JP2020049830A - Image formation apparatus, image formation method and program - Google Patents

Abstract

To provide an image formation apparatus, image formation method and program which can stably grip a printing medium and enhance the stability in conveyance of the printing medium.SOLUTION: An image formation apparatus includes: a rotor in which a gripper for gripping a printing medium at a specific rotation position on the surface is provided on the surface; a conveyance part which conveys the printing medium to the specific rotation position; a printing part which performs printing to the printing medium gripped by the gripper; a reading part which reads an image of the printing medium printed by the printing part; a calculation part which calculates a correction amount to a conveyance amount of the printing medium by the conveyance part from the physical relation between the tip in the conveyance direction of the printing medium indicated by the image read by the reading part and the gripper; a correction part which obtains the correction speed at which the conveyance part conveys the printing medium on the basis of the correction amount; and a changing part which changes the conveyance speed of the printing medium by the conveyance part to the correction speed obtained by the correction part.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, an image forming method, and a program.

  2. Description of the Related Art As a printing method by an image forming apparatus, there is known a method of performing double-sided printing by transporting a sheet, which is a printing medium, by a chain gripper while holding the sheet. In order to reduce the cost by such a method, there is a method in which a sheet is gripped only by a gripper in a printing unit and conveyed by a roller and a belt in other places. In the case of such a method, it is necessary to convey the sheet by rollers in accordance with the timing of opening and closing the gripper.

  In such a technique of gripping and transporting a sheet with a gripper at the time of printing, one point, for example, at the center of the leading end of the sheet is detected, and the opening and closing timing of the gripper is adjusted (for example, Patent Document 1).

  However, in the case of the duplex printing method, the paper may be deformed by passing through the drying unit. At this time, only one point, for example, at the center of the leading edge of the paper is detected, and the opening / closing timing of the gripper is determined. When combined, there is a problem that the gripper may not be able to hold the sheet stably (hereinafter, sometimes referred to as gripping).

  SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus, an image forming method, and a program that can perform stable grip on a print medium and increase the stability of transport of the print medium. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, the present invention provides a rotating body provided with a gripper for gripping a print medium at a specific rotational position on the surface, the print medium, A transport unit that transports the print medium toward the rotational position, a printing unit that prints on a print medium gripped by the gripper, a reading unit that reads an image of the print medium printed by the print unit, and the reading unit. A calculation unit that calculates a correction amount for the transport amount of the print medium by the transport unit from the positional relationship between the leading end of the print medium indicated by the image read in the transport direction of the image and the gripper, and based on the correction amount. A correction unit that determines a correction speed at which the transport unit transports a print medium, and a change unit that changes the transport speed of the print medium by the transport unit to the correction speed determined by the correction unit. Characterized by comprising a.

  ADVANTAGE OF THE INVENTION According to this invention, a stable grip can be performed with respect to a print medium, and the stability of conveyance of a print medium can be improved.

FIG. 1 is a diagram illustrating an example of the entire configuration of the image forming apparatus according to the embodiment. FIG. 2 is a diagram illustrating an example of a schematic configuration of an image forming unit of the image forming apparatus according to the embodiment. FIG. 3 is a diagram illustrating an example of a hardware configuration of an image forming unit of the image forming apparatus according to the embodiment. FIG. 4 is a diagram illustrating an example of a functional block configuration of an image forming unit of the image forming apparatus according to the embodiment. FIG. 5 is a diagram for explaining a speed change for eliminating a timing deviation due to conveyance unevenness or the like. FIG. 6 is a diagram illustrating an example of a state in which the sheet is gripped by the gripper without deformation. FIG. 7 is a diagram illustrating an example of a state where the paper is deformed and gripped by the gripper. FIG. 8 is a diagram illustrating an example of an image obtained by reading the state of the sheet gripped by the gripper. FIG. 9 is a diagram illustrating an example of a graph in which read values in a sub-scanning direction in a read image are plotted. FIG. 10 is a diagram for explaining a method of correcting the sheet conveyance. FIG. 11 is a diagram for explaining the timing at which the correction amount of the sheet conveyance is reflected. FIG. 12 is a flowchart illustrating an example of the flow of a printing operation in the image forming apparatus according to the embodiment.

  Hereinafter, embodiments of an image forming apparatus, an image forming method, and a program according to the present invention will be described in detail with reference to the drawings. Further, the present invention is not limited by the following embodiments, and components in the following embodiments may be easily conceived by those skilled in the art, may be substantially the same, and may have a so-called equivalent range. Is included. Furthermore, various omissions, substitutions, changes, and combinations of the components can be made without departing from the spirit of the following embodiments.

(Configuration of Image Forming Apparatus)
FIG. 1 is a diagram illustrating an example of the entire configuration of the image forming apparatus according to the embodiment. The overall configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feeding unit 11, a pre-coating unit 12, an image forming unit 13, a drying / cooling unit 14, a reversing unit 15, and a paper discharging unit 16. Have.

  The paper feed unit 11 is a unit that feeds paper, which is a print medium, one sheet at a time and transports the paper to the pre-coating unit 12.

  The pre-coating unit 12 is a unit for pre-applying a pre-coating liquid for fixing ink on paper. Since there are some papers on which the ink is difficult to be fixed, it is possible to easily fix the ink by applying the pre-coating liquid by the pre-coating unit 12 in advance. Further, the pre-coating unit 12 applies a pre-coating liquid to the sheet, and then dries the sheet by a heater, and conveys the sheet to the image forming unit 13.

