Image forming apparatus

Abstract

To improve the accuracy of an image formation position even in a case where a skew occurs in a sheet.SOLUTION: A skew feed correcting portion that corrects skew of a sheet conveyed by a conveyance unit, and a detection unit that detects an angle of a leading edge and an angle of a side edge of the sheet before the sheet conveyed by the conveyance unit passes through the skew feed correcting portion, are provided. A control unit is configured to be capable of selectively executing: a leading edge registration correction mode in which, based on the angle of the leading edge of the sheet detected by the detection unit, the skew of the sheet is corrected so as to align the leading edge of the sheet with a width direction perpendicular to a sheet conveyance direction, and an image formation position for forming an image with respect to the sheet after the skew correction is set in the sheet conveyance direction; and a lateral registration correction mode in which, based on the angle of the side edge of the sheet detected by the detection unit, the skew of the sheet is corrected so as to align the side edge of the sheet with the sheet conveyance direction, and an image formation position for forming an image with respect to the sheet after the skew correction is set in the width direction.SELECTED DRAWING: Figure 15

Description

Technical Field

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet.

Background Art

[0002] In recent years, in an image forming apparatus, the image position accuracy with respect to a sheet has become important. For this reason, a technique has been developed in which a test chart is read to adjust the image position in order to adjust the image forming position (see Patent Document 1).

[0003] On the other hand, as a series of printing systems including an image forming apparatus, an image forming system including a folding machine, cutting, and bookbinding has become widespread. In this type of image forming system, the image forming position with respect to the sheet required by the post-processing method is different. For example, in the case of saddle stitching bookbinding, adjustment is required so that the image is positioned at the center of the sheet in the transport direction and the width direction. Also, in the case of spiral binding, since the sheet is cut based on the end, adjustment is required so that the image is positioned based on the sheet end in the paper transport direction and the width direction. Therefore, in image position adjustment, a technique that takes into account the post-processing process is required. Therefore, a technique has been developed to switch the image forming position in the transport direction of printing on the sheet according to the post-processing process and the like (see Patent Document 2).

[0004] From the above, the image forming position is important in an image forming apparatus, and it is required to improve the accuracy of the image forming position in both cases where the post-processing step is performed and where it is not performed, considering the sheet cutting accuracy and the sheet shape including sheet deformation as disturbances.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the image forming apparatuses described in Patent Documents 1 and 2 mentioned above, skewing of the sheet is not taken into consideration. That is, the cutting error of the sheet needs to consider not only the conveyance direction and the width direction but also the inclination component. Due to the error of the inclination component of the sheet, the printing position on the sheet is different between the case where the skew component of the printing position is aligned with reference to the paper leading edge and the case where it is aligned at the left end of the sheet. Therefore, when the inclination component of the sheet is not considered, there is a risk that the accuracy of the image forming position deteriorates.

[0007] An object of the present invention is to provide an image forming apparatus capable of improving the accuracy of the image forming position even when skewing occurs in the sheet.

Means for Solving the Problems

[0008] One aspect of the present invention includes an image forming unit that forms an image on a sheet, a conveyance unit that conveys the sheet to the image forming unit, a skew correction unit that corrects the skew of the sheet conveyed by the conveyance unit, a detection unit that detects the angle of the leading edge and the side edge of the sheet before the sheet conveyed by the conveyance unit passes through the skew correction unit, and a control unit that controls the skew correction unit and the image forming unit. The control unit corrects the skew of the sheet so as to align the leading edge of the sheet in the width direction orthogonal to the sheet conveyance direction based on the angle of the leading edge of the sheet detected by the detection unit, and sets an image forming position for forming an image with respect to the skew-corrected sheet in the sheet conveyance direction. A first mode and a second mode in which the skew of the sheet is corrected so as to align the side edge of the sheet in the sheet conveyance direction based on the angle of the side edge of the sheet detected by the detection unit, and an image forming position for forming an image with respect to the skew-corrected sheet in the width direction is set. It is an image forming apparatus characterized in that it can be switched and executed.

[0009] Another aspect of the present invention includes an image forming unit that forms an image on a sheet, a conveyance unit that conveys the sheet to the image forming unit, a detection unit that detects the angle of the leading edge and the side edge of the sheet conveyed toward the image forming unit by the conveyance unit, and a control unit that controls the image forming unit to change the image forming position based on the angle of the leading edge or the side edge of the sheet detected by the detection unit. The control unit can switch between and execute a third mode in which the image forming position is changed with reference to the leading edge of the sheet based on the angle of the leading edge of the sheet, and a fourth mode in which the image forming position is changed with reference to the side edge of the sheet based on the angle of the side edge of the sheet. The image forming apparatus is characterized by this.

Effect of the Invention

[0010] According to the present invention, the accuracy of the image forming position can be improved even when skewing occurs in the sheet.

Brief Description of the Drawings

[0011]

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Figure 20

Mode for Carrying Out the Invention

[0012] Hereinafter, this embodiment will be described with reference to the drawings. In this embodiment, the case where an image forming apparatus is applied to an inkjet recording system 1 will be described. FIG. 1 is a schematic diagram showing an example of the schematic configuration of the inkjet recording system 1. This inkjet recording system 1 is a sheet-fed inkjet recording system for manufacturing a recording material in which an ink image is formed on a sheet S using two liquids, a reaction liquid and ink. As shown in FIG. 1, the inkjet recording system 1 includes a feeding module 100, a printing module 200, a drying module 300, a fixing module 400, a cooling module 500, a reversing module 600, and a discharging module 700. The cut-sheet-like sheet S supplied from the feeding module 100 is conveyed along a conveyance path, processed by each module, and discharged by the discharging module 700. In this embodiment, the drying module 300, the fixing module 400, the cooling module 500, the reversing module 600, and the discharging module 700 are examples of a sheet processing unit that performs processing on a sheet on which an image has been formed by the printing module 200.

