JP2015107866A - Sheet transport device, image reading device, and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce double feeding of originals.SOLUTION: An original automatic transport device, when an original is fed to a nip NP between a transportation roller 5 and a separation roller 6, being press-contacted each other by a pressurizing spring 64, makes a depressurizing spring 185 pull the separation roller 6 along the direction coming away from the transportation roller 5 against the pressurizing spring 64, to prevent double feeding of the original while lowering a nip pressure. By totally separating the separation roller 6 from the transportation roller 5, an impact caused when an original comes out of between the separation roller 6 and the transportation roller 5 is reduced.

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet, an image reading apparatus that includes the sheet conveying apparatus and reads a document conveyed instead of the sheet, and a sheet that includes the sheet conveying apparatus and is conveyed by the sheet conveying apparatus. The present invention relates to an image forming apparatus for forming an image.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines, facsimile machines, and printers that form an image on a sheet are provided with an image reading apparatus that reads an original in the apparatus main body, and the original is converted into a sheet based on image reading information of the image reading apparatus. It is supposed to be copied. The image reading apparatus may include an automatic document conveying device (sheet conveying device) that automatically conveys the document to the image reading unit.

  In general, such an automatic document feeder generally separates a document tray on which a document is placed, a pickup roller that picks up and conveys a document from the document tray, and a document that is conveyed from the pickup roller one by one. A separation unit or the like is provided to convey downstream. The separation unit includes a separation pad method in which the separation conveyance roller and the separation pad are in contact with each other with a predetermined contact pressure. Furthermore, the separation unit includes a simple retard method in which a separation roller that rotates only at a predetermined torque or more and a conveyance roller are brought into contact with each other with a predetermined contact pressure, and the separation conveyance roller is rotated in a direction to push the document back upstream. There is a retard method.

  As an automatic document feeder using the retard method, there is one described in Patent Document 1. This automatic document feeder includes the following components. That is, a separation roller that is driven to rotate. A resistance member disposed to face the separation roller. A nip pressure adjusting unit for adjusting the nip pressure between the separation roller and the resistance member. A sheet thickness detector that detects the thickness of the sheet. A sheet missing detection unit that detects a state in which the sheet is removed from between the separation roller and the resistance member. After the state where the sheet is removed from between the separation roller and the resistance member is detected by the sheet missing detection unit, the nip pressure adjustment unit automatically adjusts the nip pressure according to the thickness detected by the sheet thickness detection unit. Control unit.

JP 2010-95373 A

  However, the conventional automatic document feeder adjusts the nip pressure to the characteristics such as the thickness and surface roughness of the first document among a plurality of documents placed on the document tray. Even if the characteristics of the original document are changed, the nip pressure suitable for the original document cannot be adjusted. For this reason, the conventional automatic document feeder sometimes double feeds when the document characteristics change. Further, when the trailing edge of the sheet passes through the nip between the separation roller and the conveyance roller, the conveyance speed of the sheet may change. In such a case, there is a problem that an impact is generated on the sheet.

  The present invention provides a sheet conveying apparatus that reduces the double feeding of sheets and reduces the impact when the sheet passes through the separation roller and the conveying roller, an image reading apparatus including the sheet conveying apparatus, and an image forming apparatus. There is.

  The sheet conveying apparatus according to the present invention includes a rotating body, a conveying resistance unit, and a plurality of sheets conveyed by a nip between the rotating body and the conveying resistance unit, with the rotating body and the conveying resistance unit being pressed against each other. Separation means that separates and conveys the sheet, and a separation operation unit that separates the rotating body and the conveyance resistance unit, the separation operation unit between the start and the end of conveyance of the sheet The rotary body and the conveyance resistance section are separated after the pressure contact pressure of the nip is lowered.

  An image reading apparatus according to the present invention includes a document conveying device that conveys a document and a reading unit that reads a document conveyed by the document conveying device, and the document conveying device is the sheet conveying device described above. It is said.

  An image forming apparatus of the present invention includes a sheet conveying apparatus that conveys a sheet, and an image forming unit that forms an image on a sheet conveyed by the sheet conveying apparatus, and the sheet conveying apparatus is the above-described sheet conveying apparatus. It is characterized by that.

