Sheet transport device and image forming apparatus

Abstract

The present invention provides a sheet transport device that can properly correct sheet misalignment with a simple configuration that suppresses the increase in the drive mechanism, including the drive source. [Solution] The sheet conveying device 4 is positioned upstream of the resist roller pair 44 with respect to the sheet conveying direction Dc and includes a conveying roller pair 46 composed of a first roller 461 and a second roller 462. The first roller 461 includes a first conveying section 463 having a first roll shaft 463x to which a first roll section 463r is fixed. The first conveying section 463 includes a pair of bearing sections 463a and a pair of first biasing members 463b. The pair of bearing sections 463a rotatably support both ends of the first roll shaft 463x in the sheet width direction Dw and are movable in the sheet width direction Dw together with the first roll shaft 463x. The pair of first biasing members 463b bias the pair of bearing sections 463a in opposite directions in the sheet width direction Dw.

Description

Technical Field

[0001] The present invention relates to a sheet conveyance device and an image forming apparatus.

Background Art

[0002] Image forming apparatuses such as copiers and printers include a sheet conveyance device. The sheet conveyance device includes a pair of conveyance rollers for conveying a sheet. The sheet conveyance device conveys sheets one by one from a sheet supply unit that stacks and accommodates sheets, which are recording media used for printing (recording) images, toward an image forming unit (transfer unit), a fixing unit, and a sheet discharge unit. And a technique for correcting the positional deviation of the conveyed sheet is known.

[0003] A conventional relay conveyance device disclosed in Patent Document 1 includes a first conveyance means for conveying a sheet, a detection means for detecting a sheet end portion in a direction orthogonal to the sheet conveyance direction, and a first moving means for moving the first conveyance means in a direction orthogonal to the sheet conveyance direction. Then, the first moving means moves the first conveyance means in a direction orthogonal to the sheet conveyance direction according to the detection result of the sheet end portion. At this time, in a second conveyance means disposed upstream of the first conveyance means in the sheet conveyance direction, the clamping of the sheet is switched to a released state. Thereby, it is possible to prevent the movement of the first conveyance means by the first moving means (correction of the positional deviation of the sheet) from being hindered by the second conveyance means.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, conventional technology had a problem in that when moving the first conveying means in a direction perpendicular to the sheet conveying direction to correct sheet misalignment, a drive mechanism including a motor or other drive source was required to switch the roller pair of the second conveying means to a state where the sheet was not gripped. As a result, the number of parts increased, the cost of the device increased, and there were concerns that noise would be generated during operation.

[0006] The present invention has been made in view of the above points, and aims to provide a sheet conveying device that can properly correct sheet misalignment with a simple configuration that suppresses the increase in the drive mechanism including the drive source. [Means for solving the problem]

[0007] To solve the above problems, the sheet conveying device of the present invention comprises a pair of resist rollers and a pair of conveying rollers. The pair of resist rollers extends in the sheet width direction perpendicular to the sheet conveying direction and corrects the positional displacement of the conveyed sheet in the sheet width direction. The pair of conveying rollers is composed of a first roller and a second roller that are arranged upstream of the pair of resist rollers with respect to the sheet conveying direction and are rotatably opposed to each other to convey the sheet. The first roller comprises a drive shaft, a first conveying section, and a joint section. The drive shaft extends in the sheet width direction and transmits rotational driving force. The first conveying section is arranged parallel to the drive shaft in the sheet width direction and has a first roll shaft to which a first roll section that contacts the second roller is fixed. The joint section connects the drive shaft and the first roll shaft in the sheet width direction and holds the first roll shaft so as to be movable in the sheet width direction. The first conveying section comprises a pair of bearing sections and a pair of first biasing members. The pair of bearing portions rotatably support each of the two ends of the first roll shaft in the sheet width direction and are movable together with the first roll shaft along the sheet width direction. The pair of first biasing members bias each of the pair of bearing portions in opposite directions in the sheet width direction. [Effects of the Invention]

