JP2006176296A - Sheet carrying device and image forming device having this device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce uneven carrying of sheets, by forming a complete loop in a sheet, even if an interval between first rotary body pairs and second rotary body pairs is narrow. <P>SOLUTION: This sheet carrying device 21 has first carrier roller pairs 3 for carrying the sheet, second carrier roller pairs 4 for carrying the sheet carried by the first carrier roller pairs at a sheet carrying speed slower than the first carrier roller pairs, a sheet carrying guide 1 for guiding the sheet between the first carrier roller pairs and the second carrier roller pairs 4, and a carrying guide moving mechanism 5 for moving the sheet carrying guide to a retreat position from a sheet guide position after the sheet arrives at the second carrier roller pairs. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus that once bends and conveys a sheet, and an image forming apparatus including the apparatus in a main body of the apparatus.

  2. Description of the Related Art Conventionally, a sheet conveying apparatus that conveys a sheet is equipped in an apparatus that handles sheets such as an image forming apparatus that forms an image on a sheet and a sheet processing apparatus that performs processing on a sheet.

  An example of the image forming apparatus is a color printer that forms a color toner image by electrostatically adsorbing powdery toner onto a sheet using an electrophotographic system.

  FIG. 6 is a cross-sectional view along the sheet conveying direction of a color printer provided with a conventional sheet conveying apparatus. The color printer 101 conveys the sheet supplied from the sheet conveying apparatus 102 by electrostatically adsorbing the sheet to the transfer conveying belt 106a passing between the photosensitive drum 107 and the transfer device 106d, and the sheet is the photosensitive drum 7 of each color. The color toner images of Y (yellow), M (magenta), C (cyan), and black (B) are sequentially transferred to the sheet to form a color image.

  However, in this type of color printer 101, if the sheet conveyance speed with respect to the photosensitive drum 107 is uneven, the color toner images are displaced from each other, and the image quality is deteriorated.

  On the other hand, the sheet conveying device 102 includes a first roller pair 103 that conveys a sheet, a second roller pair 104 that conveys a sheet conveyed from the first roller pair 103, and first and second roller pairs 103, A guide member 105 or the like for guiding sheets between 104 is provided.

  The sheet conveyance speeds of the first and second roller pairs 103 and 104 and the transfer conveyance belt 106a are V1, V2, and V3, respectively. If V2 is the same as V3 and V2 and V3 are always constant, there is no deviation between the color toner images. However, the outer diameter of the driving roller 104a of the second roller pair 104 has a tolerance. Also, the outer diameter changes due to wear. For this reason, it is difficult to make V2 the same as V3. In addition, the outer diameter of the drive roller 106b of the transfer mechanism 106 also intersects and changes due to wear, so it is difficult to keep V2 and V3 constant at all times.

  Therefore, the sheet conveying speed V2 of the second roller pair 104 is made higher than the sheet conveying speed V3 of the transfer conveying belt 106a (V2> V3), and the sheet is conveyed between the transfer conveying belt 106a and the second roller pair 104. It is conceivable to cause a loop in the sheet so that the conveyance of the second roller pair 104 does not affect the sheet conveyance of the transfer conveyance belt 106a.

However, when the conveying force that the second roller pair 104 conveys while sandwiching the sheet is larger than the sheet adsorbing force of the transfer conveying belt 106a and the rigidity of the conveyed sheet is strong, for example, thick paper of about 163 g / m ² or more Is difficult to loop. For this reason, the second roller pair 104 pushes the sheet into the transfer / conveying belt 106a and slides the sheet to the downstream side with respect to the transfer / conveying belt 6a.

  Further, it is conceivable that the sheet conveyance speed V2 of the second roller pair 104 is made slower than the sheet conveyance speed V3 of the transfer conveyance belt 106a (V2 <V3) (see Patent Document 1). When V2 <V3 is set, the transfer conveyance belt 106a pulls and conveys the sheet conveyed by the second roller pair 104 from the second roller pair 104. For this reason, the second roller pair 104 becomes a sheet conveyance resistance of the transfer conveyance belt 106a, and the sheet conveyance speed V3 of the transfer conveyance belt 106a may be uneven.