  In the sheet conveying apparatus of the present invention, the pressure contact pressure between the rotating body and the conveyance resistance portion is lowered during the conveyance of the sheet. , Sheet double feeding can be prevented. In addition, the sheet conveying apparatus of the present invention is configured to separate the rotating body and the conveyance resistance unit before the sheet passes between the rotating body and the conveyance resistance unit. It is possible to prevent the occurrence of an impact when passing between the rotating body and the conveyance resistance portion.

  The image reading apparatus according to the present invention includes a sheet conveying device that can prevent double feeding even if the sheet characteristics change, so that the sheet reading failure is eliminated, and the sheets can be read one by one. Further, since the rotating body and the conveyance resistance portion are separated before the sheet passes between the rotation body and the conveyance resistance portion, the sheet conveyed downstream passes between the rotation body and the conveyance resistance portion. It is possible to prevent a decrease in image reading accuracy due to fluctuations in the sheet conveyance speed.

  The image forming apparatus of the present invention includes a sheet conveying device that can prevent double feeding even if the sheet characteristics change, so that sheets that do not form an image due to overlapping of sheets do not occur. Images can be formed one by one. Further, the rotating body and the conveyance resistance portion are separated from each other before the sheet passes between the rotation body and the conveyance resistance portion. For this reason, it is possible to prevent occurrence of a decrease in image magnification failure due to fluctuations in the sheet conveyance speed when the sheet conveyed downstream passes between the rotating body and the conveyance resistance unit.

FIG. 3 is a cross-sectional view of the image forming apparatus according to the embodiment of the present invention along the sheet conveying direction. FIG. 3 is a schematic cross-sectional view along the document conveyance direction of an automatic document conveyance device as a sheet conveyance device according to an embodiment of the present invention. FIG. 3 is a partially enlarged view of a pressure adjusting / separating mechanism in FIG. 2 and its periphery. FIG. 4 is an enlarged view of a pressure adjustment / separation mechanism in FIG. 3. FIG. 5 is an external perspective view of a pressure adjusting / separating mechanism having a separation roller unit in the automatic document feeder of FIG. 4. FIG. 6 is a rear view of FIG. 5. It is an external appearance perspective view of a separation roller unit and its peripheral part. It is a bottom view of a separation roller unit. FIG. 3 is a control block diagram of a portion related to the present invention in the automatic document feeder of FIG. 2. 3 is a flowchart of document processing of the automatic document feeder in the automatic document feeder of FIG. 2. 6 is a flowchart for separating a transport roller and a separation roller when a document is not transported. It is a table | surface which shows the predetermined time T1 by the document size in embodiment of this invention. It is a figure which shows the relationship between the nip pressure by the document size and time in embodiment of this invention.

  Hereinafter, an image forming apparatus as an embodiment of the present invention and an automatic document conveying apparatus as a sheet conveying apparatus will be described.

(Image forming apparatus 101)
FIG. 1 is a cross-sectional view of the image forming apparatus according to the embodiment of the present invention along the sheet conveying direction.

  The image forming apparatus 101 is, for example, a copying machine, and includes an apparatus main body 101A, an image reading apparatus 102 provided on the upper part of the apparatus main body, and an automatic document feeder 1 provided on the image reading apparatus 102. Has been.

  The automatic document feeder 1 automatically feeds a document D as a sheet placed on a document feed tray 2 as a sheet stacking unit to an image reading device 102 by a user. The document feed tray is provided with document size detection sensors 3, 31, 32 as sheet size detection means, and these sensors can detect the sheet size. The image reading device 102 receives the reflected light of the light applied to the original conveyed by the image reading unit R, optically reads the original and converts it into an electrical signal, and image data (image data) based on the electrical signal. Reading information).

  The apparatus main body 101A of the image forming apparatus 101 forms a copy image on a sheet based on image data. The apparatus main body 101 </ b> A operates the exposure unit 123 based on an electrical signal or image data of an image of a document to form an electrostatic latent image on the surface of the rotating photosensitive drum 121. The electrostatic latent image is developed (supplied with toner) by the developing device 124 and becomes a toner image.

  On the other hand, sheet placement units 137a, 137b, 137c, and 137d loaded with sheets S of various sizes are disposed below the apparatus main body 101A. The sheets S of the sheet placement units 137a, 137b, 137c, and 137d are taken out one by one by the feeding rollers 138a, 138b, 138c, and 138d and transferred to the conveying roller 131. The sheet is also delivered from the manual feed tray 137e to the feeding roller 138e.

