Image forming apparatus

Abstract

To provide an image forming apparatus that can sufficiently correct deviation of a recording material with a shaking operation of a registration roller.SOLUTION: An image forming apparatus comprises: a conveying unit that conveys a recording material; a transfer unit having a transfer roller that transfers toner images to the recording material; a fixing unit having a fixing roller that fixes the toner images formed on the recording material; a deviation detection unit that detects the position of the recording material in a conveyance intersection direction; a deviation correction unit that is located on the upstream side of the transfer unit and moves the recording material in the conveyance intersection direction to correct deviation of the recording material; and a control unit that controls the amount of drive of the deviation correction unit based on a result of detection performed by the deviation detection unit and a contact pressure at a nip part that sandwiches the recording material being conveyed.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] In an image forming apparatus, when a recording material is conveyed from a paper feeding unit or a reversing path to a transfer unit, due to mechanical factors of the apparatus or the like, the recording material may be displaced in a direction orthogonal to the conveying direction (hereinafter sometimes referred to as the conveyance crossing direction, the recording material width direction, or the main scanning direction). When image formation is performed in a state where such displacement of the recording material occurs, the formation position of the image with respect to the recording material deviates from the original proper position.

[0003] Therefore, in an image forming apparatus, in order to accurately align the image and the recording material in consideration of the displacement of the recording material, registration rocking correction is performed in which the recording material is sandwiched by registration rollers and rocked in the conveyance crossing direction to correct the displacement of the recording material. In this registration rocking correction, a displacement sensor is arranged on the downstream side of the registration rollers, and control is performed to rock the recording material in the conveyance crossing direction based on the amount of displacement of the recording material to correct the displacement of the recording material.

[0004] However, in the above-described registration rocking correction, the registration rollers are rocked before the leading end of the recording material reaches the secondary transfer roller to align the position of the end of the recording material. By simply rocking before the recording material reaches the secondary transfer roller in this way, due to misalignment of the alignment of the secondary transfer roller and the fixing roller, or a difference in the roller diameter in the recording material width direction of each roller, the recording material may be displaced after reaching the secondary transfer roller. In particular, long paper is easily affected by this, and even after reaching the secondary transfer roller, displacement of the recording material in the main scanning direction is likely to occur. As a result, in the conventional registration rocking correction, the image formation position on the recording material may deviate during an image forming job.

[0005] Therefore, an image forming apparatus has been proposed which corrects the deviation of the recording material by performing the rocking operation of the resist roller even after the recording material has passed through the secondary transfer roller (see, for example, Patent Document 1). In this image forming apparatus, the recording material on which the image has been transferred after passing through the secondary transfer roller is read by the image reading unit, and the image forming position on the recording material is detected. Then, the rocking control information of the resist roller is corrected based on the reading result of the formed image, and the rocking operation is performed with a driving amount corresponding to the amount of deviation of the image forming position on the recording material.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in an image forming apparatus, the pressure contact forces of the secondary transfer roller, the fixing roller, the conveyance roller, etc. vary depending on the image forming conditions and are not constant. For this reason, depending on the pressure contact force of each roller, the degree of slippage that occurs between the recording material and the roller during the rocking operation is different. For example, the higher the pressure contact force of the roller, the greater the resistance to the movement of the recording material during the rocking operation, and the smaller the movement amount of the recording material. As a result, even if the rocking operation of the resist roller is performed with a driving amount based on the amount of deviation of the image forming position on the recording material, depending on the movement amount of the recording material that changes depending on the pressure contact force of the roller, the deviation of the recording material may not necessarily be sufficiently eliminated.

[0008] In order to solve the above-described problems, the present invention provides an image forming apparatus capable of sufficiently correcting the deviation of the recording material by the rocking operation of the resist roller.

Means for Solving the Problems

[0009] The image forming apparatus of the present invention includes a conveyance unit that conveys a recording material, a transfer unit that has a transfer roller for transferring a toner image onto the recording material, a fixing unit that has a fixing roller for fixing the toner image formed on the recording material, a deviation detection unit that detects the position of the recording material in the conveyance crossing direction, a deviation correction unit that is located upstream of the transfer unit and moves the recording material in the conveyance crossing direction to correct the deviation of the recording material, and a control unit that controls the driving amount of the deviation correction unit based on the detection result of the deviation detection unit and the pressure contact force of a nip unit that sandwiches the recording material during conveyance.

Effects of the Invention

[0010] According to the present invention, it is possible to provide an image forming apparatus capable of sufficiently correcting the deviation of the recording material by the swinging operation of the registration roller.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0012] Hereinafter, examples of embodiments for carrying out the present invention will be described, but the present invention is not limited to the following examples. Note that the description will be made in the following order. 1. First Embodiment of the Image Forming Apparatus 2. Second Embodiment of Image Forming Apparatus

[0013] 〈1. First Embodiment of Image Forming Apparatus〉 Hereinafter, the first embodiment of the image forming apparatus will be described. FIG. 1 shows a schematic configuration diagram of the image forming apparatus of this embodiment. The image forming apparatus 100 shown in FIG. 1 is an electrophotographic image forming apparatus 100, and is a so-called tandem type color image forming apparatus that forms a color image by arranging a plurality of photoreceptors facing an intermediate transfer belt in the vertical direction. The image forming apparatus 100 mainly includes an image forming unit 10, a control unit 11, a recording material conveyance unit 20, and a fixing unit 50, and these are housed in one housing.

