Sheet conveying device and image forming device

Abstract

To suppress variations of a state of backlash of a drive train between a state before start of first sheet conveyance and a state before starts of second and following each conveyance when performing backlash reducing control, in a conveyance job for conveying the sheet.SOLUTION: A sheet conveying device comprises a pair of registration rollers for conveying a sheet, and a control unit for executing backlash reducing process for reducing backlash of a transfer mechanism by driving and stopping a drive motor before the sheet is butted to the pair of registration rollers. The control unit, before executing the backlash reducing process, acquires target rotational speed of the drive motor when the sheet is conveyed by the pair of registration rollers after the backlash reducing process (S2), and, when the backslash reducing process is executed, the drive motor is accelerated to the target rotational speed so as to be the same as an operation that the drive motor is stopped from the target rotational speed after conveying the sheet by the pair of registration rollers after the backlash reducing process, and then stops from the target rotational speed (S6).SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a sheet conveying device that conveys a sheet, and an image forming apparatus that uses the same to form an image on the sheet. [Background technology]

[0002] In conventional image forming devices, the leading edge registration value, which is the distance between the leading edge of the sheet and the leading edge of the image, is adjusted to a desired value by synchronizing the image formation timing with the start of rotation of the pair of registration rollers that feed the sheet. In this configuration, play can occur in the drive mechanism, such as the gears and timing belt from the drive motor (the drive source) to the drive gear of the pair of registration rollers. From the second sheet onward after the start of a print job, a certain amount of play and belt tension stabilize when the device stops after feeding the preceding sheet.

[0003] However, before the first sheet of a print job is conveyed, for example, due to jam clearance or internal part replacement, the rollers may rotate, causing backlash between the gears or changes in belt tension. In this case, a time lag may occur between the start of rotation of the drive motor and the start of rotation of the pair of registration rollers, potentially delaying the arrival of the sheet at the image forming unit. To address this issue, an image forming apparatus has been proposed that performs control to eliminate backlash by rotating the drive motor for a predetermined time and then stopping it before the leading edge of the first sheet reaches the pair of registration rollers (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-66447 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for image forming apparatuses that can print on a variety of sheets, such as sheets with a large basis weight and sheets with a coated surface (coated paper). Because these sheets require a large amount of heat when fixing the toner, the image forming unit and each conveying roller are conveyed at a slower speed than sheets with a small basis weight. In other words, a single image forming apparatus may have multiple conveying speeds depending on the type of sheet on which an image is formed.

[0006] However, the image forming apparatus described in Patent Document 1 makes no mention of the speed of the control for eliminating backlash. The drive motor vibrates when it stops after rotating, and the amount of vibration varies depending on the motor's individual characteristics and drive speed. Furthermore, the amount of vibration affects the degree of backlash elimination between gears and the belt tension. Therefore, in an image forming apparatus that changes the conveying speed depending on the type of sheet, if the conveying speed for the sheet-passing job differs from the speed during the backlash elimination rotation performed before passing the first sheet of the job, the following problems may occur. In other words, in this case, the responsiveness of the registration roller pair from its stopped state to its start of rotation to convey the sheet varies, resulting in inconsistent timing for the sheet's arrival at the image forming unit and a risk of variations in the leading edge registration value.

[0007] The present invention aims to provide a sheet conveying device and an image forming device that can suppress variations in the state of backlash in the drive train before the start of conveying the first sheet and before the start of conveying each of the second and subsequent sheets when backlash elimination control is performed in a conveying job for conveying sheets. [Means for solving the problem]

[0008] One aspect of the present invention is a sheet conveying device comprising: a pair of registration rollers having a first roller and a second roller that contact each other to form a nip portion, against which a sheet is abutted while stationary and then rotates to convey the sheet; a drive motor that drives and rotates the first roller; a transmission mechanism having an endless member that transmits the power of the drive motor to the first roller via the endless member; and a control unit that performs a backlash reduction process that reduces backlash in the transmission mechanism by driving and stopping the drive motor before the sheet abuts against the pair of registration rollers, wherein the control unit, before performing the backlash reduction process, obtains a target rotational speed of the drive motor when the sheet is conveyed by the pair of registration rollers after the backlash reduction process, and, during the backlash reduction process, accelerates the drive motor to the target rotational speed and then stops it from the target rotational speed so that the operation is the same as the operation of stopping the drive motor from the target rotational speed after the sheet is conveyed by the pair of registration rollers after the backlash reduction process.

[0009] Another aspect of the present invention is an image forming apparatus comprising the above-mentioned sheet conveying device and an image forming unit that forms an image on a sheet at an image forming position, wherein the control unit controls the drive motor to strike the sheet while the registration roller pair is stopped and convey the sheet to the image forming position in accordance with the timing of image formation. [Effects of the Invention]

[0010] According to the present invention, in a conveying job for conveying sheets, when backlash elimination control is performed, the variation in the state of backlash in the drive train can be suppressed between before the start of conveying the first sheet and before the start of conveying the second sheet and thereafter. [Brief explanation of the drawings]

[0011] [Figure 1] 3 is a cross-sectional view showing the image forming apparatus according to the first embodiment in a state where the right door unit is closed. FIG. [Figure 2]3 is a cross-sectional view showing the image forming apparatus according to the first embodiment in a state where the right door unit is open. FIG. [Figure 3] FIG. 2 is a front view showing the drive mechanism according to the first embodiment. [Figure 4] FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the first embodiment. [Figure 5] 10 is a flowchart showing a processing procedure for eliminating backlash in the image forming apparatus according to the first embodiment. [Figure 6] 6 is a time chart showing the rotation speed of a registration drive motor when a backlash eliminating process is performed in the image forming apparatus according to the first embodiment. [Figure 7] 10 is a time chart showing the rotation speed of a registration drive motor when a backlash eliminating process is performed in an image forming apparatus according to a second embodiment. [Figure 8] FIG. 10 is an explanatory diagram showing vector control of a registration drive motor according to a second embodiment. [Figure 9] FIG. 10 is a block diagram showing the control functions of a motor control unit according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] First Embodiment A first embodiment of the present invention will be described in detail below with reference to Figures 1 to 6. First, the schematic configuration of an image forming apparatus 1 according to this embodiment will be described with reference to Figure 1. Unless otherwise specified, the dimensions, materials, relative positions, etc. of the components of the image forming apparatus 1 are not intended to limit the scope of the present invention to those alone.