  Thereafter, the sheet S is straightly corrected by the registration roller pair 136 and aligned with the toner image on the photosensitive drum 121, and is supplied between the photosensitive drum 121 and the transfer charger 125. The The toner image on the photosensitive drum is transferred to the sheet S by the transfer charger 125 and separated from the photosensitive drum 121 by the separation charger 126. The cleaner 127 cleans the surface of the photosensitive drum 121 to which the toner image is transferred. The charger 122 charges the surface of the photosensitive drum 121 in preparation for the next exposure.

  On the other hand, the sheet S to which the toner image has been transferred is conveyed to the fixing device 129 by the conveying unit 128 and is heated and pressurized by the fixing device 129 to fix the toner image on the surface. Then, the sheet S on which the toner image is fixed is discharged to the discharge tray 130.

  The image forming apparatus 101 described above is controlled by a control unit 132 (FIG. 1) having a CPU. Further, the photosensitive drum 121, the charger 122, the developing device 124, the fixing device 129, and the like form an image forming unit 133. The control unit 132 exchanges signals with the control unit 70 described later so that the operation of the entire image forming apparatus can be performed smoothly, and the control unit 70 may be incorporated.

(Automatic document feeder 1)
FIG. 2 is a schematic cross-sectional view of the automatic document feeder 1 along the document conveyance direction.

  The automatic document feeder 1 includes the following components. That is, the document feed tray 2 on which the document D is loaded. Document size detection sensors 3, 31, 32 which detect that the document D is placed on the document feed tray and detect the size of the document. A pickup roller 4 that picks up the document D loaded on the document feed tray 2. A separation unit 7 having a conveying roller 5, a separation roller 6, and a pressure spring 64 that separates and feeds only one of the originals sent from the pickup roller 4 and separates the multi-fed originals. A pressure adjusting / separating mechanism 180 that adjusts and separates the pressure contact between the conveying roller 5 and the separating roller 6. A pressure adjustment timing sensor 17 as detection means for detecting the leading edge of the document conveyed by the separation unit 7. A resist that corrects the skew of the original by abutting the leading edge of the original sent from the separation unit 7 and conveys the original of the image reading apparatus 102 toward the contact glass 103 that is a reading area in accordance with the reading timing. Roller pair 8. A registration sensor 9 that is disposed between the pressure adjustment timing sensor 17 and the registration roller pair 8 and detects the leading edge of the document sent from the separation unit 7. A document transport path 20 for transporting a document. An opening 21 formed so that the document D passes through the upper side of the contact glass 103 of the image reading apparatus 102 in the middle of the document transport path 20. A white roller 10 that brings the document D into close contact with the contact glass 103 at the center of the opening 21. A pair of lead rollers 11 and 12 disposed upstream and downstream of the white roller 10. A paper discharge roller pair 13 that discharges a document on the downstream side of the read roller pair 12. A document discharge tray 14 on which documents discharged by the discharge roller pair 13 are stacked. A control unit 70 that controls the automatic document feeder 1.

(Pressure adjustment and separation mechanism 180 having the separation roller unit 60)
FIG. 5 is an external perspective view of the pressure adjusting / separating mechanism 180. FIG. 6 is a rear perspective view of FIG. FIG. 7 is an external perspective view of the separation roller unit and its peripheral portion. FIG. 8 is a bottom view of the separation roller unit.

  In the automatic document feeder 1 described above, the separation roller 6 is connected coaxially to the separation roller shaft 61 that is the rotation shaft of the separation roller 6 and the separation roller shaft 61, and gives a predetermined rotational load to the separation roller 6. A separation roller unit 60 is constituted by the torque limiter 62. The separation roller unit 60 is detachably supported by a pair of separation roller holders 63. The separation roller unit 60 can be attached to and detached from the separation roller holder 63 by the user holding the handle 69 and passing the separation roller shaft 61 through the opening 63 d of one separation roller holder 63. The pair of separation roller holders 63 are formed in an L shape and are connected and integrated by a connecting plate 66. The separation roller holder 63 is rotatably supported by a fixing member (not shown) of the automatic document feeder 1 by a support shaft 65 protruding from a rotation base end portion 63a that is one end.

