JP2009263085A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can continuously perform image formation on a plurality of sheets of paper without the risk of collision between sheets and without impairing productivity even when a sheet being fed slips. <P>SOLUTION: The image forming apparatus 1 includes: an image forming section 2 to form an image on paper P; transport rollers 63, 65 disposed upstream and downstream of a transport path 50 for transporting the paper P stored in a paper cassette 6 toward the image forming section 2; upstream and downstream drive sections 71, 73 to drive the upstream and downstream transport rollers 63, 65 at variable linear speeds; upstream and downstream paper detection sections 76, 77 to detect each sheet of paper passing through the upstream and downstream transport rollers 63, 65; and a control section 81. When the downstream paper detection section 77 detects a sheet of paper passing, the control section 81 controls a transport roller linear speed of the upstream drive section 71 to transport and drive the next sheet at a predetermined interval from the detected sheet based on the transport roller linear speed of the downstream drive section 73 transporting and driving the detected sheet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using the electrophotographic method, and more particularly to an image forming apparatus provided with a sheet conveyance path to an image forming unit.

  Conventionally, as this type of image forming apparatus, a primary sheet feeding unit that feeds sheets one by one from a sheet cassette, and a sheet fed to the registration roller by the primary sheet feeding unit is timed by the registration roller. Paper feeding to the image forming unit is performed by a two-stage paper feeding operation with a secondary paper feeding unit to be supplied to the image forming unit. The conveyance roller of the primary paper feed unit and the registration roller of the secondary paper feed unit are driven by a single drive motor, and on / off of the drive is controlled using an electromagnetic clutch or the like as necessary. The sheet fed from the sheet cassette is conveyed to the registration roller by the conveyance roller, and the leading end of the sheet is abutted against the registration roller and is temporarily stopped. Here, the registration roller is driven by turning on an electromagnetic clutch that controls on / off of the registration roller drive in accordance with the image formation timing of the image forming unit, and the sheet is conveyed toward the image forming unit. In the image forming unit, a toner image formed on a plurality of photoconductors arranged in parallel is transferred to an intermediate transfer belt, and the toner image on the intermediate transfer belt is transferred onto a sheet in the transfer unit. After the transfer is completed, the toner image is fixed by a fixing device disposed downstream, and the fixed paper is discharged out of the apparatus.

  However, in special paper such as thick paper and OHP sheets, the amount of heat required for fixing increases, so if the transport speed of the fixing device is slowed down, transport from the paper feed to the registration roller, and further until the sheet comes out of the fixing device, When transporting at a substantially constant transport speed, more time is required until the output of the first sheet, and there is a drawback in that productivity deteriorates.

  Therefore, in Patent Document 1, the conveyance speed of the sheet conveyed by the transfer unit of the image forming unit and the conveyance speed of the sheet conveyed by the registration roller of the secondary sheet feeding unit are substantially the same. The conveyance speed by the conveyance roller of the next sheet feeding unit is variable. Specifically, the feeding of the first sheet is stopped at the primary sheet feeding unit at a constant speed, the sheet leading edge reaches the registration roller, and the sheet leading edge hits the registration roller. After that, in the secondary paper feeding unit, the speed of the transport drive motor is reduced from a constant speed to a quarter speed, and the registration roller and the pre-registration transport roller pair are driven to form an image at a quarter speed. The sheet is conveyed to the image forming unit at a quarter speed. When feeding the second and subsequent sheets, a predetermined time after the trailing edge of the previous sheet comes out of the registration roller, the conveyance drive motor is shifted from the 1/4 speed to the constant speed, and then the next sheet is moved at a constant speed. Primary feeding is performed.

