JP2016075756A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of print errors when a transfer material length of a fed transfer material is different from a specified transfer length upon printing either surface.SOLUTION: In order for a cartridge 6 forming an image on a photosensitive drum 1 to form the image on either surface of a transfer materia, an image forming apparatus is configured to form an image corresponding to a first surface and an image corresponding to a second surface at an interval based on a predetermined size of the transfer material, and a CPU205 is configured to accelerate or decelerate a rotation velocity of the photosensitive drum 1 for transferring the image corresponding to the second surface formed on the photosensitive drum 1 to the transfer material when a size of the transfer material determined based on a detection result of a registration sensor 20 detecting a tip end and a rear end of the transfer material to be conveyed to a sheet ejection roller pair 17 inverting the transfer material passing through a secondary transfer roller 12 and conveying the inverted transfer material is different from a preliminarily set size of the transfer material.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus using an electrophotographic process.

  Conventionally, as an image forming apparatus using an electrophotographic process, there is an image forming apparatus that forms a color image (multicolor image) on a transfer material by a primary transfer process and a secondary transfer process. In this image forming apparatus, an intermediate transfer member is used, and in the primary transfer step, the toner image formed on the photosensitive drum is transferred to the intermediate transfer member. By repeating this primary transfer process in a plurality of colors, a toner image in which a plurality of color toner images are superimposed on the intermediate transfer member is formed. In the secondary transfer process, the toner images of a plurality of colors formed on the intermediate transfer member are transferred to a transfer material such as paper.

  When performing double-sided printing with such an image forming apparatus, the transfer material that has undergone the secondary transfer process for the first side is reversed, and the transfer material reaches the secondary transfer portion where the secondary transfer is performed again. The toner image formation on the second side is started at the timing calculated backward from the timing at which it is performed. Thereby, optimum productivity can be realized. In the image forming apparatus, the timing at which the secondary transfer is performed on the second surface of the transfer material is calculated based on the transfer material length designated by the controller unit. However, when the actual transfer material is longer than the transfer material length designated by the controller unit, the reversal timing of the transfer material is delayed by an amount longer than the designated transfer material length. Therefore, at the secondary transfer timing calculated based on the designated transfer material length, the transfer material cannot reach the secondary transfer portion, and a print error occurs. Therefore, for example, in Patent Document 1, the timing for starting the toner image formation on the second surface is determined based on the timing at which the trailing edge of the transfer material passes the registration sensor, that is, the timing at which the length of the transfer material is actually measured. Therefore, even when the specified transfer material length is different from the actual transfer material length, printing is performed at the timing according to the actual transfer material length, so optimal productivity is achieved without causing print errors. it can.

JP 2010-009024 A

  However, depending on the configuration of the image forming apparatus, when the method proposed in Patent Document 1 described above is applied, optimal productivity may not be realized. The image forming apparatus in this case has the following configuration. That is, the time from when the trailing edge of the transfer material passes through the registration sensor to when the transfer material is reversed and reaches the secondary transfer portion again is formed on the photosensitive drum and transferred to the intermediate transfer member 2. It has a configuration that is shorter than the time until the toner image on the first surface reaches the secondary transfer portion. When the method proposed in Patent Document 1 is applied to this image forming apparatus, the timing at which the inverted transfer material reaches the secondary transfer portion is the second toner image transferred to the intermediate transfer member. It is earlier than the timing of reaching the next transfer portion. For this reason, the formation start timing of the toner image on the second surface is delayed as compared with the method for determining the formation start timing of the toner image on the second surface based on the designated transfer material length described above, thereby realizing optimum productivity. I can't.

  The present invention has been made under such circumstances, and prevents double-sided printing from generating a printing error when the transfer material length of the transferred transfer material is different from the designated transfer material length. Objective.

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

  (1) An image carrier, an image forming unit that forms an image on the image carrier, a transfer unit that transfers an image formed on the image carrier by the image forming unit to a transfer material, and the transfer unit A reversing unit that reverses and conveys the transferred transfer material, a conveying unit that conveys the transfer material conveyed from the reversing unit to the transfer unit, and a front end and a rear end of the transfer material conveyed to the reversing unit In the image forming apparatus having a detecting unit for detecting the image and a control unit for determining the size of the transfer material based on a detection result of the detecting unit, the image forming unit forms images on both sides of the transfer material. In addition, an image corresponding to the first surface and an image corresponding to the second surface are formed on the image carrier at intervals based on a preset size of the transfer material, and the size of the transfer material determined by the control unit Is the preset transfer material support. The rotational speed of the image carrier is accelerated or decelerated in order to transfer the image corresponding to the second surface formed on the image carrier to the transfer material. apparatus.

  According to the present invention, it is possible to prevent a print error from occurring when the transfer material length of the fed transfer material is different from the designated transfer material length during double-sided printing.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to first and second embodiments, and a block diagram illustrating a system configuration. The figure which shows the behavior of the transfer material at the time of double-sided printing of Example 1, 2 and an intermediate transfer belt, and the time chart which shows the basic operation at the time of double-sided printing Time chart showing a printing operation when the paper size of the first embodiment is large 7 is a flowchart illustrating a control sequence during duplex printing according to the first exemplary embodiment. Time chart showing a printing operation when the paper size of the second embodiment is large 7 is a flowchart illustrating a control sequence during duplex printing according to the second embodiment.

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

[Entire configuration of image forming apparatus]
FIG. 1A is a schematic configuration diagram illustrating the overall configuration of the image forming apparatus used in the first embodiment. The image forming apparatus illustrated in FIG. 1A includes a plurality of cartridges 6Y, 6M, 6C, and 6K that can be attached to and detached from the image forming apparatus. In the drawing, yellow (Y) and magenta (M) are sequentially arranged from the left side. , Cyan (C), and black (K) toner. Further, the image forming apparatus includes a scanner unit 8Y, 8M, 8C, 8K, an intermediate transfer belt 9, a primary transfer roller 7Y, 7M, 7C, 7K, a secondary transfer roller 12, a fixing device 14, a paper feed roller 10, and a registration. A roller 11 and a residual toner charging roller 13 are provided. In the drawing, suffixes Y, M, C, and K at the end of the reference numerals represent toner colors, and the registration roller 11 is hereinafter referred to as a registration roller 11. Further, the cartridges 6Y, 6M, 6C, and 6K that are image forming units have the same configuration, and in the following description, subscripts of Y, M, C, and K are attached unless a specific cartridge is indicated. Suppose that there is no. The configuration of each part will be described below according to the image forming operation.

  Each cartridge 6 includes a photosensitive drum 1, a charging roller 2, a developing roller 3, a developing device 4 that contains toner, a cleaner blade 26 that is a cleaning unit that removes and collects toner remaining on the photosensitive drum 1, and a residual toner container. 5 The photosensitive drum 1 that is an image carrier is rotated in the direction of the arrow (counterclockwise direction) in the drawing by a drive motor (not shown) according to the image forming operation. Exposure light to the photosensitive drum 1 is emitted from a scanner unit 8 provided corresponding to each cartridge 6, and an electrostatic latent image is formed on the photosensitive drum 1 by selectively exposing the surface of the photosensitive drum 1. It is formed. Prior to the formation of the electrostatic latent image, the charging roller 2 applies a DC voltage to charge the surface of the photosensitive drum 1 at each station to a uniform potential. The developing roller 3 is driven to rotate with the rotation of the photosensitive drum 1 and is applied with a DC voltage, whereby the electrostatic latent image formed on the photosensitive drum 1 is transferred to the toner stored in the developing device 4 by the toner. Develop to form a toner image.

  The primary transfer roller 7 is provided to face the photosensitive drum 1 of each cartridge 6, and a toner image formed on the photosensitive drum 1 of each cartridge 6 is applied to the intermediate transfer belt 9 by applying a DC voltage. Multiple transcribed. The intermediate transfer belt 9 as an intermediate transfer member is in contact with the photosensitive drum 1 and rotates in the direction of the arrow (clockwise direction) in the drawing along with the rotation of the photosensitive drum 1 when forming a color image. The toner image formed in (1) is transferred (primary transfer). The intermediate transfer belt 9 transfers (secondary transfer) a toner image on the intermediate transfer belt 9 to the transfer material 19 by holding and transferring a transfer material 19 described later together with a secondary transfer roller 12 as a transfer portion. . The secondary transfer roller 12 rotates in the arrow direction (counterclockwise direction) in the drawing as the intermediate transfer belt 9 rotates. Then, by applying a DC voltage to the secondary transfer roller 12, the toner image on the intermediate transfer belt 9 is transferred to the transfer material 19 fed from the paper feed cassette 18 and conveyed from the registration roller 11. Is done.