[0013] The feeding module 100 has three storage bins 110a, 110b, and 110c for storing the sheet S. Each storage bin 110a, 110b, 110c is configured to be pull-outable to the front side of the apparatus. The sheet S is fed one by one by a separation belt and a conveyance roller (not shown) in each storage bin 110a, 110b, 110c and conveyed to the printing module 200. Note that the number of the storage bins 110a, 110b, 110c is not limited to three, and a configuration having one, two, or four or more may be used.

[0014] A print module 200, which is an example of an image forming apparatus, includes a registration unit 210 that is a pre-image formation registration correction unit, a print belt unit 220, a recording unit 230, and a control unit 60 (see FIG. 9). The sheet S conveyed from the feeding module 100 has its inclination and position corrected by the registration unit 210 and is then conveyed to the print belt unit 220. The recording unit 230 is disposed at a position facing the print belt unit 220 with respect to the conveyance path. The recording unit 230 is an example of an image forming unit that forms an image by performing a recording process (printing) on the sheet S from above with a recording head 231 with respect to the conveyed sheet S. Also, in the present embodiment, the print module 200 is assumed to have the control unit 60, but the present invention is not limited to this, and any module of the inkjet recording system 1 may have it. Alternatively, an external computer may be applied as the control unit.

[0015] The drying module 300 includes a decoupling unit 320, a drying belt unit 330, and a hot air blowing unit 340, and reduces the liquid content included in the ink applied on the sheet S by the recording unit 230 of the print module 200, and enhances the fixing property between the sheet S and the ink. The sheet S printed by the recording unit 230 of the print module 200 is conveyed to the decoupling unit 320 disposed on the upstream side in the sheet conveyance direction of the drying module 300. In the decoupling unit 320, the sheet S can be conveyed by the wind pressure and the friction of the belt from above, and by weakly holding and conveying the sheet S on the belt, the deviation of the sheet S on the print belt unit 220 that forms the ink image is prevented. The drying belt unit 330 is disposed below the belt, and the hot air blowing unit 340 is disposed above the belt, facing each other with the belt interposed therebetween. The sheet S conveyed from the decoupling unit 320 is adsorbed and conveyed by the drying belt unit 330, and at the same time, receives hot air from the hot air blowing unit 340 to dry the ink application surface. Note that, in addition to the method of applying hot air, the drying method may be configured by combining a method of irradiating the surface of the sheet S with electromagnetic waves (such as ultraviolet rays and infrared rays) or a conduction heat transfer method by contact with a heating element.

[0016] The fixing module 400 has a fixing belt unit 410. The fixing belt unit 410 has an upper belt unit and a lower belt unit, and can fix the ink to the sheet S by passing the sheet S conveyed from the drying module 300 between the heated upper belt unit and the lower belt unit.

[0017] The cooling module 500 has a plurality of cooling parts 510, and cools the high-temperature sheet S conveyed from the fixing module 400. The cooling part 510 is configured to take in outside air into the cooling box with a fan, increase the pressure in the cooling box, and cool the sheet S by blowing the air ejected from the nozzles formed in the conveying guide against the sheet S. The cooling parts 510 are arranged on both the upper side and the lower side with respect to the conveying path, and cool the sheet S from both sides.

[0018] Also, the cooling module 500 has a conveying path switching part, and can switch the conveying path of the sheet S according to whether the sheet S is conveyed to the reversing module 600 or conveyed to the duplex conveying path used during duplex printing. During duplex printing, the sheet S is conveyed to the conveying path below the cooling module 500. In this case, from the cooling module 500, it is further conveyed along the duplex conveying paths of the fixing module 400, the drying module 300, the printing module 200, and the feeding module 100. A first reversing part 420 for reversing the front and back of the sheet S is provided in the duplex conveying path of the fixing module 400. Then, again, it is conveyed from the feeding module 100 to the registration unit 210, the printing belt unit 220, and the recording unit 230 of the printing module 200, and is printed by the recording unit 230.

[0019] The reversing module 600 has a second reversing part 640, can reverse the front and back of the conveyed sheet S, and can change the front and back orientation of the discharged sheet S. The discharging module 700 has a top tray 720 and a stacking part 750, and stacks the sheets S conveyed from the reversing module 600 in an aligned manner.

[0020] [Print Module] Next, the configuration of the print module 200 will be described. FIG. 2 is a cross-sectional view showing the print belt unit 220 and the recording unit 230 of the print module 200. In the print module 200, recording processing is performed on the conveyed sheet S from above by the recording head 231 to form an image on the sheet. The print belt unit 220 is disposed directly below the recording unit 230, and sucks and conveys the sheet so that the sheet conveyance behavior directly below the recording head 231 is stabilized when the sheet is conveyed in the recording unit 230.

[0021] In the print belt unit 220 according to the present embodiment, the print belt 225 is stretched by four stretching rollers 221, 222, 223, and 224. The outer surface of the print belt 225 stretched between the stretching roller 221 and the stretching roller 224 directly below the recording head 231 of the print belt unit 220 forms an image forming surface 226 which is a surface for performing image formation. The print belt 225 is formed with suction holes (not shown) for sucking the sheet S, and conveys the sheet S while sucking and adsorbing it on the inner peripheral side of the print belt 225 on the image forming surface 226. The sheet S conveyed on the image forming surface 226 is conveyed in a state where a clearance is secured between the recording head 231 by being sucked and conveyed by the print belt unit 220.

