CN1782921A - Image heating device and image forming apparatus using the same - Google Patents

Abstract

Provided is an image heating device capable of obtaining a predetermined calorific value with a small current. An image heating device is constituted by using a magnetic and conductive heating roller (1), and an exciting coil (5) arranged opposite to the peripheral surface of the heating roller (1) to heat the heating roller (1) by electromagnetic induction. The excitation coil (5) is formed by extending a bundle of 60 surface-insulated copper wires with an outer diameter of 0.2 mm in the direction of the rotation axis of the heating roller (1) and coiling it along the circumferential direction of the heating roller (1). form. In addition, the excitation coil (5) makes the wire bundles close to each other along the circumferential direction of the heating roller (1), and is arranged to cover the upper half of the heating roller (1).

Description

Image heating device and image forming device using the same

This application is a divisional application of:

Title of Invention: Image Heating Device and Image Forming Device Using the Device

Application number: 00807125.X

Application date: February 19, 2000

technical field

The present invention relates to an image heating device suitable for use in a fixing device for fixing an unfixed image used in an image forming device such as an electrophotographic device, an electrostatic recording device, and an image forming device using the image heating device.

Background technique

As this image heating device, there are known types using electromagnetic induction disclosed in JP-1074007, JP-7295414 and the like.

JP-A-1074007 describes an exciting coil in which a coil is wound around an iron core as an exciting device for generating electromagnetic induction. FIG. 34 is a cross-sectional view of the image heating device disclosed in this publication.

In FIG. 34 , 310 is a coil for generating a high-frequency magnetic field, and 311 is a metal sleeve that rotates while generating heat by induction heating. 312 is an internal pressure member provided inside the metal sleeve 311 . In addition, 313 is an external pressing member provided outside the metal sleeve 311 , the external pressing member 313 rotates in the direction of arrow a in the figure, and the metal sleeve 311 rotates with the rotation of the external pressing member 313 .

The recording paper 314 serving as a recording material carrying an unfixed toner image is conveyed to the nip portion as indicated by the arrows in the figure. Then, the unfixed toner image on the recording paper 314 is fixed by the heat of the metal sleeve 311 and the pressure of the two pressing members 312 , 313 .

The coil 310 has a plurality of separate winding parts 310a, 310b. These winding parts 310a, 310b are formed by winding conductive wires in multiple turns around the core post parts 315b, 315d of the iron core 315 provided with a plurality of post parts 315a-315e via an insulating member not shown in the figure. And formed. Here, the iron core 315 is made of ferrite which is a magnetic material, and forms a magnetic path of magnetic flux generated by an alternating current applied to the coil 310 .

However, in the image heating device disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 1074007, the following problems should be considered.

That is, in the structure of the above-mentioned excitation device, since the lead wire is wound around the iron core post part of the iron core 315, the arrangement of the lead wire is restricted by the position of the iron core post part of the iron core. Therefore, the degree of freedom in design is limited when arranging the wires, and it is difficult to arrange the wires in a wide width along the peripheral surface in the circumferential direction of the metal sleeve 311 .

On the other hand, in Japanese Unexamined Patent Publication No. 7295414, a kind of structure is described as the excitation device that conductive coil is arranged on the insulating support body by helix. FIG. 35 is a sectional view of the image heating device disclosed in this publication, and FIG. 36 is a perspective view of a heating coil used in the image heating device.

As shown in FIG. 35 , the heat roller 201 rotates in the direction of the arrow in the figure while contacting the pressure roller 202 , and the pressure roller 202 rotates with the rotation of the heat roller 201 . In addition, the pressure roller 202 is driven to rotate so as to be pressed against the heating roller 201 . In addition, the recording paper 203 carrying the unfixed toner image and conveyed between the two rollers 201, 202 is heated and pressed between the two rollers 201, 202, so that the unfixed toner image on the recording paper 203 is The toner image is fixed.

The heating coil 204 is disposed inside the insulating support 205 in a buried state. As shown in Fig. 35 and Fig. 36, the heating coil 204 extends and lays a thin conductive film along the curved surface of the semi-cylindrical insulating support 205, and arranges it spirally on the entire insulating support 205 as a whole. width. An alternating current is applied to the heating coil 204 from a power source for induction heating. Then, the heating coil 204 is excited by alternating magnetic flux generated by the alternating current applied to the heating coil 204 , and an eddy current opposite to the alternating current flowing through the heating coil 204 is generated in the heating roller 201 . When this eddy current is generated in the heating roller 201 , Joule heat is generated in the heating roller 201 , and the heating roller 201 is heated.

According to the structure of the excitation device described in the Japanese Patent Application Publication No. 7295414, compared with the structure of the excitation device in the above-mentioned Japanese Patent Application Publication No. 10 74007, the restriction on the degree of freedom in design when arranging the wires is reduced, and the wires can be arranged in the form of The wide width is arranged in the circumferential direction of the heating roller 201 along the circumferential surface.

However, in the image heating device disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 7295414, there are the following problems.

That is, since the heating coil 204 has the conductive film arranged in a helical shape, there is a space where no current flows between the helically wound currents. Therefore, as shown by the dotted line S in FIG. 35 , the magnetic flux passes between the respective coils to form a small loop. In this case, however, the magnetic flux cannot be guided to the heating roller 201 with high efficiency, thus increasing the magnetic flux that does not pass through the heating roller 201 . Therefore, in order to obtain the power required to heat the heating roller 201 , it is necessary to flow a large current through the heating coil 204 . On the other hand, in order to allow a large current to flow through the heating coil 204, it is necessary to use parts withstanding high current in the power supply for induction heating, which increases the cost of the power supply for induction heating.

Further, as an image heating device typified by a heating and fixing device, conventionally, an image heating device of a heat roller type, a belt type, or a contact heating method is generally used.

In recent years, a belt-type device that can set the heat capacity to a small value has attracted more and more attention in response to the requirements of shortening the heating time and saving energy (see JP-A-6 318001, etc.).

In FIG. 37, there is shown a sectional view of a belt image heating device disclosed in JP-A-6318001. As shown in FIG. 37, the rotating endless endless fixing belt 401 is suspended on the fixing roller 402 and the heating roller 403, and the heating roller 403 is heated by the heating source H1 arranged inside the heating roller 403, so that the fixing belt 401 heated to the specified temperature.

In this image heating device, by using the fixing belt 403 with a small heat capacity, it is possible to achieve non-uniform fixing with an oil-free structure.

In the general belt-type image heating device that also includes the above-mentioned conventional example, there is an advantage that the heat capacity of the fixing belt can be set very small so that the heating time can be shortened. Therefore, the temperature of the fixing belt itself can be raised to within a short time specified temperature. However, on the other hand, the smaller the heat capacity, the stronger the tendency that the temperature of the fixing belt is likely to drop very low due to heat taken from the recording paper etc. when the toner image is fixed. Therefore, before reaching the fixing section again, the lowered fixing belt temperature must be stably and uniformly returned to a necessary temperature for reliable fixing.

Furthermore, there is a problem that the temperature drop of the fixing belt when passing through the fixing unit varies greatly depending on the temperature state of the recording paper and members used in the pressurizing device at that time. Therefore, regardless of these temperature states, that is, no matter how much the temperature drop of the fixing belt after passing through the fixing part is different, the temperature of the fixing belt must always be restored to a certain temperature most suitable for fixing when it reaches the fixing part again, so that Performs stable fixing.

In order to stabilize and uniformly restore the temperature of the fixing belt to the specified temperature, the heat transfer structure from the heating part to the fixing belt and the structure of the heating part itself are crucial, but in the existing belt-type image heating device, the No special consideration has been given to this point.

In addition, in general belt-type image heating devices including the above-mentioned conventional ones, the heat capacity of the fixing belt is set to be small in order to shorten the heating time, but there are problems of uneven temperature and excessive local temperature rise. This problem becomes more prominent when recording paper (recording paper with a narrow width) smaller than the size of the image heating device in the depth direction (direction of the rotation axis of the heating roller 403 ) in FIG. 37 is continuously used. That is, the passing portion of the recording paper must be heated accordingly because the heat is continuously taken away by the recording paper. Thus the temperature will rise continuously. Then, when the temperature rises abnormally, if a large-sized recording paper (recording paper with a wide width) is used in this state, thermal deviation will occur.

Conversely, when heat generation is limited to prevent thermal deviation, the portion of the recording paper that has lost heat becomes cold, and thus cold deviation may occur, or fixing may not be possible.

disclosure of invention

The present invention was developed to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide an image heating device capable of obtaining a predetermined amount of heat generation with a small current, and an image forming apparatus using the image heating device. Another object of the present invention is to provide an image heating device using a fixing belt, that is, an image heating device capable of shortening the heating time and stably controlling the temperature of the fixing belt, and an image forming apparatus using the image heating device.

In order to achieve the above-mentioned object, the first structure of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, disposed opposite to the peripheral surface of the above-mentioned heat-generating member, and the above-mentioned heat-generating member is moved by electromagnetic induction. In the image heating device, the exciting coil is formed by extending a bundle of surface-insulated wires in the direction of the rotation axis of the heating member and coiling it in the circumferential direction of the heating member, and The harnesses extending in the direction of the rotation axis of the heat generating member are brought into close contact with each other at least at one location. According to the first structure of the image heating device, since the magnetic flux generated by the alternating current flowing through the excitation coil cannot pass between the wire harnesses at the position where the wire harnesses are close to each other, it can be efficiently compared with the prior art. The magnetic flux is passed through the heat generating member. Therefore, it is not necessary to flow a large current through the exciting coil to obtain the power required to heat the heat generating member.

In addition, in the above-mentioned first configuration of the image heating device of the present invention, it is preferable that the number of overlapping layers of the wire harness is greater at both ends in the direction of the rotation axis of the heat generating member than at the center. According to this preferred example, it is possible to uniformly heat a wider range in the rotation axis direction of the heat generating member. In addition, since the distance between the wire harness overlapping the both ends of the heat-generating component in the direction of the rotation axis increases from the heat-generating component, eddy currents are not concentrated at these portions to cause excessive local temperature rise.

In addition, in the first configuration of the image heating device of the present invention, it is preferable to set the outer diameter of the wire rod to be 0.1 mm to 0.3 mm, and to set the outer diameter of the wire bundle to be 5 mm or less. According to this preferred example, the resistance of the wire harness to high-frequency alternating current can be reduced, so that heat generation of the exciting coil can be suppressed. In addition, since the wire harness can have appropriate thickness, rigidity, and durability, the exciting coil can be easily formed.

In addition, in the above-mentioned first structure of the image heating device of the present invention, it is preferable that the inductance of the above-mentioned exciting coil is 10 μH or more and 50 μH or less, and the resistance is preferably 0.5 Ω or more and 5 Ω in the state where the exciting coil is opposed to the heat-generating member. the following. According to this preferred example, it is possible to obtain sufficient input power and heat generation for the heat-generating components only by constituting the excitation circuit with circuit elements that are not so high in withstand current and withstand voltage.

