JP2015196547A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align sheets even if load for conveyance of the sheets varies during control of alignment of the sheets.SOLUTION: An image forming apparatus includes: second transfer rollers 229; register rollers 240; a register sensor 241 for detecting arrival of a recording medium; conveying rollers 239; a motor 300 for driving the register rollers 240 and the conveying rollers 239; and a printer controller 303. The printer controller 303 controls the motor 300 to vary a speed of conveyance of the recording medium by the register rollers 240 (S108) on the basis of information on timing of detection of the recording medium by the register sensor 241 (S104) and information on a variation in load for conveyance in the register rollers 240 (S106).

Description

  The present invention relates to an image forming apparatus, and more particularly to sheet conveyance control.

  In a printer that is one of image forming apparatuses using electrophotographic technology, it is necessary to accurately superimpose a sheet conveyed on a conveyance path on an image generated through an image forming process. For this reason, a motor for driving the paper and a conveyance control of the paper require a highly accurate alignment function. As a sheet alignment control method, there is a method in which a sensor that detects the passage of a sheet is disposed on the conveyance path, and the position of the sheet is corrected based on the detection result. In this control method, the front end of the paper passing on the transport path is detected by a sensor, and the paper transport error (delay or advance from the ideal paper front end passage timing) is calculated from the detected timing. Then, the rotational speed of the motor that drives the transport roller that transports the paper is adjusted so as to cancel the calculated transport error, and the transport position of the paper is corrected until it is superimposed on the image (for example, Patent Documents). 1, see Patent Document 2).

  By executing this alignment control, the image can be transferred to an accurate position on the paper. Note that the above-described sensor placement positions are determined based on mechanical placement restrictions of the printer, the amount of paper transport error to be corrected, and the like. In addition, a plurality of the above-described sensors may be arranged, and the alignment correction may be performed multiple times. By using such a configuration and control method, a highly accurate alignment function is realized.

JP 2001-341898 A JP 2006-343726 A

  As described above, in the conventional alignment control, correction for the paper transport error is performed based on the paper passage timing detected by the sensor. However, for example, when the trailing edge of the sheet passes through the conveying roller that has held the sheet until the alignment correction is performed, or when the driving force of the conveying roller changes, there are the following problems. In other words, if the paper transport load fluctuates during the alignment correction for canceling the transport error, the paper registration correction amount changes before and after the transport load change, so that a new error occurs in the registration amount. There was a problem that occurred.

  The present invention has been made under such circumstances, and it is an object of the present invention to accurately align a sheet even if a variation in the sheet conveyance load occurs during sheet alignment control.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) A transfer unit that transfers an image formed on the image carrier to a recording material, a first conveyance unit that conveys the recording material to the transfer unit, and a conveyance path through which the recording material is conveyed, Detection means for detecting that the recording material has reached the first conveying means, second conveying means for conveying the recording material to the first conveying means, the first conveying means, and the second conveying means A drive unit that drives the conveyance unit; and a control unit that controls the drive unit. The control unit includes information on timing at which the detection unit detects the recording material, and a conveyance load in the first conveyance unit. And an image forming apparatus that controls the driving unit to change the conveyance speed of the recording material by the first conveyance unit based on the information related to the fluctuation of the recording medium.

  According to the present invention, it is possible to accurately align a sheet even if a variation in the sheet conveyance load occurs during the sheet alignment control.

Schematic sectional view and control block diagram of image forming apparatuses according to first to third embodiments Diagram for explaining speed transition and behavior of paper during conveyance in motor speed change control FIG. 6 is a diagram for explaining an alignment correction error in the first and third embodiments. 7 is a flowchart showing a control flow of motor shift control according to the first embodiment. FIG. 6 is a diagram illustrating the behavior of the leading edge of a sheet during conveyance according to the first exemplary embodiment. FIG. 6 is a diagram for explaining an alignment correction error in the second and third embodiments. 7 is a flowchart showing a control flow of motor shift control according to the second embodiment. FIG. 6 is a diagram illustrating the behavior of the leading edge of a sheet during conveyance according to the second exemplary embodiment. 7 is a flowchart showing a control flow of motor shift control according to the third embodiment. FIG. 10 is a diagram illustrating the behavior of the leading edge of a sheet during conveyance according to a third embodiment.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  In the first exemplary embodiment, during the alignment control of the recording material paper, the conveyance load torque fluctuates due to the trailing edge of the paper that is the target of the motor speed change control passing the conveyance roller (in this case, the conveyance load torque). Will be described. Hereinafter, the sheet alignment control is referred to as motor shift control.

<< Configuration of image forming apparatus >>
First, the configuration of an electrophotographic color image forming apparatus used in this embodiment will be described. FIG. 1A is a cross-sectional view of a tandem type color image forming apparatus employing an intermediate transfer member, and includes four colors, that is, yellow (Y), magenta (M), cyan (C), and black (K). Each image forming unit is provided. Further, each image forming unit includes a photosensitive drum, a charging unit, an exposure unit, and a developing unit. In FIG. 1A, Y, M, C, and K at the end of the code indicate yellow, magenta, cyan, and black, respectively. The configurations of the image forming units for the respective colors are the same, and Y, M, C, and K are omitted in the following description unless necessary.

  The charging unit as charging means includes a charger 223 for charging the photosensitive drum 222 for each color station, and the charger 223 includes a charging roller 223S. The photosensitive drum 222, which is an image carrier, has a configuration in which an organic optical transmission layer is applied to the outer periphery of an aluminum cylinder, and is driven by a motor (not shown). The photosensitive drum 222 rotates counterclockwise (in the direction of the arrow in the drawing) according to the image forming operation. An exposure unit as an exposure unit includes a laser scanner 224. The laser scanner 224 irradiates the photosensitive drum 222 with exposure light, and selectively exposes the surface of the photosensitive drum 222 to form an electrostatic latent image. The developing unit as a developing unit includes a developing device 226 for each color station in order to visualize the electrostatic latent image on the photosensitive drum 222 (on the image carrier). The developing device 226 supplies toner to the developing device. A toner container 225 to be sent out and a developing roller 226S are provided. Each developing device 226 can be detached.

  The transfer unit as a transfer unit applies a voltage to the primary transfer roller 227 and also makes a difference between the rotation speed of the photosensitive drum 222 and the rotation speed of the intermediate transfer belt 228 to transfer the toner image on the photosensitive drum 222 to the intermediate transfer member. Are transferred onto the intermediate transfer belt 228. This is called primary transfer. Further, the transfer unit as transfer means superimposes the toner image on the intermediate transfer belt 228 for each station, and conveys the superimposed multicolor toner image to the secondary transfer roller 229 as the intermediate transfer belt 228 rotates. The sheet 211 placed in the sheet feeding cassette 212 is fed and conveyed by a feeding roller 238 and a conveying roller 239 that use a motor 300 (FIG. 1B) as a driving source, and further uses the motor 300 as a driving source. The registration roller 240 is nipped and conveyed to the secondary transfer roller 229. At the time of transfer, a predetermined voltage is applied to the secondary transfer roller 229, whereby the toner image on the intermediate transfer belt 228 is transferred to the sheet 211. This is called secondary transfer.