  The cleaner blade 26 cleans the photosensitive drum 1 by scraping the toner remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 9, and the remaining toner container 5 is the toner scraped off by the cleaner blade 26. Store. The toner remaining on the intermediate transfer belt 9 without being transferred to the transfer material 19 is charged by the residual toner charging roller 13 and is applied to the photosensitive drum 1 at the primary transfer portion where the photosensitive drum 1 and the intermediate transfer belt 9 come into contact with each other. The toner is reversely transferred electrostatically and collected in one of the remaining toner containers 5. In the primary transfer portion, the residual toner is reversely transferred to one of the photosensitive drums 1 and the toner image on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 9.

  The registration sensor 20 (hereinafter referred to as a registration sensor 20) is provided to synchronize the toner image transferred from the photosensitive drum 1 onto the intermediate transfer belt 9 and the transfer material 19 fed from the paper feed cassette 18. It has been. The registration sensor 20 serving as a detection unit is arranged on the upstream side of the secondary transfer roller 12 in the transport direction of the transfer material 19. When the leading edge of the transfer material 19 fed from the paper feed cassette 18 is detected by the registration sensor 20, the transfer of the transfer material 19 is temporarily stopped. When the toner image transferred onto the intermediate transfer belt 9 is transferred to a predetermined position on the transfer material 19 by the secondary transfer roller 12, the transfer of the transfer material 19 is resumed. The fixing device 14 includes a pressure roller 15 and a fixing roller 16, and a heater (not shown) and a thermistor (not shown) are provided in the fixing roller 16. A thermistor (not shown) detects the surface temperature of the fixing roller 16 and performs power supply control to the heater based on the detection result. The transfer material 19 onto which the toner image has been transferred from the intermediate transfer belt 9 is introduced into the fixing device 14, and the unfixed toner image is heated and pressurized to be fixed on the transfer material 19.

  The fixing paper discharge sensor 21 detects the transfer material 19 being conveyed from the fixing device 14. The reverse flapper 22 changes the conveyance direction of the transfer material 19. When the position of the reverse flapper 22 is at the position indicated by the solid line in FIG. 1A, the transfer material 19 is discharged in a direction to be discharged onto a paper discharge tray (not shown) by the paper discharge roller pair 17 as a reverse portion. Be transported. On the other hand, when the position of the reverse flapper 22 is at the position indicated by the dotted line in FIG. 1, the transfer material 19 sandwiched between the paper discharge roller pair 17 passes through the reverse path 25 provided with the transport roller pairs 23 and 24. Be transported. Therefore, when forming an image on both surfaces of the transfer material 19, the transfer material 19 on which image formation on the first surface has been completed is conveyed to the paper discharge roller pair 17, and the rear end in the conveyance direction of the transfer material 19 forms the reverse flapper 22. When it passes, the transfer of the transfer material 19 is stopped. Then, in order to form an image on the second surface of the transfer material 19, the direction of the reverse flapper 22 is changed to the direction indicated by the dotted line in FIG. It is conveyed to the reverse path 25. The paper discharge roller pair 17, the transport roller pairs 23 and 24, and the reverse path 25 constitute a transport unit that reverses the transfer material on which an image is formed on the first surface and transports the transfer material to the secondary transfer roller 12 again.

[System configuration of image forming apparatus]
Next, the system configuration of the image forming apparatus will be described. FIG. 1B is a block diagram for explaining the system configuration of the image forming apparatus. In FIG. 1B, the image forming apparatus includes a controller unit 201 and an engine control unit 202. The controller unit 201 can communicate with the host computer 200 and the engine control unit 202 which are external devices. The engine control unit 202 includes a video interface unit 203, a CPU 205, an exposure control unit 208, a drive control unit 209, a high voltage control unit 210, a fixing control unit 211, and a sensor input unit 212. The CPU 205 includes a ROM 206 that stores programs and data executed by the CPU 205 to control the engine control unit 202, and a RAM 207 that is used for temporary data storage. The CPU 205 has a timer function for measuring time.

  The host computer 200, which is an external device, transmits print conditions, print image data, and a print command to the controller unit 201 of the image forming apparatus. The controller unit 201 converts the image data received from the host computer 200 into exposure data necessary for the image forming apparatus, and creates printing reservation information for each transfer material based on the received printing conditions. Then, the controller unit 201 transmits a print reservation instruction to the CPU 205 via the video interface unit 203. The print reservation information is, for example, a paper feed port (paper feed cassette) indicating a supply source of the transfer material 19, a transfer material size, a print mode, and the like. Furthermore, when the conversion from the image data to the exposure data is completed, the controller unit 201 transmits a print start instruction to the CPU 205. When the CPU 205 receives a print start instruction from the controller unit 201, the CPU 205 outputs a / TOP signal as a reference timing for exposure data output to the controller unit 201, and starts a printing operation according to the print reservation information.

  A drive control unit 209 of the engine control unit 202 controls driving of the photosensitive drum 1, the primary transfer roller 7, the intermediate transfer belt 9, the paper feed roller 10, the registration roller 11, the fixing device 14, and the paper discharge roller pair 17. The main motor 204 controlled by the drive control unit 209 is a motor that drives the photosensitive drum 1, the primary transfer roller 7, and the intermediate transfer belt 9, and uses a DC brushless motor. The CPU 205 performs drive control of the main motor 204 and setting of a target rotation speed via the drive control unit 209. When the drive control unit 209 receives a drive instruction from the CPU 205, the current is supplied to the motor coil to rotate the main motor 204 so that the main motor 204 starts driving, and the rotation speed of the main motor 204 is monitored. Adjust the speed to reach the target rotational speed.

  In response to an instruction from the CPU 205, the exposure control unit 208 rotates a scanner motor (not shown) of the scanner unit 8 and corrects the amount of light, and performs light on the photosensitive drum 1 based on exposure data received from the controller unit 201. Irradiation. The high voltage controller 210 controls a power source that applies a DC voltage to each member in the image forming apparatus, for example, the charging roller 2, the developing roller 3, the primary transfer roller 7, and the secondary transfer roller 12. The fixing control unit 211 detects the surface temperature of the fixing roller 16 with a thermistor (not shown), and controls power supply to a heater (not shown) based on the detection result. The sensor input unit 212 acquires detection information from the registration sensor 20 and the fixing paper discharge sensor 21 and outputs the detection information to the CPU 205.

[Double-sided printing]
FIG. 2A shows the behavior of the transfer material 19 and the operation of the intermediate transfer belt 9 when double-sided printing is performed. 2 (A) (i) to (vi) on the upper side of FIG. 2 (A) are diagrams showing the conveyance state of the transfer material 19 during the double-sided printing operation, while the lower side of FIG. 2 (A). FIGS. 2A to 2I are views showing how the toner image on the intermediate transfer belt 9 moves.

  First, FIG. 2 (A) (i) to (vi) will be described. At the time of duplex printing, the transfer material 19 fed from the paper feed cassette 18 is conveyed to the registration roller 11 (FIGS. 2A and 2I), and image formation on the first surface of the transfer material 19 (intermediate transfer belt 9). Transfer of the upper toner image onto the transfer material 19) is performed (FIG. 2 (A) (ii)). Then, the rear end of the transfer material 19 in the conveyance direction passes through the registration sensor 20 (FIG. 2A (iii)). Thereafter, when the rear end of the transfer material 19 in the transport direction reaches the paper discharge roller pair 17, the reverse flapper 22 changes the direction of the reverse flapper 22 to transport the transfer material 19 to the reverse path 25 (FIG. 2A). ) (Iv)). By rotating the paper discharge roller pair 17 in the reverse direction, the transfer material 19 is reversed and conveyed to the reversing path 25 (FIGS. 2A and 2V), and the leading edge of the transfer material 19 in the conveying direction is again the registration sensor 20. (Fig. 2 (A) (vi)). In the time T1 in the figure, after the rear end of the transfer material 19 in the transport direction passes through the registration sensor 20 (FIG. 2 (A) (iii)), the tip of the inverted transfer material 19 in the transport direction reaches the registration sensor 20. The time to reach (FIG. 2 (A) (vi)) is shown. The time T1 is determined by the length of a double-sided conveyance path (the registration sensor 20 to the discharge roller pair 17 to the conveyance roller pair 23 to the conveyance roller pair 24 to the conveyance path of the registration sensor 20) in which the transfer material 19 is conveyed. The time T1 is constant regardless of the length of the transfer material 19 in the conveyance direction (hereinafter also referred to as transfer material size).

