JP2007308266A - Sheet delivery device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet delivery device capable of securing sheet delivery conveying force and preventing roller marks from being left on sheets, and to provide an image forming device. <P>SOLUTION: A plurality of driven rollers 19 are brought into pressure contact with a plurality of roller bodies 28a coaxially provided at a roller shaft 28c of a paper delivery roller 28, and a stiffening means 28b larger in diameter than the roller bodies 28a is provided coaxially with the plurality of roller bodies 28a and between the roller bodies 28a. The sheet clamped and conveyed by the roller bodies 28a and the driven roller 19 is pressed down by the stiffening means 28b to stiffen the sheet. A small diameter part is formed at the stiffening means 28b to reduce press-down force by the stiffening means 28b. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sheet discharging apparatus and an image forming apparatus, and more particularly to a sheet discharging apparatus with a waist attached.

  In conventional image forming apparatuses such as copiers, printers, and facsimile machines, a toner image formed on a photosensitive drum, which is an image carrier provided in an image forming unit, is transferred to a sheet, and then the sheet is used as a fixing device. I am trying to carry it. In the fixing device, the toner image is fixed on the sheet by heating and pressurizing the sheet, and then the sheet on which the toner image is fixed is discharged to the sheet discharge stacking unit by the sheet discharge device. .

  In the case of such an image forming apparatus, when passing through the fixing device, the sheet may be curled due to the moisture absorption amount, the printing rate, or the like. When the curl is generated in this way, the leading edge of the sheet discharged to the sheet discharge stacking unit comes into contact with the sheet discharged previously to the sheet discharge stacking unit, and the previously discharged sheet is pushed out, or May cause the sheets to curl up and cause poor loading.

  Therefore, in order to prevent the occurrence of poor stacking when discharging such sheets, for example, a sheet discharging device is provided with a waist ring, and the sheet is waved in the width direction perpendicular to the sheet discharge direction by this waist ring. Therefore, there is a seat that is seated on the seat P. Then, by sitting on the sheet P in this way, the discharged sheet can be skipped far away, and the leading edge of the discharged sheet comes into contact with the sheet discharged earlier to the sheet discharge stacking unit. Can be prevented (see, for example, Patent Document 1).

  FIG. 10 is a diagram showing a schematic configuration of an image forming apparatus provided with such a conventional sheet discharging apparatus. In this image forming apparatus, the sheet P is gently reversed from the sheet feeding tray 1A in order to obtain reliability. A system is used in which a sheet path is used to convey to the paper discharge tray 20A.

  In such an image forming apparatus, the sheet P set on the sheet feeding tray 1A is first fed by a feeding roller 3A that is rotated by the operation of a drive motor 2A, and then separated by a separation pad 4A. Thereafter, the toner is conveyed to a transfer nip composed of the photosensitive drum 8A and the transfer roller 9A in the process cartridge 7A as a transfer portion through the conveyance roller pair 5A.

  By this time, after the latent image is formed on the surface of the photosensitive drum by the exposure by the image writing scanner 6A, the latent image is developed to form a toner image on the photosensitive drum 8A.

  Next, the sheet P conveyed to the transfer nip is transferred with the toner image on the photosensitive drum 8A as an unfixed image at the transfer nip. Thereafter, the sheet P is sent to a fixing device 30A including a film guide unit 11A including a pressure roller 10A and a fixing heater in order to heat and fix the transferred toner image. Then, an unfixed image is heated and fixed at a fixing nip formed by the pressure roller 10A and the film guide unit 11A, and then conveyed toward the sheet discharge device 31A.

  Then, the sheet P conveyed toward the sheet discharge device 31A is discharged from the discharge roller 19A in pressure contact with the roller rubber portion 18b of the discharge roller 18A by the discharge roller 18A and the discharge roller spring 22A along the separation guide 14A. It goes to the paper discharge roller pair 18A, 19A. The paper is discharged onto the paper discharge tray 20A by the paper discharge roller pair 18A, 19A.

  Here, when discharging the sheets, in order to prevent occurrence of poor stacking of the sheets P, a plurality of waist rings 18a are provided on the same axis as the sheet discharge roller 18A, and the sheets P are waved in the width direction by the waist rings 18a. The seat P is attached to the seat P.