[0014] The image forming unit 10 includes four sets of image forming units 10Y, 10M, 10C, 10K, an intermediate transfer belt 6, a secondary transfer roller 9, and the like. The image forming units 10Y, 10M, 10C, 10K are composed of an image forming unit 10Y that forms a yellow (Y) image, an image forming unit 10M that forms a magenta (M) image, an image forming unit 10C that forms a cyan (C) image, and an image forming unit 10K that forms a black (K) image.

[0015] The image forming unit 10Y is composed of a photoreceptor drum 1Y and a charging unit 2Y, an optical writing unit 3Y, a developing device 4Y, and a drum cleaner 5Y arranged around it. Similarly, the image forming units 10M, 10C, 10K are composed of photoreceptor drums 1M, 1C, 1K and charging units 2M, 2C, 2K, optical writing units 3M, 3C, 3K, developing devices 4M, 4C, 4K, and drum cleaners 5M, 5C, 5K arranged around them.

[0016] The photoreceptor drums 1Y, 1M, 1C, and 1K have their surfaces uniformly charged by the charging units 2Y, 2M, 2C, and 2K, and latent images are formed on the photoreceptor drums 1Y, 1M, 1C, and 1K by scanning exposure with the light writing units 3Y, 3M, 3C, and 3K. Further, the developing devices 4Y, 4M, 4C, and 4K develop the latent images on the photoreceptor drums 1Y, 1M, 1C, and 1K by developing with toner. As a result, a toner image of a predetermined color corresponding to any one of yellow, magenta, cyan, and black is formed on the photoreceptor drums 1Y, 1M, 1C, and 1K. The toner image formed on the photoreceptor drums 1Y, 1M, 1C, and 1K is primarily transferred to a predetermined position on the rotating intermediate transfer belt 6 by the primary transfer rollers 7Y, 7M, 7C, and 7K.

[0017] The toner images of each color transferred onto the intermediate transfer belt 6 are transferred to a recording material S conveyed at a predetermined timing by a recording material conveyance unit 20 described later, by a secondary transfer roller 9. The secondary transfer roller 9 is disposed on the back surface (the surface opposite to the image forming surface) side of the recording material S, and is disposed in pressure contact with a counter roller 8 disposed on the back surface (the surface opposite to the transfer surface) side of the intermediate transfer belt 6 via the intermediate transfer belt 6. By the pressure contact between the secondary transfer roller 9 and the counter roller 8, a nip portion (hereinafter referred to as a "transfer nip portion") is formed between the secondary transfer roller 9 and the intermediate transfer belt 6. Then, by driving the intermediate transfer belt 6 and the secondary transfer roller 9, transfer of the toner image to the recording material S and conveyance of the recording material S are performed at the transfer nip portion.

[0018] The recording material conveyance unit 20 conveys the recording material S along the conveyance path of the recording material S. The recording material S is stored in a paper feed tray 21. The recording material S stored in the paper feed tray 21 is taken in by a paper feed unit 22 and sent out to the conveyance path. Further, the recording material S may be configured to be stored in a paper feed tray of an external paper feed device (not shown) connected to the image forming apparatus 100, supplied from the paper feed device to the image forming apparatus 100, and sent out to the conveyance path.

[0019] In this conveyance path, upstream of the transfer nip section, a plurality of pairs of rollers (roller pairs) that are pressed against each other are provided as conveyance rollers for conveying the recording material S. The roller pair conveys the recording material S by rotationally driving at least one of the rollers through a drive mechanism mainly composed of an electric motor. Also, the roller pairs constituting each conveyance section are configured so that the state between the rollers can be switched between a pressed state and a separated state. And when the roller pairs are pressed against each other, a nip section (hereinafter referred to as "conveyance nip section") is formed in each roller pair.

[0020] In the recording material conveyance section 20, as conveyance rollers, intermediate conveyance rollers 23, 24, 25 and a loop roller 26 are provided from the upstream side to the downstream side of the conveyance path of the recording material S. Further, in the recording material conveyance section 20, as a conveyance roller, a registration roller 27 for adjusting the conveyance timing of the recording material S and correcting the inclination of the conveyed recording material S is provided. Note that, in addition to being composed of roller pairs, the recording material conveyance section 20 can widely adopt a configuration in which a conveyance nip section is formed by a pair of rotating members such as a combination of roller pairs via a belt or a combination of a belt and a roller.

[0021] In the conveyance path of such a recording material conveyance section 20, the recording material S fed from the paper feed tray 21 or the paper feed tray of the paper feeding device is sequentially conveyed by a plurality of intermediate conveyance rollers 23, 24, 25 and the loop roller 26 provided from the upstream side to the downstream side. When the leading end of the recording material S approaches the registration roller 27, the recording material S conveyed by the loop roller 26 or the like is abutted against the registration roller 27 in a rotationally stopped state. Then, by the loop roller 26 continuing to rotate for a predetermined time, a loop is formed in the recording material S. By this action of loop formation, the bending of the leading end of the recording material S is corrected (skew correction).

[0022] Near the upstream side of the registration roller 27, a registration sensor SE1 for detecting the arrival of the recording material S is provided. In the vicinity of the downstream side of the resist roller 27, a position detection sensor SE2 for detecting the arrival of the recording material S and the position in the recording material width direction CD of the side end portion of the recording material S is provided. As the position detection sensor SE2, for example, a linear image sensor (such as a CCD line sensor or the like) in which a plurality of light receiving elements are linearly arranged along the recording material width direction CD is used.

