JP2016050108A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which comprises inversion means, can perform two-sided printing, and can position images on a front face and a back face so as to prevent image positions of the front face and the back face from being shifted even in printing a sheet having a difference in parallelism between a front end and a rear end of the sheet.SOLUTION: An image formation apparatus comprises: a pair of register rollers 5 for performing skew correction of a conveyed sheet; a shift unit 13 for supporting the pair of register rollers, which is movable in a direction to change the angle of the pair of register rollers with respect to a sheet width direction Y; a unit drive motor 21 for moving the shift unit 13 in the direction to change the angle; sheet detection sensors 18a, 18b for detecting a difference in parallelism between a front end and a rear end of the sheet; and a control unit for controlling the unit drive motor 21 so as to change the angles of the pair of register rollers 5 as well as gate members 4 through the shift unit 13 in response to signals from the sheet detection sensors 18a, 18b when performing the skew correction of the sheet, which is inverted by the inversion means and in which an image is formed on one side.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of forming images on both sides of a sheet-like recording medium.

  In an image forming apparatus, a wide range of paper compatibility such as various paper types, paper thicknesses, and paper sizes is required in the current market. On the other hand, in order to reduce the amount of paper used as part of resource saving from the viewpoint of environmental problems, an image forming apparatus capable of forming images on both sides of a sheet as a sheet is frequently used. It is coming. In this specification, “forming an image” and “printing an image” are used synonymously. In particular, in the printing industry, higher speeds are demanded while dealing with the various papers described above, and the market requirements for image position accuracy are becoming stricter.

2. Description of the Related Art An image forming apparatus capable of duplex printing that forms images on both sides of a sheet is known that corrects image positional deviations on the front and back sides during duplex printing. (For example, refer to Patent Document 1).
The conventional image forming apparatuses capable of double-sided printing including a reversing unit that reverses a single-sided image-formed sheet having an image formed on one side thereof, including Patent Document 1, have the following problems. That is, at the time of double-sided printing, the front end of the sheet at the time of front side printing is reversed by the switchback at the time of back side printing and becomes the rear end of the sheet. The tip is aligned with the nip portion and the skew is corrected. For this reason, if printing is performed on a sheet having a large parallelism difference between the leading edge and the trailing edge of the same sheet, the image positions on the front and back surfaces are shifted, and the front and back image alignment cannot be performed (see FIG. 2).

  According to the present invention, in an image forming apparatus equipped with a reversing unit and capable of double-sided printing, even when double-sided printing is performed on a sheet having a parallelism difference between the leading edge and the trailing edge of the sheet, the image positions on the front and back surfaces are shifted. An object of the present invention is to provide an image forming apparatus capable of aligning front and back images.

  To achieve the above object, the present invention provides a registration roller pair for correcting skew feeding of a conveyed sheet, a registration driving means for rotationally driving the registration roller pair, and supporting the registration roller pair, A registration unit that is movable in a direction that changes the angle of the registration roller pair with respect to the sheet width direction orthogonal to the conveyance direction, unit drive means that moves the registration unit in a direction that changes the angle, and a conveyance from the registration roller pair An image forming unit that forms an image on the incoming sheet, a reversing unit that inverts the sheet on which one side image has been formed, and a parallel that detects a parallelism difference between the leading edge and the trailing edge of the sheet. Parallelism difference recognition means including at least one of degree difference detection means and parallelism difference setting means for setting the parallelism difference, and the inversion means When performing skew correction of a more reversed single-sided image formed sheet, the unit drive so as to change the angle of the registration roller pair via the registration unit in accordance with a signal from the parallelism difference recognition means And a first control unit that controls the image forming apparatus.

  According to the present invention, with the above-described configuration, the skew correction of the inverted single-sided image-formed sheet is performed with respect to the parallelism difference between the leading edge and the trailing edge of the sheet, so that even a sheet with a difference in parallelism can be used on the front and back surfaces. Image alignment can be performed.

1 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied. (A) is a plan view for explaining a sheet having a large parallelism difference, and (b) is a plan view of a sheet on which a surface image is formed with the sheet of (a). (C) is a plan view showing a state in which the paper on which the front image of (b) is formed is switched back, and (d) is a state of the paper on which the back image is formed on the back surface of the paper on which the front image of (c) is formed. FIG. FIG. 2 is a schematic configuration diagram of a main part of the image forming apparatus according to the first embodiment. FIG. 3 is a partial cross-sectional front view illustrating a main configuration of a skew feeding correction mechanism in the paper position correction mechanism according to the first embodiment. FIG. 5 is a plan view of FIG. 4. (A) is sectional drawing explaining the structure of a gate member, (b) is a partial cross section front view explaining the nip part of a registration roller pair, and the gate position of a gate member. (C), (d) is an enlarged sectional view for explaining the relationship between the nip portion of the registration roller pair and the position where the leading edge of the sheet hits the contact surface of the gate member. (A)-(e) is a simplified front view explaining the operation | movement transition of the skew feeding correction mechanism provided with the gate member. It is a top view explaining a structure and operation | movement of a skew position correction mechanism. FIG. 6 is a partial cross-sectional front view of the skew position correcting mechanism as seen from the direction of arrow B in FIG. 5. It is a perspective view which shows the principal part structure of the shift unit drive means of a main scanning correction | amendment mechanism. It is a top view of the shift unit drive means connected with the shift unit. (A), (b), (c) is explanatory drawing explaining the operation | movement transition of a shift unit drive means. FIG. 6 is a block diagram illustrating a main control configuration of a paper position correction mechanism according to the first embodiment, and a main control configuration of Modification 3 and Modification 4. FIG. 6 is a plan view for explaining a state of correction operation transition of a sheet by a skew position correction mechanism and a main scanning correction mechanism in front surface print conveyance according to the first embodiment. (A) is a plan view of a sheet detection sensor when the leading edge of the sheet is detected, and (b) is a plan view of the sheet detection sensor when a trailing edge of the sheet is detected. FIG. 6 is a plan view for explaining a correction operation transition state of a sheet in back surface printing conveyance according to the first embodiment. It is a block diagram which shows the control structure of the principal part of the modification 1 and the modification 2. FIG. (A), (b) is the enlarged front view of the principal part explaining the relationship between the sheet thickness and the gate position in Modification 1 and Modification 2. (A)-(g) is a simplified front view explaining the skew correction operation | movement transition of the modification 3. FIG. (A) is a front view which shows mesh | engagement of gears, (b) is an enlarged front view which expands and shows the meshing part of gears.

  Hereinafter, embodiments of the present invention including examples will be described in detail with reference to the drawings. In each embodiment and the like, components (members and components) having the same function and shape are described once unless they are confused, and the description thereof is omitted by giving the same reference numerals. In order to simplify the drawings and the description, even if the components are to be represented in the drawings, the components that do not need to be specifically described in the drawings may be omitted as appropriate. When quoting and explaining constituent elements such as published patent gazettes, the reference numerals are shown in parentheses to distinguish them from those of the embodiments.

First, with reference to FIG. 1, the operation and the basic configuration of an electrophotographic printer as an image forming apparatus to which the present invention is applied will be described. FIG. 1 is a schematic configuration diagram of an image forming apparatus to which the present invention is applied.
The image forming apparatus shown in FIG. 1 includes four process units 35Y, 35M, 35C, and 35K for forming toner images of different colors of yellow (Y), magenta (M), cyan (C), and black (K). It has. In addition, a paper feed path 43, a pre-transfer conveyance path 44, a manual paper feed path 45, a manual feed tray 46, a registration roller pair 5, a conveyance belt unit 48, a fixing unit 52, a conveyance switching device 53, a paper discharge path 54, and a paper discharge roller. A pair 52, a paper discharge tray 56, a first paper feed cassette 101, a second paper feed cassette 102, a retransmission device, and the like are also provided. Two optical writing units 34YM and 34CK are also provided. The process units 35Y, 35M, 35C, and 35K have drum-shaped photoconductors 36Y, 36M, 36C, and 36K as image carriers corresponding to toner images of different colors.

