JP2006267193A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which achieves paper conveyability of high precision by easily and stably detecting exact characteristics about conveyance of paper for use, including rigidity etc., without employing a cost increasing means by installing as sensors rigidity coefficient and thickness measuring instruments for exclusive use in a paper carrying line of the image forming apparatus. <P>SOLUTION: The image forming apparatus includes: an image forming portion for forming an image on a paper; and the carrying line for carrying the paper, which is provided with a carrying path having a bending part. First and second sensors for detecting the paper are provided in an upstream side and a downstream side respectively in a paper carrying direction of the carrying path having the bending part, and a judgement means is provided which detects a passage time in which the paper passes between the first and the second sensors is detected, and judges the degree of rigidity of the paper on the detected passage time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that detects sheet rigidity by a sensor provided in a sheet conveyance path and controls sheet conveyance.

  In an image forming apparatus, it is necessary to transfer a toner image formed on a photoreceptor or the like onto a sheet having various different characteristics in a timely manner so that image formation without deviation or distortion can be stably performed. is there. As a characteristic that affects the transportability of paper, for example, there is rigidity such as strength of paper. Conventionally, it is known that the transport state is adjusted by the thickness of the paper instead of the paper.

  In Patent Document 1, when the sheet holding force of the sheet feeding roller is small in the manual sheet feeding, the sheet is moved in the conveyance direction due to the difference in rigidity (meaning waist strength) of the sheet itself after the loop is formed. When the leading edge of the sheet moves away from the nip portion of the registration roller, the registration roller starts to rotate after that. Even when the sheet is not conveyed, a problem that a jam occurs is described. In order to achieve this problem, the occurrence of a jam is solved by driving the registration roller during the loop formation according to the rigidity of the sheet and temporarily holding it in the holding portion. In the detection of the sheet rigidity, instead of directly measuring, the thickness of the sheet is used instead. For this reason, detection means for detecting the thickness of the sheet is provided. However, even if the rigidity of the sheet is determined based on the detection result substituted by the paper thickness, the accuracy is not high. That is, factors that determine the rigidity of the sheet include factors such as the type and amount of additive, whether the sheet is vertical or horizontal, which is determined by the direction in which the paper is drawn during manufacture, in addition to the paper thickness. Therefore, the determination of the sheet rigidity in the conventional example is low in accuracy. As described above, since the sheet conveyance control is performed based on the determination result based on the paper thickness, the first problem is that the solution is not an essential solution.

In addition, correction of paper bending is performed by applying a force to press the paper against the registration roller side by forming a loop on the paper after the leading edge of the paper is abutted against the registration roller. If it is large, the force that presses the paper against the registration roller is too great, so the paper cannot be held at a predetermined position at the entrance of the nip, and the paper may penetrate deeply into the nip of the registration roller, In this case, there is a problem of passing through the nip portion. As described above, when the paper cannot be stopped at a predetermined position and the stop position of the leading edge of the paper is deviated, a deviation of the paper conveyance timing occurs, and an erroneous determination such as the occurrence of a jam occurs in the conveyance control. Thus, there is a second problem that a problem such as stopping of the image forming apparatus occurs.
JP 2002-179292 A

  In order to solve the above problems, it is necessary to detect the rigidity of the sheet with high accuracy, but there is currently no small and compact measuring means that can be incorporated into the image forming apparatus.

  It is an object of the present invention to provide an image forming apparatus that solves such problems of the prior art and detects the rigidity of a sheet with high accuracy.

  Another object of the present invention is to provide an image forming apparatus capable of improving the paper transportability based on the detection result of the paper rigidity.

  This object is achieved by any one of the following technical means (1) to (6).

(1) In an image forming apparatus having an image forming unit that forms an image on a sheet and a conveyance path that conveys the sheet, and a conveyance path having a bent portion in the conveyance path.
A first sensor and a second sensor for detecting paper are provided on the upstream side in the paper transport direction and the downstream side in the paper transport direction of the transport path having the bent portion, respectively, and the paper passes between the first sensor and the second sensor. An image forming apparatus, comprising: a determination unit that detects a passage time and determines the strength of the sheet based on the detected passage time.

  (2) The image forming apparatus according to (1), wherein the determination unit determines that the rigidity of the sheet is strong when a predetermined reference passage time is provided and is shorter than the reference passage time.

(3) A registration roller and a loop forming roller which are provided on the downstream side in the paper conveyance direction of the conveyance path having the bent portion, and which correct the paper bending of the paper by forming a loop on the paper after abutting the paper, Control means for controlling the driving of the loop forming roller,
(1) or (2), wherein the control unit controls a loop amount formed by the loop forming roller based on a determination result of the rigidity of the paper by the determination unit. Image forming apparatus.