  Therefore, the apparatus described in Patent Document 1 is provided with a one-way clutch or the like on the drive shaft of the second roller pair 104 so that the sheet conveying speed V1 of the first roller pair 103 is faster than the sheet conveying speed V2 of the second roller pair 104. Thus (V1> V2), the sheet is looped on the upstream side of the second roller pair 104 so that the sheet conveying speed of the transfer conveying belt 106a does not vary.

JP 2002-249258 A

  However, in recent years, the distance between the first roller pair 103 and the second roller pair 104 has become narrower as the main body size of the image forming apparatus is reduced. Further, the conveyance guide 105 that guides the sheet between the first roller pair 103 and the second roller pair 104 forms a bent path with a small curvature. Furthermore, the inner width of the conveyance guide 105 is narrowed due to the downsizing of the apparatus. The conveyance guide 105 is curved so that a manual sheet inserted by the user can be easily received from the side of the apparatus main body.

  For this reason, in the conventional sheet conveying apparatus 102, since the sheet conveying speed V1 of the first roller pair 103 is higher than the sheet conveying speed V2 of the second roller pair 104, the sheet loop gradually increases and the conveying guide becomes larger. The sheet may be pushed into the second roller pair 104 due to the reaction force that is in contact with the sheet 105 and the conveyance guide 105. Such a phenomenon occurred even when the conveyance guide 105 was straight.

  For example, when the conveyance speed of the sheet at the second roller pair 104 is 100 mm / sec and the conveyance speed of the upstream first roller pair 103 is 1% faster, the loop length generated by the longitudinal feeding of the A4 size sheet Becomes about 3 mm.

  Further, the image forming apparatus provided with such a sheet conveying apparatus 102 does not feed the sheet to the transfer conveying belt 106a at a predetermined sheet conveying speed, and it is difficult to form a high-quality image on the sheet. It was.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus that can form a complete loop on a sheet and reduce sheet conveyance unevenness.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that includes a sheet conveying device that reduces the unevenness of conveying the sheet and that has less image color expansion and contraction and color misregistration.

  In order to achieve the above object, a sheet conveying apparatus according to the present invention includes a first rotating body pair that conveys a sheet and a sheet that has been conveyed by the first rotating body pair that is slower than the first rotating body pair. A second rotating body pair that conveys at a speed; a conveying guide that guides a sheet between the first rotating body pair and the second rotating body pair; and after the sheet has reached the second rotating body pair, Conveyance guide moving means for moving the conveyance guide from the sheet guide position to the retracted position.

  In order to achieve the above object, an image forming apparatus according to the present invention includes the sheet conveying device and an image forming unit that forms an image on a sheet conveyed by the sheet conveying device.

  In the sheet conveying apparatus of the present invention, the conveying guide moving means moves the conveying guide from the sheet guide position to the retracted position after the sheet reaches the second rotating body pair. When the loop is formed on the sheet between the second rotating body pair and the second rotating body pair, the conveyance guide is configured to escape and not interfere with the formation of the loop, so that the sheet is not pushed by the conveyance guide. , Sheet conveyance unevenness can be reduced.

  The image forming apparatus according to the present invention includes a sheet conveying device that reduces the unevenness of conveying the sheet. Therefore, the expansion and contraction of the image and the color misregistration can be reduced for the color, and the image quality can be improved. .

  Hereinafter, a sheet conveying apparatus according to an embodiment of the present invention and a color printer as an image forming apparatus including the sheet conveying apparatus in an apparatus main body will be described with reference to the drawings.

  FIG. 1 is a schematic front view of the sheet conveying apparatus according to the first embodiment. FIG. 2 is a diagram illustrating a state in which the sheet is fed to the color printer in the sheet conveying apparatus of FIG. 1. FIG. 3 is a cross-sectional view of the color printer including the sheet conveying apparatus according to the first embodiment along the sheet conveying direction.

(Color printer)
In FIG. 3, the color printer 20 is configured to electrostatically attract powdered toner onto a sheet and form a color toner image using an electrophotographic system. The color printer 20 includes a sheet conveying device 21 to be described later, a transfer mechanism 6 disposed on the downstream side of the second conveying roller pair 4 of the sheet conveying device 21, four photosensitive drums 7 facing the transfer mechanism 6, and the like. have. The transfer mechanism 6 and the photosensitive drum 7 constitute an image forming unit.

