Image forming apparatus and program

Abstract

To prevent occurrence of damage to a transfer member and transfer failure, while maintaining a pressure-contact state of the transfer member when a sheet has a step in an image forming apparatus.SOLUTION: An image forming apparatus has an image forming unit that forms an image, a transfer unit that transfers the image to a sheet, and a control unit. The control unit acquires step information on a step in the sheet, and changes the contact pressure on the transfer member in a pressure-contact state on the basis of the acquired step information.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a program.

Background Art

[0002] When there is a step in the paper due to, for example, connecting roll paper with tape or cutting out the paper on the seal side of label paper, transfer failure may occur when the step passes through the nip of the transfer unit. In addition, the transfer member may be damaged, and image defects may occur during subsequent transfer.

[0003] To avoid this, Patent Document 1 describes providing detection means for detecting a seam upstream of paper conveyance and separating the transfer member in accordance with the arrival of the seam.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the technology of Patent Document 1, when a seam is detected, the transfer member is separated. However, when the transfer member is separated, it takes time until transfer resumes, resulting in a decrease in productivity. In addition, the impact of the separation operation is transmitted to the primary transfer unit, causing transfer deviation, problems such as the relationship between the image positions before and after being shifted, or the occurrence of waste paper to align the image positions.

[0006] An object of the present invention is to enable suppression of damage to the transfer member and transfer failure while maintaining the pressure contact state of the transfer member when there is a step in the paper in an image forming apparatus.

Means for Solving the Problems

[0007] To solve the above problems, an image forming apparatus according to the present invention includes an image forming unit that forms an image, a transfer unit that transfers the image onto a recording medium by passing the image formed by the image forming unit and the recording medium through a transfer nip formed by a transfer member in a pressure-contact state, and a control unit that acquires step information of a step in the recording medium and changes the pressure applied to the transfer member in the pressure-contact state based on the acquired step information. The image forming apparatus according to the present invention is provided with the above components.

[0008] A program according to the present invention causes a computer of an image forming apparatus including an image forming unit that forms an image, and a transfer unit that transfers the image onto a recording medium by passing the image formed by the image forming unit and the recording medium through a transfer nip formed by a transfer member in a pressure-contact state to function as a control unit that acquires step information of a step in the recording medium and changes the pressure applied to the transfer member in the pressure-contact state based on the acquired step information.

Advantages of the Invention

[0009] According to the present invention, in an image forming apparatus, when there is a step on a sheet, it is possible to suppress the occurrence of damage to the transfer member and transfer failure while maintaining the pressure-contact state of the transfer member.

Brief Description of the Drawings

[0010] The advantages and features provided by one or more embodiments of the present invention will be more fully understood from the following detailed description and the accompanying drawings. However, these drawings are for illustrative purposes only and are not intended to limit the scope of the present invention.

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[0011] Hereinafter, the present embodiment will be described in detail with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

[0012] [Configuration of Image Forming Apparatus 100] FIG. 1 is a diagram showing an overall configuration example of an image forming apparatus 100 according to an embodiment of the present invention as viewed from the front. FIG. 2 is a diagram showing a main part of the control system of the image forming apparatus 100. The image forming apparatus 100 is an apparatus that forms an image on a recording medium. The recording medium includes, for example, paper, film, cloth, and the like. In the present embodiment, a case where an image is formed on a roll-shaped paper P will be described as an example.

[0013] As shown in FIG. 1, the image forming apparatus 100 is configured by connecting a paper feeding device 1, a main body unit 2, and a winding device 3 in this order from the upstream side along the paper passing direction (paper conveyance direction) of the paper P.

[0014] The paper feeding device 1 is a device that feeds the paper P to the main body unit 2. The paper feeding device 1 conveys the paper P wound around the support shaft X to the main body unit 2 at a constant speed via a plurality of pairs of conveying rollers such as a feeding roller and a paper feeding roller. The paper feeding operation of the paper feeding device 1 is controlled by a control unit 21 provided in the main body unit 2.

[0015] The main body unit 2 forms an image by an intermediate transfer method using electrophotographic process technology. As shown in FIG. 2, the main body unit 2 includes a control unit 21, an image processing unit 22, an image forming unit 23, a paper conveyance unit 24, a storage unit 25, an operation display unit 26, a communication unit 27, a detection unit 28, and the like. Each unit of the main body unit 2 is connected by a bus.

[0016] The control unit 21 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU of the control unit 21 reads a program corresponding to the processing content from the ROM and expands it in the RAM, and centrally controls the operations of each unit of the main body unit 2, the paper feeding device 1, the winding device 3, and the like in cooperation with the expanded program.

[0017] The image processing unit 22 performs image processing such as density correction processing, rasterization processing, color conversion processing, and halftone processing on the image data of the job input via the communication unit 27 and the like, and outputs the processed data to the image forming unit 23.

