JP2006227481A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of maintaining fixing conveying speed at which recording paper is not abnormally loosened on a conveying path to a fixing device. <P>SOLUTION: The image forming apparatus is equipped with: an image carrier; an image forming means for forming a toner image on the image carrier; a transfer means for transferring the toner image to transfer material; a fixing means for fixing the toner image transferred to the transfer material; a fixing speed control means; and a loop detection means capable of detecting the degree of the looseness of the transfer material conveyed on the conveying path, and performs fixing speed control so as to keep the amount of the looseness constant according to output from the loop detection means. The apparatus stops the fixing speed control when the looseness in one direction changes to that in a reverse direction in a direction nearly perpendicular to the transfer material traveling on the conveying path. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a printer, and a fax machine, and more particularly to an image forming apparatus in which a conveying speed of a fixing device that fixes a transfer material holding a toner image is variable.

  In a conventional image forming apparatus, particularly an apparatus that conveys a transfer material in a vertical direction that is close to vertical, image quality, particularly image misalignment (transfer misalignment) when the transfer material is loosened or pulled in the conveyance path passes through the conveyance roller. ) Is greatly affected.

  This is conspicuous in a transfer system such as roller transfer or belt transfer where transfer material adhesion at the transfer point is not so good as in electrostatic transfer.

As a countermeasure, a slack detection sensor that is a loop detection means detects a speed difference between the fixing speed and the transport speed due to a change in the transport position, and performs control to maintain a constant slack amount between the fixing and the transfer material. (For example, refer to Patent Document 1).
JP-A-1-267237

  However, there are cases where the fixing speed is extremely slow, or in the case of a curled transfer material, the transfer material is extremely loosened due to poor insertion due to catching when inserted into the fixing device. In this case, since the conveyance path has only a certain gap, there is no escape space for the sheet, and the transfer material, which has been U-shaped until then, rapidly changes to an S-shape. As a result, the conveyance position becomes an abnormal state that does not reflect the slack state, and the slack detection sensor cannot detect normally.

  The above-mentioned Patent Document 1 does not touch on handling such an abnormal state.

  The present invention is proposed as a technique for dealing with the abnormal state as described above in the transfer material conveyance. By detecting the variation of the time change rate of the curl of the transfer material and controlling the fixing speed, the stable fixation conveyance can be achieved. An object of the present invention is to provide an image forming apparatus that can be maintained.

An image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image onto a transfer material, and a fixing unit that fixes the toner image transferred onto the transfer material A fixing speed control means, a loop detection means capable of detecting the degree of looseness of the transfer material conveyed to the conveyance path, and fixing so that the amount of looseness can be maintained constant according to the output of the loop detection means. In the image forming apparatus that performs speed control, the fixing speed control is stopped when the slack in one direction of the transfer material traveling on the transport path changes in the opposite direction. Image forming apparatus.

  Even when abnormal loosening of the transfer material is detected in the conveyance path to the fixing device, the fixing speed control is performed so that no malfunction occurs, so that stable fixing conveyance is possible.

  Embodiments according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing the overall configuration of an image forming apparatus according to an embodiment of the present invention.

  FIG. 2 is an enlarged view of the photoconductor, the fixing device region, and the conveyance path of FIG.

  In FIG. 1, an image forming apparatus 1 includes an automatic document feeder (commonly referred to as ADF) A, a document image reading unit B, an image control unit C for processing a read document image, and a writing unit D including a writing unit. , An image forming unit E including a transfer unit 19, a fixing device H, a storage unit F that stores recording paper P that is a transfer material for forming an image, an automatic reversing paper feeding mechanism ADU that reverses the recording paper, and the like. ing.

  First, the automatic document feeder A mainly includes a document table 26 and a document transport processor 28 including a roller group including a roller R1 and a switching unit for appropriately switching a document moving path (no reference symbol). It is plain.

  The document image reading unit B is a reading unit for reading an image of a document conveyed by the automatic document conveying device A. Under the platen glass G, it comprises a lamp 34, two mirror units 30 and 31, which can move back and forth while maintaining the optical path length, a fixed imaging lens 33, a line-shaped image sensor 35, and the like.

  The image control unit C is a control unit that controls recording paper conveyance driving in addition to processing of the read document image.

  The writing unit D includes a laser light source 40, a polygon mirror 42, and the like, and includes a writing unit 12 that performs writing on an image carrier (also referred to as a photosensitive member) 10 in accordance with image data after image processing.

