Patent Publication Number: US-11390097-B2

Title: Recording-medium transport device and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-186325 filed Oct. 9, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a recording-medium transport device and an image forming apparatus. 
     (ii) Related Art 
     Japanese Unexamined Patent Application Publication No. 2007-52112 discloses a structure that includes multiple loop sensors arranged between a transfer unit and a fixing unit in a recording medium direction, and in which a motor controller controls a fixing motor on the basis of loop detection results of these. 
     Japanese Unexamined Patent Application Publication No. 2011-90092 discloses processing of avoiding problems by changing the driving speed of a fixing device or changing the orientation of a transport guide when the measurement value of any of the loop sensors exceeds a predetermined value. 
     SUMMARY 
     A device to which a recording medium is transported includes a mover that moves in response to an arrival of a recording medium at a predetermined position, and is capable of detecting the arrival of the recording medium at the predetermined position by detecting movement of the mover. 
     In the structure including multiple movers and sensors corresponding to these movers to detect these movers, the sensors correspond in number to the movers. 
     Aspects of non-limiting embodiments of the present disclosure relate to reduction of sensors that detect movers that move in response to an arrival of a recording medium at a predetermined position, compared to the case where sensors that detect movers are provided for corresponding movers that move in response to an arrival of a recording medium at a predetermined position. 
     Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above. 
     According to an aspect of the present disclosure, there is provided a recording-medium transport device that includes a first pressed portion that moves by being pressed by a transported recording medium; a second pressed portion disposed at a different position from the first pressed portion in a width direction of the transported recording medium, the second pressed portion moving by being pressed by the transported recording medium; a mover that moves in association with the first pressed portion and the second pressed portion, the mover moving in response to the recording medium being pressed by at least one of the first pressed portion and the second pressed portion; and a sensor that detects movement of the mover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  illustrates an entire structure of an image forming apparatus; 
         FIG. 2  illustrates a structure of a controller; 
         FIG. 3  illustrates a sheet detecting device; 
         FIG. 4  is a perspective view of a sheet detecting device viewed in a direction of arrow IV in  FIG. 3 ; 
         FIGS. 5A and 5B  illustrate a first pressed portion to a third pressed portion, a first mover to a third mover, a first sensor, and a second sensor; 
         FIG. 6  illustrates a sheet detecting device viewed in a direction of arrow VI in  FIG. 3 ; 
         FIGS. 7A and 7B  illustrate each portion in the state where “the sheet P has a small swell”; 
         FIG. 8  illustrates a determination table; 
         FIGS. 9A and 9B  illustrate each portion when “the sheet P has a large swell”; 
         FIGS. 10A and 10B  illustrate each portion when the sheet P has an uneven swell; 
         FIGS. 11A and 11B  illustrate each portion when the sheet P has an uneven swell; 
         FIGS. 12A and 12B  illustrate each portion when the sheet P has an uneven swell; 
         FIGS. 13A and 13B  illustrate each portion when the sheet P has an uneven swell; 
         FIG. 14  illustrates a comparative example; and 
         FIGS. 15A and 15B  illustrate another arrangement example of a first detection position and a second detection position. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will be described below with reference to the attached drawings. 
       FIG. 1  illustrates an entire structure of an image forming apparatus  1 . More specifically,  FIG. 1  is a view of the image forming apparatus  1  viewed from the front side of the image forming apparatus  1 . 
     The image forming apparatus  1  includes an image forming portion  10 , as an example of an image forming device. The image forming portion  10  performs image formation on a sheet P, which is an example of a recording medium, based on image data for different colors. 
     The image forming apparatus  1  also includes a sheet transport device  400 , which transports sheets P. 
     The sheet transport device  400 , which is an example of a recording-medium transport device, transports sheets P contained in a sheet container  1 B to a sheet receiver  1 E via a second transfer portion T and a fixing device  40 . 
     Here, the sheet transport device  400  includes transport rollers  52  and discharge rollers  500 . The sheet transport device  400  transports the sheets P using the transport rollers  52  and the discharge rollers  500 . 
     The image forming apparatus  1  also includes a controller  30  and an image processing portion  35 . 
     The controller  30  controls functional units of the image forming apparatus  1 . The image processing portion  35  performs image processing on image data from, for example, a personal computer (PC)  3  or an image reading device  4 . 
     As illustrated in  FIG. 2  (illustrating the structure of the controller  30 ), the controller  30  includes a central processing unit (CPU)  401 , which is an example of a processor, a random access memory (RAM)  402 , a read only memory (ROM)  403 , and a storage  404 , formed from a hard disk or other devices. 
     The ROM  403  and the storage  404  store programs to be executed by the CPU  401 . The CPU  401  reads programs stored in the ROM  403  or the storage  404 , and executes each program using the RAM  402  as a work area. 
     The CPU  401  implements various functions by executing the programs stored in the ROM  403  or the storage  404 . 
     Here, the programs to be executed by the CPU  401  may be provided to the image forming apparatus  1  in the form of being stored in a computer-readable recording medium such as a magnetic recording medium (such as a magnetic tape or a magnetic disk), an optical recording medium (such as an optical disk), an optical magnetic recording medium, or a semiconductor memory. The programs to be executed by the CPU  401  may also be provided to the image forming apparatus  1  through a communication device such as the Internet. 
     In the present exemplary embodiment, a processor refers to a broadly interpreted processor, and includes a general-purpose processor (such as a central processing unit (CPU)), and an exclusive-use processor (such as a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a programmable logical device). 
     The operation may be performed not only by a single processor, but also by multiple processors physically spaced apart from each other in cooperation. The order in which processing is performed by the processor is not limited to the order described in the present exemplary embodiment, but may be changed. 
