JP2009292590A - Sheet carrying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve skew correction accuracy regardless of thickness of a sheet. <P>SOLUTION: An upper guide 100 and a lower guide 101 for guiding a sheet S to a reference block 102 keep a predetermined gap G. The upper guide is energized toward the lower guide 101 via an energization pin 104 and the reference block 102 by a compression spring 103. Buckling of a thin sheet is restrained to not more than the gap G. When a thick sheet having buckling exceeding the gap G is to be guided, the upper guide is pressed by the sheet and moves in a direction, in which the gap G is enlarged. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet conveying device that is provided in an image forming apparatus such as a printing machine, a copying machine, a FAX, or a printer and that can accurately align sheets, and an image forming apparatus including the sheet conveying device.

  2. Description of the Related Art Conventionally, a sheet correction device that corrects a positional deviation of a sheet being conveyed is incorporated in a sheet conveyance device for sheet alignment used in an image forming apparatus. As a correction method using this sheet correction mechanism, there is a correction method based on a side registration standard that corrects a positional deviation of the sheet with reference to the side edge of the sheet being conveyed (see Patent Document 1).

  In this sheet correction mechanism, an abutting reference member is provided on one side of the sheet conveyance path along the sheet conveyance direction, and a skew feeding correction roller is disposed on the sheet conveyance path. Then, the skew feeding correction roller causes the sheet being conveyed to be brought closer to the abutting reference member side, the side edge of the sheet is abutted against the abutting reference member, and the positional deviation of the sheet side edge in the direction perpendicular to the conveying direction is detected. And the inclination of the sheet side edge with respect to the conveyance direction are corrected.

  The sheet conveying apparatus having such a correction method based on the side registration standard has the following problems. That is, when the side edge of the sheet is abutted against the abutting reference member, if the pressing force of the sheet against the abutting reference member (the width-adjusting force by the skew feeding correction roller) is too strong, buckling or looping occurs in the sheet. As a result, the sheet is jammed and the correction accuracy is deteriorated. For this reason, conventionally, a guide groove is formed with a U-shaped cross section of the abutting reference member, and a seat generated in the vertical direction (sheet thickness direction) of the sheet by inserting a side portion of the sheet into a gap portion by the guide groove. Regulating bending and looping.

  The width of the guide groove of the abutting reference block is set to a width that can correct the thickest sheet to be passed. In addition, since a thin sheet or the like cannot sufficiently suppress the occurrence of buckling and loops, the width of the guide groove of the abutting reference member (hereinafter referred to as an interval) can be adjusted to match the thickness of the sheet. Some have variable interval means (see Patent Document 2).

  Hereinafter, the above-described sheet conveying apparatus with a variable interval will be schematically described. FIG. 8 is a block diagram showing an outline of the control configuration of this conventional sheet conveying apparatus. In the figure, a controller 901 controls the overall operation of the sheet conveying apparatus in accordance with preset control procedures, control conditions, control information, and the like. The humidity detection sensor 48 detects humidity that is one of environmental information during sheet conveyance. The paper thickness detection sensor 903 detects the thickness of the sheet to be conveyed. The controller 901 controls the driving of the interval adjustment motor 602 via the interval adjustment motor driver 904 based on the information of these sensors 902 and 903. The controller 901 controls the driving of the nip pressure changing roller 906 via the nip pressure changing motor driver 905.

  FIG. 9 is a diagram illustrating a configuration of the guide member and the periphery of the sheet conveying apparatus illustrated in FIG. In FIG. 9, the interval is changed by a variable eccentric cam 601, an interval adjusting motor 602, a tension spring 603, and the upper guide 100.

  The upper guide 100 is urged away from the lower guide 101 by a tension spring 603, and the position of the upper guide 100 is determined based on the rotation angle of the variable eccentric cam 601. By rotating the variable eccentric cam 601 by the interval adjusting motor 602, the interval G of the upper guide 100 changes following the variable eccentric cam 601. The interval G is adjusted to a width suitable for the sheet thickness based on the sheet thickness detected by the paper thickness detection sensor 903. The sheet S is brought close to the reference surface of the lower guide 101 by the rubber roller 301 and the driven roller 302.