  The image forming unit E is an image forming unit including an image forming unit such as a charging electrode 14, a developing device 16, a transfer electrode 18, a separation electrode 20, and a cleaning unit 21 around the photoreceptor 10. When viewed from the moving direction of the recording paper P, reference numeral 85 shown on the front side of the transfer electrode 18 is a registration roller, and the fixing device H is on the downstream side of the separation electrode 20.

  In FIG. 2, the fixing device H includes a fixing roller pair 91. The fixing roller pair 91 is in contact with the surface of the recording paper, and a pressure roller 912 that rotates while being in pressure contact with the fixing roller 911 and contacts the back surface of the recording paper. It consists of and. The fixing roller 911 has a metal shaft, a glass pipe or the like as a base, a PFA layer or the like formed on the outer periphery thereof, and a heating source 94 such as a halogen heater is disposed inside the base. The separation claw 93 is a member for peeling off the leading end of the recording paper P to be wound around the outer peripheral surface of the fixing roller 911. The pressure roller 912 has a metal shaft as a base and the outer periphery is formed of an elastic body such as silicon rubber. The recording paper P to which the toner image is transferred from the photoreceptor 10 is conveyed upward in the vertical direction, and is sandwiched between press contact portions formed by a pair of fixing rollers 91 disposed adjacent to each other in the horizontal direction. After fixing, it is further conveyed upward.

  Returning to FIG. 1, the storage unit F is a storage unit for the paper feed trays 22 and 24 that store the recording paper P on which an image is formed. The reference symbol S in the paper feed tray 24 is a movable plate, and the recorded bundle is pushed up by the movable plate S. As a result, the uppermost sheet comes into contact with a feed roller described later. The paper feed tray 22 also has the same configuration as described above. Of the paper feed trays, the bottom of the paper feed tray 24 and the bottom wall of the apparatus main body are arranged in the lower stage (in the embodiment, the paper feed tray is a two-tiered stack, which is the lower stage, meaning the lower stage). A space 25 having a predetermined gap is formed between the two. The space portion 25 is used in a mode in which images are formed on both sides of the recording paper P, and contributes to achieving reversal of the recording paper in cooperation with the automatic reversing conveyance path 86 for reversing the recording paper. To do.

  Reference numerals 50 and 53 shown at the top of the leading ends of the paper feeding trays 22 and 24 (corresponding to the leading edge of the stored recording paper P as viewed from the paper feeding direction) are paper feeding means (hereinafter referred to as feeding rollers). , 51 and 54 are feed rollers, and 52 and 55 are double feed prevention rollers. 73 and 75 are conveyance rollers.

  The recording paper conveyance switching lever 90 directs the recording paper P image-formed on the surface of the recording paper to the paper discharge path 78 which is one of the plurality of conveyance paths, or the other conveyance path. It is controlled so as to be directed to the automatic reversing conveyance path 86 via the curved conveyance path section 80.

  The automatic reversing paper feeding mechanism ADU is composed of a curved conveying path 80, a pair of reversing conveying rollers 81, 82, 83, etc., and is a mechanism for reversing the front and back of the recording paper. However, the description of the inversion operation is omitted.

  The swingable recording paper transport switching lever 90 is disposed in the vicinity of the branch point DP between the paper discharge path 78 and the curved transport path 80 downstream of the fixing device H in the recording paper transport direction (arrow). In recording and conveyance (other than reverse conveyance), the fixed recording sheet is guided to the paper discharge passage 78 at a position shown by a dotted line.

  The paper discharge passage 78 is formed with an R-shaped guide portion (no reference numeral) downstream in the recording paper conveyance direction, and a pair of discharge rollers 79 is disposed in the vicinity of the R-shaped guide portion.

  The recording paper P on which the toner image is formed on the front surface (hereinafter, the surface contacting the fixing roller 911 of the recording paper is referred to as the front surface and the surface contacting the pressure roller 912 is referred to as the back surface) is the fixing roller of the fixing device H. The pair 91 is pressed and fixed, passes through a pair of recording paper guide members 95 and 96, and goes to the branch point DP where the recording paper conveyance switching lever 90 is disposed. The recording paper conveyance switching lever 90 is connected to a switching lever driving means (not shown) constituted by a solenoid or the like. The switching lever driving means is driven by a command from the control unit, and the recording paper conveyance switching lever 90 is rotated clockwise or It is rotated counterclockwise.

