JP2011145334A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus, capable of shortening a warm-up time and a recovery time from a standby mode, and also, suppressing an increase in cost. <P>SOLUTION: The fixing device includes: a fixing belt 55 which is stretched and wound on at least two rollers, that is, a fixing roller 51 and a heat roller 54 to be rotated and driven; a pressure member 52 which comes into press contact with the surface of the fixing belt 55; and a tension member 56 which applies a tension to the fixing belt 55. A recording medium S carrying a toner image to be fixed is made to pass through a gap, between the fixing belt 55 and the pressure member 52, in the direction in which the toner image comes into contact with the fixing belt 55, and the toner image is heated and pressed on passing through the gap, thereby, the toner image is fixed on the recording medium S. The tension member 56 includes a pair of pressing parts 56b separately coming into contact with both ends in a width direction perpendicular to the traveling direction of the fixing belt 55. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention is used for an image forming apparatus for recording an image on a sheet material (recording medium) such as a sheet or an OHP film, such as a copying machine, a printer, a facsimile machine, a multifunction machine equipped with these, and such an image forming apparatus. The present invention relates to a fixing device.

  Conventionally, for example, in an image forming apparatus using an electrophotographic system, a toner image is formed on an image carrier, the toner image is transferred to a sheet material (recording medium), and the sheet material after the image transfer is used as a fixing device. Put in. Then, heat and pressure are applied by the fixing device, and the unfixed toner image on the recording medium is fixed on the sheet material and discharged.

  In the fixing device, as shown in FIGS. 11 and 12, a fixing belt 75 is wound around a fixing roller 71 and a heating roller 74 having a heat source therein, and the fixing roller 71 is pressed against the fixing roller 75. There is a belt fixing device in which a roller 72 is pressed and a sheet material (paper) is fixed between the nips.

  The belt fixing device needs to apply tension to the belt 75. In the belt stretching method for applying the tension, the position of the fixing roller 71 is fixed, the heating roller 74 is energized to stretch the fixing belt 75, and the positions of both the fixing roller and the heating roller are set. There is a method in which the fixing belt 75 is stretched by pressing the tension roller 76 against the fixing belt 75 (Patent Document 1 and Patent Document 2).

  The former method (method of energizing the heating roller) has an advantage that the number of parts can be reduced because no tension roller is used. However, it is necessary to move the position of the heating roller. Therefore, there are the following problems (1) to (3).

(1) Installation accuracy is required, and it becomes difficult to attach a safety device such as a thermostat or temperature detection means such as a thermistor.
(2) It is necessary to increase the parallelism to prevent the belt from shifting, and it is necessary to increase the installation accuracy of the side plate (belt locking member) and to increase the rigidity of the side plate.
(3) The heating roller must be uniformly urged, resulting in poor maintainability.

  On the other hand, the latter method (method of pressing the tension roller) uses an extra tension roller, but fixes the positions of the fixing roller and the heating roller, so the problems (1), (2), (3), etc. There is almost no. For this reason, it can be said that the latter method is preferable to the former.

  In the fixing device shown in FIG. 11, the tension roller 76 is pressed from the inside of the fixing belt 75. In the fixing device shown in FIG. 12, the tension roller 76 is pressed from the outside of the fixing belt 75. Is.

  As shown in FIG. 13, the tension roller 76 generally has a cylindrical shaft portion 79a made of a rigid metal such as iron or aluminum, and an outer periphery of the shaft portion 79a. It comprises a pressing portion 79b that presses and applies tension directly. Both end portions of the shaft portion 79a are rotatably supported by a support member (not shown) such as a bearing. The pressing portion 79b is required to have a rigidity that applies pressure to the fixing belt 75, a frictional force that rotates the fixing belt 75 by itself, and a heat insulating property that does not take heat of the fixing belt 75 more than necessary. In view of heat insulation, heat-resistant felt materials are often used.

  The surface of the heating roller 74 is warmed by a heating source (not shown) disposed therein. The fixing belt 75 is warmed by the contact between the outer peripheral surface of the heating roller 74 and the inner peripheral surface of the fixing belt 75. The heated fixing belt 75 rotates to heat the entire circumference of the fixing belt. The heated fixing belt 75 passes through the nip formed by the fixing member 71 and the pressure member 72 together with the recording paper, so that heat is transferred to the toner on the recording paper and the toner is fixed to the recording medium (paper). Here, as described above (purpose), the tension roller 76 is necessary for the stable running of the fixing belt 75 spanned between the fixing member 71 and the heating roller 74.