  The image forming unit 13 is a unit that winds and conveys a sheet around a drum and performs a printing process (image formation) by a line head type recording head. Details of the configuration of the image forming unit 13 will be described later. The image forming unit 13 conveys the printed paper to the drying / cooling unit 14.

  The drying / cooling unit 14 is a unit that dries the moisture of the ink on the paper on which the image is printed and fixes the ink on the paper. After drying and cooling the paper, the drying / cooling unit 14 cools the heated paper to a lower temperature, and conveys the paper to the reversing unit 15.

  The reversing unit 15 performs switchback reversal on the paper on the front side printed from the drying / cooling unit 14 and conveys the paper to the image forming unit 13 when duplex printing is set. Unit. Here, the switchback reversal is perpendicular to the transport direction of the sheet, and is performed after the leading edge of the sheet passes through the reversing roller in order to exchange two opposing sides (the leading edge of the sheet and the trailing edge of the sheet). This is a reversing method in which the rotation direction of the reversing roller is reversed before the trailing end passes, and the trailing end of the sheet is conveyed with the leading end. When the normal printing (single-sided printing) is set instead of the double-sided printing, the reversing unit 15 conveys the sheet to the sheet discharging unit 16 without performing the switchback reversal on the sheet.

  The paper discharge unit 16 is a unit that discharges the printed paper conveyed from the reversing unit 15 to the stack unit.

  The unit configuration of the image forming apparatus 1 shown in FIG. 1 is an example, and other unit configurations may be used. For example, when the paper feed unit 11 has a large paper feed volume, a paper feed unit configured by connecting a plurality of units may be used. Further, for example, a registration unit that adjusts the transport timing and the position of the sheet may be disposed between the pre-coating unit 12 and the image forming unit 13.

  FIG. 2 is a diagram illustrating an example of a schematic configuration of an image forming unit of the image forming apparatus according to the embodiment. The schematic configuration of the image forming unit 13 of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 2, the image forming unit 13 of the image forming apparatus 1 includes a roller 131 (conveying unit), an inlet cylinder 132 (rotating body), a drum 133, and recording heads 134C, 134M, 134Y, and 134K (printing). ), An in-line sensor unit 135, an outlet cylinder 136, a registration timing sensor 137 (detection unit), a print timing sensor 138, and a home position sensor 139.

  The roller 131 adjusts the paper 20 (an example of a print medium) conveyed from the pre-coating unit 12 to the grip timing by the gripper 132a of the entrance cylinder 132 based on the timing at which the paper 20 is detected by the registration timing sensor 137. Rollers that convey the paper 20 as described above. Since the gripper 132a of the inlet cylinder 132 opens and closes at the point A (specific rotation position) only once per rotation of the inlet cylinder 132, the roller 131 is opened when the gripper 132a reaches the point A. At the timing, the sheet 20 is conveyed so that the leading end of the sheet 20 is located at the point A. Here, point A is a rotational position on the surface of the entrance cylinder 132 for gripping the paper 20 with the gripper 132a.

  The inlet cylinder 132 is connected to the drum 133 and the outlet cylinder 136 by a gear, rotates at a constant rotation speed, includes a gripper 132a that opens and closes mechanically, and conveys the paper 20 to the drum 133 while gripping the paper 20 with the gripper 132a. Cylinder. The structure of the gripper 132a will be described later.

  The drum 133 is a drum that conveys the paper 20 conveyed by the inlet cylinder 132 to a print area by the recording heads 134C, 134M, 134Y, and 134K by rotation.

  The recording heads 134C, 134M, 134Y, and 134K are line-type inkjet heads that perform processing of printing an image by discharging ink onto the paper 20 transported by the rotation of the drum 133. The recording heads 134C, 134M, 134Y, and 134K are based on the timing at which the print timing sensor 138 detects that the leading end of the sheet 20 has passed, and the relationship between an encoder (not shown) that detects the rotational position of the drum 133. Then, a printing process is performed on the paper 20. Note that the recording heads 134C, 134M, 134Y, and 134K are simply referred to as “recording heads 134” when any recording head is indicated or collectively referred to.

  The in-line sensor unit 135 is a unit that reads an image printed by the recording head 134 using an in-line sensor. The inline sensor unit 135 detects missing nozzles, bends, uneven density, and the like based on the read image, and eliminates or prevents grip failure caused by the gripper 132a due to deformation of the sheet. A correction amount for the transport amount is detected. The configuration of the in-line sensor unit 135 will be described later.

  The outlet cylinder 136 is a cylinder that conveys the printed paper 20 conveyed by the rotation of the drum 133 to the subsequent stage (drying / cooling unit 14).

  The registration timing sensor 137 is a sensor that detects the leading end of the sheet 20 conveyed by the roller 131. The detection timing of the leading end of the sheet 20 by the registration timing sensor 137 is used for the transport operation of the sheet 20 by the roller 131 as described above.

  The print timing sensor 138 is a sensor that detects the leading end of the paper 20 conveyed by the rotation of the drum 133. The detection timing of the leading end of the sheet 20 by the print timing sensor 138 is used for the printing process by the recording head 134 on the sheet 20 conveyed by the drum 133 as described above.