[0022] The recording heads 231 are arranged in a plurality along the conveyance direction. In the present embodiment, in addition to the four colors of Y (yellow), M (magenta), C (cyan), and Bk (black), the recording head 231 applies eight line-type recording heads corresponding to the reaction liquid and three special features (see FIG. 2). Note that the number of colors and the number of recording heads 231 are not limited to eight. For example, five line-type recording heads may be applied without providing for the three special features. The inkjet method can employ a method using a heating element, a method using a piezo element, a method using an electrostatic element, a method using a MEMS element, or the like. The ink of each color is supplied from an ink tank (not shown) to the recording head 231 via an ink tube. The sheet S printed by the recording unit 230 has the deviation and color density of the image formed on the sheet S detected by the in-line scanner unit 10 disposed on the downstream side in the sheet conveyance direction of the recording unit 230. The detection result is used for correcting the printed image. That is, the in-line scanner unit 10 is an example of a reading unit, and reads the leading edge and side edges of the sheet and the image formed on the sheet downstream in the sheet conveyance direction from the recording unit 230.

[0023] [Print Belt Unit] Next, the control in the belt width direction of the print belt unit 220 in the present embodiment will be described with reference to FIG. 3. The belt width direction is the same direction as the sheet width direction orthogonal to the sheet conveyance direction in the print belt 225. FIG. 3 is a schematic perspective view of the print belt unit 220.

[0024] In the print belt unit 220 according to this embodiment, the tension roller 221 rotates the print belt 225 and is a roller that is movable in the roller axis direction. Further, the tension roller 222 is a tension roller that applies a force to stretch the print belt 225 from the inner peripheral side to the outer peripheral side of the belt with respect to the print belt 225. The tension roller 223 is a steering roller that can move one axial end of the roller and tilt the roller in order to suppress the meandering of the print belt 225. The steering roller of the tension roller 223 is operated by a drive source 227. The tension roller 224 is a driven roller that follows the rotation of the print belt 225 and is movable in the roller axis direction.

[0025] An upstream sensor 228 and a downstream sensor 229 that read the position detection shapes arranged at the ends of the print belt 225 are arranged in the vicinity of the tension rollers 221 and 224 that are movable in the roller axis direction, respectively. Since the sheet S is adsorbed to the image forming surface 226, the accuracy of the image can also be improved by accurately positioning the position of the image forming surface 226. For this purpose, it is desirable that the rollers movable in the roller axis direction for adjusting the position of the print belt 225 be the two tension rollers 221 and 224 that form the image forming surface 226.

[0026] The upstream sensor 228 and the downstream sensor 229 for detecting the position of the print belt 225 are provided in the vicinity of the tension rollers 221 and 224, respectively. The tension roller 221 operates the roller in the roller axis direction based on the belt position detection result of the downstream sensor 229 to adjust the position of the print belt 225. The tension roller 224 operates the roller in the roller axis direction based on the belt position detection result of the upstream sensor 228 to adjust the position of the print belt 225. By adjusting the positions of the tension roller 221 and the tension roller 224 that form the image forming surface 226, the entire image forming surface 226 can be accurately positioned.

[0027] [Cashier unit] Next, the schematic configuration of the registration unit 210 as an example of the skew correction unit before image formation will be described. FIG. 4 is a plan view showing the peripheral configuration including the registration unit 210, FIG. 5 is a perspective view showing the peripheral configuration including the registration unit 210, FIG. 6 is a cross-sectional view showing the peripheral configuration including the registration unit 210, and FIG. 7 is an operation state diagram of the roller by the registration unit 210.

[0028] [Flow of operation of the registration unit] The registration unit 210 has a left image sensor 31, a right image sensor 41, a left front registration sensor 32, a right front registration sensor 42, a left resist roller pair 33, and a right resist roller pair 43. The left resist roller pair 33 and the right resist roller pair 43 are an example of a turning roller pair. The registration unit 210 receives the sheet S from a conveyance roller pair 50 provided upstream in the sheet conveyance direction of the left resist roller pair 33 and the right resist roller pair 43. The conveyance roller pair 50 has a lower roller made of an EPDM roller and an upper roller made of a urethane rubber roller, and the lower roller is biased by a biasing spring (not shown) to the upper roller. The conveyance roller pair 50 is an example of a conveyance unit that conveys the sheet S to the recording unit 230. The registration unit 210 corrects the skew of the sheet S conveyed by the conveyance roller pair 50.

[0029] The registration unit 210 has a left registration drive motor 34, a right registration drive motor 44, a left steering motor 35, and a right steering motor 45. The left resist roller pair 33 is composed of a urethane rubber roller and has an upper roller that rotates to convey the sheet by the left registration drive motor 34 and a driven roller disposed opposite to the upper roller. The right resist roller pair 43 is composed of a urethane rubber roller and has an upper roller that rotates to convey the sheet by the right registration drive motor 44 and a driven roller disposed opposite to the upper roller.

