JP2005148302A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve detection precision of a moving speed of a belt used for forming images. <P>SOLUTION: The image forming apparatus rotates an intermediate transfer belt 10 used for forming images with a drive means, and detects a scale 70 for detecting the moving speed of the intermediate transfer belt 10 provided on the intermediate transfer belt 10 with an optical sensor 71. The structure is such that the intermediate transfer belt 10, in the neighborhood of a detection region A of the scale 70 on the intermediate transfer belt 10 by the optical sensor 71, is depressed by a position-fixing member 72. Thereby, the movement of the intermediate transfer belt 10 in the detection region A is stabilized. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a belt used for image formation.

  2. Description of the Related Art Nowadays, in electrophotographic apparatuses that are electrophotographic image forming apparatuses, there are an increasing number of color electrophotographic apparatuses that output color images, such as color copiers and color printers, in response to demands from the market.

  A color electrophotographic apparatus is provided with a developing device of a plurality of colors around one photosensitive member, and these developing devices attach toner on the photosensitive member to form a synthetic toner image on the photosensitive member, and the synthetic toner A so-called 1-drum type that transfers an image onto a sheet-like transfer paper and records a color image on the transfer paper, and a plurality of photoconductors arranged side by side, a developing device is provided on each photoconductor, There is a so-called tandem type that forms a single color toner image, transfers the single color toner image onto a transfer sheet, and records a composite color image on the transfer sheet.

  Comparing the one-drum type and the tandem type, the former has only one photoconductor, so that there is an advantage that the size can be relatively reduced and the cost can be reduced. However, an image is obtained multiple times (usually four times) using one photoconductor. Since a full color image is formed by repeating the formation, it is difficult to speed up the image formation. The latter, on the contrary, has the disadvantage that it is easy to increase the speed of image formation, although it has the disadvantage of increasing the size and cost. Recently, tandem type has been attracting attention because the demand for full-color monochrome speed is desired.

  The tandem type color electrophotographic apparatus includes a direct transfer type in which an image on each photoconductor is sequentially transferred by a transfer device onto a transfer paper conveyed by a transfer paper conveyance belt, and a primary transfer of the image on each photoconductor. There is an indirect transfer type in which images are sequentially transferred to an intermediate transfer belt by an apparatus, and then images on the intermediate transfer belt are collectively transferred to transfer paper by a secondary transfer apparatus. As the transfer device, a transfer conveyance belt is used.

  In this tandem type color electrophotographic apparatus, there are a plurality of transfer positions of the toner image on the photoconductor. For example, in the direct transfer method, if the transfer paper transport speed to each transfer position is uneven, color misregistration occurs. Will occur. In addition, in the indirect transfer method, color misregistration occurs when uneven rotation speed of the intermediate transfer belt occurs. Therefore, it is necessary to accurately drive a belt used for image formation such as a transfer paper conveyance belt and an intermediate transfer belt at a constant speed.

  One of the countermeasures against this problem is measurement of surface velocity using a linear encoder (see, for example, Patent Document 1). The linear encoder is composed of a scale on a rotating body such as a belt and a photoconductor, and scale detecting means for optically reading the scale on the rotating body that is driven to rotate, and measures the surface speed of the rotating body. The belt can be moved at a constant speed by applying feedback to the drive source from the output of the detected linear encoder.

JP 11-24507 A

  However, when the surface speed of the rotating body is measured using the linear encoder in this way, when the rotating body is a belt, the belt is driven to rotate when the belt sag occurs due to a change in belt tension or the like. May exhibit anomalous behavior such as belt flapping. In this case, since the scale also behaves in the same manner as the belt, there is a problem that the detection accuracy of the moving speed of the belt is lowered.

  An object of the present invention is to improve detection accuracy of a moving speed of a belt used for image formation.

  According to the first aspect of the present invention, there is provided a belt used for image formation and rotationally driven by a driving means, a scale provided on the belt for detecting the moving speed of the belt, and a scale detecting means for detecting the scale. The image forming apparatus includes a position fixing member that presses the belt in the vicinity of the scale detection area on the belt by the scale detection unit.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the position fixing member presses the back of the belt with respect to the detection area as the vicinity of the detection area.