[0023] In addition, the recording material conveyance unit 20 is provided with a media sensor SE4 as a recording material property detection unit capable of detecting the recording material properties of the recording material S sent out to the conveyance path. The media sensor SE4 may be arranged on the upstream side of the loop roller 26. As the media sensor SE4, a conventionally known one capable of detecting the recording material properties of the recording material S can be used.

[0024] Next, when the resist roller 27 starts rotating at a predetermined timing so as to be synchronized with the toner image carried by the intermediate transfer belt 6, the intermediate conveyance rollers 23, 24, 25 and the loop roller 26 are switched from the pressure contact state to the separated state. That is, after the loop roller 26 transitions to the separated state, the recording material S is conveyed only by the resist roller 27. This resist roller 27, as a swing roller, performs a swing operation described later while conveying the recording material S, and conveys the recording material S to the transfer nip portion between the intermediate transfer belt 6 as an image carrier and the secondary transfer roller 9 as a transfer portion.

[0025] The fixing unit 50 performs a fixing process on the recording material S onto which the toner image has been transferred, that is, the recording material S sent out from the transfer nip portion. The fixing unit 50 includes a fixing roller 51 arranged on the image forming surface side of the recording material S, a pressure roller 52 arranged at a position facing the recording material S conveyed to the fixing roller 51 with the recording material S interposed therebetween, and a heater (not shown) for heating the fixing roller 51. When the pressure roller 52 is pressed against the fixing roller 51, a nip portion (hereinafter referred to as "fixing nip portion") is formed between the fixing roller 51 and the pressure roller 52.

[0026] The fixing unit 50 fixes the toner image onto the recording material S by heating and pressing with the fixing roller 51 and the pressure roller 52 in the fixing nip portion during the conveyance process of the recording material S. The recording material S subjected to the fixing process by the fixing unit 50 is discharged to a paper discharge tray 29 attached to the outer side surface of the housing by a paper discharge roller 28.

[0027] Furthermore, a pressure detection sensor SE3 is provided as a pressure detection unit for detecting the pressure contact force of each nip portion on the secondary transfer roller 9, the intermediate transfer rollers 23, 24, 25, the loop roller 26, and the fixing roller 51 and the pressure roller 52 of the fixing unit 50. The pressure detection sensor SE3 detects, for example, the pressure contact force of the nip portion disposed within each roller. The pressure detection sensor SE3 can use, for example, a photointerrupter that detects the rotation angle of a pressure switching cam. Also, the pressure detection sensor SE3 may directly detect the pressure of the nip portion using a pressure transducer or the like. In addition to the above-described pressure detection sensor SE3, as a configuration of the pressure detection unit that detects the pressure contact force of the nip portion, for example, the drive amount of the pressure contact motor of each roller (not shown) may be used, or a configuration that calculates the pressure amount of the nip portion by detecting fluctuations in the drive torque of the roller may also be used. Note that in FIG. 1, only the pressure detection sensor SE3 that detects the pressure contact force of the secondary transfer roller 9 is shown, but this pressure detection sensor SE3 may also be provided on the intermediate transfer rollers 23, 24, 25, the loop roller 26, and the fixing unit 50.

[0028] [System Block Diagram] FIG. 2 shows a system block diagram of the image forming apparatus 100. As shown in FIG. 2, the image forming apparatus 100 includes a control unit 11, a storage unit 12, a communication unit 13, an operation unit 14, an image forming unit 10, a recording material conveyance unit 20, a fixing unit 50, an image reading unit 60, a registration sensor SE1, a position detection sensor SE2, a pressure detection sensor SE3, a media sensor SE4, and a registration swing drive unit 34.

[0029] The memory unit 12, communication unit 13, operation unit 14, image forming unit 10, recording material conveyance unit 20, fixing unit 50, image reading unit 60, resist sensor SE1, position detection sensor SE2, pressure detection sensor SE3, media sensor SE4, and resist swing drive unit 34 are communicably connected to the control unit 11, and the control unit 11 performs control such as drive control and signal processing.

[0030] The control unit 11 is composed of a CPU (Central Processing Unit), RAM (Random Access Memory), ROM (Read Only Memory), etc. The CPU of the control unit 11 reads out the system program and various processing programs stored in the ROM and the memory unit 12 and expands them in the RAM, and centrally controls the operations of each part of the image forming apparatus 100 according to the expanded programs. For example, when a job execution command is input by the operation unit 14, the control unit 11 executes the job and performs control to form a toner image on the recording material S based on the image data input from the communication unit 13, etc. Further, when a job execution command is input by the operation unit 14, the control unit 11 executes the swing control process described later and performs swing control of the resist roller 27 during job execution.

[0031] The memory unit 12 is composed of a non-volatile semiconductor memory, HDD (Hard Disk Drive), etc., and stores various parameters and data necessary for each part in addition to the various programs executed by the control unit 11. For example, the memory unit 12 stores swing control information for controlling the swing operation of the resist roller 27.

[0032] For example, as swing control information for the swing operation (first swing operation) of the resist roller 27 before the recording material S enters the secondary transfer roller 9, information for calculating the swing direction (+, -), swing speed, and drive amount, etc. of the resist swing drive unit 34 according to the deviation amount (offset amount) between the position of the side end portion of the recording material S and the target position Tp is stored.