The paper feed unit 80 includes a first paper feed cassette 101 and a second paper feed cassette 102. Each of the first paper feed cassette 101 and the second paper feed cassette 102 accommodates a bundle of sheets P as sheets and recording media. Then, the uppermost sheet P in the bundle of sheets P is sent out toward the sheet feed path 43 by the rotational driving of the sheet feed rollers 101 a and 102 a. Connected to the paper feed path 43 is a pre-transfer conveyance path 44 for conveying a sheet immediately before a secondary transfer nip described later. The paper selectively sent out from the first paper feed cassette 101 or the second paper feed cassette 102 enters the pre-transfer conveyance path 44 through the paper feed path 43.
A manual feed tray 46 is disposed on the side surface of the printer chassis so as to be openable and closable with respect to the chassis (meaning that the manual feed tray 46 is disposed and positioned). A bundle or one sheet of paper (not shown) is manually fed onto the upper surface of the tray 46. The topmost sheet in the bundle of manually fed sheets is sent out toward the pre-transfer conveyance path 44 by the feed roller of the manual feed tray 46.

  The two optical writing units 34YM and 34CK each have a laser diode, a polygon mirror, various lenses, and the like. Each optical writing unit 34YM, 34CK drives a laser diode based on image information read by a scanner outside the printer or image information sent from a personal computer. Then, the photoconductors 36Y, 36M, 36C, and 36K of the process units 35Y, 35M, 35C, and 35K are optically scanned. Specifically, the photoreceptors 36Y, 36M, 36C, and 36K of the process units 35Y, 35M, 35C, and 35K are rotationally driven in the counterclockwise direction in the drawing by driving means (not shown). The optical writing unit 34YM performs an optical scanning process by irradiating the driven photoconductors 36Y and 36M while deflecting the laser light in the rotation axis direction. Thereby, electrostatic latent images based on the Y and M image information are formed on the photoreceptors 36Y and 36M. Further, the optical writing unit 34CK performs an optical scanning process by irradiating the driven photoconductors 36C and 36K while deflecting the laser light in the direction of the rotation axis. Thereby, electrostatic latent images based on the C and K image information are formed on the photoreceptors 36C and 36K. The optical writing units 34YM and 34CK are exposure means for exposing the surfaces of the photoconductors 36Y and 36M and the photoconductors 36C and 36K to form an electrostatic latent image.

  The process units 35Y, 35M, 35C, and 35K each support the photosensitive member and various devices disposed around it as a single unit on a common support, and these support the printer unit main body. Can be removed. The configuration is the same except that the colors of the toners used are different. The Y process unit 35Y will be described as a representative. In addition to the photoconductor 36Y, a developing device 37Y as a developing unit for developing an electrostatic latent image formed on the surface of the photoconductor 36Y into a Y toner image is provided. doing. In addition, a charging device 38Y is provided as a charging unit that uniformly charges the surface of the rotationally driven photoreceptor 36Y. Further, it also includes a drum cleaning device 39Y as a cleaning means for cleaning the transfer residual toner adhering to the surface of the photoreceptor 36Y after passing through a Y primary transfer nip described later.

  The illustrated printer has a so-called tandem configuration in which four process units 35Y, 35M, 35C, and 35K are arranged along an endless movement direction with respect to an intermediate transfer belt 61 described later. As the photoreceptor 36Y, a drum-shaped member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a base tube made of aluminum or the like. However, an endless belt-shaped so-called photoreceptor belt may be used.

  The developing device 37Y develops the electrostatic latent image using a two-component developer (hereinafter simply referred to as “developer”) containing a magnetic carrier (not shown) and non-magnetic Y toner. The developing device 37Y is appropriately replenished with Y toner in the Y toner bottle 103Y by a Y toner replenishing device (not shown). A toner density detecting means (not shown) is provided in the developing device 37Y. This toner concentration detecting means detects the magnetic permeability caused by the carrier that is a magnetic material, and calculates the toner concentration from the amount of carrier contained in a certain volume. The toner density detection means detects the toner density in the developing device Y, and controls the toner density in the developing device Y to be kept within a certain range.

  As the drum cleaning device 39Y, a system that presses a cleaning blade made of polyurethane rubber against the photoreceptor 36Y is used, but another system may be used. In order to improve the cleaning property, this printer employs a system in which a rotatable fur brush is brought into contact with the photoreceptor 36Y. The fur brush also serves to apply the lubricant to the surface of the photoreceptor 36Y while scraping the lubricant from a solid lubricant (not shown) to make a fine powder.

An unillustrated neutralizing lamp is disposed above the photoreceptor 36Y, and this neutralizing lamp is also a part of the process unit 35Y. The neutralization lamp neutralizes the surface of the photoreceptor 36Y after passing through the drum cleaning device 39Y by light irradiation. The surface of the removed photoreceptor 36Y is uniformly charged by the charging device 38Y and then subjected to optical scanning by the optical writing unit 34YM described above. The charging device 38Y is of a charging roller type that is rotated while being supplied with a charging bias from a power source (not shown) (contacted with the photoconductor 36Y or placed in close proximity without contact). Instead of such a method, a scorotron charger method that performs a non-contact charging process on the photoreceptor 36Y may be employed.
Although the Y process unit 35Y has been described above, the M, C, and K process units 35M, 35C, and 35K have the same configuration as the Y process unit 35Y.

  A transfer unit 60 is disposed below the four process units 35Y, 35M, 35C, and 35K. The transfer unit 60 is either one in which an intermediate transfer belt 61 as an endless intermediate transfer member stretched by a plurality of support rollers 63, 67 is brought into contact with the photosensitive members 36Y, 36M, 36C, 36K. The roller is endlessly moved in the clockwise direction in the figure by the rotational drive of one roller. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 36Y, 36M, 36C, and 36K abut on the intermediate transfer belt 61 are formed. Of the support rollers 63 and 67, the support roller 63 is a driving roller, and the support roller 67 is a driven roller. “Tension” means to hang up in a state where tension is applied, and “abutment” means to make contact in a state of abutment.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is exposed to light by primary transfer rollers 62Y, 62M, 62C, and 62K as primary transfer rotators disposed inside the belt loop. It is pressing toward the bodies 36Y, 36M, 36C, 36K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, and 62K by a primary transfer bias power source (not shown) for each color. As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 36Y, 36M, 36C, and 36K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. Has been. “Pressing” means pressing with pressure. Each primary transfer roller 62Y, 62M, 62C, 62K and a primary transfer bias power source (not shown) for each color constitute a primary transfer device as a primary transfer unit.

  In the drawing, the photosensitive drum passes through the primary transfer nip for Y, M, C, and K in sequence with the endless movement in the clockwise direction on the front surface of the intermediate transfer belt 61 at each primary transfer nip. The toner images on the bodies 36Y, 36M, 36C, and 36K are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as “four-color toner image”) is formed on the front surface of the intermediate transfer belt 61.

A secondary transfer roller 72 as a secondary transfer rotator is disposed below the intermediate transfer belt 61 in the drawing. The secondary transfer roller 72 abuts from the front surface of the intermediate transfer belt 61 to a place where the intermediate transfer belt 61 is wound around the secondary transfer backup roller 68, and a secondary transfer nip as a contact portion or a contact / holding portion. Is forming. As a result, a secondary transfer nip where the front surface of the intermediate transfer belt 61 and the secondary transfer roller 72 abut is formed.
A secondary transfer bias is applied to the secondary transfer roller 72 by a secondary transfer bias power source (not shown). On the other hand, the secondary transfer backup roller 68 in the belt loop of the intermediate transfer belt 61 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip. A secondary transfer unit 70 is configured by the secondary transfer roller 72 and the secondary transfer bias power source (not shown).

