JP2011230880A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device that allows retries to feed the second and subsequent recording materials without reducing throughput when continuously forming an image on a plurality of recording materials.SOLUTION: The image forming device is configured as follows. In order to form an image to be formed by an image forming part in a predetermined position on a sheet, the sheet conveying speed is adjusted to a first conveying speed at a first position on the side upper, with respect to the sheet conveying direction, than the position of the image formed on the sheet by the image forming device on a conveying path. When no sheet is detected by a resist sensor provided on the conveying path, before the lapse of a predetermined period of time after the first sheet is fed from a sheet feeding cassette, the second sheet is fed and the sheet is conveyed at a second conveying speed faster than the first conveying speed.

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus such as a laser beam printer using an electrophotographic system, jamming may occur due to a defective recording material feeding or a poor conveyance due to a failure in picking up a recording material from a paper feeding cassette. . The image forming apparatus, for example, feeds a recording material when the recording material is not detected at a predetermined position downstream of the conveyance direction on the conveyance of the recording material within a predetermined time after the recording material is fed. It is determined that a jam has occurred, and the image forming operation is stopped. As a technology for eliminating such a paper jam and reducing a delay in image formation caused by the paper jam, there is a technology for retrying a paper feed operation when a failure of the paper feed operation is detected. Are known.

  For example, Patent Document 1 proposes a method of arbitrarily setting the number of paper feed retries in accordance with the state of the paper feed roller. In this method, the image forming apparatus repeats feeding retry up to the set number of times when the recording material is not detected at a predetermined position on the conveyance path within a predetermined time after the start of feeding of the recording material. Eliminate jams. This prevents unnecessary jams from occurring.

  Also, in an image forming apparatus, in general, when images are continuously formed on a plurality of recording materials, an image is formed on each recording material at a constant time interval in order to keep the throughput constant. There is a need to. In order to prevent a decrease in throughput in the image forming apparatus that executes the above-described paper feed retry, it is necessary to complete the paper feed retry within the time interval. For this reason, when images are continuously formed on a plurality of recording materials in one print job, the opportunity of paper feed retry relating to the second and subsequent recording materials is very limited in terms of time. In such a case, for the purpose of reducing the jam occurrence rate while maintaining the throughput, for example, a paper feed retry may be executed only when forming an image on the first recording material. is there.

JP 11-334935 A

  However, for example, when forming an image continuously on a plurality of recording materials, if a paper interval is widened in order to enable feeding retry of the second and subsequent recording materials, a problem of reducing throughput is caused. There is. For this reason, in the above-described prior art, if a failure in the paper feeding operation occurs when feeding the second and subsequent recording materials when images are continuously formed on a plurality of recording materials, the feeding is not reduced. It is difficult to eliminate jams by paper retry.

  The present invention has been made in view of the above-described problem. When images are continuously formed on a plurality of recording materials, the second and subsequent recording materials are fed without causing a decrease in throughput. An object of the present invention is to provide an image forming apparatus capable of retrying.

  The present invention can be realized as an image forming apparatus, for example. The image forming apparatus includes an image forming unit for forming an image on a recording material, a stacking unit on which the recording material is stacked, a sheet feeding unit that feeds the recording material stacked on the stacking unit, and a sheet feeding unit. A conveying unit that conveys the recording material fed to the conveying path to an image forming position where the image forming unit forms an image on the recording material, and an image formed by the image forming unit is formed at a predetermined position on the recording material. Therefore, an adjustment unit that adjusts the conveyance speed of the recording material to the first conveyance speed at a first position upstream of the image forming position in the conveyance path is provided. If the recording material is not fed by the paper operation, a second feeding operation of the recording material is performed by the paper feeding unit, and if the recording material is fed by the second recording material feeding operation, the conveying unit The recording material is directed to the first position by the first transport speed. Characterized by conveying a fast second transport speed.

  According to the present invention, for example, when images are continuously formed on a plurality of recording materials, an image forming apparatus capable of retrying feeding of the second and subsequent recording materials without causing a decrease in throughput. Can provide.

1 is a diagram illustrating a configuration of a laser printer 100 according to a first embodiment. It is a block diagram which shows the control mechanism of the laser printer 100 which concerns on 1st Embodiment. It is a figure which shows the signal transmitted in the laser printer 100 which concerns on 1st Embodiment. It is a figure which shows the relationship of the output timing of the / TOP signal and image data signal in the laser printer 100 which concerns on 1st Embodiment. FIG. 4 is an enlarged view of the vicinity of a registration roller pair 3 and a secondary transfer position in the laser printer 100 according to the first embodiment. FIG. 10 is a diagram illustrating a temporal change in the position of a sheet on a conveyance path in a comparative example in which high-speed sheet feeding control is not performed. FIG. 10 is a diagram illustrating a temporal change in the position of a sheet on a conveyance path in a comparative example in which high-speed sheet feeding control is performed. FIG. 6 is a diagram illustrating a temporal change in the position of a sheet on a conveyance path by sheet feeding and conveyance control according to the first embodiment. FIG. 6 is a diagram illustrating a temporal change in the position of a sheet on a conveyance path by sheet feeding and conveyance control according to the first embodiment. 4 is a flowchart illustrating a procedure of paper feed control and transport control according to the first embodiment. FIG. 10 is a diagram illustrating a temporal change in the position of a sheet on a conveyance path by sheet feeding and conveyance control according to the second embodiment. 10 is a flowchart illustrating a procedure of sheet feeding and conveyance control according to the second embodiment.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following embodiments do not limit the invention according to the claims, and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described. In the present embodiment, a case where the present invention is applied to an electrophotographic color (multicolor) laser printer will be described as an example of an image forming apparatus according to the present invention. However, the image forming apparatus of the present invention may be a mono-color (single color) type image forming apparatus or a complex machine.

<Overall configuration of image forming apparatus>
First, the overall configuration of the laser printer 100 according to the present embodiment will be described with reference to FIG. The laser printer 100 includes a plurality of image forming stations respectively corresponding to development colors of yellow (Y), magenta (M), cyan (C), and black (K). Each image forming station includes toner cartridges 11Y, 11M, 11C, and 11K, scanner units 10Y, 10M, 10C, and 10K, process cartridges 22Y, 22M, 22C, and 22K, and primary transfer rollers 4Y, 4M, 4C, and 4K. . Each process cartridge 22Y, 22M, 22C, 22K includes photosensitive drums 5Y, 5M, 5C, 5K, injection chargers (primary chargers) 7Y, 7M, 7C, 7K, and developing devices 8Y, 8M, 8C, 8K. It is mounted in a form that is detachable from the laser printer 100 main body. The laser printer 100 further includes an intermediate transfer member 12, a paper feed cassette 1 corresponding to a stacking unit on which sheets 2 as recording materials are stacked, and a fixing unit 13.

