JP5434901B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus capable of forming a color image on a sheet by superimposing images of a plurality of colors by an image forming unit while the sheet is conveyed by a conveyance roller and a belt unit.

  2. Description of the Related Art Conventionally, an image forming apparatus transports a sheet by a conveying roller and a belt unit, and superimposes a plurality of color images constituting a color image by an image forming unit disposed above the belt unit. Are formed on the surface of the paper.

  As an invention relating to such an image forming apparatus, an invention according to Patent Document 1 is known. When forming a color image on a sheet, the image forming apparatus described in Patent Document 1 uses a conveyance roller (paper supply roller) that forms a sheet feeding unit to form a sheet with respect to a belt unit having a conveyance belt formed in an endless shape. Feed paper. Then, the image forming apparatus conveys an image of each color (magenta, cyan, yellow, black) constituting the color image while conveying the sheet fed to the belt unit in a predetermined conveyance direction. The forming unit sequentially transfers the color image on the paper in a superimposed manner. Thereafter, the image forming apparatus conveys the color image transferred to the sheet while conveying the sheet that has passed through the belt unit in the conveying direction by a conveying roller (heating roller, pressure roller) that constitutes the fixing unit. A color image is formed on a sheet by fixing to the sheet.

JP 2010-064263 A

  Here, as in the image forming apparatus described in Patent Document 1, when a color image is formed on a sheet while conveying the sheet in the order of the paper feeding unit, the belt unit, and the fixing unit, each color constituting the color image is formed. In order to superimpose images without deviation, it is necessary for the paper to be appropriately bent between the paper feeding unit and the belt unit and between the belt unit and the fixing unit. When the amount of bending of the paper between the units is small, tension is applied to the paper so that the paper is pulled in the paper conveyance direction, and thus a deviation occurs when the images of the respective colors are superimposed. In addition, when the amount of deflection of the paper between the units is large, the large amount of deflection causes a shift between images of each color or a jam due to the paper.

  The amount of sheet deflection between the units corresponds to the sheet conveyance speed in each unit (sheet feeding unit, belt unit, fixing unit). If the transport speed in the upstream unit in the transport direction (for example, the paper feeding unit) is too low than the transport speed in the downstream unit in the transport direction (for example, the belt unit), the tension in the direction in which the paper is pulled increases. When the images of the respective colors are superimposed, a deviation occurs, and if the speed is higher than the transport speed in the unit on the downstream side in the transport direction, the paper is greatly bent and causes a jam or the like.

  In the conventional image forming apparatus, the sheet conveyance speed in each unit is set by a value obtained by experiments or the like. However, each image forming apparatus has a slight error with respect to the conveyance speed based on a value obtained by an experiment or the like due to a manufacturing process, accuracy of parts constituting the apparatus, or the like. Therefore, even if the conveyance speed is based on a value obtained by experiments or the like, the conveyance speed is not necessarily optimal for each image forming apparatus, and there is a case where the amount of deflection between the units cannot be ensured appropriately. Furthermore, the conveyance speed in each unit may change due to consumption due to continuous use of the image forming apparatus and changes in the environment surrounding the image forming apparatus. Accordingly, there is a case where the amount of bending between the units cannot be appropriately secured due to the continuous use of the image forming apparatus and the change in environment.

  Further, in the conventional image forming apparatus, there is no method for confirming the sheet conveyance speed in each unit. Therefore, if the amount of paper deflection between units is not in the proper range, the conventional image forming unit cannot properly adjust the conveyance speed in each unit, and the amount of paper deflection cannot be corrected to the appropriate range. . As a result, the image forming apparatus cannot prevent image misalignment or paper jam based on the amount of paper deflection.

  The present invention relates to an image forming apparatus capable of forming a color image on a sheet by superimposing a plurality of color images by an image forming unit while the sheet is conveyed by a conveyance roller and a belt unit. Provided is an image forming apparatus capable of preventing image misalignment and paper jam by adjusting to an appropriate range.

  An image forming apparatus according to a first aspect of the present invention includes a main body housing, an image forming unit, a belt unit, a conveying roller, a pattern forming unit, a first detecting unit, a second detecting unit, and a conveying speed. Adjusting means. The image forming apparatus forms an image composed of a plurality of colors on the sheet by superimposing the images of the respective colors by the image forming unit while conveying the sheet by the belt unit and the conveying roller. Then, when the sheet is conveyed to the belt unit, the image forming apparatus forms a detection pattern in the first range and the second range by the pattern forming unit. Thereafter, the image forming apparatus conveys the sheet on which the detection pattern is formed from the belt unit in a predetermined conveyance direction, and then, by the first detection unit, the first detection unit and the second range on the surface of the conveyance belt. The first transit time is measured by detecting the interval between the remaining detection patterns. In addition, the image forming apparatus measures the second passage time required for the sheet to pass through the conveyance roller by detecting the upstream end and the downstream end of the sheet by the second detection unit. Here, since the first range includes the upstream end of the paper and the second range includes the downstream end of the paper, the interval between the detection patterns remaining in the first range and the second range on the surface of the conveyor belt is as follows. This corresponds to the length dimension along the paper conveyance direction. Therefore, the image forming apparatus can specify the sheet conveyance speed by the belt unit based on the first passage time and the length along the sheet conveyance direction, and further, the second passage time and the sheet conveyance direction. The conveyance speed of the sheet by the conveyance roller can be specified based on the length along. Then, the image forming apparatus uses the conveyance speed adjusting unit to determine between the conveyance speed of the sheet by the belt unit and the conveyance speed of the sheet by the conveyance roller based on the first passage time and the second passage time. The conveyance speed of the paper by the conveyance roller is adjusted so that a predetermined speed difference is generated. As a result, the image forming apparatus can impart an appropriate amount of bending to the sheet between the transport roller and the belt unit, thereby preventing image misalignment and sheet jamming.

  3. The image forming apparatus according to claim 2, wherein the transport speed adjusting means is configured such that the transport speed of the sheet increases toward the upstream side in the transport direction based on the first passage time and the second passage time, and the belt unit. The conveyance speed of the paper by the conveyance roller is automatically adjusted so that a predetermined speed difference occurs between the conveyance speed of the paper by and the conveyance speed of the paper by the conveyance roller. As a result, the image forming apparatus can adjust the amount of bending of the paper between the belt unit and the conveyance roller to an appropriate range, and can prevent image misalignment and paper jamming.

