JP4594170B2 - Image reading device - Google Patents

Description

  The present invention relates to an image reading apparatus that reads an image of a document.

  The prior art will be described with reference to FIG.

  FIG. 8 shows an image reading apparatus including an ADF (Auto Document Feeder) 1100 and a reader 1200.

  In FIG. 8, the ADF 1100 has a paper feed tray 1111 as a document table on the upper side. Documents on the sheet feed tray 1111 are sequentially fed out from the uppermost document by a sheet feed roller 1112 serving as a feeding unit. The original fed by the paper feed roller 1112 is conveyed by a pair of conveyance rollers 1113, 1114, and 1115. The documents conveyed by the conveyance roller pairs 1113, 1114, and 1115 are conveyed to the platen glass 1102 by the upstream lead roller pair 1103.

  The document conveyed to the platen glass is discharged onto the discharge tray 1116 by the downstream lead roller pair 1118.

  The reader 1200 optically reads an image of a document conveyed by the ADF 1100 by the reading unit 1201.

  Here, in the conventional machine, the upstream lead roller pair 1103 and the downstream lead roller pair 1118 are widely provided with a predetermined peripheral speed difference. The purpose is to prevent document loop formation on the platen glass 102. A loop generated in the original in the reading unit causes a shock or pitch unevenness in the read image due to resistance from the conveyance path including the platen glass 102.

  Therefore, the peripheral speed of the upstream lead roller pair 1103 is set to be higher than the peripheral speed of the downstream lead roller pair 1118. Further, by providing a difference in the roller clamping pressure between the upstream lead roller pair 1103 and the downstream lead roller pair 1118, when the document is pulled while the document is clamped between both roller pairs, the roller pair with the lower clamping pressure is used. Slips between the document and the document.

Patent Document 1 discloses that the driving speed of the downstream lead roller pair is set to be faster than the upstream conveying roller pair, and the sheet conveying force of the downstream lead roller pair is set to be weaker than the upstream conveying roller pair. ing. Furthermore, it is disclosed that when the trailing edge of the original comes out of the upstream conveying roller pair, the original conveying speed of the downstream lead roller pair is controlled to be substantially the same as the original conveying speed of the upstream conveying roller pair. ing.
Japanese Patent Application Laid-Open No. 07-304537

  However, in the configuration of Patent Document 1, the behavior of the document is disturbed by a shock when the trailing edge of the document passes through the upstream-side read roller pair, and the reading accuracy may be adversely affected by the disturbance of the document behavior. . SUMMARY OF THE INVENTION An object of the present invention is to reduce deterioration in reading accuracy due to a shock when a trailing edge of a document passes through an upstream side lead roller pair.

In order to achieve the above object, the configuration of the present invention includes a transport path for transporting a document, a reading unit for reading an image of a document transported on the transport path at a reading speed at a reading position, and a document transport direction from the reading position. An upstream side document transporting unit disposed on the upstream side and sandwiching and transporting the document; a downstream side document transporting hand disposed downstream from the reading position and transporting the document while sandwiching; and the upstream side document transporting unit When the document is being conveyed by both the upstream document conveying unit and the downstream document conveying unit, the document conveying speed of the upstream document conveying unit is set to be the downstream document. A control unit that controls the upstream side document transport unit and the downstream side document transport unit so that the speed is lower than the document transport speed of the transport unit, and the pressure changing unit includes the upstream side document transport unit. Higher than the clamping pressure of the downstream document conveying means when the leading edge of the document starts to be clamped by the downstream document conveying means while the document is being transported by both the device and the downstream document conveying means The clamping pressure of the upstream document conveying unit is changed from the clamping pressure to a clamping pressure lower than the clamping pressure of the downstream document conveying unit, and the clamping pressure of the upstream document conveying unit is lowered by the pressure changing unit. While the document is changed, the trailing edge of the document is detached from the upstream document conveying unit, and the document is held between both the upstream document conveying unit and the downstream document conveying unit, and the upstream document When the clamping pressure of the conveying means is higher than the clamping pressure of the downstream document conveying means, the conveying speed of the upstream document conveying means is equal to the reading speed, and the clamping pressure of the upstream document conveying means is the downstream document conveying. Means When lower than pressure, and controls the control unit is the upstream document conveying means and the lower stream side original conveying means as conveying speed is equal to the reading speed of the downstream document transport means .

  It is possible to reduce the deterioration of the reading accuracy due to a shock when the trailing edge of the original leaves the upstream conveying unit.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a cross-sectional view of an image reading apparatus including an ADF (Auto Document Feeder) 110 and a reader 120.

  In FIG. 1, the ADF 100 has a paper feed tray 111 serving as a document placement table on the upper side. Documents on the sheet feed tray 111 are sequentially fed out from the uppermost document by a sheet feed roller 112 serving as a feeding unit. The documents fed out by the sheet feeding roller 112 are separated one by one by a separation conveying roller 113 and a separation pad 114 constituting a separating unit. The separated document is conveyed at a predetermined reading position onto the platen glass 102 by the conveyance roller pairs 117 and 101 and the upstream side read roller pair 103 as the upstream side document conveyance means.

  A document detection sensor S that detects the leading edge and the trailing edge of the document being conveyed is provided immediately upstream of the upstream read roller pair 103.

  Here, before the original enters the platen glass 102, the leading edge of the original is brought into contact with the nip portion of the upstream lead roller pair 103 to form a loop, thereby performing skew feeding and leading edge registration. Thereafter, the original is discharged onto the discharge tray 116 by the downstream lead roller pair 118 and the discharge roller pair 115.