[0008] According to the configuration of the present invention, the first roll shaft, to which the first roll section that contacts the second roller and conveys the sheet is fixed, can move in the sheet width direction without obtaining driving force from a drive mechanism. That is, when the sheet moves in the sheet width direction when the misalignment is corrected by the resist roller pair, the first roll shaft can move in the sheet width direction in accordance with the movement of the sheet without hindering the movement of the sheet. Therefore, it becomes possible to properly correct the misalignment of the sheet in the sheet width direction with a simple configuration that suppresses the increase in the drive mechanism including the drive source. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional front view of an image forming apparatus according to one embodiment of the present invention. [Figure 2] Figure 1 is a cross-sectional front view of the sheet transport device of the image forming apparatus. [Figure 3] Figure 2 is a front view of the area around the conveyor roller pair of the sheet conveying device. [Figure 4] Figure 3 is a side view of the first roller of the conveyor roller pair. [Figure 5] Figure 4 is a cross-sectional side view of the joint portion of the first roller. [Figure 6] Figure 4 is a cross-sectional side view of the area around the bearing portion of the first roll shaft of the first roller. [Figure 7] Figure 3 is a side view of the second roller of the conveyor roller pair. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following.

[0011] Figure 1 is a schematic cross-sectional front view of an image forming apparatus 1 according to an embodiment. An example of the image forming apparatus 1 in this embodiment is a tandem-type color printer that transfers a toner image to a sheet S using an intermediate transfer belt 71. The image forming apparatus 1 may be a so-called multifunction device equipped with functions such as printing, scanning (image reading), and facsimile transmission.

[0012] As shown in Figure 1, the image forming apparatus 1 comprises a sheet supply unit 3, a sheet transport device 4, an exposure unit 5, an image forming unit 6, a transfer unit 7, a fixing unit 8, a sheet discharge unit 9, and a control unit 10, all of which are located on the apparatus body 2.

[0013] The sheet supply unit 3 is located at the bottom of the main body 2 of the device. The sheet supply unit 3 stores multiple sheets S before printing and separates and feeds out the sheets S one by one during printing. The sheet transport device 4 extends vertically along the side wall of the main body 2 of the device. The sheet transport device 4 transports the sheets S fed from the sheet supply unit 3 to the secondary transfer unit 73 and the fixing unit 8, and then discharges the fixed sheets S from the sheet discharge port 4a to the sheet discharge unit 9. When double-sided printing is performed, the sheet transport device 4 distributes the fixed sheets S of the first side to the inversion transport path 42 via the branching unit 4b and transports the sheets S again to the secondary transfer unit 73 and the fixing unit 8. The exposure unit 5 is located above the sheet supply unit 3. The exposure unit 5 irradiates the image forming unit 6 with laser light controlled based on image data.

[0014] The image forming unit 6 is positioned above the exposure unit 5 and below the intermediate transfer belt 71. The image forming unit 6 includes an image forming unit 6Y for yellow, an image forming unit 6C for cyan, an image forming unit 6M for magenta, and an image forming unit 6B for black. These four image forming units 6 have the same basic configuration. Therefore, in the following description, the identification symbols "Y," "C," "M," and "B" representing each color may be omitted unless specifically required.

[0015] The image forming unit 6 includes a photosensitive drum that is supported to be rotatable in a predetermined direction (clockwise in Figure 1). The image forming unit 6 further includes a charging unit, a developing unit, and a drum cleaning unit arranged around the photosensitive drum along its rotational direction. A primary transfer unit 72 is positioned between the developing unit and the drum cleaning unit.

[0016] The photoreceptor drum is formed in a cylindrical shape extending horizontally and has a photosensitive layer on its outer surface. The charging unit charges the outer surface of the photoreceptor drum to a predetermined surface potential. The exposure unit 5 exposes the outer surface of the photoreceptor drum, which has been charged by the charging unit, and forms an electrostatic latent image of the original image with the charge attenuated on the outer surface of the photoreceptor drum. The developing unit supplies toner to the electrostatic latent image on the outer surface of the photoreceptor drum and develops it to form a toner image. Each of the four image forming units 6 forms a toner image of a different color. The drum cleaning unit cleans the outer surface of the photoreceptor drum by removing any remaining toner, etc., after the toner image has been primary transferred to the outer surface of the intermediate transfer belt 71. In this way, the image forming unit 6 forms the image (toner image) that will later be transferred to the sheet S.