[0018] The image forming unit 23 includes an image forming section 200, an intermediate transfer member 201, a secondary transfer section 202 (transfer section), and a fixing section 203. The image forming section 200 includes four sets of exposure sections 2a, photoreceptors 2b, developing sections 2c, charging sections 2d, cleaning sections 2e, and primary transfer rollers 2f (primary transfer sections) corresponding to the color components of Y (yellow), M (magenta), C (cyan), and K (black), respectively. First, based on the input image data, the image forming unit 23 forms color toner images on the photoreceptors 2b of each color in the image forming section 200, sequentially performs primary transfer onto the intermediate transfer member 201 by the primary transfer rollers 2f, and superimposes the four-color toner images. Next, the image forming unit 23 conveys the toner image on the intermediate transfer member 201 to the secondary transfer section 202 and performs secondary transfer onto the sheet P fed from the paper feeding device 1, thereby forming an image on the sheet P. Then, the image forming unit 23 fixes the formed image onto the sheet P by the fixing section 203.

[0019] FIG. 3 is a diagram showing an example of the secondary transfer section 202 in the present embodiment. The secondary transfer section 202 includes an upper roller 202a and a lower roller 202b as transfer members. The upper roller 202a and the lower roller 202b can be brought into pressure contact / separated. By bringing the upper roller 202a and the lower roller 202b into pressure contact, a transfer nip is formed. The secondary transfer section 202 transfers the image formed by the image forming section 200 and the sheet P through this transfer nip, thereby transferring the image onto the sheet P.

[0020] At both ends of the upper roller 202a, a cam 202c and a pressing spring 202d are respectively and independently provided. By pressing the pressing springs 202d at both ends with the cams 202c at both ends respectively, the pressure contact force at both ends between the upper roller 202a and the lower roller 202b can be adjusted independently and continuously. With such a configuration, in the secondary transfer unit 202, an optimal balanced pressure contact force can be set at both ends of the transfer member according to the uneven state of the paper P. Note that, by configuring the surfaces of the upper roller 202a and the lower roller 202b with an elastic body such as a sponge so as to follow the unevenness of the paper P, the transfer performance can be ensured even for larger unevenness.

[0021] The paper conveyance unit 24 has a plurality of conveyance rollers 241, its drive source, a conveyance path 242, etc., and conveys the paper P conveyed from the paper feeding device 1.

[0022] The storage unit 25 is constituted by, for example, a non-volatile semiconductor memory, a hard disk drive, or the like. The storage unit 25 stores various programs executed by the control unit 21, parameters necessary for executing the processing by the programs, or data such as processing results. Further, the storage unit 25 stores the input job information and the like. The job information is the image data of the job and the setting information of the job. Note that these data etc. may be stored in the RAM of the control unit 21.

[0023] The operation display unit 26 is constituted by, for example, a liquid crystal display (LCD: Liquid Crystal Display) with a touch screen. The operation display unit 26 functions as a display unit 261 and an operation unit 262. The display unit 261 performs displays such as various operation screens, the state of the image, and the operation status of each function according to the display control signal input from the control unit 21. The operation unit 262 is provided with various operation keys such as a numeric keypad and a start key. The operation unit 262 receives various input operations by the user and outputs an operation signal to the control unit 21.

[0024] The communication unit 27 is composed of a communication control card such as a LAN (Local Area Network) card. The communication unit 27 performs transmission and reception of various data with an external device (such as a personal computer) connected to a communication network such as a LAN or a WAN (Wide Area Network).

[0025] The detection unit 28 is provided upstream of the secondary transfer unit 202 that transfers an image onto the sheet P in the sheet conveyance direction. The detection unit 28 detects the state of the sheet P, specifically, the unevenness (change in thickness) in the sheet P, and outputs the detection result to the control unit 21.

[0026] FIG. 4 is a diagram showing an example of the detection unit 28. In the drawings of the present application, a step in the sheet P is indicated by the reference sign ST. The detection unit 28 shown in FIG. 4 is arranged, for example, above the conveyance path 242 of the sheet P. The detection unit 28 includes a plurality of distance sensors 280 arranged in the width direction of the sheet P. The width direction of the sheet P is a direction orthogonal to the sheet conveyance direction. The detection unit 28 detects the unevenness in the sheet P passing through the detection unit 28 based on the distance from each distance sensor 280 to the sheet P. With such a configuration, the detection unit 28 can detect unevenness parallel to the width direction of the sheet P, diagonal unevenness, unevenness at multiple positions, etc.

[0027] FIG. 5 is a diagram showing another example of the detection unit 28. The detection unit 28 shown in FIG. 5 sandwiches the sheet P from both sides with an upper roller 281 and a lower roller 282 whose axial direction is the width direction of the sheet P, and detects the unevenness in the width direction of the sheet P passing through the detection unit 28 from the displacement amounts at both ends of the upper roller 281. With such a configuration, the detection unit 28 can detect the unevenness in the width direction of the sheet P with a simple configuration. Also, when there is unevenness biased in the width direction of the sheet P, the pressure balance at both ends of the roller of the secondary transfer unit 202 can be set accurately.

[0028] FIG. 6 is a diagram showing another example of the detection unit 28. The detection unit 28 shown in FIG. 6 presses a plurality of rollers 285 arranged in the width direction of the sheet P against a roller 286 that presses from the back surface of the sheet P, and detects irregularities in the sheet P passing through the detection unit 28 from the displacement amount of each roller 285. With such a configuration, even when the behavior of the sheet P is unstable or when there are irregularities on both sides of the sheet P, the irregularities in the width direction of the sheet P can be accurately detected.