[0033] In addition to the swing control information according to the deviation amount between the position of the side end portion of the recording material S and the target position Tp as swing control information for controlling the swing operation (second swing operation) of the resist roller 27 after the recording material S enters the secondary transfer roller 9, a swing control table for correcting the swing operation of the resist roller 27 based on the pressure contact force of the nip portion that sandwiches the recording material S during conveyance is stored.

[0034] An example of the swing control table for correcting the swing operation of the resist roller 27 is shown in FIG. 3. The swing control table shown in FIG. 3 describes correction amounts corresponding to the pressure contact force of the nip portion and the recording material characteristics. After the recording material S enters the secondary transfer roller 9, the control unit 11 controls the resist roller 27 to swing at a plurality of predetermined timings (referred to as swing timings). For this reason, the swing control table shown in FIG. 3 stores the pressure contact force information of the nip portion that sandwiches the recording material and the correction amount for correcting the swing operation of the resist roller 27 based on the recording material property information.

[0035] In the swing control table shown in FIG. 3, as an example of the pressure contact force information, the pressure contact force at each nip portion (nip portion a, nip portion b) such as the transfer nip portion, the fixing nip portion, and the conveyance nip portion, and the distance between each nip portion and the resist roller 27 are stored. In the swing control table, as an example of the recording material property information, the type, thickness, basis weight, recording material size, and surface smoothness are stored. Then, the correction amount is calculated according to each condition of the stored pressure contact force and distance of each nip portion and the recording material property information.

[0036] Therefore, in the second swing operation described above, the control unit 11 corrects the swing control information according to the deviation amount between the position of the side end portion of the recording material S stored in the storage unit 12 and the target position Tp based on the correction amount stored in the swing control table, and controls the swing operation of the resist roller 27. As a result, it is possible to correct the shift of the recording material S in consideration of the magnitude of the resistance due to the pressure contact force of the nip portion with respect to the movement of the recording material S during the swing operation, and it becomes possible to form the toner image at the optimal position of the recording material S.

[0037] Further, not only the pressing force of the nip portion but also the resistance of the recording material S to the swinging operation of the resist roller 27 differs depending on the characteristics of the recording material S even when the pressing force of the nip portion is the same. For example, in the case of a recording material S with low surface smoothness, the resistance tends to be large with respect to the pressing force of the nip portion. Therefore, it is preferable to increase the correction amount of the swinging operation and increase the driving amount of the resist roller 27. Further, in the case of a recording material S with a large thickness, the resistance tends to be large with respect to the pressing force of the nip portion. Therefore, it is preferable to increase the correction amount of the swinging operation and increase the driving amount of the resist roller 27. Thus, in order to accurately perform the offset correction of the recording material S, it is preferable that in the swing control table, in addition to the pressing force of the nip portion, a correction amount corresponding to conditions such as the correction amount corresponding to the recording material characteristics is stored.

[0038] The communication unit 13 is provided with various interfaces such as a NIC (Network Interface Card), a MODEM (Modulator-DEModulator), and a USB (Universal Serial Bus), and connects to an external device.

[0039] The operation unit 14 outputs various information set by the user to the control unit 11. As the operation unit 14, for example, a touch panel capable of performing an input operation according to the information displayed on the display can be used. Through such an operation unit 14, the user can set printing conditions, that is, the type of the recording material S (for example, basis weight, size, paper quality, etc.), the paper feed tray to be used, the density of the image, the magnification, the presence or absence of double-sided printing, and the like. Further, the user can input an execution command for a job or an operation instruction in an adjustment mode through the operation unit 14. Further, the control unit 11 can display various messages to the user via the operation unit 14 by controlling the operation unit 14.

[0040] The resist sensor SE1 detects the arrival of the tip of the recording material S and transmits the detection result to the control unit 11. As a result, the detection result of the resist sensor SE1 is used in the control unit 11 to detect the rotation start timing of the resist roller 27 and the like.

[0041] The position detection sensor SE2 detects the position of the recording material S in the recording material width direction CD at the side end of the recording material S and transmits the detection result to the control unit 11. The detection result of the position detection sensor SE2 is used in the control unit 11 to determine the moving amount in the swinging operation of the resist roller 27 and to grasp the timing when the tip of the recording material S enters the secondary transfer roller 9.

[0042] The resist swing drive unit 34 is connected to the resist roller 27 and is mainly composed of an electric motor. By driving the resist roller 27 by the resist swing drive unit 34, a so-called swinging operation is performed in which the resist roller 27 is moved in the conveyance crossing direction CD starting from a predetermined home position.

[0043] The pressure detection sensor SE3 is used to detect the pressure contact force of the nip portions in the intermediate conveyance rollers 23, 24, 25, the loop roller 26 of the recording material conveyance unit 20, the fixing roller 51 of the fixing unit 50, and the pressure roller 52. The pressure detection sensor SE3 receives information from the pressure detection sensors SE3 arranged in each roller of the recording material conveyance unit 20 and detects the pressure contact force of the nip portions in each roller.

[0044] Also, the adjustment of the pressure contact force of each nip portion and the switching between the pressure contact state and the separated state are controlled by the control unit 11. For example, the control unit 11 adjusts the interval between the roller pairs constituting each nip portion, thereby controlling the pressure contact force of the conveyance nip portion by the intermediate conveyance rollers 23, 24, 25 and the loop roller 26 of the recording material conveyance unit 20 during the conveyance of the recording material S, the pressure contact force of the fixing nip portion between the secondary transfer roller 9 of the image forming unit 10 and the counter roller 8, and the pressure contact force of the fixing nip portion between the fixing roller 51 and the pressure roller 52 of the fixing unit 50.