[0013] [Image forming equipment] 1 is a schematic diagram of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 forms an image on a sheet used as a recording medium based on image information input from an externally connected computer 204 (see FIG. 4) or image information read from an original. Sheets used as recording media include various sheet materials of different materials and sizes, such as paper of different basis weights, such as cardboard, plain paper, and thin paper, envelopes, plastic film for overhead projectors, and cloth.

[0014] The image forming apparatus 1 includes an apparatus main body 1A that houses an image forming unit 15 that forms an image on a sheet S, and an image reading device 2 that is disposed above the apparatus main body 1A and reads image information from a document. The image forming unit 15 is an electrophotographic unit of an intermediate transfer type that includes four image forming stations PY, PM, PC, and PK for yellow, magenta, cyan, and black, an intermediate transfer belt 155, and a fixing unit 160. The image forming unit 15 forms an image on the sheet S at a secondary transfer unit 161, which will be described later and is an example of an image forming position.

[0015] Each of the image forming stations PY to PK performs an electrophotographic process to form a toner image on the surface of a photosensitive drum 151, which is an image carrier. Since the image forming stations PY to PK have the same configuration except for the color of the toner, the configuration of the yellow image forming station PY will be described below as a representative example. When a request is made to form a toner image at the image forming station PY, the photosensitive drum 151, which serves as a photosensitive member, is rotated, and a charging device uniformly charges the surface of the photosensitive drum 151. An exposure device 152, located below the photosensitive drum 151, irradiates the photosensitive drum 151 with laser light based on image information to expose the drum surface and writes an electrostatic latent image onto the photosensitive drum 151. A developing device 153 supplies charged toner particles to the photosensitive drum 151 and develops the electrostatic latent image on the drum surface into a toner image.

[0016] The toner images of each color formed on the surface of each photosensitive drum 151 in the image forming stations PY to PK are finally transferred onto the sheet S via an intermediate transfer belt 155 and a secondary transfer roller 159. First, the toner images carried on each photosensitive drum 151 are primarily transferred onto the intermediate transfer belt 155 by a primary transfer roller 154. Adherents such as toner remaining on the photosensitive drum 151 are removed by a cleaning device provided in each of the image forming stations PY to PK.

[0017] An intermediate transfer belt 155, which is an intermediate transfer body, is wound around a secondary transfer inner roller 156, a tension roller 157, and a tension roller 158, and is driven to rotate in the direction R1 in the drawing. The toner image carried on the intermediate transfer belt 155 is secondarily transferred to a sheet S at a secondary transfer section 161 formed between the intermediate transfer belt 155 and a secondary transfer roller 159 facing the secondary transfer inner roller 156. Adherents such as toner remaining on the intermediate transfer belt 155 are removed by a belt cleaning device.

[0018] The sheet S onto which the toner image has been transferred is delivered to a fixing device 160. The fixing device 160, which is a fixing means in this embodiment, has a fixing roller 162 as a rotating body that conveys the sheet S, a pressure roller 163 that holds the sheet S together with the fixing roller 162, and a heat source (e.g., a halogen lamp) (not shown) that heats the toner image on the sheet. The fixing device 160 applies heat and pressure to the toner image while conveying the sheet S, melting the toner, and then the toner is fixed to the sheet S.

[0019] In this embodiment, the image forming apparatus 1 is an example of a sheet conveying apparatus. A configuration for conveying a sheet S in the image forming apparatus 1 will be described below. In parallel with the image formation process described above, sheets S are fed one by one from the cassette feeding unit 10 or the manual feeding unit 11 toward the image forming unit 15. The cassette feeding unit 10 includes two upper and lower feeding cassettes 100, 100 that store sheets S inside the apparatus main body 1A, and a feeding unit 101 that feeds the sheets S from each feeding cassette 100. The feeding unit 101 includes a pickup roller 102, a feeding roller 103, and a separation roller 104. During image formation, when feeding a sheet S from the feeding cassette 100, the control unit 30 issues a print signal, and the pickup roller 102 feeds the sheet S stored in the feeding cassette 100. Thereafter, the sheet S is fed as a single sheet to a conveying path by a roller pair consisting of a feeding roller 103 and a separation roller 104. The fed sheet S is conveyed by a drawing roller pair 114 and a pre-registration roller pair (hereinafter referred to as a pre-registration roller pair 121). Furthermore, the sheet S is conveyed toward a registration roller pair (hereinafter referred to as a registration roller pair 20) arranged downstream of the pre-registration roller pair 121 in the sheet conveying direction.

[0020] The manual feed section 11 has a manual tray 113 on which a user places sheets S outside the housing 3 of the apparatus main body 1A, and a feed unit 112 that feeds the sheets S from the manual tray 113. When feeding sheets S from the manual tray 113 during image formation, when the control section 30 issues a print signal, a pickup roller feeds the sheets S stacked on the manual tray 113. Thereafter, the sheets S are fed as a single sheet to a conveyance path by a roller pair of a feed roller and a separation roller, and the fed sheets S are conveyed by a pull-out roller pair 115 and a pre-registration roller pair 121 toward the registration roller pair 20.

[0021] When the sheet S abuts against the nip portion of the registration roller pair 20 while the registration roller pair 20 is stopped, the pre-registration roller pair 121 pushes the sheet S into this nip portion, causing the sheet S to bend between the pre-registration roller pair 121 and the registration roller pair 20. As a result, the orientation of the sheet S is corrected so that the leading edges of the sheet S are aligned, and as the registration roller pair 20 rotates in this state, the sheet S is corrected for skew and is transported to the secondary transfer unit 161, which is an example of an image forming position of the image forming unit 15.

