JP4526510B2 - Image forming apparatus - Google Patents

Description

  In the present invention, a registration roller and a pre-registration roller are arranged on the upstream side of the electrostatic latent image carrier, the leading end of the conveyance paper is brought into contact with the registration roller, and the rear end side is sandwiched by the pre-registration roller After the paper is temporarily stopped by the above, the registration roller and the pre-registration roller are moved at a timing at which the leading edge of the image information visualized on the electrostatic latent image carrier and the leading edge of the paper stopped by the registration roller coincide with each other. The present invention relates to an image forming apparatus including a conveyance control unit that resumes conveyance of the paper by starting driving, and more specifically, corresponds to a high-speed machine in which the number of sheets conveyed to a transfer unit exceeds 100 sheets per minute. The present invention relates to an image forming apparatus.

  In recent image forming apparatuses, a vertical conveyance type that does not take up space is mainly used due to the installation space. That is, a plurality of paper feed cassettes are arranged in a multi-stage at the lower part of the apparatus main body, and a transfer part and a fixing part are arranged at the upper part. In such a structure, the transport paper fed from the paper feed cassette is transported upward once, is bent approximately 90 degrees in front of the transfer unit, and is converted into transport in the horizontal direction, and then transferred to the transfer unit. It is intended to be conveyed toward

  FIG. 6 shows the configuration of the paper transport path on the front side of the transfer unit.

  As described above, a pair of conveying rollers R31 and R32, pre-registration rollers R41 and R42, and registration rollers R51 and R52 are provided along the sheet conveying direction S from the upstream side in the sheet conveying path 28 arranged in a curved shape. The registration rollers R51 and R52 face each other at a distance of about 50 mm from the nip portion N1 that is a contact portion between the electrostatic latent image carrier (photosensitive drum) 14 and the transfer roller 17a. Yes.

  FIG. 7 is a chart showing the operation timing of the registration rollers R51 and R52 and the pre-registration rollers R41 and R42.

  That is, when the sheet P is conveyed through the sheet conveyance path 28 to the registration rollers R51 and R52 and the leading edge of the sheet contacts the nip portion N5 of the registration rollers R51 and R52, the registration rollers R51 and R52 first stop at time t1, At slightly later time t2, the pre-registration rollers R41 and R42 are stopped. Due to such a time difference stop, the paper P sandwiched between the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 is held in a slightly bent state as shown in FIG.

Thereafter, the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 align the leading edge of the paper P with the leading edge of the image information visualized on the electrostatic latent image carrier (photosensitive drum) 14. At time t3, which is the timing, the conveyance of the paper P is started again. At that time, the paper P is slightly bent, so that the feeding timing of the front end of the paper P from the registration rollers R51 and R52 can be matched in the width direction of the paper. the distortion of the formed image with respect to the width direction of P so that the free camphor. That is, the paper P once stopped by the registration rollers R51 and R52 is finely adjusted in the direction parallel to the paper transport direction S by the registration rollers R51 and R52, the center of the transport paper, and transported during the stop. The skew of time is corrected.

  Incidentally, recent image forming apparatuses are required to have a higher printing processing speed than conventional image forming apparatuses. For example, in the past, 60 sheets / min (in the case of A4 horizontal transport) or more was regarded as a high-speed machine, but in recent years, 80 sheets / min or more has been called a high-speed machine, and further 100 to 120 sheets. Development of an image forming apparatus of more than / min is also in progress.

  In such an image forming apparatus, it is necessary to improve the printing quality when the toner image on the electrostatic latent image carrier (photosensitive drum) is transferred onto the paper. In order to ensure this printing quality, Increases the accuracy of alignment between the leading edge of the image information visualized on the electrostatic latent image carrier (photosensitive drum) and the leading edge of the paper P stopped by the registration rollers R51 and R52. Is an important factor.

  As a technique for improving the accuracy of such alignment, a paper conveying device described in Patent Document 1 has been proposed.

