JP2009053617A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing a non-paper-passing area (area near an end part) of a fixing roller from reaching excessively high temperature without causing increase in power consumption and without causing scattering of toner, deterioration in image quality and fixing defects. <P>SOLUTION: The image forming apparatus is equipped with a thermal fixing device equipped with a cylindrical fixing roller for thermally fixing a toner image by rotating while making its surface come into contact with recording paper to which the toner image is transferred and fixing an unfixed toner image on paper. The image forming apparatus is equipped with a heat conduction member which is attached to the inside of the end of the fixing roller and whose outside diameter is variable, and a heat conduction member deforming means which deforms the heat conduction member between a state where the outside diameter of the heat conduction member is enlarged, so that the outer peripheral surface of the heat conduction member is brought into contact with the inner peripheral surface of the end of the fixing roller and a state where the outside diameter of the heat conduction member is contracted, so that the outer peripheral surface of the heat conduction member is separated from the inner peripheral surface of the end of the fixing roller. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thermal fixing device including a cylindrical fixing roller for fixing an unfixed toner image on a sheet by heating and fixing the toner image by rotating the recording sheet onto which the toner image is transferred while contacting the surface. The present invention relates to an image forming apparatus comprising:

An electrophotographic image forming apparatus (such as a copying machine, a printer, or a facsimile machine) includes a fixing device that heats and fixes a toner image onto a recording sheet. Usually, the fixing device includes a cylindrical fixing roller that heats and fixes the toner image on the recording paper by rotating the recording paper on which the unfixed toner image is transferred while contacting the surface thereof, a heater that heats the fixing roller, A pressure roller or a pressure belt is provided to press the recording paper against the surface of the fixing roller.
A predetermined control device controls the power supplied to the heater, so that the surface temperature of the fixing roller is maintained at a predetermined target temperature necessary for fixing the toner.

  In addition, the image forming apparatus can perform image formation and heat fixing on recording papers of a plurality of sizes, and the fixing roller and the heater are the largest recording paper that can be handled by the image forming apparatus in the rotation axis direction. It is formed to have a length equal to or greater than the width (the length in the direction orthogonal to the recording paper conveyance direction) (hereinafter referred to as the maximum size recording paper). For this reason, when heat fixing is performed on a recording paper having a width smaller than the maximum recording paper (hereinafter referred to as a small-size recording paper), the fixing roller comes into contact with the small-size recording paper. In an area outside the area (hereinafter referred to as a paper passing area) in the rotation axis direction (hereinafter referred to as a non-paper passing area), it is in direct contact with the opposing pressure roller or pressure belt.

By the way, when continuous image formation and heat fixing (hereinafter referred to as continuous printing) are performed on a large number of the small size recording papers, the fixing roller supplies the surface temperature of the paper passing area from the heater. The heat and heat transfer to the recording paper are balanced and maintained at a substantially appropriate fixing temperature.
However, when the continuous printing is performed, the surface temperature of the non-sheet passing area is increased because the temperature of the pressure roller and the pressure belt rises due to heat accumulation, but there is no heat transfer to the recording sheet. It will rise to a temperature higher than the surface temperature of the paper area.

FIG. 3A is a graph schematically showing the distribution of the surface temperature of the fixing roller in the rotation axis direction at the start of printing (solid line) and during continuous printing (broken line) in the conventional image forming apparatus. is there.
As shown in the figure, when the continuous printing is started in a state where the heater control is performed so that the surface temperature of the sheet passing area does not fall below the target temperature, the number of printed sheets (that is, the number of sheets to be heat-fixed) ) Increases, the target temperature (fixing temperature) is substantially maintained while the surface temperature of the paper passing area is slightly decreased, while the surface temperature of the non-paper passing area is much higher than the target temperature. End up.

As described above, when a recording sheet having a size in which the area near the end of the fixing roller is excessively hot and the area is a sheet passing area is passed, the recording sheet is wrinkled, high temperature offset, the fixing roller. Fixing abnormalities such as wrapping of recording paper on the sheet are likely to occur. Further, the excessive high temperature tends to cause a problem that the fixing roller is deteriorated. For example, a release layer (coating layer) bonded to the core metal peels off or the release layer is thermally damaged.
In particular, the recent fixing roller is formed with a small thickness in order to reduce the heat capacity for the purpose of power saving by shortening the warm-up time. In such a thin fixing roller, FIG. The occurrence of excessively high temperature at the end of the fixing roller (non-sheet passing area) shown in a) becomes remarkable. In addition, the occurrence of the excessively high temperature is remarkable even in a high-speed machine (an image forming apparatus having a high printing speed) in which the amount of heat transfer per unit time from the fixing roller to the recording paper in the paper passing area is large.