  As shown in FIGS. 11 and 12, in the system in which the tension roller 76 is pressed, the tension roller 76 is pressed against the fixing belt 75 over almost the entire width of the fixing belt 75. For this reason, the heat of the fixing belt 75 escapes to the tension roller 76, and there has been a problem that the temperature of the fixing belt 75 rises slowly during warm-up or when returning from the energy-saving standby mode (remaining heat mode).

  In particular, since the tension roller 76 is usually installed at a position away from the heat source, the tension roller 76 is often held at a temperature lower than the temperature of the heating roller 74 and at 100 ° C. or less, which is the in-machine atmosphere temperature. As a result, the heat radiation from the tension roller 76 increases, and the warm-up time and the return time from the standby mode become longer, which is a problem in terms of energy saving.

  For this reason, some conventional belt fixing devices of this type use a heat insulating material having a small heat capacity for the tension roller, as described in Japanese Patent Application Laid-Open No. H10-228707. Even when such a heat insulating material is used, there is a problem that the warm-up time and the return time from the standby mode become long.

  Further, in Patent Document 2, auxiliary heating means for heating the tension member is provided in order to shorten the warm-up time and the return time from the standby mode. However, by providing the auxiliary heating means, there are problems of increase in energy and cost increase due to the addition of the heating source of the auxiliary heating means.

  In view of such circumstances, the present invention is intended to provide a fixing device and an image forming apparatus that can shorten the warm-up time and the return time from the standby mode, and can suppress the cost increase. is there.

  The fixing device according to the present invention includes a fixing roller, a fixing belt that is wound around at least two rollers of a heating roller, is rotated, a pressure member that is in pressure contact with the surface of the fixing belt, and tension is applied to the fixing belt. A recording medium carrying a toner image to be fixed is passed between the fixing belt and the pressure member in a direction in which the toner image is in contact with the fixing belt. In the fixing device for fixing the toner image to the recording medium by applying heat and pressure to the tension member, the tension member includes a pair of pressing portions respectively contacting both end portions in the width direction orthogonal to the traveling direction of the fixing belt. It is.

  According to the fixing device of the present invention, since it is not necessary to move the fixing roller or the heating roller for applying tension, the problems (1), (2), and (3) do not occur. In addition, the tension member has a pair of pressing portions that are in contact with both end portions in the width direction orthogonal to the running direction of the fixing belt, and the heat of the fixing belt is recorded within a range through which the recording paper (recording medium) passes. The tension member can be set so as not to be in contact with the fixing belt in a range where the paper is taken away, and heat can be prevented from being taken away from the tension member. For this reason, it is preferable that the pressing portion applies tension only on the outer side of the widthwise maximum end portion of the recording medium that passes.

  The tension member may be pressed from the outer surface side of the fixing belt or may be pressed from the inner surface side of the fixing belt.

  By the way, when pressing pressure is applied only to the end portion of the fixing belt, the fixing pressure is not applied depending on various conditions such as arrangement of members, rotation speed, pressing force of the pressing portion, pressing width of the pressing portion, and the like. There may be a case where a defective portion such as wrinkles or sagging occurs near the center of the belt. When such a wrinkle phenomenon occurs, the contact between the fixing belt near the center and the heating roller may be non-uniform, not in contact, or may be lifted. In such a location, the fixing belt cannot properly receive the amount of heat from the heating roller, and there is a risk that the temperature of that portion will be locally lowered. In places where the amount of heat cannot be properly received, problems such as poor fixing and uneven gloss will occur.

  Therefore, the tension member is preferably set so that tension is applied to the fixing belt outward in the width direction. Thus, by setting, wrinkles and sagging can be prevented from occurring near the center of the fixing belt.

In addition, the tension member may be provided with an auxiliary support portion that supports the fixing belt when the slack of the fixing belt occurs between the pressing portions. By providing the auxiliary support portion, it is possible to prevent the occurrence of wrinkles and sagging that cause defects such as poor fixing and uneven gloss in the vicinity of the center of the fixing belt.

  An image forming apparatus according to the present invention includes the fixing device described above.

