Conveyance device

Abstract

To provide a conveyance device that can suppress skew correction of paper from being insufficiently performed.SOLUTION: A control part controls resist conveying parts 31A and 31B so that a conveying speed of paper being conveyed by one resist conveying part 31 conveying paper ahead becomes lower than a conveying speed of a paper being conveyed by the other resist conveying part 31, on the basis of a skew amount of paper detected by a skew detecting part 5A, so as to execute a skew-correction process for correcting skewing of the paper. When the skew amount of the paper detected by the skew detecting part 5A is larger than a predetermined skew-correction amount in the skew-correction process, the control part temporarily stops the one resist conveying part 31 conveying the paper ahead, and executes a butting operation by which the skew amount of the paper is reduced below the maximum skew-correction amount by making the paper butt to the stopped one resist conveying part 31, and thereafter executes the skew-correction process.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a transport device that transports paper. [Background technology]

[0002] 2. Description of the Related Art In a conveying device that conveys paper on which printing is performed by a printing device, skew correction of the paper is performed.

[0003] A technique for correcting skew of paper is disclosed in Patent Document 1. The image forming apparatus in Patent Document 1 includes two pairs of skew correction rollers that are spaced apart from each other in a direction perpendicular to the paper transport direction and can transport paper independently. In this image forming apparatus, the skew of paper is corrected by providing a difference in transport speed between the two pairs of skew correction rollers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5355021 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the technique of Patent Document 1, there is a risk that the skew correction will be insufficient if a sheet with a skew amount larger than the range that can be corrected by the two skew correction roller pairs is conveyed.

[0006] The present invention has been made in view of the above, and has an object to provide a transport device that can prevent insufficient correction of skew of paper. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the conveying device of the present invention comprises a pair of conveying units arranged at a distance from each other in a direction perpendicular to the conveying direction of the paper and each driven independently to convey the paper, a detection unit that detects the amount of skew of the paper, and a control unit that performs a skew correction process to correct the skew of the paper by controlling the paper conveying speed by one of the pair of conveying units, which is the one in which the paper is leading, to be slower than the paper conveying speed by the other conveying unit based on the amount of skew detected by the detection unit, and is characterized in that when the amount of skew detected by the detection unit is greater than a predetermined maximum skew correction amount in the skew correction process, the control unit temporarily stops one of the conveying units and causes the paper to strike the one of the stopped conveying units, thereby performing a striking operation to reduce the amount of skew of the paper to less than the maximum skew correction amount, and then performs the skew correction process. Effect of the Invention

[0008] According to the conveying device of the present invention, it is possible to prevent insufficient correction of skew of the paper. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a printing device according to an embodiment. [Diagram 2] 2 is a front view showing a schematic configuration of a registration transport unit and a skew detection unit of the printing apparatus shown in FIG. [Diagram 3] 2 is a plan view showing a schematic configuration of a registration transport unit and a skew detection unit of the printing apparatus shown in FIG. 1. [Figure 4] 2 is a control block diagram of the printing apparatus shown in FIG. 1. [Diagram 5] 6 is a timing chart for explaining the operation of the resist transport unit when performing skew correction processing. [Figure 6] 10 is a timing chart for explaining the operation of the resist transport unit when performing abutment operation and skew correction processing. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 10] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 11] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 12] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 13] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 14] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 15] 11A and 11B are diagrams illustrating an example of a transition of a paper transport state during double-sided printing. [Figure 16] 10 is a flowchart for explaining a paper transport operation during double-sided printing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0011] The following embodiments are examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0012] FIG. 1 is a schematic diagram of a printing device provided with a conveying device according to an embodiment of the present invention. FIG. 2 is a front view showing the schematic configuration of a registration conveying unit and a skew detection unit of the printing device shown in FIG. 1. FIG. 3 is a plan view showing the schematic configuration of a registration conveying unit and a skew detection unit of the printing device shown in FIG. 1. FIG. 4 is a control block diagram of the printing device shown in FIG. 1. In the following description, the direction perpendicular to the paper surface of FIG. 1 is defined as the front-rear direction, and the front direction of the paper surface is defined as the forward direction. Additionally, the top, bottom, left, and right directions of the paper surface in FIG. 1 are defined as the top, bottom, left, and right directions.

[0013] 1, the path indicated by the thick line is the transport path along which the print medium, paper P, is transported. Of the transport paths, the path indicated by the solid line is the normal path RC, the path indicated by the dashed line is the reversing path RR, the paths indicated by the dashed line are the paper discharge paths RD1 and RD2, and the path indicated by the two-dot chain line is the paper feed path RS. In the following description, upstream and downstream refer to upstream and downstream in the transport direction of the paper P transported along the transport path.

[0014] 1 to 4, the printing device 1 according to the present embodiment includes an external paper feed section 2, an internal paper feed section 3, a transport printing section 4, skew detection sections 5A, 5B, a face-up paper discharge section 6, an upper surface transport section 7, a face-down paper discharge section 8, an inversion section 9, a control section 10, and a housing 11 that houses or holds each section. The transport device includes registration transport sections 31A, 31B, which will be described later, a skew detection section 5A, an upper surface transport section 7, an inversion section 9, and a control section 10. The alphabetical suffixes in the reference numerals of the skew detection sections 5A, 5B, etc. may be omitted to generally indicate the components.

[0015] The external paper feed unit 2 feeds paper P, which is partially exposed outside the housing 11 and stacked thereon, to the transport and print unit 4. The external paper feed unit 2 includes an external paper feed tray 21, an external paper feed roller 22, and an external paper feed motor .

[0016] The external paper feed tray 21 is provided on which paper sheets P to be used for printing are stacked. The external paper feed tray 21 is installed with a part thereof exposed to the outside of the housing 11.

[0017] The external paper feed rollers 22 take out the paper sheets P stacked on the external paper feed tray 21 one by one, and transport the paper sheets P toward the transport printing unit 4 along the paper feed path RS.

[0018] The external paper feed motor 23 rotates the external paper feed roller 22. The external paper feed motor 23 also rotates the most downstream vertical transport roller 28 of a plurality of pairs of vertical transport rollers 28 described later. The external paper feed motor 23 is connected to the external paper feed roller 22 and the most downstream vertical transport roller 28 via a one-way clutch (not shown). As a result, the external paper feed roller 22 is rotated by the rotational drive of the external paper feed motor 23 in one direction, and the most downstream vertical transport roller 28 is rotated by the rotational drive of the external paper feed motor 23 in the other direction.

[0019] The internal paper feed unit 3 feeds paper P loaded inside the housing 11 to the transport printing unit 4. The internal paper feed unit 3 includes a plurality of internal paper feed trays 26, a plurality of internal paper feed rollers 27, a plurality of pairs of vertical transport rollers 28, and an internal paper feed motor 29.

[0020] The internal paper feed tray 26 is disposed inside the housing 11 and supports paper P to be used for printing.

[0021] The internal paper feed rollers 27 take out the paper P one by one from the internal paper feed tray 26 and send it out to the paper feed path RS.

[0022] The vertical transport rollers 28 transport the paper P taken out from the internal paper feed tray 26 toward registration transport units 31A and 31B, which will be described later. The vertical transport rollers 28 are disposed along the paper feed path RS.

[0023] The internal paper feed motor 29 rotates the internal paper feed rollers 27 and the vertical transport rollers 28. The internal paper feed motor 29 can be connected / disconnected to each of the internal paper feed rollers 27 and the vertical transport rollers 28 via a clutch (not shown). The clutch switches between the internal paper feed rollers 27 and the vertical transport rollers 28 that are rotated.

[0024] The transporting and printing unit 4 transports the paper P and prints on the paper P. The transporting and printing unit 4 includes registration transport units 31A and 31B (corresponding to a pair of transport units), registration motors 32A and 32B, a belt platen unit 33, a printing unit 34, and a paper sensor 35.

[0025] The registration conveying units 31A and 31B convey the paper P conveyed from any one of the external paper feeding unit 2, the internal paper feeding unit 3, and the inverting unit 9 toward the belt platen unit 33. The registration conveying units 31A and 31B also correct the skew of the paper P.

[0026] The registration transport sections 31A and 31B are disposed at the same position in the transport direction (left-right direction) of the paper P, and spaced apart from each other in the front-rear direction, which is a direction perpendicular to the transport direction. The registration transport sections 31A and 31B are disposed at equal distances to the front and rear from the center position of the paper P in the front-rear direction. The registration transport sections 31A and 31B are driven independently.

[0027] The registration conveying section 31 includes a pair of registration rollers 36 that nip and convey the paper P. The registration rollers 36 are fixed to a rotary shaft 36a that extends in the front-rear direction, and rotate about the rotary shaft 36a.

[0028] The registration motors 32A and 32B rotate the registration conveying sections 31A and 31B, respectively. Specifically, the registration motor 32 rotates one of a pair of registration rollers 36 of the registration conveying section 31. As a result, one of the pair of registration rollers 36 is rotationally driven by the registration motor 32, and the other registration roller 36 is rotated by the one registration roller 36.

[0029] The belt platen unit 33 conveys the paper P conveyed by the registration conveyance unit 31 while adsorbing and holding the paper P on the belt.

[0030] The printing unit 34 has an inkjet head (not shown), and ejects ink from the inkjet head onto the paper P transported by the belt platen unit 33 to print an image.

[0031] The paper sensor 35 detects the paper P transported to the registration transport units 31A, 31B from any one of the external paper feed unit 2, the internal paper feed unit 3, and the reversing unit 9. The paper sensor 35 is disposed at the upstream end of the normal path RC.

[0032] The skew detection unit 5A (corresponding to a detection unit) detects the amount of skew of the sheet P transported to the registration transport units 31A and 31B from any one of the external sheet feed unit 2, the internal sheet feed unit 3, and the inversion unit 9. The skew detection unit 5A includes sheet sensors 38A and 38B.

[0033] The paper sensors 38A and 38B are disposed at the same positions near the upstream sides of the registration conveying sections 31A and 31B in the conveying direction (left-right direction) of the paper P, and spaced apart from each other in the front-rear direction. The paper sensors 38A and 38B are disposed at equal distances to the front and rear from the center position of the paper P in the front-rear direction.

[0034] The skew detection unit 5B detects the amount of skew of the sheet P conveyed from the registration conveyance units 31A and 31B to the belt platen unit 33. The skew detection unit 5B includes sheet sensors 39A and 39B.

[0035] The paper sensors 39A and 39B are disposed at the same positions between the registration conveying units 31A and 31B and the belt platen unit 33 in the conveying direction (left-right direction) of the paper P, and are spaced apart from each other in the front-rear direction. The paper sensors 39A and 39B are disposed at the same positions as the paper sensors 38A and 38B in the front-rear direction, respectively.

[0036] The face-up paper ejection unit 6 ejects the printed paper P with the printed side (the side printed later in the case of double-sided printing) facing up. The face-up paper ejection unit 6 includes a switching unit 41, a solenoid 42, a pair of face-up paper ejection rollers 43, a face-up paper ejection motor 44, and a face-up paper ejection tray 45.

[0037] The switching unit 41 switches the transport path of the paper P between the normal path RC and the paper discharge path RD1. The switching unit 41 is disposed at a branch point between the normal path RC and the paper discharge path RD1.

[0038] The solenoid 42 drives the switching unit 41 .

[0039] The face-up paper discharge rollers 43 convey the paper P conveyed by the belt platen unit 33 and discharge the paper P onto a face-up paper discharge tray 45 .

[0040] The face-up paper discharge motor 44 drives the face-up paper discharge rollers 43 to rotate.

[0041] The face-up paper ejection tray 45 is a tray on which printed paper P conveyed by the face-up paper ejection rollers 43 is stacked.

[0042] The upper surface transport section 7 transports the paper P transported by the belt platen section 33 to the face-down paper discharge section 8 or the inversion section 9. The upper surface transport section 7 includes multiple pairs of upward transport rollers 51, an upward transport motor 52, multiple pairs of horizontal transport rollers 53, a horizontal transport motor 54, and paper sensors 55-57.

[0043] The upward transport rollers 51 transport the paper P transported by the belt platen unit 33 to the upper horizontal transport rollers 53. The upward transport rollers 51 are disposed along the upward portion of the middle stream area of ​​the normal route RC.

[0044] The lifting conveying motor 52 drives the pairs of lifting conveying rollers 51 to rotate.

[0045] The horizontal transport rollers 53 transport the paper P transported by the ascending transport rollers 51 to the face-down discharge section 8 or the reversing section 9. The most downstream horizontal transport rollers 53 are disposed in the upstream part of the reversing route RR. The other horizontal transport rollers 53 are disposed in the horizontal parts in the downstream area of ​​the normal route RC.

[0046] The horizontal conveying motor 54 drives the pairs of horizontal conveying rollers 53 to rotate.

[0047] The paper sensors 55 and 56 detect the paper P being transported in the upper surface transport section 7. The paper sensor 55 is disposed near the upstream side of the most upstream ascending transport roller 51. The paper sensor 56 is disposed near the downstream side of the most upstream horizontal transport roller 53. The paper sensor 57 is disposed near the upstream side of the most downstream horizontal transport roller 53.

[0048] The face-down paper discharge unit 8 discharges the printed paper P with the printed side (the side printed later in the case of double-sided printing) facing down. The face-down paper discharge unit 8 includes a switching unit 61, a solenoid 62, a pair of face-down paper discharge rollers 63, a face-down paper discharge motor 64, and a face-down paper discharge tray 65.

[0049] The switching unit 61 switches the transport path of the paper P between the paper discharge path RD2 and the reverse path RR. The switching unit 61 is disposed at a branch point between the paper discharge path RD2 and the reverse path RR.

[0050] The solenoid 62 drives the switching unit 61 .

[0051] The face-down paper discharge rollers 63 convey the paper P conveyed by the upper conveying section 7 and discharge it onto the face-down paper discharge tray 65 .

[0052] The face-down paper discharge motor 64 drives the face-down paper discharge rollers 63 to rotate.

[0053] The face-down paper ejection tray 65 is a tray on which printed paper P conveyed by the face-down paper ejection rollers 63 is stacked.

[0054] Inversion unit 9, during double-sided printing, inverts paper P that has been printed on one side and transports it to registration transport units 31A and 31B. Inversion unit 9 includes a pair of inversion rollers 71, an inversion motor 72, a pair of re-feed rollers 73 (corresponding to the re-feed transport unit), a re-feed motor 74, a switching gate 75, and paper sensors 76 and 77.

[0055] In addition, the upper transport section 7 and the reversing section 9 form a circulating transport section that, during double-sided printing, transports the paper P that has been transported from the registration transport sections 31A, 31B to the belt platen section 33 and printed on one side back to the registration transport sections 31A, 31B.

[0056] The reversing rollers 71 switch back the paper P conveyed by the horizontal conveying rollers 53 of the upper conveying section 7 and convey it to the paper re-feed rollers 73. The reversing rollers 71 are configured to be capable of rotating forward and backward in order to perform the switch back conveyance of the paper P.

[0057] The reversing motor 72 drives the reversing roller 71 to rotate.

[0058] The re-feed rollers 73 transport the sheet P transported by the reversing rollers 71 and deliver it to the registration transport sections 31A and 31B.

[0059] The re-feed motor 74 drives the re-feed roller 73 to rotate.

[0060] The switching gate 75 guides the paper P conveyed by the horizontal conveyance rollers 53 to the inversion rollers 71. The switching gate 75 also guides the paper P switched back by the inversion rollers 71 to the re-feed rollers 73.

[0061] The paper sensors 76 and 77 detect the paper P transported along the reversing path RR. The paper sensor 76 is disposed near the downstream side of the reversing rollers 71 in the transport direction of the paper P before being reversed. The paper sensor 77 is disposed near the downstream side of the re-feed rollers 73.

[0062] The control unit 10 controls the operation of each part of the printing device 1. The control unit 10 includes a CPU, a RAM, a ROM, a hard disk, and the like.

[0063] Specifically, the control unit 10 controls the feeding of paper P from the external paper feed unit 2 or the internal paper feed unit 3 to the transporting and printing unit 4, and the transporting and printing unit 4 to print on the paper P. During single-sided printing, the control unit 10 controls the ejection of the single-sided printed paper P by the face-up paper ejection unit 6 or the face-down paper ejection unit 8. During double-sided printing, the control unit 10 controls the reversing unit 9 to feed the single-sided printed paper P again to the transporting and printing unit 4, the transporting and printing unit 4 to print on the unprinted side of the paper P, and the ejection of the double-sided printed paper P by the face-up paper ejection unit 6 or the face-down paper ejection unit 8.

[0064] Furthermore, the control unit 10 executes a skew correction process by the registration conveying units 31A and 31B when feeding the paper P from the external paper feeding unit 2 or the internal paper feeding unit 3 to the conveying and printing unit 4 and when re-feeding the paper P to the conveying and printing unit 4 by the reversing unit 9. Specifically, the control unit 10 executes a skew correction process to correct the skew of the paper P by controlling the conveying speed of the paper P by one of the registration conveying units 31A and 31B on which the paper P is leading, to be slower than the conveying speed of the paper P by the other registration conveying unit 31, based on the amount of skew of the paper P detected by the skew detection unit 5A.

[0065] At this time, if the skew amount of paper P detected by the skew detection unit 5A is greater than the predetermined maximum skew correction amount in the above-mentioned skew correction process, the control unit 10 temporarily stops one of the registration conveying units 31 on the side where the paper P is leading, and causes the paper P to abut against the stopped registration conveying unit 31, thereby performing a collision operation to reduce the skew amount of the paper P to below the maximum skew correction amount, and then performs the above-mentioned skew correction process.

[0066] Here, the maximum skew correction amount is set as the maximum amount of skew that can be corrected in the skew correction process before the paper P reaches the belt platen unit 33. The maximum skew correction amount is set according to the distance between the registration conveying units 31A, 31B and the belt platen unit 33, and the conveying speed of the paper P by the registration conveying units 31A, 31B.

[0067] Next, the operation of the printer 1 during printing will be described.

[0068] In the case of single-sided printing, the control unit 10 controls so that unprinted paper P is fed from the external paper feed unit 2 or the internal paper feed unit 3 to the transport and print unit 4 in sequence.

[0069] The fed paper P is transported by the registration transport units 31A and 31B to the belt platen unit 33. While being transported by the belt platen unit 33, the paper P is printed by the printing unit .

[0070] When the discharge destination is the face-up discharge tray 45, the paper P printed on one side is guided from the normal route RC to the discharge route RD1 by the switching unit 41 and discharged onto the face-up discharge tray 45 by the face-up discharge rollers 43.

[0071] When the discharge destination is the face-down discharge tray 65, the paper P printed on one side is transported from the belt platen unit 33 to the upper transport unit 7, where it is transported by the upward transport rollers 51 and the horizontal transport rollers 53. The paper P is then guided by the switching unit 61 to the discharge path RD2, and discharged to the face-down discharge tray 65 by the face-down discharge rollers 63.

[0072] In double-sided printing, unprinted paper P fed in sequence from the external paper feed unit 2 or the internal paper feed unit 3 is printed on by the printing unit 34 while being transported by the belt platen unit 33, in the same manner as in single-sided printing. After single-sided printing, the paper P is transported from the belt platen unit 33 to the upper surface transport unit 7, where it is transported by the upward transport rollers 51 and horizontal transport rollers 53. The paper P is then guided by the switching unit 61 to the reversing route RR.

[0073] The paper P guided to the reversing path RR is guided by a switching gate 75 to reversing rollers 71 in the reversing unit 9, and is switched back by the reversing rollers 71. The paper P is then guided by the switching gate 75 to re-feed rollers 73, and is refed by the re-feed rollers 73 to the transporting and printing unit 4. The refed paper P is transported to the belt platen unit 33 by the registration transport units 31A and 31B in the transporting and printing unit 4.

[0074] After single-sided printing, the paper P is inverted by the inverting unit 9 and sent to the belt platen unit 33 with the unprinted side facing up. Then, while the paper P is being transported by the belt platen unit 33, the unprinted side is printed by the printing unit 34. The paper P that has been printed on both sides is discharged to the face-up paper output tray 45 or the face-down paper output tray 65, similar to the case of single-sided printing described above.

[0075] Next, the skew correction process performed by the registration transport units 31A and 31B during the above-mentioned printing operation will be described.

[0076] First, the operation of the registration transport sections 31A and 31B when performing the skew correction process in the case where the skew amount of the sheet P that arrives at the registration transport sections 31A and 31B is equal to or less than the maximum skew correction amount will be described with reference to the timing chart of FIG.

[0077] Here, the registration transport sections 31A and 31B are driven to transport the paper P at a transport speed V1. The paper P is transported to the registration transport sections 31A and 31B at the transport speed V1.

[0078] When paper P is transported from either external paper feed unit 2, internal paper feed unit 3, or inversion unit 9 toward registration transport units 31A, 31B, the leading edge of the paper P is detected by paper sensors 38A, 38B of skew detection unit 5A.

[0079] In the example of Fig. 5, after the leading edge of the paper P is detected by the paper sensor 38A at time t1, the leading edge of the paper P is detected by the paper sensor 38B at time t2. That is, in the example of Fig. 5, the paper P is skewed so that the front side (the paper sensor 38A side) leads.

[0080] The control unit 10 calculates the amount of skew of the paper P that arrives at the registration conveyance units 31A and 31B (the amount of skew detected by the skew detection unit 5A) based on the timing difference between the detection timings of the leading edge of the paper P by the paper sensors 38A and 38B. Next, the control unit 10 judges whether the calculated amount of skew is equal to or less than the maximum amount of skew correction. In the example of FIG. 5, it is assumed that the amount of skew detected by the skew detection unit 5A is equal to or less than the maximum amount of skew correction.

[0081] Furthermore, the control unit 10 calculates a skew correction speed V2 based on the calculated skew amount. The skew correction speed V2 is calculated so that the skew amount of the paper P becomes zero by the time the paper P reaches the belt platen unit 33 by decelerating the registration conveying unit 31 on the side where the paper P is leading from the conveying speed V1 to the skew correction speed V2 for a predetermined skew correction time. Here, the skew correction time is preset as the time of the skew correction process for completing the skew correction process by the time the leading edge of the paper P reaches the belt platen unit 33.

[0082] After the paper P reaches the registration transport units 31A and 31B, the control unit 10 decelerates the transport speed of the paper P by the registration transport unit 31 on the side where the paper P is leading from the transport speed V1 to the skew correction speed V2. After this, the control unit 10 controls the registration transport unit 31 on the side where the paper P is leading to start decelerating and then returns the transport speed from the skew correction speed V2 to the transport speed V1 after the above-mentioned skew correction time.

[0083] 5, the control unit 10 starts decelerating the registration transport unit 31A at time t3 after the paper P reaches the registration transport units 31A and 31B. After this, the control unit 10 controls the transport speed of the registration transport unit 31A to return from the skew correction speed V2 to the transport speed V1 at time t4, which is the skew correction time after time t3. This ends the skew correction process.

[0084] By this skew correction process, the resist conveying section 31 on the side where the paper P is leading (the front side in the example of Figure 5) slows down to the skew correction speed V2, so that the leading edge of the paper P becomes parallel in the front-to-back direction, and the skew of the paper P is corrected.

[0085] Here, while the paper P is being transported from the registration transport units 31A and 31B to the belt platen unit 33, the leading edge of the paper P is detected by the paper sensors 39A and 39B of the skew detection unit 5B. If the amount of skew calculated based on the timing difference between the detection timings of the leading edge of the paper P by the paper sensors 39A and 39B is greater than the theoretical value when the above-mentioned skew correction process is being performed, the control unit 10 adjusts the transport speed of the registration transport unit 31 on the side where the paper P is leading so that the amount of skew becomes zero by the time the paper P reaches the belt platen unit 33.

[0086] Next, the operation of the registration transport sections 31A and 31B when performing the abutment operation and the skew correction process when the skew amount of the sheet P that arrives at the registration transport sections 31A and 31B is greater than the maximum skew correction amount will be described with reference to the timing chart of FIG.

[0087] In the example of Fig. 6, after the leading edge of the paper P is detected by the paper sensor 38A at time t11, the leading edge of the paper P is detected by the paper sensor 38B at time t12. That is, in the example of Fig. 6, similar to the example of Fig. 5 described above, the paper P is skewed so that the front side (the paper sensor 38A side) leads.

[0088] When the leading edge of the sheet P is detected by the sheet sensors 38A, 38B of the skew detection unit 5A, the control unit 10 calculates the amount of skew of the sheet P that arrives at the registration conveyance units 31A, 31B (the amount of skew detected by the skew detection unit 5A) based on the timing difference between the detection timings of the leading edge of the sheet P by the sheet sensors 38A, 38B. Next, the control unit 10 judges whether the calculated amount of skew is equal to or smaller than the maximum amount of skew correction. In the example of FIG. 6, it is assumed that the amount of skew detected by the skew detection unit 5A is greater than the maximum amount of skew correction.

[0089] In this case, the control unit 10 stops the registration conveying unit 31 on the side where the paper P is leading before the paper P reaches the registration conveying units 31A and 31B. After this, the leading end of the paper P hits the registration conveying unit 31 and stops. Since the lagging side of the paper P does not stop, the amount of skew of the paper P is reduced.

[0090] In the example of Fig. 6, the control unit 10 stops the registration transport unit 31A at time t13 before the sheet P reaches the registration transport units 31A and 31B. After that, as shown in Fig. 7, the leading edge of the front side of the sheet P hits the registration transport unit 31A and stops. Since the rear side of the sheet P does not stop, the amount of skew of the sheet P is reduced.

[0091] Then, when the skew amount of the paper P decreases to the maximum skew correction amount or less, the control unit 10 starts driving the registration transport unit 31 on the side where the paper P is leading. In the example of Fig. 6, when the skew amount of the paper P decreases to the maximum skew correction amount or less, the control unit 10 starts driving the registration transport unit 31A at transport speed V1 at time t14, as shown in Fig. 8.

[0092] Furthermore, the control unit 10 calculates the skew correction speed V2 based on the skew amount of the paper P at the time when the driving of the registration transport unit 31 on the leading side of the paper P is started. The skew amount of the paper P at the time when the driving of the registration transport unit 31 on the leading side of the paper P is started can be calculated by subtracting the reduction in the skew amount corresponding to the time during which the leading edge of the paper P on the leading side hits the registration transport unit 31 and stops, from the skew amount detected by the skew detection unit 5A.

[0093] Here, the control unit 10 starts driving the registration transport unit 31 on the side where the paper P is leading before the skew amount of the paper P becomes zero. For example, the control unit 10 starts driving the registration transport unit 31 on the side where the paper P is leading at the timing when the skew amount of the paper P becomes the maximum skew correction amount. This reduces the time that the paper P is stopped, thereby preventing a decrease in productivity.

[0094] The control for temporarily stopping the registration transport unit 31 on the side where the paper P is leading as described above may be trapezoidal control rather than the on / off control as shown in FIG.

[0095] After starting the drive of the registration transport section 31 on the side where the paper P is leading, the control section 10 decelerates the transport speed of the paper P by the registration transport section 31 on the side where the paper P is leading from transport speed V1 to skew correction speed V2, similar to the skew correction process when the skew amount of the paper P arriving at the registration transport sections 31A and 31B described above is equal to or less than the maximum skew correction amount. After this, the control section 10 controls the registration transport section 31 on the side where the paper P is leading to start decelerating and then returns the transport speed from the skew correction speed V2 to the transport speed V1 after the above-mentioned skew correction time.

[0096] 6, the control unit 10 starts decelerating the resist transport unit 31A at time t15 after the drive of the resist transport unit 31A is started. After this, the control unit 10 controls the transport speed of the resist transport unit 31A to return from the skew correction speed V2 to the transport speed V1 at time t16, which is the skew correction time after time t15. This ends the skew correction process.

[0097] Here, similar to the skew correction process when the skew amount of the paper P reaching the aforementioned registration conveying sections 31A, 31B is less than the maximum skew correction amount, if the timing difference between the detection timing of the leading edge of the paper P by the paper sensors 39A, 39B of the skew detection section 5B is greater than the theoretical value when the skew correction process is being performed, the control section 10 adjusts the conveying speed of the registration conveying section 31 on the side where the paper P is leading so that the skew amount becomes zero by the time the paper P reaches the belt platen section 33.

[0098] As described above, if the skew amount of the paper P arriving at the registration conveying sections 31A, 31B is greater than the maximum skew correction amount, the control section 10 temporarily stops one of the registration conveying sections 31 on the side where the paper P is leading, and causes the paper P to abut against the stopped registration conveying section 31, thereby performing abutment operation to reduce the skew amount of the paper P to below the maximum skew correction amount, and then performs skew correction processing.

[0099] Here, when performing the above-mentioned abutting operation during double-sided printing, the control unit 10 temporarily suspends, after the abutting operation, the transport of the paper P being transported in the upper surface transport unit 7 and the inversion unit 9 at the time of the abutting operation, other than the paper that was abutted against one of the registration transport units 31 during the abutting operation. Here, the paper P being transported in the upper surface transport unit 7 and the inversion unit 9 at the time the abutting operation is performed is the paper P that has passed through the belt platen unit 33 at that time, and is in the upper surface transport unit 7 and the inversion unit 9.

[0100] In addition, when the control unit 10 temporarily stops the re-feed roller 73 to temporarily stop the paper P being transported in the upper conveying unit 7 and the inversion unit 9, the control unit 10 abuts the paper P to be temporarily stopped against the re-feed roller 73 to correct the skew of the paper P.

[0101] In the example of FIG. 6, control unit 10 stops horizontal conveyance rollers 53 and re-feed rollers 73 at time t17 after performing the abutting operation by temporarily stopping registration conveyance unit 31A.

[0102] 6, the sheet P that is abutted against one of the registration conveying units 31 during the abutting operation is not one that has been re-fed by the inverting unit 9, but one that has been fed from the external sheet feeding unit 2 or the internal sheet feeding unit 3. Also, in the example of Fig. 6, at the time when the abutting operation is performed, there is a sheet P being conveyed in each of the upper conveying unit 7 and the inverting unit 9. Also, the conveying speed of the sheet P by the horizontal conveying rollers 53 and the re-feeding rollers 73 is V1.

[0103] At time t18, which is the same time as the temporary suspension time of the registration conveying unit 31A from time t17 when the horizontal conveying roller 53 and the re-feed roller 73 are stopped, the control unit 10 starts driving the horizontal conveying roller 53 and the re-feed roller 73.

[0104] During the period in which re-feed roller 73 is temporarily stopped, control unit 10 causes reversing roller 71 to abut sheet P temporarily stopped by re-feed roller 73 against re-feed roller 73, thereby correcting skew of sheet P. In other words, control unit 10 controls the timing of temporarily stopping horizontal transport roller 53 and re-feed roller 73 so that sheet P located furthest downstream on the upstream side of re-feed roller 73 at the time of the abutting operation can be abutted against stopped re-feed roller 73 to correct skew of sheet P.

[0105] The control for temporarily stopping horizontal conveyance rollers 53 and sheet re-feed rollers 73 may be trapezoidal control, similar to the control for temporarily stopping registration conveyance section 31.

[0106] As described above, the reason why the sheet P being transported in the upper transport section 7 and the reversing section 9 is temporarily stopped when the abutting operation is performed is to prevent the gap between the sheet P abutted against one of the registration transport sections 31 during the abutting operation and the succeeding sheet P from shrinking, causing transport failures such as collisions between the sheets P. Also, the sheet P is abutted against the re-feed roller 73 to correct skew, in order to reduce skew of the sheet P being re-fed to the registration transport sections 31A and 31B.

[0107] 6, if the sheet P abutted against one of the registration transport sections 31 in the abutting operation is one that has been re-fed by the reversing section 9, the sheet P abutted against one of the registration transport sections 31 at the time of the abutting operation is being nipped by the re-feed roller 73 and being transported. This sheet P abutted against one of the registration transport sections 31 is not included in the sheets P that are temporarily stopped after the abutting operation.

[0108] Also, in this case, instead of stopping the paper P that is most downstream on the upstream side of the re-feed roller 73 at the time of the abutting operation by abutting it against the temporarily stopped re-feed roller 73, the paper P can be temporarily stopped by temporarily stopping the reversing roller 71.

[0109] Next, an example of the transition of the transport state of the paper P during double-sided printing will be described.

[0110] Here, it is assumed that the external paper feed unit 2 feeds the paper P to the transfer and printing unit 4. It is also assumed that the face-up paper discharge unit 6 discharges the paper P that has been printed on both sides.

[0111] 9 to 11, the first to third sheets of paper P1 to P3 are sequentially fed to the transport and printing unit 4. Here, it is assumed that the amount of skew detected by the skew detection unit 5A when the paper P3 is transported from the external paper feed unit 2 to the registration transport units 31A and 31B is greater than the maximum skew correction amount.

[0112] In this case, the registration transport units 31A and 31B execute the above-mentioned abutting operation and skew correction process. At the time when the abutting operation is executed during feeding of the sheet P3 shown in FIG. 11, the sheet P1 is being transported by the inversion unit 9, and the sheet P2 is being transported by the upper surface transport unit 7.

[0113] 12, after the abutting operation when feeding paper P3, horizontal conveyance rollers 53 and re-feed rollers 73 are temporarily stopped, so that paper P1 and P2 are temporarily stopped at inversion section 9 and upper conveyance section 7, respectively. Here, paper P1 is abutted against stopped re-feed rollers 73 and temporarily stopped. This corrects the skew of paper P1.

[0114] Thereafter, as shown in FIG. 13, the conveyance of the papers P1 and P2 is resumed, and the papers P1 and P2 which have been printed on both sides are sequentially discharged by the face-up paper discharge section 6 as shown in FIGS.

[0115] Also, as shown in FIG. 15, between the time when paper P2 is re-fed to the transporting and printing unit 4 by the inversion unit 9 and the time when paper P3 is re-fed, a fourth sheet of paper P4 is fed from the external paper feed unit 2 to the transporting and printing unit 4.

[0116] Thereafter, sheet P3 is re-fed, and then the fifth sheet P is fed from external sheet feeder 2. Thereafter, re-feeding from reversing section 9 and feeding from external sheet feeder 2 are alternately repeated.

[0117] Here, when the sheet P1 is re-fed as shown in FIG. 13, if the amount of skew detected by the skew detection unit 5A is greater than the maximum amount of skew correction, the registration transport units 31A and 31B execute the above-mentioned abutment operation and skew correction process.

[0118] In this case, as paper P1 is temporarily stopped during the abutting operation, paper P2 is temporarily stopped at the reversing unit 9. Paper P3 being transported by the belt platen unit 33 is not temporarily stopped because the belt platen unit 33 is not stopped during the printing operation. For this reason, the distance between the papers P2 and P3 is reduced, and there is a risk that, for example, paper P3 will collide with paper P2 while paper P2 is being switched back and transported by the reversing rollers 71.

[0119] Therefore, if the distance between sheets P2 and P3 is equal to or less than a predetermined threshold value that is smaller than a prescribed value, the control unit 10 determines this to be an error and stops the transport of sheet P in the printing device 1. Here, the distance between two sheets P transported in succession during double-sided printing can be calculated based on the detection timing of each sheet P by the sheet sensors 35, 55-57, 76, and 77.

[0120] Next, the paper transport operation during double-sided printing will be described with reference to the flowchart in FIG.

[0121] In step S1 of FIG. 16, the control unit 10 determines whether the paper sensors 38A, 38B of the skew detection unit 5A have detected the paper P or not.

[0122] If it is determined that the paper sensors 38A, 38B of the skew detection unit 5A have detected the paper P (step S1: YES), in step S2, the control unit 10 calculates the amount of skew of the paper P detected by the skew detection unit 5A, and determines whether the calculated amount of skew is greater than the maximum skew correction amount.

[0123] When it is determined that the skew amount is greater than the maximum skew correction amount (step S2: YES), in step S3, the control unit 10 executes the above-mentioned abutment operation.

[0124] Next, in step S4, the control unit 10 executes the above-mentioned skew correction process.

[0125] Next, in step S5, the control unit 10 judges whether or not a sheet interval equal to or less than a threshold value has been detected from the sheet interval between the sheets P being conveyed.

[0126] If it is determined that the paper gap is equal to or smaller than the threshold value (step S5: YES), then in step S6, the control unit 10 stops the transport of the paper P in the printing device 1 as an error.

[0127] Here, as described above, when performing abutting operation during double-sided printing, the distance between two sheets of paper P being transported in succession may decrease, possibly resulting in collision between the sheets of paper P. For this reason, when a distance between the sheets that is equal to or less than the threshold is detected (step S5: YES), an error is detected and the transport of the sheets of paper P is stopped (step S6).

[0128] When it is determined that the sheet gap equal to or smaller than the threshold value has not been detected (step S5: NO), the control unit 10 returns to step S1.

[0129] In step S2, when it is determined that the skew amount is equal to or less than the maximum skew correction amount (step S2: NO), in step S7, the control unit 10 executes a skew correction process. After that, the control unit 10 returns to step S1.

[0130] If it is determined in step S1 that the paper sensors 38A, 38B of the skew detection unit 5A have not detected the paper P (step S1: NO), then in step S8, the control unit 10 determines whether or not re-feeding of the last paper P in the ongoing double-sided printing operation to the transport printing unit 4 has been completed. If it is determined that re-feeding of the last paper P has not been completed (step S8: NO), the control unit 10 returns to step S1.

[0131] When the control unit 10 determines that re-feeding of the last sheet P has been completed (step S8: YES), the series of operations ends.

[0132] As described above, in the printing device 1, when the skew amount of the paper P detected by the skew detection unit 5A is greater than the maximum skew correction amount in the skew correction process, the control unit 10 temporarily stops one of the registration transport units 31 on the side where the paper P is leading, and executes abutment operation to reduce the skew amount of the paper P to the maximum skew correction amount or less by abutting the paper P against the stopped registration transport unit 31, and then executes the skew correction process. As a result, even if the skew amount of the paper P is greater than the maximum skew correction amount in the skew correction process, the abutment operation is performed to reduce the skew amount to the maximum skew correction amount or less, thereby preventing insufficient skew correction of the paper P.

[0133] Furthermore, when the control unit 10 executes the abutting operation, it temporarily suspends the conveyance of the sheets P being conveyed in the upper conveying unit 7 and the reversing unit 9 at the time of the abutting operation, other than the sheet P abutted against one of the registration conveying units 31 during the abutting operation, after the abutting operation. This makes it possible to prevent conveyance failures such as collisions between sheets P caused by a reduction in the sheet gap, even when the abutting operation is executed.

[0134] Furthermore, when the control unit 10 temporarily stops the re-feed rollers 73 in order to temporarily stop the sheet P being transported in the upper transport unit 7 and the inversion unit 9 at the time when the abutting operation is performed, the control unit 10 abuts the sheet P to be temporarily stopped against the stopped re-feed rollers 73 to correct the skew of the sheet P. This can reduce the skew of the sheet P re-fed to the registration transport units 31A and 31B, thereby reducing the frequency of the abutting operation.

[0135] In the above-described embodiment, in the skew correction process, the conveying speed of the paper P by one of the registration conveying sections 31 on the side where the paper P is ahead is slowed down to be slower than the conveying speed of the paper P by the other registration conveying section 31. However, this is not limited to the above, and for example, the conveying speed of the paper P by the registration conveying section 31 on the side where the paper P is behind may be accelerated to make the conveying speed of the paper P by one of the registration conveying sections 31 on the side where the paper P is ahead slower than the conveying speed of the paper P by the other registration conveying section 31.

[0136] The present invention is not limited to the above-described embodiment, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[0137] [Note] This application discloses the following inventions.

[0138] (Appendix 1) a pair of transport units arranged apart from each other in a direction perpendicular to the sheet transport direction and independently driven to transport the sheet; a detection unit for detecting an amount of skew of the paper; a control unit that executes a skew correction process to correct skew of the paper by controlling a paper conveying speed by one of the pair of conveying units, which is a conveying unit on the side where the paper is leading, to be slower than a paper conveying speed by the other conveying unit, based on the amount of skew detected by the detection unit; The control unit, when the amount of skew detected by the detection unit is greater than a predetermined maximum skew correction amount in the skew correction process, temporarily stops one of the transport units and causes the paper to strike the one of the stopped transport units, thereby performing a striking operation to reduce the amount of skew of the paper to below the maximum skew correction amount, and then performs the skew correction process.

[0139] (Appendix 2) a circulating conveying unit that conveys the paper conveyed by the pair of conveying units back to the pair of conveying units, The control unit of the conveying device described in Appendix 1 is characterized in that, when the abutting operation is performed, the control unit temporarily suspends the transport of sheets of paper being transported by the circulating transport unit at the time the abutting operation is performed, other than the sheet of paper that was abutted against one of the transport units in the abutting operation, after the abutting operation.

[0140] (Appendix 3) the circulating conveyance unit has a paper re-feed conveyance unit which transfers the paper to the pair of conveyance units, The control unit is characterized in that when the control unit temporarily stops the re-feeding transport unit in order to temporarily stop a sheet of paper being transported by the circulating transport unit at the time the abutting operation is performed, other than the sheet of paper that has been abutted against one of the transport units during the abutting operation, the control unit abuts the sheet of paper to be temporarily stopped against the stopped re-feeding transport unit to correct the skew of the sheet of paper. [Explanation of symbols]

[0141] 1 Printing device 2 External paper feed section 3 Internal paper feed section 4. Transport and printing section 5A, 5B Oblique detection section 6 Face-up paper ejection section 7 Upper conveyor section 8 Face-down paper output section 9. Reversal section 10 Control section 31, 31A, 31B Resist transport section 32A, 32B Register motor 33 Belt platen part 34 Printing Department 51 Ascending conveying roller 52 Lifting conveyor motor 53 Horizontal conveyor roller 54 Horizontal conveying motor 71 Reversing roller 72 Reverse Motor 73 Refeed roller 74 Refeed motor

Claims

1. a pair of transport units arranged apart from each other in a direction perpendicular to the sheet transport direction and independently driven to transport the sheet; a detection unit for detecting an amount of skew of the paper; a control unit that executes a skew correction process to correct skew of the paper by controlling a paper conveying speed by one of the pair of conveying units, which is a conveying unit on the side where the paper is leading, to be slower than a paper conveying speed by the other conveying unit, based on the amount of skew detected by the detection unit; The control unit, when the amount of skew detected by the detection unit is greater than a predetermined maximum skew correction amount in the skew correction process, temporarily stops one of the transport units and causes the paper to strike the one of the stopped transport units, thereby performing a striking operation to reduce the amount of skew of the paper to below the maximum skew correction amount, and then performs the skew correction process.

2. a circulating conveying unit that conveys the paper conveyed by the pair of conveying units back to the pair of conveying units, The conveying device according to claim 1, characterized in that, when the control unit executes the abutment operation, it temporarily suspends the transport of sheets of paper being transported by the circulating transport unit at the time the abutment operation is executed, other than the sheet of paper that was abutted against one of the transport units during the abutment operation, after the abutment operation.

3. the circulating conveyance unit has a paper re-feed conveyance unit which transfers the paper to the pair of conveyance units, The conveying device described in claim 2, characterized in that when the control unit temporarily stops the re-feeding conveying unit in order to temporarily stop a sheet of paper being conveyed by the circulating conveying unit at the time the abutting operation is performed, other than the sheet of paper that has been abutted against one of the conveying units during the abutting operation, the control unit abuts the sheet of paper to be paused against the stopped re-feeding conveying unit to correct the skew of the sheet of paper.

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