On the other hand, increasing the thickness of the fixing roller in order to prevent the excessively high temperature by reducing the temperature difference of the fixing roller surface temperature in the rotation axis direction is contrary to power saving.
It is also conceivable that a plurality of heaters having a length corresponding to the size (width) of the recording paper is arranged in the fixing roller, and the heater that generates heat is switched according to the size of the recording paper. However, it is impossible to arrange a large number of heaters corresponding to each of a large number of sizes in the fixing roller in a small space provided in the fixing path. Eventually, in the non-sheet passing area in the heating area by the heater. The excessive high temperature problem arises.
Patent Document 1 discloses an image forming apparatus that cools the non-sheet passing area by blowing air from a fan. However, in the configuration shown in Patent Document 1, it is inevitable that the cooling air is blown to the sheet passing area, and the cooling air disturbs the surface temperature of the fixing roller and the detection value of the temperature sensor that measures the temperature. In addition, the cooling air blows off the toner on the surface of the recording paper in the paper passing area, causing new problems such as image quality deterioration and toner scattering.
Further, in Patent Document 2 and Patent Document 3, a member having high thermal conductivity is brought into contact with the outer surface (circumferential surface) of the non-sheet passing area of the fixing roller, so that the excess temperature in the non-sheet passing area is reduced. A fixing device for preventing the occurrence is shown. However, in the configurations shown in Patent Document 2 and Patent Document 3, the surface of the fixing roller is liable to be damaged due to contact of the members, and the image quality may be deteriorated due to defective fixing or adhesion of offset toner due to scratches on the surface. There is. Furthermore, the configurations shown in Patent Document 2 and Patent Document 3 are difficult to apply to a general reverse crown shaped fixing roller as a countermeasure against paper wrinkles.
Japanese Patent Laying-Open No. 2005-77792 JP-A-9-160423 JP 2000-321902 A

  Accordingly, the present invention has been made in view of the above circumstances, and the problem is that the non-passage of the fixing roller without causing an increase in power consumption, toner scattering, image quality deterioration, and fixing failure. An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of an excessively high temperature in a region (region near the end).

In order to solve the above problems, the present invention
A thermal fixing device including a cylindrical fixing roller for fixing an unfixed toner image for fixing the toner image on the paper by rotating the recording paper on which the toner image has been transferred while contacting the surface thereof; In an image forming apparatus,
A heat conducting member mounted on the inner side of the fixing roller and having a variable outer diameter;
A state in which the outer diameter of the heat conducting member is enlarged to bring the outer peripheral surface of the heat conducting member into contact with the inner peripheral surface of the end of the fixing roller; and the outer diameter of the heat conducting member is reduced by reducing the outer diameter of the heat conducting member. A heat conducting member deforming means for deforming the surface between a state where the surface is separated from the inner peripheral surface of the end portion of the fixing roller;
It is comprised as an image forming apparatus characterized by comprising.
As a result, it is possible to prevent the occurrence of an excessively high temperature in the non-sheet-passing area (area near the end) of the fixing roller without causing an increase in power consumption, toner scattering, image quality deterioration, and fixing failure.
Further, the heat conducting member deforming means used in the present invention is exemplified by one that enlarges the outer diameter of the heat conducting member when the temperature of the end portion of the fixing roller exceeds a predetermined temperature.
In this case, as the heat conducting member deforming means, it is preferable to supply recording paper narrower than the maximum sheet passing width and to enlarge the outer diameter of the heat conducting member when the time exceeds a predetermined time. is there.
Specifically, the heat conducting member is formed in a substantially cylindrical shape with slit-shaped notches in the axial direction, and the heat conducting member deforming means is wound around the substantially cylindrical heat conducting member. A strip that is applied to the heat conducting member wound by applying tension and deforms in a direction to reduce the outer diameter, and the outer diameter of the wound heat conducting member is increased by releasing the tension; And a means provided with means for changing the tension of the strip.