  In the fixing device of the present invention, the problems (1), (2), and (3) do not occur, and an increase in cost can be suppressed. In addition, when the same energy is applied when the temperature of the fixing belt is raised from room temperature to a fixable temperature, the rate of temperature increase is increased. For this reason, the energy used can be reduced and energy saving can be achieved. Furthermore, the effect of shortening the waiting time of the operator of this apparatus can be obtained. Even during printing in which the recording medium (paper) passes through the fixing nip, heat transfer to the tension member is eliminated, so that energy saving can be achieved and the temperature of the fixing belt is stabilized because the heat transfer is small. For this reason, it is possible to improve the fixing performance, such as preventing the occurrence of fixing failure and stabilizing the glossiness of the image by stabilizing the temperature. Therefore, in the fixing device of the present invention, it is possible to shorten the warm-up time and the return time from the standby mode.

  The pressing part can stably prevent the escape of heat from the tension member by applying the tension only outside the maximum end in the width direction of the recording medium passing therethrough. As a result, the warm-up time and the return time from the standby mode can be further shortened.

  By applying a tension to the fixing belt outward in the width direction or by providing an auxiliary support portion, it is possible to prevent problems such as poor fixing and uneven gloss.

  In the image forming apparatus of the present invention, the warm-up time and the return time from the standby mode can be shortened, and the cost increase can be suppressed, and further, the occurrence of defects such as poor fixing and uneven gloss is prevented. And an image forming apparatus can be provided.

1 is an overall simplified view of an image forming apparatus of the present invention. 1 is a simplified diagram of a first fixing device of the present invention. FIG. 3 is a simplified perspective view of the fixing device shown in FIG. 2. FIG. 6 is a simplified diagram of a second fixing device of the present invention. FIG. 5 is a simplified perspective view of the fixing device shown in FIG. 4. FIG. 6 is a simplified diagram of a third fixing device. FIG. 10 is a simplified diagram of a fourth fixing device. FIG. 10 is a simplified diagram of a fifth fixing device. FIG. 3 is a simplified diagram of the fixing device in a state where wrinkles are generated in the fixing belt. FIG. 3 is a perspective view of the fixing device in a state where wrinkles are generated in the fixing belt. It is a perspective view of a conventional fixing device. FIG. 10 is a perspective view of another conventional fixing device. It is sectional drawing of a general tension member.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention according to embodiments shown in the drawings will be described.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is a color laser printer, and includes a tandem image forming unit including four image forming units 101Y, 101C, 101M, and 101K arranged at regular intervals. Note that subscripts Y, C, M, and K of the image forming unit indicate yellow, cyan, magenta, and black members.

  Each of the image forming units 101Y, 101C, 101M, and 101K forms a latent image on the photoconductors (photoconductor drums) 21Y, 21C, 21M, and 21K as image carriers and the photoconductor drums 21Y, 21C, 21M, and 21K. A developing device 10Y, 10C, 10M for developing a latent image on the photosensitive drums 21Y, 21C, 21M, and 21K with toner (for example, an optical writing unit 9 and a charging device 30). 10K and a cleaning device 40 for cleaning the surface of the photosensitive drum.

  At the top of the printer, toner bottles 2Y, 2C, 2M, and 2K are arranged. That is, the toner bottle 2Y is filled with yellow toner, the toner bottle 2C is filled with cyan toner, the toner bottle 2M is filled with magenta toner, and the toner bottle 2K is filled with blackener. Each color developing device 10Y, 10C, 10M, and 10K is replenished from the toner bottles 2Y, 2C, 2M, and 2K by a predetermined replenishment amount via a conveyance path (not shown).

  In addition, an optical writing unit 9 as a latent image forming unit is provided below the tandem image forming unit. The optical writing unit 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like. The surface of each photoconductor 1 is irradiated with laser light while scanning based on the image data.

  Above the tandem image forming unit, an endless belt-like intermediate transfer belt 1 is provided as an intermediate transfer member. The intermediate transfer belt 1 is wound around support rollers 1a and 1b, and a drive motor (not shown) serving as a drive source is connected to a rotation shaft of the drive roller 1a among the support rollers. When this drive motor is driven, the intermediate transfer belt 1 travels (rotates) in the counterclockwise direction while being wound around the support rollers 1a and 1b. At this time, the followable support roller 1b rotates. Inside the intermediate transfer belt 1, primary transfer devices 11Y, 11C, 11M, and 11K for transferring the toner images formed on the photoreceptors 21Y, 21C, 21M, and 21K onto the intermediate transfer belt 1 are provided. .