[0045] The media sensor SE4 is a recording material property detection unit for detecting the properties of the recording material S. The media sensor SE4 detects, for example, the type (paper type) and size of the recording material S, the physical properties of the recording material S, and the like. The media sensor SE4 detects, as the physical properties of the recording material S, for example, the surface state such as thickness, basis weight, smoothness, stiffness, charge amount, moisture content, and grain direction (angle of the fiber direction of the recording material).

[0046] [Resist Oscillation Unit] (Configuration of the Oscillation Unit) Next, the oscillation process of the recording material S by the resist roller 27 in the image forming apparatus 100 will be described. FIG. 4 shows the configuration around the resist roller 27 related to the oscillation process in the image forming apparatus 100.

[0047] FIG. 4 shows a resist roller 27 that oscillates the recording material S, a resist oscillation drive unit 34 that oscillates the resist roller 27, a resist sensor SE1 that detects the arrival of the recording material S disposed upstream of the resist roller 27, and a position detection sensor SE2 that detects the deviation of the recording material S disposed downstream of the resist roller 27. Further, in FIG. 4, the distances from the resist roller 27 to the transfer nip portion by the secondary transfer roller 9 and the conveyance nip portion by the loop roller 26 are indicated by arrows.

[0048] Furthermore, FIG. 4 shows a secondary transfer roller 9 disposed downstream of the resist roller 27, a loop roller 26 disposed upstream of the resist roller 27, and a pressure detection sensor SE3 that detects the pressure contact force of the nip portions provided on the secondary transfer roller 9 and the loop roller 26. In the image forming apparatus 100, the position detection sensor SE2 corresponds to a deviation detection unit that detects the deviation of the recording material S. Also, the resist roller 27 and the resist oscillation drive unit 34 correspond to a deviation correction unit that moves the recording material S in the conveyance crossing direction to correct the deviation of the recording material.

[0049] The resist roller 27 is configured to be swingable in a direction perpendicular to the recording material conveyance direction FD (conveyance cross direction CD, main scanning direction). A resist swing drive unit 34 mainly composed of an electric motor is connected to the resist roller 27. Then, by driving the resist swing drive unit 34, the resist roller 27 moves in the conveyance cross direction CD starting from a predetermined home position.

[0050] The resist roller 27 moves along the conveyance cross direction CD in accordance with the period during which the recording material S passes, thereby moving the conveyed recording material S along the conveyance cross direction CD (swing process). As a result, the resist roller 27 corrects the deviation of the conveyed recording material S in the conveyance cross direction CD and adjusts the conveyance position of the recording material S so as to match the position of the toner image to be transferred.

[0051] Here, the position where the side end portion of the recording material S passes when there is no deviation in the conveyance cross direction CD is defined as the target position Tp. This target position Tp is the position (optimal image position) where the positional relationship between the recording material S and the toner image becomes optimal if the side end portion of the recording material S passes through that position in the conveyance cross direction CD. The resist roller 27 adjusts the conveyance position of the recording material S in the conveyance cross direction CD so that the side end portion of the recording material S reaches the target position Tp.

[0052] A resist sensor SE1 and a position detection sensor SE2 are provided in the conveyance path. The control unit 11 controls the operation of the resist roller 27 based on the detection results of the resist sensor SE1 and the position detection sensor SE2. The resist sensor SE1 is disposed between the resist roller 27 and the loop roller 26 in the conveyance path. The resist sensor SE1 detects the arrival of the leading end of the recording material S at a predetermined position upstream of the resist roller 27. The position detection sensor SE2 is disposed between the resist roller 27 and the secondary transfer roller 9 in the conveyance path. The position detection sensor SE2 detects the deviation amount (offset amount) between the passing position of the side end portion of the recording material S in the conveyance cross direction CD and the target position Tp.

[0053] (Resist Oscillation Control) Next, the control process of the oscillation operation by the resist roller 27 will be described. FIG. 5 shows a flowchart of the oscillation control process for controlling the oscillation operation of the resist roller 27.

[0054] First, when the job is started, the position detection sensor SE2 detects the position of the side end of the recording material S (step S101). The control unit 11 determines whether the side end of the recording material S is deviated from the target position Tp based on the detection result by the position detection sensor SE2 and the target position Tp (step S102).

[0055] When the side end of the recording material S is deviated from the target position Tp (Yes in step S102), based on the deviation amount (offset amount) between the position of the side end of the recording material S detected by the position detection sensor SE2 and the target position Tp, the oscillation amount and oscillation direction of the resist roller 27 are determined from the oscillation control information stored in the storage unit 12 (step S103).

[0056] The control unit 11 drives the resist oscillation drive unit 34 according to the determined oscillation amount and oscillation direction of the resist roller 27, and executes the oscillation operation (first oscillation operation) of the resist roller 27 (step S104).

[0057] After the oscillation of the resist roller 27 is stopped, or when the side end of the recording material S is not deviated from the target position Tp (No in step S102), the recording material S is made to enter the secondary transfer roller 9 without performing the oscillation operation of the resist roller 27 (step S105).

[0058] Next, the control unit 11 determines whether the oscillation timing has arrived (step S106). When the oscillation timing has not arrived (No in step S106), the control unit 11 waits until the oscillation timing arrives. The oscillation timing is set every time a predetermined time elapses after the recording material S enters the secondary transfer roller 9.