  4. The image forming apparatus according to claim 3, wherein the conveyance speed adjusting means compares the difference value between the first passage time and the second passage time with a reference value based on the speed difference. Then, it is determined whether or not it is necessary to adjust the conveyance speed of the sheet by the conveyance roller. Therefore, the image forming apparatus can determine whether or not the adjustment related to the sheet conveyance speed by the conveyance roller is necessary without calculating the sheet conveyance speed by the belt unit and the sheet conveyance speed by the conveyance roller. It is possible to adjust the transport speed in a necessary state while reducing the control burden related to the necessity of speed adjustment.

  5. The image forming apparatus according to claim 4, wherein the transport roller is disposed upstream of the belt unit in the transport direction of the paper, and is driven to rotate with respect to the belt unit. Feed paper. Therefore, the image forming apparatus can apply a deflection amount in an appropriate range to the conveyance roller that feeds the sheet to the belt unit and the sheet between the belt unit. It can prevent jamming.

  6. The image forming apparatus according to claim 5, wherein the transport roller is disposed downstream of the belt unit in the transport direction of the paper, and the paper transported through the belt unit by being driven to rotate. Are transported downstream in the transport direction. Therefore, the image forming apparatus can impart a deflection amount in an appropriate range to the sheet between the conveyance roller that conveys the sheet conveyed from the belt unit further downstream in the conveyance direction and the belt unit. Image misalignment and paper jam can be prevented.

  The image forming apparatus according to claim 6, wherein the transport roller includes a first transport roller and a second transport roller. The first transport roller is disposed upstream of the belt unit in the transport direction of the paper, and supplies the paper to the belt unit by being driven to rotate. The second transport roller is disposed downstream of the belt unit in the transport direction of the paper, and is rotated to transport the paper transported through the belt unit downstream in the transport direction. The conveyance speed adjusting means is configured to cause the sheet by the first conveyance roller to have a predetermined speed difference between the conveyance speed of the sheet by the belt unit and the conveyance speed of the sheet by the first conveyance roller. , And the second conveying roller causes the sheet to be conveyed by the second conveying roller so that a predetermined speed difference occurs between the conveying speed of the sheet by the belt unit and the conveying speed of the sheet by the second conveying roller. Adjust the transport speed. Therefore, the image forming apparatus further conveys the sheet between the first conveyance roller that feeds the sheet to the belt unit and the belt unit and the sheet conveyed from the belt unit further downstream in the conveyance direction. Any amount of paper between the transport roller and the belt unit can be given an appropriate range of deflection, thereby preventing image misalignment and paper jamming.

  8. The image forming apparatus according to claim 7, wherein the first detection unit detects a density of an image formed by the image forming unit and a shift of each image when the images of the plurality of colors are superimposed. It is composed of sensors. Therefore, according to the image forming apparatus, it is possible to effectively use the detection sensor for detecting the density of the image formed by the image forming unit and the shift of each image when the images of the plurality of colors are superimposed. Further, it is possible to prevent image misalignment and paper jam caused by the amount of paper deflection during conveyance. As a result, according to the image forming apparatus, it is possible to prevent image misalignment and paper jam while reducing the number of parts constituting the image forming apparatus.

It is a sectional side view of the laser printer concerning this embodiment. It is a block diagram which shows the control system of a laser printer. It is a flowchart of a conveyance speed adjustment processing program. FIG. 6 is an explanatory diagram illustrating a state where an upstream end of a sheet is detected by a first sheet detection sensor. FIG. 6 is an explanatory diagram illustrating a state where a downstream end of a sheet is detected by a first sheet detection sensor. FIG. 10 is an explanatory diagram illustrating a state in which an upstream end of a sheet is detected by a second sheet detection sensor. FIG. 10 is an explanatory diagram illustrating a state where a downstream end of a sheet is detected by a second sheet detection sensor. It is explanatory drawing regarding the pattern for a detection formed in a conveyance belt and a paper. FIG. 6 is an explanatory diagram relating to a detection pattern in a state where a sheet is conveyed from a belt unit.

  Hereinafter, an image forming apparatus according to an embodiment of the invention embodied in a laser printer 1 will be described in detail with reference to the drawings. In the following description, a description will be given using directions based on the user when the laser printer 1 is used. That is, in FIG. 1, the right side toward the paper surface is “front side”, the left side toward the paper surface is “rear side”, the front side toward the paper surface is “left side”, and the rear side toward the paper surface is “right side”. To do. Further, the vertical direction toward the paper surface is defined as “vertical direction”.

  As shown in FIG. 1 and the like, the laser printer 1 has a main body housing 10. The main body housing 10 is formed in a box shape, and includes a paper feeding unit 20, an image forming unit 30, a belt unit 70, a fixing unit 80, and a paper discharge unit 90 inside. The paper supply unit 20 supplies paper P that is a recording medium. The image forming unit 30 forms and transfers an image on the paper P fed by the paper feeding unit 20 in cooperation with the belt unit 70. The fixing unit 80 fixes the image transferred onto the paper P on the surface of the paper P. The paper discharge unit 90 discharges the paper P on which the image is formed by the image forming unit 30 to the outside of the laser printer 1. The paper feeding unit 20, the image forming unit 30, the belt unit 70, the fixing unit 80, and the paper discharging unit 90 will be described in detail later.

  A front cover 11 is provided on the front surface of the main body housing 10 so as to be rotatable forward and backward with a lower portion as a fulcrum. A paper discharge tray 13 is formed in the upper part of the main body housing 10. The paper discharge tray 13 accumulates the paper P discharged from the main body housing 10 by the paper discharge unit 90. An LED unit 40 constituting the image forming unit 30 is disposed on the lower surface of the paper discharge tray 13. In the main body casing 10, a main body frame is fixed to the main body casing 10 and the like. The main body frame is used to fix and support each part constituting the laser printer 1 and functions as a part of the apparatus main body that detachably accommodates each process cartridge 50 described later.

  As shown in FIG. 1, the paper feeding unit 20 is provided in the lower part in the main body housing 10. The paper feed unit 20 is mainly composed of a paper feed tray 21, a paper supply mechanism 22, and a first paper detection sensor 26. The paper feed tray 21 stores paper P as a recording medium in a stacked state, and is detachably attached to the main body housing 10.