  Further, a secondary transfer roller 4 as a secondary transfer device is provided downstream of the primary transfer devices 11Y, 11C, 11M, and 11K in the driving direction of the intermediate transfer belt 1. A support roller 1b is disposed on the opposite side of the secondary transfer roller 4 and the intermediate transfer belt 1, and the support roller 1b functions as a pressing member. In addition, a paper feed cassette 8, a paper feed roller 7, a registration roller 6, and the like are disposed upstream of the secondary transfer roller 4. Further, a fixing device 5 for fixing an image on the recording medium S and a paper discharge roller 3 are disposed downstream of the secondary transfer roller 4 with respect to the traveling direction of the recording medium S to which the toner image is transferred by the secondary transfer roller 4. It has.

  The fixing device 5 includes a fixing roller 55 as a fixing member, a fixing belt 55 that is wound around at least two rollers, that is, a heating roller 54 as a heating member, and a pressure belt that is in pressure contact with the surface of the fixing belt 55. A pressure member 52 and a tension member 56 that applies tension to the fixing belt 55 are provided. The heating roller 54 has a heating source 53, and the surface of the fixing roller 51 is maintained at a predetermined temperature by a temperature control unit (not shown).

  The printer operation in the image forming apparatus configured as described above will be described. The photoreceptors 21Y, 21C, 21M, and 21K are rotated by the individual image forming units, and the photoreceptors 21Y, 21C, and 21C are first rotated by the charging devices 17Y, 17C, 17M, and 17K as the photoreceptors 21Y, 21C, 21M, and 21K rotate. The surfaces of 21M and 21K are uniformly charged.

  Next, the image data is irradiated with writing light by a laser from the optical writing unit 9 to form electrostatic latent images on the photoreceptors 21Y, 21C, 21M, and 21B. Thereafter, toner is attached by the developing devices 10Y, 10C, 10M, and 10K, and the electrostatic latent images are visualized to form yellow, cyan, magenta, and black on the photoreceptors 21Y, 21C, 21M, and 21K, respectively. A monochromatic image is formed.

  The drive roller 1a is rotationally driven by a drive motor (not shown), the other driven roller 1b and the secondary transfer roller 4 are driven to rotate, and the intermediate transfer belt 1 is rotated and conveyed. The visible images are sequentially transferred onto the intermediate transfer belt 1 by the primary transfer devices 11Y, 11C, 11M, and 11K. As a result, a composite color image is formed on the intermediate transfer belt 1. The surface of the photoconductors 21Y, 21C, 21M, and 21K after the image transfer is cleaned by removing residual toner by the photoconductor cleaning device 40 to prepare for image formation again.

  In accordance with the timing of image formation, the recording medium S is fed out from the paper feed cassette 8 by the paper feed roller 7, conveyed to the registration roller 6, and temporarily stops. Then, the sheet is conveyed between the secondary transfer roller 4 and the intermediate transfer belt 1 while taking the timing with the image forming operation. Here, the intermediate transfer belt 1 and the secondary transfer counter roller 4 form a so-called secondary transfer nip across the recording medium S, and the secondary transfer roller 4 transfers the toner image on the intermediate transfer belt 1 to the recording medium S. Secondary transfer on top.

  Then, the recording medium S after the image transfer is sent to the fixing device 5. In the fixing device 5, a recording medium (paper) is conveyed by nipping and conveying the paper to a nip portion formed by a pressure member (pressure roller) 52 that faces the fixing member (fixing roller) 51 and is pressed against the fixing member 51. The toner image on S is heated and pressed to be fixed on the paper S. Further, the paper S discharged from the nip portion is discharged from the paper discharge roller 3 to the outside of the apparatus. On the other hand, the intermediate transfer belt 1 after the image transfer is removed by the intermediate transfer body cleaning device 12 to remove residual toner remaining on the intermediate transfer belt 1 after the image transfer, so that the tandem image forming unit prepares for another image formation.

