JP2015024877A - Sheet transport device, image reader, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet transport device, an image reader, and an image forming apparatus, which are capable of correcting a skew reliably, while securing transport force by a feed roller.SOLUTION: A document D fed from a tray is caused to pass in a separation nip N1 between a feed roller 521 and a separation roller 522 of a separation-transport part 52 so as to transport the document in separating by sheet. A skew is corrected by causing a lead edge of the document D to abut to a nip portion N2 of a registration roller pair 53 in a stationary state so as to form a loop R. Then, the registration roller pair 53 is rotated to transport the document D downstream. After the lead edge of the document D is aligned by abutting to the nip portion N2 of the registration roller pair 53 (FIG. 10 (a)), a magnitude of separation pressure P applied between the feed roller 521 and the separation roller 522 is lowered from a first value p1 to a second value p2 until the lead edge is sandwiched in the nip portion N2 for a given amount by rotation start of the registration roller pair 53 (FIG.10 (b)).

Description

  The present invention relates to a sheet conveying apparatus, an image reading apparatus and an image forming apparatus provided with the sheet conveying apparatus, and more particularly to a technique for correcting sheet skew.

An image forming apparatus such as a copying machine includes a document transport device that feeds a document placed on a tray and transports the document to an image reading position (for example, Patent Document 1).
Usually, in such a document conveying device, the document fed from the tray is pressed against the paper feed roller so that the document is not double-fed or conveyed to the image reading position in a tilted state. It has a paper-carrying unit that passes between the paper-carrying rollers and conveys them one by one, and a registration roller pair that corrects the skew of the original conveyed from the paper-carrying unit. The skew correction of the document is performed by bringing the leading edge of the document into contact with the nip portion of the registration roller pair in a rotation stopped state to form a loop and rotating the back of the document by the waist of the document.

JP 2004-106995 A

However, in the conventional document feeder, document skew correction by the registration roller pair may not be sufficiently performed.
That is, when forming a loop of a document, the document is sandwiched between a paper feed roller and a separating roller that is pressed against the roller. Even if it acts, it is difficult to correct the posture of the original by rotating the rear part of the original, and there is a possibility that the skew correction is not sufficiently performed. As a result, the read image is skewed and the image quality is degraded.

As a method for facilitating the rotational movement of the rear part of the document during skew correction, it is conceivable to reduce the pressure contact force between the paper feed roller and the separation roller. May occur, and the conveyance force may be reduced and the document cannot be conveyed.
Such a problem is a problem that may occur not only in the document conveying apparatus but also in general sheet conveying apparatuses including a sheet feeding and conveying apparatus that conveys a recording sheet for printing an image.

  The present invention has been made in view of the above-described problems, and is a sheet conveying apparatus, an image reading apparatus, and an image forming apparatus that can reliably perform skew correction while ensuring a conveying force by a sheet feeding roller. The purpose is to provide.

  In order to achieve the above object, a sheet conveying apparatus according to the present invention scoops a sheet fed from a tray by passing it between a sheet feeding roller and a separating member pressed against the sheet in a sheet conveying unit. For each conveyed sheet, the tip of the sheet is brought into contact with the nip portion of the registration roller pair in the rotation stop state to form a loop to correct the skew, and then the registration roller pair is rotated to move the sheet downstream. A pressure contact force changing means for changing the magnitude of the pressure contact force between the paper feed roller and the separating member, wherein the pressure contact force change means has a leading edge of the sheet of the registration roller pair. After the contact nip is aligned and aligned, the pressure contact force is applied from the first value until the resist roller pair starts to rotate and is engaged with the nip by a predetermined amount. Wherein the reduced to smaller second value than the first value.

  In addition, an acquisition unit that acquires information relating to a conveyance condition of the conveyed sheet is provided, and the pressing force changing unit decreases the pressing force from the first value to the second value in a first time. The first change mode and the second change mode in which the first change mode is decreased from the first value to the second value in a second time longer than the first time, as the acquired sheet conveyance conditions. The configuration can be selected and executed accordingly.

Here, the information on the sheet conveyance condition includes a type according to the thickness of the sheet, and the pressing force changing unit selects the second change mode when the sheet type is thick paper, and is thinner than that. In the case of a sheet, it is desirable to select the first change mode.
Further, the information regarding the sheet conveyance condition includes a width size in a direction orthogonal to the sheet conveyance direction, and the pressing force changing unit is configured to change the second change mode when the sheet width size is equal to or larger than a predetermined size. If the sheet width size is less than the predetermined size, the first change mode may be selected.

In addition, as information on the sheet conveyance conditions, instruction information from the user whether or not to prioritize the productivity of sheet conveyance is included, and when the pressing force change means prioritizes the productivity, If the first change mode is selected and productivity is not prioritized, the second change mode may be selected.
Further, the pressing force changing means may be configured to change the magnitude of the second value in accordance with the sheet conveying condition.

Here, it is desirable that the pressure contact force changing means increase the second value when the sheet type is thick paper than when it is thin paper.
The pressing force changing means may be configured to reduce the pressing force stepwise from a first value to a second value.
In addition, an acquisition unit that acquires information related to a conveyance condition of the conveyed sheet is provided, and the pressing force changing unit is configured to change the number of steps when the pressing force is reduced according to the conveyance condition of the sheet. You can also

Here, the information regarding the sheet conveyance condition includes a type according to the thickness of the sheet, and the pressing force changing means increases the number of steps when the sheet type is thick paper than when the paper is thin. desirable.
The pressure contact between the separation member and the paper feed roller is performed by an elastic member that presses the separation member toward the paper supply roller, and the pressure contact force changing means is opposite to the separation member of the elastic member. An eccentric cam for swingably supporting the end of the shaft, a drive means for rotationally driving the eccentric cam, and a drive control means for controlling the drive means. The drive control means controls the drive means to provide eccentricity. It can be set as the structure which changes the magnitude | size of the press-contact force between the said peeling member and a paper feeding roller by rotating a cam.

  A pair of alignment plates that are in contact with and aligned with both ends of the sheet placed on the tray in the sheet width direction perpendicular to the conveyance direction; and a proximity separation mechanism that moves the pair of alignment plates close to or away from each other. And a proximity / separation control means for controlling the proximity / separation mechanism, wherein the proximity / separation control means uses the pressure contact force changing means after the leading edge of the conveyed sheet has passed between the sheet feeding roller and the separating member. Until the operation for reducing the pressure contact force from the first value to the second value is started, the proximity / separation mechanism is controlled to release the contact state of the sheet by the pair of alignment plates. It can be configured.

The present invention may be a document reading device that includes the sheet conveying device having the above-described configuration as a document conveying unit and reads a document conveyed by the document conveying unit.
Further, the present invention may be an image forming apparatus that includes the sheet conveying device having the above-described configuration as a sheet feeding unit and forms an image on a recording sheet fed from the sheet feeding unit.

  According to the sheet conveying apparatus having the above-described configuration, the pressure contact force between the sheet feeding roller and the separating member is set to the first value to convey the sheet while reliably conveying the sheet, and the leading edge of the sheet comes into contact with the nip portion of the registration roller pair. Since the pressure contact force is reduced to a second value smaller than the first value after the alignment, the rotation of the rear portion of the sheet is facilitated by the restoring force in the loop forming portion of the sheet. . As a result, skew correction can be reliably performed.

1 is a schematic cross-sectional view for illustrating an overall configuration of a copier according to a first embodiment of the present invention. FIG. 2 is an enlarged view showing a configuration of an ADF unit included in the copying machine. It is the schematic plan view which looked at the ADF unit from the upper part. (A), (b) is a figure for demonstrating the structure of the press-contacting mechanism which press-contacts a separating roller to a paper feeding roller. FIG. 6 is a diagram for explaining a relationship between an action to rotate the rear part of the original by the restoring force of the original and a frictional resistance generated when the rear part of the original rotates. FIG. 6 is a diagram illustrating a state in which a leading edge of a document is separated from a registration nip due to an inertial force when a document rear part rotates. It is a block diagram which shows the relationship between the structure of a control part, and the main component used as the control object by a control part. 4 is a flowchart showing a part of control contents of a document conveying process executed by a control unit. It is a time chart which shows the timing of the control which switches a soot pressure. (A) is a figure which shows the state of the original before switching the winding pressure, and (b) is a figure which shows the state where the rear part of the original is rotated and the posture is corrected by switching the winding pressure. (A) is a figure explaining the control of the press-contact mechanism when switching the firing pressure to the second value in the normal mode, and (b) when switching the firing pressure to the second value in the suppression mode. It is a figure explaining control of the press-contact mechanism. It is a time chart which shows the timing of the control which switches the burning pressure in 2nd Embodiment. 10 is a flowchart illustrating a part of control content of a document conveyance process executed by a control unit according to a second embodiment. It is a time chart which shows the timing of the control which switches the burning pressure in 3rd Embodiment. 14 is a flowchart illustrating a part of control content of document conveyance processing executed by a control unit according to a third embodiment. It is a time chart which shows the timing of the control which switches the burning pressure in 4th Embodiment. It is a figure for demonstrating the start timing of switching control of the burning pressure P. FIG. 14 is a flowchart illustrating a part of control content of document conveyance processing executed by a control unit according to a fourth embodiment. It is a figure for demonstrating an example of the switching control of the burning pressure which concerns on a modification. It is a figure for demonstrating another example of the switching control of the rolling pressure which concerns on a modification. It is a figure for demonstrating another example of the switching control of the rolling pressure which concerns on a modification. (A), (b) is a figure for demonstrating the operation mode of the switching control of the burning pressure which concerns on a modification. It is a figure which shows the structure of the press-contact force change means which concerns on a modification. (A), (b) is a figure for demonstrating the structure of a pair of alignment board which the original document feed tray which concerns on a modification has.