  Further, the heat conducting member is a spiral coil-like spring-like body, and the heat conducting member deforming means is configured such that one end of the spiral coil-like spring-like body is relative to the other end around the coil center. The outer diameter of the spring-like body may be enlarged by rotating the lens, or may be deformed by being reduced.

  As the material of such a fixing roller, aluminum is conceivable, and the thickness is preferably in the range of 0.5 to 1 mm.

  Since the present invention is configured as described above, an excess of the non-sheet passing region (region near the end) of the fixing roller without causing an increase in power consumption, toner scattering, image quality deterioration, and fixing failure. Generation of high temperature can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a schematic sectional view showing a non-heat dissipating state of the cooling mechanism provided at the end of the fixing roller in the image forming apparatus X according to the first embodiment, and FIG. 2 is an image according to the first embodiment. FIG. 3 is a schematic cross-sectional view showing a heat dissipation state of a cooling mechanism provided at the end of the fixing roller in the forming apparatus X. FIG. 3 is a diagram illustrating a conventional image forming apparatus and an image forming apparatus according to this embodiment at the start of printing and during continuous printing. 4 is a graph schematically showing the distribution of the surface temperature of the fixing roller in each of the rotation axis directions, and FIG. 4 shows a non-heat dissipating state of the fixing roller end cooling mechanism in the image forming apparatus X according to the second embodiment. FIG. 5 is a schematic sectional view, FIG. 5 is a schematic sectional view showing a heat radiation state of the fixing roller end cooling mechanism in the image forming apparatus X according to the second embodiment, and FIG. 6 is an image forming apparatus X according to the embodiment of the present invention. Summary of Block diagram representing the formation, Figure 7 is a schematic cross-sectional view of the printing unit and the fixing unit in the image forming apparatus X.

[Embodiment 1]
The image forming apparatus X according to the first embodiment of the present invention includes an electrophotographic system including a cylindrical fixing roller that heats and fixes a toner image by rotating the recording paper onto which the toner image is transferred while contacting the surface. This is an image forming apparatus.
The image forming apparatus X is characterized by a cooling mechanism in the vicinity of the end of the fixing roller (hereinafter, referred to as a fixing roller end cooling mechanism Z1).

First, the overall configuration of the image forming apparatus X according to the embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 6, the image forming apparatus X includes a main control unit 1, an operation / display unit 2, a data storage unit 3, an image processing calculation unit 4, a NIC 5, a scanner unit 6, a printing unit 10, a fixing unit 20, and the like. They are connected in such a way that they can exchange information.
The operation / display unit 2 includes an operation input unit for inputting information and an information display unit. The operation input unit is, for example, a touch panel or a sheet key provided on the surface of the liquid crystal display device. The display unit is, for example, a liquid crystal display device or an LED lamp. The operation / display unit 2 constitutes a man-machine interface for the user.
The data storage unit 3 is a readable / writable non-volatile memory that stores processing data as necessary when processing image data obtained by reading from a document or printing processing of image data.
The image processing arithmetic unit 4 is constituted by a dedicated signal processing circuit or a DSP (Digital Signal Processor) or the like, performs various image processing on the image data, and forms a print job described in a predetermined print job description language into an image. A process for converting to bitmap image data to be used, a process for generating image data to be transmitted to an external device (for example, image data subjected to predetermined encoding such as JPEG format), and the like are performed.

The NIC 5 is a communication that transmits and receives data (including data of an image read by the scanner unit 6) to and from an external device such as a personal computer through a network composed of a LAN and the Internet conforming to the standard IEEE 802.3, for example. Interface.
The scanner unit 6 is an apparatus provided with an optical device that reads an image formed on a document placed on a glass document table (not shown) or a document conveyed by an ADF (not shown). is there.
The main control unit 1 controls each of the scanner unit 6, the printing unit 10, the fixing unit 20, the operation / display unit 2, the data storage unit 3, and the image processing calculation unit 4.
For example, the main control unit 1 causes the printing unit 10 to execute a printing process (image forming process) based on a print job received through the NIC 5. Further, the main control unit 1 causes the scanner unit 6 to execute a scanning process for reading an image formed on the original from the original.
The print unit 10 is a so-called print engine controlled by the main control unit 9 and sequentially feeds sheets stored in a sheet feeding cassette (not shown) one by one, and passes through a predetermined image forming position to a sheet discharge tray. At the image forming position, the image is printed on the recording paper based on the image data of the document read from the document by the scanner unit 6 or the image data for printing generated by the image processing calculation unit 4 at the image forming position. It is a set of components to be formed (output) and parts such as an MPU that controls the device.
The fixing unit 20 is a device (fixing device) for fixing the toner image on the recording paper by heating the recording paper on which the unfixed toner image is transferred by the printing unit 10.

