JP2019123084A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus capable of accurately aligning image formation positions in a sheet conveyance direction of each of a first surface and a second surface of a sheet in double-sided printing.SOLUTION: An image forming apparatus 1 includes an image writing starting position specification section 85 which specifies an image writing staring position in a sheet conveyance direction A with respect to a sheet S by an image forming section 50. The image writing starting position specification section 85 has a first specification section 851 for specifying a first position P1 preset according to the size of the sheet S as an image writing starting position with respect to a first surface S1 of the sheet S, and a second specification section 852 for calculating a sheet length to be a length in the sheet conveyance direction A of the sheet S during image formation with respect to the first surface S1 of the sheet S and specifying a second position P2 to be an image writing starting position with respect to a second surface S2 of the sheet S on the basis of the calculated value LB and the first position P1.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus for forming an image on a sheet.

  An image forming apparatus such as a printer, a copier, or a facsimile includes a sheet conveying unit that conveys a sheet, and an image forming unit that forms an image on a sheet conveyed by the sheet conveying unit. In such an image forming apparatus, after an image is formed on the first side of the sheet by the image forming unit, the front and back of the sheet are reversed to form an image on the second side opposite to the first side of the sheet. May perform double-sided printing.

  When double-sided printing is performed in the image forming apparatus, accurate matching between the image forming position on the first side of the sheet and the image forming position on the second side is required. For example, Patent Document 1 discloses a technique of adjusting an image forming position with respect to a sheet in a sheet width direction orthogonal to a sheet conveyance direction. In this technique, the side end position of the sheet in the sheet width direction is detected, the off-center amount of the sheet is determined based on the detected side end position of the sheet, and the image forming unit is moved in the sheet width direction according to the off-center amount. Move to

  A reference length is set for each of the sheet conveying direction and the sheet width direction of the sheet, for example, for each sheet size such as “A4 size” or “B4 size”. However, due to the cutting accuracy and the like at the time of cutting the sheet, an error of about several millimeters with respect to the reference length exists for each sheet. That is, the length of the sheet is different for each sheet even if the sheet size is the same.

  Assuming that an error with respect to a preset reference length exists for each sheet, in double-sided printing, the image forming position in the sheet width direction of each of the first and second sides of the sheet is disclosed in Patent Document It is considered that the matching can be achieved by using the sheet width direction adjustment technique disclosed in No. 1. However, even if the adjustment technology in the sheet width direction disclosed in Patent Document 1 is applied as an adjustment technology in the sheet conveyance direction, in double-sided printing, image formation is performed in the sheet conveyance direction of each of the first surface and the second surface of the sheet. The position can not be matched exactly.

JP, 2013-11684, A

  The present invention has been made in view of such circumstances, and an object of the present invention is to correct an image forming position in the sheet conveying direction of each of the first surface and the second surface of a sheet in double-sided printing. It is an object of the present invention to provide an image forming apparatus which can be matched with

  An image forming apparatus according to one aspect of the present invention includes a sheet conveyance unit that conveys a sheet in a predetermined sheet conveyance direction, an image forming unit that forms an image on the sheet conveyed by the sheet conveyance unit, and the image A sheet reversing unit for reversing the front and back sides of the sheet on which the image is formed on the first surface by the forming unit and the second surface opposite to the first surface; and the sheet by the image forming unit An image writing position specifying unit that specifies an image writing position in the sheet conveying direction with respect to the sheet; and an image of the image forming unit with respect to each of the first surface and the second surface of the sheet with reference to the image writing position. And an image forming control unit that controls the forming operation. The image writing start position specifying unit specifies a first position set in advance according to the size of the sheet as a image writing position with respect to the first side of the sheet, and the first position of the sheet At the time of image formation on a surface, the sheet length which is the length of the sheet in the sheet conveyance direction of the sheet is calculated, and based on the calculated value and the first position, the image writing position for the second surface of the sheet And a second identification unit that identifies a second position.

  According to this image forming apparatus, the image formation control unit refers to the image writing position in the sheet conveying direction with respect to the sheet specified by the image writing position specifying unit, and detects the first and second sides of the sheet in duplex printing. The image forming operation of the image forming unit on each side is controlled. Here, the image writing position specifying unit includes a first specifying unit and a second specifying unit, and the first specifying unit specifies a first position as an image writing position in the sheet conveying direction with respect to the first surface of the sheet, and the second specifying The section specifies the second position as the image writing position in the sheet conveying direction with respect to the second side of the sheet.