  The paper supply mechanism 22 is provided on the front side of the paper feed tray 21 and transports the paper P from the paper feed tray 21 to the image forming unit 30 in the transport direction D on the transport path R. The paper supply mechanism 22 includes a paper feed roller 23, a separation roller 24, and a separation pad 25. The paper feed roller 23 feeds the paper P in the paper feed tray 21 from the paper feed tray 21 toward the separation roller 24. The separation roller 24 cooperates with the separation pad 25 to separate the fed paper P one by one. Accordingly, in the paper supply unit 20, the paper P in the paper supply tray 21 is separated one by one and sent upward. Thereafter, the paper P is turned in the rearward direction along the transport path R and supplied to the image forming unit 30.

  The first paper detection sensor 26 is disposed above the separation roller 24 and the separation pad 25 (that is, downstream in the conveyance direction D), and detects the end of the paper P conveyed by the paper supply unit 20. . The first paper detection sensor 26 is normally positioned so as to protrude into the transport path R, and comes into contact with the paper P transported through the transport path R by the paper feed unit 20 (see FIG. 4). By detecting the contact of the paper P, the first paper detection sensor 26 can detect the downstream end Eb of the paper P conveyed by the paper supply unit 20. Further, when the paper P is transported in the transport direction D, the first paper detection sensor 26 rotates in the transport direction D side. Therefore, the first paper detection sensor 26 does not hinder the movement of the paper P conveyed by the paper supply unit 20. The first paper detection sensor 26 returns to a position where it protrudes into the transport path R when the paper P passes through the vicinity of the first paper detection sensor 26. Therefore, the first paper detection sensor 26 can detect the upstream end Ea of the paper P conveyed by the paper supply unit 20. The first paper detection sensor 26 functions as one of the second detection means in the present invention.

  The image forming unit 30 includes four LED units 40 and four process cartridges 50. Each LED unit 40 and each process cartridge 50 correspond to a color used for forming a color image. That is, each LED unit 40 and each process cartridge 50 correspond to each color of black, yellow, magenta, and cyan in order from the front of the laser printer 1.

  As shown in FIG. 1, each LED unit 40 is located between predetermined process cartridges 50 at an exposure position facing the surface of the photosensitive drum 53, and each has an LED head that is an example of an exposure unit. ing. The LED head is formed on the lower side of the LED unit 40, and is configured by arranging a plurality of light emitting units made of LEDs in the left-right direction. Each light emitting unit of the LED head emits light based on a control signal from the control unit 15 (see FIG. 2), and exposes the surface of the photosensitive drum 53 based on the image data.

  The four process cartridges 50 are arranged side by side in the front-rear direction between the upper surface of the main body housing 10 and the paper feed unit 20, and are arranged at a predetermined interval from the other process cartridges 50. Has been. Each process cartridge 50 is different in only the color of toner (that is, one of black, yellow, magenta, and cyan) stored in a toner storage chamber 66 described later, and has the same configuration.

  As shown in FIG. 1, each process cartridge 50 includes a drum unit 51 and a developing unit 61. The developing unit 61 is configured to be detachable from the drum unit 51. The drum unit 51 includes a photosensitive drum 53 and a charger 54. The photosensitive drum 53 is rotatably supported at the lower part of the drum unit 51. Further, the drum unit 51 has an exposure hole into which the LED unit 40 is inserted on the surface located above the photosensitive drum 53.

  The photosensitive drum 53 is an example of a photosensitive member, and an electrostatic latent image is formed on the surface of the photosensitive drum 53 by the LED unit 40. The charger 54 is a so-called scorotron charger, and uniformly charges the surface of the photosensitive drum 53.

  The developing unit 61 includes a developing roller 63, a supply roller 64, and a toner storage chamber 66. The developing unit 61 holds the developing roller 63 and the supply roller 64 rotatably. The developing roller 63 supplies the toner supplied from the toner storage chamber 66 to the surface of the photosensitive drum 53. The supply roller 64 supplies the toner in the toner storage chamber 66 to the surface of the developing roller 63. The toner layer carried on the developing roller 63 is regulated to a certain thickness by a layer thickness regulating blade. The toner storage chamber 66 stores toner of any one of black, yellow, magenta, and cyan used for forming a color image.

  As shown in FIG. 1, the belt unit 70 is disposed between the paper feeding unit 20 and the image forming unit 30. The belt unit 70 includes a driving roller 71, a driven roller 72, a conveyance belt 73, a transfer roller 74, and a registration sensor 75. The driving roller 71 and the driven roller 72 are arranged in parallel so as to be separated in the front-rear direction. The conveyor belt 73 is constituted by an endless belt, and is stretched between the driving roller 71 and the driven roller 72. Accordingly, the conveyance belt 73 circulates with the rotation of the driving roller 71 and can convey the paper P conveyed to the belt unit 70 in the conveyance direction D. The outer surface of the conveyor belt 73 is in contact with the surface of each photosensitive drum 53, and four transfer rollers 74 are disposed inside the conveyor belt 73. Each transfer roller 74 is positioned below each photosensitive drum 53, and sandwiches a conveyance belt 73 with the photosensitive drum 53. The transfer roller 74 transfers the toner image on the surface of the photosensitive drum 53 onto the paper P by applying a transfer bias.

  The registration sensor 75 is disposed at the rear of the belt unit 70 in the main body housing 10 and at a position below the belt unit 70. The registration sensor 75 has a detection range on the surface facing the outer surface of the conveyor belt 73, and detection patterns (for example, a first detection pattern Ma and a second detection pattern) formed on the outer surface of the conveyor belt 73. Mb) is detected. Accordingly, the laser printer 1 can correct misalignment and density during image formation by performing various controls by the control unit 15 based on the detection pattern detection result by the registration sensor 75. The registration sensor 75 functions as the first detection means in the present invention.

  The fixing unit 80 is disposed on the rear side of the image forming unit 30 and the belt unit 70, and the paper P conveyed in the conveyance direction D by the belt unit 70 is discharged from the paper discharge unit 90 and the paper discharge tray 13. The image formed on the paper P is heat-fixed while being conveyed toward the front. The fixing unit 80 includes a heating roller 81, a pressure roller 82, and a second paper detection sensor 83. The heating roller 81 functions as a heat source related to thermal fixing of an image and is rotated to convey the paper P downstream in the conveyance direction D. The pressure roller 82 is disposed to face the heating roller 81, presses the paper P toward the heating roller 81, and rotates in the same manner as the heating roller 81.

