Patent Publication Number: US-2023150282-A1

Title: Conveyor and liquid discharge apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-187114, filed on Nov. 17, 2021, 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 conveyor and a liquid discharge apparatus. 
     Related Art 
     An inkjet image forming apparatus as a liquid discharge apparatus discharges ink onto a sheet such as paper to form an image. 
     In an inkjet image forming apparatus, if the position of a sheet conveyed by a conveyance roller or the like deviates from an intended position, the position of ink landing on the sheet also deviates, which degrades image quality. In order to inhibit the positional deviation of the ink with respect to the sheet, there are image forming apparatuses that include a position detector such as an optical sensor that detects the position (positional deviation) of the sheet. 
     SUMMARY 
     In one aspect, a conveyor includes a conveyance roller to convey a conveyed object, a pair of roller supports opposing to each other and supporting both ends of the conveyance roller in an axial direction of the conveyance roller, a position sensor to detect a position of the conveyed object, and a sensor support supporting the position sensor. Each of the pair of roller supports has an insertion hole into which the sensor support is inserted. The insertion hole determines a position of the sensor support in a direction intersecting an insertion direction of the sensor support. The sensor support includes a positioning portion determining the position of the sensor support with respect to at least one of the pair of roller supports. The positioning portion determines the position of the sensor support in the insertion direction, a direction opposite to the insertion direction, and a rotational direction about an axis alone the insertion direction. 
     In another aspect, a liquid discharge apparatus includes the conveyor described above; and a liquid discharge head to discharge a liquid onto the conveyed object conveyed by the conveyor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG.  1    is a schematic diagram illustrating an overall configuration of an inkjet image forming apparatus according to one embodiment; 
         FIG.  2    is a block diagram of a control system of the inkjet image forming apparatus according to one embodiment; 
         FIG.  3    is a plan view of an image forming device according to one embodiment; 
         FIG.  4    is a side view of a conveyance device according to one embodiment; 
         FIG.  5    is a plan view of an example in which a conveyed sheet meanders; 
         FIG.  6    is a block diagram illustrating a control system of position sensors and head units according to one embodiment; 
         FIG.  7    is a perspective view of a sensor mounting structure according to one embodiment; 
         FIG.  8    is an exploded perspective view of the sensor mounting structure according to one embodiment; 
         FIG.  9    is a cross-sectional view of a state in which a support shaft is attached to a pair of side plates illustrated in  FIGS.  7  and  8   ; 
         FIG.  10    is an exploded perspective view of the sensor mounting structure in a state before a fixing plate is attached, according to one embodiment; 
         FIG.  11    is an exploded perspective view of the sensor mounting structure before a sensor holder is attached to each support shaft, according to one embodiment; 
         FIG.  12    is an exploded perspective view of the sensor holder and the position sensor to be attached to the sensor holder, according to one embodiment; 
         FIG.  13    is a side view of a comparative structure in which a support shaft is attached to a pair of side plates from an inner side; 
         FIG.  14    is a side view of the comparative structure in a state after the support shaft is inserted into one of the side plate in  FIG.  13   ; 
         FIG.  15    is a side view of the comparative example in which a bearing is used to secure the support shaft attached to the side plates from the inner side; 
         FIG.  16    is a perspective view of a sensor mounting structure in which a fitting hole for positioning a support shaft in a rotational direction is provided in a side plate, according to a modification; 
         FIG.  17    is a perspective view of a sensor mounting structure in which a front end of a support shaft contacts a side plate and is positioned, according to another modification; 
         FIG.  18    is a perspective view of a support shaft including two mounting faces, according to another modification; 
         FIG.  19    is a diagram illustrating an overall configuration of an electrophotographic image forming apparatus according to another embodiment; and 
         FIG.  20    is a diagram illustrating a configuration of a cooling device in the image forming apparatus illustrated in  FIG.  19   . 
     
    
    
     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. Also, 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 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 a similar function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, embodiments of the present disclosure are described below. 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. 
     With reference to drawings, descriptions are given below of embodiments of the present disclosure. In the drawings illustrating embodiments of the present disclosure, elements or components having identical or similar functions or shapes are given similar reference numerals as far as distinguishable, and redundant descriptions are omitted. 
     First, a configuration of an inkjet image forming apparatus, which is an example of a liquid discharge apparatus according to an embodiment of the present disclosure, is described with reference to  FIGS.  1  and  2   .  FIG.  1    is a diagram illustrating an overall configuration of an inkjet image forming apparatus  100 , and  FIG.  2    is a diagram illustrating a control system of the inkjet image forming apparatus  100  (hereinafter simply referred to as the “image forming apparatus  100 ”). 
     As illustrated in  FIG.  1   , the image forming apparatus  100  according to the present embodiment includes a sheet supply device  1  that supplies a sheet S for image formation, a conveyor unit  8  that conveys the supplied sheet S, a first image forming device  3  that forms an image on a front side of the sheet S, a second image forming device  4  that forms an image on a back side of the sheet S, a front-back reverse device  5  that reverses the sheet S to turn upside down, a first drying device  6  and a second drying device  7  that dry the sheet S, and a sheet collection device  2  that collects the sheet S on which an image has been formed. The image forming apparatus  100  according to the present embodiment further includes a controller  9  (see  FIG.  2   ) that controls the sheet supply device  1 , the conveyor unit  8 , the first image forming device  3 , the second image forming device  4 , the front-back reverse device  5 , the first drying device  6 , the second drying device  7 , and the sheet collection device  2 . 
     The sheet supply device  1  includes a supply roller  11  on which a long sheet S is wound in a roll shape. The supply roller  11  is rotatable in the direction indicated by an arrow appended to the supply roller  11  in  FIG.  1   , and the sheet S is fed from the supply roller  11  as the supply roller  11  rotates. 
     The conveyor unit  8  includes a plurality of conveyance devices  20  (see  FIG.  4   ) each having a plurality of conveyance rollers  17 . The sheet S is stretched over the conveyance rollers  17 , and the sheet S is conveyed by rotation of the conveyance rollers  17 . The conveyance roller may be a pipe, a shaft, or the like having a circular cross section. 
     The first image forming device  3  includes a plurality of head units  12 Y,  12 M,  12 C, and  12 K (also collectively “head units  12 ”) that discharges liquid ink onto the sheet S. Each of the head units  12  discharges ink onto the front side of the sheet S to form an image thereon according to, of image data generated by the controller  9 , image data representing the image to be formed on the front side of the sheet S. The ink is a liquid containing a colorant, a solvent, and crystalline resin particles dispersed in the solvent. Crystalline resin is a resin that melts to changes a phase thereof from a crystal phase to a liquid phase when heated above a melting point thereof. 
     The first drying device  6  includes a heating drum  13  that heats the sheet S to dry the ink on the sheet S. The heating drum  13  has a cylindrical shape and rotates while the sheet S is wound around the outer circumferential surface thereof. The heating drum  13  includes a heating source such as a halogen heater disposed therein. The heating drum  13  is disposed below a conveyance path along which the sheet S is conveyed. In other words, the heating drum  13  is on the back side of the sheet S. When the sheet S is conveyed from the first image forming device  3 , the bottom face (back side) of the sheet S contacts the outer circumferential surface of the heating drum  13 . The heating drum  13  conveys the sheet S while heating the sheet S. Accordingly, the drying of the ink on the sheet S is promoted. The rotation speed of the heating drum  13  at this time is controlled by the controller  9  to be substantially the same as the conveyance speed of the sheet supply device  1 , the sheet collection device  2 , the conveyor unit  8 , and the like. Such control prevents detective conveyance direction of the sheet S being conveyed, such as slipping of the sheet S on the outer circumferential surface of the heating drum  13  in the direction in which the sheet S is conveyed (i.e., a sheet conveyance direction). 