[0029] The winding device 3 is a device that winds the sheet P conveyed from the main body 2 around the support shaft Y at a constant speed via a plurality of pairs of conveying rollers. The winding operation of the winding device 3 is controlled by the control unit 21 provided in the main body 2.

[0030] [Operation of the image forming apparatus 100] Next, the transfer control process based on the step of the sheet P in the image forming apparatus 100 will be described. When there is a step in the sheet used for image formation, such as when a roll paper is connected with a tape or the sheet on the seal side of a label paper is cut out, if the step enters the transfer nip of the secondary transfer unit, transfer defects such as transfer misalignment may occur due to the impact. In addition, the transfer member may be damaged, and image defects may occur during subsequent transfer.

[0031] Conventionally, in order to avoid this, it has been proposed to separate the pair of rollers of the secondary transfer unit in accordance with the arrival of the step in the sheet. However, when the transfer member is separated, it takes time until the transfer restarts and the productivity decreases. In addition, the impact of the separation operation is transmitted to the primary transfer unit and transfer misalignment occurs. If the image formation is stopped to avoid transfer misalignment, problems such as the relationship between the image positions before and after being shifted or the occurrence of skewed paper for aligning the image positions occur.

[0032] Therefore, in the image forming apparatus 100, when the execution of the job is instructed by receiving job information from the communication unit 27, the image forming process based on the job information is executed, and the transfer control process shown in FIG. 7 is executed.

[0033] In the image forming process based on job information, first, the control unit 21 causes the upper roller 202a and the lower roller 202b of the secondary transfer unit 202 to be pressed against each other with a predetermined pressing force (standard pressing force) defined in advance with respect to the paper P. The standard pressing force here is a pressing force that can ensure transfer performance when transfer is performed on a paper P without steps. Note that the standard pressing force may be configured to be selectable from a plurality according to the thickness of the paper P. Next, the control unit 21 controls the paper feeding device 1, the image processing unit 22, the image forming unit 23, the paper conveyance unit 24, and the winding device 3 based on the job information to form an image on the paper P. The control unit 21 controls the above-described units to perform image formation until the image formation based on all the job information is completed, that is, until the job is completed.

[0034] Also, the control unit 21 executes the transfer control process shown in FIG. 7 in parallel with the image forming process based on the job information. The transfer control process is a process of changing the pressing force of the transfer member of the secondary transfer unit 202 in the pressed state based on the step (step height) in the paper P in order to suppress the occurrence of damage to the transfer member and transfer defects.

[0035] Hereinafter, the transfer control process will be described with reference to FIG. 7. The transfer control process is executed by the cooperation of the program stored in the ROM of the control unit 21 and the CPU.

[0036] First, the control unit 21 causes the detection unit 28 to detect the unevenness of the conveyed paper P, and acquires step information in the paper P from the detection result of the detection unit 28 (step S1). The step information is information indicating the position and height of the steps existing in the paper P. For example, the control unit 21 stores the detection results (distance, displacement amount, etc.) of the detection unit 28 in a RAM or the like in association with the time from the start of feeding the sheet P. Based on the stored detection results, the control unit 21 acquires information on the position and height of the step in at least the region (image region) in the sheet P where the image is transferred. For example, the control unit 21 acquires the difference between the detection result of the detection unit 28 for the sheet P and the detection result when the detection unit 28 detects a standard-thickness sheet P without a step as the height of the step. The detection result when the detection unit 28 detects a standard-thickness sheet P without a step may be obtained from the detection result of the sheet P during paper passage, or may be measured in advance and stored in the storage unit 25. When obtaining the detection result of a standard-thickness sheet P without a step from the detection result of the sheet P during paper passage, the minimum value (in the case of displacement amount) or the maximum value (in the case of distance), the most frequent value, etc. of the detection result of the sheet P during paper passage can be used as the detection result of the standard-thickness sheet P without a step.

[0037] Next, the control unit 21 determines whether it is necessary to switch the pressing force of the secondary transfer unit 202 based on the acquired step information (step S2). For example, the control unit 21 determines, based on the step information, whether there is a step exceeding a predetermined threshold value TH1 (first threshold value) in the region of the sheet P where the image to be formed by the image forming unit 200 next (for example) is transferred. The threshold value TH1 is a value such that if the step (step height) in the sheet P exceeds this value, there is a possibility that damage will be caused to the transfer member of the secondary transfer unit 202 by pressing with the standard pressing force or that transfer displacement due to impact will occur when the step enters the transfer nip. The threshold value TH1 is a value obtained experimentally or empirically. For example, the threshold value TH1 is for a normal basis weight of 80 g / m 2The step is about 100 μm, which is the thickness of one sheet of paper. When it is determined that there is no step exceeding the threshold TH1 in the area of the paper P where the image to be imaged by the imaging unit 200 will be transferred, the control unit 21 determines that it is not necessary to switch the pressing force of the transfer member of the secondary transfer unit 202. When it is determined that there is a step exceeding the threshold TH1 in the area of the paper P where the image to be imaged by the imaging unit 200 will be transferred, the control unit 21 determines that it is necessary to switch the pressing force of the transfer member of the secondary transfer unit 202.