  The transfer mechanism 6 includes a transfer conveyance belt 6a, a driving roller 6b, a driven roller 6c, transfer rollers 6d (four in this embodiment), a receiving roller 6e, and the like. The driven roller 6c is pulled to the outside of the transfer / conveying belt 6a by a biasing member (not shown) such as a spring to apply tension to the transfer / conveying belt 6a. Since the driving roller 6b rotates in the direction of arrow D, the transfer conveyance belt 6a circulates in the direction D shown in the figure. The photosensitive drums 7 (four in this embodiment) are disposed adjacent to the transfer conveyance belt 6a and facing the transfer roller 6d, and rotate in the direction of arrow E.

  The color printer 20 electrostatically applies the sheet P supplied from the sheet conveying device 21 to the transfer conveying belt 6a that circulates between the photosensitive drum 7 rotating in the arrow E direction and the transfer device 6d in the arrow D direction. While adsorbed and conveyed, the color toner images of Y (yellow), M (magenta), C (cyan), and black (B) are sequentially transferred onto the sheet P while the sheet passes through the photosensitive drums 7 of the respective colors. A color image is formed.

(Sheet Conveying Device of First Embodiment)
The configuration of the sheet conveying apparatus will be described.

  1 and 2, a sheet conveying device 21 includes a sheet feeding unit 2, a first conveying roller pair 3 as a first rotating body pair, a sheet conveying guide 1 as a conveying guide, and a second rotating body pair. A conveyance roller pair 4 and a conveyance guide moving mechanism 5 as a conveyance guide moving means are provided.

  The sheet feed roller 2a of the sheet supply unit 2 rotates in the direction of arrow A in FIG. 1, and supplies and conveys the sheet P one by one to the first conveyance roller pair 3 on the downstream side.

  The first transport roller pair 3 and the second transport roller pair 4 are composed of drive rollers 3a and 4a and driven rollers 3b and 4b, respectively. The driven rollers 3b and 4b are pressed by an urging member such as a spring (not shown) and are in pressure contact with the driving rollers 3a and 4a. In FIG. 1, the first and second conveying roller pairs 3 and 4 sandwich the sheet between the driving rollers 3a and 4a and the driven rollers 3b and 4b, and the driving rollers 3a and 4a rotate in the directions of arrows B and C. As a result, the driven rollers 3b and 4b follow and rotate through the sheet to convey the sheet.

  The drive rollers 3a and 4a are provided with a one-way clutch (not shown). For this reason, the drive rollers 3a and 4a are configured to follow and rotate when the conveyed sheet is pulled downstream by a transfer conveyance belt 6a of the transfer mechanism 6 described later.

  The sheet conveying guide 1 is disposed between the first and second rotating body pairs 3 and 4, and has been conveyed by the first rotating body pair 3 by the curved outer guide plate 1c and inner guide plate 1d. The sheet is guided to the nip of the second rotating body pair 4. The outer guide plate 1c is configured such that the downstream end portion tilts about the rotation shaft 1a. The downstream end of the outer guide plate 1c is pressed by the spring 1b and is in pressure contact with the cam 8 of the transport guide moving mechanism 5 described later. The conveyance guide 5 is curved so that a manual sheet inserted by a user can be easily received from the side of the apparatus main body.

  The conveyance guide moving mechanism 5 is provided on a shaft 4c of the driving roller 4a of the second conveyance roller pair 4 so as to be rotatable, and is a registration shutter 11 that is rotated by being pushed by the leading edge of the sheet, and a cam 8 that is integrated with the registration shutter 11. It consists of and. The registration shutter 11 has an abutting surface 11a substantially perpendicular to the sheet conveyance direction. The registration shutter 11 is rotationally biased in the direction opposite to the arrow C by a biasing member such as a spring (not shown), and is normally positioned at the position shown in FIG. 1 by a stopper (not shown). For this reason, the abutting surface 11a normally stands by at the upstream side of the nip of the second conveying roller pair 4. The registration shutter 11 is configured to form a loop in the sheet while being pushed and rotated by the leading edge of the received sheet to straighten the skew of the sheet. The cam 8 is formed by a large diameter portion 8a and a small diameter portion 8b. A tilting end portion of the outer guide plate 1c is pressed against the outer periphery of the cam 8 by a spring 1b.