  The home position sensor 139 is a sensor that detects the home position of the inlet cylinder 132. For example, the home position sensor 139 detects a protrusion or the like formed at one position in the rotation direction of the inlet cylinder 132 as a home position. Since the positional relationship between the home position of the inlet cylinder 132 and the gripper 132a is known, the position of the gripper 132a in the rotational direction can be grasped by detecting the home position by the home position sensor 139.

(Hardware configuration of imaging unit)
FIG. 3 is a diagram illustrating an example of a hardware configuration of an image forming unit of the image forming apparatus according to the embodiment. The hardware configuration of the main part of the image forming unit 13 of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 3, the image forming unit 13 of the image forming apparatus 1 includes an in-line sensor unit 135, a CPU (Central Processing Unit) 201, a ROM (Read Only Memory) 202, and a memory 203 described above with reference to FIG. , A sensor I / F 204, a motor driving circuit 205, a head control circuit 206, and a gripper opening / closing unit 207. As shown in FIG. 3, the inline sensor unit 135 includes an inline sensor 1351, an A / D conversion circuit 1352, a shading correction circuit 1353, a memory 1354, and a detection circuit 1355 (an example of a calculation unit). Note that the “reading unit” of the present invention can be considered as the inline sensor 1351, or can be considered as the entire inline sensor unit 135 including the inline sensor 1351.

  The in-line sensor 1351 is a sensor that reads an image of the sheet 20 on which the print processing has been performed by the recording head 134. The in-line sensor 1351 includes a solid-state imaging device such as a charge-coupled device (CCD) or a complementary metal oxide semiconductor (CMOS), a light source such as an LED (Light Emitting Diode), a lens, and the like.

  The A / D conversion circuit 1352 is a circuit that performs A / D conversion on a signal output by the reading operation of the in-line sensor 1351 and obtains a read image.

  The shading correction circuit 1353 is a circuit that performs shading correction on the read image obtained by the A / D conversion circuit 1352 to correct unevenness in light amount and the like.

  The memory 1354 is a storage device that temporarily stores a read image (hereinafter, simply referred to as a read image) on which shading correction has been performed by the shading correction circuit 1353. The read image stored in the memory 1354 is used for correction in print processing for detecting density unevenness and the like and eliminating the density unevenness and the like. In the present embodiment, the read image is further processed by the roller 131 as described later. It is used for correcting the transport amount of the paper 20.

  The detection circuit 1355 is a circuit that detects a correction amount (ΔY described later) for the transport amount of the paper 20 by the roller 131 from the read image stored in the memory 1354.

  The CPU 201 is an arithmetic device that controls the overall operation of the image forming unit 13. The CPU 201 controls the operation of the entire image forming unit 13 using the memory 203 as a work memory according to a program stored in the ROM 202, for example.

  The sensor I / F 204 is an interface for receiving detection signals from the registration timing sensor 137, print timing sensor 138, home position sensor 139, and the like described above with reference to FIG.

  The motor drive circuit 205 is a circuit that rotationally drives the roller 131 and the inlet cylinder 132, the drum 133, and the outlet cylinder 136 according to a command from the CPU 201.

  The head control circuit 206 is a circuit that controls the ink ejection operation of the recording head 134 according to a command from the CPU 201.

  The gripper opening / closing unit 207 is an actuator or the like that performs an opening / closing operation (grip or grip release) of the gripper 132a of the inlet cylinder 132.

  Note that the hardware configuration of the image forming unit 13 shown in FIG. 3 is merely an example, and may include components other than the components shown in FIG. For example, an auxiliary storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive) for storing a read image read by the in-line sensor unit 135 or a program executed by the CPU 201 may be provided.

(Configuration of functional blocks of the imaging unit)
FIG. 4 is a diagram illustrating an example of a functional block configuration of an image forming unit of the image forming apparatus according to the embodiment. The configuration of the function lock of the image forming unit 13 of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 4, the image forming unit 13 of the image forming apparatus 1 includes a motor control unit 301, a timing acquisition unit 302, a timing correction unit 303, a speed change unit 304 (change unit), and an image acquisition unit 305. , An image processing unit 306, a conveyance correction amount calculation unit 307, a correction amount acquisition unit 308, a conveyance amount correction unit 309 (correction unit), and a storage unit 310.

  The motor control unit 301 is a functional unit that controls the rotation operation of the roller 131 and the inlet cylinder 132, the drum 133, and the outlet cylinder 136 via the motor drive circuit 205. The motor control unit 301 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The timing acquisition unit 302 is a functional unit that acquires detection signals received by the sensor I / F 204 from the registration timing sensor 137, the print timing sensor 138, and the home position sensor 139. The timing acquisition unit 302 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The timing correction unit 303 determines the transport speed of the sheet 20 by the rotation of the roller 131 when the timing at which the leading edge of the sheet 20 is detected by the registration timing sensor 137 is shifted due to uneven transport in the previous stage of the image forming unit 13. Is a functional unit that corrects The timing correction unit 303 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The speed changing unit 304 is a functional unit that changes the conveying speed of the roller 131 for the paper 20 based on the correction contents obtained by the timing correcting unit 303 and the conveying amount correcting unit 309. The speed changing unit 304 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The image acquisition unit 305 is a functional unit that acquires a read image read by the inline sensor unit 135. The image acquisition unit 305 is realized by, for example, an A / D conversion circuit 1352 that receives a signal output by a reading operation by the in-line sensor 1351, as shown in FIG. Note that the image acquisition unit 305 can be considered to be realized by a shading correction circuit 1353 that receives a read image obtained by AD conversion by the A / D conversion circuit 1352.