[0022] The registration roller pair 20 is an example of a registration roller pair, and includes a drive roller 21, which is an example of a first roller, and a driven roller 22, which is an example of a second roller, which come into contact with each other to form a nip portion N. The registration roller pair 20 is stopped while the sheet S is abutted against it, and then rotates to convey the sheet S. The registration roller pair 20 is located upstream of the secondary transfer portion 161 in the sheet conveying direction along the vertical direction, and sandwiches the sheet S at the nip portion N (see FIG. 3) to convey it to the secondary transfer portion 161. In this embodiment, the axial direction of the drive roller 21 is the sheet width direction, which intersects with the sheet conveying direction.

[0023] The sheet S, on which an image has been formed by passing through the secondary transfer unit 161 and the fixing device 160, is conveyed to discharge rollers 171. The discharge rollers 171 discharge the sheet S on which the image has been formed, and stack it on a discharge tray 180 provided at the top of the apparatus main body 1A. Note that this embodiment employs a so-called internal discharge type configuration in which a discharge space (above the discharge tray 180) for stacking the sheet S is provided between the apparatus main body 1A and the image reading device 2 in the vertical direction.

[0024] In the case of double-sided printing, the discharge rollers 171 convey the sheet S with an image formed on its first side, and when the trailing edge of the sheet S passes the branching section 172, the discharge rollers 171 reverse the conveying direction and switch back the sheet S. As a result, the sheet S is delivered to the double-sided conveying section 190, and is conveyed by the re-conveying roller pair of the double-sided conveying section 190 toward the pre-registration roller pair 121 via the double-sided path 191. After passing through the pre-registration roller pair 121 and being corrected for skew again by the registration roller pair 20, the sheet S, with an image formed on its second side by passing through the secondary transfer section 161 and the fixing device 160, is discharged by the discharge rollers 171 and stacked on the discharge tray 180.

[0025] In the above description, a direct transfer electrophotographic unit, or an inkjet or offset printing image forming unit may be used as the image forming section 15. Also, in this embodiment, a full-color electrophotographic copying machine equipped with multiple photosensitive drums is applied, but the present invention is not limited to this and can also be applied to a monochrome or mono-color copying machine or printer equipped with one photosensitive drum.

[0026] [Opening and closing mechanism of the device body] Next, the opening and closing mechanism of the right side of the apparatus main body 1A, i.e., the side where the manual feed unit 11 is provided, will be described using Fig. 2. Fig. 2 is a cross-sectional view of the state in which the right door unit 701 is open. As shown in Fig. 2, the apparatus main body 1A has a housing 3 which is an example of a fixed side unit, and a right door unit 701 which is an example of an opening and closing side unit that opens and closes the housing 3 by rotating on the right side of the housing 3.

[0027] In this embodiment, some of the sheet conveying means are mounted on the right door unit 701, and the right door unit 701 is configured to be able to open around a rotation shaft 702 when, for example, a sheet S becomes jammed inside the main body. That is, the right door unit 701 opens and closes by rotating left and right relative to the housing 3 around the rotation shaft 702, which is arranged in the axial direction of the drive roller 21, which is the sheet width direction. The rotation shaft 702 is arranged, for example, near directly below the feeding unit 112 of the manual feed tray 113. The position of the rotation shaft 702 is not limited to being near directly below the feeding unit 112, and may be near directly above the feeding unit 112. In addition, in this embodiment, the right door unit 701 opens and closes by rotating around the rotation shaft 702, but the invention is not limited thereto and may be configured to open and close by, for example, a sliding or pivoting action.

[0028] When the right door unit 701 is opened, one roller of a pair of rollers, such as the drive roller 21, is held by the right door unit 701, so that the sheet S can be removed without tearing, and the pair of rollers can be separated. For this reason, the right door unit 701 supports the drive roller 21, secondary transfer roller 159, duplex conveying section 190, etc. In addition, the housing 3 supports the driven roller 22, inner secondary transfer roller 156, fuser 160, etc. As a result, when the right door unit 701 closes the housing 3, the drive roller 21 and driven roller 22 come into contact with each other, and when the right door unit 701 opens the housing 3, the drive roller 21 and driven roller 22 are separated from each other.

[0029] [Registration Roller Pair Drive Mechanism] Next, a drive mechanism that drives and rotates the pair of registration rollers 20 will be described with reference to FIG. 3. FIG. 3 is a front view showing the drive mechanism for the drive roller 21 when the right door unit 701 is closed. As shown in FIG. 3, the image forming apparatus 1 includes a registration drive motor 212, which is an example of a drive motor, and a transmission mechanism 230 that transmits the power of the registration drive motor 212 to the drive roller 21 to rotate the drive roller 21. The transmission mechanism 230 includes a motor pulley 231 attached to the rotation shaft of the registration drive motor 212, a timing belt 232, a gear pulley 233, and an idler gear 234. The driving force is transmitted from the motor pulley 231 attached to the registration drive motor 212 to the gear pulley 233 via the timing belt 232, and further transmitted via the idler gear 234 to a registration drive gear 235 attached to the end of the drive roller 21. The timing belt 232 is an example of an endless member and is a toothed belt made of an elastic material. In this embodiment, the timing belt 232 made of a toothed belt is used as the endless member, but the present invention is not limited to this, and a toothless belt, a chain, or the like may also be used.

[0030] Here, the registration drive motor 212 and the transmission mechanism 230 are supported by the housing 3, and their positions are fixed regardless of whether the right door unit 701 is open or closed. In contrast, as shown in FIG. 2, the drive roller 21 moves in accordance with the opening and closing of the right door unit 701. Therefore, when the right door unit 701 closes the housing 3, the drive roller 21 is connected to the transmission mechanism 230, and when the right door unit 701 opens the housing 3, the connection between the drive roller 21 and the transmission mechanism 230 is released. In other words, when the right door unit 701 is opened, the registration drive gear 235 and the idler gear 234 are separated, and the first sheet S to be conveyed after the right door unit 701 is opened or closed may have play between the gears and the belt. In addition, in this embodiment, a case has been described in which the drive roller 21 is supported by the rotating right door unit 701, but this is not limited to this. The drive roller 21 may be supported by the housing 3 so that the registration roller pair 20 continues to be clamped regardless of whether the right door unit 701 is open or closed, but even in such a configuration, rattles may occur when, for example, a jammed sheet remaining in the apparatus main body 1A is processed. Therefore, in this embodiment, rattle elimination processing is performed before the first sheet S of the image forming job is conveyed.

