JP7200573B2 - Image forming apparatus, image forming method and program - Google Patents

Description

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

As a printing method using an image forming apparatus, a method is known in which a chain gripper grips and conveys a sheet, which is a printing medium, to perform double-sided printing. In order to reduce the cost of such a system, there is a system in which the paper is gripped by a gripper only in the printing section and conveyed by rollers and belts in other locations. In such a method, it is necessary to convey the paper by the rollers in accordance with the opening and closing timing of the gripper.

In such a technique of gripping and conveying a sheet with a gripper during printing, one point at the leading edge of the sheet, for example, the central portion, is detected to match the opening and closing timing of the gripper (for example, Japanese Patent Application Laid-Open No. 2002-100001).

However, in the case of the double-sided printing method, the paper may be deformed by passing through the drying unit. In this case, only one point at the leading edge of the paper, for example, the center, is detected to determine the opening and closing timing of the gripper. When combined, there is a problem that the gripper may not be able to stably grip the paper (hereinafter sometimes referred to as "gripping").

The present invention has been made in view of the above-described problems, and provides an image forming apparatus, an image forming method, and a program capable of stably gripping a print medium and improving the stability of transport of the print medium. intended to provide

In order to solve the above-described problems and achieve the object, the present invention provides a rotating body having a gripper provided on the surface thereof for gripping a print medium at a specific rotational position on the surface thereof, and a conveying unit that conveys toward a rotational position of; a drum that receives the print medium conveyed by the rotating body and gripped by the gripper and conveys the print medium by rotation ; a printing unit that prints on the printing medium gripped by the gripper ; a reading unit that reads an image of the printing medium printed by the printing unit; a calculation unit that calculates a correction amount for the amount of conveyance of the print medium by the conveyance unit from the positional relationship between the gripped leading end of the print medium in the conveyance direction and the gripper; A correcting unit that obtains a corrected speed for conveying a print medium, and a changing unit that changes the conveying speed of the print medium by the conveying unit to the corrected speed obtained by the correcting unit.

According to the present invention, it is possible to stably grip the print medium and improve the stability of transport of the print medium.

FIG. 1 is a diagram illustrating an example of the overall configuration of an image forming apparatus according to an 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 configuration of functional blocks of an image forming unit of the image forming apparatus according to the embodiment; 5A and 5B are diagrams for explaining speed change for eliminating timing deviations due to unevenness in conveyance or the like. FIG. 6 is a diagram showing an example of a state in which the paper is gripped by the gripper without deformation. FIG. 7 is a diagram showing an example of a state in which the paper is gripped by the gripper while the paper is deformed. FIG. 8 is a diagram showing an example of an image obtained by reading the state of the paper gripped by the gripper. FIG. 9 is a diagram showing an example of a graph plotting reading values in the sub-scanning direction in a read image. FIG. 10 is a diagram for explaining a correction method for paper conveyance. FIG. 11 is a diagram for explaining the timing of reflecting the correction amount for paper conveyance. FIG. 12 is a flow chart showing an example of the flow of printing operation in the image forming apparatus according to the embodiment.

Exemplary embodiments of an image forming apparatus, an image forming method, and a program according to the present invention will be described in detail below with reference to the drawings. In addition, the present invention is not limited by the following embodiments, and the constituent elements in the following embodiments can be easily conceived by those skilled in the art, substantially the same, and so-called equivalent ranges. is included. Furthermore, various omissions, replacements, changes and combinations of components can be made without departing from the gist of the following embodiments.

(Configuration of image forming apparatus)
FIG. 1 is a diagram illustrating an example of the overall configuration of an image forming apparatus according to an embodiment. An overall configuration of an 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. I have.

The paper feed unit 11 is a unit that feeds sheets of paper, which are print media, one by one and conveys them to the pre-coating unit 12 .

The pre-coating unit 12 is a unit that pre-applies a pre-coating liquid for fixing the ink on the paper. Since there are some papers on which the ink is difficult to fix, the pre-coating unit 12 pre-applies the pre-coating liquid so that the ink can be easily fixed. Also, the pre-coating unit 12 applies the pre-coating liquid to the paper, dries it with a heater, and conveys the paper to the image forming unit 13 .