[0017] The transfer unit 7 comprises an intermediate transfer belt 71, primary transfer units 72Y, 72C, 72M, and 72B, a secondary transfer unit 73, and a belt cleaning unit 74. The intermediate transfer belt 71 is positioned above the four image forming units 6. The intermediate transfer belt 71 is supported so as to be rotatable in a predetermined direction (counterclockwise in Figure 1), and is an endless intermediate transfer body on which the toner images formed in each of the four image forming units 6 are sequentially superimposed and primary transferred. The four image forming units 6 are arranged in a so-called tandem configuration, lined up in a row from the upstream side to the downstream side in the rotational direction of the intermediate transfer belt 71.

[0018] The primary transfer units 72Y, 72C, 72M, and 72B are disposed above the image forming units 6Y, 6C, 6M, and 6B for respective colors, sandwiching the intermediate transfer belt 71. The secondary transfer unit 73 is disposed on the upstream side of the fixing unit 8 with respect to the sheet conveyance direction of the sheet conveyance device 4 and on the downstream side of the four image forming units 6Y, 6C, 6M, and 6B with respect to the rotation direction of the intermediate transfer belt 71. The belt cleaning unit 74 is disposed on the downstream side of the secondary transfer unit 73 with respect to the rotation direction of the intermediate transfer belt 71.

[0019] The primary transfer unit 72 transfers the toner image formed on the outer peripheral surface of the photosensitive drum to the intermediate transfer belt 71. In other words, the toner image is primarily transferred to the outer peripheral surface of the intermediate transfer belt 71 by the primary transfer units 72Y, 72C, 72M, and 72B for respective colors. Then, with the rotation of the intermediate transfer belt 71, the toner images of the four image forming units 6 are successively and continuously overlapped and transferred to the intermediate transfer belt 71 at a predetermined timing, whereby a color toner image in which toner images of yellow, cyan, magenta, and black are overlapped is formed on the outer peripheral surface of the intermediate transfer belt 71.

[0020] The color toner image on the outer peripheral surface of the intermediate transfer belt 71 is transferred to the sheet S synchronized and sent by the sheet conveyance device 4 at the secondary transfer nip portion formed in the secondary transfer unit 73. The belt cleaning unit 74 removes and cleans deposits such as toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. In this way, the transfer unit 7 transfers (records) the toner image formed on the outer peripheral surface of the photosensitive drum to the sheet S.

[0021] The fixing unit 8 is disposed on the downstream side of the secondary transfer unit 73 with respect to the sheet conveyance direction and above the secondary transfer unit 73. The fixing unit 8 heats and presses the sheet S to which the toner image has been transferred to fix the toner image to the sheet S.

[0022] The sheet discharge unit 9 is located downstream of the fixing unit 8 with respect to the sheet transport direction and is positioned on the upper surface of the main body 2 of the device. Sheets S on which the toner image has been fixed and printing is complete are transported through the sheet discharge port 4a to the sheet discharge unit 9. The sheet discharge unit 9 ejects the printed sheets (printed materials) from above.

[0023] The control unit 10 includes a CPU, an image processing unit, a memory unit, and other electronic circuits and electronic components (none of which are shown). The CPU controls the operation of each component provided in the image forming apparatus 1 based on control programs and data stored in the memory unit, and performs processing related to the functions of the image forming apparatus 1. The sheet supply unit 3, sheet transport device 4, exposure unit 5, image forming unit 6, transfer unit 7, and fixing unit 8 each receive individual commands from the control unit 10 and perform printing on the sheet S in conjunction. The memory unit is composed of a combination of a non-volatile memory device (not shown), such as a program ROM (Read Only Memory) or data ROM, and a volatile memory device (not shown), such as a RAM (Random Access Memory).