     The image forming apparatus  1  will be described further with reference to  FIG. 1 . 
     The image forming portion  10  includes four image forming units  11 Y,  11 M,  11 C, and  11 K (hereinafter also simply referred to as “image forming units  11 ”, collectively) arranged side by side at regular intervals. 
     The image forming units  11  have the same structure except for accommodating different types of toner in respective developing devices  15 . The image forming units  11  form toner images (images) of yellow (Y), magenta (M), cyan (C), and black (K). 
     Each image forming unit  11  includes a photoconductor drum  12 , a charging device  200 , which electrically charges the photoconductor drum  12 , and a LED print head (LPH)  300 , which exposes the photoconductor drum  12  to light. 
     The photoconductor drum  12  is electrically charged by the charging device  200 . The photoconductor drum  12  is also exposed to light by the LPH  300  to have an electrostatic latent image formed thereon. 
     Each image forming unit  11  also includes a developing device  15 , which develops an electrostatic latent image formed on the photoconductor drum  12 , and a cleaner (not illustrated) that cleans the surface of the photoconductor drum  12 . 
     The image forming portion  10  includes an intermediate transfer belt  20 , to which toner images of different colors formed by the photoconductor drums  12  are transferred, and first transfer rollers  21 , which sequentially transfer (first-transfer) the toner images of different colors formed by the photoconductor drums  12  to the intermediate transfer belt  20 . 
     The image forming portion  10  also includes a second transfer roller  22 , which collectively transfers (second-transfers) the toner images transferred onto the intermediate transfer belt  20  to a sheet P, and a fixing device  40 , which fixes the toner images transferred to the sheet P onto the sheet P. 
     The exemplary embodiment also includes a sheet detecting device  600 , which detects a sheet P, downstream of the second transfer roller  22  and upstream of the fixing device  40 . 
     The fixing device  40  includes a fixing belt module  41  including a heating member, and a pressing roller  46 . 
     The fixing belt module  41  is disposed on the right of a sheet transport path R 1  in the drawing. The pressing roller  46  is disposed on the left of the sheet transport path R 1  in the drawing. The pressing roller  46  is pressed against the fixing belt module  41 . 
     The fixing belt module  41  includes a film-shaped fixing belt  411 , which comes into contact with the sheet P. The fixing belt  411  is a device for fixing a toner image (image) on the sheet P onto the sheet P. 
     The fixing belt  411  includes, for example, a release layer disposed outermost to come into contact with the sheet P, an elastic layer disposed adjacent to and on the inner side of the release layer, and a base layer that supports the elastic layer. 
     The fixing belt  411  is annular and rotates clockwise in the drawing. In other words, the fixing belt  411  is endless and circularly moves along a predetermined path. 
     The fixing belt  411  comes into contact with the sheet P transported from below in the drawing. More specifically, the fixing belt  411  has an outer peripheral surface  411 B, which comes into contact with the sheet P. 
     The portion of the fixing belt  411  that is in contact with the sheet P moves together with the sheet P. The fixing belt  411  holds the sheet P together with the pressing roller  46  to press and heat the sheet P. 
     The fixing belt module  41  also includes a heating member on the inner side of the fixing belt  411  to heat the fixing belt  411 . 
     The pressing roller  46  serving as an example of a pressing member is disposed on the left side of the sheet transport path R 1  in the drawing. The pressing roller  46  is pressed against the outer peripheral surface  411 B of the fixing belt  411  to press the sheet P passing between the fixing belt  411  and the pressing roller  46 . 
     The pressing roller  46  is rotated counterclockwise in the drawing by a motor (not illustrated). When the pressing roller  46  rotates counterclockwise, the fixing belt  411  rotates clockwise with the driving force received from the pressing roller  46 . 
     In the exemplary embodiment, the fixing device  40  also has a function of transporting downstream a sheet P transported thereto from upstream. While transporting the sheet P, the fixing device  40  fixes a toner image on the sheet P. 
     In the exemplary embodiment, the transport speed of the sheet P in the fixing device  40  is changeable. More specifically, in the exemplary embodiment, the transport speed of the sheet P with the fixing device  40  is changeable by changing the number of rotations of the pressing roller  46 . 
     In the image forming apparatus  1 , the image processing portion  35  performs image processing on image data from the PC  3  or the image reading device  4 , and the image data undergoing image processing is fed to each image forming unit  11 . 
     Then, for example, in the image forming unit  11 K for black (K), the photoconductor drum  12  is electrically charged by the charging device  200  while rotating in the direction of arrow A, and exposed to light emitted from the LPH  300  on the basis of the image data transmitted from the image processing portion  35 . 
     Thus, an electrostatic latent image for a black (K) image is formed on the photoconductor drum  12 . The electrostatic latent image formed on the photoconductor drum  12  is developed by the developing device  15  into a toner image for black (K) formed on the photoconductor drum  12 . 
     Similarly, the image forming units  11 Y,  11 M, and  11 C respectively form toner images of yellow (Y), magenta (M), and cyan (C). 
     The toner images of respective colors formed by the respective image forming units  11  are sequentially electrostatically attracted by the first transfer rollers  21  to the intermediate transfer belt  20  moving in the direction of arrow B, so that a superposed toner image including toner of different colors is formed on the intermediate transfer belt  20 . 
     The toner image formed on the intermediate transfer belt  20  is transported to a position (second transfer portion T) where the second transfer roller  22  is located by the movement of the intermediate transfer belt  20 . 
     At the timing when the toner image is transported to the second transfer portion T, a sheet P is fed from the sheet container  1 B to the second transfer portion T. 