  A pre-registration roller pair 42 and a registration roller pair 3 for adjusting the conveyance of the sheet 2 are sequentially arranged in the conveyance direction along a conveyance path along which the sheet 2 fed from the sheet cassette 1 is conveyed. . The pre-registration roller pair 42 and the registration roller pair 3 are driven by a paper feed motor 41. A stepping motor may be used as the paper feed motor 41.

On the downstream side of the position of the registration roller pair 3 on the conveyance path, a sheet detection sensor (registration sensor) 19 that detects the presence or absence of the sheet 2 fed from the sheet feeding cassette 1 and conveyed. The registration sensor 19 is used, for example, to detect the leading edge and the trailing edge of the sheet 2. In FIG. 1, a position P ₁ on the conveyance path of the sheet 2 is a position of a sheet feeding port (sheet feeding position) for feeding the sheet 2 from the sheet feeding cassette 1 to the conveyance path. P ₂ is the position of the nip portion of the registration roller pair 3. P ₃ is a detection position by the registration sensor 19. P ₄ is the position of the nip portion between the intermediate transfer body 12 and the secondary transfer roller 9 and corresponds to the secondary transfer position.

  The photosensitive drums 5Y, 5M, 5C, and 5K are formed by applying an organic optical conductive layer to the outer periphery of an aluminum cylinder, and are rotated by a driving force by a driving motor (not shown). The photosensitive drums 5Y, 5M, 5C, and 5K are rotated clockwise in FIG. 1 by a drive motor in accordance with an image forming operation. The scanner units 10Y, 10M, 10C, and 10K form electrostatic latent images on the respective photosensitive drums by exposing the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K with laser beams in accordance with input image data signals. To do. The injection chargers 7Y, 7M, 7C, and 7K include sleeves 7YS, 7MS, 7CS, and 7KS, respectively. The developing devices 8Y, 8M, 8C, and 8K develop the electrostatic latent images formed on the photosensitive drums 5Y, 5M, 5C, and 5K using toner supplied from the toner cartridges 11Y, 11M, 11C, and 11K. Thus, the electrostatic latent images are visualized respectively.

The intermediate transfer body 12 rotates counterclockwise in FIG. 1 while being in contact with the photosensitive drums 5Y, 5M, 5C, and 5K during execution of the image forming process. As the photosensitive drums 5Y, 5M, 5C, and 5K rotate, a nip portion between the intermediate transfer body 12 and the photosensitive drums 5Y, 5M, 5C, and 5K is formed on the photosensitive drums 5Y, 5M, 5C, and 5K. It is conveyed to (primary transfer position). At the primary transfer position, each toner image is superimposed on the intermediate transfer body 12 from the photosensitive drums 5Y, 5M, 5C, and 5K by the primary transfer bias applied to the primary transfer rollers 4Y, 4M, 4C, and 4K. Primary transfer. The color toner image primarily transferred to the intermediate transfer body 12 is transferred to the sheet 2 at the secondary transfer position P ₄ (image forming position).

  The sheet 2 on which the color toner image is transferred is conveyed to the fixing unit 13, and the toner image is fixed to the sheet 2 by the fixing process by the fixing unit 13. The fixing unit 13 includes a fixing roller 14 that heats the sandwiched sheet 2 and a pressure roller 15 that presses the sheet 2 against the fixing roller 14. The fixing roller 14 and the pressure roller 15 are formed in a hollow shape, and incorporate heaters 16 and 17 respectively. The sheet 2 holding the toner image is nipped and conveyed by the fixing roller 14 and the pressure roller 15, and heat and pressure are applied thereto. As a result, the toner image on the sheet 2 is fixed on the surface of the sheet 2.

  After the fixing process, the sheet 2 is discharged to the paper discharge unit, whereby the image forming process for the sheet 2 is completed. The engine control unit 203 (not shown in FIG. 1) conveys the sheet 2 using the registration sensor 19, the pre-fixing sensor 27, the fixing paper discharge sensor 20, and the double-sided conveyance sensor 28 on the conveyance path of the sheet 2. Manage the situation.

<Control mechanism of image forming apparatus>
Next, the control mechanism of the laser printer 100 will be described with reference to FIG. Note that FIG. 2 particularly shows portions related to paper feed / conveyance control according to the present embodiment. As shown in the figure, the laser printer 100 includes a controller unit 201 and an engine control unit 203 as control mechanisms. The controller unit 201 can mutually communicate with the external host computer 200 and the engine control unit 203, and transmits and receives various commands and signals described below. The engine control unit 203 includes a video interface unit 204 connected to the controller unit 201 and a central processing unit (CPU) 205 connected to the video interface unit 204.

  The engine control unit 203 is connected to an image forming unit 206 and a paper feed motor 41 that drives a pair of conveyance rollers 40 for conveying a sheet on the conveyance path, a pair of pre-registration rollers 42, a pair of registration rollers 3, and the like. Yes. The image forming unit 206 includes each of the image forming stations described with reference to FIG. 1, the intermediate transfer body 12, the secondary transfer roller 9, and the like, and is connected to the video interface unit 204 in the engine control unit 203. The image forming unit 206 and the paper feed motor 41 are connected to the CPU 205 in the engine control unit 203. The CPU 205 controls the image forming unit 206 to form an image on the sheet 2 based on the image data signal input from the controller unit 201 to the video interface unit 204. Further, the CPU 205 drives the paper feed motor 41 at an appropriate timing and adjusts the rotation speed (drive speed) in order to form an image formed by the image forming unit 206 at a predetermined position on the sheet 2. By doing so, the conveying speed of the sheet 2 is adjusted.

  Next, signals transmitted between the controller unit 201 and the engine control unit 203 will be described with reference to FIG. Note that the direction of the arrow in FIG. 3 indicates the transmission direction of the signal transmitted through the signal line provided between the controller unit 201 and the engine control unit 203. The controller unit 201 transmits various commands (commands) to the engine control unit 203 by serial communication using the serial command transmission signal 103. In response to receiving the command, the engine control unit 203 transmits status data to the controller unit 201 by serial communication using the serial status transmission signal 104.

  The engine control unit 203 further transmits to the controller unit 201 a vertical synchronization signal (/ TOP signal) 105 that serves as a reference for the timing at which the controller unit 201 outputs the image data signals 110 to 113 to the engine control unit 203. In addition, the engine control unit 203 transmits horizontal synchronization signals 106 to 109 of each color of yellow (Y), magenta (M), cyan (C), and black (K) to the controller unit 201. The controller unit 201 synchronizes with the / TOP signal 105 and the horizontal synchronization signals 106 to 109 received from the engine control unit 203, and outputs the image data signals 110 to 113 of each color of Y, M, C, and K to the engine control unit 203. Send.