  Next, FIGS. 2A to 2I will be described. 2A and 2I show the timing at which the / TOP signal for the first surface of the transfer material 19 is output, and exposure of the photosensitive drum 1Y is started from the scanner unit 8Y according to the first surface image. FIGS. 2A and 2II show the timing at which the / TOP signal is output for the second surface of the transfer material 19, and the exposure to the photosensitive drum 1Y is started from the scanner unit 8Y according to the second image. At this time, the toner image on the intermediate transfer belt 9 is also transferred to the first surface of the transfer material 19. 2A and 2III show the timing at which the toner image on the second surface of the transfer material 19 formed on the photosensitive drum 1Y is transferred onto the intermediate transfer belt 9. FIG. At this time, the transfer of the toner image on the intermediate transfer belt 9 to the first surface of the transfer material 19 is completed, and the transfer material 19 is conveyed to the paper discharge roller pair 17. 2A and 2IV show the movement state of the toner image on the intermediate transfer belt 9 at the timing (FIGS. 2A and 2V) that the leading end of the reversed transfer material 19 in the conveyance direction reaches the registration sensor 20. FIG. FIG. In the time T2 in the figure, the tip of the reversed transfer material 19 in the transport direction reaches the registration sensor 20 from the timing (FIGS. 2A and 2) that the / TOP signal for the second surface of the transfer material 19 is output. The time until timing (FIG. 2 (A) (IV)) is shown. The time T2 is determined by the length of the intermediate transfer belt 9, and is constant regardless of the transfer material size of the transfer material 19.

  The / TOP signal output timing (FIGS. 2 (A) (II)) on the second surface of the transfer material 19 was inverted with the output timing (FIGS. 2 (A) (I)) of the first surface as the base point. It is determined in consideration of the time until the transfer material 19 reaches the registration sensor 20. The output timing of the / TOP signal on the second surface of the transfer material 19 depends on the length of the intermediate transfer belt 9 and the length of the above-described duplex conveyance path. 2A and 2V, the time from when the conveyance is restarted until the transfer material 19 reaches the secondary transfer roller 12, and the state of FIGS. The time until the leading edge of the toner image reaches the secondary transfer roller 12 is equal. In the image forming apparatus of this embodiment, the time from the start of image formation until the leading edge of the toner image on the intermediate transfer belt 9 reaches the secondary transfer roller 12 is the transfer material 19 whose trailing edge has passed the registration sensor 20. Is longer than the time until the leading edge of the toner reaches the secondary transfer roller 12. Therefore, in the image forming apparatus having such a configuration, the relationship between the times T1 and T2 described above is T1 <T2. Therefore, after the rear end of the transfer material 19 in the conveyance direction passes through the registration sensor 20 (FIG. 2A (iii)), a / TOP signal for the second surface of the transfer material 19 is output (FIGS. 2A and II). )), It takes a long time for the transfer material 19 to be temporarily stopped by the registration sensor 20. Therefore, the inversion time of the transfer material 19 is predicted based on the transfer material size designated in advance by the controller unit 201. Then, based on the predicted reversal time, before the rear end of the transfer material 19 in the transport direction passes through the registration sensor 20 (FIG. 2A (iii)), the / TOP signal for the second surface of the transfer material 19 is It outputs (FIG. 2 (A) (II)). Thereby, the maximum throughput (the number of printed sheets per unit time) is realized.

[Timing chart for double-sided continuous printing]
FIG. 2B is a timing chart of the duplex continuous printing operation of this embodiment. FIG. 2B shows, in order from the top, (a) shows the output timing of the / TOP signal, (b) shows the exposure operation in the cartridges 6Y, 6M, 6C, and 6K, and the hatched portion is the photosensitive drum 1 by the scanner unit 8. The exposure period is shown. (C) shows the driving state of the registration roller 11 (shown as registration roller driving in the figure), ON indicates the state where the registration roller 11 is rotated and the transfer material 19 is conveyed, and OFF indicates that the registration roller 11 is stopped. It shows the state. (D) shows the pick-up operation (paper feeding operation) of the transfer material 19 of the paper feed cassette 18, and one transfer material is conveyed from the paper feed cassette 18 to the registration sensor 20 for each ON-state pulse. (E) indicates a detection state by the registration sensor 20, ON indicates a state in which the registration sensor 20 detects the transfer material 19, and OFF indicates a state in which the registration sensor 20 does not detect the transfer material 19. (F) shows the reversal operation section of the transfer material 19, and the ON state represents the reversal operation section from when the transfer material 19 is reversed to when the leading end in the transfer material transport direction reaches the registration sensor 20. (G) indicates a detection state by the fixing paper discharge sensor 21, ON indicates a state in which the fixing paper discharge sensor 21 detects the transfer material 19, and OFF indicates that the fixing paper discharge sensor 21 has detected the transfer material 19. Indicates no state. In FIG. 2B, the horizontal axis indicates time, and t311 to t321 in the figure indicate timing (time). Further, T1 and T2 in the figure indicate the above-described times T1 and T2.

  2B, when the CPU 205 receives a print start command from the controller unit 201, the CPU 205 prepares for a printing operation. When the preparation is completed, the CPU 205 outputs a / TOP signal for the first surface of the transfer material 19 (t311), and the feeding operation of the transfer material 19 from the paper feed cassette 18 is started (t312). The CPU 205 stops the driving of the registration roller 11 when the leading end of the fed transfer material 19 in the conveyance direction reaches the registration sensor 20 disposed in the vicinity of the registration roller 11 (t313). The conveyance is temporarily stopped (t314). Then, the CPU 205 resumes the conveyance of the transfer material 19 in accordance with the timing when the leading edge of the toner image transferred onto the intermediate transfer belt 9 reaches the secondary transfer roller 12 (t315). The toner image on the intermediate transfer belt 9 is transferred to the transfer material 19 by the secondary transfer roller 12, and the unfixed toner image is heated and fixed to the transfer material 19 by the fixing device 14.

  Thereafter, the rear end of the transfer material 19 in the conveyance direction passes through the fixing paper discharge sensor 21 (t316), and the transfer material 19 is conveyed to a reversible position. At the timing when the transfer material 19 is conveyed to a position where it can be reversed, the CPU 205 turns on the reverse flapper 22 and a reverse solenoid (not shown) to start a reversing operation for conveying the transfer material in the reverse direction. (T317). Then, the transfer path of the transfer material 19 is switched to the reverse path 25 side by the reverse flapper 22, and the transfer material 19 is transferred to the reverse path 25.

  The CPU 205 outputs a / TOP signal for the second surface of the transfer material 19 (t318) before the transfer material 19 passes the registration sensor 20 (t323) in order to perform double-sided printing with the maximum throughput. Then, when the transfer material 19 conveyed through the reversing path 25 reaches the registration sensor 20 (t319), the CPU 205 stops the driving of the registration roller 11 and temporarily stops the transfer material 19 (t320). The CPU 205 drives the registration roller 11 in accordance with the timing at which the toner image on the second surface of the transfer material 19 formed on the intermediate transfer belt 9 reaches the secondary transfer roller 12 and resumes the transfer of the transfer material 19. (T321), the toner image is transferred to the transfer material 19. When performing continuous printing, the / TOP signal for the first surface of the succeeding second transfer material 19 is output before the rear end in the transport direction of the preceding first transfer material 19 passes the registration sensor 20 ( t322), the same double-sided printing operation as the first sheet of the transfer material 19 described above is repeated.

  In the timing chart of FIG. 2B described above, the / TOP signal for the second surface is output before the transfer material 19 passes through the registration sensor 20. The / TOP signal for the second side is output at the timing when the time (interval) based on the transfer material size specified in advance has elapsed from the timing at which the / TOP signal for the first side was output. Therefore, when the actual transfer material size is larger than the transfer material size designated in advance, the time from when the / TOP signal is output until the transfer material 19 starts the reversing operation becomes longer. As a result, before the transfer material 19 reaches the secondary transfer roller 12, the leading edge of the second-side toner image formed on the intermediate transfer belt 9 reaches the secondary transfer roller 12, resulting in a print error. End up.

  Therefore, in this embodiment, in such a case, the speed control of the intermediate transfer belt 9 described below is performed. That is, when the toner image formed on the black photosensitive drum 1K on the second surface is transferred to the intermediate transfer belt 9, the rotational speed of the intermediate transfer belt 9 is temporarily reduced, and the transfer material 19 reaches the secondary transfer roller 12. Control to return to the original speed before deceleration is performed at the same timing. The black photosensitive drum 1 </ b> K is a photosensitive drum of the cartridge 6 arranged on the most downstream side in the rotation direction of the intermediate transfer belt 9.

[Double-sided printing when transfer material size is larger than specified size]
In FIG. 3, the length A in the transport direction of the transfer material 19 placed on the paper feed cassette 18 is larger than the length B in the transport direction of the transfer material designated in advance by the controller unit 201 (A> B). ) Is a timing chart showing a continuous double-sided printing operation to which the present embodiment is applied. Hereinafter, the length A of the actual transfer material 19 in the conveyance direction is also referred to as a transfer material length A, and the length B of the transfer material designated by the controller unit 201 is also referred to as a transfer material length B.

  (A) to (g) in the vertical axis direction of FIG. 3 are the same as those in FIG. FIG. 3H shows the rotation speed of the main motor 204 controlled by the drive control unit 209. The speed Vp is the rotation speed of the main motor 204 in the normal state, and the speed Vl adjusts the speed of the intermediate transfer belt 9 when the length A of the transfer material 19 is longer than the designated transfer material length B. The deceleration speed of the main motor 204 when performing is shown. The horizontal axis in FIG. 3 indicates time, and t511 to t522 in the figure indicate timing (time). Further, T1 and T3 in the figure indicate the time T1 described above and a time T3 described later.