In addition, in the above-mentioned first structure of the image heating device of the present invention, it is preferable that an iron core made of a magnetic material is further provided outside the excitation coil. According to this preferred example, all the magnetic flux on the back side of the exciting coil can pass through the inside of the iron core, so that the magnetic flux can be prevented from leaking backward. As a result, heat generation due to electromagnetic induction of surrounding conductive members can be prevented, and radiation of unnecessary electromagnetic waves can be prevented. In addition, since the inductance of the exciting coil is increased, the electromagnetic coupling between the exciting coil and the heating element can be improved, so that even with the same coil current, a larger power can be input to the heating element. In addition, in this case, it is preferable to make the length of the iron core in the direction of the rotation axis of the heat generating member shorter than the length of the heat generating member in the direction of the rotation axis. According to this preferred example, it is possible to prevent excessive heating of the end surface of the heat generating member due to an increase in the eddy current density at the end surface of the heat generating member. In addition, in this case, it is preferable to make the length in the direction of the rotation axis of the heat generating member at the outer peripheral portion of the exciting coil longer than the width of the maximum width of the material to be recorded, and to make the length of the iron core in the direction of the rotation axis of the heat generating member longer than the width of the material to be recorded. The maximum width used is the width of the recorded material. According to this preferred example, even if the winding of the exciting coil is uneven to some extent, the magnetic field radiated from the exciting coil to the heat generating member can be made uniform in the direction of the rotation axis of the heat generating member. Therefore, the heat generation distribution of the heat generating member in the portion through which the recording material passes can be made uniform. According to this structure, the temperature distribution in the fixing portion can be made uniform, so that a stable fixing effect can be obtained. In addition, it is also possible to reduce the length of the heat generating member in the direction of the rotation axis and the length of the exciting coil in the direction of the rotation axis of the heat generating member while making the heat generation distribution of the heat generating member uniform. As a result, the size of the device can be reduced and the cost can be reduced. Also, in this case, it is preferable that the distance from the end face of the iron core to the end face of the heat generating member in the direction of the rotation axis of the heat generating member be longer than the relative interval between the iron core and the heat generating member. According to this preferred example, the magnetic lines of force radiated from the iron core toward the end of the heating element are not concentrated in a narrow range, so it is possible to prevent the induced current from concentrating on the end surface of the heating element and its vicinity, thereby preventing the end of the heating element from overheat. In addition, in this case, it is preferable that the iron core has an opposing portion facing the heat generating member without passing through the exciting coil, and a magnetic conduction portion facing the heat generating member passing through the exciting coil. According to this preferred example, since the magnetic flux generated by the alternating current (coil current) flowing through the exciting coil is passed between the opposing portion and the heat generating member, most of the magnetic circuit can be made of high magnetic permeability material. Therefore, the portion of the air with low magnetic permeability through which the magnetic flux generated by the coil current passes is only a narrow gap portion between the heat generating member and the iron core. Therefore, the inductance of the exciting coil is increased, and almost all of the magnetic flux generated by the coil current can be guided to the heat generating member. As a result, the electromagnetic coupling between the heating element and the exciting coil is further improved, so that even with the same coil current, a larger power can be input to the heating element. Furthermore, since the magnetic circuit is defined by the opposing portion and the heat generating member, it is possible to freely design the magnetic circuit. In this case, further, the heat generating member is preferably supported by a supporting member made of a magnetic material, and the distance between the above supporting member and the iron core is preferably equal to the relative distance between the above iron core and the above heat generating member. More than 2 times. According to this preferred example, most of the magnetic flux passing through the iron core passes through the heat generating member without being guided to the supporting member. Therefore, the electromagnetic energy supplied to the exciting coil can be efficiently transmitted to the heat generating member, and heat generation of the support member can be prevented. In this case, further, the length between ends of the outermost ends of the magnetic conduction portion along the rotation axis direction of the heat generating member is preferably smaller than the length between ends of the outermost ends of the opposing portion along the rotation axis direction of the heat generating member. According to this preferred example, the amount of material used in the magnetically permeable part can be reduced while ensuring the range of the opposite part that determines the range of the heat generating part along the direction of the rotation axis of the heat generating part, so that the heat distribution can be made more efficient with a lower cost structure. uniform. In this case, further preferably, at least a part of the facing portion is closer to the heat generating member than the magnetically permeable portion to form the proximity portion. According to this preferred example, more power can be input to the heat generating element. In this case, furthermore, it is preferable to provide a plurality of approaching portions such that one of the plurality of approaching portions is located at the center of the winding of the exciting coil. Since the magnetic flux generated by the coil current must pass through the center of the excitation coil, the magnetic flux generated by the coil current can be efficiently guided to the heat generating member by locating the approach portion at this portion. In addition, in this case, it is preferable that at least a part of the iron core has a gap in the direction of the rotation axis of the heat generating member. According to this preferred example, by changing the arrangement of the iron cores, it is possible to freely design the distribution of heat generation. In addition, uniform temperature distribution can be obtained even when an inexpensive, small-volume iron core is used. Furthermore, heat can be dissipated from gaps in the iron core, and at the same time, since the surface area of the iron core itself is increased, heat dissipation can be promoted. In this case, it is further preferable that the iron core has an opposing portion facing the heat-generating component without passing through the exciting coil and a magnetic-conductive portion facing the heat-generating component through the exciting coil, and the above-mentioned conductive portion of the iron core It is preferable that the distribution of the gaps in the magnetic portion is not uniform in the direction of the rotation axis of the heat generating member. Furthermore, in this case, it is preferable to make the gap of the magnetically permeable part of the iron core narrower at the ends in the rotation axis direction of the heat generating member than at the center. According to this preferred example, the temperature distribution of the heat generating member can be made uniform, thereby preventing fixing failures. In this case, it is further preferable that the iron core has an opposing portion facing the heat-generating member without passing through the exciting coil and a magnetically conductive portion facing the heat-generating member through the exciting coil, and the above-mentioned The facing portion is arranged at an asymmetrical position with respect to the center line of the field coil in the direction of the rotation axis of the heat generating member. According to this preferred example, the distribution of heat generation in the direction of the rotation axis of the heat generating member can be made uniform using a small number of iron cores. On the contrary, if it is the same amount of iron core, the heat distribution can be made more uniform. In this case, it is further preferable that the iron core has an opposing portion facing the heat-generating member without passing through the exciting coil and a magnetic-conductive portion facing the above-mentioned heat-generating member through the exciting coil, and the above-mentioned iron core The gap of the opposed part is smaller than the gap of the said magnetic transmission part of the said iron core in the rotation axis direction of the said heat generating member. According to this preferred example, the amount of material used in the magnetic permeable part can be reduced while securing the length of the iron core at the opposing part that determines the range of the heat generating part. Therefore, even if the amount of iron core material is less than before, it is a low-cost structure. , can also make the heat distribution become uniform. In this case, it is further preferable that the iron core has an opposing portion facing the heat-generating member without passing through the exciting coil and a magnetic-conductive portion facing the above-mentioned heat-generating member through the exciting coil, and the above-mentioned iron core The facing portion is continuous in the direction of the rotation axis of the heat generating member. According to this preferred example, even if gaps are provided in the iron core of the magnetic permeable part and the distribution is uneven, the magnetic field reaching the heat generating member from the opposing part can be made uniform in the direction of the rotation axis. According to this structure, the heat generation distribution of the heat generating member on the portion where the recording material passes can be made uniform while reducing the iron core of the magnetic conduction portion, so that the temperature on the fixing portion becomes uniform. Therefore, a stable fixing effect can be obtained. In addition, it is possible to reduce the number of iron cores of the magnetic permeable part while making the heat distribution of the heat generating member uniform, so that the size of the device can be reduced and the cost can be reduced. Also, in this case, it is preferable to form the heat generating member in a tubular shape, and make the cross-sectional area of the surface perpendicular to the rotation axis inside the heat generating member smaller than the maximum cross-sectional area of the iron core and the field coil. According to this preferred example, a heat generating member with a small heat capacity, an exciting coil with a large number of turns, and an appropriate amount of ferrite (iron core) can be used in combination. Therefore, it is possible to input more power to the heat generating member with a predetermined coil current while suppressing the heat capacity of the fixing device. Also, in this case, it is preferable to divide a part of the iron core to form a movable part, and to hold the movable part so as to be movable relative to other parts of the iron core. In this case, further, it is preferable that the movable portion located outside the region through which the recording material used is to be movable relative to other portions of the iron core. According to this preferred example, it is possible to prevent excessive temperature rise in the range where the recording material does not pass, and to prevent the temperature of components such as the fixing belt and the bearing at the end from exceeding the heat-resistant temperature. In addition, even if a large-sized recording material is used after a small-sized recording material is continuously used, the temperature of the fixing portion remains normal, so occurrence of thermal deviation can be prevented. Therefore, it is possible to use a large-sized recorded material immediately after using a small-sized recorded material.

In addition, in the above-mentioned first configuration of the image heating device of the present invention, it is preferable to further include a shielding member made of a conductive material covering at least a part of the back surface of the exciting coil. According to this preferred example, it is possible to prevent the high-frequency electromagnetic waves generated from the excitation coil from propagating inside and outside the device. According to this configuration, it is possible to prevent malfunctions of circuits inside and outside the device due to electromagnetic noise.

In addition, in the above-mentioned first configuration of the image heating apparatus of the present invention, it is preferable to further include cooling means for cooling the exciting coil by air flow.

In addition, in the above-mentioned first configuration of the image heating apparatus of the present invention, it is preferable to further include a heat insulating member for shielding heat transfer between the exciting coil and the heat generating member. According to this preferred example, the exciting coil can be cooled without cooling the heat-generating components. In addition, in this case, it is preferable to provide an iron core made of a magnetic material on the outside of the exciting coil, and to make the length of the exciting coil along the rotation axis of the heat generating member longer than the length of the heat insulating member along the rotating axis of the heat generating member. The length in the axial direction is shorter, but longer than the length of the iron core along the rotation axis of the heat generating member. According to this preferred example, even when the iron core is close to the heating element, the temperature of the iron core can be prevented from rising.

In addition, in the above-mentioned first configuration of the image heating apparatus of the present invention, it is preferable to further include a fixing roller, and a fixing belt suspended from the fixing roller and the heat generating member. In addition, in this case, an iron core made of a magnetic material is preferably provided outside the exciting coil, and the iron core preferably has an opposing portion facing the heat-generating member without passing through the exciting coil and passing through the exciting coil. The coil is used to excite the magnetic conduction portion facing the heat generating member, and the length between the ends of the outermost end of the facing portion along the rotation axis direction of the heat generating member is smaller than the width of the fixing belt. According to this preferred example, since the heat-generating member in the portion where heat is not taken away by the fixing belt is not overheated, it is possible to prevent the end of the heat-generating member from overheating,

In addition, the second configuration of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. A coil, the image heating device is characterized in that: the excitation coil is formed by extending a bundle of surface insulated wires in the direction of the rotation axis of the heat generating member and coiling it along the circumferential direction of the heat generating member. At both end portions in the direction of the rotation axis of the member, the number of layers of the wire harness is overlapped and coiled more than that at the central portion.

In addition, the third structure of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. The image heating device is characterized in that: an iron core made of magnetic material is provided outside the above-mentioned exciting coil, and the length of the above-mentioned iron core along the direction of the rotation axis of the above-mentioned heating element is larger than the maximum width of the used Record the width of the material.

In addition, the fourth configuration of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. A coil, the image heating device is characterized in that: on the side opposite to the above-mentioned heat-generating member with respect to the outside of the above-mentioned exciting coil, there is also an opposing coil made of a magnetic material that is opposed to the above-mentioned heat-generating member without passing through the above-mentioned exciting coil. part and the iron core of the magnetically permeable part opposed to the above-mentioned heat-generating component through the above-mentioned exciting coil, and make at least a part of the above-mentioned opposing part closer to the heat-generating component than the above-mentioned magnetically permeable part to form a close part, and at the same time make at least part of the above-mentioned iron core A part has a gap in the rotation axis direction of the heat generating member.

In addition, the fifth structure of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. A coil, the image heating device is characterized in that: on the side opposite to the above-mentioned heat-generating member with respect to the outside of the above-mentioned exciting coil, there is also an opposing coil made of a magnetic material that is opposed to the above-mentioned heat-generating member without passing through the above-mentioned exciting coil. part and the iron core of the magnetically permeable part facing the heat-generating component through the above-mentioned exciting coil, and make the opposing area of the opposing part and the above-mentioned heat-generating component larger than the cross-sectional area of the magnetic-conducting part perpendicular to the circumferential direction of the heat-generating component. According to the fifth configuration of the image heating device, the electromagnetic coupling between the exciting coil and the heat generating member can be improved, thereby improving the heat generation efficiency. In addition, since the magnetic flux generated by the coil current is concentrated on the opposing part of the iron core, by making the opposing area of the opposing part and the heat generating member larger than the cross-sectional area of the magnetic conduction part perpendicular to the circumferential direction of the heat generating member, it is possible to make The heat generation amount in the rotation axis direction of the heat generating member becomes uniform. Furthermore, a gap can be provided on the iron core while ensuring the cross-sectional area of the magnetic flux, thereby forming a part of the exciting coil that does not face the iron core, so that heat dissipation from the exciting coil can be promoted, and the leakage of the magnetic flux to the outside can be prevented at the same time. .

In addition, the sixth configuration of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. A coil, the image heating device is characterized in that an iron core made of a magnetic material is further provided on a side opposite to the above-mentioned heat generating member on the outside of the above-mentioned exciting coil, and a part of the iron core is divided to form a movable part, And the above-mentioned movable part is held to be movable relative to other parts of the above-mentioned iron core.

In addition, the seventh structure of the image heating device of the present invention is characterized in that: a fixing belt, a pressurizing device that is in pressure contact with the fixing belt to form a nip portion on the surface side of the fixing belt, at least a part of which is made of conductive The material constitutes a heating roller that movably suspends the fixing belt, and an exciting coil that is disposed opposite to the peripheral surface of the heating roller across the fixing belt and that excites and heats the contact portion of the heating roller with the fixing belt. According to the seventh structure of the image heating device, since the heat is heated at the contact portion of the heating roller with the fixing belt and the heat is immediately transferred to the fixing belt, it is not necessary to raise the temperature of the heating roller more than necessary. As a result, heating time can be shortened.

In addition, in the seventh configuration of the image heating apparatus of the present invention, it is preferable that the excitation width in the moving direction of the fixing belt is substantially equal to or smaller than the contact width between the fixing belt and the heating roller. According to this preferred example, since only the area of the heating roller that contacts the fixing belt is heated, an abnormal increase in the temperature of the heating roller can be prevented.

In addition, in the seventh configuration of the image heating device of the present invention, it is preferable to further include a temperature detection device that contacts the surface of the heating roller other than the contact portion with the fixing belt to detect the temperature, and an output signal based on the output of the temperature detection device. A control device that controls the output of the field coil. According to this preferred example, the temperature of the fixing belt can always be kept at an optimum temperature for fixing.

In addition, in the seventh configuration of the image heating device of the present invention, it is preferable to apply an exciting current having a predetermined frequency to the exciting coil, and make the conductive member of the heating roller have a skin thickness greater than that determined by its material and the predetermined frequency. Depth of thickness. According to this preferred example, most of the induced current can be generated in the heating roller at a low temperature.

In addition, an eighth configuration of the image heating device of the present invention is characterized in that a fixing belt is provided, a pressurizing device that is in pressure contact with the fixing belt and forms a nip portion on the surface side of the fixing belt, and the Curie temperature The heating roller which is composed of a magnetic material set to a predetermined value and movably suspends the above-mentioned fixing belt, the conductive member provided in the above-mentioned heating roller, and the peripheral surface of the above-mentioned heating roller is arranged opposite to each other with the above-mentioned fixing belt interposed therebetween. An exciting coil for exciting and heating a portion of the heating roller in contact with the fixing belt. According to the eighth structure of the image heating device, since the contact portion of the heating roller and the fixing belt is heated and the heat is immediately transferred to the fixing belt, it is not necessary to raise the temperature of the heating roller more than necessary. As a result, heating time can be shortened.

In addition, in the eighth configuration of the image heating apparatus of the present invention described above, it is preferable to provide a conductive member so as to be thermally insulated from the heating roller. According to this preferred example, the heat generated in the heating roller is hardly transmitted to the conductive member.

In addition, in the eighth configuration of the image heating device of the present invention, it is preferable to apply an exciting current having a predetermined frequency to the exciting coil, and to make the heating roller thicker than the skin depth determined by its material and the predetermined frequency.

In addition, in the ninth structure of the image heating device of the present invention described above, a heat generating member composed of a magnetic and conductive rotating body is provided, and a heat generating member is arranged to face the outer peripheral surface of the heat generating member, and the heat generating member is heated by electromagnetic induction. In this image heating device, the exciting coil is formed by extending a bundle of surface-insulated wires in the direction of the rotation axis of the heat generating member and coiling it along the circumferential direction of the heat generating member, and The wire harnesses extending in the direction of the rotation axis of the heat generating member are in close contact with each other at least at one location.

In addition, in the tenth configuration of the image heating device of the present invention described above, a heat generating member composed of a magnetic and conductive rotating body is provided, and a heat generating member is arranged to face the outer peripheral surface of the heat generating member, and the heat generating member is heated by electromagnetic induction. An excitation coil, the image heating device is characterized in that the above-mentioned excitation coil is formed by extending a bundle of surface-insulated wires in the direction of the rotation axis of the above-mentioned heat-generating member and coiling along the circumferential direction of the above-mentioned heat-generating member. At both end portions in the direction of the rotating shaft of the heat generating member, the number of layers of the wire harness to be overlapped and coiled is greater than that at the central portion.

In addition, the eleventh configuration of the image heating device of the present invention is provided with a heat-generating member composed of a magnetic and conductive rotating body, and an excitation element that is arranged to face the peripheral surface of the heat-generating member and heats the heat-generating member by electromagnetic induction. The image heating device is characterized in that: an iron core made of magnetic material is provided outside the above-mentioned exciting coil, and the length of the above-mentioned iron core along the direction of the rotation axis of the above-mentioned heating element is larger than the maximum width of the used Record the width of the material.

In addition, the structure of the image forming apparatus of the present invention is equipped with an image forming unit for forming and carrying an unfixed image on the recording material, and a fixing device for fixing the above-mentioned unfixed image on the above-mentioned recording material. , The image forming apparatus is characterized in that the above-mentioned image heating device of the present invention is used as the above-mentioned fixing device.

A brief description of the drawings

Fig. 1 is a sectional view showing a fixing device as an image heating device according to a first embodiment of the present invention.

2 is a partially cutaway plan view showing a heat generating unit of a fixing device as an image heating device according to a first embodiment of the present invention.

