JP2006078875A - Fixing unit and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing unit and an image forming device which can surely prevent the temperature from rising at both ends of the heater and the fixing unit in the width direction. <P>SOLUTION: This device has a component 23 heated by induction, a magnetic flux adjusting means 29 for reducing the magnetic flux to the component 23 within a predetermined width, and a drive means for driving the magnetic flux adjusting means 29. The magnetic flux adjusting means 29 has two or more steps 29a, formed continuously for changing the adjustable range in a stepwise manner. The drive means moves the magnetic flux adjusting means 29, until one of its steps 29a comes to a position to reduce the magnetic flux in the range desired to adjust. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile, or a multifunction machine thereof, and a fixing device installed therein, and in particular, a fixing device using an electromagnetic induction heating method. And an image forming apparatus.

  Conventionally, in an image forming apparatus such as a copying machine or a printer, a fixing device using an electromagnetic induction heating method has been known for the purpose of saving energy by reducing the rise time of the device (see, for example, Patent Document 1). .)

  In Patent Document 1, etc., an electromagnetic induction heating type fixing device mainly includes a support roller (heating roller), a fixing auxiliary roller (fixing roller), and a fixing belt (heat-resistant belt) stretched between the supporting roller and the fixing auxiliary roller. ), Magnetic flux generating means facing the support roller via the fixing belt, and a pressure roller facing the fixing auxiliary roller via the fixing belt. The magnetic flux generation means includes a coil portion extending in the width direction (a direction perpendicular to the recording medium conveyance direction), a core portion (excitation coil core) facing the coil portion, and the like.

The fixing belt is heated at a position facing the magnetic flux generating means. The heated fixing belt heats and fixes the toner image on the recording medium conveyed to the positions of the auxiliary fixing roller and the pressure roller. Specifically, when a high-frequency alternating current is passed through the coil portion, a magnetic field is formed around the coil portion, and an eddy current is generated on the surface of the support roller. When an eddy current is generated in the support roller, Joule heat is generated by the electrical resistance of the support roller itself. The fixing belt wound around the support roller is heated by the Joule heat.
It is known that a fixing device using such an electromagnetic induction heating method can raise the surface temperature (fixing temperature) of a fixing belt to a desired temperature with a small start-up time with low energy consumption.

On the other hand, Patent Document 2 discloses a fixing device that uses an electromagnetic induction heating method, and suppresses a temperature rise in a non-sheet-passing region (non-passing portion) in a fixing roller (film-like metal fixing roller). For this purpose, a technique for providing a magnetic flux shielding plate for shielding a part of magnetic flux generated from magnetic flux generating means (excitation coil) provided in the fixing roller is disclosed.
Specifically, on the magnetic flux shielding plate, strip-shaped nonmagnetic material portions having different lengths corresponding to various recording medium sizes are formed in a stepped shape with a gap. Then, according to the size of the recording medium to be passed, the magnetic flux shielding plate is driven to vary the range in which the magnetic flux is shielded by the fixing roller. This technique aims to block the magnetic flux reaching the fixing roller in the non-sheet passing area and suppress the temperature rise in the non-sheet passing area.

JP 2002-123106 A JP 2002-83676 A

  The conventional technology described above cannot reliably suppress the temperature rise at both ends in the width direction of the heating member (or the fixing member) that occurs when a recording medium having a short width direction size is continuously fixed. .

Details are as follows.
A general image forming apparatus is configured to form an image on several types of recording media having different sizes in the width direction. Here, the recording media having different sizes in the width direction include non-standard size recording media in addition to various standard size recording media in the A and B rows of JIS dimensions. Further, even in the case of recording media of the same size (for example, A4 size), the transport direction is the short direction (the direction perpendicular to the longitudinal direction) when the longitudinal direction is the transport direction. In some cases, recording media having different sizes in the width direction are handled.

  When fixing such a recording medium having different width direction sizes with the fixing device, the temperature distribution in the width direction of the fixing belt varies depending on the width direction size of the recording medium, resulting in temperature unevenness. was there. For example, when fixing by passing a recording medium having a small size in the width direction, a lot of heat is taken away at the position of the fixing belt corresponding to the size in the width direction of the recording medium (the paper passing area). The fixing temperature is lower than at other positions (non-sheet passing area). Such a phenomenon becomes particularly prominent when a recording medium having a small size in the width direction is continuously fed.

  Therefore, when trying to control the fixing temperature in the entire width direction of the fixing belt with reference to the fixing temperature in the center portion in the width direction of the fixing belt, the fixing temperature in the center portion in the width direction of the fixing belt can be controlled to a desired temperature. The fixing temperature at both ends in the direction will increase. As described above, when a large recording medium in the width direction is fixed in a state where the fixing temperature at both ends in the width direction of the fixing belt is increased, a hot offset occurs on the recording medium corresponding to the temperature increase position. Further, when the fixing temperature at both ends in the width direction exceeds the heat resistance temperature of the fixing belt, it is also conceivable that the fixing belt is thermally damaged.