FIG. 7 is a cross-sectional view of the process from the printing unit 10 to the fixing unit 20.
As shown in FIG. 7, the printing unit 10 includes a photosensitive drum 11, a cleaning device 12, a charging device 13, a laser light source 14, a developing device 15, and a transfer device 16.
The surface of the photosensitive drum 11 is charged by the charging device 13, and an electrostatic latent image is written on the surface by the beam light emitted from the laser light source 14. The electrostatic latent image on the photosensitive drum 11 is visualized (developed) as a toner image by the developing device 15, and the toner image is transferred onto the recording paper by the transfer device 16. In FIG. 7, a path R indicated by an arrow is a recording paper conveyance path.
Further, the recording paper on which the unfixed toner image is transferred is conveyed to the fixing unit 20.
The fixing unit 20 includes a cylindrical fixing roller 21 including a heater 23 and a pressure roller 22 (or pressure belt) pressed against the roller. The fixing roller 21, the pressure roller 22, The toner image is heated and fixed on the recording paper by passing the recording paper on which the unfixed toner image has been transferred through the nip between the two.
The fixing roller 21 is, for example, a cylindrical member made of aluminum (Al) having a thickness of about 0.5 mm to 1.0 mm, and a release layer (coating layer) on the surface (outer circumferential surface). Is formed. Note that the outer surface of the fixing roller 21 may have an inverted crown shape as a countermeasure against paper wrinkles, but even in that case, the space formed inside is a columnar shape as in the case of the cylindrical fixing roller.
Further, as shown in FIG. 6, the fixing unit 20 includes a heat conducting member 31, a wire 41, a rotary solenoid S1, a cooling fan 40, a central thermistor 24, an end thermistor 25, and the like, which will be described later. .

Next, the fixing roller end cooling mechanism Z1 provided in the image forming apparatus X will be described with reference to the cross-sectional views shown in FIGS. The cross-sectional views shown in FIGS. 1 and 2 are cross-sectional views on a plane including the rotation axis of the fixing roller 21 around the end portion of the fixing roller 21.
As shown in FIG. 1, the fixing roller end cooling mechanism Z1 is mounted on the inner side of the end of the cylindrical fixing roller 21, and has a heat conduction member 31 having a variable outer diameter, and FIG. 2 (a), As shown in FIG. 1B, the outer diameter of the heat conducting member 31 is enlarged to bring the outer peripheral surface 31a of the heat conducting member 31 into contact with the inner peripheral surface 21a of the fixing roller 21. (A), (b)) a state in which the outer diameter of the heat conducting member 31 is reduced and the outer peripheral surface 31a of the heat conducting member 31 is separated from the end inner peripheral surface 21a of the fixing roller 21; And a heat conducting member deforming means including a rotary solenoid S1 for driving the wire 41 and the like.

The heat conducting member deforming means will be described in more detail.
The heat conducting member 31 is provided coaxially with the fixing roller 21 via a non-illustrated elastic member by a non-illustrated bearing, and has a slit shape in the direction of the rotation axis of the fixing roller 21 as shown in FIG. The heat conducting member deforming means is wound around the substantially cylindrical heat conducting member 31 and is formed of an elastic body. A strip which gives deformation in the direction of reducing the outer diameter to the heat conducting member 31 wound by applying tension and expands the outer diameter of the wound heat conducting member 31 by releasing its tension by its own elasticity. A wire 41 as an example of a body is provided.