  At the time of double-sided reading, after the front image is conveyed on the platen glass 102 and the rear end of the original on which the image has been read passes through the flapper 119, the paper discharge roller pair 115 is driven in reverse. By rotating the discharge roller pair 115 in the reverse direction, the document is reversed and conveyed to the conveyance roller pair 101. Thereafter, after the image on the back side of the original is read by the platen glass 102, the original is reversed again by the paper discharge roller pair 115 for the orientation of the original. Further, after passing through the platen glass 102, the paper is discharged onto a paper discharge tray 116.

  The platen glass 102 is provided with a platen roller 120 and rollers 121 and 122 for stabilizing the document transportability on the platen glass 102. The platen roller 120 and the rollers 121 and 122 are arranged with a predetermined gap with respect to the platen glass 102.

  The reader 200 as a reading unit optically reads image information recorded on a document to be read such as a document, photoelectrically converts it, and inputs it as image data. The reader 200 is provided with the transparent platen glasses 202 and 102 described above. The reader 200 is provided with a first mirror unit 201 having a lamp 204 that irradiates light to the original, a reflection shade 205, and a mirror 206 that reflects light reflected from the original. The reader 200 receives the second mirror unit 209 having mirrors 207 and 208 that reflect the light from the mirror 206, the lens unit 210 through which the light from the second mirror unit passes, and the light that has passed through the lens of the range unit 210. A CCD 211 is provided.

  The reader 200 reads an image of the document conveyed by the ADF 100 to the reading position of the platen glass 102 through the platen glass 102. The reader 200 can also read an image by causing the first mirror unit 201 and the second mirror unit 209 to scan the document placed on the platen glass 202.

  The operations of the ADF 100 and the reader 200 are controlled by the control unit C. That is, the control unit C controls the operations of the first mirror unit 201, the second mirror unit, and the CCD 211 of the reader 200. The control unit C controls operations of the paper feed roller 112, the separation transport roller 113, the transport roller pair 117, 101, the upstream lead roller pair 103, the downstream lead roller pair 118, and the like of the ADF 100. A signal from the document detection sensor S is input to the control unit C.

  FIG. 3 is a diagram showing a drive configuration of the upstream lead roller pair 103 and the downstream lead roller pair. In FIG. 3, reference numeral 301 denotes a stepping motor 301 for driving the upstream lead roller pair 103 and the downstream lead roller pair. A gear 302 is press-fitted into the rotating shaft of the stepping motor 301. The gear 302 is engaged with a gear 303 that is integrally disposed with the driving roller 103 (a) of the upstream lead roller pair 103 and a gear 304 that is integrally disposed with the driving roller 118 (a) of the downstream lead roller pair 118. ing. The rotation speed of the stepping roller 301 is controlled by the control unit C.

  The number of teeth of the gear 303 is larger than the number of teeth of the gear 304. The driving side roller 103 (a) of the upstream side lead roller pair 103 and the driving side roller 118 (a) of the downstream side lead roller pair 118 are common parts and have the same outer diameter. Therefore, the downstream side lead roller pair 118 has a higher peripheral speed than the upstream side lead roller pair 103 at the gear ratio between the gear 303 and the gear 304. In this embodiment, the gear 303 has 31 teeth and the gear 304 has 30 teeth. That is, as the peripheral speed ratio, the peripheral speed of the upstream lead roller pair 103: the peripheral speed of the downstream lead roller pair 118 = 30: 31.

  The clamping pressure of the upstream lead roller pair 103 can be changed by a clamping pressure changing mechanism.

  One form of the clamping pressure changing mechanism is shown in FIG. In FIG. 2, a pressure lever 1901 is provided on the shaft 103 a of one roller of the upstream lead roller pair 103. The pressure lever 1901 is provided with a lever shaft 1901a. A torsion coil spring 1901b is provided between the pressure lever 1901 and the lever shaft 1901a. The torsion coil spring 1901b biases the pressure lever 1901 in the counterclockwise direction of FIG.

  By the biasing force of the torsion coil spring 1901b, the upstream side read roller pair 103 is given a clamping force via the pressure lever 1901 so as to clamp the document. The lever shaft 1901a is swingable and is moved by the cam 1991 to the position shown in FIG. 2A and the position shown in FIG. Depending on the rotational position of the cam 1991 (lever shaft 1901a position), the urging force by the torsion coil spring 1901b differs. By changing the rotational position of the cam 1991, the clamping pressure of the upstream lead roller pair 103 is changed. 2A shows a state where the clamping pressure is low, and FIG. 2B shows a state where the clamping pressure is high.

  The clamping pressure changing mechanism is controlled by the control unit C. That is, when the motor or the like that controls the rotational position of the cam 1991 is controlled by the control unit C, the clamping pressure of the upstream lead roller pair 103 is changed.

  In the present embodiment, the clamping pressure of the upstream lead roller pair 103 can be changed in two stages of 400 (gf) and 800 (gf) by the clamping pressure changing mechanism.

  The clamping pressure of the downstream side lead roller pair 118 is set to 600 (gf). Therefore, the clamping pressure changing mechanism (the clamping pressure of the upstream lead roller pair 103> the clamping pressure of the downstream lead roller pair 118) and the clamping pressure of the upstream lead roller pair 103 <the clamping of the downstream lead roller pair 118 Pressure) state can be set.