  Here, the back part is the back side of the detection area, the back side periphery, or the back side and the back side periphery.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the position fixing member is arranged around the detection area on the surface of the belt on the side where the scale is provided as the vicinity of the detection area. Hold down.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the periphery of the detection region on the surface of the belt on the side where the scale is provided is pressurized toward the position fixing member side. A pressure member is provided.

  A fifth aspect of the present invention is the image forming apparatus according to the first or third aspect, further comprising a pressing member that pressurizes a back portion of the belt with respect to the detection area toward the position fixing member.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the portion of the pressure member that contacts the belt is a sponge material.

  According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the portion of the position fixing member that contacts the belt is a brush material.

  According to the present invention, the detection accuracy of the moving speed of the belt used for image formation can be improved.

  A first embodiment of the present invention will be described with reference to FIGS. The present embodiment is an application example to a tandem type indirect transfer type full-color electrophotographic copying machine (hereinafter simply referred to as “copying machine”) as an image forming apparatus. Here, FIG. 1 is a schematic configuration diagram showing the entire copying machine of the present embodiment, FIG. 2 is a plan view showing the inner peripheral surface of the intermediate transfer belt, and FIG. 3 is a scale as seen from the inner peripheral surface side of the intermediate transfer belt. FIG. 4 is a perspective view showing the scale detection unit viewed from the outer peripheral surface side of the intermediate transfer belt.

  First, the configuration of the entire copying machine according to the present embodiment will be described. As shown in FIG. 1, the copying machine includes a copying machine main body 100 that forms an image, and a paper feed that places the copying machine main body 100 and supplies transfer paper 5 that is a recording material to the copying machine main body 100. The apparatus 200 includes a scanner 300 that is mounted on the copying machine main body 100 and reads a document image, and an automatic document feeder (ADF) 400 that is mounted on the scanner 300. The copying machine main body 100 is provided with a manual feed tray 6 for manually feeding the transfer paper 5 and a paper discharge tray 7 for discharging the transfer paper 5 on which an image has been formed.

  The copying machine main body 100 is provided with an endless belt-shaped intermediate transfer belt 10 that is a belt. The intermediate transfer belt 10 is rotationally driven in a clockwise direction in FIG. 1 by a motor (not shown) as a driving means while being stretched around three support rollers 14, 15 and 16.

  As shown in FIG. 2, a scale 70 on which a scale is formed is provided around one end of the inner peripheral surface 10a at one end in the width direction of the inner peripheral surface 10a of the intermediate transfer belt 10. As shown in FIG. 3, an optical sensor 71 that is a scale detecting means for optically detecting the scale 70 is fixedly provided at a position facing the scale 70. The optical sensor 71 detects the moving speed of the intermediate transfer belt 10 based on the detected scale 70.

  The scale 70 is an optically readable and detectable scale, and a fine and precise pitch light reflecting surface 70 a and non-reflecting surface 70 b are alternately formed in the rotational movement direction of the intermediate transfer belt 10 in a plastic sheet shape. Then, the optical sensor 71 detects the scale 70 by irradiating the condensed beam toward the scale 70 and optically reading and detecting the reflected light from the light reflecting surface 70a of the scale 70.

  As shown in FIGS. 3 and 4, a position fixing member 72 is disposed on the outer peripheral surface 10 b side of the intermediate transfer belt 10. A pressure member 73 is disposed on the inner peripheral surface 10a side of the intermediate transfer belt 10 where the scale 70 is formed. The position fixing member 72 and the pressure member 73 together with the optical sensor 71 constitute a scale detection unit 74.

  The position fixing member 72 is configured by attaching a brush material 76 to one surface of a plate-like base material 75. The brush material 76 is made of electrodeposited flocking such as nylon or rayon. The position fixing member 72 is an inner peripheral surface 10 a of the intermediate transfer belt 10, and a brush material 76 is attached to the back of the intermediate transfer belt 10 with respect to the detection area A of the scale 70 on the intermediate transfer belt 10 of the optical sensor 71. The back surface is pressed by contacting. Here, the back part is the back side of the detection area A and the periphery of the back side.

