JP2013180894A - Document feeder, document reader, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a document feeder capable of preventing the deterioration of a read image of a document by suppressing a variation of feeding speed which is caused when the trailing edge of the document comes off out of a separating roller as much as possible while surely separating the document, and to provide a document reader and an image forming apparatus.SOLUTION: An ADF unit which conveys a fed document to a document reading position after separating the document by the application of feeding resistance by a separating roller is provided with a load torque generating mechanism which gives load torque as the feeding resistance to the separating roller and is constituted so that the magnitude of the load torque can be changed. The load torque generated by the load torque generating mechanism when starting paper feeding is set to a first value (S101), and the load torque is changed from the first value to a second value smaller than the first value (S104) in a period from a time when the tip of the fed document passes through a resist nip on the downstream side of the separating roller (S103) until a time when it reaches the document reading position. Thus, the feeding resistance by the separating roller is made small.

Description

  The present invention relates to a document conveying device, a document reading device and an image forming apparatus provided with the document conveying device, and more particularly to an improvement of a document separation mechanism.

Many image forming apparatuses such as copiers are provided with a document transport device that feeds a document to be scanned by a pickup roller, rolls it by a scooping section, and then transports it to a document reading position.
Usually, the separation unit forms a nip by pressing the separation roller on the peripheral surface of the feed roller, and the document fed by the pickup roller is passed through the separation nip, so that the document being fed is It is configured to apply a force (hereinafter referred to as “conveyance resistance”) acting in a direction opposite to the direction in which the document is fed.

  The document that has passed through the separation nip is conveyed further downstream in the document direction and passes the document reading position. At this time, the image of the document that has passed through is read by an image reading element such as a CCD array.

JP 2001-146337 A Japanese Patent Laid-Open No. 11-124245

  However, if the length of the document in the transport direction is long, when reading of the leading edge of the document is started, the trailing edge of the document has not yet passed through the nip, and the trailing edge of the document has passed the nip. Until then, the tension in the transport direction is applied to the document, but the tension applied to the document at the moment of passing is drastically reduced and the document transport load is reduced, so the document transport speed fluctuates at the document reading position. Instantly gets faster.

When the document transport speed is instantaneously increased, the magnification of the read image in the sub-scanning direction is compressed, resulting in deterioration of the read image.
In order to avoid this, it is conceivable to reduce the conveyance resistance by the roller, but if this is done, there arises a problem that the paper feeding ability is lowered and the document is frequently fed. Such a problem similarly occurs even when, for example, a whirling pad or the like is used as a whispering member instead of a whispering roller.

  The present invention has been made in view of the above-described problems, and suppresses fluctuations in the conveyance speed that occur as a result of detachment from the trailing edge of the document as much as possible while reliably scanning the document. An object of the present invention is to provide a document conveying device, a document reading device, and an image forming apparatus capable of preventing deterioration of a document read image.

  In order to achieve the above object, the document conveying device according to the present invention is configured to feed a document stacked on a document tray with a pickup roller, and apply a conveyance resistance by a separating member pressed by a feeding roller at a separation unit. After that, the conveyance resistance changing means for changing the magnitude of the conveyance resistance by the separation member and the conveyance roller pair arranged on the downstream side in the document conveyance direction from the separation section are rotated. A conveying unit that drives and conveys the document, and the conveyance resistance changing unit moves the leading end of the document that has passed through the curving unit to the document reading position after passing through the nip of the conveying roller pair in the conveying unit. In the meantime, the conveyance resistance applied by the rolling member is changed from the first value to a smaller second value.

  According to the document conveying device having the above-described configuration, the conveyance resistance in the separation unit is reduced after the leading end of the document passes through the separation unit and before reaching the document reading position. Can make the document sufficiently large by making the conveyance resistance sufficiently large, and thereafter, to reduce the conveyance resistance, the variation in the conveyance speed when the trailing edge of the document passes through the curling part is made smaller than before. Therefore, the compressed image is less likely to be compressed.

Here, a thickness detection unit that detects the thickness of the document in the middle of the conveyance path from the winding unit to the nip of the conveyance roller pair is provided, and the conveyance resistance changing unit sets the second value from a plurality of different values. It is possible to determine the second value in accordance with the thickness of the original detected by the thickness detecting means.
Further, it is provided with a carry detecting means for detecting that the carry has occurred in the winding portion, and when the carry resistance changing means detects the carry, the second value is corrected to increase by a predetermined amount. desirable.

Here, the rolling member includes a rolling roller that is pressed by the paper feed roller to form a rolling nip, and a plurality of torque limiters that apply a rotational load to the winding roller, and the conveyance resistance changing means includes a plurality of torque limiters. It is desirable to change the conveyance load from the first value to the second value by cutting a part of the rotational load on the roller.
The present invention may be a document reading apparatus provided with the document conveying device having the above-described configuration, and thereby, the same effects as those of the document conveying device having the above-described configuration can be obtained.

  Furthermore, an image forming apparatus provided with this document reading device may be used, and the same effects as those of the document conveying device having the above-described configuration can be obtained.