3 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a first embodiment of the present invention.

4 is an equivalent circuit diagram showing a heat generating unit of a fixing device as an image heating device according to a first embodiment of the present invention.

5 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a second embodiment of the present invention.

Fig. 6 is a bottom view showing a heat generating portion of a fixing device as an image heating device according to a second embodiment of the present invention without a heat generating roller.

7 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a third embodiment of the present invention.

8 is a cross-sectional view showing a heat generating unit of another example of a fixing device as an image heating device according to a third embodiment of the present invention.

Fig. 9 is a cross-sectional view showing an image forming apparatus using an image heating device as a fourth embodiment of the present invention as a fixing device.

10A is a sectional view showing a fixing device as an image heating device according to a fourth embodiment of the present invention.

10B is a cross-sectional view showing another example of the fixing device as the image heating device according to the fourth embodiment of the present invention.

FIG. 11 is a projected view showing the heat generating portion viewed from the direction of arrow G in FIG. 10A .

12 is a cross-sectional view showing a heating portion on a plane including the rotation shaft of the heating roller and the center of the exciting coil of the fixing device as the image heating device according to the fourth embodiment of the present invention.

13 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a fourth embodiment of the present invention.

14 is a cross-sectional view showing a heating roller of a fixing device as an image heating device according to a fourth embodiment of the present invention.

15 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a fifth embodiment of the present invention.

16 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a sixth embodiment of the present invention.

FIG. 17 is a projected view showing a heat generating unit of a fixing device as an image heating device according to a sixth embodiment of the present invention viewed from the direction of arrow A in FIG. 16 .

18 is a perspective view showing another example of a heat generating unit of a fixing device as an image heating device according to a sixth embodiment of the present invention.

Fig. 19 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a seventh embodiment of the present invention.

FIG. 20 is a projected view showing a heat generating unit of a fixing device as an image heating device according to a seventh embodiment of the present invention viewed from the direction of arrow A in FIG. 19 .

Fig. 21 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to an eighth embodiment of the present invention.

FIG. 22 is a projected view showing a heat generating unit of a fixing device as an image heating device according to an eighth embodiment of the present invention viewed from the direction of arrow A in FIG. 21 .

Fig. 23 is a perspective view showing a heat generating unit of a fixing device as an image heating device according to a ninth embodiment of the present invention.

Fig. 24 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a ninth embodiment of the present invention.

25 is a cross-sectional view showing another example of a heat generating unit of a fixing device as an image heating device according to a ninth embodiment of the present invention.

Fig. 26 is a sectional view showing an image forming apparatus using an image heating device as a tenth embodiment of the present invention as a fixing device.

Fig. 27 is a sectional view showing a fixing device as an image heating device according to a tenth embodiment of the present invention.

Fig. 28 is a sectional view showing a fixing belt used in a fixing device as an image heating device according to a tenth embodiment of the present invention.

29 is a front view showing an exciting coil and a core material used in a fixing device as an image heating device according to a tenth embodiment of the present invention.

Fig. 30 is a sectional view showing a heating roller used in a fixing device as an image heating device according to a tenth embodiment of the present invention.

Fig. 31 is a diagram for explaining the flow of magnetic flux passing through a heating roller used in a fixing device as an image heating device according to a tenth embodiment of the present invention at a low temperature state.

Fig. 32 is a diagram for explaining a flow of magnetic flux passing through a heating roller used in a fixing device as an image heating device according to a tenth embodiment of the present invention at a high temperature state.

Fig. 33 is a sectional view showing a fixing device for fixing a color image as an image heating device according to an eleventh embodiment of the present invention.

Fig. 34 is a sectional view showing a conventional image heating device.

Fig. 35 is a cross-sectional view showing another example of a conventional image heating device.

Fig. 36 is a perspective view showing a heating coil used in another example of the conventional image heating device.

Fig. 37 is a cross-sectional view showing still another example of a conventional image heating device.

Best Mode for Carrying Out the Invention

Hereinafter, the present invention will be described in more detail using embodiments.

[First Embodiment]

1 is a sectional view showing a fixing device as an image heating device according to a first embodiment of the present invention, and FIG. 2 is a partially cutaway plan view showing a heat generating portion of the fixing device.

In Fig. 1 and Fig. 2, 1 is a heat-generating roller as a heat-generating member, 2 is a supporting side plate made of galvanized steel sheet, and 3 is fixed to the supporting side plate 2 and supports the heating roller at both ends in a rotatable manner. bearings. The heating roller 1 is driven to rotate by the driving device of the device body not shown in the figure. The heating roller 1 is made of a magnetic material which is an alloy of iron, nickel, and chromium, and its Curie point is adjusted to be 300° C. or higher. In addition, the heating roller 1 is formed in a tubular shape with a thickness of 0.3 mm.

The surface of the heating roller 1 is covered with a 20 μm thick release layer (not shown) made of a fluorine-containing resin so as to have release properties. In addition, as the mold release layer, resins or rubbers having good mold release properties such as PTFE, PFA, FEP, silicone rubber, and fluorine-containing rubber may be used alone or in combination. When the heating roller 1 is used for fixing monochrome images, it is enough to ensure only the releasability, but if the heating roller 1 is used for fixing color images, it is better to make it elastic. , must further form a thick rubber layer.

4 is a pressure roller as a pressure means. The pressure roller 4 is made of silicone rubber with a hardness of JISA 65, and is pressed against the heating roller 1 with a pressing force of 20 kgf to form a nip. Therefore, in this state, the pressure roller 4 rotates with the rotation of the heating roller 1 . In addition, as the material of the pressure roller 4, other heat-resistant resins or rubbers such as fluorine-containing rubber and fluorine-containing resin may also be used. In addition, it is preferable to cover the surface of the pressure roller 4 with resin or rubber such as PFA, PTFE, FEP alone or in combination to improve its wear resistance and mold release properties. In addition, in order to prevent heat loss, the pressure roller 4 is preferably made of a material with low thermal conductivity.

5 is an exciting coil as an exciting device. The field coil 5 is formed by extending a bundle of 60 surface-insulated copper wires with an outer diameter of 0.2 mm in the direction of the rotation axis of the heating roller 1 and coiling it in the circumferential direction of the heating roller 1 . In addition, the cross-sectional area of the wire harness is about 7 mm ² including the insulating sheath of the wire.

The cross section of the excitation coil 5 perpendicular to the rotation axis of the heating roller 1 is arranged so that the wire bundles are closely arranged along the circumferential direction of the heating roller 1 so as to cover the upper half of the heating roller 1 and formed in two overlapping layers. shape. In this case, adjacent wire bundles in the wire bundle from one end to the other end of the heating roller 1 are arranged to abut each other, and adjacent wire bundles in the wire bundle from the other end to the end of the heating roller 1 are abutted to each other.

In addition, the coiling order of the wire bundles extending and coiling in the direction of the rotation axis of the heating roller 1 is not necessarily the order starting from the center of the coils, and the order may be changed in the middle.

The number of turns of the exciting coil 5 is 18 in total, and the wire bundles are bonded to each other with an adhesive on the surface, so as to maintain the shape shown in Fig. 1 and Fig. 2 . In addition, the exciting coil 5 is opposed to the outer peripheral surface of the heating roller 1 at a distance of about 2 mm. The range where the exciting coil 5 faces the outer peripheral surface of the heating roller 1 is a wide range of about 180 degrees at an angle centered on the rotation axis of the heating roller 1 .

An alternating current of 30 kHz is applied to the exciting coil 5 from the exciting circuit 6 which is a semi-oscillating inverter. According to the temperature signal measured by the temperature sensor 7 provided on the surface of the heating roller 1, the AC current applied to the exciting coil 5 is controlled so that the surface of the heating roller 1 reaches a predetermined fixing temperature of 170°C. Hereinafter, the alternating current applied to the exciting coil 5 is also referred to as "coil current".

In this embodiment, A4 size (210 mm wide) recording paper is used as the recording paper of the maximum width, and the length of the heating roller 1 in the direction of the rotation axis is set to 270 mm, and the edge of the outer peripheral portion of the exciting coil 5 generates heat. The length in the direction of the rotation axis of the roller 1 was set to 230 mm, and the length of the inner peripheral portion of the exciting coil 5 in the direction of the rotation axis of the heating roller 1 was set to 200 mm.

The recording paper 8 as a recording material carrying the toner 10 on its surface is inserted into the fixing device configured as above from the direction of the arrow in FIG. 1 , whereby the toner 10 on the recording paper 8 is fixed.

In this embodiment, the exciting coil 5 heats the heating roller 1 by electromagnetic induction. Hereinafter, the mechanism thereof will be described with reference to FIG. 3 .

The magnetic flux generated by the excitation coil 5 by the alternating current from the excitation circuit 6 (FIG. 2), as shown by the dotted line M in FIG. Generate and disappear. The induced current generated in the heating roller 1 due to the change of the magnetic flux flows almost only on the surface of the heating roller 1 due to the skin effect, thereby generating Joule heat.

In this embodiment, since the excitation coil 5 is configured so that the adjacent wire bundles in the wire bundle from one end to the other end of the heating roller 1 are close to each other and the adjacent wire bundles in the wire bundle from the other end to this end of the heating roller 1 are The wire bundles are close together so magnetic flux does not pass between the wire bundles. In addition, as shown by the dotted line M in FIG. 3 , since there is no harness at the central portion of the exciting coil 5 but a gap through which the magnetic flux passes is provided, the magnetic flux forms a large loop that rotates around the exciting coil 5 . Further, since the exciting coil 5 is disposed opposite to the heating roller 1 along the circumferential direction of the heating roller 1 over a wide range of angles of about 180 degrees centered on the rotation axis of the heating roller 1, the magnetic flux can be made to flow along the circumferential direction. It runs through a very wide range of the heating roller 1 . Therefore, since the heating roller 1 generates heat over a wide range, a predetermined power can be supplied to the heating roller 1 even if the coil current is small and the generated magnetic flux is small.

As described above, since there is no magnetic flux passing between the wire harnesses without passing through the heating roller 1 , the electromagnetic energy applied to the exciting coil 5 is transmitted to the heating roller 1 without leakage. Therefore, even if the coil current is small, predetermined power can be supplied to the heating roller 1 . Furthermore, by making the wire harnesses close to each other, it is also possible to reduce the size of the field coil 5 .

In addition, since the harness of the exciting coil 5 is positioned close to the heating roller 1, the magnetic flux generated by the coil current can be transmitted to the heating roller 1 with high efficiency. Furthermore, the flow of the eddy current generated in the heating roller 1 by this magnetic flux can cancel the change of the magnetic field caused by the coil current. In this case, since the coil current and the eddy current generated in the heating roller 1 are close to each other, the canceling effect is greater, so that the magnetic field generated by all currents in the surrounding space can be suppressed.

In addition, since the heat dissipation from the outer periphery of the exciting coil 5 is not hindered at all, it is possible to prevent the insulation sheath of the wire rod from melting due to a temperature rise due to heat storage, or to prevent the resistance value of the exciting coil 5 from increasing.

In FIG. 4 , an equivalent circuit of the exciting coil and the heating roller in a state where the exciting coil is opposed to the heating roller is shown. In FIG. 4 , r is the resistance of the exciting coil 5 itself, R is the resistance when the exciting coil 5 faces the heating roller and is electromagnetically coupled, and L is the total inductance of the circuit. r can be obtained by removing the exciting coil 5 from the heating roller 1 and measuring the individual resistance of the exciting coil 5 at a predetermined angular frequency ω with an LCR meter. R can be obtained as a value obtained by subtracting r from the resistance in a state where the exciting coil 5 is opposed to the heating roller 1 . L does not differ much from the individual inductance of the field coil 5 . When the current I flows through the circuit, the product of the square of the current I and the resistance value is consumed as effective power, thereby generating heat. The power consumed by r heats the exciting coil 5 , and the power consumed by R heats the heating roller 1 . Assuming that the electric power supplied to the heat-generating roller 1 is W, the relationship is expressed by the following formula 1.

[Formula 1]

W=(R+r)×I ²

In addition, if the voltage applied to the excitation coil 5 by the facility is V, the following Expression 2 is established.

[Formula 2]

I=V/{(R+r) ² +(ωL) ² }

It can be seen from the above (Formula 2) that when L and R are too large, sufficient current I cannot be obtained at a certain voltage V. Therefore, as shown in the above (Formula 1), since the input power W is insufficient, sufficient heat cannot be obtained. On the contrary, when R is too small, no effective power is consumed even if the current I flows, and thus sufficient heat cannot be obtained. And when L is too small, the semi-oscillating inverter, that is, the exciting circuit 6 will not work normally. When the frequency of the AC current applied from the exciting circuit 6 to the exciting coil 5 is in the range of 25 kHz to 50 kHz, R is not less than 0.5Ω and not more than 5Ω, and L is not less than 10 μH and not more than 50 μH. In this case, the excitation circuit 6 is formed of circuit elements with relatively low withstand current and withstand voltage, so that sufficient input power and heat generation can be obtained. In addition, if the values of R and L are within this range, even if the specifications of the exciting coil 5 such as the number of turns of the exciting coil 5 and the distance between the exciting coil 5 and the heating roller 1 are changed, the same effect can be obtained.

In addition, in the present embodiment, as described above, 60 wires having an outer diameter of 0.2 mm are bundled together to constitute the wire harness of the exciting coil 5 . The structure of the wire harness is not necessarily limited to this structure, but it is preferably formed by bundling 50 to 200 wires having an outer diameter of 0.1 mm or more and 0.3 mm or less. If the outer diameter of the wire rod is less than 0.1mm, there is a possibility that the wire may break due to mechanical load. On the other hand, if the outer diameter of the wire exceeds 0.3 mm, the resistance to high-frequency alternating current (r in FIG. 4 ) increases, thereby excessively heating the exciting coil 5 . In addition, if the number of wires constituting the wire harness is less than 50, the electric resistance increases due to the decrease in the cross-sectional area, so that the exciting coil 5 generates excessive heat. On the other hand, if the number of wires constituting the wire harness exceeds 200, it is difficult to wind the excitation coil 5 into any shape because the wire bundle becomes thick, and it is difficult to obtain a predetermined number of turns in a predetermined space. The above-mentioned conditions can be satisfied by roughly setting the outer diameter of the wire harness to 5 mm or less. According to the above structure, the number of turns of the exciting coil 5 can be increased in a small space, so that the size of the exciting coil 5 can be reduced and the necessary power can be supplied to the heating roller.

It is also effective that the wire bundles of the coiled field coil 5 are partly spaced apart from one another but largely close to one another. In addition, the wiring harness of the coiled exciting coil 5 may also be configured in such a way that the overlap is partially changed, so that a lower portion of the exciting coil 5 can input more power to the heat-generating roller with a smaller current. As the shape of the exciting coil 5 , it is only necessary that the width (length in the circumferential direction) of the coil arrangement is greater than the height (thickness of the stack) of the exciting coil 5 .