The image forming unit 13 is a unit that conveys a sheet of paper wrapped around a drum and performs print processing (image formation) using a recording head of a line head type. 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 to the paper. After drying the paper, the drying/cooling unit 14 cools the hot paper to lower the temperature, and conveys the paper to the reversing unit 15 .

When double-sided printing is set, the reversing unit 15 performs switchback reversal on the paper conveyed from the drying/cooling unit 14 and printed on the front side, and conveys the paper to the image forming unit 13. is a unit. Here, the switchback inversion is perpendicular to the paper conveying direction, and is performed after the leading edge of the paper passes through the inverting rollers in order to switch two opposite sides (the edge of the leading edge of the sheet and the edge of the trailing edge of the sheet). , the rotation direction of the reversing roller is reversed before the trailing edge passes through, and the edge of the sheet that was the trailing edge is conveyed as the leading edge. Further, when normal printing (single-sided printing) is set instead of double-sided printing, the reversing unit 15 conveys the paper to the paper discharge unit 16 without performing switchback inversion on the paper.

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

Note that 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, if the paper feeding unit 11 has a large paper feeding volume, the paper feeding unit may be configured by connecting a plurality of units. Further, for example, a registration unit may be arranged between the pre-coating unit 12 and the image forming unit 13 to adjust the transport timing and the position of the paper.

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; A 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 (conveyance unit), an inlet cylinder 132 (rotating body), a drum 133, and recording heads 134C, 134M, 134Y, 134K (printing section), an in-line sensor unit 135 , an exit cylinder 136 , a registration timing sensor 137 (detection section), a print timing sensor 138 and a home position sensor 139 .

The roller 131 adjusts the gripping timing of the paper 20 (an example of the print medium) conveyed from the pre-coating unit 12 by the gripper 132a of the entrance cylinder 132 based on the timing at which the registration timing sensor 137 detects the paper 20. It is a registration roller that conveys the paper 20 as shown in FIG. Since the gripper 132a of the inlet cylinder 132 opens and closes at point A (specific rotational position) only once per rotation of the inlet cylinder 132, the roller 131 reaches the point A and is in an open state. The paper 20 is conveyed so that the leading edge of the paper 20 is positioned at the point A at the timing. Here, point A is the rotational position on the surface of inlet cylinder 132 for gripping sheet 20 with gripper 132a.

The entrance cylinder 132 is connected to the drum 133 and the exit cylinder 136 by gears, rotates at a constant rotational speed, and has a gripper 132a that mechanically opens and closes. It is a cylinder that The structure of the gripper 132a will be described later.

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

The recording heads 134C, 134M, 134Y, and 134K are line-type inkjet heads that print images by ejecting ink onto the paper 20 conveyed by the rotation of the drum 133 . The recording heads 134C, 134M, 134Y, and 134K are based on the relationship between the timing at which the print timing sensor 138 detects that the leading edge of the paper 20 has passed, and the encoder (not shown) that detects the rotational position of the drum 133. Then, the 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 indicating arbitrary recording heads or when collectively referring to them.

The inline sensor unit 135 is a unit that reads an image printed by the recording head 134 with an inline sensor. The in-line sensor unit 135 detects missing nozzles, bending, density unevenness, etc. from the read image, and also detects or prevents poor gripping by the gripper 132a due to deformation of the paper. A correction amount for the transport amount is detected. The configuration of the in-line sensor unit 135 will be described later.

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

The registration timing sensor 137 is a sensor that detects the leading edge of the paper 20 conveyed by the rollers 131 . The detection timing of the leading edge of the paper 20 by the registration timing sensor 137 is used for the conveying operation of the paper 20 by the rollers 131 as described above.

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

A 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 projection or the like formed at one position in the rotational direction of the inlet cylinder 132 as the home position. Since the positional relationship between the home position of the inlet cylinder 132 and the gripper 132a is known, detection of the home position by the home position sensor 139 allows the position of the gripper 132a in the rotational direction to be grasped.

(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 this 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 the in-line sensor unit 135 described above with reference to FIG. , a sensor I/F 204 , a motor drive circuit 205 , a head control circuit 206 , and a gripper opening/closing unit 207 . The inline sensor unit 135, as shown in FIG. 3, has 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 section). The “reading unit” of the present invention can be considered as the in-line sensor 1351 or the entire in-line sensor unit 135 including the in-line sensor 1351 .