1 is a schematic cross-sectional view for illustrating an overall configuration of a copier according to a first embodiment of the present invention. It is a figure which shows the structure of the scanner unit and ADF unit which the said copying machine has. It is a figure which shows the structural example of the mechanism for giving conveyance resistance to a rolling roller and a rolling roller. (A) is a figure for demonstrating the winding operation | movement when the torque limit value of a roller is made into the 1st value, (b) is when the torque limit value of a roller is made into the 2nd value It is a figure for demonstrating a whispering operation | movement. 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. (A)-(c) is an operation | movement diagram for demonstrating the outline | summary of the document conveyance process in an ADF unit, and the load torque change process of a winding roller. It is a flowchart which shows the control content of the "loading torque change process of a rolling roller" performed by a control part. (A) is a schematic diagram for explaining a configuration for determining the type of original paper, and (b) is a schematic diagram for explaining a configuration for detecting and determining the accompanying document. It is a figure which shows the structural example of the load torque generation mechanism of the rolling roller which the ADF unit which concerns on 2nd Embodiment has. It is a table which shows an example of the 1st value of the torque limit value of a winding roller, the 2nd value for every paper type of thick paper, plain paper, and thin paper, and the operation control of the torque limiter at each value. It is a flowchart which shows the control content of the "loading torque change process of a roller roller" performed by the control part of 2nd Embodiment.

<First Embodiment>
Hereinafter, a case where an embodiment of an original conveying apparatus according to the present invention is applied to an image reading apparatus of a tandem type color copying machine (hereinafter simply referred to as “copying machine”) will be described with reference to the drawings.
(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.

A 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.
(1-1) Configuration of Printer Unit The printer unit 2 includes an image forming unit 10, a paper feeding unit 20, and a control unit 30. The printer unit 2 transmits image data generated by the image reading unit 3 or an external terminal device. Based on the received 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.
(1-2) 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 and the ADF unit 50 will be described with reference to the enlarged view of FIG.
As shown in the drawing, 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. Prepare.

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 operates in a mirror scan mode in which when the document is placed on the first platen glass 45, the light source unit 41 and the mirror unit 42 are moved in the direction of arrow B by a moving mechanism (not shown) to read the document. Control is performed by the control unit 30 as described above. On the other hand, when the document is placed on the document feed tray 52 of the ADF unit 50, the control unit is operated so that the document is transported so as to pass over the second platen glass 46 and operates in a sheet through mode for reading the image. 30.

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 freely opened and closed. Accordingly, 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 the document feed tray 52, the ADF unit main body 51, and the document discharge tray 53.

The ADF unit main body 51 includes a conveyance path 510 formed so that a document passes over the second platen glass 46, and a pickup roller 54, a pair of rolling rollers 55 for feeding the document through the conveyance path 510, A registration roller pair 56, a pre-reading roller pair 57, a post-reading roller pair 58, a paper discharge roller pair 59, and the like are provided.
In the sheet through mode, the original is conveyed and read as follows.

  First, a bundle of documents (not shown) placed on the document feed tray 52 is unwound by the pick-up roller 54 in order from the topmost document, and is wound when passing through the separation nip N1 of the pair of separation rollers 55. As a result, the sheets are fed one by one into the conveyance path 510 in the ADF unit main body 51. The separating roller pair 55 includes a sheet feeding roller 551 (with a one-way clutch) and a sheet separating roller 552 that is pressed against the sheet feeding roller 551 to form a sheeting nip N1. A load torque generating mechanism (described later) for applying a rotational load to the rotation shaft is mounted on the roller 552, and a resistance (hereinafter referred to as “carrying”) acting on the document passing through the nip N1 in the direction opposite to the carrying direction. Resistance ”). Due to this conveyance resistance, when a document is fed to the separation nip N 1, the document in contact with the separation roller 552 is separated and separated from other documents.

The document sent to the conveyance path 510 is conveyed to the registration roller pair 56 where skew correction is performed.
The original after skew correction is conveyed in the conveyance path 510 by the registration roller pair 56, the pre-reading roller pair 57, and the post-reading roller pair 58, and passes through the original reading position P on the second platen glass 46. The image on the first surface (the second platen glass 46 side) is read by the scanner unit 40. The document whose image has been read is discharged from a pair of discharge rollers 59 onto a document discharge tray 53. When performing double-sided copying or double-sided scanning, the paper discharge roller pair 59 is reversed to switch back the original, and the original is returned from the switchback conveyance path 511 to the conveyance path 510, whereby the second side of the original (first page). The image is re-conveyed in the conveyance path 510 with the side opposite to the first surface facing the second platen glass 46, and the image on the second surface is read by the scanner unit 40. The document whose image has been read is discharged from a pair of discharge rollers 59 onto a document discharge tray 53.

  The pickup roller 54 and the paper feed roller 551 of the pair of separation rollers 55 are connected via a timing belt (not shown) and are rotationally driven by a drive motor M1. The registration roller pair 56 is rotationally driven by a driving motor M2, the pre-reading roller pair 57 and the post-reading roller pair 58 are rotationally driven by the driving motor M3, and the paper discharge roller pair 59 is rotationally driven by the driving motor M4.

