JP2006119473A - Image forming apparatus and belt device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform steady belt drive control for a long period of time by preventing an object to be detected from being soiled, wearing, or peeling with time, without shortening the service life of an apparatus nor increasing the size and cost of the apparatus. <P>SOLUTION: The belt drive device rotates a transfer conveyance belt 60 stretched over a plurality of rollers, by driving at least one of the rollers. An bias-stop guide 104 disposed at the end of the internal circumferential face of the transfer conveyance belt is made a multilayer structure having a surface layer 102 and a lower layer 101 whose hardness is higher than that of the surface layer 102 and fixed to the transfer conveyance belt. A marking member 103 is disposed in the multilayer of the bias-stop guide. The marking member is detected by a photo-sensor 105. On the basis of the detection result of the detecting means, the belt drive device is controlled. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a belt device used for a copying machine, a fax machine, a printer, and the like, and an image forming apparatus employing the belt device.

  2. Description of the Related Art Conventionally, image forming apparatuses are known in which an endlessly movable belt is provided, such as an intermediate transfer belt for intermediate transfer of a toner image and a paper conveyance belt for conveying transfer paper. In addition, in order to prevent a situation in which the belt is excessively offset in the width direction on the stretching roller for running the belt and is separated from the stretching roller, the belt is moved closer to both ends on the inner circumferential surface of the belt. There is also known one provided with a stop guide. Further, there are also known ones that take measures to minimize the belt speed fluctuation. When speed fluctuations occur in the belt, for example, if the transfer belt is formed by superimposing a plurality of toner images on the surface or the transfer paper held on the surface, misalignment may occur, or the transfer paper may be moved toward the transfer position. This is because if the belt is transported, the transfer position is shifted.

  Therefore, in order to keep the belt speed constant, a method of detecting the belt speed fluctuation and correcting the rotation of the driving roller for rotating the belt based on the detection result by feedback control is performed. This means that the belt speed is detected based on the detection time interval of the detected object provided at a predetermined pitch in the belt circumferential direction or the belt speed based on the detection timing of only one reference mark provided in the belt circumferential direction. Is to detect. As an example, as shown in Patent Document 1 and Patent Document 2, transfer of obtaining a color image by transferring each color toner image formed on a photosensitive member directly on a transfer belt or via a transfer member. Various things related to the belt device are disclosed.

Japanese Patent Laid-Open No. 2000-231283 JP 2003-173067 A

  In Patent Document 1 or Patent Document 2 described above, a marking is provided on the inner peripheral surface of the transfer belt as an object to be detected, and a difference in reflectance between the inner peripheral surface of the transfer belt and this marking is detected by an optical sensor as a detecting means. is doing. For this reason, the reflective surface of the marking is damaged over time due to adhesion of dirt due to toner scattering inside the apparatus or wear due to contact between the inner peripheral surface of the transfer belt and the roller, resulting in a difference in reflectance between the marking and the transfer belt. May become small and cause poor detection. Moreover, there is a possibility that a detection failure due to the peeling of the marking may occur.

  In order to solve this, it is conceivable to prevent the surface of the marking from being exposed. As one of them, a simple method of covering the surface of the marking without increasing the number of parts by using a detent guide provided at the end portion of the inner peripheral surface of the belt can be considered. Specifically, a transparent material is used as the detent guide, and the marking is sandwiched between the transfer belt and the detent guide. As a result, the surface of the marking is not exposed, the surface is less likely to become dirty, and it is strong against abrasion and peeling.

  Here, a rubber with a relatively low hardness is suitable as a detent guide because of its function, and when a cheap and transparent material having such characteristics is selected and used, the detent guide becomes a belt. The problem of being peeled off occurred. This is because when a low hardness stopper guide and a belt member made of a material that is not easily distorted due to its function are fixed, even if the low hardness stopper guide deforms, the belt member follows and deforms. Is easy to peel off. Here, if the rubber is relatively low in hardness and transparent, the number of materials that can be selected is reduced, and among those that are inexpensive, it can be said that the rubber is peeled off from the belt. In addition, there are materials with relatively low hardness, which are transparent and difficult to peel off, but they are very expensive.

  In addition, instead of marking as an object to be detected, a method is also conceivable in which a hole is formed directly in the transfer belt and this is detected by a transmission optical sensor. However, stress concentration occurs around the hole, and if the apparatus is operated for a long time, the transfer belt is damaged due to fatigue, resulting in a problem that the life of the transfer belt is shortened.