The in-line sensor 1351 is a sensor that reads an image on the paper 20 printed by the recording head 134 . The in-line sensor 1351 includes a solid-state imaging device such as a CCD (Charge-Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), 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 AD conversion on the signal output by the reading operation of the in-line sensor 1351 and acquires it as a read image.

The shading correction circuit 1353 is a circuit that executes shading correction for correcting unevenness in the amount of light on the read image obtained by the A/D conversion circuit 1352 .

The memory 1354 is a storage device that temporarily stores a read image that has been subjected to shading correction by the shading correction circuit 1353 (hereinafter simply referred to as a read image). The read image stored in the memory 1354 is used for correction in printing processing for detecting density unevenness and the like and eliminating the density unevenness. It is used for correction of the transport amount of the paper 20 .

A detection circuit 1355 is a circuit for detecting a correction amount (.DELTA.Y to be described later) for the conveying amount of the paper 20 by the roller 131 from the read image stored in the memory 1354. FIG.

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

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

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

A head control circuit 206 is a circuit that controls the ink ejection operation of the print head 134 in accordance with 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 132 a of the inlet cylinder 132 .

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

(Structure of Functional Blocks of Imaging Unit)
FIG. 4 is a diagram illustrating an example of a configuration of functional blocks 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 this 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 rotational operations of the roller 131 , the inlet cylinder 132 , the drum 133 and the outlet cylinder 136 via the motor drive circuit 205 . The motor control unit 301 is implemented by, for example, a program executed by the CPU 201 shown in FIG.

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

The timing correction unit 303 adjusts the conveying speed of the paper 20 by rotating the roller 131 when the timing at which the registration timing sensor 137 detects the leading edge of the paper 20 is deviated due to uneven conveyance in the front stage of the image forming unit 13 or the like. It is a functional unit that corrects the The timing correction unit 303 is realized by, for example, a program executed by the CPU 201 shown in FIG.

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

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

The image processing unit 306 is a functional unit that performs various image processing (such as shading correction) on the read image acquired by the image acquiring unit 305 . The image processing unit 306 is implemented by, for example, the shading correction circuit 1353 shown in FIG.

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

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

The conveyance amount correction unit 309 uses the correction amount ΔY acquired by the correction amount acquisition unit 308 to calculate the distance (conveyance It is a functional unit that corrects the amount of The transport amount correction unit 309 is realized by, for example, a program executed by the CPU 201 shown in FIG.

The storage unit 310 is a functional unit that stores programs executed by the CPU 201, various data, correction data calculated by the timing correction unit 303 and the transport amount correction unit 309, and the like. The storage unit 310 is realized by the ROM 202 and the memory 203 shown in FIG. 3, for example.

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 - Programmable Gate Array) or hardware circuits such as ASIC (Application Specific Integrated Circuit).

Further, although the image acquisition unit 305, the image processing unit 306, and the transport correction amount calculation unit 307 are implemented by circuits included in the inline sensor unit 135, they are not limited to this, and are executed by the CPU 201. It may be implemented by a program that

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

(Speed change due to transport unevenness, etc.)
5A and 5B are diagrams for explaining speed change for eliminating timing deviations due to unevenness in conveyance or the like. Referring to FIG. 5, an operation for correcting the conveying speed of the paper 20 of the roller 131 when the timing at which the registration timing sensor 137 detects the leading edge of the paper 20 is deviated due to uneven conveyance or the like will be described.

First, the moving speed of the cylinder surface due to the rotation of the inlet cylinder 132 is V1, and the position of the gripper 132a when the home position sensor 139 detects the home position due to the rotation of the inlet cylinder 132 until the gripper 132a reaches the point A. on the cylinder surface is defined as D1. The time when the home position sensor 139 detects the home position due to the rotation of the inlet cylinder 132 is defined as zero. In this case, the time T1 at which the gripper 132a reaches the point A is obtained by D1/V1.

Also, the transport speed of the paper 20 by the rotation of the roller 131 is V2, and the leading edge of the paper 20 is detected by the registration timing sensor 137 as the paper 20 is transported by the roller 131, and the leading edge is at the point A. Let D2 be the conveying distance of the paper 20 until it reaches the destination. The time when the leading edge of the paper 20 is detected by the registration timing sensor 137 as the paper 20 is conveyed by the rollers 131 is T2.

