Image forming apparatus

Abstract

An image forming apparatus includes: a device body; a photosensitive drum; a belt unit including a transfer belt and a belt memory that stores a sheet conveyance speed of the transfer belt, i.e., a first sheet conveyance speed; a fixing unit; a belt motor; a fixing motor; a body memory that stores a sheet conveyance speed of the fixing unit, i.e., a second sheet conveyance speed, and stores a reference value, i.e., a first reference value, of a speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit; and a control unit that performs: a reading process of reading the first and second sheet conveyance speeds; and a motor control process of setting a rotation speed of the belt motor or the fixing motor based on a speed difference, i.e., a first speed difference, between the first sheet conveyance speed and the second sheet conveyance speed read in the reading process and the first reference value so that the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit approaches the first reference value.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus including an apparatus main body and a belt unit that can be attached to and detached from the apparatus main body. Background Art

[0002] In the prior art, an image forming apparatus is known that includes an apparatus main body, a photosensitive drum, a belt unit that can be attached to and detached from the apparatus main body, a fixing unit disposed behind the belt unit, and a conveying roller for conveying a sheet such as paper toward the belt unit (see Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-10839). In this technology, the belt unit includes a conveyor belt configured to convey a sheet between the conveyor belt and the photosensitive drum.

[0003] When the speed difference between the sheet conveyance speed of the conveyor belt and the sheet conveyance speed of the fixing unit becomes large, the sheet may be excessively bent between the conveyor belt and the fixing unit. When the speed difference between the sheet conveyance speed of the conveying roller and the sheet conveyance speed of the conveyor belt becomes large, the sheet may be excessively bent between the conveying roller and the conveyor belt.

[0004] On the other hand, when the speed difference between the sheet conveyance speed of the conveyor belt and the sheet conveyance speed of the fixing unit becomes small, the sheet may slide in the belt unit or the fixing unit. When the speed difference between the sheet conveyance speed of the conveying roller and the sheet conveyance speed of the conveyor belt becomes small, the sheet may slide on the conveying roller or the belt unit.

[0005] When the sheet is excessively bent or the sheet slides, for example, the printed surface may be rubbed, resulting in a reduction in image quality. Summary of the Invention

[0006] Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing excessive bending of a sheet and sliding of the sheet.

[0007] To achieve the above object, the present invention provides an image forming apparatus, including: a device main body; a photosensitive drum; a belt unit that can be mounted on the device main body and can be detached from the device main body, the belt unit including a transfer belt and a belt memory, the transfer belt being configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet, the belt memory storing a first sheet conveyance speed, the first sheet conveyance speed being the sheet conveyance speed of the transfer belt; a fixing unit configured to fix the toner image on the sheet conveyed by the transfer belt to the sheet in a state where the belt unit is mounted on the device main body; a belt motor configured to drive the transfer belt; a fixing motor configured to drive the fixing unit; a main body memory storing a second sheet conveyance speed, the second sheet conveyance speed being the sheet conveyance speed of the fixing unit, the main body memory storing a first reference value, the first reference value being a reference value of a speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit; and a control unit. The control unit performs: a reading process of reading the first sheet conveyance speed from the belt memory and reading the second sheet conveyance speed from the main body memory; and a motor control process of setting a rotation speed of the belt motor or a rotation speed of the fixing motor based on a first speed difference and the first reference value such that the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit approaches the first reference value, the first speed difference being a speed difference between the first sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process.

[0008] According to this structure, by setting the rotation speed of the motor based on the first sheet conveyance speed stored in the belt memory of the replaceable belt unit, the motor can be controlled. Therefore, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit can be maintained within a certain range. Thereby, excessive bending of the sheet between the transfer belt and the fixing unit can be suppressed, and sliding of the sheet in the belt unit or the fixing unit can be suppressed.

[0009] In the image forming apparatus of the present invention, the first sheet conveyance speed is the sheet conveyance speed of the transfer belt based on a pre-measured value.

[0010] In the image forming apparatus of the present invention, the second sheet conveyance speed is the sheet conveyance speed of the fixing unit based on a predetermined measured value.

[0011] In the image forming apparatus of the present invention, the belt motor drives the photosensitive drum.

[0012] Therefore, the number of motors can be reduced.

[0013] An image forming apparatus according to the present invention, wherein, in the motor control process, the control unit sets the rotational speed of the fixing motor based on the first speed difference and the first reference value.

[0014] An image forming apparatus according to the present invention, wherein, in the motor control process, the control unit decreases the rotational speed of the fixing motor when the first speed difference is greater than the first reference value, and increases the rotational speed of the fixing motor when the first speed difference is less than the first reference value.

[0015] An image forming apparatus according to the present invention, wherein the transfer belt conveys a sheet between the transfer belt and the photosensitive drum.

[0016] An image forming apparatus according to the present invention, wherein the transfer belt is an endless belt.

[0017] An image forming apparatus according to the present invention, wherein the first sheet conveyance speed is an actual measurement value of the sheet conveyance speed of the transfer belt measured in advance.

[0018] An image forming apparatus according to the present invention, wherein the belt unit includes a belt driving roller and a belt driven roller, the belt driving roller drives the transfer belt, the belt driving roller is in contact with the inner peripheral surface of the transfer belt, the belt driven roller rotates by being driven by the transfer belt, the belt driven roller is spaced apart from the belt driving roller, the belt driven roller is in contact with the inner peripheral surface of the transfer belt, and the first sheet conveyance speed is a calculated value calculated based on the thickness of the transfer belt measured in advance and the outer diameter of the belt driving roller.

[0019] An image forming apparatus according to the present invention, wherein the first sheet conveyance speed stored in the belt memory is faster than the second sheet conveyance speed stored in the main body memory.

[0020] An image forming apparatus according to the present invention, wherein the second sheet conveyance speed is an actual measurement value of the sheet conveyance speed of the fixing unit measured in advance.

[0021] An image forming apparatus according to the present invention, wherein the fixing unit includes a fixing roller configured to heat the sheet, and the second sheet conveyance speed is a calculated value calculated based on the outer diameter value of the fixing roller measured in advance.

[0022] The image forming apparatus of the present invention further includes: a cover, the apparatus main body including the cover that can be opened and closed, the cover being opened when the belt unit is installed and removed; a first sensor configured to detect the opening and closing of the cover; and a second sensor configured to detect whether the belt unit is installed in the apparatus main body. When the first sensor detects that the cover is closed and the second sensor detects that the belt unit is installed in the apparatus main body, the control unit starts the reading process.

[0023] Therefore, when the belt unit is replaced and the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit is likely to change, the rotational speed of the motor can be set. Thus, over-bending of the sheet and sheet slippage can be more reliably suppressed.

[0024] The image forming apparatus according to the present invention, wherein the main body memory stores a reference sheet conveyance speed, which is a reference value of the sheet conveyance speed of the transfer belt. In the reading process, when the first sheet conveyance speed cannot be read from the belt memory, the control unit reads the reference sheet conveyance speed from the main body memory. In the motor control process, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process as the first speed difference.

[0025] Therefore, even when the first sheet conveyance speed cannot be read from the belt memory, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit can be kept within a certain range.

[0026] The image forming apparatus of the present invention, wherein the main body memory stores a reference sheet conveyance speed, which is a reference value of the sheet conveyance speed of the transfer belt. In the reading process, the control unit reads the reference sheet conveyance speed from the main body memory. In the motor control process, when the speed difference between the first sheet conveyance speed read in the reading process and the reference sheet conveyance speed read in the reading process is outside the range of the determination threshold, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process as the first speed difference.

[0027] Therefore, even when the value of the first sheet conveyance speed read in the reading process is an abnormal value, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit can be kept within a certain range.