  The separation roller holder 63 is urged so as to press the separation roller 6 against the transport roller 5 by a pressure spring 64 (FIG. 4). The pressure spring 64 is a compression spring, and is provided between the fixing member 1 </ b> A of the automatic document feeder 1 and the connecting plate 66 of the separation roller holder 63. A pressure adjustment timing sensor 17 that detects the leading edge of the document conveyed by the separation unit 7 is provided downstream of the separation roller 6 and the conveyance roller 5. The separation roller unit 60 approaches and separates from the transport roller 5 around the support shaft 65 according to or against the pressure spring 64 by the operation of a pressure adjusting / separating mechanism 180 described later.

  The pressure adjusting / separating mechanism 180 detachably holds the separation roller unit 60, and changes the pressure contact pressure (nip pressure) of the nip NP (FIG. 4) between the separation roller 6 and the conveyance roller 5 under the control of the control unit 70. Or the separation roller 6 is separated from the conveying roller 5. The pressure adjustment / separation mechanism 180 includes a pressure adjustment motor 181, a rotation transmission mechanism 189, a pressure adjustment cam 182, a pressure adjustment shaft 183, a pair of pressure adjustment levers 184 A and 184 B, a pair of separation roller holders 63, and a pair of pressure reductions. A spring 185, a pressure spring (FIGS. 6 and 8) 64, and the like are included. The separation roller 6 and the torque limiter 62 constitute a conveyance resistance unit, and the conveyance resistance unit, the conveyance roller 5 as a rotating body, and the pressure spring 64 as a first elastic body constitute a separation unit. Yes. The pressure adjusting / separating mechanism 180 and the control unit 70 constitute pressure contact pressure changing means.

  The rotation transmission mechanism 189 is a mechanism that transmits the rotation of the pressure adjustment motor 181 to the pressure adjustment cam 182, and includes a belt 190 and gears 191, 192, and 193. The rotation shaft 194 of the gear 193 is also a rotation center shaft of the pressure adjustment cam 182 that is an eccentric cam and the rotation flag 186. For this reason, the gear 193, the pressure adjusting cam 182 and the rotation flag 186 are rotated together. The rotation flag 186 is formed with a step 186 a and a plurality of radial slits 186 b around the rotation shaft 194. A separation detection sensor 187 is opposed to the rotation flag 186. The separation detection sensor 187 detects the slit 186b of the rotation flag 186 that rotates, and the counter 74 of the control unit 70 (FIG. 9) described later counts the slit 186b. Accordingly, the control unit 70 can adjust the pressure contact pressure of the separation roller 6 with respect to the transport roller 5. When the separation detection sensor 187 detects the step 186 a of the rotation flag 186, the control unit 70 can detect that the separation roller 6 is completely separated from the transport roller 5.

  The pressure adjusting shaft 183 is rotatably supported by a fixing member (not shown). Rotating base end portions 184Aa and 184Ba, which are one end of a pair of pressure adjusting levers 184A and 184B, are integrally provided at both ends of the pressure adjusting shaft 183. A pair of tension springs as a second elastic body is provided between both corners of the rotation end 184Bb which is the other end of one pressure adjusting lever 184B and a corner 63b of the pair of separation roller holders 63. A pressure reducing spring 185 is provided. On both sides of the rotation end 184Bb of the pressure adjusting lever 184B, a rotation restricting pin 67 (one is not shown) protrudes. The rotation restriction pin 67 is engaged with a rotation restriction hole 68 that is a long hole formed in the rotation end portion 63 c of the separation roller holder 63. The pressure spring (FIG. 4) 64 is a compression spring and is provided between the fixing member 1 </ b> A of the automatic document feeder 1 and the connecting plate 66 of the separation roller holder 63. The rotation restricting pin 67 and the rotation restricting hole 68 are separation operation portions.

  In the above configuration, the pressure reducing spring 185 normally pulls (acts) the pressure adjusting lever 184B upward (in the direction of arrow A). The pressure adjustment lever 184B is integral with the pressure adjustment shaft 183. The pressure adjusting shaft 183 is integrally provided with another pressure adjusting lever 184A. For this reason, when the pressure reducing spring 185 pulls the pressure adjusting lever 184A upward (in the direction of arrow A), the pressure adjusting lever 184A also rotates upward. However, the pressure adjusting lever 184A is received by the pressure adjusting cam 182 and is restricted from rotating. As a result, the pressure adjusting lever 184B is also restricted from rotating upward. At this time, the rotation restricting pins 67 projecting on both sides of the pressure adjusting lever 184B are located in the middle of the rotation restricting hole 68 indicated by the broken line in FIG.

  On the other hand, the pressure spring 64 (FIG. 4) pushes the separation roller holder 63 upward (in the direction of arrow A) via the connecting plate 66. The separation roller holder 63 rotates counterclockwise in FIG. 4 about the support shaft 65, and presses the separation roller 6 against the transport roller 5 against the pressure reducing spring 185. Therefore, the pressure contact pressure (nip pressure P) between the separation roller 6 and the conveyance roller 5 is a difference (P = PA−PB) between the push-up force PA of the pressure spring 64 and the tensile force PB of the pressure-reduction spring 185. In this case, at least the separation roller 6 out of the conveying roller 5 and the separation roller 6 is a rubber roller or a resin roller having a large friction coefficient and elasticity, so that the elastic roller is elastically deformed. The rollers are in pressure contact.

  FIG. 9 is a control block diagram of a portion related to the present invention in the automatic document feeder 1. The controller 70 controls the pressure adjustment motor 181 based on the document detection operation of the pressure adjustment timing sensor 17 and the registration sensor 9 to operate the pressure adjustment / separation mechanism 180. The control unit 70 controls the paper feed driving unit 71 having a motor for rotating the transport roller 5 and the pickup roller 4 to rotate the transport roller 5. Similarly, the control unit 70 controls the paper feed driving unit 72 having a motor for rotating the registration roller pair 8 to stop the rotation of the registration roller pair 8.

  Next, in the above configuration, the operation of the automatic document feeder 1 with the pressure adjusting / separating mechanism 180 as a main component will be described based on the flowchart of FIG.

  The control unit 70 rotates the pickup roller 4 to convey the original G to the nip NP between the conveyance roller 5 and the separation roller 6 and starts feeding. At this time, when the pushing force of the pressure spring 64 is PA1, the tensile force of the pressure reducing spring 185 is PB1, and the nip pressure is P1, the initial value of the nip pressure is (P1 = PA1-PB1). As a result, the conveying roller 5 and the separation roller 6 sandwich the document with the nip pressure P1 and rotate and convey it. When the pressure adjustment timing sensor 17 detects the leading edge of the document (S101), the control unit 70 rotates the pressure adjustment motor 181.

  In FIG. 5, the pressure adjusting motor 181 rotates at the rotation speed V1, thereby rotating the pressure adjusting cam 182 in the arrow B direction and rotating the pressure adjusting lever 184A in the arrow B direction. In this case, in FIG. 5, the rotation restricting pin 67 is in contact with the lower end 68a of the rotation restricting hole 68, but starts to rotate in the arrow B direction from the position indicated by the broken line in FIG. Then, the pressure adjusting shaft 183 and the pressure adjusting lever 184B integrated with the pressure adjusting lever 184A also rotate in the arrow B direction. At this time, the pressure adjusting lever 184B moves in the direction of the arrow B while moving the rotation restricting pin 67 (FIGS. 3 and 4) below the rotation restricting hole 68 and pulls the pressure reducing spring 185 downward.

  Then, the tensile force PB of the pressure reducing spring 185 becomes PB2 (> PB1) larger than PB1, and a certain nip pressure P is changed from the initial value P1 by the difference between the tensile force of the pressure reducing spring 185 and the pushing force of the pressure spring. It changes to the nip pressure of P2 (= PA1-PB2). In this case, since (PB2> PB1), (P1> P2) is established, and the nip pressure is smaller than that at the start of the document (S105). Since the controller 70 continuously rotates the pressure adjustment motor 181 at the rotation speed V1, the nip pressure gradually decreases (FIG. 13).

  As a result, first, when the nip pressure between the separation roller 6 and the conveying roller 5 is the initial value P1, the separation roller 6 as the driven rotating body overcomes the load applied to the separation roller 6 by the torque limiter 62, The conveyance roller 5 is driven to rotate. For this reason, the separation roller 6 conveys the original document with the conveying roller 5 without separating the original document even when the originals are being fed.

  However, since the nip pressure P gradually becomes smaller than the initial nip pressure P1, the separation roller 6 becomes difficult to rotate or rotates depending on the load of the torque limiter 62 from the middle of the decrease. No longer. For this reason, the separation roller 6 prevents the conveyance of the original that is in contact with the separation roller 6 when the originals are being fed in a double manner, and the original that is in contact with the conveyance roller 5 is conveyed to the registration roller pair 8. Go.

  When the nip pressure is P1, which is the initial value, the friction between the originals pressed against each other at the initial value is greater than the friction between the separation roller 6 to which the rotational load of the torque limiter 62 is applied and the original. For this reason, at first, the document is nipped between the conveying roller 5 and the separation roller 6 and rotated and conveyed even in the double feeding state. After that, as the nip pressure gradually decreases, the friction between the originals brought into pressure-contact with each other becomes smaller than the friction between the separation roller 6 to which the rotational load of the torque limiter 62 is applied and the originals. . As a result, the document that is in contact with the transport roller 5 is transported, but the document that is in contact with the separation roller 6 is not transported, and the double feed of the documents is efficiently eliminated. In this case, since the nip pressure gradually decreases, it is possible to reliably eliminate the double feeding of the originals.

  As described above, the automatic document feeder 1 first sets the nip pressure between the transport roller 5 and the separation roller 6 to the initial value P1, and then gradually decreases the nip pressure from the initial value P1. Yes. For this reason, the automatic document feeder 1 first reliably conveys a document, and thereafter, when the document is a double-fed document, the document can be separated even if the document has different characteristics. Even in this case, it is possible to prevent double feeding of documents. If the nip pressure is set to a small nip pressure from the beginning, the separation roller 6 becomes difficult to rotate due to the load of the torque limiter 62, so that the transport roller 5 and the separation roller 6 can grip and transport the document. Can not. Therefore, it is preferable that the nip pressure is initially increased and then gradually decreased.

  Thereafter, the registration sensor 9 detects the leading edge of the document conveyed downstream by the conveyance roller 5 in the document conveyance direction (sheet conveyance direction). After the detection (S105), when the predetermined time T1 has elapsed (S107), the control unit 70 changes the rotation speed of the pressure adjusting motor 181 from the initial value V1 to V2 (V1 <V2). The predetermined time T1 is counted by the counter 74 in the control unit 70, and is determined by the sheet size detected by the document size detection sensors 3, 31, 32 (FIG. 12). Then, the rotation restricting pin 67 projecting on the side of the pressure adjusting lever 184B that has been tilted with the rotation of the pressure adjusting motor 181 contacts the lower end 68a of the rotation restricting hole 68 (FIG. 4). Then, the separation roller holder 63 is rotated in the direction of arrow B in FIG. The separation roller holder 63 rotates in the arrow B direction around the support shaft 65. As the separation roller holder 63 rotates, the separation roller 6 supported by the separation roller holder 63 is completely separated from the transport roller 5 (FIG. 13).

  Of the transport roller 5 and the separation roller 6, at least the separation roller 6 is a rubber roller or a resin roller having a large friction coefficient and elasticity. Hereinafter, although the separation roller 6 will be described as having elasticity, the conveying roller 5 may also have elasticity. Initially, when the nip pressure is the initial value P1, the separation roller 6 is elastically deformed, and the separation roller 6 is pressed against the conveying roller 5. Then, when the nip pressure starts to decrease, the separation roller 6 starts to restore to the original shape, and when the separation roller holder 63 rotates slightly, the separation roller 6 is completely restored to the original shape, The separation roller 6 is completely separated from the transport roller 5 (S109). Thus, when the separation roller 6 is completely separated from the conveyance roller 5, the contact with the conveyance roller 5 is not suddenly released, but the shape of the separation roller 6 is restored. Is gradually released and then completely separated from the conveying roller 5. For this reason, the pressure contact pressure (nip pressure) between the separation roller 6 and the transport roller 5 gradually decreases, so even if the document characteristics change, the double feed of the documents is eliminated when the nip pressure according to the characteristics is reached. can do. The limit of separation of the separation roller 6 from the conveyance roller 5 is limited to the separation detection sensor 187 detecting the step 186a of the rotation flag 186 integrated with the pressure adjustment cam 182 (FIG. 5).

  Before the separation roller 6 is completely separated from the conveyance roller 5, the document reaches the registration roller pair 8 and is conveyed by the registration roller pair 8. For this reason, the predetermined time T1 varies depending on the length of the document, and from the time when the registration sensor 9 detects the leading edge of the document to the time when the trailing edge of the same document comes out between the separation roller 6 and the conveying roller 5. (FIG. 12). Thus, since the predetermined time T1 is set, even if the trailing edge of the document is located between the separation roller 6 and the conveying roller 5 that are completely separated from each other, the leading edge of the same document is the registration roller. Since the pair 8 is held, the conveyance of the document is continued. Accordingly, it is possible to prevent a decrease in image reading accuracy due to fluctuations in the sheet conveyance speed when the document passes through the separation roller 6 and the conveyance roller 5.

  When the trailing edge of the document is detected by the registration sensor 9 after the separation roller 6 is completely separated from the conveyance roller 5 (S111), the control unit 70 reverses the pressure adjusting motor 181 to rotate the pressure reducing spring 185. The original state is restored, and the separation roller 6 is brought into contact with the conveying roller 5. The nip pressure returns to the initial value P1 (S113). Then, when the pressure adjustment timing sensor 17 detects the leading edge of the subsequent document (YES in S115), the control unit 70 returns to the process S103, and performs the multifeed process when the subsequent document is overlapped. Even when the pressure adjustment timing sensor 17 has not detected the leading edge of the subsequent document (NO in S115), the control unit 70 causes the document size detection sensor 3 to load the subsequent document on the document feed tray 2. If it is detected (YES in S117), the process returns to S101. If the document size detection sensor 3 does not detect a document (NO in S117), the control unit 70 ends the document separation processing conveyance operation.

  If the leading edge of the document is not detected by the pressure adjustment timing sensor 17 in step S101, or if the leading edge of the document is not detected by the registration sensor 9 in step S105, the trailing edge of the document is not detected by the registration sensor 9 in step S111. There is. In these cases, the control unit 70 notifies the user that a document jam has occurred via the operation panel 73 (S119, S121, S123). This eliminates the need for the user to separate the separation roller 6 and the transport roller 5 from each other.

  The separation roller 6 described above is difficult to rotate following the conveyance roller 5 by a torque limiter (a driven load is applied), and prevents the double-fed original from being conveyed downstream in the original conveyance direction. There is only doing. However, the separation roller 6 is connected to a reversing clutch and a motor, and rotates following the original when the original is not double fed. When the original is double fed, the rotation of the motor is received via the reverse clutch. Thus, the double-fed document may be returned to the document feed tray 2. Further, instead of the separation roller 6, a friction plate pressed against the conveyance roller may be used. Therefore, the conveyance resistance portion is not limited to the separation roller in the present embodiment.

  By the way, at least the separation roller 6 of the conveying roller 5 and the separation roller 6 is a rubber roller or a resin roller having a large friction coefficient and elasticity. For this reason, when the automatic document feeder 1 is not used, if the carry roller 5 and the separation roller 6 are kept in pressure contact, the separation roller 6 may be plastically deformed and distorted. . If the separation roller 6 is distorted, it is difficult to prevent double feeding of the originals even if the conveyance of the originals is started.

  Therefore, the controller 70 rotates the pressure adjustment motor 181 (FIG. 5) when the conveyance of the document is completed, and when the separation detection sensor 187 detects the step 186a of the rotation flag 186, the pressure adjustment motor 181 (FIG. 5). ) Is stopped and kept in that state. As a result, the separation roller 6 is completely separated from the conveyance roller 5, the pressure contact between the separation roller 6 and the conveyance roller 5 is released, and plastic deformation of the separation roller 6 can be prevented.

  When the start key provided on the operation panel 73 is pressed by the user (YES in FIG. 11, S201), the control unit 70 rotates the pressure adjusting motor 181 in the reverse direction to move the separation roller 6 to the transport roller 5. Make contact. The control unit also controls the paper feed driving unit 71 to rotate the pickup roller 4 and the transport roller 5 (S203). As a result, the separation roller 6 and the conveyance roller 5 convey the document while preventing the document from being double-fed.

  Note that the state where the separation roller 6 is separated from the transport roller 5 is maintained as it is unless the start key is pressed by the user (NO in S201, S211 and S213).

  Thereafter, the control unit 70 determines that the conveyance of the document has been completed when a predetermined time T2 has elapsed since the pressure adjustment timing sensor 17 detected the trailing edge of the last document (YES in S205). The predetermined time T2 is counted by a counter 74 in the control unit 70. The controller 70 rotates the pressure adjustment motor 181 (FIG. 5), and when the separation detection sensor 187 detects the step 186a of the rotation flag 186, the controller 70 stops the pressure adjustment motor 181 (FIG. 5) and maintains the state. To do. As a result, the separation roller 6 is completely separated from the transport roller 5 (S207), the pressure contact between the separation roller 6 and the transport roller 5 is released, and the state is maintained (S209). As a result, plastic deformation of the separation roller 6 can be prevented.

  In the above description, the case where the separation roller 6 is completely separated from the conveyance roller 5 has been described. However, the separation roller 6 may be pressed against the conveyance roller 5 to the extent that the separation roller 6 is not plastically deformed. Good. In this case, the control unit 70 needs to stop the rotation of the pressure adjustment motor 181 before the stepped portion 186a of the rotation flag 186 is detected by the separation detection sensor 187.

  Since the image reading apparatus 102 includes the automatic document feeder 1 that can prevent double feeding, it is possible to read documents one by one without losing reading errors.

  Further, the pressure adjusting / separating mechanism 180 having the separation roller unit 60 is provided between the sheet placement portions 137a to 137d in the apparatus main body of the image forming apparatus or between the tray 137e and the registration roller pair 136 so that the weight of the sheets is increased. You may enable it to perform a transmission / separation process. In this case, the image forming apparatus can form an image on each sheet by preventing double feeding of the sheets.

  1: automatic document conveying device (sheet conveying device, document conveying device), 2: document feeding tray (sheet stacking unit), 3, 31, 32: document size detecting sensor (sheet size detecting means), 5: conveying roller ( Rotating body, separating means), 6: Separating roller (driven rotating body, conveying resistance portion, separating means), 17: Pressure adjustment timing sensor (detecting means), 62: Torque limiter (conveying resistance portion, separating means), 64: Pressure spring (first elastic body, separation means), 67: rotation restriction pin (separation operation part), 68: rotation restriction hole (separation operation part), 70: control part (pressure contact pressure changing means), 101 : Image forming apparatus, 101A: apparatus main body of image forming apparatus, 102: image reading apparatus, 133: image forming unit, 180: pressure adjusting / separating mechanism (pressure contact pressure changing means), 185: pressure reducing spring (second elastic body) ), R: image reading unit, S: DOO, G: document, NP: nip between the conveying roller 5 and the separation roller 6.

Claims (7)

Separation for conveying a sheet by separating a plurality of sheets conveyed at a nip between the rotating body and the conveyance resistance unit by bringing the rotation body, the conveyance resistance unit, and the rotation body and the conveyance resistance unit into pressure contact with each other. Means,
A separation operation unit that separates the rotating body and the conveyance resistance unit, and the separation operation unit lowers the pressure contact pressure of the nip between the start and the end of conveyance of the sheet, Separating the rotating body and the conveyance resistance portion;
A sheet conveying apparatus. The separation operation unit lowers the pressure contact between the rotating body and the conveyance resistance unit after the leading edge of the sheet passes through the nip.
The sheet conveying apparatus according to claim 1. The separation operation unit separates the rotating body and the conveyance resistance unit before a rear end of the sheet passes through the nip.
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. A sheet stacking unit on which a sheet is placed, and a sheet size detecting unit that detects the size of the sheet stacked on the sheet stacking unit,
The separation operation unit changes the pressure contact pressure according to the sheet size detected by the sheet size detection unit and changes the separation timing between the rotating body and the conveyance resistance unit.
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. The conveyance resistance unit includes a driven rotating body that is driven to rotate while being pressed against the rotating body, and a torque limiter that applies a load to the driven rotating body.
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. A document transport device for transporting a document;
Reading means for reading a document conveyed by a document conveying device,
The document conveying device is the sheet conveying device according to any one of claims 1 to 5.
An image reading apparatus. A sheet conveying device for conveying a sheet;
An image forming unit that forms an image on a sheet conveyed by a sheet conveying device;
The sheet conveying apparatus is the sheet conveying apparatus according to any one of claims 1 to 5.
An image forming apparatus.

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