  However, in recent years, in order to increase the speed of image formation, it is necessary to increase the processing speed (copy speed and print speed) in the image forming apparatus to further improve productivity. The processing speed is determined by the time interval from the start of the previous secondary paper feed to the start of the next secondary paper feed. For example, when image formation is continuously performed on a plurality of sheets, when the secondary sheet feeding interval is set to 1000 msec, a maximum of 60 sheets can be sent to the image forming unit per minute. In other words, if the sheet to be secondarily fed has reached the registration roller before 1000 msec has elapsed since the start of the previous secondary paper feed, a new secondary paper feed is started every 1000 msec. Can do. As described above, in order to reduce the period of the secondary paper feeding, a plurality of sheets must be continuously fed and conveyed to the conveying path of the primary paper feeding unit. However, in Patent Document 1, when the previous sheet is being conveyed from the registration roller to the second sheet feeding unit at a quarter speed, the next sheet is continuously directed toward the registration roller toward the first sheet feeding unit. Is conveyed at a constant speed, the leading edge of the next sheet may collide with the trailing edge of the preceding sheet. In order to avoid this collision, it is necessary to start feeding after the next sheet waits until the previous sheet is conveyed to some extent, and it is difficult to increase the processing speed.

Further, when a paper slip or the like occurs during the primary paper feeding, the next paper to be secondary fed has not reached the registration roller when 1000 msec has elapsed from the start of the secondary paper feeding of the previous paper. Can occur. In this case, the start of the secondary paper feed is delayed by the delay time of the primary paper feed, and the time required for copying / printing becomes long. If this delay time becomes longer, the image formation timing is not met, and the toner image formed on the image forming unit is not transferred to the paper, the image forming unit is cleaned to discard the toner image on the image forming unit. In addition, there is a disadvantage that productivity is greatly reduced.
JP 2002-59601 A (paragraphs [0014], [0067], [0068], FIG. 6)

  The present invention has been made to solve the above-described problems. When images are continuously formed on a plurality of sheets, there is no possibility of collision between the sheets, and the sheet is being fed. It is an object of the present invention to provide an image forming apparatus that does not impair productivity even when paper slipping occurs.

  In order to achieve the above object, the present invention is arranged on an upstream side and a downstream side of an image forming unit that forms an image on a sheet and a conveyance path that conveys the sheet stored in a sheet cassette toward the image forming unit. A transport roller, an upstream and downstream drive unit that drives the upstream and downstream transport rollers with variable linear speed, an upstream side that detects each sheet passing through the upstream and downstream transport rollers, and When the downstream paper detection unit and the downstream paper detection unit detect the passage of the previous paper, the next paper is detected based on the linear speed of the conveyance roller of the downstream drive unit that conveys and drives the previous paper. And a control unit that controls the linear speed of the conveyance roller of the upstream drive unit so as to convey and drive the sheet with a predetermined interval.

  According to this configuration, the conveying roller linear speed for conveying and driving the next sheet is controlled based on the conveying roller linear speed for conveying the preceding sheet so as to have a predetermined sheet interval.

  According to a second aspect of the present invention, there is provided a paper detection unit disposed on the conveyance path with the predetermined interval with respect to the paper cassette, and the control unit is configured such that the paper detection unit When the trailing edge is detected, control is performed so that the next sheet starts to be conveyed from the sheet cassette.

  According to a third aspect of the present invention, the upstream side and downstream side drive units include respective stepping motors that rotate the upstream side and downstream side conveyance rollers, and the control unit is based on the downstream side paper detection unit. The number of rotations of the downstream stepping motor is counted from detection of the previous sheet, and the upstream of the next sheet with respect to the previous sheet is set at the predetermined interval based on the number of rotations of the downstream stepping motor. It is characterized by controlling the rotation speed of the side stepping motor.

  According to a fourth aspect of the present invention, there is provided a registration roller that abuts on a sheet that is fed along a conveyance path by the downstream side conveyance roller, and the control unit abuts the sheet on the registration roller, and the downstream side When the drive unit stops, the upstream drive unit is stopped.

  According to the first aspect of the present invention, since the conveying roller linear speed for conveying and driving the next sheet is controlled based on the conveying roller linear speed for conveying the preceding sheet so as to have a predetermined sheet interval. When a plurality of sheets are continuously conveyed, image formation is reliably performed continuously, and productivity is improved. Further, when the transport speed of the previous paper decreases due to slipping or the like, the transport speed of the next paper is controlled to be slow and always has a predetermined paper interval, so there is a possibility that the previous paper will collide with the next paper. Absent.