     The front-back reverse device  5  has a known structure to reverse the sheet S to turn the sheet S upside down. When the sheet S conveyed from the first drying device  6  passes through the front-back reverse device  5 , the sheet S is turned upside down and sent to the second image forming device  4 . That is, when the sheet S is conveyed with the front side facing up to the front-hack reverse device  5 , the sheet S is reversed so that the front side faces down (the back side faces up). 
     The second image forming device  4  has a structure similar to that of the first image forming device  3  and includes a plurality of head units  14 Y,  14 M,  14 C, and  14 K that discharges ink. The second image forming device  4  forms an image on the back side of the sheet S. That is, since the sheet S is conveyed to the second image forming device  4  after the sheet S is reversed (turned upside down) by the front-back reverse device  5 , the second image forming device  4  discharges ink onto the back side of the sheet S to form an image thereon according to, of the image data generated by the controller  9 , image data representing the image to be formed on the back side of the sheet S. 
     Similar to the first drying device  6 , the second drying device  7  includes a heating drum  15  that heats the sheet S. As illustrated in  FIG.  1   , similar to the heating drum  13  of the first drying device  6 , the heating drum  15  of the second drying device  7  is disposed below the conveyance path. Since the sheet S is reversed (turned upside down), the front side of the sheet S contacts the outer circumferential surface of the heating drum  15 . Even if the front side of the sheet S bears an image (ink is applied thereto), the ink has already been dried by the first drying device  6 . Accordingly, the image on the front side is not disturbed by the contact with the heating drum  15 . 
     The sheet collection device  2  includes a collection roller  16  that winds and collects the sheet S. The collection roller  16  is rotatable in the direction indicated by an arrow appended thereto in  FIG.  1   , and the sheet S is wound in a roll shape around the collection roller  16  as the collection roller  16  rotates. The sheet collection device  2  may include a post-processing unit that performs post-processing such as cutting the sheet S to a predetermined length and aligning the cut sheet S. 
     The controller  9  is implemented by an information processing apparatus such as a personal computer (PC). The controller  9  generates image data representing images to be formed on the front side and the back side of the sheet S, and controls various operations of the sheet supply device  1 , the first image forming device  3 , the second image forming device  4 , the front-back reverse device  5 , the first drying device  6 , the second drying device  7 , and the sheet collection device  2 . For example, the controller  9  controls, in addition to the rotation speeds of the supply roller  11 , the collection roller  16 , and the conveyance rollers  17 , the temperatures of the heating sources that heat the heating drums  13  and  15 . 
     Next, with reference to  FIG.  3   , a description is given of the configuration of the image forming devices according to the present embodiment. In the present embodiment, the first image forming device  3  and the second image forming device  4  has similar configurations. Accordingly, the configuration of the first image forming device  3  is described, and the description of the configuration of the second image forming device  4  is omitted. 
     As illustrated in  FIG.  3   , in the first image forming device  3  according to the present embodiment, the four head units  12 K,  12 C,  12 M, and  12 Y that discharge black (K), cyan (C), magenta (M), and yellow (Y) inks, respectively, are disposed in that order from the upstream side in the direction indicated by arrow A (hereinafter “sheet conveyance direction A”) in which the sheet S is conveyed. The order of the head units  12 K,  12 C,  12 M, and  12 Y of the respective colors is not limited to the illustrated order. The color of the ink to be used may be a color other than yellow, magenta, cyan, and black. 
     Each of the head units  12 K,  12 C,  12 M, and  12 Y includes four liquid discharge heads  18 . Each liquid discharge head  18  has a plurality of nozzles  19  and discharges ink (liquid) onto the sheet S from each nozzle  19 . The liquid discharge heads  18  are alternately arranged to cover an image formation area of the sheet S entirely in the width direction of the sheet S. When the sheet S is conveyed to the position facing the head units  12 K,  12 C,  12 M, and  12 Y, the liquid discharge heads  18  discharge ink, and an image is formed on the sheet S. 
     In this specification, the term “width direction” of the sheet S is a direction parallel to a conveyance plane on which the sheet is conveyed and orthogonal to the sheet conveyance direction A. The width direction is indicated by arrow B  FIG.  3   . Further, the term “conveyance plane” is a plane through which the conveyed sheet passes. The conveyance plane includes, for example, an imaginary plane connecting contact portions between the sheet and a plurality of conveyance rollers to convey the sheet, or a face of a conveyance belt on which the sheet is placed and conveyed. The “width direction” of the sheet may be referred to “sheet width direction” in the following description. 
     With reference to  FIG.  4   , a description is given of a configuration of the conveyance device  20  (serving as a conveyor) of the conveyor unit  8  disposed in the first image forming device  3 . 
     As illustrated in  FIG.  4   , the conveyance device  20  includes the plurality of conveyance rollers  17 . The plurality of the conveyance rollers  17  illustrated in  FIG.  4    includes drive roller pairs  17 A and  17 B, a drive roller  17 C, and a plurality of driven rollers  17   d  to  17   k . The drive roller pair  17 A disposed extreme upstream in the sheet conveyance direction A and the drive roller pair  17 B disposed extreme downstream in the sheet conveyance direction A are two drive roller pairs that convey the sheet S while sandwiching the sheet S from the front side and the back side. In addition to the drive roller pairs  17 A and  17 B (drive roller pairs), the drive roller  17 C not paired with another roller) disposed adjacent to and downstream from the upstream drive roller pair  17 A conveys the sheet S. 
     The plurality of driven rollers  17   d  to  17   k  is disposed between the drive roller  17 C on the upstream side and the drive roller pair  17 B on the downstream side. Instead of the driven rollers  17   d  to  17   k , a plurality of drive rollers may be disposed. In  FIG.  4   , the head units  12 K,  12 C,  12 M, and  12 Y discharge ink at liquid discharge positions  10 K,  10 C,  10 M, and  10 Y (also collectively “liquid discharge positions  10 ”), respectively. The driven rollers  17   d  to  17   k  are disposed such that each liquid discharge position  10  is interposed between two of the driven rollers  17   d  to  17   k  in the sheet conveyance direction. With the arrangement in which the driven rollers  17   d  to  17   k  are respectively disposed on upstream and downstream from the liquid discharge positions  10 K,  10 C,  10 M, and  10 Y, fluttering of the sheet S particularly at the liquid discharge positions  10 K,  10 C,  10 M, and  10 Y is inhibited, and the sheet S can be stably conveyed. 
     When the conveyance roller  17  is eccentric or thermally expanded, as illustrated in  FIG.  5   , the conveyed sheet S may he displaced in the width direction indicated by arrow B, and the sheet S may be conveyed in a meandering manner. When such meandering of the sheet S occurs, the position of the ink landing on the sheet S also deviates, and image quality deteriorates. Therefore, in the present embodiment, in a case where meandering of the sheet S occurs, the head units  12 C,  12 M, and  12 Y for cyan, magenta, and yellow are movable in the width direction of the sheet S indicated by arrow B, so as to follow the meandering (positional deviation in the width direction). In  FIG.  5   , chain double-dashed lines indicate the move of the head units  12 C,  12 M, and  12 Y. 
     In order to move the head units  12 C,  12 M, and  12 Y to follow the meandering of the sheet S, it is necessary to grasp a positional deviation (the direction in which the position deviates and the amount of deviation) in the width direction indicated by arrow B of the sheet S. For that, as illustrated in  FIG.  4   , the conveyance device  20  according to the present embodiment is provided with a plurality of position sensors  30  (first to fourth position sensors  30 A to  30 D) serving as a position detector to detect the position of the sheet S. 