[0028] To achieve the above object, the present invention further provides an image forming apparatus, including: a device main body; a photosensitive drum; a belt unit that can be mounted on the device main body and detached from the device main body, the belt unit including a transfer belt and a belt memory, the transfer belt being configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet, the belt memory storing a first sheet conveyance speed, the first sheet conveyance speed being the sheet conveyance speed of the transfer belt; a conveyance roller configured to convey the sheet toward the transfer belt in a state where the belt unit is mounted on the device main body; a belt motor configured to drive the transfer belt; a conveyance motor configured to drive the conveyance roller; a main body memory storing a third sheet conveyance speed, the third sheet conveyance speed being the sheet conveyance speed of the conveyance roller, the main body memory storing a second reference value, the second reference value being a reference value of a speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller; and a control unit. The control unit performs: a reading process of reading the first sheet conveyance speed from the belt memory and reading the third sheet conveyance speed from the main body memory; and a motor control process of setting a rotation speed of the belt motor or a rotation speed of the conveyance motor based on a second speed difference and the second reference value so that a speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller approaches the second reference value, the second speed difference being a speed difference between the first sheet conveyance speed read in the reading process and the third sheet conveyance speed read in the reading process.

[0029] According to this structure, by setting the rotation speed of the motor based on the first sheet conveyance speed stored in the belt memory of the replaceable belt unit, the motor can be controlled. Therefore, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller can be maintained within a certain range. Thereby, excessive bending of the sheet between the transfer belt and the fixing unit can be suppressed, and sliding of the sheet in the belt unit or the fixing unit can be suppressed.

[0030] In the image forming apparatus of the present invention, the first sheet conveyance speed is the sheet conveyance speed of the transfer belt based on a pre-measured value.

[0031] In the image forming apparatus of the present invention, the third sheet conveyance speed is the sheet conveyance speed of the conveyance roller based on a predetermined measured value.

[0032] In the image forming apparatus of the present invention, in the motor control process, the control unit sets the rotation speed of the conveyance motor based on the second speed difference and the second reference value.

[0033] The image forming apparatus of the present invention, wherein, in the motor control process, when the second speed difference is greater than the second reference value, the control unit decreases the rotational speed of the conveyance motor, and when the second speed difference is less than the second reference value, the control unit increases the rotational speed of the conveyance motor.

[0034] The image forming apparatus of the present invention, wherein the first sheet conveyance speed stored in the tape memory is slower than the third sheet conveyance speed stored in the main body memory.

[0035] The image forming apparatus of the present invention, wherein the third sheet conveyance speed is an actual measurement value of the sheet conveyance speed of the conveyance roller measured in advance.

[0036] The image forming apparatus of the present invention, wherein the conveyance roller includes a conveyance drive roller and a conveyance driven roller, a driving force from the conveyance motor is input to the conveyance drive roller, the conveyance driven roller is driven by the conveyance drive roller to rotate, and the third sheet conveyance speed is a calculated value calculated based on the value of the outer diameter of the conveyance drive roller measured in advance.

[0037] The image forming apparatus of the present invention, wherein the main body memory stores a reference sheet conveyance speed which is a reference value of the sheet conveyance speed of the transfer belt. In the reading process, when the first sheet conveyance speed cannot be read from the tape memory, the control unit reads the reference sheet conveyance speed from the main body memory. In the motor control process, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the third sheet conveyance speed read in the reading process as the second speed difference.

[0038] Therefore, even when the first sheet conveyance speed cannot be read from the tape memory, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller can be maintained within a certain range.

[0039] The image forming apparatus of the present invention, wherein the main body memory stores a reference sheet conveyance speed which is a reference value of the sheet conveyance speed of the transfer belt. In the reading process, the control unit reads the reference sheet conveyance speed from the main body memory. In the motor control process, when the speed difference between the first sheet conveyance speed read in the reading process and the reference sheet conveyance speed read in the reading process is outside the range of the determination threshold, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the third sheet conveyance speed read in the reading process as the second speed difference.

[0040] Therefore, even when the value of the first sheet conveyance speed read in the reading process is an abnormal value, the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller can be kept within a certain range.

[0041] According to the present invention, over-bending of the sheet and sheet slippage can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a cross-sectional view of an image forming apparatus according to an embodiment;

[0043] Figure 2 is a diagram showing a structure related to the control of the image forming apparatus;

[0044] Figure 3 is an enlarged view of the electrical contact points of the belt unit and the image forming apparatus;

[0045] Figure 4 is a block diagram of the control unit;

[0046] Figure 5 is a flowchart showing a process of setting the rotational speed of the fixing motor; and

[0047] Figure 6 is a flowchart showing a process of setting the rotational speed of the conveyance motor. DETAILED DESCRIPTION OF THE INVENTION

[0048] Next, embodiments of the present invention will be described in detail with appropriate reference to the accompanying drawings. In the following description, the axial direction of the photosensitive drum 41 is referred to as the first direction. The direction in which a plurality of photosensitive drums 41 are arranged is referred to as the second direction. The second direction intersects the first direction. Preferably, the second direction is perpendicular to the first direction. The direction in which the discharge tray 12, the image forming unit 3, and the sheet tray 21 are arranged is referred to as the third direction. The third direction intersects the first direction and the second direction. Preferably, the third direction is perpendicular to the first direction and the second direction.

[0049] As Figure 1As shown, the image forming apparatus 1 includes an apparatus main body 10, a sheet supply unit 2, an image forming unit 3, a sheet discharge unit 4, a first sensor 5, and a second sensor 6.

[0050] The apparatus main body 10 includes a lid 11 that can be opened and closed on one end side in the second direction. The lid 11 is opened when installing and removing a later-described processing unit 40 and a belt unit 50. The apparatus main body 10 includes a discharge tray 12.

[0051] The first sensor 5 is a sensor that detects the opening and closing of the lid 11. The first sensor 5 is, for example, an interlocking switch having a rod. When the lid 11 is closed and a part of the lid 11 presses the rod, the first sensor 5 detects that the lid 11 is closed. When the lid 11 is opened and the pressure on the rod is released, the first sensor 5 detects that the lid 11 is opened.

[0052] The sheet supply unit 2 includes a sheet tray 21, a pickup roller 22, a separation roller 23, a separation pad 24, a paper dust removing roller 25, and a registration roller 26 as an example of a conveying roller. The sheet tray 21 accommodates sheets S such as paper.

[0053] The pickup roller 22 supplies the sheet S in the sheet tray 21 toward the separation roller 23. The separation roller 23 and the separation pad 24 separate the sheets S one by one and convey the sheets S toward the image forming unit 3. The paper dust removing roller 25 conveys the sheet S toward the image forming unit 3. The registration roller 26 controls the leading edge position of the sheet S and then supplies the sheet S to the image forming unit 3.

[0054] The image forming unit 3 includes an exposure unit 30, a processing unit 40, a belt unit 50, and a fixing unit 70.

[0055] The exposure unit 30 is located on one end side in the third direction in the apparatus main body 10. The exposure unit 30 emits a light beam (see the dashed line) to expose the surface of the photosensitive drum 41.

[0056] The processing unit 40 includes: a plurality of photosensitive drums 41 arranged in the second direction; a plurality of chargers 42 and developing cartridges 43 corresponding to the respective photosensitive drums 41; and a processing frame 44 for supporting the photosensitive drums 41 and the like. By opening the lid 11, the processing unit 40 can be installed in and removed from the apparatus main body 10. The processing unit 40 is located between the sheet tray 21 and the exposure unit 30 in a state of being installed in the apparatus main body 10.

[0057] The developing cartridge 43 can be individually installed in and removed from the processing frame 44. The developing cartridge 43 can be installed in and removed from the apparatus main body 10 together with the processing unit 40 in a state of being installed in the processing unit 40. Each developing cartridge 43 includes a developing housing 45 for accommodating a developer and a developing roller 46.

[0058] The belt unit 50 includes a belt driving roller 51, a belt driven roller 52, a transfer belt 53, and a plurality of transfer rollers 54.

[0059] The belt driving roller 51 is a roller that drives the transfer belt 53. The belt driven roller 52 rotates by being driven by the transfer belt 53. The belt driven roller 52 is spaced apart from the belt driving roller 51 in the second direction. The belt driving roller 51 and the belt driven roller 52 are in contact with the inner peripheral surface of the transfer belt 53.