  The first position specified by the first specifying unit is a position set in advance according to the size of the sheet. On the other hand, the second position specified by the second specifying unit is a position based on the calculated value of the sheet length in the sheet conveyance direction calculated at the time of image formation on the first surface of the sheet and the first position. . That is, while the first position which is the image writing position with respect to the first side of the sheet is a preset position set in advance according to the sheet size, the second position which is the image writing position with respect to the second side of the sheet is The actual value of the sheet length in the sheet conveying direction is added to the setting position. As a result, even if an error with respect to the reference length preset according to the sheet size is present for each sheet due to the cutting accuracy etc. at the time of cutting the sheet, the first side of the sheet in double-sided printing The image forming position in the sheet conveying direction of each of the first and second surfaces can be exactly matched.

  In the above-described image forming apparatus, the sheet conveying unit conveys the sheet toward the image forming unit by rotating at a predetermined timing around a rotation axis extending in a sheet width direction orthogonal to the sheet conveying direction. The conveyance roller pair is included, and the second identification unit calculates the sheet length based on the amount of rotation of the conveyance roller pair about the rotation axis.

  In this aspect, the second identification unit can calculate the sheet length in the sheet conveyance direction by referring to the amount of rotation about the rotation axis of the conveyance roller pair.

  In the above-described image forming apparatus, the second specifying unit relates to a length of the sheet in the sheet conveying direction, and a difference between calculated values of the sheet length with respect to a reference length preset according to the size of the sheet. And the second position based on the first position.

  In this aspect, the second identification unit identifies the difference between the calculated value of the actual sheet length and the reference length in the sheet conveyance direction set in advance according to the sheet size, and the image writing position of the first surface of the sheet. By referring to the first position, it is possible to specify the second position as the image writing position of the second side of the sheet.

  According to the present invention, it is possible to provide an image forming apparatus capable of accurately matching the image forming position in the sheet conveying direction of each of the first surface and the second surface of the sheet in double-sided printing.

FIG. 1 schematically shows an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a view showing the vicinity of a resist roller pair provided in the image forming apparatus. FIG. 2 is a block diagram showing a control system of the image forming apparatus. FIG. 6 is a diagram for describing initial setting information regarding a sheet size referred to in an image forming operation by an image forming unit of the image forming apparatus. FIG. 6 is a diagram for describing an image forming operation by the image forming unit.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described based on the drawings. In the following, the directional relationship will be described using XYZ orthogonal coordinate axes. The X direction is equivalent to the front and back direction (+ X is after, -X is front), the Y direction is the left and right direction (+ Y is left, -Y is right), and the Z direction is up and down (+ Z is up, -Z is down) Do. Further, in the following description, the term "sheet" refers to copy paper, coated paper, OHP sheet, cardboard, postcard, tracing paper, other sheet material subjected to an image forming process, or any process other than an image forming process Means sheet material that is subject to

<Overall Configuration of Image Forming Apparatus>
FIG. 1 is a view schematically showing an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 shown in FIG. 1 is an ink jet recording apparatus that discharges ink droplets to form (print) an image on a sheet S. The image forming apparatus 1 includes an apparatus main body 10, a sheet feeding unit 20, a sheet reversing unit 30, a sheet conveying unit 40, an image forming unit 50, and a sheet discharging unit 60.

  The apparatus main body 10 is a box-shaped housing that accommodates various apparatuses for forming an image on the sheet S. In the apparatus main body 10, a first conveyance passage 11, a second conveyance passage 12, and a third conveyance passage 13 which are conveyance passages of the sheet S are formed.

  The sheet feeding unit 20 feeds the sheet S to the first conveyance path 11. The sheet feeding unit 20 includes a sheet feeding cassette 21 and a pickup roller 22. The sheet feeding cassette 21 is attachable to and detachable from the apparatus main body 10, and accommodates the sheet S therein. The pickup roller 22 is disposed on the −Y side and on the + Z side of the sheet feeding cassette 21. The pickup roller 22 picks up the sheet S of the uppermost layer of the sheet bundle stored in the sheet feeding cassette 21 one by one and sends it out to the first conveyance path 11.

  The sheet S fed to the first conveyance path 11 is disposed at the downstream end of the first conveyance path 11 by the first conveyance roller pair 111 provided in the first conveyance path 11. The sheet is conveyed to the registration roller pair 44. A sheet feed tray 25 is disposed on the side surface on the −Y side of the apparatus main body 10, and the sheet S can be placed on the upper surface portion of the sheet feed tray 25. The sheet S placed on the sheet feed tray 25 is fed toward the registration roller pair 44 by the sheet feed roller 24.