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

D1/V1-T2=D2/V2 (1)

Therefore, the motor control unit 301 should control the rotation of the roller 131 so that the sheet 20 is conveyed at the conveying speed V2 given by the following equation (2).

V2=D2/(D1/V1-T2) (2)

Basically, the gripper 132a grips the leading edge of the paper 20 by conveying the paper 20 such that V1=V2 with respect to the moving speed V1 and the conveying speed V2. However, at time T2 when the leading edge of the paper 20 is detected by the registration timing sensor 137, the operation of the transport mechanism preceding the rollers 131 varies depending on the paper type or thickness of the paper 20, resulting in uneven transport. An example of the correcting operation of the conveying speed by the rollers 131 when the time at which the registration timing sensor 137 detects the leading edge of the paper 20 deviates from the time T2 due to the uneven conveyance will be described below. FIG. 5 shows an example in which the leading edge of the paper 20 is delayed from the original time T2 detected by the registration timing sensor 137 to time T2'. In this case, in order to eliminate the delay from time T2 to time T2', the conveying speed of the roller 131 by the motor control unit 301 is corrected as follows. Since time T1 (=D1/V1) is the timing at which the gripper 132a grips, the timing correction unit 303 adjusts the roller 131 so that the position of the leading edge of the paper 20 is at the original position by time T3 before that. correct the transport speed of the Here, the timing at which the leading edge of the paper 20 is brought to the original position is not time T1, but time T3, which is the time before that, is because, if the timing is time T1, the gripper 132a This is because when the paper 20 is gripped, the conveying speed by the rollers 131 changes from the original conveying speed, and there is a possibility that the paper 20 collides with the gripper 132a.

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

D3=(T3-T2)×V2 (3)

Since it is necessary to convey the paper 20 by the conveying distance D3 from the time T2′ when the leading edge of the paper 20 is actually detected by the registration timing sensor 137 to the time T3, the timing correction unit 303 does not replace the original roller 131 A corrected speed V2′, which is a speed obtained by correcting the conveying speed V2 by using the following equation (4), is calculated.

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

Therefore, the speed changing unit 304 increases the conveying speed of the rollers 131 by the motor control unit 301 to the corrected speed V2′ (>V2) from time T2′ to time T3, and after time T3, increases the conveying speed to the original conveying speed V2. It can be switched.

(Speed change according to grip condition)
FIG. 6 is a diagram showing an example of a state in which the paper is gripped by the gripper without deformation. FIG. 7 is a diagram showing an example of a state in which the paper is gripped by the gripper while the paper is deformed. A state in which the paper 20 is gripped by the gripper 132a will be described with reference to FIGS. 6 and 7. FIG.

FIG. 6 shows a state in which the paper 20 is gripped by the gripper 132a on the entrance cylinder 132 when 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 conveying direction of the paper 20, and a plurality of claws extending from the frame 1321 at predetermined intervals in the conveying direction. 1322 and . The paper 20 is gripped by the gripper 132a 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 the reference for the print timing of the recording head 134 .

On the other hand, as described above, in the case of performing double-sided printing, the paper 20 is transported again to the image forming unit 13 via the drying/cooling unit 14 and the reversing unit 15, but passes through the drying/cooling unit 14. By doing so, the paper 20 may be deformed. In particular, in an inkjet image forming apparatus, unevenness of ink in the paper (for example, an image with a large amount of ink applied on the right side) may cause the paper to shrink and deform unevenly. 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 to have a curved front end. In this case, since the print timing sensor 138 performs detection at the center of the paper 20 (one point in the main scanning direction even if it is not at the center), it is determined that the paper is gripped at a normal position. 7, both ends of the paper 20 may come out of the grips. Further, there is a possibility that the paper 20 is deformed not only in the case of printing on the back side of double-sided printing, but also in the case of printing on the front side. For example, in the pre-coating unit 12 on the front side of the image forming unit 13, the paper 20 is deformed by the heat of the heater for drying the pre-coating liquid. The operation of correcting the conveying speed of the paper 20 of the roller 131 in order to eliminate the poor gripping of the paper 20 by the gripper 132a or to prevent the occurrence of such failure will be described below. to explain.