  It is assumed that the sheet conveying speeds V1, V2, and V3 of the first conveying roller pair 3, the second conveying roller pair 4, and the transfer conveying belt 6a are set to have a relationship of V1, V3> V2.

  The operation of the sheet conveying apparatus will be described.

  The sheet P conveyed from the sheet supply unit 2 to the first conveyance roller pair 3 is conveyed downstream by the first conveyance roller pair 3 while being guided by the sheet conveyance guide 1. The leading edge of the sheet P comes into contact with the sheet conveyance guide 1 and approaches the nip of the second conveyance roller pair 4. Thereafter, the leading edge of the sheet comes into contact with the abutting surface 11 a of the registration shutter 11 of the conveyance guide moving mechanism 5. Since the first conveyance roller pair 3 continues to convey the upstream portion of the sheet P, a loop is formed in the sheet within the sheet conveyance guide 1. The loop portion of the sheet comes into contact with the outer guide plate 1c of the sheet conveying guide 1, and a force is generated that pushes the abutting surface 11a to the downstream side against the sheet. Thus, when the sheet is skewed, the skew is corrected and straightened along the sheet conveyance direction.

  Since the sheet is further conveyed by the first conveying roller pair 3, the leading edge of the sheet pushes against the abutting surface 11 a of the registration shutter 11 and resists the rotational urging force of the registration shutter 11. Is rotated in the direction of arrow C. The sheet reaches the nip of the second conveying roller pair 4 and enters the nip. Further, the cam 8 rotates integrally with the registration shutter 11.

  As the cam 8 rotates, the portion in contact with the outer guide plate 1c changes from the small diameter portion 8b to the large diameter portion 8a, and tilts the outer guide plate 1c against the spring 1b. The outer guide plate 1c tilts in a direction away from the seat (a direction away from the fixed inner guide plate 1d). That is, the outer guide plate 1c is tilted from the sheet guide position to the retracted position. A wide space S is formed in the sheet conveyance guide 1 by the tilting of the outer guide plate 1c.

  Then, the sheet is conveyed to the transfer conveyance belt 6a by the conveyance of the second conveyance roller pair 4, and the toner image formed on the surface of the photosensitive drum 7 is sequentially transferred for each color to form a color image. The

  In the above operation, the sheet is conveyed to the registration shutter 11 along the outer guide plate 1c, and when the leading edge of the sheet rotates the registration shutter 11 in the direction of arrow C against the rotational urging force of the registration shutter 11. Since the sheet receives a reaction force from the outer guide plate 1c, the sheet is strongly pressed and the skew of the sheet is corrected straight. After the skew of the sheet is corrected and the sheet is conveyed by the second conveying roller pair 4, the second conveying roller pair 3, 4 has a second sheet conveying speed difference (V 1 −V 2), so that the second A loop is gradually formed on the upstream side of the conveying roller pair 4. At this time, since the outer guide plate 1c is moved to the retracted position, the sheet loop is released into the wide space S formed in the sheet conveying guide 1 and contacts the outer guide plate 1c. Therefore, the leading edge of the sheet is not pushed into the nip of the second conveying roller pair 4 due to the reaction force from the outer guide plate 1c. Even if contact is made, the loop is in an escaped state, so the sheet is hardly pushed into the nip of the second conveying roller pair 4 due to the rigidity of the loop.

  Therefore, the sheet conveying apparatus 21 of the present embodiment does not push the sheet into the nip of the second conveying roller pair 4 due to the rigidity of the formed loop. That is, the sheet conveying device 21 can reduce the unevenness of sheet conveyance and supply the sheet to the transfer mechanism 6 of the color printer.

  Further, the sheet conveying device 21 does not disturb the sheet conveying speed V3 of the transfer conveying belt 6a because the sheet is not pushed into the nip of the second conveying roller pair 4. As a result, the color printer can form an image with less expansion and contraction and less color shift on the sheet.

  Of course, in the state before the leading edge of the sheet reaches the nip of the second conveying roller pair 4, the outer guide plate 1c is in a position to regulate the loop, and therefore the skew is corrected by the rigidity of the sheet.