  FIG. 2 is a view showing the vicinity of the resist roller pair 44. As shown in FIG. The registration roller pair 44 is a conveyance roller pair disposed at the upstream end of the sheet conveyance unit 40. The registration roller pair 44 rotates at a predetermined timing around a rotation shaft 441 extending in the sheet width direction (X direction) orthogonal to the sheet conveyance direction A, whereby the sheet conveyance unit 40 conveys the sheet conveyance unit 40. Send toward the belt 41. The registration roller pair 44 is rotationally driven by a drive motor 442. The registration roller pair 44 corrects the skew of the sheet S, and feeds the sheet S toward the conveyance belt 41 via the sheet introduction guide unit 23 in accordance with the timing of the image forming process by the image forming unit 50. Thus, the registration roller pair 44 conveys the sheet S toward the image forming unit 50. The sheet conveyance direction A is a direction from the −Y side to the + Y side in the Y direction.

  The sheet introduction guide unit 23 guides the sheet S delivered by the registration roller pair 44 toward the outer peripheral surface 411 of the conveyance belt 41 in the sheet conveyance unit 40.

  When the leading end of the sheet S guided by the sheet introduction guide portion 23 contacts the outer peripheral surface 411 of the conveyance belt 41, the sheet S is conveyed in the sheet conveyance direction A while being held on the outer peripheral surface 411 by the drive of the conveyance belt 41 Be done.

  The sheet conveying unit 40 is disposed to face the line head 51 on the −Z side of the image forming unit 50. The sheet conveyance unit 40 conveys the sheet S guided and introduced by the sheet introduction guide unit 23 in the sheet conveyance direction A so that the sheet S passes through the −Z side of the image forming unit 50. The sheet conveyance unit 40 includes a conveyance belt 41 and a suction unit 43 in addition to the registration roller pair 44.

  The transport belt 41 is an endless belt having a width in the Y direction and extending in the X direction. The conveyance belt 41 is disposed to face the image forming unit 50, and conveys the sheet S in the sheet conveyance direction A on the outer peripheral surface 411. More specifically, the conveyance belt 41 holds the sheet S on the outer circumferential surface 411 in a predetermined conveyance area facing the line head 51 of the image forming unit 50 and conveys the sheet S in the sheet conveyance direction A.

  The transport belt 41 is stretched around the first roller 421, the second roller 422, the third roller 423, and the pair of fourth rollers 424. Inside the stretched conveyor belt 41, a suction unit 43 is disposed to face the inner circumferential surface 412. The first roller 421 is a drive roller that extends along the Y direction, which is the width direction of the conveyance belt 41, and is disposed downstream of the suction unit 43 in the sheet conveyance direction A. The first roller 421 is rotationally driven by a drive motor (not shown) and causes the transport belt 41 to rotate in a predetermined rotation direction. As the conveyance belt 41 circulates, the sheet S held on the outer circumferential surface 411 is conveyed in the sheet conveyance direction A.

  The second roller 422 is a belt speed detection roller extending along the Y direction, and is disposed upstream of the suction portion 43 in the sheet conveyance direction A. The second roller 422 cooperates with the first roller 421, and an area of the outer circumferential surface 411 of the conveyance belt 41 facing the line head 51 and an area of the inner circumferential surface 412 of the conveyance belt 41 facing the suction portion 43 It is arrange | positioned so that planarity may be maintained. Here, in the outer circumferential surface 411 of the conveyance belt 41, the area between the first roller 421 and the second roller 422, which is an area facing the line head 51, is for holding and conveying the sheet S. It becomes a predetermined conveyance area. The second roller 422 is driven to rotate in conjunction with the rotation of the transport belt 41. A pulse plate (not shown) is attached to the second roller 422, and the pulse plate rotates integrally with the second roller 422. The rotational speed of the transport belt 41 is detected by measuring the rotational speed of the pulse plate.

  The third roller 423 is a tension roller extending along the Y direction, and applies tension to the conveyance belt 41 so that the conveyance belt 41 does not bend. The third roller 423 is driven to rotate in conjunction with the rotation of the transport belt 41. Each of the pair of fourth rollers 424 is a guide roller extending along the Y direction, and guides the transport belt 41 so that the transport belt 41 passes through the −Z side of the suction portion 43. The pair of fourth rollers 424 is driven to rotate in conjunction with the circulation of the conveyance belt 41.