FIG. 8 is a diagram showing an example of an image obtained by reading the state of the paper gripped by the gripper. FIG. 9 is a diagram showing an example of a graph plotting reading values in the sub-scanning direction in a read image. FIG. 10 is a diagram for explaining a correction method for paper conveyance. 8 to 10, the operation of correcting the conveying speed of the paper 20 of the roller 131 according to the gripping state of the paper 20 by the gripper 132a will be described.

A 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 leading edge is deformed as shown in FIG. The read image 500 includes a sheet portion 501 corresponding to the sheet 20 , a gripper portion 502 corresponding to the gripper 132 a and a drum surface portion 503 corresponding to the surface of the drum 133 .

First, the conveyance 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 in which the read values (pixel values) thus extracted are plotted in the sub-scanning direction (example of position X1). 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 higher the luminance, the larger the read value. As shown in FIG. 9, the gripper portion 502 reading is Zb, the drum surface portion 503 drops to Za, and the paper portion 501 rises to Zc. Here, the conveyance correction amount calculation unit 307 obtains the boundary position Ya between the gripper section 502 and the drum surface section 503 and the boundary position Yb between the drum surface section 503 and the paper section 501 . As a specific method of obtaining the positions Ya and Yb, for example, first, the above read values Za, Zb and Zc are obtained, and the position in the sub-scanning direction that is the intermediate value of the read values Zb and Za is set as the position Ya. , and the intermediate value of the read values Za and Zc is assumed to be Yb.

Note that the larger the difference between the read value Zb of the gripper portion 502 and the read value Za of the drum surface portion 503, the higher the detection accuracy of the boundary between the gripper portion 502 and the drum surface portion 503 on the read image, that is, the position Ya. higher accuracy. Therefore, the difference in light reflectance between the surfaces of the gripper 132a and the drum 133 (the surface of the member that conveys the print medium) is greater than or equal to a predetermined value that ensures a certain level of detection accuracy for the boundary described above. It is desirable to have

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 to the leading edge of the paper 20 at the position X1. Similarly, the transport correction amount calculator 307 calculates the distances from the frame 1321 of the gripper 132a to the leading edge of the paper 20 at the positions X2 to X7 as distances Y2 to Y7, respectively. Distances Y1 to Y7 correspond to distances indicated by arrows in FIG. Further, the transport correction amount calculation unit 307 extracts the minimum value as the distance Ymin and the maximum value as the distance Ymax from the distances Y1 to Y7, and extracts the central value Ytpy between the distances Ymin and Ymax.

Next, let Y be the target value of the distance from the frame 1321 to the tip of the paper 20 when the paper 20 is gripped by the original gripper 132a, and the length of the claw 1322, that is, the distance from the frame 1321 to the tip of the claw 1322 FIG. 10 shows an example of plotting the distances Ymin, Ymax, Ytpy, Y, and Ylim, with the length being the distance Ylim. Then, the conveyance correction amount calculation unit 307 calculates a correction amount ΔY for the conveyance amount of the paper 20 by the rollers 131 using the following formula (5).

ΔY=Ytyp−Y (5)

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

V2a=(D2+ΔY)/(D1/V1-T2) (6)

However, when ΔY is a positive value and Ymin−ΔY<0, the leading edge of the paper 20 collides with the gripper 132a (frame 1321). It is necessary to limit to ΔY. Further, when ΔY is a negative value and Ymax−ΔY>Ylim, the paper 20 comes off the pawl 1322 and cannot be gripped. 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 to a range of Ymax−Ylim<ΔY<Ymin.

FIG. 11 is a diagram for explaining the timing of reflecting the correction amount for paper conveyance. Next, referring to FIG. 11, the speed changing unit 304 changes the timing of reflecting the corrected speed V2a calculated by the conveying amount correcting unit 309 to the conveying speed of the paper 20 of the roller 131, that is, the conveying speed of the paper 20. The timing of changing to the correction speed V2a will be described.