(Sheet Conveying Device of Second Embodiment)
FIG. 4 is a schematic front view of the sheet conveying apparatus according to the second embodiment. FIG. 5 is a diagram showing a state in which the sheet is fed to the color printer in the sheet conveying apparatus of FIG.

  The sheet conveying apparatus 22 of the second embodiment is different from the sheet conveying apparatus 21 of the first embodiment in the configuration of the conveyance guide moving mechanism, and the other parts are almost the same. The same parts are denoted by the same reference numerals, and description thereof is omitted.

  A conveyance guide moving mechanism 25 serving as a conveyance guide moving means is provided on the shaft 4c of the driving roller 4a of the second conveyance roller pair 4 so as to be rotatable, and a registration shutter 11 that rotates by being pushed by the leading edge of the sheet. The plate 9 is integrated with the shutter 11, and the arm 10 connects the arcuate long hole 9 a of the plate 9 and the tilting end of the outer guide plate 1 c. The registration shutter 11 has an abutting surface 11a substantially perpendicular to the sheet conveyance direction. The registration shutter 11 is rotationally biased in the direction opposite to the arrow C by a biasing member such as a spring (not shown), and is normally positioned at the position of FIG. 1 by a stopper (not shown). For this reason, the abutting surface 11a normally stands by at the upstream side of the nip of the second conveying roller pair 4. The arm 10 and the long hole 9a constitute a linear motion mechanism.

  It is assumed that the sheet conveying speeds V1, V2, and V3 of the first conveying roller pair 3, the second conveying roller pair 4, and the transfer conveying belt 6a are set to have a relationship of V1, V3> V2.

  The operation of the sheet conveying apparatus of this embodiment will be described. An operation different from the operation of the sheet conveying apparatus 21 of the first embodiment will be described, and the description of the similar operation will be omitted.

  When the leading edge of the sheet is upstream of the nip of the second conveying roller pair 4, the sheet conveying guide 1 is at a position for guiding the leading edge of the sheet to the nip as shown in FIG. The registration shutter 11 is pushed and rotates integrally with the plate 9 by the contact of the leading end of the sheet. However, since there is play in the connecting portion between the long hole 9a and the arm 10, the arm 10 does not move. For this reason, the sheet conveyance guide 1 also does not rotate. During this time, if the sheet is skewed, the skew is corrected and straightened along the sheet conveyance direction.

  When the leading edge of the sheet reaches the nip of the second conveying roller pair 4, the play between the long hole 9 a of the plate 9 and the arm 10 is eliminated by the rotation of the registration shutter 11. For this reason, when the sheet passes through the nip of the second conveying roller pair 4, the outer guide plate 1c of the sheet conveying guide 1 is moved away from the sheet (from the fixed inner guide plate 1d) by the operation of the arm 10. Tilt in the direction). That is, the outer guide plate 1 c is tilted from the sheet guide position to the retracted position, so that a wide space S is formed in the sheet conveyance guide 1.

  As a result, also in the sheet conveying apparatus 22 of the present embodiment, the sheet is caused upstream of the second conveying roller pair 4 by the speed difference (V1−V2) between the first conveying roller pair 3 and the second conveying roller pair 4. Even if a loop occurs, the loop can be released into the wide space S formed in the sheet conveyance guide 1 and the sheet is not pushed into the nip of the second conveyance roller pair 4. Even if contact is made, the loop is in an escaped state, so the sheet hardly pushes the leading edge of the sheet into the nip of the second conveying roller pair 4 due to the rigidity of the loop.

  Therefore, the sheet conveying apparatus 22 of the present embodiment also does not push the sheet into the nip of the second conveying roller pair 4 due to the rigidity of the formed loop. In other words, the sheet conveying device 22 can reduce the unevenness in conveying the sheet and supply the sheet to the transfer mechanism 3 of the color printer.

  Further, the sheet conveying device 22 does not disturb the sheet conveying speed V3 of the transfer conveying belt 6a because the sheet is not pushed into the nip of the second conveying roller pair 4. As a result, the color printer forms an image with less expansion and contraction and color shift on the sheet.