  The secondary transfer roller 229 contacts the sheet 211 at the position P252 while transferring the toner image to the sheet 211, and is separated after the printing process. Whether or not the sheet 211 is conveyed at a desired timing is detected by the registration sensor 241. If it is not the desired timing, motor shift control for the sheet 211 described later is performed. Further, when the sheet 211 is not conveyed, various jams (for example, conveyance delay jam) are notified to a video controller (not shown). The paper 211 placed in the paper feed cassette 212 is fed at a desired timing by the paper feed roller 238, but slips when the surface of the paper feed roller 238 is worn and the paper 211 cannot be fed at the desired timing. There is. In such a case, motor shift control for the sheet 211 is performed.

  The fixing unit 231 as a fixing unit includes a fixing roller 232 that heats the paper 211 and a pressure roller 233 that presses the paper 211 against the fixing roller 232 in order to melt and fix the toner image transferred to the paper 211 on the paper 211. It has. The fixing unit 231 sandwiches and conveys the sheet 211 holding the toner image between the fixing roller 232 and the pressure roller 233 and applies heat and pressure to fix the toner image on the sheet 211. The sheet 211 after the toner image is fixed is then discharged to a discharge tray (not shown) by a discharge roller (not shown), and the image forming operation ends. The cleaning unit 230 cleans toner remaining on the intermediate transfer belt 228 without being transferred to the sheet 211, and waste toner collected by cleaning is stored in a cleaner container (not shown).

  The paper feed roller 238 feeds the paper 211 placed on the paper feed cassette 212. A transport roller 239 as a second transport unit transports the paper 211 fed from the paper feed cassette 212 to the paper transport path. A registration roller 240 serving as a first transport unit sandwiches and transports the sheet 211 transported by the transport roller 239 to a secondary transfer roller 229 serving as a transfer unit. A registration sensor 241 provided on the conveyance path of the sheet 211 detects the passage of the sheet 211.

  A position P250 at which the registration sensor 241 serving as a detection unit is disposed indicates a start position of the motor shift control, and a position P251 provided downstream in the sheet transport direction indicates an end position (end point) of the motor shift control. A position P252 where the secondary transfer roller 229 and the intermediate transfer belt 228 contact each other indicates a secondary transfer position. In this embodiment, the paper feed roller 238, the transport roller 239, and the registration roller 240 are driven by the same motor 300 (FIG. 1B to be described later) that is a driving unit. Further, transmission / cutoff of the driving force to the paper feed roller 238 and the transport roller 239 is switched by an electromagnetic clutch (not shown). The motor speed change control is performed by adjusting the rotational speed of the motor 300 that drives the registration roller 240 in the section L243 from the position P250 to the position P251, and the adjustment method will be described later.

≪Printer control part≫
Next, the printer control unit and its operation in this embodiment will be described. FIG. 1B is a diagram illustrating a configuration of a control IC 302 that controls the printer of this embodiment. The control IC 302 is configured by a one-chip microcomputer or the like, and controls various operations of the printer. The control IC 302 includes a host I / F (interface) unit 310, a RAM 308, a ROM 307, a printer control unit 303, an image formation control unit 304, and a paper conveyance control unit 305. In addition, the printer control unit 303, the image formation control unit 304, and the paper conveyance control unit 305 have a timer function.

  The host I / F unit 310 communicates with a host computer (hereinafter simply referred to as a host) that is an external device such as a personal computer (hereinafter referred to as a PC) that transmits a print request or image data. The RAM 308 temporarily stores image data, paper type information, control data necessary for printer operation control, and the like. A ROM 307, which is a non-volatile storage unit, stores tables and data necessary for microcomputer programs and printer operation control. The printer control unit 303 controls image forming processing by an electrophotographic process, paper transport processing, and the like according to a print request from the host. In response to an instruction to start image formation processing from the printer control unit 303, the image formation control unit 304 performs laser control for forming an electrostatic latent image, high-pressure control for developing the electrostatic latent image with toner, and the like. Do. The paper conveyance control unit 305 receives the image forming process start instruction from the printer control unit 303 and performs conveyance control of the paper 211.

  Further, the registration sensor 241 detects the paper on the conveyance path and notifies the printer control unit 303 of it. The motor driver IC 301 supplies power to the motor 300 in response to a drive instruction from the paper transport control unit 305. The motor 300 is a drive source for the paper feed roller 238, the transport roller 239, and the registration roller 240 that transport the paper 211. In addition to the motor 300, the sheet conveyance control unit 305 also controls a motor (not shown) that drives the intermediate transfer belt 228 and the fixing unit 231.

  Next, the operation of the printer control unit 303 during image formation will be described. When the printer control unit 303 receives a print request from the PC via the host I / F unit 310, the printer control unit 303 stores the image data received from the PC and information about the recording material such as the paper size and paper type in the RAM 308. Then, the printer control unit 303 instructs the image formation control unit 304 to start an image formation process and instructs the sheet conveyance control unit 305 to start conveying a sheet at a predetermined timing. The image formation control unit 304 converts the image data stored in the RAM 308 into raster data suitable for the image output format by the laser scanner 224, and then performs laser light emission control and development so that latent images, development, and transfer are sequentially performed. High pressure control accompanying, high pressure control accompanying transfer.

  On the other hand, the sheet conveyance control unit 305 sequentially transmits drive instructions to the motor driver IC 301 so as to rotate the motor 300 at a desired speed. When the motor driver IC 301 receives a driving instruction from the paper conveyance control unit 305, the motor driver IC 301 supplies power corresponding to the driving instruction to the motor 300. On the other hand, the motor 300 starts rotating by the power supply from the motor driver IC 301, and the sheet 211 is transported on the transport path. Thereafter, the sheet 211 conveyed on the conveyance path reaches a position P250 where the registration sensor 241 is disposed. When the registration sensor 241 detects that the leading edge of the sheet 211 has arrived, the registration sensor 241 notifies the printer control unit 303 of the detection result. The printer control unit 303 determines whether the paper 211 is transported or transported at a time ΔTr based on the paper arrival timing from the registration sensor 241 and the image formation processing status executed by the image formation control unit 304. Ask for. Further, the printer control unit 303 calculates an alignment correction amount ΔDr that is a shift amount based on the conveyance delay or the conveyance advance time ΔTr.