  The pressure member 73 is configured by attaching a sponge material 78 to one surface of a plate-like base material 77. The width of the pressure member 73 is set larger than the width of the scale 70. Examples of the material of the sponge material 78 include foamed polyurethane and foamed rubber. The pressure member 73 is disposed to face the position fixing member 72 with the sponge material 78 in contact with the scale 70 with the scale 70 and the intermediate transfer belt 10 interposed therebetween. In addition, a hole 79 is formed in a portion of the pressing member 73 that faces the detection area A of the optical sensor 71, and the optical sensor 71 can detect the scale 70 through the hole 79. The pressure member 73 is positioned by fixing the base material 77 at a position where the intermediate transfer belt 10 around the detection area A is pressed toward the position fixing member 72 by the elasticity of the sponge material 78. . Here, when the sponge material 78 slides on the inner peripheral surface 10 a of the intermediate transfer belt 10 and the scale 70 and there is a concern about wear, a tape (Teflon (registered trademark) series) that is difficult to wear on the surface of the sponge material 78. Etc.) is effective.

  Here, as a method of pressing the intermediate transfer belt 10 by the pressing member 73, besides using the sponge material 78, a method of urging the base material 77 against the intermediate transfer belt 10 with a spring or the like can be considered. In this method, uneven pressure may occur in each part of the intermediate transfer belt 10 due to irregularities on the surfaces of the position fixing member 72 and the pressure member 73. In particular, when the position fixing member 72 and the pressure member 73 are hard, a portion that is in contact with the intermediate transfer belt 10 and a portion that is not in contact with each other are generated via the intermediate transfer belt 10, and a large bias pressure is applied to the intermediate transfer belt 10. Occurs. Therefore, it is more difficult for the intermediate transfer belt 10 to generate a bias pressure when one of the surfaces of the position fixing member 72 and the pressure member 73 is softer. From the above, as the pressurizing method, the method using the sponge material 78 is one of the effective methods.

  As shown in FIG. 1, the belt stretched portion between the first support roller 14 and the second support roller 15 among the support rollers 14, 15, 16 has yellow, cyan, magenta, and black (black). Four image forming units 18Y, 18C, 18M, and 18K corresponding to the four colors are arranged side by side. An exposure device 21 is provided above the image forming units 18Y, 18C, 18M, and 18K. The exposure apparatus 21 emits writing light by driving a semiconductor laser (not shown) by a laser control unit (not shown) based on the image information of the document read by the scanner 300, and each image forming unit. This is for forming an electrostatic latent image on the photoconductive drums 20Y, 20C, 20M, and 20K as image carriers provided on 18Y, 18C, 18M, and 18K. Here, the emission of the writing light is not limited to the laser, but may be an LED, for example.

  The configuration of the image forming units 18Y, 18C, 18M, and 18K will be described. In the following description, the image forming unit 18K that forms a black toner image will be described as an example, but the other image forming units 18Y, 18C, and 18M have the same configuration. In addition, in the code | symbol in a figure, the symbol of "M" and "K" which shows distinction of a color is abbreviate | omitted, and a symbol is abbreviate | omitted suitably also in the following description.

  In the image forming unit 18, a charging device 60, a developing device 61, a photoconductor cleaning device 63, and a charge removal device 64 are provided around the photoconductor drum 20. Further, a primary transfer device 62 is provided at a position facing the photosensitive drum 20 via the intermediate transfer belt 10. In this structure, as the photosensitive drum 20 rotates, the charging device 60 first charges the surface of the photosensitive drum 20 uniformly. Next, based on the image information read by the scanner 300, the exposure light is irradiated from the exposure device 21 to form an electrostatic latent image on the photosensitive drum 20. Thereafter, the electrostatic latent image is visualized by the developing device 61 to form a toner image. This toner image is primarily transferred onto the intermediate transfer belt 10 by the primary transfer device 62. The transfer residual toner remaining on the surface of the photosensitive drum 20 after the primary transfer is removed by the photosensitive member cleaning device 63, and thereafter, the surface of the photosensitive drum 20 is discharged by the static eliminating device 64, and the next image formation is performed. Provided.