<First Embodiment>
Hereinafter, a case where the first embodiment of the sheet conveying apparatus according to the present invention is applied to an original conveying apparatus in an image reading apparatus of a tandem type color copying machine (hereinafter simply referred to as “copier”) will be described with reference to the drawings. I will explain.
(1) Overall Configuration of Copying Machine FIG. 1 is a schematic cross-sectional view for illustrating the overall configuration of a copying machine according to the present embodiment.

The copying machine 1 shown in FIG. 1 includes a printer unit 2 and an image reading unit 3 (image reading device) provided on the printer unit 2. The copying machine 1 is connected to a network (for example, a LAN), and is configured to be able to transmit and receive data with an external terminal device.
(2) Configuration of Printer Unit The printer unit 2 includes an image forming unit 10, a paper feeding unit 20, and a control unit 30, and is sent from image data generated by the image reading unit 3 or an external terminal device. Based on the coming image data, a toner image is printed on the recording sheet S by a known electrophotographic method.

The image forming unit 10 includes image forming units 11Y, 11M, 11C, and 11K corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K), an intermediate transfer belt 12, two A next transfer roller pair 13, a fixing unit 14, a paper discharge tray 15 and the like are provided.
The image forming units 11Y, 11M, 11C, and 11K form toner images of corresponding colors under the control of the control unit 30, and electrostatic transfer (primary transfer) to the intermediate transfer belt 12 so that the toner images of the respective colors overlap each other. ) The intermediate transfer belt 12 is an endless belt, rotates in the direction of arrow A, and conveys the toner image to the secondary transfer position 16.

The paper feeding unit 20 includes a plurality of paper feeding cassettes 21 that store the recording sheets S, feeds the recording sheets S from one of the paper feeding cassettes 21 one by one, and matches the timing of the toner image on the intermediate transfer belt 12. To the secondary transfer position 16.
The recording sheet S on which the toner image (unfixed image) is formed by the secondary transfer is conveyed to the fixing unit 14, and the toner image is heated and pressurized in the fixing unit 14 and thermally fixed on the recording sheet S. The The thermally fixed recording sheet S is discharged onto the paper discharge tray 15.

The control unit 30 controls the image forming unit 10, the paper feeding unit 20, and the image reading unit 3 described below. Details will be described later.
(3) Configuration of Image Reading Unit The image reading unit 3 includes a scanner unit 40 that reads a document image and an ADF unit (automatic document transport mechanism) 50 that transports the document to the document reading position of the scanner unit 40.

The scanner unit 40 includes a light source unit 41, a mirror unit 42, a lens 43, a line sensor 44, and the like in a housing 400 in which first and second platen glasses 45 and 46 are fitted on the upper surface.
The light source unit 41 includes a lamp 411 serving as a light source, a mirror 412 and the like, and the mirror unit 42 includes folding mirrors 421 and 422 and the like. The line sensor 44 is composed of a CCD (Charge Coupled Device) having a plurality of photoelectric conversion elements.

  The scanner unit 40 includes a mirror scan mode for reading an image of a document placed on the first platen glass 45 by moving the light source unit 41 and the mirror unit 42 in the direction of arrow B by a slide mechanism (not shown), and ADF. When the document placed on the document feed tray 502 of the unit 50 is transported and passes over the second platen glass 46, the document image is read by selectively executing the sheet-through mode for reading the image.

(4) Configuration of ADF Unit The ADF unit 50 is attached to the scanner unit 40 by a hinge mechanism (not shown) so that the front side (the front side of the paper) can be opened and closed. Thus, when reading the document in the mirror scan mode, the ADF unit 50 can be opened upward and the document can be placed on the first platen glass 45.

The ADF unit 50 includes an ADF unit main body 501, a document feed tray 502, and a document discharge tray 503. Hereinafter, a description will be given with reference to the enlarged view of FIG.
(4-1) ADF Unit Main Body The ADF unit main body 501 includes a pick-up roller 51, a paper transport unit 52, a registration roller pair 53, first to third transport roller pairs 54 to 56, a paper discharge roller pair 57, and a back surface reading unit. A CCD line sensor 58 and the like are provided, and when the original is read in the sheet-through mode of the scanner unit 40, the original is conveyed as follows.

First, a bundle of documents (not shown) placed on the document feed tray 502 is unwound by the pickup roller 51 in order from the topmost document, and is rolled when passing through the separation nip N1 of the separation conveyance unit 52. As a result, the sheets are fed one by one toward the registration roller pair 53, and the skew is corrected.
Here, “skew correction” refers to forming a loop by bringing the edge on the leading end side of the document into contact with the registration nip N2 of the stopped registration roller pair 53, and conveying the original sheet by the waist of the document in the loop portion. This refers to correcting the inclination in the direction.

  The paper transport unit 52 includes a paper feed roller 521 (with a one-way clutch) and a paper feed roller 522 that is pressed against the paper feed roller 521. A torque limiter (not shown) that restricts the rotation is attached to the roller 522. As a result, when the originals are double-fed, the conveyance of the originals on the side of the separating roller 522 whose rotation is restricted (stopped) by the torque limiter is blocked and the originals are turned. A pressure contact mechanism that presses the separation roller 522 against the paper feed roller 521 will be described later.

  The original after skew correction is conveyed further downstream by the registration roller pair 53 and the first to third conveyance roller pairs 54 to 56, and passes through the original reading position P on the second platen glass 46. An image on one surface (the second platen glass 46 side) is read by the line sensor 44 of the scanner unit 40. Further, when performing double-sided copying or double-sided scanning, the image on the second side (the side opposite to the first side) of the document is read by the CCD line sensor 58 for reading the back side. The document from which the image has been read is discharged from the discharge roller pair 57 onto the document discharge tray 503.

  The pickup roller 51 and the paper feed roller 521 of the paper transport unit 52 are rotationally driven by a transport drive motor M1 (hereinafter also referred to as “paper feed motor M1”). Among these, a paper feed clutch CL made up of an electromagnetic clutch is inserted in the power transmission path between the pickup roller 51 and the paper feed motor M1, thereby performing transmission control of the rotational driving force. The registration roller pair 53 is rotationally driven by a conveyance drive motor M2 (hereinafter also referred to as “registration motor M2”), and the first to third conveyance roller pairs 54 to 56 are connected to the conveyance drive motor M3 and the discharge roller pair. 57 are each driven to rotate by a conveyance drive motor M4.

In the present embodiment, DC motors are used for the transport drive motors M1 to M4.
Document transport sensors S1 to S3 for detecting a document to be transported are provided on a transport path 510 from the paper transport unit 52 to the document reading position P. The document conveyance sensor S1 is disposed on the downstream side in the conveyance direction of the paper conveyance unit 52, the document conveyance sensor S2 is disposed on the upstream side of the registration roller pair 53, and the document conveyance sensor S3 is disposed on the upstream side of the document reading position P. ing.

  The document conveyance sensors S1 to S3 are formed of, for example, a reflection type photoelectric sensor, and an on (Hi level) signal is output to the control unit 30 while a document is detected, and an off (Low level) signal is detected when the document is not detected. Output. The control unit 30 detects the leading edge and the trailing edge of the document from the rising edge (change point from Low to Hi level) and the falling edge (change point from Hi to Low level) of the output of the document transport sensors S1 to S3, respectively. It is possible to detect that each of the document transport sensors S1 to S3 has passed, and based on the detection result, the rotation drive of each of the transport drive motors M1 to M4 is controlled to perform document transport and document skew correction. Control the behavior.

Hereinafter, the document conveyance sensor S1 is referred to as “after-rolling sensor S1”, and the document conveyance sensor S2 is referred to as “pre-registration sensor S2”. The post-rolling sensor S1 and the pre-registration sensor S2 are arranged on the center line L1 in the width direction Y of the conveyance path 510 (see FIG. 3).
FIG. 3 is a schematic plan view of a part of the ADF unit main body 501 and a document feeding tray 502 as viewed from above.

  As shown in the figure, the pickup roller 51 has a roller 51b attached to the rotating shaft 51a, and is arranged so that the center of the roller 51b in the axial direction is located on the center line L1 of the transport path 510. ing. In addition, the paper feed roller 521 of the paper transport unit 52 is disposed so that the center of the roller 521b attached to the rotation shaft 521a is located on the center line L1. The roller 522 also has one roller attached to the rotation shaft, and is arranged so that the center of the roller in the axial direction is located on the center line L1.