  Further, a method is conceivable in which a protrusion that is integrated with the belt in the width direction of the transfer belt is provided as an object to be detected, and this protrusion is detected by a transmission type optical sensor. However, it is difficult to form the protrusions integrally with the transfer belt, and the protrusions protrude in the width direction, so that a space is required and the unit becomes large.

  Further, as a detection method, it is conceivable to use a magnetic detection object and a magnetic detection means in addition to the optical detection means using the above-described optical sensor. Even in such a case, since the surface of the detection object is exposed, problems such as contamination, wear, and peeling of the detection object may occur over time, which may cause detection failure.

  The present invention has been made in view of such a background. The purpose is to provide stable belt drive control over a long period of time by preventing contamination, wear, and peeling of the detected object over time without shortening the service life, increasing the size, and increasing the cost. It is an object of the present invention to provide a belt device and an image forming apparatus that can be used.

In order to achieve the above-mentioned object, the invention according to claim 1 is characterized in that an endless belt stretched around a plurality of rollers and at least one of the plurality of rollers are driven to rotationally drive the belt. A belt drive device; a detent guide provided at an end portion of the inner peripheral surface of the belt; a detection object provided on the belt; and a detection means for detecting the detection object. In the image forming apparatus for controlling the belt driving device based on the detection result, the detent guide has a multilayer structure having at least a surface layer and a lower layer fixed to the belt with higher hardness than the surface layer, and the detected object Is disposed between multiple layers of the detent guide.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the surface layer of the detent guide is transparent, the object to be detected is disposed under the surface layer, and the detection means is an optical sensor. It is a feature.
According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the image forming apparatus includes an image carrier on which a toner image is formed, and the toner image is transferred from the image carrier directly or via a transfer target. It is a transfer belt to be carried, or a conveyance belt that conveys a transfer object carried on the surface toward a transfer position.
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the image forming apparatus further comprises a plurality of image forming portions for forming toner images on the plurality of image carriers, and the belt passes through a portion facing the plurality of image carriers. Thus, a multicolor image is formed by superimposing and transferring toner images from the respective image carriers.
The invention of claim 5 includes an endless belt stretched around a plurality of rollers, a belt driving device that drives at least one of the plurality of rollers to rotationally drive the belt, A detent guide provided at an end portion of the inner peripheral surface of the belt to prevent meandering, a detected object provided on the belt, and a detecting means for detecting the detected object, the detection In the belt device for controlling the belt driving device based on the detection result of the means, the detent guide has a multilayer structure having at least a surface layer and a lower layer fixed to the belt with higher hardness than the surface layer, and the object to be detected Is disposed between multiple layers of the detent guide.
According to a sixth aspect of the present invention, in the belt device according to the fifth aspect, the surface layer of the detent guide is transparent, the object to be detected is disposed under the surface layer, and the detection means is an optical sensor. It is what.

  In the inventions of claims 1 to 6, as the detent guide, the surface layer uses a material having an appropriate rubber hardness to fulfill the detent function, and the lower layer fixed to the belt uses a higher hardness than this, An object to be detected is disposed between the multilayers. With such a configuration, the surface layer effectively prevents the belt from being offset, protects the surface of the detection object, and prevents contamination, abrasion, and peeling. Also, the lower layer fixed to the belt is difficult to peel off from the belt. This is to suppress peeling by interposing a lower layer harder than the surface layer between the surface layer that is relatively low hardness and easy to deform and a belt member that is not easily distorted, and functions as a cushioning material to buffer the deformation. is there. By adopting such a configuration, the selectivity of the material is widened as compared with the case where the detection target is covered with the single-layer detent guide, and as a result, the cost is reduced. Further, since the surface of the detection object is covered by using the detent guide, the entire apparatus has a simple configuration as compared with the method of providing another member. And since a belt drive device is controlled based on a detection result based on such a stable position detection result, a stable belt drive can be performed over a long period of time.