[0024] Next, the configuration of the sheet conveying device 4 will be described. Figure 2 is a cross-sectional front view of the sheet conveying device 4 of the image forming apparatus 1 shown in Figure 1. Note that in Figure 2, components other than the main parts related to the detailed explanation have been omitted from the drawing.

[0025] As shown in Figure 2, the sheet conveying device 4 includes a sheet conveying path 41, a reversing conveying path 42, a sheet detection unit 43, a pair of resist rollers 44, a pair of conveying rollers 45, and a pair of conveying rollers 46.

[0026] The sheet transport path 41 extends substantially vertically from the downstream side of the sheet supply unit 3 in the sheet transport direction, through the secondary transfer unit 73 and the fixing unit 8, to the upstream side of the sheet discharge unit 9 in the sheet transport direction. A sheet discharge port 4a is provided at the downstream end of the sheet transport path 41 in the sheet transport direction, facing the sheet discharge unit 9. Between the fixing unit 8 and the sheet discharge port 4a of the sheet transport path 41, a branching section 4b is provided where the reversal transport path 42 branches off.

[0027] The sheet transport path 41 is provided with multiple transport roller pairs 45, including a resist roller pair 44. Each of the multiple transport roller pairs 45 extends in the sheet width direction (the paper depth direction in Figure 2) perpendicular to the sheet transport direction of the sheet transport path 41. The sheet transport path 41 uses the multiple transport roller pairs 45 to transport the sheet S sent from the sheet supply unit 3 to the secondary transfer unit 73 and the fixing unit 8, and then discharges the fixed sheet S from the sheet discharge port 4a to the sheet discharge unit 9.

[0028] The reversal conveying path 42 is even closer to the side wall of the device body 2 than the sheet conveying path 41, and extends vertically just inside the side wall. At the branching section 4b, the reversal conveying path 42 branches off from the sheet conveying path 41 and extends downward, rejoining the sheet conveying path 41 below the pair of resist rollers 44, i.e., downstream in the sheet conveying direction.

[0029] The reversing conveying path 42 is provided with multiple pairs of conveying rollers 46. Each of the multiple pairs of conveying rollers 46 extends in the sheet width direction of the reversing conveying path 42. The reversing conveying path 42 uses the multiple pairs of conveying rollers 46 to convey the sheets S that were allocated to the reversing conveying path 42 at the branching section 4b downward along the side wall of the main body of the device 2, and merges with the sheet conveying path 41 below the pair of resist rollers 44, i.e., downstream in the sheet conveying direction.

[0030] Furthermore, an opening / closing section (not shown) is provided in the area where the sheet transport path 41 and the reversing transport path 42 are located. The opening / closing section extends vertically along the side wall of the main body of the device 2. The opening / closing section is supported by the main body of the device 2 so as to be able to swing around a rotation axis that extends along the front-to-back direction of the main body of the device 2 (the depth direction of the paper in Figures 1 and 2), with its upper end being a free end. By tilting the upper end of the opening / closing section sideways (to the right in Figures 1 and 2) away from the main body of the device 2, the sheet transport path 41, including the area around the resist roller pair 44, can be exposed. In other words, the opening / closing section is attached to the main body of the device 2 so as to be able to be opened and closed.

[0031] The sheet detection unit 43 is positioned on the sheet transport path 41, upstream of the secondary transfer unit 73 and downstream of the resist roller pair 44 with respect to the sheet transport direction (below the secondary transfer unit 73 and above the resist roller pair 44 in Figure 2). The sheet detection unit 43 includes, for example, a contact image sensor (CIS). The contact image sensor extends across the entire sheet width direction of the sheet transport path 41.

[0032] The contact image sensor emits light from its built-in light source toward the sheet transport path 41 and receives the reflected light. Based on the difference in light intensity between the parts of the sheet S that are blocked and the parts that are not, it detects the edges of the sheet S in the sheet transport direction (up and down direction in Figure 2) and the edges in the sheet width direction (paper depth direction in Figure 2). As a result, the sheet detection unit 43 detects the amount of displacement of the sheet S in the sheet width direction as it is transported along the sheet transport path 41.