  Unlike the sheet conveying device 21 of the first embodiment, the sheet conveying device 22 of the present embodiment does not apply the force of the spring 1b to the outer guide plate 1c in the direction of approaching the sheet. With the pressing force, the space can be formed reliably, and a complete loop can be formed on the sheet.

  The conveyance guide moving mechanisms 5 and 25 in the above-described sheet conveyance apparatus rotate the cam 8 or the plate 9 interlocked with the registration shutter 11 to retract the outer guide plate 1c from the sheet guide position to the retracted position. However, a sensor is arranged on the downstream side of the second conveying roller pair 4, and it is detected by this sensor that the sheet has reached the second conveying roller pair 4, and a solenoid (not shown) The guide plate 1c may be retracted from the sheet guide position to the retracted position. Further, the solenoid may be controlled using a sensor that detects the rotation of the registration shutter 11.

  Further, a belt pair may be used instead of the first and second transport roller pairs for transporting the sheet.

  In the above description, the sheet conveying apparatus is incorporated in a color printer. However, the sheet conveying apparatus is also incorporated in a copying machine that forms a monochrome toner image on a sheet with a rotating photosensitive drum and a transfer device without using a transfer conveying belt. be able to. Also in this case, the copying machine can form an image with less image expansion / contraction on the sheet.

It is a front schematic diagram of a sheet conveying device of a 1st embodiment. FIG. 2 is a diagram illustrating a state where a sheet is being fed into a color printer in the sheet conveying apparatus of FIG. FIG. 3 is a cross-sectional view of the color printer including the sheet conveying apparatus according to the first embodiment along the sheet conveying direction. It is a front schematic diagram of a sheet conveying device of a 2nd embodiment. FIG. 5 is a diagram illustrating a state where a sheet is being fed into a color printer in the sheet conveying apparatus of FIG. 4. FIG. 10 is a cross-sectional view of a color printer including a conventional sheet conveying device along the sheet conveying direction.

Explanation of symbols

P sheet S space 1 sheet conveyance guide (conveyance guide)
1a Rotating shaft 1b Spring 1c Outer guide plate 1d Inner guide plate 3 First conveying roller pair (first rotating body pair)
4 Second conveying roller pair (second rotating body pair)
5 Transport guide moving mechanism (transport guide moving means)
6 Transfer mechanism (image forming means)
6a Transfer conveyor belt 7 Photosensitive drum (image forming means)
8 Cam 9 Plate 9a Long hole (Linear motion mechanism)
10 Arm (Linear motion mechanism)
11 Registration shutter 11a Abutting surface 20 Color printer (image forming apparatus)
21 Sheet Conveying Device of First Embodiment 22 Sheet Conveying Device of Second Embodiment 25 Conveying Guide Moving Mechanism (Conveying Guide Moving Means)

Claims (6)

A first rotating body pair for conveying the sheet;
A second rotating body pair that conveys the sheet conveyed by the first rotating body pair at a sheet conveying speed slower than the first rotating body pair;
A conveyance guide for guiding a sheet between the first rotating body pair and the second rotating body pair;
Transport guide moving means for moving the transport guide from the sheet guide position to the retracted position after the sheet reaches the second pair of rotating bodies;
A sheet conveying apparatus comprising:   2. The conveyance guide moving means includes: a registration shutter that is rotated by being pushed by a leading edge of a sheet; and a cam that moves the conveyance guide to a retracted position in conjunction with the registration shutter. The sheet conveying apparatus according to the description.   The transport guide moving means includes a registration shutter that is rotated by being pushed by a leading end of a sheet, and a linear motion mechanism that converts the rotational motion of the registration shutter into a linear motion and moves the transport guide to a retracted position. The sheet conveying apparatus according to claim 1.   The sheet conveying apparatus according to claim 1, wherein the conveying guide moving unit includes a sensor that detects a sheet and a solenoid that is operated by the sensor and retracts the conveying guide to a retracted position.   5. The sheet conveyance according to claim 1, wherein the conveyance guide has a pair of guide members that are curved to be opposed to each other, and the guide member on the outer side of the curve can be retracted. apparatus. The sheet conveying apparatus according to any one of claims 1 to 5, which conveys a sheet to an image forming unit;
Image forming means for forming an image on the sheet conveyed by the sheet conveying device;
An image forming apparatus comprising:

Images