Further, in the conveyance path 510, a document conveyance sensor S1 for detecting a document to be conveyed is provided at an upstream position of the registration roller pair 56, and a document conveyance sensor S2 is provided at an upstream position of the document reading position P. .
The document transport sensors S1 and S2 include, for example, reflective photoelectric sensors, and an on (Hi level) signal is detected when the document is detected, and an off (Low level) signal is detected when the document is not detected. Output. The control unit 30 determines that the leading edge and the trailing edge of the document are at the leading 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 conveyance sensors S1 and S2, respectively. It can be detected that the document transport sensors S1 and S2 have been passed. Thereby, the control unit 30 can acquire the document position in the conveyance path 510, and various timings for controlling the rotational drive of the drive motors M1 to M4 such as the skew correction timing and the document reading timing. Can be obtained.

  The document feed tray 52 is provided with an elevating plate 521 for raising a placed document bundle (not shown) and placing the uppermost document at a position where it can be fed out by the pickup roller 54. . The elevating plate 521 is rotated (lifted / lowered) by a driving motor (not shown) (eg, a stepping motor) around a rotating shaft 523 provided at the upstream end in the transport direction C.

Further, the document feed tray 52 is provided with side guides 522 (a pair) for positioning the document bundle in the width direction (depth direction on the paper surface), a plurality of document placement sensors S11, and the like.
The document placement sensor S11 includes a known contact sensor, and when a document is placed, the actuator S11a is pressed to output an ON signal to the control unit 30. The control unit 30 can detect that a document is placed by an ON signal. Here, since the plurality of document placement sensors S11 are arranged at a predetermined interval in the conveyance direction C, the document size in the conveyance direction C can be detected based on the output of each sensor S11.

(1-3) Configuration of Load Torque Generating Mechanism FIG. 3 is a diagram illustrating a configuration example of the load torque generating mechanism mounted on the roller 552.
As shown in the figure, the rolling roller 552 includes a roller body 552a and a rotating shaft 552b, and the load torque generating mechanism 70 includes a torque limiter TL1 coaxially connected to one end of the rotating shaft 552b, and the other end. And a torque limiter TL2 connected via the gears 71 and 72 and the clutch CL1.

A gear 71 is attached to the rotary shaft 552b, a gear 72 is attached to the output shaft J11 of the clutch CL1, and the gears 71 and 72 are engaged with each other. The torque limiter TL2 is connected to the input shaft J12 of the clutch CL1.
The torque limiters TL1 and TL2 and the clutch CL1 are held by a holding member (not shown). Each shaft 552b, J11, J12 is rotatably supported by a holding member (not shown).

The torque limiters TL1 and TL2 are, for example, those of a coil spring type, and are set to predetermined torque limit values, respectively.
The clutch CL <b> 1 is a known electromagnetic clutch, and is turned on / off under the control of the control unit 30. When the clutch CL1 is on, a load torque combining the torque limiter TL1 and the torque limiter TL2 is applied to the rolling roller 552, and when the clutch CL1 is off, the load torque of only the torque limiter TL1 is rolled. To be granted. Thereby, the control part 30 can selectively switch the load torque (torque limit value) given to the rolling roller 552 by performing on / off control of the clutch CL1. The magnitude of the load torque indicates the magnitude of the conveyance resistance of the separation roller 552 for scooping the document. As the load torque increases, the conveyance resistance also increases. When the load torque decreases, the conveyance resistance also decreases.

Hereinafter, the torque limit value when the clutch CL1 is turned on is referred to as a “first value t1”, and the torque limit value when the clutch CL1 is turned off is referred to as a “second value t2.”
The magnitudes of the first and second values t1, t2 are set as follows.
The first value t1 is that when one original is fed to the separation nip N1, the separation roller 552 is driven by the rotation of the paper feed roller 551, and when the original is double-fed to the separation nip N1, The size is set such that the original can be separated and separated by the conveyance resistance due to the load torque applied to the roller 552. Hereinafter, the magnitude of the conveyance resistance at the first value t1 is referred to as “first resistance value”.

This “first resistance value” will be described more specifically. For example, as shown in FIG. 4A, when the document D2 is fed together with the document D1 to the separation nip N1 (multiple feed). In addition, the rotation of the winding roller 552 can be suppressed and stopped against the frictional force (maximum static frictional force) between the documents D1 and D2.
With the rotation of the rolling roller 552 stopped in this way, a conveyance resistance opposite to the conveyance direction C can be applied to the document D2, so that a slip can be generated between the document D1 and the document D2. Then, the document D2 can be separated and only the document D1 can be conveyed (document D1 indicated by a broken arrow in the figure).

The second value t2 is such that the conveyance resistance of the roller 552 (hereinafter referred to as “second resistance value”) slips between the documents D1 and D2 as shown in FIG. The size is set so as to be able to suppress and stop the rotation of the roller 552 against the sliding frictional force at the time. The second resistance value is smaller than the first resistance value.
Therefore, even when the torque limit value of the separating roller 552 is switched from the first value t1 to the second value t2 in a state where slippage occurs between the documents as shown in FIG. 4A, FIG. ), It is possible to maintain the rotation stop state of the separating roller 552, and it is possible to apply a conveyance resistance to the document D2. As a result, the sliding state between the documents D1 and D2 can also be maintained, so that the document D2 can be prevented from being fed to the document D1.