[0060] The transfer belt 53 is an endless belt. By applying a bias voltage to the transfer roller 54, the transfer belt 53 transfers the toner image on the photosensitive drum 41 to the sheet S. At the same time, the transfer belt 53 conveys the sheet S. Specifically, the transfer roller 54 is provided inside the transfer belt 53. The transfer roller 54 and the photosensitive drum 41 sandwich the transfer belt 53 therebetween. Thus, when the photosensitive drum 41, the transfer belt 53, and the transfer roller 54 rotate, the transfer belt 53 conveys the sheet S between the transfer belt 53 and the photosensitive drum 41 toward the fixing unit 70.

[0061] By opening the cover 11 and removing the processing unit 40, the belt unit 50 can be installed in the apparatus main body 10 and can be removed from the apparatus main body 10. The belt unit 50 is located between the sheet tray 21 and the exposure unit 30 in a state of being installed in the apparatus main body 10. In addition, by installing the processing unit 40 in the apparatus main body 10, the belt unit 50 is located between the sheet tray 21 and the processing unit 40.

[0062] The second sensor 6 is a sensor for detecting whether the belt unit 50 is installed in the apparatus main body 10. The second sensor 6 is, for example, a sensor that detects the current flowing through the transfer belt 53. When the current flowing through the transfer belt 53 is detected, the second sensor 6 detects that the belt unit 50 is installed in the apparatus main body 10. When the current flowing through the transfer belt 53 cannot be detected, the second sensor 6 detects that the belt unit 50 is not installed in the apparatus main body 10.

[0063] The fixing unit 70 is located in the apparatus main body 10. In a state where the belt unit 50 is installed in the apparatus main body 10, the fixing unit 70 fixes the toner image on the sheet S conveyed by the transfer belt 53 to the sheet S. The fixing unit 70 includes a fixing roller 71 for heating the sheet S, and a pressure roller 72 for pressing the fixing roller 71. The fixing roller 71 is a cylindrical member made of metal. The pressure roller 72 is a member having an elastic layer around a metal mandrel.

[0064] The image forming unit 3 charges the surface of the photosensitive drum 41 through the charger 42. Next, the image forming unit 3 exposes the surface of the photosensitive drum 41 through the exposure unit 30. Thus, the image forming unit 3 forms an electrostatic latent image on the photosensitive drum 41. Then, the image forming unit 3 supplies the developer from the developing roller 46 to the photosensitive drum 41. Thus, the image forming unit 3 visualizes the electrostatic latent image and forms a developer image on the photosensitive drum 41.

[0065] Next, the image forming unit 3 transports the sheet S supplied from the sheet supply unit 2 to between the photosensitive drum 41 and the transfer belt 53. Thus, the image forming unit 3 transfers the developer image on the photosensitive drum 41 to the sheet S. Then, the image forming unit 3 transports the sheet S with the transferred developer image to between the fixing roller 71 and the pressure roller 72. Thus, the image forming unit 3 thermally fixes the developer image on the sheet S, thereby forming an image on the sheet S.

[0066] The sheet discharge unit 4 has a discharge path 81 and a plurality of discharge rollers 82. The discharge rollers 82 discharge the sheet S with the formed image to the discharge tray 12 of the apparatus main body 10 through the discharge path 81.

[0067] As Figure 2 shown, the image forming apparatus 1 includes a control unit 100, a main body memory 200, a conveyance motor M1, a belt motor M2, and a fixing motor M3. The belt unit 50 also includes a belt memory 300.

[0068] The conveyance motor M1 drives the registration roller 26. Specifically, the registration roller 26 includes a conveyance drive roller 26A and a conveyance driven roller 26B. By inputting the driving force from the conveyance motor M1 to the conveyance drive roller 26A via a plurality of gears (not shown) etc., the conveyance drive roller 26A rotates. The conveyance driven roller 26B is driven by the conveyance drive roller 26A to rotate. When the registration roller 26 is driven in a state where the processing unit 40 and the belt unit 50 are mounted on the apparatus main body 10, the sheet S is conveyed toward the space between the photosensitive drum 41 and the transfer belt 53.

[0069] The belt motor M2 drives the transfer belt 53. Specifically, the belt motor M2 drives the belt drive roller 51 through a plurality of gears (not shown) etc., whereby the transfer belt 53 is driven. The belt motor M2 drives the photosensitive drum 41 through a plurality of gears (not shown) etc. When the photosensitive drum 41 and the transfer belt 53 are driven, the sheet S is conveyed toward the fixing unit 70.

[0070] The fixing motor M3 drives the fixing unit 70. Specifically, by inputting the driving force from the fixing motor M3 to the pressure roller 72 via a plurality of gears (not shown) etc., the pressure roller 72 rotates. The fixing roller 71 is driven by the pressure roller 72 to rotate. When the fixing roller 71 and the pressure roller 72 rotate, the sheet S is conveyed to the discharge path 81 (seeFigure 1 )。

[0071] As Figure 3 shown, the tape memory 300 is supported by the tape frame body 55 of the tape unit 50. The tape frame body 55 is a member that rotatably supports the tape drive roller 51, the tape driven roller 52, and the transfer roller 54. The tape memory 300 includes a storage element 310 and an electrical contact surface 320. The electrical contact surface 320 is electrically connected to the storage element 310.

[0072] The image forming apparatus 1 includes an electrical contact point 15. In a state where the tape unit 50 is mounted on the apparatus main body 10, the electrical contact point 15 can be in electrical contact with the electrical contact surface 320 of the tape unit 50. The electrical contact point 15 is held by a contact holding portion 16 in the apparatus main body 10. In a state where the tape unit 50 is mounted on the apparatus main body 10, the storage element 310 of the tape memory 300 can be electrically connected to the control unit 100 through the electrical contact surface 320 and the electrical contact point 15.

[0073] The tape memory 300 (storage element 310) stores information about the tape unit 50. Storing information about the tape unit 50 in the tape memory 300 is performed when the tape unit 50 is manufactured in a manufacturing factory. The tape memory 300 stores the first sheet conveyance speed VBs as one of the information about the tape unit 50.

[0074] The first sheet conveyance speed VBs is the sheet conveyance speed of the transfer belt 53 based on a pre-measured value. The first sheet conveyance speed VBs stored in the tape memory 300 is, for example, the measured value of the actual sheet conveyance speed of the pre-measured transfer belt 53. The first sheet conveyance speed VBs is the moving speed of the transfer belt 53 obtained by applying a driving force to the tape drive roller 51 to rotate the transfer belt 53 and measuring at this time after the tape unit 50 is assembled.

[0075] The first sheet conveyance speed VBs stored in the tape memory 300 can be a calculated value calculated based on the thickness of the pre-measured transfer belt 53 and the outer diameter value of the tape drive roller 51. The first sheet conveyance speed VBs (unit: mm / s) can be calculated from the measured values of the thickness T53 (unit: mm) of the transfer belt 53, the outer diameter D51 (unit: mm) of the tape drive roller 51, and the rotational speed N51 (unit: rpm) of the tape drive roller 51 according to the following formula.

[0076] VBs = (D51 + T53 × 2) × Π × N51 / 60

[0077] The first sheet conveyance speed VBs is a value unique to the tape unit 50. Therefore, when the tape unit 50 is replaced with a new tape unit 50, the first sheet conveyance speed VBs is usually a different value.

[0078] ReturnFigure 2 The main body memory 200 is electrically connected to the control unit 100. Although the main body memory 200 and the control unit 100 are shown separately in the drawings, the control unit 100 may include the main body memory 200.

[0079] The main body memory 200 stores information about the image forming apparatus 1. Storing information about the image forming apparatus 1 in the main body memory 200 is performed when the image forming apparatus 1 is manufactured at a manufacturing factory.