The registration roller pair 5 described above is disposed on the right side of the secondary transfer nip in the drawing, and the sheet sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61 at a timing 2. Send to next transfer nip. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred to the sheet collectively due to the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the sheet.
Note that one roller of the registration roller pair 5 is formed of rubber, for example, and the other roller of the registration roller pair 5 is formed of metal, and a nip is formed by both rollers. The image forming apparatus shown in FIG. 1 employs a nip system that corrects the skew of a sheet by abutting the leading end of the sheet against the nip of the registration roller pair 5.

Untransferred toner that has not been transferred to the paper P at the secondary transfer nip adheres to the front surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This untransferred toner is cleaned by a belt cleaning device 75 having a cleaning blade in contact with the intermediate transfer belt 61. A cleaning blade backup roller 69 is disposed at a position facing the cleaning blade of the belt cleaning device 75 with the intermediate transfer belt 61 interposed therebetween. A tension roller 66 that applies a predetermined tension to the intermediate transfer belt 61 is disposed near the downstream of the belt cleaning device 75 in the rotational traveling direction.
The paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 48. The conveyor belt unit 48 is endlessly moved in the counterclockwise direction in the figure by the rotational driving of the driving roller 50 while the endless conveyor belt 49 is stretched between the driving roller 50 and the driven roller 51. Then, while the sheet transferred from the secondary transfer nip is held on the upper stretched surface of the conveyance belt 49, the sheet is conveyed along with the endless movement of the conveyance belt 49 and is transferred to the fixing unit 52.

  The paper P that has passed through the secondary transfer nip described above is sent into the fixing unit 52 and sandwiched between the fixing nips. Then, the toner image is fixed by an action such as pressurization and heating. The paper P on which the toner image has been transferred to the first surface at the secondary transfer nip and the toner image has been fixed on the first surface by the fixing unit 52 is sent out toward the conveyance switching device 53.

  In the present printer, the transfer switching device 53, the retransmission path 57, the switchback path 58, the post-switchback transfer path 59, and the like constitute a retransmission means. Specifically, the conveyance switching device 53 includes a first switching claw 64 that switches the subsequent conveyance destination of the paper P received from the fixing unit 52 to the paper discharge path 54 or the retransmission path 57. When a single-side mode print job for forming an image only on the first side of the paper P is executed, the conveyance destination is set to the paper discharge path 54. As a result, the paper P on which the image is formed only on the first surface is sent to the paper discharge roller pair 52 via the paper discharge path 54 and discharged onto the paper discharge tray 56 outside the apparatus. In addition, when a double-sided mode print job for forming images on both sides of the paper P is executed, when the paper P having images fixed on both sides is received from the fixing unit 52, the transport destination is discharged. Set to Road 54. As a result, the paper P on which images are formed on both sides is discharged onto a discharge tray 56 outside the apparatus.

  On the other hand, when a sheet P having an image fixed only on the first side is received from the fixing unit 52 during execution of a double-side mode print job, the transport destination is set to the retransmission path 57. A switchback path 58 is connected to the retransmission path 57, and the sheet P sent to the retransmission path 57 is guided by the second switching claw 65 and enters the switchback path 58. When the entire area in the transport direction of the paper P enters the switchback path 58, the transport direction of the paper P is reversed and the paper P is switched back. The switchback path 58 is connected to a post-switchback conveyance path 59 in addition to the retransmission path 57, and the switched-back paper P is guided by the second switching claw 65 and enters the post-switchback conveyance path 59. . At this time, the upper and lower sides of the paper P are reversed. Then, the vertically inverted paper P is retransmitted to the secondary transfer nip via the post-switchback transport path 59 and the paper feed path 43 described above. The paper P on which the toner image is also transferred to the second surface at the secondary transfer nip is fixed on the second surface via the fixing unit 52, and then the conveyance switching device 53, the paper discharge path 54, The paper is discharged onto a paper discharge tray 56 via the paper discharge roller pair 52.

As described above, at the branch point between the retransmission path 57, the switchback path 58, and the post-switchback transport path 59, the paper P on which the image is fixed only on the first surface is fed to the switchback path 58 or the post-switchback transport path. A second switching claw 65 for switching to 59 is provided. The first switching claw 64 and the second switching claw 65 described above have a well-known configuration for switching the sheet conveyance path by swinging and displacing with a combination of a solenoid and a spring.
Single-sided image-formed paper on which an image is formed on one side by the conveyance switching device 53, the retransmission path 57, the switchback path 58, the post-switchback conveyance path 59, the first switching claw 64, the second switching claw 65, etc. Inversion means for inverting the (sheet) is configured.

Currently, the double-sided switchback method shown in FIG. 1 is mainly employed as a sheet conveyance path during double-sided printing. This has the advantage that the machine size can be reduced.
However, at the time of double-sided printing in the image forming apparatus provided with the reversing means, the leading edge Pa of the paper P at the time of front side printing is reversed at the time of backside printing to become the rear end Pb of the paper P. In some cases, the tips are aligned on different paper surfaces. Therefore, when skew correction is performed on a sheet having a large parallelism difference between the leading end Pa and the trailing end Pb of the sheet P as shown in FIG. 2A, printing is performed as shown in FIG. The paper PA on which the surface image has been formed is formed. Note that the rear end Pb of the rectangular paper P, which is a normal normal paper shape, is indicated by a broken line. In FIG. 2B, parentheses indicate that the leading edge PAa of the paper PA on which the surface image is formed is the leading edge Pa of the paper P before the surface image is formed. Here, the paper PA on which the front surface image has been formed means a sheet on which a single-sided image has been formed.

  On the other hand, as shown in FIG. 2C, the leading edge PAa of the paper PA on which the front surface image has been formed is switched back and reversed to become the rear end Pb of the paper PA on which the front surface image has been formed. For this reason, as shown in FIG. 2D, the front and back image positions of the double-side printed paper PB on which the front image and the back image are formed are shifted, and the front and back images cannot be aligned.

(Embodiment 1)
The image forming apparatus 100 according to the first embodiment of the present invention will be described with reference to FIG. 3 (claims 2, 7, and 8). FIG. 3 is a schematic configuration diagram of a main part of the image forming apparatus according to the first embodiment.
The image forming apparatus 100 is an electrophotographic printer, and has a sheet position correcting mechanism 2 including a plurality of correcting mechanisms, which will be described later, as compared with the image forming apparatus shown in FIG. The point which has the control part 30 to control mainly differs. The image forming apparatus 100 other than this difference is the same as the image forming apparatus of FIG. Hereinafter, the printer of the first embodiment will be described in detail focusing on the above differences. The image forming apparatus 100 shown in FIG. 3 is an electrophotographic printer similar to that shown in FIG. Any image forming apparatus may be used as long as it is an image forming apparatus.

  The image forming apparatus 100 includes an image forming unit 1, a secondary transfer unit 70 as an image transfer unit, a paper position correction mechanism 2, a double-side reversing unit 3, a paper feeding unit 80, and a fixing unit 52. ing. The image forming unit 1 is not shown in detail, but corresponds to the two optical writing units 34YM and 34CK and the four process units 35Y, 35M, 35C, and 35K in the image forming apparatus of FIG. To do. The double-side reversing unit 3 includes a retransmission path 57, a switchback path 58, a post-switchback conveyance path 59, a first switching claw 64, and a second switching claw 65 in the image forming apparatus of FIG. The fixing unit 52 is illustrated in the configuration in which the fixing belt is used in the image forming apparatus of FIG. 1 instead of the two heating rollers and the pressure roller, but is functionally the same.