  According to the second aspect of the present invention, since the sheet detection unit is disposed on the conveyance path with the predetermined interval with respect to the sheet cassette, the next sheet is fed out from the sheet cassette. The sheet is conveyed while maintaining a predetermined sheet interval with respect to the previous sheet, and there is no possibility that the previous sheet and the next sheet collide in the conveyance path from the start of conveyance.

  According to the third aspect of the present invention, the upstream and downstream conveying rollers are driven to rotate by the stepping motor, and the controller rotates the upstream stepping motor based on the number of rotations of the downstream stepping motor. Since the number is controlled, the linear velocity of the transport roller can be accurately controlled with a simple configuration.

  According to the fourth aspect of the present invention, when the previous paper arrives at the registration roller and stops, the next paper stops with a predetermined paper interval. The timing with the sheet conveyed to the image forming unit can be surely matched.

  Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. The embodiment of the present invention shows the most preferable form of the invention, and the use of the invention and the terms shown here are not limited thereto.

  FIG. 1 is a cross-sectional view schematically showing the overall configuration of an image forming apparatus 1 used in a color printer of the present invention. The image forming unit 2 includes photoreceptors 10a to 10d, an intermediate transfer belt 5, primary transfer roller rotations 26a to 26d, a secondary transfer roller 7, and the like.

  In the free photosensitive members 10a to 10d, an amorphous silicon photosensitive member or an organic photosensitive member (OPC photosensitive member) is used as a photosensitive material for forming a photosensitive layer, and black (Bk), yellow (Y), cyan (C) and It corresponds to each color of magenta (M). The developing devices 100a to 100d, the chargers 40a to 40d, and the optical exposure device (not shown) are disposed around the respective photoreceptors 10a to 10d. The developing devices 100a to 100d each include a developing roller and a toner container for each color. Based on document image data input to an image input unit (not shown) from a personal computer or the like, a laser beam is irradiated onto the photoconductors 10a to 10d from the optical exposure unit.

  The intermediate transfer belt 5 is stretched around a tension roller 9, a driving roller 25, and a driven roller 27, and the photoreceptors 10a to 10d are conveyed in the transport direction of the intermediate transfer belt 5 (in FIG. 1) so as to contact the intermediate transfer belt 5. Are arranged opposite to each other so as to be adjacent from the upstream side along the arrow direction. The primary transfer rollers 26a to 26d are arranged so as to face the photoreceptors 10a to 10d and contact the intermediate transfer belt 5 with the intermediate transfer belt 5 interposed therebetween. Further, the secondary transfer roller 7 is disposed so as to face the driving roller 25 and contact the intermediate transfer belt 5 with the intermediate transfer belt 5 interposed therebetween.

  When the image forming start operation is performed, the photoconductors 10a to 10d rotate counterclockwise in FIG. 1, and the chargers 40a to 40d uniformly charge the surfaces of the photoconductors 10a to 10d. The optical exposure unit irradiates the surfaces of the photoconductors 10a to 10d with light based on the image data, and electrostatic latent images are formed on the surfaces of the photoconductors 10a to 10d. Next, toner of each color adheres to the electrostatic latent images formed on the surfaces of the photoconductors 10a to 10d by the developing bias voltage applied to the developing rollers of the developing devices 100a to 100d, thereby forming toner images.

  Each color toner image formed on the surface of each photoconductor 10a to 10d is moved in the direction of the arrow in FIG. 1 by primary transfer rollers 26a to 26d to which a primary transfer bias potential (a polarity opposite to the charging polarity of the toner) is applied. The primary transfer is sequentially performed on the intermediate transfer belt 5 being conveyed, and the colors are superimposed, so that a color toner image is formed on the intermediate transfer belt 5.

  In the conveyance path 50, the paper P stacked on the paper cassette 6 is conveyed between the intermediate transfer belt 5 and the secondary transfer roller 7 by the conveyance rollers 62 to 65 and the registration roller 66. The color toner image formed on the intermediate transfer belt 5 is secondarily transferred onto the paper P by the secondary transfer roller 7 to which a secondary transfer bias potential (polarity opposite to the toner charging polarity) is applied. Details of the conveyance path 50 will be described later.

  The paper P to which the toner image has been transferred is conveyed to the fixing device 8 and heated and pressed by the fixing roller to fix the toner image on the surface of the paper, thereby forming an image. The paper on which the image is formed is discharged out of the apparatus main body by a discharge roller (not shown).