  Next, a secondary transfer roller 24 as a secondary transfer device is provided at a position facing the third support roller 16 among the support rollers. When the toner image on the intermediate transfer belt 10 is secondarily transferred onto the transfer paper 5, the secondary transfer roller 24 is pressed against the portion of the intermediate transfer belt 10 wound around the third support roller 16. Next transfer is performed. The secondary transfer device may not be configured using the secondary transfer roller 24 but may be configured using, for example, a transfer belt or a non-contact transfer charger. The secondary transfer roller 24 is in contact with a roller cleaning unit 91 that cleans toner adhering to the secondary transfer roller 24.

  Further, an endless belt-like transport belt 22 stretched between the two rollers 23a and 23b is provided on the downstream side of the secondary transfer roller 24 in the transfer paper transport direction. Further, a fixing device 25 for fixing the toner image transferred onto the transfer paper 5 is provided further downstream in the transport direction. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a heating roller 26. Further, a belt cleaning device 17 is provided at a position facing the second support roller 15 among the support rollers of the intermediate transfer belt 10. The belt cleaning device 17 is for removing residual toner remaining on the intermediate transfer belt 10 after the toner image on the intermediate transfer belt 10 is transferred to the transfer paper 5.

  Further, the copying machine main body 100 is provided with a conveyance path 48 for guiding the transfer paper 5 fed from the paper feeding device 200 to the paper discharge tray 7 via the secondary transfer roller 24. A conveying roller 49a, a registration roller 49b, a discharge roller 56, and the like are provided along the line 48. A switching claw 55 is provided on the downstream side of the transport path 48 to switch the transport direction of the transfer paper 5 after transfer to the paper discharge tray 7 or the paper reversing device 93. The paper reversing device 93 reverses the transfer paper 5 and sends it again toward the secondary transfer roller 24. Further, the copying machine main body 100 is provided with a manual feed path 53 that joins from the manual feed tray 6 to the transport path 48, and the transfer paper 5 set in the manual feed tray 6 is located upstream of the manual feed path 53. A sheet feeding roller 50 and a separation roller 51 are provided for feeding sheets one by one.

  The paper feeding device 200 includes a plurality of paper feeding cassettes 44 that store the transfer paper 5, a paper feeding roller 42 and a separation roller 45 that feed the transfer papers stored in these paper feeding cassettes 44 one by one, and the fed transfer paper Is composed of a transport roller 47 that transports the paper along the paper feed path 46. The paper feed path 46 is connected to the conveyance path 48 of the copying machine main body 100.

  The scanner 300 will be briefly described. In the scanner 300, first and second traveling bodies 33 and 34 mounted with a document illumination light source and a mirror reciprocate in order to read and scan a document (not shown) placed on the contact glass 31. To do. The image information scanned by the traveling bodies 33 and 34 is collected by the imaging lens 35 on the imaging surface of the reading sensor 36 installed behind the imaging lens 35 and read by the reading sensor 36 as an image signal.

  The copier is provided with a computer-configured control unit that drives and controls each unit of the copier, although not particularly shown.

  Next, the operation of the copying machine of this embodiment will be described. When copying a document using the copying machine having the above configuration, first, the document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 31 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. Thereafter, when the user presses a start switch (not shown), when the document is set on the automatic document feeder 400, the document is conveyed onto the contact glass 31. Then, the scanner 300 is driven and the first traveling body 33 and the second traveling body 34 start traveling. Thereby, the light from the first traveling body 33 is reflected by the document on the contact glass 31, and the reflected light is reflected by the mirror of the second traveling body 34 and guided to the reading sensor 36 through the imaging lens 35. . In this way, the image information of the original is read.

  When the start switch is pressed by the user, a drive motor (not shown) is driven, and one of the support rollers 14, 15, 16 is rotationally driven to rotate the intermediate transfer belt 10. At the same time, the photosensitive drums 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K are also rotationally driven. Thereafter, based on the image information read by the reading sensor 36 of the scanner 300, writing light is emitted from the exposure device 21 onto the photosensitive drums 20Y, 20C, 20M, and 20K of the image forming units 18Y, 18C, 18M, and 18K. Each is irradiated. As a result, electrostatic latent images are formed on the respective photosensitive drums 20Y, 20C, 20M, and 20K, and are visualized by the developing devices 61Y, 61C, 61M, and 61K. Then, yellow, cyan, magenta, and black toner images are formed on the photosensitive drums 20Y, 20C, 20M, and 20K, respectively.