[0031] [Control system] Next, we will explain the control unit that controls the functional configuration of the image forming apparatus 1. Fig. 4 is a block diagram for explaining the control system of the image forming apparatus 1. The control unit 30 has various functional units such as a CPU 201 (Central Processing Unit), memory 202, an operation unit 203, an image formation control unit 205, a sheet conveyance control unit 206, and a sensor control unit 207. Note that, for example, the control unit 30 may be configured to be able to receive various information related to the sheet S used for printing via a computer 204 connected via a network.

[0032] The CPU 201 executes predetermined control programs and the like to realize various processes performed by the image forming apparatus 1. The memory 202 is, for example, a RAM (Random Access Memory) or a ROM (Read Only Memory), and stores various programs and various data in predetermined storage areas. The operation unit 203 accepts various information (size information, basis weight information, surface property information, etc.) related to the sheet S used by the user for printing, and various operations performed by the user, such as instructions to execute or interrupt printing.

[0033] The image formation control unit 205 issues instructions to the image forming unit 15 including the exposure device 152, and controls image formation. The sheet transport control unit 206 issues instructions to the feed motor 211, the registration drive motor 212, the double-sided motor 213, the extraction motor 214, and the like, and controls the transport of the sheet S. The feed motor 211 drives the feed unit 101. The registration drive motor 212 drives the registration roller pair 20. The double-sided motor 213 drives the re-transport roller pair, and the like.

[0034] The sensor control unit 207 controls the start or stop of detection by the sheet size detection sensor 221, the registration sensor 222, the image position detection sensor 301, the sheet position detection sensor 302, etc., and receives the detection results of these sensors. The sheet size detection sensor 221 and the registration sensor 222 are disposed upstream of the registration roller pair 20 in the sheet conveying direction.

[0035] [Reducing backlash] The following describes the backlash reduction process in this embodiment with reference to FIGS. 5 and 6. In this embodiment, the image forming apparatus 1 controls the image formation speed and sheet conveyance speed to be slower for sheets S, such as thick paper with a heavy basis weight or coated paper with a coated surface, compared to thin paper with a light basis weight or plain paper without a coating, for reasons such as ensuring toner fixability. For example, when the registration drive motor 212 rotates the registration roller pair 20, the target rotation speed of the registration drive motor 212 is changed. For example, a high target rotation speed V1 is set for thin paper, a medium target rotation speed V2 is set for medium paper, and a low target rotation speed V3 is set for thick paper or coated paper. For example, if the sheet information is basis weight, the control unit 30 acquires V1 (first speed) as the target rotation speed when it acquires a first basis weight as the sheet information. At this time, the control unit 30 acquires V2 (second speed), which is slower than V1 (first speed), as the target rotation speed when it acquires a second basis weight, which is greater than the first basis weight, as the sheet information. That is, the sheet S is conveyed at a speed selected from a plurality of conveying speeds depending on the type of the sheet S.

[0036] In this embodiment, after the image formation job (such as the print image, the type and number of sheets S) is determined, the registration drive motor 212 rotates for a predetermined time at a speed corresponding to the conveyance speed before the first sheet S reaches the registration roller pair 20, and then stops. This causes the state to transition to one in which the backlash between the gears is eliminated as described above. That is, the control unit 30 executes a backlash elimination process to eliminate backlash in the transmission mechanism 230 by driving and stopping the registration drive motor 212 before the sheet S abuts against the registration roller pair 20. Note that in this embodiment, the backlash elimination process is sufficient as long as it eliminates at least backlash in the transmission mechanism 230, and may further include a process to eliminate backlash between the transmission mechanism 230 and the drive roller 21. Alternatively, it may include a process to eliminate backlash inside the registration drive motor 212.

[0037] In this embodiment, when the control unit 30 stops the registration drive motor 212 from the target rotation speed during the backlash removal process, the control unit 30 decelerates the rotation speed in two stages: a first deceleration gradient and a second deceleration gradient that is steeper than the first deceleration gradient. The first deceleration gradient is a gradient used when decelerating from the target rotation speed to a threshold speed that is slower than the target rotation speed, and the second deceleration gradient is a gradient used when decelerating from the threshold speed until the motor stops.

[0038] In this manner, in the backlash elimination process, the control unit 30 acquires the target rotation speed of the registration drive motor 212 when the sheet S is conveyed by the pair of registration rollers 20 after the backlash elimination process before executing the backlash elimination process. Then, during the backlash elimination process, the control unit 30 accelerates the registration drive motor 212 to the target rotation speed and then stops it from the target rotation speed. At this time, the control unit 30 stops the registration drive motor 212 from the target rotation speed so that the operation is the same as the operation of stopping the registration drive motor 212 from the target rotation speed after the sheet S is conveyed by the pair of registration rollers 20 after the backlash elimination process. As a result, the state of backlash in the transmission mechanism 230 immediately after the backlash elimination process is the same as the state of backlash in the transmission mechanism 230 when the pair of registration rollers 20 is stopped when the sheet S is actually conveyed thereafter. Therefore, in an image formation job, when the backlash elimination process is performed, variation in the state of backlash in the transmission mechanism 230 between before the start of conveyance of the first sheet and before the start of conveyance of each of the second and subsequent sheets can be suppressed.