  The sheet thickness can be detected by using a displacement sensor having a contactor (actuator) or by detecting the vertical movement of the driven roller when the sheet passes through a reflective optical sensor and determining the thickness of the sheet from the amount of displacement. There is an optical detection method for detecting the above.

JP-A-11-189355 JP 2002-356250 A

  However, the conventional sheet conveying apparatus configured to detect the sheet thickness and adjust the gap G according to the thickness has the following problems.

  The detection accuracy of the contact type sensor or the reflection type optical sensor for detecting the thickness of the sheet has many variations, and the variation amount is about 60 μm in terms of the sheet thickness. Furthermore, there is also a variation in the sheet thickness itself, which is 10% of the sheet thickness and a variation of about 30 μm in thickness. Therefore, the detection variation is about 90 μm in total.

  On the other hand, the sheet thickness is 60 μm to 400 μm depending on the type, the range is as narrow as 400-60 = 360 μm, and the detection error due to the detection variation of the previous 90 μm is as large as 90/360 × 100 = 25%. For this reason, in the conventional sheet conveying apparatus that adjusts the gap G by feeding back the detected sheet thickness value, the sheet thickness exceeds the adjusted gap due to the detection error of the sheet thickness, and the sheet is well in the guide groove. There was a risk of jamming without entering.

  The present invention has been made in view of the above points. SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus with improved skew correction accuracy by regulating buckling at the time of sheet abutting against the abutting reference member regardless of the thickness of the sheet, and image formation using the same To provide an apparatus.

  In order to achieve the above object, a sheet conveying apparatus of the present invention is a sheet conveying apparatus that conveys a sheet in a predetermined conveying direction, and for positioning a side end of the conveyed sheet along the conveying direction. A reference member having a reference position, a width adjusting means for adjusting the side edge of the conveyed sheet to the reference member, and a side portion of the sheet when the sheet is conveyed while being adjusted by the width adjusting means. A pair of guide members guided to the reference member, the pair of guide members being held at a predetermined interval, and when guiding a sheet having a thickness exceeding the predetermined interval, It is possible to move in the direction in which the interval is widened.

  According to the sheet conveying apparatus of the present invention, buckling can be reduced at the time of abutting skew correction to the abutting reference member, and stable skew correction can be performed regardless of the thickness of the sheet. Further, the use of the sheet conveying apparatus for the image forming apparatus can increase the image position accuracy.

  A sheet conveying apparatus and an image forming apparatus including the same according to an embodiment of the present invention will be described with reference to the drawings.

[Overall configuration of image forming apparatus]
First, the overall configuration of the image forming apparatus according to the present embodiment will be described. Color image forming apparatuses are mainly classified into a rotary system having a configuration in which a plurality of image forming units are arranged side by side and a tandem system having a configuration in which a plurality of image forming units are arranged in a cylindrical shape. Transfer methods are classified into a direct transfer method in which a toner image is directly transferred from a photosensitive member to a sheet material, and an intermediate transfer method in which the toner image is once transferred to an intermediate transfer member and then transferred to a sheet material.

  FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention using an intermediate transfer tandem system in which four color image forming units are arranged side by side on an intermediate transfer belt. The intermediate transfer method does not need to hold the transfer material on the transfer drum or the transfer belt unlike the direct transfer method, and thus can cope with various transfer materials such as ultra-thick paper and coated paper. Furthermore, the intermediate transfer method is suitable for realizing high productivity due to the features of parallel processing in a plurality of image forming units and batch transfer of full-color images. The configuration and operation of the image processing apparatus according to this embodiment will be described below.