This paper conveying device compares the time from the start of rotation of the timing roller until the sensor detects the leading edge of the paper with a preset reference time, and based on the difference between the two, the timing roller is moved upstream in the paper conveying direction. The leading edge of the paper is made to coincide with the leading edge of the image forming area on the photosensitive drum by being moved to the side or the downstream side.
JP 09-156802 A

  However, in recent high-speed machines, the paper conveyance speed has been increased, and the variation in the stop position of the paper leading edge at the registration roller has increased, and the timing of the subsequent conveyance paper excluding the first sheet can be adjusted when printing multiple sheets continuously. It has become difficult in terms of time. That is, since there is a time margin for the first printed sheet in the initialization process of the apparatus, it is possible to secure a time margin for adjustment at the registration roller portion by increasing the paper feeding timing from the paper feeding unit. Can do. However, the sheet conveyance timing for the second and subsequent sheets depends on the printing processing speed, that is, the conveyance speed, and for the second and subsequent sheets, the electrostatic latent image carrier (photosensitive member) before the leading end of the sheet contacts the nip portion of the registration roller. Since writing of image information onto the drum) has started, there is no time margin for adjusting the paper leading edge position at the registration roller portion.

  By the way, the most important thing in the alignment between the leading edge of the transport paper P and the leading edge of the image information visualized on the electrostatic latent image carrier (photosensitive drum) 14 is transport of the transport paper P. The speed and stop timing of the registration rollers R51 and R52. That is, the amount of biting when the leading edge of the paper P is stopped in a state where the leading edge of the paper P is bitten by the registration rollers R51 and R52 is most important for positioning the leading edge. The amount of biting depends on the stop timing of the registration rollers R51 and R52, but the transport speed at which the leading edge of the paper P is transported to the registration rollers R51 and R52 is a more important factor. For this purpose, it is necessary to detect and control the sheet conveyance speed of the pre-registration rollers R41 and R42 disposed immediately before the registration rollers R51 and R52. Since the paper conveyance speed changes depending on the paper type (basis weight, paper size, etc.) and the history change (roller surface property, scraping, etc.) of the pre-registration rollers R41, R42, the accurate paper conveyance speed is measured. Therefore, it is important for the alignment of the leading end of the sheet to determine the stop timing of the registration rollers R51 and R52 based on the result.

  The present invention was devised in view of such circumstances, and its purpose is to place a conveyance paper detection sensor before and after the pre-registration roller and to input to the pre-registration roller based on the paper conveyance speed detected by both sensors. An object of the present invention is to provide an image forming apparatus capable of fixing the timing at which the leading edge of the paper reaches the registration roller by determining the number of pulses and the energization time.

In order to solve the above-described problems, the image forming apparatus of the present invention has a registration roller and a pre-registration roller arranged upstream of the electrostatic latent image carrier, and makes the leading edge of the conveyance paper abut against the registration roller. After temporarily stopping the sheet with the end side being sandwiched between the pre-registration rollers, the leading edge of the image information visualized on the electrostatic latent image carrier and the leading edge of the sheet stopped by the registration roller In the image forming apparatus provided with a conveyance control unit that resumes conveyance of the sheet by starting driving of the registration roller and the pre-registration roller at the timing of matching, the pre-registration roller is disposed before and after the sheet conveyance direction. , it is composed of two sensors consisting of the upstream sensor and the downstream sensor for detecting the passage timing and rate of passage of the paper tip that passes through the upstream roller That a detecting means, the pre-registration drive means are constituted by a pulse motor for driving the roller, Bei example, said conveyance control means, based on a detection result of said detecting means, said pre-registration in the paper passage A control unit that controls the driving of the roller, and the control unit of the pre-registration roller controls the number of input pulses and energization time of the pulse motor, and monitors the upstream sensor and the downstream sensor, The number of pulses (X) required for driving the pulse motor after checking whether the leading edge has passed each sensor and before the leading edge of the sheet passes through the upstream sensor. The number of pulses (α) necessary for adjusting the speed of the transported paper by comparing the appropriate number of pulses (Y) calculated from the paper transport speed stored in advance in the memory and the number of measured pulses (X) Calculate The calculated pulse number (α) is added to the appropriate pulse number (Y) to obtain the input pulse number (Z) of the pulse motor, and the registration roller is stopped based on the input pulse number (Z). The timing A is calculated .