[0039] Thereafter, the control unit 30 controls the registration drive motor 212 to start rotating in accordance with the timing of image formation when the leading edge of the sheet S hits the pair of registration rollers 20. The control unit 30 stops the rotation of the registration drive motor 212 at the timing when the trailing edge of the sheet S leaves the pair of registration rollers 20. When conveying the second or subsequent sheets in the image forming job, the leading edge of the next sheet S hits the stopped pair of registration rollers 20, and image formation is performed in the same manner.

[0040] The procedure for performing backlash reduction processing when an image forming job is executed will be described with reference to the flowchart shown in Fig. 5. When an image forming job (paper passing job) is determined (S1), the control unit 30 acquires the target rotation speed of the registration drive motor 212 according to the sheet information of the job (S2). For example, for thin paper, the target rotation speed is a high speed V1 (S3), for medium paper, the target rotation speed is a medium speed V2 (S4), and for thick paper or coated paper, the target rotation speed is a low speed V3 (S5). The control unit 30 acquires the target rotation speed based on the sheet information, for example, by referring to a table.

[0041] The control unit 30 drives the registration drive motor 212 to rotate in accordance with the acquired target rotation speed, and stops it after a predetermined time. This is the backlash elimination process. The predetermined time T1 here is set shorter than the time (T2) for which the sheet S is subsequently transported at the target rotation speed, for example, about 0.1 to 0.5 seconds (see FIG. 6). That is, the control unit 30 sets the time for which the registration drive motor 212 is driven at the target rotation speed in the backlash elimination process to be shorter than the time for which the registration drive motor 212 is driven at the target rotation speed when the sheet S is transported by the registration roller pair 20 after the backlash elimination process. This makes it possible to suppress a decrease in productivity even when the backlash elimination process is performed.

[0042] 6 is a time chart that schematically shows the command values ​​for rotating the registration drive motor 212, and is shown for each target rotation speed. The actual rotation speed may not completely match the command value. FIG. 6 is a schematic diagram, and in reality, if the size of the sheet S is the same, the time it takes for the sheet S to pass through the pair of registration rollers 20 will differ depending on the target rotation speed, so the time chart will not be like this.

[0043] After the registration roller pair 20 stops due to backlash reduction processing, the control unit 30 causes the leading edge of the first sheet S to reach the registration roller pair 20 (S7). The control unit 30 acquires a target rotation speed for the registration drive motor 212 according to the sheet information of the job (S8). For example, for thin paper, the target rotation speed is a high speed V1 (S9), for medium paper, the target rotation speed is a medium speed V2 (S10), and for thick paper or coated paper, the target rotation speed is a low speed V3 (S11). The control unit 30 rotates the registration drive motor 212 in accordance with the image formation timing (S12) to transport the sheet S. When the control unit 30 detects that the trailing edge of the sheet S has passed through the registration roller pair 20 (S13), it determines whether the image formation job has ended (S14). If the control unit 30 determines that the image formation job has not ended (S14; NO), it transports the next sheet S (S12). When the control unit 30 determines that the image forming job has ended (S14; YES), the process ends.

[0044] By controlling in this way, the rotation speed of the registration drive motor 212 before the leading edges of the first and second and subsequent sheets of a job reach the registration roller pair 20 is made uniform, and the degree of vibration when stopped is made equivalent (shown by the dashed line in FIG. 6). This reduces differences in the play between the transmission mechanisms 230 and the tension of the timing belt 232, and the time lag from the start of rotation of the registration drive motor 212 to the start of rotation of the drive roller 21 is also made equivalent for the first and second and subsequent sheets, thereby reducing variations in the leading edge registration value.

[0045] In this embodiment, the image formation job forms images on multiple sheets S of the same size and type. Therefore, there is no need to perform backlash elimination processing after the image formation job starts. In other words, when executing a conveyance job to convey multiple sheets having the same target rotation speed, the control unit 30 performs backlash elimination processing before the first sheet abuts against the pair of registration rollers 20, and then does not perform backlash elimination processing until the conveyance job is completed. In contrast, in a mixed job in which multiple types of sheets are included in one image formation job, the control unit 30 may perform backlash elimination processing each time the conveyance speed changes.

[0046] As described above, according to the image forming apparatus 1 of the present embodiment, the registration drive motor 212 is stopped from the target rotation speed so as to be the same as the operation of stopping the registration drive motor 212 from the target rotation speed after the sheet S is conveyed by the registration roller pair 20 after the backlash elimination process. As a result, the state of backlash in the transmission mechanism 230 immediately after the backlash elimination process is the same as the state of backlash in the transmission mechanism 230 when the registration roller pair 20 is stopped when the sheet S is actually conveyed thereafter. Therefore, in an image forming job, when backlash elimination process is performed, variation in the state of backlash in the transmission mechanism 230 between before the start of conveyance of the first sheet and before the start of conveyance of each of the second and subsequent sheets can be suppressed. Therefore, by aligning the state of the registration drive train between the first sheet and the second and subsequent sheets in a paper passing job, variation in the leading edge registration value can be reduced.

[0047] In this embodiment, the transmission mechanism 230 has a timing belt 232. The timing belt 232 is an elastic member, and is prone to play due to the expansion and contraction of the belt. However, according to this embodiment, even in such cases, the variation in the play state of the transmission mechanism 230 can be suppressed.

[0048] In the above embodiment, the registration roller pair 20 that conveys the sheet S to the secondary transfer unit 161 is used as the registration roller pair, but the present invention is not limited to this. For example, the present invention can be applied to all registration roller pairs that convey the sheet S in accordance with a predetermined timing, and can also be applied to an image reading device that reads an image on the sheet S, for example.

[0049] <Second embodiment> Next, a second embodiment of the present invention will be described in detail with reference to Figures 7 to 9. This embodiment differs from the first embodiment in that vector control and open control are performed to control the registration drive motor 212. However, other configurations are the same as those of the first embodiment, so the same reference numerals are used and detailed description will be omitted.

[0050] 7, the control unit 30 executes vector control and open control in the backlash eliminating process. The control unit 30 controls the registration drive motor 212 by vector control, which controls the d-axis current and the q-axis current, to rotate it at a target rotation speed V1. When decelerating from the target rotation speed to a threshold speed V0, the control unit 30 performs deceleration by vector control, and when decelerating from the threshold speed V0 to a stop, the control unit 30 performs deceleration by open control, which turns on and off the supply of a constant current.