  It should be noted that the second resistance value is desirably smaller for the reason described later. Therefore, here, the second value t2 (torque limit value) is not only smaller than the first value t1, but also at that time. , That is, the second resistance value is such that the rotation of the roller 552 cannot be stopped against the frictional force (maximum static frictional force) between the documents D1 and D2. Is set to

Such first and second values t1 and t2 are obtained in advance by experiments.
In the present embodiment, the combination of the separation roller 552 and the load torque generation mechanism 70 functions as a separation member for separating the document fed by the pickup roller 54.
(2) Configuration of Control Unit FIG. 5 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 an image data storage. Part 35 and the like.
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 controls the rotational driving of the driving motors M1 to M4 to rotate the rollers and the roller pairs 54 to 59 of the ADF unit 50 and place them on the document feed tray 52. A document transport process for transporting the document to the document reading position P is performed.
During the document conveyance process, the CPU 31 further controls the on / off of the clutch CL1 of the ADF unit 50, and changes the load torque for switching the torque limit value of the winding roller 552 between the first value t1 and the second value t2. Execute the process.

(3) Rolling Roller Load Torque Changing Process FIGS. 6A to 6C are operation diagrams for explaining an outline of the rolling roller load torque changing process associated with the document conveying process in the ADF unit.
First, FIG. 6A shows a state at the start of feeding of the document D1. In the figure, a pick-up roller 54, a roller pair 55, such as a pair of rollers 56 to 59, a document conveyance path 510, and the like are schematically shown. The same applies to FIGS. 6B and 6C.

Here, the control unit 30 sets the torque limit value of the rolling roller 552 to the first value t1.
Then, as shown in FIG. 6B, when the leading edge D1a of the document D1 fed out by the pickup roller 54 passes through the winding nip N1, is corrected for skew, and then passes through the registration nip N2, the control unit 30 The torque limit value of the rolling roller 552 is switched from the first value t1 to the second value t2. The control unit 30 stops the rotational driving of the paper feed roller 551 after skew correction, and controls the drive motors M1 and M2 so that the registration roller pair 56 is rotationally driven. In this case, since the paper feed roller 551 is connected to the drive motor M1 via the one-way clutch, the original is conveyed as it is.

The switching to the second value t2 is preferably performed after the leading edge D1a of the document D1 passes through the registration nip N2 and reaches the document reading position P. This is due to the following reason.
When the leading edge D1a of the document D1 passes through the registration nip N2, the document D1 is bridged between the registration roller pair 56 and the separation roller pair 55. At this time, one registration roller pair 56 is driven to rotate in the transport direction C. The rotation driving of the paper feed roller 551 of the other pair of roller rollers 55 is stopped, but it is rotated by the action of the one-way clutch. However, back tension (tension indicated by arrow E in FIG. 6B) is generated due to the conveyance resistance of the roller 552.

  In this case, when the length of the document D1 in the conveyance direction C is long (for example, A4 longitudinal), the leading edge D1a passes the document reading position P and image reading is started as shown in FIG. After that, the rear end D1b passes through the nip N1. As a result, the back tension of the document D1 is reduced and the transport load of the document D1 is reduced and the transport speed is instantaneously increased. Therefore, the read image is compressed in the sub-scanning direction and the magnification fluctuation occurs. It will occur. As a result, there is a problem that the read image is deteriorated.

This problem can be avoided or alleviated by suppressing the decrease in back tension. However, in order to reduce the back tension of the document, simply reducing the torque limit value of the separating roller 552, which serves as a conveyance resistance, reduces the separation ability. This causes a problem of frequent double feeds.
Therefore, in order to suppress the deterioration of the image due to the fluctuation of the back tension while preventing the double feeding of the original, as described above, from the start of the original feeding until the leading edge of the original passes the registration nip. The torque limit value of the roller 552 is set to the first value t1 having a high scribing ability, and the manuscript is surely scooped. After that, the scoring ability is lowered, but if the slippage is generated between the manuscripts, the manuscript is switched. The second value t2 is set to be able to suppress the accompanying feed.

  Here, the first value t1 is maintained until the leading edge of the document passes through the registration nip. After skew correction (before the leading edge of the document passes through the registration nip), the roller that transports the document is This is because when the sheet feeding roller 551 is switched to the registration roller pair 56, the conveyance of the document is temporarily stopped. At this time, if the document has already been switched to the second value t2 and a plurality of documents are caught in the separation nip N1, there is a high possibility that the documents will be double-fed by the start of conveyance.

The first value t1 is switched to the second value t2 until the leading edge of the document reaches the document reading position P. After the image reading is started, the first value t1 is switched to the second value t2. This is because sometimes the back tension of the document fluctuates, causing a problem of magnification fluctuation.
Note that the problem of image deterioration due to such back tension fluctuations is that the conveyance path is made sufficiently long so that the document leading edge passes through the document reading position after the document trailing edge passes through the nip. It is clear that this will be solved. However, in that case, the size of the apparatus is increased. Therefore, by switching the torque limit value of the rolling roller 552 from the first value t1 to the second value t2 within the above-described period, it is possible to suppress image deterioration due to back tension variation and increase the size of the apparatus. It is configured to avoid this.