  The sheet S is stored on the lift-up device 52 included in the sheet feeding device 51 and is fed by the sheet feeding unit 53 in accordance with the image forming timing of the image forming apparatus. Here, as the sheet feeding means 53, there are a system using friction separation by a feeding roller or the like, a system using separation adsorption by air, etc., but this image forming apparatus adopts a feeding system by air. .

  The sheet S sent out by the sheet feeding unit 53 passes through a transport path 54 a included in the transport unit 54 and is transported to the skew correction device 55. After the skew correction and timing correction are performed in the skew correction device 55, it is sent to the secondary transfer unit. The secondary transfer portion is a toner image transfer nip portion to the sheet S formed by the substantially opposite secondary transfer inner roller 503 and secondary transfer outer roller 56, and applies a predetermined pressure and electrostatic load bias. As a result, the unfixed image is transferred onto the transfer paper.

  Next, a process for forming an image sent to the secondary transfer unit at the same timing as the conveyance process of the sheet S to the secondary transfer unit will be described. The image forming apparatus 513 mainly includes a photosensitive member 508, an exposure device 511, a developing device 510, a primary transfer device 507, a photosensitive member cleaner 509, and the like. The exposure device 511 emits light based on the image information signal sent to the photosensitive member 508 whose surface is uniformly charged in advance by the charging means and rotates in the direction of arrow A in the figure, and the diffraction means 512 and the like are transmitted. A latent image is formed via an appropriate route. The electrostatic latent image formed on the photoconductor 508 in this way is subjected to toner development by the developing device 510 to form a toner image on the photoconductor. Thereafter, a predetermined pressing force and an electrostatic load bias are applied by the primary transfer device 507, and the toner image is transferred onto the intermediate transfer belt 506. Thereafter, the transfer residual toner slightly remaining on the photoconductor 508 is collected by the photoconductor cleaner 509, and is prepared for the next image formation again. In the present embodiment, the image forming apparatus 513 described above includes four sets of yellow (Y), magenta (M), cyan (C), and black (Bk). Of course, it is not limited to four colors, and the order of colors is not limited to this.

  Next, the intermediate transfer belt 506 will be described. The intermediate transfer belt 506 is stretched by rollers such as a driving roller 504, a tension roller 505, and a secondary transfer inner roller 503, and is conveyed and driven in the direction of arrow B in the drawing. Therefore, the image forming process of each color processed in parallel by the above-described Y, M, C, and Bk image forming apparatuses 513 is performed at the timing of superimposing on the upstream toner image primarily transferred onto the intermediate transfer belt. As a result, a full-color toner image is finally formed on the intermediate transfer belt 506 and conveyed to the secondary transfer unit.

  As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer portion by the sheet conveying process and the image forming process described above. Thereafter, the sheet S is conveyed to the fixing device 58 by the pre-fixing conveyance unit 57. The fixing device 58 melts and fixes the toner on the sheet S by applying a predetermined pressurizing force by a substantially opposing roller or belt and generally a heating effect by a heat source such as a heater. Whether the sheet S having a fixed image obtained in this way is discharged as it is onto the discharge tray 500 by the branch conveyance device 59, or is conveyed to the reverse conveyance device 501 when double-sided image formation is required. Is selected.

  A transport operation when double-sided image formation is required will be described. The sheet S sent to the reverse conveying apparatus 501 is switched back and then conveyed to the duplex conveying apparatus 502 by performing a switchback operation. Thereafter, the transfer unit 54 joins from the refeed path 54b of the transport unit 54 in synchronization with the transfer material of the subsequent job transported from the sheet feeding device 51, and is similarly sent to the secondary transfer unit. The image forming process on the back side is the same as that on the front side, and is therefore omitted.

  A large number of conveyance roller devices are arranged in the sheet conveyance path of the conveyance unit 54, the branch conveyance device 59, the reverse conveyance device 501, and the double-side conveyance device 502. In these conveyance roller devices, the sheet is conveyed in a state where the sheet is nipped between the driving roller and the driven roller. Further, in the conveyance roller device arranged in the sheet conveyance path, an urging member such as a spring is arranged on the driven roller, and a pressure for nipping the sheet between both rollers is set.