[0059] When the rocking timing arrives (Yes in step S106), the control unit 11 determines whether the side end of the recording material S is displaced from the target position Tp based on the detection result by the position detection sensor SE2 and the target position Tp (step S107). When the side end of the recording material S is not displaced from the target position Tp (No in step S107), the control unit 11 waits until the next rocking timing arrives.

[0060] When the side end of the recording material S is displaced from the target position Tp (Yes in step S107), the rocking amount and rocking direction of the registration roller 27 are determined based on the amount of deviation of the recording material S detected by the position detection sensor SE2 and the pressure contact force of the nip portion during conveyance of the recording material S (step S108). In this step S108, the control unit 11 calculates provisional values of the rocking amount and rocking direction of the registration roller 27 from the rocking control information stored in the storage unit 12 based on the amount of deviation detected by the position detection sensor SE2. Further, the control unit 11 calculates a correction amount of the rocking amount from the rocking control table for correcting the rocking operation stored in the storage unit 12 based on the pressure contact force of the nip portion during conveyance of the recording material S and the recording material characteristics of the recording material S. Then, the provisional value of the calculated rocking amount is corrected by the correction value to calculate the execution values of the rocking amount and rocking direction of the registration roller 27.

[0061] In the correction of the rocking amount by the pressure contact force of the nip portion, one or more pressure contact forces of any of the nip portions sandwiching (nipping) the recording material S being rocked by the registration roller 27 are considered. For example, one or more pressure contact forces of the transfer nip portion, fixing nip portion, and conveyance nip portion that nip the conveyed recording material S are considered. Further, as the conveyance nip portion, one or more of the intermediate conveyance rollers 23, 24, 25 and the loop roller 26, preferably the pressure contact force of the loop roller 26 closest to the registration roller 27, are considered.

[0062] In the image forming apparatus 100, the pressure contact force at the transfer nip of the secondary transfer unit and the fixing nip portion of the fixing unit 50 can be switched in order to satisfy conveyance performance and image quality. For example, when the recording material S is an envelope, the pressure contact force of the transfer nip is lowered in order to suppress wrinkles. Further, when the recording material S is embossed paper or the like with large irregularities, the pressure contact force of the transfer nip of the secondary transfer unit is increased in order to enhance the adhesion between the irregular portion and the transfer member (intermediate transfer belt) and improve transfer performance. Further, each conveyance roller in the recording material conveyance unit 20 can be switched according to the position within the recording material S during conveyance, and the pressure contact force of the nip portion can be changed at the front end portion, the center portion, and the rear end portion of the recording material S, respectively.

[0063] In the swinging operation of the registration roller 27, the greater the pressure contact force of the nip portion where the recording material S is nipped, the greater the resistance to the swing of the recording material S in the conveyance crossing direction CD. When the recording material S is swung in such a state, it becomes difficult to slip between the recording material S and the roller, and the swing amount of the recording material S becomes smaller than the swing amount of the registration roller 27. Therefore, when the pressure contact force of the nip portion is large, it is necessary to correct the swing amount determined based on the amount of deviation of the recording material S in a direction of increasing it according to the pressure contact force of the nip portion.

[0064] In the swinging operation of the registration roller 27, the influence of the pressure contact force of the nip portion becomes greater as the roller or the like sandwiching the recording material S is closer to the registration roller 27. Therefore, the correction amount of the final swing amount according to the pressure contact force of the nip portion may be determined according to the pressure contact force of the nip portion of each roller and the distance between each roller and the registration roller 27. For example, it is preferable that an increase in the pressure contact force of the transfer nip portion having a short distance from the registration roller 27 has a greater influence on the swing amount (correction amount) than an increase in the pressure contact force of the nip portion of a roller having a long distance from the registration roller 27 (fixing nip portion or conveyance nip portion).

[0065] In addition, due to misalignment of the secondary transfer roller 9 and the fixing roller 51, or the difference in roller diameters between the front side and the back side of each roller (such as a conveyance roller), the recording material S will shift (skew) in the conveyance cross direction CD even during recording material conveyance. After passing through the secondary transfer roller, the recording material performs a registration swing motion determination every time a predetermined time elapses until the recording material is discharged by the registration roller 27. If it is shifted from the target position, a swing motion is performed. Therefore, position correction of the side end portion of the recording material S can be performed not only at the leading end of the recording material S but also at the intermediate portion and the trailing end side, and the skew of the recording material S can be corrected. For example, it is possible to correct the sub-scanning curvature that significantly occurs in a recording material that is long in the recording material conveyance direction, such as a long sheet.

[0066] Next, the control unit 11 drives the registration swing drive unit 34 according to the determined swing amount and swing direction of the registration roller 27, and swings (second swing operation) the registration roller 27 (step S109). After the swing process of the registration roller 27, it is determined whether the recording material S has been discharged from the registration roller 27 (step S110). The control unit 11 detects the passage of the trailing end portion of the recording material S by the registration sensor SE1 and the position detection sensor SE2, and determines whether the recording material S has been discharged from the registration roller 27 based on this. If the recording material S has not been discharged from the registration roller 27 (No in step S110), it waits until the next swing timing arrives. If the recording material S has been discharged from the registration roller 27 (Yes in step S110), the processing according to this flowchart is terminated.