  The conveyance path 50 will be described. The conveyance path 50 includes a primary sheet feeding unit 51 that conveys the sheet P stored in the sheet cassette 6 to the registration roller 66, and a secondary sheet feeding unit 52 that conveys the sheet P from the registration roller 66 to the secondary transfer roller 7. Is provided. The conveyance path 50 includes a pickup roller 61, conveyance rollers 62 to 65, a registration roller 66, and paper detection units 75 to 78.

  The pick-up roller 61 is rotated by a stepping motor (not shown) in order to separate the sheets P stacked on the sheet cassette 6 one by one and feed them out to the conveyance path 50. The pickup roller 61 is held on a drive shaft driven by a stepping motor via a one-way clutch. Thereby, even when the stepping motor is stopped, the driven rotation is possible in the paper feeding direction.

  The transport rollers 62 to 65 are rotated by a stepping motor (not shown) in order to transport the paper P sent out by the pickup roller 61 on the transport path 50 and to primarily feed the paper P to the registration roller 66.

  The registration roller 66 is for performing secondary paper feeding at the timing of paper feeding to the image forming unit 2. The registration roller 66 stops rotating when the leading edge of the sheet P conveyed from the conveying roller 65 approaches. The registration roller 66 stops rotating for a predetermined time after the leading edge of the sheet P comes into contact. And the rotation of the toner image on the intermediate transfer belt 5 and the paper P is started at the timing when the secondary transfer roller 7 aligns the position of the toner image.

  The paper detection unit 78 detects the passage of the paper P and is disposed at a predetermined position on the upstream side of the conveyance path 50 with respect to the registration roller 66 and is sent from the primary paper supply unit 51. This switch is turned on when the leading edge of P is detected, and is turned off when the paper P is fed from the registration roller 66 toward the image forming unit 2 and the trailing edge of the paper P has passed. After a predetermined time has elapsed since the leading edge of the paper P has turned on the paper detection unit 78, the rotation of the registration roller 66 that has been stopped is resumed. This time is set by the distance between the paper detection unit 78 and the registration roller 66 and the conveyance speed of the paper P by the registration roller 66.

  Each of the paper detection units 75 to 77 is turned on when the leading edge of the paper P sent from the paper cassette 6 is detected, and detects the passage of the paper P that is turned off when the trailing edge of the paper P has passed. It is a switch to do. The sheet detection unit 75 is disposed at a predetermined position from the sheet cassette 6, the sheet detection unit 76 is disposed at a predetermined position on the downstream side of the conveyance path 50 of the conveyance roller 63, and the sheet detection unit 77 is disposed on the conveyance roller 65. It is disposed at a predetermined position on the upstream side of the conveyance path 50.

  The paper detection units 75 to 78 are contact type sensors that rotate when a contact lever is brought into contact with the paper P to block between the light projecting unit and the light receiving unit. Note that the paper detection units 75 to 78 may be contact sensors that mechanically contact and separate the switch by the rotation of the sensing lever. Instead of the contact sensor, the presence or absence of the paper P is detected without contact, and the paper is detected. A signal corresponding to the presence or absence of P may be output.

  FIG. 2 is a block diagram showing an electrical configuration relating to paper feed control of the image forming apparatus according to the embodiment of the present invention. The image forming apparatus 1 rotationally drives the image forming unit 2, the control unit 81, the storage unit 82, the image forming drive unit 36 that drives the image forming unit 2 and the fixing unit 8, and the transport rollers 62 to 65. The control unit 81 includes a drive unit 70 to 73, a drive unit 74 that rotationally drives the registration roller 66, and paper detection units 75 to 78. The control unit 81 includes a storage unit 82, an image forming drive unit 36, and a drive unit 70. To 74 and the paper detection units 75 to 78 are connected.

  The storage unit 82 includes an image memory 85, a RAM 83, and a ROM 84, and the RAM 83 and the ROM 84 store a processing program, processing contents, and the like of the control unit 81 including a CPU.

  The image forming drive unit 36 includes a motor and drives the photoconductor 10, the transfer unit 45, and the fixing unit 8 in accordance with a control signal from the control unit 81.