[0033] The resist roller pair 44 is positioned upstream of the sheet detection unit 43 in the sheet transport direction. Sheets S sent from the sheet supply unit 3 and sheets S transported along the inversion transport path 42 reach the location of the resist roller pair 44. The control unit 10 corrects the positional misalignment of the sheet S in the sheet width direction using the resist roller pair 44, and adjusts the transport timing of the sheet S with the toner image formation of the image forming unit 6 and the primary transfer of the transfer unit 7, and sends the sheet S toward the secondary transfer nip of the secondary transfer unit 73.

[0034] Next, the configuration of the transport roller pair 46 of the reversing transport path 42 will be described. Figure 3 is a front view of the area around the transport roller pair 46 of the sheet transport device 4 shown in Figure 2. The reversing transport path 42 includes a first transport guide member 421 and a second transport guide member 422 that are arranged opposite each other on the sheet transport path on the reversing transport path 42. The first transport guide member 421 and the second transport guide member 422 are formed in a flat plate shape that extends in the sheet transport direction Dc and the sheet width direction (the depth direction of the paper in Figure 3) of the sheet S.

[0035] The transport roller pair 46 is positioned upstream of the register roller pair 44 with respect to the sheet transport direction. The transport roller pair 46 is composed of a first roller 461 and a second roller 462. The first roller 461 and the second roller 462 are positioned opposite each other, with the sheet transport path on the reversing transport path 42 in between. The first roller 461 and the second roller 462 transport the sheet S with the sheet S sandwiched between them.

[0036] The first roller 461 is rotatably supported by the first transport guide member 421. The first roller 461 is a drive roller that rotates when a driving force is input from the drive motor 471 of the drive mechanism 47.

[0037] The drive mechanism 47 for the first roller 461 includes, for example, a drive motor 471, two pulleys 472, and a drive belt 473. The two pulleys 472 are fixed to the rotation shaft 471x of the drive motor 471 and the drive shaft 461x of the first roller 461, respectively, and the drive belt 473 is wound around them.

[0038] The second roller 462 is rotatably supported by the second transport guide member 422. The second roller 462 is a driven roller that rotates in conjunction with the first roller 461 by contacting the first roller 461. An opposing biasing member 48 is positioned at the location of the second roll axis 462x of the second roller 462.

[0039] The opposing biasing member 48 is composed of, for example, a compression coil spring arranged to expand and contract radially in the direction of the second roller 462. One end of the opposing biasing member 48 in the direction of expansion and contraction is supported by the second transport guide member 422, and the other end is in contact with the circumferential surface of the second roll axis 462x of the second roller 462. The opposing biasing member 48 biases the second roller 462 with respect to the second transport guide member 422 in the direction that the second roller 462 approaches the first roller 461, that is, to the right in Figure 3.

[0040] Next, the configuration of the first roller 461 of the conveyor roller pair 46 will be described in detail. Figure 4 is a side view of the first roller 461 of the conveyor roller pair 46 shown in Figure 3. Figure 5 is a cross-sectional side view of the joint portion 461j of the first roller 461 shown in Figure 4. Figure 6 is a cross-sectional side view of the area around the bearing portion 463a of the first roll shaft 463x of the first roller 461 shown in Figure 4. Note that Figure 6 is a diagram showing the bearing portion 463a on one end of the first roll shaft 463x in the axial direction, but the bearing portion 463a on the other end in the axial direction has a similar configuration. Also, arrows indicating the sheet conveying direction Dc and the sheet width direction Dw are drawn in Figures 4, 5, 6, and 7.

[0041] The first roller 461 comprises a drive shaft 461x, a joint portion 461j, and a first conveying portion 463.