     Each position sensor  30  is disposed opposite the corresponding head unit  12  (on the lower side of the sheet S in  FIG.  4   ) relative to the conveyance path through which the sheet S is conveyed, and in the vicinity of the liquid discharge position  10  at which the head unit  12  discharges ink. That is, each position sensor  30  is disposed between, out of the driven rollers  17   d  to  17   k , two driven rollers respectively disposed upstream and downstream from the corresponding one of the liquid discharge positions  10 K,  10 C,  10 M, and  10 Y. The “liquid discharge position” in this specification refers to a liquid discharge position in a state where the sheet does not meander, that is, a state where the head unit does not move in the sheet width direction and is disposed at a reference position (initial position) set in advance. 
     The position sensor  30  is an optical sensor or the like that detects surface information of a conveyed object to be conveyed. Examples include a charge-coupled device (CCD) camera and a complementary metal oxide semiconductor (CMOS) camera using air pressure, photoelectricity, ultrasonic wave, or light such as visible light, laser, or infrared light. 
       FIG.  6    is a block diagram illustrating a control system of the position sensors and the head units according to the present embodiment. With reference to  FIG.  6   , a description is given below of control of the position sensors  30  and the head units  12  using an example of a combination of the first position sensor  30 A and the second position sensor  30 B. The first position sensor  30 A detects the position of the sheet S at the position of the head unit  12 K for black. The second position sensor  30 B detects the position of the sheet S at the position of the head unit  12 C for cyan. 
     As illustrated in  FIG.  6   , the controller  9  includes a calculation unit  36 . Each of the first position sensor  30 A and the second position sensor  30 B includes an imaging device  31 , an image capture controller  32 , and an image storage unit  33 . 
     The imaging device  31  captures an image of the sheet S being conveyed. 
     The image capture controller  32  includes a shutter control unit  34  and an image acquisition unit  35 . The shutter control unit  34  controls the timing at which the imaging device  31  captures an image. The image acquisition unit  35  acquires data of an image captured by the imaging device  31 . 
     The image storage unit  33  stores the image data obtained by the image capture controller  32 . 
     The sheet S has diffusiveness on or inside thereof. Accordingly, when the sheet S is irradiated with laser beam from a laser light source of the position sensor  30 A or  30 B, the reflected light is diffused. The diffuse reflection creates a pattern on the sheet S. The pattern is made of spots called “speckles” and called a “speckle pattern,” which is an example of the surface information. When an image of the sheet S is captured, image data representing the speckle pattern is obtained. From the image data, the position of the pattern is known, and the position of a specific portion of the sheet S is detected. 
     That is, when the sheet S is conveyed, the pattern of the sheet S is also conveyed. Therefore, by detecting the same pattern at different times, the movement amount or the movement speed of the sheet S can be obtained. 
     The image data obtained by the first position sensor  30 A and image data obtained by the second position sensor  30 B are sent to the calculation unit  36  of the controller  9 . The calculation unit  36  calculates how much the predetermined portion on the sheet S has moved in the sheet width direction based on the image data sent from the first position sensor  30 A and the second position sensor  30 B. By moving the head unit  12 C for cyan in the sheet width direction based on the movement amount (positional deviation amount) of the sheet S calculated by the calculation unit  36 , the discharge position in the sheet width direction is controlled. In other combinations of the position sensors  30 , the positional deviation of the sheet S is detected in the same manner, and the magenta and yellow head units  12 M and  12 Y are moved in the sheet width direction based on the detected positional deviation amount, thereby controlling the respective discharge positions in the sheet width direction. 
     Based on the image data obtained by each position sensor  30 , in addition to the positional deviation in the sheet width direction, the positional deviation in the sheet conveyance direction is also detected. For example, the calculation unit  36  calculates how much the predetermined portion on the sheet S has moved in the sheet conveyance direction based on the image data sent from the first position sensor  30 A and the second position sensor  30 B, so as to calculate the positional deviation amount of the sheet S in the sheet conveyance direction. In other combinations of the position sensors  30 , the positional deviation in the sheet conveyance direction is similarly detected. The sheet S may extend in the sheet conveyance direction due to permeation of the ink. In such a case, the discharge timing of each of the head units  12 K,  12 C,  12 M, and  12 Y is controlled based on the calculated positional deviation amount in the sheet conveyance direction. Thus, the discharge position in the sheet conveyance direction can be controlled. 
     In order to improve the detection accuracy of each position sensor  30 , as illustrated in  FIG.  4   , each position sensor  30  is preferably disposed between rollers such as the driven rollers  17   d  to  17   k . Since the conveyance speed of the sheet S is relatively stable between the rollers, the position sensors  30  disposed between the rollers can accurately detect the movement amount or the movement speed of the sheet S in at least one of the sheet conveyance direction and the sheet width direction. 
     Preferably, the position of the position sensor  30  is close to the corresponding liquid discharge position  10  where ink is discharged. That is, the shorter the distance between the position sensor  30  and the liquid discharge position  10 , the smaller the detection error. Therefore, the positional deviation of the sheet S can be detected with high accuracy. 
     Further, the position sensor  30  is preferably disposed upstream from the liquid discharge position  10 . When the position sensor  30  is disposed upstream from the liquid discharge position  10 , the movement or discharge timing of the head unit  12  can be controlled after the position of the sheet S is detected by the position sensor  30  and before the sheet S is conveyed to the liquid discharge position  10 . 
     By contrast, in a case where the position sensor  30  is disposed directly below the liquid discharge position  10 , there is a concern that the landing position of the ink deviates due to a delay by the amount of the control operation. If the control operation is performed quickly, as the position of the position sensor  30 , directly below the liquid discharge position  10  is preferred to upstream from the liquid discharge position  10  for accurately detecting the movement amount of the sheet S directly below the liquid discharge position  10 . Alternatively, when the error by the amount of the control operation is allowable, the position sensor  30  may be disposed downstream from the liquid discharge position  10 . 
     In the present embodiment, intervals D 1  to D 3  (see  FIG.  4   ) between the position sensors  30  in the sheet conveyance direction A are set to be integral multiples of a circumferential length X of the drive roller that conveys the sheet S (for example, the lower drive roller of the drive roller pair  17 B disposed extreme downstream in the sheet conveyance direction A in  FIG.  4   ). That is, in  FIG.  4   , the respective distances D 1  to D 3  from the extreme upstream position sensor  30 A to the position sensors  30 B to  30 D downstream from the position sensor  30 A are respectively set to one, two, and three multiples of the circumferential length X of the drive roller (D 1 =X, D 2 = 2 X, D 3 = 3 X). 
     Setting the intervals D 1  to D 3  between the position sensors  30  to integral multiples of the circumferential length X of the drive roller is advantageous as follows. Even if the drive roller is eccentric, this setting can cancel out the speed unevenness of the sheet S due to the eccentricity at the detection positions of the position sensors  30 . Therefore, each position sensor  30  can accurately detect the positional deviation of the sheet S. 
     Similarly, intervals E 1  to E 3  between the head units  12 K,  12 C,  12 M, and  12 Y in the sheet conveyance direction A are set to one, two, and three multiples of the circumferential length X of the drive roller (E 1 =X, E 2 = 2 X, and E 3 = 3 X). This setting can cancel out the speed unevenness of the sheet S due to the eccentricity of the drive roller at each of the liquid discharge positions  10 K,  10 C,  10 M, and  10 Y, thereby securing accurate discharge of ink from the head units  12 K,  12 C,  12 M, and  12 Y to the sheet S. 