  Then, by seating the sheet P in this way, when the sheet P is discharged to the discharge tray 20A, the trajectory of the sheet P becomes P ″ shown in FIG. 10 and is indicated by P ′. The sheet flies farther than the path of the sheet P that is not seated, so that a sheet curled toward the printing surface or a sheet that tends to curl is landed directly under the sheet discharge outlet 21A and discharged first. It is possible to prevent the sheet from curling or pushing out the sheet, and the alignment is improved.

JP 2004-059277 A

  By the way, in such a conventional sheet discharging apparatus and image forming apparatus, when the sheet P is thin paper having a basis weight of about 60 g, since the waist of the sheet is weak, as shown in FIG. 11, the rubber roller portion 18b and the waist ring portion The sheet P1 can be bent and corrugated between 18a. That is, it is possible to sufficiently apply the nip pressure of the sheet discharge roller while the sheet P1 is seated.

  However, depending on the type of seat, the seating may be performed and the seat landing point may not be extended far away. For example, when the sheet is a thick sheet P2 such as an envelope, as shown in FIG. 12, the urging pressure F of the sheet discharge roller 19A is lost to the waist of the sheet P2 bent by the waist ring 18a, and the sheet is discharged. There is a problem that the roller 19A and the rubber roller portion 18b are separated from each other and the conveying force is lost.

  Furthermore, in recent miniaturized image forming apparatuses, as shown in FIG. 13, the nip line (discharge direction) of the discharge roller pair 18A and 19A determined from the discharge stacking performance and the fixing device 30A. Deviation occurs in the fixing nip direction (fixing nip line) determined from the conveyance conditions. For this reason, in the sheet discharge device 31A, the conveyance path from the fixing device 30A to the discharge roller pair 18A, 19A cannot be linear.

  In this way, when the conveyance path is not linear, when the sheet passes through the fixing nip, the rear end of the sheet comes into contact with the sheet discharge guide 14A, and thus the sheet direction is deviated from the nip line of the sheet discharge roller pair 18A, 19A. It will be. When the orientation (posture) of the sheet deviates from the nip line between the discharge roller pair 18A and 19A as described above, the sheet is bent in the vertical direction.

  In other words, when the sheet is conveyed while being waved in the width direction by the waist ring 18a, vertical deflection also occurs in a very narrow conveyance path between the fixing device 30A and the discharge roller pair 18A, 19A.

  For this reason, if the sheet is waved, the sheet becomes very strong. If the sheet becomes very strong in this way, the sheet discharge roller 19A is separated from the roller rubber portion 18b and the conveying force is increased. It will drop greatly. If there is a high conveyance load region where the conveyance force is greatly reduced, the sheet may stagnate and jam may occur when passing through the high conveyance load region. In addition, the sheet that has been discharged first may come into contact with the sheet, or the sheet may be pushed out.

  In order to prevent such a paper discharge jam or the like, the spring force of the paper discharge roller spring 22A is increased to increase the pressure contact pressure of the paper discharge roller 19A, or the diameter of the waist ring 18a is increased. There are methods such as reducing the amount of bending of the sheet to make it easy to apply pressure. However, when the pressure contact pressure is increased, there is a problem that the sheet has a roller mark, and reducing the ring diameter causes a problem that the sheet cannot be sufficiently corrugated, leading to a decrease in discharge stacking performance. is there.

  As described above, there is a trade-off relationship between securing the sheet discharge conveyance force for thick sheets of thick paper and envelopes and preventing roller traces on thin sheets. Therefore, the setting range of the spring force of the discharge roller spring 22A is limited to a narrow range, and it is necessary to strictly manage the tolerance of the discharge roller spring 22A.

  In addition, since the spread of image forming apparatuses has recently been promoted, the types of sheets used by end users tend to increase further, and a device that can stably discharge various paper types regardless of basis weight. Is the situation that is awaited. Further, it is desirable that such an image forming apparatus is not contrary to the downsizing of the apparatus, is simple and has a small number of parts.

  Accordingly, the present invention has been made in view of such a current situation, and provides a sheet discharge device and an image forming apparatus that can secure a sheet discharge conveying force and can prevent a roller from being traced. It is intended to provide.

  In a sheet discharge device for discharging a sheet on which an image is formed with a waist, a discharge roller having a roller shaft and a plurality of roller bodies coaxially provided on the roller shaft, and a plurality of roller bodies A plurality of driven rollers that are in pressure contact with each other, and the roller main body that is provided coaxially with the plurality of roller main bodies and between the roller main bodies and seats on a sheet that is nipped and conveyed by the roller main bodies and the driven rollers And a small diameter portion is formed in the waist-resting means so as to reduce the seating force by the waist-mounting means.