The main operation of the image forming apparatus 100 will be described. The paper P stacked in the first paper feed cassette 101 of the paper feed unit 80 is transported to the paper position correction mechanism 2, and the skew of the paper and the deviation in the main scanning direction are corrected and pass through the secondary transfer unit 70. The image is transferred and formed on the paper. Thereafter, the sheet on which the image is formed on one surface is reversed from the fixing unit 52 through the duplex reversing unit 3 and the like. The sheet that has been turned upside down passes through the conveyance path 59 after switchback and passes again through the sheet position correction mechanism 2 and the secondary transfer unit 70, so that the image is also transferred and formed on the back side, which is the other side of the sheet. Then, double-sided printing is performed.
The paper position correction mechanism 2 includes a skew correction mechanism that corrects the skew of the paper, a skew position correction mechanism 14 shown in FIGS. 5 and 8 that corrects the skew of the paper during front and back printing, and a sheet width. A main scanning correction mechanism 16 shown in FIGS. 9 to 12 for correcting the image in the direction (main scanning direction) and the paper position is included.

The sheet position correcting mechanism 2 according to the first embodiment will be described with reference to FIGS. FIG. 4 is a partial cross-sectional front view showing the main configuration of the skew correction mechanism in the skew position correction mechanism 14 of the first embodiment, and FIG. 5 is a plan view of FIG.
As shown in FIGS. 4 and 5, the sheet position correction mechanism 2 includes a feed roller pair 6, a registration roller pair 5, a contact image sensor 8, and a conveyance roller pair from the upstream side to the downstream side in the sheet conveyance direction X. 7. Two paper detection sensors 18a and 18b are arranged in this order. The feed roller pair 6 and the conveyance roller pair 7 are configured as a pair of rollers facing each other across the sheet conveyance path, and can be rotated via a shaft with a pair of frames 15a and 15b fixedly disposed on the apparatus main body side. It is supported by.

  In the sheet conveyance path between the feed roller pair 6 and the registration roller pair 5, a lower conveyance guide 153 and a lower conveyance guide 153 that are arranged to extend substantially parallel to the tangential direction of the nip portion of the feed roller pair 6. And an upper conveyance guide 154 disposed opposite to each other. A part in the extending direction of the upper conveyance guide 154 is formed in a shape bulging upward in a direction away from the lower conveyance guide 153. The bulging portion of the upper conveyance guide 154 is a portion where a loop (curved portion) generated when a part of a sheet described later is bent is located.

The registration roller pair 5 includes a gate-side registration roller 5a as one registration roller positioned on the lower side in FIG. 4 across the sheet conveyance path, and a registration roller positioned on the upper side in FIG. 4 so as to face the registration roller 5a. 5b. The registration roller 5a is a driving roller to which a rotational driving force is transmitted, and the registration roller 5b is a driven roller that is driven by the registration roller 5a.
The upper registration roller 5b is configured to abut against or separate from the lower registration roller 5a by a contact / separation mechanism (not shown). The contact / separation mechanism (not shown) includes, for example, a nipping / conveying roller contact / separation cam (151C) provided on the drive roller side similar to that shown in FIG. 5 of Japanese Patent Application Laid-Open No. 2012-030971 proposed by the present applicant. It is configured. Note that the contact / separation mechanism of the registration roller pair 5 is not limited to the above-described one, and may be another known contact / separation mechanism that separates the registration roller pair 5 using another drive motor and a cam.

A gate member 4 as a gate portion that is coaxially supported adjacent to the axial end surface of the registration roller 5a is integrally attached to the shaft 5c of the registration roller 5a that is a driving roller. The gate member 4 is also provided in the vicinity of both ends of the shaft 5c corresponding to the maximum sheet size in the sheet width direction Y used in the image forming apparatus of the present embodiment. In the present embodiment, the gate member 4 is made of a metal such as aluminum and formed separately from the registration roller 5a. However, the gate member 4 is not limited to this and may be a gate portion formed integrally with the registration roller 5a. Good.
As shown in FIG. 6A, the gate member 4 has a contact surface 4a for aligning the leading edge of the paper, a guide surface 4c, and a registration roller pair 5 stopped, and the registration roller 5b is connected to the registration roller 5a. A conveyance guide surface 4b is formed as a guide when being separated from the sheet. As shown in FIGS. 6A and 6B, the contact surface 4a is formed in a contact portion protruding from the outer peripheral surface of the registration roller 5a. The guide surface 4c is a part continuous with the contact surface 4a of the gate member 4, and is formed to have the same diameter as the outer diameter of the registration roller 5a.
The gate member 4 rotates integrally with the registration roller 5a, so that the contact surface 4a is between the initial position where the contact surface 4a is located at the gate position Gp shown in FIG. It is configured to be able to move.

In the skew correction mechanism provided with the gate member 4, as shown in FIG. 6B and FIG. 7B described later, the position where the leading edge of the conveyed paper P abuts is pressed by the registration roller pair 5. It is not the position of the nip portion N to be formed. That is, the position where the leading edge of the conveyed paper P abuts is set to the gate position Gp where the contact surface 4a of the gate member 4 is located, which is biased to the upstream side in the sheet conveyance direction X from the position of the nip portion N. Has been.
Thereafter, the gate-integrated registration roller pair 5 is rotated, and the sheet must be conveyed to the nip portion N of the registration roller pair 5 while following the gate member 4. At that time, the stiffness of the sheet generated when the sheet is bent in FIG. 7B (force to return the sheet to a straight line when the sheet is bent) is caused to follow the gate member 4 and the nip of the registration roller pair 5 is detected. It is transported to the part N (FIGS. 6C and 6D).
Therefore, when the sheet whose skew has been corrected by the gate member 4 is transported to the nip portion N of the registration roller pair 5, the gate position Gp is closer to the nip portion N even if the sheet stiffness is weaker. It is smoothly conveyed to the position of the nip portion N.

The contact image sensor 8 (hereinafter abbreviated as “CIS8”) functions as a sheet width detection unit that detects the position of the conveyed sheet in the sheet width direction Y. The CIS 8 is attached and fixed to the frame 15a so as to protrude on the sheet conveyance path in the vicinity of the shift unit 13 in order to detect the side end position in the sheet width direction Y of the conveyed sheet.
The two sheet detection sensors 18a and 18b are formed of, for example, a reflection type photosensor, and a parallelism difference detection unit that detects a difference in parallelism by detecting the passage timing between the leading edge and the trailing edge of the sheet. Functions as a parallelism difference recognition means.

With reference to FIG. 5, a registration driving means for rotationally driving the registration roller pair 5 will be described. The registration driving means includes a drive motor 9, a gear 11, a two-stage gear 17, and a gear 10. The drive motor 9 is composed of a stepping motor or a DC motor that can rotate forward and backward, is fixed to the frame 15a via a bracket (not shown), and functions as a drive source for rotationally driving the registration roller pair 5. A gear 11 is fixed to the output shaft of the drive motor 9. The two-stage gear 17 includes a small-diameter gear 17a and a large-diameter gear 17b that always mesh with the gear 11, and is rotatably supported by the frame 15a. The large-diameter gear 17 b always meshes with the gear 10 fixed to the shaft 5 c of the registration roller pair 5.
A home position sensor for detecting the initial position of the gate member 4 may be provided in the gear 10 or the like.