  As shown in FIGS. 3 and 4, the tension roller (tension member) 56 of the present invention includes a cylindrical shaft portion 59a made of a rigid metal such as iron or aluminum, and an end of the shaft portion 59a. It consists of a pair of press parts 59b and 59b arrange | positioned by the part side. The pressing portions 59b and 59b are formed of a short cylindrical body, and the pressing portions 59b and 59b press the fixing belt 55 to directly apply tension. Note that both end portions of the shaft portion 79a are rotatably supported by a support member (not shown) such as a bearing.

  The pressing portions 59b and 59b are required to have a rigidity that applies pressure to the fixing belt 55, a frictional force that rotates the fixing belt 55 by itself, and a heat insulating property that does not take heat of the fixing belt 75 more than necessary. In view of heat insulation, a heat-resistant felt material is often used. However, the material is not limited as long as the above functions are satisfied.

  The dimension W between the pressing portions 59b and 59b is set larger than the maximum width dimension W1 of the paper (recording medium) S. For this reason, the pressing portions 59b and 59b apply tension only outside the maximum width direction end portion of the recording medium S that passes therethrough.

  3, the tension roller 56 is disposed inside the fixing belt 55, and in the one illustrated in FIG. 4, the tension roller 56 is disposed outside the fixing belt 55.

  In the tension roller 56 as shown in FIGS. 3 and 4, the tension roller 56 and the fixing belt 55 are within the range where the heat of the fixing belt 55 is taken away by the recording paper (recording medium S) within the range through which the recording medium S passes. Not touching. For this reason, it is possible to prevent heat from being removed from the tension roller 56.

  As a result, when the same energy is applied when the temperature of the fixing belt 55 is raised from room temperature to a fixable temperature, the temperature increase rate is increased. For this reason, the energy used can be reduced and energy saving can be achieved. At the same time, the effect of shortening the waiting time of the equipment operator can be obtained. Even during printing in which the recording paper (recording medium S) passes through the fixing nip, the heat transfer to the tension roller 56 is eliminated, so that energy saving can be achieved and the temperature of the fixing belt 55 is stabilized because the heat transfer is small. It is possible to improve the fixing performance such as preventing the occurrence of fixing failure and stabilizing the gloss of the image by stabilizing the temperature. This effect can be obtained similarly when the tension roller 56 is disposed outside the fixing belt 55 and when the tension roller 56 is disposed inside.

  Incidentally, as described above, when pressing pressure is applied only to the end portion of the fixing belt 55, depending on various conditions such as arrangement of members, rotation speed, tension roller pressing force, tension roller pressing width, etc., FIG. As shown in FIG. 10, there may be a case where a defective portion 50 such as wrinkles or sagging occurs near the center of the fixing belt 55 to which no pressing pressure is applied.

  When such a wrinkle phenomenon occurs, the contact between the fixing belt 55 near the center and the heating roller 54 may be non-uniform, not in contact, or may have floated. It is conceivable that the fixing belt 55 at such a location cannot properly receive the amount of heat from the heating roller 54, and the temperature at that portion locally decreases. In such a case, problems such as poor fixing and uneven gloss will occur in places where the temperature of the fixing belt 55 is inappropriate.

  Therefore, in FIG. 6, the configuration is such that the defective portion 50 as shown in FIGS. 9 and 10 does not occur. The tension member 56 applies tension to the fixing belt 55 outward in the width direction. That is, in this case, the tension member 56 is configured such that the pressing portions 59b and 59b can reciprocate along the axial direction with respect to the shaft portion 59a. Elastic members 59c and 59c for pressing in the direction. The elastic members 59c and 59c are made of a coil spring or the like and are received by the support pieces 59d and 59d supported by the shaft portion 59a.

  Further, detent guides 58 and 58 as shown in FIG. 6 are provided at both ends in the width direction of the fixing belt 55. That is, the detent guide 58 is affixed (adhered) to both ends of the fixing belt 55, and when the fixing belt 55 is close to either one of the axial directions, it interferes with either end of the member to be included, This interference prevents the fixing belt 55 from further approaching the opposite end, and prevents the fixing belt 55 from falling off the inner member. In the case of the embodiment, the heating roller 54 and the detent guide 58 are configured to interfere with each other.