  The drive units 70 to 73 include stepping motors (not shown) that rotationally drive the conveyance rollers 62 to 65. For example, the drive units 70 to 73 normally convey the paper P at a conveyance speed of 600 m / s, but a control signal from the control unit 81. Accordingly, the rotation speed of the stepping motor is controlled to increase or decrease the conveyance speed. In addition, the drive units 70 to 73 output a stop signal and a rotation speed signal regarding the stop and rotation speed of the stepping motor to the control unit 81.

  The drive unit 74 includes a stepping motor (not shown) that rotationally drives the registration roller 66. For example, the drive unit 74 normally conveys the paper P at a conveyance speed of 400 m / s.

  The paper detection unit 75 outputs a level signal (on / off signal) corresponding to detection of the leading edge of the paper P and passage of the trailing edge thereof to the control unit 81.

  The paper detection units 76 and 77 output a level signal (on / off signal) corresponding to the detection of the leading edge of the paper P and the passage of the trailing edge thereof to the control unit 81. In the control unit 81, the sheet P is conveyed based on the time point when the sheet P is detected or passed through the sheet detection units 76, 77 and the number of rotations of the stepping motors of the conveyance rollers 63, 65 corresponding to the sheet detection units 76, 77. Set the paper interval.

  The paper detection unit 78 outputs a level signal (on / off signal) according to detection of the leading edge of the paper P and passage of the trailing edge thereof to the control unit 81. In the control unit 81, after a predetermined time has elapsed since the leading edge of the paper P has turned on the paper detection unit 78, the rotation of the registration roller 66 that has been stopped is resumed. This time is set by the distance between the paper detection unit 78 and the registration roller 66 and the conveyance speed of the paper P by the registration roller 66.

  The control unit 81 inputs an on / off signal of the paper detection units 75 to 78, a stop signal of the driving units 70 to 74, and a rotation speed signal, and outputs a control signal to the driving units 70 to 74 in accordance with a set program. The conveyance speed of the rollers 62 to 65 is controlled.

  Based on FIGS. 3 and 4, the control of the control unit 81 will be described with reference to FIGS. 1 and 2. 3 and 4 are diagrams showing the relationship between the time and position of the paper P conveyed on the conveyance path 50. The horizontal axis represents time, the vertical axis represents the movement distance on the conveyance path 50, and the paper feed start is shown. The leading edge of the sheet in the sheet cassette 6 is set to 0, and the positions of the sheet detection unit 75 and the registration roller 66 are shown. The moving state of the leading edge of the sheet is indicated by a solid line, and the moving state of the trailing edge of the sheet is indicated by a broken line. FIG. 3 shows a state in which the sheet is normally conveyed without slipping, and FIG. 4 is a diagram showing a state in which the sheet slip is corrected.

  As shown in FIG. 3, the paper detection unit 75 sets a paper feed start position in order to set a transport paper interval m between the first paper as the first paper and the second paper as the next paper. To a predetermined position on the conveyance path. The transport paper interval m is the time from when the paper P is transported toward the secondary transfer roller 7 by the secondary paper feed unit 52 and leaving the registration roller 66 until the next paper abuts and the registration roller 66 stops. Further, this corresponds to the distance that the registration roller 66 rotates at the conveyance speed and conveys the sheet. The conveyance sheet interval m is stored in the ROM 84 of the storage unit 82. By setting the conveyance sheet interval m, it is possible to shorten the secondary sheet feeding interval when performing image formation continuously, and to convey a plurality of sheets to the primary sheet feeding unit 51 continuously. . In addition, the ROM 84 stores a paper feed time t from the start position to the registration roller 66 when transported at a transport speed of 600 m / s in the primary paper feed. In this embodiment, since the primary paper feeding is performed at a conveyance speed of 600 m / s, the first sheet P1 is conveyed at this conveyance speed, and the rear end of the sheet P1 passes through the sheet detection unit 75 to detect the sheet. When the pickup roller 61 is driven to rotate based on the off signal of the section 75 and the pickup roller 61 starts to convey the second sheet P2 from the start position, the interval between the trailing edge of the sheet P1 and the leading edge of the sheet P2 is increased. Control is performed so that the conveyance sheet interval is m.

