Patent Publication Number: US-10788779-B2

Title: Belt deviation detection device, belt device, image forming apparatus, and method of manufacturing contact member

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2018-157986, filed on Aug. 27, 2018, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Embodiments of the present disclosure relate to a belt deviation detection device configured to detect a lateral displacement of a belt in a width direction of the belt, such as an intermediate transfer belt, a transfer conveyance belt, a photoconductor belt, or the like that rotates in a predetermined direction, a belt device, an image forming apparatus incorporating the belt deviation detection device, and a method of manufacturing a contact member included in the belt deviation detection device. 
     Description of the Related Art 
     Certain image forming apparatuses include a belt deviation detection device configured to detect a displacement of an intermediate transfer belt, which rotates in a predetermined direction, in a width direction of the intermediate transfer belt. 
     SUMMARY 
     Embodiments of the present disclosure describe an improved belt deviation detection device to detect lateral displacement of a rotary belt in a width direction of the belt. The belt deviation detection device includes a contact member in contact with the belt at a contact portion of the contact member, a biasing member configured to bias the contact member toward the belt to press the contact member against the belt, and a displacement detector configured to detect the displacement of the belt in the width direction. The contact member is configured to track the displacement of the belt in the width direction of the belt. The contact member is made of a metal material, and a hardening treatment is applied to at least the contact portion of the contact member. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view illustrating a configuration of an image forming apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic cross-sectional view of an image forming unit of the image forming apparatus in  FIG. 1 ; 
         FIG. 3  is a schematic view of a belt device of the image forming apparatus in  FIG. 1 ; 
         FIG. 4  is a perspective view of a belt deviation detection device according to an embodiment of the present disclosure; 
         FIG. 5  is a schematic view of a part of the belt device in  FIG. 3  as viewed in a width direction of a belt included in the belt device; 
         FIGS. 6A-1, 6B-1, and 6C-1  are schematic views illustrating a vicinity of a transmissive photosensor included in the belt deviation detection device; 
         FIGS. 6A-2, 6B-2, and 6C-2  are graphs illustrating an output change of the transmissive photosensor; and 
         FIGS. 7A and 7B  are top views illustrating a state in which a contact member of the belt deviation detection device is in contact with the belt of the belt device. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. In addition, identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It is to be noted that the suffixes Y, M, C, and K attached to each reference numeral indicate only that components indicated thereby are used for forming yellow, magenta, cyan, and black images, respectively, and hereinafter may be omitted when color discrimination is not necessary. 
     Embodiments of the present disclosure are described in detail with reference to the appended drawings. It is to be understood that identical or similar reference numerals are assigned to identical or corresponding components throughout the drawings, and redundant descriptions are omitted or simplified below as required. 
     With reference to  FIGS. 1 and 2 , a configuration and operation of an image forming apparatus  100  according to the present embodiment are described below. 
       FIG. 1  is a schematic view illustrating the configuration of the image forming apparatus  100 , which in the present embodiment is a printer.  FIG. 2  is an enlarged cross-sectional view illustrating a part of an image forming unit  6 Y of the image forming apparatus  100 . 
     As illustrated in  FIG. 1 , the image forming apparatus  100  includes an intermediate transfer belt device  15  as a belt device at the center of the apparatus body of the image forming apparatus  100 . The image forming units  6 Y,  6 M,  6 C, and  6 K are arranged in parallel, facing an intermediate transfer belt  8  as a belt of the intermediate transfer belt device  15  to form toner images of yellow, magenta, cyan, and black, respectively. Below the intermediate transfer belt device  15 , a secondary transfer belt device  69  is disposed. 
     With reference to  FIG. 2 , the image forming unit  6 Y for yellow includes a photoconductor drum  1 Y and further includes a charging device  4 Y, a developing device  5 Y, a cleaning device  2 Y, a lubricant applicator  3 , and a discharger disposed around the photoconductor drum  1 Y. Image forming processes, namely, charging, exposure, development, transfer, and cleaning processes, are performed on the photoconductor drum  1 Y, and thus a yellow toner image is formed on a surface of the photoconductor drum  1 Y. 
     The other three image forming units  6 M,  6 C, and  6 K have a similar configuration to that of the yellow image forming unit  6 Y except for the color of toner used therein and form magenta, cyan, and black toner images, respectively. Thus, only the image forming unit  6 Y is described below and descriptions of the other three image forming units  6 M,  6 C, and  6 K are omitted. 
     With reference to  FIG. 2 , the photoconductor drum  1 Y is rotated counterclockwise in  FIG. 2  by a main motor. The charging device  4 Y uniformly charges the surface of the photoconductor drum  1 Y at a position opposite the charging device  4 Y (a charging process). 
     Then, the charged surface of the photoconductor drum  1 Y reaches a position to receive a laser beam L emitted from an exposure device  7 , and the photoconductor drum  1 Y is scanned with the laser beam L in a width direction at the position, thereby forming an electrostatic latent image for yellow on the surface of the photoconductor drum  1 Y (an exposure process). The width direction is a main-scanning direction perpendicular to the surface of the paper on which  FIGS. 1 and 2  are drawn. 
     The surface of the photoconductor drum  1 Y carrying the electrostatic latent image reaches a position opposite the developing device  5 Y, and the electrostatic latent image is developed into a toner image of yellow at the position (a development process). 
     When the surface of the photoconductor drum  1 Y carrying the toner image reaches a position opposite a primary transfer roller  9 Y via the intermediate transfer belt  8 , the toner image on the surface of the photoconductor drum  1 Y is transferred onto a surface of the intermediate transfer belt  8  at the position (a primary transfer process). After the primary transfer process, a certain amount of untransferred toner remains on the photoconductor drum  1 Y. 