One end 41a of the wire 41 is fixed to the machine base as shown, and the other end 41b is wound around a pulley 43 that is rotationally driven by a rotary solenoid S1, and is driven by the rotary solenoid S1. When the pulley 43 rotates in one direction, the wire 41 is pulled, and when the tension increases, the heat conducting member 31 is tightened and elastically deformed to reduce the outer diameter.
Further, when the rotary solenoid S1 rotates in the opposite direction, the wire 41 is loosened due to the rotation of the pulley 43, and the tension is lost, so that the tightening force on the heat conducting member 31 is eliminated and elastic deformation occurs. The outer diameter increases.

In FIG. 1, as a result of the wire 41 being pulled as described above and the tension being increased, the heat conducting member 31 is elastically deformed and the outer diameter is reduced. As a result, the outer peripheral surface 31a of the heat conducting member 31 is A state (non-cooled state) is shown in which the heat is not taken away from the end portion of the fixing roller 21 while being separated from the inner peripheral surface 21a of the end portion of the fixing roller 21.
Further, FIG. 2 shows that the outer diameter 31a of the heat conducting member 31 is increased in the end portion of the fixing roller 21 as a result of the outer diameter of the heat conducting member 31 being expanded by loosening the wire 41 and reducing the tension as described above. A state (cooling state) in which the peripheral surface 21a is touched and heat is taken from the end of the fixing roller 21 is shown.

  The heat conducting member 31 is a cylindrical member having a sufficiently high thermal conductivity, like the material of the fixing roller 21 (for example, a metal such as iron or aluminum). A material with high conductivity is preferred.

The main control unit 1 drives the rotary solenoid S1 to rotate in the opposite direction when the temperature at the end of the fixing roller 21 detected by the end thermistor 25 exceeds a predetermined temperature. The tension applied to the wire 41 is reduced, the outer diameter of the heat conducting member 31 is enlarged, heat is taken from the end of the fixing roller 21, and the temperature of the end is lowered.
Further, the main control unit 1 does not perform the image forming process, and therefore the fixing process detected by the end thermistor 25 when the fixing process is not performed or because the image forming process does not take a long time. While the temperature at the end of the roller 21 is lower than the predetermined temperature, the rotary solenoid S1 is rotationally driven in the one direction to increase the tension applied to the wire 41 to increase the outer diameter of the heat conducting member 31. The heat conducting member 31 is separated from the inner peripheral surface 21 a of the end portion of the fixing roller 21 by reducing the size. As a result, the temperature of the fixing roller 21 rises quickly in the initial state of the image forming process.

  Accordingly, when the continuous printing is started in a state where the heater control is performed so that the surface temperature of the sheet passing area does not fall below the target temperature, as shown in FIG. The target temperature (fixing temperature) is substantially maintained while the surface temperature of the sheet passing area is slightly decreased as the number of heat-fixed sheets is increased). As shown by the broken line, the target temperature is significantly higher than the target temperature, but in this embodiment, as described above, the heat conducting member 31 that has been separated from the fixing roller 21 comes into contact with the fixing roller 21 to fix it. Since the heat at the end (non-sheet passing area) of the roller 21 is deprived, the temperature distribution in the axial direction of the fixing roller 21 is lowered at the end of the fixing roller 21 as indicated by the solid line, resulting in an excessively high temperature. Problems such as the increase in power consumption, toner scattering, image quality degradation and fixing failure are solved, and the occurrence of excessively high temperature in the non-sheet passing area (area near the end) of the fixing roller can be prevented.

  In the above description, the main controller 1 reduces the tension applied to the wire 41 when the temperature at the end of the fixing roller 21 detected by the end thermistor 25 exceeds a predetermined temperature. Thus, the outer diameter of the heat conducting member 31 is increased, heat is taken from the end of the fixing roller 21, and the temperature of the end is lowered. However, this is merely an example. Even if the temperature of the end of the fixing roller 21 is not strictly measured, a recording sheet narrower than the maximum sheet passing width is supplied to the fixing roller 21 for image formation, and fixing for image formation is performed. When the time for performing a predetermined time exceeds a predetermined time, it can be considered that the temperature of the end portion of the fixing roller 21 is higher than the predetermined temperature. Therefore, the main control unit supplies the recording roller narrower than the maximum sheet passing width to the fixing roller 21 for image formation, and when the time for fixing for image formation exceeds a predetermined time, The outer diameter of the heat conducting member 31 may be enlarged to remove heat from the end of the fixing roller 21 and reduce the temperature of the end.