[0067] 〈2. Second Embodiment of the Image Forming Apparatus〉 Next, a second embodiment of the image forming apparatus will be described. The image forming apparatus according to the second embodiment includes a machine learning unit that learns, by machine learning, the amount of swing of the registration roller (offset correction unit) according to the nip pressure contact force. Note that, for the configuration other than including the machine learning unit, the same configuration as that of the image forming apparatus according to the first embodiment described above can be applied. Therefore, detailed description of the same configuration as that of the first embodiment described above will be omitted.

[0068] [Configuration of Machine Learning Unit] FIG. 6 is a block diagram showing the functional configuration of the machine learning unit in the control unit. In FIG. 6, an example in which the machine learning unit 70 is provided in the control unit 11 is shown. The machine learning unit 70 determines, by machine learning (reinforcement learning), the amount of swing according to the pressure contact force of the nip portion in the image forming apparatus 100 and the characteristics of the recording material.

[0069] The control unit 11 includes a state information notification unit 81 and an update processing unit 82. The control unit 11 outputs and inputs information to and from the position detection sensor SE2, the pressure detection sensor SE3, the media sensor SE4, and the storage unit 12 of the image forming apparatus 100. The machine learning unit 70 includes a state information acquisition unit 71, a learning unit 72, a reward calculation unit 73, and a control information output unit 74.

[0070] In FIG. 6, the position detection sensor SE2 detects the deviation amount (offset amount) between the position of the side end portion of the recording material S on the registration roller 27 and the target position Tp, and transmits it to the state information notification unit 81. The pressure detection sensor SE3 detects the nip pressure contact force of the recording material S being conveyed, and transmits it to the state information notification unit 81. The media sensor SE4 detects the recording material characteristics of the recording material S, and transmits it to the state information notification unit 81. The state information notification unit 81 notifies the machine learning unit 70 of the offset amount, the nip pressure contact force, and the recording material characteristics received from the position detection sensor SE2, the pressure detection sensor SE3, and the media sensor SE4 as the state information of the recording material S in the image forming apparatus 100. The update processing unit 82 receives the new rocking control information calculated by the machine learning unit 70 from the control information output unit 74, and updates the information of the rocking control table for correcting the rocking control stored in the storage unit 12.

[0071] The state information acquisition unit 71 acquires the offset amount, the nip pressure, and the recording material characteristics from the state information notification unit 81 as state information. The learning unit 72 starts learning with the nip pressure of the nip unit and the recording material characteristics of the recording material S input from the state information acquisition unit 71, and outputs the rocking amount of the resist rocking drive unit 34. Further, the learning unit 72 calculates, as the rocking control information, the rocking amount of the resist rocking drive unit 34 having the highest action value based on the nip pressure of the nip unit of the recording material S during conveyance, the recording material physical properties, and the reward calculated by the reward calculation unit 73.

[0072] The reward calculation unit 73 calculates the reward to be stored based on the detection value (offset amount) of the position detection sensor SE2 after the rocking operation of the resist roller 27. The reward calculation unit 73 calculates and stores a positive reward if the deviation amount (offset amount) between the position of the side end portion of the recording material S and the target position Tp is less than a certain amount, and calculates and stores a negative reward if it is equal to or more than the certain amount.

[0073] The control information output unit 74 receives and outputs the new rocking control information calculated by the learning unit 72 based on the nip pressure and the recording material physical properties and the reward calculated by the reward calculation unit 73, and updates the rocking control information stored in the storage unit 12 of the image forming apparatus 100.

[0074] The image forming apparatus 100 can determine the optimal correction amount according to the combination of the nip pressure of each nip unit of the recording material S in the conveyance path such as the secondary transfer unit and the fixing unit and the recording material characteristic data by performing machine learning (reinforcement learning). Therefore, it is possible to reduce the image position shift due to the offset of the recording material S.

[0075] [Machine learning process] Next, the machine learning process by the machine learning unit 70 described above will be explained. FIG. 7 shows a flowchart of the machine learning process by the machine learning unit 70. The machine learning unit 70 starts learning with the nip pressure of each roller pair of the recording material and the recording material characteristics as inputs and the swing amount of the resist roller 27 as the output.

[0076] First, the state information acquisition unit 71 of the machine learning unit 70 acquires the state information of the recording material S in the image forming apparatus 100 from the state information notification unit 81 (step S201). The state information acquisition unit 71 acquires, as state information, for example, the amount of deviation detected by the position detection sensor SE2 of the image forming apparatus 100, the nip pressure at each nip portion of the recording material S being conveyed detected by the pressure detection sensor SE3, and the recording material characteristics detected by the media sensor SE4 from the state information notification unit 81.

[0077] Next, the resist swing drive unit 34 is driven to perform a swing operation of the resist roller 27 (step S202). This swing operation of the resist roller 27 executes a first swing operation and a second swing operation according to the flowchart shown in FIG. 4 of the above-described first embodiment.

[0078] Next, after the second swing operation of the resist roller 27, the reward calculation unit 73 calculates a reward from the amount of deviation detected by the position detection sensor SE2 (step S203). The reward calculation unit 73 calculates a positive reward if the deviation amount between the position of the side end portion of the recording material P and the target position Tp is less than a certain amount, and a negative reward if it is equal to or more than the certain amount, based on the value of the position detection sensor after the second swing operation.

[0079] Next, the learning unit 72 learns the swing operation of the resist roller 27 by calculating the swing operation (correction amount) with the highest action value according to the nip pressure and the recording material physical properties of the recording material S and the reward calculated by the reward calculation unit 73 (step S204). Then, the learning unit 72 outputs control information of the swing operation (correction amount) with the highest action value determined based on the learning result to the control information output unit 74 (step S205).