[0038] When it is determined that it is not necessary to switch the pressing force of the secondary transfer unit 202 (step S2; NO), the control unit 21 proceeds to step S18. That is, the control unit 21 maintains the upper roller 202a and the lower roller 202b in pressure contact with a predetermined pressing force (standard pressing force).

[0039] When it is determined that it is necessary to switch the pressing force of the secondary transfer unit 202 (step S2; YES), the control unit 21 determines the pressing force of the transfer member of the secondary transfer unit 202 based on the acquired step information (step S3). For example, the storage unit 25 stores a pressing force table that associates the height of the step with the optimal pressing force when transferring an image to a sheet of paper including the step of that height. The optimal pressing force is, for example, the maximum pressing force that does not damage the transfer member of the secondary transfer unit 202 even when the step of that height enters the transfer nip and does not cause transfer deviation due to impact. This optimal pressing force is the largest for the standard pressing force and decreases as the step increases. The control unit 21 refers to the pressing force table and determines the pressing force of the transfer member of the secondary transfer unit 202 based on the step information. It should be noted that the control unit 21 preferably specifies the position of the step in the paper width direction from the step information and determines the respective pressing forces at both ends of the transfer member of the secondary transfer unit 202 based on the position of the step. Thereby, the control unit 21 can change the respective pressing forces at both ends of the transfer member of the secondary transfer unit 202 according to the steps in the paper P. Further, the pressure contact force table may be provided for each thickness of the sheet P. Then, the control unit 21 may determine the pressure contact force based on the thickness of the sheet P and the step information.

[0040] Next, the control unit 21 determines whether the transfer performance can be maintained with the determined pressure contact force (step S4). Here, as described above, the optimum pressure contact force decreases as the step increases. However, when the step exceeds the threshold value TH2 (second threshold value; TH1 < TH2), the pressure contact force corresponding to that step falls below the minimum pressure contact force capable of ensuring the transfer performance. Therefore, the transfer performance cannot be maintained. Thus, when the step is equal to or less than the threshold value TH2, the control unit 21 determines that the transfer performance can be maintained with the determined pressure contact force. When the step exceeds the threshold value TH2, the control unit 21 determines that the transfer performance cannot be maintained with the determined pressure contact force. Note that the minimum pressure contact force capable of ensuring the transfer performance may be stored in the storage unit 25, and based on the comparison between the pressure contact force corresponding to the step in the sheet P and the minimum pressure contact force, it may be determined whether the transfer performance can be maintained with the determined pressure contact force.

[0041] When it is determined that the transfer performance can be maintained with the determined pressure contact force (step S4; YES), the control unit 21 decreases the pressure contact force so that the pressure contact force of the transfer member of the secondary transfer unit 202 becomes the determined pressure contact force when the step reaches the transfer nip of the secondary transfer unit 202 (step S5).

[0042] FIG. 8 is a diagram showing the changes in the stepped portions (ST1, ST2) within the sheet P and the pressure contact state of the transfer member in the secondary transfer unit 202. "Normal pressure contact" in FIGS. 8 and 9 indicates pressure contact at the above-described standard pressure contact force. As shown in FIG. 8, the control unit 21 performs the switching of the pressure contact force starting from the time of arrival at point A1, which reaches the transfer nip by the transfer time before the tip A2 of the step ST1 reaches the transfer nip, taking into account the transfer time from the standard pressure contact force in the secondary transfer unit 202 to the determined pressure contact force. When the rear end A3 of the step ST1 passes through the transfer nip, the control unit 21 returns the pressure contact force to the standard pressure contact force. Similarly, the control unit 21 performs the switching of the pressure contact force starting from the time of arrival at point A5, which reaches the transfer nip by the transfer time before the tip A6 of the step ST2 reaches the transfer nip. When the rear end A7 of the step ST2 passes through the transfer nip, the control unit 21 returns the pressure contact force to the standard pressure contact force. Here, as shown in FIG. 8, since the larger the step, the larger the reduction width of the pressure contact force, the start of the switching of the pressure contact force is earlier. Thus, by performing the switching of the pressure contact force taking into account the transfer time from the standard pressure contact force to the determined pressure contact force, transfer to the step can be performed in a stable state.

[0043] Next, the control unit 21 determines whether or not the transfer nip of the secondary transfer unit 202 has passed through the step (step S6). When it is determined that the transfer nip of the secondary transfer unit 202 has not passed through the step (step S6; NO), the control unit 21 repeats step S6. When it is determined that the step has passed through the secondary transfer unit 202 (step S6; YES), the control unit 21 returns the pressure contact force of the transfer member of the secondary transfer unit 202 to the standard pressure contact force (step S7), and proceeds to the process of step S18.

[0044] On the other hand, in step S4, when it is determined that the transfer performance cannot be maintained at the determined pressure contact force (step S4; NO), the control unit 21 stops the image formation in the image forming unit 200 so that the image does not pass through the secondary transfer unit 202 at the timing when the step passes through the transfer nip of the secondary transfer unit 202 (step S8).

[0045] Next, the control unit 21 determines whether or not the height of the step is equal to or less than a predetermined value TH3 (step S9). The predetermined value TH3 mentioned here is, for example, a value that becomes the maximum paper thickness usable in the image forming apparatus 100 when the thickness (standard thickness) of the paper P is added to the predetermined value. TH1 < TH2 < TH3. When it is determined that the height of the step is equal to or less than the predetermined value TH3 (step S9; YES), the control unit 21 decreases the pressure contact force of the secondary transfer unit 202 so that the pressure contact force becomes the pressure contact force determined when the step reaches the secondary transfer unit 202 (step S10). The process of step S10 is the same as that described in the process of step S5, so the description is incorporated herein.