  In the first embodiment, as shown in FIG. 1, when the heat conducting member 31 is clamped by the wire 41 and integrated with the wire 41, the heat conducting member 31 is separated from the fixing roller 21, so that the fixed heat conducting member 31 is fixed. The member 31 does not resist the rotation of the fixing roller 21. In addition, when the wire 41 is loose as shown in FIG. 2, the wire 41 and the heat conducting member 31 are separated from each other or slip, so that the heat conducting member 31 rotates together with the fixing roller 21. I can do it.

[Embodiment 2]
As the heat conductive member and the heat conductive member deforming means for deforming the heat conductive member according to the present invention, as shown in FIG. 4 and FIG. It may be a spiral coil-like spring-like body 51 mounted around the shaft 50 mounted coaxially with the fixing roller 21 on the surface portion. In the case of such a fixing roller end cooling mechanism Z2, as the heat conducting member deformation means, one end of the helical coil spring 51 is rotated relative to the other end with respect to the coil center. Thus, it is conceivable that the outer diameter of the spring-like body is enlarged or reduced to be deformed.

Specifically, for example, a cylinder whose inner diameter is smaller than the inner diameter of the end inner peripheral surface 21 a of the fixing roller 21 at the end inner peripheral surface 21 a of the fixing roller 21 at a depth L from the end 21 b of the fixing roller 21. A heat insulating member 53 is fixed. The heat insulating member 53 is desirably made of a low friction material while having heat insulating properties, such as Teflon (registered trademark). Alternatively, the heat insulating member 53 can be attached to the fixing roller 21 via a bearing (not shown).
A solenoid S2 (see FIG. 6) for moving the shaft 50 forward and backward in the axial direction of the fixing roller 21 is connected to the main control unit 1 instead of the rotary solenoid S1.
In the state where no external force is applied, the spring-like body 51 has such a size that the outer diameter portion 51 a contacts the inner peripheral surface 21 a of the end portion of the fixing roller 21 as shown in FIG. Therefore, when the fixing process is not performed, or even when the fixing process is performed, the recording paper having the maximum size is supplied or the recording paper having a smaller size than the maximum size recording paper is passed. Even if the main thermistor 25 detects that the end of the fixing roller 21 has not reached the predetermined temperature because the number is small, the main controller 1 turns the solenoid S2 on. Energized to push the shaft 50 in the back direction of the fixing roller 21. As a result, the outer periphery 51b of the tip of the spring-like body 51 is inserted inside the heat insulating member 53 having a smaller diameter than the inner peripheral surface 21a of the end of the fixing roller 21 and comes into contact with the heat insulating member 53. Is twisted to reduce its outer diameter, and is separated from the inner peripheral surface 21 a of the end portion of the fixing roller 21. Thereby, the heat of the fixing roller 21 is not transmitted to the spring-like body 51 which is an example of the heat conducting member (uncooled state).

On the other hand, when the end thermistor 25 detects that a considerable number of recording sheets smaller than the maximum size have been passed and the end of the fixing roller 21 has become higher than a predetermined temperature, the main controller 1 Drives the solenoid S <b> 2 to move the shaft 50 to a position where the outer periphery 51 b of the distal end portion of the spring-like body 51 is separated from the heat insulating member 53. In this state, the outer periphery 51b of the distal end portion of the spring-like body 51 does not come into contact with the electric heating member 53. Therefore, the outer diameter portion 51a of the spring-like body 51 comes into contact with the inner peripheral surface 21a of the end portion of the fixing roller 21. 51 and the shaft 50 rotate together with the fixing roller 21.
As a result, the heat at the end of the fixing roller 21 flows to the spring-like body 51, and the temperature at the end of the fixing roller 21 falls below the predetermined temperature (cooled state).

Thus, it is desirable to connect the solenoid S2 side and the shaft 50 via a thrust bearing so that the shaft 50 can rotate with respect to the solenoid S2 fixed to the machine base.
In this case as well, as in the first embodiment, the main control unit preliminarily sets the time during which the fixing paper 21 is supplied for recording the recording paper narrower than the maximum sheet passing width and the fixing for the image forming is performed. When the predetermined time is exceeded, the outer diameter of the heat conducting member 31 may be enlarged to take heat away from the end of the fixing roller 21 and lower the temperature of the end.