After the paper 20 is gripped by the gripper 132a, the image of the paper 20 is read by the in-line sensor unit 135, and the detection circuit 1355 detects the correction amount ΔY. The gripping operation by the gripper 132a is completed for about three sheets. Therefore, the speed changing unit 304 reflects the correction amount ΔY calculated by the conveying correction amount calculating unit 307 in the conveying speed of the roller 131 only after that, that is, after the sheet that has already been gripped by the gripper 132a. This is to be performed for the conveying operation after the first sheet.

Further, the presence or absence of deformation and the state of deformation differ between the case where the paper 20 is gripped when printing on its front surface and the case where it is gripped 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 depends on the transport speed of the paper transported for printing the front surface. It is necessary to reflect it as the correction speed (first correction speed), and the correction amount ΔY (second correction amount) calculated based on the read image (second image) of the back side (second side) of the paper 20 is is reflected as a correction speed (second correction speed) in the transport speed of the paper transported for printing.

The example shown in FIG. 11 shows an example in which the correction amount ΔYm obtained from the read image of the _m -th page (front) sheet is reflected in the conveying speed of the (m+4)-th page (front) sheet. Note that the example shown in FIG. 11 shows an operation in which the correction amount ΔY is detected for each printed sheet 20 and reflected in the conveying speed each time, but the present invention is not limited to this, and the correction amount A moving average (that is, average) of ΔY or a weighted average may be reflected, or the correction amount ΔY may be detected and reflected at predetermined number of sheets or at predetermined time intervals. For example, when reflecting the moving average of the correction amount _ΔY , in FIG. An average value of _m and correction amount Y _m+2 may be used. In this way, by using a correction amount using a moving average, weighted average, or the like, variations in detection results can be reduced.

In the example shown in FIG. 11, the correction amount ΔY is detected for each printed sheet 20 and reflected in the conveying speed each time. and the read image of the back side may be acquired to calculate each correction amount .DELTA.Y, and the correction amount .DELTA.Y may be reflected in the conveying speed during normal printing. Further, the correction amount ΔY calculated during test printing may be calculated only for the read image on the front side.

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

<Step S11>
The motor control unit 301 causes the roller 131 to convey the paper 20 toward the point A shown in FIG. Then, the process proceeds to step S12.

<Step S12>
The gripper opening/closing unit 207 closes the gripper 132 a at the timing when the gripper 132 a reaches the point A due to the rotation of the inlet cylinder 132 to grip the leading edge of the paper 20 . Then, the process proceeds to step S13.

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

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

<Step S15>
The in-line sensor unit 135 reads images printed by the recording head 134 . The image acquisition unit 305 acquires the read image read by the inline sensor unit 135 . An image processing unit 306 executes various image processing (for example, shading correction, etc.) on the read image acquired by the image acquisition unit 305 . Then, the process proceeds to step S16.

<Step S16>
A conveyance correction amount calculation unit 307 calculates (detects) a correction amount ΔY for the conveyance amount of the paper 20 by the rollers 131 from the read image after image processing by the image processing unit 306 . A specific method for calculating the correction amount ΔY is as described above. Then, the process proceeds to step S17.

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

According to the flow of steps S11 to S17 described above, the printing operation including the 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, calculates (detects) the correction amount ΔY for the conveyance amount (conveyance distance D2) of the paper 20 from the read image, Using the correction amount ΔY, a corrected speed V2a, which is a speed obtained by correcting the original conveying speed V2 of the rollers 131, is calculated. Then, the image forming apparatus 1 reflects the calculated correction speed V2a on the conveying speed of the paper 20 of the roller 131 at a predetermined timing. As a result, the gripper 132a can stably grip the paper 20, and the stability of the transportation of the paper 20 can be improved.