     When the surface of the photoconductor drum  1 Y reaches a position opposite the cleaning device  2 Y, a cleaning blade  2   a  of the cleaning device  2 Y collects the untransferred toner from the photoconductor drum  1 Y into the cleaning device  2 Y (a cleaning process). 
     The cleaning device  2 Y includes a lubricant supply roller  3   a , a solid lubricant  3   b , and a compression spring  3   c , which constitute the lubricant applicator  3  for the photoconductor drum  1 Y. The lubricant supply roller  3   a  rotating clockwise in  FIG. 2  rubs a small amount of lubricant from the solid lubricant  3   b  and applies the lubricant to the surface of the photoconductor drum  1 Y. 
     Subsequently, the surface of the photoconductor drum  1 Y reaches a position opposite the discharger, and the discharger eliminates a residual potential from the photoconductor drum  1 Y. 
     Thus, a sequence of image forming processes performed on the photoconductor drum  1 Y is completed. 
     The above-described image forming processes are performed in the image forming units  6 M,  6 C, and  6 K similarly to the yellow image forming unit  6 Y. That is, the exposure device  7  disposed above the image forming units  6 M,  6 C, and  6 K irradiates photoconductor drums  1 M,  1 C, and  1 K of the image forming units  6 M,  6 C, and  6 K with the laser beams L based on image data. Specifically, the exposure device  7  includes a light source to emit the laser beams L, multiple optical elements, and a polygon mirror that is rotated by a motor. The exposure device  7  directs the laser beams L to the photoconductor drums  1 M,  1 C, and  1 K via the multiple optical elements while deflecting the laser beams L with the polygon mirror. Alternatively, an exposure device  7  in which a plurality of light emitting diodes (LEDs) is arranged side by side in the width direction can be used. 
     Then, the toner images formed on the photoconductor drums  1 M,  1 C, and  1 K through the development process of developing devices  5 M,  5 C, and  5 K are primarily transferred therefrom and superimposed onto the intermediate transfer belt  8 . Thus, a multicolor toner image is formed on the intermediate transfer belt  8 . 
     The intermediate transfer belt  8  as the belt is stretched and supported around a plurality of rollers  16  through  19  and  40  and is rotated by a drive roller  16  driven by a drive motor in a direction indicated by arrow A 2  in  FIG. 3 . 
     The four primary transfer rollers  9 Y,  9 M,  9 C, and  9 K are pressed against the corresponding photoconductor drums  1 Y,  1 M,  1 C, and  1 K, respectively, via the intermediate transfer belt  8  to form primary transfer nips. Transfer voltages (primary transfer biases) opposite in polarity to that of toner are applied to the primary transfer rollers  9 Y,  9 M,  9 C, and  9 K. 
     While rotating in the direction indicated by arrow A 2  in  FIG. 3 , the intermediate transfer belt  8  passes through the primary transfer nips between the photoconductor drums  1 Y,  1 M,  1 C, and  1 K and the respective primary transfer rollers  9 Y,  9 M,  9 C, and  9 K. Then, the single-color toner images on the photoconductor drums  1 Y,  1 M,  1 C, and  1 K are primarily transferred and superimposed onto the intermediate transfer belt  8 , thereby forming the multicolor toner image on the intermediate transfer belt  8  (a primary transfer process). 
     Then, the intermediate transfer belt  8  carrying the multicolor toner image reaches a position opposite a secondary transfer belt  72 . A secondary-transfer backup roller  40  and a secondary transfer roller  70  press against each other via the intermediate transfer belt  8  and the secondary transfer belt  72 , thereby forming a secondary transfer nip. The multicolor (four-color) toner image on the intermediate transfer belt  8  is transferred onto a sheet P (e.g., a paper sheet) conveyed to the secondary transfer nip (a secondary transfer process). At that time, toner that is not transferred onto the sheet P remains on the surface of the intermediate transfer belt  8 . 
     Then, the intermediate transfer belt  8  reaches a position opposite a belt cleaner  10  of the intermediate transfer belt device  15 . At this position, the belt cleaner  10  removes substances adhering to the intermediate transfer belt  8  (e.g., untransferred toner) to complete a series of image transfer processes performed on the intermediate transfer belt  8 . 
     With reference to  FIG. 1 , the sheet P is conveyed from a sheet feeder  26  disposed in a lower portion of the apparatus body of the image forming apparatus  100  to the secondary transfer nip via a feed roller  27  and a registration roller pair  28 . 
     Specifically, the sheet feeder  26  contains a stack of multiple sheets P such as paper sheets piled one on another. As the feed roller  27  rotates counterclockwise in  FIG. 1 , the topmost sheet P of the stack of multiple sheets P in the sheet feeder  26  is fed toward a nip between the registration roller pair  28  via a first conveyance path K 1 . 
     The registration roller pair (a timing roller pair)  28  temporarily stops rotating, stopping the sheet P with a leading edge of the sheet P nipped in the registration roller pair  28 . The registration roller pair  28  rotates to convey the sheet P to the secondary transfer nip, timed to coincide with the arrival of the multicolor toner image on the intermediate transfer belt  8 . Thus, the desired multicolor toner image is transferred onto the sheet P. 
     The sheet P, onto which the multicolor toner image is secondarily transferred at the secondary transfer nip, is conveyed on the secondary transfer belt  72  and separated from the secondary transfer belt  72 , and then a conveyance belt  60  conveys the sheet P to a fixing device  50 . In the fixing device  50 , a fixing belt and a pressing roller apply heat and pressure to the sheet P to fix the multicolor toner image on the sheet P (a fixing process). 
     The sheet P is conveyed through a second conveyance path K 2  and ejected by an output roller pair to the outside of the image forming apparatus  100 . The sheets P ejected by the output roller pair are sequentially stacked as output images on a stack tray to complete a series of image forming processes (printing operations) performed by the image forming apparatus  100 . 