  The image processing unit 306 is a functional unit that executes various types of image processing (for example, shading correction) on the read image acquired by the image acquisition unit 305. The image processing unit 306 is realized by, for example, the shading correction circuit 1353 shown in FIG.

  The transport correction amount calculation unit 307 is a functional unit that calculates (detects) a correction amount (ΔY described later) for the transport amount of the paper 20 by the roller 131 from the read image after the image processing by the image processing unit 306. The transport correction amount calculation unit 307 is realized, for example, by the detection circuit 1355 shown in FIG.

  The correction amount acquisition unit 308 is a functional unit that acquires the correction amount ΔY calculated by the transport correction amount calculation unit 307. The correction amount acquisition unit 308 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The conveyance amount correction unit 309 uses the correction amount ΔY acquired by the correction amount acquisition unit 308 to detect the distance (conveyance) from the position where the registration timing sensor 137 detects the leading end of the sheet 20 to the point A shown in FIG. This is a functional unit for correcting the amount. The transport amount correction unit 309 is realized by, for example, a program executed by the CPU 201 illustrated in FIG.

  The storage unit 310 is a functional unit that stores programs executed by the CPU 201, various data, and correction data calculated by the timing correction unit 303 and the transport amount correction unit 309. The storage unit 310 is realized by, for example, the ROM 202 and the memory 203 illustrated in FIG.

  Some or all of the motor control unit 301, the timing acquisition unit 302, the timing correction unit 303, the speed change unit 304, the correction amount acquisition unit 308, and the transport amount correction unit 309 are not software programs but FPGA (Field). -It may be realized by a hardware circuit such as a Programmable Gate Array or an ASIC (Application Specific Integrated Circuit).

  In addition, the image acquisition unit 305, the image processing unit 306, and the transport correction amount calculation unit 307 are realized by circuits included in the in-line sensor unit 135, but are not limited thereto, and are executed by the CPU 201. The program may be realized by a program that executes the program.

  Further, each functional unit shown in FIG. 4 conceptually shows a function, and is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in the image forming unit 13 illustrated in FIG. 4 may be configured as one functional unit. On the other hand, the function of one function unit in the image forming unit 13 shown in FIG. 4 may be divided into a plurality of functions and configured as a plurality of function units.

(Change speed due to uneven transport)
FIG. 5 is a diagram for explaining a speed change for eliminating a timing deviation due to conveyance unevenness or the like. With reference to FIG. 5, a description will be given of a correction operation of the roller 131 with respect to the transport speed of the paper 20 when the timing at which the leading end of the paper 20 is detected by the registration timing sensor 137 is shifted due to transport unevenness or the like.

  First, the moving speed of the cylinder surface due to the rotation of the inlet cylinder 132 is V1, and from the position of the gripper 132a when the home position is detected by the home position sensor 139 by the rotation of the inlet cylinder 132, until the gripper 132a reaches the point A. The moving distance on the cylinder surface is D1. The time when the home position is detected by the home position sensor 139 due to the rotation of the inlet cylinder 132 is set to 0. In this case, the time T1 at which the gripper 132a reaches the point A is determined by D1 / V1.

  Further, the transport speed of the paper 20 due to the rotation of the roller 131 is V2, and the leading edge of the paper 20 is detected by the registration timing sensor 137 by the transport of the paper 20 by the roller 131. The transport distance of the paper 20 until it reaches is D2. The time when the leading end of the paper 20 is detected by the registration timing sensor 137 by the conveyance of the paper 20 by the roller 131 is defined as T2.

  In this case, the time from the time T2 until the gripper 132a reaches the point A is calculated by D1 / V1-T2. The time from the time T2 until the leading end of the sheet 20 reaches the point A is calculated as D2 / V2. Therefore, in order for the leading end of the sheet 20 to reach the point A at the timing when the gripper 132a reaches the point A, the following expression (1) may be satisfied.

  D1 / V1-T2 = D2 / V2 (1)

  Therefore, the motor control unit 301 only needs to control the rotation of the roller 131 so as to convey the sheet 20 at the conveyance speed V2 represented by the following equation (2).

  V2 = D2 / (D1 / V1-T2) (2)

  Basically, the paper 20 is transported such that V1 = V2 for the moving speed V1 and the transport speed V2, and the timing is adjusted so that the gripper 132a grips the leading end portion of the paper 20. However, at the time T2 when the leading end of the paper 20 is detected by the registration timing sensor 137, the operation of the transport mechanism in the preceding stage of the roller 131 varies depending on the paper type or thickness of the paper 20, and transport unevenness occurs. Hereinafter, an example of the operation of correcting the transport speed by the rollers 131 when the time at which the leading end of the sheet 20 is detected by the registration timing sensor 137 due to the transport unevenness is shifted from the time T2 will be described. FIG. 5 shows an example in which the leading end of the sheet 20 is delayed from the original time T2 detected by the registration timing sensor 137 to a time T2 '. In this case, in order to eliminate the delay from time T2 to time T2 ', the transport speed of the roller 131 by the motor control unit 301 is corrected as follows. Since the time T1 (= D1 / V1) is the timing at which the gripper 132a grips, the timing correction unit 303 adjusts the position of the leading end of the sheet 20 to the original position by the time T3 immediately before the roller 131a. Is corrected. Here, the timing at which the position of the leading end of the sheet 20 is set to the original position is not the time T1 but the time T3 which is the time immediately before the time T1. This is because when the paper 20 is gripped, the transport speed of the roller 131 changes from the original transport speed, and the paper 20 may collide with the gripper 132a.