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

1 Image Forming Apparatus 11 Paper Feed Unit 12 First Coating Unit 13 Image Forming Unit 14 Drying/Cooling Unit 15 Reversing Unit 16 Paper Discharge Unit 20 Paper 131 Roller 132 Entrance 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 ROMs
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 Conveyance correction amount calculation unit 308 Correction amount acquisition unit 309 Conveyance amount Correction unit 310 storage unit 500 read image 501 paper unit 502 gripper unit 503 drum surface unit 1321 frame 1322 claw 1351 in-line 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 with a gripper on the surface for gripping the print medium at a specific rotational position on the surface;
a transport unit that transports the print medium toward the specific rotational position;
a drum that receives the print medium gripped by the gripper that is transported by the rotating body and transports the print medium by rotation;
a printing unit that prints on a print medium conveyed by the drum and gripped by the gripper ;
a reading unit that reads an image on a printing medium printed by the printing unit;
calculating a correction amount for the conveying amount of the print medium by the conveying unit from the positional relationship between the gripper and the tip of the print medium gripped by the gripper in the conveying direction indicated by the image read by the reading unit; a calculation unit;
a correction unit that determines a correction speed for conveying the print medium by the conveying unit based on the correction amount;
a changing unit that changes the transport speed of the print medium by the transport unit to the corrected speed obtained by the correcting unit;
image forming apparatus. The calculation unit calculates the correction amount based on each distance between a leading end of the print medium in the conveying direction indicated by the image and a plurality of positions of the gripper on a frame extending in the main scanning direction. Item 1. The image forming apparatus according to item 1. further comprising a detection unit that detects the print medium transported by the transport unit,
3. The image formation according to claim 1, wherein the calculation unit calculates the correction amount for the distance from the position where the print medium is detected by the detection unit to the specific rotation position as the transport amount. Device. The printing unit prints 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. read the image of as the second image,
The calculation unit calculates a first correction amount as the correction amount from the first image, calculates a second correction amount as the correction amount from the second image, and
Based on the first correction amount, the correction unit obtains a first correction speed as the correction speed for conveying the print medium for printing on the first surface by the conveying unit, and calculates a first correction speed based on the second correction amount. obtaining a second corrected speed as the corrected speed at which the conveying unit conveys the print medium for printing on the second surface;
The change unit changes the transport speed when the transport unit transports the print medium for printing on the first side to the first correction speed, 4. The image forming apparatus according to any one of claims 1 to 3, wherein the conveying speed for conveying the print medium is changed to the second corrected speed. The image forming apparatus according to any one of claims 1 to 4, wherein the changing unit changes the conveying speed of the print medium after the print medium gripped by the gripper to the corrected speed. The image forming apparatus according to any one of claims 1 to 5, 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 the printing medium printed by the printing unit during test printing,
The calculation unit calculates the correction amount based on the image read by the reading unit during the test printing,
The correction unit obtains the correction speed based on the correction amount calculated by the correction unit during the test printing,
The image forming apparatus according to any one of claims 1 to 6, wherein the change unit changes the transport speed of the print medium by the transport unit to the correction speed during normal printing that is not the test printing. 8. The difference between the light reflectance of the gripper gripping the print medium and the light reflectance of the surface of the member conveying the print medium is equal to or greater than a predetermined value. 10. The image forming apparatus according to claim 1. a first conveying step of conveying the print medium by a conveying unit toward a specific rotational position on a rotating body having a gripper provided on the surface for gripping the print medium at a specific rotational position on the surface;
a second conveying step of receiving the print medium gripped by the gripper conveyed by the rotating body with a drum and conveying the print medium by rotation of the drum;
printing on a print medium conveyed by the drum and gripped by the gripper ;
a reading step of reading an image of the printed print medium;
a calculation 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 gripped by the gripper in the transport direction and the gripper indicated by the read image;
a correction step of obtaining a correction speed for conveying the print medium by the conveying unit based on the correction amount;
a changing step of changing the conveying speed of the print medium by the conveying unit to the corrected speed;
An image forming method comprising: a first conveying step of conveying the print medium by a conveying unit toward a specific rotational position on a rotating body having a gripper provided on the surface for gripping the print medium at a specific rotational position on the surface;
a second conveying step of receiving the print medium gripped by the gripper conveyed by the rotating body with a drum and conveying the print medium by rotation of the drum;
printing on a print medium conveyed by the drum and gripped by the gripper ;
a reading step of reading an image of the printed print medium;
A correction amount calculated by a calculation unit for the transport amount of the print medium by the transport unit, based on the positional relationship between the leading edge of the print medium gripped by the gripper in the transport direction and the gripper, which is indicated by the read image. a correction step of obtaining a corrected speed at which the transport unit transports the print medium based on
a changing step of changing the conveying speed of the print medium by the conveying unit to the corrected speed;
A program that causes a computer to run

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