  In the present invention, the detection means is constituted by two sensors arranged before and after the pre-registration roller along the sheet conveyance direction. The sensor may be a mechanical switch such as a limit switch or the like, but a reflective or transmissive photocoupler may be used. Further, a pulse motor can be used as a driving means for driving the pre-registration roller. In this case, the drive control of the pre-registration roller is performed by controlling the number of input pulses of the pulse motor and the energization time.

  In other words, the transport control unit performs drive control of the pre-registration rollers so that a time during which a predetermined process can be performed on the paper after the leading edge of the transported paper reaches the registration roller can be secured. Specifically, the predetermined processing includes a paper front end alignment process for matching the front end of the transport paper and the front end of the image information on the electrostatic latent image carrier at the transfer unit, and the paper transport direction of the transport paper For example, a conveyance reference position alignment process in a direction orthogonal to the.

  That is, according to the present invention, the number of pulses of the drive source of the pre-registration roller when the front end of the paper passes between the two sensors arranged before and after the pre-registration roller is counted, so that the paper conveyance speed is appropriate. And the stop timing of the registration roller after passing the sensor can be confirmed. As a result, if the paper conveyance speed is not appropriate, the number of input pulses may be changed to an appropriate speed as described above, thereby making it possible to optimize the number of print processing sheets. In addition, by confirming the stop timing of the registration rollers, it is possible to secure an appropriate paper ejection amount and paper deflection amount, improve the alignment accuracy of the paper leading edge and image information leading edge at the transfer section, and also prevent the skew of the paper. It becomes possible to correct appropriately.

  According to the image forming apparatus of the present invention, it is possible to check whether or not the paper conveyance speed is appropriate and to check the stop timing of the registration roller by detecting the passage timing and the passage speed of the leading edge of the paper passing through the pre-registration roller. As a result, if the paper transport speed is not appropriate, the number of print processing sheets can be optimized by changing the number of input pulses to an appropriate speed. Further, by confirming the stop timing of the registration rollers, it is possible to ensure an appropriate amount of paper protrusion and amount of paper deflection, and to accurately align the front end of the paper and the front end of the image information at the transfer unit. Furthermore, the skew of the paper can be corrected appropriately.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing the overall configuration of the image forming apparatus according to the present embodiment.

  The image forming apparatus 1 of the present embodiment is a digital image forming apparatus having copy, printer, scanner, and fax modes, for example, and an operation panel 10 is provided on the front side.

  On the upper surface of the image forming apparatus 1, a manuscript table 11 made of a hard transparent glass body is arranged, an automatic manuscript feeder 12 is arranged above the manuscript table 11, and an optical unit 13 is arranged below the manuscript table 11. .

  Below the optical unit 13, a photosensitive drum 14 whose surface is made of a photoconductive material is rotatably supported. Around the photosensitive drum 14, a charger 15, a developing device 16, a transfer unit 17, and a cleaner 18 are disposed so as to face the peripheral surface of the photosensitive drum 14.

  In the image forming apparatus 1 configured as described above, when the start of the image forming process is instructed by operating the operation panel 10, the optical unit 13 scans the image surface of the document placed on the document table 11, and the inside of the optical unit 13 The light reflected from the copy lamp on the original image surface is irradiated onto the surface of the photosensitive drum 14.

  Prior to the irradiation of the reflected light from the original, the surface of the photosensitive drum 14 is uniformly charged with a single polarity charge by the charger 15, and the photoconductor is caused by the photoconductive action caused by the irradiation of the reflected light from the original. An electrostatic latent image is formed on the surface of the drum 14. Developer is supplied from the developing device 16 to the surface of the photosensitive drum 14 on which the electrostatic latent image is formed, and the electrostatic latent image is visualized as a developer image.