[0051] In this embodiment, the control of the registration drive motor 212 by the control unit 30 during paper feed is performed using so-called sensorless vector control, which considers the current component that generates torque and the current component that generates magnetic flux in the rotor and controls each current component independently. This enables optimal operation tailored to the rotational state of the registration drive motor 212, providing effective control for reducing operating noise. However, because the induced voltage is small at low speeds during acceleration and deceleration, open excitation control is required, which generates a rotating magnetic field by passing a constant current and performs synchronous drive. This can cause vibration (shock) due to motor phase alignment, and this vibration during deceleration may affect the leading edge registration value. Therefore, by performing a backlash reduction process similar to the first embodiment, the registration drive motor 212 rotates at the same speed as the second and subsequent sheets before the first sheet of a paper feed job, thereby aligning the vibration when the control is changed. This reduces the impact on variations in the leading edge registration value.

[0052] [Vector control] The control unit 30 has a motor control unit 193 that performs vector control. The functional configuration of the motor control unit 193 that controls the rotation speed and torque of the registration drive motor 212 and its general control (processing) will be described with reference to FIGS. 8 and 9. FIG. 8 is an explanatory diagram showing the vector control of the motor. FIG. 9 is a block diagram showing the control function of the motor control unit. Note that the technology of the motor control unit that performs speed control based on the difference between the torque when the sheet is not being conveyed and the torque when the sheet is being conveyed is described in Japanese Patent Application Laid-Open No. 2019-151486.

[0053] (Vector control) First, vector control by the motor control unit will be described with reference to Fig. 8. The motor control unit 193 controls the registration drive motor 212 using vector control. Note that the motor in the following description is not provided with a sensor such as a rotary encoder for detecting the rotational phase of the rotor of the motor, but a sensor such as a rotary encoder may be provided.

[0054] FIG. 8 illustrates the relationship between the resist drive motor 212, which is a two-phase stepping motor consisting of an A phase (first phase) and a B phase (second phase), and a rotating coordinate system represented by the d-axis and q-axis. In FIG. 8, the α-axis, which corresponds to the A-phase winding, and the β-axis, which corresponds to the B-phase winding, are defined in the stationary coordinate system. Also in FIG. 8, the d-axis is defined along the direction of the magnetic flux generated by the magnetic poles of the permanent magnet used in the rotor 402, and the q-axis is defined along the direction 90 degrees counterclockwise from the d-axis (the direction perpendicular to the d-axis). The angle between the α-axis and the d-axis is defined as θ, and the rotational phase of the rotor 402 is represented by the angle θ. In vector control, a rotating coordinate system based on the rotational phase θ of the rotor 402 is used. Specifically, vector control uses a q-axis component (torque current component) that generates torque in rotor 402 and a d-axis component (excitation current component) that affects the strength of the magnetic flux that penetrates windings 401a-401d. The torque current component is a current component in a rotating coordinate system of a current vector that corresponds to the drive current that flows through windings 401a-401d. In other words, vector control is a method of controlling a motor by performing speed feedback control that controls the value of the torque current component and the value of the excitation current component so as to reduce the deviation between a command speed that represents a target speed of rotor 402 and the actual rotation speed.

[0055] (Functional configuration of the motor control unit) Next, the functional configuration of the motor control unit 193 that controls the registration drive motor 212 will be described with reference to Fig. 9. The motor control unit 193 is configured with at least one ASIC (Application Specific Integrated Circuit) and executes the functions described below.

[0056] Motor control unit 193 has, as circuits for performing vector control, speed controller 502, current controller 503, coordinate inverse converter 505, coordinate converter 511, PWM inverter 506 that supplies drive current to windings 401a to 401d of the motor, and the like.

[0057] The coordinate converter 511 converts the current vectors corresponding to the drive currents flowing through the A-phase and B-phase windings 401a-401d of the registration drive motor 212 from a stationary coordinate system represented by the α-axis and β-axis to a rotating coordinate system represented by the q-axis and d-axis. As a result, the drive currents flowing through the windings 401a-401d are represented by the current value of the q-axis component (q-axis current) and the current value of the d-axis component (d-axis current), which are current values ​​in the rotating coordinate system. The q-axis current corresponds to a torque current that generates torque in the rotor 402 of the registration drive motor 212. The d-axis current corresponds to an excitation current that affects the strength of the magnetic flux passing through the windings 401a-401d of the registration drive motor 212, but does not contribute to the generation of torque in the rotor 402. The motor control unit 193 can independently control the q-axis current and the d-axis current. As a result, motor control unit 193 can efficiently generate the torque required to rotate rotor 402 by controlling the q-axis current in accordance with the load torque applied to rotor 402. That is, in vector control, the magnitude of the current vector shown in FIG.

[0058] The motor control unit 193 determines the rotation speed ω of the rotor 402 of the register drive motor 212 using a method described below, and performs vector control based on the determination result. The CPU 201 outputs a command to drive the register drive motor 212 to the speed command determiner 194. The command output from the CPU 201 includes a command speed ω_ref1 that indicates a target speed of the rotor 402 of the register drive motor 212. The speed command determiner 194 generates and outputs a command speed ω_ref2 that indicates the target speed of the rotor 402 of the register drive motor 212 based on the command speed ω_ref1.

[0059] A subtractor 601 calculates and outputs the deviation between the rotation speed ω of the rotor 402 of the registration drive motor 212 output from the speed determiner 514 and the command speed ω_ref.