  Here, when the tension member 56 is installed in the fixing belt 55, the pressing portion 59b biased by the elastic member 59c is pressed against the detent guide 58, and as a result, a force for pulling the fixing belt 55 outward is given. As a result, the defective portion 50 such as sagging and wrinkles near the center of the fixing belt 55 is improved.

  In FIG. 7, the rollers constituting the pressing portions 59 b and 59 b have a trapezoidal cross section (Tsumami shape) whose outer diameter surface expands from the axially inner side toward the axially outer side. For this reason, the fixing belt 55 in contact with the pressing portion 59b receives a force that is rotated at a higher speed because the outer diameter of the fixing belt 55 is larger on the outer side. It is known that a member rotatably supported by such a knob-shaped rotating body receives an external tension, and as a result, the fixing belt 55 receives a pulling force to the outside, resulting in a defective portion such as a wrinkle around the center. 50 is improved. In addition, in the press parts 59b and 59b shown in FIG. 7, the inclination angle of an outer diameter surface is exaggerated and drawn. Actually, the difference between the small-diameter portion and the large-diameter portion can function sufficiently when the difference is about 0.1 mm.

  The tension member 56 is provided with an auxiliary support portion 60 that supports the center in the width direction of the fixing belt 55 when the fixing belt 55 sags between the pressing portions 59b and 59b. The auxiliary support portion 60 is composed of a roller body that is externally fitted and fixed to the central portion in the axial direction of the shaft portion 59a. As the material of the roller body, the same material as the pressing portions 59b and 59b can be used. In this case, the auxiliary support portion 60 has an outer diameter dimension set smaller than the outer diameter dimensions of the pressing portions 59b and 59b.

  For this reason, when the fixing belt 55 is operating normally, the auxiliary support portion 60 does not contact the fixing belt 55. As a result, the heat of the fixing belt 55 is not taken away. However, when sagging or the like occurs in the fixing belt 55 due to various conditions, the auxiliary support portion 60 supports the fixing belt 55 in an auxiliary manner. For this reason, it can return to a normal form, ie, the defective part 50 is not produced, and generation | occurrence | production of wrinkles, slack, etc. can be prevented.

  In addition, this invention is not limited to the above-mentioned Example, Of course, a various change can be added in the range which does not deviate from the summary of this invention. Examples of the image forming apparatus according to the present invention include an electrophotographic copying machine, a laser beam printer, and a facsimile machine. The length of the pressing portion 56b in the axial direction can be variously changed as long as the tension can be applied only on the outer side of the widthwise maximum end portion of the recording medium passing therethrough. Further, when the auxiliary support portion 60 is provided, the position of the auxiliary support portion 60 is not limited to the central portion in the axial direction, and the number of roller bodies constituting the auxiliary support portion 60, the axial length, etc. Various modifications can be made based on the material of the roller body and the like within a range in which it is difficult to remove heat from the fixing belt 55.

51 Fixing roller (fixing member)
52 Pressure Member 54 Heating Roller 55 Fixing Belt 56 Tension Roller (Tension Member)
56b Pressing part 60 Auxiliary supporting part S Recording medium

JP 2002-123111 A JP 2005-10249 A

Claims (7)

A fixing roller; a fixing belt that is wound around at least two rollers of a heating roller and driven to rotate; a pressure member that presses against the surface of the fixing belt; and a tension member that applies tension to the fixing belt. The recording medium carrying the toner image to be fixed is passed between the fixing belt and the pressure member so that the toner image is in contact with the fixing belt, and heat and pressure are applied to the toner image during the passage. In a fixing device for fixing the toner image on a recording medium,
The fixing device is characterized in that the tension member includes a pair of pressing portions that are in contact with both end portions in the width direction orthogonal to the traveling direction of the fixing belt.   The fixing device according to claim 1, wherein the pressing portion applies a tension only on an outer side of a width direction maximum end portion of the recording medium that passes therethrough.   The fixing device according to claim 1, wherein the tension member is pressed from an outer surface side of the fixing belt.   The fixing device according to claim 1, wherein the tension member is pressed from an inner surface side of the fixing belt.   The fixing device according to claim 1, wherein the tension member applies tension to the fixing belt outward in the width direction.   5. The fixing device according to claim 1, wherein the tension member includes an auxiliary support portion that supports the fixing belt when a slack of the fixing belt occurs between the pressing portions.   An image forming apparatus comprising the fixing device according to claim 1.

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