  FIG. 4 is a diagram showing the relationship between the position in the sub-scanning direction (document transport direction) and the document transport speed in the reading unit (platen glass) 102. A solid line in FIG. 4 indicates the conveyance speed of the document on the platen glass 102. The broken lines in FIG. 4 indicate the peripheral speeds (conveyance speeds) of the upstream lead roller pair 103 or the downstream lead roller pair 118, respectively.

  In FIG. 4, a region before the leading edge of the document enters the downstream side lead roller pair 118 is defined as a region (A). A region where the document is sandwiched between both the upstream lead roller pair 103 and the downstream lead roller pair 118 is defined as a region (B). A region after the rear end of the document is detached from the upstream side lead roller pair 103 is defined as a region (C).

  An area (E) from when the leading edge of the document enters the downstream side lead roller pair 118 until the clamping pressure of the upstream side lead load roller pair 103 is lowered from 800 (gf) to 400 (gf) by the clamping pressure changing mechanism. ), And then the area until the original passes through the reading section is defined as area (F).

  The clamping pressure of the upstream side lead roller pair 103 is set to be 800 (gf) in the region (A) and the region (E). Shortly before the trailing edge of the document at the boundary between the regions (E) and (F) is released from the upstream side lead roller pair 103, it is lowered to 400 (gf), and between the region (C) or the space between the next document and the paper Is again increased to 800 (gf).

  Here, before the trailing edge of the original comes off the upstream side read roller pair 103, the clamping pressure of the roller pair is lowered from 800 (gf) to 400 (gf). The reason for this is to reduce the shock of the read image when it is removed from the upstream-side read roller 103 at the trailing edge of the original, and this is particularly a reduction in color misregistration in the case of a color image reading apparatus.

  The clamping pressure is again increased from 400 (gf) to 800 (gf). The reason for this is that when the document shown in the area (A) pushes the leading edge toward the downstream lead roller pair 118 at the peripheral speed of the upstream lead roller pair 103, it is sufficiently conveyed to the upstream lead roller pair 103. To gain power. If there is not a sufficient conveyance force, there is a risk that document non-feeding or a decrease in conveyance efficiency may occur in a paper type having a large basis weight such as thick paper. A reduction in document conveyance efficiency causes a magnification failure (large magnification) in the sub-scanning direction (conveyance direction).

  For the above reasons, the upstream side lead roller pair 103 is provided with a clamping pressure changing mechanism. The clamping pressure of the upstream-side read roller pair 103 is set to a value that does not hinder the document conveyance efficiency in the region (A) when the clamping pressure is large. The set value when the clamping pressure is small is set so small that no shock is removed from the upstream lead roller pair 103.

Then the peripheral speed of the control clogging of the upstream-side lead roller pair 103 and the downstream-side lead roller pair 118 will be described with respect to the driving frequency control of the motor 301 with reference to FIG.

  Before the leading edge of the document enters the downstream lead roller pair 118 (area (A)), the motor 301 has a drive frequency set so that the peripheral speed of the upstream lead roller pair 103 is 101 mm / sec. At this time, the peripheral speed of the downstream side lead roller pair 118 is 104.36 (= 101 * 31/30) (mm / sec).

  The motor 301 is upstream until the nipping pressure of the upstream lead roller pair 103 is reduced to 400 (gf) by the pressure changing mechanism after the leading edge of the document enters the downstream lead roller pair 118 (area (E)). The drive frequency is set so that the peripheral speed of the side lead roller pair 103 is 100 (mm / sec). At this time, the peripheral speed of the downstream-side lead roller pair 118 is 103.33 (= 100 * 31/30) (mm / sec). The control unit C determines the timing at which the leading edge of the document reaches the downstream-side read roller pair 118 based on the document detection sensor S detecting the leading edge of the document.

  After the clamping pressure of the upstream lead load roller pair 103 is lowered from 800 (gf) to 400 (gf) by the pressure changing mechanism (region (F)), the motor 301 causes the peripheral speed of the downstream lead roller pair 118 to be The drive frequency is set to 100 (mm / sec). The peripheral speed of the upstream lead roller pair at this time is 96.77 (= 100 * 30/31) (mm / sec).

  Next, the document conveyance speed on the platen glass 102 by controlling the peripheral speeds of the upstream lead roller pair 103 and the downstream lead roller pair 118 will be described with reference to FIG.

  In (Area (A)), the document is conveyed by a system in which the leading edge is pushed into the downstream lead roller pair 118 at the peripheral speed of the upstream lead roller pair 103. The leading edge of the document is conveyed while receiving resistance of a bent conveyance path including the platen glass 102. Therefore, the reading unit (platen glass) 102 is conveyed at a conveyance speed that is about 1% slower than the peripheral speed of the upstream side read roller pair 103, and the conveyance speed of the original on the platen glass 102 is 100 (mm / sec). Become. Here, 100 (mm / sec) is a reading speed when the reader 200 reads the original, and is a speed equal to the theoretical value of the original conveyance speed at the reading position for setting the sub-scan magnification of the reading unit to 100%. It is.

  In (Area (E)), the upstream lead roller pair 103 and the downstream lead roller pair 118 are conveyed by the platen glass 102 at the peripheral speed of the upstream lead roller pair 103 which is the roller pair having the larger roller clamping pressure. The Therefore, the document conveyance speed at the reading position is 100 (mm / sec). At this time, slip occurs between the original and the downstream side lead roller pair 118.