  Since the lower roller in FIG. 3 is hidden in the registration roller pair 53, when viewed from the upper roller, the upper roller 531 has seven rollers 531b to 531h attached to the rotation shaft 531a. The center of the middle roller 531e in the axial direction is located on the center line L1, and the rollers 531b to 531d and the rollers 531f to 531h are arranged at symmetrical positions with respect to the center line L1 on both sides thereof. The configuration of the lower roller is the same.

Further, the roller pairs 54 to 57 (see FIG. 2) on the downstream side of the registration roller pair 53 are also similar to the registration roller pair 53. Each of the upper and lower rollers has seven rollers, respectively, with respect to the center line L1. Are configured to be symmetrical.
The number of rollers in each roller is not limited to seven. For example, the number of rollers may be six or less, or eight or more. The number and arrangement of rollers in each roller can be appropriately selected according to the specifications of the ADF unit 50.

(4-2) Document Feeding Tray In the document feeding tray 502, the document D is brought into contact with both edges of the width direction (the direction Y orthogonal to the transport direction C) of the placed document D, and the document D is transported in the transport direction C. A pair of alignment plates 505a and 505b that are aligned so as to be parallel are provided.
The document feed tray 502 is a so-called center reference system, and the pair of alignment plates 505a and 505b are configured to move symmetrically with respect to the center line L1 of the transport path 510 as will be described later.

A reference wall 504 for positioning the leading edge of the document D is provided on the downstream side in the transport direction C of the document feed tray 502 (see also FIG. 2).
The document feed tray 502 is provided with a document placement sensor S11 that detects a placed document. The document placement sensor S11 includes, for example, a reflective photoelectric sensor, and can be detected even when a document of a minimum size (for example, A5 lengthwise) that can be transported by the ADF unit 50 is placed (all sizes that can be transported). While the document is being detected, an ON signal is output to the control unit 30. Here, the maximum size that can be transported is A3 vertical.

The document placement sensor S11 and the document transport sensors S1 to S3 are not limited to reflective photoelectric sensors, and for example, contact-type limit switches may be used. Each sensor can be appropriately selected according to the specification of the ADF unit 50 and the like.
(4-3) Configuration of the Pressing Mechanism of the Rolling Conveying Section FIGS. 4A and 4B are diagrams for explaining the configuration of the pressing mechanism 70 that presses the rolling roller 522 against the paper feed roller 521.

The pressure contact mechanism 70 has two sets including a compression coil spring 71, a piston 72, a cylinder 73, and an eccentric cam 74 (only one set is shown in FIGS. 4A and 4B).
As shown in FIG. 4A, one compression coil spring 71 has one end attached to one of a pair of bearing members 523 that rotatably supports the rotating shaft 522a of the roller 522, and the other end a piston 72. The piston 72 is inserted into the cylinder 73 together with the piston 73. The same applies to the other compression coil spring 71, and one end is attached to the other bearing member 523 and is inserted into the cylinder 73 together with the piston 72.

Each of the pair of bearing members 523 is held so as to be movable in the vertical direction in a long hole of a support frame (not shown).
The lower end 73 b of the piston 72 is brought into contact with the outer peripheral surface of the eccentric cam 74 and moves up and down in conjunction with the rotation of the eccentric cam 74 to compress the compression coil spring 71.
As shown in FIG. 4A, the outer diameter of the eccentric cam 74 is brought into contact with the piston 72, and when the piston 72 is pushed up most, the pressure contact force that presses the roller 522 against the paper feed roller 521 (hereinafter referred to as "contact force"). , “The soaking pressure P”) is the maximum value (hereinafter, this maximum value is referred to as “first value p1”). On the other hand, as shown in FIG. 4 (b), when the short diameter portion 74b of the eccentric cam 74 is brought into contact with the piston 72 and the piston 72 is lowered most, the firing pressure P becomes the minimum value (hereinafter, this minimum value). The value is “second value p2”.)

The rotating shafts of the eccentric cams 74 in each group are the same (rotating shaft 741), and a cam motor M5 is attached to the rotating shaft 741.
The rotation shaft 741 of the cylinder 73 and the eccentric cam 74 is supported by a support frame (not shown).
The cam motor M5 is formed of, for example, a stepping motor, and rotates in a specified direction by a predetermined angle based on a control signal (including a drive pulse signal, a rotation direction signal, etc.) from the control unit 30, and each set of the eccentric cams 74 is set. Rotate synchronously. Here, the eccentric cam 74 is configured to rotate once by one rotation of the cam motor M5. Further, the cam motor M5 rotates 10 ° with one drive pulse signal, and the cam motor M5 rotates 360 ° (one rotation) with 36 drive pulse signals.

Here, the eccentric cam 74 shown in FIG. 4A is set as the rotation reference position (rotation angle 0 °). The eccentric cam 74 is provided with a positioning mark 742 for detecting whether or not it is at the rotation reference position. In the axial direction of the eccentric cam 74, a so-called mark detection sensor S12 that detects the positioning mark 742 is provided. (See FIG. 7).
The control unit 30 drives and controls the cam motor M5 while checking the output result from the mark detection sensor S12 to rotate the eccentric cam 74 to the rotation reference position, and sets the firing pressure P to the first value p1. Can do. Further, the control unit 30 can switch the firing pressure P from the first value p1 to the second value p2 by driving and controlling the cam motor M5 to rotate the eccentric cam 74 by 180 ° from the rotation reference position. .

(4-4) Regarding the Separation Pressure In the present embodiment, when the document is conveyed by the document conveying unit 52, the document is conveyed by the document conveying unit 52 with the document pressure P set to the first value p1. When the leading edge of the original is brought into contact with the registration nip N2 and the loop R is formed, the winding pressure P is reduced and switched to the second value p2.

When a document is conveyed while being conveyed, if the document pressure P is large, when the document is fed to the document nip N1, the frictional resistance between the fed documents is increased, so that slippage is less likely to occur. In contrast, if the squeezing pressure P is small, a slip occurs between the paper feed roller 521 and the original, and the original cannot be conveyed.
Therefore, the magnitude of the first value p1 is obtained and set in advance by experiments (for example, about 4.3 N) so that the originals can be conveyed one by one while preventing double feeding of the originals.

On the other hand, as shown in FIG. 5, the second value p2 indicates that the skewed leading edge Da of the document D is brought into contact with the registration nip N2 and the loop R is formed. The size is set such that the frictional force is reduced, and the rear portion Dc of the document D is rotated by the restoring force of the document D to correct the document posture. This will be described in detail below.
FIG. 5 shows a state in which the document D conveyed in a skewed state to the left side in the conveyance direction C (front side of the copying machine 1) is brought into contact with the registration nip N2 and a loop R is formed. .

Hereinafter, the front side of the copying machine 1 is simply referred to as “front side”, and the back side of the copying machine 1 is simply referred to as “back side”.
The loop R is larger on the back side R1 than the front side R2, and the restoring force of the document D by the loop R is larger on the back side than the front side (F1> F2). An action (rotational moment Mt1) to rotate in the direction occurs.

  The center of the rotational moment Mt1 is the corner K2 on the front side of the tip Da that is in contact with the registration nip N2. Therefore, when the force due to the restoring force of the document D acting on the opposite corner K1 is Fx, the rotational moment Mt1 is the product of the force Fx and the document width W (distance between the corners K1 and K2). (Mt1 = Fx × W). The force Fx acting on the corner portion K1 can be measured using, for example, a push-pull gate.

On the other hand, a resistance moment Mt2 in the direction opposite to the rotation moment Mt1 is generated in the document D to be rotated due to the frictional resistance F3 between the document conveying section 52 and the document D.
The resistance moment Mt2 is obtained by the product of the frictional resistance force F3 (= rolling pressure P × friction coefficient μ) and the distance L2 from the corner K2 to the center point N1a of the rolling nip N1 (M2 = F3 × L2). Here, the friction coefficient μ is a static friction coefficient between the document D and the paper conveying unit 52.

When the skew exceeding the allowable range occurs in the document D, the magnitude of the second value p2 is set so that the resistance moment Mt2 is smaller than the rotation moment Mt1 (Mt2 <Mt1 (condition 1)). Is done. As a result, the rear portion Dc of the document D rotates to correct the document posture.
Here, the “allowable range” of the magnitude of the skew is, for example, a skew angle (a document inclination with respect to a direction orthogonal to the conveyance direction C) of about −0.3 ° to + 0.3 °, and the ADF unit 50. These are revised according to the specifications of the scanner unit 40.

  Since the resistance moment Mt2 decreases as the second value p2 decreases, it is convenient to consider only the rotation of the rear portion D of the document D. However, the inertial force when the document D rotates is easily increased. As a result, the leading edge Da of the document D may be separated from the registration nip N2 (see FIG. 6). In this case, there arises a problem that the document D cannot be conveyed downstream due to the rotation of the registration roller pair 53. In order to prevent this, the second value p2 satisfies the above condition 1 and leaves a resistance moment Mt2 (frictional resistance force F3) that can prevent the leading edge Da of the document D from leaving the registration nip N2. (Condition 2) Set.