[0060] The speed controller 502 acquires the deviation output from the subtractor 601 at a period T (for example, 200 microseconds). The speed controller 502 generates and outputs a q-axis current command value iq_ref and a d-axis current command value id_ref based on proportional control (P), integral control (I), and differential control (D) so that the deviation acquired from the subtractor 601 becomes small. Specifically, the speed controller 502 generates and outputs a q-axis current command value iq_ref and a d-axis current command value id_ref based on P control, I control, and D control so that the deviation acquired from the subtractor 601 becomes "0". Note that P control is a control method in which the value of a controlled object is controlled based on a value proportional to the deviation between a command value and an estimated value. I control is a control method in which the value of a controlled object is controlled based on a value proportional to the time integral of the deviation between a command value and an estimated value. D control is a control method in which the value of a controlled object is controlled based on a value proportional to the time change in the deviation between a command value and an estimated value. The speed controller 502 shown in FIG. 9 generates the q-axis current command value iq_ref and the d-axis current command value id_ref based on PID control, but the present invention is not limited to this. For example, the speed controller 502 may generate the q-axis current command value iq_ref and the d-axis current command value id_ref based on PI control. When a permanent magnet is used for the rotor 402, the d-axis current command value id_ref, which affects the strength of the magnetic flux penetrating the windings 401a to 401d, is usually set to 0, but the present invention is not limited to this.

[0061] The drive currents flowing through the A-phase and B-phase windings 401a to 401d of the registration drive motor 212 are detected by current detectors 507 and 508, and then converted from analog values ​​to digital values ​​by an A / D converter 510. The cycle at which the current detectors 507 and 508 detect the current is, for example, equal to or shorter than the cycle T at which the speed controller 502 acquires the deviation (for example, 25 microseconds).

[0062] The current value of the drive current converted from an analog value to a digital value by the A / D converter 510 is expressed as the current values ​​iα and iβ in the stationary coordinate system by the following equation using the phase θe of the current vector shown in Fig. 8. The phase θe of the current vector is defined as the angle between the α axis and the current vector. Furthermore, I indicates the magnitude of the current vector. iα=I*cosθe (1) iβ=I*sinθe (2) These current values ​​iα and iβ are input to a coordinate converter 511 and an induced voltage determiner 512 .

[0063] The coordinate converter 511 converts the current values ​​iα and iβ in the stationary coordinate system into a current value iq of the q-axis current and a current value id of the d-axis current in the rotating coordinate system using the following equations. id=cosθ*iα+sinθ*iβ ···(3) iq=-sinθ*iα+cosθ*iβ (4) The coordinate converter 511 outputs the converted current value iq to the subtractor 602 and the speed command determiner 194. The coordinate converter 511 also outputs the converted current value id to the subtractor 603. The speed command determiner 194 will be described later.

[0064] The subtractor 602 calculates the deviation between the q-axis current command value iq_ref and the current value iq, and outputs the deviation to the current controller 503. The subtractor 603 calculates the deviation between the d-axis current command value id_ref and the current value id, and outputs the deviation to the current controller 503.

[0065] The current controller 503 generates drive voltages Vq and Vd based on PID control so that the input deviations are each reduced. Specifically, the current controller 503 generates drive voltages Vq and Vd so that the input deviations are each reduced to "0" and outputs them to the coordinate inverse converter 505. That is, the current controller 503 functions as a means for generating drive voltages Vq and Vd. Note that the current controller 503 shown in FIG. 9 generates drive voltages Vq and Vd based on PID control, but this is not limiting. For example, the current controller 503 may generate drive voltages Vq and Vd based on PI control.

[0066] The coordinate inverse converter 505 inversely converts the drive voltages Vq and Vd in the rotating coordinate system output from the current controller 503 into drive voltages Vα and Vβ in the stationary coordinate system using the following equations. Vα=cosθ*Vd-sinθ*Vq (5) Vβ=sinθ*Vd+cosθ*Vq (6) The coordinate inverse converter 505 outputs the inversely converted drive voltages Vα and Vβ to the induced voltage determiner 512 and the PWM inverter 506 .

[0067] The PWM inverter 506 has a full-bridge circuit. The full-bridge circuit is driven by a PWM (Pulse Width Modulation) signal based on the drive voltages Vα and Vβ input from the coordinate inverse converter 505. As a result, the PWM inverter 506 generates drive currents iα and iβ according to the drive voltages Vα and Vβ, and supplies the drive currents iα and iβ to the windings 401a to 401d of each phase of the registration drive motor 212, thereby driving the registration drive motor 212. In other words, the PWM inverter 506 functions as a supply means for supplying current to the windings 401a to 401d of each phase of the registration drive motor 212. Note that although the PWM inverter 506 shown in FIG. 9 has a full-bridge circuit, the PWM inverter 506 may also be a half-bridge circuit, etc.

[0068] Next, a method for determining the rotation phase θ will be described. The rotation phase θ of the rotor 402 is determined using the values ​​of induced voltages Eα and Eβ induced in the A-phase and B-phase windings 401a to 401d of the register drive motor 212 by the rotation of the rotor 402. The values ​​of the induced voltages Eα and Eβ are determined (calculated) by an induced voltage determiner 512. Specifically, the induced voltages Eα and Eβ are determined by the following equations from the current values ​​iα and iβ input to the induced voltage determiner 512 from the A / D converter 510 and the drive voltages Vα and Vβ input to the induced voltage determiner 512 from the coordinate inverse converter 505. Eα=Vα-R*iα-L*diα / dt ···(7) Eβ=Vβ-R*iβ-L*diβ / dt ···(8) Here, R is the winding resistance and L is the winding inductance. The values ​​of winding resistance R and winding inductance L are specific to the motor 509 being used, and are stored in advance in ROM 190b or a memory (not shown) provided in the motor control unit 193. The induced voltages Eα and Eβ determined by the induced voltage determiner 512 are output to a phase determiner 513.

[0069] The phase determiner 513 determines the rotational phase θ of the rotor 402 of the registration drive motor 212 based on the ratio between the induced voltages Eα and Eβ output from the induced voltage determiner 512, using the following equation: θ=tan^-1(-Eβ / Eα) (9) 9 determines the rotation phase θ by performing a calculation based on equation (9), but this is not limiting. For example, the phase determiner 513 may determine the rotation phase θ by referring to a table stored in a ROM or the like that indicates the relationship between the induced voltages Eα and Eβ and the rotation phase θ corresponding to the induced voltages Eα and Eβ. The rotation phase θ of the rotor 402 obtained as described above is input to the coordinate inverse converter 505, the coordinate converter 511, and the speed determiner 514.