     At the second transfer portion T, the toner image on the intermediate transfer belt  20  is collectively and electrostatically transferred to the sheet P transported to the second transfer portion T with a transfer electric field formed by the second transfer roller  22 . 
     Thereafter, the sheet P to which the toner image is electrostatically transferred is separated from the intermediate transfer belt  20 , and transported to the fixing device  40 . 
     In the exemplary embodiment, while the sheet P is transported from the intermediate transfer belt  20  to the fixing device  40 , the sheet detecting device  600  detects the sheet P. 
     The fixing device  40  holds the sheet P between the fixing belt module  41  and the pressing roller  46 . More specifically, the fixing device  40  holds the sheet P with the fixing belt  411 , circularly moving clockwise, and the pressing roller  46 , rotating counterclockwise. 
     Thus, the sheet P undergoes pressing and heating to have a toner image thereon fixed thereto. The sheet P undergoing fixing is transported to the sheet receiver  1 E by the discharging rollers  500 . 
       FIG. 3  illustrates the sheet detecting device  600 . 
     The sheet detecting device  600  according to the exemplary embodiment includes a pressed portion  610 , which moves by being pressed by a transported sheet P. 
     The sheet detecting device  600  includes movers  700  that move in association with the pressed portion  610 . The movers  700  move in response to the pressed portion  610  being pressed by the sheet P. 
     The sheet detecting device  600  also includes guide members  498 , which guide the transported sheet P downstream. The exemplary embodiment also includes pressed portions  610  on the side closer to the sheet transport path R 1  than the guide members  498 . 
     The sheet detecting device  600  according to the present exemplary embodiment also includes a second guide member  499  that guides the transported sheet P downstream at a position opposite to the guide members  498 . 
     In the exemplary embodiment, the guide members  498 , the movers  700 , and sensors S (described below) are disposed on a first side RX of the sheet transport path R 1 , and the second guide member  499  is disposed on a second side RY of the sheet transport path R 1 . 
     In the exemplary embodiment, the movers  700  are disposed opposite to the pressed portions  610  with respect to the guide members  498 . 
     The exemplary embodiment includes sensors S, which are an example of sensors that detect movement of the mover  700 . 
     Here, as described with reference to  FIG. 4 , the exemplary embodiment includes multiple pressed portions  610 , multiple movers  700 , and multiple sensors S. 
       FIG. 4  is a perspective view of the sheet detecting device  600  viewed in a direction of arrow IV in  FIG. 3 . 
     The exemplary embodiment includes three pressed portions  610  including a first pressed portion  611  to a third pressed portion  613 . 
     Here, the first pressed portion  611  to the third pressed portion  613  are arranged at different positions in the width direction of the transported sheet P. 
     The exemplary embodiment includes three movers  700 , which are movers of a first mover  710  to a third mover  730 . 
     The first mover  710  (an example of a first mover) and the third mover  730  (an example of a third mover) move in association with the first pressed portion  611  (an example of a first pressed portion) and the second pressed portion  612  (an example of a second pressed portion). The first mover  710  and the third mover  730  move when at least one of the first pressed portion  611  and the second pressed portion  612  is pressed by the sheet P. 
     The second mover  720  (an example of a second mover) moves in association with the third pressed portion  613  (an example of a third pressed portion). The second mover  720  moves when the third pressed portion  613  is pressed by the sheet P. 
     The exemplary embodiment includes a connector  650 , which connects the first pressed portion  611  and the second pressed portion  612 . The connector  650  is formed into a round rod-like member, and extends in the width direction of the transported sheet P. 
     In the exemplary embodiment, the first pressed portion  611 , the second pressed portion  612 , the first mover  710 , and the third mover  730  are fixed to the connector  650 . A gap G is disposed between the first mover  710  and the third mover  730 . 
     The first mover  710  and the third mover  730  are disposed on the left side of the connector  650  in the drawing. The first pressed portion  611  is disposed on the right side of the connector  650  in the drawing. 
     The connector  650  is rotatably supported by a body (not illustrated) of the sheet detecting device  600 . More specifically, the round bar-shaped connector  650  is supported at both ends in the longitudinal direction, and rotatable in the circumferential direction. 
     The exemplary embodiment includes an urging member (not illustrated) that urges the connector  650  clockwise in the drawing. The urging member protrudes the first pressed portion  611  and the second pressed portion  612  toward the sheet transport path R 1  (refer to  FIG. 3 ). 
     A rodlike member  660 , extending in the width direction of the sheet P, is disposed near the third pressed portion  613 . In the exemplary embodiment, the rodlike member  660  supports the third pressed portion  613  and the second mover  720 . 
     The second mover  720  is disposed on the left of the rodlike member  660  in the drawing. The third pressed portion  613  is disposed on the right of the rodlike member  660  in the drawing. 
     As in the connector  650 , the rodlike member  660  is rotatable. 
     The exemplary embodiment includes an urging member (not illustrated) that urges the rodlike member  660  clockwise in the drawing. The third pressed portion  613  protrudes toward the sheet transport path R 1  (refer to  FIG. 3 ). 
     The sensors S of the exemplary embodiment include a first sensor S 1 , which is an example of a first sensor that detects movement of the first mover  710  and the third mover  730 . 
     The sensors S of the exemplary embodiment also include a second sensor S 2 , which is an example of a second sensor that detects movement of the second mover  720 . 
     The first sensor S 1  and the second sensor S 2  are so-called transmissive sensors, and each include a light source  605 , which emits light, and a light receiving portion  606 , which receives light from the light source  605 . 
     In the exemplary embodiment, each of the first mover  710 , the second mover  720 , and the third mover  730  passes between the corresponding light source  605  and the corresponding light receiving portion  606 . Thus, the first sensor S 1  detects the first mover  710  and the third mover  730 , and the second sensor S 2  detects the second mover  720 . 