FIG. 7 is a flowchart showing the control content of the “rolling roller load torque changing process” executed by the control unit 30.
This control is performed as a subroutine of a main flowchart (not shown) for controlling the entire copying machine 1. This control is executed at the time of reading a document in the sheet through mode, and is performed in parallel with the above-described document transport process.

As shown in the figure, the control unit 30 first sets the torque limit value of the rolling roller 552 to the first value t1 (step S101).
Then, the feeding of the document is started (step S102), and the document fed out by the pickup roller 54 is passed through the pair of rolling rollers 55 and skew corrected, and then the leading edge of the document passes through the registration nip N2 of the registration roller pair 56. If it passes (step S103: Yes), the control unit 30 switches the torque limit value of the rolling roller 552 to the second value t2 (step S104).

In step S103, whether the leading edge of the document has passed the registration nip N2 of the registration roller pair 56 is determined using the output information of the document conveyance sensor S1 on the upstream side of the registration roller pair 56 as follows. Can be done.
As described above, the control unit 30 can detect that the leading edge of the document passes the detection position of the document conveyance sensor S1 by detecting the rising edge of the output of the document conveyance sensor S1. The time (J1) (including the time required for skew correction) from when the leading edge of the document passes the registration nip N2 from the detection position can be obtained in advance by experiments. Accordingly, the control unit 30 checks whether or not time (J1) has elapsed from the time when the leading edge of the document has passed the detection position of the document conveyance sensor S1, so that the leading edge of the document has passed the registration nip N2. It can be determined whether or not.

  Next, if the rear end of the original passes through the original reading position P (step S106: Yes) and the image reading is completed and there is a next original (step S107: Yes), the process returns to step S101, and the separation roller 552 is returned. The torque limit value is returned to the first value t1, and the processes in subsequent steps S102 to S106 are repeated. If there is no next original (step S107: No), the process returns to the main flowchart (not shown).

In step S106, whether or not the trailing edge of the document has passed the document reading position P is determined by using the output information of the document transport sensor S2 on the upstream side of the document reading position P and the determination in step S103. Similarly, it can be performed as follows.
As described above, the control unit 30 can detect that the trailing edge of the document passes the detection position of the document conveyance sensor S2 by detecting the falling edge of the output of the document conveyance sensor S2. Further, the time (J2) until the trailing edge of the document passes from the detection position to the document reading position P can be obtained in advance by experiments or from the conveyance speed and the distance from the detection position to the document reading position P. Accordingly, the control unit 30 checks whether or not the time (J2) has elapsed since the trailing edge of the document has passed the detection position of the document conveyance sensor S2, so that the trailing edge of the document is at the document reading position P. It is possible to determine whether or not it has passed.

In step S107, whether or not there is a next document can be determined by whether or not the document placement sensor S11 is switched on.
The ADF unit 50 configured as described above sets the torque limit value of the separating roller 552 to the first value t1 before reaching the document reading position P after the leading edge D1a of the document D1 passes through the registration nip N2 of the registration roller pair 56. To the second value t2 to reduce the transport resistance (from the first resistance value to the second resistance value). As a result, until the leading edge D1a of the document D1 passes through the registration nip N2, the conveyance resistance for the document passing through the separation nip N1 can be made large enough to be able to be crushed, and the subsequent conveyance resistance is reduced. Since the size is reduced, fluctuations in the back tension and the conveyance speed when the trailing edge D1b of the document D1 passes through the nip N1 can be made smaller than before. Thereby, it is possible to suppress the magnification fluctuation due to partial compression of the read image, and it is possible to suppress deterioration of the read image.
<Second Embodiment>
In the ADF unit of the second embodiment, the second value of the torque limit value of the separating roller 552 is changed for each paper type of thick paper, plain paper, and thin paper according to the thickness of the document to be fed. In the first embodiment, when the document is fed due to the switching to the second value, correction is performed to increase the second value. It is different from the ADF unit 50.

Here, “document feed” caused by switching to the second value means that the leading edge of the document that has been fed to the separation nip passes through the separation nip after switching to the second value. It means a phenomenon.
Since other configurations are basically the same as those of the ADF unit 50 of the first embodiment, the same configurations are denoted by the same reference numerals and description thereof is omitted.

(1) Configuration for Determining Document Paper Type FIG. 8A is a schematic diagram for explaining a configuration for determining the document paper type provided in the ADF unit according to the present embodiment.
As shown in the figure, a document transport sensor S3 and a document thickness detection sensor S4 are provided on the downstream side of the pair of roller 55.

  The document conveyance sensor S3 is composed of, for example, a reflection type photoelectric sensor like the document conveyance sensors S1 and S2 described in the first embodiment, and outputs a detection result to the control unit 30 (see FIG. 5). The document thickness detection sensor S4 is composed of two well-known distance measuring sensors arranged opposite to each other so as to sandwich the document conveyance path, and is detected by the distance between the two distance measuring sensors and each distance measuring sensor. The difference (original thickness) from the distance to the original is output to the control unit 30.