  As in the present invention, by forming a small-diameter portion on the seating means for seating the sheet, and reducing the seating force by the seating means, it is possible to secure the sheet discharge conveying force and It is possible to prevent the roller marks from sticking.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of a laser beam printer which is an example of an image forming apparatus provided with a sheet discharging apparatus according to a first embodiment of the present invention. This laser beam printer is a small image forming apparatus having a sheet reversing path.

  The laser beam printer 100 is transferred by an image forming unit 101, a paper feeding unit 102 that feeds a sheet P to the image forming unit 101, a transfer unit 103 that transfers a toner image to the sheet P, and a transfer unit 103. And a fixing unit 104 for fixing the toner image on the sheet P. Further, a sheet discharge device 105 that discharges a sheet on which image formation has been formed is provided.

  Here, the image forming unit 101 exposes the surface of the photosensitive drum 8 by exposing the surface of the photosensitive drum 8 and the process cartridge 7 including the photosensitive drum 8 that is an image carrier, the developing sleeve 8a, the charging roller 8b, and the like. And a laser scanner 6 for forming an electrostatic latent image.

  The sheet feeding unit 102 is a sheet feeding tray 1 on which sheets P are stacked, a feeding roller 3 that feeds the sheets P on the sheet feeding tray 1 one by one, and a separation member that is in pressure contact with the feeding roller 3. And a separation pad 4. The separation pad 4 has a friction coefficient, a contact angle, and a shape of the surface set so that only one uppermost sheet is fed for each sheet feeding.

  The transfer unit 103 presses against the photosensitive drum 8 to form a transfer nip, and when the sheet P passes through the transfer nip, the toner image on the photosensitive drum 8 is transferred to the sheet P. It is comprised by the transfer roller 9 which is a transfer means to transfer to. The fixing unit 104 includes a pressure roller 10 and a film guide unit 11 including a ceramic heater, a thin film, and a guide member.

  Further, the sheet discharge device 105 includes a separation guide 14 and a pair of discharge rollers 19 and 28 including a discharge roller 28 and a discharge roller 19.

  Next, an image forming operation in the laser beam printer 100 configured as described above will be described.

  When the power is turned on from a main switch (not shown), a driving force is transmitted to a gear train (not shown) by the motor 2, and various rollers such as the photosensitive drum 8, the feeding roller 3, the charging roller 8b, the pressure roller 10 and the like. Starts rotating. As a result, the sheets P set in the sheet feeding tray 1 are separated and fed one by one by the separation feeding mechanism including the feeding roller 3 and the separation pad 4.

  On the other hand, in the image forming unit 101, the photosensitive drum 8 rotates in the direction of the arrow and is uniformly charged to a predetermined polarity and a predetermined potential by a charging roller 8b fed from a high voltage power source (not shown). Then, laser light is irradiated from the laser scanner 6 to the photosensitive drum 8 whose surface has been charged in this way, whereby an electrostatic latent image is formed on the photosensitive drum 8.

  Next, the electrostatic latent image is developed as a toner image when toner that has been appropriately charged with the rotation of the developing sleeve 8a is supplied onto the photosensitive drum 8 and adheres to the electrostatic latent image. Visualized. Then, the sheet P separated and fed one by one is conveyed to the transfer unit 103 including the photosensitive drum 8 and the transfer roller 9 along the reverse path R curved in a substantially vertical direction by the conveying roller pair 5, and this transfer The toner image is transferred in the portion 103.

  Next, the sheet P onto which the toner image has been transferred in this manner is conveyed to a fixing nip constituted by a pressure roller 10 and a film guide unit 11 provided in the fixing unit 104, and is not fixed in the fixing nip. The toner image is heated and pressurized and fixed on the sheet surface. The sheet P on which the toner image has been fixed in this way is reversed and conveyed by the separation guide 14 to a pair of paper discharge rollers 19 and 28 including a paper discharge roller 28 and a paper discharge roller 19. The paper is discharged to the paper discharge tray 20 by the roller pairs 19 and 28.

  Incidentally, the sheet discharge device 105 of the laser beam printer 100 conveys (discharges) the sheet P while being sandwiched by a pair of discharge roller pairs 19 and 28 in order to reduce the size of the laser beam printer 100 as shown in FIG. Like to do.