The magnitude of the rotational moment Mt1 due to the restoring force of the original D is larger as the original width W is larger even if the original skew is the same, and is lower than that of thin paper (for example, about 50 g / m ² basis weight). Strong cardboard (for example, basis weight of about 128 g / m ² ) is larger.
Therefore, in the present embodiment, the second value p2 indicates that the above condition 1 and condition 2 are satisfied for each document size that can be transported by the ADF unit 50 and each document type (thick paper, plain paper, thin paper, etc.). It is set to an appropriate size that can be satisfied (for example, about 3.0 N).

(5) Configuration of Control Unit FIG. 7 is a block diagram illustrating a relationship between the configuration of the control unit 30 and main components that are controlled by the control unit 30.
As shown in the figure, the control unit 30 includes a CPU (Central Processing Unit) 31, a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a communication interface (I / F) unit 34, and image data. A storage unit 35 and the like are provided.

  The CPU 31 executes a program for controlling the image forming unit 10, the paper feeding unit 20, the scanner unit 40, the ADF unit 50, the operation panel 60, and the like. The ROM 32 is a storage that stores various programs executed by the CPU 31. The RAM 33 is a work area when the CPU 31 executes a program. The communication I / F unit 34 is an interface for connecting to a LAN such as a LAN card or a LAN board.

The image data storage unit 35 stores image data for printing input via the communication I / F unit 34 or the scanner unit 40.
The operation panel 60 is disposed at an easy-to-operate position on the upper side of the copier 1, and is a touch panel type liquid crystal display for displaying various information such as an operation screen such as a print setting screen and a print result, and for inputting various instructions. It consists of operation buttons and the like, and receives various instruction inputs from the user through operations such as a touch panel and operation buttons.

In the sheet-through mode, the CPU 31 performs a “document transport process” in which the uppermost document is sequentially fed from the document stack placed on the document feed tray 502 and transported to the document reading position P.
During the document conveying process, the CPU 31 sets the winding pressure P to the first value p1 when the unwound document is rolled by the conveying unit 52, and rotates the rear portion of the document when correcting the skew after being rolled. The control for switching the firing pressure P from the first value p1 to the second value p2 is executed so that the posture can be easily corrected. The ROM 32 stores the number of drive pulse signals (18) and the drive pulse signal input period (about 1.4 ms) as control information for the cam motor M5 for switching the firing pressure P.

Hereinafter, the document conveying process including the control for switching the winding pressure P will be described in detail.
(6) Document Conveying Process FIG. 8 is an example of a flowchart showing a part of the control content of the “document conveying process” executed by the control unit 30.
This control is carried out as a subroutine of a main flowchart (not shown) for controlling the entire copying machine 1, and here, control for switching the firing pressure P is mainly shown.

FIG. 9 is a time chart showing the timing of control for switching the firing pressure P, and this figure is also referred to hereinafter.
First, as illustrated in FIG. 8, the control unit 30 places a bundle of documents on the document feed tray 502 by the user and receives a copy job or scan job start instruction via the operation panel 60 (Step S 30). S101), the paper feed motor M1 is driven to rotate (step S102), and the document feed is started (time T0 in FIG. 9). The firing pressure P at this time T0 is the first value p1.

  After the fed document passes through the paper transporting section 52, the leading edge of the paper that has passed through the paper transporting section 52 has passed the pre-registration sensor S2 position (step S103: Yes) (in FIG. 9). T1) If the predetermined time Ta has elapsed (step S104: Yes) (time point T3 in FIG. 9), control for switching the firing pressure P from the first value p1 to the second value p2 is started (step S105). .

  The predetermined time Ta here is the time Ta1 until the portion (α) at the leading edge of the document that has passed the position of the pre-registration sensor S2 reaches the registration nip N2, and the portion (α) reaches the registration nip N2. After that, the time Ta2 required for conveying the trailing edge of the original by about 3 mm, for example, is added. The time Ta2 is a time provided so that the entire leading edge of the document is in contact with and aligned with the registration nip N2.

The time Ta1 is calculated from the transport distance from the pre-registration sensor S2 position to the registration nip N2 and the document transport speed (system speed).
The above-mentioned transport amount of the trailing edge of the document used for calculating the time Ta2 is the maximum skew (for example, skew angle ± 1.0 °) expected for the maximum size (A3 longitudinal) document that can be transported here. ) Occurs, the necessary and sufficient size is set to convey the corner (β) delayed by the skew to the registration nip N2 among both corners of the leading edge. The time Ta2 is calculated from the transport amount thus set (for example, 3 mm) and the document transport speed (system speed).

For example, if the transport distance between the pre-registration sensor S2 position and the resist nip N2 is 5 mm and the system speed is 520 mm / s, the time Ta1 is about 9.6 ms (= 5/520), and the time Ta2 is about 5.8 ms (= 3/520), the predetermined time Ta is about 15.4 ms.
Therefore, at the time T3 when the predetermined time Ta has elapsed, the entire leading edge of the document is reliably aligned with the registration nip N2, and a loop is formed on the document.

  In step S105, the control unit 30 determines the cam information based on the control information of the cam motor M5 (number of drive pulse signals (18), input period of drive pulse signal (about 1.4 ms)) stored in the ROM 32. The motor M5 is driven to rotate forward. Thereby, the eccentric cam 74 is rotated 180 degrees from the basic posture, and the magnitude of the firing pressure P is switched to the second value p2 (see FIG. 4B).

In the control for switching the firing pressure P to the second value p2, as shown in FIG. 9, the firing pressure P is gradually reduced by taking time Ts for switching. The switching time Ts here is about 24 ms (switching time Ts≈input period of drive pulse signal × number of input periods).
As described above, the page pressure P is gradually reduced because when the page pressure P is reduced all at once, the restoring force of the original works and the rear part of the original is rotated. This is because there is a risk of separation from the nip N2. In particular, this problem becomes significant in the case of stiff paper. On the other hand, if the switching time Ts is long, the action of rotating the rear part of the document due to the restoring force of the document is weakened in the case of thin paper that is weak, and the effect of rotating the rear part of the document may be reduced. As for the switching time Ts, an appropriate time length is obtained in advance by experiments. Further, the input period of the drive pulse signal for driving and controlling the cam motor M5 is calculated based on the switching time Ts thus obtained.

Next, if the time Tb has elapsed from the start timing of the control for switching the firing pressure P in step S105 (step S106: Yes) (time T4 in FIG. 9), the paper feed motor M1 is stopped (step S107).
In this manner, the stop timing of the paper feed motor M1 is delayed from the start timing of the control for switching the paper pressure P to the second value p2, and the paper pressure P is applied while the document is being conveyed by the paper feed roller 521. I try to lower it. Thereby, compared with the case where the paper pressure P is lowered after the document conveyance is stopped, the restoring force of the document can be prevented from acting at once due to the conveyance force applied by the paper feed roller 521 to the document. It is possible to further prevent the front end of the document from being separated from the registration nip N2.

The time Tb is, for example, about 1 to 20 ms, and is determined in advance at the design stage.
Thereafter, the braking time until the paper feed motor M1 stops (time T5 in FIG. 9) passes, and after waiting for the time Tc to pass (step S108: Yes), the registration motor M2 is driven to rotate. (Step S109) (time T6 in FIG. 9), the registration roller pair 53 is rotated to convey the document downstream.

The time Tc here is set to a sufficient time (for example, about 20 to 30 ms) for the rear part of the document to rotate to complete (correct) the posture change.
As described above, when the skew correction is performed, the skew pressure P is changed from the first value p1 to the second value p2, so that skew remains in the rear portion Dc of the document D as shown in FIG. From the state, the rear portion Dc of the document D is rotated by the restoring force of the loop R portion of the document D, and as shown in FIG. 10B, the skew of the rear portion Dc can be reduced and the posture can be corrected.

Returning to FIG. 8, after the registration motor M2 is rotationally driven in step S109, if the trailing edge of the document passes the post-scanning sensor S1 position (step S110: Yes) (time T7 in FIG. 9), the rolling pressure P To the original first value p1 (step S111).
Here, the control unit 30 drives the cam motor M5 in reverse rotation based on the control information of the cam motor M5 stored in the ROM 32. As a result, the eccentric cam 74 is rotated 180 ° in the opposite direction to step S105 to return to the basic posture, and the firing pressure P is set to the first value p1 (see FIG. 4A).

Next, after the trailing edge of the document has passed the pre-registration sensor S2 position (time T8 in FIG. 9), if a sufficient time Td required to pass the registration nip N2 has elapsed (step S112: Yes). (Time point T9 in FIG. 9), the registration motor M2 is stopped (step S113). The time Td is obtained in advance by experiments.
Thereafter, it is confirmed whether or not there is a next original (step S114). Whether or not there is a next document can be determined by referring to the output of the document placement sensor S11.