[0046] The control unit 21 resumes image formation in the image forming unit 200 so that the formed image passes through the secondary transfer unit 202 at a predetermined timing after the step has passed through the secondary transfer unit 202 (step S11). Based on the time required for image formation in the image forming unit 200, the distance from the image forming unit 200 to the secondary transfer unit 202, the conveyance speed of the paper P and the image, etc., the control unit 21 resumes image formation in the image forming unit 200 so that the formed image passes through the transfer nip of the secondary transfer unit 202 at a predetermined timing after the step has passed through the transfer nip of the secondary transfer unit 202.

[0047] Next, the control unit 21 determines whether or not the step has passed through the transfer nip of the secondary transfer unit 202 (step S12). When it is determined that the step has not passed through the transfer nip of the secondary transfer unit 202 (step S12; NO), the control unit 21 repeats step S12. When it is determined that the step has passed through the transfer nip of the secondary transfer unit 202 (step S12; YES), the control unit 21 returns the pressure contact force of the secondary transfer unit 202 to the standard pressure contact force (step S13), and proceeds to the process of step S18.

[0048] On the other hand, in step S9, when it is determined that the height of the step exceeds a predetermined value TH3 (step S9; NO), the control unit 21 determines that it is abnormal and separates the transfer member of the secondary transfer unit 202 (step S14). Here, when the height of the step exceeds the predetermined value TH3, if the pressure contact force is decreased and the step is allowed to pass through the transfer nip of the secondary transfer unit 202, damage will occur to the transfer member. Therefore, when the height of the step exceeds the predetermined value TH3, the control unit 21 determines that it is abnormal and separates the transfer member of the secondary transfer unit 202. Note that the allowable step height in the secondary transfer unit 202 varies depending on the stiffness and basis weight of the paper P. Therefore, the control unit 21 may change the predetermined value TH3 based on the paper information of the paper P stored in the storage unit 25. The paper information is information that can specify the stiffness of the paper, such as, for example, the type, material, and basis weight of the paper.

[0049] Next, the control unit 21 resumes imaging in the imaging unit 200 at a predetermined timing after the step has passed through the transfer nip of the secondary transfer unit 202, so that the imaged image passes through the nip of the secondary transfer unit 202 (step S15). The control unit 21 resumes imaging in the imaging unit 200 at a predetermined timing after the step has passed through the secondary transfer unit 20 based on the time required for imaging in the imaging unit 200, the distance from the imaging unit 200 to the secondary transfer unit 202, the conveyance speed of the paper P and the image, etc., so that the imaged image passes through the transfer nip of the secondary transfer unit 20.

[0050] Next, the control unit 21 determines whether or not the step has passed through the transfer nip of the secondary transfer unit 202 (step S16). When it is determined that the step has not passed through the secondary transfer unit 202 (step S16; NO), the control unit 21 repeats step S16. When it is determined that the step has passed through the secondary transfer unit 202 (step S16; YES), the control unit 21 presses the transfer member of the secondary transfer unit 202 with the standard pressure contact force (step S17) and proceeds to the process of step S18.

[0051] In step S18, the control unit 21 determines whether the job has ended (step S18). If it is determined that the job has not ended (step S18; NO), the control unit 21 returns to step S1 and repeatedly executes the processes of steps S1 to S18. If it is determined that the job has ended (step S18; YES), the control unit 21 ends the transfer control process.

[0052] Note that the operation of the transfer control process shown in FIG. 7 is a case where imaging is also performed on the step of the sheet P, such as a label sheet cut out in a necessary shape on the release paper. In the case where imaging is not performed on a step, such as a portion where the sheets are connected with tape, the pressing force of the secondary transfer unit 202 is switched, but for imaging, the operation stops regardless of the height of the step.

[0053] FIG. 9 is a graph showing the relationship between the height of the step on the surface of the sheet, the pressing force of the transfer member of the secondary transfer unit 202, and the continuation / stop of imaging in the transfer control process of FIG. 7. The horizontal axis of the graph indicates step information (height of the step). The vertical axis of the graph shows the pressing force of the transfer member of the secondary transfer unit 202 in the lower part and the continuation or stop of imaging in the upper part. The dotted line of the graph showing the pressing force indicates the separated state. In FIG. 9, for example, TH1 is about 100 μm, TH2 is about 400 μm, and TH3 is about 1000 μm.

[0054] In FIG. 9, when the height of the step is up to TH1, transfer performance can be ensured with the standard pressing force, and there is no damage to the transfer member of the secondary transfer unit 202 or transfer deviation due to the impact when entering the transfer nip of the step. Therefore, the switching of the pressing force of the transfer member of the secondary transfer unit 202 is not performed, the standard pressing force is maintained, and imaging by the imaging unit 200 is continued.