  Each color toner image formed in this way is primarily transferred by the primary transfer devices 62Y, 62C, 62M, and 62K so as to sequentially overlap each other on the intermediate transfer belt 10. As a result, a composite toner image in which the toner images of the respective colors overlap is formed on the intermediate transfer belt 10. The transfer residual toner remaining on the intermediate transfer belt 10 after the secondary transfer is removed by the belt cleaning device 17.

  When the user presses the start switch, the paper feed roller 42 of the paper feed device 200 corresponding to the transfer paper 5 selected by the user rotates, and the transfer paper 5 is sent out from one of the paper feed cassettes 44. The transferred transfer paper 5 is separated into one sheet by the separation roller 45 and enters the paper feed path 46, and is conveyed by the conveyance roller 47 to the conveyance path 48 in the copying machine main body 100. The transfer sheet 5 thus transported is stopped when it abuts against the registration roller 49b. When the transfer paper 5 not set in the paper feed cassette 44 is used, the transfer paper 5 set on the manual feed tray 6 is fed out by the paper feed roller 50 and separated into one sheet by the separation roller 52, and then manually fed. It is conveyed through the paper path 53. Then, it stops when it hits the registration roller 49b.

  The registration roller 49 b starts to rotate in accordance with the timing at which the composite toner image formed on the intermediate transfer belt 10 as described above is conveyed to the secondary transfer unit facing the secondary transfer roller 24. The transfer paper 5 sent out by the registration roller 49b is sent between the intermediate transfer belt 10 and the secondary transfer roller 24, and the secondary transfer roller 24 causes the composite toner image on the intermediate transfer belt 10 to be transferred onto the transfer paper 5. Secondary transfer is performed. Thereafter, the transfer paper 5 is conveyed to the fixing device 25 while being attracted to the secondary transfer roller 24, and heat and pressure are applied by the fixing device 25 to perform a toner image fixing process. The transfer paper 5 that has passed through the fixing device 25 is discharged to the paper discharge tray 7 by the discharge roller 56 and stacked. When image formation is performed also on the back surface of the surface on which the toner image is fixed, the transfer paper 5 that has passed through the fixing device 25 is switched by the switching claw 55 and sent to the paper reversing device 93. The transfer paper 5 is then reversed and guided to the secondary transfer roller 24 again.

  In such an image forming operation, in this embodiment, the moving speed of the intermediate transfer belt 10 is detected using the optical sensor 71, and the detection result is fed back to a drive system including a motor for driving the intermediate transfer belt 10. Thus, the moving speed of the intermediate transfer belt 10 is kept constant. The detection of the moving speed of the intermediate transfer belt 10 is performed based on the detection of the scale 70 provided on the intermediate transfer belt 10 by the optical sensor as described above. At this time, in the present embodiment, the position fixing member 72 presses the back side (outer peripheral surface 10 b side) of the intermediate transfer belt 10 with respect to the detection area A of the scale 70 by the optical sensor 71. The movement of the intermediate transfer belt 10 is stabilized, and irregular behavior such as flapping of the intermediate transfer belt 10 in the detection area A is prevented from occurring. Thereby, the detection accuracy of the scale 70 by the optical sensor 71 is improved, and the detection accuracy of the moving speed of the intermediate transfer belt 10 is improved. Accordingly, the moving speed of the intermediate transfer belt 10 can be kept constant, and color misregistration during the transfer of toner images from the four photosensitive drums 20 to the intermediate transfer belt 10 can be prevented. A highly accurate toner image is formed. Therefore, a highly accurate color image is formed on the transfer paper 5.