  (4) In the item (3), the control unit controls the loop amount formed by the loop forming roller to be small when the determination unit determines that the rigidity of the sheet is strong. The image forming apparatus described.

  (5) The image according to any one of (1) to (4), wherein the conveyance path having the bent portion is provided in a reversal conveyance path for reversing and re-feeding the paper. Forming equipment.

  (6) The image forming apparatus according to any one of (1) to (4), wherein the conveyance path having the bent portion is provided in a conveyance path for feeding a sheet to the photosensitive member.

  The present inventors pay attention to a phenomenon that causes a difference in paper conveyance time due to a difference in strength of the paper when the paper is conveyed in a conveyance path having a bent portion. It has been found that the rigidity of the paper can be judged. In other words, the paper is transported through a transport path having a bent portion, and the rigidity is determined based on the difference in transport time, so that the detection accuracy can be improved and a new small and compact rigidity detection means is not provided. This achieves the detection of paper rigidity at low cost.

  Further, by adjusting the loop formation amount based on the determination result of the sheet rigidity detected by the above-described detection method, it is possible to eliminate the shift in the sheet conveyance timing and improve the sheet conveyance property.

  Embodiments of the image forming apparatus of the present invention will be described below.

  An image forming apparatus 1 shown in FIG. 1 is a digital image forming apparatus as an example of the present invention, and is an image reading unit A, an image processing unit B, an image forming unit C, and a paper supply conveyance for supplying and conveying a paper P. It consists of part D.

  An automatic document feeder that automatically conveys the document is provided above the image reading unit A. The document placed on the document table 11 is separated and conveyed by the document conveyance roller 12 to the reading position 13a. The image is read. The document after the document reading is completed is discharged onto the document discharge tray 14 by the document transport roller 12.

  On the other hand, the image of the original when placed on the platen glass 13 is read at a speed v of the first mirror unit 15 including the illumination lamp and the first mirror constituting the scanning optical system, and the V-shaped first image is located. Reading is performed by the movement of the second mirror unit 16 including the two mirrors and the third mirror in the same direction at the speed v / 2.

  The read image is formed on the light receiving surface of the image sensor CCD through the projection lens 17. The line-shaped optical image formed on the image sensor CCD is sequentially photoelectrically converted into an electric signal (luminance signal) and then A / D converted, and the image processing unit B performs processing such as density conversion and filter processing. Then, the image data is temporarily stored in the memory.

  In the image forming unit C, as an image forming unit, a drum-shaped photoconductor 21, a charging unit 22 for charging the photoconductor 21, a developing unit 23, a transfer electrode 24, a separation electrode 25, and the photoconductor 21 on the outer periphery thereof. The cleaning devices 26 are arranged in the order of operation. The photoconductor 21 is formed by coating a photoconductive compound on a drum base. For example, an organic photoconductor (OPC) is preferably used and is driven to rotate in the clockwise direction shown in the drawing.

  After the rotating photosensitive member 21 is uniformly charged by the charging means 22, the exposure optical system 30 performs image exposure based on the image signal called from the memory of the image processing unit B. The exposure optical system 30 uses a laser diode as a light emitting light source, passes through a rotating polygon mirror 31, an fθ lens 34, and a cylindrical lens 35, and an optical path is bent by a reflection mirror 32 to perform main scanning. In this position, image exposure is performed, and a latent image is formed by sub-scanning by rotation of the photoconductor 21.

  The latent image on the photoreceptor 21 is subjected to reversal development by the developing unit 23, and a visible toner image is formed on the surface of the photoreceptor 21. In the paper transport unit D, paper feed units 41 (A), 41 (B), 41 (C) and a transport roller 43D are provided below the image forming unit as paper storage means for storing paper P of different sizes. The paper P selected from any of them is fed along the transport path 40 by the guide roller 43.

  The sheet P is temporarily stopped by the registration roller pair 44 that corrects the bending of the sheet P to be fed. Thereafter, the sheet P is fed again from the registration roller 44 toward the transfer position, guided by the pre-transfer roller 43a and the entry guide plate 47, and conveyed to the transfer position Bo. The sheet P is transferred by the transfer pole 24 at the transfer position Bo. A toner image is transferred on top. The sheet on which the toner image has been transferred is separated from the surface of the photoreceptor by the separation pole 25 and is conveyed to the fixing device 50 by the conveyance belt device 45.

  The fixing device 50 includes a heating roller 51 provided with a heating source and a pressure roller 59, and heats and presses the sheet P by passing between the heating roller 51 and the pressure roller 59. To fix the toner image on the paper.

  The paper P on which the toner image is fixed passes through the path switching gate 171 and is linearly conveyed and discharged onto the paper discharge tray 81.

  The above describes the case where the single-side mode for performing image formation on only one side of the paper P is set.