[0042] As shown in Figure 4, the drive shaft 461x is positioned outside the sheet width direction Dw relative to the center of the sheet width direction Dw, and further outward than the joint portion 461j and the first conveying portion 463. The drive shaft 461x extends in the sheet width direction Dw and is rotatably supported by the first conveying guide member 421 via bearing portions 461b located near both ends in the sheet width direction Dw (axial direction). A pulley 472 of the drive mechanism 47 is fixed to one end of the drive shaft 461x in the axial direction, and a joint portion 461j is fixed to the other end. Rotational driving force is transmitted to the drive shaft 461x from the drive mechanism 47 via the pulley 472.

[0043] As shown in Figures 4 and 5, the joint portion 461j is positioned between the drive shaft 461x and the first roll shaft 463x of the first conveying unit 463 in the sheet width direction Dw. The joint portion 461j is formed in a substantially cylindrical shape extending in the sheet width direction Dw. The drive shaft 461x and the first roll shaft 463x are inserted into the joint portion 461j from each of its axial ends. The joint portion 461j connects the drive shaft 461x and the first roll shaft 463x in the sheet width direction Dw. Within the joint portion 461j, the drive shaft 461x and the first roll shaft 463x are positioned with a predetermined distance between them.

[0044] One end of the drive shaft 461x is fixed to the joint portion 461j. One end of the first roll shaft 463x is held in the joint portion 461j so as to be movable in the sheet width direction Dw. More specifically, in the portion where the first roll shaft 463x is inserted into the joint portion 461j, the inner circumference of the joint portion 461j and the outer circumference of the first roll shaft 463x each have a D-shaped cross-sectional shape perpendicular to the axial direction, and are composed of a so-called D-cut. As a result, the first roll shaft 463x is movable in the sheet width direction Dw relative to the joint portion 461j, and rotational driving force around the axis is transmitted from the joint portion 461j.

[0045] The first conveying unit 463 is positioned in the center of the sheet width direction Dw. The first conveying unit 463 comprises a first roll shaft 463x, a pair of holders 463h, a pair of bearing units 463a, and a pair of first biasing members 463b.

[0046] As shown in Figure 4, the first roll shaft 463x is positioned parallel to the drive shaft 461x in the sheet width direction Dw via a joint portion 461j. A first roll portion 463r, which contacts the second roller 462, is fixed to the first roll shaft 463x. The first roll portion 463r has a larger outer diameter than the first roll shaft 463x and extends in the sheet width direction Dw. In this embodiment, the first roller 461 has two first roll portions 463r that are spaced apart in the sheet width direction Dw.

[0047] Each of the pair of holders 463h is positioned at each of the axial ends of the first roll shaft 463x, as shown in Figure 4. The holder 463h positioned on the joint portion 461j side of the first roll shaft 463x is positioned inward (towards the first roll portion 463r) of the joint portion 461j in the sheet width direction Dw. The pair of holders 463h are formed in a cylindrical shape extending in the sheet width direction Dw and are fixed to the first transport guide member 421. Within their cylindrical shape, the pair of holders 463h support each of the axial ends of the first roll shaft 463x via a pair of bearing portions 463a.

[0048] Each of the pair of bearing portions 463a is located inside each of the pair of cylindrical holders 463h, as shown in Figure 6. Each of the pair of bearing portions 463a rotatably supports each of the ends of the first roll shaft 463x in the axial direction (sheet width direction Dw). Furthermore, the bearing portions 463a are located inside the holders 463h so as to be movable in the sheet width direction Dw relative to the holders 463h. More specifically, the bearing portions 463a are movable in the sheet width direction Dw such that their outer circumferential surface slides on the inner circumferential surface of the holders 463h. That is, the pair of bearing portions 463a are movable along the sheet width direction Dw together with the first roll shaft 463x.

[0049] Each of the pair of first biasing members 463b is positioned inside each of the pair of cylindrical holders 463h, as shown in Figure 6. The first biasing member 463b consists of a compression coil spring that expands and contracts in the axial direction (sheet width direction Dw) of the first roll shaft 463x, and is positioned so that the first roll shaft 463x passes through the coil portion of the spring.