  The second paper detection sensor 83 is disposed between the belt unit 70 and the fixing unit 80 and detects the end of the paper P conveyed by the fixing unit 80. The second paper detection sensor 83 normally protrudes on the transport path R and comes into contact with the paper P transported by the fixing unit 80 (see FIG. 6). By detecting the contact of the paper P, the second paper detection sensor 83 can detect the downstream end Eb of the paper P conveyed by the fixing unit 80. Further, when the paper P is further transported in the transport direction D, the second paper detection sensor 83 rotates in the transport direction D side. Therefore, the second paper detection sensor 83 does not hinder the movement of the paper P conveyed by the fixing unit 80. The second paper detection sensor 83 returns to a position where it protrudes into the transport path R when the paper P passes through the vicinity of the second paper detection sensor 83. Therefore, the second paper detection sensor 83 can detect the upstream end Ea of the paper P conveyed by the fixing unit 80. The second paper detection sensor 83 functions as one of the second detection means in the present invention.

  The paper discharge unit 90 is disposed on a conveyance path R extending from the fixing unit 80 toward the paper discharge tray 13 and includes a plurality of rollers 92. Each roller 92 is disposed along a transport path R downstream of the fixing unit 80 in the transport direction D, and the paper P that has passed through the fixing unit 80 is directed toward the paper discharge tray 13 along the transport path R. Transport. The paper P on which the toner image has been thermally fixed is discharged out of the main body housing 10 by the roller 92 and stored in the paper discharge tray 13.

  Next, printing on the paper P in the laser printer 1 will be described. When printing on the paper P is performed, first, the surface of each photosensitive drum 53 is uniformly charged by the charger 54. Thereafter, the surface of each photosensitive drum 53 is exposed by LED light emitted from each LED unit 40. Thereby, an electrostatic latent image based on the image data is formed on each photosensitive drum 53.

  The toner in the toner storage chamber 66 is supplied to the developing roller 63 by the rotation of the supply roller 64. The toner enters between the developing roller 63 and the layer thickness regulating blade by the rotation of the developing roller 63 and is carried on the developing roller 63 as a thin layer having a constant thickness. The toner carried on the developing roller 63 is supplied onto the photosensitive drum 53 when the developing roller 63 comes into contact with the surface of the photosensitive drum 53. As a result, the toner is selectively carried on the photosensitive drum 53 and the electrostatic latent image is visualized. That is, a toner image is formed on the photosensitive drum 53 by reversal development.

  When the paper P fed by the paper feeding unit 20 passes between the photosensitive drum 53 and the transfer roller 74 by the driving of the transport belt 73, the toner image formed on each photosensitive drum 53 becomes the paper P. Transcribed above. In other words, the laser printer 1 transfers the toner images of the respective colors on the paper P in the order of black, yellow, magenta, and cyan while conveying the paper P by the belt unit 70. The laser printer 1 can form a color image on the paper P by superimposing the toner images of the respective colors without deviation. The toner image transferred onto the paper P is heat-fixed on the paper P as the paper P passes between the heating roller 81 and the pressure roller 82. Thereafter, the paper P on which the image is thermally fixed is conveyed by the paper discharge unit 90 and discharged onto the paper discharge tray 13.

  Next, the configuration of the control system in the laser printer 1 according to the present embodiment will be described in detail with reference to FIG. As shown in FIG. 2, the laser printer 1 has a control unit 15. The control unit 15 includes a CPU, a ROM, and a RAM, and performs various controls of the laser printer 1. The ROM stores various data and control programs necessary for controlling the laser printer 1. The control program stored in the ROM includes a conveyance speed adjustment processing program (see FIG. 3) described later.

  As shown in FIG. 2, the control unit 15 is connected to the paper feeding unit 20, the image forming unit 30, the belt unit 70, and the fixing unit 80. Therefore, the control unit 15 can perform image formation on the paper P by controlling the paper feeding unit 20, the image forming unit 30, the belt unit 70, and the fixing unit 80 in accordance with a known image forming processing program. The control unit 15 can form a detection pattern on the outer surface of the conveyance belt 73 by controlling the image forming unit 30. Further, the control unit 15 controls the image forming unit 30 in accordance with a conveyance speed control program (see FIG. 3) to be described later, so that the first detection pattern Ma, the first detection pattern Ma, and the like are within a predetermined range such as the outer surface of the conveyance belt 73. 2 The detection pattern Mb can be formed (see FIG. 8).

  The control unit 15 is connected to the first paper detection sensor 26 and the second paper detection sensor 83. Accordingly, the control unit 15 detects the detection timing of the upstream end Ea of the paper P conveyed by the paper supply unit 20 and the detection of the downstream end Eb of the paper P based on the detection signal from the first paper detection sensor 26. The time can be specified. Similarly, the control unit 15 detects the detection timing of the upstream end Ea of the paper P conveyed by the fixing unit 80 and the detection of the downstream end Eb of the paper P based on the detection signal from the second paper detection sensor 83. The time can be specified.

  Further, the control unit 15 is connected to a registration sensor 75 located below the belt unit 70. Therefore, the control unit 15 can perform control related to the positional deviation and density correction during image formation based on the detection pattern detection signal from the registration sensor 75. Further, the control unit 15 can specify the detection timing of the first detection pattern Ma and the detection timing of the second detection pattern Mb based on the detection signal from the registration sensor 75.

  Next, the conveyance speed adjustment processing program of the laser printer 1 according to the present embodiment will be described in detail with reference to FIG. The conveyance speed adjustment processing program is executed by the control unit 15 when a predetermined operation is performed at the time of shipment adjustment of the laser printer 1 or maintenance work by the user. In the following description, it is assumed that the laser printer 1 stores the sheets P in the sheet feeding tray 21 in a stacked state.

  As shown in FIG. 3, when the execution of the conveyance speed adjustment processing program is started, the control unit 15 first executes a required conveyance time detection process (S1). In the required conveyance time detection process, the control unit 15 conveys one sheet P along the conveyance path R from the paper feed tray 21 to the paper discharge tray 13, so that the paper feed unit conveyance required time Ta, the belt The required conveyance time Tb and the fixing portion conveyance required time Tc are measured. The control unit 15 stores the paper feed unit conveyance time Ta, the belt conveyance time Tb, and the fixing unit conveyance time Tc in the RAM of the control unit 15, and then proceeds to S2.