[0055] When the height of the step is between TH1 and TH2, if transfer is performed with the standard pressure contact force, damage may occur to the transfer member of the secondary transfer unit 202, or transfer misalignment may occur due to the impact when entering the transfer nip of the step. Therefore, when the height of the step is between TH1 and TH2, the pressure contact force of the transfer member is switched to decrease according to the height of the step. Since the pressure contact force corresponding to the step from TH1 to TH2 is a pressure contact force that can ensure transfer performance, image formation by the image forming unit 200 is continued.

[0056] When the height of the step is between TH2 and TH3, if transfer is performed with the standard pressure contact force, damage may occur to the transfer member of the secondary transfer unit 202, or transfer misalignment may occur due to the impact when entering the transfer nip of the step. However, when the height of the step is between TH2 and TH3, if the pressure contact force is decreased to a level that can avoid damage to the transfer member and transfer misalignment due to impact, transfer performance cannot be ensured. Therefore, when the height of the step is between TH2 and TH3, image formation by the image forming unit 200 is stopped so that image formation is not performed on the step. However, if the transfer member of the secondary transfer unit 202 is separated when image formation is stopped, it takes time until transfer is resumed and productivity decreases. In addition, problems such as the impact of the separation operation being transmitted to the primary transfer unit and causing transfer misalignment, or the relationship between the image positions before and after being shifted, or the occurrence of paper wrinkles to align the image positions, occur. Therefore, when the height of the step is between TH2 and TH3, the transfer member is not separated, and the pressure contact force is decreased to maintain the pressure contact state. When the height of the step exceeds TH3, damage to the transfer member cannot be avoided even if the pressure contact force of the transfer member of the secondary transfer unit 202 is set to the lowest level. Therefore, the transfer member of the secondary transfer unit 202 is separated, and image formation is also stopped.

[0057] That is, in the above transfer control process, the control unit 21, for example, for a step of about 100 μm which is the thickness of one sheet of paper with a general basis weight of about 80 g / m 2 transfer is performed without switching the pressure contact force of the transfer member of the secondary transfer unit 202. From 100 μm to a basis weight of 400 g / m 2If the step is up to about 400 μm, which is the thickness of one sheet of paper, the control unit 21 continues image formation while reducing the pressure contact force of the transfer member of the secondary transfer unit 202. If the step is from 400 μm to 1000 μm, which is the maximum step allowable in the image forming apparatus 100, the control unit 21 interrupts image formation but continues the pressure contact state. In the case of a step exceeding 1000 μm, which is the maximum step allowable in the image forming apparatus 100, the control unit 21 separates the transfer member of the secondary transfer unit 202.

[0058] Thus, in the transfer control process, when there is a step on the sheet P, if the step does not exceed the maximum step allowable in the image forming apparatus 100, by maintaining the pressure contact state of the transfer member of the secondary transfer unit 202 and reducing the pressure contact force, the occurrence of damage to the transfer member and transfer failure can be suppressed. Therefore, the occurrence of damage to the transfer member and transfer failure can be suppressed while minimizing the separation of the transfer member and the stop of image formation.

[0059] (Modification 1) In the above embodiment, in the transfer control process of FIG. 7, the step information is acquired based on the detection result of the sheet P by the detection unit 28. However, the method of acquiring the step information is not limited to this example. For example, the step information of the sheet P may be stored in the storage unit 25 in advance, and the control unit 21 may read and acquire the step information of the sheet P from the storage unit 25.

[0060] FIG. 10 is a diagram for explaining an example of the step information stored in the storage unit 25. In FIG. 10, the step is indicated by attaching the symbol ST. In FIGS. 10 and 11, the circle indicates the writing reference position, and the double arrow indicates the period of the image. The step information stored in the memory unit 25 includes information on the position and height of the steps within the paper P. The information on the position of the steps is represented by the distance from the reference position. For example, in the case of continuous paper such as roll paper, the end of the writing reference position of the image in the paper conveyance direction and the lower end of the paper are used as the reference positions. In the case of single sheets (sheet-fed paper), the paper end at the leading edge of the paper and the lower end of the paper are used as the reference positions. As the information on the position of the steps, the conveyance direction distance from the reference position to the steps (e.g., X1 to X4 in FIG. 10) and the distance in the direction orthogonal to the conveyance direction (e.g., Y1 to Y4 in FIG. 10) are stored.

[0061] FIG. 11 is a diagram for explaining another example of the step information stored in the memory unit 25. For example, the information on the height of the steps at each position of the intersection G of the grid arranged in the area corresponding to the writing cycle of the image from the above-mentioned reference position is stored in the memory unit 25 as the step information. The interval of the step information may be equivalent to the resolution of the image, or may be an interval of around 5 mm that the transfer pressure of the secondary transfer unit 202 follows.

[0062] As described above, in the first modification, since the step information of the paper P used for image formation is stored in the memory unit 25, the transfer control process of FIG. 7 can be performed even if the image forming apparatus 100 is not provided with the detection unit 28. Note that the format of the step information shown in FIGS. 10 and 11 may be applied to the step information obtained from the detection result of the detection unit 28 described in the above embodiment.

[0063] (Second Modification) When the image forming apparatus 100 is connected to a post-processing apparatus, it is also possible to store in the memory unit 25 the post-processing information regarding the post-processing performed after the transfer by the secondary transfer unit 202. Then, the control unit 21 may determine the timing of resuming the image formation when the image formation in the image forming unit 200 is stopped based on the post-processing information. The post-processing information includes information on whether to perform the post-processing at each specified length of the image cycle or to perform the post-processing in accordance with the image position, on the premise that the post-processing apparatus processes continuous paper.