     To improve the detection accuracy of each position sensor  30 , the position of the position sensor  30  relative to the liquid discharge position is set as described above, and, preferably, the mounting accuracy of the position sensor is improved. For improving the mounting accuracy of the sensor, generally, there is a method of increasing the dimensional accuracy of a mounting component or performing position adjustment after mounting. However, higher accuracy of component dimensions increases the cost, and adjusting the position after mounting increases the mounting work time, which are not desirable. Therefore, in the present embodiment, the following configuration is adopted to easily and accurately mount the position sensor. Hereinafter, a sensor mounting structure according to the present embodiment will be described. 
       FIG.  7    is a perspective view of a part of the conveyance device  20  including the sensor mounting structure according to the present embodiment. 
     As illustrated in  FIG.  7   , the position sensor  30  is attached between a pair of side plates  21 A and  21 B via two support shafts  22  and a sensor holder  23 . The pair of side plates  21 A and  21 B serves as a pair of roller supports to support both ends (or the vicinity thereof) of each of the plurality of conveyance rollers  17 , The side plates  21 A and  21 B are disposed in parallel with each other with an interval therebetween. The sensor holder  23  holds the position sensor  30 . The sensor holder  23  extends across the two support shafts  22  and is attached to the two support shafts  22 . Each support shall  22  is a component of a sensor support that supports the position sensor  30  held by the sensor holder  23 , and is attached between the pair of side plates  21 A and  21 B. On the side plate  21 A, a flat fixing plate  24  serving as a fixing member that fixes each support shaft  22  is attached. The flat fixing plate  24  is another component of the sensor support. That is, the sensor support includes the pair of support shafts  22  and the fixing plate  24 . As described above, the conveyance device  20  according to the present embodiment includes the pair of side plates  21 A and  21 B, the two support shafts  22 , the sensor holder  23 , and the fixing plate  24  as the sensor mounting structure for mounting the position sensor  30 . 
     Next, a description is given of details of the sensor mounting structure and a mounting method according to the present embodiment with reference to the exploded perspective views of  FIGS.  8  to  12   . In the following description, of the side plates  21 A and  21 B illustrated in  FIG.  8   , the side plate  21 A on the near side in the drawing is also referred to as a “first side plate  21 A,” and the side plate  21 B on the far side is also referred to as a “second side plate  21 B.” In addition, the side on which the side plates  21 A and  21 B face each other (face a center in the sheet width direction) is referred to as an “inner side” or “opposing side.” and an opposite side thereof is referred to as an “outer side.” 
     As illustrated in  FIG.  8   , each of the first side plate  21 A and the second side plate  21 B has two insertion holes  25  into which the respective support shafts  22  are inserted. Each insertion hole  25  has a circular cross section. The insertion holes  25  are positioned at the same height and at the same interval so that the support shafts  22  inserted in the insertion holes  25  are horizontal and parallel to each other. 
     As illustrated in  FIG.  8   , each support shaft  22  is inserted from the outer side of the first side plate  21 A toward the second side plate  21 B in the direction indicated by arrow C (also “insertion direction C”). A front end of each support shaft  22  in the insertion direction C includes a protruding portion  220  having a circular cross section. The protruding portion  220  is to be inserted into the insertion hole  25  of the second side plate  21 B. The protruding portion  220  has a smaller diameter than other portion (a large-diameter portion  221 ) of the support shaft  22 . As illustrated in  FIG.  9   , when the protruding portion  220  is inserted into the insertion hole  25  of the second side plate  21 B, an end-side portion (on the protruding portion  220  side) of the large-diameter portion  221  of the support shaft  22  is also inserted into the insertion hole  25  of the second side plate  21 B. 
     After the support shafts  22  are inserted into the insertion holes  25  of the first and second side plates  21 A and  21 B, the fixing plate  24  is attached to the first side plate  21 A. Then, the movement of the support shafts  22  in the insertion direction C and the direction opposite thereto and the rotation of the support shafts  22  about the axes along the insertion direction C are restricted. 
     Specifically, as illustrated in  FIG.  10   , a rear end (an end opposite to a front end in the insertion direction C) of each support shaft  22  includes a rotation prevention protrusion  222 . The rotation prevention protrusion  222  has a D-shaped cross section and restricts rotation of the support shaft  22 . Relating to this, the fixing plate  24  has fitting holes  241 , each having a D-shaped cross section, into which the rotation prevention protrusions  222  of the support shafts  22  fit. As the rotation prevention protrusion  222  of the support shaft  22  is inserted and fitted into the fitting hole  241  of the fixing plate  24 , the rotation of the support shaft  22  with respect to the fixing plate  24  is restricted. The shape of the cross section of the rotation prevention protrusion  222  and the fitting hole  241  is not limited to a D-shape but may be another non-circular shape such as a quadrangular shape, a polygonal shape, or an elliptical shape. 
     Further, as illustrated in  FIG.  10   , a screw hole  224  is provided in the rotation prevention protrusion  222 . The support shaft  22  is screwed to the fixing plate  24  by a screw  27  inserted into the screw hole  224  from the outer side of the fixing plate  24 . Further, the fixing plate  24  has a screw insertion hole  240  for attaching the fixing plate  24  to the first side plate  21 A. Relating to this, the first side plate  21 A has a screw hole  210  for attaching the fixing plate  24 . A screw  26  is inserted into the screw insertion hole  240  of the fixing plate  24  and screwed in the screw hole  210  of the first side plate  21 A. Then, the fixing plate  24  is attached to the outer face of the first side plate  21 A. 
     As illustrated in  FIG.  9   , in a state in which the support shaft  22  is secured to the fixing plate  24  and the fixing plate  24  is secured to the first side plate  21 A, movement of the support shaft  22  in the insertion direction C and the direction opposite thereto with respect to the first side plate  21 A is restricted. Further, in this state, since the respective rotation prevention protrusions  222  of the support shafts  22  are fitted to the fitting holes  241  of the fixing plate  24 , the rotation of the support shafts  22  with respect to the first side plate  21 A is also restricted. 
       FIG.  11    is an exploded perspective view of the sensor holder  23 , the position sensor  30 , and the support shafts  22  in a state before the sensor holder  23  is attached to the support shafts  22 . 
     As illustrated in  FIG.  11   , each support shaft  22  includes a mounting face  225  for mounting the sensor holder  23  on the surface thereof. The mounting face  225  is a flat face. In a state in which rotation of the support shaft  22  with respect to the first side plate  21 A is restricted, the mounting face  225  faces upward (conveyance path side) and is disposed horizontally. 
     The mounting face  225  includes two positioning recesses  226   a  and  226   b  as 5 positioning portions for positioning the sensor holder  23 . Of the two positioning recesses  226   a  and  226   b , the positioning recess  226   a  has a round shape and serves as a main reference for positioning. The other positioning recess  226   b  has a slot shape and serves as a sub-reference for positioning. The mounting face  225  further has two screw holes  227  for mounting the sensor holder  23 . 
     As illustrated in  FIG.  11   , the sensor holder  23  includes a base portion  230  attached to the mounting face  225  of the support shaft  22 , and a sensor mounting portion  231  to which the position sensor  30  is mounted. The base portion  230  and the sensor mounting portion  231  are orthogonal to each other. When the base portion  230  is disposed horizontally, the sensor mounting portion  231  extends vertically downward from the base portion  230 . The base portion  230  includes two positioning projections  232 , as positioning portions, to be inserted into the positioning recesses  226   a  and  226   b  in the mounting face  225 . When the positioning projections  232  are inserted into the positioning recesses  226   a  and  226   b , the sensor holder  23  is prevented from moving horizontally (in a direction parallel to the mounting face  225 ) with respect to the support shaft  22 . At this time, since the base portion  230  is placed on the mounting face  225  of the support shaft  22 , movement of the sensor holder  23  in a downward direction (a direction perpendicular to the mounting face  225 ) with respect to the support shaft  22  is also restricted. 