If there is a next original (step S114: Yes), the process returns to step S102, and the processes of steps S102 to S113 are repeated. If there is no next document (step S114: No), the process returns to the main flowchart (not shown).
This completes the document conveyance process.
In the present embodiment, an eccentric cam 74 that supports the end of the compression coil spring 71 opposite to the roller 522 so as to be swingable via a piston 72, and a cam motor M5 that rotationally drives the eccentric cam 74; The control unit 30 that drives and controls the cam motor M5 functions as a pressing force changing unit.

<Second Embodiment>
The second embodiment includes two modes, a normal mode and a suppression mode, as operation modes for reducing the firing pressure P from the first value p1 to the second value p2, and operates according to the thickness (paper type) of the document. This is different from the first embodiment in which there is one operation mode (normal mode) in that the mode is switched.
(1) Outline When the original is thick paper, the restoring force of the original is large and the action of rotating the back of the original is stronger than when using plain paper or thin paper. There is a high risk of separation from the resist nip N2. Therefore, in the present embodiment, when the original is thick paper, the second value p2 of the squeezing pressure P is increased (the amount of pressure reduction from the first value p1 is smaller) than in the normal mode when the original is thin paper. ) And a suppression mode in which the decompression speed when decompressing is reduced is executed.

  Thereby, in the normal mode, since it is not necessary to consider thick paper, the second value p2 is made smaller (the amount of pressure reduction from the first value p1 is larger) and the pressure is reduced than when thick paper is considered. The speed can be increased, and it can be set so that the action by the restoring force (the action of rotating the rear part of the original) in the loop forming portion of the original can be obtained more effectively in the plain paper or thin paper original. Therefore, the effect of correcting the document orientation can be further enhanced as compared with the first embodiment configured to cope with thick paper, plain paper, and thin paper documents in one operation mode.

For example, in the normal mode, as shown in FIG. 11A, the eccentric cam 74 is rotated 180 ° from the rotation reference position (the position indicated by the broken line) to switch the firing pressure P to the second value p2. Hereinafter, the second value p2 in the normal mode is also referred to as “second value p2a”.
On the other hand, in the suppression mode, as shown in FIG. 11B, the eccentric cam 74 is rotated 90 ° from the rotation reference position (the position indicated by the broken line) to switch the firing pressure P to the second value p2. . At this time, the eccentric cam 74 abuts the intermediate portion 74c between the long diameter portion 74a and the short diameter portion 74b against the piston 72, so that the position of the piston 72 is more than that in the normal mode of FIG. Is also a little higher. Hereinafter, the second value p2 in this suppression mode is also referred to as “second value p2b”.

In the present embodiment, the second value p2a in the normal mode is, for example, about 2.5N, and the second value p2b in the suppression mode is, for example, about 3.5N. Here, the wire diameter and the number of turns of the compression coil spring 71 are appropriately selected, the spring constant is changed, and the winding pressure P is adjusted so as to have the above design values.
FIG. 12 is a time chart showing the timing of control for switching the firing pressure P in the present embodiment.

As shown in the figure, the time required for reducing the firing pressure P from the first value p1 to the second values p2a and p2b is the same time Ts in both the normal mode (solid line) and the suppression mode (broken line). Therefore, the decompression speed is higher in the normal mode with a large decompression amount than in the suppression mode.
The ROM 32 (see FIG. 7) stores control information of the cam motor M5 for switching the firing pressure P in the normal mode and the suppression mode. That is, as the control information for the normal mode, the number of drive pulse signals (18) and the input period of the drive pulse signal (about 1.4 ms), the number of the drive pulse signals (9) as the control information for the suppression mode, the drive pulse The signal input period (about 2.8 ms) is stored.

In the normal mode, the rotational speed of the cam motor M5 is increased and the decompression speed is increased because the input period of the drive pulse signal is shorter than in the suppression mode.
The paper type information of the original is obtained when the user inputs paper type information (thin paper, plain paper, thick paper, etc.) from the operation panel 60 when setting the original on the original feed tray 502. The input paper type information is stored in a predetermined area in the RAM 33 of the control unit 30. The default value is plain paper.

Since the other configuration is basically the same as that of the copying machine 1 of the first embodiment, the following description will mainly focus on the different parts of the “document conveying process”.
(2) Document Conveying Process FIG. 13 is a flowchart showing a part of the control content of the “document conveying process” executed by the control unit 30 in the present embodiment, and mainly only processes different from the flowchart of FIG. It is shown. Note that the same steps as those in FIG. 8 are given the same step numbers or omitted.

As shown in the figure, after step S101, the control unit 30 first reads the paper type information of the original stored from a predetermined area of the RAM 33 (step S121), and the original set on the original feed tray 502 is read. It is determined whether the paper is thick (step S122).
If the document is thick paper (step S122: Yes), the suppression mode is set to On as the operation mode for reducing the squeezing pressure P from the first value p1 to the second value p2 (step S123). On the other hand, if the paper is not plain paper but plain paper or thin paper (step S122: No), the normal mode is turned on (step S124).

  For the setting of the suppression mode and the normal mode (On), for example, an area for writing a setting flag for setting the operation mode is provided in the RAM 33. In step S123, “1” is set in the setting flag (the suppression mode is On). In step S124, the setting flag is set to “0” (normal mode is on). In this case, in the subsequent step, it is possible to confirm which of the suppression mode and the normal mode is set (On) by the value set in the setting flag.

Thereafter, in steps S102 to S104, the leading edge of the fed document passes the pre-registration sensor S2 position (time T1 in FIG. 12), and after a predetermined time Ta has elapsed (time T3 in FIG. 12), the control unit 30 confirms whether the suppression mode is On (step S125), and performs subsequent processing based on the confirmation result.
That is, when the suppression mode is On (setting flag = “1”) (step S125: Yes), the cam motor M5 is rotated forward based on the control information of the cam motor M5 in the suppression mode stored in the ROM 32. The drive control is performed to rotate the eccentric cam 74, and control for switching the firing pressure P from the first value p1 to the second value p2b is started (step S126). Here, as described above, the control information of the cam motor M5 in the suppression mode is the number of drive pulse signals (18) and the input period of drive pulse signals (about 1.4 ms).

  On the other hand, when the suppression mode is not On and the normal mode is On (setting flag = “0”) (step S125: No), based on the control information of the cam motor M5 in the normal mode stored in the ROM 32, The cam motor M5 is controlled to rotate forward to rotate the eccentric cam 74, and control for switching the firing pressure P from the first value p1 to the second value p2a is started (step S127). As described above, the control information of the cam motor M5 in the normal mode is the number of drive pulse signals (9) and the drive pulse signal input period (about 2.8 ms).

The switching time Ts required for switching the firing pressure P in the suppression mode in step S126 and the normal mode in step S127 is about 24 ms.
The subsequent steps are the same as steps S106 to S114 in FIG. In step S111, the cam motor M5 is reversely rotated and controlled based on the control information of the cam motor M5 in the corresponding operation mode stored in the ROM 32, and the eccentric cam 74 is opposite to the steps S126 and S127. Is rotated to return the firing pressure P to the first value p1.

  In the present embodiment, the paper type information (thin paper, plain paper, thick paper, etc.) of the document has been described as being obtained by the user inputting from the operation panel 60. However, the present invention is not limited to this. A sensor for detecting the thickness of the document may be provided in the middle of the conveyance path 510 (for example, at a downstream position of the paper conveyance unit 52), and the paper type may be determined based on the acquired thickness. In this case, it is possible to deal with a paper type mixed original in which different paper types are mixedly loaded.

<Third Embodiment>
The third embodiment is configured such that the operation mode for reducing the squeezing pressure P from the first value p1 to the second value p2 is switched depending on the thickness (paper type) of the document. Common with form.
However, in the second embodiment, between the operation modes (between the normal mode and the suppression mode), the magnitude of the second value p2 and the pressure reduction speed when the pressure is reduced from the first value p1 to the second value p2. However, the third embodiment differs in that the second value p2 is the same between the operation modes, and only the pressure reduction speed is changed. .
(1) Outline In the present embodiment, when the original is thick paper, the low-speed mode is executed in which the decompression speed when reducing the squeezing pressure P is slower than the normal mode when plain paper or thin paper is used.

When the document is thick paper, even if the decompression speed is slowed down, the restoring force at the loop forming part of the document can be suppressed at once, so the action of rotating the back of the document can be weakened, and the inertial force It is possible to prevent the front end of the document from being separated from the registration nip N2.
Further, in the normal mode, as in the second embodiment, it is not necessary to consider stiff paper, so that the decompression speed can be made faster than when thick paper is considered, and restoration in the loop formation portion of the document is possible. It can be set so that an action by force (an action of rotating the rear part of the document) can be obtained effectively.

The second value p2 in the present embodiment is about 3.0N, which is the same size as in the first embodiment. Further, the switching of the firing pressure P from the first value p1 to the second value p2 is such that the eccentric cam 74 is rotated 180 ° from the rotation reference position and the short diameter portion 74b is in contact with the piston 72. (See FIG. 4B).
Further, as shown in the time chart of FIG. 14, in the normal mode (solid line), the switching pressure P is switched from the first value p1 to the second value p2 over the first time Tf. In the low speed mode (broken line), the firing pressure P is switched over a second time Tg longer than the first time Tf.