  On the other hand, when the duplex mode for performing duplex copying is set, the path switching gate 171 is switched in the direction of the first conveyance path 174 for duplex copying, and the sheet P on which the toner image is fixed on one side is indicated by a broken arrow. Conveyed in the direction.

  The following description will be made with reference to the cross-sectional configuration diagram of the reverse conveyance path for double-sided copying in FIG. 2, which is a partially enlarged view of FIG.

  The sheet P is transported in the downstream direction by the drive roller pair 175 and a plurality of drive roller pairs 176A and 177A arranged on the downstream side thereof, and is transported to the second transport path 181 of the duplex copy reversing unit 180. The conveyance direction is switched in the forward and reverse directions by 182 and is switched back, and the conveyance path 183 having a bent portion with the rear end portion of the sheet P so far formed as the leading end portion and the passage width is greatly expanded, and a pair of conveyance rollers 184, and is conveyed into the third conveyance path 185 for double-sided copying.

  Further, the sheet P reaches the pre-registration roller 188 through the transport roller 186, the loop forming roller 187, and the photo sensor 187S in the third transport path 185. The first, second, and third transport paths are referred to as a reverse transport path.

  Then, the paper P is fed again from the pre-registration roller 188, and is conveyed to the registration roller 44 through the paper supply roller 132, a conveyance path 133 having a bent portion whose passage width is greatly expanded, and a loop forming roller 43D2.

  Further, the sheet P is conveyed from the registration roller 44 to the sheet discharge tray 81 in the same manner as the single-sided image formation.

  Next, the main part of the present invention will be described with reference to FIG.

  A photo sensor 182S as a first sensor and a photo sensor 184S as a second sensor are provided on the upstream side and the downstream side in the paper conveyance direction of the conveyance path 183 having a bent portion, respectively. A passing time for the sheet to pass between the first sensor and the second sensor is detected.

  FIG. 7 is a block diagram showing a hardware configuration for performing control in the present invention. Reference numeral 60 denotes control means. The control means 60 is provided with a determination means 61 for determining the rigidity of the paper and a memory 62 in which data on the reference passage time is stored. The leading edge of the sheet is detected by the photosensor 182S as the first sensor and the photosensor 184S as the second sensor, and a detection signal is sent to the control means 60, and the sheet between the first sensor and the second sensor is detected by the detection signal. The passing time for passing is calculated. Based on the detected passage time, the determination means 61 determines the strength of the sheet rigidity. In the determination means 61, if the detected passage time is shorter than the reference passage time, it is determined that the rigidity of the sheet is strong. For the reference passage time, the passage time of plain paper or the like having low rigidity is applied, and whether the time difference is strong is determined by whether or not the time difference is a predetermined threshold, for example, a time difference of 3 ms or more.

Incidentally, as shown in the graph (b) of the passage time difference in FIG. 4, the passage time of the sheet from the detection of the leading edge of the photosensor 182S as the first sensor to the detection of the leading edge of the photosensor 184S as the second sensor is rigid. weak when plain paper reference transit time transit time of, while plain paper passage time is the reference transit time basis weight 64 g / m ² is 286.41Ms, heavy basis weight 200 g / m ² The paper passage time is 282.04 ms, which is a time difference of 4.37 ms.

  5 and 6, when a conveyance path having a bent portion with a wide passage width is provided in the conveyance path of the paper P, the conveyance path having the bent portion is divided into a thick sheet having high rigidity and a thin sheet having low rigidity. A behavior that causes a passage time difference when a sheet is conveyed will be described.

  The rigid paper P is transported by the upstream transport roller while the leading edge hits the outer periphery of the inner surface of the transport path having a bent portion. Is done. On the other hand, paper such as plain paper having low rigidity is flexible, and after being bent in the direction of the arrow after contacting the outer peripheral surface of the guide member, the paper is conveyed along the outer peripheral side of the inner surface of the guide member. As a result, the passage time is delayed as compared with a rigid sheet.

  Therefore, paying attention to the difference in the passage time passing through the conveyance path having the bent portion as the rigidity of the paper that is substantially closely related to the conveyance performance of the paper to be used, the rigidity of the paper is based on the difference in the passage time. By determining the strength of the paper, it is possible to detect the rigidity with higher detection accuracy than the conventional example because it is detected directly, and without the need for a new compact and compact rigidity detecting means, the paper can be manufactured at low cost. It can be seen that the detection of the stiffness of the can be achieved.

  Next, a method of using the determination result obtained by determining the rigidity of the paper will be described.