  The operation of correcting the transport speed of the roller 131 by the timing correction unit 303 is specifically performed as follows. First, the transport distance D3 for transporting the paper 20 from the original time T2 to the time T3 is calculated by the following equation (3).

  D3 = (T3−T2) × V2 (3)

  Since the paper 20 needs to be transported by the transport distance D3 from time T2 ′ to time T3 when the leading end of the paper 20 is actually detected by the registration timing sensor 137, the timing correction unit 303 The corrected speed V2 ', which is the speed obtained by correcting the transport speed V2 according to the above, is calculated by the following equation (4).

V2 '= D3 / (T3-T2')
= {(T3-T2) / (T3-T2 ′)} × V2 (4)

  Therefore, from time T2 ′ to time T3, the speed changing unit 304 increases the transport speed of the roller 131 by the motor control unit 301 to the correction speed V2 ′ (> V2), and after time T3, returns to the original transport speed V2. What is necessary is just to switch.

(Change speed according to grip state)
FIG. 6 is a diagram illustrating an example of a state in which the sheet is gripped by the gripper without deformation. FIG. 7 is a diagram illustrating an example of a state where the paper is deformed and gripped by the gripper. A state in which the paper 20 is gripped by the gripper 132a will be described with reference to FIGS.

  FIG. 6 shows a state in which the paper 20 is gripped by the gripper 132a on the entrance cylinder 132 in a state where the paper 20 is not deformed. As shown in FIG. 6, the gripper 132a includes a frame 1321 extending in a direction (main scanning direction) perpendicular to the transport direction of the paper 20 and a plurality of claws extending in the transport direction at predetermined intervals from the frame 1321. 1322. The gripping of the paper 20 by the gripper 132a is performed by gripping the paper 20 with a plurality of claws 1322 as shown in FIG. In this state, the print timing sensor 138 detects the leading edge of the paper 20, and this detection timing is used as a reference for the print timing by the recording head 134.

  On the other hand, as described above, when performing double-sided printing, the paper 20 is again conveyed to the image forming unit 13 via the drying / cooling unit 14 and the reversing unit 15, but is transmitted via the drying / cooling unit 14. By doing so, the paper 20 may be deformed. In particular, in the image forming apparatus of the ink jet system, the sheet may be unevenly contracted and deformed due to the unevenness of the ink in the sheet (for example, an image on the right side with a large amount of applied ink). FIG. 7 shows a state in which the paper 20 is gripped by the gripper 132a in a state where the paper 20 is deformed and the leading end has a curved surface. In this case, the print timing sensor 138 detects at the center of the sheet 20 (any point in the main scanning direction even if not at the center), so it is determined that the paper 20 is held at a normal position. When the paper 20 is deformed as shown in FIG. 7, both ends of the paper 20 may come off the grip. Further, the paper 20 may be deformed not only in the case of the back side printing at the time of the duplex printing but also in the case of the front side printing. For example, there is a case where the paper 20 is deformed by the heat of the heater for drying the pre-coating liquid in the pre-coating unit 12 which is the former stage of the image forming unit 13. The following describes the operation of correcting the transport speed of the paper 20 by the rollers 131 in order to eliminate such a failure when the gripper 132a causes grip failure of the paper 20 or to prevent the failure from occurring. Will be described.

  FIG. 8 is a diagram illustrating an example of an image obtained by reading the state of the sheet gripped by the gripper. FIG. 9 is a diagram illustrating an example of a graph in which read values in a sub-scanning direction in a read image are plotted. FIG. 10 is a diagram for explaining a method of correcting the sheet conveyance. With reference to FIGS. 8 to 10, a description will be given of an operation of correcting the transport speed of the sheet 20 by the roller 131 according to the grip state of the sheet 20 by the gripper 132a.

  The read image 500 shown in FIG. 8 is an image obtained by reading a state in which the gripper 132a grips the paper 20 whose tip is deformed, as shown in FIG. 7 described above. The read image 500 includes a sheet portion 501 corresponding to the sheet 20, a gripper portion 502 corresponding to the gripper 132a, and a drum surface portion 503 corresponding to the surface of the drum 133.

  First, the transport correction amount calculation unit 307 extracts read values (pixel values) at positions X1 to X7 indicating positions between the claws 1322 in the main scanning direction in the read image. FIG. 9 shows an example of a graph (an example of the position X1) in which the extracted read values (pixel values) are plotted in the sub-scanning direction. In the graph shown in FIG. 9, the + direction of the sub-scanning direction on the horizontal axis corresponds to the downward direction in FIG. 8, and the read value shows a larger value as the luminance is higher. As shown in FIG. 9, the read value of the gripper unit 502 is Zb, which decreases to Za at the drum surface 503 and increases to Zc at the paper unit 501. Here, the conveyance correction amount calculation unit 307 obtains the position Ya of the boundary between the gripper unit 502 and the drum surface unit 503 and the position Yb of the boundary between the drum surface unit 503 and the paper unit 501. As a specific method of obtaining the positions Ya and Yb, for example, first, the above-described read values Za, Zb, and Zc are obtained, and a position in the sub-scanning direction that is an intermediate value between the read values Zb and Za is defined as a position Ya. The position in the sub-scanning direction that is an intermediate value between the read values Za and Zc is Yb.