  When the printer control unit 303 determines that a change in the transport load torque occurs during the motor shift control, the timing at which the change in the transport load torque occurs and the alignment error amount corresponding to the change amount are stored in the ROM 307. Obtained from the alignment error amount table 309. As will be described later, the alignment error amount table 309 (hereinafter referred to as the error amount table 309) has a plurality of tables according to the types of associated data, and is stored in the ROM 307. The printer control unit 303 adds or subtracts the alignment error amount acquired from the error amount table 309 from the alignment correction amount ΔDr according to the increase / decrease of the alignment correction amount due to the conveyance load fluctuation torque. ΔD is calculated. Then, the printer control unit 303 shifts the speed correction information of the motor 300 corresponding to the alignment correction amount ΔD, that is, the change speed Vc and the execution time Tc of the motor 300 described later, a shift control information table 306 (third) Table). The printer control unit 303 transmits the speed correction information acquired from the shift control information table 306 to the paper transport control unit 305. The paper transport control unit 305 executes the shift control of the motor 300 based on the speed correction information received from the printer control unit 303. A shift control method and a method for calculating the alignment correction amount ΔD will be described later.

  When the motor shift control is executed, the sheet 211 is conveyed on the conveyance path at a timing synchronized with the toner image formed by the image formation control unit 304, and the toner image is transferred by the secondary transfer unit. The toner image is melted and fixed by the fixing unit 231. When the printing process is completed, the printer control unit 303 notifies the image formation control unit 304 and the sheet conveyance control unit 305 of the end of control. In the present embodiment, an example in which various controls such as motor and image formation are performed by a control unit configured by hardware such as an ASIC is described, but other means, for example, control by a program of a microcomputer may be used.

≪Motor shift control≫
Next, a description will be given of motor speed change control, which is paper position alignment control by the motor 300. FIG. 2A is a diagram illustrating an example of speed transition (conveyance delay correction) of the motor 300 during motor speed change control, where the horizontal axis represents time [unit: seconds] and the vertical axis represents motor speed [unit: mm / s]. The graph shown by the solid line in FIG. 2A shows the speed transition of the motor 300 when the motor shift control is executed, and the graph shown by the dotted line maintains the motor 300 at the steady rotational speed Vref, and the motor shift control. The speed transition of the motor 300 when not executing is shown. In FIG. 2A, the timing T10 indicates the start time of the motor shift control, and is also the time when the leading edge of the sheet 211 reaches the registration sensor 241 (the time when it reaches the position P250 (FIG. 1A)). Timing T11 indicates the time when the rotation speed of the motor 300 reaches the speed change rotation speed Vc, and timing T12 indicates the time when the control of returning the speed of the motor 300 from the speed change rotation speed Vc to the steady rotation speed Vref is started. Further, timing T13 indicates the time when the speed of the motor 300 returns to the steady rotational speed Vref, and is also the time when the leading edge of the sheet 211 reaches the end position P251 (FIG. 1A) of the motor shift control. As shown in FIG. 2A, the control of changing the rotation speed of the motor 300 is performed in a section L243 from the position P250 which is the start point to the position P251 which is the end point, and thereby the sheet 211 generated at the position P250. The conveyance delay is eliminated. Note that the speed Vc at the time of the motor shift control and the execution time Tc during which the motor shift control is performed differ depending on the alignment correction amount ΔD of the sheet 211. The change speed Vc and the execution time Tc, which are correction information at the time of motor shift control corresponding to the alignment correction amount ΔD, are stored in the ROM 307.

  Next, the behavior of the sheet 211 when the motor shift control is executed will be described. Here, a case will be described in which there is no variation in the sheet transport load torque during motor shift control. FIG. 2B is a diagram illustrating the conveyance state of the sheet 211 when there is no conveyance delay and the conveyance state of the sheet 211 when the conveyance delay occurs. This shows the situation where the tip of the sword moves on the transport path. 2B, the horizontal axis represents time [unit: second (s)], the vertical axis represents the position on the conveyance path (conveyance path position), and the positions P250, P251, and P252 represent the paper in FIG. Regarding the position of the conveyance path, a section L243 indicates a section (distance) between the position P250 and the position P251. A graph (ideal paper leading edge position) indicated by a dotted line in the drawing shows how the leading edge of the paper 211 moves on the transport path when the paper 211 is ideally transported. Here, ideal conveyance of the sheet 211 means that there is no conveyance advance or conveyance delay with respect to the image writing timing in the image forming unit in the conveyance of the sheet from the sheet feeding cassette 212 to the secondary transfer position P252, and the motor speed change. This refers to a transport state that does not require control. That is, ideal conveyance of the sheet 211 indicates a conveyance state of the sheet 211 that is synchronized with the movement of the toner image formed on the intermediate transfer belt 228 that is assumed in design. On the other hand, a graph (actual paper leading edge position) indicated by a solid line in the figure is the case where the motor shift control is performed on the paper 211 in which the conveyance delay has actually occurred with respect to the image writing timing in the image forming unit. An example of how the leading edge of the sheet 211 moves on the conveyance path is shown. A graph indicated by a two-dot chain line shows an example of a state in which the leading end of the sheet 211 moves on the conveyance path when the motor shift control is not performed on the sheet 211 in which the conveyance delay actually occurs. .

  In FIG. 2B, when the leading edge of the sheet 211 is detected by the registration sensor 241 (position P250), the printer control unit 303 causes the conveyance at the position P250 not to be delayed (dotted line graph) and the conveyance delay to occur. The time difference ΔTr with respect to (solid line graph) is calculated. Here, the timing at which the sheet 211 reaches the position P250 when there is no conveyance delay is calculated as follows. That is, the printer control unit 303 obtains the timing at which the toner image on the photosensitive drum 222 is transferred to the intermediate transfer belt 228 from the image formation control unit 304, and the toner image is transferred to the secondary transfer position based on the driving speed of the intermediate transfer belt 228. The timing to reach P252 is calculated. The printer control unit 303 can calculate the timing at which the sheet 211 reaches the registration sensor 241 (position P250) based on the calculated conveyance speed of the sheet 211 from the calculated timing. The printer control unit 303 calculates a time difference ΔTr calculated from the calculated timing (time) and the timing (time) when the detection result from the registration sensor 241 is received. Then, the printer control unit 303 multiplies the calculated time difference ΔTr and the design transport speed of the paper 211 to obtain a paper that is the difference in the transport distance of the paper 211 when there is no transport delay at the position P250. An alignment correction amount ΔDr 211 is calculated. The printer control unit 303 acquires correction information at the time of motor shift control based on the calculated alignment correction amount ΔDr from the shift control information table 306 described above, and instructs the sheet conveyance control unit 305 to execute motor shift control. As shown in FIG. 2B, the conveyance error is eliminated so that the leading end of the sheet after the start of the motor shift control coincides with the leading end position of the sheet 211 when ideally conveyed at the position P251 on the conveyance path. Yes. Then, after the motor speed change control is completed at the position P251, the sheet 211 advances on the same track as the sheet 211 in the ideal transport state.