  When the first sheet P1 is conveyed through the primary sheet feeding unit 51 by the conveyance rollers 62 to 65, for example, is nipped and conveyed by the conveyance roller 65, and the rear end of the sheet P1 passes through the sheet detection unit 75, the control unit 81 calculates the position of the trailing edge of the paper P1 on the primary paper feeding unit 51 according to the passage of time, based on the rotation speed of the stepping motor of the driving unit 73 that rotationally drives the transport roller 65 at this time. At the same time, the second sheet P2 starts to be conveyed by the rotational drive of the pickup roller 61, and is nipped and conveyed by the conveyance roller 63. The leading edge reaches the sheet detection unit 75 and is detected, and then the sheet detection unit 76 is turned on. To do. At this time, the control unit 81 determines 1 of the leading end of the paper P2 based on the number of rotations of the stepping motor of the driving unit 71 that rotationally drives the transport roller 63 and the time after the ON signal is input from the paper detection unit 76. The position on the next sheet feeding unit 51 is calculated.

  The control unit 81 calculates the transport distance (P1-P2) between the rear end of the paper P1 and the front end of the paper P2 from the position on the primary paper feed unit 51 between the rear end of the paper P1 and the front end of the paper P2. A difference between (P1-P2) and the conveyance sheet interval m stored in the ROM 84 is calculated, and the rotation of the stepping motor of the drive unit 71 is controlled according to the difference. When the transport distance (P1-P2) is smaller than the transport paper interval m, the rotation speed of the stepping motor of the driving unit 71 is decreased to decrease the transport speed of the transport roller 63, and conversely, the transport distance (P1- When P2) is larger than the conveyance sheet interval m, the rotation speed of the stepping motor of the drive unit 71 is increased, and the conveyance speed of the conveyance roller 63 is increased. Accordingly, the transport distance (P1-P2) between the rear end of the paper P1 and the front end of the paper P2 holds the transport paper interval m, and the paper P1 and the paper P2 are transported on the primary paper feed unit 51. The control unit 81 calculates a transport distance (P1-P2) for each predetermined time during the paper transport, and compares the transport distance (P1-P2) with the transport paper interval m.

  Further, when the first sheet P1 is transported through the primary paper feed unit 51 and comes into contact with the registration roller 66 and stops on the primary paper feed unit 51, the control unit 81 drives the transport roller 65 to rotate. The stepping motor of the driving unit 73 is stopped. When the control unit 81 inputs a stop signal from the drive unit 73 along with the stop of the stepping motor, the control unit 81 stops the stepping motor of the drive unit 71 that rotationally drives the transport roller 63 based on the stop signal. The second sheet P2 stops. If the difference between the conveyance distance (P1-P2) and the conveyance sheet interval m is smaller than the movement distance during the stop time of the registration roller 66, the controller 81 drives the stepping motor of the conveyance roller 73 to stop. By slightly delaying the stop of the stepping motor 71, it is also possible to stop the paper P2 with respect to the paper P1 at the conveyance paper interval m.

  Before the sheet P1 comes into contact with the registration roller 66, the leading edge of the sheet P1 turns on the sheet detection unit 78. After a predetermined time has elapsed since the sheet detection unit 78 was turned on, the registration roller 66 stopped. Rotates. That is, the control unit 81 sets the number of rotations of the stepping motor of the driving unit 74 and the stepping motors of the driving units 71 to 73 so that the conveyance speed of the registration roller 66 for conveying the paper P1 is 400 m / s. The rotational speed is made the same as the rotational speed of the stepping motor of the drive unit 74. The paper P2 is also transported at the transport speed of 400 m / s by the transport rollers 63 and 64 simultaneously with the paper P1, and the transport distance (P1-P2) between the rear end of the paper P1 and the front end of the paper P2 is set to the transport paper interval m. Is done. When the trailing edge of the paper P2 passes through the paper detection unit 75, the pickup roller 61 in the stopped / driven rotation state starts to rotate, and the third paper P3 is conveyed.