  Further, the transport belt 41 has a plurality of suction holes penetrating in the thickness direction from the outer peripheral surface 411 to the inner peripheral surface 412.

  The suction unit 43 is disposed to face the image forming unit 50 via the conveyance belt 41. More specifically, the suction portion 43 faces the inner circumferential surface 412 inside the transport belt 41 stretched by the first roller 421, the second roller 422, the third roller 423, and the pair of fourth rollers 424. Are arranged. The suction unit 43 brings the sheet S into close contact with the outer circumferential surface 411 of the conveyance belt 41 by generating a negative pressure between the sheet S held by the outer circumferential surface 411 of the conveyance belt 41 and the conveyance belt 41. The suction unit 43 includes a belt guide member 431, a suction case 432, a suction device 433, and an exhaust duct 434.

  The belt guide member 431 is disposed to face the area between the first roller 421 and the second roller 422 on the inner circumferential surface 412 of the conveyance belt 41, and has a length in the width direction (Y direction) of the conveyance belt 41. It is a plate-like member having substantially the same width dimension. The belt guide member 431 constitutes an upper surface portion of the suction case 432 and has substantially the same shape as the suction case 432 when viewed from the + Z side. The belt guide member 431 guides the circumferential movement of the transport belt 41 interlocked with the rotation of the first roller 421 between the first roller 421 and the second roller 422.

  Further, the belt guide member 431 has a plurality of grooves formed in a belt guide surface facing the inner circumferential surface 412 of the transport belt 41. Each groove is formed corresponding to the suction hole of the conveyance belt 41. Further, the belt guide member 431 has a through hole provided corresponding to each groove. The through hole is a hole penetrating in the thickness direction of the belt guide member 431 in each groove, and communicates with the suction hole of the transport belt 41 through each groove.

  The suction portion 43 provided with the belt guide member 431 configured as described above is from the space on the + Z side of the conveyance belt 41 via the groove portion and the through hole of the belt guide member 431 and the suction hole of the conveyance belt 41. Suction is generated by suctioning air. Due to this suction force, an air flow (suction wind) toward the suction portion 43 is generated in the space above the transport belt 41. When the sheet S is guided on the conveying belt 41 by the sheet introduction guide portion 23 and covers a part of the outer peripheral surface 411 of the conveying belt 41, a suction force (negative pressure) acts on the sheet S to convey the sheet S to the conveying belt. It is in close contact with the outer peripheral surface 411 of 41.

  In the suction unit 43, the suction case 432 is a box-shaped case opened on the + Z side, and the opening on the + Z side is covered by the belt guide member 431 that constitutes the upper surface portion of the suction case 432, It is disposed on the −Z side of the transport belt 41. The suction housing 432 cooperates with the belt guide member 431 constituting the upper surface thereof to define a suction space 432A. That is, a space surrounded by the suction case 432 and the belt guide member 431 is a suction space 432A. The suction space 432 </ b> A communicates with the suction hole of the conveyance belt 41 via the groove portion of the belt guide member 431 and the through hole.

  An opening 432B is formed in the bottom wall of the suction housing 432, and a suction device 433 is disposed corresponding to the opening 432B. An exhaust duct 434 is connected to the suction device 433. The exhaust duct 434 is connected to an exhaust port (not shown) provided in the apparatus main body 10.

  An image forming unit 50 is disposed on the + Z side of the sheet conveyance unit 40. Specifically, the image forming unit 50 is disposed on the + Z side of the sheet conveyance unit 40 so as to face the outer circumferential surface 411 of the conveyance belt 41. The image forming unit 50 forms an image by performing an image forming process on the sheet S conveyed in the sheet conveying direction A while being held on the outer peripheral surface 411 of the conveying belt 41. In the present embodiment, the image forming unit 50 is an inkjet type image forming system, and discharges ink droplets to form an image on the sheet S.

  The image forming unit 50 includes line heads 51Bk, 51C, 51M, and 51Y. The line head 51Bk ejects a black ink droplet, the line head 51C ejects a cyan ink droplet, the line head 51M ejects a magenta ink droplet, and the line head 51Y ejects a yellow ink droplet. Do. The line heads 51Bk, 51C, 51M, and 51Y are arranged in parallel from the upstream side to the downstream side in the sheet conveyance direction A. The line heads 51Bk, 51C, 51M, and 51Y may be collectively referred to as line heads 51 because they have the same configuration except that the colors of the ink droplets to be ejected are different.