  The time difference ΔTr, which is the variation in the detection timing of the leading edge of the paper shown in FIG. 2B, is caused by an electrical and mechanical delay at the time of paper feeding, a variation in the leading edge position of the paper 211 on the paper feeding cassette 212, a conveyance roller, and the like. It occurs due to various factors such as a change in the roller diameter of 239 over time. Therefore, by performing the motor shift control described above, the conveyance variation of the sheet 211 is corrected, and the alignment with the toner image on the intermediate transfer belt 228 can be realized.

≪Positioning error due to transfer load torque fluctuation≫
Next, a description will be given of an alignment error caused by a conveyance load torque fluctuation generated during the motor shift control. FIG. 3A is a graph showing the relationship between the position of the sheet 211 and the alignment error when the conveyance load torque fluctuation occurs. In FIG. 3A, the horizontal axis indicates the position (Pt1) [unit: mm] on the transport path at the leading end of the sheet 211 when the transport load torque variation occurs, and the vertical axis indicates the alignment error [unit: mm]. Show. The position (Pt1) on the transport path is indicated by a distance (unit: mm) in the upstream direction of the transport path from position P251, which is the end position of the motor shift control. 3A, “P251 position” indicates a position P251 where Pt1 is 0, and “P251 upstream 10” indicates a position where Pt1 is 10 mm away from the position P251 in the upstream direction of the conveyance path.

  Further, the position of the sheet 211 on which the conveyance load torque fluctuation occurs on the conveyance path is based on the sheet length α of the sheet 211, the distance β of the section L243, and the distance γ of the conveyance path between the registration roller 240 and the conveyance roller 239. Can be calculated. That is, the position of the sheet 211 on the conveyance path where the conveyance load torque fluctuation can be calculated by (β + γ) −α, and if (β + γ) ≦ α, the conveyance load fluctuation does not occur. Note that the distance β of the section L243 and the distance γ of the conveyance path between the registration roller 240 and the conveyance roller 239 are stored in advance in the ROM 307 as control data. In FIG. 3A, the conveyance load torque varies from the state in which the sheet 211 under motor shift control is sandwiched between the conveyance rollers 239 to the rear end of the sheet 211 passing through the conveyance roller 239, and the sheet 211 is conveyed to the conveyance roller 239. Occurs from the point of change to a state where it is not pinched. That is, the variation in the conveyance load torque occurs when the trailing end of the sheet 211 passes the conveyance roller 239 during the motor shift control, and as a result, an alignment error occurs. From the graph of FIG. 3A, the position of the sheet is adjusted as the fluctuation in the conveyance load torque occurs earlier, that is, as the sheet 211 has a shorter length and the rear end of the sheet 211 is generated upstream of the conveyance path. It can be seen that the error becomes larger. This is because the sheet 211 is not held between the conveyance rollers 239, thereby reducing the conveyance load on the sheet conveyance by the registration roller 240, and as a result, the sheet conveyance force of the registration roller 240 increases.

  FIG. 3B shows an example of the behavior of the sheet 211 when the conveyance load torque decreases during the motor shift control. In FIG. 3B, the horizontal axis represents time [unit: second (s)], the vertical axis represents the position on the conveyance path (conveyance path position), and the graph indicated by the solid line represents the conveyance load torque during motor shift control. A state is shown in which the leading edge of the sheet 211 moves on the transport path when it decreases. On the other hand, the alternate long and short dash line portion shows how the leading edge of the sheet 211 moves on the conveyance path when there is no change in the conveyance load torque during motor shift control. A graph indicated by a dotted line shows how the leading edge of the sheet 211 moves on the conveyance path when the sheet 211 is ideally conveyed. Further, the graph indicated by a two-dot chain line shows an example of a state in which the leading end of the sheet 211 moves on the conveyance path when the motor shift control is not performed on the sheet 211 in which the conveyance delay has actually occurred. . As shown in FIG. 3B, the position correction by the motor shift control is excessively applied from the position Pt1 when the conveyance load torque is reduced, and the shift amount is deviated from the assumed correction position at the end of the shift control. An alignment error amount ΔD1 is generated. As a result, the leading edge of the sheet 211 moves as shown in the graph in the case where the motor shift control is performed without considering the fluctuation of the generated transport load torque indicated by the solid line. As described above, when the conveyance load torque varies during the motor shift control, an alignment error (ΔD1) that is a first alignment error amount corresponding to the variation amount of the conveyance load torque is further generated. Therefore, when the motor speed change control is performed, the final alignment correction amount ΔD is calculated by correcting the alignment correction amount ΔDr due to the conveyance delay of the sheet 211 based on the error amount ΔD1 corresponding to the variation of the conveyance load torque. To do. Then, it is necessary to perform motor shift control based on the calculated final alignment correction amount ΔD.

  As shown in FIG. 3B, at the position P250, the actual paper 211 has a transport delay time ΔTr as compared with an ideal paper transport, and at the position P250 due to the transport delay of the paper 211. An alignment correction amount ΔDr is generated. Then, in order to align the front end of the actually conveyed paper 211 with the ideal paper transport at the position P251, i.e., the paper front that is assumed in design, according to the alignment correction amount ΔDr. The motor shift control is performed at the shift speed Vc and the execution time Tc. However, at the position Pt1, the trailing edge of the sheet 211 passes through the conveyance roller 239, so that the conveyance load applied to the registration roller 240 is reduced (decreased), and the conveyance speed of the sheet 211 is increased. As a result, the leading end of the sheet 211 arrives earlier than the time when the leading end of the sheet in the case of ideal sheet conveyance reaches the position P251, and an alignment error amount ΔD1 occurs. Therefore, the final alignment correction amount ΔD necessary for aligning the leading end of the actually conveyed sheet 211 with the leading end of the sheet in the case of ideal sheet conveyance at the position P251 is ΔD = alignment correction amount ΔDr−position. The alignment error amount is ΔD1.

  Further, for example, when there is a difference in peripheral speed between the registration roller 240 and the conveyance roller 239, or when the conveyance roller has no driving force, that is, the conveyance roller 239 is driven to rotate by the driving force of the registration roller 240. In particular, the variation in the conveyance load torque becomes large. As a result, the alignment error amount ΔD1 also increases, and thus the above-described alignment correction amount ΔDr needs to be corrected.