In addition, when the length of the exciting coil 5 in the direction of the rotation axis of the heating roller 1 is longer than the length of the heating roller 1 , the magnetic flux passes through conductive members at the ends of the heating roller 1 such as the side plate 2 . Therefore, the surrounding constituent members are heated, thereby reducing the transmission ratio of electromagnetic energy to the heating roller 1 . In this embodiment, since the length of the heating roller 1 is longer than the length of the excitation coil 5 in the direction of the rotation axis of the heating roller 1, almost all the magnetic flux generated by the coil current reaches the heating roller 1 and does not reach the side plate 2. surrounding components. According to this structure, the electromagnetic energy applied to the exciting coil 5 can be efficiently transmitted to the heating roller 1 . In particular, when the magnetic flux passes through the end surface of the heating roller 1 in the direction of the rotation axis, the eddy current density at the end surface of the heating roller 1 is increased. In this case, the problem of excessive heating of the end surface of the heating roller 1 arises.

In the present embodiment, as described above, the inner peripheral portion of the exciting coil 5, the recording paper with the largest width, the outer peripheral portion of the exciting coil 5, and the heating roller 1 are sequentially arranged in ascending order of the length in the direction of the rotating shaft of the heating roller 1 . The roller 1 and the excitation coil 5 are uniformly coiled along the rotation axis direction and parallel to the rotation axis direction of the heating roller 1 on the portion where the recording paper 8 passes. Therefore, the distribution of heat generation by the heat generation roller 1 on the portion where the recording paper 8 passes can be made uniform. As a result, the temperature distribution in the fixing portion can be made uniform, so that a stable fixing action can be obtained.

[Second Embodiment]

5 is a cross-sectional view showing a heating portion of a fixing device as an image heating device according to a second embodiment of the present invention, and FIG. 6 is a bottom view showing a heating portion of the fixing device without a heating roller. In addition, the same code|symbol is attached|subjected to the member whose function is the same as that of the said 1st Embodiment, and the description is abbreviate|omitted.

This embodiment differs from the first embodiment in that the wire bundle is wound along the circumferential direction of the heating roller 1 instead of overlapping in two layers, and a pair of back iron cores 9 are provided on the back of the exciting coil 5 .

As the material of the back core 9 , ferrite with a relative magnetic permeability of 1000 to 3000, a saturation magnetic flux density of 200 to 300 mT, and a volume resistivity of 1 to 10 Ω·m is used. In addition, as the material of the back iron core 9 , other than ferrite, a material with high magnetic permeability and high resistivity such as permalloy can be used.

The cross section of the back core 9 is formed in a shape in which a cylinder having an outer diameter of 36 mm and a thickness of 5 mm is cut at an angle of about 90 degrees in the axial direction. Therefore, the cross-sectional area of the back core 9 is 243 mm ² . In addition, the cross-sectional area of the exciting coil 5 is 7mm ² ×9 turns×2, that is, 126mm ² .

The heating roller 1 is formed in a tubular shape with an outer diameter of 20 mm and a thickness of 0.3 mm. Therefore, the cross-sectional area of the surface perpendicular to the rotation axis inside the heating roller 1 is about 295 mm ² . Therefore, the cross-sectional area of the field coil 5 including the back iron core 9 is larger than the cross-sectional area of the surface perpendicular to the rotation axis inside the heating roller 1 . In addition, the distance between the back iron core 9 and the heating roller 1 was 5.5 mm.

In addition, in this embodiment, A4 size (width 210 mm) recording paper is used as the recording paper of the maximum width, and the length of the heating roller 1 in the direction of the rotation axis is set to 240 mm, and the outer circumference of the exciting coil 5 wound The length of the portion along the rotation axis of the heating roller 1 is set to 200 mm, the length of the inner peripheral portion of the exciting coil 5 along the rotation axis of the heating roller 1 is set to 170 mm, and the length of the back core 9 along the heating axis is set to 200 mm. The length in the rotation axis direction of the roller 1 was set to 220 mm. A bearing 3 (see FIG. 2 ) as a supporting member of the heating roller 1 is made of steel as a magnetic material. The distance between the bearing 3 and the back iron core 9 is 10 mm, which is larger than the distance between the back iron core 9 and the heating roller 1 .

Other structures are the same as those of the above-mentioned first embodiment.

Hereinafter, the operation of the fixing device configured as described above will be described.

By providing the back iron core 9, the inductance of the exciting coil 5 can be increased, thereby improving the electromagnetic coupling between the exciting coil 5 and the heating roller 1, and increasing R in the equivalent circuit of FIG. 4 . Therefore, even with the same coil current, a larger power can be input to the heating roller 1 . Therefore, an inexpensive excitation circuit 6 with a low withstand current and a withstand voltage can be used, and a fixing device with a short heating time can be realized.

In addition, as shown by the dotted line M in FIG. 5 , since all the magnetic flux on the back side of the field coil 5 passes through the inside of the back core 9 , it is possible to prevent the magnetic flux from leaking backward. As a result, heat generation due to electromagnetic induction of surrounding conductive members can be prevented, and unnecessary radiation of electromagnetic waves can be prevented.

Further, since the coiled wire bundles do not overlap each other, all the wire bundles of the exciting coil 5 are brought close to the heating roller 1 . Therefore, the magnetic flux generated by the coil current can be transmitted to the heat generating roller 1 with higher efficiency.

In this embodiment, since the exciting coil 5 and the back core 9 are provided outside the heating roller 1 (heating part), it is possible to prevent the heating of the exciting coil 5 and the like due to the influence of the temperature of the heating part. Therefore, the heat generation amount can be kept stable. In particular, since the exciting coil 5 and the back iron core 9 with a cross-sectional area larger than the cross-sectional area of the plane perpendicular to the rotating shaft inside the heating roller 1 are used, the heating roller 1 with a small heat capacity and the exciting coil 5 with a large number of turns can be combined. , An appropriate amount of ferrite (back iron core 9) is used in combination. Therefore, it is possible to input more power to the heat generating member with a predetermined coil current while suppressing the heat capacity of the fixing device.

In this embodiment, as described above, the lengths of the heating roller 1 in the direction of the rotation axis are in ascending order of the inner peripheral portion of the exciting coil 5, the outer peripheral portion of the exciting coil 5, the largest width of recording paper, the back surface Iron core 9, heating roller 1. In this way, the length of the outer peripheral portion of the exciting coil 5 along the direction of the rotation axis of the heating roller 1 is smaller than the width of the recording paper of the maximum width, and on the other hand, the length of the back iron core 9 along the rotation axis of the heating roller 1 is Therefore, even if the winding of the exciting coil 5 is uneven to some extent, the magnetic field reaching the heating roller 1 from the exciting coil 5 can be made uniform in the direction of the rotation axis. Therefore, the distribution of heat generation by the heat generation roller 1 on the portion where the recording paper passes can be made uniform. Thereby, the temperature distribution on the fixing portion can be made uniform, so that a stable fixing action can be obtained. In addition, since it is also possible to reduce the length of the heating roller 1 in the direction of the rotation axis of the heating roller 1 and the length of the exciting coil 5 along the direction of the rotation axis of the heating roller 1 while making the distribution of heat generation of the heating roller 1 uniform, the device can be realized. Miniaturization and cost reduction. Further, since the length of the back iron core 9 along the direction of the rotation axis of the heating roller 1 is shorter than the length of the direction of the rotation axis of the heating roller 1, the eddy current density of the end surface of the heating roller 1 can be prevented from becoming high and the Excessive heating of the end face.

In addition, as described above, the bearing 3 (refer to FIG. 2 ), which is a supporting member of the heating roller 1, is generally made of magnetic steel to ensure mechanical strength. Therefore, the magnetic flux generated by the coil current is easily attracted by the bearing 3, and will be generated when the magnetic flux passes through the bearing 3. Therefore, the transmission ratio of the electromagnetic energy to the heating roller 1 is reduced. At the same time, the temperature of the bearing 3 rises to shorten the life span. In this embodiment, as described above, the distance between the bearing 3 and the back iron core 9 is set to be greater than the distance between the back iron core 9 and the heating roller 1, so the magnetic flux passing through the back iron core 9 will not be blocked. The guide bearing 3 is thus made to pass through the heating roller 1 for the most part. Therefore, the electromagnetic energy supplied to the exciting coil 5 can be efficiently transmitted to the heat generating roller 1, and heat generation of the bearing 3 can be prevented.

The distance between the bearing 3 and the back iron core 9 (10 mm in this embodiment) should be greater than the distance between the back iron core 9 and the heating roller 1 (5.5 mm in this embodiment), preferably twice or more.

In addition, since the back iron core 9 has a uniform thickness, heat is not locally accumulated inside the back iron core 9 . Furthermore, since there is no hindrance to the heat dissipation from the outer periphery of the back iron core 9, it is possible to prevent a decrease in the saturation magnetic flux density of the back iron core 9 due to an increase in temperature due to heat storage, thereby preventing a sudden decrease in the magnetic permeability as a whole. . Therefore, it is possible to stably maintain the heating roller 1 at a predetermined temperature for a long period of time.

[third embodiment]

7 is a cross-sectional view showing a heating unit of a fixing device as an image heating device according to a third embodiment of the present invention. Members having the same functions as those in the second embodiment are denoted by the same reference numerals and their descriptions are omitted.

The difference between this embodiment and the above-mentioned second embodiment is that, as shown in FIG. "Counterpart F". Hereinafter, a portion of the back core 9 that faces the heating roller 1 via the exciting coil 5 is referred to as a "magnetic conduction portion T". In addition, the cross section of the back core 9 is formed in a shape in which the cylinder is cut at an angle of about 180 degrees in the axial direction.

In this case, the magnetic circuit can be formed by more ferrite (back core 9). Therefore, the portion of the air with low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heating roller 1 and the back core 9 . Therefore, the inductance of the exciting coil 5 is increased, and almost all of the magnetic flux generated by the coil current can be guided to the heating roller 1 . As a result, the electromagnetic coupling between the heating roller 1 and the exciting coil 5 is further improved, and R in the equivalent circuit of FIG. 4 is further increased. According to this configuration, even with the same coil current, a larger power can be input to the heat generating member.

In addition, the magnetic flux guided to the heating roller 1 from the back surface core 9 passes through the opposing portion F as shown by a dotted line M in FIG. 7 . The length of the opposing portion F in the direction of the rotation axis of the heating roller 1 is equal to the length of the back core 9 in the direction of the rotation axis of the heating roller 1 , and thus longer than the width of the recording paper. Therefore, it is possible to uniformly make the magnetic flux enter the portion through which the recording paper passes from the opposing portion F. FIG. Therefore, it is possible to uniformly heat the range required for the fixing of the heating roller 1 .

In addition, in this embodiment, the exciting coil 5 is arranged on the side of the back iron core 9 facing the heating roller 1, but as shown in FIG. The excitation coil 5 is formed by extending and winding in the axial direction and coiling in the circumferential direction of the heating roller 1 . In this case, the magnetic flux generated by the coil current not only passes through the side of the circumference of the heating roller 1 close to the excitation coil 5 but also passes through the side of the pressure roller (dotted line M' in the figure). As a result, since the entire circumference of the heating roller 1 is heated, the overall heating value can be increased even with the same coil current. In addition, since the cross-sectional area through which the magnetic flux passes increases, even if more magnetic flux passes through the heating roller 1, the saturation magnetic flux density of the heating roller 1 will not be exceeded. Therefore, since the magnetic flux can be prevented from passing through the space other than the heating roller 1, the pair of heating rollers 1 can be heated by electromagnetic induction with higher efficiency.

[Fourth Embodiment]

9 is a sectional view showing an image forming apparatus using an image heating device as a fourth embodiment of the present invention as a fixing device, and FIG. 10A is a sectional view showing a fixing device as an image heating device according to a fourth embodiment of the present invention. 11 is a projection view showing the heating portion viewed from the direction of arrow G in FIG. 10A, and FIG. 12 is a cross-sectional view of the heating portion on a plane including the rotation axis of the heating roller and the center of the exciting coil.

In FIG. 9, 11 is an electrophotographic photoreceptor (hereinafter referred to as "photosensitive drum"). The photosensitive drum 11 is driven to rotate at a predetermined peripheral speed in the direction of the arrow, and the surface of the photosensitive drum 11 is uniformly charged by the charger 12 with a negative dark potential V0. 13 is a laser beam scanner, which outputs a laser beam 14 modulated according to time-series electrical digital pixel signals of image information input from an image reading device not shown in the figure or a host device such as a computer. The charged surface of the photosensitive drum 11 is scanned and exposed with the laser beam 14 . As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 11 is lowered to a bright potential VL, whereby an electrostatic latent image is formed. The latent image is developed by the negatively charged toner of the developing device 15, and becomes a visible image.

The developing device 15 includes a developing roller 16 that is driven to rotate. The developing roller 16 is arranged to face the photosensitive drum 11 and forms a thin layer of toner on its outer peripheral surface. On the developing roller 16, a developing bias whose absolute value is smaller than the dark potential V0 of the photosensitive drum 11 and greater than the bright potential VL is applied. Print to make a latent image into a visible image.

On the other hand, the recording paper 8 is supplied one by one from the paper feeding section 17, and is conveyed to the photosensitive drum 11 and the transfer roller 19 by a pair of registration rollers 18 at precise timing synchronized with the rotation of the photosensitive drum 11. the gap between the rollers. Next, the toner image on the photosensitive drum 11 is sequentially transferred onto the recording paper 8 by the transfer roller 19 to which a transfer bias is applied. The photosensitive drum 11 after the recording paper 8 has been separated is repeatedly used for the next image formation after the cleaning device 20 removes residues such as transfer residual toner on the surface.

21 is a fixing paper guide plate, and the movement of the transferred recording paper 8 to the fixing device 22 is guided by the fixing paper guide plate 21 . After the recording paper 8 is separated from the photosensitive drum 11 , it is transported to the fixing device 22 , and the toner image transferred on the recording paper 8 is fixed by the fixing device 22 . Reference numeral 23 denotes a paper discharge guide plate, and the recording paper 8 passing through the fixing device 22 is guided to the outside of the device by the paper discharge guide plate 23 . The above-mentioned fixing paper guide 21 and paper discharge guide 23 are made of resin such as ABS. In addition, the fixing paper guide 21 and the paper discharge guide 23 may be made of non-metallic materials such as aluminum. The recording paper 8 on which the toner image has been fixed is discharged onto the paper discharge tray 24 .

25 is the bottom plate of the device body, 26 is the top plate of the device body, and 27 is the body casing, and these components form an integral body to ensure the strength of the device body. These members use steel as a magnetic material as a base material and are made of galvanized materials.