[Sheet conveying device]
Next, a sheet conveying device for sheet alignment used in the image forming apparatus will be described.

  The sheet conveying apparatus of the present embodiment incorporates a skew correction device 55 for correcting the positional deviation of the sheet being conveyed. As a correction method used in the skew feeding correction device 55, there is a correction method based on a side registration reference that corrects a positional deviation of a sheet with reference to a side edge of the sheet being conveyed. In the present embodiment, a case where the skew feeding correction device 55 is arranged in front of the secondary transfer portion will be described. The skew correction device 55 using the side registration method may be used for a discharge-type sheet post-processing device after fixing as well as before secondary transfer.

  The conveyance roller device 50 includes a plurality of conveyance rollers that allow the driven roller to be attached to and detached from the sheet, and that a nip state and a nip release state can be arbitrarily set. The skew correction device 55 includes a plurality of skew correction rollers that are provided downstream of the conveying roller device 50 and that can arbitrarily set a nip state and nip release. The conveyance roller device 50 and the skew feeding correction device 55 constitute a sheet aligning device. The skew correction device 55 and the registration roller 7 constitute a register device.

  FIGS. 2A to 2C are top views of the sheet conveying apparatus having the conveying roller device 50, the skew feeding correction device 55, and the registration roller 7, and are diagrams illustrating a state in which the skew of the sheet is corrected. . The skew correction device 55 is mainly composed of a movable guide 30 and a fixed guide 33. The movable guide 30 is movable in the width direction (arrow direction) according to the size of the sheet S, and is configured by an abutting reference member 31 and a plurality of skew correction rollers.

  The skew feeding correction roller 32 is inclined by an angle α with respect to the conveyance direction, and is set so that an abutting conveyance component with respect to the abutting reference member 31 is obtained. In this embodiment, the skew correction roller 32 applies a force in the width-adjusting direction to the abutting reference member 31 and a force in the transport direction to the sheet S. However, the force in the width-adjusting direction is applied to the sheet S. It is also possible to add by means different from the row correction roller 32.

  The fixed guide 33 does not move regardless of the size of the sheet S and functions as a conveyance guide for the sheet S. As shown in FIG. 2A, it is assumed that the sheet S enters the skew correction device 55 in a state where the sheet S has a skew angle β with respect to the transport direction. The sheet S sent to the skew feeding correction roller 32 by the conveying roller 34 is conveyed obliquely toward the abutting reference member 31 as shown in FIG. Note that when the sheet S starts to be conveyed by the skew feeding correction roller 32, the nip of the conveyance roller 34 is released. Then, as shown in FIG. 2C, the side edge of the sheet S is brought closer to the reference surface of the abutting reference member 31 to correct skewing.

  FIG. 3 is a diagram showing details of the abutting reference member 31. The cross section of the abutting reference member 31 is U-shaped and includes an upper guide 100, a lower guide 101, and a reference block 102. The reference block 102 provides a reference position for positioning the sheet S. The upper guide 100 and the lower guide 101 constitute a pair of guide members. The upper guide 100 is urged toward the lower guide 101 by a compression spring (biasing means) 103 via an urging pin 104 and a reference block (reference member) 102 and is slidable up and down. . That is, the upper guide 100 is slidably biased so as to approach the lower guide 101. The shape of the entrance of the upper and lower guides is tapered so that the side edge of the sheet S can be guided. The upper guide 100 can slide up and down and is pressurized toward the lower guide 101. A certain predetermined amount of gap (guide gap) G between the upper and lower guides is secured. The skew correction roller 32 includes a rubber roller 301 and a driven roller 302.