  The controller unit 201 receives image information and a print command from the host computer 200, analyzes the received image information, and converts it into bit data. Further, the controller unit 201 transmits a print reservation command to the engine control unit 203 via the video interface unit 204 in accordance with a print command for each sheet. The engine control unit 203 prepares for execution of printing according to the print reservation command received from the controller unit 201, and waits for a print start command from the controller unit 201. Thereafter, when the engine control unit 203 is ready for printing, the controller unit 201 transmits a print start command to the engine control unit 203. When the engine control unit 203 receives the print start command, the engine control unit 203 outputs to the controller unit 201 a / TOP signal that is a reference for the output timing of the image data signals 110 to 113. The controller unit 201 starts transmission of image data signals (video signals) 110 to 113 at a timing according to the received / TOP signal (shown in FIG. 4 described later). The engine control unit 203 starts a printing operation using the received image data signals 110 to 113 according to the settings included in the print reservation command.

(Transmission timing of image data signals 110 to 113)
Next, with reference to FIG. 4, transmission timings of the image data signals 110 to 113 for the respective colors output from the controller unit 201 to the engine control unit 203 in the image forming process of the laser printer 100 according to the present embodiment will be described. . FIG. 4 is a timing chart of the / TOP signal 105 and the image data signal 110 for each color in the laser printer 100 during the printing operation. ΔT _{1 to} ΔT ₄ represent elapsed times from when the controller unit 201 receives the / TOP signal 105 from the engine control unit 203 until the Y, M, C, and K image data signals 110 to 113 are output.

  When the controller unit 201 receives a print command from the host computer 200, the controller unit 201 shifts to an image print mode in which image printing is executed and issues a print reservation command to the engine control unit 203 using the serial command transmission signal 103. Upon receiving the print reservation command, the engine control unit 203 starts a printing operation and transmits a signal indicating that the printing operation has started to the controller unit 201 using the serial status transmission signal 104. When the printing operation starts, the laser printer 100 rotates the photosensitive drums 5Y, 5M, 5C, and 5K, the intermediate transfer belt drive motor that rotates the intermediate transfer body 12, and the scanner units 10Y and 10M. Start driving 10C and 10K.

When the preparation for printing each color is completed, the engine control unit 203 outputs a / TOP signal 105 to the controller unit 201. After receiving the / TOP signal 105, the controller unit 201 waits until the output timing of the Y image data signal 110 arrives (until the predetermined time ΔT ₁ elapses). After the output timing, the controller unit 201 synchronizes the image data signal for Y printing (specifically, the ON / OFF signal for the laser beam emitted from the scanner unit 10Y) 110 with the horizontal synchronization signal 106. To the engine control unit 203. In the engine control unit 203, the laser beam scanning system in the Y scanner unit 10Y emits a laser beam in accordance with the image data signal 110 input from the controller unit 201, thereby forming an electrostatic latent image on the photosensitive drum 5Y. To do. Further, the developing unit 8Y forms a toner image on the photosensitive drum 5Y by developing the electrostatic latent image formed on the photosensitive drum 5Y using Y toner. The toner image on the photosensitive drum 5Y is conveyed to the nip portion (primary transfer position) between the photosensitive drum 5Y and the primary transfer portion 4Y according to the rotation of the photosensitive drum 5Y, where the intermediate transfer is performed by the primary transfer portion 4Y. Primary transferred to the body 12.

The controller unit 201 matches the timing at which the toner image of Y toner on the intermediate transfer body 12 reaches the nip portion between the photosensitive drum 5M and the primary transfer portion 4M, and the M toner image reaches the nip portion. In this way, the image data signal 111 is output. Specifically, after receiving the / TOP signal, the controller unit 201 outputs the M image data signal 111 to the engine control unit 203 at a timing when a predetermined time (ΔT ₂ ) satisfying such a condition has elapsed. To do. Thereafter, the same process as the process for forming the Y toner image described above is executed, so that the M toner image is superimposed on the toner image at the position where the Y toner image is formed on the intermediate transfer body 12. Is primarily transferred. C and B toner images are also formed on the photosensitive drums 5C and 5K, respectively, by the same processing as described above, and are primarily applied to the intermediate transfer member 12 so as to overlap the toner images of the Y and M toners on the intermediate transfer member 12. Transcribed.

Through the above processing, a full-color toner image formed on the intermediate transfer body 12 based on the four color image data signals is formed. The full-color toner image is conveyed to the nip portion (secondary transfer position P ₄ ) between the intermediate transfer body 12 and the secondary transfer roller 9 as the intermediate transfer body 12 rotates.

<Sheet feeding and conveyance control>
Next, the conveyance control of the sheet 2 in the conveyance path in the laser printer 100 will be described with reference to FIG. FIG. 5 shows a portion upstream of the secondary transfer position P ₄ in the conveyance path of the sheet 2 shown in FIG. 1, and between the position P ₂ of the registration roller pair 3 and the secondary transfer position P ₄ . The distance is L ₀ .

When printing on the sheet 2, the engine control unit 203 starts conveying the sheet 2 from the sheet feeding port (sheet feeding position P ₁ ) and conveys the sheet 2 toward the registration roller pair 3. When the leading edge of the sheet 2 reaches the position (standby position) P _w1 corresponding to the predetermined pop-out amount L ₁ from the position P ₂ of the nip portion of the registration roller pair 3, the engine control unit 203 temporarily conveys the sheet 2. To stop. Specifically, the engine control unit 203, after detecting the leading end of the sheet 2 with a resist sensor 19, after a predetermined time required for the leading end of the sheet 2 is moved from the position P ₂ by a distance L _1, the resist The operations of the roller pair 3 and the pre-registration roller pair 42 are temporarily stopped. In the laser printer 100 according to the present embodiment, for example, L ₀ is about 90 mm and L ₁ is about 10 mm. In general, the conveyance control of the sheet 2 is performed so that the predetermined pop-out amount L ₁ is always a constant amount. However, in the present embodiment, as will be described later, when the sheet 2 is fed again, a pop-out amount different from L ₁ may be used.

Thereafter, the engine control unit 203 waits for the standby position P so that the sheet 2 reaches the secondary transfer position P ₄ at the timing when the toner image formed on the intermediate transfer body 12 reaches the secondary transfer position P _4. The conveyance of the sheet 2 is restarted from _w1 . Specifically, by resuming the operation of the registration roller pair 3 at the timing necessary for the leading edge of the toner image on the intermediate transfer body 12 and the leading edge of the sheet 2 to reach the secondary transfer position P ₄ simultaneously. Then, the conveyance of the sheet 2 is resumed. (Hereinafter, this timing is referred to as “re-feed timing”.)

  When the sheet conveyance is resumed at the refeed timing, the engine control unit 203 accelerates the rotation speed (sheet conveyance speed) of the registration roller pair 3 at a predetermined constant acceleration. After the rotational speed of the registration roller pair 3 reaches the process speed (first transport speed) of the apparatus, the engine control unit 203 maintains the rotational state of the registration roller pair 3 at the process speed.