  On the other hand, if it is attempted to control the fixing temperature in the entire width direction of the fixing belt based on the fixing temperature at both ends in the width direction of the fixing belt, the fixing temperature at both ends in the width direction of the fixing belt can be controlled to a desired temperature. However, the fixing temperature at the center in the width direction is lowered. As described above, when the recording medium is fixed in a state where the fixing temperature at the center portion in the width direction of the fixing belt is lowered, fixing failure or cold offset occurs on the recording medium corresponding to the temperature lowered position.

  In order to solve such a problem, in the above-mentioned Patent Document 2 and the like, the position of the magnetic flux shielding plate is changed in accordance with the size of the recording medium, and one corresponding non-magnetic material among the plurality of non-magnetic material portions. Since the magnetic flux in the non-sheet passing area is shielded by the portion, an effect of suppressing the temperature rise in the non-sheet passing area can be expected to some extent even when a recording medium having a small width direction size is continuously fed.

  However, in the above-described technique, since the plurality of nonmagnetic material portions having different lengths in the width direction are installed with gaps therebetween, the position of the magnetic flux shielding plate after the variable movement is shifted from the target position. In such a case, the non-magnetic material part is insufficiently shielded from the magnetic flux. That is, when an error occurs in the position control of the magnetic flux shielding plate, there is a possibility that the magnetic flux is not sufficiently shielded in the non-sheet passing area and the temperature of the non-sheet passing area is increased.

  The present invention has been made to solve the above-described problems, and provides a fixing device and an image forming apparatus that can reliably suppress a temperature rise at both ends in the width direction of a heating member and a fixing member. It is in.

  According to a first aspect of the present invention, there is provided a fixing device for fixing a toner image on a recording medium, a magnetic flux generating means for generating a magnetic flux, a heating member induction-heated by the magnetic flux, A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member with respect to a predetermined adjustment range in the width direction; and a driving unit that drives and controls the magnetic flux adjusting member. A plurality of stepped portions that are continuously formed, and the driving means includes a stepped portion corresponding to a variable adjustment range among the plurality of stepped portions. The magnetic flux adjusting member is driven and controlled so as to move to a position to be lowered.

  According to a second aspect of the present invention, there is provided the fixing device according to the first aspect of the present invention, further comprising first detection means for detecting a range in the width direction of the recording medium corresponding to the heating member, and the driving. The means selects one of the plurality of steps according to the range in the width direction detected by the first detection means, and the one step moves to a position where the magnetic flux is reduced. Thus, the magnetic flux adjusting member is driven and controlled.

  According to a third aspect of the present invention, in the fixing device according to the second aspect, the first detection means is a size detection sensor for detecting the size of the recording medium.

  According to a fourth aspect of the present invention, there is provided a fixing device according to any one of the first to third aspects, further comprising second detection means for detecting environmental fluctuations, wherein the drive means is the first one. The magnetic flux adjusting member is selected such that one step portion is selected from the plurality of step portions according to the environmental change detected by the two detecting means, and the one step portion moves to a position where the magnetic flux is reduced. Drive control is performed.

  A fixing device according to a fifth aspect of the present invention is the fixing device according to any one of the first to fourth aspects, further comprising third detecting means for detecting the thickness of the recording medium, and the driving means. Selects one of the plurality of steps according to the thickness of the recording medium detected by the third detection means, and the one step moves to a position where the magnetic flux is reduced. Thus, the magnetic flux adjusting member is driven and controlled.

  A fixing device according to a sixth aspect of the present invention is the fixing device according to any one of the first to fifth aspects, further comprising fourth detection means for detecting the type of the recording medium, wherein the driving means is According to the type of the recording medium detected by the fourth detecting means, one step portion is selected from the plurality of step portions, and the one step portion moves to a position where the magnetic flux is reduced. The magnetic flux adjusting member is driven and controlled.

  A fixing device according to a seventh aspect of the present invention is the fixing device according to any one of the first to sixth aspects, further comprising fifth detection means for detecting a conveyance speed of the recording medium, and the driving means. Selects one of the plurality of steps according to the conveyance speed of the recording medium detected by the fifth detection means, and the one step moves to a position where the magnetic flux is reduced. Thus, the magnetic flux adjusting member is driven and controlled.

  The fixing device according to an eighth aspect of the present invention is the fixing device according to any one of the first to seventh aspects, wherein the magnetic flux generating means extends in the width direction so as to face the heating member. A magnetic flux shielding member disposed between the coil portion and the inner core, the coil portion and an inner core facing the coil portion via the heating member. It is a thing.

  According to a ninth aspect of the present invention, in the fixing device according to the eighth aspect, the magnetic flux shielding member can increase or decrease the range covering the outer periphery of the inner core facing the coil portion in a stepwise manner. It is formed as follows.

  According to a tenth aspect of the present invention, there is provided the fixing device according to the ninth aspect, wherein the driving means is configured to increase or decrease the magnetic flux shielding member so as to gradually increase or decrease the range covering the outer periphery of the inner core. It is a means for driving control.

  According to an eleventh aspect of the present invention, in the fixing device according to any one of the eighth to tenth aspects, the magnetic flux generating means faces the coil portion on a side not facing the heating member. In addition, a core portion having a center core is provided, and the magnetic flux shielding member covers an outer periphery of the inner core facing the center core.