28 is a cooling fan, and the cooling fan 28 generates air flow in the device. 29 is a coil cover as a shielding member made of a non-magnetic metal material such as aluminum, and the coil cover 29 is configured to cover the back core 9 of the exciting coil 5 (see FIG. 10A ).

Hereinafter, the fixing device as the image heating device of the present embodiment will be described in detail.

In FIG. 10A , the thin fixing belt 31 is an endless endless belt with a diameter of 50 mm and a thickness of 100 μm made of polyamide resin. The surface of the fixing belt 31 is covered with a 20 μm thick release layer (not shown) made of a fluorine-containing resin so as to have release properties. As the base material, in addition to heat-resistant polyamide resins and fluororesins, extremely thin metals such as nickel produced by electroforming can also be used. As the mold release layer, resins or rubbers having good mold release properties such as PTFE, PFA, FEP, silicone rubber, and fluororubber may be used alone or in combination. When the fixing belt 31 is used for fixing a monochrome image, it is sufficient to only ensure the releasability, but if the fixing belt 31 is used for fixing a color image, it is preferable to make it elastic. , must further form a thick rubber layer.

The excitation coil 5 as an excitation device is formed by extending a bundle of 60 surface-insulated copper wires with an outer diameter of 0.2 mm in the direction of the rotation axis of the heating roller 1 and coiling it along the circumferential direction of the heating roller 1 . The cross-sectional area of the wire harness is about 7mm ² including the insulating sheath of the wire.

As shown in FIGS. 10A to 12 , the exciting coil 5 has a cross-sectional shape covering the fixing belt 31 wound around the heating roller 1 . In this case, the exciting width of the exciting coil 5 in the moving direction of the fixing belt 31 is smaller than the contact range (winding range) of the fixing belt 31 and the heating roller 1 . When the portion of the heat-generating roller 1 that is not deprived of heat by the fixing belt 31 generates heat, there is a problem that the heat-resistant temperature of the material of the fixing belt 31 is exceeded and the temperature of the heat-generating roller 1 is likely to rise. However, according to the configuration of the present embodiment, since only the area of the heating roller 1 that is in contact with the fixing belt 31 generates heat, the temperature of the heating roller 1 can be prevented from rising abnormally. In addition, the wire harness overlaps only at both ends of the exciting coil 5 (both ends in the direction of the rotation axis of the heating roller 1 ), and is coiled 9 times in close contact with each other along the circumferential direction of the heating roller 1 . Both end portions of the field coil 5 in the direction of the rotation axis of the heat generating roller 1 protrude in a state in which wire bundles are overlapped in two rows. That is, the exciting coil 5 is formed in a saddle-like shape as a whole. Therefore, it is possible to uniformly heat a wider range in the direction of the rotation axis of the heating roller 1 . In addition, since the distance between the bundle of wires that overlaps at both ends of the exciting coil 5 and the heating roller 1 is increased, eddy currents are not concentrated in this portion to cause excessive local temperature rise.

The back iron core 9 is composed of a C-shaped iron core 32 and a center iron core 33 . Seven C-shaped iron cores 32 have a width of 10 mm and are arranged at intervals of 25 mm along the rotation axis direction of the heating roller 1 . According to this structure, magnetic flux leaking to the outside can be captured. The central iron core 33 is located at the center of the excitation coil 5 and forms a shape protruding from the C-shaped iron core 32 . That is, the center iron core 33 constitutes one approach portion N to the heating roller 1 in the facing portion F of the rear iron core 9 (see FIG. 13 ). In addition, the cross-sectional area of the center iron core 33 is 3 mm×10 mm.

In addition, the central iron core 33 may be divided into several structurally along the direction of the rotation axis of the heating roller 1 for the convenience of ferrite processing. In addition, the center iron core 33 may be configured in a shape integrated with the C-shaped iron core 32 . Furthermore, it may be configured as a shape integrated with the C-shaped iron core 32 and divided into several pieces along the rotation axis direction of the heating roller 1 .

Reference numeral 34 is a heat insulating member having a thickness of 1 mm made of a resin having a high heat-resistant temperature such as PEEK material or PPS. At the end of the heat insulating member 34, there are provided both end holding portions 34a for holding raised portions of both end portions of the field coil 5 in the direction of the rotation axis of the heating roller 1. As shown in FIG. According to this structure, the protrusions at both ends of the exciting coil 5 can be prevented from collapsing, and at the same time, the position of the outer side of the exciting coil 5 can be restricted.

The material of the back core 9 is the same as that of the above-mentioned second embodiment. Except for the center iron core 33, the sectional shape of the back iron core 9 on the cross section including the C-shaped iron core 32 and the shape of the heating roller 1 are also the same as those of the second embodiment. Therefore, the sectional area of the exciting coil 5 including the back core 9 is larger than the sectional area of the inner surface of the heating roller 1 perpendicular to the rotation axis, which is the same as the second embodiment.

The AC current applied to the exciting coil 5 from the exciting circuit 6 (see FIG. 2 ) is the same as that in the above-mentioned first embodiment. According to the temperature signal measured by the temperature sensor provided on the surface of the fixing belt 31, the AC current applied to the excitation coil 5 is controlled so that the temperature of the fixing belt 31 reaches 190° C. which is a predetermined fixing temperature.

As shown in FIG. 10A , the fixing belt 31 is suspended at a predetermined tension on a low-thermal-conductivity fixing roller 35 with a diameter of 20 mm and a diameter of 20 mm made of silicone rubber having a surface of low hardness (JISA 30 degrees) and elastic foam. On the heating roller 1, it can rotate and move in the direction of arrow B. Here, at both ends of the heating roller 1, ribs (not shown) for preventing lateral oscillation of the fixing belt 31 are provided. In addition, the pressure roller 4 as a pressure means is in pressure contact with the fixing roller 35 via the fixing belt 31 , thereby forming a nip portion.

In this embodiment, A4-inch (210 mm wide) recording paper is used as the recording paper of the maximum width, the width of the fixing belt 31 is set to 230 mm, and the length of the heating roller 1 in the direction of the rotation axis is set to 260 mm. The length between the outermost ends of the back iron core 9 in the direction of the rotation axis of the heating roller 1 is set to 225 mm, and the length of the outer peripheral portion of the wound exciting coil 5 along the direction of the rotation axis of the heating roller 1 is set to be 245 mm, and the length of the heat insulating member 34 in the direction of the rotation axis of the heating roller 1 was set to 250 mm.

In this embodiment, the exciting coil 5, the back core 9, and the heating roller 1 are configured as described above, and the exciting coil 5 heats the heating roller 1 by electromagnetic induction. Hereinafter, the mechanism thereof will be described with reference to FIG. 13 .

As shown in FIG. 13 , the magnetic flux generated by the coil current enters the heating roller 1 from the facing portion F of the back iron core 9 . In this case, as indicated by a dotted line M in the figure, the magnetic flux generated by the coil current penetrates the heating roller 1 in the circumferential direction due to the magnetism of the heating roller 1 . Then, the magnetic flux forms a large circuit from the center core 33 , which is the portion N close to the heat-generating roller 1 of the back core 9 , via the magnetic conduction portion T, and repeatedly generates and disappears. The induced current generated by the change of the magnetic flux generates Joule heat, which is the same as that of the first embodiment described above.

In this embodiment, as shown in FIG. 11 , a plurality of narrow C-shaped iron cores 32 are arranged at equal intervals along the direction of the rotation axis of the heating roller 1 . The magnetic flux flowing in the circumferential direction is concentrated in the portion of the C-shaped cores 32 and hardly flows through the air between the adjacent C-shaped cores 32 . Therefore, the magnetic flux entering the heating roller 1 tends to concentrate on the portion where the C-shaped iron core 32 exists. Therefore, the part of the heating roller 1 facing the C-shaped iron core 32 is more likely to generate heat. Continuously arranged in the direction of the rotation axis, so the magnetic flux entering the heating roller 1 from the opposite part F of the C-shaped iron core 32 also flows along the direction of the rotation axis in the heating roller 1, thereby making the distribution uniform. Therefore, the unevenness of the heat generation amount of the heat generating roller 1 can be alleviated.

The function of guiding the magnetic flux of the magnetic conduction part T from the facing part F of the C-shaped iron core 32 to the other facing part F is not directly related to the incident distribution of the magnetic flux to the heating roller 1 . Therefore, it is very effective to optimize the shape of the back core 9 by configuring the magnetically permeable part T and the facing part F separately. The magnetically conductive part T is not necessarily required to be uniform in the axial direction, and it is only necessary to make the opposite part F as uniform as possible in the axial direction.

Since the approach portion N to the heating roller 1 is provided by making the center iron core 33 a shape protruding from the C-shaped iron core 32 , the magnetic circuit can be constituted by more ferrite. Therefore, the air part with low magnetic permeability through which the magnetic flux generated by the coil current passes is only a narrow gap part between the heating roller 1 and the back core 9 . Therefore, the inductance of the exciting coil 5 is further increased, and the magnetic flux generated by the coil current can be guided to the heating roller 1 more, thereby improving the electromagnetic coupling between the heating roller 1 and the exciting coil 5 . According to this configuration, even with the same coil current, a larger power can be input to the heat generating member. In particular, since the magnetic flux generated by the coil current must pass through the center portion where the excitation coil 5 is wound, by providing the proximity portion N consisting of the central iron core 33 continuous in the direction of the rotation axis of the heating roller 1 at this portion, The magnetic flux generated by the coil current can be efficiently guided to the heating roller 1 .

The cross-sectional area of the C-shaped iron core 32 in the circumferential direction of the magnetic transmission part T is set so that the density of the magnetic flux derived from the exciting coil 5 does not exceed the maximum magnetic flux density of the material used. This magnetic flux density is set to about 80% of the saturation magnetic flux density of ferrite at the maximum. The ratio of the maximum magnetic flux density to the saturation magnetic flux density only needs to be 100% or less, but it is practically preferable to set it within a range of 50% to 85%. If the ratio is too high, the maximum magnetic flux density may exceed the saturation magnetic flux density due to environmental or component variations. In this case, the magnetic flux will flow to the back of the back iron core 9, thereby heating the components behind. Conversely, if the ratio is too low, it will be necessary to use more expensive ferrite than necessary, which will increase the cost of the device.

In addition, since a plurality of C-shaped iron cores 32 are arranged at large intervals along the rotation axis direction of heating roller 1 with a uniform width, heat is not stored in back surface iron core 9 and exciting coil 5 . Further, since there is no hindrance to the heat dissipation from the outer periphery of the back iron core 9 and the field coil 5, it is possible to prevent the temperature rise caused by heat storage from reducing the saturation magnetic flux density of the ferrite of the back iron core 9, thereby preventing A drastic decrease in the magnetic permeability as a whole. In addition, it is also possible to prevent a short circuit between the wires due to melting of the insulating sheath of the wires. Therefore, it is possible to stably maintain the heating roller 1 at a predetermined temperature for a long period of time.

In addition, since both ends of the wire harness 5 in the direction of the rotation axis of the heating roller 1 are overlapped, the excitation coil 5 can be uniformly extended in the direction of the rotation axis of the heating roller 1 over a wider range. On the contrary, since the width of both end portions of the exciting coil 5 in the direction of the rotation axis of the heat generating roller 1 can be reduced while ensuring a uniform heat generating region, the overall size of the device can be reduced.

In addition, in this embodiment, the recording paper with the largest width, the back iron core 9, the fixing belt 31, the outer peripheral portion of the exciting coil 5, the heat insulating material, and the heat insulating roller 1 are listed in descending order of the length of the heating roller 1 in the direction of the rotation axis. Component 34, heating roller 1. That is, the length of the heat insulating member 34 is longer than the lengths of the field coil 5 and the back core 9 . Furthermore, since back iron core 9 faces heating roller 1 and fixing belt 31 through heat insulating member 34 , even when back iron core 9 is brought close to heating roller 1 , the temperature of back iron core 9 can be prevented from rising. In addition, it is also possible to prevent the cooling air flow from coming into contact with the fixing belt 31 to cool the fixing belt 31 .

In addition, since the width of the fixing belt 31 is longer than the length of the rear iron core 9 along the rotation axis direction of the heating roller 1, the heating roller 1 at the portion not in contact with the fixing belt 31 will not be heated, so that this portion can be prevented from being heated. The temperature of the heating roller 1 rises excessively.

In addition, by providing the coil cover 29, a small amount of magnetic flux leaking to the back of the back core 9 and high-frequency electromagnetic waves generated from the exciting coil 5 can be prevented from propagating inside and outside the device. As a result, malfunctions of circuits inside and outside the device due to electromagnetic noise can be prevented.

Further, since the space surrounded by the coil cover 29 and the heat insulating member 34 is used as a ventilation path to allow the airflow from the cooling fan to flow, the heating roller 1 and the fixing belt 31 are not cooled, but only the exciting coil 5 and the back surface are cooled. The iron core 9 is cooled.

In addition, the bottom plate 25, the top plate 26, and the main body casing 27 of the device main body constitute the magnetic members of the device, and the nearest distance from the excitation coil 5 is set to 20 mm. According to this structure, it is possible to prevent the magnetic flux passing through the inside of the back core 9 from radiating to the outside of the exciting coil 5 from a position other than the facing portion F and entering into magnetic members such as the main body casing 27. The components of the device are heated unnecessarily, and the electromagnetic energy supplied to the exciting coil 5 can be efficiently injected into the heating roller 1 . Though the minimum value of the distance between the exciting coil 5 and the magnetic components such as the main body casing 27 is set to 20mm, the distance between the magnetic components such as the back iron core 9 and the main body casing 27 is greater than the distance between the back iron core 9 and the heating roller 1 It is preferably at least 1.5 times the interval, so that the magnetic flux can be prevented from leaking to the back surface of the exciting coil 5 . In this embodiment, since the fixing paper guide 21 and paper discharge guide 23 that must be close to the fixing device 22 are made of resin, a sufficient distance can be easily ensured between the back core 9 and other magnetic members.

In addition, in this embodiment, the heating roller 1 (heating part) is provided inside the fixing belt 31, and the excitation coil 5 and the back iron core 9 are provided outside the fixing belt 31, so that it is possible to prevent the excitation coil 5, etc. The temperature rises under the influence of the temperature of the heat generating part. Therefore, the heat generation amount can be kept stable. In particular, since the excitation coil 5 and the back iron core 9 whose cross-sectional area is larger than the cross-sectional area of the plane perpendicular to the rotating shaft inside the heating roller 1 are used, the heating roller 1 with a small heat capacity and the excitation coil with a large number of turns can be used. The coil 5 is used in combination with an appropriate amount of ferrite (back iron core 9). Therefore, it is possible to input more power to the heat generating member with a predetermined coil current while suppressing the heat capacity of the fixing device 22 . As a result, an inexpensive excitation circuit 6 (see FIG. 2 ) with low withstand current and withstand voltage can be used, and a fixing device 22 with a short heating time can be realized. In the present embodiment, the AC current from the excitation circuit 6 can input a power of 800W to the heating roller 1 at an effective value voltage of 140V (voltage amplitude: 500V) and an effective value current of 22A (peak current: 55A).