  The CPU 205 outputs a / TOP signal for the first surface of the transfer material 19 (t511), and starts a paper feeding operation (t512). When the leading edge of the fed transfer material 19 in the conveyance direction reaches the registration sensor 20 (t513), the CPU 205 temporarily stops the conveyance of the transfer material 19 (t514). Then, the CPU 205 resumes the conveyance of the transfer material 19 at the timing when the leading edge of the toner image transferred from the photosensitive drum 1 onto the intermediate transfer belt 9 reaches the secondary transfer roller 12 and Measurement of the transfer material length is started (t515). Thereafter, the CPU 205 outputs a / TOP signal for the second surface of the transfer material 19 at a timing calculated based on the transfer material length B of the transfer material designated by the controller unit 201 (t516). That is, the CPU 205 outputs a / TOP signal before the registration sensor 20 detects the rear end of the transfer material 19 in the transport direction. The CPU 205 ends the measurement of the transfer material length at the timing (t517) when the rear end of the transfer material 19 in the conveyance direction passes the registration sensor 20. Then, the CPU 205 compares the measured transfer material length A of the transfer material 19 with the transfer material length B designated from the controller unit 201. If the transfer material length A is longer than the transfer material length B, the intermediate transfer is performed. The speed and control time for carrying out the speed control of the belt 9 are determined. On the other hand, when the transfer material length A is equal to the transfer material length B, or when it is determined that the transfer material length A is shorter than the transfer material length B, the speed of the intermediate transfer belt 9 is a speed Vp which is a print speed described later. The speed control is not performed. The transfer material length A is determined from the transfer speed of the transfer material 19 and the transfer material 19 being resumed (t515) until the rear end of the transfer material 19 in the transfer direction passes the registration sensor 20 (t517). It can be calculated by multiplying time.

  Here, a method for controlling the speed of the intermediate transfer belt 9 of this embodiment will be described. First, the symbols newly added in FIG. 3 as compared with FIG. 2B will be described. The time T3 is the timing at which the tip of the reversed transfer material 19 in the conveyance direction reaches the registration sensor 20 from the timing (t518) when the transfer of the toner image formed on the black photosensitive drum 1K to the intermediate transfer belt 9 is completed. The time until (t520) is shown. The time Td indicates the time required to reduce the speed of the main motor 204 from the speed Vp (printing speed) to the speed Vl (deceleration speed). On the other hand, the time Tu indicates the time required to increase the speed of the main motor 204 from the speed Vl to the speed Vp. The time Tc indicates a speed limit time during which the speed of the main motor 204 is maintained at the speed Vl. The speed Vp indicates a steady speed when the main motor 204 is printing. The speed Vl indicates a steady speed at the time of deceleration control of the main motor 204, and in this embodiment, the minimum speed that can be rotated is set so that the time Tc of the speed limit time becomes the minimum time.

  Accordingly, the speeds Vp and Vl are fixed values determined in advance, and the times Td and Tu are also determined according to the speeds Vp and Vl, and thus are fixed values. On the other hand, the time T3 is a fluctuation value that varies depending on the difference between the transfer material lengths A and B, and the time Tc that is the speed limit time is also a fluctuation value that varies depending on the difference between the transfer material lengths A and B.

  In this embodiment, the above-described print error is prevented by controlling the speed of the intermediate transfer belt 9 as follows. That is, the position of the tip of the toner image on the intermediate transfer belt 9 when the transfer material having the transfer material length B reaches the registration sensor 20 is the same as the position of the leading edge of the toner image on the intermediate transfer belt 9 when the transfer material having the transfer material length A reaches the registration sensor 20. Speed control is performed so that the upper toner image reaches the same position. Referring to FIG. 3, the intermediate transfer belt 9 moves between the timing (t518) when the transfer of the toner image to the intermediate transfer belt 9 is completed and the timing (t520) when the transfer material 19 reaches the registration sensor 20. The distance may be reduced by the difference in transfer material length. For this purpose, a speed limit time Tc that satisfies the following equations (1) to (3) is calculated, and the speed of the intermediate transfer belt 9 is controlled by the main motor 204 according to the calculated speed limit time Tc. Good. The distance Du used in the expressions (1) and (2) indicates the distance that the intermediate transfer belt 9 travels at time Tu, and the distance Dd indicates the distance that the intermediate transfer belt 9 travels at time Td. The distances Du and Dd are eigenvalues determined according to the times Tu and Td, which are eigenvalues described above.

  The difference between the transfer material length of the transfer material 19 actually transported and the designated transfer material (transfer material length A-transfer material length B) (hereinafter abbreviated as (AB)) is as follows. Can be calculated.

(A−B) = (Vp × (Td + Tc + Tu)) − (Dd + Vl × Tc + Du)
= (Vp-Vl) * Tc + Vp * (Td + Tu)-(Dd + Du) (1)
Note that (Vp × (Td + Tc + Tu)) indicates the distance that the intermediate transfer belt 9 moves when speed control is not performed, and (Dd + Vl × Tc + Du) indicates that the intermediate transfer belt 9 moves when speed control is performed. Indicates the distance to perform.
Furthermore, when Expression (1) is transformed into an expression for obtaining the speed limit time Tc, the following Expression (2) is obtained.

Speed limit time Tc = [(A−B) −Vp × (Td + Tu) + (Dd + Du)] / (Vp−Vl) (2)
The speed of the intermediate transfer belt 9 is controlled during the time T3, that is, after the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 has been completed, It must be completed before the registration sensor 20 is reached. Therefore, the speed limit time Tc must be a time that satisfies the following conditional expression (3).

(Td + Tc + Tu) <T3 (3)
Here, when the speed control of the intermediate transfer belt 9 is executed ((Td + Tc + Tu in FIG. 3)), the / TOP signal for the first surface of the second transfer material 19 is output (t521). The toner image is disturbed. Therefore, in the case of continuous duplex printing, it is necessary to output the / TOP signal after completing the speed control of the intermediate transfer belt 9. Therefore, in order to make the output timing of the / TOP signal on the first surface of the second transfer material 19 as fast as possible, the speed of the main motor 204 is the minimum speed at which the speed limit time Tc is minimized and which can be rotated. The speed limit time Tc is calculated by setting the speed Vl. Then, the CPU 205 controls the speed of the intermediate transfer belt 9 by setting the rotation speed of the main motor 204 to the speed Vl for the calculated speed limit time Tc. As a result, the drive instruction timing (t522) of the registration roller 11 based on the / TOP signal output timing (t516) on the second surface of the transfer material 19 is the same when the transfer material lengths A and B are the same and speed control is unnecessary. Compared to the time required for speed control of the intermediate transfer belt 9, the time is delayed. As a result, before the transfer material 19 reaches the secondary transfer roller 12, a print error occurs in which the leading edge of the second-side toner image formed on the intermediate transfer belt 9 reaches the secondary transfer roller 12. Can be prevented.

  Subsequently, the CPU 205 determines the speed of the main motor 204 at the timing when the image formation on the second surface of the transfer material 19 is completed, that is, when the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 is completed (t518). Is changed from the speed Vp to the speed Vl. Then, the CPU 205 changes the speed of the main motor 204 to the speed Vp again after the speed limit time Tc described above has elapsed while maintaining the speed Vl that is the deceleration speed. The CPU 205 outputs a / TOP signal for the first surface of the second transfer material 19 at the timing when the speed of the main motor 204 returns to the speed Vp (t521). The CPU 205 starts driving the registration roller 11 after the leading edge of the first transfer material 19 in the conveyance direction reaches the registration sensor 20 (t520) (t522), and conveys the transfer material 19 to the secondary transfer roller 12. Then, the toner image on the intermediate transfer belt 9 is transferred to the transfer material 19.

[Control sequence for duplex printing]
FIG. 4A is a flowchart showing a control sequence during the double-sided printing operation of this embodiment. The flowchart of FIG. 4A is activated when the CPU 205 that has received a print start command from the controller unit 201 completes preparation for a print operation. It is assumed that the time Td, Tu, the distance Dd, Du, the print speed Vp and the deceleration speed Vl of the main motor 204 are stored in the ROM 206. Also, the time from the output of the / TOP signal to the completion of the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 (the time between t516 and t518 in FIG. 3) is determined in advance by design. It is assumed that the stored time (fixed value) is stored in the ROM 206. The above-described time T1 is also a predetermined fixed value regardless of the transfer material length, and is stored in the ROM 206.