[0030] The upper roller of the left resist roller pair 33 is rotatably supported by a left steering shaft 36 having a vertical rotation center, and the left steering shaft 36 is drivingly connected to a left steering motor 35 via a sector gear 37 and a motor gear 38. When the left steering motor 35 is driven, the upper roller of the left resist roller pair 33 pivots about the left steering shaft 36. Similarly, the upper roller of the right resist roller pair 43 is rotatably supported by a right steering shaft 46 having a vertical rotation center, and the right steering shaft 46 is drivingly connected to a right steering motor 45 via a sector gear 47 and a motor gear 48. When the right steering motor 45 is driven, the upper roller of the right resist roller pair 43 pivots about the right steering shaft 46. Thereby, the registration unit 210 corrects the skew of the sheet S by conveying the sheet S so as to pivot it with the left resist roller pair 33 and the right resist roller pair 43.

[0031] As shown in FIG. 7(a), by rotating the left resist roller pair 33 and the right resist roller pair 43 in the sheet conveyance direction at the same rotational speed (VL = VR), the sheet S is conveyed straight along the sheet conveyance direction toward the recording unit 230. As shown in FIG. 7(b), by rotating the left resist roller pair 33 and the right resist roller pair 43 in the sheet conveyance direction at different rotational speeds (VL < VR), the sheet S can be pivoted and the skew can be corrected. As shown in FIG. 7(c), by pivoting the left resist roller pair 33 and the right resist roller pair 43 by the same angle from the sheet conveyance direction and rotating them at the same rotational speed (VL = VR), the sheet S can be moved in an oblique direction without being inclined, and the horizontal position can be corrected.

[0032] [Detection of skew amount] The left front sensor 32 and the right front sensor 42 are arranged at the same position with respect to the sheet conveyance direction and at different positions with respect to the sheet width direction in the vicinity of the nip of the left resist roller pair 33 and the right resist roller pair 43. As the left front sensor 32 and the right front sensor 42, an optical sensor having a light emitting portion that emits light and a light receiving portion that receives the reflected light of the light emitted from the light emitting portion and reflected by the sheet is applied. The control unit 60 calculates the current skew amount of the sheet S from the timing when the left front sensor 32 and the right front sensor 42 detect the sheet S and the speed at which the sheet S is conveyed. That is, the left front sensor 32 and the right front sensor 42 are an example of a detection unit, and detect the angle of the leading end of the sheet S before the sheet S conveyed by the conveyance roller pair 50 passes through the registration unit 210. In the present embodiment, the case where two sensors, the left front sensor 32 and the right front sensor 42, are provided as the front sensors has been described, but the present invention is not limited to this, and three or more sensors may be provided. Alternatively, as long as it measures the skew amount of the sheet, other types of sensors such as an image sensor may be used instead of the above-described optical sensor.

[0033] [Detection of Width Direction Position] The left image sensor 31 and the right image sensor 41 are provided in the vicinity of the nip of the left resist roller pair 33 and the right resist roller pair 43. The left image sensor 31 detects the edge position of the left end of the sheet S, and the right image sensor 41 detects the edge position of the right end of the sheet S. The control unit 60 calculates the width direction position of the sheet S based on the edge position of the left end and the edge position of the right end of the sheet S. That is, the left image sensor 31 and the right image sensor 41 are an example of a detection unit, and detect the angle of the side end of the sheet S before the sheet S conveyed by the conveyance roller pair 50 passes through the registration unit 210. In the present embodiment, the case where image sensors are provided at two locations, left and right, so as to detect both side ends of the sheet S has been described, but the present invention is not limited to this. For example, only one image sensor longer than the width of the sheet S may be provided. Alternatively, only one side end of the sheet S may be detected and controlled based on one side end reference.

[0034] [Control System] Next, the control unit 60 of the print module 200 and the control system will be described with reference to FIG. 8. The control unit 60 includes a CPU 61 (Central Processing Unit), a RAM 62 (Random Access Memory), and a ROM 63 (Read only memory). The CPU 21 realizes various processes performed by the print module 200 by executing a predetermined control program and the like. The RAM 62 and the ROM 63 store various programs and various data in a predetermined storage area. The CPU 21 reads and executes the control program stored in the ROM 63 based on signals input from an external computer via an interface (not shown), and controls the operation of the registration unit 210 while using the RAM 62 as a work memory.

[0035] The control unit 60 includes functional units such as an image formation control unit 64, a sheet conveyance control unit 65, and a skew correction control unit 66. The image formation control unit 64 transmits instructions to the recording unit 230 to control image formation. The sheet conveyance control unit 65 transmits instructions to a drive source to drive a pair of conveyance rollers 50 and the like, and controls the driving of various conveyance rollers to control the conveyance of the sheet S.

[0036] The skew correction control unit 66 controls the registration unit 210. Specifically, the skew correction control unit 66 acquires detection results input by the left image sensor 31, the right image sensor 41, the left front registration sensor 32, and the right front registration sensor 42. Based on the detection results, the skew correction control unit 66 controls the left registration drive motor 34, the right registration drive motor 44, the left steering motor 35, and the right steering motor 45 to perform skew correction and correction of lateral displacement of the sheet S. Here, the lateral displacement (or lateral registration deviation) means the amount of deviation from a reference in the width direction orthogonal to the conveyance direction.

[0037] Also, a patch image (inspection image) is formed on the sheet S using the recording unit 230 to create a test chart St (see FIG. 10), and the test chart St is read by the in-line scanner unit 10. At this time, the skew correction control unit 66 acquires the correction value set by reading the sheet shape and patch position of the test chart St on the print belt 225 by the in-line scanner unit 10. Then, by adding and adjusting for skew correction and horizontal position shift, it is possible to correct the front-back shift caused by factors such as the sheet shape. At this time, the accuracy of the image formation position depends on the shape of the sheet S. The skew correction control unit 66 can change the correction reference position of the printing position with respect to the sheet S by offsetting the front reference correction value, the horizontal reference correction value, and the skew correction value. Thereby, even if there is an error in the sheet shape, the image formation position can be adjusted to a desired position with respect to the sheet S. Note that hereinafter, the front reference is also referred to as the front register, and the horizontal reference is also referred to as the horizontal register.