  FIG. 4 is a diagram illustrating a state of the abutting reference member 31 when a sheet thicker than the predetermined (initial state) gap G has been conveyed. As shown in the figure, when a sheet S thicker than the gap G is conveyed, it spreads according to the sheet thickness and becomes the same gap G1 as the sheet thickness. The pressure for urging the upper guide 100 is set to such an extent that no abutting failure occurs even when a thick sheet is conveyed. Details of the pressure setting are described below.

  FIG. 5 is a graph showing the relationship between sheet stiffness and thickness. The stiffness is the strength of the sheet, and is a physical property value indicating how much force is required to bend the sheet. The distance G between the upper and lower guides was set to 1 mm, and the thickness, rigidity, and static friction coefficient of the buckling sheet were obtained by experiments. The conditions of the seat that buckles when abutting are as follows. Although there were variations depending on the environment, the thickness was 90 μm, the static friction coefficient μ was 0.25 to 0.35, the stiffness was 400 to 500 mgf, and the nip pressure N of the skew feeding correction roller was 450 gf to 480 gf. As shown in FIG. 5, there is a correlation between the rigidity and the thickness of the sheet. If a sheet having a rigidity of 400 mgf or less is given, the sheet is classified into a sheet having a thickness of less than 200 μm. Therefore, the buckling of the thin sheet can be regulated by setting the predetermined amount of the gap G to 200 μm.

FIG. 6 is a diagram illustrating the relationship between the force F that pushes up the upper guide 100 when the thin sheet buckles and the conveying force of the skew feeding correction roller. As shown in the figure, F = μNsinθ, where θ is the angle between the width direction of the sheet edge and the horizontal direction, μ is the static friction coefficient, and N is the nip pressure. Substituting the above-mentioned values into this equation yields 0.35 × 480 × sin (tan ⁻¹ (1/15)) = 11 gf. Therefore, if the urging force P of the upper guide 100 is set to 11 gf or more, the upper guide 100 is not pushed up due to buckling of thin paper.

  Regarding the buckling of the thick sheet, referring to FIG. 5, when the thickness is 200 μm or more, the stiffness is 715 mgf or more. Therefore, when the nip pressure of the skew correction roller 32 that buckles at 200 μm is obtained from the above-mentioned buckling condition, 450 is obtained. × 715/400, and the value is approximately 800 gf. Since the nip pressure N of the skew feeding correction roller 32 when passing a sheet having a thickness of 200 μm or more is set to 600 to 700 gf, N <800 gf or less and no buckling occurs. That is, in the case of a thick sheet of 200 μm or more, there is no buckling of the sheet at the time of skew correction. Therefore, the lower limit value of the urging force P for preventing the upper guide 100 from lifting due to buckling is 11 gf, and P> 11 gf.

  Conversely, the upper limit value of the urging force P of the upper guide 100 is set to a pressure at which the thick sheet is not conveyed poorly. The upper limit value of P is determined by the resistance value when the thickest sheet is sandwiched between the guide grooves. Actually, since the trailing edge of the sheet flowing through the oblique feeding reference member 31 straddles the conveyance roller device 50 at the time of skew correction, it is necessary to subtract the conveyance resistance of the conveyance roller device 50.

  FIG. 7 is a graph showing the transport load of the transport roller device 50 on thick large-size paper. As shown in the figure, since the curl amount is defined to be 10 mm or less, the maximum conveying load at the trailing edge of the conveying roller device 50 is 135 gf. Therefore, the feeding force for skew feeding at the time of skew feeding correction is a value obtained by subtracting 135 gf, which is the maximum conveyance load value at the trailing edge of the sheet, from 0.30 × 600 = 180 gf.

  Further, the surface of the upper and lower guide plates (100, 101, 102) of the abutting reference member is subjected to fluorine plating to improve the slidability and manage the friction coefficient. The friction coefficient of the guide plate is 0.06, which is about 1/5 of the friction coefficient of the sheet, and the upper limit of the urging force P of the upper guide 100 is (180−135) /0.06=750 gf.