  In this embodiment, a table (first table) in which the leading end position (Pt1) of the sheet 211 when the conveyance load torque fluctuation shown in FIG. Is stored in advance in the error amount table 309 of the ROM 307. Further, the relationship between the alignment error amounts in FIG. 3A also changes depending on the type of paper (for example, the thickness of the paper and the material). Therefore, a table of alignment error amounts may be provided for each paper type. Further, a table of alignment error amounts according to the degree of wear of the transport roller 239 and the registration roller 240 may be provided.

≪Motor shift control considering load torque fluctuation≫
Next, motor shift control in the present embodiment will be described with reference to FIGS. FIG. 4 is a flowchart showing a control sequence of the motor speed change control according to the present embodiment, which is activated during the printing operation. FIG. 5 is a diagram illustrating the behavior of the sheet 211 when the motor shift control according to the present exemplary embodiment is performed when the transport load torque is reduced during the motor shift control. FIG. 5 is a diagram similar to FIG. 3B described above, in which the horizontal axis indicates time [unit: seconds (s)], and the vertical axis indicates a position on the transport path (transport path position). Further, the solid line indicates that the leading edge of the sheet 211 actually moves on the conveyance path by the control shown in FIG. It shows how it moves. A dotted line shows how the leading edge of the sheet 211 moves on the conveyance path in an ideal conveyance state assumed in design, and a two-dot chain line indicates a motor shift control when a conveyance delay actually occurs. It shows a state in which the leading edge of the sheet 211 moves on the conveyance path when the operation is not performed.

  In step (hereinafter referred to as S) 100 in FIG. 4, the printer control unit 303 issues an instruction to start image formation processing to the image formation control unit 304, and instructs the sheet conveyance control unit 305 to start conveying the sheet. Start the timer you have. Then, the printer control unit 303 initializes a storage area in which information necessary for motor shift control is stored, and sets, for example, 0 in a storage area in which an alignment error amount ΔD1 described later is stored. In step S <b> 101, the printer control unit 303 obtains information about the paper length α of the paper 211, the paper type, here, the thickness and material of the paper from the print information regarding the recording material such as the paper type received from the host stored in the RAM 308. get. In step S102, the printer control unit 303 determines whether a notification that the leading edge of the sheet 211 is detected has been received from the registration sensor 241. If it is determined that the notification has not been received, the printer control unit 303 repeats the processing in step S102 and determines that it has been received. If so, the process proceeds to S103.

  In step S103, the printer control unit 303 calculates a time (timer value) for the leading edge of the sheet 211 to reach the position P250 when the sheet 211 indicated by the dotted line in FIG. Since the calculation method has been described above, a description thereof is omitted here. Then, based on the calculated timer value and the timer value when the notification is received from the registration sensor 241, the printer control unit 303 calculates a difference time ΔTr (FIG. 5) between the time when the sheet 211 reaches the position P 250. To do. In step S <b> 104, the printer control unit 303 calculates the alignment correction amount ΔDr by multiplying the calculated difference time ΔTr by the conveyance speed when the sheet 211 is ideally conveyed.

  In step S <b> 105, the printer control unit 303 determines whether there is a change in the conveyance load torque during the motor shift control, that is, whether the rear end of the sheet 211 passes the conveyance roller 239 during the motor shift control. The printer control unit 303 reads the distance β of the section L243 and the distance γ of the conveyance path between the registration roller 240 and the conveyance roller 239 from the ROM 307. Then, the printer control unit 303 determines whether the relationship between the sheet length α of the sheet 211 acquired in S101, the distance β of the section L243, and the distance γ is (β + γ)> α. If (β + γ)> α, the printer control unit 303 determines that a change in the conveyance load torque occurs, and proceeds to S106. If (β + γ) ≦ α, the printer control unit 303 determines that a change in the conveyance load torque does not occur (position) The alignment error amount ΔD1 is set to 0), and the process proceeds to S107.

  In step S <b> 106, the printer control unit 303 acquires an alignment error amount ΔD <b> 1 corresponding to the position Pt <b> 1 on the transport path at the leading edge of the paper 211 where the variation in the paper type and transport load torque occurs from the error amount table 309 of the ROM 307. In step S107, the printer control unit 303 calculates the final alignment correction amount ΔD by ΔD = alignment correction amount ΔDr−alignment error amount ΔD1. In step S108, the printer control unit 303 acquires motor shift information corresponding to the calculated final alignment correction amount ΔD from the shift control information table 306 stored in the ROM 307. Then, the printer control unit 303 transmits the change speed Vc and the execution time Tc of the motor 300, which is the acquired motor shift information, to the sheet transport control unit 305, and instructs the start of the motor shift control, thereby correcting the transport correction. Start.

  As a result of the motor shift control explained in FIG. 4, as shown in FIG. 5, it corresponds to the alignment time error T1 (positioning error amount ΔD1 shown in FIG. 3B) that occurs after the position Pt1 where the conveyance load torque fluctuates. The motor shift control according to the As a result, the leading end position of the sheet 211 can be made to coincide with the leading end position of the sheet 211 during ideal sheet conveyance at the position P251 where the motor speed change control ends. As described above, by performing the motor shift control in consideration of the alignment error due to the fluctuation of the transfer load torque during the motor shift control, the sheet being conveyed accurately with respect to the sheet conveyance path configurations and the sheet lengths of various printers. Can be aligned. In this embodiment, the alignment error amount corresponding to the sheet length is tabulated and stored in the ROM 307. The alignment error amount is measured in advance according to not only the paper length but also, for example, the type of paper, the durable wear state of the registration roller 240 and the transport roller 239, and the correspondence with the alignment error amount is stored in the ROM 307 as a table. May be. As described above, according to the present exemplary embodiment, even when the paper conveyance load fluctuates during the paper positioning control, the paper positioning can be performed with high accuracy.

  In the first embodiment, the control when the conveyance load torque during the motor shift control is changed in the decreasing direction has been described. In the second embodiment, a description will be given of the control in the case where the conveyance load torque during the motor shift control is changed in the increasing direction and an alignment error occurs during the motor shift control. Note that the configuration of the image forming apparatus, the configuration of the printer control unit, and the motor shift control method are the same as those in the first embodiment, and thus the description thereof is omitted.

≪Positioning error due to transfer load torque fluctuation≫
An alignment error due to a change in the conveyance load torque during the motor shift control will be described with reference to FIG. FIG. 6A is a graph showing the relationship between the position of the sheet 211 and the alignment error when the conveyance load torque fluctuation occurs. In FIG. 6A, the horizontal axis indicates the position (Pt2) [unit: mm] on the transport path at the leading edge of the sheet 211 when the transport load torque variation occurs, and the vertical axis indicates the alignment error [unit: mm]. Show. The position (Pt2) on the conveyance path is indicated by a distance (unit: mm) in the upstream direction of the conveyance path from the position P251 that is the end position of the motor shift control. In FIG. 6A, “P251 position” indicates a position P251 where the position Pt2 is 0, and “P251 upstream 25” indicates a position where the position Pt2 is 25 mm away from the position P251 in the upstream direction of the conveyance path. .

  6A is not transmitted from the state in which the driving force from the motor 300 is transmitted to the transport roller 239 by the connection / disconnection process of the motor power by the electromagnetic clutch during the motor shift control. Occurs when switching to a state. Here, the electromagnetic clutch that transmits the driving force of the motor 300 to the paper feed roller 238 and the transport roller 239 will be described. The electromagnetic clutch realizes connection / disconnection with motor power by supplying electric power to the electromagnet. When the electromagnetic clutch is connected, power is supplied to the electromagnet, and when it is disconnected, the power supply is stopped. The electromagnet that continues to supply electric power has a feature that the temperature gradually increases and the coupling force decreases accordingly. For this reason, in order to maintain the coupling force, there is a usage limitation that the electromagnetic clutch must be disconnected at predetermined time intervals. The same applies to the electromagnetic clutch that controls the driving force applied to the paper feed roller 238 and the transport roller 239 in this embodiment, and the electromagnetic clutch must be disconnected according to usage restrictions. Due to this restriction, the electromagnetic clutch may be disconnected during the motor speed change control. When the electromagnetic clutch is disconnected, the paper feed roller 238 and the transport roller 239 are stopped.

  The fluctuation of the conveyance load torque in FIG. 6A occurs when the electromagnetic clutch is disengaged and the conveyance roller 239 stops rotating in a state where the sheet 211 under the motor shift control is sandwiched between the conveyance rollers 239. That is, the variation in the conveyance load torque occurs when the conveyance roller 239 that is nipping and conveying the sheet 211 is stopped during the motor shift control, and an alignment error occurs. From the graph of FIG. 6A, it can be seen that the alignment error becomes larger as the fluctuation of the conveyance load torque occurs earlier, that is, upstream of the conveyance path. This is because the sheet 211 is held by the conveyance roller 239 when the conveyance roller 239 is stopped, so that the conveyance load applied to the sheet conveyance by the registration roller 240 is increased. As a result, the sheet conveyance by the registration roller 240 is performed. This is because power is reduced.

  FIG. 6B shows an example of the behavior of the sheet 211 when the conveyance load torque increases during the motor shift control. In FIG. 6B, the horizontal axis indicates time [unit: second (s)], the vertical axis indicates the position on the conveyance path (conveyance path position), and the solid line (actual paper leading edge position) indicates during motor speed change control. A state in which the leading edge of the sheet 211 moves on the conveyance path when the conveyance load torque increases is shown. On the other hand, the alternate long and short dash line portion shows how the leading edge of the sheet 211 moves on the conveyance path when there is no change in the conveyance load torque during motor shift control. A dotted line (ideal paper front end position) indicates a state in which the front end of the paper 211 moves on the transport path when the paper 211 is transported ideally (as designed and assumed). Further, the graph indicated by a two-dot chain line shows an example of a state in which the leading end of the sheet 211 moves on the conveyance path when the motor shift control is not performed on the sheet 211 in which the conveyance delay has actually occurred. .

  As shown in FIG. 6B, the position correction by the motor shift control is insufficient from the position Pt2 at the time when the conveyance load torque is increased, and the position P251 at which the shift control ends is out of the assumed correction position. An alignment error amount ΔD2 that is a shift amount is generated. As a result, the leading edge of the sheet 211 moves as shown in the graph in the case where the motor shift control is performed without considering the fluctuation of the generated transport load torque indicated by the solid line. As described above, when the conveyance load torque varies during the motor shift control, an alignment error (ΔD2) corresponding to the variation amount of the conveyance load torque further occurs. Therefore, when the motor shift control is performed, the final alignment correction amount ΔD is calculated by correcting the alignment correction amount ΔDr due to the conveyance delay of the sheet 211 based on the error amount ΔD2 corresponding to the variation of the conveyance load torque. To do. Then, it is necessary to perform motor shift control based on the calculated final alignment correction amount ΔD.

  As shown in FIG. 6B, at the position P250, the actual paper 211 has a transport delay time ΔTr as compared with the ideal paper transport, and at the position P250 due to the transport delay of the paper 211. An alignment correction amount ΔDr is generated. Then, in order to align the leading end of the actually conveyed sheet 211 with the leading end of the sheet in the case of ideal sheet conveyance (designed sheet conveyance in design) at the position P251, a shift corresponding to the alignment correction amount ΔDr is performed. Motor speed change control is performed at the speed Vc and the execution time Tc. However, since the rotation of the transport roller 239 stops at the position Pt2, the transport load applied to the registration roller 240 that transports the sheet 211 becomes heavy (increases), and the transport speed of the sheet 211 decreases. As a result, the leading end of the sheet 211 arrives later than the time when the leading end of the sheet reaches the position P251 in the case of ideal sheet conveyance, and a second alignment error amount ΔD2 is generated. . Therefore, the final alignment correction amount ΔD necessary for aligning the front end of the actually conveyed paper 211 with the front end of the paper in the ideal paper conveyance at the position P251 is ΔD = alignment correction amount ΔDr + alignment. The error amount is ΔD2.

  As described above, when the transport load torque fluctuates during the motor shift control, an error occurs in alignment according to the variation amount of the transport load torque. Therefore, when the motor shift control is performed, the error amount is corrected. It is necessary to control with. In particular, when there is a peripheral speed difference between the registration roller 240 and the conveyance roller 239, the variation in the conveyance load torque is large, and the above-described motor shift control is necessary. In this embodiment, a table (second table) in which the leading end position (Pt2) of the sheet 211 when the conveyance load torque fluctuation shown in FIG. Is stored in advance in the error amount table 309 of the ROM 307. Further, the relationship between the alignment error amounts in FIG. 6A also changes depending on the paper type (for example, the thickness of the paper and the material). Therefore, a table of alignment error amounts may be provided for each paper type. Further, a table of alignment error amounts according to the degree of wear of the transport roller 239 and the registration roller 240 may be provided.

≪Motor shift control considering load torque fluctuation≫
Next, motor shift control in this embodiment will be described with reference to FIGS. FIG. 7 is a flowchart showing a control sequence of the motor speed change control according to the present embodiment, which is activated during the printing operation. FIG. 8 is a diagram illustrating the behavior of the sheet 211 when the motor shift control according to this embodiment is executed when the conveyance load torque is increased during the motor shift control. FIG. 8 is a diagram similar to FIG. 6B described above, in which the horizontal axis indicates time [unit: second (s)], and the vertical axis indicates a position on the transport path (transport path position). Further, the solid line indicates that the leading edge of the sheet 211 is actually moved on the conveyance path by the control shown in FIG. It shows how it moves. A dotted line shows how the leading edge of the sheet 211 moves on the conveyance path in an ideal conveyance state assumed in design, and a two-dot chain line indicates a motor shift control when a conveyance delay actually occurs. It shows a state in which the leading edge of the sheet 211 moves on the conveyance path when the operation is not performed.

  In S200 of FIG. 7, the printer control unit 303 instructs the image formation control unit 304 to start image forming processing, instructs the paper transport control unit 305 to start transporting paper, and starts an internal timer. Then, the printer control unit 303 initializes a storage area in which information necessary for motor shift control is stored, and sets, for example, 0 in a storage area in which an alignment error amount ΔD2 described later is stored. In step S <b> 201, the printer control unit 303 acquires information about the paper type, here, the thickness and material of the paper from the print information regarding the recording material received from the host stored in the RAM 308. Further, the printer control unit 303 cuts after connecting the sheet length, the distance β of the section L243, the distance γ between the registration roller 240 and the conveying roller 239, the conveying speed of the sheet 211 of the conveying roller 239, and the electromagnetic clutch. Get the time until. The processing of S202 to S204 is the same as the processing of S102 to S104 of FIG.

  In step S <b> 205, the printer control unit 303 determines whether there is a change in the conveyance load torque during the motor shift control, that is, the conveyance roller 239 holds the sheet 211 when the conveyance roller 239 stops due to the electromagnetic clutch being disconnected. Determine if there is. The printer control unit 303 compares the conveyance speed of the conveyance roller 239 acquired in step S <b> 201 with the conveyance length calculated based on the time from when the electromagnetic clutch is connected to when the electromagnetic clutch is disconnected, and the sheet length of the sheet 211. The printer control unit 303 determines that the variation in the conveyance load torque occurs if the sheet length> the conveyance length, and proceeds to S206, and determines that the variation in the conveyance load torque does not occur if the sheet length ≦ the conveyance length (position). The alignment error amount ΔD2 is set to 0), and the process proceeds to S207.

  In step S206, the printer control unit 303 calculates a position Pt2 on the transport path of the leading edge of the paper 211 where the transport load torque varies based on the print information acquired in step S201. Then, the printer control unit 303 acquires a registration error amount ΔD2 corresponding to the paper type and the calculated position Pt2 from the error amount table 309 stored in the ROM 307. In step S207, the printer control unit 303 calculates the final alignment correction amount ΔD by ΔD = alignment correction amount ΔDr + alignment error amount ΔD2. The processing of S208 is the same as the processing of S108 of FIG.

  As a result of the motor shift control explained in FIG. 7, as shown in FIG. 8, it corresponds to the alignment time error T2 that occurs after the position Pt2 where the conveyance load torque fluctuates (corresponding to the alignment error amount ΔD2 shown in FIG. 6B). The motor shift control according to the As a result, the leading end position of the sheet 211 can be made to coincide with the leading end position of the sheet 211 at the time of sheet conveyance, which is assumed in design, at the position P251 where the motor speed change control ends. In this way, by carrying out motor speed change control that takes into account positioning errors due to fluctuations in the load torque during motor speed change control, it is possible to accurately carry paper for various printer paper path configurations, paper lengths, and paper types. The position of the paper inside can be adjusted. As described above, according to the present exemplary embodiment, even when the paper conveyance load fluctuates during the paper positioning control, the paper positioning can be performed with high accuracy.

  In the first embodiment, the control when the conveyance load torque during the motor shift control is changed in the decreasing direction has been described, and in the second embodiment, the control when the conveyance load torque during the motor shift control is changed in the increasing direction has been described. In the third embodiment, the electromagnetic clutch control is executed during the motor shift control, and further, the sheet passes through the transport roller, whereby the transport load torque applied to the registration roller is increased and decreased, and an alignment error occurs during the motor shift control. The case control will be described. Note that the configuration of the image forming apparatus, the configuration of the printer control unit, the motor speed change control method, and the alignment error due to the variation in the conveyance load torque are the same as those in the first and second embodiments, and thus description thereof is omitted.

≪Motor shift control considering load torque fluctuation≫
The motor speed change control in this embodiment will be described with reference to FIGS. FIG. 9 is a flowchart showing a control sequence of the motor speed change control according to the present embodiment, which is activated during the printing operation. FIG. 10 is a diagram illustrating the behavior of the sheet 211 when the motor shift control according to the present exemplary embodiment is performed when the conveyance load torque is increased or decreased during the motor shift control. FIG. 10 is a diagram similar to FIGS. 5 and 8 described above, in which the horizontal axis indicates time [unit: seconds (s)], and the vertical axis indicates a position on the transport path (transport path position). Further, the solid line indicates that the leading edge of the sheet 211 is actually moved on the conveyance path by the control shown in FIG. It shows how it moves. A dotted line shows how the leading edge of the sheet 211 moves on the conveyance path in an ideal conveyance state assumed in design, and a two-dot chain line indicates a motor shift control when a conveyance delay actually occurs. It shows a state in which the leading edge of the sheet 211 moves on the conveyance path when the operation is not performed.

  In S300 of FIG. 9, the printer control unit 303 instructs the image formation control unit 304 to start image forming processing and instructs the paper transport control unit 305 to start transporting paper, and starts an internal timer. Then, the printer control unit 303 initializes a storage area in which information necessary for motor shift control is stored, and sets, for example, 0 in a storage area in which alignment error amounts ΔD1 and ΔD2 described later are stored. In step S <b> 301, the printer control unit 303 acquires information about the sheet length and sheet type of the sheet 211, here the sheet thickness and material, from the print information regarding the recording material received from the host stored in the RAM 308. Further, the printer control unit 303 cuts after connecting the sheet length, the distance β of the section L243, the distance γ between the registration roller 240 and the conveying roller 239, the conveying speed of the sheet 211 of the conveying roller 239, and the electromagnetic clutch. Get the time until.

  The processing in S302 to S304 is the same as the processing in S102 to S104 in FIG. 4 of the first embodiment and the processing in S202 to S204 in the second embodiment, and a description thereof will be omitted. Further, the processes of S305 and S306 are the same as the processes of S105 and S106 of FIG. Further, the processing of S307 and S308 is the same as the processing of S205 and S206 of FIG.

  In step S309, the printer control unit 303 calculates the final alignment correction amount ΔD by ΔD = alignment correction amount ΔDr−alignment error amount ΔD1 + alignment error amount ΔD2. In step S <b> 310, the printer control unit 303 acquires motor shift information corresponding to the calculated final alignment correction amount ΔD from the shift control information table 306 stored in the ROM 307. Then, the printer control unit 303 transmits the change speed Vc and the execution time Tc of the motor 300, which is the acquired motor shift information, to the sheet transport control unit 305, and instructs the start of the motor shift control, thereby correcting the transport correction. Start.

  As a result of the motor shift control explained in FIG. 9, as shown in FIG. 10, the alignment time error T3 (corresponding to the alignment error amounts ΔD1 and ΔD2) occurring after the position Pt1 and the position Pt2 where the conveyance load torque fluctuates. The motor shift control according to the As a result, the leading end position of the sheet 211 can be made to coincide with the leading end position of the sheet 211 at the time of sheet conveyance, which is assumed in design, at the position P251 where the motor speed change control ends. In this way, by carrying out motor speed change control that takes into account positioning errors due to fluctuations in the load torque during motor speed change control, it is possible to accurately carry paper for various printer paper path configurations, paper lengths, and paper types. The position of the paper inside can be adjusted.

  In the first to third embodiments described above, the paper feed roller, the transport roller, and the registration roller are driven by the same motor 300, but the control of the above-described embodiment is applied even if they are driven by different motors. be able to. In addition, although the first to third embodiments have been described with respect to the case where the conveyance delay occurs, the present invention can be applied to the case where the conveyance advance occurs. The situation in which the conveyance progress occurs is, for example, that the following sheet 211 is brought out to the nip portion of the conveyance roller 239 as the preceding sheet 211 is fed due to the frictional force between the sheets 211 placed in the sheet feeding cassette 212. This is the case. In the embodiment described above, a conveyance delay has occurred, so the calculated alignment correction amount ΔDr is a positive value. On the other hand, when the conveyance progress has occurred, the calculated alignment correction amount ΔDr becomes a negative value, and as a result, the final alignment correction amount ΔD may also become a negative value. The sheet 211 is conveyed at a speed slower than the steady rotation speed Vref. As a result, the leading end position of the sheet 211 can be made to coincide with the leading end position of the sheet 211 at the time of sheet conveyance, which is assumed in design, at the position P251 where the motor speed change control ends. Further, the image forming apparatuses according to the first to third embodiments have been described using the color image forming apparatus. However, the image forming apparatus is not limited to the color image forming apparatus. The present invention is applied to an image forming apparatus that performs alignment control of a sheet for accurately superimposing a sheet conveyed on a conveyance path on an image generated through an image forming process. The embodiments described above can also be applied to the apparatus. As described above, according to the present exemplary embodiment, even when the paper conveyance load fluctuates during the paper positioning control, the paper positioning can be performed with high accuracy.

229 Secondary transfer roller 239 Conveying roller 240 Registration roller 241 Registration sensor 300 Motor 303 Printer control unit

Claims (15)

Transfer means for transferring an image formed on the image carrier to a recording material;
First conveying means for conveying the recording material to the transfer means;
A detection unit provided in a conveyance path through which the recording material is conveyed, and detecting that the recording material has reached the first conveyance unit;
Second conveying means for conveying the recording material to the first conveying means;
Drive means for driving the first transport means and the second transport means;
Control means for controlling the drive means;
With
The control means, based on the information related to the timing when the detection means detects the recording material and the information related to the fluctuation of the conveyance load in the first conveyance means, the recording material conveyance speed by the first conveyance means. An image forming apparatus that controls the driving unit to change   The control means obtains a registration correction amount of the recording material based on information related to the timing at which the detection means detects the recording material, and based on information related to a change in transport load in the first transport means, The image forming apparatus according to claim 1, wherein an alignment error amount of the recording material is obtained.   The alignment correction amount is a time difference between the arrival timing of the recording material detected by the detection means and a predetermined arrival timing at which the recording material reaches the detection means for the transfer means to transfer an image. The image forming apparatus according to claim 2, wherein the image forming apparatus calculates a deviation amount at a position of a conveyance path in which the detection unit is provided, which is calculated based on the image.   4. The change in the transport load occurs when a recording material is transported in a predetermined section of a transport path between the first transport unit and the transfer unit. The image forming apparatus described. The amount of alignment error is
A first alignment error amount corresponding to fluctuations in the transport load generated by the trailing edge of the recording material being transported by the first transport means passing through the second transport means;
The image forming apparatus according to claim 4, further comprising:   6. The image formation according to claim 5, wherein the first alignment error amount is a shift amount corresponding to the conveyance progress of the recording material at an end point downstream in the conveyance direction of the recording material in the predetermined section. apparatus.   6. The apparatus according to claim 5, further comprising: a first table in which the position of the recording material in the predetermined section when the change in the transport load occurs and the first alignment error amount are associated with each other. 6. The image forming apparatus according to 6. The amount of alignment error is
A second alignment error amount corresponding to a change in the transport load generated when the second transport unit that transports the same recording material as the recording material transported by the first transport unit stops driving. The image forming apparatus according to claim 4, further comprising:   9. The image formation according to claim 8, wherein the second alignment error amount is a shift amount corresponding to a conveyance delay of the recording material at an end point downstream in the conveyance direction of the recording material in the predetermined section. apparatus.   9. The apparatus according to claim 8, further comprising: a second table in which the position of the recording material in the predetermined section when the change in the transport load occurs and the second alignment error amount are associated with each other. The image forming apparatus according to 9. The amount of alignment error is
A first alignment error amount corresponding to fluctuations in the transport load generated by the trailing edge of the recording material being transported by the first transport means passing through the second transport means;
A second alignment error amount corresponding to a change in the transport load generated when the second transport unit that transports the same recording material as the recording material transported by the first transport unit stops driving. The image forming apparatus according to claim 4, further comprising:   A deviation amount of the recording material at an end point downstream of the recording material in the conveyance direction in the predetermined section, calculated based on the alignment correction amount, the first alignment error amount, and the second alignment error amount. The image forming apparatus according to claim 11, further comprising: a third table that associates a recording material conveyance speed by the first conveyance unit in the predetermined section of the recording material. An electromagnetic clutch for transmitting or interrupting the driving force by the driving means to the second conveying means;
The image forming apparatus according to claim 8, wherein the control unit stops driving of the second transport unit by controlling the electromagnetic clutch. The driving means has one motor,
The image forming apparatus according to claim 1, wherein the first transport unit and the second transport unit are driven by the motor. The drive means has a plurality of motors,
The image forming apparatus according to claim 1, wherein the first transport unit and the second transport unit are driven by different motors.

Images