  Here, when the speed of the transport roller 63 cannot be changed and the paper can be transported only at 600 mm / s as in the configuration of the prior art, the start of the paper P2 is delayed in order to match the secondary paper feed transport at 400 mm / s. . Since the paper is transported at 600 mm / s, even if the delay with respect to the paper P1 is recovered, the trailing edge of the paper P2 is delayed to pass through the paper detection unit 75, and the time margin for transporting the third paper P3 is lost. Is called. When the pick-up roller 61 slips, a standby state occurs in the registration roller 66, leading to a delay in processing time, and a possibility of jamming increases.

  Next, correction of the conveyance speed when the sheet slides with a roller or the like during conveyance to reduce the conveyance speed of the sheet will be described.

  As shown in FIG. 4, the first sheet P1 and the second sheet P2 are each transported at a transport speed of 600 m / s while maintaining the transport distance (P1-P2) from the start position at the transport sheet interval m. However, when the transport speed of the sheet P1 decreases in the section ST in the transport path due to the slip of the transport roller 65, the control unit 81 starts from the position on the transport path between the rear end of the sheet P1 and the front end of the sheet P2. Then, the transport distance (P1-P2) between the rear end of the paper P1 and the front end of the paper P2 is calculated, and the difference between the transport distance (P1-P2) and the transport paper interval m stored in the ROM 84 is calculated. In this case, since the transport distance (P1-P2) is smaller than the transport paper interval m, the number of rotations of the stepping motor of the drive unit 71 is decreased, the transport speed of the transport roller 63 is decreased, and the transport distance (P1) -P2) is corrected to the conveyance sheet interval m.

  Although the sheet P1 has not reached the conveyance distance conveyed at the conveyance speed of 600 m / s due to the decrease in the conveyance speed in the section ST, the control unit 81 determines the distance between the sheet detection unit 77 and the conveyance roller 65. At this time, the position of the leading edge of the sheet P2 on the conveying path is calculated based on the number of rotations of the stepping motor of the driving unit 73 that rotationally drives the conveying roller 65 and the time after the ON signal is input from the sheet detecting unit 77. To do. Further, the control unit 81 calculates the remaining transport distance to the registration roller 66 from the calculated position, and the registration roller 66 receives the required time t from the start position stored in the ROM 84 to the registration roller 66. The remaining time required for reaching the vehicle is determined, and the number of rotations of the stepping motor of the drive unit 73 in the section TG is set based on the remaining transport distance and the remaining time. In this way, even if the paper is slipped by a roller or the like during transport, the paper is transported from the start position to the registration roller 66 in the required paper feed time t.

  In the section TG, as the transport speed of the paper P1 increases, the control unit 81 for the paper P2 starts from the position on the transport path between the rear edge of the paper P1 and the front edge of the paper P2 and the paper. A transport distance (P1−P2) from the leading edge of P2 is calculated, and a difference between the transport distance (P1−P2) and the transport sheet interval m stored in the ROM 84 is calculated. In this case, since the transport distance (P1-P2) is larger than the transport paper interval m, the rotation speed of the stepping motor of the driving unit 71 is increased to increase the transport speed of the transport roller 63, and the transport distance (P1). -P2) is corrected to the conveyance sheet interval m.

  According to the above-described embodiment, the image forming apparatus 1 includes the image forming unit 2 that forms an image on the paper P and the upstream of the conveyance path 50 that conveys the paper P stored in the paper cassette 6 toward the image forming unit 2. Conveying rollers 63 and 65 arranged on the side and downstream side, upstream and downstream drive units 71 and 73 that drive the upstream and downstream conveying rollers 63 and 65 with variable linear speed, and upstream side And upstream and downstream sheet detection units 76 and 77 for detecting each sheet passing through the downstream conveyance rollers 63 and 65, and a control unit 81. When the downstream paper detection unit 77 detects the passage of the previous paper, the control unit 81 sets the next paper as the previous paper based on the linear velocity of the conveyance roller of the downstream drive unit 73 that conveys and drives the previous paper. The conveyance roller linear velocity of the upstream drive unit 71 is controlled so that the conveyance drive is performed with a predetermined interval.

  According to this configuration, the conveying roller linear speed for driving the next sheet is controlled so as to have a predetermined sheet interval based on the conveying roller linear speed for conveying the previous sheet. When continuously transporting, image formation is reliably performed continuously, and productivity is improved. Further, when the transport speed of the previous paper decreases due to slipping or the like, the transport speed of the next paper is controlled to be slow and always has a predetermined paper interval, so there is a possibility that the previous paper will collide with the next paper. Absent.