  The line head 51 discharges ink droplets onto the sheet S conveyed in the sheet conveyance direction A in a state of being held on the outer peripheral surface 411 of the conveyance belt 41, and forms an image on the sheet S. Specifically, the line head 51 discharges ink droplets toward the sheet S which is conveyed by the conveyance belt 41 and passes a position facing the line head 51. Thus, an image is formed on the sheet S.

  Ink droplets are ejected from the line head 51, and the sheet S on which an image is formed is conveyed by the conveyance belt 41 and is delivered to the conveyance unit 45 disposed on the downstream side of the conveyance direction A of the conveyance belt 41. . The transport unit 45 further transports the sheet S received from the sheet transport unit 40 to the downstream side in the sheet transport direction A. A decurler unit 46 is disposed downstream of the transport unit 45. The decurler unit 46 further transports the sheet S to the downstream side in the sheet transport direction A while correcting the curl of the sheet S received from the transport unit 45. The sheet S conveyed by the decurler unit 46 is delivered to the second conveyance path 12.

  The second transport path 12 is extended along the side surface on the + Y side of the apparatus main body 10. The sheet S delivered to the second transport path 12 is transported by the second transport roller pair 121 provided on the second transport path 12 toward the discharge port 12A formed on the + Y side of the apparatus main body 10 , And the sheet is discharged onto the sheet discharge unit 60 from the sheet discharge outlet 12A.

  On the other hand, when the sheet S sent to the second conveyance path 12 is for double-sided printing on which the image formation processing of the first surface (surface) is completed, the sheet S is sent to the sheet reversing unit 30. Be The sheet reversing unit 30 is a conveyance path branched in the middle of the second conveyance path 12 and is a portion where the sheet S is reversed (switched back). The sheet S whose front and back is reversed by the sheet reversing unit 30 is delivered to the third conveyance path 13. The sheet S sent to the third conveyance path 13 is reversely fed by the third conveyance roller pair 131 provided in the third conveyance path 13, and the front and back are conveyed via the registration roller pair 44 and the sheet introduction guide portion 23. It is again supplied onto the outer peripheral surface 411 of the transport belt 41 in the reversed state. The sheet S supplied on the outer peripheral surface 411 of the transport belt 41 with the front and back reversed in this manner is transported by the transport belt 41 and the second surface opposite to the first surface is formed by the image forming unit 50. Image formation processing is performed on the (rear surface). The sheet S for which double-sided printing has been completed passes through the second conveyance path 12 and is discharged onto the paper discharge unit 60 from the paper discharge port 12A.

  In addition, the image forming apparatus 1 according to the present embodiment further includes a sheet detection sensor 70 (see FIG. 1) and a rotation detection unit 71 (see FIG. 2). The sheet detection sensor 70 is a sensor that is disposed on the downstream side of the registration roller pair 44 and close to the registration roller pair 44 and detects the sheet S conveyed by the registration roller pair 44.

  The rotation detection unit 71 is a mechanism for detecting the amount of rotation of the registration roller pair 44 about the rotation axis 441. The rotation detection unit 71 includes a pulse plate 711 and a PI sensor (photo interrupter sensor) 712. The pulse plate 711 is a disk-like member provided concentrically with the rotation shaft 411 and integrally provided with the rotation. The pulse plate 711 controls the passage of light from the light emitting unit 712A of the PI sensor 712 by rotating in conjunction with the rotation of the resist roller pair 44 about the rotation axis 441. In the pulse plate 711, a plurality of light passing openings through which light from the light emitting unit 712 A of the PI sensor 712 passes are formed at equal intervals along the circumferential direction.

  The PI sensor 712 is a sensor for detecting the amount of rotation of the registration roller pair 44 about the rotation axis 441. The PI sensor 712 includes a light emitting unit 712A and a light receiving unit 712B which are disposed to face each other with the pulse plate 711 interposed therebetween. The light emitting unit 712A may be one in which one light source emitting diffused light is disposed, or a plurality of light emitting elements may be arranged in a line. The light receiving unit 712B has a light receiving surface that receives light emitted from the light emitting unit 712A and having passed through the light passing opening according to the rotation of the pulse plate 711. A plurality of light receiving elements are arranged on the light receiving surface of the light receiving unit 712B. The light receiving unit 712B outputs a light receiving signal based on the light received by each light receiving element. The light reception signal output from the light reception unit 712B is a pulse signal, and is a detection signal that represents the amount of rotation of the registration roller pair 44.