The operation of the skew feeding correction mechanism will be described with reference to FIGS. FIG. 7A to FIG. 7E are front views of the main part showing the operation transition of the gate member and the registration roller of the skew feeding correction mechanism.
In FIG. 5, when the drive motor 9 is rotationally driven, the rotational driving force of the drive motor 9 is transmitted to the registration roller 5a through a gear train including the gear 11, the second gear 17, and the gear 10, and the registration roller pair 5 rotates. First, the registration roller pair 5 is rotated so that the contact surface 4a of the gate member 4 integral with the registration roller 5a protrudes into the sheet conveyance path as shown in FIGS. Perform positioning. At this time, the leading edge Pa of the sheet P is positioned on the sheet conveyance path between the feed roller pair 6 and the registration roller pair 5 by the rotation of the feed roller pair 6.
Next, as shown in FIG. 7B, the paper P is conveyed to the contact surface 4a of the positioned gate member 4 by the rotation of the feed roller pair 6, the leading end Pa of the paper P is abutted, and the paper P The front end portion is bent along the upper conveyance guide 154 to correct the front end position of the paper P (skew correction). Thereafter, the drive motor 9 is driven to rotate again, and the skew-corrected paper P is transported again (FIG. 7C).

  Next, as shown in FIG. 7D, when the leading edge Pa of the paper P is transported to the downstream transport roller pair 7, the registration roller 5 b on the driven side of the resist roller pair 5 is separated and transports the gate member 4. It waits for the paper P to come off on the guide surface 4b and the registration roller 5a. Next, when the trailing edge Pb of the paper P passes through the registration roller pair 5, the registration roller 5b is pressed against the registration roller 5a, and the registration roller pair 5 is rotated to the gate position (FIG. 7E). At this time, similarly to the above operation, positioning is performed so that the contact surface 4a of the gate member 4 occupies the gate position.

  In the skew correction mechanism of the type in which the registration roller 5a and the gate member 4 are integrally formed, the operations from FIG. 7A to FIG. 7E are all performed by one rotation of the registration roller pair 5. Yes. Accordingly, the skew correction of the paper can be performed in a short time, so that the skew of the paper conveyed at high speed can be corrected, and the interval of the conveyed paper can be further reduced. Further, since the gate member 4 has the conveyance guide surface 4 b, the registration roller 5 b of the registration roller pair 5 is separated when the gate member 4 is conveyed to the downstream conveyance roller pair 7. Then, after the trailing edge of the sheet has been removed, the method of performing press contact → registration roller pair rotation → repositioning of the gate member again can perform high-speed skew correction regardless of the sheet length.

The skew position correcting mechanism 14 will be described with reference to FIGS. 5, 8, and 9. The skew position correcting mechanism 14 includes unit driving means for moving the shift unit 13 in a direction in which the angle of the gate member 4 and the registration roller pair 5 with respect to the sheet width direction Y is changed. 9 is a partial cross-sectional front view seen from the direction of arrow B in FIG.
Each gate member 4 and registration roller pair 5 are attached to and supported by a flat unit main body 12 via a shaft 5c so as to be rotatable (meaning circular movement in forward and reverse directions). Each gate member 4, the registration roller pair 5, and the unit main body 12 constitute an integral shift unit 13.
As shown in FIG. 8, a long hole 15 c is formed in the frame 15 b so as to be substantially parallel to the sheet conveyance direction X. In the figure of the shift unit 13, the upper end side of the registration roller pair 5 with respect to the sheet width direction Y is centered on the lower end side of the shaft 5 c of the shift unit 13 by inserting the shaft 5 c of the registration roller 5 a through the elongated hole 15 c. It can move in the direction of changing the angle. In other words, the shift unit 13 functions as a registration unit that supports the gate member 4 and the registration roller pair 5 and is movable in a direction that changes the angle of the gate member 4 and the registration roller pair 5 with respect to the sheet width direction Y.

  The skew position correcting mechanism 14 includes a fixing member 19, a rack 20, a unit moving motor 21, and a pinion 21a. The fixing member 19 is a member that couples and fixes the upper end side in the drawing of the shift unit 13 and the left end side in the drawing of the rack 20. Rack teeth 20 a are formed on the rack 20 extending in the sheet conveying direction X. The unit moving motor 21 is composed of a stepping motor or a DC motor that can rotate forward and backward, and is fixed to the frame 15b via a bracket (not shown), and functions as a drive source for moving the shift unit 13. A pinion 21 a that always meshes with the rack teeth 20 a is attached and fixed to the output shaft of the unit moving motor 21.

A home position sensor for detecting the home position of the shift unit 13 may be provided in the pinion 21 a or the shift unit 13. Further, a guide member that smoothly guides the fixing member 19 in the sheet conveyance direction X may be provided.
The skew position correcting mechanism 14 is not limited to the one constituted by the rack 20, the unit moving motor 21, the pinion 21a, and the like, but the rotational drive of the gear is moved in the moving direction by using a timing belt and a toothed pulley. You may take the structure to convert.

The shift unit driving means constituting the main scanning correction mechanism 16 that moves the shift unit 13 in the sheet width direction Y will be described with reference to FIGS. FIG. 10 is a perspective view showing the configuration of the main part of the shift unit driving means of the main scanning correction mechanism, and FIG. 11 is a plan view of the shift unit driving means connected to the shift unit. 12 (a), 12 (b), and 12 (c) are explanatory diagrams for explaining the operation transition of the shift unit driving means. In FIG. 11, illustration of the gate member 4 and the resist roller pair 5 attached and supported by the shift unit 13 is omitted.
As shown in FIGS. 10 and 11, the main scanning correction mechanism 16 mainly includes a shift motor 22, a toothed drive pulley 23, a timing belt 24, a toothed driven pulley 25, an eccentric cam 26, and a cam clamping member 27. It is configured. The shift motor 22 is composed of a stepping motor or a DC motor that can rotate forward and backward, is fixed to the apparatus main body via a bracket (not shown), and functions as a drive source for rotating the eccentric cam 26. A toothed drive pulley 23 is fixed to the output shaft of the shift motor 22.

The toothed driven pulley 25 is coupled and fixed integrally with the eccentric cam 26 via a cam shaft 26a serving as a common pivot. The cam shaft 26a is rotatably supported by the apparatus main body. A timing belt 24 is wound around the toothed driving pulley 23 and the toothed driven pulley 25, and the rotational driving force of the shift motor 22 is transmitted to the eccentric cam 26. The cam clamping member 27 is a member that holds the eccentric cam 26 so as to be clamped, and is attached and fixed to the shift unit 13. The eccentric cam 26 and the cam clamping member 27 constitute a kind of positive cam from the relationship of converting the rotation of the shift motor 22 into the movement of the shift unit 13 in the sheet width direction.
Note that a home position sensor for detecting the home position of the shift unit 13 may be provided in the shift motor 22 or the shift unit 13 as appropriate.

The transition of the operation of the shift unit driving means will be described with reference to FIGS. 12 (a), 12 (b), and 12 (c). In the state shown in FIG. 12A, the eccentric cam 26 where the shift motor 22 is not rotating is in the home position.
As shown in FIG. 12B, when the shift motor 22 is rotated by a predetermined amount in the counterclockwise direction, the eccentric cam 26 is rotated via the drive pulley 23, the timing belt 24, and the driven pulley 25. As a result, the position of the end portion of the eccentric cam 26 clamped by the cam clamping member 27 (not shown) is changed to the right side in the sheet width direction Y, so that the shift unit 13 (not shown) is moved in the sheet width direction. Shift and move to the right of Y.
As shown in FIG. 12 (c), when the shift motor 22 is rotated by a predetermined amount in the clockwise direction opposite to that shown in FIG. 12 (b), via the drive pulley 23, the timing belt 24, and the driven pulley 25, The eccentric cam 26 rotates. As a result, the position of the end portion of the eccentric cam 26 clamped by the cam clamping member 27 (not shown) is changed to the left side in the sheet width direction Y, so that the shift unit 13 (not shown) is moved in the sheet width direction. Shift and move to the left of Y.