     Here, in the exemplary embodiment, when each of the first mover  710  and the third mover  730  is located between the light source  605  and the light receiving portion  606  of the first sensor S 1 , light emitted from the light source  605  is blocked and the first sensor S 1  is turned off. 
     When neither the first mover  710  nor the third mover  730  is located between the light source  605  and the light receiving portion  606  of the first sensor S 1 , light emitted from the light source  605  arrives at the light receiving portion  606 , and the first sensor S 1  is turned on. 
     In the exemplary embodiment, when the second mover  720  is located between the light source  605  and the light receiving portion  606  of the second sensor S 2 , light emitted from the light source  605  is blocked, and the second sensor S 2  is turned off. 
     When the second mover  720  is not located between the light source  605  and the light receiving portion  606  of the second sensor S 2 , light emitted from the light source  605  arrives at the light receiving portion  606 , and the second sensor S 2  is turned on. 
       FIGS. 5A and 5B  illustrate the first pressed portion  611  to the third pressed portion  613 , the first mover  710  to the third mover  730 , the first sensor S 1 , and the second sensor S 2 . 
       FIG. 5A  illustrates the second sensor S 2 , the second mover  720 , and the third pressed portion  613 , viewed in the direction of arrow VA in  FIG. 4 . 
       FIG. 5B  illustrates the first sensor S 1 , the first mover  710 , the third mover  730 , the first pressed portion  611 , and the second pressed portion  612 , viewed in the direction of arrow VB in  FIG. 4 . 
     In the exemplary embodiment, when pressed by the transported sheet P, the first pressed portion  611 , the second pressed portion  612 , and the third pressed portion  613  move toward the first side RX of the sheet transport path R 1 , as illustrated in arrow  5 A in  FIGS. 5A and 5B . 
     In the exemplary embodiment, when pressed by the transported sheet P, each of the first pressed portion  611  to the third pressed portion  613  moves in a first direction of arrow  5 A. 
     Herein, the above first direction (direction of arrow  5 A), in which each of the first pressed portion  611  to the third pressed portion  613  moves, is referred to as a pressed-portion movement direction  5 A. 
     In the exemplary embodiment, when the first pressed portion  611 , the second pressed portion  612 , and the third pressed portion  613  move downstream in the pressed-portion movement direction  5 A, each of the first mover  710  to the third mover  730  moves in the first direction of arrow  5 X, as illustrated in  FIGS. 5A and 5B . 
     Herein, the first direction of arrow  5 X is referred to as a mover movement direction  5 X, below. 
     In the exemplary embodiment, when the first pressed portion  611  (refer to  FIG. 5B ) and the second pressed portion  612  move downstream in the pressed-portion movement direction  5 A, the first mover  710  and the third mover  730  move downstream in the mover movement direction  5 X, and the first mover  710  and the third mover  730  are detected by the first sensor S 1 . 
     More specifically, when the first mover  710  and the third mover  730  arrive at a detection position KP (position where light from the light source  605  passes), which is the target of detection of the first sensor S 1 , the first mover  710  and the third mover  730  are detected by the first sensor S 1 . 
     More specifically, as described above, the first sensor S 1  according to the exemplary embodiment is a transmissive sensor. In the exemplary embodiment, when arriving at the position at which a light beam for detection passes, the first mover  710  and the third mover  730  are detected by the first sensor S 1 . 
     In the exemplary embodiment, when the third pressed portion  613  (refer to  FIG. 5A ) is pressed by the transported sheet P, the third pressed portion  613  moves downstream in the pressed-portion movement direction  5 A. 
     Thus, the second mover  720  moves downstream in the mover movement direction  5 X. The second mover  720  is thus detected by the second sensor S 2 . 
     More specifically, when the second mover  720  arrives at the detection position KP for the second sensor S 2 , the second mover  720  is detected by the second sensor S 2 . 
     More specifically, as in the first sensor S 1 , the second sensor S 2  is a transmissive sensor. In the exemplary embodiment, when arriving at the position at which a light beam for detection passes, the second mover  720  is detected by the second sensor S 2 . 
     In the exemplary embodiment, the detection position KP at which the first sensor S 1  detects a mover is referred to as a first detection position KP 1 , and the detection position at which the second sensor S 2  detects a mover is referred to as a second detection position KP 2 , below. 
     In the exemplary embodiment, as illustrated in  FIG. 5B , the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611 . 
     More specifically, in the exemplary embodiment, the second pressed portion  612  is located further apart from the second guide members  499  (refer to  FIG. 3 ) than the first pressed portion  611 . 
     More specifically, the first pressed portion  611  and the second pressed portion  612  rotate (move) counterclockwise about the connector  650  (refer to  FIG. 4 ). In the exemplary embodiment, the second pressed portion  612  is located further downstream than the first pressed portion  611  in this rotation direction. 
     In the exemplary embodiment, the second pressed portion  612  is located closer to the first side RX than the first pressed portion  611 . 
     In the exemplary embodiment, when the positions of the first mover  710  to the third mover  730  in the mover movement direction  5 X are compared to each other while the sheet P is not in contact with the first pressed portion  611  to the third pressed portion  613 , the first mover  710  is located further downstream than the second mover  720 , as illustrated in  FIGS. 5A and 5B . The third mover  730  is located further upstream than the second mover  720 . 
     More specifically, in the exemplary embodiment, while the sheet P is not in contact with the first pressed portion  611  to the third pressed portion  613 , the second mover  720  is located between the first mover  710  and the third mover  730  in the mover movement direction  5 X. 