  A fixing unit 20 including a heating roller and a pressure roller is disposed on the downstream side of the photosensitive drum 14. A transfer belt 50 and a paper guide 19 of the transfer unit 17 are disposed between the fixing unit 20 and the photosensitive drum 14. The transfer belt 50 and the paper guide 19 allow the transfer belt 50 and the paper guide 19 to move from the photosensitive drum 14. A sheet conveyance path to the fixing unit 20 is formed.

  A sheet discharge tray 33 is provided on the side surface of the image forming apparatus 1, and a sheet discharge conveyance path 22 is formed between the fixing unit 20 and the sheet discharge tray 33. A part of the paper discharge conveyance path 22 branches through a branch gate 25 into a re-conveyance path 24 that is continuous with an automatic double-sided paper feeder 23 disposed below the photosensitive drum 14.

  Below the image forming apparatus 1, four paper feed cassettes 26 that are detachably mounted from the front side of the image forming apparatus 1 are provided. Each sheet cassette 26 stores sheets of different sizes, and the sheet from any one of the four sheet cassettes 26 is fed by a sheet feed roller 27 prior to the rotation of the photosensitive drum 14. Is fed through. The fed paper is conveyed in the direction of the photosensitive drum 14 by the conveyance rollers R31 and R32 via the common conveyance path 28, the rear end is sandwiched by the pre-registration rollers R41 and R42, and the front end is registered by the registration rollers R51 and R51. Stops in contact with R52. The basic configuration of this part is the same as the configuration shown in FIG. The operation timings of the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 are also the same as the operation timing shown in FIG.

  Further, the image forming apparatus 1 of the present embodiment includes a large-capacity paper feeding unit (LCC) 60. Although details of the structure of the large-capacity paper feed unit 60 are omitted, the paper fed from the large-capacity paper feed unit 60 is joined to the common transport path 28 before the transport rollers R31 and R32. , And is conveyed in the direction of the photosensitive drum 14 by the conveying rollers R31 and R32, the rear end is held between the pre-registration rollers R41 and R42, and the front end is brought into contact with the registration rollers R51 and R52 and stopped.

  The registration rollers R51 and R52 rotate in synchronization with the rotation of the photosensitive drum 14, and guide the sheet to the nip portion (image forming region) N5 between the photosensitive drum 14 and the transfer unit 17. The paper guided to the image forming area is subjected to corona discharge of the transfer unit 17, and the developer image carried on the surface of the photosensitive drum 1 is transferred to the surface of the paper.

  The sheet on which the developer image has been transferred is conveyed to the fixing unit 20 along the transfer belt 50 and the paper guide 19, and is heated and pressurized in the fixing unit 20, and the developer image is melted and fixed on the surface of the sheet. To do.

  In the single-sided printing mode in which an image is printed on one side of the paper, the paper that has passed through the fixing unit 20 is discharged from the paper discharge port 32 onto the paper discharge tray 33 by the paper discharge roller 31 via the paper discharge conveyance path 22. At this time, the paper discharge roller 31 is driven to reciprocate in the paper transport direction by a paper discharge roller drive unit (not shown).

  In the double-sided printing mode in which images are printed on both sides of the paper, the branch gate 25 is exposed in a part of the paper delivery conveyance path 22, and the paper that has passed through the fixing unit 20 passes through the re-conveyance path 24 including the conveyance roller 34. Then, it is conveyed to the automatic double-sided paper feeder 23. The paper transported to the automatic duplex paper feeder 23 is fed in a state where the front and back are reversed by the refeed roller 35, and again with the front and back surfaces reversed by the retransport roller 36 via the common transport path 28. It is conveyed in the direction of the photosensitive drum 14, the rear end is sandwiched between the registration rollers R41 and R42, and the front end is brought into contact with the registration rollers R51 and R52 and stopped.