[0080] The control information output unit 74 receives the new rocking control information calculated by the machine learning unit 70 and outputs it to the update processing unit 82, and the update processing unit 82 updates the correction amount of the rocking control table stored in the storage unit 12 (step S206). Based on the information in the updated rocking control table, the control unit 11 controls the second rocking operation of the resist roller 27 (step S207). Then, by repeating the processes from step S201 to step S207, the machine learning unit 70 performs machine learning (reinforcement learning).

[0081] The above-mentioned machine learning unit 70 can determine an optimal correction amount for the rocking operation of the resist roller 27 according to the combined state of the pressure contact force of the nip portion (transfer nip portion, fixing nip portion, conveying nip portion, etc.) where the recording material S is sandwiched during conveyance and the recording material characteristics by machine learning (reinforcement learning). Thereby, the deviation of the recording material can be sufficiently corrected by the rocking operation of the resist roller 27, and the positional deviation of image formation with respect to the recording material S can be reduced.

[0082] Note that the present invention is not limited to the configuration described in the above-described embodiment examples, and various modifications and changes are possible without departing from the configuration of the present invention.

Explanation of Reference Numerals

[0083] 1Y, 1M, 1C, 1K photoreceptor drum, 2Y, 2M, 2C, 2K charging unit, 3Y, 3M, 3C, 3K optical writing unit, 4Y, 4M, 4C, 4K developing device, 5Y, 5M, 5C, 5K drum cleaner, 6 intermediate transfer belt, 7Y, 7M, 7C, 7K primary transfer roller, 8 counter roller, 9 secondary transfer roller, 10 image forming section, 10C, 10K, 10M, 10Y image forming unit, 11 control section, 12 storage section, 13 communication section, 14 operation section, 20 recording material conveyance section, 21 paper feed tray, 22 paper feed section, 23 intermediate conveyance roller, 26 loop roller, 27 registration roller, 28 paper discharge roller, 29 paper discharge tray, 34 registration swing drive section, 50 fixing section, 51 fixing roller, 52 pressure roller, 60 image reading section, 70 machine learning section, 71 state information acquisition section, 72 learning section, 73 reward calculation section, 74 control information output section, 81 state information notification section, 82 update processing section, 100 image forming apparatus, SE1 registration sensor, SE2 position detection sensor, SE3 pressure detection sensor, SE4 media sensor

Claims

1. In an image forming apparatus that sandwiches and conveys a recording material at a nip portion, a conveyance unit that conveys the recording material, a transfer unit having a transfer roller that transfers a toner image onto the recording material, a fixing unit having a fixing roller that fixes the toner image formed on the recording material, a deviation detection unit that detects the position of the recording material in the direction intersecting the conveyance direction, a deviation correction unit that is located upstream of the transfer unit and moves the recording material in the direction intersecting the conveyance direction to correct the deviation of the recording material, a pressure detection unit that detects the pressing force of the nip portion, and a control unit that controls the driving amount of the deviation correction unit based on the detection result of the deviation detection unit and the pressing force of the nip portion detected by the pressure detection unit. An image forming apparatus.

2. The control unit controls the driving amount of the deviation correction unit based on the pressing force of any one or more of the conveyance nip portion formed by the roller pair of the conveyance unit, the transfer nip portion formed by the transfer roller of the transfer unit, and the fixing nip portion formed by the fixing roller that fixes the toner image, as the nip portion. The image forming apparatus according to claim 1.

3. The control unit stores a control table for controlling the driving amount of the deviation correction unit, and controls the driving amount of the deviation correction unit based on the detection result of the deviation detection unit and the control table. The image forming apparatus according to claim 1 or 2.

4. The control unit controls the pressing force of the nip portion. The image forming apparatus according to any one of claims 1 to 3.

5. When the control unit increases the pressing force of the nip portion, the control unit increases the driving amount of the deviation correction unit. The image forming apparatus according to claim 4.

6. The shorter the distance between the deviation correction unit and the nip portion, the more the control unit increases the driving amount of the deviation correction unit. The image forming apparatus according to any one of claims 1 to 5.

7. Comprising a pressure detection unit that detects the pressing force of the nip portion. The image forming apparatus according to any one of claims 1 to 6.

8. Comprising a recording material characteristic detection unit that detects the characteristics of the recording material, and the control unit controls the driving amount of the deviation correction unit according to the recording material characteristics detected by the recording material characteristic detection unit. The image forming apparatus according to any one of claims 1 to 7.

9. When the recording material is embossed paper, the control unit increases the driving amount of the deviation correction unit. The image forming apparatus according to claim 8.

10. When the recording material is an envelope, the control unit increases the driving amount of the skew correction unit. The image forming apparatus according to claim 8.

11. The recording material characteristic detection unit detects, as the recording material characteristics, any one or more of paper type, paper thickness, basis weight, recording material size, and surface smoothness. The image forming apparatus according to any one of claims 8 to 10.

12. The control unit includes a machine learning unit that learns the driving amount of the skew correction unit by machine learning. The machine learning unit inputs at least one of the pressure contact force of the transfer roller and the roller pair and the physical properties of the recording material, outputs the driving amount of the recording material by the skew correction unit, and calculates a reward value according to whether the skew amount of the recording material after skew correction is within a predetermined range. It has a learning model. The control unit controls the skew correction unit based on the driving amount of the skew correction unit obtained by the learning model. The image forming apparatus according to claim 2.

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