       FIG. 6  illustrates the sheet detecting device  600  viewed in a direction of arrow VI in  FIG. 3 . More specifically,  FIG. 6  illustrates the sheet detecting device  600  when viewed in a direction perpendicular to the transport direction of the sheet P. 
     Here, in the exemplary embodiment, when a A4-size sheet P is transported while having its short side at the leading end, the first pressed portion  611  opposes a first end of the A4-size sheet P in the width direction. 
     The second pressed portion  612  opposes a center portion of the A4-size sheet P in the width direction. The third pressed portion  613  opposes a second end of the A4-size sheet P in the width direction. 
     Here, “the width direction” refers to the direction perpendicular to the transport direction of the sheet P. More specifically, “the width direction” refers to the direction in which the side at the leading end of the transported sheet P extends. 
     In the exemplary embodiment, when a A4-size sheet P, which is an example of a sheet P of a predetermined size, is transported in the predetermined position, the first pressed portion  611  opposes the first end of the sheet P in the width direction. 
     More specifically, in the exemplary embodiment, when the A4-size sheet P, which is an example of a predetermined-sized sheet P, is transported while having its short side at the leading end, the first pressed portion  611  opposes the first end of the sheet P in the width direction. 
     The second pressed portion  612  opposes the center portion of the sheet P in the width direction. The third pressed portion  613  opposes the second end of the sheet P in the width direction. 
     More specifically, in the exemplary embodiment, the sheet P is transported with reference to the center. In the exemplary embodiment, the center portion of the sheet P in the width direction passes a position opposite to the second pressed portion  612 . 
     The first end of the sheet P in the width direction passes the position opposite to the first pressed portion  611 . The second end of the sheet P in the width direction passes the position opposite to the third pressed portion  613 . 
     In the exemplary embodiment, as illustrated in  FIG. 5B , the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611 . 
     In the exemplary embodiment, the first pressed portion  611  and the third pressed portion  613  are aligned in the pressed-portion movement direction  5 A. 
     In the exemplary embodiment, as illustrated in  FIG. 4 , the first mover  710  and the third mover  730  are arranged closer to either one of the first pressed portion  611  and the second pressed portion  612 . 
     Specifically, in the exemplary embodiment, the first mover  710  and the third mover  730  are arranged closer to the first pressed portion  611 . 
     More specifically, in the exemplary embodiment, the first mover  710  and the third mover  730  are arranged on the side closer to the first pressed portion  611  than a middle point C of a line segment SB extending in the width direction of the sheet P, the line segment SB connecting the first pressed portion  611  and the second pressed portion  612 . 
     In the exemplary embodiment, as illustrated in  FIG. 4 , the first mover  710  and the third mover  730  are located on an extension line of a plate-shaped member  615 . 
     More specifically, in the exemplary embodiment, a line denoted with a reference sign  6 A in  FIG. 6  indicates an extension line  29  of the plate-shaped member  615 . In the exemplary embodiment, the first mover  710  and the third mover  730  are disposed on the extension line  29 . 
     Here, in the exemplary embodiment, as illustrated in  FIG. 4 , the plate-shaped member  615  is disposed at a portion where the first pressed portion  611  is disposed. 
     In the exemplary embodiment, the first mover  710  and the third mover  730  are disposed on the extension line  29  (refer to  FIG. 6 ) of the plate-shaped member  615 . 
     In the exemplary embodiment, an edge  32  (edge  32  located closer to the sheet transport path R 1 ) located on a side of the plate-shaped member  615  (refer to  FIG. 4 ) on which the sheet P passes functions as the first pressed portion  611 . More specifically, in the exemplary embodiment, part of the plate-shaped member  615  functions as the first pressed portion  611 . 
     In the exemplary embodiment, the first mover  710  and the third mover  730 , which also have a plate shape, are disposed on the extension line  29  (refer to  FIG. 6 ) of the plate-shaped member  615 . 
     More specifically, in the exemplary embodiment, the plate-shaped member  615 , the first mover  710 , and the third mover  730  are disposed in the thickness direction of the transported sheet P. In the exemplary embodiment, the first pressed portion  611  is formed from part of the plate-shaped member  615  extending in the thickness direction of the sheet P. 
     In the exemplary embodiment, the first mover  710  and the third mover  730  are disposed on the extension line  29  of the plate-shaped member  615 . 
     More specifically, the first mover  710 , the third mover  730 , and the plate-shaped member  615  are disposed on the same (common) plane extending in the direction perpendicular to the width direction of the sheet P. 
     More specifically, in the exemplary embodiment, in comparison with the positions in the width direction of the sheet P, the first mover  710  and the third mover  730  are aligned with the plate-shaped member  615 . 
     More specifically, in the exemplary embodiment, when the first mover  710 , the third mover  730 , and the plate-shaped member  615  are projected in a direction perpendicular to the width direction of the sheet P and toward a virtual plane H 1  (refer to  FIG. 4 ) extending in the width direction of the sheet P, the first mover  710 , the third mover  730 , and the plate-shaped member  615  are disposed so that they overlap each other. 
     The same holds true to the third pressed portion  613 . In the exemplary embodiment, a plate-shaped member  616  (refer to  FIG. 4 ) is disposed at a portion where the third pressed portion  613  is disposed. In the exemplary embodiment, the second mover  720  having a plate shape is disposed on an extension line of the plate-shaped member  616 . 
     Here, the sheet detecting device  600  according to the exemplary embodiment detects an arrival of the sheet P at the position where the sheet detecting device  600  is disposed. The sheet detecting device  600  also detects a swell of the sheet P that has arrived at the sheet detecting device  600 . 
     Here, detection of a swell of the sheet P will be described. 