  FIG. 2 shows the structure near the pre-registration rollers R41 and R42 according to this embodiment.

  That is, in the present embodiment, two sensors 71 for detecting the passage timing and passage speed of the leading edge of the paper passing through the pre-registration rollers R41 and R42 before and after the pre-registration rollers R41 and R42 along the paper conveyance direction S. , 72 are arranged. Here, a sensor disposed upstream of the pre-registration rollers R41 and R42 is referred to as an upstream sensor 71, and a sensor disposed downstream is referred to as a downstream sensor 72. These sensors 71 and 72 are configured as mechanical switches such as limit switches in FIG. 2, but are not limited to such mechanical switches, and for example, transmissive or reflective photocouplers can also be used. is there. Further, reference numerals 81 and 82 in the drawing are an upper paper guide and a lower paper guide that form a paper conveyance path between the registration rollers R51 and R52 and the pre-registration rollers R41 and R42.

  Next, the configuration of the control system in the image forming apparatus 1 having the above configuration will be described with reference to the block diagram shown in FIG.

  The central processing unit (control unit) 101 manages each drive mechanism unit constituting the image forming apparatus 1 such as the automatic document feeder 12, the optical unit 13, the image forming unit 102, and the sheet conveying system 103 by sequence control. Based on the detection values of the various sensor units 106 including the sensors 71 and 72, a control signal is output to each unit.

  An operation panel 10 is connected to the control unit 101 in a state where mutual communication is possible, and the operation of the operation panel 10 causes the image forming apparatus 1 to operate in accordance with print processing conditions set and input by the user. Yes.

  In addition, a memory 104 and an image data communication unit 105 are connected to the control unit 101. The memory 104 stores various control information necessary for controlling each drive mechanism unit constituting the image forming apparatus 1. The image data communication unit 105 is a communication unit provided for enabling information communication of image information and image control signals with other digital image devices.

  The control unit 101 performs print processing control in accordance with print processing conditions input and set by the user by operating the operation panel 10. At this time, the passage timing and passage speed of the leading edge of the paper passing through the pre-registration rollers R 41 and R 42 are controlled. Are detected by the two sensors 71 and 72, and based on the detection results, drive control of the pre-registration rollers R41 and R42 during paper passage is performed. Here, in the present embodiment, a pulse motor is used as a driving means for driving the pre-registration rollers R41 and R42. That is, the drive control of the pre-registration roller is performed by controlling the number of input pulses of the pulse motor and the energization time.

  That is, the control unit 101 sets the number of input pulses of the pulse motor and the energization time so that a predetermined processing time can be secured on the paper after the leading edge of the conveyed paper reaches the registration rollers R51 and R52. To control. Here, the predetermined processing includes a paper front end alignment process for matching the front end of the transport paper and the front end of the image information on the photosensitive drum 14 at the nip portion N5 that is a transfer unit, and transport of the transport paper. For example, a conveyance reference position alignment process in a direction orthogonal to the direction S.

  Hereinafter, drive control of the pre-registration rollers R41 and R42 during sheet conveyance (that is, sheet conveyance speed control) will be described with reference to the flowchart shown in FIG.

  When receiving a print request for a continuous printing process for a plurality of sheets by operating the operation panel 10 (step S1), the control unit 101 starts an initialization process of the apparatus (step S2). For example, in the photosensitive drum 14, an initialization process such as adjustment of the charging potential by the charger 15 and removal of toner contamination on the surface of the photosensitive drum 14 by the cleaner 18 is started. Then, it is confirmed whether or not the initialization process of the apparatus is completed (step S3). When the initialization process is completed, the control unit 101 feeds the first sheet from one sheet feeding cassette 26 ( Step S4).