  From the above, the range of the guide biasing force P is 11 gf <P <750 gf. That is, the urging force P is set to be equal to or greater than the force that prevents the upper guide 100 from moving even if the thin sheet buckles between the upper and lower guides. The urging force P is set to be equal to or less than the urging force that does not cause a conveyance failure when the thick sheet held between the urged lower guide 101 and the upper guide 100 is conveyed.

  For this reason, in this embodiment, the range of the guide biasing force P is set to 11 gf <P <750 gf, so that the upper guide 100 does not move due to buckling of the thin sheet, and the lower guide 101 and the upper guide are moved by the thick sheet. Even if the sheet is sandwiched between the guide 100, a conveyance failure does not occur.

  In addition, since the maximum thickness of the sheet is about 400 μm, the slide amount of the upper guide 100 is very small, 400−200 = 200 μm (0.2 mm), and the spring pressure increases extremely due to the thickness of the thick sheet. There is no resistance. A sheet of 200 μm or more is guided by the taper of the upper guide 100 and the lower guide 101, and pushes up the upper guide 100 to hit the reference block 102.

  As described above, by setting the urging force of the upper guide 100 to 11 gf <P <750 gf, the buckling amount is regulated to 0.2 mm or less for the paper thickness of 50 μm to 200 μm, and for the paper of 200 to 400 μm. The paper passes through the gap G between the upper and lower guides depending on the paper thickness. For this reason, the skew amount can be regulated to 0.2 mm or less as a whole.

  From the above, in the case of the guide fixed type as in the conventional case, the thin sheet buckle is bad, and it is possible to suppress the skew to about 1/3 compared with the worst case of about 0.6 mm. Thus, the image position accuracy can be greatly improved.

  Further, since the lower limit value of the urging force P is as small as 11 gf, the urging means may be only the own weight of the upper guide 100 without attaching the compression spring 103.

1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows a mode that skew feeding of a sheet | seat is corrected. It is a figure which shows the detailed structure of an abutting reference | standard member. It is a figure which shows the state of an abutting member when the sheet | seat thicker than the space | interval of an initial upper and lower guide has been conveyed. It is a graph which shows the relationship between the rigidity of a sheet | seat, and thickness. It is a figure which shows the relationship between the force which pushes up an upper guide when a thin sheet buckles, and the conveyance force of a skew feeding correction roller. It is a graph which shows the conveyance load in the thick large sized paper of a conveyance roller apparatus. It is a block diagram which shows the outline of the control structure of the conventional sheet conveying apparatus. FIG. 9 is a diagram illustrating a configuration of a guide member and its periphery of the sheet conveying apparatus illustrated in FIG. 8.

Explanation of symbols

31 Abutting reference member
32 Skew correction roller
100 Top guide
101 Lower guide
102 Reference block
103 Compression spring
104 Biasing pin
301 Rubber roller
302 Follower roller S Sheet G Interval

Claims (4)

A sheet conveying apparatus for conveying a sheet in a predetermined conveying direction,
A reference member having a reference position for positioning the side edge of the conveyed sheet along the conveyance direction;
Width adjusting means for adjusting the side edge of the conveyed sheet to the reference member;
A pair of guide members for guiding the side of the sheet to the reference member when the sheet is conveyed while being width-adjusted by the width-adjusting means;
Have
The pair of guide members are held at a predetermined interval, and when guiding a sheet having a thickness exceeding the predetermined interval, the pair of guide members can be moved in a direction in which the interval is increased by being pushed by the sheet. Sheet conveying device. At least one of the pair of guide members is slidably provided;
The sheet conveying apparatus according to claim 1, further comprising a biasing unit that biases the pair of guide members toward each other. The sheet conveying apparatus according to claim 1, wherein the width adjusting unit includes a conveying roller provided so as to form a predetermined angle with respect to the conveying direction. Comprising the sheet conveying apparatus according to any one of claims 1 to 3,
An image forming apparatus that conveys a sheet on which an image is formed by the sheet conveying apparatus.

Images