     In the exemplary embodiment, two sensors S, which are the first sensor S 1  and the second sensor S 2 , are used to determine which of the three states of “the sheet P having a small swell”, “the sheet P having a large swell”, and “the sheet P having an uneven swell”, the sheet P is in. 
     Here, “the sheet P having an uneven swell” is a state where the degree of a swell of the sheet P at the first end in the width direction of the sheet P is different from that of a swell of the sheet P at the second end in the width direction of the sheet P. 
       FIGS. 7A and 7B  illustrate each portion when “the sheet P has a small swell”. 
     In the drawings subsequent to  FIGS. 7A and 7B , the second pressed portion  612  is not illustrated. 
       FIGS. 7A and 7B  illustrate the state of each portion when the degree of a swell at the first end in the width direction of the sheet P is equal to the degree of a swell at the second end, and the degree of the swell is a first degree, which is a small degree. 
     When the degree of a swell is the first degree, only the first mover  710  arrives at the first detection position KP 1  for the first sensor S 1 , and the second mover  720  does not arrive at the second detection position KP 2  for the second sensor S 2 . 
     In this case, the controller  30  according to the present exemplary embodiment detects the sheet P having a small swell. 
     More specifically, in the state illustrated in  FIGS. 7A and 7B , the first mover  710  arrives at the first detection position KP 1  for the first sensor S 1 , and the first sensor S 1  is turned off, while the second mover  720  does not arrive at the second detection position KP 2 , and the second sensor S 2  is turned on. 
     More specifically, in the exemplary embodiment, the first mover  710  is located further downstream than the second mover  720  in the mover movement direction  5 X, as described above. 
     In the exemplary embodiment, when the degree of a swell at the first end in the width direction of the sheet P is equal to the degree of a swell at the second end and the degree of this swell is a first degree, which is a small degree, the first mover  710  arrives at the first detection position KP 1  and the first sensor S 1  is turned off, while the second mover  720  does not arrive at the second detection position KP 2  and the second sensor S 2  is turned on. 
     In this case, the controller  30  detects the sheet P having a small swell. 
     More specifically, in the exemplary embodiment, a determination table illustrated in  FIG. 8  (illustrating the determination table) is registered in the storage  404  (refer to  FIG. 2 ), and the controller  30  detects the sheet P having a small swell with reference to this determination table. 
     More specifically, when the first sensor S 1  is turned off and the second sensor S 2  is turned on, the state corresponds to the state denoted with a reference sign  8 A in  FIG. 8 , and the controller  30  detects the sheet P having a small swell. 
       FIGS. 9A and 9B  illustrate each portion when “the sheet P has a large swell”. 
     When the sheet P has a large swell, each portion has the state illustrated in  FIGS. 9A and 9B . 
     More specifically, when the sheet P has a large swell and the degree of a swell at the first end in the width direction of the sheet P is equal to the degree of a swell at the second end, each portion has the state illustrated in  FIGS. 9A and 9B . 
     More specifically, when the sheet P has a large swell and the degree of a swell at the first end in the width direction of the sheet P and the degree of a swell at the second end are a second degree, which is larger than the first degree, each portion has the state illustrated in  FIGS. 9A and 9B . 
     When the degree of a swell of the sheet P is the second degree, the first mover  710  passes by the first detection position KP 1 , whereas the second mover  720  arrives at the second detection position KP 2 . Here, the controller  30  detects the sheet P having a large swell. 
     More specifically, when the swell of the sheet P is in the second degree, the first sensor S 1  is turned on, and the second sensor S 2  is turned off. This state corresponds to the state denoted with the reference sign  8 B in  FIG. 8 , and the controller  30  detects the sheet P having a large swell. 
     In the exemplary embodiment, when the sheet P has an uneven swell, for example, the degree of a swell at the first end in the width direction of the sheet P is the second degree and the degree of a swell at the second end in the width direction of the sheet P is a third degree, which is larger than the second degree, each portion has the states illustrated in  FIGS. 10A and 10B  (illustrating the state of each portion when the sheet P has an uneven swell). 
     Here, the first sensor S 1  is turned on, and the second sensor S 2  is turned on. 
     This state corresponds to the state denoted with the reference sign  8 D in  FIG. 8 , and the controller  30  detects the sheet P having an uneven swell. 
     When the sheet P has an uneven swell, for example, the degree of a swell at the first end in the width direction of the sheet P is the second degree and the degree of a swell at the second end in the width direction of the sheet P is the first degree, each portion has the state illustrated in  FIGS. 11A and 11B  (illustrating the state of each portion when the sheet P has an uneven swell). 
     Here, the first sensor S 1  is turned on, and the second sensor S 2  is turned on. 
     This state corresponds to the state denoted with the reference sign  8 D in  FIG. 8 , and the controller  30  detects the sheet P having an uneven swell. 
     When the sheet P has an uneven swell, for example, the degree of a swell at the second end in the width direction of the sheet P is the second degree and the degree of a swell at the first end in the width direction of the sheet P is the third degree, each portion has the state illustrated in  FIGS. 12A and 12B  (illustrating the state of each portion when the sheet P has an uneven swell). 
     In this case, the first sensor S 1  is turned off, and the second sensor S 2  is turned off. More specifically, in the state illustrated in  FIGS. 12A and 12B , the third mover  730  is located at the first detection position KP 1 , and the first sensor S 1  is turned off. 
     This state corresponds to the state denoted with the reference sign  8 C in  FIG. 8 , and the controller  30  detects the sheet P having an uneven swell. 
     When the sheet P has an uneven swell, for example, the degree of a swell at the second end in the width direction of the sheet P is the second degree, and the degree of a swell at the first end in the width direction of the sheet P is the first degree, each portion has the state illustrated in  FIGS. 13A and 13B  (illustrating the state of each portion when the sheet P has an uneven swell). 