  The control unit 30 obtains the detection timing of the document thickness from the output of the document transport sensor S3. Specifically, when the rising edge of the output of the document transport sensor S3 is detected (the leading edge of the document is detected), the thickness of the document is detected from the output result of the document thickness detection sensor S4. Then, if the detected thickness of the original is within a specified range of the thickness of “plain paper”, the control unit 30 determines that the paper type of the original is “plain paper” and specifies the thickness of “plain paper”. When it is larger than the range, it is determined as “thick paper”, and when it is smaller than the specified range of the thickness of “plain paper”, it is determined as “thin paper”.

Information indicating the prescribed range of the thickness of “plain paper” (hereinafter also referred to as “paper type information”) is stored in the ROM 32 of the control unit 30. The paper type information may be configured to store the prescribed ranges of the thickness of “thick paper” and “thin paper” together with the prescribed range of the thickness of “plain paper”.
The document thickness detection sensor S4 may be arranged downstream of the document transport sensor S3. In this case, the thickness of the document may be detected when a predetermined time elapses after the leading edge of the document is detected by the document conveyance sensor S3 and the leading edge passes the position of the document thickness detection sensor S4.

(2) Configuration for Determining Document Advancing FIG. 8B is a schematic diagram for explaining a configuration for detecting and determining document advancing. Here, the output information of the document transport sensor S3 is used as follows.
If document feeding has occurred, for example, as shown in the figure, when the trailing edge D1b of the document D1 transported in the transport path 510 passes through the document reading position P, the nip N1 is viewed. The leading edge D2a of the next document D2 is in a state of passing through the nip N1 and coming to the downstream side. At this time, since the ON signal indicating the detection of the document is output from the document conveyance sensor S3, the control unit 30 can determine that the document is being fed.

It should be noted that the timing for detecting the document feed is not limited to when the trailing edge D1b of the document D1 passes the document reading position P. It may be any time after the trailing edge D1b of the document D1 has passed the detection position of the document transport sensor S3 and before the next document D2 is fed out and transported.
(3) Mechanism for generating load torque to roller roller FIG. 9 is a diagram showing a configuration example of the load torque generating mechanism of the present embodiment.

As shown in the figure, the load torque generating mechanism 170 has a configuration in which, in addition to the torque limiters TL1 and TL2, three torque limiters TL3 to TL5 are connected to the rotating shaft 552b of the roller 552.
Torque limiter TL3 is connected to gear 73 via clutch CL2, torque limiter TL4 is connected to gear 74 via clutch CL3, and torque limiter TL5 is connected to gear 75 via clutch CL4.

The clutches CL <b> 2 to CL <b> 4 are known electromagnetic clutches similar to the clutch CL <b> 1 and are turned on / off under the control of the control unit 30.
The controller 30 can selectively switch the load torque (torque limit value) applied to the roller 552 by changing the combination of the torque limiters TL2 to TL5 to be operated by controlling the clutches CL1 to CL4 on and off. it can.

FIG. 10 is a table showing an example of the first value t1, the second value t2 set for each paper type, and the operation control of the torque limiters TL1 to TL5 at each value.
As shown in the figure, in the present embodiment, the torque limit values of the torque limiters TL1 to TL5 are 90 gf · cm, 100 gf · cm, 110 gf · cm, 120 gf · cm, and 130 gf · cm.

The first value t1 is a value obtained by operating (turning on) all of the torque limiters TL1 to TL5, which is 550 gf · cm.
Further, the second value t2 when the original is thick paper can be switched to three stages of 420 gf · cm, 430 gf · cm, and 440 gf · cm, and the initial value is a value obtained by turning on the torque limiters TL1 to TL4, 420 gf. -It is cm (◎ mark). When the follow-up occurs at the initial value, the control unit 30 turns off the torque limiter TL4 and turns on the torque limiter TL5, and switches the second value t2 to 430 gf · cm. If the feed still occurs, the torque limiter TL3 is turned off, the torque limiter TL4 is turned back on, and the second value t2 is controlled to be switched to 440 gf · cm.

Similarly, the second value t2 when the original is plain paper and thin paper can also be switched to three stages, and the initial values are 320 gf · cm and 200 gf · cm (◎).
The second value t2 for each of thick paper, plain paper, and thin paper is obtained by experiments. The second value t2 is larger for thick paper than for thin paper. For example, when two originals are rolled and bitten into the nip N1, the thicker the original is, the more the distance between the original is. Since the friction force is increased due to the pressure contact, the feeding is likely to occur.

  Also, even if the document has the same thickness, the frictional force between the document and the document changes depending on the amount of moisture absorbed by the document and the type of image (photograph, text, etc.). The second value t2 cannot be made too small. Note that the original state (moisture absorption amount), image type, and the like do not vary greatly when viewed in units of a bundle of originals set on the original feed tray. For this reason, the initial value of the second value t2 is assumed here based on a predetermined document state (moisture absorption amount) and on the premise of a document of an image type (for example, characters) that is generally frequently used. It is set, and when the feed occurs, the value is corrected (increased). This is because the second value t2 (particularly the initial value) can be set smaller.

The maximum value of the second value t2 of each paper type is set to a size that can suppress the document feed regardless of the document state and the image type. Here, an intermediate value between these is set as a value between the initial value and the maximum value.
The initial value and maximum value of the second value t2 for each paper type are obtained in advance by experiments. In addition, a value between the initial value and the maximum value is obtained by experiment and set in advance so that the carry can be suppressed on the premise of a document that is different from the original state (moisture absorption amount) and the image type. It doesn't matter.