The main control configuration of the paper position correction mechanism 2 will be described with reference to FIG. FIG. 13 is a block diagram illustrating a main control configuration of the paper position correction mechanism 2 according to the first embodiment.
The control unit 30 includes, for example, a microcomputer including a CPU, an I / O (input / output) port, a ROM, a PROM, a RAM, a timer, and the like, which are connected by a signal bus. In the ROM and PROM, a program (an operation order of a sheet position correction mechanism 2 described later) and related data for exhibiting the calculation function and control function of the CPU and related data are stored in advance. The RAM has a function of temporarily storing calculation results and input / output data of the CPU.

The control unit 30 transmits command signals to the drive motor 9, the unit moving motor 21, and the shift motor 22 based on output signals from the paper detection sensors 18 a and 18 b, the CIS 8, the various home position sensors, or the operation unit 31. To control them.
When the control unit 30 performs skew correction of the reversed single-sided image-formed paper, the angle of the gate member 4 and the registration roller pair 5 via the shift unit 13 according to a signal from the parallelism difference recognition unit. It functions as a first control means for controlling the unit moving motor 21 so as to change.

  Here, the parallelism difference recognizing means is at least one of the parallelism difference detecting means for detecting the parallelism difference between the leading edge and the trailing edge of the sheet (sheet) and the parallelism difference setting means for setting the parallelism difference. It is sufficient if the difference in parallelism can be recognized. In the present embodiment, the parallelism difference detection means corresponds to the paper detection sensors 18a and 18b, and the parallelism difference setting means corresponds to the operation unit 31. The operation unit 31 gives an operation instruction to the image forming apparatus and recognizes the state of each unit and each device, and includes various keys and switches such as a numeric keypad and an enter key, and an LCD (liquid crystal display device). Yes.

  The control unit 30 functions as a third control unit that controls the shift motor 22 so that the shift unit 13 moves a predetermined amount in the sheet width direction Y based on a signal from the CIS 8.

The overall operation of the paper position correction mechanism 2 during double-sided printing will be described with reference to FIGS. 14 to 16. After the operation of the skew position correction mechanism 14 is described for convenience of explanation, The operation will be described. Actually, the operation of the skew feeding position correction mechanism 14 and the operation of the main scanning correction mechanism 16 are performed in parallel.
FIG. 14 shows a correction operation transition for the sheet P when the sheet P having a large parallelism difference between the leading end Pa and the trailing end Pb is conveyed from the upstream side to the downstream side of the sheet position correcting mechanism 2 for surface printing. It is a top view. The three sheets P shown in the figure are all the same sheet.
As shown on the right side of FIG. 14, the sheet P in a state where the parallelism difference between the leading end Pa and the trailing end Pb is skewed greatly is conveyed by the rotation of the feed roller pair 6. At that time, the leading edge Pa of the sheet P in the skewed state is aligned by the skew correcting operation by the gate member 4 and the registration roller pair 5 described in FIG. The sheet P is conveyed downstream in the sheet conveying direction X when the gate member 4 and the registration roller pair 5 are rotationally driven by the drive motor 9 (see the sheet P shown in the center of FIG. 14).

When the skew-corrected sheet P is transported to the downstream transport roller pair 7, as shown in FIGS. 14 and 15A, the leading edge Pa of the sheet P has two sheet detection sensors 18a and 18b. Is detected, the detection time difference T1 is detected by the paper detection sensors 18a and 18b. At this time, since the leading edge Pa of the paper P is aligned and parallel to the sheet width direction Y, the detection time difference T1 is negligible, and the detection time T1 is detected.
Next, as shown in FIG. 14 and FIG. 15B, the paper P is transported further downstream by the transport roller pair 7, and when the rear end Pb of the paper P passes through the two paper detection sensors 18a and 18b, A detection time difference T2 is detected by the paper detection sensors 18a and 18b. The CPU of the control unit 30 calculates a parallelism difference between the leading edge Pa and the trailing edge Pb of the paper P from the difference between the detection time T1 and the detection time difference T2 transmitted from the paper detection sensors 18a and 18b.
Then, the sheet P conveyed by the conveying roller pair 7 is transferred to and formed on the surface image by the secondary transfer unit 70 in FIG. The paper PA on which the front surface image has been formed is switched back in the above-described reversing unit so as to form a back surface image on the remaining back surface, and the front surface and the reverse side of the paper PA on which the front surface image has been formed is reversed. The image-formed paper PA is conveyed to the feed roller pair 6.

Further, the paper PA on which the front surface image has been formed is conveyed by the rotation of the feed roller pair 6, and the front end of the paper PA on which the front surface image has been formed (the rear end Pb of the paper P) shown in the center of FIG. Re-transported to the line correction mechanism. At this time, the CPU of the control unit 30 rotates the unit moving motor 21 of the skew feeding position correction mechanism 14 according to the previously calculated parallelism difference, and moves the rack 20 meshing with the pinion 21a, thereby moving the rear of the paper PA. The shift unit 13 is angled so as to have an angle corresponding to the skew on the end PAb side. Thereafter, the skew correction is performed on the paper PA to be printed on the back side while keeping the angle.
By performing the above operation, the image position on the back surface can be matched with the image position on the front surface as in the double-side printed paper PB shown in FIG. It can be done with high accuracy.

  The parallelism difference detection means is not limited to the sheet detection sensors 18a and 18b that detect the difference in parallelism using a time difference, but uses a contact image sensor (CIS) that can detect the entire sheet conveyance width. The parallelism between the leading end side and the trailing end side of the sheet may be detected.

Next, the operation of the main scanning correction mechanism 16 will be described with reference to FIGS. 7, 10 to 12, 14, and 16.
The operation of the main scanning correction mechanism 16 is the leading edge Pa of the paper P or the trailing edge PAb of the reversed paper PA (the trailing edge Pb of the paper P) between FIG. 7C and FIG. This is performed before the front end side reaches the downstream conveying roller pair 7.
As shown in FIG. 14, after the leading edge Pa of the paper P is skew-corrected by the skew-correcting mechanism using the gate member 4 and the registration roller pair 5, the side edge position of the sheet P in the sheet width direction Y is detected by the CIS8. The The CPU of the control unit 30 calculates the amount of deviation from the reference position of the sheet in the sheet width direction Y from the side edge position data of the sheet P in the sheet width direction Y transmitted from the CIS 8. Then, the CPU obtains a shift amount for moving the shift unit 13 in the sheet width direction Y by the calculated deviation amount, and controls the shift motor 22 to move the shift unit 13 in the sheet width direction Y by this shift amount. It becomes.

On the other hand, as shown in FIG. 16, the rear end PAb (the rear end Pb of the paper P) on which the reversed surface image is formed is skew-corrected by the skew correction mechanism using the gate member 4 and the registration roller pair 5. Thereafter, the side end position in the sheet width direction Y of the paper PA is detected by the CIS8. The CPU of the control unit 30 calculates a deviation amount from the reference position of the sheet in the sheet width direction Y from the side edge position data of the sheet PA in the sheet width direction Y transmitted from the CIS 8. Then, the CPU obtains a shift amount for moving the shift unit 13 in the sheet width direction Y by the calculated deviation amount, and controls the shift motor 22 to move the shift unit 13 in the sheet width direction Y by this shift amount. It becomes.
As described above, the operation of the skew feeding position correction mechanism 14 and the operation of the main scanning correction mechanism 16 are performed in parallel, and only the rotation control of the registration roller pair 5 is performed, so that the skew feeding position and the main scanning position of the sheet are of course. Since the position in the sub-scanning direction can also be accurately conveyed, the image position accuracy is further improved.

  In the present embodiment, the conveyance member adjacent to the downstream of the registration roller pair 5 is the conveyance roller pair 7, but instead, a secondary transfer unit 70 that is an image transfer unit is disposed downstream of the registration roller pair 5. (See FIG. 2).

  In the present embodiment, the paper detection sensors 18a and 18b, which are parallelism difference detection means, are used as the parallelism difference recognition means. However, the present invention is not limited to this, and the following may be used. That is, the parallelism difference between the leading edge and the trailing edge of the sheet before passing is measured, and a signal related to the parallelism difference is generated using the numeric keypad, enter key, etc. of the operation unit 31, and the signal related to the parallelism difference is generated. May be input to the control unit 30.