The exciting coil 5 located outside the heating roller 1 heats the surface of the heating roller 1 , so the fixing belt 31 can be in contact with the part of the heating roller 1 that generates the most heat. Therefore, the largest heat generating portion constitutes a heat transfer portion to the fixing belt 31 , so that generated heat can be transferred to the fixing belt 31 without heat conduction in the heat generating roller 1 . In this way, since the distance for heat transfer is small, quick-response control can be performed for temperature changes of the fixing belt 31 .

A temperature sensor (not shown) is provided near a position where the heating roller 1 passes through the contact portion with the fixing belt 31 . By controlling the temperature of this portion to a constant value, the temperature of the fixing belt 31 when it enters the nip portion between the fixing roller 35 and the pressure roller 4 can be kept constant at all times. As a result, even when a plurality of consecutive sheets of recording paper 8 are fixed, the fixing can be performed stably.

In addition, since the exciting coil 5 and the back iron core 9 cover almost half of the circumference of the heating roller 1 , the entire contact portion between the fixing belt 31 and the heating roller 1 can be heated. Therefore, the heating energy transferred from the exciting coil 5 by electromagnetic induction can be more transferred to the fixing belt 31 .

In addition, in this embodiment, the material, thickness, etc. of the heating roller 1 and the fixing belt 31 can be independently set. Therefore, as the material and thickness of the heating roller 1 , the most suitable material and thickness for electromagnetic induction heating of the exciting coil 5 can be selected. On the other hand, as the material and thickness of the fixing belt 31 , the most suitable material and thickness for fixing can be selected.

In this embodiment, in order to shorten the heating time, the heat capacity of the fixing belt 31 is set as small as possible, and the heat capacity of the heating roller 1 is set to a small value by reducing the thickness and outer diameter. Therefore, at an input power of 800W, the specified temperature can be reached within about 15 seconds from the temperature rise for fixing.

In addition, in the present embodiment, the C-shaped iron cores 32 are arranged at equal intervals along the rotation axis direction of the heating roller 1, but the intervals do not necessarily have to be equal. The interval can be adjusted according to the heat dissipation conditions and the presence or absence of contact members such as temperature sensors, so that the heat distribution can be freely designed to make the temperature distribution uniform.

In addition, in this embodiment, the back iron core 9 includes a plurality of C-shaped iron cores 32 made of ferrite and uniform in thickness arranged at equal intervals along the direction of the rotation axis of the heating roller 1 and also made of ferrite. The central core 33, but not necessarily limited to this structure. For example, a plurality of holes may be provided in the integral back core 9 continuous in the direction of the rotation axis of the heating roller 1 . Alternatively, a plurality of members made of ferrite may be independently distributed on the back surface of the field coil 5 .

In addition, in this embodiment, the base material of the fixing belt 31 is made of resin, but instead of resin, it may be made of ferromagnetic metal such as nickel. In this case, part of the heat generated by electromagnetic induction is generated in the fixing belt 31 to heat the fixing belt 31 itself, so that electromagnetic energy can be transmitted to the fixing belt 31 more efficiently.

In addition, in this embodiment, the bottom plate 25 of the device body, the top plate 26 of the device body, and the body casing 27 are made of magnetic materials, but they may be made of resin materials instead of magnetic materials. In this case, the members ensuring the strength of the device body do not have any influence on the lines of magnetic force, so these members can be arranged close to the back core 9 . As a result, overall miniaturization of the device can be achieved.

In addition, in this embodiment, both ends of the heating roller 1 are structurally supported by the bearings 3, but as shown in FIG. Flanges 36 made of thermal resin and a center shaft 37 passing through the two flanges 36 are supported. According to such a structure, leakage of heat or magnetic flux from both ends of the heating roller 1 can be suppressed.

In addition, in this embodiment, the excitation width of the exciting coil 5 in the moving direction of the fixing belt 31 is set to be smaller than the contact range (winding range) between the fixing belt 31 and the heating roller 1, but it is not necessarily limited to this. kind of structure. For example, as shown in FIG. 10B , the excitation width of the exciting coil 5 in the moving direction of the fixing belt 31 may also be set from the contact range between the fixing belt 31 and the heating roller 1 (winding range: boundary line b) to the fixing roller 35. side extended. According to this structure, compared with the structure of Fig. 10A, the heat generation of the heat generating roller 1 can be made to reach a wider range (range a in Fig. 10B), so a sufficient heat generation can be obtained even with a small coil current. Also, in this case, after the wire harness is coiled to form the excitation coil 5, the cross section of the coiled wire harness is made substantially square by compressing the excitation coil 5, and the wire harnesses are further brought into closer contact with each other. According to this structure, the volume occupied by the exciting coil 5 can be reduced, so that the exciting coil 5 can be wound more times. As a result, the current density of the coil current is increased, so the density of the eddy current generated in the heating roller 1 is also increased, thereby increasing the heat generation amount. Therefore, it is possible to reduce the required coil current or reduce the diameter of the heat generating roller 1 . Further, since the distance between the back iron core 9 and the exciting coil 5 can be increased, the heat dissipation of the back iron core 9 is facilitated, thereby preventing the temperature rise of the back iron core 9 . In addition, since the wire harnesses are brought closer to each other, the bonding between the wire harnesses is made stronger, thereby enabling the exciting coil 5 to maintain its single-body shape. Therefore, the assembly process of the fixing device 22 is simplified.

[Fifth Embodiment]

15 is a cross-sectional view showing a heat generating unit of a fixing device as an image heating device according to a fifth embodiment of the present invention. Members having the same functions as those in the fourth embodiment are denoted by the same reference numerals and their descriptions are omitted.

As shown in FIG. 15 , in this embodiment, unlike the above-mentioned fourth embodiment, the portion facing the heating roller 1 of the facing portion F of the back core 9 is formed in a convex shape closer to the heating roller 1 .

Other structures are the same as those of the above-mentioned fourth embodiment.

According to the present embodiment, the magnetic circuit can basically be entirely made of ferrite. Therefore, the portion of the air with low magnetic permeability through which the magnetic flux generated by the coil current passes is only the narrow gap portion between the heating roller 1 and the back core 9 . Therefore, the inductance of the exciting coil 5 is further increased, and almost all of the magnetic flux generated by the coil current can be guided to the heating roller 1 . As a result, the electromagnetic coupling between the heating roller 1 and the exciting coil 5 is improved, and R in the equivalent circuit of FIG. 4 is increased. Therefore, even with the same coil current, a larger power can be input to the heat generating member. In this embodiment, an electric power of 800 W is applied to the heating roller 1 with an effective value current of 20 A (peak current of 50 A).

In addition, since the back core 9 faces the heating roller 1 and the fixing belt 31 through the heat insulating member 34 , even when the back core 9 is brought close to the heating roller 1 , the temperature of the back core 9 can be prevented from rising.

[Sixth Embodiment]

16 is a cross-sectional view showing a heat generating portion of a fixing device as an image heating device according to a sixth embodiment of the present invention, and FIG. 17 is a projected view of the heat generating portion viewed from the direction of arrow A in FIG. 16 . In addition, the same code|symbol is attached|subjected to the member whose function is the same as said 5th Embodiment, and the description is abbreviate|omitted.

As shown in FIGS. 16 and 17 , in this embodiment, unlike the above-mentioned fifth embodiment, as the facing portion F of the back iron core 9 , a facing iron core continuous in the direction of the rotation axis of the heating roller 1 is provided. Core 38. In addition, A4 size (210 mm wide) recording paper was used as the recording paper of the maximum width, and the length in the direction of the rotation axis of the heating roller 1 was set to 240 mm, and the C-shaped iron core 32 other than the opposing iron core 38 was placed The length between the outermost ends in the direction of the rotation axis of the heating roller 1 was set to 200 mm, the length of the inner peripheral portion of the exciting coil 5 in the direction of the rotation axis of the heating roller 1 was set to 210 mm, and the opposing iron core 38 The length in the direction of the rotation axis of the heating roller 1 was set to 220 mm.

Other structures are the same as those of the above-mentioned fifth embodiment.

In this embodiment, the length of the magnetic conduction portion T of the exciting coil 5 along the rotation axis direction of the heating roller 1 (the length of the inner peripheral portion of the exciting coil 5 along the rotation axis direction of the heating roller 1 ) is made smaller than the maximum width. The width of the recording paper, on the other hand, makes the length of the opposing portion F of the back core 9 in the direction of the rotation axis of the heating roller 1 (the length of the opposing iron core 38 in the direction of the rotation axis of the heating roller 1) larger than the maximum Therefore, even if gaps are provided on the back iron core 9 of the magnetic conduction part T and the distribution is uneven, the magnetic field reaching the heating roller 1 from the opposing part F can be made uniform in the direction of the rotation axis . According to this structure, the heat distribution of the heating roller 1 on the recording paper passing portion can be made uniform while reducing the back iron core 9 of the magnetic conducting portion T, so that the temperature on the fixing portion becomes uniform. Therefore, a stable fixing effect can be obtained. In addition, the number of rear iron cores 9 of the magnetic permeable part T can be reduced while making the heat distribution of the heating roller 1 uniform, so that the size of the device can be reduced and the cost can be reduced.

In addition, in this embodiment, the opposing iron core 38 which is the opposing part F of the back iron core 9 is provided continuously in the rotation axis direction of the heating roller 1, but it is not necessarily limited to this structure. For example, as shown in FIG. 18 , opposing iron core 38 may be divided and back surface iron core 9 may be configured such that opposing portion F has a wider width in the direction of the rotation axis of heating roller 1 than magnetic-conducting portion T. According to this configuration, since the number of rear iron cores 9 in the opposing portion F is reduced, the weight of the rear iron cores 9 can be reduced. In addition, since the surface area of the facing portion F where the temperature tends to rise can be increased, cooling can be promoted by heat dissipation.

[Seventh Embodiment]

19 is a cross-sectional view showing a heat generating portion of a fixing device as an image heating device according to a seventh embodiment of the present invention, and FIG. 20 is a projected view of the heat generating portion viewed from the direction of arrow A in FIG. 19 . In addition, the same code|symbol is attached|subjected to the member whose function is the same as said 5th Embodiment, and the description is abbreviate|omitted.

As shown in FIGS. 19 and 20 , in this embodiment, unlike the above-mentioned fifth embodiment, the C-shaped iron core 38 is formed in a shape covering a range of about 90 degrees with respect to the direction of the rotation axis of the heating roller 1 . The C-shaped iron cores 38a and 38b whose installation directions are changed are alternately arranged in the direction of the rotation axis of the heating roller 1 . That is, the opposing portion F of the back core 9 is arranged at an asymmetrical position with respect to the center line of the exciting coil 5 in the direction of the rotation axis of the heating roller 1 .

In the above-mentioned fifth embodiment, the same circumferential portion of the heating roller 1 is rotated relative to the opposing portion F of the two C-shaped iron cores 32, so the opposing portion of the heating roller 1 to the C-shaped iron core 32 is The calorific value of the parts other than the difference is very large, so it is easy to cause a large unevenness in the temperature distribution. In this embodiment, however, the same circumferential portion of the heating roller 1 rotates with respect to the facing portion F of one part of the C-shaped iron core 38, so the portion facing the C-shaped iron core 38 of the heating roller 1 and other parts The calorific value will not produce a large deviation. In addition, the volume of the back iron core 9 used can be reduced, and at the same time, the track interval of the portion facing the facing portion F of the back iron core 9 on the surface of the heating roller 1 when the heating roller 1 rotates can be shortened. That is, if the length of the opposing portion F in the direction of the rotation axis of the heating roller 1 is set to 220 mm as in the sixth embodiment, five C-shaped iron cores 38 are arranged side by side in a row with a pitch of 44 mm. Since the two rows of C-shaped iron cores 38a, 38b are arranged in a staggered manner, when the heating roller 1 rotates, the distance between the parts facing the staggered facing part F is only half of the distance on the surface of the heating roller 1. 22mm. Therefore, in the present embodiment, there is no large difference in the amount of heat generated between the portion facing the C-shaped iron core 38 and other portions of the heat generating roller 1, and since the distance between the facing portion F where heat is concentrated is reduced, Therefore, the heat distribution can be made uniform. As a result, the temperature unevenness of the heating roller 1 and the fixing belt can be suppressed.

In addition, since the number of rear iron cores 9 in the facing portion F is reduced, the weight of the rear iron core 9 can be reduced. Further, since it is possible to increase the surface area of the facing portion F where the temperature tends to rise, cooling can be promoted by heat dissipation. Therefore, heat is not locally accumulated inside the back core 9 . According to this configuration, it is possible to prevent a decrease in the saturation magnetic flux density of the back core 9 due to a temperature rise due to heat storage, and thus prevent a sudden decrease in the magnetic permeability as a whole. As a result, the heating roller 1 can be stably maintained at a predetermined temperature for a long period of time.

[Eighth Embodiment]

21 is a cross-sectional view showing a heat generating portion of a fixing device as an image heating apparatus according to an eighth embodiment of the present invention, and FIG. 22 is a projected view of the heat generating portion viewed from the direction of arrow A in FIG. 21 . In addition, the same code|symbol is attached|subjected to the member whose function is the same as that of the said 4th Embodiment, and the description is abbreviate|omitted.

As shown in FIGS. 19 and 20 , this embodiment differs from the above-mentioned fourth embodiment in that the interval between adjacent C-shaped iron cores 32 is changed along the rotation axis direction of the heating roller 1 . In FIG. 22, d1=21mm, d2=21mm, and d3=18mm. Therefore, the relationship of d1=d2>d3 is established. That is, at the end of the heating roller 1, the distance between the adjacent back surface cores 9 is narrowed. In addition, a 5 mm square member 40 made of ferrite was provided at the same position as the temperature sensor 7 for measuring the temperature in contact with the surface of the fixing belt.

However, when the intervals between adjacent back iron cores 9 are equalized, the temperatures of the ends of the heating roller 1 and the fixing belt may decrease. Furthermore, the unevenness in temperature in the direction of the rotation axis of the heating roller 1 leads to defective fixing.

In this embodiment, as described above, the distance between the adjacent back cores 9 is made narrower than the distance between the central parts at the end of the heating roller 1, so that the magnetic flux generated by the coil current flows at the end of the heating roller 1. The central part is correspondingly more than the central part. Therefore, the amount of heat generated at the end portion of the heat generating roller 1 increases. On the other hand, at the end of the heat-generating roller 1, due to heat conduction to bearings and the like, more heat tends to be taken away than at the center. Therefore, these two effects cancel each other out, that is, the temperature distribution of the heating roller 1 and the fixing belt becomes uniform, so that fixing failure can be prevented.