[0038] As shown in FIG. 8, the print module 200 is provided with an operation unit 51. The operation unit 51 is composed of, for example, a liquid crystal touch panel having a display function for displaying information and an input function for the user to input information, and is provided on the upper surface of the print module 200. Alternatively, it may display information on the screen of a monitor of an externally connected computer and perform input operations using a mouse, keyboard, etc. The operation unit 51 is an example of a reception unit, and receives mode information about the mode selected from the front register correction mode and the horizontal register correction mode (see FIG. 19).

[0039] [In-line Scanner Unit] FIG. 9 shows an in-line scanner unit 10 that reads a sheet on the print belt 225 and an image formed on the sheet downstream of the recording head 231 in the sheet conveyance direction. The in-line scanner unit 10 has an optical box 12 and a processing unit 16 in a housing 11. The optical box 12 reads the sheet shape and patch position of the test chart St through a reading glass 13 and transmits the result to the processing unit 16. The processing unit 16 is connected to a control unit 60, processes the information obtained by the optical box 12, and transmits it to the control unit 60. The optical box 12 can apply an appropriate image sensor such as a CIS. The in-line scanner unit 10 can be moved in the left-right direction in the figure by a driving unit (not shown). Then, at a predetermined timing, the reading position 14 of the optical box 12 is moved from the position for reading the sheet S to the shading position facing the shading sheet 15, thereby performing shading processing.

[0040] [Image Processing Process] As shown in FIG. 8, the image information read by the optical box 12 is processed by the processing unit 16, the sheet shape and patch position of the test chart St are digitized, and correction values for the image position, sheet position, and image magnification are generated from the digitized results. The generated correction values are transmitted to the control unit 60. The control unit 60 reflects the above correction values in the processing of the registration unit 210, the print belt unit 220, and the recording unit 230, thereby adjusting the image position, sheet position, and image magnification.

[0041] [Digitization of Sheet Shape and Patch Position] FIG. 10 is a schematic diagram showing a test chart St for explaining a method of digitizing a sheet shape and a patch position. By reading the test chart St with the in-line scanner unit 10, an image as shown in FIG. 10 is acquired. The positions of the four corners and four patch points of the test chart St are coordinated as (X1, Y1) to (X8, Y8) from the acquired image. At this time, the conveyance direction is the Y direction, and the width direction orthogonal to the conveyance direction is the X direction.

[0042] [Image Formation Position Adjustment] First, examples of the front margin and the side margin are shown. As described above, in the case of the saddle-stitch binding, adjustment is required so that the image is positioned at the center of the sheet in the conveyance direction and the width direction. Also, in the case of the perfect binding, since the sheet is cut based on the end reference, adjustment is required so that the image is positioned at the sheet end reference in the conveyance direction and the width direction of the sheet.

[0043] [Front Margin Adjustment] As shown in FIG. 11(a), a test chart St for image formation position adjustment is printed and read by the in-line scanner unit 10, and the positions of the four corners and the four patch points of the test chart St are coordinated as (X1, Y1) to (X8, Y8). From the coordinates, the distances La and Lb between the sheet leading edge and the two patch positions on the sheet leading edge side are obtained. As shown in FIG. 11(b), when aligning the front margin based on the sheet leading edge, if the reference distance from the sheet leading edge to the patch position is Ls, the front margin correction value is calculated by Equation 1. Front margin correction value = (La + Lb) / 2 - Ls ··· Equation 1

[0044] As shown in FIG. 11(c), when aligning the front margin based on the sheet center, with the center coordinate of the sheet in the Y direction being Y1 and the center coordinate of the image being Y2 from the coordinate values, the front margin correction value is calculated by Equation 2. From this correction, a correction result as shown in FIG. 11 is obtained. Front margin correction value = Y2 - Y1 ··· Equation 2

[0045] [Side Margin Adjustment] As shown in FIG. 12(a), a test chart St for image formation position adjustment is printed and read by the in-line scanner unit 10, and the positions of the four corners and the four patch points of the test chart St are coordinated as (X1, Y1) to (X8, Y8). From the coordinates, the distances Lc and Ld between the sheet left end and the two patch positions on the sheet left end side are obtained. As shown in FIG. 12(b), when aligning the side margin based on the sheet left end, if the reference distance from the sheet left end to the patch position is Ls, the side margin correction value is calculated by Equation 3. Side margin correction value = (Lc + Ld) / 2 - Ls ··· Equation 3

[0046] As shown in FIG. 12(c), when aligning the horizontal registration with respect to the center of the sheet, taking the center coordinate of the sheet in the Y direction as Y1 and the center coordinate of the image as Y2 with respect to the coordinate values, the horizontal registration correction value is calculated by Equation 4. From this correction, a correction result as shown in FIG. 12 is obtained. Previous registration correction value = Y1 - Y2 ··· Equation 4

[0047] By changing the correction reference as described above, the formation positions in the conveyance direction and the front-back direction for printing on the sheet can be changed according to the post-processing method or the like. Here, in an image forming apparatus that handles cut sheets, there are those that provide high-precision print position stability by sheet posture and alignment (registration). However, usually, registration is performed with reference to one side of a rectangular sheet, so the accuracy variation of each sheet depends on the cutting accuracy of the sheet and the deformation of the sheet. Examples of the sheet shape including the cutting accuracy and deformation of the sheet include right-angledness and parallelism in addition to the length, but the accuracy is greatly affected by the cutting lot difference of the sheet and the surrounding environment. Therefore, the print position accuracy depends on the quality according to the shape of the sheet. Therefore, in order to provide print position accuracy equivalent to offset printing with a cut-sheet printer, it is necessary to adjust the print position deviation every time the cutting lot of the sheet or the setting environment changes.