  According to the present invention, the belt can be stably driven over a long period of time by preventing contamination, abrasion, and peeling of the detection target over time without shortening the life, increasing the size, and increasing the cost of the apparatus. There is an excellent effect of being able to.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic tandem color laser printer (hereinafter referred to as “laser printer”) as an image forming apparatus will be described.
The tandem type laser printer includes a plurality of photoconductors arranged in parallel, and includes a toner image forming portion that forms each toner image on each photoconductor, and superimposes the color toner images formed on each photoconductor. To obtain a color image. In the tandem type laser printer, there are a method of directly transferring to a transfer sheet (direct transfer method) and a method of final transfer via an intermediate transfer member (intermediate transfer method). The direct transfer method is a method in which an image is directly formed by a toner image forming unit for each color on a transfer sheet conveyed by a transfer conveyance belt. On the other hand, the intermediate transfer method is a method in which an image formed by each color toner image forming unit is once formed on an intermediate transfer belt and then further transferred from the intermediate transfer belt to a transfer sheet.

  Since a tandem type laser printer uses a plurality of photoconductors, toner images of each color can be formed in parallel. Therefore, there is an advantage that the number of output sheets per unit time is larger than that of a so-called revolver type laser printer that repeatedly uses a single photosensitive drum to form each color toner image. On the other hand, since the transfer conveyance belt or the intermediate transfer belt passes through each toner image forming section one after another and obtains a color image, there is a problem that it is difficult to align each color.

  FIG. 1 is a schematic configuration diagram of a laser printer according to the present embodiment. The laser printer according to this embodiment will be described using a direct transfer system. This laser printer transfers four sets of toner image forming portions 1Y, 1M, 1C, and 1K for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K). They are arranged in order from the upstream side in the moving direction of the paper 100 (the direction in which the belt 60 travels along the arrow A in the figure). Note that the subscripts Y, M, C, and K of the respective symbols indicate members for yellow, magenta, cyan, and black, respectively. Each of the toner image forming units 1Y, 1M, 1C, and 1K includes photosensitive drums 11Y, 11M, 11C, and 11K as image carriers and a developing unit. In addition, the arrangement of the toner image forming units 1Y, 1M, 1C, and 1K is set so that the rotation axes of the photosensitive drums are parallel and arranged at a predetermined pitch in the transfer paper moving direction. .

  In addition to the toner image forming units 1Y, 1M, 1C, and 1K, the laser printer carries the optical writing unit 2, the paper feed cassettes 3, 4, the resist roller pair 5, and the transfer paper 100, and each toner image forming unit. A transfer unit 6 as a belt driving device having a transfer conveyance belt 60 as a transfer conveyance member that conveys the sheet so as to pass through the transfer position, a belt fixing type fixing unit 7, a paper discharge tray 8, and the like. In addition, a manual feed tray MF and a toner supply container TC are provided, and a waste toner bottle, a duplex / reversing unit, a power supply unit, and the like (not shown) are also provided in a space S indicated by a two-dot chain line.

  The optical writing unit 2 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K while scanning the laser beam based on the image data. .

FIG. 2 is an enlarged view showing a schematic configuration of the transfer unit 6. The transfer conveyance belt 60 used in the transfer unit 6 is a high-resistance endless single-layer belt having a volume resistivity of 10 ⁹ to 10 ¹¹ Ωcm, and the material thereof is PVDF (polyvinylidene fluoride). The transfer / conveying belt 60 is wound around rollers 61 to 68 so as to pass through the transfer positions that contact and face the photosensitive drums 11Y, 11M, 11C, and 11K of the toner image forming units. Among these rollers, the entrance roller 61 on the upstream side in the transfer paper moving direction is disposed on the outer peripheral surface of the transfer conveyance belt 60 so that the electrostatic adsorption roller 80 to which a predetermined voltage is applied from the power source 65a is opposed. . The transfer paper 100 that has passed between the two rollers 61 and 65 is electrostatically attracted onto the transfer conveyance belt 60.

  A roller 63 is a drive roller that frictionally drives the transfer conveyance belt 60, and is connected to a drive source (not shown) and rotates in the direction of the arrow. As a transfer electric field forming means for forming a transfer electric field at each transfer position, transfer bias applying members 67Y, 67M, 67C, and 67K are provided at positions facing the photosensitive drum so as to be in contact with the back surface of the transfer conveyance belt 60. ing. These are bias rollers provided with a sponge or the like on the outer periphery, and a transfer bias is applied to the roller metal from each transfer bias power source 9Y, 9M, 9C, 9K. Due to the action of the applied transfer bias, a transfer charge is applied to the transfer conveyance belt 60, and a transfer electric field having a predetermined strength is formed between the transfer conveyance belt 60 and the surface of the photosensitive drum at each transfer position. In addition, a backup roller 68 is provided to keep the contact between the transfer paper and the photoconductor in the area where the transfer is performed, and to obtain the best transfer nip.