(4) Rolling Roller Load Torque Changing Process FIG. 11 is a flowchart showing the control content of the “rolling roller load torque changing process” executed by the controller 30 in the present embodiment.
Here, the above-described paper type information (information indicating the prescribed range of the thickness of plain paper) and various types of information in the setting table F shown in FIG. 10 are stored in the ROM 32 of the control unit 30. The RAM 33 also stores second value storage units R1, R2, and R3 that store second value setting values for thick paper, plain paper, and thin paper, and a paper type that stores the paper type that is detected and determined for the document thickness. An area for the storage unit R4 is provided.

  As shown in FIG. 11, first, the control unit 30 sets an initial value to the second value setting value of each paper type (step S201). Specifically, the initial values (420 gf · cm, 320 gf · cm, 200 gf · cm) of the second values corresponding to the thick paper, plain paper, and thin paper are acquired from the setting table F stored in the ROM 32. , Are set in the second value storage units R1, R2, R3 of the RAM 33, respectively.

Next, the control unit 30 sets the torque limit value of the rolling roller 552 to the first value t1 (step S202).
When the feeding of the document is started (step S203), the thickness of the fed document is detected (step S204). The control unit 30 determines the paper type of the original by comparing the detected thickness of the original, the paper type information stored in the ROM 32, and the specified range of the thickness of the plain paper (steps S205 and S207). At this time, the determined paper type is stored in the paper type storage unit R4 of the RAM 33.

As a result of the determination, in the case of plain paper (step S205: Yes), the “second value set value of plain paper” stored in the second value storage unit R2 of the RAM 33 is set to the second value t2. (Step S206).
If the determined result is thick paper (step S207: Yes), the “second value setting value of thick paper” stored in the second value storage unit R1 is set to the second value t2 (step S208). If it is neither plain paper nor thick paper (steps S205 and 207: No), the “second value setting value for thin paper” stored in the second value storage unit R3 is set to the second value t2. Set (step S209).

Thereafter, if the skew-corrected leading edge of the document passes through the registration nip N2 of the registration roller pair 56 (step S210: Yes), the control unit 30 sets the torque limit value of the separation roller 552 to the above-described steps S206 and S208. , S209 to switch to the second value t2 set (step S211).
Then, when the trailing edge of the document passes the document reading position P (step S212: Yes) and the image reading is completed, it is confirmed whether or not the document is being fed (step S213).

  If document feeding has occurred (step S213: Yes), the control unit 30 raises the second value setting value of the fed document sheet type (step S214). Here, the control unit 30 transfers the second value storage unit (any one of R1, R2, and R3) corresponding to the paper type stored in the paper type storage unit R4 of the RAM 33 from the setting table F of the ROM 32. A second value greater than is obtained and set.

Thus, when the original of the same paper type is fed next time, the carry-forward can be suppressed.
On the other hand, if no document feed has occurred (step S213: No), step S214 is skipped.
If there is a next original (step S215: Yes), the process returns to step S202, the torque limit value of the rolling roller 552 is returned to the first value t1, and the processes of subsequent steps S203 to S215 are repeated. If there is no next original (step S215: No), the process returns to the main flowchart (not shown).

  In the present embodiment, the second value t2 is set for each paper type of the document, and means for correcting the second value t2 is provided. Therefore, the second value t2 (especially the initial value) is set to be larger than that in the first embodiment in which the second value t2 corresponds to all paper types and is fixed. It becomes possible to make it smaller. In particular, it can be reduced in the case of thin paper or plain paper (see FIG. 10).

As a result, the back tension when the trailing edge of the original passes through the nip and the fluctuation in the conveyance speed can be made smaller than in the first embodiment, and the deterioration of the read image is further suppressed. can do.
[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 above embodiment, the configuration has been described in which the scooping member for scooping the document fed by the pickup roller 54 is a combination of the scooping roller 552 and the load torque generating mechanism 70, but is not limited thereto. .
For example, the separating roller 552 can be configured to rotate in the direction opposite to the document conveying direction in response to the driving force from the driving motor, and to convey the document by conveying resistance due to rotational torque. In this case, for example, when a DC motor is used as the drive motor, the rotational torque can be switched by changing the supply current value, and the magnitude of the conveyance resistance applied to the document can be changed.

  For example, instead of a rolling roller, a rolling pad can be used as a rolling member. In this case, the separation pad is pressed against the paper feed roller by an appropriate actuator mechanism such as a spring and solenoid to form a separation nip, and the conveyance resistance applied to the document can be changed by switching the pressing force. Can be configured. Moreover, it may replace with a solenoid and may be made to press a spreading pad using a cam mechanism. When a cam mechanism or the like is used, the pressing force can be changed in multiple steps or continuously, so that, for example, the conveyance resistance may be controlled more finely.

  (2) In the above embodiment, a load torque generating mechanism is shown in which the torque limiter TL1 is attached to one end of the rotating shaft 552b of the roller 552, and another torque limiter (TL2 or the like) is attached to the other end. However, the present invention is not limited to this. For example, all of the torque limiter TL1 and other torque limiters (TL2 and the like) may be attached to one end or the other end of the rotating shaft 552b.