[0048] For example, in post-processing steps such as cutting, it is often aligned based on the transport direction. Therefore, it is desirable to align the skew at the tip. Also, in the case of a product without post-processing, especially for large sizes, it is desirable to align the skew with the long side (for example, when transporting the A3 size in the longitudinal direction, it is based on the left end). Thus, not only is it necessary to switch the formation position in the transport direction for printing on the sheet, but it is also necessary to switch the reference for the skew component. Therefore, in the present embodiment, the reference position (front registration, horizontal registration, skew) for image formation position adjustment can be changed according to whether a post-processing step is assumed or a long sheet without such is assumed. Also, the in-line scanner unit 10 reads the sheet shape and patches of the test chart St to detect the shape of the entire sheet, and performs image formation position adjustment. At that time, the reference position of the image formation position can be arbitrarily selected.

[0049] [Skew correction] Next, the skew correction of the image formation position adjustment will be described. As described above, it is desirable to consider not only the cutting error of the sheet in the transport direction and the front-back direction but also the inclination component. Due to the error of the inclination component of the sheet, the image formation position on the sheet is different between the case of aligning the skew component of the image formation position based on the sheet tip and the case of aligning it based on the sheet left end. In post-processing steps such as cutting, it is often aligned based on the transport direction. Therefore, it is desirable to align the skew at the tip. Also, in the case of a product without post-processing, especially for large sizes, it is desirable to align the skew with the long side (for example, when transporting the A3 size in the longitudinal direction, it is based on the left end).

[0050] Here, assume the case of a long (large size) sheet without post-processing, as shown in FIGS. 13(a) and (b). As shown in FIG. 13(a), when aligning the skew based on the tip, the blank space becomes excessively small at the rear end of the sheet, which is not preferable. On the other hand, as shown in FIG. 13(b), by aligning the skew based on the left end, the blank space also looks uniform at the rear end of the sheet, which is more preferable than the example of FIG. 13(a).

[0051] Next, assume a case of three-way arbitration, as shown in FIGS. 14(a) and 14(b). As shown in FIG. 14(a), when aligning the skew with the left end as a reference, the blank space after cutting becomes non-uniform with respect to the cutting position indicated by the dashed line, which is not preferable. On the other hand, as shown in FIG. 14(b), by aligning the skew with the tip as a reference, the blank space after cutting becomes uniform with respect to the cutting position indicated by the dashed line, which is more preferable than the example of FIG. 14(a). On the other hand, when aligning the skew with the left end as a reference as shown in FIG. 14(a), therefore, it is desirable to switch the reference also in the skew component with respect to the technique of switching the formation position in the conveyance direction for printing on the sheet.

[0052] Hereinafter, a method for calculating the skew correction value in the present embodiment will be described with reference to FIGS. 15(a) to 15(c). As shown in FIG. 15(a), a test chart St for image formation position adjustment is created and read by the in-line scanner unit 10, and the positions of the four corners and the four patch points of the test chart St are coordinated as (X1, Y1) to (X8, Y8). From the coordinates, the distances La and Lb between the sheet tip and the two patch positions on the sheet tip side, and the distances Lc and Ld between the sheet left end and the two patch positions on the sheet left end side are obtained.

[0053] As shown in FIG. 15(b), when aligning the skew with the sheet left end as a reference, the skew correction value is calculated by Equation 5. Skew correction value = Lc - Ld ··· Equation 5 As shown in FIG. 15(c), when aligning the skew with the sheet tip as a reference, the skew correction value is calculated by Equation 6. Skew correction value = La - Lb ··· Equation 6

[0054] By the above-described correction, a correction result as shown in FIG. 15 is obtained. The correction value can change the image formation position with respect to the sheet S by offsetting the pre-registration correction value, the horizontal registration correction value, and the skew correction value to the registration unit 210 and the recording unit 230.

[0055] In this embodiment, the control unit 60 can be set to switch between a leading-edge registration correction mode and a side-edge registration correction mode for skew correction. The leading-edge registration correction mode is an example of the first mode, and the skew of the sheet is corrected so that the leading edge of the sheet is aligned in the width direction based on the angle of the leading edge of the sheet detected by the sensor. Further, in the leading-edge registration correction mode, the control unit 60 sets an image formation position for forming an image with respect to the sheet after skew correction in the sheet conveyance direction, and forms an image. The side-edge registration correction mode is an example of the second mode, and the skew of the sheet is corrected so that the side edge of the sheet is aligned in the sheet conveyance direction based on the angle of the side edge of the sheet detected by the sensor. Further, in the side-edge registration correction mode, the control unit 60 sets an image formation position for forming an image with respect to the sheet after skew correction in the width direction, and forms an image.

[0056] Next, the processing procedure when adjusting the correction reference when adjusting the image formation position will be described according to the flowchart shown in FIG. 16. The adjustment timing is preferably performed before the execution of the image formation job so that the state of the sheet does not change. Here, for each image formation job, adjustment is performed on the media to be used.