[0050] The first biasing member 463b has one end in the expansion / contraction direction (towards the center in the sheet width direction Dw) in contact with the holder 463h, and the other end (outside in the sheet width direction Dw) in contact with the bearing portion 463a. Each of the pair of first biasing members 463b biases each of the pair of bearing portions 463a in opposite directions in the sheet width direction Dw. That is, in this embodiment, each of the pair of first biasing members 463b biases each other to move the first roll shaft 463x (first roll portion 463r) outward in the sheet width direction Dw.

[0051] According to the above configuration, the first roll shaft 463x, to which the first roll section 463r that contacts the second roller 462 to transport the sheet S is fixed, can move in the sheet width direction Dw without obtaining driving force from the drive mechanism. That is, when the sheet S moves in the sheet width direction Dw when the misalignment is corrected by the resist roller pair 44, the first roll shaft 463x can move in the sheet width direction Dw in accordance with the movement of the sheet S without hindering the movement of the sheet S. Therefore, the sheet transport device 4 can properly correct the misalignment of the sheet S in the sheet width direction with a simple configuration that suppresses the increase in the drive mechanism including the drive source.

[0052] Next, the configuration of the second roller 462 of the conveyor roller pair 46 will be described in detail. Figure 7 is a side view of the second roller 462 of the conveyor roller pair 46 shown in Figure 3.

[0053] The second roller 462 is positioned in the center of the sheet width direction Dw. The second roller 462 comprises a second roll shaft 462x, a second roll section 462r, and a pair of second biasing members 462b.

[0054] The second roll shaft 462x extends in the sheet width direction Dw. The second roll shaft 462x is rotatably supported by the second transport guide member 422 via bearing portions 462a located near both ends in the sheet width direction Dw (axial direction). As mentioned above, an opposing biasing member 48 is positioned at the location of the second roll shaft 462x. The opposing biasing member 48 biases the second roller 462 with respect to the second transport guide member 422 in the direction that the second roller 462 approaches the first roller 461 (see Figure 3).

[0055] The second roll portion 462r is rotatably supported with respect to the second roll shaft 462x and is in contact with the first roll portion 463r. The second roll portion 462r has a larger outer diameter than the second roll shaft 462x and extends in the sheet width direction Dw. In this embodiment, the second roller 462 has two second roll portions 462r spaced apart in the sheet width direction Dw.

[0056] Each pair of second biasing members 462b is composed of a compression coil spring arranged to expand and contract in the axial direction (sheet width direction Dw) of the second roll shaft 462x, with the second roll shaft 462x passing through the coil portion. Each pair of second biasing members 462b is positioned outside both ends of a second roll section 462r in the axial direction (sheet width direction Dw). In other words, in this embodiment, the second roller 462 has two pairs of second biasing members 462b, each positioned for two second roll sections 462r that are spaced apart in the sheet width direction Dw.

[0057] The second biasing member 462b has one end in the expansion / contraction direction in contact with the second transport guide member 422, and the other end in contact with the second roll portion 462r. The pair of second biasing members 462b bias the second roll portion 462r in opposite directions in the sheet width direction Dw. That is, in this embodiment, each of the pair of second biasing members 462b biases the second roll portion 462r so that it moves in the sheet width direction Dw so as to press against the second roll portion 462r.

[0058] With the above configuration, the second roll section 462r, which contacts the first roll section 463r to transport the sheet S, can move in the sheet width direction Dw without obtaining driving force from the drive mechanism, just like the first roll section 463r. In other words, when the sheet S moves in the sheet width direction Dw while the misalignment is corrected by the resist roller pair 44, the effect of not hindering the movement of the sheet S can be enhanced. Therefore, the sheet transport device 4 can correct the misalignment of the sheet S in the sheet width direction more effectively.

[0059] Furthermore, as described above, the first roller 461 comprises a plurality (e.g., two) of first roll sections 463r fixed to the first roll shaft 463x. The second roller 462 comprises a plurality (e.g., two) of second roll sections 462r and a plurality (e.g., two pairs) of second biasing members 462b. The two second roll sections 462r contact each of the two first roll sections 463r individually. The two pairs of second biasing members 462b individually bias each of the two second roll sections 462r in opposite directions in the sheet width direction Dw.