  Here, the specific content of the conveyance time detection process (S1) will be described in detail with reference to FIGS. The transport direction D means a direction from the paper feed tray 21 toward the paper discharge tray 13 between the image forming unit 30 and the belt unit 70 via the fixing unit 80 along the transport path R. . Further, in the paper P that is transported in the transport time detection process (S1), the end on the upstream side in the transport direction D (that is, the paper feed tray 21 side) is referred to as “upstream end Ea”, and the downstream in the transport direction D That is, the end on the paper discharge tray 13 side is referred to as “downstream end Eb”. Further, the paper P has a paper length L as a dimension in the direction along the transport direction D.

  In the required conveyance time detection process (S1), first, the control unit 15 controls the paper supply unit 20 to transfer one sheet P from the paper supply tray 21 in the conveyance direction D along the conveyance path R. Transport. Along with the conveyance by the paper supply unit 20, the paper P moves in the conveyance direction D with the downstream end Eb at the head.

  As shown in FIG. 4, when a predetermined amount of paper P is transported from the paper feed tray 21 along the transport path R, the downstream end Eb of the paper P comes into contact with the first paper detection sensor 26. Since the paper P is continuously conveyed downstream in the conveyance direction D, the first paper detection sensor 26 rotates in a predetermined direction by contact with the paper P and outputs a detection signal to the control unit 15. To do. Therefore, the control unit 15 can specify the time point when the downstream end Eb of the paper P passes the first paper detection sensor 26 based on the detection signal of the first paper detection sensor 26.

  When the downstream end Eb of the paper P comes into contact with the first paper detection sensor 26 and the paper P is transported along the transport path R by a transport amount corresponding to the paper length L, the upstream end Ea of the paper P is Passes the first paper detection sensor 26 (see FIG. 5). At this time, the first sheet detection sensor 26 is released from the contact with the sheet P conveyed along the conveyance path R, and returns to a state where the first sheet detection sensor 26 protrudes on the conveyance path R from the state rotated in a predetermined direction. Therefore, the control unit 15 can specify the time point when the upstream end Ea of the paper P passes through the first paper detection sensor 26 based on the detection signal of the first paper detection sensor 26.

  That is, the control unit 15 can specify the time when the downstream end Eb and the upstream end Ea of the paper P have passed through the first paper detection sensor 26 based on the detection signal from the first paper detection sensor 26. That is, the control unit 15 specifies “the time required for the paper P having the paper length L to pass through the first paper detection sensor 26 by the conveyance by the paper feeding unit 20”, and the paper feeding unit conveyance time It can be stored in RAM as Ta.

  In the required transport time detection process (S1), the control unit 15 determines that the downstream end Eb of the paper P has a predetermined position on the upstream side in the vicinity of the photosensitive drum 53 of the predetermined process cartridge 50 (for example, the black process cartridge 50). At the time of passing, the formation of the second detection pattern Mb is started. Specifically, the control unit 15 conveys the sheet P by the belt unit 70 until the downstream end Eb of the sheet P passes a predetermined position on the downstream side of the photosensitive drum 53, and the outer surface of the conveyance belt 73 and the surface. The black toner image is transferred to the second range Ab including a part of the paper P. Accordingly, the second detection pattern Mb is formed on the outer surface of the paper P and the conveyance belt 73 included in the second range Ab (see FIG. 8).

  Further, when the upstream end Ea of the paper P passes a predetermined position on the upstream side in the vicinity of the photosensitive drum 53 of the predetermined process cartridge 50 (for example, the black process cartridge 50), the control unit 15 performs the first detection. The formation of the pattern Ma is started. Specifically, the controller 15 conveys the sheet P by the belt unit 70 until the upstream end Ea of the sheet P passes a predetermined position downstream of the photosensitive drum 53, and the outer surface of the conveyance belt 73 and the surface. The black toner image is transferred to the first range Aa including a part of the paper P. Thus, the first detection pattern Ma is formed on the surface of the paper P and the outer surface of the conveyance belt 73 included in the first range Aa (see FIG. 8).

  Here, in the belt unit 70, an endless conveyance belt 73 is stretched between the driving roller 71 and the driven roller 72, and the conveyance belt 73 is rotated in a predetermined direction (see FIG. 1 in a counterclockwise direction). The belt unit 70 can transport the paper P in the transport direction D between the image forming unit 30 and the belt unit 70 as the transport belt 73 circulates. In the rear portion of the belt unit 70, the paper P is transported toward the second paper detection sensor 83 and the fixing unit 80, while the transport belt 73 moves along the circumferential surface of the drive roller 71. That is, the paper P on which the first detection pattern Ma and the second detection pattern Mb are formed is removed from the outer surface of the conveyance belt 73.

  As shown in FIG. 9, when the paper P is removed from the outer surface of the transport belt 73, the first detection pattern Ma and the second detection pattern Mb are only portions formed on the outer surface of the transport belt 73. That is, after the paper P is transported from the belt unit 70 to the fixing unit 80, the first detection pattern Ma is a portion of the first range Aa on the upstream side in the transport direction D with the upstream end Ea of the paper P as a boundary (that is, , A portion formed on the outer surface of the conveyor belt 73. Similarly, the second detection pattern Mb is a portion on the downstream side in the transport direction D with respect to the downstream end Eb of the paper P in the second range Ab (that is, a portion formed on the outer surface of the transport belt 73). .

  As described above, the conveyance belt 73 circulates between the driving roller 71 and the driven roller 72 by conveying the paper P in the conveyance direction D. Therefore, as the paper P is transported, first, the second detection pattern Mb on the transport belt 73 moves along the circumferential surface of the drive roller 71 and passes through the detection range of the registration sensor 75. At this time, the registration sensor 75 outputs a detection signal to the control unit 15 based on the presence / absence of the second detection pattern Mb on the outer surface of the conveyance belt 73. As a result, the control unit 15 detects the upstream boundary of the second detection pattern Mb (that is, the position corresponding to the downstream end Eb of the paper P) based on the detection signal of the registration sensor 75, and thereby the second detection pattern Mb. The timing when the upstream boundary of the detection pattern Mb passes the detection range of the registration sensor 75 can be specified.

  When the second detection pattern Mb on the transport belt 73 passes through the detection range of the registration sensor 75, the first detection pattern Ma on the transport belt 73 further transports the paper P in the transport direction D. , Passing through the detection range of the registration sensor 75. At this time, the registration sensor 75 outputs a detection signal to the control unit 15 based on the presence / absence of the first detection pattern Ma on the outer surface of the conveyance belt 73. As a result, the control unit 15 detects the downstream boundary of the first detection pattern Ma (that is, the position corresponding to the upstream end Ea of the paper P) based on the detection signal of the registration sensor 75, and thereby the first detection pattern Ma. The timing at which the downstream boundary of the detection pattern Ma passes the detection range of the registration sensor 75 can be specified.

  Therefore, the control unit 15 can specify the time when the downstream boundary of the first detection pattern Ma and the upstream boundary of the second detection pattern Mb have passed through the registration sensor 75 based on the detection signal from the registration sensor 75. . Here, as shown in FIGS. 8 and 9, the downstream boundary of the first detection pattern Ma corresponds to the position of the upstream end Ea of the paper P, and the upstream boundary of the second detection pattern Mb is the paper. This corresponds to the position of the downstream end Eb of P. The distance between the downstream boundary of the first detection pattern Ma and the upstream boundary of the second detection pattern Mb is the sheet length of the sheet P when the first detection pattern Ma and the second detection pattern Mb are formed. Corresponds to L. That is, the control unit 15 can specify “the time required for the conveyance belt 73 to circulate and move a distance corresponding to the paper length L of the paper P by driving the belt unit 70”. In other words, the control unit 15 specifies “the time required for the paper P having the paper length L to pass through a predetermined position in the belt unit 70 by the conveyance by the belt unit 70”, and the belt conveyance time Tb. Can be stored in the RAM.

  When the paper P on which the first detection pattern Ma and the second detection pattern Mb are formed is transported further from the belt unit 70 toward the downstream side in the transport direction D, the downstream end Eb of the paper P is It contacts the second paper detection sensor 83 (see FIG. 6). Then, since the paper P is continuously conveyed in the conveyance direction D by the fixing unit 80 or the like, the second paper detection sensor 83 rotates in a predetermined direction by contact with the paper P, and the detection signal is transmitted to the control unit. 15 is output. Accordingly, the control unit 15 can specify the time point when the downstream end Eb of the paper P passes through the second paper detection sensor 83 based on the detection signal of the second paper detection sensor 83.

  When the downstream end Eb of the sheet P comes into contact with the second sheet detection sensor 83 and the sheet P is conveyed by a conveyance amount corresponding to the sheet length L, the upstream end Ea of the sheet P is moved to the second sheet detection sensor 83. (See FIG. 7). At this time, the second paper detection sensor 83 is released from the contact with the paper P, and returns from the state rotated in a predetermined direction to the state protruding on the transport path R. Accordingly, the control unit 15 can specify the time when the upstream end Ea of the paper P passes the second paper detection sensor 83 based on the detection signal of the second paper detection sensor 83.

  Therefore, the control unit 15 can specify the time when the downstream end Eb and the upstream end Ea of the paper P pass through the second paper detection sensor 83 based on the detection signal from the second paper detection sensor 83. That is, the control unit 15 specifies “the time required for the paper P having the paper length L to pass through the second paper detection sensor 83 by the conveyance by the fixing unit 80”, and the fixing unit conveyance time Tc. Can be stored in the RAM. Thereafter, the sheet P is transported on the transport path R in the transport direction D by the fixing unit 80 and discharged to the paper discharge tray 13.

  As described above, the paper feed unit conveyance time Ta, the belt conveyance time Tb, and the fixing unit conveyance time Tc all indicate “time required to move the distance corresponding to the paper length L”. Therefore, the paper feed unit transport time Ta corresponds to the transport speed of the paper P by the paper feed unit 20, and the belt transport time Tb and the fixing unit transport time Tc are respectively the transport speed of the paper P by the belt unit 70. This corresponds to the conveyance speed of the paper P by the fixing unit conveyance time Tc. Also, the paper feed unit transport time Ta, the belt transport time Tb, and the fixing unit transport time Tc indicate the time required to move the same distance (paper length L). You can compare.

  The control unit 15 can specify “time” based on the paper feed unit conveyance time Ta, the belt conveyance time Tb, and the fixing unit conveyance time Tc, and can also specify the “distance” of the paper length L. Therefore, the conveyance speed of the paper P by the paper supply unit 20, the conveyance speed of the paper P by the belt unit 70, and the conveyance speed of the paper P by the fixing unit 80 can be calculated.

  Returning to FIG. 3 again, the conveyance speed adjustment processing program will be described. In S2, the control unit 15 executes a difference value calculation process. In the difference value calculation process (S2), the control unit 15 is based on the paper feed unit conveyance time Ta, the belt conveyance time Tb, and the fixing unit conveyance time Tc detected and measured in the conveyance time detection process (S1). Thus, the first difference value Da and the second difference value Db are calculated.

  Specifically, the control unit 15 subtracts the belt conveyance time Tb from the paper feed unit conveyance time Ta to calculate the first difference value Da. The first difference value Da corresponds to the difference between the conveyance speed of the paper P by the paper supply unit 20 and the conveyance speed of the paper P by the belt unit 70. Further, the control unit 15 subtracts the fixing unit conveyance time Tc from the belt conveyance time Tb to calculate the second difference value Db. The second difference value Db corresponds to the difference between the conveyance speed of the paper P by the belt unit 70 and the conveyance speed of the paper P by the fixing unit 80. Then, the control part 15 stores 1st difference value Da and 2nd difference value Db in RAM, and transfers a process to S3.

  In S3, the control unit 15 compares the difference values (first difference value Da and second difference value Db) calculated in the difference value calculation process (S2) with the reference values stored in the ROM. The reference value includes a difference in conveyance speed between the units necessary for causing a predetermined amount of bending in the sheet P conveyed between the units (the paper feeding unit 20, the belt unit 70, the fixing unit 80), and each unit. It is defined based on the distance along the transport path R between.

  That is, in S3, the control unit 15 compares the first difference value Da with the reference value, and determines that “the sheet conveyance speed in the sheet feeding unit 20 is larger than the conveyance speed in the belt unit 70, and the conveyance of the two is performed. It is determined whether or not the speed difference is within a predetermined reference range. Further, the control unit 15 compares the second difference value Db with the reference value, and “the sheet conveyance speed in the belt unit 70 is larger than the conveyance speed in the fixing unit 80, and the difference between the two conveyance speeds is predetermined. It is determined whether or not it is within the reference range. In other words, the control unit 15 is transported between the belt unit 70 and the fixing unit 80 and “whether or not an appropriate amount of bending occurs in the paper P transported between the paper feeding unit 20 and the belt unit 70”. Whether or not an appropriate amount of bending occurs in the paper P to be printed is determined. When the difference value is equal to or larger than the reference value (S3: YES), the control unit 15 shifts the process to S4. When the difference value is less than the reference value (S3: NO), the control unit 15 ends the conveyance speed adjustment processing program.

  If transfering to S4, the control part 15 will perform a conveyance speed adjustment process. In the transport speed adjustment process (S4), the control unit 15 performs the transport speed and fixing of the paper P in the paper feed unit 20 based on the paper feed unit transport time Ta, the belt transport time Tb, and the fixing unit transport time Tc. The conveyance speed of the paper P in the unit 80 is adjusted. Thereafter, the control unit 15 ends the conveyance speed adjustment processing program.

  Specifically, in the conveyance speed adjustment process (S4), the control unit 15 adjusts the conveyance speed of the paper P in the paper supply unit 20 to be faster than the conveyance speed of the paper P in the belt unit 70 by a predetermined value. . By adjusting in this way, when the paper P is transported between the paper feeding unit 20 and the belt unit 70, the paper P is caused by a difference in transport speed between the paper feeding unit 20 and the belt unit 70. Thus, an appropriate amount of bending occurs. As a result, the laser printer 1 can cause an appropriate amount of bending of the paper P transported between the paper feeding unit 20 and the belt unit 70, so that the color image is superimposed on the paper P by superimposing the images of the respective colors. When forming, it is possible to prevent the image of each color from being shifted. In addition, since the laser printer 1 causes the paper P to bend an appropriate amount, the paper P is jammed in the transport path R on the upstream side of the belt unit 70, unlike when the large deflection is applied to the paper P. This can be prevented.

  In the conveyance speed adjustment process (S4), the control unit 15 adjusts the conveyance speed of the paper P in the fixing unit 80 to be slower than the conveyance speed of the paper P in the belt unit 70 by a predetermined value. By adjusting in this way, when the paper P is transported between the belt unit 70 and the fixing unit 80, the paper P is caused by a difference in transport speed between the belt unit 70 and the fixing unit 80. An appropriate amount of bending will occur. As a result, the laser printer 1 can cause an appropriate amount of bending of the paper P conveyed between the belt unit 70 and the fixing unit 80, so that a color image is formed by superimposing the images of the respective colors on the paper P. In this case, it is possible to prevent the image of each color from being shifted. In addition, since the laser printer 1 causes the paper P to bend an appropriate amount, the paper P is jammed in the transport path R on the upstream side of the fixing unit 80, unlike when the large deflection is applied to the paper P. This can be prevented.

  As described above, the laser printer 1 according to this embodiment includes the paper feeding unit 20, the image forming unit 30, the belt unit 70, and the fixing unit 80, and transports the paper P along the transport path R in the transport direction D. A color image can be formed by superimposing the images of the respective colors on the paper P while being conveyed to the paper.

  Further, the laser printer 1 has a first paper detection sensor 26 that detects the upstream end Ea and the downstream end Eb of the paper P on the transport path R from the paper supply unit 20 toward the belt unit 70. The laser printer 1 executes the conveyance speed adjustment processing program by the control unit 15, so that “the paper P having the paper length L is fed by the paper feeding unit 20 based on the detection signal from the first paper detection sensor 26. The time required for passing through the first paper detection sensor 26 by the transport (the time required for transporting the paper feed unit Ta) can be specified.

  Then, the laser printer 1 executes a conveyance speed adjustment processing program by the control unit 15, whereby the first range Aa including the upstream end Ea of the paper P being conveyed on the conveyance belt 73, and the downstream of the paper P. A first detection pattern Ma and a second detection pattern Mb are formed in the second range Ab including the end Eb, respectively. In the laser printer 1, the registration sensor 75 detects the first detection pattern Ma and the second detection pattern Mb with the paper P removed from the transport belt 73. Therefore, the laser printer 1 determines that the sheet unit P having the sheet length L is conveyed by the belt unit 70 based on the detection signals of the first detection pattern Ma and the second detection pattern Mb by the registration sensor 75. The time required for passing through a predetermined position at 70 (belt conveyance time Tb) can be specified.

  Further, the laser printer 1 has a second paper detection sensor 83 that detects the upstream end Ea and the downstream end Eb of the paper P on the transport path R from the belt unit 70 to the fixing unit 80. The laser printer 1 executes the conveyance speed adjustment processing program by the control unit 15, so that “the sheet P having the sheet length L is conveyed by the fixing unit 80 based on the detection signal from the second sheet detection sensor 83. By this, it is possible to specify “the time required for passing through the second paper detection sensor 83 (fixed portion conveyance time Tc)”.

  Then, the laser printer 1 calculates the first difference value Da based on the paper feed unit conveyance time Ta and the belt conveyance time Tb (S2), and compares the first difference value Da with the reference value. Then, it is determined whether or not “a proper amount of bending occurs in the sheet P conveyed between the sheet feeding unit 20 and the belt unit 70” (S3). If it is out of the proper range for the paper P, the laser printer 1 controls the paper feed mechanism 22 in the paper feed unit 20 to control the conveyance speed of the paper P in the paper feed unit 20. It is adjusted so as to be faster than the transport speed by a predetermined value. As a result, when the paper P is transported between the paper feed unit 20 and the belt unit 70, the paper P has an appropriate amount due to the difference in transport speed between the paper feed unit 20 and the belt unit 70. Deflection occurs. As a result, when the laser printer 1 forms a color image by superimposing the image of each color on the paper P, it can prevent the image of each color from being shifted. Further, since the laser printer 1 causes the paper P to bend an appropriate amount, the paper P is jammed in the transport path R on the upstream side of the belt unit 70 as in the case where the large deflection is applied to the paper P. This can be prevented.

  Then, the laser printer 1 calculates the second difference value Db based on the belt conveyance time Tb and the fixing unit conveyance time Tc (S2), and compares the second difference value Db with the reference value. , “Whether or not an appropriate amount of bending occurs in the sheet P conveyed between the belt unit 70 and the fixing unit 80” is determined (S3). When it is out of the proper range for the paper P, the laser printer 1 controls the heating speed of the heating roller 81 and the like in the fixing unit 80 to control the transport speed of the paper P in the fixing unit 80 and the transport of the paper P in the belt unit 70. The speed is adjusted to be slower than the speed by a predetermined value. Thus, when the paper P is transported between the belt unit 70 and the fixing unit 80, the paper P is subjected to an appropriate amount of bending due to the difference in transport speed between the belt unit 70 and the fixing unit 80. Arise. As a result, when the laser printer 1 forms a color image by superimposing the image of each color on the paper P, it can prevent the image of each color from being shifted. Further, since the laser printer 1 causes the paper P to bend an appropriate amount, the paper P is jammed in the transport path R on the upstream side of the fixing unit 80 as in the case where the large deflection is applied to the paper P. This can be prevented.

  Further, in the laser printer 1, the first detection pattern Ma and the second pattern on the conveyor belt 73 are used by using the registration sensor 75 that is used for density adjustment related to image formation on the paper P and for correcting the deviation of the superimposed image. The detection pattern Mb is detected, and the belt conveyance time Tb is measured. Therefore, according to the laser printer 1, it is not necessary to provide a dedicated sensor or the like for measuring the belt conveyance time Tb, and a color image is formed by superimposing the images of each color on the paper P with a small number of components. In this case, it is possible to prevent the image of each color from being shifted.

  Although the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. For example, in the present embodiment, the laser printer 1 is configured to directly transfer the toner image on the surface of the photosensitive drum 53 onto the paper P conveyed on the conveyance belt 73, but the present invention is limited to this mode. It is not a thing. For example, it is possible to adopt an intermediate transfer method in which the toner image on the surface of the photosensitive drum 53 is transferred to the surface of the conveying belt 73 and then transferred again from the surface of the conveying belt 73 to the paper P.

  In the present embodiment, the first paper detection sensor 26 and the second paper detection sensor 83 are mechanical sensors provided with actuators that protrude on the conveyance path R, but the present invention is not limited to this mode. . In other words, the first sheet detection sensor 26 and the second sheet detection sensor 83 may employ various sensors as long as they can detect the upstream end Ea and the downstream end Eb of the sheet P transported on the transport path R. obtain. If an optical sensor or the like is employed, the upstream end Ea and the downstream end Eb of the paper P can be detected with higher accuracy. Further, the arrangement positions of the first paper detection sensor 26 and the second paper detection sensor 83 are not limited to the positions in the above-described embodiment, and are arranged as close as possible to the paper feed unit 20 and the fixing unit 80. It is desirable.

DESCRIPTION OF SYMBOLS 1 Laser printer 10 Main body housing | casing 20 Paper feed part 22 Paper supply mechanism 26 1st paper detection sensor 30 Image formation part 70 Belt unit 75 Registration sensor 80 Fixing unit 83 2nd paper detection sensor P Paper Ma 1st detection pattern Mb 2nd Detection pattern

Claims (7)

The main body housing,
Each of the plurality of colors has a photosensitive drum on which an electrostatic latent image corresponding to any one of a plurality of colors used for image formation is formed, and the plurality of photosensitive drums are arranged in one direction in the main body housing. An arranged image forming unit;
The image forming unit is provided with an endless conveying belt disposed at a position facing each photosensitive drum and having a surface facing each photosensitive drum, and a sheet on which an image is formed is driven by driving the conveying belt. A belt unit for conveying in a predetermined conveying direction;
An image forming apparatus having a conveyance roller disposed along a predetermined conveyance path in which the sheet is conveyed in the main body casing and conveying the sheet along the conveyance path;
An upstream end positioned on the upstream side in the transport direction of the paper on the transport belt, a predetermined first range including a transport belt surface adjacent to the upstream end, and a downstream end positioned on the downstream side in the transport direction of the paper And pattern forming means for forming a detection pattern for the second range including the surface of the conveyor belt adjacent to the downstream end,
After the sheet on which the detection pattern is formed by the pattern forming unit is conveyed from the belt unit in a predetermined conveyance direction, the interval between the detection patterns remaining in the first range and the second range on the surface of the conveyance belt is set. First detecting means for measuring a first passing time required for the paper to pass through the belt unit by detecting;
Second detection means for measuring a second passage time required for the paper to pass through the transport roller by detecting an upstream end and a downstream end of the paper transported by the transport roller;
Based on the first passage time detected by the first detection means and the second passage time detected by the second detection means, the paper conveyance speed by the belt unit and the paper conveyance speed by the conveyance roller. An image forming apparatus comprising: a conveyance speed adjusting unit configured to adjust a conveyance speed of the sheet by the conveyance rollers so that a predetermined speed difference is generated between the two. The image forming apparatus according to claim 1,
The transport speed adjusting means is
Based on the first passage time detected by the first detection means and the second passage time detected by the second detection means,
The upstream side of the transport direction has a higher paper transport speed, and a predetermined speed difference is generated between the transport speed of the paper by the belt unit and the transport speed of the paper by the transport roller. An image forming apparatus, wherein the sheet conveyance speed is automatically adjusted. The image forming apparatus according to claim 1, wherein:
The transport speed adjusting means is
Determining whether or not it is necessary to adjust the conveyance speed of the sheet by the conveyance roller by comparing the difference value between the first passage time and the second passage time with a reference value based on the speed difference. An image forming apparatus. An image forming apparatus according to any one of claims 1 to 3,
The transport roller is
An image forming apparatus, wherein the image forming apparatus is disposed upstream of the belt unit in a conveyance direction of the sheet and feeds the sheet to the belt unit by being driven to rotate. An image forming apparatus according to any one of claims 1 to 3,
The transport roller is
The image forming apparatus is disposed downstream of the belt unit in the conveyance direction of the sheet, and rotates to convey the sheet conveyed through the belt unit to the downstream side in the conveyance direction. apparatus. An image forming apparatus according to any one of claims 1 to 3,
The transport roller is
A first transport roller that is disposed upstream of the belt unit in the transport direction of the paper and that rotates and supplies the paper to the belt unit;
A second transport roller that is disposed downstream of the belt unit in the transport direction of the paper and that rotates and transports the paper transported through the belt unit to the downstream side of the transport direction;
The transport speed adjusting means is
Adjusting the conveyance speed of the paper by the first conveyance roller so that a predetermined speed difference occurs between the conveyance speed of the paper by the belt unit and the conveyance speed of the paper by the first conveyance roller;
The paper transport speed of the second transport roller is adjusted so that a predetermined speed difference is generated between the paper transport speed of the belt unit and the paper transport speed of the second transport roller. An image forming apparatus. An image forming apparatus according to any one of claims 1 to 6,
The first detection means includes
An image forming apparatus comprising: a detection sensor that detects a density of an image formed by the image forming unit and a shift of each image when the images of a plurality of colors are superimposed.

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