     Thus, in single-side printing, the sheet P is ejected after the toner image is fixed on the front side of the sheet P. By contrast, in duplex printing to form toner images on both sides (front side and back side) of the sheet P, the sheet P is guided to a third conveyance path K 3 . After a direction of conveyance of the sheet P is reversed, the sheet P is conveyed again to the secondary transfer nip (a secondary transfer belt device  69 ) via a fourth conveyance path K 4 . Then, through the image forming processes (the printing operations) similar to those described above, the toner image is transferred onto the back side of the sheet P at the secondary transfer nip and fixed thereon by the fixing device  50 , after which the sheet P is ejected from the image forming apparatus  100  via the second conveyance path K 2 . 
     Next, a detailed description is provided of a configuration and operations of the developing device  5 Y with reference to  FIG. 2 . 
     The developing device  5 Y includes a developing roller  51 Y opposed to the photoconductor drum  1 Y, a doctor blade  52 Y opposed to the developing roller  51 Y, two conveying screws  55 Y disposed in a developer storage of the developing device  5 Y, and a toner concentration sensor  56 Y to detect a toner concentration in a developer G. The developing roller  51 Y includes stationary magnets, a sleeve that rotates around the magnets, and the like. The developer storage contains the two-component developer G including carrier and toner. 
     The developing device  5 Y with such a configuration operates as follows. 
     The sleeve of the developing roller  51 Y rotates in the direction indicated by arrow A 1  in  FIG. 2 . The developer G is carried on the developing roller  51 Y by a magnetic field generated by the magnets. As the sleeve rotates, the developer G moves along a circumference of the developing roller  51 Y. A ratio of toner to carrier (i.e., toner concentration) in the developer G contained in the developing device  5 Y is adjusted within a predetermined range. Specifically, when low toner concentration is detected by the toner concentration sensor  56 Y disposed in the developing device  5 Y, fresh toner is supplied from a toner container  58  to the developer storage of the developing device  5 Y to keep the toner concentration within the predetermined range. 
     The two conveying screws  55 Y stir and mix the developer G with the toner supplied from the toner container  58  to the developer storage while circulating the developer G in the developer storage separated into two compartments. In this case, the developer G moves in the direction perpendicular to the surface of the paper on which  FIG. 2  is drawn. The toner in developer G is triboelectrically charged by friction with the carrier and electrostatically attracted to the carrier. Then, the toner is carried on the developing roller  51 Y together with the carrier by magnetic force generated on the developing roller  51 Y. 
     The developer G on the developing roller  51 Y is carried in the direction indicated by arrow A 1  in  FIG. 2  to the doctor blade  52 Y. An amount of developer G on the developing roller  51 Y is adjusted by the doctor blade  52 Y, after which the developer G is carried to a development range opposed to the photoconductor drum  1 Y. The toner in the developer G is attracted to the latent image formed on the photoconductor drum  1 Y due to the effect of an electric field generated in the development range. As the sleeve rotates, the developer G remaining on the developing roller  51 Y reaches an upper part of the developer storage and separates from the developing roller  51 Y. 
     The replaceable toner container  58  is detachably attached to the developing device  5 Y (the image forming apparatus  100 ). When the toner container  58  runs out of fresh toner, the toner container  58  is detached from the developing device  5 Y (the image forming apparatus  100 ) and replaced with a new one. 
     Now, a detailed description is given of a belt deviation detection device  80  included in the intermediate transfer belt device  15  of the image forming apparatus  100  according to the present embodiment, with reference to  FIGS. 3 through 7B . 
     With reference to  FIGS. 3 and 4 , the intermediate transfer belt device  15  as the belt device includes the intermediate transfer belt  8  as the belt, the four primary transfer rollers  9 Y,  9 M,  9 C, and  9 K, the drive roller  16 , a correction roller  17 , a correction unit  91 , a pre-transfer roller  18 , a tension roller  19 , the belt cleaner  10  for the intermediate transfer belt  8 , the secondary-transfer backup roller  40 , the belt deviation detection device  80 , and the like. 
     The intermediate transfer belt  8  is disposed in contact with the four photoconductor drums  1 Y,  1 M,  1 C, and  1 K to bear the toner images of the respective colors, thereby forming the primary transfer nips. The intermediate transfer belt  8  is stretched taut around and supported by multiple rollers: the drive roller  16 , the correction roller  17 , the pre-transfer roller  18 , the tension roller  19 , the secondary-transfer backup roller  40 , and the like. 
     According to the present embodiment, the intermediate transfer belt  8  includes a single layer or multiple layers including, but not limited to, polyimide (PI), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), and polycarbonate (PC), with conductive material such as carbon black dispersed therein. The volume resistivity of the intermediate transfer belt  8  is adjusted within a range of from 10 7  to 10 12  Ωcm, and the surface resistivity of a back surface of the intermediate transfer belt  8  is adjusted within a range of from 10 8  to 10 12  Ω/sq. The thickness of the intermediate transfer belt  8  ranges from 80 to 100 μm. In the present embodiment, the thickness of the intermediate transfer belt  8  is 90 μm. 
     In some embodiments, the intermediate transfer belt  8  may include a release layer coated on the surface of the intermediate transfer belt  8  as needed. Examples of a material usable for the release layer include, but are not limited to, fluorocarbon resins such as ETFE, polytetrafluoroethylene (PTFE), PVDF, perfluoroalkoxy polymer resin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and polyvinyl fluoride (PVF). 
     The intermediate transfer belt  8  is manufactured through a casting process, a centrifugal molding process, or the like. The surface of the intermediate transfer belt  8  may be polished as necessary. 