     Here, the first sensor S 1  is turned off, and the second sensor S 2  is turned off. 
     This state corresponds to the state denoted with the reference sign  8 C in  FIG. 8 , and the controller  30  detects the sheet P having an uneven swell. 
     In the exemplary embodiment, three states of a swell of the sheet P is detected with two sensors S, as described above. 
       FIG. 14  illustrates a comparative example. 
     In this example, three states of a swell of the sheet P is detected with four sensors S. 
     More specifically, this comparative example includes a first sensor S 11  and a second sensor S 12 , which are disposed on the side closer to the first end in the width direction of the sheet P and at different positions in the mover movement direction  5 X. 
     This comparative example also includes a third sensor S 13  and a fourth sensor S 14 , which are disposed on the side closer to the second end in the width direction of the sheet P and at different positions in the mover movement direction  5 X. 
     In this comparative example, three states are detected with these four sensors S. 
     Specifically, in this comparative example, when, for example, the first sensor S 11  detects the first mover  710  and the third sensor S 13  detects the second mover  720 , it is determined that “the sheet P has a small swell”. 
     In this comparative example, when, for example, the second sensor S 12  detects the first mover  710  and the fourth sensor S 14  detects the second mover  720 , it is determined that “the sheet P has a large swell”. 
     In this comparative example, when, for example, the first sensor S 11  detects the first mover  710  and the fourth sensor S 14  detects the second mover  720 , it is determined that “the sheet P has an uneven swell”. 
     When, for example, the second sensor S 12  detects the first mover  710  and the third sensor S 13  detects the second mover  720 , it is determined that “the sheet P has an uneven swell”. 
     This comparative example is also capable of detecting three states, that is, “the sheet P having a small swell”, “the sheet P having a large swell”, and “the sheet P having an uneven swell”. However, this comparative example involves four sensors S for detection of these three states. 
     On the other hand, the exemplary embodiment is capable of detecting three states, that is, “the sheet P having a small swell”, “the sheet P having a large swell”, and “the sheet P having an uneven swell” with two sensors, that is, the first sensor S 1  and the second sensor S 2 . 
     In the above structure, three states are detected with the first mover  710  and the second mover  720  shifted from each other. Instead, the three states may be detected by shifting the first detection position KP 1  and the second detection position KP 2  without shifting the first mover  710  and the second mover  720 . 
     More specifically, the three states may be detected by shifting the first detection position KP 1  and the second detection position KP 2  in the mover movement direction  5 X, which is a movement direction in which the first mover  710  to the third mover  730  move. 
     More specifically, for example, three states, that is, “the sheet P having a small swell”, “the sheet P having a large swell”, and “the sheet P having an uneven swell” may be detected with the structure illustrated in  FIGS. 15A and 15B  (another arrangement example of the first detection position KP 1  and the second detection position KP 2 ). 
     In the structure example illustrated in  FIGS. 15A and 15B , the position of the first mover  710  in the mover movement direction  5 X and the position of the second mover  720  in the mover movement direction  5 X are aligned. 
     On the other hand, in this structure example, the second detection position KP 2  for the second sensor S 2  is located further downstream in the mover movement direction  5 X than the first detection position KP 1  for the first sensor S 1 . 
     In this structure example, the state where “the sheet P has a small swell” is the first state where the first mover  710  arrives at the first detection position KP 1  for the first sensor S 1 . Thus, “the sheet P having a small swell” is detected. 
     The state where “the sheet P has a large swell” is a second state where the first mover  710  passes by the first detection position KP 1  whereas the second mover  720  arrives at the second detection position KP 2  for the second sensor S 2 . Thus, “the sheet P having a large swell” is detected. 
     The state where, for example, the sheet P has an uneven swell” is the state other than the first state and the second state. In this case, when this another state is detected, “the sheet P having an uneven swell” is detected. 
     Here, in the exemplary embodiment, when the sheet P is transported to arrive at the sheet detecting device  600 , the sheet P comes into contact with any of the first pressed portion  611  to the third pressed portion  613 . 
     Thus, an arrival of the sheet P at the position where the sheet detecting device  600  is installed is detected in the exemplary embodiment. 
     Here, in the exemplary embodiment, when the sheet detecting device  600  fails to detect the sheet P by predetermined timing, the sheet P is determined to be jammed and, for example, transportation of the sheet P is stopped. 
     Here, in the exemplary embodiment, when an A4-size or greater sheet P is transported to the sheet detecting device  600 , the sheet P comes into contact with the first pressed portion  611  and the third pressed portion  613 . 
     More specifically, in the exemplary embodiment, as described above, the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611 . Thus, when the A4-size or greater sheet P is transported to the sheet detecting device  600 , the sheet P comes into contact with the first pressed portion  611  and the third pressed portion  613 . 
     Thus, in the exemplary embodiment, an arrival of the A4-size or greater sheet P at the position where the sheet detecting device  600  is installed is detected. 
     In the exemplary embodiment, when the A4-size or greater sheet P is transported, the sheet P comes into contact with the first pressed portion  611  and the third pressed portion  613 , and the first mover  710  to the third mover  730  move. 
     Here, in the exemplary embodiment, as described above, the controller  30  detects the state of a swell of the sheet P. 
     More specifically, the controller  30  determines which of the states where “the sheet P has a small swell”, “the sheet P has a large swell”, and “the sheet P has an uneven swell” the transported sheet P is in. 
     In the exemplary embodiment, the controller  30  adjusts the transport speed of the sheet P at the fixing device  40  in accordance with the detected state of a swell. 