  The ROM 32 (see FIG. 7) stores control information of the cam motor M5 for switching the firing pressure P in the normal mode and the low speed mode. That is, as the control information for the normal mode, the number of drive pulse signals (18) and the input period of the drive pulse signal (about 0.7 ms), the number of the drive pulse signals (18) as the control information for the low speed mode, and the drive pulse The signal input period (about 1.4 ms) is stored.

Since other configurations are basically the same as those of the copying machine 1 of the second embodiment, the following description will mainly focus on different parts of the “document conveying process”.
(2) Document Conveying Process FIG. 15 is a flowchart showing a part of the control contents of the “document conveying process” executed by the control unit 30 in the present embodiment, and mainly the flowcharts of FIGS. Only the different processing is shown. Note that the same steps as those in FIGS. 8 and 13 are given the same step numbers or omitted.

  As shown in the figure, after step S121, it is determined whether or not the document set on the document feed tray 502 is thick paper. If the document is thick paper (step S122: Yes), the firing pressure P is set to the first value. The low speed mode is set to On as the operation mode for reducing the pressure from the value 1 to the second value p2 (step S131). On the other hand, if the paper is not plain paper but plain paper or thin paper (step S122: No), the normal mode is turned on (step S132).

In step S131, “1” is set to the setting flag provided in the RAM 33 (low speed mode is On), and in step S132, “0” is set to the setting flag (normal mode is On).
Thereafter, in steps S102 to S104, the leading edge of the fed document passes the pre-registration sensor S2 position (time T1 in FIG. 14), and after a predetermined time Ta has elapsed (time T3 in FIG. 14), the control unit 30 confirms whether or not the low-speed mode is On (step S133), and performs subsequent processing based on the confirmation result.

  That is, when the low speed mode is On (setting flag = “1”) (step S133: Yes), the cam motor M5 is rotated forward based on the control information of the cam motor M5 in the low speed mode stored in the ROM 32. The drive control is performed to rotate the eccentric cam 74, and control for switching the firing pressure P from the first value p1 to the second value p2 is started (step S134). The control information of the cam motor M5 in the low speed mode here is the number of drive pulse signals (18) and the drive pulse signal input period (about 1.4 ms) as described above.

  On the other hand, when the low speed mode is not On and the normal mode is On (setting flag = “0”) (step S133: No), based on the control information of the cam motor M5 in the normal mode stored in the ROM 32. Then, the cam motor M5 is controlled to rotate forward to rotate the eccentric cam 74, and control for switching the firing pressure P from the first value p1 to the second value p2a is started (step S135). As described above, the control information of the cam motor M5 in the normal mode includes the number of drive pulse signals (18) and the input period of drive pulse signals (about 0.7 ms).

The switching time Tg required for switching the firing pressure P in the low speed mode in step S134 is about 24 ms, and the switching time Ts in the firing pressure P in the normal mode in step S135 is about 12 ms.
The subsequent steps are the same as steps S106 to S114 in FIG. In step S111, the cam motor M5 is reversely rotated and controlled based on the control information of the cam motor M5 in the corresponding operation mode stored in the ROM 32, and the eccentric cam 74 is reverse to the steps S134 and S135. Is rotated to return the firing pressure P to the first value p1.

<Fourth embodiment>
In the fourth embodiment, switching of the firing pressure P from the first value p1 to the second value p2 is performed after the rotation of the registration roller pair 53 is started. This is different from the first embodiment performed while the rotation of the registration roller pair 53 is stopped.
Even after the rotation of the registration roller pair 53 starts, the document loop remains, so if the switching pressure P is switched immediately, the trailing edge of the document is rotated by the restoring force in the loop forming portion of the document. Is possible, and the posture of the manuscript can be corrected. On the other hand, when the registration roller pair 53 rotates and the original is caught in the registration nip N2 and conveyed, the restoring force of the original acts so as to push the original into the registration nip N2. If it remains, there is a possibility that the skew returns to the original document pushed in by the restoring force. In order to prevent this, in the present embodiment, the rolling pressure P is switched immediately after the rotation of the registration roller pair 53 starts.
(1) Control start timing for switching the firing pressure P FIG. 16 is a time chart showing the control timing for switching the firing pressure P in the present embodiment.

  A time point T6 shown in the figure is a time point when the rotation driving of the registration motor M2 is started, and a time point when the rotation of the registration roller pair 53 starts. A time point T62 is a time point when the rotation speed of the registration motor M2 reaches the target speed V, and indicates a time point when the peripheral speed of the registration roller pair 53 reaches the system speed. The control for switching the firing pressure P from the first value p1 to the second value p2 is started (decompression start) within the rising time Ti of the motor between the time points T6 and T62 (time point T61).

The start timing of the switching control of the firing pressure P will be described in more detail with reference to FIGS. 17 (a) and 17 (b).
FIG. 17A shows a state in which the leading edge Da of the document D is brought into contact with the registration nip N2 of the registration roller pair 53 whose rotation is stopped, and a loop R is formed on the document D.
Further, as shown in the figure, the registration nip N2 has a predetermined width (about several mm) in the conveyance direction C, and the leading edge Da of the document D is brought into the entrance of the registration nip N2 by the restoring force of the loop R portion. It is in a state of being inserted a little into the part.

Thereafter, the registration motor M2 is rotated and the registration roller pair 53 is rotated, whereby the leading edge Da of the document D is caught in the registration nip N2 and the document D is conveyed.
During the start-up of the registration motor M2 at this time, as shown in FIG. 17B, when the leading edge Da of the document D passes the center point N2a in the conveyance direction C of the registration nip N2, switching control of the rolling pressure P is performed. To start.

The reason for starting the switching control of the firing pressure P at this timing will be described.
The center point N2a of the registration nip N2 is the intersection of the registration nip N2 with the straight line F connecting the rotation center point E1 of the upper roller 531 and the rotation center point E2 of the lower roller 532 in the registration roller pair 53, and the nip pressure Is the strongest position. If the leading edge Da of the document D passes through the center point N2a, the document D is firmly held by the registration nip N2. Therefore, after passing through the center point N2a, there is no possibility that the leading edge Da of the document D is separated from the registration nip N2 as the squeezing pressure P is reduced.

  Further, in the present embodiment, as the conveyance of the document by the registration roller pair 53 proceeds, the document D is pushed into the registration nip N2 by the restoring force of the loop R portion, and the risk of the skew returning increases. The page pressure P is switched to the second value p2 until the document conveyance amount by the registration roller pair 53 reaches a predetermined amount J so as to be within an allowable range (about −0.3 ° to + 0.3 °). It is configured as follows.

  The predetermined amount J here is, for example, the relationship between the amount of skew generated in the document conveyed by the registration roller pair 53 and the conveyance amount when the maximum expected skew remains at the rear of the document by experiment. It is obtained and set by acquiring the magnitude of the conveyance amount at which the skew becomes the limit value of the allowable range (for example, about 5 mm). This predetermined amount J corresponds to the amount by which the document D is caught in the registration nip N2.

  Further, after the rotation of the registration roller pair 53 starts, the time Th until the leading edge Da of the conveyed document D reaches the center point N2a of the registration nip N2 and the time Tj until the document conveyance amount reaches the predetermined amount J are also included. These are obtained by experiments (see FIGS. 16A and 16B for times Th and Tj). Here, the time Th is obtained as the time for which the registration roller pair 53 rotates by a predetermined angle θ (FIG. 17B).

In the present embodiment, using the times Th and Tj thus obtained, as shown in FIG. 16, after the rotation of the registration roller pair 53 starts (time T6), the firing pressure P is reached at time T61 when the time Th has elapsed. Switching control is started, and the firing pressure P is controlled to be switched to the second value p2 from time T6 to time T63 when the time Tj elapses.
The switching time Tt required for switching the firing pressure P is obtained from the difference between the time Tj and the time Th. Based on the obtained switching time Tt, the input period of the drive pulse signal for controlling the drive of the cam motor M5 is calculated. ROM 32 (see FIG. 7).

  In this way, if the switching control of the separation pressure P is performed after passing through the center point N2a so that the leading edge of the document does not separate from the registration nip N2, for example, the separation roller 522 is separated from the sheet feeding roller 521 and the separation roller N A configuration in which the pressure P is set to “0” is conceivable. In this case, since the rear part of the document is more easily rotated, there is an advantage that the posture of the document can be effectively corrected by the restoring force in the loop forming portion of the document, but the trailing edge of the document flutters during conveyance. The manuscript may be wrinkled. Therefore, in this embodiment, the separation roller 522 is not separated from the paper feed roller 521, and the document is sandwiched by the separation conveyance unit 52 to such an extent that the document fluttering can be suppressed.

Since the other configuration is basically the same as that of the copying machine 1 of the first embodiment, the following description will mainly focus on the different parts of the “document conveying process”.
(2) Document Conveying Process FIG. 18 is a part of a flowchart showing the control content of the “document conveying process” executed by the control unit 30 in the present embodiment. Mainly, only the processes different from the flowchart of FIG. It is shown. Note that the same steps as those in FIG. 8 are given the same step numbers or omitted.