     The primary transfer rollers  9 Y,  9 M,  9 C, and  9 K are disposed in contact with the photoconductor drums  1 Y,  1 M,  1 C, and  1 K via the intermediate transfer belt  8 , respectively. Specifically, the primary transfer roller  9 Y for yellow is disposed in contact with the photoconductor drum  1 Y for yellow via the intermediate transfer belt  8 . The primary transfer roller  9 M for magenta is disposed in contact with the photoconductor drum  1 M for magenta via the intermediate transfer belt  8 . The primary transfer roller  9 C for cyan is disposed in contact with the photoconductor drum  1 C for cyan via the intermediate transfer belt  8 . The primary transfer roller  9 K for black is disposed in contact with the photoconductor drum  1 K for black via the intermediate transfer belt  8 . Each of the primary transfer rollers  9 Y,  9 M,  9 C, and  9 K is an elastic roller including a core and a conductive foamed layer on the core. The volume resistivity of each of the primary transfer rollers  9 Y,  9 M,  9 C, and  9 K is adjusted within a range of from 10 6  to 10 12  Ωcm, preferably from 10 7  to 10 9  Ωcm. 
     The drive roller  16  is disposed in contact with an inner circumferential surface of the intermediate transfer belt  8  by an angle of belt winding of about 120 degrees at a position downstream from the four photoconductor drums  1 Y,  1 M,  1 C, and  1 K in a direction of rotation of the intermediate transfer belt  8 . The drive roller  16  is rotated clockwise in  FIG. 3  by the drive motor, which is controlled by a controller  90 . Such a configuration allows the intermediate transfer belt  8  to rotate in a predetermined direction (i.e., clockwise in  FIG. 3 ) as indicated by arrow A 2  in  FIG. 3 . 
     The correction roller  17  is disposed in contact with the inner circumferential surface of the intermediate transfer belt  8  by the angle of belt winding of about 180 degrees at a position upstream from the four photoconductor drums  1 Y,  1 M,  1 C, and  1 K in the direction of rotation of the intermediate transfer belt  8 . A portion of the intermediate transfer belt  8  from the correction roller  17  to the drive roller  16  is arranged approximately horizontal. The correction roller  17  is rotated clockwise in  FIG. 3  as the intermediate transfer belt  8  rotates. 
     The correction roller  17  is coupled to the correction unit  91 . The correction roller  17  together with the correction unit  91  functions as a correction device that corrects a belt deviation (a displacement in the width direction) of the intermediate transfer belt  8  based on the detection result of the belt deviation of the intermediate transfer belt  8  by the belt deviation detection device  80 . Detailed descriptions of the belt deviation detection device  80  and the correction device are deferred. 
     The tension roller  19  is in contact with an outer circumferential surface of the intermediate transfer belt  8 . The pre-transfer roller  18  and the secondary-transfer backup roller  40  are in contact with the inner circumferential surface of the intermediate transfer belt  8 . 
     As the intermediate transfer belt  8  rotates, the plurality of rollers  17  through  19  and  40  other than the drive roller  16  is driven to rotate. 
     The belt cleaner  10  is disposed between the secondary-transfer backup roller  40  and the tension roller  19 . The belt cleaner  10  includes a cleaning blade. 
     With reference to  FIG. 3 , the secondary-transfer backup roller  40  is in contact with the secondary transfer roller  70  via the intermediate transfer belt  8  and the secondary transfer belt  72 . The secondary-transfer backup roller  40  includes a cylindrical core made of, for example, stainless steel or the like, having an elastic layer on an outer circumferential surface of the core. The elastic layer is made of acrylonitrile-butadiene rubber (NBR). The elastic layer has the volume resistivity ranging from approximately 10 7  to 10 8  Ωcm, and a hardness ranging from approximately 48 to 58 degrees on Japanese Industrial Standards A hardness (hereinafter, referred to as JIS-A hardness) scale. The elastic layer has a thickness of approximately 5 mm. 
     According to the present embodiment, the secondary-transfer backup roller  40  is electrically connected to a power source that applies a high voltage of approximately −5 kV as a secondary transfer bias to the secondary-transfer backup roller  40 . With the secondary transfer bias applied to the secondary-transfer backup roller  40 , the toner image primarily transferred to the surface of the intermediate transfer belt  8  is secondarily transferred onto the sheet P conveyed to the secondary transfer nip. The secondary transfer bias has the same polarity as the polarity of toner. In the present embodiment, the secondary transfer bias is a direct current (DC) voltage and has a negative polarity to transfer the toner image by repulsion. With this configuration, the toner carried on the outer circumferential surface (a surface bearing the toner) of the intermediate transfer belt  8  electrostatically moves from the secondary-transfer backup roller  40  side toward the secondary transfer belt device  69  due to a secondary transfer electric field. 
     In another embodiment, the secondary transfer bias may be an alternating current (AC) voltage superimposed on a DC voltage. In yet another embodiment, the secondary transfer bias may be applied to the secondary transfer roller  70  to transfer the toner image by attraction. 
     The secondary transfer belt device  69  includes the secondary transfer belt  72 , the secondary transfer roller  70 , a separation roller  71 , and a secondary-transfer cleaning blade  73 . 
     The secondary transfer belt  72  is an endless belt stretched taut around multiple rollers (i.e., the secondary transfer roller  70  and the separation roller  71 ). The secondary transfer belt  72  is made of a material similar to that of the intermediate transfer belt  8 . The secondary transfer belt  72  is in contact with the intermediate transfer belt  8  to form the secondary transfer nip and conveys the sheet P fed from the secondary transfer nip. 
     The secondary-transfer backup roller  40  and the secondary transfer roller  70  press against each other via the intermediate transfer belt  8  and the secondary transfer belt  72 , thereby forming the secondary transfer nip. 
     The separation roller  71  is disposed downstream from the secondary transfer nip in the direction of conveyance of the sheet P. Ejected from the secondary transfer nip, the sheet P is conveyed along the secondary transfer belt  72  rotating counterclockwise in  FIG. 3  and separated from the secondary transfer belt  72  at a curved portion of the secondary transfer belt  72  wound around an outer circumference of the separation roller  71  due to self-stripping. 