  The transfer bias applying members 67Y, 67M, and 67C and the backup roller 68 disposed in the vicinity thereof are integrally held by the swing bracket 93 so as to be rotatable, and can be rotated around a rotation shaft 94. This rotation is clockwise when the cam 96 fixed to the cam shaft 97 is rotated in the direction of the arrow.

  The entrance roller 61 and the suction roller 80 are integrally supported by the entrance roller bracket 90, and can be rotated clockwise from the state shown in FIG. A hole 95 provided in the swing bracket 93 and a pin 92 fixed to the entrance roller bracket 90 are engaged with each other, and rotate in conjunction with the rotation of the swing bracket 93. By the clockwise rotation of these brackets 90, 93, the bias applying members 67Y, 67M, 67C and the backup roller 68 disposed in the vicinity thereof are separated from the photoreceptors 11Y, 11M, 11C, and the entrance roller 61 and the suction roller 80 also moves downward. It is possible to avoid contact between the photoconductors 11Y, 11M, and 11C and the transfer conveyance belt 60 when forming a black-only image.

  On the other hand, the transfer bias applying member 67K and the backup roller 68 adjacent to the transfer bias applying member 67K are rotatably supported by the outlet bracket 98, and are rotatable about a shaft 99 coaxial with the outlet roller 62. When attaching / detaching the transfer unit 6 to / from the main body, the transfer unit 6K is rotated clockwise by operating a handle (not shown), and the transfer bias applying member 67K and the backup roller 68 adjacent thereto are moved from the black image forming photosensitive member 11K. They are separated.

  A cleaning device 85 composed of a brush roller and a cleaning blade is disposed on the outer peripheral surface of the transfer conveyance belt 60 wound around the driving roller 63. The cleaning device 85 removes foreign matters such as toner adhering to the transfer conveyance belt 60.

  A roller 64 is provided downstream of the driving roller 63 in the traveling direction of the transfer conveyance belt 60 in a direction to push the outer peripheral surface of the transfer conveyance belt, and a winding angle around the drive roller 83 is ensured. A tension roller 65 that applies tension to the belt with a pressing member (spring) 69 is provided in the loop of the transfer conveyance belt 60 further downstream from the roller 64.

  The one-dot chain line in FIG. 1 shown above indicates the conveyance path of the transfer paper 100. The transfer paper 100 fed from the paper feed cassettes 3 and 4 or the manual feed tray MF is transported by transport rollers while being guided by a transport guide (not shown), and is transported to a temporary stop position where the registration roller pair 5 is provided. The transfer paper 100 delivered at a predetermined timing by the registration roller pair 5 is carried on the transfer conveyance belt 60, conveyed toward the toner image forming units 1Y, 1M, 1C, and 1K, and passes through the transfer nips. .

  The toner images developed on the toner drums 11Y, 11M, 11C, and 11K of the toner image forming units 1Y, 1M, 1C, and 1K are superimposed on the transfer paper 100 at the transfer nips, respectively. It is transferred onto the transfer paper 100 under the action of pressure. By this superposition transfer, a full-color toner image is formed on the transfer paper 100. The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the toner image transfer are cleaned by a cleaning device, and are further discharged to prepare for the formation of the next electrostatic latent image.

  On the other hand, the transfer paper 100 on which the full-color toner image is formed is fixed in the first paper discharge direction B or the second in accordance with the rotation posture of the switching guide G after the full-color toner image is fixed by the fixing unit 7. In the paper discharge direction C. When the paper is discharged from the first paper discharge direction B onto the paper discharge tray 8, it is stacked in a so-called face-down state with the image surface down. On the other hand, when the paper is discharged in the second paper discharge direction C, it is conveyed toward another post-processing device (such as a sorter or a binding device) (not shown), or is registered again for double-sided printing via a switchback unit. It is conveyed to the roller pair 5.

  In such a laser printer, it is essential that the transfer conveyance belt 60 moves endlessly while maintaining a constant movement speed. If the transfer belt speed fluctuates during image formation, color misregistration occurs and the image quality of the color image is significantly reduced.

  One of the fluctuations in the speed of the transfer / conveyance belt 60 is caused by the eccentricity of the diameter of the drive roller 63 that regulates the speed of the transfer / conveyance belt 60. In this regard, the eccentricity of the driving roller 63 does not contribute to color misregistration by setting the distances 1Y, 1M, 1C, and 1K between the toner image forming portions to an integral multiple of the circumference of the driving roller of the transfer conveyance belt 60. Can be.