As described above, according to the present embodiment, the following effects can be obtained.
First, the skew feeding position correction mechanism 14 and the main scanning correction mechanism 16 are substantially integrated, and both mechanisms are controlled by the control unit 30. Therefore, the skew feeding deviation and the main scanning deviation of the paper at a high speed are configured. The image alignment during double-sided printing can be performed with high accuracy. Further, the skew correction of the inverted sheet on which the single-sided image is formed is performed with respect to the difference in parallelism between the leading edge and the trailing edge of the sheet, so that the front and back images can be aligned even on a sheet having a difference in parallelism. .

Second, since the shift unit 13 includes a shift unit driving unit that moves the shift unit 13 in the sheet width direction Y, a predetermined shift amount can be moved in the sheet width direction, thereby improving the accuracy of the paper position in the main scanning direction. can do.
Thirdly, since the main scanning correction mechanism 16, the CIS 8, and the control unit 30 are included, the shift in the main scanning direction, which is the sheet width direction Y, can be corrected, so that more accurate paper position correction can be performed.

  In the first embodiment, the gate member 4 is integrally provided on the shaft 5c of the registration roller 5a. However, the present invention is not limited to this, and only the gate member 4 is shown in FIGS. 4 to 8, 14, 16, and the like. Alternatively, the skew correction may be performed only by the registration roller pair 5 from which is removed (claim 1). With such a configuration, skew correction of a sheet conveyed at high speed cannot be expected, but the problems of the prior art including Patent Document 1 described in the above problem column can be solved.

(Modification 1)
A first modification of the first embodiment will be described with reference to FIGS. 17 and 18 (claim 3). FIG. 17 is a block diagram showing the control configuration of the main part of the first and second modifications. FIG. 18A and FIG. 18B are enlarged front views of the main part for explaining the relationship between the sheet thickness and the gate position in the first modification. In FIG. 17, the paper thickness detection device 28 and the encoder 29 surrounded by a broken line are not used in the first modification, but are used in the second modification.
The modification 1 is mainly different from the first embodiment in that the operation unit 31 is used as a sheet thickness setting unit that sets the sheet thickness, and the control unit 30A is used instead of the control unit 30. Is different. The configuration of the first modification other than this difference is the same as that of the first embodiment.

The operation unit 31 sets a signal related to the paper thickness using a numeric keypad, an enter key, and the like, and inputs the signal related to the paper thickness to the control unit 30A.
In addition to the function of the control unit 30, the control unit 30 </ b> A determines the position of the contact surface 4 a of the gate member 4 with respect to the nip N of the registration roller pair 5 in accordance with a signal related to the sheet thickness from the operation unit 31. Only the point of having the function of the second control means for controlling the drive motor 9 to be changed is different. The control unit 30A includes the same microcomputer as the control unit 30. In the ROM of the control unit 30A, relational data between “sheet thickness” and “stop position of the pair of registration rollers 5 corresponding to the distance d shown in FIG. 18” is stored in advance.

In the skew feeding correction mechanism including the gate member 4, as described with reference to FIGS. 6C, 6D, and 7B, the sheet generated when bent in FIG. It is conveyed to the nip portion N of the registration roller pair 5 by following the gate member 4 using the stiffness. Therefore, when the sheet whose skew has been corrected by the gate member 4 is transported to the nip portion N of the registration roller pair 5, the gate position Gp is closer to the nip portion N even if the sheet stiffness is weaker. It is smoothly conveyed to the position of the nip portion N. In the first modification, the drive motor 9 is changed so that the distance d from the nip portion N of the registration roller pair 5 to the contact surface 4a of the gate member 4 is changed according to the thickness of the sheet by utilizing the phenomenon described above. It is something to control.
For example, as shown in FIG. 18A, in the case of performing skew correction of a sheet P such as a relatively thin paper, the gate member 4 and the resist are set so that the distance d is a relatively short distance d1. The stop position of the roller pair 5 is determined. On the other hand, as shown in FIG. 18B, in the case of performing skew correction of the paper P such as a thick paper having a relatively large thickness, the gate member 4 and the resist so that the distance d becomes a relatively long distance d2. The stop position of the roller pair 5 is determined. The stop position of the gate member 4 and the registration roller pair 5 can be determined by controlling the drive motor 9 by the CPU of the control unit 30A.

  As described above, according to the present modification, the skew correction of the paper can be performed with higher accuracy on both the front surface and the back surface according to the thickness of the paper (sheet). In addition, the thickness of the paper can be set finely.

(Modification 2)
A second modification of the first modification will be described with reference to FIGS. 17 and 18 (claim 4).
The modification 2 is different from the modification 1 in that a paper thickness detection device 28 provided with an encoder 29 as a thickness detection means for detecting the thickness of the sheet is used instead of the operation unit 31, and the control unit 30A. Instead, the main difference is that the control unit 30B is used. The configuration of Modification 2 other than this difference is the same as that of Modification 1.

The paper thickness detection device 28 automatically detects the thickness of the paper P, and is disposed around the feed roller pair 6 shown in FIG. 3 upstream of the registration roller pair 5 in the sheet conveyance direction X. The paper thickness detection device 28 has the same configuration as the paper thickness detection device (40) disclosed in paragraphs [0053] to [0058] of Japanese Patent Application Laid-Open No. 2014-031275 and FIG. And the function similar to the calculation part (45) relevant to a paper thickness detection apparatus (40) should just be added to the control part 30B of this modification. According to the paper thickness detection device 28, it is possible to detect the sheet thickness with high accuracy with the same effect as the paper thickness detection device (40), that is, with a simple configuration.
The thickness detecting means is not limited to the paper thickness detecting device 28, but may be other known means, for example, detecting the thickness of the paper by detecting the amount of transmitted light passing through the paper. .

  The control unit 30B controls the drive motor 9 to change the position of the contact surface 4a of the gate member 4 with respect to the nip portion N of the registration roller pair 5 in accordance with a signal related to the sheet thickness from the sheet thickness detection device 28. It functions as a second control means for controlling. The control unit 30B includes the same microcomputer as the control unit 30. The ROM of the control unit 30B stores in advance relational data between “sheet thickness” and “stop position of the registration roller pair 5 corresponding to the distance d shown in FIG. 18”.

  In the second modification, the same operation as that in the first modification shown in FIGS. 18A and 18B can be performed by the above configuration. Therefore, according to the present modification, the skew correction of the paper on both the front surface and the back surface is more accurately and easily performed according to the thickness of the paper without the user setting the thickness of the paper (sheet). be able to.

(Modification 3)
A third modification of the first embodiment will be described with reference to FIGS. 13 and 19 (Claim 5).
The modification 3 is mainly different from the first embodiment in that a control unit 30C is used instead of the control unit 30. The configuration of Modification 3 other than this difference is the same as that of the first embodiment.
The control unit 30C is different from the control unit 30 in that it has the following control function. That is, the control unit 30C rotates the registration roller pair 5 by a predetermined rotation angle in the sheet conveyance direction X, and then rotates the registration roller pair 5 by a predetermined rotation angle in the direction opposite to the sheet conveyance direction X. The drive motor 9 is controlled so that the gate member 4 is stopped at the position and skew correction is performed.