[0057] As shown in FIG. 17, the control unit 60 displays a media library screen 52 on the operation unit 51. The user designates the media on the media library screen 52 and touches and selects the print position adjustment button (step S1). The control unit 60 displays a print position adjustment screen 53 on the operation unit 51 as shown in FIG. 18. The print position adjustment screen 53 has an auto-registration adjustment button and a manual registration adjustment button, and an option button is provided for auto-registration adjustment. The user touches and selects the option button (step S2).

[0058] As shown in FIG. 19, the control unit 60 displays a selection screen 54 for the correction reference of the printing position on the operation unit 51. On the selection screen 54 for the correction reference of the printing position, slant correction, leading-edge correction, and horizontal registration correction are displayed as selectable correction references, and the user makes a selection for each (step S3). That is, the operation unit 51 receives mode information for the mode selected from among the leading-edge correction mode and the horizontal registration correction mode.

[0059] Regarding the leading-edge correction, the operation unit 51 receives one selected from among the first information (front end, center, rear end) regarding the image formation position in the sheet conveyance direction. When executing the leading-edge correction mode, the control unit 60 sets the image formation position in the sheet conveyance direction based on the first information. The center in the first information is, for example, a reference position and is the center position of the sheet in the sheet conveyance direction. Note that the center position here is also the standard setting position of the margin or the initial setting position when there is no specific designation. The front end in the first information is an example of a downstream end side position that is a position downstream from the center. The rear end in the first information is an example of an upstream end side position that is a position upstream from the center.

[0060] Regarding the horizontal registration correction, the operation unit 51 receives one selected from among the second information (left end, center, right end) regarding the image formation position in the width direction. When executing the horizontal registration correction mode, the control unit 60 sets the image formation position in the width direction based on the second information. The center in the second information is, for example, a reference position and is the center position of the sheet in the width direction. Note that the center position here is also the standard setting position of the margin or the initial setting position when there is no specific designation. The left end in the second information is an example of a one-end side position that is a position on one side in the width direction from the center. The right end in the second information is an example of a the-other-end side position that is a position on the other side in the width direction from the center.

[0061] After the user selects the correction standard, the user touches the return button to close the options and return to the print position adjustment screen 53 shown in FIG. 18 (step S4). The user touches the auto registration adjustment start button on the print position adjustment screen 53 shown in FIG. 18, and the control unit 60 starts the print position adjustment (step S5). The control unit 60 forms a patch image on the sheet to create a test chart St (step S6). The control unit 60 reads the positions of the four corners of the test chart St and the four patch points using the in-line scanner unit 10 (step S7).

[0062] The control unit 60 coordinates the positions of the four corners of the test chart St and the four patch points as (X1, Y1) to (X8, Y8) from the measurement results by the in-line scanner unit 10. The control unit 60 obtains the distances La and Lb between the sheet leading edge and the two patch positions on the sheet leading edge side, and the distances Lc and Ld between the sheet left end and the two patch positions on the sheet left end side based on the coordinates, calculates each correction value, and stores it in the sheet library (step S8). Thereafter, the control unit 60 executes one of the pre-registration correction mode and the horizontal registration correction mode based on the mode information input by the user.

[0063] That is, before executing the pre-registration correction mode or the horizontal registration correction mode, the control unit 60 forms a patch image on the sheet by the recording unit 230 without performing skew correction by the registration unit 210 to create a test chart St. Then, the in-line scanner unit 10 reads the leading edge and side edges of the test chart St and the patch image. When executing the pre-registration correction mode, the control unit 60 sets the image formation position based on the positional relationship between the leading edge and side edges of the sheet and the patch image read by the in-line scanner unit 10, and the angle of the leading edge of the sheet to be corrected by the registration unit 210. When executing the horizontal registration correction mode, the control unit 60 sets the image formation position based on the positional relationship between the leading edge and side edges of the sheet and the patch image read by the in-line scanner unit 10, and the angle of the side edge of the sheet to be corrected by the registration unit 210.

[0064] By changing the correction criteria as described above, when there is a post-processing step such as cutting in the forming position in the conveyance direction for printing on the sheet as shown in Fig. 20, good print position adjustment can be performed on the sheet by changing according to whether there is post-processing or not. That is, as shown in Fig. 20(a), by aligning the skew with the left end as a reference, the margins also look uniform at the rear end of the sheet, which is more preferable than the example in Fig. 13(a). Also, as shown in Fig. 20(b), by aligning the skew with the front end as a reference, the margins after cutting become uniform with respect to the cutting position indicated by the dashed-dotted line, which is more preferable than the example in Fig. 14(a).

[0065] As described above, according to the print module 200 of the present embodiment, it is possible to switch between and execute the pre-registration correction mode or the horizontal registration correction mode. Therefore, the error of the inclination component of the sheet can be suppressed, and the accuracy of the image formation position can be improved even when a skew occurs on the sheet. Thereby, for example, when there is a post-processing step such as cutting in the forming position in the conveyance direction for printing on the sheet, good print position adjustment can be performed on the sheet in any case by changing according to whether there is post-processing or not.