     In the present embodiment, the positioning recesses  226   a  and  226   b  are provided in both of the support shafts  22  for commonality of components. However, the positioning projections  232  of the sensor holder  23  are inserted into the positioning recesses  226   a  and  226   b  of only one of the support shafts  22 . In this manner, the sensor holder  23  is positioned with reference to the positioning recesses  226   a  and  226   b  of at least one of the support shafts  22 . Alternatively, the sensor holder  23  may be positioned with reference to the positioning recesses  226   a  and  226   b  of both support shafts  22 . In addition, the projection-recess relationship between the positioning portions of the sensor holder  23  and the support shaft  22  may be opposite to that in the present embodiment. That is, the sensor holder  23  may have positioning recesses, and the mounting face  225  of the support shaft  22  may have positioning projections. 
     As illustrated in  FIG.  11   , the base portion  230  of the sensor holder  23  has a plurality of screw insertion holes  233  for attaching the sensor holder  23  to the support shafts  22 , in a state in which the sensor holder  23  is positioned with respect to the mounting faces  225  of the support shafts  22 , screws  28  are inserted into the screw insertion holes  233  of the sensor holder  23  and screwed to the screw holes  227  in the mounting faces  225 . Then, the sensor holder  23  is mounted to the mounting faces  225  of the support shafts  22 . 
       FIG.  12    is an exploded perspective view of the sensor holder  23  and the position sensor  30  to be attached to the sensor holder  23 . 
     As illustrated in  FIGS.  11  and  12   , the sensor mounting portion  231  of the sensor holder  23  includes a plurality of positioning projections  234  as positioning portions for positioning the position sensor  30 . As indicated by a chain double-dashed line in  FIG.  12   , the position sensor  30  is restricted from moving downward and rightward in the drawing by the contact with the positioning projections  234  of the sensor holder  23 . Specifically, the position sensor  30  includes a main body  301  including the imaging device  31 , a lens unit  302 , and an illumination unit  303 , and the main body  301  has a hexahedral shape (a cubic shape or a rectangular parallelepiped shape). As the positioning projections  234  contact two planes (the bottom face and the right face in  FIG.  12   ) of the main body  301  orthogonal to each other, movement of the position sensor  30  in a direction orthogonal to the two planes of the main body  301  is restricted. 
     Further, the sensor mounting portion  231  of the sensor holder  23  includes a plurality of screw insertion holes  235  for mounting the position sensor  30 . Relating to this, the main body  301  of the position sensor  30  has a plurality of screw holes  304 . In a state in which the position sensor  30  is positioned with respect to the sensor holder  23 , screws  29  are inserted into the screw insertion holes  235  of the sensor mounting portion  231  and screwed to the screw holes  304  in the position sensor  30 . Then, the position sensor  30  is mounted to the sensor holder  23 . In the present embodiment, the two screw insertion holes  235  and the two positioning projections  234  are provided in the sensor mounting portion  231  so that the number of position sensors  30  attached to the sensor holder  23  can be increased to two or the mounting position can be selected. 
     In the above-described structure according to the present embodiment, in order to mount the position sensor  30  between the side plates  21 A and  21 B, first, as illustrated in  FIG.  8   , the two support shafts  22  are inserted into the insertion holes  25  from the outer side of the first side plate  21 A. Further, the front ends (the protruding portions  220 ) of the support shafts  22  in the insertion direction C are inserted into the insertion holes  25  of the second side plate  21 B. In the present embodiment, the diameter of the insertion holes  25  of the first side plate  21 A are larger on the near side than on the far side in the insertion direction C (see  FIG.  9   ). Therefore, for example, even when the positions of the insertion holes  25  of the side plates  21 A and  21 B are slightly shifted from each other, the support shaft  22  can be smoothly inserted from the insertion hole  25  of the first side plate  21 A into the insertion hole  25  of the second side plate  21 B when the support shaft  22  is inclined in the insertion hole  25  of the first side plate  21 A. 
     Next, the mounting faces  225  of the support shafts  22  inserted into the insertion holes  25  are aligned so as to face upward, and the fixing plate  24  is attached from the outer side of the first side plate  21 A. At this time, as illustrated in  FIG.  10   , the fixing plate  24  is disposed such that the rotation preventing protrusions  222  of the support shafts  22  fit in the fitting holes  241  of the fixing plate  24 . Then, the screw  26  is screwed to the screw insertion hole  240  in the fixing plate  24 , and the screws  27  are screwed to the screw holes  224  in the rotation prevention protrusions  222  of the support shafts  22 . Thus, the fixing plate  24  is secured to the first side plate  21 A, and the support shafts  22  are secured to the fixing plate  24 . 
     Subsequently, as illustrated in  FIG.  12   , the position sensor  30  is mounted to the sensor holder  23 . 
     First, the position sensor  30  is brought into contact with the plurality of positioning projections  234  of the sensor holder  23  to be positioned. While this state is maintained, the screws  29  are screwed to the screw holes  304  of the position sensor  30  through the screw insertion holes  235  of the sensor holder  23 . Thus, the position sensor  30  is mounted to the sensor holder  23 . 
     Then, the sensor holder  23  to which the position sensor  30  is mounted is mounted on the support shafts  22  secured between the pair of side plates  21 A and  21 B. First, as illustrated in  FIG.  11   , the positioning projections  232  of the sensor holder  23  are inserted into the positioning recesses  226   a  and  226   b  in the mounting face  225  of one of the support shafts  22 , to determine the position thereof. Next, the screws  28  are screwed to the screw holes  227  in the mounting face  225  through the screw insertion holes  233  of the sensor holder  23 , and the sensor holder  23  is mounted on each support shaft  22 . Thus, the mounting operation of the position sensor  30  is completed. 
     As described above, in the present embodiment, the position sensor  30  can be mounted while the position of each member is determined. Accordingly, the position sensor  30  can be easily and accurately mounted without strict dimension management of components or position adjustment after the mounting. 
     That is, in the present embodiment, as the support shafts  22  supporting the position sensor  30  are inserted into the insertion holes  25  in the pair of side plates  21 A and  21 B, the positions of the support shafts  22  in a direction (radial direction) intersecting the insertion direction C are determined. In addition, in a state in which the support shafts  22  are inserted into the insertion holes  25 , the support shaft  22  are secured to the first side plate  21 A via the fixing plate  24 . Then, the positions of the support shafts  22  with respect to the first side plate  21 A in the insertion direction C and the direction opposite thereto (axial direction) are determined. Further, the rotation prevention protrusions  222  at the rear ends of the support shafts  22  are fitted into the fitting holes  241  of the fixing plate  24 . This fitting determines the position of the support shafts  22  with respect to the first side plate  21 A in the rotational direction about the axes along the insertion direction C. 
     As described above, in the present embodiment, the paired side plates  21 A and  21 B have the insertion holes  25  into which the support shafts  22  are inserted to position the support shafts  22  in the direction intersecting the insertion direction C. Additionally, the fixing plate  24  functions as a positioning portion for positioning the support shafts  22  in the insertion direction C and the direction opposite thereto and in the rotational direction about the axis along the insertion direction C with respect to the first side plate  21 A. With this structure, the positions of the support shafts  22  can be easily determined by inserting the support shafts  22  into the insertion holes  25  and attaching the fixing plate  24  to the first side plate  21 A. 