  According to a twelfth aspect of the present invention, in the fixing device according to any one of the first to eleventh aspects, the heating member heats the fixing member that melts the toner image.

  The fixing device according to a thirteenth aspect of the present invention is the fixing device according to the twelfth aspect of the present invention, wherein the fixing member is a fixing belt, and the heating member stretches the fixing belt together with a fixing auxiliary roller. The magnetic flux generating means is arranged to face the fixing belt.

  According to a fifteenth aspect of the present invention, in the fixing device according to the thirteenth aspect, the fixing auxiliary roller is configured such that the pressure roller that presses the conveyed recording medium is interposed via the fixing belt. It is arrange | positioned so that it may contact | abut.

  According to a fifteenth aspect of the present invention, in the fixing device according to any one of the first to fourteenth aspects, the heating member is a fixing member that melts a toner image.

  The fixing device according to a sixteenth aspect of the present invention is the fixing device according to the fifteenth aspect, wherein the fixing member is a fixing belt, and the magnetic flux generating means is arranged to face the fixing belt. It was established.

  According to a fifteenth aspect of the present invention, in the fixing device according to the sixteenth aspect, the fixing belt is stretched between a support roller and a fixing auxiliary roller, and the fixing auxiliary roller is conveyed. It is disposed so as to abut against a pressure roller for pressing the recording medium via the fixing belt.

  The fixing device according to an eighteenth aspect of the invention is the fixing device according to the fifteenth aspect of the invention, wherein the fixing member is a fixing roller that abuts against a pressure roller that presses a recording medium to be conveyed. The magnetic flux generating means is disposed so as to face the fixing roller.

  An image forming apparatus according to a nineteenth aspect includes the fixing device according to any one of the first to eighteenth aspects.

  In the present invention, the adjustment range is varied by driving and controlling a magnetic flux adjusting member in which a plurality of step portions are continuously formed without any gaps. Therefore, even if an error occurs in the driving control, the adjustment is performed. Range variable errors can be reduced. Accordingly, it is possible to provide a fixing device and an image forming apparatus in which a temperature rise at both ends in the width direction of the heating member and the fixing member is reliably suppressed.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the entire image forming apparatus will be described with reference to FIG.
In FIG. 1, 1 is a main body of a laser printer as an image forming apparatus, 3 is an exposure unit that irradiates a photosensitive drum 18 with exposure light L based on image information, and 4 is detachably installed on the apparatus main body 1. A process cartridge as an image forming unit; 7, a transfer unit for transferring a toner image formed on the photosensitive drum 18 to a recording medium P; 10, a paper discharge tray on which an output image is placed; A paper feeding unit in which a recording medium P such as paper is stored, 13 is a registration roller that conveys the recording medium P to the transfer unit 7, 15 is a manual paper feeding unit, and 20 is a fixing unit that fixes an unfixed image on the recording medium P. Indicates the device.

With reference to FIG. 1, an operation during normal image formation in the image forming apparatus will be described.
First, exposure light L such as laser light based on image information is emitted from the exposure unit 3 (writing unit) toward the photosensitive drum 18 of the process cartridge 4. The photosensitive drum 18 rotates counterclockwise in the figure, and a toner image corresponding to image information is formed on the photosensitive drum 18 through a predetermined image forming process (charging process, exposure process, development process). Is done.
Thereafter, the toner image formed on the photosensitive drum 18 is transferred onto the recording medium P conveyed by the registration roller 13 in the transfer unit 7.

On the other hand, the recording medium P conveyed to the transfer unit 7 operates as follows.
First, one of the plurality of paper feeding units 11, 12, and 15 of the image forming apparatus main body 1 is automatically or manually selected (for example, the uppermost paper feeding unit 11 is selected). To do.) Each of the plurality of paper feeding units 11 and 12 stores a recording medium P having a different size and a recording medium P having the same size and different transport directions.

  Then, the uppermost sheet of the recording medium P stored in the paper feeding unit 11 is transported toward the position of the transport path K. Thereafter, the recording medium P passes through the conveyance path K and reaches the position of the registration roller 13. Then, the recording medium P that has reached the position of the registration roller 13 is conveyed toward the transfer unit 7 at the same timing in order to align with the toner image formed on the photosensitive drum 18.

After the transfer process, the recording medium P passes through the position of the transfer unit 7 and then reaches the fixing device 20 through the conveyance path. The recording medium P that has reached the fixing device 20 is fed between the fixing belt and the pressure roller, and the toner image is fixed by the heat received from the fixing belt and the pressure received from the pressure roller. The recording medium P on which the toner image has been fixed is sent from between the fixing belt and the pressure roller, and then is discharged from the image forming apparatus main body 1 as an output image and placed on the paper discharge tray 10.
Thus, a series of image forming processes is completed.

Next, the configuration / operation of the fixing device 20 installed in the image forming apparatus main body 1 will be described in detail with reference to FIG.
As shown in FIG. 2, the fixing device 20 mainly includes a fixing auxiliary roller 21, a fixing belt 22, a support roller 23 (heating roller), an induction heating unit 24, a pressure roller 30, a thermopile 37, a thermistor 38, and an oil application roller. 34, a guide plate 35, a separation plate 36, and the like.

Here, the fixing auxiliary roller 21 has an elastic layer such as silicone rubber formed on the surface thereof, and is driven to rotate counterclockwise in FIG. 2 by a driving unit (not shown).
The support roller 23 is a cylindrical body made of a nonmagnetic material such as SUS304 and rotates counterclockwise in the figure. An inner core 28 made of a ferromagnetic material such as ferrite and a magnetic flux shielding member 29 covering a part of the outer periphery of the inner core 28 are rotatably installed inside the support roller 23. The inner core 28 faces the coil portion 25 through the fixing belt 22 and the support roller 23. The rotational drive of the inner core 28 and the magnetic flux shielding member 29 is performed separately from the rotational drive of the support roller 23. The configuration and operation of the support roller 23 provided with the inner core 28 and the magnetic flux shielding member 29 will be described in detail later.

The fixing belt 22 as a fixing member is stretched and supported by a support roller 23 and a fixing auxiliary roller 21. The fixing belt 22 is a multi-layered endless belt in which a heating layer, an elastic layer, and a release layer are formed on a base material.
The base material of the fixing belt 22 is made of a heat-resistant resin material. For example, polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), PPS (polyphenylene sulfide), fluororesin, or the like can be used. . As the heating layer, nickel, stainless steel, iron, copper, cobalt, chromium, aluminum, gold, platinum, silver, tin, palladium, an alloy composed of a plurality of these metals, or the like can be used. As the elastic layer, silicone rubber, fluorosilicone rubber, or the like can be used. As the release layer, fluorine resins such as tetrafluoroethylene resin (PTFE) and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (FEP), or a mixture of these resins can be used.

  In the first embodiment, the base material of the fixing belt 22 and the heating layer are mixed layers. Specifically, three heating layers made of silver are formed at intervals in a base material made of polyimide. Then, an elastic layer and a release layer are sequentially formed on the hybrid layer.

The induction heating unit 24 as a magnetic flux generation unit includes a coil unit 25, a core unit 26, a coil guide 27, and the like.
Here, the coil portion 25 is wound around a litz wire in which fine wires are bundled so as to cover the outer peripheral surface of the fixing belt 22 wound around the support roller 23 and is in the width direction (in the direction perpendicular to the paper surface of FIG. 2). It is extended. The coil guide 27 is made of a highly heat-resistant resin material or the like, and holds the coil part 25 and functions as a frame of the induction heating part 24. The core portion 26 is made of a ferromagnetic material such as ferrite having a relative permeability of about 2500, and is provided with a center core portion 26a and a side core 26b. The core part 26 is installed so as to face the coil part 25 extending in the width direction. The center core 26a is at a substantially central position in the circumferential direction of the coil portion 25, and is a position where the density of magnetic flux formed around the coil portion 25 is the highest. The coil unit 25 is connected to a high frequency power supply unit (not shown), and an alternating current of 10 k to 1 MHz is applied from the high frequency power supply unit.

  The pressure roller 30 is formed by forming an elastic layer such as fluorine rubber or silicone rubber on a cylindrical member made of aluminum, copper, stainless steel or the like. The elastic layer of the pressure roller 30 has a thickness of 1 to 5 mm and an Asker hardness of 20 to 50 degrees. The pressure roller 30 is in contact with the fixing auxiliary roller 21 via the fixing belt 22. Then, the recording medium P is conveyed to a contact portion (a fixing nip portion) between the fixing belt 22 and the pressure roller 30.

A guide plate 35 for guiding the conveyance of the recording medium P is disposed on the entrance side of the contact portion between the fixing belt 22 and the pressure roller 30.
A separation plate 36 that guides conveyance of the recording medium P and promotes separation of the recording medium P from the fixing belt 22 is disposed on the exit side of the contact portion between the fixing belt 22 and the pressure roller 30.

  An oil application roller 34 is in contact with a part of the outer peripheral surface of the fixing belt 22. The oil application roller 34 supplies oil such as silicone oil onto the fixing belt 22. Thereby, the toner releasability on the fixing belt 22 is further ensured. The oil application roller 34 is in contact with a cleaning roller 33 that removes dirt on the surface.

A non-contact type thermopile 37 is installed at a position facing the outer peripheral surface of the fixing belt 22 and in a central portion in the width direction (a position that does not become an adjustment range described later). In addition, a contact type thermistor 38 is installed at a position in contact with the outer peripheral surface of the fixing belt 22 and at an end portion in the width direction (a position within an adjustment range described later).
The surface temperature (fixing temperature) on the fixing belt 22 is detected by the thermopile 37 and the thermistor 38, and the output in the induction heating unit 24 having an inverter circuit is adjusted. Thus, the fixing temperature on the fixing belt 22 is kept constant.

The fixing device 20 configured as described above operates as follows during normal operation.
By the rotation driving of the auxiliary fixing roller 21, the fixing belt 22 rotates in the arrow direction in FIG. 2, the support roller 23 also rotates counterclockwise, and the pressure roller 30 also rotates in the arrow direction. The fixing belt 22 is heated at a position facing the induction heating unit 24. Specifically, the magnetic field lines are alternately switched between the core part 26 and the inner core 28 by passing a high-frequency alternating current through the coil part 25. At this time, an eddy current is generated on the surface of the support roller 23 and the heating layer of the fixing belt 22, and Joule heat is generated by the electrical resistance of the support roller 23 and the heating layer. Thus, the fixing belt 22 is heated by the heat received from the heat-generating support roller 23 and the heat generated by its own heating layer. That is, the support roller 23 functions as a heating member, and the fixing belt 22 functions as a heating member as well as a member to be heated.

Thereafter, the surface of the fixing belt 22 heated by the induction heating unit 24 passes through the position of the thermistor 38 and then reaches the contact portion with the pressure roller 30. Then, the toner image T on the conveyed recording medium P is heated and melted.
Specifically, the recording medium P carrying the toner image T through the image forming process described above is fed between the fixing belt 22 and the pressure roller 30 while being guided by the guide plate 35 (indicated by the arrow Y). It is movement in the transport direction.) The toner image T is fixed to the recording medium P by the heat received from the fixing belt 22 and the pressure received from the pressure roller 30, and the recording medium P is sent from between the fixing belt 22 and the pressure roller 30.

The surface of the fixing belt 22 that has passed through the position of the pressure roller 30 sequentially passes through the positions of the oil application roller 34 and the thermopile 37, and then reaches the position facing the induction heating unit 24 again.
Such a series of operations is continuously repeated to complete the fixing step in the image forming process.

The configuration and operation of the support roller 23 will be described in detail with reference to FIG.
FIG. 3 is a view of the support roller 23 installed in the fixing device 20 of FIG. 2 as viewed in the width direction from the induction heating unit 24 side, and shows the inside of the support roller 23.
As shown in FIG. 3, an inner core 28 and a magnetic flux shielding member 29 are rotatably installed in the cylindrical body of the support roller 23.

  Magnetic flux shielding members 29 made of a diamagnetic material such as copper are integrally installed at both ends in the width direction of the cylindrical inner core 28 made of a ferromagnetic material. The magnetic flux shielding member 29 is a step-like member formed with a plurality of step portions 29a so as to increase or decrease the range in which the outer peripheral surface of the inner core 28 is shielded from the end surface side. Thereby, by rotating the inner core 28 together with the magnetic flux shielding member 29, the shielding range (adjustment range) in the width direction of the inner core 28 facing the coil portion 25 of the induction heating unit 24 can be varied stepwise. .

  Specifically, referring to FIG. 4, magnetic flux shielding member 29 is provided between center core 26 a of induction heating unit 24 (the position where the magnetic flux density is highest in the configuration of the first embodiment) and internal core 28. When the (selected step portion 29a) is interposed, a normal magnetic flux (indicated by a broken line B in FIG. 4) formed when there is no magnetic flux shielding member 29 is weakened. Thereby, in the position of the support roller 23 which has arrange | positioned the magnetic flux shielding member 29, a heating efficiency falls with the fall of the magnetic flux which acts.

  Here, the range (adjustment range) in the width direction in which the magnetic flux is reduced can be changed stepwise by changing the posture of the magnetic flux shielding member 29 facing the coil portion 25. Specifically, by rotating and driving (driving control) the magnetic flux shielding member 29 together with the inner core 28, the adjustment range for reducing the magnetic flux is varied within the range of Mmax to Mmin in FIG. 3 by the number of the plurality of step portions 29a. be able to. That is, the adjustment range (shielding range) is varied in 7 steps in the range of 0 to (Mmax−Mmin), and the heating range is varied in 7 steps in the range of Mmax to Mmin.

Specifically, referring to FIG. 5, the magnetic flux shielding member 29 corresponds to the adjustment ranges of the recording medium P of A3 size, B4 size, A4 size, B5 size, A5 size, B6 size, and A6 size, respectively. Two stepped portions 29a are provided. FIG. 5 is a schematic diagram showing a state where the magnetic flux shielding member 29 faces the center core 26 a of the core portion 26. FIG. 5A shows the optimum position of the magnetic flux shielding member 29 when the A5 size recording medium P is passed (fixed). That is, the outer range (non-sheet passing region) of the A5 size width direction range is shielded by the magnetic flux shielding member 29, and the A5 size width direction range becomes the heating range.
As described above, the magnetic flux shielding member 29 functions as a magnetic flux adjusting member that reduces the magnetic flux acting on the support roller 23 (or the fixing belt 22) in the adjustment range in the width direction.

  The rotational drive (drive control) of the inner core 28 and the magnetic flux shielding member 29 is performed by a stepping motor (not shown) as drive means connected to the shaft portion 28a of the inner core 28. The stepping motor is a drive system different from a drive motor (not shown) that drives the auxiliary fixing roller 21, the fixing belt 22, the support roller 23, and the like.

Specifically, referring to FIG. 3, the inner core 28 and the magnetic flux shielding member 29 are rotated by a predetermined angle (predetermined number of steps) in the circumferential direction so that the maximum range of the magnetic flux shielding member 29 is opposed to the center core 26 a. At this time, the adjustment range in which the magnetic flux is reduced is maximized, and the outside of the adjustment range (the region having the central width Mmin) is the main heating range of the fixing belt 22.
On the other hand, the inner core 28 and the magnetic flux shielding member 29 are further rotated by a predetermined angle in the circumferential direction so that the magnetic flux shielding member 29 does not face the center core 26a. At this time, the adjustment range in which the magnetic flux is reduced becomes zero, and the entire range (the region of the width Mmax) becomes the main heating range of the fixing belt 22.

  In the first embodiment, the magnetic flux shielding member 29 is driven and controlled so that the heating range substantially coincides with the width direction range (paper passing area) of the recording medium P corresponding to the support roller 23 (or the fixing belt 22).

Specifically, a case where an A5 size recording medium P is passed will be described with reference to FIG.
First, when an A5 vertical size recording medium P set in the paper feeding unit is selected by a print command input by the user, the size of the recording medium P based on the information is a size detection sensor (not shown). ) Is detected. The size detection sensor is a photo that detects the position of a paper feed fence (a member for fixing the recording medium P, which moves according to the size of the recording medium P) installed in the paper feeding units 11 and 12. It is a sensor, and functions as a first detection unit that collates input information that is instructed to be printed by a user and detects the size in the width direction of the recording medium P on the support roller 23. Thus, the width direction size (or size and transport direction) of the recording medium P to be passed (fixed) is detected by the first detection unit. The size of the recording medium P detected by the size detection sensor as the first detection means specifies the width direction range (paper passing area) of the recording medium P corresponding to the support roller 23 and the fixing belt 22. That is, in the support roller 23 and the fixing belt 22, a non-sheet passing region that may overheat is specified.

Thereafter, the magnetic flux shielding member 29 is driven and controlled based on the range in the width direction detected by the first detection means. That is, the A5 size step 29a is selected from the seven steps 29a according to the width direction range detected by the first detection means. Then, the magnetic flux shielding member 29 is started to rotate together with the inner core 28 so that the selected A5 size step 29a moves to a position facing the center core 26a (a position where the magnetic flux is reduced). .
The magnetic flux shielding member 29 is driven and controlled so that the heating range substantially coincides with the width direction range of the A5 size by the adjustment range (shielding range) facing the center core 26a (the state shown in FIG. 5A). .

Thereafter, in the state of FIG. 5A, the switch of the inverter power supply (high frequency power supply unit) of the fixing device 20 is turned on, and heating by the induction heating unit 24 is started. Note that the heating start timing is not limited to this timing, and can be performed before the drive control of the magnetic flux shielding member 29 is started.
Thus, in the support roller 23 and the fixing belt 22, the magnetic flux acting on the non-sheet passing area exceeding the A5 size is reduced, and excessive temperature rise in the non-sheet passing area can be suppressed.

  Here, FIG. 5B is a diagram showing the positional relationship between the magnetic flux shielding member 29 and the center core 26a when an error occurs in the positional accuracy due to the drive control of the magnetic flux shielding member 29. FIG. In the first embodiment, since the adjacent step portions 29a in the magnetic flux shielding member 29 are continuously formed without a gap, even if an error occurs in the drive control, a variable error in the adjustment range. Can be reduced.

Specifically, according to the configuration of the first embodiment, as shown in FIG. 5B, even if an error occurs in the drive control of the magnetic flux shielding member 29, the heating range is only the distance G. It stays longer (the adjustment range becomes shorter by the distance G).
On the other hand, according to the conventional configuration in which the strip-shaped magnetic flux shielding members 29A and 29B (nonmagnetic material portions) having different lengths are formed in a stepped shape with a gap, as shown in FIG. When an error occurs in the drive control of the member 29, the heating range becomes longer by the distance H and almost the entire region becomes the heating range (distance H> distance G). That is, the effect of lowering the magnetic flux by the magnetic flux shielding member 29 is almost lost.

FIG. 7 is a graph showing the temperature distribution in the width direction on the fixing belt 22 in the fixing device of the first embodiment.
In FIG. 7, the horizontal axis indicates the position in the width direction of the fixing belt 22, and the vertical axis indicates the temperature of the fixing belt 22 (fixing temperature). Here, “0” in the width direction position on the horizontal axis indicates the center position in the width direction of the fixing belt 22. A solid line R1 indicates a temperature distribution when the recording medium P having a width direction size L1 is continuously fed. A solid line R2 indicates a temperature distribution when the recording medium P having a width direction size L2 is continuously fed.

  Even if an error occurs in the drive control of the magnetic flux shielding member 29 by making the magnetic flux shielding member 29 driven and controlled according to the range in the width direction of the recording medium P into a stepped member without a gap, the fixing belt The temperature distribution 22 can be maintained in the state shown in FIG. Thereby, in the range exceeding the sheet passing width of the recording medium P, the temperature of the fixing belt 22 does not increase, and thermal damage to the fixing belt 22 is suppressed.

  As described above, in the first embodiment, the adjustment range is varied by driving and controlling the magnetic flux shielding member 29 in which the plurality of step portions 29a are continuously formed without leaving a gap. Even when an error occurs, the variable error in the adjustment range can be reduced. As a result, the temperature rise at both ends in the width direction of the support roller 23 and the fixing belt 22 can be reliably suppressed.

  In the first embodiment, the fixing belt 22 having a heating layer and the support roller 23 are used as heating members. On the other hand, only one of the fixing belt 22 and the support roller 23 can be used as a heating member. In this case as well, the magnetic flux shielding member 29 in which the plurality of stepped portions 29a are continuously formed without gaps is driven and controlled in accordance with the size in the width direction of the recording medium P, thereby being the same as in the first embodiment. An effect can be obtained.

  In the first embodiment, a halogen heater can be installed inside the pressure roller 30. Further, a thermistor or an oil application roller can be brought into contact with the outer peripheral surface of the pressure roller 30. In the first embodiment, the present invention is applied to the monochrome image forming apparatus 1. However, the present invention can also be applied to a color image forming apparatus. In these cases, the same effect as in the first embodiment can be obtained.

  In the first embodiment, the magnetic flux shielding member 29 is driven and controlled in accordance with the range in the width direction of the recording medium P detected by the first detection unit, and the adjustment range (or heating range) is varied. On the other hand, the magnetic flux shielding member 29 is driven and adjusted according to the detection result of the second detection means for detecting the environmental fluctuation (temperature, humidity, etc.) in which the apparatus main body 1 is installed. The range (or heating range) can also be varied. Such control is particularly effective when the heating efficiency of the support roller 23 and the fixing belt 22 changes due to environmental fluctuations. That is, the temperature rise at both ends in the width direction of the support roller 23 and the fixing belt 22 can be reliably suppressed regardless of environmental fluctuations.

  Further, the adjustment range (or heating range) can be varied by drivingly controlling the magnetic flux shielding member 29 according to the detection result of the third detection means for detecting the thickness (paper thickness) of the recording medium P. Such control is particularly effective when the heating efficiency of the support roller 23 and the fixing belt 22 varies depending on the thickness of the recording medium P. That is, the temperature rise at both ends in the width direction of the support roller 23 and the fixing belt 22 can be reliably suppressed regardless of the thickness of the recording medium P.

  Further, the adjustment range (or heating range) can be varied by drivingly controlling the magnetic flux shielding member 29 according to the detection result of the fourth detection means for detecting the type (paper type) of the recording medium P. Such control is particularly effective when the heating efficiency of the support roller 23 and the fixing belt 22 varies depending on the type of the recording medium P. That is, the temperature rise at both ends in the width direction of the support roller 23 and the fixing belt 22 can be reliably suppressed regardless of the type of the recording medium P.

  Further, the adjustment range (or heating range) can be varied by drivingly controlling the magnetic flux shielding member 29 in accordance with the detection result of the fifth detection means for detecting the conveyance speed (linear speed) of the recording medium P. Such control is particularly effective in the image forming apparatus 1 in which the conveyance speed of the recording medium P is variable and the heating efficiency of the support roller 23 and the fixing belt 22 varies depending on the conveyance speed of the recording medium P. . That is, the temperature rise at both ends in the width direction of the support roller 23 and the fixing belt 22 can be reliably suppressed regardless of the conveyance speed of the recording medium P.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 8 is a sectional view showing the fixing device 20 according to the second embodiment. The fixing device according to the second embodiment uses the fixing roller 31 as a heating member and a fixing member, and the above embodiment uses a fixing belt as a fixing member using a support roller and a fixing belt as the heating member. It is different from one.

As shown in FIG. 8, the fixing device 20 according to the second embodiment is mainly composed of a fixing roller 31 (fixing member), a pressure roller 30, an induction heating unit 24, and the like.
The fixing roller 31 includes a heat generating layer 31a, an elastic layer made of silicone rubber, a release layer made of a fluorine compound, and the like. The inside of the fixing roller 31 has a hollow structure, and the inner core 28 and the magnetic flux shielding member 29 are rotatably installed.

The induction heating unit 24 includes a coil unit 25, a core unit 26, a coil guide 27, and the like, as in the first embodiment. Then, when an alternating current of 10 k to 1 MHz is supplied to the coil portion 25, magnetic lines of force are formed between the core portion 26 and the inner core 28, and the fixing roller 31 is heated by electromagnetic induction. In this way, the heated fixing roller 31 heats and melts the toner image on the recording medium P conveyed from the arrow Y direction, and fixes the toner image on the recording medium P.
Also in the second embodiment, similarly to each of the embodiments described above, the adjustment range is varied by driving and controlling the magnetic flux shielding member 29 in which the plurality of step portions 29a are continuously formed without leaving a gap. Yes.

  As described above, in the second embodiment, as in each of the above embodiments, even if an error occurs in the drive control of the magnetic flux shielding member 29 as the magnetic flux adjusting member, the variable error of the adjustment range is reduced. Can be reduced. Thereby, the temperature rise at both ends in the width direction of the fixing roller 31 can be reliably suppressed.