[0080] The main body memory 200 stores the second sheet conveyance speed VFs as information about the image forming apparatus 1. The second sheet conveyance speed VFs is the sheet conveyance speed of the fixing unit 70 based on a pre-measured value.

[0081] The second sheet conveyance speed VFs stored in the main body memory 200 is, for example, an actually measured value of the sheet conveyance speed of the pre-measured fixing unit 70. The second sheet conveyance speed VFs is the circumferential speed of the fixing roller 71 obtained by rotating the fixing roller 71 by applying a driving force to the pressure roller 72 and measuring at this time after assembling the fixing unit 70 or the image forming apparatus 1.

[0082] The second sheet conveyance speed VFs stored in the main body memory 200 may be a calculated value calculated based on a value of the outer diameter of the pre-measured fixing roller 71. The second sheet conveyance speed VFs (unit: mm / s) can be calculated from the measured value of the outer diameter D71 (unit: mm) of the fixing roller 71 and the rotational speed N71 (unit: rpm) of the fixing roller 71 according to the following formula.

[0083] VFs = D71 × Π × N71 / 60

[0084] Here, the first sheet conveyance speed VBs of the transfer belt 53 stored in the belt memory 300 is set to be faster than the second sheet conveyance speed VFs of the fixing unit 70 stored in the main body memory 200.

[0085] The main body memory 200 stores the third sheet conveyance speed VCs as information about the image forming apparatus 1. The third sheet conveyance speed VCs is the sheet conveyance speed of the registration roller 26 based on a pre-measured value.

[0086] The third sheet conveyance speed VCs stored in the main body memory 200 is, for example, an actually measured value of the sheet conveyance speed of the pre-measured registration roller 26. The third sheet conveyance speed VCs is the circumferential speed of the conveyance drive roller 26A obtained by rotating the conveyance drive roller 26A by applying a driving force to the conveyance drive roller 26A and measuring at this time after assembling the image forming apparatus 1.

[0087] The third sheet conveyance speed VCs stored in the main body memory 200 may be a calculated value calculated based on the value of the outer diameter of the conveyance drive roller 26A measured in advance. The third sheet conveyance speed VCs (unit: mm / s) can be calculated from the measured value of the outer diameter D26 (unit: mm) of the conveyance drive roller 26A and the rotational speed N26 (unit: rpm) of the conveyance drive roller 26A according to the following formula.

[0088] VCs = D26 × Π × N26 / 60

[0089] Here, the first sheet conveyance speed VBs stored in the tape memory 300 is set to be slower than the third sheet conveyance speed VCs of the registration roller 26 stored in the main body memory 200.

[0090] The main body memory 200 stores a reference sheet conveyance speed VBr. The reference sheet conveyance speed VBr is, for example, a reference value of the sheet conveyance speed of the transfer belt 53, and is set in advance based on experimental and simulation results.

[0091] The main body memory 200 stores a first reference value VA1. The first reference value VA1 is a reference value of the speed difference between the sheet conveyance speed of the transfer belt 53 and the sheet conveyance speed of the fixing unit 70. The first reference value VA1 is the speed difference between the reference sheet conveyance speed VBr and the reference value VFr of the sheet conveyance speed of the fixing unit 70 set in advance. The control unit 100 controls the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fixing unit 70 to be close to the first reference value VA1.

[0092] Here, the "speed difference" may be, for example, a value obtained by subtracting the value of the sheet conveyance speed of the transfer belt 53 from the value of the sheet conveyance speed of the fixing unit 70. However, in the present embodiment, the speed difference is a speed ratio. The first reference value VA1 is represented by the following formula.

[0093] VA1 = VFr / VBr

[0094] The main body memory 200 also stores a second reference value VA2. The second reference value VA2 is a reference value of the speed difference between the sheet conveyance speed of the transfer belt 53 and the sheet conveyance speed of the registration roller 26. The second reference value VA2 is the speed difference between the reference sheet conveyance speed VBr and the reference value VCr of the sheet conveyance speed of the registration roller 26 set in advance. The control unit 100 controls the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 to be close to the second reference value VA2. The second reference value VA2 is represented by the following formula.

[0095] VA2 = VCr / VBr

[0096] The main body memory 200 is capable of rewriting the stored information. For example, since the second sheet conveyance speed VFs of the fixing unit 70 is a value unique to the fixing unit 70, when a service person replaces the fixing unit 70, the service person rewrites the second sheet conveyance speed VFs to a value unique to the replaced fixing unit 70.

[0097] For example, since the third sheet conveyance speed VCs of the registration roller 26 is a value unique to the registration roller 26, when a service person replaces the registration roller 26, the service person rewrites the third sheet conveyance speed VCs to a value unique to the replaced registration roller 26.

[0098] As Figure 4 shown, the control unit 100 controls, for example, motors M1 to M3 according to a preset program or the like. The control unit 100 is electrically connected to the first sensor 5 and the second sensor 6. The control unit 100 includes a CPU, a RAM, a ROM, an input / output circuit, etc. (not shown in the figure). The control unit 100 includes a reading unit 110, a calculation unit 120, a motor control unit 130, and a storage unit 190.

[0099] The reading unit 110 performs a reading process. When the first sensor 5 detects that the cover 11 is closed and the second sensor 6 detects that the belt unit 50 is installed on the apparatus main body 10, the reading unit 110 starts the reading process.

[0100] In the reading process, the reading unit 110 reads the first sheet conveyance speed VBs from the belt memory 300, and reads the second sheet conveyance speed VFs and the third sheet conveyance speed VCs from the main body memory 200. The reading unit 110 also reads the reference sheet conveyance speed VBr, the first reference value VA1, and the second reference value VA2 from the main body memory 200.

[0101] Even when the first sheet conveyance speed VBs cannot be read from the belt memory 300, the reading unit 110 reads the second sheet conveyance speed VFs, the third sheet conveyance speed VCs, the reference sheet conveyance speed VBr, the first reference value VA1, and the second reference value VA2 from the main body memory 200. A case where the belt unit 50 is installed on the apparatus main body 10 but information cannot be read from the belt memory 300 is, for example, a case where foreign matter adheres to the electrical contact surface 320 of the belt memory 300 or the electrical contact point 15 of the image forming apparatus 1, resulting in a contact failure.

[0102] The reading unit 110 outputs the read information to the calculation unit 120 and the motor control unit 130.

[0103] The calculation unit 120 performs calculation processing. In the calculation processing, the calculation unit 120 calculates a first speed difference VD1. The first speed difference VD1 is the speed difference between the first sheet conveyance speed VBs of the transfer belt 53 read in the reading process and the second sheet conveyance speed VFs of the fixing unit 70 read in the reading process. The calculation unit 120 calculates the first speed difference VD1 according to the following formula.

[0104] VD1 = VFs / VBs

[0105] The calculation unit 120 calculates a second speed difference VD2. The second speed difference VD2 is the speed difference between the first sheet conveyance speed VBs and the third sheet conveyance speed VCs of the registration roller 26 read in the reading process. The calculation unit 120 calculates the second speed difference VD2 according to the following formula.

[0106] VD2 = VCs / VBs

[0107] The calculation unit 120 also calculates a third speed difference VD3. The third speed difference VD3 is the speed difference between the reference sheet conveyance speed VBr of the transfer belt 53 read in the reading process and the second sheet conveyance speed VFs. The calculation unit 120 calculates the third speed difference VD3 according to the following formula.

[0108] VD3 = VFs / VBr

[0109] The calculation unit 120 calculates a fourth speed difference VD4. The fourth speed difference VD4 is the speed difference between the reference sheet conveyance speed VBr and the third sheet conveyance speed VCs. The calculation unit 120 calculates the fourth speed difference VD4 according to the following formula.

[0110] VD4 = VCs / VBr

[0111] The calculation unit 120 calculates a fifth speed difference VBD. The fifth speed difference VBD is the speed difference between the first sheet conveyance speed VBs and the reference sheet conveyance speed VBr. The calculation unit 120 calculates the fifth speed difference VBD according to the following formula.