     In addition, in the present embodiment, each support shaft  22  is inserted into the insertion hole  25  from the outer side of the first side plate  21 A. This configuration is advantageous in reducing the number of attachment components and facilitating the mounting work as compared with a configuration in which each support shaft  22  is inserted into the insertion hole  25  from the inner side (opposing side) of the first side plate  21 A as illustrated in  FIG.  13   . Specifically, in the comparative example illustrated in  FIG.  13   , the support shaft  22  is inclined, and the front end thereof is inserted into the insertion hole  25  from the inner side of the first side plate  21 A. After that, as illustrated in  FIG.  14   , the support shaft  22  is disposed horizontal, and the rear end thereof is inserted into the insertion hole  25  of the second side  21 B. In such a mounting method, the insertion hole  25  in the first side plate  21 A has a diameter larger than that of the support shaft  22  since the support shaft  22  is inserted into the insertion hole  25  in an inclined posture. Therefore, in a state in which the support shaft  22  is horizontally disposed, as illustrated in  FIG.  15   , another member such as a bearing  40  for supporting the rear end of the support shaft  22  with respect to the insertion hole  25  of the first side plate  21 A is used. By contrast, in the present embodiment, since the support shaft  22  is inserted into the insertion hole  25  from the outer side of the first side plate  21 A, the insertion hole  25  of the first side plate  21 A can have the same size as the support shaft  22 , and there is no need to separately provide a bearing or the like. Therefore, the support shaft  22  can be easily attached with a small number of parts. Note that the present disclosure does not exclude a configuration in which the support shaft  22  is inserted from the inner side of the first side plate  21 A as illustrated in  FIGS.  13  to  15   . A member such as the bearing  40  may be provided, or such a configuration may be adopted. 
     In addition, in the present embodiment, since the support shafts  22  can be inserted from the insertion holes  25  of the same one (the first side plate  21 A) of the pair of side plates  21 A and  21 B to the insertion hole  25  of the other side plate (the second side plate  21 B), the support shafts  22  can be attached easily. For example, there may an obstacle on the second side plate  21 B side that makes it difficult to insert the support shafts  22  and screwing the support shafts  22  from the second side plate  21 B side. In such a case, the mounting work is facilitated by inserting and screwing the support shafts  22  from the first side plate  21 A side. In addition, since it is not necessary to change the insertion direction for each support shaft  22 , work efficiency is also improved. 
     Further, in the present embodiment, as the support shafts  22  are secured to the first side plate  21 A via the fixing plate  24 , the support shafts  22  are positioned with respect to the first side plate  21 A in the insertion direction C and the direction opposite thereto (positioning in the axial direction). By contrast, with respect to the second side plate  21 B, since only the front end of each support shaft  22  is inserted into the insertion hole  25  (see  FIG.  9   ), positioning of each support shaft  22  in the insertion direction C and the direction opposite thereto (positioning in the axial direction) is not performed. Thus, in the present embodiment, the support shafts  22  are not positioned in the insertion direction C and in the direction opposite thereto (positioned in the axial direction) with respect to the second side plate  21 B and are allowed to move in the axial direction with respect to the second side plate  21 B. With this structure, even if the support shafts  22  expand or contract in the axial direction due to a temperature rise after attachment, the side plates  21 A and  21 B are less likely to be directly affected by the expansion and contraction of the support shafts  22 . This feature can inhibit deformation such as bending of the side plates  21 A and  21 B caused by expansion and contraction of the support shafts  22 , thereby improving positional accuracy of the support shafts  22 . 
     Further, as described above, since the support shafts  22  are positioned with respect to the same side plate (the first side plate  21 A) via the fixing plate  24 , the positioning accuracy of the support shafts  22  improves. That is, since the positioning of the support shafts  22  in the insertion direction C and the direction opposite thereto is performed with reference to the same side plate (first side plate  21 A), the accuracy of positioning can he high compared with a case in which the positioning is performed with reference to different side plates. As described above, in the present embodiment, since the support shafts  22  can be positioned with high accuracy, the mounting accuracy of the position sensor  30  supported by the support shafts  22  are also improved. 
     In addition, the sensor mounting structure of the present embodiment facilitates installation of an additional position sensor  30 , maintenance work, and the like. For example, additional insertion holes  25  for the additional position sensor are provided in advance in each of the side plates  21 A and  21 B so that, when necessary, another support shaft  22  is inserted into the additional insertion holes  25  from the outer side of the first side plate  21 A and easily attached. Further, since the sensor holder  23  can be screwed and secured to the added support shaft  22  from above, the mounting work can be easily performed. Similarly, the position sensor  30  can be easily replaced or rearrangement from above the support shafts  22 . 
     Further, as in the example illustrated in  FIG.  16   , fitting holes  211  (positioning portions in the rotational direction) having a D-shaped cross section to be fitted to the rotation prevention protrusions  222  of the support shafts  22  may be directly provided in one (the side plate  21 A) of the pair of side plates  21 A and  21 B. In this case, the rotation prevention protrusion  222  on each of the support shafts  22  and the fitting hole  211  in the side plate  21 A together serve as the positioning portion for positioning the support shaft  22  in the rotational direction. In the example illustrated in  FIG.  16   , the support shaft  22  is inserted into the fitting hole  211  in the direction indicated by arrow C 1  (insertion direction C 1 ) from the inner side of the side plate side  21 A. Each fitting hole  211  in the side plate  21 A serves as both the positioning portion for the rotational direction and the positioning portion for the radial direction (the insertion hole  25 ). In other words, each fitting hole  211  fits with the rotation prevention protrusion  222  in the support shaft  22  to restrict the rotation of the support shaft  22 , and supports the support shaft  22  in the direction intersecting the insertion direction C 1 . In this case, when the rotation prevention protrusion  222  of the support shaft  22  is inserted into the fitting hole  211  from the inner side of the side plate side  21 A, the position of the support shaft  22  is determined in the rotational direction and in a direction (radial direction) intersecting the insertion direction C 1 . Further, as the front end face of the support shaft  22  in the insertion direction C 1  contacts the side plate side  21 A, the position of the support shaft  22  is determined also in the insertion direction C 1  (axial direction). In this case, at least one of the pair of side plates  21 A and  21 B is movable toward and away from the other. After the front end of each support shaft  22  in the insertion direction C 1  is inserted into the fitting hole  211  of the side plate  21 A, the other side plate  21 B is moved toward the rear end of each support shaft  22 , so as to insert the rear end of each support shaft  22  into the insertion hole  25  of the side plate  21 B. Thus, each support shaft  22  is sandwiched between the pair of side plates  21 A and  21 B, and the support shafts  22  are positioned with respect to the side plates  21 A and  21 B in the insertion direction C 1  and the direction opposite thereto. 
     Alternatively, the position of each support shaft  22  in the in the insertion direction C may be determined as in another example illustrated in  FIG.  17   . Specifically, in  FIG.  17   , when the protruding portion  220  at the front end of each support shaft  22  in the insertion direction C is inserted into the insertion hole  25  of the second side plate  21 B, the end face of the large-diameter portion  221  on the front end side (the protruding portion  220  side) of each support shaft  22  contacts the rim of the insertion hole  25  of the second side plate  21 B (the inner face of the second side plate  21 B enclosing the insertion hole  25 ), thereby determining the position of each support shaft  22  in the insertion direction C. In this case, each insertion hole  25  of the second side plate  21 B has a diameter larger than the diameter of the projecting portions  220  and smaller than the diameter of the end face of the large-diameter portion  221  so that the end face of the large-diameter portions  221  of the support shaft  22  contacts the rim of the insertion hole  25 . 