[0064] For example, in steps S11 and S15 of FIG. 7, the control unit 21 obtains information from the post-processing information stored in the storage unit 25 on whether the post-processing device performs post-processing on the premise that the period of the image is every specified length or performs post-processing according to the image position. When the post-processing device performs post-processing on the premise that the period of the image is every specified length, the control unit 21 causes the image forming unit 200 to resume image formation at the timing when the stoppage of image formation of the specified length ends. When the post-processing device performs post-processing according to the image position, the control unit 21 causes the image forming unit 200 to resume image formation so that the image is conveyed to the secondary transfer unit 202 when the step passes through the secondary transfer unit 202.

[0065] FIG. 12 is a diagram showing post-processing timing in a post-processing device that performs post-processing on the premise that the period of the image is every specified length and the image formation stop period in Modification 2. In FIG. 12, the circles indicate the timing of post-processing, and the double-headed arrows indicate the period of the image. As shown in FIG. 12, in the post-processing device, post-processing is performed every period (specified length) of the image. Therefore, when the post-processing device performs post-processing on the premise that the period of the image is every specified length, the control unit 21 causes the image forming unit 200 to resume image formation at the timing when the stoppage of image formation for the length of one period of the image ends. By doing so, the timing from the stoppage to the resumption of image formation due to the step can be appropriately set according to the timing of post-processing, and the generation of streaky paper can be minimized.

[0066] FIG. 13 is a diagram showing post - processing timing in a post - processing apparatus that performs post - processing in accordance with the image position and the imaging stop period in Modification 2. In FIG. 13, the circles indicate the timing of post - processing, and the double - headed arrows indicate the period of the image. As shown in FIG. 13, in the post - processing apparatus, post - processing is performed in accordance with the image position. Therefore, when the post - processing apparatus performs post - processing in accordance with the image position, the control unit 21 causes the imaging unit 200 to resume imaging at a timing such that after imaging stops and when the step passes through the secondary transfer unit 202, the image arrives at the secondary transfer unit 202. By doing so, it is possible to minimize the timing from the stop to the resumption of imaging due to the step, and minimize the occurrence of streaky paper.

[0067] As described above, according to the image forming apparatus 100, the control unit 21 acquires step information of the step in the sheet P, and changes the pressure contact force of the transfer member in the pressure contact state based on the acquired step information. Therefore, when there is a step in the sheet P, it is possible to suppress the occurrence of damage to the transfer member and transfer failure while maintaining the pressure contact state of the transfer member in the secondary transfer unit 202.

[0068] For example, the image forming apparatus 100 includes a detection unit 28 that is located upstream of the secondary transfer unit 202 in the sheet conveyance direction and detects the state of the sheet P, and the control unit 21 acquires step information from the detection result of the detection unit 28. Therefore, it is possible to easily acquire the step information of the sheet P. For example, the detection unit 28 has a plurality of sensors (280 or 285) arranged in the width direction of the sheet P, and detects the unevenness in the width direction of the sheet P by the plurality of sensors (280 or 285). Therefore, it is possible to accurately detect the partial unevenness in the width direction of the sheet P. Further, the detection unit 28 sandwiches the sheet P from both sides with an upper roller 281 and a lower roller 282 having the width direction of the sheet P as the axial direction, and detects the unevenness in the width direction of the sheet P from the displacement amounts at both ends of the upper roller 281. Therefore, it is possible to accurately detect the unevenness of the sheet even when the sheet behavior is unstable or when there is unevenness on both sides of the sheet.

[0069] Further, for example, the image forming apparatus 100 includes a storage unit 25 that stores the step information of the sheet P, and the control unit 21 acquires the step information from the storage unit 25. Therefore, the control unit 21 can acquire the step information even without including the detection unit 28.

[0070] Also, the secondary transfer unit 202 can independently adjust the pressure contact forces at both ends in the width direction of the sheet P of the transfer member, and the control unit 21 changes the respective pressure contact forces at both ends in the width direction of the sheet P of the transfer member of the secondary transfer unit 202 based on the acquired step information. Therefore, the transfer member can be pressure contacted with an optimal balanced pressure contact force according to the uneven state of the sheet.

[0071] Also, the control unit 21 changes so that the pressure contact force becomes smaller as the step is larger. Therefore, it is possible to prevent problems such as transfer deviation due to damage or impact of the transfer member by reducing the pressure contact force as the step is larger.

[0072] For example, when the step is equal to or less than the first threshold value, the control unit 21 pressure contacts the transfer member with a predetermined pressure contact force, and when the step exceeds the first threshold value, the control unit 21 pressure contacts the transfer member with a pressure contact force smaller than the predetermined pressure contact force. Therefore, when the step exceeds the first threshold value, it is possible to prevent problems such as transfer deviation due to damage or impact of the transfer member by reducing the pressure contact force.

[0073] When the step exceeds a second threshold value that is larger than the first threshold value, the control unit 21 further stops the image formation in the image forming unit 200. Therefore, it is possible to prevent the printing of an image for which the transfer performance cannot be maintained.