     The secondary-transfer cleaning blade  73  is in contact with the surface of the secondary transfer belt  72  to remove substances such as toner and paper dust adhering to the surface of the secondary transfer belt  72 . 
     The intermediate transfer belt device  15  according to the present embodiment includes the belt deviation detection device  80  configured to detect the displacement of the intermediate transfer belt  8  (i.e., the belt deviation) laterally in the width direction (the direction perpendicular to the surface of the paper on which  FIG. 3  is drawn) when the intermediate transfer belt  8  rotates in the predetermined direction. 
     Specifically, with reference to  FIG. 4 , the belt deviation detection device  80  includes a contact member  82  in contact with the intermediate transfer belt  8 , an arm  81  to which the contact member is attached, a transmissive photosensor (a photo interrupter)  83  as a displacement detector configured to indirectly detect the lateral displacement of the intermediate transfer belt  8 , and a tension spring  84  as a biasing member to bias the contact member  82  attached to the arm  81  so that the contact member  82  contacts the intermediate transfer belt  8 . The displacement of the intermediate transfer belt  8  (i.e., the belt deviation) includes an amount of displacement and a direction of displacement of the intermediate transfer belt  8 . 
     The contact member  82  is in contact with the intermediate transfer belt  8  due to the biasing force of the tension spring  84  as the biasing member and tracks the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8 . 
     Specifically, the contact member  82  is cylindrical and held in a non-rotational manner so as to stand on one end side of the L-shaped arm  81 . Further, the contact member  82  is in contact with the intermediate transfer belt  8  such that a longitudinal direction of the contact member  82  is substantially perpendicular to the end in the width direction (i.e., the side edge) of the intermediate transfer belt  8 . In the present embodiment, the contact member  82  is made of a metal material such as stainless steel or the like to which a hardening treatment such as a heat treatment or a surface modification treatment is applied, which is described in detail later. 
     The arm  81  is a substantially L-shaped plate made of a resin material and held by a casing of the intermediate transfer belt device  15  so as to be swingable around a spindle  81   a  in the direction indicated by the solid double arrow A 3  in  FIG. 4 . The cylindrical contact member  82  is fitted to the one end side of the arm  81 . On the other end side of the arm  81 , a slit  81   b  penetrates the arm  81  in the thickness direction. In the present embodiment, the arm  81  and the contact member  82  are individually formed as separated pieces. Alternatively, the arm  81  and the contact member  82  can be formed as a single piece. 
     One end of the tension spring  84  as the biasing member is coupled to the other end side of the arm  81 , the side on which the contact member  82  is not disposed. The other end of the tension spring  84  is coupled to the casing of the intermediate transfer belt device  15 . 
     With such a configuration, the arm  81  swings along with the contact member  82  in the direction indicated by solid double arrow A 3  in  FIG. 4 , following the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8 , which is the direction of the belt deviation indicated by the double-headed arrow A 4  in  FIG. 4 . 
     Specifically, when the intermediate transfer belt  8  shifts to the left in  FIG. 5 , the contact member  82  moves in the same direction against the biasing force of the tension spring  84 , and the arm  81  swings around the spindle  81   a  clockwise in  FIG. 5 . On the other hand, when the intermediate transfer belt  8  shifts to the right in  FIG. 5 , the contact member  82  moves in the same direction by the biasing force of the tension spring  84 , and the arm  81  swings around the spindle  81   a  counterclockwise in  FIG. 5 . 
     The transmissive photosensor  83  as the detector detects the direction of displacement and the amount of displacement of the intermediate transfer belt  8  when the intermediate transfer belt  8  shifts toward one side (i.e., the belt deviation occurs). In other words, the transmissive photosensor  83  detects a direction of movement and an amount of movement of the contact member  82  (or the arm  81 ). 
     The transmissive photosensor  83  is disposed facing the slit  81   b  formed in the arm  81 . Specifically, with reference to  FIGS. 6A-1, 6B-1, and 6C-1 , in the present embodiment, the transmissive photosensor  83  includes one light emitting element  83   a  and two light receiving elements  83   b   1  and  83   b   2  disposed across the slit  81   b  of the arm  81 . The light receiving element  83   b   1  is positioned on the right side, and the light receiving element  83   b   2  is positioned on the left side in  FIGS. 6A-1, 6B-1, and 6C-1 . The transmissive photosensor  83  detects the direction of displacement and the amount of displacement of the intermediate transfer belt  8  (, the contact member  82 , or the arm  81 ) based on an output change of the two light receiving elements  83   b   1  and  83   b   2 . 
     By using such a transmissive photosensor  83  as the detector, the cost of the detection device can be reduced as compared with the cases in which a rangefinder is used as the detector, or a transmissive photosensor including a plurality of pairs of light emitting elements and light receiving elements is used as the detector. 
     Further, by using such a transmissive photosensor  83  as the detector, the detection accuracy by the detector can be improved as compared with the case in which a transmissive photosensor including one pair of light emitting element and light receiving element is used as the detector. 
     More specifically, the light emitted from the light emitting element  83   a  spreads radially and enters the two light receiving elements  83   b   1  and  83   b   2  through the slits  81   b . The outputs of the light receiving elements  83   b   1  and  83   b   2  (i.e., sensor outputs) change according to an incident light level from the light emitting element  83   a .  FIGS. 6A-2, 6B-2, and 6C-2  are graphs illustrating waveforms of the sensor outputs of the light receiving elements  83   b   1  and  83   b   2 . A right side peak of the waveform corresponds to the sensor output of the light receiving element  83   b   1  positioned on the right side, and a left side peak of the waveform corresponds to the sensor output of the light receiving element  83   b   2  positioned on the left side in  FIGS. 6A-1, 6B-1, and 6C-1 . The light receiving elements  83   b   1  and  83   b   2  are of the same type. 