  Next, with reference to FIG. 6, a description will be given of a relationship between start timings related to printing, paper feeding, and refeeding in the laser printer 100. In FIG. 6, the horizontal axis represents the elapsed time, the vertical axis represents the position of the leading edge and the trailing edge of the sheet on the conveying path, and the inclination of the line corresponds to the sheet conveying speed. First, the transmission interval of the / TOP signal 105 from the engine control unit 203 will be described with reference to 601 in FIG. When the engine control unit 203 receives the N-th print reservation command from the controller unit 201, the sub-scanning direction size (that is, the sheet conveyance direction size) L_paper_size [N ] Is memorized. Further, in the laser printer 100, the minimum paper gap necessary for reliably detecting the trailing edge of the preceding sheet and the leading edge of the succeeding sheet in consideration of the return time of the sensor flag in the registration sensor 19 and the chattering removal time. A distance L_gap_min is determined in advance.

The engine control unit 203 uses these pieces of information to transmit a transmission interval of the / TOP signal 105 during normal printing (corresponding to the Nth sheet // TOP signal corresponding to the N + 1th sheet from the transmission of the TOP signal 105). (Time interval until transmission of 105) ΔT_top_interval [N] is calculated as follows. However, V_process is the rotational speed (process speed) of the intermediate transfer body 12 and corresponds to the image forming speed of the laser printer 100.
ΔT_top_interval [N] = (L_paper_size [N] + L_gap_min) / V_process (1)
In FIG. 6A, ΔT_gap_min represents a time interval (= L_gap_min / V_process) corresponding to the above-described minimum paper distance.

As described above, the toner image formed on the intermediate transfer body 12 reaches the secondary transfer position P ₄ after a predetermined time has elapsed from the output timing T ₀ of the / TOP signal 105 by the engine control unit 203. In order to transfer the toner image to an appropriate position on the sheet, the engine control unit 203 needs to convey the sheet to the secondary transfer position in accordance with the arrival timing of the toner image to the secondary transfer position. Here, the time required to convey the sheet on the conveyance path from the sheet feeding position P ₁ of the sheet feeding port to the position P ₃ of the registration sensor 19 is normally slip at the start of sheet feeding, sheets in the sheet feeding cassette 1. May be changed due to a difference in the position of the transport path, a transport path difference in the transport path, and the like. That is, in the required time, an error from the design value may occur for each sheet. For this reason, the sheet conveyance time from P ₁ to P ₃ may vary from sheet to sheet. On the other hand, on the downstream side of the conveyance direction with respect to the registration roller pair 3 on the conveyance path, a relatively stable time depends on the conveyance path being flat and the setting of the clamping force of the registration roller pair 3. It is possible to convey the sheet. For this reason, there is little variation in the conveyance time from the registration roller pair 3 to the secondary transfer position P ₄ .

Therefore, as indicated by reference numeral 601 in FIG. 6, the engine control unit 203 starts sheet feeding and conveyance at timing T ₁ after a predetermined time ΔT_pick has elapsed from the output timing T ₀ of the / TOP signal. The engine control unit 203 temporarily stops the conveyance of the sheet being conveyed on the conveyance path at the above-described predetermined standby position P _w1 after detection by the registration sensor 19 (position P ₃ ). In this way, the engine control unit 203 sets the front end of the sheet to the standby position P _w1 downstream from the position P ₂ of the registration roller pair 3 with respect to the conveyance direction (the distance L ₁ from the position P ₂ of the registration roller pair 3). Transport to a remote location. Thereafter, /, based on the output timing T ₀ of the TOP signal, from T ₀ to re-feed timing T _R after a predetermined time ΔT_refeed elapsed, resumes the conveyance of the sheet at the process speed and the same conveying speed. This ΔT_refeed is determined in advance on the condition that the leading edge of the toner image on the intermediate transfer body 12 and the leading edge of the sheet reach the secondary transfer position P _{4 at} the same timing. Through the above processing, the toner image on the intermediate transfer body 12 can be transferred to an appropriate position on the sheet. Further, the feeding and conveyance of subsequent sheets are performed in the same manner.

  However, in the laser printer 100, a sheet conveyance failure (jam) may occur due to a failure in picking up a sheet from the sheet feeding cassette 1 or a paper jam at any location in the conveyance path. is there. When the jam occurs, it becomes difficult to normally transfer the toner image formed on the intermediate transfer body 12 to a predetermined position on the sheet. For example, when the sheet is not detected by the registration sensor 19 within a predetermined time (ΔT_jamwin of 601 in FIG. 6) after starting the sheet feeding, the engine control unit 203 determines that a jam has occurred. Stop printing operation. The predetermined time ΔT_jamwin is allowed in consideration of, for example, a difference in sheet position in the sheet feeding cassette 1, a sheet slip that may occur in the conveyance process to the registration sensor 19, a conveyance path difference in the conveyance path, and the like. Set to the maximum time. (Hereinafter, ΔT_jamwin is also referred to as “paper feed allowable time”.)

In the laser printer 100, when sheet pickup fails, the sheet is retried as indicated by 602 in FIG. 6 (hereinafter, also referred to as “sheet feeding retry control”), thereby performing sheet feeding. The pickup may be successful. As a result, it is possible to eliminate the pickup failure once occurred without stopping the printing operation. As a result, the occurrence rate of jam can be substantially reduced. The paper feed retry control retries the paper feed operation when the registration sensor 19 does not detect the leading edge of the sheet from the start of the paper feed operation (T ₁ of 602 in FIG. 6) until the paper feed allowable time ΔT_jamwin elapses. It is realized by doing. In this case, as indicated by reference numeral 602 in FIG. 6, the engine control unit 203 retries the paper feeding operation at time T ₂ after the elapse of the paper feed allowable time ΔT_jamwin from time T ₁ . If the sheet is detected by the registration sensor 19 after retrying the paper feeding operation and before the allowable paper feeding time ΔT_jamwin has elapsed, the engine control unit 203 determines that the sheet has been successfully fed and conveyed. Continue operation. On the other hand, if the sheet is not detected by the registration sensor 19 even after the allowable paper feed time ΔT_jamwin has elapsed since the start of retrying the paper feeding operation, the engine control unit 203 repeats the retry or stops the printing operation.