The skew correction operation of Modification 3 will be described focusing on the difference from the skew correction operation of the first embodiment shown in FIG. In the third modification, the registration roller pair 5 occupies a predetermined position (gate position or initial position) where the contact surface 4a of the gate member 4 abuts the leading edge of the conveyed sheet, as in the first embodiment. It is configured so that it can be stopped (FIG. 19D).
The first difference is that in FIGS. 19A to 19B, the registration roller pair 5 is rotated from the gate position in FIG. 19A in the sheet conveying direction X by a predetermined rotation angle α °. (Forward rotation). The second difference is that in FIG. 19C, the registration roller pair 5 is immediately rotated by α ° in the opposite direction to the sheet conveying direction X (reverse rotation), and then the gate member 4 is stopped at the gate position. The skew correction is performed (FIG. 19D). As shown in FIGS. 19A to 19C, the operation of rotating the registration roller pair 5 forward and backward as described above is performed when the leading edge Pa of the paper P conveyed by the feed roller pair 6 is gated. It is performed quickly so as to be before the contact surface 4a of the member 4 is reached. By performing such a rotation operation of the registration roller pair 5, for example, the play of the drive transmission member including the above-described gear train that transmits the rotational driving force of the drive motor 9 to the registration roller pair 5 is reduced.

Needless to say, the third modification can be applied to the first and second modifications.
As described above, according to this modification, when the conveyed paper P hits the contact surface 4a of the gate member 4, the rotational positions of the gate member 4 and the registration roller pair 5 do not vary, and the height is further increased. Accurate skew correction can be performed.

(Modification 4)
Modification 4 of Modification 3 will be described with reference to FIGS. 13 and 20 (Claim 6).
The modification 4 is mainly different from the modification 3 in that a control unit 30D is used instead of the control unit 30C. The configuration of the modification 4 other than this difference is the same as that of the modification 3.
The control unit 30D is different from the control unit 30C in that it has the following control function. That is, the control unit 30D rotates the registration roller pair 5 by a predetermined rotation angle in the sheet conveyance direction X, and then sets an angle for rotating the registration roller pair 5 in the direction opposite to the sheet conveyance direction X. The drive motor 9 is controlled so as to change according to the drive time.

In the gear train of the registration driving means shown in FIG. 5, the meshing portion of the gear 10 fixed to the shaft 5c of the registration roller 5a and the large diameter gear 17b transmits the rotational driving force of the drive motor 9 to the registration roller 5a. ing. Therefore, as shown in FIGS. 20A and 20B, the backlash in the sheet conveying direction X is zero. For this reason, the meshing part of the gear 10 and the large-diameter gear 17b is heavily worn over time.
Therefore, in the present modification, instead of the α ° of Modification 3 in which the angle at which the registration roller pair 5 is rotated in the direction opposite to the sheet conveying direction X is replaced with the driving time of the registration roller pair 5, the above-mentioned wear over time. Focusing on the occurrence of this, α ° + correction amount β ° (t) is set. t is the driving time of the registration roller pair 5. In the ROM of the control unit 30D, relational data between “registration roller pair 5 driving time” and “correction amount β °” is stored in advance. This relational data can be grasped in advance by conducting an experiment or the like.

Of course, the modification 4 can also be applied to the modifications 1 and 2.
As described above, according to the present modification, even when the backlash increases due to the wear of the gear 10 and the large-diameter gear 17b with the passage of time, by changing the angle of rotation in the reverse direction according to the driving time, Also, the accuracy of the paper position correction can be ensured.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above. For example, the technical matters described in the above embodiments and examples may be appropriately combined.

  The image forming apparatus to which the present invention is applied is not limited to the electrophotographic printer shown in FIG. 1, and an image provided with a reversing unit for reversing a sheet on which a single-sided image is formed with an image formed on one side. Any image forming format may be used as long as it is a forming apparatus. That is, the present invention can also be applied to an image forming apparatus capable of double-sided printing provided with a reversing means such as a copying machine, a facsimile machine, a plotter, an ink jet recording apparatus, a stencil printing machine, and an offset printing machine.

  The effects appropriately described in the embodiments of the present invention are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. It is not a thing.

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Paper position correction mechanism 3 Double-side inversion part (inversion means)
4 Gate member (gate part)
4a Contact surface 5 Registration roller pair 6 Feed roller pair 7 Conveyance roller pair 8 CIS (sheet width detection means)
9 Drive motor (drive source for registration drive means)
10 Gear 13 Shift unit (Registration unit)
14 Skew position correction mechanism 16 Main scanning correction mechanism 18a, 18b Paper detection sensor (parallelism difference detection means, parallelism difference recognition means)
21 Unit moving motor (drive source for skew position correction mechanism)
22 Shift motor (drive source for main scanning correction mechanism)
26 Eccentric cam 28 Paper thickness detection device (thickness detection means)
30, 30A, 30B, 30C, 30D control unit (first control means to third control means)
31 Operation unit (parallelism difference setting means, parallelism difference recognition means)
Gp Gate position N Nip part P Paper (sheet, recording medium)
X Sheet conveyance direction Y Sheet width direction

JP 2012-101904 A

Claims (8)

A pair of registration rollers for correcting skew feeding of the conveyed sheet,
Registration driving means for rotationally driving the registration roller pair;
A registration unit that supports the registration roller pair and is movable in a direction to change an angle of the registration roller pair with respect to a sheet width direction orthogonal to a sheet conveyance direction;
Unit driving means for moving the resist unit in a direction to change the angle;
An image forming unit that forms an image on a sheet conveyed from the pair of registration rollers;
A reversing means for reversing the sheet on which the image is formed on one side and having the image formed on one side;
A parallelism difference recognition means including at least one of a parallelism difference detection means for detecting a parallelism difference between the leading edge and the trailing edge of the sheet and a parallelism difference setting means for setting the parallelism difference;
When skew correction is performed on a sheet on which a single-sided image is formed reversed by the reversing unit, the angle of the registration roller pair is changed via the registration unit in accordance with a signal from the parallelism difference recognizing unit. First control means for controlling the unit driving means;
An image forming apparatus comprising:   The registration roller pair is provided coaxially with one registration roller, protrudes from the peripheral surface of the one registration roller, and the leading edge of the conveyed sheet is upstream of the nip portion of the registration roller pair in the sheet conveyance direction. The image forming apparatus according to claim 1, further comprising a gate portion having an abutting surface that abuts on the side, and performing skew correction of a sheet conveyed by the gate portion. A thickness setting means for setting the thickness of the sheet;
Second control means for controlling the registration driving means to change the position of the contact surface of the gate portion with respect to the nip portion of the registration roller pair in response to a signal from the thickness setting means;
The image forming apparatus according to claim 2, further comprising: A thickness detecting unit disposed upstream of the registration roller pair in the sheet conveying direction and detecting a thickness of the sheet;
Second control means for controlling the registration driving means to change the position of the contact surface of the gate portion with respect to the nip portion of the registration roller pair in response to a signal from the thickness detection means;
The image forming apparatus according to claim 2, further comprising: The registration roller pair can be stopped when the contact surface occupies a predetermined position where the leading edge of the sheet conveyed is abutted,
After rotating the registration roller pair by a predetermined rotation angle in the sheet conveyance direction, the registration roller pair is rotated by the predetermined rotation angle in a direction opposite to the sheet conveyance direction, and the gate is moved to the predetermined position. The image forming apparatus according to claim 2, wherein the skew correction is performed by stopping a section.   6. The image forming apparatus according to claim 5, wherein an angle at which the registration roller pair is rotated in a direction opposite to the sheet conveying direction is changed according to a driving time of the registration roller pair. A shift unit that supports the pair of registration rollers including the gate portion and is movable in a sheet width direction orthogonal to the sheet conveyance direction;
Shift unit driving means for moving the shift unit in the sheet width direction;
The image forming apparatus according to claim 2, further comprising: Sheet width position detecting means for detecting a side end position in the sheet width direction of the sheet conveyed to the shift unit;
Third control means for controlling the shift unit driving means so that the shift unit moves a predetermined amount in the sheet width direction based on a signal from the sheet width position detecting means;
The image forming apparatus according to claim 7, further comprising:

Images