     For example, when the controller  30  detects “the sheet P having a small swell”, the controller  30  reduces the transport speed of the sheet P at the fixing device  40  to increase the swell of the sheet P. 
     More specifically, when the controller  30  detects “the sheet P having a small swell” and the sheet P is of a predetermined type, the controller  30  reduces the transport speed of the sheet P at the fixing device  40  to increase the swell of the sheet P. 
     When the transport speed of the sheet P at the fixing device  40  is reduced, the distance by which the sheet P is transported by the fixing device  40  per unit time is reduced. On the other hand, the sheet P is transported at the predetermined speed from upstream of the fixing device  40 . More specifically, the sheet P is transported at the same, unchanged speed from upstream of the fixing device  40 . 
     In this case, transportation of the sheet P is slowed at the fixing device  40  to increase the swell of the sheet P. 
     For example, when the controller  30  detects “the sheet P having a large swell”, the controller  30  increases the transport speed of the sheet P at the fixing device  40  to reduce the swell of the sheet P. 
     More specifically, when the controller  30  detects “the sheet P having a large swell” and the sheet P is of a predetermined type, the controller  30  increases the transport speed of the sheet P at the fixing device  40  to reduce the swell of the sheet P. 
     For example, when the controller  30  detects “the sheet P having an uneven swell”, the controller  30  increases the transport speed of the sheet P at the fixing device  40  to reduce the swell of the sheet P. 
     In the exemplary embodiment, when an A4-size or smaller sheet P such as a postcard-size sheet is transported, the sheet P comes into contact with only the second pressed portion  612 . 
     More specifically, in the exemplary embodiment, when a sheet P (referred to as a “small-size sheet P”, below) smaller than a specific size such as the A4 size is transported, this small-size sheet P comes into contact with only the second pressed portion  612 . 
     As in the above case, an arrival of the small-size sheet P at a portion where the sheet detecting device  600  is installed is detected. 
     When the small-size sheet P is transported, the small-size sheet P does not come into contact with the first pressed portion  611  and the third pressed portion  613 . No detection is performed on the state of a swell of the small-size sheet P. 
     In the exemplary embodiment, as described above, the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611 . 
     Thus, in the exemplary embodiment, when an A4-size or greater sheet P (hereinafter referred to as a “large-size sheet P”) is transported, a load exerted on the large-size sheet P is reduced further than in the case where the first pressed portion  611  to the third pressed portion  613  are aligned in the pressed-portion movement direction  5 A. 
     Here, the first pressed portion  611  to the third pressed portion  613  may be aligned. In this case, however, the second pressed portion  612  comes into contact with the large-size sheet P every time when the large-size sheet P is transported, and the load exerted on the large-size sheet P is increased. 
     On the other hand, when, as in the exemplary embodiment, the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611  and the third pressed portion  613 , the load exerted on the large-size sheet P is reduced. 
     More specifically, when, as in the exemplary embodiment, the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611  and the third pressed portion  613 , the load exerted on the large-size sheet P is reduced while detection of a small-size sheet P is enabled. 
     In the exemplary embodiment, the case where the large-size sheet P does not come into contact with the second pressed portion  612  is described. However, this does not exclude the structure where the large-size sheet P comes into contact with the second pressed portion  612 . The large-size sheet P may come into contact with the second pressed portion  612 . 
     Also in this case, as in the above case, preferably, the second pressed portion  612  is located further downstream in the pressed-portion movement direction  5 A than the first pressed portion  611  and the third pressed portion  613 , and the contact pressure exerted when the sheet P and the second pressed portion  612  come into contact with each other is smaller than the contact pressure exerted when the sheet P and the first pressed portion  611  and the third pressed portion  613  come into contact with each other. 
     As above, the exemplary embodiment has described the case where the first mover  710  and the third mover  730  are located closer to the side where the first pressed portion  611  is disposed. Instead, the first mover  710  and the third mover  730  may be located closer to the second pressed portion  612 , such as on the extension line of a plate-shaped member  617  (refer to  FIG. 4 ) disposed closer to the second pressed portion  612 . 
     Nevertheless, as in the exemplary embodiment, the structure including the first mover  710  and the third mover  730  disposed closer to the first pressed portion  611  detects a swell more highly accurately, as described above. 
     When the first mover  710  and the third mover  730  are disposed closer to the second pressed portion  612 , the distance between the first pressed portion  611  for swell detection and the first mover  710  and the third mover  730  is increased. 
     More specifically, when the first mover  710  and the third mover  730  are disposed closer to the second pressed portion  612 , a round bar-shaped connector  650  (refer to  FIG. 4 ) is disposed between the first mover  710  and the third mover  730  and the first pressed portion  611 . 
     In this case, due to, for example, a twist of the connector  650 , the distance by which the first mover  710  and the third mover  730  move may be smaller than the distance by which the first pressed portion  611  moves. 
     More specifically, the distance by which the first pressed portion  611  moves may differ from the distance by which the first mover  710  and the third mover  730  move. 
     In this case, the swell detection accuracy may degrease. 
     On the other hand, in the structure where the first mover  710  and the third mover  730  are disposed closer to the side where the first pressed portion  611  is disposed, the effect of the twist is reduced, and reduction of the swell detection accuracy is thus prevented. 
     In a more preferable aspect, as described above, the first mover  710  and the third mover  730  are disposed on the extension line  29  of the plate-shaped member  615  disposed on the first pressed portion  611 . In this case, reduction of the swell detection accuracy is further reduced. 
     The present disclosure is not only applicable to an electrophotographic image forming apparatus, and is also applicable to other image forming apparatuses such as an inkjet or thermal printer. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.