  A registration roller 188 and a loop forming roller 187 are provided on the downstream side of the conveyance path 183 having the bent portion in the sheet conveyance direction to correct the sheet bending of the sheet by forming a loop on the sheet after abutting the sheet. . The driving of the loop forming roller 187 is controlled by the control means 60. The control unit 60 controls the loop amount formed by the loop forming roller based on the determination result of the rigidity of the sheet by the determination unit 61. Specifically, when the determination unit 61 determines that the sheet has a high rigidity, the control unit 60 controls the loop formation roller 187 to stop the loop formation roller 187 so as to be earlier by, for example, 10 msec. The amount of loop formed by the roller 187 is reduced. By this control, it is possible to prevent a rigid sheet from being strongly pressed against the registration roller 188 and entering deeply into the nip.

  Of course, the above-described determination of rigidity can also be applied when feeding from the first sheet feeding unit.

  In this case, it is applied to a conveyance path 430 having a bent portion with a greatly expanded passage width. Each member includes a photosensor 431 as a first sensor, a photosensor (PS) 432 as a second sensor, a registration roller 44, and A loop forming roller 43D2 is used and is the same as described above.

As shown in (a) of the graph of difference in passage time in FIG. 4, the passage time of plain paper as the reference passage time is 285.50 ms, whereas the thickness of thick paper having a strong basis weight of 200 g / m ² is strong. The passing time is 281.15 ms, with a time difference of 4.35 ms, and a determination threshold of 3 msec can be similarly applied.

  Furthermore, the above-described determination of rigidity can of course be applied at the time of refeeding.

  In this case, it is applied to a conveyance path 133 having a bent portion with a large passage width, and each member includes a photo sensor 188S as a first sensor, a photo sensor 432 as a second sensor, a registration roller 44, and a loop forming roller. 43D2 is used and is the same as described above.

  As shown in FIG. 4 (c), the passage time of plain paper as the reference passage time is 409.56 ms, while the passage time of thick paper is 404.51 ms. It has a time difference of 0.04 ms, and a determination threshold of 3 msec can be similarly applied.

  In addition, although demonstrated using the photo sensor as a 1st sensor and a 2nd sensor, a sensor is not limited to these.

1 is a cross-sectional configuration diagram of an image forming apparatus to which the present invention is applied. It is a cross-sectional block diagram of the reverse conveyance path for double-sided copying. FIG. 3 is a partially enlarged view of FIG. 2. It is a graph of the passage time when a sheet passes through each bent part. It is a figure showing the behavior of the rigid paper conveyed in the guide member of a bending part. It is a figure showing the behavior of the paper with low rigidity conveyed in the guide member of a bending part. It is a block diagram which shows the hardware constitutions for performing control in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 21 Photoconductor 24 Transfer device 25 Separator 43D1 Conveyance drive roller 43D2 Loop forming roller 44 Registration roller pair 50 Fixing device 170 Discharge reversing part 171 Path switching gate 174 First conveyance path 175, 176A for double-sided copying 177A Driving roller pair 180 Double-sided copying reversing unit 181 Second conveying path for double-sided copying 182 Conveying roller pair 182S, 188S, 431 Photosensor as first sensor 184S, 432 Photosensor as second sensor 183, 133, 430 Conveying path having a bent portion 184 Conveying roller pair 185 Third conveying path for double-sided copying 187 Loop forming roller 188 Pre-registration roller P Paper

Claims (6)

In an image forming apparatus having an image forming unit that forms an image on a sheet and a conveyance path that conveys the sheet, and a conveyance path having a bent portion in the conveyance path is provided.
A first sensor and a second sensor for detecting paper are provided on the upstream side in the paper transport direction and the downstream side in the paper transport direction of the transport path having the bent portion, respectively, and the paper passes between the first sensor and the second sensor. An image forming apparatus, comprising: a determination unit that detects a passage time and determines the strength of the sheet based on the detected passage time. The image forming apparatus according to claim 1, wherein the determination unit determines that the rigidity of the sheet is strong when a predetermined reference passage time is provided and is shorter than the reference passage time. A registration roller, a loop forming roller, which is provided on the downstream side of the sheet conveying direction of the conveying path having the bent portion and corrects the sheet bending of the sheet by forming a loop on the sheet after hitting the sheet, and the loop forming roller Control means for controlling the drive of
The image forming apparatus according to claim 1, wherein the control unit controls a loop amount formed by the loop forming roller based on a determination result of the rigidity of the paper by the determination unit. . The image forming apparatus according to claim 3, wherein the control unit performs control so as to reduce a loop amount formed by the loop forming roller when the determination unit determines that the sheet has high rigidity. apparatus. The image forming apparatus according to claim 1, wherein the conveyance path having the bent portion is provided in a reverse conveyance path that reversely conveys and re-feeds the paper. The image forming apparatus according to claim 1, wherein the conveyance path having the bent portion is provided in a conveyance path that feeds a sheet to a photosensitive member.

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