As shown in the figure, the control unit 30 first receives a copy job or scan job start instruction in steps S101 to S104, and then the leading edge of the fed document passes the pre-registration sensor S2 position ( At time T1) in FIG. 16, it waits for a predetermined time Ta to elapse.
If the predetermined time Ta has elapsed (step S104: Yes), the control unit 30 stops the paper feed motor M1 (step S107) (time T2 in FIG. 16), and after the paper feed motor M1 is stopped, further, the time Tc. (Step S108: Yes), the registration motor M2 is driven to rotate (step S109) (time point T6 in FIG. 16).
When the time Th required for the registration roller pair 53 to rotate by the predetermined angle θ has elapsed (step S141: Yes), the control unit 30 determines that the leading edge Da of the document D has reached the center point N2a of the registration nip N2. Determination is made, and control for switching the firing pressure P from the first value p1 to the second value p2b is started (step S142). The control unit 30 controls the cam motor M5 to rotate forward based on the control information of the cam motor M5 stored in the ROM 32, so that the document conveyance amount by the registration roller pair 53 reaches the predetermined amount J ( At time T63 in FIG. 16, the firing pressure P is switched to the second value p2.

The subsequent steps are the same as steps S110 to S114 in FIG.
[Modification]
As described above, the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described embodiment, and the following modifications can be implemented.
(1) In the first to third embodiments, after the leading edge of the document is brought into contact with the registration nip N2 and aligned, the control for switching the sheet pressure P is started first, and then the sheet feeding roller 521 is rotated. Although the configuration for stopping is shown, the present invention is not limited to this.

For example, it is possible to adopt a configuration in which the control for switching the firing pressure P is started after the paper feed roller 521 is synchronized with the rotation stop timing or after the rotation is stopped.
(2) Further, in the fourth embodiment, the configuration is shown in which the control for switching the squeezing pressure P is started after the leading edge of the document passes the center point N2a of the registration nip N2 by the rotation of the registration roller pair 53. However, the control for switching the firing pressure P may be started before the leading edge of the document passes through the center point N2a of the registration nip N2.

In this case, the page pressure P is gradually reduced until the leading edge of the document passes the center point N2a of the registration nip N2 so that the leading edge of the document is not separated from the registration nip N2 by the restoring force of the document. After passing through the point N2a, it is desirable to reduce the squeezing pressure P at a stretch so that the action due to the restoring force of the document is effectively exhibited.
If the control for switching the squeezing pressure P from the first value p1 to the second value p2 is performed while the loop is formed on the document, the document posture is determined by rotating the rear part of the document by the restoring force of the document. Can be corrected, and the skew correction effect can be enhanced as compared with the prior art.

Here, “while the loop is formed on the original” specifically means that the front end of the original is brought into contact with the registration nip N2 and then aligned with the registration nip N2 by the rotation of the registration roller pair 53. It means a predetermined amount J (see the fourth embodiment) until it is bitten.
(3) In the first embodiment, the time Ta2 provided so that the entire leading edge of the document is in contact with and aligned with the registration nip N2 is the size of the document and the amount of skew generated in the document. Regardless of the above, the configuration in which the conveyance amount of the trailing edge of the document is fixed (here, 3 mm) is shown, but the present invention is not limited to this.

  For example, the size of the fed document or the skew generated in the document is acquired, and based on the acquired result, the trailing edge of the document required for aligning the entire leading edge of the document with the registration nip N2 The transport amount may be calculated and obtained for each document fed. In this case, the smaller the original skew and the same skew, the smaller the original width, the smaller the conveyance amount of the rear end of the original necessary to align the entire leading edge of the original with the registration nip N2. Therefore, compared to the first embodiment in which the conveyance amount at the trailing edge of the document is determined on the assumption that the maximum skew that can be expected has occurred in the maximum size document that can be conveyed, The end conveyance amount can be reduced as a whole, and productivity can be increased.

For example, when the document is set in the document feed tray 502, the user inputs the document size (A5 vertical length or the like) from the operation panel 60 or is set in the document feed tray 502. This can be obtained by providing a sensor for obtaining the length of the original and a sensor for obtaining the width.
In addition, acquisition of the magnitude of the skew generated in the document is performed by, for example, registering two photoelectric sensors that detect the document to be conveyed in the middle of the conveyance path 510 between the paper conveyance unit 52 and the registration roller pair 53. The skew amount (skew angle) can be calculated and acquired by the time difference when the leading edge of the document is detected from the output of each sensor.

(4) In the above embodiment, the configuration is shown in which the firing pressure P is changed linearly from the first value p1 to the second value p2, but the present invention is not limited to this.
For example, as shown in FIG. 19, the firing pressure P may be switched by changing in a curve. In this case, in the normal mode of plain paper or thin paper, it is desirable to first increase the pressure reduction and change the pressure gradually. First, the restoring force of the document is applied at once to rotate the rear part of the document, and thereafter the action due to the restoring force of the document is gradually weakened to prevent the leading edge of the document from being separated from the registration nip N2. Because it becomes like this. On the other hand, in the cardboard suppression mode, it is desirable to weaken the initial decompression, gradually increase it, and gradually reduce the pressure. This is because the restoring force of the original can be gradually exerted, whereby the leading edge of the original can be reliably prevented from separating from the registration nip N2.

(5) Moreover, as shown in FIG. 20, it can also be set as the structure which changes the burning pressure P in steps.
In the normal mode of plain paper or thin paper, the first value p1 can be reduced in two steps from the second value p2, and in the thick paper suppression mode, a reduction can be considered in three steps. The reason why the number of steps is increased in the suppression mode as compared with the normal mode is that the amount of pressure reduction per step can be reduced (pressure reduction amount Pa> pressure reduction amount Pb). This is to suppress the action of the restoring force of the original when the pressure is gradually reduced, and to prevent the front end of the original from being separated from the registration nip N2.

(6) The above embodiment shows a configuration in which the pressure reduction rate when switching the firing pressure P from the first value p1 to the second value p2 is the same as the pressure increase rate when returning to the first value p1. However, the present invention is not limited to this.
For example, as in the above-described embodiment, when the trailing pressure of the document is returned to the first value p1 after the trailing edge of the document has passed the position after the sensor S1, the document is not affected. As shown in FIG. 21, the pressure may be increased at a stroke regardless of whether the paper is thick or thin. Conversely, the pressure can be increased slowly. From the viewpoint of productivity, it is desirable to increase the pressure at a stroke and return the firing pressure P to the first value p1, since the document feeding interval can be shortened.

(7) Alternatively, the trailing pressure P may be returned to the first value p1 before the trailing edge of the document passes the position of the sensor S1 after scanning.
In this case, since the back tension of the document fluctuates with the increase of the winding pressure P, a problem such as wrinkling may occur in the document. Therefore, since the thin paper is more susceptible to the back tension than the thick paper, for example, as shown in FIG. 19, it is desirable to slowly increase the pressure to return to the first value p1.

(8) In the second and third embodiments, the configuration including two operation modes of the suppression (or low speed) mode in the case of thick paper and the normal mode in the case of plain paper and thin paper is shown. It is not limited to.
For example, the operation mode for plain paper and thin paper may be separated. By subdividing the operation mode according to the strength of the document, the document posture can be corrected more effectively by the restoring force of the document.

(9) In the second and third embodiments, the configuration in which the operation mode is switched depending on the thickness (paper type) of the document has been described. However, the present invention is not limited to this.
For example, the operation mode can be switched depending on the width size of the document.
Even when the skew is the same, the larger the width of the document, the larger the front edge R2 and the backside loop R1 when the entire leading edge of the document is aligned with the registration nip N2 (see FIG. 10A). There is a difference in the height, and the action due to the restoring force of the original works strongly.

  Therefore, as shown in FIG. 22A, when the document width size is large (for example, A3 portrait orientation, A4 landscape orientation), the low-speed mode in which the reduction pressure of the squeezing pressure P is reduced is set to the document width size. Is small (for example, A5 lengthwise, A4 lengthwise), it is desirable to switch to the high speed mode in which the decompression speed is higher than the low speed mode. In addition, regarding the amount of reduction of the squeezing pressure P, it is desirable to select a mode in which the amount of decompression is small when the width size of the document is large, and to a mode in which the amount of decompression is larger than that when the width size of the document is small.

By switching the operation mode according to the document width size in this way, the document posture can be effectively corrected by the restoring force of the loop portion of the document.
Note that a configuration in which three or more operation modes are switched according to the document width size may be employed.
(10) Also, as shown in FIG. 22B, the operation mode may be switched depending on the conveyance conditions such as productivity.

When giving priority to productivity, it is possible to adopt a high speed mode in which the pressure reduction speed of the burning pressure P is increased, and when not giving priority to productivity, it is possible to adopt a low speed mode in which the pressure reduction speed is slower than the high speed mode. .
Whether or not to give priority to productivity can be acquired by setting from the operation panel 60 by the user when setting a document on the document feed tray 502, for example.