[0112] VBD = VBs / VBr

[0113] The calculation unit 120 outputs the information of each calculated speed difference to the motor control unit 130. When the first sheet conveyance speed VBs cannot be read from the belt memory 300 in the reading process, the calculation unit 120 outputs the information about the third speed difference VD3 and the fourth speed difference VD4 to the motor control unit 130.

[0114] The motor control unit 130 performs motor control processing. In the motor control processing, the motor control unit 130 sets the rotational speed N3 of the fixing motor M3 according to the first speed difference VD1 and the first reference value VA1. The motor control unit 130 also sets the rotational speed N1 of the conveyance motor M1 according to the second speed difference VD2 and the second reference value VA2.

[0115] Then, when receiving an instruction to drive the motors M1 to M3, the motor control unit 130 drives the conveyance motor M1 at the set rotational speed N1, drives the belt motor M2 at the rotational speed N2, and drives the fixing motor M3 at the set rotational speed N3. In the present embodiment, the rotational speed N2 of the belt motor M2 is a preset default value and does not change due to the first speed difference VD1 and the second speed difference VD2.

[0116] Thus, the motor control unit 130 controls the rotational speed of the fixing motor M3 such that the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fixing unit 70 when the image forming apparatus 1 is operating approaches the first reference value VA1. The motor control unit 130 controls the rotational speed of the conveyance motor M1 such that the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 when the image forming apparatus 1 is operating approaches the second reference value VA2.

[0117] When the first speed difference VD1 is greater than the first reference value VA1, the motor control unit 130 decreases the rotational speed N3 of the fixing motor M3. When the first speed difference VD1 is less than the first reference value VA1, the motor control unit 130 increases the rotational speed N3 of the fixing motor M3. As an example, the motor control unit 130 can calculate the rotational speed N3 of the fixing motor M3 according to the following formula. Here, N3d is a preset default value of the rotational speed of the fixing motor M3.

[0118] N3 = N3d × VA1 / VD1

[0119] When the second speed difference VD2 is greater than the second reference value VA2, the motor control unit 130 decreases the rotational speed N1 of the conveyance motor M1. When the second speed difference VD2 is less than the second reference value VA2, the motor control unit 130 increases the rotational speed N1 of the conveyance motor M1. As an example, the motor control unit 130 can calculate the rotational speed N1 of the conveyance motor M1 according to the following formula. Here, N1d is a preset default value of the rotational speed of the conveyance motor M1.

[0120] N1 = N1d × VA2 / VD2

[0121] When the rotation speed N3 (current value N3n) of the fixing motor M3 is newly set, the motor control unit 130 replaces the previous value (N3 n-1 ) of the rotation speed N3 of the fixing motor M3 with the current value, and stores the current value in the storage unit 190. Then, the fixing motor M3 is driven using the rotation speed N3 n until the rotation speed N3 (next value N3 n+1 ) of the fixing motor M3 is newly set.

[0122] Similarly, when the rotation speed N1 (current value N1 n ) of the conveyance motor M1 is newly set, the motor control unit 130 replaces the previous value (N1 n-1 ) of the rotation speed N1 of the conveyance motor M1 with the current value, and stores the current value in the storage unit 190. Then, the conveyance motor M1 is driven using the rotation speed N1 n until the rotation speed N1 (next value N1 n+1 ) of the conveyance motor M1 is newly set.

[0123] In the present embodiment, when the fifth speed difference VBD is outside the range of the preset determination threshold, specifically, when the fifth speed difference VBD is less than the minimum value VBD1 of the determination threshold and when it is greater than the maximum value VBD2 of the determination threshold, the value of the first sheet conveyance speed VBs read from the tape memory 300 in the reading process is considered an abnormal value.

[0124] Therefore, when the fifth speed difference VBD is outside the range of the determination threshold, the motor control unit 130 does not use the first speed difference VD1 calculated by the calculation unit 120, and uses the third speed difference VD3 as the first speed difference VD1. When the fifth speed difference VBD is outside the range of the determination threshold, the motor control unit 130 does not use the second speed difference VD2 calculated by the calculation unit 120, and uses the fourth speed difference VD4 as the second speed difference VD2.

[0125] Even when the first sheet conveyance speed VBs cannot be read from the tape memory 300 in the reading process, the motor control unit 130 uses the third speed difference VD3 as the first speed difference VD1. Similarly, when the first sheet conveyance speed VBs cannot be read from the tape memory 300 in the reading process, the motor control unit 130 uses the fourth speed difference VD4 as the second speed difference VD2.

[0126] Next, the process of the control unit 100 setting the rotation speed N3 of the fixing motor M3 will be described. When the cover 11 is closed from the open state, the control unit 100 starts the process of setting the rotation speed N3 of the fixing motor M3.

[0127] As Figure 5As shown, when the cover 11 is closed (start), the control unit 100 determines whether the belt unit 50 is installed on the apparatus main body 10 (S101). When it is determined that the belt unit 50 is not installed on the apparatus main body 10 (No in S101), the control unit 100 ends the process of setting the rotational speed.

[0128] On the other hand, when it is determined that the belt unit 50 is installed on the apparatus main body 10 (Yes in S101), the control unit 100 reads the second sheet conveyance speed VFs of the fixing unit 70 and the reference sheet conveyance speed VBr of the transfer belt 53 from the main body memory 200 (S102) (reading process). The control unit 100 reads the first sheet conveyance speed VBs of the transfer belt 53 from the belt memory 300 (S103) (reading process).

[0129] Then, when it is determined that the first sheet conveyance speed VBs has been read from the belt memory 300 (Yes in S104), the control unit 100 calculates a fifth speed difference VBD based on the first sheet conveyance speed VBs and the reference sheet conveyance speed VBr (S105). Then, the control unit 100 determines whether the fifth speed difference VBD is within the determination threshold range (S106).

[0130] When it is determined that the fifth speed difference VBD is within the determination threshold range (Yes in S106), the control unit 100 calculates a first speed difference VD1 based on the first sheet conveyance speed VBs and the second sheet conveyance speed VFs (S107), and the process proceeds to step S110.

[0131] When it is determined in step S104 that the first sheet conveyance speed VBs cannot be read from the belt memory 300 (No in S104), and when it is determined in step S106 that the fifth speed difference VBD is not within the determination threshold range (No in S106), the control unit 100 calculates a third speed difference VD3 based on the reference sheet conveyance speed VBr and the second sheet conveyance speed VFs (S108). Then, the control unit 100 uses the third speed difference VD3 as the first speed difference VD1 (S109).

[0132] In step S110, the control unit 100 sets the rotational speed N3 of the fixing motor M3 based on the first speed difference VD1 and the first reference value VA1 (S110) (motor control process). Then, the control unit 100 stores the set rotational speed N3 as the rotational speed of the fixing motor M3 (S111), and the process of setting the rotational speed of the fixing motor M3 ends.

[0133] Next, the process in which the control unit 100 sets the rotation speed N1 of the conveyance motor M1 will be described. The same reference numerals are used for the same processes as those for setting the rotation speed N3 of the fixing motor M3, and the description thereof will be appropriately omitted.

[0134] As Figure 6 shown, when it is determined that the belt unit 50 is installed in the apparatus main body 10 (Yes in S101), the control unit 100 reads the third sheet conveyance speed VCs of the positioning roller 26 and the reference sheet conveyance speed VBr of the transfer belt 53 from the main body memory 200 (S202) (reading process).

[0135] When it is determined in step S106 that the fifth speed difference VBD is within the determination threshold (Yes in S106), the control unit 100 calculates the second speed difference VD2 based on the first sheet conveyance speed VBs and the third sheet conveyance speed VCs (S207), and the process proceeds to step S210.

[0136] When it is determined in step S104 that the first sheet conveyance speed VBs cannot be read (No in S104), and when it is determined in step S106 that the fifth speed difference VBD is not within the determination threshold (No in S106), the control unit 100 calculates the fourth speed difference VD4 based on the reference sheet conveyance speed VBr and the third sheet conveyance speed VCs (S208). Then, the control unit 100 uses the fourth speed difference VD4 as the second speed difference VD2 (S209).

[0137] In step S210, the control unit 100 sets the rotation speed N1 of the conveyance motor M1 based on the second speed difference VD2 and the second reference value VA2 (S210) (motor control process). Then, the control unit 100 stores the set rotation speed N1 as the rotation speed of the conveyance motor M1 (S211), and the process of setting the rotation speed of the conveyance motor M1 ends.

[0138] According to the above-described embodiment, by setting the rotation speed N3 of the fixing motor M3 based on the first sheet conveyance speed VBs stored in the belt memory 300 of the replaceable belt unit 50, the fixing motor M3 can be controlled. Therefore, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fixing unit 70 can be kept within a certain range. As a result, it is possible to suppress the excessive bending of the sheet S between the transfer belt 53 and the fixing unit 70, and to suppress the slippage of the sheet s in the belt unit 50 or the fixing unit 70.

[0139] Since the belt motor M2 drives not only the transfer belt 53 but also the photosensitive drum 41, the number of motors provided in the image forming apparatus 1 can be reduced.

[0140] When the cover 11 is closed and the belt unit 50 is installed, the reading process starts. Therefore, when a new belt unit 50 is replaced and the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fixing unit 70 is likely to change, the rotational speed N3 of the fixing motor M3 and the rotational speed N1 of the conveyance motor M1 can be set. Thus, it is possible to more reliably suppress excessive bending of the sheet S and slippage of the sheet s.

[0141] When the first sheet conveyance speed VBs cannot be read from the belt memory 300 or when the value of the first sheet conveyance speed VBs read during the reading process is an abnormal value, since the third speed difference VD3 is used as the first speed difference VD1, even in such a case, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fixing unit 70 can be kept within a certain range.

[0142] According to the present embodiment, since the rotational speed N1 of the conveyance motor M1 can be set according to the first sheet conveyance speed VBs to control the conveyance motor M1, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 can be kept within a certain range. Thus, it is possible to more reliably suppress excessive bending of the sheet S between the registration roller 26 and the transfer belt 53, and to suppress slippage of the sheet on the registration roller 26 or the belt unit 50.

[0143] When the first sheet conveyance speed VBs cannot be read from the belt memory 300 or when the value of the first sheet conveyance speed VBs read during the reading process is an abnormal value, since the fourth speed difference VD4 is used as the second speed difference VD2, even in such a case, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 can be kept within a certain range.

[0144] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be implemented with appropriate modifications.

[0145] For example, the control unit 100 or the main body memory 200 stores a first wear prediction value and a second wear prediction value. The first wear prediction value is a deceleration value of the sheet conveyance speed of the fixing unit 70 predicted when the pressure roller 72 of the fixing unit 70 is worn by the conveyance of the sheet S. The second wear prediction value is a deceleration value of the sheet conveyance speed of the registration roller 26 predicted when the registration roller 26 is worn by the conveyance of the sheet S.

[0146] When the second sensor 6 or the like detects that the belt unit 50 has been replaced with a new belt unit, the control unit 100 determines whether the number of sheets S printed after the fusing unit 70 has been replaced by the service personnel is a predetermined number or more. When the control unit 100 determines that the number of sheets printed after the fusing unit 70 has been replaced is a predetermined number or more, the control unit 100 subtracts the first wear prediction value from the second sheet conveyance speed VFs. Then, the control unit 100 controls the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fusing unit 70 to be close to the first reference value VA1.

[0147] As a result, even when the fusing unit 70 wears due to the conveyance of the sheet S and the sheet conveyance speed of the fusing unit 70 decreases, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the fusing unit 70 can be kept within a certain range.

[0148] When the second sensor 6 or the like detects that the belt unit 50 has been replaced with a new belt unit, the control unit 100 determines whether the number of sheets S printed after the registration roller 26 has been replaced by the service personnel is a predetermined number or more. When the control unit 100 determines that the number of sheets S printed after the registration roller 26 has been replaced is a predetermined number or more, the control unit 100 subtracts the second wear prediction value from the third sheet conveyance speed VCs. Then, the control unit 100 controls the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 to be close to the second reference value VA2.

[0149] As a result, even when the registration roller 26 wears due to the conveyance of the sheet S and the sheet conveyance speed of the registration roller 26 decreases, the speed difference between the actual sheet conveyance speed of the transfer belt 53 and the actual sheet conveyance speed of the registration roller 26 can be kept within a certain range.

[0150] Although the belt motor M2 is configured to drive the transfer belt 53 and the photosensitive drum 41 in the above-described embodiment, the photosensitive drum may be driven by a motor other than the belt motor.

[0151] Although the control unit 100 is configured to start the reading process when the cover 11 is closed and the belt unit 50 is installed in the above-described embodiment, the present invention is not limited thereto. For example, the control unit may start the reading process for each predetermined control period in a state where an instruction for driving the motor is not received, and set the conveyance speed of the motor. That is, the timing for starting the reading process and setting the motor conveyance speed is arbitrary.

[0152] In the above-described embodiment, when the first sheet conveyance speed VBs cannot be read from the memory 300, or when the value of the first sheet conveyance speed VBs read in the reading process is an abnormal value, the control unit 100 uses the third speed difference VD3 as the first speed difference VD1 to set the rotation speed N3 of the fixing motor M3. However, the present invention is not limited thereto. For example, in the above case, the control unit may set the rotation speed of the fixing motor to a default value. In the above case, the control unit may output an error message or the like without setting the rotation speed of the fixing motor. This also applies to the setting of the rotation speed of the conveyance motor.

[0153] In the above-described embodiment, the rotation speed N3 of the fixing motor M3 is set by the first speed difference VD1 and the first reference value VA1 in the motor control process. However, the present invention is not limited thereto, and the rotation speed N2 of the belt motor M2 may be set. The rotation speed N2 of the belt motor M2 and the rotation speed N3 of the fixing motor M3 may be set. The first reference value may not be a single value but a value having a certain range.

[0154] In the above-described embodiment, the rotation speed N1 of the conveyance motor M1 is set by the second speed difference VD2 and the second reference value VA2 in the motor control process. However, the present invention is not limited thereto, and the rotation speed N2 of the belt motor M2 may be set. The rotation speed N2 of the belt motor M2 and the rotation speed N1 of the conveyance motor M1 may be set. The second reference value may not be a single value but a value having a certain range.

[0155] In the above-described embodiment, as the fixing unit, the fixing unit 70 including the cylindrical fixing roller 71 made of metal is shown. However, the present invention is not limited thereto. For example, the fixing unit may be a belt fixing type fixing unit including a flexible annular fixing belt. The second sheet conveyance speed stored in the main body memory may be a calculated value calculated based on the value of the outer diameter of the pressure roller measured in advance.

[0156] In the above-described embodiment, the registration roller 26 is shown as the conveyance roller. However, the present invention is not limited thereto. For example, the pickup roller 22, the separation roller 23, the paper powder removing roller 25, etc. in the above-described embodiment may be controlled in the same manner as the registration roller 26.

[0157] In the above-described embodiment, the transfer belt 53 (conveyance belt) that conveys the sheet S between the transfer belt 53 and the photosensitive drum 41 is shown as the transfer belt. However, the present invention is not limited thereto. For example, the transfer belt may be an intermediate transfer belt or the like, and the toner image is transferred from the photosensitive drum through the intermediate transfer belt or the like, and the transferred toner image is transferred to the sheet.

[0158] In the above-described embodiment, the present invention is used to control the speed difference between the sheet conveyance speed of the transfer belt 53 and the sheet conveyance speed of the fixing unit 70, and to control the speed difference between the sheet conveyance speed of the transfer belt 53 and the sheet conveyance speed of the registration roller 26. However, the present invention is not limited thereto. For example, the present invention can be used to control only the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit. The present invention can be used to control only the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the registration roller.

[0159] In the above-described embodiment, as the image forming apparatus, an image forming apparatus 1 for color printing provided with a plurality of photosensitive drums 41 is shown. However, the present invention is not limited thereto. For example, the image forming apparatus may be a monochrome printing image forming apparatus having only one photosensitive drum. The image forming apparatus may be a printer, or may be a multifunction machine, a copying machine, etc. provided with an original reading device such as a flatbed scanner.

[0160] In the above-described embodiment, the sheet conveyance speed based on the pre-measured value is stored in the belt memory or the main body memory. However, the present invention is not limited thereto. For example, the thickness of the transfer belt, the value of the outer diameter of the belt driving roller, etc. can be stored in the belt memory, and the sheet conveyance speed of the transfer belt can be calculated in the control unit of the image forming apparatus. The same applies to the information stored in the main body memory.

[0161] Each of the components in the above-described embodiment and the above-described modification examples can be appropriately combined and implemented.

Claims

1. An image forming apparatus, comprising: A device body; A photosensitive drum; A belt unit that can be mounted on and detached from the device body, the belt unit including a transfer belt and a belt memory, the transfer belt configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet, and the belt memory storing a first sheet conveyance speed, which is the sheet conveyance speed of the transfer belt; A fixing unit configured to fix the toner image on the sheet conveyed by the transfer belt to the sheet in a state where the belt unit is mounted on the device body; A belt motor configured to drive the transfer belt; A fixing motor configured to drive the fixing unit; A body memory storing a second sheet conveyance speed, which is the sheet conveyance speed of the fixing unit, and storing a first reference value, which is a reference value for the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit; And A control unit, The control unit performs: A reading process that reads the first sheet conveyance speed from the belt memory and reads the second sheet conveyance speed from the body memory; And A motor control process that sets the rotational speed of the belt motor or the rotational speed of the fixing motor according to a first speed difference and the first reference value so that the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit approaches the first reference value, the first speed difference being the speed difference between the first sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process, The body memory stores a reference sheet conveyance speed, which is a reference value for the sheet conveyance speed of the transfer belt, In the reading process, when the first sheet conveyance speed cannot be read from the belt memory, the control unit reads the reference sheet conveyance speed from the body memory, In the motor control process, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process as the first speed difference.

2. The image forming apparatus according to claim 1, wherein, The first sheet conveyance speed is the sheet conveyance speed of the transfer belt based on a pre-measured value.

3. The image forming apparatus according to claim 1, wherein, The second sheet conveyance speed is the sheet conveyance speed of the fixing unit based on a predetermined measured value.

4. The image forming apparatus according to any one of claims 1 to 3, wherein, The belt motor drives the photosensitive drum.

5. The image forming apparatus according to any one of claims 1 to 3, wherein, In the motor control process, the control unit sets the rotational speed of the fixing motor according to the first speed difference and the first reference value.

6. The image forming apparatus according to claim 5, wherein, In the motor control process, when the first speed difference is greater than the first reference value, the control unit decreases the rotational speed of the fixing motor, and when the first speed difference is less than the first reference value, the control unit increases the rotational speed of the fixing motor.

7. The image forming apparatus according to any one of claims 1 to 3, wherein, The transfer belt conveys a sheet between the transfer belt and the photosensitive drum.

8. The image forming apparatus according to any one of claims 1 to 3, wherein, The transfer belt is an endless belt.

9. The image forming apparatus according to any one of claims 1 to 3, wherein, The first sheet conveyance speed is an actual measurement value of the sheet conveyance speed of the transfer belt measured in advance.

10. The image forming apparatus according to any one of claims 1 to 3, wherein, The belt unit includes a belt driving roller and a belt driven roller. The belt driving roller drives the transfer belt, and the belt driving roller contacts the inner peripheral surface of the transfer belt. The belt driven roller rotates by being driven by the transfer belt, and the belt driven roller is spaced apart from the belt driving roller. The belt driven roller contacts the inner peripheral surface of the transfer belt. The first sheet conveyance speed is a calculated value calculated based on the thickness of the transfer belt measured in advance and the outer diameter of the belt driving roller.

11. The image forming apparatus according to any one of claims 1 to 3, wherein, The first sheet conveyance speed stored in the belt memory is faster than the second sheet conveyance speed stored in the main body memory.

12. The image forming apparatus according to any one of claims 1 to 3, wherein, The second sheet conveyance speed is an actual measurement value of the sheet conveyance speed of the fixing unit measured in advance.

13. The image forming apparatus according to any one of claims 1 to 3, wherein, The fixing unit includes a fixing roller configured to heat the sheet. The second sheet conveyance speed is a calculated value calculated based on the outer diameter value of the fixing roller measured in advance.

14. The image forming apparatus according to any one of claims 1 to 3, further comprising: A cover, the apparatus main body including the cover that can be opened and closed, and the cover is opened when the belt unit is installed and removed; A first sensor configured to detect the opening and closing of the cover; And A second sensor configured to detect whether the belt unit is installed on the apparatus main body. When the first sensor detects that the cover is closed and the second sensor detects that the belt unit is installed on the apparatus main body, the control unit starts the reading process.

15. An image forming apparatus, comprising: An apparatus main body; A photosensitive drum; A belt unit that can be installed on and removed from the apparatus main body. The belt unit includes a transfer belt and a belt memory. The transfer belt is configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet. The belt memory stores a first sheet conveyance speed, which is the sheet conveyance speed of the transfer belt. A fixing unit configured to fix the toner image on the sheet conveyed by the transfer belt to the sheet in a state where the belt unit is installed on the apparatus main body. A belt motor configured to drive the transfer belt; A fixing motor configured to drive the fixing unit; A main body memory that stores a second sheet conveyance speed, which is the sheet conveyance speed of the fixing unit, and stores a first reference value, which is a reference value for the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit; And A control unit, The control unit performs: A reading process that reads the first sheet conveyance speed from the belt memory and reads the second sheet conveyance speed from the main body memory; And A motor control process that sets the rotational speed of the belt motor or the rotational speed of the fixing motor according to a first speed difference and the first reference value so that the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the fixing unit approaches the first reference value. The first speed difference is the speed difference between the first sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process, The main body memory stores a reference sheet conveyance speed, which is a reference value for the sheet conveyance speed of the transfer belt, In the reading process, the control unit reads the reference sheet conveyance speed from the main body memory, In the motor control process, when the speed difference between the first sheet conveyance speed read in the reading process and the reference sheet conveyance speed read in the reading process is outside the range of the determination threshold, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the second sheet conveyance speed read in the reading process as the first speed difference.

16. The image forming apparatus according to claim 15, wherein, The first sheet conveyance speed is the actually measured value of the sheet conveyance speed of the transfer belt based on a pre-measured value.

17. The image forming apparatus according to claim 15, wherein, The second sheet conveyance speed is the sheet conveyance speed of the fixing unit based on a predetermined measured value.

18. The image forming apparatus according to any one of claims 15 to 17, wherein, The belt motor drives the photosensitive drum.

19. The image forming apparatus according to any one of claims 15 to 17, wherein, In the motor control process, the control unit sets the rotational speed of the fixing motor according to the first speed difference and the first reference value.

20. The image forming apparatus according to claim 19, wherein, In the motor control process, the control unit decreases the rotational speed of the fixing motor when the first speed difference is greater than the first reference value, and increases the rotational speed of the fixing motor when the first speed difference is less than the first reference value.

21. The image forming apparatus according to any one of claims 15 to 17, wherein, The transfer belt conveys the sheet between the transfer belt and the photosensitive drum.

22. The image forming apparatus according to any one of claims 15 to 17, wherein, The transfer belt is an endless belt.

23. The image forming apparatus according to any one of claims 15 to 17, wherein, The first sheet conveyance speed is the actually measured value of the sheet conveyance speed of the transfer belt based on a pre-measured value.

24. The image forming apparatus according to any one of claims 15 to 17, wherein, The belt unit includes a belt driving roller and a belt driven roller. The belt driving roller drives the transfer belt, contacts the inner peripheral surface of the transfer belt, the belt driven roller rotates by being driven by the transfer belt, the belt driven roller is spaced apart from the belt driving roller, and the belt driven roller contacts the inner peripheral surface of the transfer belt. The conveying speed of the first sheet is a calculated value calculated based on the thickness of the transfer belt measured in advance and the outer diameter of the belt driving roller.

25. The image forming apparatus according to any one of claims 15 to 17, wherein, The first sheet conveying speed stored in the belt memory is faster than the second sheet conveying speed stored in the main body memory.

26. The image forming apparatus according to any one of claims 15 to 17, wherein, The second sheet conveying speed is an actually measured value of the sheet conveying speed of the fixing unit measured in advance.

27. The image forming apparatus according to any one of claims 15 to 17, wherein, The fixing unit includes a fixing roller configured to heat the sheet. The second sheet conveying speed is a calculated value calculated based on the value of the outer diameter of the fixing roller measured in advance.

28. The image forming apparatus according to any one of claims 15 to 17, further comprising: A cover, the apparatus main body including the cover that can be opened and closed, the cover being opened when the belt unit is installed and removed; A first sensor configured to detect the opening and closing of the cover; And A second sensor configured to detect whether the belt unit is installed in the apparatus main body. When the first sensor detects that the cover is closed and the second sensor detects that the belt unit is installed in the apparatus main body, the control unit starts the reading process.

29. An image forming apparatus, comprising: An apparatus main body; A photosensitive drum; A belt unit that can be installed on and removed from the apparatus main body, the belt unit including a transfer belt and a belt memory, the transfer belt being configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet, the belt memory storing a first sheet conveying speed, the first sheet conveying speed being the sheet conveying speed of the transfer belt; A conveying roller configured to convey the sheet toward the transfer belt in a state where the belt unit is installed in the apparatus main body; A belt motor configured to drive the transfer belt; A conveying motor configured to drive the conveying roller; A main body memory storing a third sheet conveying speed, the third sheet conveying speed being the sheet conveying speed of the conveying roller, the main body memory storing a second reference value, the second reference value being a reference value of the speed difference between the sheet conveying speed of the transfer belt and the sheet conveying speed of the conveying roller; And A control unit. The control unit performs: A reading process that reads the first sheet conveying speed from the belt memory and reads the third sheet conveying speed from the main body memory; and A motor control process that sets the rotational speed of the belt motor or the rotational speed of the conveying motor according to a second speed difference and the second reference value so that the speed difference between the sheet conveying speed of the transfer belt and the sheet conveying speed of the conveying roller approaches the second reference value, the second speed difference being the speed difference between the first sheet conveying speed read in the reading process and the third sheet conveying speed read in the reading process. The main body memory stores a reference sheet conveyance speed, which is a reference value of the sheet conveyance speed of the transfer belt. In the reading process, when the first sheet conveyance speed cannot be read from the belt memory, the control unit reads the reference sheet conveyance speed from the main body memory. In the motor control process, the control unit uses the speed difference between the reference sheet conveyance speed read in the reading process and the third sheet conveyance speed read in the reading process as the second speed difference.

30. The image forming apparatus according to claim 29, wherein, The first sheet conveyance speed is the sheet conveyance speed of the transfer belt based on a pre-measured value.

31. The image forming apparatus according to claim 29, wherein, The third sheet conveyance speed is the sheet conveyance speed of the conveyance roller based on a predetermined measured value.

32. The image forming apparatus according to any one of claims 29 to 31, wherein, In the motor control process, the control unit sets the rotational speed of the conveyance motor according to the second speed difference and the second reference value.

33. The image forming apparatus according to claim 32, wherein, In the motor control process, when the second speed difference is greater than the second reference value, the control unit decreases the rotational speed of the conveyance motor, and when the second speed difference is less than the second reference value, the control unit increases the rotational speed of the conveyance motor.

34. The image forming apparatus according to any one of claims 29 to 31, wherein, The first sheet conveyance speed stored in the belt memory is slower than the third sheet conveyance speed stored in the main body memory.

35. The image forming apparatus according to any one of claims 29 to 31, wherein, The third sheet conveyance speed is the actual measured value of the sheet conveyance speed of the conveyance roller measured in advance.

36. The image forming apparatus according to any one of claims 29 to 31, wherein, The conveyance roller includes a conveyance drive roller and a conveyance driven roller. Driving force from the conveyance motor is input to the conveyance drive roller, and the conveyance driven roller is driven by the conveyance drive roller to rotate. The third sheet conveyance speed is a calculated value calculated based on the value of the outer diameter of the conveyance drive roller measured in advance.

37. An image forming apparatus, comprising: A device main body; A photosensitive drum; A belt unit that can be mounted on and removed from the device main body. The belt unit includes a transfer belt and a belt memory. The transfer belt is configured to transfer a toner image on the photosensitive drum to a sheet and convey the sheet. The belt memory stores a first sheet conveyance speed, which is the sheet conveyance speed of the transfer belt; A conveyance roller configured to convey the sheet toward the transfer belt in a state where the belt unit is mounted on the device main body; A belt motor configured to drive the transfer belt; A conveyance motor configured to drive the conveyance roller; A main body memory that stores a third sheet conveyance speed, which is the sheet conveyance speed of the conveyance roller, and stores a second reference value, which is a reference value of the speed difference between the sheet conveyance speed of the transfer belt and the sheet conveyance speed of the conveyance roller; And A control unit, The control unit performs: A reading process that reads the first sheet conveyance speed from the belt memory and reads the third sheet conveyance speed from the main body memory; and Motor control processing, wherein the motor control processing sets the rotational speed of the belt motor or the rotational speed of the conveying motor according to a second speed difference and the second reference value, such that the speed difference between the sheet conveying speed of the transfer belt and the sheet conveying speed of the conveying roller approaches the second reference value, and the second speed difference is the speed difference between the first sheet conveying speed read in the reading processing and the third sheet conveying speed read in the reading processing. The main body memory stores a reference sheet conveying speed, which is a reference value for the sheet conveying speed of the transfer belt. In the reading processing, the control unit reads the reference sheet conveying speed from the main body memory. In the motor control processing, when the speed difference between the first sheet conveying speed read in the reading processing and the reference sheet conveying speed read in the reading processing is outside the range of the judgment threshold, the control unit uses the speed difference between the reference sheet conveying speed read in the reading processing and the third sheet conveying speed read in the reading processing as the second speed difference.

38. The image forming apparatus according to claim 37, wherein, The first sheet conveying speed is the sheet conveying speed of the transfer belt based on a pre-measured value.

39. The image forming apparatus according to claim 37, wherein, The third sheet conveying speed is the sheet conveying speed of the conveying roller based on a predetermined measured value.

40. The image forming apparatus according to any one of claims 37 to 39, wherein, In the motor control processing, the control unit sets the rotational speed of the conveying motor according to the second speed difference and the second reference value.

41. The image forming apparatus according to claim 40, wherein, In the motor control processing, when the second speed difference is greater than the second reference value, the control unit decreases the rotational speed of the conveying motor, and when the second speed difference is less than the second reference value, the control unit increases the rotational speed of the conveying motor.

42. The image forming apparatus according to any one of claims 37 to 39, wherein, The first sheet conveying speed stored in the belt memory is slower than the third sheet conveying speed stored in the main body memory.

43. The image forming apparatus according to any one of claims 37 to 39, wherein, The third sheet conveying speed is the actual measured value of the sheet conveying speed of the conveying roller measured in advance.

44. The image forming apparatus according to any one of claims 37 to 39, wherein, The conveying roller includes a conveying drive roller and a conveying driven roller. A driving force from the conveying motor is input to the conveying drive roller, and the conveying driven roller is driven by the conveying drive roller to rotate. The third sheet conveying speed is a calculated value calculated based on the value of the outer diameter of the conveying drive roller measured in advance.

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