[0060] According to the above configuration, each of the two second roll sections 462r moves independently in the sheet width direction Dw. This allows for flexible response to sheets S exhibiting unexpected behavior and does not hinder the movement of the sheet S in the sheet width direction Dw. As a result, the sheet conveying device 4 can more effectively correct misalignment of the sheet S in the sheet width direction.

[0061] Although embodiments of the present invention have been described above, the scope of the present invention is not limited thereto, and various modifications can be made to implement the invention without departing from the spirit of the invention.

[0062] For example, in the above embodiment, the configuration of the present invention described with reference to Figures 3 to 7 was applied to the transport roller pair 46 of the reversal transport path 42, but it is not limited to this. The configuration of the present invention may also be applied to any transport roller pair on the upstream side in the sheet transport direction of the resist roller pair 44, for example, the transport roller pair 45 of the sheet transport path 41.

[0063] Furthermore, in the above embodiment, the image forming apparatus 1 is a so-called tandem-type color printing image forming apparatus that sequentially superimposes images of multiple colors, but it is not limited to this type of model. The image forming apparatus may be a color printing image forming apparatus that is not of the tandem type, or a monochrome printing image forming apparatus. [Industrial applicability]

[0064] The present invention can be used in sheet transport devices and image forming devices. [Explanation of Symbols]

[0065] 1. Image forming apparatus 2. Main unit of the device 4 Sheet conveying device 41 Sheet transport path 42 Reversal transport path 43 Sheet detection unit 44 Resist Roller vs 46 Conveyor Roller Pair 421 First transport guide member 422 Second transport guide member 461 First Roller 461b Bearing section 461j Joint 461x drive shaft 462 Second Roller 462a Bearing section 462b Second biasing member 462r Second Roll Section 462x Second Roll Axis 463 First Conveyor Unit 463a Bearing section 463b First biasing member 463h holder 463r First Roll Section 463x First Roll Axis Dc Sheet transport direction Dw Seat width direction S Seat

Claims

1. A pair of resist rollers extending in the sheet width direction perpendicular to the sheet transport direction, which corrects the positional misalignment of the transported sheet in the sheet width direction, A conveying roller pair consisting of a first roller and a second roller arranged upstream of the resist roller pair with respect to the sheet conveying direction, and arranged rotatably opposite to each other to convey the sheet, Equipped with, The first roller is, A drive shaft extending in the width direction of the sheet and through which rotational driving force is transmitted, The first conveying unit has a first roll shaft that is positioned parallel to the drive shaft in the sheet width direction and has a first roll section fixed to it that contacts the second roller, A joint portion connects the drive shaft and the first roll shaft in the sheet width direction, and holds the first roll shaft so as to be movable in the sheet width direction, Equipped with, The first transport unit is, A pair of bearing portions that rotatably support each of the two ends of the first roll shaft in the sheet width direction and are movable together with the first roll shaft along the sheet width direction, A pair of first biasing members that bias each of the pair of bearing portions in opposite directions in the sheet width direction, A sheet conveying device characterized by comprising the following features.

2. The second roller is, The second roll shaft extending in the sheet width direction, A second roll portion is rotatably supported with respect to the second roll shaft and is in contact with the first roll portion, A pair of second biasing members that bias the second roll portion in opposite directions in the sheet width direction, The sheet conveying device according to claim 1, characterized by comprising the following:

3. The first roller comprises a plurality of first roll sections fixed to the first roll shaft, The second roller is, Multiple second roll sections, each of the multiple first roll sections, in contact with each of the multiple second roll sections, A plurality of pairs of second biasing members, each of the plurality of second roll sections, individually biases each of them in opposite directions in the sheet width direction, The sheet conveying device according to claim 1, characterized by comprising the following:

4. An image forming apparatus comprising a sheet transport device according to any one of claims 1 to 3.

Images