  The larger the difference between the read value Zb of the gripper unit 502 and the read value Za of the drum surface unit 503 is, the greater the detection accuracy of the boundary between the gripper unit 502 and the drum surface unit 503 on the read image, that is, the position Ya Accuracy increases. Therefore, with respect to the surfaces of the gripper 132a and the drum 133 (the surface of the member carrying the print medium), the difference in the light reflectance is equal to or greater than a predetermined value that ensures a certain detection accuracy at the above-described boundary. Desirably.

  Then, the transport correction amount calculation unit 307 calculates the distance obtained by Yb-Ya as the distance Y1 from the frame 1321 of the gripper 132a at the position X1 to the leading end of the sheet 20. Similarly, the transport correction amount calculation unit 307 calculates the distance from the frame 1321 of the gripper 132a at the position X2 to X7 to the leading end of the sheet 20 as the distance Y2 to Y7, respectively. The distances Y1 to Y7 correspond to the distances indicated by arrows in FIG. Further, the transport correction amount calculation unit 307 extracts a minimum value as the distance Ymin and a maximum value as the distance Ymax from the distances Y1 to Y7, and extracts a center value Ytpy between the distance Ymin and the distance Ymax.

  Next, the target value of the distance from the frame 1321 to the leading end of the paper 20 when the paper 20 is gripped by the original gripper 132a is defined as a distance Y, and the length of the nail 1322, that is, the distance from the frame 1321 to the leading end of the nail 1322 FIG. 10 shows an example in which the length is set to the distance Ylim and the distances Ymin, Ymax, Ytpy, Y, and Ylim are plotted. Then, the transport correction amount calculation unit 307 calculates a correction amount ΔY with respect to the transport amount of the sheet 20 by the roller 131 using the following equation (5).

  ΔY = Ytype−Y (5)

  The correction amount acquisition unit 308 acquires the correction amount ΔY calculated (detected) by the transport correction amount calculation unit 307. Then, the transport amount correction unit 309 corrects the transport distance of the sheet 20 from the position of the leading edge when the leading edge of the paper 20 is detected by the registration timing sensor 137 until the leading edge reaches the point A to D2. The value obtained by adding the amount ΔY is applied to the above equation (2). Specifically, the transport amount correction unit 309 calculates a corrected speed V2a, which is a speed corrected for the original transport speed V2, by the following equation (6).

  V2a = (D2 + ΔY) / (D1 / V1-T2) (6)

  However, when ΔY is a positive value and Ymin−ΔY <0, the leading end of the sheet 20 collides with the gripper 132a (the frame 1321), so that the transport amount correction unit 309 sets the correction amount ΔY to Ymin> It is necessary to limit it to ΔY. Further, when ΔY is a negative value and Ymax−ΔY> Ylim, the paper 20 is disengaged from the nail 1322 and cannot be gripped. Therefore, the transport amount correction unit 309 restricts Ymax−ΔY <Ylim. There is a need to. That is, for example, the transport amount correction unit 309 limits the correction amount ΔY acquired by the correction amount acquisition unit 308 so that Ymax−Ylim <ΔY <Ymin.

  FIG. 11 is a diagram for explaining the timing at which the correction amount of the sheet conveyance is reflected. Next, referring to FIG. 11, the timing at which the speed changing unit 304 reflects the correction speed V2a calculated by the conveyance amount correction unit 309 on the conveyance speed of the paper 20 of the roller 131, that is, the conveyance speed of the paper 20, The timing for changing to the correction speed V2a will be described.

  After the gripping of the paper 20 by the gripper 132a, the in-line sensor unit 135 reads the image on the paper 20 and the detection circuit 1355 detects the correction amount ΔY. About three sheets, the grip operation by the gripper 132a has been completed. Therefore, the reason that the speed changing unit 304 reflects the correction amount ΔY calculated by the conveyance correction amount calculation unit 307 on the conveyance speed of the roller 131 is that the subsequent sheet, that is, the sheet that has already been gripped by the gripper 132a, This operation is performed for the transport operation after the first sheet.

  Also, the presence or absence and state of deformation are different between the case where the grip is performed when printing on the front surface of the paper 20 and the case where the grip is performed when printing on the back surface of the paper 20. Therefore, the correction amount ΔY (first correction amount) calculated based on the read image (first image) of the front surface (first surface) of the paper 20 is equal to the transport speed of the paper transported for printing the front surface. The correction amount ΔY (second correction amount) calculated based on the read image (second image) of the back surface (second surface) of the paper 20 needs to be reflected as the correction speed (first correction speed). Needs to be reflected as the correction speed (second correction speed) on the conveyance speed of the paper conveyed for printing.

In the example shown in FIG. 11, m-th page the correction amount [Delta] Y _m obtained from the read image on paper (Table), m + 4-page shows an example in which reflected in the conveying speed of the sheet (Table). Note that, in the example shown in FIG. 11, the operation of detecting the correction amount ΔY for each printed sheet 20 and reflecting the correction amount ΔY on the transport speed each time is shown. However, the present invention is not limited to this. The moving average (that is, the average) of ΔY or the multiple addition average may be reflected, or the correction amount ΔY may be detected and reflected at every predetermined number of sheets or every predetermined time. For example, in the case where the moving average of the correction amount ΔY is reflected, in FIG. 11, instead of the correction amount ΔY _{m + 2} , the correction amount Y calculated last time is used as the correction amount to be reflected on the sheet conveyance speed of the m + 6th page (table). The average value of _m and the correction amount Ym _{+ 2} may be used. As described above, by using the correction amount using the moving average, the multiple addition average, or the like, it is possible to reduce the variation in the detection result.