〔Example〕
In the above-described embodiment, the end portion of the fixing roller 21 is cooled by pressing the heat conducting member 31 or the spring-like body 51 which is an example of the heat conducting member against the inner peripheral surface of the end portion of the fixing roller 21. Thus, if the heat conducting member pressed against the inner peripheral surface of the end portion of the fixing roller 21 can be further forcibly cooled, the cooling effect of the end portion of the fixing roller 21 is further enhanced. In order to achieve such an effect, it is desirable to have a cooling means for forcibly cooling the end portion of the heat conducting member 31 or the spring-like body 51. As an example of such a cooling means, a heat pump type heat exchanger connected to the end portion of the heat conducting member 31 or the spring-like body 51 can be considered, but it is also possible to apply wind from a cooling fan. In this case, since the cooling air is not directly blown onto the surface of the fixing roller 21, the unfixed toner image on the recording paper passing through the fixing roller 21 is disturbed or the fixing roller 21 is cooled more than necessary. The problem that the heating efficiency of the fixing roller 21 is reduced does not occur.

  The present invention can be used for an image forming apparatus.

FIG. 3 is a schematic cross-sectional view illustrating a non-heat dissipating state of a cooling mechanism provided at an end portion of a fixing roller in the image forming apparatus X according to the first embodiment. FIG. 3 is a schematic cross-sectional view illustrating a heat dissipation state of a cooling mechanism provided at an end portion of a fixing roller in the image forming apparatus X according to the first embodiment. 6 is a graph schematically showing the distribution of the surface temperature of the fixing roller in the rotation axis direction at the start of printing and during continuous printing in a conventional image forming apparatus. FIG. 10 is a schematic cross-sectional view illustrating a non-heat dissipating state of a fixing roller end cooling mechanism in an image forming apparatus X according to a second embodiment. FIG. 10 is a schematic cross-sectional view illustrating a heat dissipation state of a fixing roller end cooling mechanism in an image forming apparatus X according to a second embodiment. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus X according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus X according to an embodiment of the present invention.

Explanation of symbols

21 ... Fixing roller 21a ... End inner peripheral surface 31 ... Heat conductive member 31a ... Outer peripheral surface 41 ... Wire (form)
50 ... Shaft 51 ... Spring-like body 53 ... Heat insulation member

Claims (7)

A thermal fixing device including a cylindrical fixing roller for fixing an unfixed toner image for fixing the toner image on the paper by rotating the recording paper on which the toner image has been transferred while contacting the surface thereof; In an image forming apparatus,
A heat conducting member mounted inside the end of the fixing roller and having a variable outer diameter;
A state in which the outer diameter of the heat conducting member is enlarged to bring the outer peripheral surface of the heat conducting member into contact with the inner peripheral surface of the end of the fixing roller; and the outer diameter of the heat conducting member is reduced by reducing the outer diameter of the heat conducting member. A heat conducting member deforming means for deforming the surface between a state where the surface is separated from the inner peripheral surface of the end portion of the fixing roller;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the heat conducting member deforming unit enlarges the outer diameter of the heat conducting member when the temperature of the end portion of the fixing roller exceeds a predetermined temperature.   2. The heat conduction member deforming means is configured to increase the outer diameter of the heat conduction member when a recording sheet narrower than a maximum sheet passing width is supplied and the time exceeds a predetermined time. Image forming apparatus.   The heat conducting member is formed in a substantially cylindrical shape with a slit-shaped notch in the axial direction, and the heat conducting member deforming means is wound around the substantially cylindrical heat conducting member to generate a tension. A strip which gives deformation in a direction to reduce the outer diameter to the heat conducting member wound by applying a tension and expands the outer diameter of the wound heat conducting member by releasing the tension, and The image forming apparatus according to claim 1, further comprising means for changing a tension.   The heat conducting member is a spiral coil-like spring-like body, and the heat conducting member deforming means rotates one end of the helical coil-like spring-like body relative to the other end around the center of the coil. The image forming apparatus according to claim 1, wherein the outer diameter of the spring-like body is enlarged by being moved, or is deformed by being reduced.   The image forming apparatus according to claim 1, wherein the fixing roller is made of aluminum and has a thickness of 0.5 to 1 mm.   The image forming apparatus according to claim 1, further comprising a cooling unit that forcibly cools an end of the heat conducting member.

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