  In order to suppress the speed fluctuation of the transfer belt, as disclosed in Japanese Patent Laid-Open No. 63-81370, a driven roller that contacts the back surface of the transfer belt and rotates at the same speed as the transfer belt is used for speed detection. There is also a method in which the rotation speed of the driven roller is detected by an encoder, and the detected speed is fed back to a servo control circuit so that the drive speed is always equal to a predetermined speed. However, in the method in which the rotation of the driven roller is detected by an encoder and corrected by feedback control, when the thickness of the transfer belt varies, the variation in the thickness of the transfer belt occurs at the location where the rotationally driven drive roller is wound around the transfer belt. As a result, the distance from the center of the driving roller to the belt surface changes, so the belt speed fluctuates. In particular, in the case of an integrally formed seamless belt, a thickness deviation easily occurs around the belt.

  Japanese Patent Application Laid-Open No. 2003-173067 discloses one that corrects a speed fluctuation caused by a change in the thickness of a transfer belt. In this case, first, a detection object is provided on the inner peripheral surface of the transfer belt, and thickness change data of the transfer belt is stored in advance for one rotation of the belt with reference to the position of the detection object. Then, along with the rotation of the transfer belt, the detection object is detected by the detection means, and the rotation of the driving roller is corrected and controlled based on the stored thickness change data based on the stored thickness change data. To do. According to this method, it is possible to prevent color misregistration due to speed fluctuation of the transfer belt due to thickness deviation of the transfer belt.

  Therefore, in the laser printer of this embodiment, in order to keep the speed of the transfer conveyance belt 60 constant, a marking member is provided on the inner peripheral surface of the transfer conveyance belt 60 as a detection target, and the inner peripheral surface of the transfer conveyance belt 60 is provided. And a difference in reflectance between the marking member and the marking member are detected by an optical sensor as a detecting means. Then, the belt speed is detected based on the detection timing of the marking member, and the rotation of the driving roller that rotationally drives the belt is corrected by feedback control based on the detection result.

  Next, the characteristic part of this embodiment is demonstrated. FIG. 3A shows a detent guide 104 for the transfer conveyance belt 60. The stopper guide 104 has a two-layer structure composed of a rubber material for the lower layer 101 and a rubber material for the upper layer 102. The upper layer 102 is a transparent rubber material, and a material having an optimum rubber hardness (low hardness) is used as a guide. The lower layer 101 is a rubber material for strengthening the adhesive strength, and has a higher hardness than the upper layer. Specifically, a transparent thermoplastic urethane rubber (hardness 66 °) was used as the rubber material of the upper layer 102, and a thermoplastic urethane rubber (hardness 90 °) was used as the rubber material of the lower layer 101. A typical example of such a stopper guide is MA-W manufactured by Ashiya Co., Ltd. Further, as shown in FIG. 3B, a marking member 103 as a detection object is sandwiched and welded between two layers of rubber material. The lower layer 101 of such a detent guide 104 is adhered to the inner peripheral surface of the transfer conveyance belt 60 with a double-sided tape. The material of the transfer conveyance belt 60 is PVDF and transmits light.

  FIG. 4 is an explanatory diagram of the marking member detection means. An optical sensor 105 as a detection unit is provided at a position facing the detent guide 104 inside the transfer conveyance belt 60. A marking member is detected by this optical sensor, and driving of the driving roller 63 is controlled based on the detection result. In this way, the marking surface can be protected and the adhesive strength of the guide can be maintained while providing the characteristics as a detent guide.

  In the above-described embodiment, a tandem image forming apparatus in which a plurality of photosensitive drums 11Y, 11M, 11C, and 11K are arranged side by side on the transfer conveyance belt 60. The present invention is applied to the transfer unit 6 that employs a two-layer urethane rubber as a stop guide. The image forming apparatus and the belt apparatus to which the present invention can be applied are not limited to this configuration. Needless to say, the present invention is applicable to an intermediate transfer belt in which an image formed by each color toner image forming unit of a tandem image forming apparatus is formed on a transfer belt and then transferred from the transfer belt to a transfer sheet. Furthermore, any belt device can be used as long as it is a belt device that rotates and drives an endless belt stretched around a plurality of rollers by at least one of the rollers, and a belt device of an image forming apparatus that has a guide at the end of the belt. Is also applicable. In the above embodiment, the present invention has been described using detection by an optical detection unit. However, the present invention can also be applied to other detection units such as a magnetic detection unit.