  In the printing operation, the photosensitive member 10 is rotated in the counterclockwise direction indicated by an arrow by starting a photosensitive member driving motor (not shown), and at the same time, application of a potential to the photosensitive member 10 is started by the charging action of the charging electrode 14.

  After the photoconductor 10 is given a potential, writing of an image corresponding to the image data from the writing unit D is started, and an electrostatic latent image corresponding to the document image is formed on the surface of the photoconductor 10.

  The electrostatic latent image is reversely developed in a non-contact state by the developing device 16 to form a toner image on the photoreceptor 10.

  On the other hand, the recording paper P is fed from the paper feed tray 22 by the feed roller 50, is transported by the feed roller 51, is further transported by the transport roller 75, and is detected by the registration sensor 85A disposed near the upstream of the registration roller 85. In synchronization with the toner image formed on the body 10, the registration roller 85 suppresses paper bending or the like and temporarily stops. Thereafter, the registration roller 85 starts to drive again, feeds the recording paper P to the transfer region S of the transfer electrode 18 to which a DC voltage having a polarity opposite to that of the toner is applied, and the toner image is applied to the recording paper P. Transcribed. Thereafter, the photosensitive member 10 is cleaned of residual toner by the cleaning means 21 and enters the next image forming cycle.

  The recording paper P onto which the toner image has been transferred is further sent to the fixing device H, and is sandwiched between the heating roller 911 and the pressure roller 912 of the fixing roller pair 91 and fixed by being pressed. Since the change in the fixing speed causes the transfer material to be loosened or curled due to pulling in the conveyance path 70 between the transfer and fixing, a looseness detection sensor 70B is disposed in the conveyance path 70, and this looseness (loop) is detected. The amount is dynamically monitored and the time change rate is calculated by the control unit C, and the fixing speed is feedback controlled so that a constant loop amount is obtained.

  The recording paper P on which the toner image has been fixed advances along the paper discharge path 78. When the recording paper P passes through the fixed paper discharge sensor 91A, the feedback control stops, and the paper discharge roller 79 (see FIG. 1) further discharges the paper shelf. It is loaded onto T.

  However, as described above, when the fixing speed is extremely slow or when the curled transfer material is inserted into the fixing roller 91 due to being caught in the fixing device, the recording paper P is extremely loosened. There is a case. In this case, since the conveyance path 70 has only a certain gap, there is no escape space for the sheet, and the recording sheet P that has been U-shaped until then changes rapidly to an S-shaped, and an abnormal state occurs.

  Here, the detection of the curl state of the recording paper and the control of the fixing speed in the conveyance path 70 in the prior art will be specifically described with reference to FIGS.

  FIG. 3 is a perspective view of the suction guide communicating with the suction fan.

  FIG. 4 is a diagram illustrating a state in which the recording paper is conveyed along a conveyance path between transfer and fixing.

  4A and 4B, in a normal conveyance state, the recording paper communicates with a suction fan (not shown) as indicated by a two-point difference line P1 in the conveyance path 70 and after the transfer process. While being slightly drawn by the duct-shaped suction guide 70A as described above, the vehicle travels while being detected by the slack detection sensor 70B while maintaining the passing height h from the suction guide 70A, and is sandwiched between the fixing roller pair 91. The slack detection sensor 70B can detect the passage height h of the recording paper in multiple stages. In the present embodiment, the feeding speed of the recording paper is 250 mm / sec, the passing height h is in the range of 2 mm to 6 mm, and when the fixing speed tends to be pulled relatively fast, the suction guide 70A is used. The output h shifts to the plus side (left direction in the figure). FIG. 4C shows a state in which the recording paper P2 has reached the top of the tension, and the toner image touches the guide and looseness detection sensor 70B, causing image blurring. On the other hand, when the fixing speed is slow and the film tends to be slack, it shifts to the minus side (rightward in the figure). If the recording paper is too slack or too small, an image defect such as the above-described transfer error occurs.

  Therefore, if the recording paper is too slack or too small, an image defect problem due to dirt or conveyance slip of the recording paper occurs. In order to prevent the image defect problem, the fixing speed is varied by performing feedback control according to the detection output so as to make the amount of slackness constant. That is, the slackness is made constant by increasing the fixing speed when the passing height h is low (from the right) and decelerating when the passing height h is high (from the left).