  In the region (G)), the reading unit (platen glass) 102 is moved to the reading unit (platen glass) 102 by the peripheral speed of the downstream lead roller pair 103 which is the roller pair having the larger roller clamping pressure of the upstream lead roller pair 103 and the downstream lead roller pair 118. Are transported. Therefore, the document conveyance speed at the reading unit is 100 (mm / sec). At this time, slip occurs between the document and the upstream side lead roller pair 103.

  In (area (C)), the document is conveyed by the reading unit (platen glass) 102 at the peripheral speed of the downstream-side read roller pair 118, so the document conveying speed at the reading unit is 100 (mm / sec).

  The transport speed Vj of the upstream lead roller pair 103 and the transport speed Vk of the downstream lead roller pair 118 are set. Vk> Vj is always satisfied when transported by both the upstream side lead roller pair 103 and the downstream side lead roller pair 118.

  A speed equal to the theoretical value of the document transport speed on the platen glass 102 for setting the sub-scan magnification at the reader 200 to 100% is defined as Vs. Before the leading edge of the document conveyed by the upstream lead roller pair 103 reaches the downstream lead roller pair 118, Vj = Vs or Vj> Vs. Further, the document clamping pressure of the upstream lead roller pair 103 is Tj, and the document clamping pressure of the downstream lead roller pair 118 is Tk. When the document is sandwiched between the upstream lead roller pair 103 and the downstream lead roller pair 118, Vj = Vs when Tj> Tk, and Vk = Vs when Tj <Tk. Further, Vk = Vs when the trailing edge of the original is removed from the upstream lead roller pair 103 and is conveyed by the downstream lead roller pair 118. The control unit C controls the stepping motor 301 and the pressure changing mechanism that drive the upstream lead roller pair 103 and the downstream lead roller pair 118 so as to achieve the above settings.

  Here, in the present embodiment, a drive configuration as shown in FIG. 3 is used to control the peripheral speeds of the upstream lead roller pair 103 and the downstream lead roller pair 118. However, the present invention is not limited to this. For example, a similar effect can be obtained by arranging one motor for each roller pair drive configuration and independently controlling the drive frequency of each motor.

  In addition, the timings of the regions (A), (E), (G), and (C) vary depending on the size of the document. However, the above-mentioned effect depends on the size of the document by appropriately measuring the timing according to each size. Can be obtained.

  In the region (A), the upstream lead roller pair is rotated at a peripheral speed higher than the reading speed. However, it goes without saying that the peripheral speed of the upstream-side read roller pair 103 may be a speed that coincides with the reading speed in the case of a path shape with a small original transport load.

  With the configuration described above, the following effects can be obtained.

  A region before the leading edge of the document enters the downstream side lead roller pair 118 is a region (A), and the clamping pressure of the upstream side lead roller pair 103 is high. Accordingly, when the leading edge of the document conveyed by the upstream lead roller pair 103 pushes the leading edge toward the downstream lead roller pair 118, a sufficient conveying force is obtained. Accordingly, it is difficult for document non-feeding and conveyance efficiency to be reduced.

  Before the trailing edge of the original comes off the upstream lead roller pair 103, the clamping pressure of the upstream lead roller pair 103 becomes low. Therefore, it is possible to reduce the shock of the read image when the trailing edge of the document is detached from the upstream lead roller 103.

  The downstream lead roller pair 118 is set to have a higher peripheral speed at a constant ratio than the upstream lead roller pair 103. Therefore, while preventing the formation of a document loop in the reading unit, and in the areas (A), (E), (G), and (C) (area (B) = area (E) + area (G)) By controlling the peripheral speeds of the upstream-side read roller pair 103 and the downstream-side read roller pair 118, the document conveyance speed in the reading unit is always constant. Therefore, the magnification of the read image in the sub-scanning direction (original transport direction) is always constant.

  Further, in this embodiment, the decrease in the document conveyance speed at the reading unit with respect to the peripheral speed of the upstream-side read roller pair 103 in the region (A) is set to about 1%. However, since the reduction rate is not constant depending on the paper type and paper size, the probability of the reduction rate may be set for a general-purpose paper type and paper size. In addition, by registering the paper type and paper size in the image reading device or automatically detecting them by the image reading device before reading the image, and appropriately changing the mode for each mode based on the value, the above effects can be obtained. It is obtained regardless of.

(Second Embodiment)
Hereinafter, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 shows an image reading apparatus including an ADF 600 and a reader 700.

  In FIG. 5, a first reading mode in which a user reads a document set on a platen glass 702 of the image reading apparatus main body by moving a reading traveling body 701 (a light source, a first mirror, etc.), and the reading mode. There is a second reading mode in which the traveling body 701 is stopped at a predetermined position and the original set on the ADF is read while being fed onto the original glass of the image reading apparatus main body and conveyed.

  The ADF 100 has a paper feed tray 611 serving as a document placement table on the upper side, and the document on the paper feed tray 611 is sequentially fed out from the uppermost document by a paper feed roller 612 serving as a feeding unit. The sheets are separated one by one by the separating and conveying roller 613 and the separating pad 614 that are configured. The separated document is conveyed by a conveyance roller pair 617 and an upstream side read roller pair 603 to a platen glass 602 having a surface reading position which is a reading position of the surface image reading apparatus. Here, before the document enters the reading unit 602, the leading edge of the document abuts against the nip portion of the upstream lead roller pair 603 to form a loop, thereby performing skew feeding and leading edge registration.

  A document detection sensor S that detects conveyance of a document is provided immediately upstream of the upstream-side read roller pair 603.

  Thereafter, the document passes through the front surface reading position (platen glass 602), and is then conveyed by the intermediate lead roller pair 651 to the back surface reading position 802, which is the reading position of the back surface image reading device. Thereafter, the original is discharged onto the discharge tray 616 by the downstream read roller pair 618.

  A surface reading roller 620 is provided on the platen glass 602 so as to face the reading position of the surface image reading apparatus. The surface reading roller 620 is a white roller.

  The back side reading unit optically reads image information recorded on a document to be read such as a document, photoelectrically converts it, and inputs it as image data. The back surface reading unit includes a lamp 804, mirrors 806, 807, 808, a lens unit 810, and a CCD 817.

  The back side reading unit reads the image of the document conveyed to the reading unit 802 by the ADF 600.

  The back side reading unit 802 is provided with a white conveyance guide 652 facing the reading position of the back side image reading apparatus. The white reference adjustment of the document reading unit of the back side reading unit 802 is performed using the white conveyance guide 652.

  The reader 700 optically reads image information recorded on a document to be read such as a document, photoelectrically converts it, and inputs it as image data. The reader 700 includes platen glass 702 and 602, a lamp 704, a reflective shade 705, a 1 mirror unit 701 having a mirror 706, a 2 mirror unit 709 having mirrors 707 and 708, a lens unit 710, and a CCD 716. The reader 700 reads an image of the original conveyed by the ADF 600 to the surface reading unit via the platen glass 602.

  A document abutting portion 901 is provided for the reading mode in which the document set on the document table glass 702 is read by moving the reading traveling body 701 (light source, first mirror, etc.). A white reference member 902 serving as a white reference for the document image reading unit is provided at a position opposite to the document table glass 702 of the reader 700.

  The operations of the ADF 100 and the reader 200 are controlled by the control unit C. That is, the control unit C controls the operations of the first mirror unit 201, the second mirror unit, and the CCD 211 of the reader 200. The control unit C controls the operations of the paper feed roller 112, the separation transport roller 113, the transport roller pair 117, 101, the upstream lead roller pair 103, the downstream lead roller pair 118, and the like of the ADF 100. A signal from the document detection sensor S is input to the control unit C.

  Here, one motor is provided for each drive configuration of the upstream side lead roller pair 603 and the downstream side lead roller pair 618. The independent motors that drive the upstream side lead roller pair 603 and the downstream side lead roller pair 618 are controlled in driving frequency. By controlling the drive frequency of each motor, it is possible to independently change the peripheral speed of the upstream lead roller pair 603 and the downstream lead roller pair 618. The intermediate lead roller pair 651 is always driven to rotate at a constant speed (100 (mm / sec)).

  Next, the setting of the clamping pressure of the upstream lead roller pair 603, the intermediate lead roller pair 651, and the downstream lead roller pair 618 will be described.

  The clamping pressure can be changed on the upstream lead roller pair 603 by a clamping pressure changing mechanism having the same configuration as the clamping pressure changing mechanism described in the first embodiment. The clamping pressure of the roller pair can be changed in two stages of 400 (gf) and 800 (gf) by the clamping pressure changing mechanism.

  The clamping pressure of the intermediate lead roller pair 651 is set to 1200 (gf).

  Therefore, the clamping pressure of the upstream lead roller pair 603 is always smaller than the clamping pressure of the intermediate lead roller pair 651.

  The clamping pressure of the downstream side lead roller pair 618 is set to 800 (gf).

  Therefore, the clamping pressure of the intermediate lead roller pair 651 is always greater than the clamping pressure of the downstream lead roller pair 618.

  With reference to FIG. 6, control of the holding pressure change timing of the upstream lead roller pair 603 and the peripheral speeds of the upstream lead roller pair 603 and the downstream lead roller pair 618 by the pressure changing mechanism in the above configuration will be described.

  FIG. 6 is a diagram showing the relationship between the position of the front side document in the sub-scanning direction (document feeding direction) at the front side reading unit and the feeding speed of the document at the reading unit (platen glass) 602. The solid line indicates the document conveyance speed on the platen glass 602, and the broken line indicates the peripheral speed of the upstream-side read roller pair 603.

  The lower diagram in FIG. 6 is a diagram showing the relationship between the position of the back side document in the sub-scanning direction (document transport direction) at the back side reading unit and the document transport speed at the reading unit 802. The solid line indicates the document conveyance speed (= the peripheral speed of the intermediate lead roller 651) in the reading unit 802 on the back surface, and the broken line indicates the peripheral speed of the downstream-side read roller pair 618.

  In the upper diagram of FIG. 6, when the document on the front side is sandwiched between the upstream lead roller pair 603 and is not sandwiched between the intermediate lead roller pair 651 (area (H) shown in FIG. 6), the document is the upstream lead roller pair. At the peripheral speed of 603, it is conveyed so as to push its tip toward the downstream side lead roller pair 118. Here, since the leading edge of the document is conveyed while receiving the resistance of the bending conveyance path including the platen glass 602, the document is conveyed by the reading unit (platen glass) 602 at a conveyance speed slightly lower than the peripheral speed of the upstream lead roller pair 603. Is done.

  When the leading edge of the document enters the intermediate lead roller pair 618 and is sandwiched between the upstream lead roller pair 603 and the intermediate lead roller pair 651 (region (I) shown in FIG. 6), the upstream lead roller pair 603 and the intermediate lead roller pair 651 are conveyed by the reading unit (platen glass) 602 at the peripheral speed of the intermediate lead roller pair 651 that is the roller pair having the larger roller clamping pressure.

  Here, since the roller clamping pressure of the intermediate lead roller pair 651 is larger than that of the upstream lead roller pair 603, the document slips between the upstream lead roller pair 603 in the region (I) where the document is sandwiched between both roller pairs. It is conveyed while generating.

  6, after the leading edge of the document enters the intermediate lead roller pair 651, the clamping pressure of the upstream lead load roller pair 603 is lowered from 800 (gf) to 400 (gf) by the pressure changing mechanism described later. The area up to the area (N) and the area until the original passes through the reading section thereafter are the area (O).

  Here, the clamping pressure of the upstream side lead roller pair 603 is set to be 800 (gf) in the region (H) and the region (N), and after the document that is the boundary between the regions (N) and (O). The edge is lowered to 400 (gf) just before the end of the upstream side lead roller pair 603 is removed, and again raised to 800 (gf) between the area (J) or the sheet between the next original.

  Here, immediately before the trailing edge of the document is removed from the upstream lead roller pair 603, the clamping pressure of the roller pair is reduced from 800 (gf) to 400 (gf). The reason for this is to reduce the shock of the read image when the document is removed from the upstream lead roller 603 at the trailing edge of the document. In particular, in the case of a color image reading apparatus, color misregistration or the like is reduced.

  The reason why the clamping pressure is again increased from 400 (gf) to 800 (gf) is that the original shown in the region (H) is moved to the intermediate lead roller pair 651 at the peripheral speed of the upstream lead roller pair 603 and the leading edge thereof. This is because a sufficient conveying force is obtained for the upstream-side lead roller pair 603 when pressing the. If there is no conveyance force, original paper is not fed or conveyance efficiency is lowered in a paper type having a large basis weight such as thick paper, and a magnification failure (large magnification) occurs in the sub-scanning direction (conveyance direction).

  For the above reasons, the upstream side lead roller pair 603 is provided with a clamping pressure changing mechanism. The high setting value of the clamping pressure is set to a level that does not hinder the document conveyance efficiency in the region (H), and the low setting value is set to a level that does not cause a shock release from the upstream side read roller pair 603. ing.

  Further, after the trailing edge of the original leaves the upstream side lead roller pair 603 (region (J) shown in FIG. 6), it is conveyed by the reading unit (platen glass) 102 at the peripheral speed of the intermediate lead roller pair 118. The

  In the lower diagram of FIG. 6, when the document on the back side is sandwiched between the intermediate lead roller pair 651 and is not sandwiched between the downstream lead roller pair 618 (region (K) shown in FIG. 6), the document is placed on the intermediate lead roller pair 651. It is conveyed by a system that pushes its tip to the downstream side lead roller pair 118 at a peripheral speed. At this time, the shape of the path through which the document is conveyed is substantially flat. Therefore, the document is unlikely to receive resistance that is affected by conveyance from the conveyance path including the guide portion 652. Therefore, the back surface reading unit 802 is transported at a transport speed equal to the peripheral speed of the intermediate lead roller pair 651.

  A state in which the leading edge of the document enters the downstream lead roller pair 618 and is sandwiched between the intermediate lead roller pair 651 and the downstream lead roller pair 618 (region (L) shown in FIG. 6) will be described. In the region (L), the sheet is conveyed by the back surface reading unit 802 at the peripheral speed of the intermediate lead roller pair 651 that is the roller pair having the larger roller clamping pressure of the intermediate lead roller pair 603 and the downstream lead roller pair 618.

  Here, the roller clamping pressure of the intermediate lead roller pair 651 is larger than that of the downstream lead roller pair 618. Therefore, in the area (I) where the document is sandwiched between both roller pairs, the document is conveyed while slipping between the pair of downstream side lead rollers 618.

  Next, the setting of the peripheral speeds of the upstream lead roller pair 603 and the downstream lead roller pair 618 will be described.

  First, the upstream side lead roller pair 603 will be described.

  The driving frequency of a motor (not shown) is set so that the peripheral speed of the upstream lead roller pair 603 is 101 mm / sec before the leading edge of the document enters the intermediate lead roller pair 118 (region (H)).

  The period from when the original begins to be sandwiched between the pair of upstream lead roller pair 603 and intermediate lead roller pair 651 to when the original passes through the surface reading unit 602 (areas (I) and (J)) is the upstream side read roller pair. The drive frequency is set so that the peripheral speed of a motor 603 (not shown) is 97 (mm / sec).

  Thereafter, the upstream lead roller 603 is set to have a motor driving frequency so that the peripheral speed is again 101 mm / sec before the next original reaches the upstream lead roller pair 603.

  Next, the downstream side lead roller pair 618 will be described.

  Between the time when the leading edge of the document enters the downstream lead roller pair 651 and the time when the trailing edge of the document leaves the intermediate lead roller 651 (regions (K) and (L)), the peripheral speed of the downstream lead roller pair 618 is low. A motor driving frequency (not shown) is set so as to be 103 mm / sec.

  After the trailing edge of the document leaves the intermediate lead roller 651 (region (M)), the motor drive frequency (not shown) is set so that the peripheral speed of the downstream lead roller pair 618 is 100 (mm / sec). Yes.

  Thereafter, the downstream lead roller 618 is set to a motor driving frequency (not shown) so that the peripheral speed is again 103 mm / sec before the next original reaches the downstream lead roller pair 618.

  With the above configuration, the document transport speed is as follows in the document front side reading unit 602 and the back side reading unit 802.

  In the (region (H)) of the front surface reading unit, the document is conveyed by a system in which the leading edge is pushed into the intermediate lead roller pair 651 at the peripheral speed of the upstream lead roller pair 603. The leading edge of the document is conveyed while receiving the resistance of a bent conveyance path including the platen glass 602. Therefore, the platen glass 602 is transported at a transport speed that is approximately 1% slower than the peripheral speed of the upstream side lead roller pair 603, and the transport speed of the original on the platen glass 602 is 100 (mm / sec).

  In (Area (I)), the reading unit (platen glass) 602 uses a peripheral speed of the intermediate lead roller pair 651, which is the roller pair having the larger roller clamping pressure of the upstream lead roller pair 603 and the intermediate lead roller pair 651, at the reading unit (platen glass) 602. Be transported. The conveyance speed of the original on the platen glass 602 is 100 (mm / sec). At this time, a slip occurs between the document and the upstream side lead roller pair 603.

  (Region (J)) is conveyed by the platen glass 602 at the peripheral speed of the intermediate lead roller pair 651. Therefore, the document conveyance speed at the reading unit is 100 (mm / sec).

  In the (region (K)) of the back surface reading unit, the document is conveyed by a system in which the leading edge is pushed into the downstream side lead roller pair 651 at the peripheral speed of the intermediate lead roller pair 651. The path shape is a substantially flat shape, and the document is less likely to receive resistance from the conveyance path including the guide portion 652 that is influenced by the conveyance. Therefore, since the back surface reading unit 802 is transported by the peripheral speed of the pair of intermediate lead rollers 651, the document transport speed at the back surface reading unit is 100 (mm / sec).

  In (Region (L)), the intermediate reading roller pair 651 and the downstream reading roller pair 618 are conveyed by the back surface reading unit 802 at the peripheral speed of the intermediate reading roller pair 651 that is the roller pair having the larger roller clamping pressure. . Therefore, the conveyance speed of the document in the back side scanning unit is 100 (mm / sec). At this time, a slip has occurred between the original and the downstream lead roller pair 618.

  In (Area (M)), the back surface reading unit 802 transports the document at the back surface reading unit 802 at the peripheral speed of the downstream side read roller pair 618, so that the document transport speed at the back surface reading unit is 100 (mm / sec).

  The following effects can be obtained by the second embodiment described above.

  The intermediate lead roller pair 651 is set to have a higher peripheral speed than the upstream lead roller pair 603 in (region I). Further, the peripheral lead roller pair 618 is set to have a higher peripheral speed than the intermediate lead roller pair 651 in (region L). Therefore, it is possible to prevent document loop formation at the front side reading unit 102 and the back side reading unit. In addition, the conveyance speed of the original on the platen glass 602 is always constant by controlling the peripheral speed of the upstream-side read roller pair 603 in the areas (H) to (J) of the original image read by the surface reading unit 102. Further, the conveyance speed of the document in the back surface reading unit 802 is always constant by controlling the peripheral speed of the downstream read roller pair 618 in the regions (K) to (M) of the document image read by the back surface reading unit 802. Therefore, the magnification in the sub-scanning direction (document transport direction) of the read image is always constant on both the front and back surfaces.

  Here, the timings of the respective regions ((H) to (P)) shown in FIG. 6 vary depending on the size of the document. However, by appropriately measuring the timing according to each size, the above-described effect is achieved by the size of the document. It can be obtained regardless.

  Furthermore, in this embodiment, the decrease in the document conveyance speed at the reading unit with respect to the peripheral speed of the upstream-side read roller pair 603 in the region (H) is set to about 1%. However, since the reduction rate is not constant depending on the paper type and paper size, the probability of the reduction rate may be set for a general-purpose paper type and paper size. In addition, by registering the paper type and paper size in the image reading device or automatically detecting them by the image reading device before reading the image, and appropriately changing the mode for each mode based on the value, the above effects can be obtained. It is obtained regardless of.

(Reference form)
The reference form according to the embodiment of the present invention will be additionally described. This reference form is different from the first embodiment in that it does not have a pressure changing mechanism. Differences will be described, and the rest of the configuration is the same as that of the first embodiment, and a description thereof will be omitted. The same configuration as that of the first embodiment will be described using the same reference numerals. Refer to FIG. 1 for a schematic configuration.

  FIG. 7 is an explanatory diagram regarding the control of the peripheral speeds of the upstream lead roller pair 103 and the downstream lead roller pair 118 in the present embodiment, that is, the drive frequency control of the motor 301.

  The broken lines in FIG. 7 indicate the peripheral speeds of the upstream lead roller pair 103 and the downstream lead roller pair 118, respectively.

  Before the leading edge of the document enters the downstream lead roller pair 118 (area (A)), the motor 301 has a drive frequency set so that the peripheral speed of the upstream lead roller pair 103 is 101 mm / sec. At this time, the peripheral speed of the downstream side lead roller pair 118 is 104.36 (= 101 * 31/30) (mm / sec).

  When the document is sandwiched between both the upstream lead roller pair 103 and the downstream lead roller pair 118 (area (B)), the motor 301 has a peripheral speed of 100 (mm / sec) of the upstream lead roller pair 103. The drive frequency is set so that

  At this time, the peripheral speed of the downstream-side lead roller pair 118 is 103.33 (= 100 * 31/30) (mm / sec).

  After the trailing edge of the document is detached from the lower lead roller pair 118 (area (C)), the motor 301 has a drive frequency set so that the peripheral speed of the downstream lead roller pair 118 is 100 (mm / sec). ing. The peripheral speed of the upstream lead roller pair at this time is 96.77 (= 100 * 30/31) (mm / sec).