  Further, according to the above embodiment, the paper detection unit 75 is provided on the conveyance path 50 with the predetermined interval with respect to the paper cassette 6, and the control unit 81 includes the paper detection unit 75 as the previous paper. When the trailing edge is detected, control is performed so that the next sheet starts to be conveyed from the sheet cassette 6, so that when the next sheet is fed out from the sheet cassette 6, a predetermined sheet interval is maintained with respect to the previous sheet. Thus, there is no possibility that the previous sheet and the next sheet collide in the conveyance path from the start of conveyance.

  Further, according to the above embodiment, the upstream and downstream drive units 71 and 73 include the respective stepping motors that rotate the upstream and downstream transport rollers 63 and 65, and the control unit 81 has the downstream sheet detection unit 77. The upstream stepping motor counts the number of rotations of the downstream stepping motor from the detection of the previous sheet by the step, and based on the number of rotations of the downstream stepping motor, the upstream stepping motor is set at a predetermined interval with respect to the previous sheet. By controlling the number of rotations, the linear velocity of the transport roller can be accurately controlled with a simple configuration.

  In addition, according to the above embodiment, the registration roller 66 is in contact with the paper P sent through the conveyance path 50 by the downstream side conveyance roller 65, and the control unit 81 is in contact with the registration roller 66, and the downstream side When the drive unit 73 is stopped, the upstream drive unit 71 is stopped, so that the timing of the image formation of the image forming unit 2 and the sheet conveyed to the image forming unit 2 can be reliably matched.

  INDUSTRIAL APPLICABILITY The present invention can be used for an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system, and in particular, an image forming apparatus provided with a sheet conveyance path to an image forming unit. Can be used.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus that is an embodiment of the present invention. FIG. 4 is a diagram illustrating a relationship between time and position of a sheet conveyed by the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram illustrating a relationship between a time and a position of a sheet that is corrected and conveyed by the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 5 Intermediate transfer belt 6 Paper cassette 7 Secondary transfer roller 10a-10d Photoconductor 50 Conveying path 51 Primary paper feeding part 52 Secondary paper feeding part 61 Pickup roller 62-65 Conveying roller 66 Resist Roller 70 to 74 Drive unit 75 to 78 Paper detection unit 81 Control unit 100a to 100d Developing device P Paper

Claims (4)

  An image forming unit that forms an image on a sheet; a conveyance roller that is disposed on an upstream side and a downstream side of a conveyance path that conveys a sheet stored in a sheet cassette toward the image forming unit; and the upstream side and the downstream side An upstream side and a downstream side drive unit that drives the conveyance roller with variable linear speed, an upstream side and a downstream side sheet detection unit that detects each sheet passing through the upstream side and the downstream side conveyance roller, and the downstream side sheet When the detection unit detects the passage of the preceding sheet, the next sheet is conveyed and driven with a predetermined interval from the preceding sheet based on the linear velocity of the conveying roller of the downstream drive unit that conveys and drives the preceding sheet. As described above, an image forming apparatus comprising: a control unit that controls a linear speed of a conveyance roller of the upstream drive unit.   A sheet detection unit disposed on the conveyance path with the predetermined interval with respect to the sheet cassette; and when the sheet detection unit detects the trailing edge of the previous sheet, The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to start conveyance from a paper cassette.   The upstream and downstream drive units include respective stepping motors that rotate the upstream and downstream transport rollers, and the control unit detects the previous sheet from the detection of the previous sheet by the downstream sheet detection unit. And controlling the number of revolutions of the upstream stepping motor based on the number of revolutions of the downstream stepping motor so that the next sheet is at the predetermined interval with respect to the preceding sheet. The image forming apparatus according to claim 1, wherein:     A registration roller that abuts the sheet fed through the conveyance path by the downstream side conveyance roller; and the control unit detects that the upstream side drive unit stops when the sheet contacts the registration roller and the downstream side drive unit stops. The image forming apparatus according to claim 1, wherein the image forming apparatus is stopped.

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