  Further, in the example shown in FIG. 11, the operation of detecting the correction amount ΔY for each printed sheet 20 and reflecting the correction amount ΔY on the transport speed each time is shown. However, the present invention is not limited to this. Alternatively, the correction amount ΔY may be calculated by acquiring the read image on the back side, and the correction amount ΔY may be reflected on the transport speed during normal printing. In addition, the correction amount ΔY calculated at the time of test printing may be calculated only for the image corresponding to the read image on the front surface.

(Flow of printing operation of image forming apparatus)
FIG. 12 is a flowchart illustrating an example of the flow of a printing operation in the image forming apparatus according to the embodiment. A flow of a printing operation including a correction operation in the image forming apparatus 1 (image forming unit 13) according to the present embodiment will be described with reference to FIG.

<Step S11>
The motor control unit 301 causes the paper 131 to be conveyed toward the point A shown in FIG. Then, control goes to a step S12.

<Step S12>
The gripper opening / closing unit 207 closes the gripper 132a at the timing when the gripper 132a reaches the point A by the rotation of the entrance cylinder 132, and grips the leading end of the paper 20. Then, control goes to a step S13.

<Step S13>
The paper 20 gripped by the gripper 132a is conveyed to the print area of the recording head 134 by the rotation of the entrance cylinder 132 and the drum 133. Then, control goes to a step S14.

<Step S14>
The head control circuit 206 causes the recording head 134 to perform an image printing process on the paper 20 based on the acquisition timing of the detection signal of the paper 20 by the print timing sensor 138 by the timing acquisition unit 302. Then, control goes to a step S15.

<Step S15>
The inline sensor unit 135 reads an image printed by the recording head 134. The image acquisition unit 305 acquires a read image read by the inline sensor unit 135. The image processing unit 306 performs various image processing (for example, shading correction) on the read image acquired by the image acquisition unit 305. Then, control goes to a step S16.

<Step S16>
The transport correction amount calculation unit 307 calculates (detects) a correction amount ΔY with respect to the transport amount of the paper 20 by the roller 131 from the read image after the image processing by the image processing unit 306. A specific method of calculating the correction amount ΔY is as described above. Then, control goes to a step S17.

<Step S17>
The correction amount acquisition unit 308 acquires the correction amount ΔY calculated (detected) by the transport correction amount calculation unit 307. The transport amount correction unit 309 calculates the transport distance of the sheet 20 from the position of the leading edge when the leading edge of the paper 20 is detected by the registration timing sensor 137 until the leading edge reaches the point A to D2, and the correction amount ΔY Is applied to the above equation (2). Specifically, the transport amount correction unit 309 calculates a correction speed V2a, which is a speed corrected for the original transport speed V2 of the roller 131, by using the above-described equation (6). Then, the speed changing unit 304 changes the transport speed of the roller 131 for transporting the paper 20 to the correction speed V2a calculated by the transport amount correction unit 309 according to the timing described above with reference to FIG.

  According to the flow of steps S11 to S17, a printing operation including a correction operation in the image forming apparatus 1 (image forming unit 13) is performed.

  As described above, the image forming apparatus 1 according to the present embodiment reads the printed image of the paper 20 and calculates (detects) the correction amount ΔY for the transport amount (the transport distance D2) of the paper 20 from the read image, Using the correction amount ΔY, a correction speed V2a, which is a speed corrected for the original transport speed V2 by the roller 131, is calculated. Then, the image forming apparatus 1 reflects the calculated correction speed V2a on the conveyance speed of the paper 20 of the roller 131 at a predetermined timing. Thus, stable gripping of the paper 20 by the gripper 132a can be performed, and the conveyance stability of the paper 20 can be enhanced.

  In each of the above embodiments, when at least one of the functional units of the image forming apparatus 1 (the image forming unit 13) is realized by executing a program, the program is previously installed in a ROM (Read Only Memory) or the like. Provided. The program executed by the image forming apparatus 1 (imaging unit 13) according to the above-described embodiment is a file in an installable format or an executable format, such as a CD-ROM (Compact Disc Read Only Memory) or a flexible disk. (FD), CD-R (Compact Disk-Recordable), or DVD (Digital Versatile Disc) or other computer-readable recording medium may be provided for recording. Also, a program to be executed by the image forming apparatus 1 (imaging unit 13) according to the above-described embodiment may be stored on a computer connected to a network such as the Internet, and provided by being downloaded via the network. You may comprise. Further, the program executed by the image forming apparatus 1 (imaging unit 13) according to the above-described embodiment may be provided or distributed via a network such as the Internet. The program executed by the image forming apparatus 1 (the image forming unit 13) of the above-described embodiment has a module configuration including at least one of the above-described functional units, and the actual hardware is a CPU. When the (CPU 201) reads and executes a program from the above-described storage device (such as the ROM 202), each of the above-described functional units is loaded on the main storage device (such as the memory 203) and generated.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Paper feed unit 12 Pre-coating unit 13 Image forming unit 14 Drying / cooling unit 15 Reversing unit 16 Paper discharge unit 20 Paper 131 Roller 132 Inlet cylinder 132a Gripper 133 Drum 134, 134C, 134K, 134M, 134Y Recording head 135 In-line sensor unit 136 Exit cylinder 137 Registration timing sensor 138 Print timing sensor 139 Home position sensor 201 CPU
202 ROM
203 Memory 204 Sensor I / F
205 Motor drive circuit 206 Head control circuit 207 Gripper opening / closing unit 301 Motor control unit 302 Timing acquisition unit 303 Timing correction unit 304 Speed change unit 305 Image acquisition unit 306 Image processing unit 307 Transport correction amount calculation unit 308 Correction amount acquisition unit 309 Transport amount Correction section 310 Storage section 500 Read image 501 Paper section 502 Gripper section 503 Drum surface section 1321 Frame 1322 Claw 1351 Inline sensor 1352 A / D conversion circuit 1353 Shading correction circuit 1354 Memory 1355 Detection circuit