  Next, the document conveyance speed in the reading unit by controlling the peripheral speeds of the upstream side lead roller pair 103 and the downstream side lead roller pair 118 will be described with reference to FIG.

  In (Area (A)), the document is conveyed by a system in which the leading edge is pushed into the downstream lead roller pair 118 at the peripheral speed of the upstream lead roller pair 103. Since the leading edge of the document is conveyed while receiving the resistance of the bending conveyance path including the platen glass 102, the document is conveyed by the reading unit (platen glass) 102 at a conveyance speed that is approximately 1% slower than the peripheral speed of the upstream-side read roller pair 103. Thus, the document conveyance speed at the reading unit is 100 (mm / sec).

  In (Area (B)), the reading unit (platen glass) 102 depends on the peripheral speed of the upstream lead roller pair 103 that is the roller pair having the larger roller clamping pressure of the upstream lead roller pair 103 and the downstream lead roller pair 118. Therefore, the document conveyance speed at the reading unit is 100 (mm / sec). At this time, a slip has occurred between the original and the downstream lead roller pair 118.

  In (area (C)), the document is conveyed by the reading unit (platen glass) 102 at the peripheral speed of the downstream-side read roller pair 118, so the document conveying speed at the reading unit is 100 (mm / sec).

Sectional drawing which shows 1st Embodiment. The figure explaining a clamping pressure change mechanism. The figure which shows a drive structure. The figure explaining 1st Embodiment. Sectional drawing which shows 2nd Embodiment. The figure explaining a 2nd Example and the prior art. The figure explaining a reference form. The figure explaining a prior art.

Explanation of symbols

100 ADF
103 Upstream Lead Roller Pair 118 Upstream Lead Roller Pair 200 Leader C Control Unit

Claims (3)

A transport path through which the document is transported;
A reading unit that reads an image of a document conveyed through the conveyance path at a reading speed at a reading position;
An upstream side document conveying means disposed upstream of the reading position in the document conveying direction and configured to sandwich and convey the document;
A downstream document conveying means disposed downstream from the reading position and configured to sandwich and convey the document;
Pressure changing means for changing the clamping pressure of the upstream document conveying means;
When a document is being transported by both the upstream document transport unit and the downstream document transport unit, the document transport speed of the upstream document transport unit is lower than the document transport speed of the downstream document transport unit. A control unit for controlling the upstream document conveying unit and the downstream document conveying unit,
The pressure changing unit is configured to prevent the downstream side from being sandwiched by a pressure higher than the sandwiching pressure of the downstream side document transport unit when transporting the document by both the upstream side document transport unit and the downstream side document transport unit. Changing the clamping pressure of the upstream document conveying means to a clamping pressure lower than the clamping pressure of the document conveying means;
The trailing edge of the document is detached from the upstream document conveying unit in a state where the clamping pressure of the upstream document conveying unit is changed to be low by the pressure changing unit;
While the document is being sandwiched between the upstream document transport unit and the downstream document transport unit, when the clamping pressure of the upstream document transport unit is higher than the clamping pressure of the downstream document transport unit When the conveying speed of the upstream document conveying means is equal to the reading speed and the clamping pressure of the upstream document conveying means is lower than the clamping pressure of the downstream document conveying means, the conveying speed of the downstream document conveying means is image reading apparatus, wherein the control unit so as to be equal to the reading speed to control the lower stream side document conveying means and the upstream document conveying means.   The upstream document transporting unit and the downstream document transporting unit are driven by a common motor, and the control unit controls the operation of the common motor so that the document transporting speed of the upstream document transporting unit and the downstream document transporting unit are controlled. 2. The image reading apparatus according to claim 1, wherein the document conveying speed of the side document conveying means is changed. A transport path through which the document is transported;
A reading unit that reads an image of a document conveyed through the conveyance path at a reading speed at a reading position;
An upstream side document conveying means disposed upstream of the reading position in the document conveying direction and configured to sandwich and convey the document;
A downstream document conveying means disposed downstream from the reading position and configured to sandwich and convey the document;
Pressure changing means for changing the clamping pressure of the upstream document conveying means,
The pressure changing unit is configured to prevent the downstream side from being sandwiched by a pressure higher than the sandwiching pressure of the downstream side document transport unit when transporting the document by both the upstream side document transport unit and the downstream side document transport unit. as the lower clamping Ji圧than nipping Ji圧the document conveying means, and change the pinching Ji圧of the upstream document conveying means,
The trailing edge of the document is detached from the upstream document conveying unit in a state where the clamping pressure of the upstream document conveying unit is changed to be low by the pressure changing unit;
The speed relationship when a document is sandwiched between both the upstream document transport unit and the downstream document transport unit is expressed by the transport speed Vj of the upstream document transport unit and the transport speed Vk of the downstream document transport unit. When
Vk> Vj,
A speed equal to the theoretical value of the document conveying speed at the reading position for setting the sub-scan magnification of the reading unit to 100% is Vs, the clamping pressure of the upstream document conveying means is Tj, and the downstream document conveying means The clamping pressure is Tk,
Vj = Vs or Vj> Vs before the leading edge of the original conveyed by the upstream original conveying means reaches the downstream original conveying means.
When a document is sandwiched between both the upstream document transport unit and the downstream document transport unit,
If Tj> Tk, Vj = Vs,
In the case of Tj <Tk, Vk = Vs,
Vk = Vs when the trailing edge of the original is removed from the upstream original conveying means and is conveyed by the downstream original conveying means.
An image reading apparatus set to be

Images