When such a paper feed retry control is performed (602 in FIG. 6), the time interval of the output timing of the / TOP signal needs to be increased as compared with a case where the pause retry control is not performed (601 in FIG. 6). It becomes. This is within the period from the timing T _R to start the re-fed from the timing T ₁ to start the first paper feed (ΔT_refeed), it is necessary to at least twice of the paper feeding allowed time ΔT_jamwin is ensured Because. That is, in addition to the first paper feeding operation, it is necessary to secure in advance a time for executing the second paper feeding operation. Furthermore, when printing continuously on a plurality of sheets, it is necessary to set ΔT_refeed in consideration of the time ΔT_gap_min necessary for securing the above-mentioned minimum paper distance L_gap_min as the space between sheets. There is. As described above, when the time interval of the output timing of the / TOP signal is extended for paper feed retry control, the printing speed (throughput) is reduced, leading to a reduction in productivity.

  As a technique for dealing with the above time constraint when performing the paper feed retry control, for example, the paper feed retry control is limited to the first sheet of the print job, and the second and subsequent sheets are fed. There is a method for preventing paper retry control. Thereby, a decrease in throughput can be avoided without increasing the output timing interval of the / TOP signal. However, by not performing the paper feed retry control for the second and subsequent prints, there is no possibility of the pickup failure occurring after the second page being eliminated. As a result, it becomes difficult to substantially reduce the jam occurrence rate.

(High-speed paper feed control)
In order to deal with the above-described problem, the present embodiment uses high-speed paper feed control described below. In an image forming apparatus such as a laser printer, speed control is usually performed to change process speeds in a transfer unit and a fixing unit in accordance with the type of a sheet to be printed. According to such speed control, for example, when the process speed for plain paper (for example, basis weight 90 [g / mm ² ]) is 250 [mm / sec], thick paper (for example, basis weight 220 [g / mm]). mm ² ]) is reduced to about 60 mm / sec. Even for thick paper, when carrying out the pickup operation from the paper feed port, the conveyance speed may be set to be equal to the normal paper process speed from the viewpoint of sheet conveyance stability. As described above, the speed control is appropriately performed in accordance with each process executed in the image forming apparatus, thereby improving the quality of the image formed on the sheet.

One such speed control is high-speed paper feed control. Fast feeding control, sheet feeding to execute the sheet conveyance of the feed position P ₁ of the paper feed port at the time of feeding the sheet to the conveying path to the standby position P _w1, than the process speed faster transport speed Control. FIG. 7 shows an example of high-speed paper feed control. In FIG. 7, the primary transfer of the toner image to the intermediate transfer body 12 and the secondary transfer from the intermediate transfer body 12 to the sheet are performed at a process speed of 60 [mm / sec], and high-speed paper feed control is performed for conveying the sheet. The case where is applied is shown. FIG. 7 shows how the positions of the leading and trailing edges of the sheet change with time as the sheet is conveyed in the upper part, and shows the driving speed (conveying speed) of the sheet feeding motor 41 in the lower part. A straight line G indicates a virtual position of the leading edge of the toner image on the intermediate transfer body 12, and the time T ₄ when the leading edge reaches the secondary transfer position P ₄ and the process speed of the printing process on the sheet. A straight line drawn based on

When images are continuously formed on a plurality of sheets, the paper feed motor 41 needs to drive each roller at a process speed until the trailing edge of the Nth sheet passes the registration roller pair 3. There is. After the trailing edge of the Nth sheet has passed the registration roller pair 3, there is no influence on the conveyance of the Nth sheet, so that the conveyance speed is increased in preparation for feeding control of the (N + 1) th sheet. Change the transport speed. After the speed change, feeding of the (N + 1) th sheet is started at a timing T ₁ when a predetermined time has elapsed and the motor driving speed is stabilized. Here, as an example, an example in which the sheet is conveyed at high speed to the standby position P _w1 is shown, but when the sheet reaches the standby position P _w1 , the sheet is earlier than the leading edge of the toner image on the intermediate transfer body 12. If the secondary transfer position P ₄ can be reached, the conveyance speed to the standby position P _w1 can be arbitrarily set. Further, where the position for conveying the sheet at a high speed as an example was to the standby position P _w1, at a timing earlier than the toner image tip end of it is on the intermediate transfer body 12 of the sheet when it reaches the standby position P _w1 If it can reach the secondary transfer position P4, it can be transported at a high speed to any position upstream of the standby position _Pw1 .

The engine control unit 203, when performing fast feed control, and feeding from the feed port to the sheet to the conveyance path at T _1, the process speed 60 [mm / sec] faster than a conveying speed 250 [mm / sec], the conveyance of the sheet is started. The engine control unit 203, in the high-speed conveying speed, the sheet is conveyed from the feed position P ₁ of the sheet feeding port to the standby position P _w1, where it is temporarily stopped (time T _2). Thereafter, the engine control unit 203 in a predetermined re-feed timing T _R, resumes the conveyance of the sheet at the process speed equivalent to the transport speed. With such high-speed paper feed control, for example, even when the sheet feeding is started after the image formation on the intermediate transfer body 12 is started, the toner image is placed at an appropriate position on the sheet at the secondary transfer position. It becomes possible to transfer.

(Paper retry control according to this embodiment)
The laser printer 100 that performs paper feed retry control according to the present embodiment uses the above-described high-speed paper feed control in order to enable the paper feed retry of the second and subsequent sheets without causing a decrease in throughput. In this embodiment, when printing is continuously performed on a plurality of sheets, high-speed paper feed control is executed at the time of retrying the paper feed operation in order to avoid widening the space for paper feed retry control. That is, by increasing the sheet conveyance speed when retrying the sheet feeding operation, the delay of the sheet feeding and conveying time caused by the failure of the sheet feeding operation is compensated. The sheet conveyance speed at the time of retrying the sheet feeding operation is a speed at which the sheet can reach the secondary transfer position P ₄ earlier than the leading edge of the toner image on the intermediate transfer body 12 on condition that the space between the sheets is not widened. It is necessary to be.

FIG. 8 shows sheet feed retry control using high-speed sheet feed control according to the present embodiment. FIG. 8 shows, as an example, a case where the sheet fed by the first sheet feeding operation is transported at the same transport speed as the process speed. Here, depending on the difference in sheet conveyance speed between the first paper feeding operation and the second (retry) paper feeding operation, different paper feed allowable times ΔT_jamwin1 and ΔT_jamwin2 are set. The engine control unit 203, after the start of the sheet of paper feeding at time T _1, when the tip of the sheet by the registration sensor 19 prior to the expiration of the feeding time allowed ΔT_jamwin1 is not detected, retrying the feeding operation of the sheet. Retry the sheet feeding operation, as well as carried out from time T ₁ to time T _2, after the lapse Derutati_jamwin1, the process speed (the first conveying speed) faster transport speed than the (second conveying speed) sheet Be transported. In FIG. 8, the success of the retry makes the leading edge of the sheet reach the standby position P _w1 (first position) at time T ₃ .