Moreover, although the structure which used the gear for connecting a some torque limiter was shown, it may replace with a gear and may be set as the structure connected with a belt.
The structure of the torque limiter mounting structure can be selected as appropriate according to the specifications of the ADF unit (such as the layout of the internal space).
(3) In the above-described embodiment, the configuration using the document thickness detection sensor including the two distance measuring sensors is shown, but the present invention is not limited to this. For example, in the above-described embodiment, it is only necessary to have a measurement accuracy that can determine the type of paper such as thick paper, plain paper, and thin paper. Therefore, it is possible to use a contact-type thickness measuring device that sandwiches a document from the thickness direction. In this case, it is desirable to temporarily stop the conveyance of the document when measuring the thickness so that no conveyance resistance occurs when the document is sandwiched.

  (4) In the second embodiment, the ADF unit including both the configuration for setting the second value t2 for each paper type of the document and the configuration for correcting the second value t2 has been described. It is not limited to. Even if only one of the configurations is provided, the second value t2 can be made smaller than in the first embodiment. Therefore, the back tension when the trailing edge of the original passes through the nip is adjusted. Variations can be suppressed, and deterioration of the read image can be suppressed.

  (5) In the second embodiment, the configuration is shown in which the second value t2 is set for each type of thick paper, plain paper, and thin paper classified according to the thickness of the document. However, the present invention is not limited to this. . For example, the second value t2 is set for the thick paper and the other (plain paper and thin paper) depending on the thickness of the document, and the second value t2 is set. The second value t2 may be set.

Furthermore, thick paper, plain paper, and thin paper may be classified more finely according to the thickness of the document, and the second value t2 may be set for each classification.
(6) In the second embodiment, the configuration in which the second value t2 can be switched to three levels for each paper type of the document has been described. However, the second value t2 may be two levels, four levels, and five levels. It may be configured to be switched to.

  Moreover, although the initial value of the second value t2 is set to be small and correction is performed so as to increase the value when the feed occurs, the present invention is not limited to this. For example, a configuration may be adopted in which the initial value of the second value t2 is increased, and correction is performed so that the value is decreased when no follow-up occurs. In this case, when a feed occurs because the second value t2 is reduced, it is desirable to return the value to the value before the feed and maintain the value.

In addition, an intermediate value among the switchable values is set as the initial value of the second value t2, and correction is made to increase the value if the feed occurs, and the value if the feed does not occur. A configuration may be adopted in which the correction is made to lower the value.
(7) In the above 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, but the present invention is not limited to this. For example, a configuration provided with a controller dedicated to the ADF unit 50 may be used. In this case, the controller dedicated to the ADF unit 50 is configured to execute the document transport process and the load torque change process of the winding roller in cooperation with the controller 30 of the printer unit 2.

(8) 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 improving a document separation mechanism.

DESCRIPTION OF SYMBOLS 1 Copier 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 52 Document feed tray 53 Document output tray 54 Pickup roller 55 Roller pair (roller)
551 Paper feeding roller 552 Rolling roller 56 Registration roller pair 57 Pre-reading roller pair 58 Post-reading roller pair 59 Paper discharge roller pair 70, 170 Load torque generating mechanism CL1 to CL4 Clutch N1 Rolling nip N2 Registration nip S1 to S3 Document feed sensor S4 Document thickness detection sensor TL1 to TL5 Torque limiter

Claims (6)

A document conveying device that conveys a document loaded on a document tray to a document reading position after feeding a document with a pick-up roller and applying a conveyance resistance by a separation member pressed by a feeding roller in a separation unit,
A conveyance resistance changing means for changing the magnitude of the conveyance resistance by the rolling member;
A conveying unit that conveys the document by rotationally driving a pair of conveying rollers disposed on the downstream side in the document conveying direction with respect to the separation unit;
With
The transport resistance changing means is
The conveyance resistance applied by the separation member after the leading edge of the document that has passed through the separation unit reaches the document reading position after passing through the nip of the conveyance roller pair in the conveyance unit is set to An original conveying apparatus characterized in that the value is changed to a smaller second value. A thickness detecting means for detecting the thickness of the document in the middle of the conveyance path from the webbing portion to the nip of the conveyance roller pair;
The transport resistance changing means can set the second value from a plurality of different values,
2. The document conveying apparatus according to claim 1, wherein the second value is determined according to the thickness of the document detected by the thickness detecting means. A feed detection means for detecting that a feed has occurred in the whirling section;
3. The document conveying apparatus according to claim 1, wherein the conveyance resistance changing unit performs correction to increase the second value by a predetermined amount when the follow-up is detected. The rolling member is composed of a rolling roller that is pressed by a paper feed roller to form a rolling nip, and a plurality of torque limiters that apply a rotational load to the rolling roller.
The conveyance resistance changing unit is configured to change the conveyance load from a first value to a second value by cutting a rotational load on the winding roller of a part of the plurality of torque limiters. The document conveying device according to claim 1.   An original reading apparatus comprising the original conveying apparatus according to claim 1.   An image forming apparatus comprising the document reading device according to claim 5.

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