At this time, the control unit 101 monitors the upstream sensor 71 and the downstream sensor 71 to check whether the leading edge of the sheet has passed through each sensor (steps S5 and S6). The number of pulses (X required for driving the pulse motor, which is the drive source of the pre-registration rollers R41 and R42, from the time when the leading edge of the sheet passes through the upstream sensor 71 to the time when it passes through the downstream sensor 72. ) measured (step S7), and compared to the memory 104 of the control unit 101 (FIG. 3) to the appropriate number of pulses is calculated from the sheet conveying speed which is previously stored (Y), and a measurement pulse number (X) (Step S8), the number of pulses (α) necessary for adjusting the speed of the conveyed paper is calculated (Step S9). Next, the calculated pulse number (α) is added to the appropriate pulse number (Y) obtained in step S8 to obtain the input pulse number (Z) of the pulse motor (step S10).

  Steps S7 to S10 will be specifically described. For example, when the number of pulses (X) measured in step S7 is 48 and the appropriate number of pulses obtained in step S8 is 50, in step S9, these differences 2 (= 50−48) is calculated as the required number of pulses (α). In step S10, a value 52 obtained by adding the calculated value α = 2 to the appropriate number of pulses Y = 50 is obtained as the number of input pulses (Z) to the pulse motor.

  Next, the control unit 101 calculates the stop timing (Asec) of the registration rollers R51 and R52 based on the number of input pulses (Z) (step S11). That is, the conveyance speed of the conveyance sheet can be determined by the number of input pulses (Z), and the distance between the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 is a constant distance (for example, within a range of 100 mm to 120 mm). Therefore, these conditions (however, the distance between the registration rollers R51 and R52 and the pre-registration rollers R41 and R42 are precisely between the registration rollers R51 and R52 and the downstream sensor 72). The distance at which the leading edge of the sheet reaches the registration rollers R51 and R52, that is, the stop timing (Asec) can be accurately calculated.

  Similarly, the stop timing (Bsec) of the pre-registration rollers R41 and R42 is calculated based on the number of input pulses (Z) (step S12). That is, as shown in FIG. 5, the pre-registration rollers R41 and R42 are stopped at the time t2 slightly after the registration rollers R51 and R52 are stopped (time t1), so the time ΔT from the time t1 to t2 is stopped. By adding (sec) to the stop timing (Asec) of the registration rollers R51 and R52, the stop timing (B = A + ΔT) of the pre-registration rollers R41 and R42 can be obtained accurately. Note that the times t1, t2, and t3 in the timing chart shown in FIG. 5 are the same timing as the times t1, t2, and t3 in the timing chart shown in FIG.

  When the respective stop timings (that is, energization times) A and B are calculated in this way, the control unit 101 activates an internal timer circuit (not shown) and starts from time t0 when the downstream sensor 72 detects the leading edge of the sheet. Measurement time A and B is started (step S13).

  The control unit 101 monitors the time measured by the internal timer circuit to monitor whether or not the time A has passed since the leading edge of the paper passed the downstream sensor 72 (step S14). Then, the registration rollers R51 and R52 are temporarily stopped (step S15). The control unit 101 continues to monitor whether or not the time B has passed after the leading edge of the paper has passed the downstream sensor 72 (step S16), and once the time B has passed, temporarily stops the pre-registration rollers R41 and R42. (Step S17).

Thereafter, the control unit 101 matches the leading edge of the paper stopped by the registration rollers R51 and R52 with the leading edge of the image information visualized on the photosensitive drum 14 (that is, as shown in FIG. 5 ). (Time t3), the registration rollers R51 and R52 and the pre- registration rollers R41 and R42 are re-driven to resume the conveyance of the paper P (step S18). The printing process is executed through the fixing step 20 (step S19).

  Next, the control unit 101 checks whether or not there is a next print (step S20). If there is a next print, the control unit 101 returns to step S4 and feeds the next paper from the paper feed cassette 26. On the other hand, if there is no next printing, the process ends.

  The image processing apparatus of the present invention is suitably used for a high-speed digital multi-function peripheral that has a copy mode, a printer mode, a scanner mode, and a fax mode, and that processes a large amount of printed matter at a high speed.