The fast transport speed, without increasing the Derutati_refeed, set the resumable speed conveyance of the sheet at the process speed from the standby position P _w1 at re feed timing T _R. That is, the conveying speed of the sheet in the sheet feed retry control requires that a sheet fed by the paper feed retry control is sufficiently fast in order to reach the standby position P _w1 before re-feed timing T _R It is. By performing the paper feed retry control at the transport speed satisfying such a condition, it is not necessary to widen the sheet interval for the paper feed retry control. As a result, the paper feed retry control can be executed on the second and subsequent sheets without causing a decrease in throughput.

Further, in the case of not being able to use a sufficiently high sheet conveyance speed so as not to widen the sheet interval during sheet feeding retry control, the following control may be executed as a modification of the present embodiment. In this modification, as shown in FIG. 9, when the paper feeding operation is retried, in addition to the execution of the high-speed conveyance control, the standby position is set to the conveyance direction rather than the normal position P _w1 (first position). The position is changed to a downstream position P _w2 (second position).

In this case, the laser printer 100 conveys the sheet fed at time T ₂ to the position P _w2 downstream of the conveyance direction with respect to the conveyance direction from P _w1 without stopping at the normal standby position P _w1. Let That is, at the time of paper feed retry, a position P _w2 closer to the secondary transfer position P ₄ than the normal standby position P _w1 on the conveyance path is set as a standby position for re-feeding. Here, the new standby position P _w2 is set to a position separated from the position P ₂ of the registration roller pair 3 by a distance L ₂ (> L ₁ ), as shown in FIG. Further, the standby position P _w2, as the timing at which the toner image on the intermediate transfer member 12 reaches the secondary transfer position P _4, the timing at which the leading end of the sheet reaches the secondary transfer position P ₄ match, The position is set at a position where the conveyance of the sheet can be resumed. That is, the setting of the P _w2 is slowest sheet that has passed the position of the resist sensor 19 when it reaches the standby position P _w2 at the timing, the toner image on at least the intermediate transfer body 12 in the range of the paper feed time allowed ΔT_jamwin It is necessary to make it possible for the sheet to reach the secondary transfer position P ₄ at an earlier timing than the leading edge.

Thereafter, the laser printer 100, in accordance with the timing at which the toner image on the intermediate transfer member 12 reaches the secondary transfer position P _4, resumes the conveyance of the sheet from the standby position P _w2 for when the paper feed retry. The timing corresponds to a time T _R2 when ΔT_refeed_retry has elapsed with reference to the output timing T ₀ of the / TOP signal in FIG. The laser printer 100 resumes the conveyance of the sheet at the conveyance speed equivalent to the process speed toward the secondary transfer position P ₄ at the _refeed timing T _R2 . As described above, in the present exemplary embodiment, when the sheet feeding retry is executed, the sheet standby position is set to the downstream side of the normal, thereby reducing the influence of the delay in the conveyance resumption timing caused by the sheet feeding retry. To compensate. Accordingly, the conveyance of the sheet on the conveyance path is resumed at the timing when the toner image on the intermediate transfer body 12 reaches the secondary transfer position P _4, and the toner image is transferred to an appropriate position on the sheet. Secondary transfer from 12 can be performed. Accordingly, when printing is continuously performed on a plurality of sheets, it is not necessary to widen the sheet space for the paper feed retry control. Therefore, the paper feed retry control is not performed on the second and subsequent sheets without causing a decrease in throughput. Can be executed. In this way, even if it is not sufficient only to increase the conveyance speed at the time of paper feed retry, by changing the sheet standby position to the downstream side, paper feed retry control can be performed without causing a decrease in throughput. realizable.

<Procedure for paper feed retry control>
Next, sheet feeding and conveyance control according to the present embodiment will be described based on the flowchart of FIG. Here, the embodiment shown in FIG. 9 will be described in which the sheet standby position is changed from P _w1 (first position) to P _w2 (second position) when the paper feed retry control is executed. The processing of each step in the flowchart is executed based on control by the CPU 205 of the engine control unit 203. In FIG. 10, as in FIG. 9, the printing process of the (N + 1) th sheet after the printing up to the Nth sheet is completed when the printing process is continuously performed on a plurality of sheets will be described.

First, in step S <b> 100, the CPU 205 outputs to the controller unit 201 a / TOP signal that is a temporal reference when executing the printing process for the (N + 1) th sheet. The CPU 205 starts image formation on the intermediate transfer body 12 using an image data signal transmitted from the controller unit 201 in response to the / TOP signal. Further, the CPU 205 starts a timer for measuring an elapsed time from the timing (T ₁ ) at which the / TOP signal is output. The CPU 205 monitors the sheet feeding timing (T ₂ ) and the sheet feeding timing (T ₃ ) based on the timer.

In step S <b> 101, the CPU 205 determines whether the sheet feeding timing (T ₂ ) has arrived based on the monitoring of the timer started in step S <b> 100. This determination process is executed by determining whether or not ΔT_pick has elapsed from the output timing (T ₁ ) of the / TOP signal. Here, as long as the CPU 205 determines that the sheet feeding timing has not arrived (“No” in S101), the determination processing in S101 is repeated. On the other hand, when the CPU 205 determines that the sheet feeding timing has arrived (“Yes” in S101), the CPU 205 starts sheet feeding processing in the next S102. Specifically, the CPU 205 drives the pickup solenoid of the paper feed port of the paper feed cassette 1 designated by the print job, thereby feeding the sheet from the paper feed port to the conveyance path and at the standby position P _w1. The sheet is conveyed toward. Further, the CPU 205 starts a timer for detecting a sheet feeding jam at the same time as starting the sheet feeding operation. Thereafter, the process proceeds to S103.

The transport speed (third transport speed) for transporting the sheet from the paper feed position P ₁ to the standby position P _w1 may be the same transport speed (first transport speed) as the process speed. The high-speed conveyance speed (second conveyance speed) by the above-described high-speed conveyance control may be used.

In step S103, the CPU 205 determines whether a sheet jam has occurred by determining whether the sheet has been successfully fed based on the timer activated in step S102. Specifically, the CPU 205 determines whether or not the leading edge of the sheet has been detected by the registration sensor 19 at the position P ₃ from the timing (T ₂ ) when the sheet feeding operation is started until the predetermined time ΔT_jamwin has elapsed. To do. If the leading edge of the sheet is detected within the predetermined time, the CPU 205 determines that the paper feeding operation has been successful, and the process proceeds to S105. On the other hand, if the leading edge of the sheet is not detected within a predetermined time, the CPU 205 determines that the sheet feeding operation has failed, and the process proceeds to S104.