  In step (hereinafter referred to as S) 600, the CPU 205 outputs a / TOP signal for the first surface of the first transfer material 19 to the controller unit 201 (t511 in FIG. 3), and starts the printing operation for the first surface. . In step S <b> 601, the CPU 205 resets and starts the timer 1 for measuring the timing for outputting the / TOP signal for the second surface of the transfer material 19. In step S <b> 602, the CPU 205 resets and starts the timer 2 for measuring the re-transport timing for resuming the transport of the transfer material 19. In step S <b> 603, the CPU 205 refers to the timer 2 and determines whether or not the transfer material re-conveying timing for resuming the conveyance of the transfer material 19 (t515 in FIG. 3) has been reached. If the CPU 205 determines that the transfer material re-transport timing has been reached, the process proceeds to step S604. If the CPU 205 determines that the transfer material re-transport timing has not been reached, the process of step S603 is repeated. Note that the transfer material re-conveying timing time (timer value) is stored in the ROM 206 in advance, and is read by the CPU 205 as needed.

  In step S <b> 604, the CPU 205 resets and starts the timer 3 for measuring the transfer material length of the transfer material 19. In step S605, the CPU 205 refers to the timer 1 and determines whether or not the timing (t516 in FIG. 5) for outputting the / TOP signal for the second surface has been reached. If the CPU 205 determines that the / TOP signal output timing for the second surface has been reached, the process proceeds to S606. If the CPU 205 determines that the / TOP signal output timing has not been reached, the process of S605 is repeated. The / TOP signal output timing for the second surface is determined based on the length of the transfer material in the transport direction, that is, the size of the transfer material. The CPU 205 receives the size from the controller unit 201 prior to the start of printing, and acquires the size of the transfer material 19 from the print reservation information stored in the RAM 207. The ROM 206 stores a time (timer value) corresponding to the timing for outputting the / TOP signal corresponding to the size of the transfer material. The CPU 205 determines that the / TOP signal output timing for the second surface has been reached when the timer 1 has reached the corresponding timer value. In S606, the CPU 205 outputs the / TOP signal for the second surface of the first transfer material 19 to the controller unit 201 (t516 in FIG. 3). Further, the CPU 205 resets and starts the timer 4 in order to measure the passage of time from the / TOP signal output (t516 in FIG. 3).

  In step S <b> 607, the CPU 205 acquires the detection result of the registration sensor 20 via the sensor input unit 212, and the registration sensor 20 falls (from the on state (transfer material is detected) to the off state (transfer material is not detected)). Is detected). If the CPU 205 determines that the trailing edge of the registration sensor 20 has been detected, the process proceeds to step S608. If the CPU 205 determines that the trailing edge has not been detected, the process of step S607 is repeated. In step S <b> 608, the CPU 205 determines that the trailing end of the transfer material 19 in the conveyance direction has passed the registration sensor 20 by detecting the falling edge of the registration sensor 20, and the timer 3 for measuring the transfer material length of the transfer material 19. To complete the measurement of the transfer material length. The CPU 205 calculates a transfer material length of the transfer material 19 by reading a timer value (corresponding to the time from t515 to t517 in FIG. 3) from the timer 3 and multiplying the transfer speed of the transfer material 19. Note that the conveyance speed of the transfer material 19 is stored in the ROM 206 in advance. Further, the CPU 205 reads the timer value from the timer 4 and stores it in the RAM 207. The timer value of the timer 4 read at this time indicates the time from the output of the / TOP signal until the trailing end of the transfer material 19 in the transport direction passes through the registration sensor 20. The CPU 205 calculates the time T3 (FIG. 3) as follows. The time (t516 to t520 in FIG. 3) from the output of the / TOP signal until the tip of the inverted transfer material 19 reaches the registration sensor 20 is the time stored in the RAM 207 and the time stored in the ROM 206. It is obtained by adding T1. Then, the time from the output of the / TOP signal to the completion of the transfer of the toner image to the intermediate transfer belt 9 (time from t516 to t518 in FIG. 3) stored in the ROM 206 is subtracted from the obtained time. Time T3 can be calculated.

  In S609, the CPU 205 controls the speed of the intermediate transfer belt based on the transfer material length of the transfer material 19 calculated in S608 and the time T3. In step S <b> 610, the CPU 205 determines whether there is a next print reservation from the print reservation information received from the controller unit 201 prior to the start of printing and stored in the RAM 207. If the CPU 205 determines that there is a next print reservation, the process returns to S600, and if it is determined that there is no print reservation, the process ends. In addition, although four timers were used for the time measurement mentioned above, time measurement can be performed with two timers by making the timer 2 and the timer 3 into the same timer, and making the timer 1 and the timer 4 into the same timer, for example. it can.

  FIG. 4B is a flowchart showing a control sequence of S609 in FIG. 4A for controlling the speed of the intermediate transfer belt 9. In FIG. The flowchart of FIG. 4B is activated when S609 of FIG. 4A is executed. In S620, the CPU 205 determines that the transfer material length of the transfer material 19 calculated in S608 (FIG. 4A) is set in the print reservation information received from the controller unit 201 (designated transfer material length of the transfer material). Size) or longer. If the CPU 205 determines that the transfer material length of the transfer material 19 is longer than the specified size (transfer material length> specified size), the CPU 205 proceeds to S621. On the other hand, if the CPU 205 determines that the transfer material length of the transfer material 19 is not longer than the specified size (transfer material length ≦ specified size), the CPU 205 ends the process and returns to the process of FIG.

  In step S621, the CPU 205 determines the speed described above from the difference between the designated transfer material size (corresponding to the transfer material length B described above) and the transfer material transfer material length calculated in step S608 (corresponding to the transfer material length A described above). The time limit Tc is calculated using the above-described equation (2). At this time, the CPU 205 reads the values of the times Td, Tu, distances Dd, Du, and the speeds Vp, Vl of the main motor 204 used in the equation (2) from the ROM 206. Further, the CPU 205 confirms that the calculated speed limit time Tc satisfies the above-described equation (3), that is, the total time of the time Tu, the speed limit time Tc, and the time Td is shorter than the time T3. At this time, the CPU 205 reads the time Td and Tu used in Expression (3) from the ROM 206, and uses the time T3 calculated in S608 of FIG. 4A as the time T3.

  In step S <b> 622, the CPU 205 refers to the timer 4 to determine whether the image formation on the second surface of the transfer material 19 is completed, that is, the toner image formed on the black photosensitive drum 1 </ b> K on the second surface is transferred to the intermediate transfer belt 9. Judge whether it has been transcribed. If the CPU 205 determines that the image formation on the second side has been completed, the process advances to step S623. If it is determined that the image formation has not ended, the process of step S622 is repeated. As described above, the time from when the / TOP signal is output until the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 is completed (the time between t516 and t518 in FIG. 3) in advance. It is stored in the ROM 206 and read by the CPU 205 as needed. In step S623, the CPU 205 executes speed control of the intermediate transfer belt 9. That is, the CPU 205 performs control to reduce the rotational speed of the main motor 204 from the speed Vp that is the speed at the time of printing to the speed Vl (deceleration speed) via the drive control unit 209. The CPU 205 confirms that the time Td has elapsed and the rotation speed of the main motor 204 is the speed Vl, and maintains the state of the main motor 204 that has been decelerated to the speed Vl for the speed limit time Tc. Then, after the time Tc has elapsed, the CPU 205 performs control to return the rotation speed of the main motor 204 from the speed Vl (deceleration speed) to the speed Vp that is the printing speed via the drive control unit 209. After the time Tu has elapsed, the CPU 205 confirms that the rotation speed of the main motor 204 is at the speed Vp, ends the process, and returns to the process of FIG.

  The speed control of the intermediate transfer belt 9 when the transfer material length of the fed transfer material is longer than the designated transfer material length has been described above. On the other hand, when the transfer material length of the fed transfer material is shorter than the designated transfer material length, the CPU 205 registers the registration roller when the transfer material 19 conveyed through the reverse path 25 reaches the registration sensor 20. 11 is stopped, and the conveyance of the transfer material 19 is temporarily stopped. Then, the CPU 205 drives the registration roller 11 in accordance with the timing at which the toner image on the second surface of the transfer material 19 formed on the intermediate transfer belt 9 reaches the secondary transfer roller 12 to convey the transfer material 19. Then, the toner image is transferred to the transfer material 19. As described above, when the transfer material length of the fed transfer material is shorter than the designated transfer material length, the speed control of the intermediate transfer belt 9 is not performed. However, the speed control of the intermediate transfer belt 9 is not performed. It is also possible to respond by performing In this case, the distance that the intermediate transfer belt 9 moves is increased by the difference in transfer material length between the timing at which the transfer of the toner image to the intermediate transfer belt 9 is completed and the timing at which the transfer material 19 reaches the registration sensor 20. You can do it. That is, when the toner image formed on the black photosensitive drum 1K on the second surface is transferred to the intermediate transfer belt 9, the rotational speed of the intermediate transfer belt 9 is temporarily increased, and the transfer material 19 is transferred to the secondary transfer roller 12. Control to return to the original speed before acceleration may be performed in accordance with the arrival timing.

  Therefore, when the length of the fed transfer material is short, the speed of the main motor 204 is reduced to the minimum speed limit time Tc, contrary to the minimum speed Vl when the transfer material length is long. The speed limit time Tc is calculated by setting the speed Vh that is the maximum speed that can be rotated. Then, the CPU 205 controls the speed of the intermediate transfer belt 9 by setting the rotational speed of the main motor 204 to the speed Vh for the calculated speed limit time Tc.