<Control system of image forming apparatus>
Next, a control system of the image forming apparatus 1 will be described with reference to FIGS. 3 to 5. FIG. 3 is a block diagram showing a control system of the image forming apparatus 1. FIG. 4 is a diagram for explaining the initial setting information J1 regarding the sheet size referred to in the image forming operation by the image forming unit 50 of the image forming apparatus 1. FIG. 5 is a diagram for explaining an image forming operation by the image forming unit 50. As shown in FIG. The image forming apparatus 1 includes a control unit 80 and an operation unit 90, as shown in FIG. The operation unit 90 includes a touch panel, a ten key, a start key, a setting key, and the like, and receives a user's operation on the image forming apparatus 1 and various settings.

  The control unit 80 is configured of a central processing unit (CPU), a read only memory (ROM) for storing a control program, and a random access memory (RAM) used as a work area of the CPU. The control unit 80 centrally controls the operation of the image forming apparatus 1 by the CPU executing a control program stored in the ROM. The control unit 80 includes a sheet feeding control unit 81, a sheet conveyance control unit 82, an image formation control unit 83, a storage unit 84, and an image writing position specifying unit 85.

  The sheet feeding control unit 81 controls the sheet feeding operation of the sheet feeding unit 20. The sheet conveyance control unit 82 controls the sheet conveyance operation of the sheet conveyance unit 40.

  The image forming control unit 83 controls the image forming operation of the image forming unit 50. The image forming control unit 83 controls the image forming operation of the image forming unit 50 with reference to the initial setting information J 1 regarding the sheet size stored in advance in the storage unit 84. The initial setting information J1 stored in the storage unit 84 is information in which sheet size information J11, reference length information J12, and first leading end margin length information J13 are associated as shown in FIG. The sheet size information J11 is information indicating a sheet size such as “A4 size” or “B4 size”, for example. The reference length information J12 is a length in the sheet conveyance direction A of the sheet S, and is information representing a reference length LA set in advance according to the size of the sheet S (sheet size). The first leading end margin length information J13 has a first leading end margin length L1 which is a length from the leading end of the sheet S in the sheet conveying direction A to the leading end of the image at the time of image formation on the first surface S1 of the sheet S. It is information to represent. The first leading edge margin length information J13 can be rewritten by an input operation on the operation unit 90.

  In the example shown in FIG. 4, the sheet size represented by the sheet size information J11 is "AA", "AA1" as the reference length information J12, and "AA2" as the first leading edge margin length information J13. And are associated. As a result, for the sheet S having the sheet size “AA”, the reference length LA in the sheet conveyance direction A is preset to “AA1”, and the first leading edge margin length L1 in the sheet conveyance direction A is “AA2”. It is shown that it is set in advance. Further, in the example shown in FIG. 4, when the sheet size represented by the sheet size information J11 is “BB”, “BB1” as the reference length information J12 and “BB” as the first leading edge margin length information J13 "BB2" is associated. As a result, for the sheet S having the sheet size “BB”, the reference length LA in the sheet conveyance direction A is preset to “BB1”, and the first leading edge margin length L1 in the sheet conveyance direction A is “BB2”. It is shown that it is set in advance. Furthermore, in the example illustrated in FIG. 4, when the sheet size represented by the sheet size information J11 is “CC”, “CC1” as the reference length information J12 and “C1 as the first leading edge margin length information J13 "CC2" is associated. As a result, for the sheet S having the sheet size “CC”, the reference length LA in the sheet conveyance direction A is preset to “CC1”, and the first leading edge margin length L1 in the sheet conveyance direction A is “CC2”. It is shown that it is set in advance.

  When the image forming apparatus 1 performs single-sided printing in which an image is formed only on the first surface S1 of the sheet S, the image formation control unit 83 refers to the initial setting information J1 stored in the storage unit 84 and The image of the image forming unit 50 is set such that the image writing position in the sheet conveying direction A with respect to the one side S1 is a position defined by the first leading edge margin length L1 represented by the first leading edge margin length information J13. Control the forming operation.

  On the other hand, when the image forming apparatus 1 performs double-sided printing in which an image is formed on each of the first surface S1 and the second surface S2 of the sheet S, the image formation control unit 83 is specified by the image writing position specifying unit 85. The image forming operation of the image forming unit 50 on each of the first surface S1 and the second surface S2 of the sheet S is controlled with reference to the image writing position in the sheet conveying direction A with respect to the sheet S by the image forming unit 50. .