(When paper feeding is successful)
In step S <b> 105, the CPU 205 controls the driving speed of the paper feeding motor 41 to convey the sheet on the conveyance path, and waits at a standby position P _w1 downstream by a distance L ₁ from the position P ₂ of the nip portion of the registration roller pair 3. Stop temporarily. Thereafter, in step S106, the CPU 205 determines whether or not the refeed timing (T _R1 ) has arrived. Here, the CPU 205 executes the determination process by determining whether or not a predetermined time ΔT_refeed has elapsed from the output timing (T ₁ ) of the / TOP signal based on the monitoring of the timer started in S100. If the predetermined time has not elapsed, the CPU 205 determines that the refeed timing (T _R1 ) has not arrived, and repeats the determination process. On the other hand, if the predetermined time has elapsed, it is determined that the refeed timing (T _R1 ) has arrived, and the process proceeds to S111.

(If paper feed fails)
In step S <b> 104, the CPU 205 retries (retrys) the sheet feeding operation similar to that in step S <b> 102 at time T <b> ₂ after ΔT_jamwin has elapsed from time T <b> ₁ . Thus, the CPU 205 functions as a paper feed retry unit. At this time, the CPU 205 determines that the third transport speed for transporting the sheet from the paper feed position P ₁ to the standby position P _w1 is different from the high transport speed (second transport speed) for paper feed retry. The conveyance speed is changed to the second conveyance speed before the sheet conveyance starts. On the other hand, the CPU 205 does not need to change the transport speed when the third transport speed is the same as the second transport speed.

In S104, CPU 205 further activates a timer for measuring the elapsed time from the time T _2. Thereafter, in step S107, the CPU 205 determines whether or not a paper jam has occurred by determining whether or not the retryed sheet has been successfully fed based on the timer started in step S104. Specifically, the CPU 205 determines whether or not the leading edge of the sheet has been detected by the registration sensor 19 at the position P ₃ before the predetermined time ΔT_jamwin has elapsed since the paper feed retry start time T ₂ . If the leading edge of the sheet is detected within a predetermined time, the CPU 205 determines that the retry of the sheet feeding operation has been successful, and the process proceeds to S109. On the other hand, if the leading edge of the sheet is not detected within a predetermined time, the CPU 205 determines that the retry of the sheet feeding operation has failed due to the occurrence of a sheet feeding jam, and the process proceeds to S108. In step S108, the CPU 205 performs a stop process of the image forming operation such as an emergency stop process of the engine as a countermeasure when a paper feed jam occurs, and then ends the process.

If the paper feed retry is successful, in step S109, the CPU 205 controls the drive of the paper feed motor 41 to convey the sheet to the standby position _Pw2 for paper feed retry, and temporarily stops the sheet there. As described above, the standby position P _w2 is changed to a position downstream of the position P ₂ of the nip portion of the registration roller pair 3 on the transport path and downstream of the normal standby position P _w1. .

Next, in S110, the CPU 205 determines whether or not a re-feed timing (T _R2 ) for paper feed retry has arrived. Here, the CPU 205 determines whether or not a predetermined time ΔT_refeed_retry has elapsed from the output timing (T ₁ ) of the / TOP signal based on the monitoring of the timer started in S100. As a result of the determination, if the predetermined time has not elapsed, the determination process of S110 is repeated. On the other hand, if the predetermined time has elapsed, it is determined that the re-feed timing (T _R2 ) for paper feed retry has arrived, and the process proceeds to S111.

Here, the above-described T_refeed and T_refeed_retry can be determined in advance by, for example, the following equations (2) and (3).
ΔT_refeed = ΔT_top_to_trans− (L ₀ −L ₁ −L_acc) / V_process−ΔT_acc (2)
ΔT_refeed_retry = ΔT_top_to_trans− (L ₀ −L ₂ −L_acc) / V_process−ΔT_acc (3)
In these equations, ΔT_top_to_trans represents the time from when the / TOP signal is output until the leading edge of the toner image formed on the intermediate transfer body 12 reaches the secondary transfer position P ₄ . ΔV_process represents a process speed (sheet conveyance speed after the standby position). L ₀ represents the distance between the position P ₂ of the registration roller pair 3 and the secondary transfer position P ₄ . Further, L_acc and ΔT_acc indicate the distance that the sheet is transported and the time required until the sheet rotation is resumed at the process speed after the driving of the sheet feeding motor 41 is resumed for refeeding. To express.

Finally, in S111, the CPU 205 resumes the conveyance of the sheet from the standby position _Pw1 or _Pw2 by resuming the driving of the sheet feeding motor 41 at the refeeding timing ( _TR1 or _TR2 ). . Thereafter, as described above, the sheet conveyed on the conveyance path has the secondary end of the sheet secondary to the timing at which the leading end of the toner image formed on the intermediate transfer body 12 reaches the secondary transfer position P _4. it reaches the transfer position P _4. As a result, at the secondary transfer position P ₄ , the toner image formed on the intermediate transfer body 12 is secondarily transferred to an appropriate position on the sheet.

Note that the following points should be noted when changing the standby position P _w2 for paper feed retry. In FIG. 9, the time required for stopping and starting the paper feed motor 41 is ensured from the time T ₃ to T _R2 (the time from when the sheet reaches the standby position P _w2 until the conveyance of the sheet is resumed). Need to be done. That is, after the paper feed motor 41 is temporarily stopped, the standby position P _w2 for paper feed retry is set on condition that the time required for starting again and driving at the process speed can be secured. It is necessary to. To do so, resulting in the sheet feeding and conveying process of a sheet from the paper feed position P ₁ to the standby position P _w2, in consideration of the variation from the set value of the conveying time, if the maximum delay in the conveyance time occurs P _w2 may be set so that

  As described above, in this embodiment, the sheet fed from the sheet feeding cassette is fed to the sheet feeding position where the sheet is fed to the conveyance path, and the toner image formed on the intermediate transfer member is applied to the sheet. It is detected by a registration sensor on the conveyance path between the transfer position and the transfer position. If a sheet is not detected within a predetermined time after the start of sheet feeding, the sheet feeding operation is retried. Further, when a sheet is detected within a predetermined time, the sheet is conveyed to a predetermined standby position downstream of the detection direction by the registration sensor on the conveyance path with respect to the conveyance direction. On the other hand, when the sheet is not detected within a predetermined time, the standby position of the sheet is changed to a position downstream of the predetermined standby position with respect to the conveyance direction, and at a higher speed than the process speed. The sheet is conveyed at the conveyance speed to the changed standby position. Thereafter, the conveyance of the sheet stopped at the standby position is resumed at the process speed so that the toner image on the sheet and the intermediate transfer member simultaneously reach the transfer position. According to the above processing, when images are continuously formed on a plurality of sheets, it is possible to execute the feeding retry of the second and subsequent sheets without causing a decrease in throughput. In addition, this can reduce the occurrence rate of jam.

[Second Embodiment]
Next, a second embodiment according to the present invention will be described. In the first embodiment, when a jam occurs on a sheet fed by the feed retry control, the image forming operation is stopped as described in S108 of FIG. In this embodiment, an embodiment in which the image forming operation is not stopped but the sheet feeding retry control is repeated with a predetermined number of times as an upper limit in such a case will be described.