  Specifically, the CPU 205 increases the speed of the main motor 204 at the timing when the image formation on the second surface of the transfer material 19 is completed, that is, when the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 is completed. The speed Vp is changed to the speed Vh. Then, the CPU 205 changes the speed of the main motor 204 to the speed Vp again after the speed limit time Tc described above has elapsed while maintaining the speed Vh that is the acceleration speed. The CPU 205 outputs a / TOP signal for the first surface of the second transfer material 19 at the timing when the speed of the main motor 204 returns to the speed Vp. The CPU 205 starts driving the registration roller 11 after the leading edge of the first transfer material 19 in the conveyance direction reaches the registration sensor 20, conveys the transfer material 19 to the secondary transfer roller 12, and the intermediate transfer belt 9. The upper toner image is transferred to the transfer material 19. As a result, before the leading edge of the second-side toner image formed on the intermediate transfer belt 9 reaches the secondary transfer roller 12, a print error occurs in which the transfer material 19 reaches the secondary transfer roller 12. Can be prevented.

  In this embodiment, the registration sensor 20 detects the leading edge and the trailing edge of the transfer material and measures the transfer material length. However, the registration sensor 20 is provided with a dedicated detection means for measuring the transfer material length. May be. In this case, the detection unit is not necessarily disposed on the upstream side in the conveyance direction of the transfer material 19 of the secondary transfer roller 12 as in the registration sensor 20, but may be on the downstream side.

  As described above, according to the present embodiment, it is possible to prevent the occurrence of a print error when the transfer material length of the fed transfer material is different from the designated transfer material length during duplex printing. In this embodiment, the formation of the toner image on the second surface is started based on the designated transfer material length, and optimum productivity is realized when the actual transfer material length is the same as the designation. Further, when the actual transfer material length is longer than the designated transfer material length, the speed of the intermediate transfer belt 9 is reduced at the timing when the image formation on the second side is completed, and then returned to the steady speed again. Make adjustments. On the other hand, when the actual transfer material length is shorter than the designated transfer material length, the speed of the intermediate transfer belt 9 is accelerated at the timing when the image formation on the second side is completed, and then returned to the steady speed again. Adjust the speed. As a result, even if the transfer material length of the fed transfer material is different from the designated transfer material length, it is possible to perform a double-sided printing operation without causing a print error.

  In the first exemplary embodiment, when the length of the fed transfer material in the conveyance direction (transfer material length) is longer than the transfer material length of the designated transfer material, the toner image on the intermediate transfer belt is transferred to the transfer material. The speed adjustment of the intermediate transfer belt for adjusting the transfer timing has been described. In the first embodiment, in order to make the output timing of the / TOP signal to the subsequent transfer material as early as possible, the minimum speed at which the speed of the main motor that drives the intermediate transfer belt can be rotated so that the speed limit time is minimized. It was set to. However, as the speed at the time of deceleration is lowered, the speed change of the main motor becomes larger, and the frequency of the sound accompanying the rotation driving of the main motor is modulated, so there is a possibility that the frequency belongs to the human audible band. In the second embodiment, an example in which the motor sound in the audible band is reduced by extending the speed limit time to an allowable limit and suppressing the speed change during deceleration will be described. Since the configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment, the same reference numerals are used, and detailed description of the present embodiment is omitted.

[Timing chart of double-sided printing operation when transfer material size is larger than specified]
FIG. 5 shows the case where the transfer material length A of the transfer material 19 placed in the paper feed cassette 18 is larger than the transfer material length B of the transfer material designated by the controller unit 201 (A> B). It is a timing chart which shows the continuous double-sided printing operation to which an example is applied. (A) to (h) in the vertical axis direction of FIG. 5 are the same as those of FIG. 3 of the first embodiment described above, and description of how to read the drawings is omitted. In addition, the horizontal axis of FIG. 5 indicates time, and t811 to t822 in the figure indicate timing (time). Note that timings t811 to t822 in FIG. 5 respectively correspond to t511 to t522 in FIG. 3 of the first embodiment, and the duplex printing operation shown in FIG. 5 and the duplex printing operation shown in FIG. Since it is the same except for the speed control of the transfer belt, the description is omitted here.

  Next, a method for controlling the speed of the intermediate transfer belt 9 of this embodiment will be described. First, the symbols newly added in FIG. 5 of the present embodiment compared to FIG. 3 of the first embodiment will be described. The time Td 'indicates the time required to reduce the speed of the main motor 204 from the speed Vp (printing speed) to the speed Vl' (deceleration speed). On the other hand, the time Tu ′ indicates the time required to increase the speed of the main motor 204 from the speed Vl ′ to the speed Vp. The time Tc ′ indicates a speed limit time during which the speed of the main motor 204 is maintained at the speed Vl ′. The speed Vp indicates a steady speed when the main motor 204 is printing. The speed Vl ′ indicates a steady speed during deceleration control of the main motor 204, and in this embodiment, a speed that satisfies a time (Tc ′ + Td ′ + Tu ′) = time T3 described later is set. Therefore, in this embodiment, the speed Vp is a predetermined fixed value, but the speed Vl ′ is a fluctuation value, and the times Td ′ and Tu ′ are also fluctuation values determined according to the speeds Vp and Vl ′. Become. On the other hand, the time T3 is a fluctuation value that varies depending on the difference between the transfer material lengths A and B, and the time Tc ′ that is the speed limit time is also a fluctuation value that varies depending on the difference between the transfer material lengths A and B.

  In this embodiment, the above-described print error is prevented by controlling the speed of the intermediate transfer belt 9 as follows. That is, the position of the tip of the toner image on the intermediate transfer belt 9 when the transfer material having the transfer material length B reaches the registration sensor 20 is the same as the position of the leading edge of the toner image on the intermediate transfer belt 9 when the transfer material having the transfer material length A reaches the registration sensor 20. Speed control is performed so that the upper toner image reaches the same position. Referring to FIG. 5, the intermediate transfer belt 9 moves in the entire period from the timing (t818) when the transfer of the toner image to the intermediate transfer belt 9 is completed to the timing (t820) when the transfer material 19 reaches the registration sensor 20. It is only necessary to reduce the distance to be transferred by the difference in transfer material length. That is, in Example 1, control was performed to reduce the difference between the transfer material lengths of the two transfer materials in the minimum time in the period of time T3. On the other hand, in the present embodiment, the speed difference between the speed Vp and the speed Vl ′ of the main motor 204 is reduced by performing control to reduce the difference between the transfer material lengths of the two transfer materials using the entire time T3. The frequency modulation is reduced, and the motor sound in the audible band is reduced. For this purpose, a speed Vl ′ and a speed limit time Tc ′ satisfying the following expressions (4) and (5) are calculated, and the main motor 204 performs the calculation according to the calculated speed Vl ′ and the speed limit time Tc ′. The speed of the intermediate transfer belt 9 may be controlled. The distance Du ′ used in the equation (4) or the like indicates the distance that the intermediate transfer belt 9 travels at time Tu ′, and the distance Dd ′ indicates the distance that the intermediate transfer belt 9 travels at time Td ′. The distances Du ′ and Dd ′ are determined according to the above-described times Tu ′ and Td ′.

  The difference between the transfer material length of the transfer material 19 actually transported and the designated transfer material (transfer material length A-transfer material length B) (hereinafter abbreviated as (AB)) is as follows. Can be calculated.

(AB)
= (Vp × (Td ′ + Tc ′ + Tu ′)) − (Dd ′ + Vl ′ × Tc ′ + Du ′)
= (Vp−Vl ′) × Tc ′ + Vp × (Td ′ + Tu ′) − (Dd ′ + Du ′) (4)
Note that (Vp × (Td ′ + Tc ′ + Tu ′)) indicates the distance that the intermediate transfer belt 9 moves when speed control is not performed, and (Dd ′ + Vl ′ × Tc ′ + Du ′) indicates speed control. This indicates the distance that the intermediate transfer belt 9 moves when the above is performed.

  The speed control of the intermediate transfer belt 9 is started at time T3, that is, when the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 is completed. The process ends when the registration sensor 20 is reached. Therefore, the speed limit time Tc ′ must be a time that satisfies the following conditional expression (5).

(Td ′ + Tc ′ + Tu ′) = T3 (5)
Further, for example, the proportional relationship between the time Tu ′ of the present embodiment and the time Tu of the first embodiment is obtained by using the speeds Vp, Vl, and Vl ′ of the main motor 204 and time Tu ′: time Tu = (Vp−Vl ′). ): (Vp−Vl). Therefore, the times Tu ′ and Td ′ and the distances Du ′ and Dd ′ can be expressed as follows using the times Tu, Td, the speeds Vp, Vl, and the distances Du and Dd described in the first embodiment. it can.