[0074] Also, post-processing information regarding post-processing performed after transfer by the secondary transfer unit 202 is stored in the storage unit 25, and when the control unit 21 stops the image formation in the image forming unit 200, the control unit 21 determines the timing of restarting the image formation in the image forming unit 200 based on the post-processing information. Therefore, the timing from the stop to the restart of the image formation due to the step can be appropriately set according to the post-processing, and the generation of streaky paper can be minimized.

[0075] Further, the control unit 21 compares the step information based on the detection result by the detection unit 28 with a predetermined value, and determines that an abnormality has occurred when the step exceeds the predetermined value. Therefore, for example, when there is a step exceeding the predetermined value acceptable in the image forming apparatus 100, it can be determined that an abnormality has occurred.

[0076] When the step exceeds the predetermined value, the control unit 21 separates the transfer member of the secondary transfer unit 202. Therefore, it is possible to prevent a step exceeding the predetermined value acceptable in the image forming apparatus 100 from entering the transfer nip and damaging the transfer member.

[0077] Note that the above-described embodiment is a preferred example of the present invention and is not limited thereto. For example, in the above embodiment, the case where the present invention is applied to a roll-shaped paper has been described as an example. However, the same effects can also be obtained when the present invention is applied to a cut recording medium such as a sheet of paper.

[0078] In addition, regarding the detailed configuration and detailed operation of the image forming apparatus, it can be appropriately changed without departing from the spirit of the present invention.

[0079] As described above, the embodiments of the present invention have been described and illustrated in detail. However, the disclosed embodiments are created for the purpose of illustration and exemplification only and are not restrictive. The scope of the present invention should be construed by the appended claims.

Explanation of Reference Numerals

[0080] 100 Image forming apparatus 1 Paper feeding device 2 Main body unit 21 Control unit 22 Image processing unit 23 Image forming unit 202 Secondary transfer unit 202a Upper roller 202b Lower roller 24 Paper conveyance unit 25 Storage unit 26 Operation display unit 27 Communication unit 28 Detection unit 280 Distance sensor 281 Upper roller 282 Lower roller 285 Roller 286 Roller 3 Take-up device

Claims

1. An image forming unit that forms an image; A transfer unit that transfers the image onto a recording medium by passing the image formed by the image forming unit and the recording medium through a transfer nip formed by a transfer member in a pressed state; A control unit that acquires step information of a step in the recording medium and changes the pressing force of the transfer member in the pressed state based on the acquired step information; An image forming apparatus comprising the above.

2. A detection unit that is located upstream of the transfer unit in the conveyance direction of the recording medium and detects the state of the recording medium, wherein the control unit acquires the step information from the detection result by the detection unit. The image forming apparatus according to Claim 1.

3. The image forming apparatus according to Claim 2, wherein the detection unit detects unevenness in the width direction of the recording medium.

4. The image forming apparatus according to Claim 3, wherein the detection unit has a plurality of sensors arranged in the width direction of the recording medium, and the plurality of sensors detect unevenness in the width direction of the recording medium.

5. The image forming apparatus according to Claim 3, wherein the detection unit sandwiches the recording medium from both sides with a roller having the width direction of the recording medium as the axial direction, and detects unevenness in the width direction of the recording medium from the displacement amounts at both ends of the roller.

6. A storage unit that stores step information of the recording medium, wherein the control unit acquires the step information from the storage unit. The image forming apparatus according to Claim 1.

7. The transfer unit can independently adjust the pressing forces at both ends in the width direction of the recording medium of the transfer member, wherein the control unit changes the respective pressing forces at both ends in the width direction of the recording medium of the transfer member based on the step information. The image forming apparatus according to Claim 1.

8. The control unit changes the pressing force so that the larger the step, the smaller the pressing force. The image forming apparatus according to Claim 1.

9. When the step is equal to or less than a first threshold value, the control unit presses the transfer member with a predetermined pressing force, and when the step exceeds the first threshold value, the control unit presses the transfer member with a pressing force smaller than the predetermined pressing force. The image forming apparatus according to Claim 1.

10. When the step exceeds a second threshold value greater than the first threshold value, the control unit further stops image formation by the image forming unit. The image forming apparatus according to Claim 9.

11. ​ ​ ​ A storage unit that stores post-processing information regarding post-processing performed after transfer by the transfer unit is provided. The image forming apparatus according to claim 10, wherein when the control unit stops imaging by the imaging unit, the control unit determines a timing for resuming imaging by the imaging unit based on the post-processing information.

12. The image forming apparatus according to claim 2, wherein the control unit compares a step difference based on a detection result by the detection unit with a predetermined value, and determines that an abnormality has occurred when the step difference exceeds the predetermined value.

13. The image forming apparatus according to claim 12, wherein when the step difference exceeds the predetermined value, the control unit separates the transfer member.

14. An imaging unit that forms an image; A transfer unit that transfers the image to a recording medium by passing the image formed by the imaging unit and the recording medium through a transfer nip formed by a transfer member in a pressure contact state; A program for causing a computer of an image forming apparatus including a control unit that acquires step difference information of a step difference in the recording medium and changes a pressure contact force of the transfer member in a pressure contact state based on the acquired step difference information to function as.

Images