  At this time, since the position fixing member 72 is in contact with the intermediate transfer belt 10 by the brush material 76, the intermediate transfer belt 10 is prevented from being scraped or worn due to friction between the position fixing member 72 and the intermediate transfer belt 10. The

  Further, at this time, the pressing member 73 presses the periphery of the detection area A of the inner peripheral surface 10a of the intermediate transfer belt 10 toward the position fixing member 72, so that the intermediate transfer belt 10 in the detection area A is pressed. Movement is further stabilized, and irregular behavior such as flapping of the intermediate transfer belt 10 in the detection area A is further prevented from occurring. Thereby, the detection accuracy of the scale 70 by the optical sensor 71 is further improved, and the detection accuracy of the moving speed of the intermediate transfer belt 10 is further improved. As a result, the moving speed of the intermediate transfer belt 10 can be kept more constant, and color misregistration during the transfer of toner images from the four photosensitive drums 20 to the intermediate transfer belt 10 can be further prevented. 10, a toner image with higher accuracy is formed. Therefore, a color image with higher accuracy is formed on the transfer paper 5. At this time, since the pressing member 73 pushes the intermediate transfer belt 10 from above the scale 70, deformation of the scale 70 such as undulation can be made flat. Thereby, the shape of the scale 70 is stabilized, and the detection accuracy of the scale 70 by the optical sensor 71 is further improved. In addition, since the pressure member 73 is directly pressed against the scale 70, the surface of the scale 70 is cleaned by the pressure member 73 and the foreign matter on the surface of the scale 70 is removed by the rotation of the intermediate transfer belt 10. Therefore, the detection accuracy of the scale 70 by the optical sensor 71 is further improved.

  In addition, by using the elasticity of the sponge material 78 as a pressurizing method by the pressurizing member 73, it is possible to suppress the occurrence of uneven pressure in the pressurization to the intermediate transfer belt 10, and the pressurizing member 73 is used. Can be configured at low cost.

  In the present embodiment, the intermediate transfer belt 10 has been described as an example of a belt used for image formation. However, the present invention is not limited to this. For example, when an image forming apparatus of a direct transfer system that sequentially transfers the toner image of each photosensitive drum by the transfer device to the transfer paper 5 conveyed by the transfer paper conveyance belt is applied as the image forming apparatus, the transfer paper is used as the belt. A conveyor belt may be applied.

  Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those of the first embodiment are denoted by the same reference numerals, and description thereof is also omitted. Here, FIG. 5 is a perspective view showing the scale detection unit 74 of the present embodiment as viewed from the inner peripheral surface 10a side of the intermediate transfer belt 10, and FIG. 6 is a scale detection as viewed from the outer peripheral surface 10b side of the intermediate transfer belt 10. It is a perspective view which shows the part 74. FIG.

  In the present embodiment, the arrangement of the position fixing member 82 and the pressure member 83 of the scale detection unit 74 is opposite to that of the first embodiment. That is, the position fixing member 82 is disposed on the inner peripheral surface 10 a side of the intermediate transfer belt 10, and the pressure member 83 is disposed on the outer peripheral surface 10 b side of the intermediate transfer belt 10.

  The position fixing member 82 includes a base material 85 and a brush material 86, and the width thereof is set larger than the width of the scale 70. The position fixing member 82 presses the intermediate transfer belt 10 around the detection area A in a state where the brush material 86 is in contact with the scale 70. In addition, a hole 89 is formed in a portion of the position fixing member 82 that faces the detection region A, so that the scale 70 of the optical sensor 71 can be detected.

  The pressure member 83 is configured by attaching a base material 87 and a sponge material 88. The pressure member 83 is not formed with the hole 79 described in the first embodiment. The pressure member 83 is disposed opposite to the position fixing member 82 via the intermediate transfer belt 10 and the scale 70 in a state where the sponge material 88 is in contact with the outer peripheral surface 10 b of the intermediate transfer belt 10. The pressure member 83 presses the intermediate transfer belt 10 at the back of the detection area A by the elasticity of the sponge material 88 in a state where the sponge material 88 is in contact with the outer peripheral surface 10 b of the intermediate transfer belt 10.

  In the image forming operation in such a configuration, the periphery of the detection area A on the inner peripheral surface 10a of the intermediate transfer belt 10 is pressed by the position fixing member 82. Therefore, the movement of the intermediate transfer belt 10 in the detection area A is performed. Is stabilized, and irregular behavior such as flapping of the intermediate transfer belt 10 in the detection area A is prevented from occurring. Thereby, the detection accuracy of the scale 70 by the optical sensor 71 is improved, and the detection accuracy of the moving speed of the intermediate transfer belt 10 is improved. Accordingly, the moving speed of the intermediate transfer belt 10 can be kept constant, and color misregistration during the transfer of toner images from the four photosensitive drums 20 to the intermediate transfer belt 10 can be prevented. A highly accurate toner image is formed. Therefore, a highly accurate color image is formed on the transfer paper 5.