  Further, the operation mode may be switched depending on the type of document (photo, text). For example, in the case of a photograph, if the skew is conveyed to the image reading position and the read image is tilted, the print image formed based on the read image is also tilted and the image quality is deteriorated. High nature. On the other hand, in the case of a text-only document, the user often uses it without worrying about it even if the print image is slightly inclined.

Therefore, in the case of a text-only original, it is not necessary to worry about the image quality as much as in the case of a photograph. Therefore, it is desirable to increase the productivity by setting the high-speed mode. For example, when priority is given to image quality such as a photograph, it is desirable to set the low-speed mode when the document is thick paper and the high-speed mode when the document is thin paper so that the skew can be corrected effectively.
(11) In the above embodiment, the configuration using the eccentric cam 74 as the means (pressure contact force changing means) for changing the setting pressure between the setting roller 522 and the sheet feeding roller 521 is shown, but the present invention is limited to this configuration. It is not a thing.

For example, as shown in FIG. 23, by using a rack and pinion mechanism including a pinion 174 and a rack rod 175 provided with a tooth row meshing with the pinion 174, the piston 72 is moved up and down so that the rolling pressure P It can also be set as the structure which changes.
Alternatively, the piston 72 may be moved up and down using a direct acting motor.
(12) In the above embodiment, the DC motor is used as the transport driving motors M1 to M4 including the paper feeding motor and the registration motor. However, the invention is not limited to this, and for example, a stepping motor may be used.

  (13) Although not specifically mentioned in the above embodiment, the pair of aligning plates 505a and 505b for aligning the documents placed on the document feeding tray 502 is changed from the first value p1 to the first value p1. When switching to the value p2 of 2, as shown in FIG. 24A, it is desirable to move in the direction Q away from each other to release the contact state (regulated state) of the document D. This is because the rear portion Dc of the document D is easily rotated.

  For example, a slide mechanism 270 formed of a rack and pinion mechanism as shown in FIG. 24B can be used to move the pair of alignment plates 505a and 505b apart from each other or close to each other. The slide mechanism 270 includes a pinion 271, two rack rods 272 a and 272 b provided with tooth rows that mesh with the pinion 271, a pinion drive motor M 9 that rotates the pinion 271 via a timing belt 273, and the like. Is done.

  For example, during the document conveyance process (see the flowchart of FIG. 8), the control unit 30 performs the predetermined time Ta after the leading edge of the document that has passed the paper conveyance unit 52 has passed the pre-registration sensor S2 position (step S103: Yes). Before the time elapses (step S104: No), the pinion drive motor M9 is driven and controlled, and the pair of alignment plates 505a and 505b are moved by a predetermined amount in the separating direction Q to release the original contact state. In step S111, after the firing pressure P is returned to the original first value p1, the control unit 30 controls the drive of the pinion drive motor M9, and the pair of alignment plates 505a and 505b are opposite to the direction Q. The document can be moved back by a predetermined amount to return the original to the alignment position.

As a mechanism for moving the pair of alignment plates 505a and 505b close to each other, a belt driving mechanism may be used instead of the rack and pinion mechanism.
(14) In the above embodiment, the configuration has been described in which the scooping member that scoops the document fed out by the pickup roller 51 is composed of the scooping roller 522, but the present invention is not limited to this. For example, instead of a rolling roller, a rolling pad can be used as a rolling member.

  (15) In the above-described embodiment, the configuration in which the ADF unit 50 is controlled using the control unit 30 provided (arranged) in the printer unit 2 has been described. However, the present invention is not limited to this. For example, the ADF unit 50 may have a dedicated control unit. In this case, the controller dedicated to the ADF unit 50 is configured to execute the document conveying process in cooperation with the controller 30 of the printer unit 2.

(16) In the above embodiment, the tandem type color copying machine has been described as the image forming apparatus. However, the scope of application of the present invention is not limited to this, and the present invention is applicable to other copying machines, printers, facsimile machines, and the like. Can be applied.
Further, the contents of the above-described embodiment and modification examples may be combined as much as possible.

  The present invention is useful as a technique for correcting sheet skew.

DESCRIPTION OF SYMBOLS 1 Copy machine 2 Printer part 3 Image reading part 10 Image forming part 11 Image forming unit 12 Intermediate transfer belt 13 Secondary transfer roller pair 14 Fixing part 20 Paper feed part 30 Control part 40 Scanner unit 50 ADF unit 51 Pickup roller 52 Rolling conveyance Part 53 Registration roller pair 60 Operation panel 70 Pressure contact mechanism 71 Compression coil spring 72 Piston 74 Eccentric cam 505a, 505b Alignment plate 521 Feed roller 522 Rolling roller N1 Rolling nip N2 Registration nip N2a Center point of registration nip

Claims (14)

The sheet fed from the tray is passed between the sheet feeding roller and the sheeting member pressed against the sheet in the sheet conveying unit and conveyed one by one, and the leading edge of the sheet is rotated for each conveyed sheet. A sheet conveying apparatus that abuts against a nip portion of a stopped registration roller pair to form a loop and correct skew, and then rotates the registration roller pair to convey the sheet downstream.
A pressing force changing means for changing the magnitude of the pressing force between the paper feed roller and the rolling member;
The pressure contact force changing means is
After the leading edge of the sheet comes into contact with the nip portion of the registration roller pair and is aligned, the pressure contact force is applied to the first time until the nip portion is bitten by a predetermined amount by the rotation of the registration roller pair. The sheet conveying apparatus is characterized in that the value is reduced to a second value smaller than the first value. Comprising an acquisition means for acquiring information relating to a conveyance condition of a conveyed sheet;
The pressure contact force changing means is:
A first change mode for reducing the pressure contact force from the first value to the second value in a first time, and a second time longer than the first time from the first value. 2. The sheet conveying apparatus according to claim 1, wherein the second change mode for decreasing to a second value is selected and executed according to the acquired sheet conveying condition. As the information on the sheet conveyance conditions, the type according to the thickness of the sheet is included,
The pressure contact force changing means selects the second change mode when the sheet type is thick paper, and selects the first change mode when the sheet is thinner than the sheet type. The sheet conveying apparatus according to 1. Information on the sheet conveyance conditions includes a width size in a direction orthogonal to the sheet conveyance direction,
The pressing force changing means selects the second change mode when the sheet width size is equal to or larger than the predetermined size, and selects the first change mode when the sheet width size is less than the predetermined size. The sheet conveying apparatus according to claim 2, wherein As the information on the sheet conveyance conditions, instruction information from the user whether to give priority to sheet conveyance productivity is included,
The pressure contact force changing means selects the first change mode when productivity is given priority, and selects the second change mode when productivity is not given priority. The sheet conveying apparatus according to the description.   The sheet conveying apparatus according to claim 2, wherein the pressure contact force changing unit changes the magnitude of the second value according to a conveyance condition of the sheet.   The sheet conveying apparatus according to claim 6, wherein the pressing force changing unit increases the second value when the sheet type is thick paper than when the sheet is thin paper. The sheet conveying apparatus according to claim 1, wherein the pressure contact force changing unit gradually decreases the pressure contact force from a first value to a second value. Comprising an acquisition means for acquiring information relating to a conveyance condition of a conveyed sheet;
The sheet conveying apparatus according to claim 8, wherein the pressing force changing unit changes the number of steps when the pressing force is reduced according to a sheet conveying condition. As the information on the sheet conveyance conditions, the type according to the thickness of the sheet is included,
The sheet conveying apparatus according to claim 9, wherein the pressure contact force changing unit increases the number of steps when the sheet type is thick paper than when the sheet type is thin paper. The pressure contact between the separating member and the sheet feeding roller is performed by an elastic member that presses the separating member toward the sheet feeding roller,
The pressure contact force changing means includes an eccentric cam that swingably supports an end of the elastic member opposite to the rolling member, a driving means that rotationally drives the eccentric cam, and a drive control means that controls the driving means. The drive control means controls the drive means to rotate the eccentric cam, thereby changing the magnitude of the pressure contact force between the winding member and the paper feed roller. To 10. The sheet conveying apparatus according to any one of 10 to 10. A pair of alignment plates that are in contact with and aligned with both ends of the sheet placed on the tray in the sheet width direction perpendicular to the conveying direction;
A proximity separation mechanism for approaching or separating the pair of alignment plates from each other;
A proximity separation control means for controlling the proximity separation mechanism,
The proximity / separation control means includes:
After the leading edge of the conveyed sheet passes between the paper feed roller and the separating member, until the operation for reducing the pressure contact force from the first value to the second value by the pressure contact force changing means is started. The sheet conveying apparatus according to claim 1, further comprising: controlling the proximity / separation mechanism to release the contact state of the sheet by the pair of alignment plates. An original reading device for reading an original conveyed by an original conveying means,
An original reading apparatus comprising the sheet conveying apparatus according to claim 1 as the original conveying means. An image forming apparatus for forming an image on a recording sheet fed from a sheet feeding means,
An image forming apparatus comprising: the sheet conveying device according to claim 1 as the sheet feeding unit.

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