As described above, according to the image forming apparatus according to the present embodiment, the first layer 102 is made of the material having the optimum rubber hardness as the detent guide 104 and is detected between the first layer 102 and the second layer 101. A marking member 103 as a body is disposed. Then, the second layer 101 having a higher hardness than the first layer 102 and the transfer conveyance belt 60 are bonded. In this way, the structure in which the detection target is sandwiched between the two layers can protect against the peeling from the belt while protecting the surface of the detection target. Enables stable detection.
Further, the first layer 102 of the detent guide is made transparent, and the optical sensor 105 is used as the detection means. Optical detection is possible by making the first layer 102 of the stopper guide transparent. Optical detection by the optical sensor 105 enables simple and stable detection.
The image forming apparatus includes a plurality of photosensitive drums 11 and a toner image forming unit 1, and passes through a portion facing the plurality of photosensitive drums 11 to form a multicolor image to which a toner image is transferred from the photosensitive drum 11. Used for the conveyor belt 60. As a result, it is possible to prevent the occurrence of color misregistration based on the speed fluctuation of the transfer belt over a long period of time, and it is possible to maintain a color image having a high quality image.

1 is a schematic configuration diagram of a laser printer according to an embodiment. FIG. 3 is an enlarged view showing a schematic configuration of a transfer unit. (A) The schematic block diagram of the slip stopper guide of 2 layer structure. (B) The schematic block diagram of the detent guide which pinched | interposed the marking member. Explanatory drawing of the detection means of a marking member.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Toner image formation part 2 Optical writing unit 3, 4 Paper feed cassette 5 Registration roller pair 6 Transfer unit 7 Fixing unit 8 Paper discharge tray 9 Transfer bias power supply 11 Photosensitive drum 60 Transfer conveyance belt 61-68 Support roller 63 Drive roller 80 Electrostatic adsorption roller 80a Power supply 90 Entrance roller bracket 91 Shaft 92 Pin 93 Swing bracket 94 Rotating shaft 95 Hole 96 Cam 97 Cam shaft 98 Exit bracket 99 Shaft 100 Transfer paper 101 Offset guide lower layer 102 Offset guide upper layer 103 Optical sensor 104 Stop guide A Belt running direction B First paper discharge direction C Second paper discharge direction S Space MF Manual feed tray G Switching guide

Claims (6)

An endless belt stretched around a plurality of rollers, a belt drive device that drives at least one of the plurality of rollers to rotate the belt, and an inner peripheral surface end of the belt An image forming apparatus comprising: a detent guide provided; a detected object provided on the belt; and a detecting means for detecting the detected object, and controlling the belt driving device based on a detection result of the detecting means In
The detent guide has a multilayer structure having at least a surface layer and a lower layer fixed to the belt with higher hardness than the surface layer, and the object to be detected is disposed between the multi-layers of the detent guide. Image forming apparatus.   2. The image forming apparatus according to claim 1, wherein a surface layer of the detent guide is transparent, the object to be detected is disposed under the surface layer, and the detecting means is an optical sensor. The image forming apparatus according to claim 1 or 2, further comprising: an image carrier on which a toner image is formed, and a transfer belt that carries the toner image directly or via a transfer target from the image carrier, or An image forming apparatus, wherein the image forming apparatus is a conveyance belt that conveys a transfer medium carried on a surface thereof toward a transfer position.   4. The image forming apparatus according to claim 3, further comprising: a plurality of image forming portions that form toner images on a plurality of image carriers, wherein the belt passes through a portion facing the plurality of image carriers, and each of the image carriers. An image forming apparatus for forming a multicolor image by superimposing and transferring a toner image from a body.   An endless belt stretched around a plurality of rollers, a belt drive device that drives at least one of the plurality of rollers to rotate the belt, and a belt drive device for preventing meandering of the belt A detent guide provided at an end portion of the inner peripheral surface of the belt, a detection object provided on the belt, and a detection means for detecting the detection object, and based on a detection result of the detection means, In the belt device for controlling the belt driving device, the detent guide has a multilayer structure having at least a surface layer and a lower layer fixed to the belt with higher hardness than the surface layer, and the multi-layer structure of the detent guide A belt device characterized by being disposed between.   6. The belt device according to claim 5, wherein a surface layer of the detent guide is transparent, the object to be detected is disposed under the surface layer, and the detection means is an optical sensor.

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