In addition, since the temperature sensor 7 is in contact with the surface of the fixing belt, heat may be taken from the fixing belt by the temperature sensor 7 . Therefore, only the portion in contact with the temperature sensor 7 tends to become lower in temperature in the circumferential direction of the fixing belt.

In this embodiment, as described above, since the member 40 made of ferrite is provided in this part, it is easier to concentrate the magnetic flux in this part than in other parts. Therefore, the amount of heat generated on this part is increased compared to other parts. According to this structure, the heat taken away by the temperature sensor 7 can be compensated, and the temperature distribution on the surface of the fixing belt can be made uniform, so that fixing failure can be prevented.

In addition, in the present embodiment, a uniform temperature distribution can be obtained by narrowing the distance between the adjacent back surface iron cores 9 at the end of the heating roller 1 , but it is not necessarily limited to this structure. For example, by making the intervals between adjacent back iron cores 9 equal and making the width of the back iron core 9 positioned at the end of the heating roller 1 larger than the width of the back surface iron core 9 positioned at the center of the heating roller 1, uniformity can also be obtained. temperature distribution. Also, for example, by making the intervals between adjacent back iron cores 9 equal and arranging members made of ferrite independently in the range close to the end of the heating roller 1 , a uniform temperature distribution can be similarly obtained.

[Ninth Embodiment]

23 is a projected view showing a heating portion of a fixing device as an image heating device according to a ninth embodiment of the present invention, and FIG. 24 is a cross-sectional view showing a heating portion of a fixing device as an image heating device according to a ninth embodiment of the present invention. In addition, the same code|symbol is attached|subjected to the member whose function is the same as that of the said 4th Embodiment, and the description is abbreviate|omitted.

As shown in Fig. 23 and Fig. 24, in this embodiment, unlike the above-mentioned fourth embodiment, the C-shaped iron core of the back iron core 9 located near the end of the heating roller 1 is movably held. 32a, 32b. Further, in this embodiment, the recording paper of A3 size (297mm wide) is used as the recording paper of maximum width, and the C-shaped iron core 32a is located outside the area where the recording paper of A4 size (210mm wide) passes. For recording paper of approximately A4 size, the C-shaped iron core 32a is moved in the radial direction of the heating roller 1 and separated from the heating roller 1 as shown by the dotted line 32a' in FIG. 24 . When using a recording paper having a smaller size, the C-shaped iron core 32b positioned inside the C-shaped iron core 32a is also moved in the same manner.

Other structures are the same as those of the above-mentioned fourth embodiment.

In this embodiment, the C-shaped iron core 32 outside the area where the recording paper passes is moved to increase the air portion with low magnetic permeability through which the magnetic flux generated by the coil current passes. Therefore, the magnetic flux in this part is reduced, and the heat generation amount of the heat-generating roller 1 in the opposite part is reduced. According to this structure, it is possible to prevent excessive temperature rise in the range where the recording paper does not pass, and to prevent the temperature of components such as the fixing belt and the bearing at the end from exceeding the heat-resistant temperature. Further, even if the large-size recording paper is used after the small-size recording paper is continuously used, the temperature of the fixing portion remains normal, so the occurrence of thermal deviation can be prevented. Therefore, recording paper of large size can be used immediately after recording paper of small size is used.

In addition, in the above-mentioned embodiment, the case where only the C-shaped iron core 32 is movable has been described as an example, but it is not necessarily limited to such a structure. For example, as shown in Fig. 25, the same effect can be obtained by integrating the C-shaped iron core 32a with the center iron core 33 and moving it as shown by the dotted line 9'.

In addition, in each of the above-mentioned embodiments, the exciting coil 5 is in contact with the back core 9 , but even when a gap of about 1 mm is provided therebetween, the same effect can be obtained. By providing such a gap between the exciting coil 5 and the back iron core 9 , it is possible to prevent the temperature rise of the contact portion between the exciting coil 5 and the back iron core 9 .

In addition, in each of the above-mentioned embodiments, the heat insulating member 34 is in contact with the exciting coil 5, but it is not necessarily limited to such a structure. For example, the heat insulating member 34 may be structurally separated from the exciting coil 5 , and the airflow may pass between them, so that the heat dissipation of the exciting coil 5 can be further promoted.

The structures of the exciting coil 5, the back core 9, and the heating roller 1 are not limited to the structures of the above-mentioned embodiments. In the equivalent circuit of FIG. 4, if the inductance L is 10 μH to 50 μH, and the resistance component R is 0.5Ω to 5Ω, there is no practical problem.

In addition, in each of the above-mentioned embodiments, the case where excitation is performed from the outside of the heating roller 1 (heating member) by the exciting coil 5 is exemplified, but it may also be configured to be excited from the inside of the heating roller 1 (heating member).

[Tenth Embodiment]

Fig. 26 is a sectional view showing an image forming apparatus using an image heating device as a tenth embodiment of the present invention as a fixing device.

In FIG. 26, 101 is an electrophotographic photoreceptor (hereinafter referred to as "photosensitive drum"). The photosensitive drum 101 is driven to rotate at a predetermined peripheral speed in the direction of the arrow, and the surface of the photosensitive drum 101 is uniformly charged with a negative dark potential V0 by the charger 102 .

103 is a laser beam scanner that outputs a laser beam modulated according to time-series electrical digital pixel signals of image information input from a main device such as an image reading device or a computer not shown in the figure. The surface of the photosensitive drum 101 uniformly charged as described above is scanned and exposed by the laser beam. As a result, the absolute value of the potential of the exposed portion of the photosensitive drum 101 is lowered to a bright potential VL, whereby an electrostatic latent image is formed. The latent image is developed by the negatively charged toner in the developing unit 104 to become a visible image.

The developing device 104 includes a developing roller 104a that is driven to rotate. The developing roller 104a is arranged to face the photosensitive drum 101, and forms a thin layer of toner on its outer peripheral surface. On the developing roller 104a, a developing bias whose absolute value is smaller than the dark potential V0 of the photosensitive drum 101 and larger than the bright potential VL is applied. Print to make a latent image into a visible image.

On the other hand, the recording paper 115 is supplied one by one from the paper feeding section 110, and is conveyed to the photosensitive drum 101 and the transfer unit by a pair of registration rollers 111, 112 at precise timing synchronized with the rotation of the photosensitive drum 101. The nip between the rollers 113. Next, the toner image on the photosensitive drum 101 is sequentially transferred onto the recording paper 115 by the transfer roller 113 to which a transfer bias is applied. The recording paper 115 that has passed through the transfer unit is separated from the photosensitive drum 101 and then sent to the fixing device 116 , whereby the toner image transferred on the recording paper 115 is fixed. The recording paper 115 on which the toner image has been fixed is discharged onto a paper discharge tray 117 .

The photosensitive drum 101 after the recording paper 115 is separated is repeatedly used for the next image formation after the cleaning device 5 removes residues such as transfer residual toner on the surface.

Hereinafter, the fixing device as the image heating device of the present embodiment will be described in detail.

27 is a sectional view showing a fixing device as an image heating device according to a tenth embodiment of the present invention; FIG. 28 is a sectional view showing a fixing belt used in the fixing device according to a tenth embodiment of the present invention; Fig. 30 is a sectional view showing a heating roller used in the fixing device according to the tenth embodiment of the present invention.

In FIGS. 27 and 28, the thin fixing belt 120 is an endless endless belt with a diameter of 50 mm and a thickness of 50 μm, in which the base material 121 is made of polyamide resin. The surface of the fixing belt 120 is covered with a release layer 122 made of a fluororesin with a thickness of 5 μm so as to have release properties. As the material of the base material 121, in addition to heat-resistant polyamide resins and fluorine-containing resins, extremely thin metals such as nickel produced by electroforming can be used. As the mold release layer 122 , resins or rubbers having good mold release properties, such as PTFE, PFA, FEP, silicone rubber, and fluororubber, may be used alone or in combination. When the fixing belt 120 is used for fixing monochromatic images, it is enough to ensure only the releasability, but if the fixing belt 120 is used for fixing color images, it is better to make it elastic. , must further form a thick rubber layer.

123 is an exciting coil as a heat generating device, and the exciting coil 123 has a cross-sectional shape covering the fixing belt 120 .

As shown in FIGS. 27 and 29 , a back iron core 124 made of ferrite is provided at the center and part of the back surface of the field coil 123 . As the material of the back iron core 124 , in addition to ferrite, materials with high magnetic permeability such as permalloy can also be used. In addition, the back surface core 124 on the back surface of the field coil 123 exists only in a part, so that it can capture the magnetic flux leaking to the outside. An alternating current of 30 kHz is applied from the exciting circuit 125 to the exciting coil 123 . Hereinafter, the alternating current applied to the exciting coil 123 is also referred to as "excitation current".

As shown in FIG. 27 , the fixing belt 120 is suspended at a predetermined tension on a low thermally conductive fixing roller 143 with a diameter of 20 mm made of silicone rubber having a low hardness (JISA 30 degrees) on the surface, which is an elastic foam body, and a rear roller 143 . The heat-generating roller 144 with a diameter of 30mm made of the materials mentioned above can be rotated and moved in the direction of arrow B. The heating roller 144 is made of a magnetic material with a thickness of 0.4 mm and a composition of an iron-nickel-chromium alloy, and its Curie point is adjusted to 220° C. according to the amount of nickel mixed in the material. Inside the heating roller 144, a conductive roller 45 made of aluminum and having a thickness of 0.8 mm is provided as a conductive member with a gap of 0.5 mm from the heating roller 144. As shown in FIG.

As shown in FIGS. 27 and 30, the heating roller 144 and the conductive roller 145 are supported at both ends by flanges 146 and 147 made of heat-resistant resin with low thermal conductivity such as phenolic resin. In addition, since the conductive roller 145 is disposed in a heat-insulated manner from the heat-generating roller 144 , heat generated by the heat-generating roller 144 is hardly transmitted to the conductive roller 145 . The heating roller 144 and the conductive roller 145 are driven to rotate around the shaft 148 by the driving device of the device body not shown in the figure.

In FIG. 27, a pressure roller 149 as a pressure means is made of silicone rubber with a hardness of JIS A65. Further, the pressure roller 149 is in pressure contact with the fixing roller 43 via the fixing belt 120 , thereby forming a nip portion. Here, the pressure roller 149 is provided slightly upstream in the transport direction of the recording paper 115 directly below the fixing roller 43 in the vertical direction. touch. The pressure roller 149 is supported so as to be rotatable around the metal shaft 150 as the fixing belt 120 rotates. As the material of the pressure roller 4, other heat-resistant resins or rubbers such as fluorine-containing rubber and fluorine-containing resin can also be used. In addition, it is preferable to cover the surface of the pressure roller 149 with resin or rubber such as PFA, PTFE, and FEP alone or in combination, so as to improve its wear resistance and mold releasability. In addition, in order to prevent heat loss, the pressure roller 149 is preferably made of a material with low thermal conductivity.

In this embodiment, by configuring the heating roller 144 as described above, the heating roller 144 can be provided with an automatic temperature control characteristic. Hereinafter, this action will be described with reference to FIGS. 31 and 32 .

In FIG. 31, when the temperature of the heating portion 144a of the heating roller 144 facing the exciting coil 123 is below the Curie point, as shown by the arrows D and D' in the figure, the magnetic flux generated by the exciting current will generate heat. Most of the magnetism of the roller 144 penetrates the inside of the heating roller 144 and is repeatedly generated and lost. The induced current generated by the change of the magnetic flux flows almost only on the surface of the heating roller 144 due to the skin effect, and Joule heat is generated on this part. When the heating portion 144a of the heating roller 144 approaches the Curie temperature, since the magnetism disappears, the magnetic flux is diverged to one side of the conductive roller 145 disposed inside the heating roller 144 as shown by arrows E and E′ in FIG. Therefore, most of the induced current flows out from the conductive roller 145 with low resistance. At this time, since the electric resistance of the conductive roller 145 is low, the generation of heat can be significantly reduced by limiting the current to a certain value. According to calculations, the depth of the part where the current of the skin effect flows is about 0.3 mm when the frequency of the excitation current is 30 kHz. If the thickness of the heating roller 144 is equal to or greater than the skin depth, most of the induced current can be generated in the heating roller 144 at a low temperature. If the frequency of the induced current is increased, the skin depth will be reduced, so a heat generating roller 144 with a small thickness can be used. However, when the frequency of the induced current is too high, the cost increases and the noise emitted to the outside increases.

In this embodiment, by configuring the heating roller 144 as described above, stable temperature control at approximately 190° C. can be realized.

In addition, in this embodiment, the two-layer structure of the heating roller 144 and the conductive roller 145 is adopted, but it is not necessarily limited to this structure. For example, a heating roller made of a single layer of magnetic material thicker than the skin depth may be used. In this case, when the Curie temperature is lower than the Curie temperature, the heat generation increases because the part through which the induced current flows is thin, and when the Curie point is exceeded, the induced current flows through almost the entire thickness of the magnetic body, so the resistance decreases, Thereby reducing the calorific value. Therefore, even with this structure, automatic temperature control characteristics can be obtained.

As mentioned above, if the thickness of the heating roller 144 is equal to or greater than the skin depth corresponding to the frequency of the excitation current applied to the excitation coil 123, a more significant effect of automatic temperature control can be obtained.

In addition, in this embodiment, aluminum is used as the material of the conductive roller 145, but metals having high conductivity such as copper other than aluminum may be used.

In addition, in this embodiment, an iron-nickel-chromium alloy is used as the material of the conductive roller 144, but the same effects can be obtained by using other alloys capable of setting the Curie temperature.

The fixing device constituted as above is installed in the image forming apparatus shown in FIG. 26, and the recording paper 115 on which the toner image has been transferred is moved from the direction of the arrow F so that the toner 135 is loaded on the recording paper 115 as shown in FIG. The toner image on the recording paper 115 is fixed by entering the fixing device with the face facing upward.

According to this embodiment, since the heating roller 144 itself has an automatic temperature control characteristic, it is possible to automatically perform temperature control so that the temperature is approximately close to the fixing temperature without raising the heating portion 144a to an abnormally high temperature. This control also works on the local temperature difference in the depth direction (rotation axis direction of the heating roller 144) shown in FIG. The passing portion reaches an abnormally high temperature, and even if a large-sized recording paper is used thereafter, no thermal deviation occurs.

In addition, the material, thickness, etc. of the heating roller 144 can be set independently of the material, thickness, etc. of the fixing belt 120 . Therefore, as the material and thickness of the heat-generating roller 144, the most suitable material and thickness can be selected so as to have automatic temperature control characteristics. In addition, since the heat capacity of the fixing belt 120 can also be set independently of the heat capacity of the heating roller 1 , an optimum value can be selected as the heat capacity of the fixing belt 120 .

In addition, the fixing roller 143 not only has a low thermal conductivity of the material itself, but also is made of a foam body. Therefore, due to the presence of voids inside, the heat held by the fixing belt 120 is difficult to dissipate due to contact with the fixing roller 143, thereby Can improve efficiency.