  The image writing position specifying unit 85 specifies an image writing position in the sheet conveyance direction A with respect to the sheet S by the image forming unit 50 when command information for performing double-sided printing is input through the operation unit 90. The image writing position specifying unit 85 includes a first specifying unit 851 and a second specifying unit 852 as shown in FIG.

  The first specifying unit 851 refers to the initial setting information J1 stored in the storage unit 84, and displays the first tip margin length information J13 set in advance according to the sheet size represented by the sheet size information J11. The first position P1 (see FIG. 5) defined by the first leading edge margin length L1 is specified as the image writing position in the sheet conveyance direction A with respect to the first surface S1 of the sheet S.

  By the way, as indicated by the initial setting information J1 stored in the storage unit 84, the length of the sheet S in the sheet conveyance direction A is the reference length information J12 for each sheet size represented by the sheet size information J11. The reference length LA represented by is set. However, due to the cutting accuracy and the like at the time of cutting the sheet S, an error of about several millimeters with respect to the reference length LA exists for each sheet S. That is, the length of the sheet conveyance direction A of the sheet S is different for each sheet S even if the sheet size is the same.

  Therefore, the image writing position in the sheet conveyance direction A with respect to the second surface S2 of the sheet S is the same as in the case of the first surface S1, the first leading edge margin length L1 represented by the first leading edge margin length information J13. Assuming that the position is defined by the position of the image G1, the position of the image G1 on the first surface S1 and the position of the image G2 on the second surface S2 corresponding to the error with respect to the reference length LA, as shown in FIG. But the sheet conveyance direction A is shifted.

  Therefore, the second specifying unit 852 specifies a second position P2 (see FIG. 5) which is an image writing position in the sheet conveyance direction A with respect to the second surface S2 of the sheet S. First, the second specifying unit 852 calculates a sheet length LB, which is a length in the sheet conveyance direction A of the sheet S, at the time of image formation by the image forming unit 50 on the first surface S1 of the sheet S.

  More specifically, the second specifying unit 852 sets the sheet based on the amount of rotation of the registration roller pair 44 detected by the rotation detecting unit 71 at the time of image formation by the image forming unit 50 on the first surface S1 of the sheet S. A sheet length LB, which is the length of the sheet conveyance direction A of S, is calculated. The amount of rotation of the registration roller pair 44 referred to when the second specifying unit 852 calculates the sheet length LB is a period in which a detection signal indicating that the sheet S is detected from the sheet detection sensor 70, that is, The amount of rotation detected by the rotation detection unit 71 within a period from when the leading end of the sheet S passes the sheet detection sensor 70 to when the rear end passes. The amount of rotation of the registration roller pair 44 may be derived with reference to the drive control signal of the drive motor 442 that rotationally drives the registration roller pair 44.

  The second identification unit 852 may calculate the sheet length LB by measuring the time during which the sheet detection sensor 70 outputs a detection signal of the sheet S. However, since the conveyance speed of the sheet S by the registration roller pair 44 may increase or decrease depending on the speed change, there is a possibility that the calculated value of the sheet length LB by time measurement may be deteriorated in accuracy. For this reason, it is desirable that the second specifying unit 852 be configured to calculate the sheet length LB based on the rotation amount of the registration roller pair 44.

  Further, the second specifying unit 852 is a movement amount by which the conveyance belt 41 circularly moves in a period in which a synchronization signal of the discharge of ink droplets from the line head 51 synchronized with the conveyance of the sheet S by the conveyance belt 41 is output. The sheet length LB may be calculated based on

  Then, based on the calculated value of the sheet length LB and the first position P1 specified by the first specifying unit 851, the second specifying unit 852 writes the image in the sheet conveying direction A with respect to the second surface S2 of the sheet S. The second position P2 to be the position is identified. The second specifying unit 852 is configured to perform the second specifying unit 852 before the sheet S on which the formation of the image G1 on the first surface S1 is completed is conveyed through the third conveyance path 13 and reaches the registration roller pair 44 in a state where the front and back is reversed. Identify the position P2.

  Specifically, the second specifying unit 852 sets the sheet conveyance direction in the sheet S represented by the reference length information J12, which is set in advance according to the sheet size represented by the sheet size information J11 of the initial setting information J1. The second position P2 is specified based on the difference between the calculated value of the sheet length LB and the reference length LA of A and the first position P1 specified by the first specifying unit 851.