     Further, as in the example illustrated in  FIG.  18   , the support shaft  22  may include a plurality of mounting faces  225  at different positions in the axial direction of the support shaft  22 . For example, in a configuration in which the width-direction reference position for determining the width-direction position of the sheet S in the first image forming device  3  is on the near side (left side in  FIG.  18   ), in the second image forming device  4 , in which the sheet S is thereafter reversed and conveyed, the width-direction reference position for the sheet S is on the far side (right side in  FIG.  18   ). Accordingly, the sensor holder  23  of the first image forming device  3  may be attached to the mounting face  225  on the near side of the support shaft  22 , and the sensor holder  23  of the second image forming device  4  may he attached to the mounting face  225  on the far side of the support shaft  22 . In this manner, since the support shaft  22  includes the plurality of mounting faces  225 , it is possible to appropriately select the position of the position sensor  30  according to the width-direction reference position of the sheet S or the like. 
     The embodiments of the present disclosure have been described above using an example of the conveyor mounted in an inkjet image forming apparatus. However, aspects of the present disclosure are applicable to, in addition to the above-described inkjet image forming apparatus, a conveyor mounted in an electrophotographic image forming apparatus as illustrated in  FIG.  19   . Hereinafter, a configuration of an electrophotographic image forming apparatus to which aspects of the present disclosure are applied will be described. 
     An image forming apparatus  200  illustrated in  FIG.  19    is a tandem image forming apparatus including four process units  61 Y,  61 C,  61 M, and  61 Bk as image forming units (image forming devices). 
     Each of the process units  61 Y,  61 C,  61 M, and  61 Bk includes a drum-shaped photoconductor  62  serving as a latent image bearer, a charging roller  63  serving as a charger that charges the photoconductor  62 , a developing device  64  that forms a toner image on the photoconductor  62 , and a cleaning blade  65  serving as a cleaning device that cleans the surface of the photoconductor  62 . 
     In  FIG.  19   , an exposure device  66  is disposed above the process units  61 Y,  61 C,  61 M, and  61 Bk. The exposure device  66  includes a light source, a polygon mirror, an f-θ lens, and reflection mirrors to irradiate the surfaces of the photoconductors  62  with laser beams according to the image data. 
     In  FIG.  19    a transfer device  67  is disposed below the process units  61 Y,  61 C,  61 M, and  61 Bk. The transfer device  67  includes an intermediate transfer belt  68  formed of an endless belt as a transfer member, primary transfer rollers  70  each of which is disposed in contact with corresponding one of the photoconductors  62 , forming a primary transfer nip therebetween, and a secondary transfer roller  71  disposed in contact with the intermediate transfer belt  68 , forming a secondary transfer nip therebetween. 
     The image forming apparatus  200  includes sheet feeding trays  72  that store sheets S as recording media, sheet feeding rollers  73  that feed the sheets S from the sheet feeding trays  72 , and a timing roller pair  74  that conveys the fed sheets S to the secondary transfer nip at a predetermined timing. The image forming apparatus  200  further includes a fixing device  75  that fixes images on the sheets S, a cooling device  76  that cools the sheets S, an ejection roller pair  77  that discharges the sheets S to the outside of the apparatus, and an output tray  78  on which the ejected sheets S are placed. 
     The image forming apparatus  200  illustrated in  FIG.  19    operates as follows. 
     When an image forming operation is started, the photoconductors  62  of the process units  61 Y,  61 C,  61 M, and  61 Bk rotate in a counterclockwise direction in  FIG.  19   , and the charging rollers  63  uniformly charge the surfaces of the photoconductors  62  to a predetermined polarity. Then, the exposure device  66  directs laser beams onto the charged surfaces of the photoconductors  62  according to image data of a document read by a scanner. Thus, electrostatic latent images are formed on the photoconductors  62 . Note that the image data according to which each photoconductor  62  is exposed is single-color image data obtained by separating full-color image data into individual color components of yellow, cyan, magenta, and black. The electrostatic latent images formed on the photoconductors  62  are developed into toner images with toner of respective colors supplied by the developing devices  64 . 
     In the transfer device  67 , one of a plurality of rollers  69 A to  69 D that supports the intermediate transfer belt  68  rotates as a drive roller, thereby rotating the intermediate transfer belt  68  in the direction indicated by an arrow appended to the transfer device  67  in  FIG.  19   . Each primary transfer roller  70  is applied with a voltage having a polarity opposite a charging polarity of the toner, in constant-voltage or constant-current control, so as to generate a transfer electrical field in each primary transfer nip between the primary transfer roller  70  and the corresponding photoconductor  62 . The transfer electric fields generated at the primary transfer nips sequentially transfer and superimpose the respective toner images from the photoconductors  62  one on another on the intermediate transfer belt  68 . Thus, a full-color toner image is formed on the intermediate transfer belt  68 . Residual toner on the photoconductor  62  not transferred onto the intermediate transfer belt  68  is removed by the cleaning blade  65 . 
     In accordance with rotation of the intermediate transfer belt  68 , the full-color toner image transferred onto the intermediate transfer belt  68  reaches the secondary transfer nip (position of the secondary transfer roller  71 ) and is transferred, at the secondary transfer nip, onto the sheet S conveyed by the timing roller pair  74 . The sheet S is supplied from the sheet feeding tray  72 . In the sheet feeding tray  72 , after an instruction to start a printing operation is given, the sheets S are fed one by one as the sheet feeding roller  73  rotates. The timing roller pair  74  halts the supplied sheet P and then conveys the sheet P to the secondary transfer nip timed to coincide with arrival, at the secondary transfer nip, of the full-color toner image on the intermediate transfer belt  68 . At this time, the secondary transfer roller  71  is applied with a transfer voltage having a polarity opposite to the charging polarity of the toner image on the intermediate transfer belt  68 , and the transfer electrical field generated in the secondary transfer nip transfers the toner image from the intermediate transfer belt  68  onto the sheet S. 
     Thereafter, the sheet S is conveyed to the fixing device  75 . The fixing device  75  heats and presses the toner image to the sheet S with a fixing roller  81  and a pressure roller  82 , thereby fixing the toner image on the sheet S. Then, the sheet S is conveyed to the cooling device  76  and cooled, after which the ejection roller pair  77  ejects the sheet S to the output tray  78 . Thus, a series of image forming operations is completed. 
     The cooling device  76  in the image forming apparatus  200  has the following configuration. 
     As illustrated in  FIG.  20   , the cooling device  76  includes a pair of conveyor belts  51 A and  51 B. Each of the conveyor belts  51 A and  51 B is an endless belt and is stretched by a pair of conveyance rollers  52 . At least one of the conveyance rollers  52  is a drive roller that is rotated by a drive source such as a motor. As the conveyance rollers  52 , the conveyor belts  51 A and  51 B rotate. As a result, the sheet S is conveyed while being nipped by the conveyor belts  51 A and  51 B. 
     As illustrated in  FIG.  19   , inside the pair of conveyor belts  51 A and  51 B, cooling members  53 A and  53 B are disposed, respectively. The cooling members  53 A and  53 B are pressed against the inner peripheral surfaces of the conveyor belts  51 A and  51 B by springs  54  serving as pressing members. With this configuration, the sheet S conveyed between the conveyor belts  51 A and  51 B, is cooled from both sides by the cooling members  53 A and  53 B while being conveyed by the rotating conveyor belts  51 A and  51 B. 