[0066] In addition, in the above-described embodiment, the case where skew correction is performed by changing the posture of the sheet by reflecting the correction value on the registration unit 210 has been described, but it is not limited to this. That is, in the above-described embodiment, on the premise that the front end or side end of the sheet comes straight, the pre-registration correction mode and the horizontal registration correction mode are switched so as to adjust the image only in the X direction or the Y direction. On the contrary, while adjusting the image in the rotation direction in accordance with the inclination of the front end or side end of the sheet detected by the sensor, the image may also be adjusted in the X direction or the Y direction. That is, a method may be applied in which skew correction is not performed on the sheet, and the image formation position is adjusted including the skew component when the recording unit 230 forms an image on the sheet S. In this case, the control unit 60 can switch between and execute a third mode in which the image formation position is changed with the front end of the sheet as a reference based on the angle of the front end of the sheet, and a fourth mode in which the image formation position is changed with the side end of the sheet as a reference based on the angle of the side end of the sheet.

[0067] In addition, in the above-described embodiment, the case where the image forming system is applied to the inkjet recording system 1 of the inkjet recording method has been described. However, the present invention is not limited to this, and it may be applied to an electrophotographic image forming apparatus.

Explanation of Signs

[0068] 1... Inkjet recording system (image forming apparatus), 10... Inline scanner unit (reading unit), 31... Left image sensor (detection unit), 32... Left front registration sensor (detection unit), 33... Left registration roller pair (swivel roller pair), 41... Right image sensor (detection unit), 42... Right front registration sensor (detection unit), 43... Right registration roller pair (swivel roller pair), 50... Conveyor roller pair (conveying unit), 51... Operation unit (reception unit), 60... Control unit, 210... Registration unit (skew correction unit), 230... Recording unit (image forming unit), 300... Drying module (sheet processing unit), 400... Fixing module (sheet processing unit), 500... Cooling module (sheet processing unit), 600... Inversion module (sheet processing unit), 700... Discharge module (sheet processing unit)

Claims

1. An image forming unit that forms an image on a sheet; A conveyance unit that conveys the sheet to the image forming unit; A skew correction unit that corrects the skew of the sheet conveyed by the conveyance unit; A detection unit that detects the angle of the leading edge and the side edge of the sheet before the sheet conveyed by the conveyance unit passes through the skew correction unit; A control unit that controls the skew correction unit and the image forming unit, and The control unit Based on the angle of the leading edge of the sheet detected by the detection unit, corrects the skew of the sheet so that the leading edge of the sheet is aligned in the width direction orthogonal to the sheet conveyance direction, and sets an image forming position for forming an image with respect to the sheet after skew correction in the sheet conveyance direction, a first mode; Based on the angle of the side edge of the sheet detected by the detection unit, corrects the skew of the sheet so that the side edge of the sheet is aligned in the sheet conveyance direction, and sets an image forming position for forming an image with respect to the sheet after skew correction in the width direction, a second mode, and can switch and execute. An image forming apparatus characterized by the above.

2. Comprising a reception unit that receives mode information about the mode selected from among the first mode and the second mode, The control unit executes one of the first mode and the second mode based on the mode information. The image forming apparatus according to claim 1, characterized by the above.

3. The reception unit receives first information about the image forming position in the sheet conveyance direction, When the control unit executes the first mode, it sets the image forming position in the sheet conveyance direction based on the first information. The image forming apparatus according to claim 2, characterized by the above.

4. The reception unit receives, as the first information, one selected from among a reference position, an upstream end side position that is a position upstream of the reference position, and a downstream end side position that is a position downstream of the reference position in the sheet conveyance direction. The image forming apparatus according to claim 3, characterized by the above.

5. The reception unit receives second information about the image forming position in the width direction, When the control unit executes the second mode, it sets the image forming position in the width direction based on the second information. The image forming apparatus according to claim 2, characterized by the above.

6. The reception unit receives, as the second information, one selected from among a reference position, a one-end side position that is one position in the width direction relative to the reference position, and the other-end side position that is the other position relative to the reference position. The image forming apparatus according to claim 5, characterized in that.

7. A reading unit is provided downstream of the image forming unit in the sheet conveyance direction to read the leading end and side edges of the sheet and the image formed on the sheet. The control unit Before executing the first mode or the second mode, an inspection image is formed on the sheet by the image forming unit without performing skew correction by the skew correction unit, and the leading end and side edges of the sheet and the inspection image are read by the reading unit. When the first mode is executed, the image forming position is set based on the positional relationship between the leading end and side edges of the sheet read by the reading unit and the inspection image, and the angle of the leading end of the sheet corrected by the skew correction unit. When the second mode is executed, the image forming position is set based on the positional relationship between the leading end and side edges of the sheet read by the reading unit and the inspection image, and the angle of the side edge of the sheet corrected by the skew correction unit. The image forming apparatus according to claim 1, characterized in that.

8. The skew correction unit has a pair of turning rollers that convey the sheet, and corrects the skew of the sheet by conveying the sheet so as to turn it by the pair of turning rollers. The image forming apparatus according to claim 1, characterized in that.

9. An image forming unit that forms an image on a sheet, A conveyance unit that conveys the sheet to the image forming unit, A detection unit that detects the angle of the leading end and the angle of the side edge of the sheet conveyed toward the image forming unit by the conveyance unit, A control unit that controls the image forming unit to change the image forming position based on the angle of the leading end or the angle of the side edge of the sheet detected by the detection unit. The control unit A third mode in which the image forming position is changed with reference to the leading end of the sheet based on the angle of the leading end of the sheet, and A fourth mode in which the image forming position is changed with reference to the side edge of the sheet based on the angle of the side edge of the sheet, and can be switched and executed. The image forming apparatus, characterized in that.

10. A sheet processing unit for performing processing on the sheet on which the image is formed by the image forming unit is provided. The image forming apparatus according to claim 1, characterized in that.

Images