Tu ′ = Tu × (Vp−Vl ′) / (Vp−Vl) (6)
Td ′ = Td × (Vp−Vl ′) / (Vp−Vl) (7)
Du ′ = Du × (Vp−Vl ′) / (Vp−Vl) (8)
Dd ′ = Dd × (Vp−Vl ′) / (Vp−Vl) (9)
As described in the first embodiment, the times Tu, Td, the speeds Vp, Vl, and the distances Du, Dd are fixed values (predetermined values), so that the times Tu ′, Td 'And distances Du' and Dd 'are determined according to the velocity Vl'. Further, as described above, since the time T3 can also be calculated, the time Tc ′ is determined according to the speed Vl ′ from the equations (5), (6), and (7). Therefore, the speed Vl ′ and time Tc ′ satisfying the expressions (4) and (5) are obtained, and the speed of the intermediate transfer belt 9 is controlled in accordance with the obtained speed Vl ′ and time Tc ′, so that the audible band is obtained. The motor noise can be reduced.

[Flow chart for duplex printing when the transfer material size is larger than specified]
As described above, in this embodiment, the speed control method of the intermediate transfer belt 9 is different from that in the first embodiment, but the control sequence during the continuous double-sided printing operation of the transfer material is the same as that in the first embodiment. Therefore, the flowchart showing the control sequence during the double-sided printing operation in the present embodiment uses FIG. 4A of the first embodiment, and the speed of the intermediate transfer belt 9 activated in S609 of FIG. 4A. For the control, the flowchart shown in FIG. 6 is used. In addition, description of the flowchart of FIG. 4A of Example 1 is abbreviate | omitted here.

  In S700, the CPU 205 transfers the transfer material length (designated) of the transfer material 19 set in the print reservation information received from the controller unit 201, as the transfer material length of the transfer material 19 calculated in S608 (FIG. 4A). Size) or longer. If the CPU 205 determines that the transfer material length of the transfer material 19 is longer than the specified size (transfer material length> specified size), the process proceeds to S701. On the other hand, if the CPU 205 determines that the transfer material length of the transfer material 19 is not longer than the specified size (transfer material length ≦ specified size), the CPU 205 ends the process and returns to the process of FIG.

  In step S701, the CPU 205 designates the designated transfer material size (corresponding to the transfer material length B described above) and the transfer material length calculated in step S608 (FIG. 4A) (corresponding to the transfer material length A described above). The above-described control speed Vl ′ is calculated from the difference. The speed limit time Tc 'for which the main motor 204 maintains the calculated control speed Vl' must satisfy the above-described formula (5).

  Therefore, in this embodiment, the control speed Vl ′ and the speed limit time Tc ′ are determined by the method described below. In other words, the control speed Vl ′ is discretely selected, and the selected control speed Vl ′ is substituted into the above formulas (6) and (7), thereby calculating the times Tu ′ and Td ′. The speed limit time Tc ′ is calculated by substituting the times Tu ′ and Td ′ into the above equation (5). Subsequently, the distances Du ′ and Dd ′ are calculated by substituting the selected control speed Vl ′ into the above formulas (8) and (9). Then, the selected control speed Vl ′, the calculated speed limit time Tc ′, and the distances Du ′ and Dd ′ are substituted into the above equation (4), and it is determined whether the values on the left side and the right side are equal. When the CPU 205 determines that the values on the left side and the right side are equal, the speed Vl ′ and the time Tc ′ at that time are changed to the control speed Vl ′ and the speed limit time Tc ′ used in the speed control of S703 described later. Determine and end the process. On the other hand, when the CPU 205 determines that the values on the left side and the right side are not equal, the CPU 205 selects the next control speed Vl ′ and repeats the above-described processing.

  In the present embodiment, the control speed Vl ′ described above is selected as follows. That is, the control speed Vl ′ is a speed between the speed Vp that is the speed at the time of printing and the speed Vl that is the minimum speed at which the main motor 204 can rotate as described in the first embodiment. Therefore, the control speed Vl ′ is defined as Vl ′ = Vl + (Vp−Vl) × INDEX value, and the control speed Vl ′ is discretely selected (determined) by applying a value from 0 to 1 to the INDEX value. ) In this embodiment, the INDEX values are applied in increments of 0.1 of 0, 0.1, 0.2,... 0.9, 1 and the control speed Vl ′ and the speed limit time Tc are determined by the above-described method. To decide. When the INDEX value is large, for example, 0.05 or 0.01 may be used. Further, since the control speed Vl ′ is discretely selected, there may be a case where the control speed Vl ′ and the speed limit time Tc ′ that satisfy both the above-described equations (4) and (5) cannot be determined. Therefore, for example, among the control speed Vl ′ and the speed limit time Tc ′ satisfying the expression (4), the control speed Vl ′ and the speed limit time Tc ′ satisfying the following expression obtained by modifying the expression (5) are selected. do it. That is, the time (Td ′ + Tc ′ + Tu ′) <time T3 is satisfied, and the time (Td ′ + Tc ′ + Tu ′) is substantially equal to the time T3, that is, the control speed Vl ′ having the smallest difference between the two times. The speed limit time Tc ′ may be selected.

  In step S <b> 702, the CPU 205 refers to the timer 4 to determine whether the image formation on the second surface of the transfer material 19 is completed, that is, the toner image formed on the black photosensitive drum 1 </ b> K on the second surface is transferred to the intermediate transfer belt 9. Judge whether it has been transcribed. If the CPU 205 determines that the image formation on the second side has been completed, the process advances to step S703. If it is determined that the image formation has not ended, the process of step S702 is repeated. As in the first embodiment, the time from when the / TOP signal is output until the transfer of the toner image on the photosensitive drum 1 to the intermediate transfer belt 9 is completed (the time between t816 and t818 in FIG. 3). Is stored in advance in the ROM 206 and is read by the CPU 205 as needed. In step S <b> 703, the CPU 205 executes speed control of the intermediate transfer belt 9. That is, the CPU 205 performs control to reduce the rotation speed of the main motor 204 from the speed Vp that is the speed at the time of printing to the speed Vl ′ (deceleration speed) via the drive control unit 209. The CPU 205 confirms that the time Td ′ has elapsed and the rotational speed of the main motor 204 is the speed Vl ′, and changes the state of the main motor 204 that has been decelerated to the speed Vl ′ during the speed limit time Tc ′. maintain. Then, after the time Tc ′ has elapsed, the CPU 205 performs control to return the rotation speed of the main motor 204 from the speed Vl ′ (deceleration speed) to the speed Vp that is the printing speed via the drive control unit 209. After the time Tu ′ has elapsed, the CPU 205 confirms that the rotation speed of the main motor 204 is at the speed Vp, ends the process, and returns to the process of FIG.

  The speed control of the intermediate transfer belt 9 when the transfer material length of the fed transfer material is longer than the designated transfer material length has been described above. On the other hand, even when the transfer material length of the fed transfer material is shorter than the designated transfer material length, it can be dealt with by controlling the speed of the intermediate transfer belt 9. In this case, the speed control of the intermediate transfer belt that increases the distance that the intermediate transfer belt 9 moves by the difference in the transfer material length is started from the timing when the transfer of the toner image to the intermediate transfer belt 9 is completed. What is necessary is just to complete | finish at the timing which 19 arrives at the registration sensor 20. FIG. That is, when the toner image formed on the black photosensitive drum 1K on the second surface is transferred to the intermediate transfer belt 9, the rotational speed of the intermediate transfer belt 9 is temporarily increased, and the transfer material 19 is transferred to the secondary transfer roller 12. Control to return to the original speed before acceleration may be performed in accordance with the arrival timing.

  Therefore, when the length of the fed transfer material is short, the acceleration speed Vh ′ of the main motor 204 and the speed are maintained in the same manner as the deceleration speed Vl ′ when the transfer material length is long. The current speed limit time Tc ′ is calculated. The sum of the speed limit time Tc ′, the time for acceleration to accelerate the speed of the main motor 204 from the speed Vp to the speed Vh ′, and the time for deceleration to decelerate the speed of the main motor 204 from the speed Vh ′ to the speed Vp. Must be approximately equal to time T3. Then, the CPU 205 controls the speed of the intermediate transfer belt 9 by adjusting the rotational speed of the main motor 204 according to the calculated acceleration speed Vh ′ and speed limit time Tc ′.