     In the cooling device  76  including the pair of conveyor belts  51 A and  51 B as described above, when one or more of the conveyance rollers  52  respectively supporting the conveyor belts  51 A and  51 B are eccentric, there is a concern that the conveyor belts  51 A and  51 B may meander (deviate in the sheet width direction). Therefore, the cooling device  76  illustrated in  FIG.  20    includes position sensors  55  respectively disposed inside the conveyor belts  51 A and  51 B, to detect the positions of the conveyor belts  51 A and  51 B. These position sensors  55  detect the surfaces of the conveyor belts  51 A and  51 B to determine the presence or absence of meandering of the conveyor belts  51 A and  51 B, When the conveyor belts  51 A and  51 B meander, the positions (positions in the sheet width direction) of the conveyor belts  51 A and  51 B are corrected by meandering correction units  56  provided to the conveyance rollers  52 . 
     As described above, in the cooling device  76  including the position sensors  55  to detect the meandering of the conveyor belts  51 A and  51 B, the mounting accuracy of the position sensors  55  affects the detection accuracy of the meandering. For this reason, it is preferable to apply one of the sensor mounting structures (illustrated in  FIGS.  7  to  12  and  16  to  18   ) according to the present disclosure to the cooling device  76  as well as the conveyance device  20  according to the above-described embodiment. Thus, the position sensors can be easily and accurately mounted, and the detection accuracy of meandering is also improved. Further, aspects of the present disclosure are applicable to, in addition to the conveyance device functioning as the cooling device  76 , a conveyance device other than the cooling device, such as a transfer device  67  including an intermediate transfer belt  68  illustrated in  FIG.  19   . 
     Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and appropriate design changes can be made without departing from the scope of the invention. 
     The term “liquid discharge apparatus” used in this specification also represents an apparatus including a liquid discharge head or a liquid discharge device to discharge liquid by driving the liquid discharge head. The term “liquid discharge apparatus” used in this specification includes, in addition to apparatuses to discharge liquid to materials to which the liquid adheres, for example, apparatuses to discharge the liquid into gas (air) or liquid. 
     The “liquid discharge apparatus” may include at least one of devices for feeding, conveying, and ejecting a material to which liquid adheres. The “liquid discharge apparatus” may further include at least one of a device for pre-processing (or pretreatment) and a device for post-processing (or after treatment). The liquid discharge apparatus may be, for example, an image forming apparatus to form an image on a sheet by discharging ink, or a three-dimensional fabricating apparatus (solid-object fabricating apparatus) to discharge a fabrication liquid to a powder layer in which powder material is formed in layers, so as to form a three-dimensional fabrication object (solid fabrication object). 
     The “liquid discharge apparatus” is not limited to an apparatus to discharge liquid to visualize meaningful images, such as letters or figures. For example, the liquid discharge apparatus may be an apparatus to form meaningless images, such as meaningless patterns, or fabricate three-dimensional images. 
     The term “liquid discharge apparatus” may represent an apparatus to relatively move the liquid discharge head and the material onto which liquid can adhere. However, the liquid discharge apparatus is not limited to such an apparatus. Specific examples include a serial-type liquid discharge apparatus including a liquid discharge head that ejects liquid while moving in the sheet width direction, and a line-type liquid discharge apparatus (see  FIG.  3   ) including a liquid discharge head that ejects liquid without moving in the sheet width direction. 
     In addition, the “liquid discharge apparatus” includes a treatment liquid application apparatus that discharges a treatment liquid onto a surface of a sheet for the purpose of modifying the surface of the sheet, and an injection granulation apparatus that injects a composition liquid in which a raw material is dispersed in a solution through a nozzle to granulate fine particles of the raw material. 
     In addition, the term “liquid discharge head” refers to a functional component that discharges or ejects liquid from a nozzle. The liquid to be discharged from the nozzle of the liquid discharge head is not limited to a particular liquid as long as the liquid has a viscosity or surface tension to be discharged from the liquid discharge head. However, preferably, the viscosity of the liquid is not greater than  30  MPa&#39;s under ordinary temperature and ordinary pressure or by heating or cooling. Examples of the liquid include a solution, a suspension, or an emulsion including, for example, a solvent, such as water or an organic solvent, a colorant, such as dye or pigment, a functional material, such as a polymerizable compound, a resin, a surfactant, a biocompatible material, such as DNA, amino acid, protein, or calcium, and an edible material, such as a natural colorant. Such a solution, a suspension, or an emulsion can be used for, e.g., inkjet ink, surface treatment solution, a liquid for forming components of electronic element or light-emitting element or a resist pattern of electronic circuit, or a material solution for three-dimensional fabrication. 
     Examples of a source for generating energy to discharge liquid include a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal actuator that employs an electrothermal transducer element, such as a heat element, and an electrostatic actuator including a diaphragm and opposed electrodes. 
     In this specification, the term “head unit” refers to an assembly in which functional components and mechanisms are integral with the liquid discharge head, and includes an assembly of components related to liquid discharge. For example, the “head unit” includes a combination of the head and at least one of a head tank, a carriage, a supply unit, a maintenance unit, a main-scanning moving mechanism, and a liquid circulator. The “head unit” may include one liquid discharge head or a plurality of liquid discharge heads as in the above-described embodiment. 
     In present specification, the terms “combined” or “integrated” mean attaching the liquid discharge head and the functional parts (or mechanism) to each other by fastening, screwing, binding, or engaging and holding one of the liquid discharge head and the functional parts to the other movably relative to the other. The liquid discharge head and the functional part(s) or device(s) may be detachably attached to each other. 
     For example, the liquid discharge head and the head tank are integral parts of the head unit. Alternatively, the liquid discharge head may be coupled with the head tank through a tube or the like to become one unit, A unit including a filter can be added at a position between the head tank and the liquid discharge head of the head unit. In yet another example, the liquid discharge head and the carriage are combined as the “head unit.” As yet another example, in the head unit, the liquid discharge head and the main scanning moving unit are combined into a single unit. The liquid discharge head is movably held by a guide that is a part of the main-scanning moving mechanism. The liquid discharge head, the carriage, and the main-scanning moving mechanism may be integral parts of a single unit. 
     As yet another example, in the head unit, a cap that is a part of the maintenance unit is secured to the carriage mounting the liquid discharge head such that the liquid discharge head, the carriage, and the maintenance unit are integral parts of the head unit. As yet another example, a tube is coupled to the liquid discharge head to which either the head tank or a channel member is attached such that the liquid discharge head and the supply unit are integral parts of the head unit. 
     The main-scan moving mechanism may be a guide only. The supply unit can he a tube(s) only or a loading unit only. 
     The term “material onto which liquid adheres” denotes, for example, a conveyed object that is a material to which liquid adheres at least temporarily, a material to which liquid adheres and is fixed, or a material to which liquid adheres and permeates. Examples of the “material to which liquid can adhere” include recording media, such as paper, recording paper, recording sheets, film, and cloth; electronic components, such as electronic substrate and a piezoelectric element; and media, such as a powder layer, an organ model, and a testing cell, The “material to which liquid can adhere” includes any material to which liquid adheres, unless otherwise specified. 
     The above-mentioned “material to which liquid adheres” may be any material, such as paper, thread, fiber, cloth, leather, metal, plastic, glass, wood, ceramics, or the like, as long as liquid can temporarily adhere. 
     In addition, the “sheet” may be a continuous long sheet (roll paper or the like) or a cut sheet (cut paper or the like) cut into a predetermined size in advance. Furthermore, aspects of the present disclosure are also applicable to an apparatus that conveys a conveyed object, such as a belt, other than a sheet. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention.