Paper conveying device

Abstract

The sheet conveying apparatus includes: a skew correction unit having a plurality of roller pairs arranged in parallel in a width direction of a sheet and sandwiching and conveying the sheet, the skew correction unit correcting skew of the sheet by relatively changing a rotational speed of each of the roller pairs; a skew detection unit that is provided downstream of the skew correction unit in the conveyance direction of the sheet and detects a front end and a rear end of the sheet; a skew amount calculation unit that calculates a skew amount of the sheet on the basis of a detection result detected by the skew detection unit; a roller skew amount calculation unit that calculates a roller skew amount generated when the paper passes through the skew correction unit, based on the skew amounts of the front end side and the rear end side of the paper calculated by the skew amount calculation unit, when the roller pair conveys the paper at a predetermined speed; and a correction amount calculation unit that calculates a correction amount of the skew correction unit based on the skew amount of the front end side of the paper calculated by the skew amount calculation unit and the roller skew amount calculated by the roller skew amount calculation unit.

Description

Technical Field

[0001] The invention relates to a paper conveying device for conveying paper. Background Art

[0002] Skew correction of paper is performed in a conveying device that conveys paper printed by a printing device.

[0003] As a technique for correcting the skew of a sheet, there is a technique disclosed in Patent Document 1. Patent Document 1 proposes a sheet conveying device that corrects the skew of a sheet while forming a loop on the sheet using a pair of skew correction rollers and a conveying roller for loop formation located upstream of the skew correction rollers. The sheet conveying device includes an upstream skew detection sensor and a downstream skew detection sensor that are respectively provided on the upstream and downstream sides of the skew correction rollers, and determines a correction amount based on a skew amount of the sheet detected by the upstream skew detection sensor, and adjusts the correction amount based on a relationship between the skew amounts before and after correction that is pre-calculated by the downstream skew detection sensor.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-120579 Summary of the invention

[0007] In the paper conveying device of Patent Document 1, skew detection sensors arranged on the upstream and downstream sides of the skew correction roller are used to grasp the relationship before and after skew correction (the amount of pressure applied to the looped sheet), and skew correction is performed taking the pressure amount into consideration in the next conveyance.

[0008] Therefore, when the sheet enters the skew correction roller, sometimes the front end of the sheet does not enter the clamping point but starts to clamp after colliding with the roller, so that the degree of skew changes randomly. There is a possibility that the sheet skew amount detected by the upstream skew detection sensor will change at the moment when the skew correction roller clamps the sheet and starts to convey it.

[0009] Therefore, in the method of grasping the relationship before and after skew correction using the upstream skew detection sensor and the downstream skew detection sensor disclosed in Patent Document 1, it is difficult to accurately grasp the roller deflection amount of the skew correction roller and appropriately perform skew correction.

[0010] An object of the present invention is to provide a paper conveying device capable of correcting the skew of a conveyed paper with high accuracy.

[0011] The paper conveying device of the technical solution of the present invention comprises: a skew correction unit having a roller pair, wherein a plurality of roller pairs are arranged in parallel in the width direction of the paper, clamping and conveying the paper, and correcting the skew of the paper by relatively changing the rotation speed of each of the roller pairs; a skew detection unit, which is arranged at a position downstream of the conveying direction of the conveyed paper than the skew correction unit, and detects the front end and the rear end of the paper; a skew amount calculation unit, which calculates the skew amount of the conveyed paper based on the detection result detected by the skew detection unit; A roller deflection amount calculation unit, which calculates the roller deflection amount generated when the paper passes through the skew correction unit based on the skew amounts on the front end side and the rear end side of the paper calculated by the skew amount calculation unit when the roller pair of the skew correction unit conveys the paper at a predetermined speed; and a correction amount calculation unit, which calculates the correction amount of the skew correction unit based on the skew amount on the front end side of the paper calculated by the skew amount calculation unit and the roller deflection amount calculated by the roller deflection amount calculation unit.

[0012] According to the above configuration, it is possible to correct the skew of the paper being transported with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the structure of a printing device to which a paper conveying device according to an embodiment of the present invention is applied.

[0014] Figure 2 This is an enlarged view of the periphery of a paper feed unit of a printing device according to an embodiment of the present invention.

[0015] Figure 3 This is a plan view of the periphery of a paper feed unit of a printing device according to an embodiment of the present invention.

[0016] Figure 4 This is a functional configuration diagram of a printing device to which a paper conveying device according to an embodiment of the present invention is applied.

[0017] Figure 5A and Figure 5B It is an explanatory diagram for explaining the calculation process of the roller deflection amount of the printing device according to one embodiment of the present invention.

[0018] Fig. 6A and Figure 6B It is an explanatory diagram for explaining the calculation process of the roller deflection amount of the printing device according to one embodiment of the present invention.

[0019] Fig. 7A and Figure 7B It is an explanatory diagram for explaining the skew correction process of the printing apparatus according to one embodiment of the present invention.

[0020] Fig. 8A and Figure 8B It is an explanatory diagram for explaining the skew correction process of the printing apparatus according to one embodiment of the present invention.

[0021] Fig. 9 It is an explanatory diagram for explaining the skew correction process of the printing apparatus according to one embodiment of the present invention.

[0022] Fig.10 It is an explanatory diagram for explaining calculation of the roller deflection amount.

[0023] Fig.11 It is an explanatory diagram for explaining the calculation of the conveying speed V2.

[0024] Fig.12 This is a flowchart showing the processing contents when the reversing unit of the printing apparatus according to one embodiment of the present invention is used. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings, the same or equivalent parts and components are denoted by the same or equivalent reference numerals.

[0026] The embodiments described below are examples of devices and the like for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the material, shape, structure, arrangement, etc. of each component to the following forms. The technical concept of the present invention can be modified in various ways within the scope of the claims.

[0027] Figure 1 is a schematic structural diagram of a printing device of a paper conveying device to which one embodiment of the present invention is applied, Figure 2 is an enlarged view of the periphery of a paper feed unit of a printing device according to an embodiment of the present invention. Figure 3 is a plan view of the periphery of a paper feed unit of a printing device according to an embodiment of the present invention, Figure 4 FIG. 1 is a functional block diagram of a printing device of a paper conveying device to which an embodiment of the present invention is applied. Figure 1 The direction perpendicular to the paper surface is set as the front-back direction, and the paper surface direction is set as the front. Figure 1 The up, down, left, and right directions of the paper are defined as the up, down, left, and right directions. The direction from left to right is the paper feeding direction.

[0028] exist Figure 1 The path shown by the middle bold line is a conveying path for conveying paper P as a printing medium. In the conveying path, the path shown by the solid line is the normal path RC, the path shown by the single-dot chain line is the reversing path RR, the path shown by the dotted line is the paper discharge path RD, and the path shown by the double-dot chain line is the paper supply path RS. In the following description, upstream and downstream mean the upstream and downstream of the conveying path.

[0029] As Figure 1 shown in Figure 1 , the printing apparatus 1 according to an embodiment of the present invention includes a paper feeding unit 2, a printing unit 3, a paper discharging unit 4, a control unit 6, and a housing 7 that houses or holds each part.

[0030] The paper feeding unit 2 supplies paper P to the printing unit 3. The paper feeding unit 2 is arranged on the most upstream side of the conveyance path. The paper feeding unit 2 includes a paper feeding tray 11, a paper feeding roller 12, a collating plate (Japanese: サバキ板) 12b2, positioning conveyance units 26A, 26B (skew correction units), a paper feeding detection unit 27, skew detection units 28A, 28B (skew detection units), and the control unit 6. In addition, the added letters of the reference numerals such as the positioning conveyance units 26A, 26B may sometimes be omitted and collectively expressed.

[0031] The paper feeding tray 11 stacks the paper P used for printing by a printing unit (not shown) at the paper feeding destination.

[0032] The paper feeding roller 12 includes a scraping roller 12a and a pickup roller 12b.

[0033] The scraping roller 12a is pressed against the uppermost (uppermost side) paper P among the papers P stacked on the paper feeding table 2, and the paper P is taken out by frictional force and fed along the paper feeding path RS to the pickup roller 12b. The scraping roller 12a is fixed to a rotary shaft 12a1 extending in the front-rear direction and rotates about the rotary shaft 12a1.

[0034] The pickup roller 12b conveys the paper P sent by the scraping roller 12a along the paper feeding path RS toward the positioning conveyance units 26A, 26B. The pickup roller 12b is arranged adjacent to the scraping roller 12a on the downstream side thereof. The pickup roller 12b is fixed to a rotary shaft 12b1 extending in the front-rear direction and rotates about the rotary shaft 12b1.

[0035] The collating plate 12b2 is a member that collates the paper P between the collating plate 12b2 and the pickup roller 12b so that the paper P can be conveyed one by one by the pickup roller 12b. The collating plate 12b2 is arranged on the lower side of the pickup roller 12b and abuts against the pickup roller 12b.

[0036] The paper feeding detection unit 27 detects the paper P conveyed along the paper feeding path RS by the pickup roller 12b.

[0037] The positioning conveyance units 26A, 26B convey the paper P conveyed from the pickup roller 12b toward the printing unit 3. In addition, the positioning conveyance units 26A, 26B correct the skew of the paper P.

[0038] The positioning conveying parts 26A and 26B are arranged at the same positions on the downstream side of the pickup roller 12b in the conveying direction (left-right direction) of the paper P, separated from each other in the front-back direction (width direction of the paper P) which is a direction orthogonal to the conveying direction. The positioning conveying parts 26A and 26B are arranged at the same distances from the center position of the paper P to the front and rear sides in the front-back direction. The positioning conveying parts 26A and 26B can correct the skew of the conveyed paper P by being driven independently by motors not shown.

[0039] Each of the positioning and conveying sections 26A and 26B includes a pair of positioning rollers 26a and 26a for sandwiching and conveying the paper P. The positioning rollers 26a and 26a are fixed to rotation shafts 26a1 and 26b1 extending in the front-rear direction, respectively, and rotate around the rotation shafts 26a1 and 26b1, respectively.

[0040] The skew detection units 28A and 28B detect the degree of skew of the paper P. The skew detection units 28A and 28B are each composed of an optical sensor having a light emitting element and a light receiving element, for example, and detect the leading end and the trailing end of the paper P being transported.

[0041] The skew detection units 28A and 28B are arranged to be separated from each other in the front-to-back direction on the downstream side (right side) of the positioning and conveying units 26A and 26B in the conveying direction (left-right direction) of the paper P. The skew detection units 28A and 28B are arranged to be separated from each other in the front-to-back direction by the same distance from the center position of the paper P to the front side and the rear side.

[0042] The printing section 3 prints while conveying the supplied paper P, and conveys the printed paper P to the paper discharge section 4. The printing section 3 includes a belt conveying section 22, an inkjet head section 23, an upper surface conveying section 24, and a reversing section 25 (reversing unit).

[0043] The belt transport unit 22 sucks and holds the paper P transported from the registration roller pair 26 on the belt and transports it to the upper transport unit 24. The belt transport unit 22 is arranged on the downstream side of the registration roller pair 26. The belt transport unit 22 is driven by a motor (not shown).

[0044] The inkjet head 23 includes a plurality of linear inkjet heads (not shown) in which a plurality of nozzles are arranged in a direction (front-rear direction) substantially perpendicular to the conveying direction of the paper P. The inkjet head 23 is disposed above the belt conveying unit 22. The inkjet head 23 ejects ink from the inkjet head onto the paper P conveyed by the belt conveying unit 22 to form an image.

[0045] The upper conveying unit 24 conveys the paper P conveyed from the belt conveying unit 22 from right to left in a U-turn. The upper conveying unit 24 includes a plurality of upper conveying roller pairs 29 and a plurality of motors (not shown) for driving the plurality of upper conveying roller pairs 29.

[0046] The upper conveying roller pair 29 sandwiches and conveys the paper P. The upper conveying roller pair 29 is disposed along a normal path RC between the belt conveying unit 22 and the reversing unit 25 .

[0047] The upper transport roller pair 29 includes a driving roller 29 a that is driven to rotate by a motor, and a driven roller 29 b that is disposed opposite to the driving roller 29 a with the normal path RC interposed therebetween.

[0048] The reversing unit 25 reverses the paper P printed on one side and conveys it to the positioning conveying units 26A and 26B. The reversing unit 25 includes a reversing roller pair 31, a switch roller pair 32, a re-feeding roller pair 33, a switching gate 34, a motor (not shown) for driving the reversing roller pair 31, a motor (not shown) for driving the switch roller pair 32, and a motor (not shown) for driving the re-feeding roller pair 33.

[0049] The reversing roller pair 31 conveys the paper P guided to the reversing path RR by the switching unit 36 ​​described later, while pinching the paper P, toward the switchback roller pair 32. The reversing roller pair 31 is arranged along the upstream region of the reversing path RR.

[0050] The reversing roller pair 31 includes a driving roller 31 a that is driven to rotate by a motor, and a driven roller 31 b that is provided to face the driving roller 31 a across the reversing path RR.

[0051] The switchback roller pair 32 switches the paper P fed by the reversing roller pair 31 and feeds it to the re-feeding roller pair 33. The switchback roller pair 32 is disposed between the reversing roller pair 31 and the re-feeding roller pair 33 along the reversing path RR. The switchback roller pair 32 switches the paper P forward and reversely.

[0052] The steering roller pair 32 includes a driving roller 32 a that is rotationally driven by a motor and a driven roller 32 b that is provided opposite to the driving roller 32 a with the reversing path RR interposed therebetween.

[0053] The re-feed roller pair 33 conveys the paper P turned back by the switchback roller pair 32 to the registration roller pair 26. The re-feed roller pair 33 is disposed between the switchback roller pair 32 and the registration roller pair 26 along the reverse path RR.

[0054] The re-feed roller pair 33 includes a driving roller 33 a that is driven to rotate by a motor and a driven roller 33 b that is disposed opposite to the driving roller 33 a with the reversing path RR interposed therebetween.

[0055] The switching gate 34 guides the paper P conveyed by the reverse roller pair 31 to the switchback roller pair 32 . The switching gate 34 also guides the paper P switched back by the switchback roller pair 32 to the re-feed roller pair 33 .

[0056] The paper discharge unit 4 discharges the printed paper P. The paper discharge unit 4 is disposed on the downstream side of the upper surface conveying unit 24. The paper discharge unit 4 includes a switching unit 36, a first paper discharge roller pair 37, and a paper discharge stage 39.

[0057] The switching unit 36 ​​switches the transport path of the paper P between the paper discharge path RD and the reversing path RR. The switching unit 36 ​​is disposed at a branch point between the paper discharge path RD and the reversing path RR.

[0058] The first paper discharge roller pair 37 discharges the paper P guided to the paper discharge path RD by the switching unit 36 ​​to the paper discharge stage 39 . The first paper discharge roller pair 37 is arranged on the downstream side of the switching unit 36 ​​.

[0059] The first paper discharge roller pair 37 includes a driving roller 37 a that is rotationally driven by a motor and a driven roller 37 b that is disposed opposite to the driving roller 37 a across the paper discharge path RD.

[0060] The paper discharge stage 39 stacks the paper sheets P discharged by the first paper discharge roller pair 37. The paper discharge stage 39 is disposed on the downstream side of the first paper discharge roller pair 37, and is inclined so as to become higher toward the downstream side (left side).

[0061] The control unit 6 includes a CPU, RAM, ROM, a hard disk, etc. The control unit 6 receives a print job from a computer connected via a network (not shown), and controls the operation of each unit of the printing device 1 based on the received print job.

[0062] The control section 6 functionally includes a skew amount calculation section 61 (skew amount calculation unit), a roller deflection amount calculation section 62 (roller deflection amount calculation unit), a roller deflection amount storage section 63 , a correction amount calculation section 64 (correction amount calculation unit), and a roller control section 65 .

[0063] The skew amount calculation unit 61 calculates at least one of the skew amount of the leading end side of the paper being transported and the skew amount of the trailing end side of the paper being transported based on the detection results of the skew detection units 28A and 28B.

[0064] When the respective positioning rollers 26a, 26a of the positioning conveying sections 26A, 26B convey the paper P at a predetermined speed, the roller skew amount calculation section 62 calculates the roller skew amount generated when the paper P passes through the positioning conveying sections 26A, 26B based on the skew amounts on the front and rear ends of the paper P calculated by the skew amount calculation section 61.

[0065] The roller deflection amount storage unit 63 stores the roller deflection amount calculated by the roller deflection amount calculation unit 62 .

[0066] The correction amount calculation unit 64 calculates the correction amount of the registration and conveying units 26A and 26B based on the skew amount on the leading end side of the paper P calculated by the skew amount calculation unit 61 and the roller deflection amount calculated by the roller deflection amount calculation unit 62 .

[0067] The roller control unit 65 controls the positioning and conveying units 26A and 26B based on the correction amount calculated by the correction amount calculation unit 64 .

[0068] Figure 5A to Figure 6B It is an explanatory diagram for explaining the calculation process of the roller deflection amount of the printing device 1 according to one embodiment of the present invention.

[0069] like Figure 5A As shown, the roller control unit 65 controls the paper feed roller 12 and the registration and conveying units 26A and 26B to convey the paper P placed on the paper feed tray 11 from the upstream side to the downstream side along the paper feed path RS at a conveying speed V1.

[0070] like Figure 5B As shown, when the skew detection units 28A and 28B respectively detect the front end of the paper P transported along the paper feed path RS, the skew amount calculation unit 61 calculates the time from the moment the paper feed detection unit 27 is turned on to the moment the skew detection unit 28A is turned on as TFon, and calculates the time from the moment the paper feed detection unit 27 is turned on to the moment the skew detection unit 28B is turned on as TRon.

[0071] like Fig. 6A As shown, when the skew detection units 28A and 28B respectively detect the rear end of the paper P, the skew amount calculation unit 61 calculates the time from the moment the paper feed detection unit 27 is turned off to the moment the skew detection unit 28A is turned off as TFoff, and calculates the time from the moment the paper feed detection unit 27 is turned off to the moment the skew detection unit 28B is turned off as TRoff.

[0072] like Figure 6B As shown, when the difference TRoffon between TRon and TRoff is greater than the difference TFoffon between TFon and TFoff, the paper P deflects to the rear side. In addition, when the difference TRoffon between TRon and TRoff is less than the difference TFoffon between TFon and TFoff, the paper P deflects to the front side.

[0073] Then, the skew amount calculation unit 61 calculates the skew amount of the front end side and the rear end side of the paper P based on the paper front end detection time and the sensor separation time, and the roller deflection amount calculation unit 62 calculates the roller deflection amount generated when the paper P passes through the registration conveying units 26A and 26B based on the skew amount of the front end side and the rear end side of the paper P calculated by the skew amount calculation unit 61. The calculation method of the roller deflection amount will be described later.

[0074] Figure 7A to Figure 9 It is an explanatory diagram for explaining the skew correction process of the printing device 1 according to one embodiment of the present invention.

[0075] like Fig. 7A At this time, the roller control unit 65 controls the paper feed roller 12 and the registration and conveying units 26A and 26B to convey the paper P from the upstream side to the downstream side along the paper feed path RS at a conveying speed V1. Here, the conveying speed V1 is set to 0.5 (m / s).

[0076] like Figure 7B As shown, here, first, the skew detection unit 28A detects the leading end of the paper P transported along the paper feed path RS.

[0077] Afterwards, if Fig. 8A As shown, the skew detection portion 28B detects the leading end of the paper P transported along the paper feed path RS.

[0078] The skew amount calculation unit 61 calculates the time from when the paper feed detection unit 27 turns on to when the skew detection unit 28A turns on as TFon, and calculates the time from when the paper feed detection unit 27 turns on to when the skew detection unit 28B turns on as TRon.

[0079] The correction amount calculation unit 64 calculates the correction amount of the registration and conveying units 26A and 26B based on the skew amount of the leading end of the paper P calculated by the skew amount calculation unit 61 and the roller deflection amount Lall calculated by the roller deflection amount calculation unit 62. Fig. 8A In the example shown, the paper P is tilted to the rear side, and the paper front end detection time T SNR For example, the correction amount calculation unit 64 calculates the time T calculated by the skew amount calculation unit 61 at the time of detecting the leading end of the paper. SNR The correction amount is calculated by adding the roller deflection amount Lall calculated by the roller deflection amount calculation unit 62 to the distance conveyed during the period, that is, the skew amount on the leading end side of the paper.

[0080] like Figure 8B As shown, the roller control unit 65 decelerates the positioning conveying unit 26A to the skew correction speed V2 at a desired deceleration, and corrects the skew of the paper P according to the speed difference between the positioning conveying unit 26A and the positioning conveying unit 26B. The conveying speed V2 is a value smaller than the conveying speed V1, and here, the conveying speed V2 is set to 0.342 (m / s). The calculation method of the conveying speed V2 will be described later.

[0081] After that, after the positioning conveying unit 26A is driven at the conveying speed V2 for a desired time, as shown in FIG. Fig. 9As shown, the roller control unit 65 performs speed control so as to accelerate the positioning and conveying unit 26A to the conveying speed V1, and the positioning and conveying unit 26A and the positioning and conveying unit 26B reach the same conveying speed V1 at the end of the skew correction section.

[0082] The skew correction section is a section between the belt conveying section 22 of the printing section 3 and the positioning conveying section 26A and the positioning conveying section 26B, which is downstream of the positioning conveying section 26A and the positioning conveying section 26B in the conveying direction.

[0083] When the leading end of the conveyed paper P reaches the belt conveying unit 22 , the paper P is sucked by the belt conveying unit 22 and the skew of the paper cannot be corrected. Therefore, it is necessary to provide a skew correction section in which the skew of the paper P is corrected.

[0084] Furthermore, when a roller mechanism is provided in place of the belt conveying unit 22 for conveying the paper by nipping it with a pair of conveying rollers, the skew of the paper P cannot be corrected after the leading end of the paper P is clamped by the rollers, and thus a skew correction section needs to be provided.

[0085] (Calculation of roller deflection)

[0086] Fig.10 It is an explanatory diagram for explaining calculation of the roller deflection amount.

[0087] The interval between the skew detection unit 28A and the skew detection unit 28B in the width direction (front-back direction) of the paper P is set to α, the interval between the positioning and conveying unit 26A and the positioning and conveying unit 26B in the width direction (front-back direction) of the paper P is set to α′, and the paper front end detection time T is set to SNR The conveying amount (TRon-TFon) is set to β, and the roller deflection amount Lall is set to β'. At this time, Fig.10 As shown, the triangle TR1 formed by the sides α and β is similar to the triangle TR2 formed by the sides α' and β'.

[0088] Then, the roller deflection amount calculation unit 62 calculates the roller deflection amount Lall using the following (Formula 1).

[0089] Lall=T SNR ×V1×α×(α / α′)(Formula 1)

[0090] (Calculation of conveying speed V2)

[0091] Fig.11This is an explanatory diagram for explaining the calculation of the conveying speed V2. ΔV represents the speed difference between the conveying speed V1 and the conveying speed V2. Here, when Tall is set as the skew correction time (determined by the correction distance and speed setting) and LCall is set as the correction amount (skew amount for each job), Tall and LCall are expressed by the following (Formula 2) and (Formula 3).

[0092] Tall=Tx+Ta1+Ta2(Formula 2)

[0093] LCall=Lx+La1+La2(Formula 3)

[0094] Here, La1 and La2 are areas, which are expressed by the following (Formula 4) and (Formula 5), ​​and the deceleration time Ta1 and the acceleration time Ta2 are expressed by the following (Formula 6) and (Formula 7).

[0095] La1=(1 / 2)*a1*Ta1 (Formula 4)

[0096] La2=(1 / 2)*a2*Ta2 (Formula 5)

[0097] Ta1=ΔV / a1 (Formula 6)

[0098] Ta2=ΔV / a2 (Formula 7)

[0099] Based on (Formula 4) to (Formula 7), La1 and La2 are expressed as the following (Formula 8) and (Formula 9).

[0100] La1=(ΔV^2) / (2*a1) (Formula 8)

[0101] La2=(ΔV^2) / (2a*2) (Formula 9)

[0102] In addition, the area Lx is expressed by the following (Mathematical Formula 10).

[0103] Lx=Tx*ΔV (Formula 10)

[0104] According to (Mathematical Formula 2),

[0105] Tx = Tall - Ta1 - Ta2 (Formula 11),

[0106] According to (Equation 10) and (Equation 11),

[0107] Lx=(Tall-Ta1-Ta2)*ΔV (Formula 12),

[0108] According to (Formula 3), (Formula 8), (Formula 9), (Formula 12),

[0109] LCall=(Tall-Ta1-Ta2)*ΔV+(ΔV^2) / (2*a1)+(ΔV^2) / (2a*2)(Formula 13),

[0110] When converted into a quadratic equation for ΔV,

[0111] =-(a1+a2) / (2*a1*a2)ΔV^2+TallΔV-LCall=0 (Formula 14),

[0112] Therefore, the coefficients required for the solution formula are:

[0113] a=-(a1+a2) / (2*a1*a2)

[0114] b=Tall

[0115] c=-LCall,

[0116] By setting the acceleration, the skew correction time, and the skew amount, ΔV is determined as shown in the following (Equation 15), and the conveying speed V2 is determined by determining ΔV.

[0117]

[0118] Here, the roller deflection amount is calculated by conveying the paper P. However, by using the reversing unit 25 , it is also possible to calculate the roller deflection amount using one paper P and then perform skew correction on the reversed paper P.

[0119] Specifically, the skew detection units 28A and 28B are used to detect the front and rear ends of the paper P when the paper P is transported by the positioning and conveying units 26A and 26B at a predetermined speed (conveying speed V1). The skew amount calculation unit 61 calculates the skew amount of the front and rear ends of the paper P based on the detection results detected by the skew detection units 28A and 28B. After the roller deflection amount calculation unit 62 calculates the roller deflection amount generated when passing through the positioning and conveying units 26A and 26B, the paper P with the front and back sides reversed by the turning unit 25 is conveyed to the positioning and conveying units 26A and 26B again. The correction amount calculation unit 64 calculates the correction amount of the skew detection units 28A and 28B based on the skew amount of the front end side of the turned paper P and the roller deflection amount.

[0120] Fig.12 This is a flowchart showing the processing contents when the reversing unit 25 of the printing apparatus 1 according to one embodiment of the present invention is used.

[0121] like Fig.12As shown, in step S101 , the roller control unit 65 controls the paper feed roller 12 and the registration and conveying units 26A and 26B so as to convey the paper P placed on the paper feed tray 11 at a conveying speed V1 in the paper feed path RS.

[0122] In step S103 , when the paper P transported in the paper feed path RS reaches the paper feed detection unit 27 , the paper feed detection unit 27 is turned on. That is, the paper feed detection unit 27 detects the paper P transported along the paper feed path RS.

[0123] Then, in step S105, when the paper P transported in the paper feeding path RS reaches the skew detection units 28A and 28B, the skew detection units 28A and 28B are turned on, that is, the skew detection units 28A and 28B detect the front end of the paper P transported along the paper feeding path RS. When the skew detection units 28A and 28B respectively detect the front end of the paper P, the skew amount calculation unit 61 calculates the paper front end detection time T1 (TRon-TFon). Specifically, the skew amount calculation unit 61 calculates the time from the time when the paper feeding detection unit 27 is turned on to the time when the skew detection unit 28A is turned on as TFon, and calculates the time from the time when the paper feeding detection unit 27 is turned on to the time when the skew detection unit 28B is turned on as TRon. In addition, the roller control unit 65 stops the paper feeding roller 12.

[0124] In step S107, when the paper P transported in the paper feeding path RS is separated from the skew detection parts 28A and 28B, the skew detection parts 28A and 28B are turned off, that is, the skew detection parts 28A and 28B detect the rear end of the paper P transported along the paper feeding path RS. When the skew detection parts 28A and 28B respectively detect the rear end of the paper P, the skew amount calculation part 61 calculates the sensor separation time T2 (TRoff-TFoff). Specifically, the skew amount calculation part 61 calculates the time from the time when the paper feeding detection part 27 is turned off to the time when the skew detection part 28A is turned off as TFoff, and calculates the time from the time when the paper feeding detection part 27 is turned off to the time when the skew detection part 28B is turned off as TRoff.

[0125] In step S109, the skew amount calculation unit 61 calculates the skew amount at the front end side and the rear end side of the paper P based on the paper front end detection time and the sensor detachment time, and the roller skew amount calculation unit 62 calculates the roller skew amount generated when the paper P passes through the positioning conveying units 26A, 26B based on the skew amount at the front end side and the rear end side of the paper P calculated by the skew amount calculation unit 61.

[0126] In step S111 , the control unit 6 reverses the paper P conveyed to the reversing unit 25 , and conveys the reversed paper P along the paper feed path RS.

[0127] In step S113, when the paper P transported in the paper feeding path RS reaches the skew detection units 28A and 28B, the skew detection units 28A and 28B are turned on, that is, the skew detection units 28A and 28B detect the leading edge of the paper P transported along the paper feeding path RS. When the skew detection units 28A and 28B detect the leading edge of the inverted paper P, the skew amount calculation unit 61 calculates the paper leading edge detection time T3 (TRon-TFon).

[0128] In step S115, the correction amount calculation unit 64 calculates the correction amount of the registration and conveying units 26A and 26B based on the paper leading end detection time T3 (TRon-TFon) calculated by the skew amount calculation unit 61 and the roller deflection amount calculated by the roller deflection amount calculation unit 62. The roller control unit 65 calculates the conveying speed V2 based on the correction amount calculated by the correction amount calculation unit 64, and controls the registration and conveying units 26A and 26B to correct the skew using the calculated conveying speeds V1 and V2.

[0129] In step S117, when the inverted paper P is separated from the skew detection units 28A and 28B, the skew detection units 28A and 28B are turned off, that is, the skew detection units 28A and 28B detect the rear end of the paper P transported along the paper feeding path RS. When the skew detection units 28A and 28B respectively detect the rear end of the paper P, the roller control unit 65 controls the registration transport units 26A and 26B to transport the paper P at the transport speed V1.

[0130] [Note]

[0131] The present invention has the following structure, for example.

[0132] (Note 1)

[0133] The paper conveying device includes: a skew correction unit having a roller pair, wherein a plurality of roller pairs are arranged in parallel in the width direction of the paper, clamping and conveying the paper, and correcting the skew of the paper by relatively changing the rotation speed of each of the roller pairs; a skew detection unit, which is arranged at a position downstream of the conveying direction of the conveyed paper than the skew correction unit, and detects the front end and the rear end of the paper; a skew amount calculation unit, which calculates the skew amount of the conveyed paper based on the detection result detected by the skew detection unit; a roller skew amount calculation unit; a calculation unit, which calculates the roller deflection amount generated when the paper passes through the skew correction unit based on the skew amounts on the front end side and the rear end side of the paper calculated by the skew amount calculation unit when the roller pair of the skew correction unit conveys the paper at a predetermined speed; and a correction amount calculation unit, which calculates the correction amount of the skew correction unit based on the skew amount on the front end side of the paper calculated by the skew amount calculation unit and the roller deflection amount calculated by the roller deflection amount calculation unit.

[0134] This allows accurate understanding of the roller deflection amount that occurs when the paper passes through the skew correction unit, and allows skew correction to be performed in consideration of the roller deflection amount, so that the skew of the paper being transported can be corrected with high accuracy.

[0135] (Note 2)

[0136] In the paper transport device described in Supplementary Note 1, the correction amount calculation unit may calculate the correction amount by adding the roller deflection amount calculated by the roller deflection amount calculation unit to the deflection amount on the leading end side of the paper calculated by the deflection amount calculation unit.

[0137] Thereby, the correction amount can be calculated more accurately.

[0138] (Note 3)

[0139] In the paper conveying device described in Note 1, the skew detection unit may also have a plurality of sensors separately arranged in the width direction of the paper, and the skew amount calculation unit may calculate the skew amount based on the difference between each detection time when the front end of the paper is detected by each of the plurality of sensors.

[0140] Thus, the skew amount on the leading end side of the paper can be appropriately calculated, and thus the correction amount calculation unit can calculate an appropriate correction amount based on the calculated skew amount on the leading end side.

[0141] (Note 4)

[0142] The paper conveying device described in Appendix 1 may also be provided with a reversing unit, which reverses the front and back sides of the paper in order to transfer the image to the second side of the paper. In the paper conveying device described in Appendix 1, the front end and the rear end of the paper are detected when the roller pair of the skew correction unit conveys the paper at a predetermined speed, and the skew amount calculation unit calculates the skew amount of the front end side and the rear end side of the paper based on the detection result detected by the skew detection unit. After the roller skew amount calculation unit calculates the roller skew amount generated when passing through the skew correction unit, the paper whose front and back sides are reversed by the reversing unit is conveyed to the skew correction unit again, and the correction amount calculation unit calculates the correction amount of the skew correction unit based on the skew amount of the front end side of the reversed paper and the roller skew amount.

[0143] Thus, by using the reversing unit, it is possible to perform skew correction on the reversed paper after calculating the roller deflection amount using one paper without separately preparing a paper for calculating the roller deflection amount.

Claims

1. A paper conveying device, wherein: The paper conveying device comprises: A skew correction unit includes a pair of rollers, a plurality of which are arranged in parallel in the width direction of the paper, and clamp and convey the paper, and corrects the skew of the paper by relatively changing the rotation speed of each of the pair of rollers; a skew detection unit disposed at a position downstream of the skew correction unit in a conveying direction of the conveyed paper, and detecting a front end and a rear end of the paper; a skew amount calculation unit that calculates a skew amount of the conveyed paper based on a detection result detected by the skew detection unit; a roller skew amount calculation unit that calculates a roller skew amount generated when the paper passes through the skew correction unit based on the skew amounts of the leading end side and the trailing end side of the paper calculated by the skew amount calculation unit when the roller pair of the skew correction unit conveys the paper at a predetermined speed; and A correction amount calculation unit calculates a correction amount of the skew correction unit based on the skew amount of the leading end side of the paper calculated by the skew amount calculation unit and the roller deflection amount calculated by the roller deflection amount calculation unit.

2. The paper conveying device according to claim 1, wherein: The correction amount calculation unit calculates the correction amount by adding the roller deflection amount calculated by the roller deflection amount calculation unit to the skew amount on the leading end side of the paper calculated by the skew amount calculation unit.

3. The paper conveying device according to claim 1, wherein: The skew detection unit includes a plurality of sensors that are separately arranged in the width direction of the paper. The skew amount calculation unit calculates the skew amount based on differences in respective detection times at which the leading end of the paper is detected by each of the plurality of sensors.

4. The paper conveying device according to claim 1, wherein: The paper conveying device further includes a reversing unit that reverses the front and back sides of the paper in order to transfer the image to the second side of the paper. The front end and the rear end of the paper are detected when the roller pair of the skew correction unit conveys the paper at a predetermined speed, and the skew amount calculation unit calculates the skew amount of the front end side and the rear end side of the paper based on the detection result detected by the skew detection unit. After the roller skew amount calculation unit calculates the roller skew amount generated when passing through the skew correction unit, the paper with the front and back sides reversed by the reversing unit is conveyed to the skew correction unit again, and the correction amount calculation unit calculates the correction amount of the skew correction unit based on the skew amount of the front end side of the reversed paper and the roller skew amount.

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