  As described above, according to the present embodiment, it is possible to prevent the occurrence of a print error when the transfer material length of the fed transfer material is different from the designated transfer material length during duplex printing. In this embodiment, the formation of the toner image on the second surface is started based on the designated transfer material length, and optimum productivity is realized when the actual transfer material length is the same as the designation. Further, when the actual transfer material length is longer than the designated transfer material length, the speed of the intermediate transfer belt 9 is reduced at the timing when the image formation on the second side is completed, and then returned to the steady speed again. Make adjustments. Thereby, a double-sided printing operation can be performed without causing a printing error. Furthermore, by setting the rotational speed of the motor that drives the intermediate transfer belt to a speed that is as small as possible with respect to the printing speed, it is possible to reduce the rotational noise of the motor that belongs to the human audible band. On the other hand, when the actual transfer material length is shorter than the designated transfer material length, the speed of the intermediate transfer belt 9 is accelerated at the timing when the image formation on the second side is completed, and then returned to the steady speed again. Adjust the speed. This makes it possible to perform a double-sided printing operation without causing a print error. Furthermore, by setting the rotational speed of the motor that drives the intermediate transfer belt to a speed that is as small as possible with respect to the printing speed, the motor is driven to the drive unit or the intermediate transfer belt due to a sudden change in the speed of the intermediate transfer belt. The load can be reduced.

[Other Examples]
In the image forming apparatus of the above-described embodiment, the time from the start of image formation until the leading edge of the toner image on the intermediate transfer belt reaches the secondary transfer roller is determined by the leading edge of the transfer material whose trailing edge has passed the registration sensor. It had a structure that was longer than the time required to reach the secondary transfer roller. The speed control of the intermediate transfer belt described above can also be applied to an image forming apparatus having a configuration different from the configuration of the above-described embodiment. That is, the time from the start of image formation until the leading edge of the toner image on the intermediate transfer belt reaches the secondary transfer roller is the time from when the trailing edge of the transfer material passes the registration sensor until the leading edge of the transfer material is secondary. The present invention can also be applied to an image forming apparatus having a configuration that is shorter than the time required to reach the transfer roller. Even in the image forming apparatus having such a configuration, when the actual transfer material length is longer than the designated transfer material length, the speed of the intermediate transfer belt 9 is increased at the timing when the image formation on the second surface is completed. Decelerate and adjust speed again to return to steady speed. On the other hand, when the actual transfer material length is shorter than the designated transfer material length, the speed of the intermediate transfer belt 9 is accelerated at the timing when the image formation on the second side is completed, and then returned to the steady speed again. Adjust the speed. As a result, even if the transfer material length of the fed transfer material is different from the designated transfer material length, it is possible to perform a double-sided printing operation without causing a print error.

  In addition, the transfer material length of the above-mentioned fed transfer material is also specified for an image forming apparatus capable of double-sided printing, in which an intermediate transfer belt is not provided and an image forming unit is configured from one photosensitive drum. It is possible to apply a speed control method when the length is different from the transfer material length. In the case of the image forming apparatus having this configuration, first, a difference in transfer material length is calculated before image formation is started. Then, the photosensitive drum is rotated in the same direction so that the difference in transfer material length is adjusted using the entire period from the start of image formation until the toner image formed on the photosensitive drum is transferred to the transfer material at the transfer portion. Speed control for driving at a speed is performed. In the image forming apparatus of this configuration, the toner image on the photosensitive drum is transferred to the transfer material at the transfer unit, and the electrostatic latent image on the photosensitive drum is visualized by the toner of the developing device. Done in parallel. Therefore, when the image forming unit is composed only of the photosensitive drum, the photosensitive drum is rotated after the electrostatic latent image on the photosensitive drum is developed with toner, as in the case where the intermediate transfer belt described above is provided. Speed control to adjust the speed cannot be performed.

  As described above, according to the present embodiment, it is possible to prevent the occurrence of a print error when the transfer material length of the fed transfer material is different from the designated transfer material length during duplex printing.

6 Cartridge 9 Intermediate transfer belt 12 Secondary transfer roller 17 Discharge roller pair 20 Registration sensor 205 CPU

Claims (16)

An image carrier;
An image forming unit for forming an image on the image carrier;
A transfer unit that transfers the image formed on the image carrier by the image forming unit to a transfer material;
A reversing unit that reverses and conveys the transfer material that has passed through the transfer unit;
A transport unit that transports the transfer material transported from the reversing unit to the transfer unit;
Detecting means for detecting a leading edge and a trailing edge of the transfer material conveyed to the reversing unit;
In the image forming apparatus having a control unit for determining the size of the transfer material based on the detection result of the detection unit,
In order for the image forming unit to form images on both surfaces of the transfer material, the image corresponding to the first surface and the image corresponding to the second surface are provided at intervals based on a preset size of the transfer material. When the size of the transfer material formed on the body and determined by the control means is different from the preset size of the transfer material, an image corresponding to the second surface formed on the image carrier is transferred to the transfer material. An image forming apparatus characterized by accelerating or decelerating the rotational speed of the image carrier in order to transfer the toner image onto the image forming apparatus.   The image forming apparatus according to claim 1, wherein the image carrier is a photosensitive drum. The image carrier is an intermediate transfer member,
The image forming unit includes a plurality of photosensitive drums, and images formed on the plurality of photosensitive drums are transferred to the intermediate transfer member,
The image forming apparatus according to claim 1, wherein the image transferred to the intermediate transfer member is transferred to a transfer material by the transfer unit.   The time from when the rear end of the transfer material passes through the detection means to when it is reversed by the reversing unit and the conveying unit and conveyed to the transfer unit is from when image formation is started in the image forming unit. The image forming apparatus according to claim 3, wherein an image transferred to the intermediate transfer member is shorter than a time until the image reaches the transfer portion.   The rotation speed of the intermediate transfer member is controlled by transferring an image formed on the photosensitive drum arranged on the most downstream side in the rotation direction of the intermediate transfer member to the intermediate transfer member. 5. The image forming apparatus according to claim 4, wherein the image forming apparatus is performed after the image forming process is completed until image formation by the image forming unit on a subsequent transfer material is started.   6. The image according to claim 5, wherein when the size of the transfer material determined by the control unit is longer than the preset size of the transfer material, the rotational speed of the intermediate transfer member is reduced. Forming equipment.   The rotational speed at the time of deceleration of the intermediate transfer member and the speed limit time for maintaining the rotational speed at the time of deceleration are the difference between a preset length in the transport direction of the transfer material and a length in the transport direction of the transfer material. The image forming apparatus according to claim 6, wherein the image forming apparatus is determined based on the determination.   The image forming apparatus according to claim 7, wherein the rotation speed of the intermediate transfer member at the time of deceleration is the lowest rotation speed among rotation speeds at which the intermediate transfer member can be rotated.   The total time of the time for setting the rotational speed of the intermediate transfer member to the rotational speed at the time of deceleration, the speed limit time, and the time for returning the rotational speed of the intermediate transfer member to the rotational speed before the deceleration. Is transferred to the inverted transfer material at the transfer unit, and after the transfer of the image formed on the photosensitive drum of the image forming unit to the intermediate transfer member is completed, The image forming apparatus according to claim 7, wherein the image forming apparatus is shorter than a time until image formation by the image forming unit is started.   The total time of the time for setting the rotational speed of the intermediate transfer member to the rotational speed at the time of deceleration, the speed limit time, and the time for returning the rotational speed of the intermediate transfer member to the rotational speed before the deceleration. Is transferred to the inverted transfer material at the transfer unit, and after the transfer of the image formed on the photosensitive drum of the image forming unit to the intermediate transfer member is completed, The image forming apparatus according to claim 7, wherein the time is substantially equal, not exceeding a time until image formation by the image forming unit is started.   6. The image according to claim 5, wherein when the size of the transfer material determined by the control unit is shorter than the preset size of the transfer material, the rotational speed of the intermediate transfer member is accelerated. Forming equipment.   The rotational speed at the time of acceleration of the intermediate transfer member and the speed limit time for maintaining the rotational speed at the time of acceleration are the difference between the preset length in the transport direction of the transfer material and the length in the transport direction of the transfer material. The image forming apparatus according to claim 11, wherein the image forming apparatus is determined based on the determination.   The image forming apparatus according to claim 12, wherein the rotation speed of the intermediate transfer body during acceleration is the highest rotation speed among rotation speeds capable of rotating the intermediate transfer body.   The total time of the time for setting the rotational speed of the intermediate transfer body to the rotational speed at the time of acceleration, the speed limit time, and the time for returning the rotational speed of the intermediate transfer body to the rotational speed before acceleration. Is transferred to the inverted transfer material at the transfer unit, and after the transfer of the image formed on the photosensitive drum of the image forming unit to the intermediate transfer member is completed, The image forming apparatus according to claim 12 or 13, wherein the time is shorter than a time until image formation by the image forming unit is started.   The total time of the time for setting the rotational speed of the intermediate transfer body to the rotational speed at the time of acceleration, the speed limit time, and the time for returning the rotational speed of the intermediate transfer body to the rotational speed before acceleration. Is transferred to the inverted transfer material at the transfer unit, and after the transfer of the image formed on the photosensitive drum of the image forming unit to the intermediate transfer member is completed, The image forming apparatus according to claim 12, wherein the time is substantially equal, not exceeding a time until image formation by the image forming unit is started.   16. The image formation by the image forming unit on the subsequent transfer material is started before the rear end in the transport direction of the preceding transfer material passes through the transfer unit. The image forming apparatus described in the item.

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