1 is a side view showing an overall configuration of an image forming apparatus of the present invention. It is explanatory drawing which shows the structure of the pre-registration roller vicinity concerning this invention. 3 is a block diagram illustrating a configuration of a control system of the image forming apparatus of the present invention. FIG. 6 is a flowchart showing drive control of a pre-registration roller during sheet conveyance. 6 is a chart showing operation timings of a registration roller and a pre-registration roller according to the present invention. FIG. 6 is an explanatory diagram illustrating a configuration of a sheet conveyance path on the near side of a transfer unit. It is a chart which shows the operation timing of a registration roller and a pre-registration roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Operation panel 11 Document stand 12 Automatic document feeder 13 Optical unit 14 Photosensitive drum 15 Charger 16 Developer 17 Transfer unit 18 Cleaner 20 Fixing unit 22 Paper delivery path 23 Automatic duplex paper feeder 24 Re-conveyance Path 26 paper feed cassette 28 common transport path 31 (31a, 31b) paper discharge roller 32 paper discharge port 33 paper discharge tray 50 transfer belt 60 large capacity paper feed unit 61 unit side transport path 71 sensor (upstream sensor)
72 sensors (downstream sensors)
81 Upper paper guide 82 Lower paper guide 101 Central processing unit (control unit)
DESCRIPTION OF SYMBOLS 102 Image formation part 103 Paper conveyance system 104 Memory 105 Image data communication unit R31, R32 Conveyance roller R41, R42 Pre-registration roller R51, R52 Registration roller

Claims (4)

A registration roller and a pre-registration roller are arranged on the upstream side of the electrostatic latent image carrier. After stopping, the driving of the registration roller and the pre-registration roller is started at the timing when the leading edge of the image information visualized on the electrostatic latent image carrier and the leading edge of the paper stopped by the registration roller are matched. In the image forming apparatus including a conveyance control unit that resumes conveyance of the paper by
The front roller is disposed before and after the pre-registration roller in the sheet conveyance direction, and is composed of two sensors including an upstream sensor and a downstream sensor that detect a passage timing and a passage speed of the front end of the paper passing through the pre-registration roller. and a detection means is,
E Bei and a driving means is constituted by a pulse motor for driving the upstream roller,
The transport control unit includes a control unit that performs drive control of the pre-registration roller while the sheet is passing based on a detection result of the detection unit ,
The controller for the pre-registration roller controls the number of input pulses of the pulse motor and the energization time, and monitors the upstream sensor and the downstream sensor to determine whether the leading edge of the sheet has passed each sensor. After confirming, the number of pulses (X) required for driving the pulse motor is measured from the time when the leading edge of the paper passes the upstream sensor to the time when it passes the downstream sensor, and is stored in advance in the memory. The appropriate pulse number (Y) calculated from the paper conveyance speed is compared with the measured pulse number (X) to calculate the pulse number (α) necessary for adjusting the conveyance paper speed, and this calculated pulse number (α ) Is added to the appropriate number of pulses (Y), the number of input pulses (Z) of the pulse motor is obtained, and the stop timing A of the registration roller is calculated based on the number of input pulses (Z). An image forming apparatus. The controller for the pre-registration roller stops the pre-registration roller at a stop timing B at time t2 after a lapse of a time ΔT after the stop time t1 of the registration roller based on the number of input pulses (Z). The image forming apparatus according to claim 1.   The conveyance control unit performs drive control of the pre-registration roller so as to secure a time during which a predetermined process can be performed on the paper after the leading edge of the conveyed paper reaches the registration roller. The image forming apparatus according to claim 1 or 2. The predetermined processing includes a paper front end alignment process for matching the front end of the transport paper and the front end of the image information on the electrostatic latent image carrier with a transfer unit, and a direction orthogonal to the paper transport direction of the transport paper The image forming apparatus according to claim 3 , wherein the conveyance reference position alignment process is performed.

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