JP 2014-073660 A

Claims (10)

A rotating body provided on the surface with a gripper for gripping a print medium at a specific rotational position on the surface,
A transport unit that transports the print medium toward the specific rotation position,
A printing unit that performs printing on a print medium gripped by the gripper,
A reading unit that reads an image of a print medium printed by the printing unit,
A calculating unit that calculates a correction amount for the transport amount of the print medium by the transport unit from the positional relationship between the leading end of the print medium indicated by the image read by the reading unit in the transport direction and the gripper;
A correction unit that calculates a correction speed at which the transport unit transports a print medium, based on the correction amount;
A changing unit that changes the transport speed of the print medium by the transport unit to the correction speed determined by the correction unit,
An image forming apparatus comprising:   The calculation unit may calculate the correction amount based on each distance between a leading end of a print medium indicated by the image in a transport direction and a plurality of positions on a frame of the gripper extending in a main scanning direction. Item 2. The image forming apparatus according to Item 1. A detection unit that detects a print medium conveyed by the conveyance unit, further comprising:
3. The image forming apparatus according to claim 1, wherein the calculation unit calculates the correction amount for the distance as a distance from a position at which a print medium is detected by the detection unit to the specific rotation position. 4. apparatus. The printing unit performs printing on at least one of a first surface and a second surface of a print medium,
The reading unit reads the image of the first surface as a first image when printed on the first surface by the printing unit, and reads the image of the second surface when printed on the second surface by the printing unit. Is read as a second image,
The calculation unit calculates a first correction amount as the correction amount from the first image, and calculates a second correction amount as the correction amount from the second image,
The correction unit obtains a first correction speed as the correction speed at which the conveyance unit conveys a print medium for printing on the first surface based on the first correction amount, and calculates a first correction speed based on the second correction amount. Determining a second correction speed as the correction speed at which the conveyance unit conveys a print medium for printing on the second surface;
The changing unit changes the transport speed when the transport unit transports a print medium to print the first surface to the first correction speed, and causes the transport unit to print on the second surface. The image forming apparatus according to claim 1, wherein a transport speed when transporting the print medium is changed to the second correction speed.   The image forming apparatus according to claim 1, wherein the change unit changes the correction speed to a conveyance speed of a print medium gripped by the gripper after a next print medium.   The image forming apparatus according to claim 1, wherein the calculation unit calculates an average or a weighted average of the correction amounts calculated for a plurality of print media as a new correction amount. The reading unit reads an image of a print medium printed by the printing unit during test printing,
The calculation unit calculates the correction amount based on the image read at the time of the test printing by the reading unit,
The correction unit determines the correction speed based on the correction amount calculated during the test printing by the correction unit,
The image forming apparatus according to claim 1, wherein the change unit changes a transport speed of the print medium by the transport unit to the correction speed during normal printing other than the test printing.   The difference between the reflectance of light of the gripper gripping a printing medium and the reflectance of light on the surface of a member conveying the printing medium is equal to or greater than a predetermined value. Item 10. The image forming apparatus according to item 1. A transport step in which a gripper for gripping the print medium at a specific rotational position on the surface transports the print medium by the transport unit toward the specific rotational position in the rotating body provided on the surface,
A printing step of printing on a print medium gripped by the gripper,
A reading step of reading an image of a printed print medium;
A calculating step of calculating a correction amount for the transport amount of the print medium by the transport unit from the positional relationship between the leading end of the print medium in the transport direction indicated by the read image and the gripper,
Based on the correction amount, the correction unit determines the correction speed at which the transport unit transports the print medium,
A changing step of changing the transport speed of the print medium by the transport unit to the correction speed,
An image forming method comprising: A transport step in which a gripper for gripping the print medium at a specific rotational position on the surface transports the print medium by the transport unit toward the specific rotational position in the rotating body provided on the surface,
A printing step of printing on a print medium gripped by the gripper,
A reading step of reading an image of a printed print medium;
Based on the positional relationship between the leading end of the print medium in the transport direction indicated by the read image and the gripper, the transport unit based on a correction amount calculated for the transport amount of the print medium by the transport unit by the calculation unit. A correction step for determining a correction speed for conveying the print medium,
A changing step of changing the transport speed of the print medium by the transport unit to the correction speed,
A program for causing a computer to execute.

Images