  At this time, since the position fixing member 82 is in contact with the scale 70 and the intermediate transfer belt 10 by the brush material 86, the scale 70 and the intermediate transfer due to friction between the position fixing member 82, the scale 70 and the intermediate transfer belt 10. The belt 10 is prevented from being scraped or worn. Further, since the position fixing member 82 is directly pressed against the scale 70, the surface of the scale 70 is cleaned by the pressure member 83 by the rotation of the intermediate transfer belt 10, and the foreign matter on the surface of the scale 70 is removed. Therefore, the detection accuracy of the scale 70 by the optical sensor 71 is further improved. At this time, since the position fixing member 82 directly presses the intermediate transfer belt 10 from above the scale 70, the deformation of the scale 70 such as undulation can be made flat. Thereby, the shape of the scale 70 is stabilized and the detection accuracy of the scale 70 by the optical sensor 71 is improved.

  Further, at this time, the pressure member 83 presses the back portion (outer peripheral surface 10b side) of the intermediate transfer belt 10 with respect to the detection area A toward the position fixing member 82 side, so that the intermediate transfer in the detection area A is performed. The movement of the belt 10 is further stabilized, and the occurrence of irregular behavior such as flapping of the intermediate transfer belt 10 in the detection area A is further prevented. Thereby, the detection accuracy of the scale 70 by the optical sensor 71 is further improved, and the detection accuracy of the moving speed of the intermediate transfer belt 10 is further improved. As a result, the moving speed of the intermediate transfer belt 10 can be kept more constant, and color misregistration during the transfer of toner images from the four photosensitive drums 20 to the intermediate transfer belt 10 can be further prevented. 10, a toner image with higher accuracy is formed. Therefore, a color image with higher accuracy is formed on the transfer paper 5.

1 is a schematic configuration diagram illustrating an entire copying machine according to a first embodiment of the present invention. FIG. 3 is a plan view showing an inner peripheral surface of an intermediate transfer belt. FIG. 6 is a perspective view showing a scale detector viewed from the inner peripheral surface side of the intermediate transfer belt. FIG. 4 is a perspective view showing a scale detector viewed from the outer peripheral surface side of the intermediate transfer belt. It is a perspective view which shows the scale detection part of 2nd embodiment of this invention seeing from the internal peripheral surface side of an intermediate transfer belt. FIG. 4 is a perspective view showing a scale detector viewed from the outer peripheral surface side of the intermediate transfer belt.

Explanation of symbols

10 Intermediate transfer belt (belt)
70 scale 71 optical sensor (scale detection means)
72 Position fixing member 73 Pressure member 76 Brush material 78 Sponge material 82 Position fixing member 83 Pressure member 86 Brush material 88 Sponge material A Detection region

Claims (7)

In an image forming apparatus comprising a belt used for image formation and rotationally driven by a driving means, a scale provided on the belt for detecting the moving speed of the belt, and a scale detecting means for detecting the scale.
An image forming apparatus comprising: a position fixing member for pressing the belt in the vicinity of the scale detection area on the belt by the scale detection means.   The image forming apparatus according to claim 1, wherein the position fixing member presses a back portion of the belt with respect to the detection area as a vicinity of the detection area.   The image forming apparatus according to claim 1, wherein the position fixing member presses a periphery of the detection area on a surface of the belt on a side where the scale is provided as a vicinity of the detection area.   3. The image forming apparatus according to claim 1, further comprising a pressing member that presses a periphery of the detection area on the surface of the belt on the side where the scale is provided toward the position fixing member. .   The image forming apparatus according to claim 1, further comprising a pressing member that presses a back portion of the belt with respect to the detection region toward the position fixing member.   6. The image forming apparatus according to claim 4, wherein the portion of the pressure member that contacts the belt is a sponge material. The image forming apparatus according to claim 1, wherein a portion of the position fixing member that is in contact with the belt is a brush material.

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