  More specifically, the second specifying unit 852 measures the length from the leading edge of the sheet S in the sheet conveying direction A to the leading edge of the image G2 when forming an image on the second surface S2 of the sheet S based on the following formula (1). The second leading end margin length L2 is calculated. Then, the second specifying unit 852 specifies the second position P2 defined by the second leading edge margin length L2 as the image writing position in the sheet conveyance direction A with respect to the second surface S2 of the sheet S.

L2 = L1 + (LB-LA) (1)
[In Formula (1), "L2" shows the 2nd tip margin length which prescribes the 2nd position P2, and "L1" shows the 1st tip margin length which prescribes the 1st position P1. Further, in the equation (1), “LB” indicates the sheet length in the sheet conveyance direction A in the sheet S calculated by the second identification unit 852, and “LA” indicates the sheet S set in advance according to the sheet size. Shows the reference length in the sheet conveyance direction A in ]

  The second specifying unit 852 uses the difference between the calculated value of the sheet length LB with respect to the reference length LA and the first leading edge margin length L1 defining the first position P1, and generates the second By calculating the leading end margin length L2, it is possible to specify the second position P2 defined by the second leading end margin length L2.

  As described above, the first position P1, which is the image writing position with respect to the first surface S1 of the sheet S, specified by the first specifying unit 851, has a first leading edge margin length L1 set in advance according to the sheet size. Position defined by On the other hand, the second position P2 specified by the second specifying unit 852 and serving as the image writing position with respect to the second surface S2 of the sheet S has a sheet length LB corresponding to the actual length in the sheet conveying direction A. It is added to the first position P1. As a result, even if an error with respect to the reference length LA previously set according to the sheet size is present for each sheet S due to the cutting accuracy at the time of cutting the sheet S, etc. The position of the image G1 in the plane S1 and the position of the image G2 in the second plane S2 can be exactly matched (see FIG. 5B).

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this, A various deformation | transformation embodiment can be taken.

  In the above embodiment, an inkjet recording apparatus has been described as the image forming apparatus 1. However, the image forming apparatus 1 of the present invention is not limited to the inkjet recording apparatus. The image forming apparatus 1 of the present invention may be any apparatus provided with the image writing position specifying unit 85, and various image forming methods (recording method) other than the ink jet type such as laser beam type, thermal type, wire dot type Devices can be used.

Reference Signs List 1 image forming apparatus 10 apparatus main body 20 sheet feeding unit 30 sheet reversing unit 40 sheet conveying unit 41 conveying belt 44 registration roller pair (conveying roller pair)
441 rotation shaft 442 drive motor 50 image forming unit 60 sheet discharge unit 70 sheet detection sensor 71 rotation detection unit 80 control unit 81 sheet feeding control unit 82 sheet conveyance control unit 83 image formation control unit 84 storage unit 85 image writing position specifying unit 851 1st identification part 852 2nd identification part 90 operation part P1 1st position P2 2nd position S sheet S1 1st surface S2 2nd surface

Claims (3)

A sheet conveying unit that conveys a sheet in a predetermined sheet conveying direction;
An image forming unit that forms an image on the sheet conveyed by the sheet conveyance unit;
A sheet reversing unit that reverses the sheet on which an image is formed on the first surface by the image forming unit so as to form an image on the second surface opposite to the first surface;
An image writing position specifying unit that specifies an image writing position in the sheet conveying direction with respect to the sheet by the image forming unit;
And an image forming control unit that controls the image forming operation of the image forming unit with respect to each of the first surface and the second surface of the sheet with reference to the image writing position.
The image writing position specifying unit
A first identification unit that identifies a first position preset according to the size of the sheet as an image writing position with respect to the first surface of the sheet;
At the time of image formation with respect to the first surface of the sheet, a sheet length which is a length of the sheet in the sheet conveying direction is calculated, and the second surface of the sheet is calculated based on the calculated value and the first position. An image forming apparatus including: a second specifying unit specifying a second position to be an image writing position for the image forming apparatus; The sheet conveyance unit includes a conveyance roller pair that conveys the sheet toward the image forming unit by rotating at a predetermined timing around a rotation axis extending in a sheet width direction orthogonal to the sheet conveyance direction.
The image forming apparatus according to claim 1, wherein the second identification unit calculates the sheet length based on an amount of rotation of the transport roller pair about the rotation axis.   The second identification unit relates to the length of the sheet in the sheet conveyance direction, and a difference between the calculated value of the sheet length and a reference length preset according to the size of the sheet, and the first position. The image forming apparatus according to claim 1, wherein the second position is specified on the basis of