     When the intermediate transfer belt  8  is not deviated from the specified position and is in a target posture, that is, when the slit  81   b  of the arm  81  is centered relative to the transmissive photosensor  83  as illustrated in  FIG. 6A-1 , the light emitted from the light emitting element  83   a  enters the two light receiving elements  83   b   1  and  83   b   2  substantially equally. As a result, as illustrated in  FIG. 6A-2 , the sensor output (voltage) of the two light receiving elements  83   b   1  and  83   b   2  has an output difference of almost zero. Therefore, when the transmissive photosensor  83  detects an output waveform as illustrated in  FIG. 6A-2 , the controller  90  determines that the intermediate transfer belt  8  is not deviated from the specified position (i.e., the belt deviation does not occur). 
     On the other hand, when the intermediate transfer belt  8  is deviated from the specified position toward one side, that is, when the slit  81   b  of the arm  81  moves to the right as indicated by the solid arrow in  FIG. 6B-1  relative to the transmissive photosensor  83 , a light incident level on the light receiving element  83   b   1  on one side (i.e., right side in  FIG. 6B-1 ) is greater than the incident light level on the light receiving element  83   b   2  on the other side (i.e., left side in  FIG. 6B-1 ). As a result, as illustrated in  FIG. 6B-2 , the sensor output of the light receiving element  83   b   1  on the one side is larger than that of the light receiving element  83   b   2  on the other side, and an output difference corresponding to the amount of movement of the intermediate transfer belt  8  is generated. Then, when the transmissive photosensor  83  detects such an output waveform as illustrated in  FIG. 6B-2 , the controller  90  determines the direction of movement and the amount of movement of the arm  81 . Accordingly, the direction of movement (or displacement) and the amount of movement (or displacement) of the intermediate transfer belt  8  (or the contact member  82 ) are obtained. 
     Similarly, when the intermediate transfer belt  8  is deviated from the specified position toward the other side, that is, when the slit  81   b  of the arm  81  moves to the left as indicated by the solid arrow in  FIG. 6C-1  relative to the transmissive photosensor  83 , the incident light level on the light receiving element  83   b   1  on the one side is less than the incident light level on the light receiving element  83   b   2  on the other side. As a result, as illustrated in  FIG. 6C-2 , the sensor output of the light receiving element  83   b   1  on the one side is smaller than that of the light receiving element  83   b   2  on the other side, and the output difference corresponding to the amount of movement of the intermediate transfer belt  8  is generated. Then, when the transmissive photosensor  83  detects such an output waveform as illustrated in  FIG. 6C-2 , the controller  90  determines the direction of movement and the amount of movement of the arm  81 . Accordingly, the direction of movement and the amount of movement of the intermediate transfer belt  8  (or the contact member  82 ) are obtained. 
     Then, when the belt deviation detection device  80  detects the displacement (the direction of displacement and the amount of displacement) of the intermediate transfer belt  8 , the correction roller  17  and the correction unit  91 , which constitute the correction device, corrects the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  based on the detection result. That is, the correction roller  17  and the correction unit  91  function as the correction device that corrects the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  based on the detection result by the belt deviation detection device  80 . 
     With reference to  FIG. 3 , the correction roller  17  is disposed on the upstream side in the direction of rotation of intermediate transfer belt  8  from photoconductor drums  1 Y,  1 M,  1 C, and  1 K and in contact with the inner circumference surface of intermediate transfer belt  8 . With reference to  FIG. 5 , the correction roller  17  is configured to swings in the directions X 1  and X 2  around a pivot  17   a  as a drive cam of the correction unit  91  operates by a predetermined angle. Specifically, the controller  90  causes the drive cam of the correction unit  91  to rotate based on the detection result of the belt deviation detection device  80 . The direction and angle of rotation of the drive cam is determined by the controller  90 , thereby determining the direction and amount (or duration) to swing the correction roller  17  corresponding to the direction and angle of rotation of the drive cam. 
     With such a configuration, when the intermediate transfer belt  8  is displaced to the right in  FIG. 5  (i.e., the belt deviation occurs), the transmissive photosensor  83  detects the direction of displacement and the amount of displacement, and then, based on the detection result, the correction roller  17  swings in the direction X 2  to correct the displacement of the intermediate transfer belt  8 . On the other hand, when the intermediate transfer belt  8  is displaced to the left in  FIG. 5 , the transmissive photosensor  83  detects the direction of displacement and the amount of displacement, and then, based on the detection result, the correction roller  17  swings in the direction X 1  to correct the displacement of the intermediate transfer belt  8 . As a result, a problem in which the intermediate transfer belt  8  meanders, and a problem in which the intermediate transfer belt  8  is broken when the intermediate transfer belt  8  is largely displaced in the width direction of the intermediate transfer belt  8  and in contact with other components are prevented. 
     Instead of changing the position of the shaft of the correction roller  17 , the actuator can be used as the correction device to contact and bias the side portion of the intermediate transfer belt  8 , thereby correcting the displacement of the intermediate transfer belt  8 . As another example of the correction device, a portion of the casing of the intermediate transfer belt device  15 , to which the tension spring  84  is coupled, may move to change the biasing force of the tension spring  84 , thereby correcting the displacement of the intermediate transfer belt  8 . 
     In the belt deviation detection device  80  according to the present embodiment, the contact member  82  is made of a metal material, and at least the contact portion of the contact member that contacts the intermediate transfer belt  8  is hardened (i.e., the hardening treatment is applied to the contact portion). That is, a method of manufacturing the contact member  82  includes hardening at least the contact portion that contacts the intermediate transfer belt  8 . Specifically, after the contact member  82  is formed in a cylindrical shape by cutting, the hardening treatment is applied to the cylindrical contact member  82 . Finally, the hardened contact member  82  is pressed into the arm  81 . 
     More specifically, in the present embodiment, the heat treatment such as a quenching treatment or the surface modification treatment such as a diamond-like carbon treatment is used as the hardening treatment applied to the contact member  82 . That is, in the method of manufacturing the contact member  82 , after a process of forming the cylindrical contact member  82 , a process of applying the heat treatment or the surface modification treatment to the cylindrical contact member  82  is performed. In the diamond-like carbon treatment, an amorphous hard film composed of a hydrocarbon or a carbon allotrope is formed on a target by plasma chemical vapor deposition (CVD) or physical vapor deposition (PVD). 
     Specifically, when the contact member  82  is made of stainless steel (SUS)  416  having high workability, a hardness of the contact member  82  is about 150 HV on Vickers hardness scale without the heat treatment. The hardness of the contact member  82  increases to about 300 HV with the quenching treatment, and the hardness of the contact member  82  increases to 1000 HV or more with the diamond-like carbon treatment. 
     Further, when the contact member  82  is made of SUS 440C having relatively high hardness, the hardness of the contact member  82  is about 250 HV on Vickers hardness scale without the heat treatment. The hardness of the contact member  82  increases to about 600 HV with the quenching treatment, and the hardness of the contact member  82  increases to 1000 HV or more with the diamond-like carbon treatment. 
     Furthermore, when the contact member  82  is made of SUS 630 having higher hardness than that of SUS 440C, the hardness of the contact member  82  is about 350 HV on Vickers hardness scale without the heat treatment. The hardness of the contact member  82  increases to about 600 HV with the quenching treatment, and the hardness of the contact member  82  increases to 1000 HV or more with the diamond-like carbon treatment. 
     As described above, the hardening treatment of the contact member  82  prevents the contact member  82  from wearing even if sliding contact with the intermediate transfer belt  8  lasts for a long time. Therefore, an error in the detection result of the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  by the belt deviation detection device  80  is hardly generated due to the wear of the contact member  82 . That is, the displacement of the intermediate transfer belt  8  can be accurately corrected over time. 
     In a comparative method to reduce the wear of the contact portion of the contact member  82 , a surface treatment to reduce a surface friction coefficient of the contact member  82  may be applied. However, if the surface friction coefficient of the contact member  82  is reduced, the surface hardness does not necessarily become higher. Accordingly, the wear of the contact member  82  may occur after long-term use, and the above-mentioned problems are not sufficiently solved. On the other hand, in the present embodiment, since the hardness of the contact portion of the contact member  82  is increased, the wear of the contact member  82  is reliably reduced, and the satisfactory detection accuracy of the belt deviation detection device  80  can be maintained over time. 
     In particular, in the present embodiment, the intermediate transfer belt  8  is configured to rotate at a high speed in the direction of rotation of the intermediate transfer belt  8  indicated by solid arrow A 5  in  FIG. 4 . By the high-speed rotation, the wear of the contact member  82  is likely to occur. Therefore, a configuration in which the hardness of the contact member  82  is increased is useful. 
     When the transmissive photosensor  83  is used as the detector for detecting the displacement of the contact member  82  (or the arm  81 ) based on the change of the output waveform of the light receiving elements  83   b   1  and  83   b   2 , the detection accuracy is likely to greatly change due to the wear of the contact member  82 , as compared with the case in which a rangefinder that directly detects the displacement of the contact member  82  (or the arm  81 ) is used as the detector. Therefore, a configuration in which the hardness of the contact member  82  is increased is useful in the case in which the transmissive photosensor  83  is used as the detector. 
     The hardening treatment can be applied to the entire outer circumference surface of the contact member  82  as illustrated by the dashed-dotted line in  FIG. 7A . Alternatively, the hardening treatment can be applied to only a part of the outer circumference surface of the contact member  82 , which is a part including at least the contact portion, as illustrated by the dashed-dotted line in  FIG. 7B . 
     In the former case, as compared to the latter case, the contact member  82  can be secured to the arm  81  without worrying about an area to which the hardening treatment is applied in the contact member  82  (i.e., an orientation of the contact member  82  that is secured to the arm  81 ). Therefore, assembly efficiency of the belt deviation detection device  80  can be improved. On the other hand, in the latter case, since the area of the hardening treatment is smaller than in the former case, the cost of the contact member  82  can be reduced. 
     In the present embodiment, the contact member  82  is cylindrical. 
     As a result, the contact member  82  is in line contact with the intermediate transfer belt  8 , thereby reducing the contact area between the contact member  82  and the intermediate transfer belt  8 . Therefore, even if the intermediate transfer belt  8  swings in the direction perpendicular to the width direction of the intermediate transfer belt  8  (the direction perpendicular to the surface of the paper on which  FIG. 5  is drawn), the contact member  82  is unlikely to swing due to the swing of the intermediate transfer belt  8 . In addition, even if the attachment accuracy (attachment angle) of the contact member  82  relative to the intermediate transfer belt  8  varies, the detection result of the transmissive photosensor  83  hardly varies. Furthermore, the wear due to sliding contact between the contact member  82  and the intermediate transfer belt  8  is reduced. Therefore, the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  can be detected with high accuracy over time. 
     In the present embodiment, the contact member  82  is formed in a cylindrical shape. However, even if the contact member  82  is not formed in a cylindrical shape, for example, if the contact member  82  is formed in a semi-cylindrical shape, the curved contact portion of the semi-cylindrical shape can attain the same effect. 
     In the present embodiment, the contact member  82  is secured to the arm  81  so that the contact member does not rotate. Thus, unlike the case in which the cylindrical contact member  82  is rotatably mounted on the arm  81  about the central axis of the contact member  82 , the detection accuracy of the transmissive photosensor  83  is prevented from varying due to the eccentricity of the contact member  82 . Therefore, the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  can be corrected with high accuracy. 
     In the present embodiment, the drive roller  16  is disposed in the vicinity of the belt deviation detection device  80  as illustrated in  FIG. 3 . 
     Such a configuration reduces the displacement (swing) of the intermediate transfer belt  8  in the direction perpendicular to the surface of the intermediate transfer belt  8  (the direction perpendicular to the surface of the paper on which  FIG. 5  is drawn) at the position of the belt deviation detection device  80  (or the contact member  82 ). That is, since the belt tension of the intermediate transfer belt  8  is increased by the drive roller  16 , the displacement of the intermediate transfer belt  8  at the position of the belt deviation detection device  80  in the direction perpendicular to the surface of the intermediate transfer belt  8  is restricted. Therefore, the following drawback is prevented, that is, in addition to a detection component to be originally detected (i.e., the detection component in the width direction of the intermediate transfer belt  8 ), a displacement component in a direction different from the width direction of the intermediate transfer belt  8  and the direction of rotation of the intermediate transfer belt  8  is also detected by the belt deviation detection device  80 . Therefore, the detection accuracy of the belt deviation of the intermediate transfer belt  8  by the belt deviation detection device  80  is further improved. 
     In the present embodiment, the correction roller  17  is disposed away from the belt deviation detection device  80 . Specifically, the correction roller  17  is disposed on the upstream side in the direction of rotation of the intermediate transfer belt  8  from an opposing region where the photoconductor drums  1 Y,  1 M,  1 C, and  1 K are opposed to the intermediate transfer belt  8 . The belt deviation detection device  80  is disposed downstream in the direction of rotation of the intermediate transfer belt  8  from the opposing region where the photoconductor drums  1 Y,  1 M,  1 C, and  1 K are opposed to the intermediate transfer belt  8 . 
     As described above, since the belt deviation detection device  80  is disposed away from the correction roller  17 , even if the correction roller  17  swings for correction operation, regulating force (i.e., restraint force of displacement in the perpendicular direction) on the intermediate transfer belt  8  by the drive roller  16  does not decrease, thereby improving the detection accuracy of the belt deviation detection device  80 . 
     Further, in the intermediate transfer belt device  15  according to the present embodiment, the belt deviation detection device  80  is disposed away from the opposing region where the photoconductor drums  1 Y,  1 M,  1 C, and  1 K are opposed to the intermediate transfer belt  8 . Specifically, the belt deviation detection device  80  and the drive roller  16  are disposed downstream in the direction of rotation of the intermediate transfer belt  8  from the opposing region where the photoconductor drums  1 Y,  1 M,  1 C, and  1 K are opposed to the intermediate transfer belt  8  (i.e., a position after the primary transfer process). 
     As a result, the intermediate transfer belt device  15  can be decreased in size as compared with the case in which the belt deviation detection device  80  is disposed in the opposing region where photoconductor drums  1 Y,  1 M,  1 C, and  1 K are opposed to the intermediate transfer belt  8 . Furthermore, as compared with the case where the belt deviation detection device  80  is disposed in the above-mentioned opposing region, the maintainability of the belt deviation detection device  80  is improved, and a drawback is prevented that the belt deviation detection device  80  (the transmissive photosensor  83 ) malfunctions due to the noise caused by a high voltage power supply disposed near the image forming units  6 Y,  6 M,  6 C, and  6 K. 
     As described above, the belt deviation detection device  80  according to the above embodiments includes the contact member  82  and the transmissive photosensor  83  as a displacement detector. The contact member  82  is in contact with the intermediate transfer belt  8  as a belt by the biasing force of the tension spring  84  as a biasing member and configured to track the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8 . The transmissive photosensor  83  is configured to detect the direction of displacement and the amount of displacement of the intermediate transfer belt  8 . The contact member  82  is made of a metal material and the hardening treatment is applied to at least the contact portion, which contacts the intermediate transfer belt  8 , of the contact member  82 . 
     As a result, the belt deviation detection device  80  can detect the displacement of the intermediate transfer belt  8  in the width direction of the intermediate transfer belt  8  with high accuracy over time. 
     Therefore, according to the present disclosure, a belt deviation detection device that can detect the displacement of the belt in the width direction of the belt with high accuracy over time, a belt device, an image forming apparatus incorporating the belt deviation detection device, and a method of manufacturing a contact member included in the belt deviation detection device can be provided. 
     It is to be noted that the above-described embodiments according to the present disclosure are applied to, but not limited to, the intermediate transfer belt device  15  in which the belt deviation of the intermediate transfer belt  8  as the belt is corrected. For example, the present disclosure can be applied to the secondary transfer belt device  69  to correct the belt deviation of the secondary transfer belt  72  according to the above embodiments, and further applied to a belt device including a belt such as a photoconductor belt, a direct transfer type transfer conveyance belt, a fixing belt, or the like. 
     Further, although in the above-described embodiments, the present disclosure is applied to the image forming apparatus  100  that forms color images, the present disclosure can also be applied to an image forming apparatus that forms only monochrome images. 
     Further, in the above-described embodiment, a displacement detector such as the transmissive photosensor  83  is configured to indirectly detect the direction of displacement (the direction of movement) and the amount of displacement (the amount of movement) of the intermediate transfer belt  8  (or the contact member  82 ). Alternatively, a displacement detector can be configured to directly detect the direction of displacement (the direction of movement) and the amount of displacement (the amount of movement) of the intermediate transfer belt  8  (or the contact member  82 ). 
     In such configurations, effects similar to those described above are also attained. 
     The above-described embodiments are illustrative and do not limit the present disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the present disclosure, the present disclosure may be practiced otherwise than as specifically described herein. The number, position, and shape of the components described above are not limited to those embodiments described above. Desirable number, position, and shape can be determined to perform the present disclosure.