  As described above, according to the present invention, when the recording paper P1 that has been U-shaped up to that point is suddenly changed to an S-shape like the recording paper P3 in FIG. 4D, an abnormal state occurs. It is about.

  That is, when the recording paper suddenly changes from U-shaped feeding to S-shaped, the output of the slack detection sensor 70B also changes suddenly. Therefore, the control unit C can determine whether the output is due to a change in the normal slack state or the S-shape state by dynamically monitoring the time change rate of the output.

  That is, in this embodiment, the difference between the fixing speed and the conveyance speed within the normal range is about −0.5% to + 0.5%, and the detected height output (at the passing height h) in that case. The rate of change is approximately −5 mm / sec to +5 mm / sec (when the recording paper feed speed is 250 mm / sec). However, in the case of the S-shaped state described above, the change is abrupt as about 4 mm in 50 msec. Occurs. Therefore, it can be determined that the rate of change is out of the normal range-when it is 10 mmsec or less or when it is +10 mmsec or more, it is determined as abnormal, and the control unit C stops the feedback control and switches to a standard constant speed.

  The present invention is characterized in that when it is determined that the abnormality is present, the feedback control to the fixing speed is immediately stopped.

  Hereinafter, the conveyance and fixing driving process of the present invention will be described with reference to flowcharts.

  FIG. 5 is a flowchart showing the conveyance and fixing driving process.

  In FIG. 5, simultaneously with the start of image recording, in step S1, the photosensitive drum, conveyance drive, and fixing drive motors start to rotate, and image formation starts on the photosensitive drum. Feeds the recording paper and the fixing roller rotates. In step S2, when the leading end of the recording paper reaches the registration sensor arranged in the vicinity of the registration roller and is turned on, the registration roller driving clutch is turned on in step S3, and the recording paper is nipped and conveyed by the registration roller. In synchronization with the toner image formed on the photosensitive drum, the toner image is sandwiched by the fixing roller through the transfer region S. In step S3, the registration sensor is in an OFF state until the recording paper arrives. In step S4, when the leading end of the recording paper reaches the fixing paper discharge sensor disposed in the vicinity of the fixing roller in step S4 and is turned ON, in step S5, the slack detection sensor 70B starts detecting the change in the slack of the recording paper. In step S6, the rotation speed Vf of the fixing roller to be fed back from the slack output value is calculated. In step S4, the fixing paper discharge sensor is in an OFF state until the recording paper arrives. In step S7, the rate of change is calculated by the control unit from the slack output value. In step S8, when the rate of change exceeds a predetermined value, that is, a value that causes an abrupt change in the S-shape, the feedback control is stopped and the fixing speed is set to a standard constant speed state. On the other hand, if the value is equal to or less than the value causing a sudden change in the S-shape, the feedback control is continued in step S9. In step S10, when the registration roller completes the conveyance of the recording paper, the registration sensor is turned off and the fixing speed is set to a standard constant speed. In step S10, the registration sensor continues the feedback control in the ON state while the registration roller is holding and transporting the recording paper.

  As described above, according to the present invention, the problem that the recording paper is conveyed in an abnormally slack state in the transfer and fixing conveyance area is avoided, and stable fixing conveyance is possible.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is an enlarged view of a photoconductor, a fixing device area, and a conveyance path in FIG. 1. FIG. 6 is a perspective view of a suction guide communicating with a suction fan. FIG. 6 is a diagram illustrating a state in which a recording sheet is conveyed along a conveyance path between transfer and fixing. A flowchart of the conveyance and fixing driving process is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoconductor 16 Developing device 18 Transfer electrode 70 Conveyance path 70A Suction guide 70B Looseness detection sensor 85 Registration roller 85A Registration sensor 91 Fixing roller pair 91A Fixation discharge sensor C Control unit H Fixing device

Claims (1)

An image carrier, an image forming unit that forms a toner image on the image carrier, a transfer unit that transfers the toner image onto a transfer material, and a fixing unit that fixes the toner image transferred onto the transfer material A fixing speed control means, a loop detection means capable of detecting the degree of looseness of the transfer material conveyed to the conveyance path, and fixing so that the amount of looseness can be maintained constant according to the output of the loop detection means. In the image forming apparatus that performs speed control, the fixing speed control is stopped when the slack in one direction of the transfer material traveling on the transport path changes in the opposite direction. Image forming apparatus.

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