In the present exemplary embodiment, the sheet standby position when the second and subsequent sheet feeding retries are performed is set to a position further downstream with respect to the sheet conveyance direction each time sheet feeding retries are repeated up to a predetermined number of times. change. Here, FIG. 11 shows a case where the sheet has been successfully fed by the second feeding retry. As shown in FIG. 11, a sheet fed by the sheet feed retry initiated at time T ₃ is conveyed further to the downstream of the standby position P _w3 than the standby position P _w2 in the case of the first paper feed retry The The sheet conveyed to the standby position _Pw3 is temporarily stopped at that position. Thereafter, the sheet conveyance from the standby position P _w3 to the transfer position P ₄ is resumed at the same conveyance speed as the process speed at the time T _R3 after the lapse of ΔT_refeed_retry_2 with respect to the output timing T ₀ of the / TOP signal. Regarding ΔT_refeed_retry_2, the timing at which the toner image formed on the intermediate transfer body 12 reaches the transfer position P ₄ and the timing at which the sheet conveyed from the standby position P _w3 reaches the transfer position P ₄ are matched. Is set. Through the above processing, the toner image on the intermediate transfer body 12 can be transferred to an appropriate position on the sheet conveyed to the transfer position P ₄ .

  The above control is demonstrated based on the flowchart of FIG. Parts that execute the same processing as in the first embodiment (FIG. 10) are given the same reference numerals in FIG. 12, and description thereof is omitted below. In this embodiment, if the CPU 205 determines in S107 that the retry operation for feeding the retryed sheet has failed, the CPU 205 executes the processing in S200 and subsequent steps.

In S200, CPU 205 is a time T ₃ after a lapse after the time T ₂ Derutati_jamwin elapsed in FIG. 11, to perform a second paper feed retry (third feeding operation). At the same time, the CPU 205 starts a timer to measure the elapsed time from the time T ₃ . Thereafter, in step S201, the CPU 205 determines whether the sheet feeding operation has failed again by determining whether or not the sheet feeding by the second sheet feeding retry is successful based on the timer started in step S200. Determine. Specifically, the CPU 205 determines whether or not the leading edge of the sheet is detected by the registration sensor 19 at the position P ₃ before the predetermined time ΔT_jamwin has elapsed from the start time T ₃ of the second paper feed retry. .

  In step S201, when the leading edge of the sheet is detected within a predetermined time, the CPU 205 determines that the retry of the sheet feeding operation has been successful, and the process proceeds to step S202. On the other hand, if the leading edge of the sheet is not detected within a predetermined time, the CPU 205 determines that the retry of the sheet feeding operation has failed due to the occurrence of a sheet feeding jam, and the process proceeds to S108. In step S108, as in the first embodiment, the CPU 205 performs a stop process of the image forming operation such as an emergency stop process of the engine as a countermeasure when a paper jam occurs, and then ends the process.

If the second paper feed retry is successful, in step S202, the CPU 205 sets the standby position changed at the time of the first paper feed retry from the standby position _Pw2 further downstream in the transport direction in the sheet transport path. The position is changed to the standby position _Pw3 . Further, the CPU 205 controls the drive of the paper feed motor 41 to convey the sheet to the changed standby position P _w3 for the second paper feed retry, and temporarily stops the sheet there.

Next, in S203, the CPU 205 determines whether or not a _refeed timing (TR3) for the second paper feed retry has arrived. Here, the CPU 205 is based on the monitoring of the timer started in S100. Then, it is determined whether or not the predetermined time ΔT_refeed_retry_2 has elapsed from the output timing (T ₁ ) of the / TOP signal, and if the predetermined time has not elapsed as a result of the determination, the determination result of S203 is repeated. If the predetermined time has elapsed, it is determined that the re-feed timing (T _R3 ) for the second paper feed retry has arrived, and the process proceeds to S 111. Note that ΔT_refeed_retry_2 is the first implementation. It can be obtained by the same procedure as the formulas (2) and (3) in the embodiment.

Finally, in step S111, the CPU 205 resumes the conveyance of the sheet temporarily stopped at any one of the standby positions P _w1 , P _w2 , and P _w3 (first to third positions). Thereafter, the sheet is conveyed to the secondary transfer position P ₄ , and the toner image formed on the intermediate transfer body 12 is secondarily transferred to an appropriate position on the sheet.

  As described above, according to the present embodiment, even if the first paper feed retry fails, the standby position during the second paper feed retry is changed further downstream with respect to the transport direction, Perform a paper retry. As a result, even when the paper feed retry fails, it is possible to retry the feeding of the second and subsequent sheets without reducing the throughput, and to reduce the jam occurrence rate.

Claims (5)

An image forming means for forming an image on a recording material;
Loading means loaded with recording materials;
Paper feeding means for feeding the recording material loaded on the loading means;
Conveying means for conveying the recording material fed to the conveying path by the paper feeding means to an image forming position where the image forming means forms an image on the recording material;
In order to form an image formed by the image forming unit at a predetermined position of the recording material, the recording material is conveyed at a first conveyance speed at a first position upstream of the image forming position in the conveyance path. Adjusting means for adjusting to the speed,
If the recording material is not fed by the first feeding operation of the recording material by the feeding device, the second feeding operation of the recording material is performed by the feeding device, and the second feeding of the recording material is performed. When the recording material is fed by operation, the recording material is transported by the transport means toward the first position at a second transport speed faster than the first transport speed. .   When the recording material is fed by the second feeding operation of the recording material by the paper feeding unit, the adjusting unit causes the downstream side from the first position and the upstream side from the image forming position by the adjusting unit. The image forming apparatus according to claim 1, wherein the conveyance speed of the recording material is adjusted to the first conveyance speed at the second position.   If the recording material is not fed by the second feeding operation of the recording material by the feeding device, the third feeding operation of the recording material is performed by the feeding device, and the third feeding of the recording material is performed. When the recording material is fed by the operation, the adjusting unit sets the conveyance speed of the recording material at a third position downstream of the second position on the conveyance path and upstream of the image forming position. The image forming apparatus according to claim 2, wherein the image forming apparatus is adjusted to a conveyance speed of 1.   The adjustment unit adjusts the conveyance speed to the first conveyance speed after temporarily stopping the recording material at any one of the first to third positions. Image forming apparatus. A detecting unit that is provided on the conveyance path between the sheet feeding position where the recording material is fed by the sheet feeding unit and the image forming position, and detects the presence or absence of the recording material conveyed along the conveyance path by the conveyance unit. Further comprising
The recording material is determined not to be fed if the recording material is not detected by the detecting means until a predetermined time has elapsed after the paper feeding operation by the paper feeding device is started. The image forming apparatus according to any one of 1 to 4.

Images