In this embodiment, in order to shorten the heating time, the heat capacity of the fixing belt 120 is set as small as possible, and the heat capacity of the heating roller 144 is set to a small value by reducing the thickness and outer diameter. When the heat capacity of the heating roller 144 is set to a value equal to the heat capacity of the fixing belt 120 by reducing the thickness of the heating roller 144 as shown in this embodiment to accelerate the temperature rise, since the heat stored in the heating roller 144 is very small, the Even once the heat is stored in the heating roller 144, its temperature usually drops immediately. That is, in the conventional method of heating the fixing belt 120 by supplying heat to the heating roller 144 at a position other than the contact portion with the fixing belt 120, in order to supply sufficient heat to the fixing belt 120, the heating roller 144 itself must be heated to fairly high temperature. In addition, the cooling temperature of the fixing belt 120 that is cooled when passing through the nip may vary greatly depending on the temperatures of the pressure roller 149 and the fixing roller 143 and the temperature state of the recording paper 115 when passing. Therefore, also in the above method, it is necessary to set the temperature of the heating roller 144 to a temperature with a large difference accordingly.

However, in the present embodiment, since heating is performed at the portion of the heating roller 144 in contact with the fixing belt 120, the required heat can be immediately transferred to the fixing belt 120, so it is not necessary to raise the temperature of the heating roller 144 to more than the necessary value. In addition, there is almost no heat generated near the position where the heating roller 144 passes through the contact portion with the fixing belt 120, so by controlling the temperature of this portion to a constant value, the temperature of the fixing belt 120 when entering the nip can be kept constant. kept at a constant value. As a result, stable fixing can be performed regardless of the temperature state of the pressure roller 149 or the like.

In addition, in this embodiment, the fixing belt 120 heated by the heating roller 144 is in contact with the recording paper 115 before reaching the fixing roller 143, so that the toner 135 on the recording paper 115 can be removed while maintaining the necessary temperature. melt. Further, since the heat capacity of the fixing belt 120 is small, when the fixing belt 120 comes into contact with the recording paper 115, the recording paper 115 starts to take away heat. The temperature of the fixing belt 120 is lowered considerably. As a result, generation of thermal deviation can be prevented.

In addition, in this embodiment, the heating roller 144 (heating part) is provided inside the fixing belt 120, and the excitation coil 123 and the back core 124 are provided outside the fixing belt 120, so it is possible to prevent the excitation coil 123, etc. The temperature rises under the influence of the temperature of the heat generating part. Therefore, the heat generation amount can be kept stable.

In addition, in this embodiment, the base material of the fixing belt 120 is made of resin, but it may be made of metal instead of resin. In this case, part of the heat generated by electromagnetic induction will occur in the fixing belt 120. If the thickness is made extremely thin, the magnetic flux generated by the exciting current will pass through the fixing belt 120 and reach the heating roller 144, so that the heat will be generated. The roll 144 can be automatically controlled in temperature as described above.

In addition, in this embodiment, the heat-generating roller 144 and the conductive roller 145 are disposed in a heat-insulated manner, but even if the two are arranged close to each other, the heat-generating roller 144 can also be provided with automatic temperature control characteristics. In this case, the heat capacity as the heat-generating roller 144 will slightly increase, thus making the heating time longer accordingly.

In addition, in this embodiment, the case where the surface of the fixing belt 31 is controlled at a predetermined fixing temperature by the automatic temperature control of the heating roller 144 is described as an example, but the automatic temperature control characteristic of the heating roller 144 is not necessarily applicable only to this. situation. For example, it is also possible to control the fixing temperature by detecting with a common thermistor or the like, and set the temperature of the automatic temperature control of the heating roller 144 to be slightly higher, so as to prevent abnormal temperature rise and Ensure safety against device damage due to high temperatures.

[Eleventh Embodiment]

Next, a fixing device for fixing a color image as an image heating device according to an eleventh embodiment of the present invention will be described with reference to Fig. 33 . In addition, detailed descriptions of portions having the same configuration as those of the fixing device according to the tenth embodiment described above and performing the same functions will be omitted.

The fixing belt 150 in this embodiment is an endless endless belt with a diameter of 50 mm and a thickness of 80 μm, in which the base material 151 is made of polyamide resin. The surface of the fixing belt 150 is covered with a silicone rubber 152 having a thickness of 150 µm for fixing a color image. Also in this embodiment, since heating is performed by the heating roller 154, an extremely thin metal may be used as the fixing belt 150, or a heat-resistant resin such as a fluorine-containing resin other than metal may be formed into a thin film.

The fixing belt 150 is suspended at a predetermined tension on a fixing roller 153 having a diameter of 30 mm and a heating roller 154 made of magnetic stainless steel having a thickness of 0.4 mm and made of magnetic stainless steel, and can rotate and move in the direction of the arrow C. . The pressure roller 157 is made of silicone rubber with a hardness of JIS A60, and is pressed against the fixing roller 153 via the fixing belt 150 to form a nip. In addition, the pressure roller 157 is supported so as to be rotatable around the metal shaft 160 as the fixing belt 150 rotates.

171 is an exciting coil, and 172 is a back iron core. The exciting coil 171 and the back iron core 172 are arranged opposite to the heating roller 154 with a small gap across the fixing belt 150 . The back core 172 has an E-shaped cross-section, and the exciting coil 171 is wound around a convex portion at the center. As in the above-mentioned tenth embodiment, by applying an exciting current with a frequency of 30 kHz to the exciting coil 171 from the exciting circuit 175, the magnetic flux shown by the arrows G and G' in the figure is repeatedly generated and disappeared, and the heating roller 154 The heat generating portion 154a, which is a portion in contact with the fixing belt 150, is excited to generate eddy current. Therefore, the heat generating portion 154a of the heat generating roller 154 is heated. At this time, the eddy current generated in the heating roller 154 concentrates on the surface shallower than the skin depth determined by the magnetic permeability and intrinsic resistance of the material used for the heating roller 154 and the frequency of the applied excitation current. When calculated according to the characteristics of the stainless steel material used for the heating roller 154 and the frequency of the applied excitation current, the skin depth is about 0.3 mm. Since the thickness of the heating roller 154 is set to 0.4 mm, most of the heating occurs within the thickness determined by the skin depth on the surface side of the heating roller 154 . Therefore, even if the thickness of the heat-generating roller 154 is locally uneven, unevenness in heat generation does not occur, and thus heat can be generated uniformly. In addition, since heat is intensively generated on the surface of the heating roller 154 in contact with the fixing belt 150 , the heat can be efficiently transferred to the fixing belt 150 .

A temperature sensor 158 is provided in a state where the heating roller 154 is in contact with the surface of the heating roller 154 near a position 154 b after passing through the contact portion with the fixing belt 150 . Furthermore, the output of the excitation circuit 175 is controlled by the control device 179 based on the detection output of the temperature sensor 158 . In this way, the amount of heat generation is controlled so that the near portion 154 b of the heat generating roller 154 at the position after passing the contact portion with the fixing belt 150 is always maintained at a constant temperature.

The fixing device having the structure as described above is installed in the color image forming device (not shown in the figure), and the recording paper 186 formed with the color toner image 185 by the fast-melting color toner with polyester as the base material is installed. Enter the fixing device from the direction of the arrow H, thereby fixing the color toner image 185 on the recording paper 186 .

In this embodiment, heat is generated at the contact portion of the heating roller 154 and the fixing belt 150, and the heat can be transferred to the fixing belt 150 immediately, so there is no need to raise the temperature of the heating roller 154 beyond the necessary temperature. In addition, the heating value is controlled by detecting the temperature of the vicinity portion 154b of the heating roller 154 after passing the contact portion with the fixing belt 150, so the temperature of the fixing belt 150 can always be kept at an optimum temperature for fixing.

In addition, the cooling temperature of the fixing belt 150 that is cooled when passing through the nip may vary greatly depending on the temperatures of the pressure roller 157 and the fixing roller 153 and the temperature state of the recording paper 186 when passing. However, since heat is generated at the contact portion of the heating roller 154 with the fixing belt 150 and the amount of heat generation is controlled so that the temperature of the vicinity portion 154b of the heating roller 154 after passing through the contact portion with the fixing belt 150 is kept constant, Therefore, the amount of heat generation can be stably controlled regardless of the temperature drop of the fixing belt 150 . Therefore, even if the heat capacity of the heating roller 154 is very small, there is no need to change the temperature control of the heating roller 154 as the temperature of the fixing belt 150 decreases, so the temperature of the fixing belt 150 when entering the nip can be kept constant.

Furthermore, in this embodiment, since the heat capacity of the fixing belt 150 is small, when the fixing belt 150 starts to contact the recording paper 186, the recording paper 186 starts to take away heat. When the belt 150 is separated, the temperature of the fixing belt 150 can be lowered considerably. As a result, even if the temperature of the fixing belt 150 at the time of entering the nip is set to be considerably high, thermal variation can be prevented from occurring. In this embodiment, the heat generation is controlled by detecting the temperature of the vicinity portion 154b of the heating roller 154 after passing the contact portion with the fixing belt 150, so the temperature of the front half of the nip can be finely controlled. Therefore, even when the fast-melting color toner 185 is used, fixing can be performed while maintaining the color toner 185 in a sufficiently melted state without thermal deviation.

In addition, there is almost no heat generated near the position where the heating roller 154 passes through the contact portion with the fixing belt 150, so by controlling the temperature of this portion to a constant value, the temperature of the fixing belt 150 when entering the nip can be kept constant. at a constant value. As a result, stable fixing can be performed regardless of the temperature state of the pressure roller 157 and the like.

In addition, the fixing roller 153 not only has a low thermal conductivity of its material itself, but also is made of a foam body. Therefore, due to the presence of voids inside, the heat held by the fixing belt 150 is difficult to dissipate due to contact with the fixing roller 153, thereby Can improve efficiency. Further, since the hardness of the fixing roller 153 is set much lower than that of the pressure roller 157 , the fixing belt 150 can be deformed along the pressure roller 157 at the nip portion. Therefore, when the recording paper 186 passes through the nip portion, the recording paper 186 can be extruded in a direction away from the fixing belt 150 , so the detachability is extremely good.

Industrial applicability

As described above, according to the present invention, it is possible to realize an image heating device that does not require a large current to flow through the exciting coil when obtaining the power required to heat the heat generating member, so it can be applied to applications where shortening of the heating time and energy saving are considered. Fixing devices used in image forming devices such as electrophotographic devices and electrostatic recording devices.

Claims (12)

1. image heating, have the generating component that constitutes by rotor, relatively dispose and make the field coil of above-mentioned generating component heating by electromagnetic induction with the side face of above-mentioned generating component with magnetic and electric conductivity, this image heating is characterised in that: above-mentioned field coil, by make boundling the wire harness of wire rod of surface insulation on the turning axle direction of above-mentioned generating component, extend and along the circumferential disc of above-mentioned generating component around forming, and make at the upwardly extending wire harness in the turning axle side of above-mentioned generating component and be close to mutually at a position at least;

The outside at field coil also has the iron core that is made of magnetic material;

Make the generating component of field coil peripheral part rotate the width that be recorded material of axial length, and make the generating component of iron core rotate the width that be recorded material of axial length greater than employed breadth extreme greater than employed breadth extreme.

2. image heating according to claim 1 is characterized in that: make from the iron core end face to the generating component end face to rotate axial distance along above-mentioned generating component longer than the relative spacing above-mentioned iron core and the generating component.

3. image heating according to claim 1 is characterized in that: iron core has obstructed overexcitation coil and relative with generating component opposed and by above-mentioned field coil and the magnetic conduction portion relative with above-mentioned generating component.

4. image heating according to claim 3 is characterized in that: at least a portion of opposed portion is formed near portion near generating component more than magnetic conduction portion.

5. image heating according to claim 4 is characterized in that: be provided with a plurality of near portion and make above-mentioned a plurality of middle position that is positioned at field coil coiling near a position in the portion.

6. image heating according to claim 1 is characterized in that: generating component is formed tubulose, and make above-mentioned generating component inside perpendicular to the basal area of the face of turning axle maximum basal area less than iron core and field coil.

7. image heating according to claim 1, it is characterized in that: the outside at field coil also has the iron core that is made of magnetic material, above-mentioned iron core, have not by above-mentioned field coil and relative with above-mentioned generating component opposed and by above-mentioned field coil and the magnetic conduction portion relative with above-mentioned generating component, and make above-mentioned opposed portion rotate between the end of axial outermost end length less than the width of photographic fixing band along above-mentioned generating component.

8. image heating, have the generating component that constitutes by rotor, relatively dispose and make the field coil of above-mentioned generating component heating by electromagnetic induction with the side face of above-mentioned generating component with magnetic and electric conductivity, this image heating is characterised in that: above-mentioned field coil, by make boundling the wire harness of wire rod of surface insulation on the turning axle direction of above-mentioned generating component, extend and along the circumferential disc of above-mentioned generating component around forming, and make at the upwardly extending wire harness in the turning axle side of above-mentioned generating component and be close to mutually at a position at least;

Also have cooling device with airflow cooling field coil.

9. image heating, have the generating component that constitutes by rotor, relatively dispose and make the field coil of above-mentioned generating component heating by electromagnetic induction with the side face of above-mentioned generating component with magnetic and electric conductivity, this image heating is characterised in that: above-mentioned field coil, by make boundling the wire harness of wire rod of surface insulation on the turning axle direction of above-mentioned generating component, extend and along the circumferential disc of above-mentioned generating component around forming, and make at the upwardly extending wire harness in the turning axle side of above-mentioned generating component and be close to mutually at a position at least;

Also have the heat insulating component of the transmission of between field coil and generating component, covering heat.

10. image heating according to claim 9, it is characterized in that: the outside at field coil also has the iron core that is made of magnetic material, and make above-mentioned field coil along generating component rotate axial length than heat insulating component along above-mentioned generating component rotate axial length short but than above-mentioned iron core to rotate axial length along above-mentioned generating component long.

11. image heating, have the generating component that constitutes by rotor, relatively dispose and make the field coil of above-mentioned generating component heating by electromagnetic induction with the side face of above-mentioned generating component with magnetic and electric conductivity, this image heating is characterised in that: the outside at above-mentioned field coil also has the iron core that is made of magnetic material, and make above-mentioned iron core rotate the width that be recorded material of axial length along above-mentioned generating component greater than employed breadth extreme.

12. image heating, have the generating component that constitutes by rotor, relatively dispose and make the field coil of above-mentioned generating component heating by electromagnetic induction with the outer peripheral face of above-mentioned generating component with magnetic and electric conductivity, this image heating is characterised in that: the outside at above-mentioned field coil also has the iron core that is made of magnetic material, and make above-mentioned iron core rotate the width that be recorded material of axial length along above-mentioned generating component greater than employed breadth extreme.

Images