[0070] Based on the amount of change in the input rotation phase θ over a predetermined period, speed determiner 514 determines rotation speed ω of rotor 402. Specifically, speed determiner 514 determines rotation speed ω of rotor 402 based on the following equation (10): ω=dθ / dt (10) The rotation speed ω of the rotor 402 obtained as described above is input to a subtractor 601 .

[0071] As described above, the motor control unit 193 repeatedly performs the above functions (controls) to perform vector control, which controls the current value in the rotating coordinate system so as to reduce the deviation between the command speed ω_ref2 and the rotation speed ω. By performing vector control, it is possible to prevent the motor from going out of step, and to prevent an increase in motor noise and power consumption due to excess torque.

[0072] As described above, according to the image forming apparatus 1 of the present embodiment, the registration drive motor 212 is stopped from the target rotation speed so as to be the same as the operation of stopping the registration drive motor 212 from the target rotation speed after the sheet S is conveyed by the registration roller pair 20 after the backlash elimination process. As a result, the state of backlash in the transmission mechanism 230 immediately after the backlash elimination process is the same as the state of backlash in the transmission mechanism 230 when the registration roller pair 20 is stopped when the sheet S is actually conveyed thereafter. Therefore, in an image forming job, when backlash elimination process is performed, variation in the state of backlash in the transmission mechanism 230 between before the start of conveyance of the first sheet and before the start of conveyance of each of the second and subsequent sheets can be suppressed. Therefore, by aligning the state of the registration drive train between the first sheet and the second and subsequent sheets in a paper passing job, variation in the leading edge registration value can be reduced. [Explanation of symbols]

[0073] 1...image forming apparatus (sheet conveying apparatus), 3...casing (fixed side unit), 15...image forming section, 20...registration roller pair (registration roller pair), 21...driving roller (first roller), 22...followed roller (second roller), 30...control section, 161...secondary transfer section (image forming position), 210...transmission mechanism, 212...registration drive motor (drive motor), 232...timing belt (endless member), 701...right door unit (opening / closing side unit), S...sheet

Claims

1. a pair of registration rollers, each having a first roller and a second roller that come into contact with each other to form a nip portion, against which a sheet is abutted in a stopped state, and thereafter rotating to convey the sheet; a drive motor that rotates the first roller; a transmission mechanism having an endless member and transmitting power of the drive motor to the first roller via the endless member; a control unit that executes a backlash reduction process to reduce backlash in the transmission mechanism by driving and stopping the drive motor before the sheet abuts against the pair of registration rollers, The control unit Before performing the backlash eliminating process, a target rotation speed of the drive motor when the sheet is conveyed by the pair of registration rollers after the backlash eliminating process is obtained; During the execution of the backlash eliminating process, the driving motor is accelerated to the target rotation speed and then stopped from the target rotation speed so as to be the same as an operation in which the driving motor is stopped from the target rotation speed after the sheet is conveyed by the registration roller pair after the backlash eliminating process. A sheet conveying device characterized by:

2. When the control unit stops the drive motor from the target rotation speed in the backlash elimination process, When decelerating from the target rotation speed to a threshold speed that is slower than the target rotation speed, the rotation speed is decelerated at a first deceleration gradient; When decelerating from the threshold speed to a stop, the vehicle is decelerated at a second deceleration gradient that is steeper than the first deceleration gradient.

2. The sheet transport device according to claim 1.

3. The control unit, in the backlash eliminating process, the drive motor is controlled by vector control that controls a d-axis current and a q-axis current to rotate at the target rotation speed; When decelerating from the target rotation speed to the threshold speed, deceleration is performed by the vector control, When decelerating from the threshold speed to a stop, deceleration is performed by open control that turns on and off the supply of a constant current.

3. The sheet transport device according to claim 2.

4. the control unit sets a time during which the drive motor is driven at the target rotation speed in the backlash eliminating process to be shorter than a time during which the drive motor is driven at the target rotation speed when the sheet is conveyed by the registration roller pair after the backlash eliminating process.

2. The sheet transport device according to claim 1.

5. The control unit Before performing the backlash eliminating process, acquiring sheet information of a sheet on which an image is to be formed after the backlash reduction processing; acquiring the target rotation speed based on the sheet information; 2. The sheet transport device according to claim 1.

6. the sheet information is the basis weight of the sheet, The control unit When a first basis weight is acquired as the sheet information, a first speed is acquired as the target rotation speed; When a second basis weight that is greater than the first basis weight is acquired as the sheet information, a second speed that is slower than the first speed is acquired as the target rotation speed.

6. The sheet transport device according to claim 5.

7. when executing a conveying job for conveying a plurality of sheets having the same target rotation speed, the control unit performs the backlash elimination process before a first sheet abuts against the pair of registration rollers, and then does not perform the backlash elimination process until the conveying job is completed.

2. The sheet transport device according to claim 1.

8. The endless member is a toothed belt made of an elastic material.

2. The sheet transport device according to claim 1.

9. a fixed-side unit that supports the second roller, the drive motor, and the transmission mechanism; an opening / closing side unit that supports the first roller and opens and closes the fixed side unit, When the opening / closing side unit closes the fixed side unit, the first roller and the second roller come into contact with each other, and the first roller and the transmission mechanism are connected, When the opening / closing side unit opens the fixed side unit, the first roller and the second roller are separated from each other, and the connection between the first roller and the transmission mechanism is released.

2. The sheet transport device according to claim 1.

10. The sheet conveying device according to any one of claims 1 to 9, an image forming unit that forms an image on a sheet at an image forming position; the control unit controls the drive motor so that the sheet is abutted against the pair of registration rollers while the pair of registration rollers is stopped, and is transported to the image forming position in accordance with the timing of image formation. An image forming apparatus characterized by:

Images