  In the second embodiment, the coil portion 25 is disposed so as to face the outer peripheral surface of the fixing roller 31, but the coil portion may be disposed so as to face the inner peripheral surface of the fixing roller 31. . In this case, a magnetic flux shielding member can be provided between the coil portion provided inside and the inner peripheral surface of the fixing roller without installing the inner core 28 inside the fixing roller 31. Even in such a case, the same effect as in the second embodiment can be obtained by driving and controlling the magnetic flux shielding member 29 in which the plurality of step portions 29a are continuously formed without gaps, thereby changing the adjustment range. be able to.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a cross-sectional view showing a fixing device installed in the image forming apparatus of FIG. 1. FIG. 3 is a view showing a support roller installed in the fixing device of FIG. 2. FIG. 3 is an enlarged view showing the vicinity of an induction heating unit in the fixing device of FIG. 2. It is an expanded view which shows the magnetic flux shielding member installed in the support roller of FIG. It is an expanded view which shows the magnetic flux shielding member installed in the conventional support roller. 3 is a graph showing a temperature distribution in a width direction on a fixing belt in the fixing device of FIG. 2. It is sectional drawing which shows the fixing device in Embodiment 2 of this invention.

Explanation of symbols

1 image forming apparatus body (apparatus body),
20 fixing device, 21 fixing auxiliary roller,
22 fixing belt (heating member, fixing member),
23 support roller (heating member),
24 induction heating part (magnetic flux generating means), 25 coil part,
26 core part, 26a center core, 26b side core,
28 inner core, 28a shank,
29 magnetic flux shielding member (magnetic flux adjusting member), 29a step, 30 pressure roller,
31 fixing roller (heating member, fixing member),
37 Thermopile, 38 Thermistor, P Recording medium.

Claims (19)

A fixing device for fixing a toner image on a recording medium,
Magnetic flux generating means for generating magnetic flux;
A heating member that is induction-heated by the magnetic flux;
A magnetic flux adjusting member that reduces the magnetic flux acting on the heating member for a predetermined adjustment range in the width direction;
Driving means for driving and controlling the magnetic flux adjusting member,
The magnetic flux adjusting member is a stepped member in which a plurality of steps for continuously changing the adjustment range is formed,
The driving unit drives and controls the magnetic flux adjusting member so that one step corresponding to a variable adjustment range among the plurality of steps moves to a position where the magnetic flux is reduced. . First detection means for detecting a range in the width direction of the recording medium corresponding to the heating member;
The drive unit selects one step portion from the plurality of step portions according to the range in the width direction detected by the first detection unit, and the one step portion reduces the magnetic flux. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled so as to move to the position. The fixing device according to claim 2, wherein the first detection unit is a size detection sensor that detects a size of the recording medium. Comprising a second detection means for detecting environmental changes;
The driving unit selects one step portion from the plurality of step portions according to the environmental change detected by the second detection unit, and the one step portion moves to a position where the magnetic flux is reduced. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled as described above. A third detecting means for detecting the thickness of the recording medium;
The drive unit selects one step portion from the plurality of step portions according to the thickness of the recording medium detected by the third detection unit, and the one step portion reduces the magnetic flux. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled to move to a position. Comprising a fourth detection means for detecting the type of the recording medium;
The drive unit selects one step portion from the plurality of step portions according to the type of the recording medium detected by the fourth detection unit, and the one step portion reduces the magnetic flux. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled so as to move to the position. A fifth detecting means for detecting the conveyance speed of the recording medium;
The driving unit selects one step portion from the plurality of step portions according to the conveyance speed of the recording medium detected by the fifth detection unit, and the one step portion reduces the magnetic flux. The fixing device according to claim 1, wherein the magnetic flux adjusting member is driven and controlled to move to a position. The magnetic flux generating means includes a coil portion extending in the width direction so as to face the heating member, and an inner core facing the coil portion via the heating member,
The fixing device according to claim 1, wherein the magnetic flux adjusting member is a magnetic flux shielding member disposed between the coil portion and the inner core. The fixing device according to claim 8, wherein the magnetic flux shielding member is formed so that a range covering an outer periphery of the inner core facing the coil portion can be increased or decreased stepwise. The fixing device according to claim 9, wherein the driving unit is a unit that drives and controls the magnetic flux shielding member so that a range covering an outer periphery of the inner core is increased or decreased stepwise. The magnetic flux generating means includes a core portion that faces the coil portion on the side not facing the heating member and has a center core.
The fixing device according to claim 8, wherein the magnetic flux shielding member covers an outer periphery of the inner core facing the center core. The fixing device according to claim 1, wherein the heating member heats a fixing member that melts a toner image. The fixing member is a fixing belt,
The heating member is a support roller that stretches the fixing belt together with a fixing auxiliary roller,
The fixing device according to claim 12, wherein the magnetic flux generation unit is disposed to face the fixing belt. The fixing device according to claim 13, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. The fixing device according to claim 1, wherein the heating member is a fixing member that melts a toner image. The fixing member is a fixing belt,
The fixing device according to claim 15, wherein the magnetic flux generation unit is disposed to face the fixing belt. The fixing belt is stretched between a support roller and a fixing auxiliary roller,
The fixing device according to claim 16, wherein the fixing auxiliary roller is disposed so as to come into contact with a pressure roller that presses a conveyed recording medium via the fixing belt. The fixing member is a fixing roller that contacts a pressure roller that presses a recording medium to be conveyed,
The fixing device according to claim 15, wherein the magnetic flux generation unit is disposed to face the fixing roller. An image forming apparatus comprising the fixing device according to claim 1.

Images