  In the present embodiment, the paper discharge roller 28 is a roller shaft 28c made of metal or molded resin, and a roller main body formed of an elastic material such as foamed urethane foam, silicon rubber, or EPDM. A roller rubber portion 28a is provided. The roller rubber portion 28a of the paper discharge roller 28 has a hardness of several tens of degrees.

  Further, the roller shaft 28c is provided with a plurality of waisting rings 28b having a diameter larger than that of the roller rubber portion 28a as waisting means, and the sheet P is waved in the width direction by the rings 28b. He sits on P and discharges it.

  3A is a view of the state of the sheet discharge device 105 when discharging the thin sheet P1 as viewed from the sheet discharge direction L shown in FIG. 1, and FIG. 3B shows the seating ring 28b. It is the figure seen from the side. The waist ring 28b is disposed at the center of the two roller rubber portions 28a in the sheet width direction.

  Here, when the thin sheet P1 is discharged, the thin sheet P1 is constituted by the roller rubber portion 28a and the discharge roller 19 while being pushed down by the ring 28b and attached to the waist without pushing back the discharge roller 19 because the thin sheet P1 is weak. Pass through the paper discharge nip.

  Accordingly, the sheet P1 is discharged at the discharge nip in a state (posture) indicated by a straight line connecting the end of the discharge nip and the ridge line of the waist ring 28b as shown in FIG. In the present embodiment, the waist ring 28b has a ridge line M of about 0.5 mm at the end, thereby preventing the roller marks from being attached to the sheet P1 when the sheet P1 is seated. It is out.

  4A is a view of the state of the sheet discharge device 105 when discharging the thick sheet P2 as viewed from the discharge direction L shown in FIG. 1, and FIG. 4B is a seating ring 28b. It is the figure which looked at from the side.

  Here, when the sheet P is discharged by the discharge roller pair 19, 28 as in the present embodiment, the discharge roller pair 19, 28, which is the discharge direction of the discharge roller pair 19, 28, as shown in FIG. And the sheet conveyance direction (fixing nip line) of the fixing unit 104 are shifted from each other. If a deviation occurs between the nip line of the paper discharge roller pair 19 and 28 and the fixing nip line of the fixing unit 104 as described above, the sheet is bent in the vertical direction as described above. This sheet discharging apparatus 105 has a large conveyance load area.

  As a result, when the trailing edge of the thick sheet P2 passes through the fixing unit 104 and enters the large conveyance load region, the sheet P2 is pushed down by the ring 28b and is discharged while being seated. The energizing pressure F is lost. As a result, the sheet discharge roller 19 is inclined while biting into a part of the roller rubber portion 28a opposite to the waist ring side.

  When the paper discharge roller 19 is inclined in this way, the sheet pressure contact area of the paper discharge nip becomes narrow, and a loss occurs in the conveyance force. Note that the larger the inclination (biting amount) of the paper discharge roller 19 is, the smaller the paper discharge conveyance force is.

  Therefore, in the present embodiment, at least when the rear end of the sheet P2 passes through the large conveyance load region, the lowering force of the waist ring 28b is reduced to weaken the waist of the sheet P2, and the discharge roller. The inclination (bite-in amount) of 19 is made small.

  Therefore, the shape of the waist ring 28b is a D-cut shape having a large diameter portion 28b1 having a large diameter Ra and a small diameter portion 28b2 having a small diameter Rb with reference to the center of the roller shaft 28c as shown in FIG. .

  By setting the waist ring 28b to such a shape, as shown in FIG. 5A, when the large-diameter portion 28b1 is in a position to push down the sheet, the sheet is pushed down with a large force. On the other hand, as shown in FIG. 5B, when the small diameter portion 28b2 is in a position to push down the sheet, the sheet P is pushed down with a small force.

  That is, when the small-diameter portion 28b2 of the waist ring 28b faces the seat, the seating force on the seat by the waist ring 28b decreases compared to when the large diameter portion 28b1 of the waist ring 28b faces the seat. . Therefore, by forming the waist ring 28b in such a so-called D-cut shape, the inclination (biting amount) of the paper discharge roller 19 can be changed.

  Next, a paper discharge operation of the sheet discharge device 105 including the waist ring 28b having such a shape will be described.

  When the thick sheet P2 is discharged, the shape of the discharge nip is approximately ½ of the area where the discharge roller 28 rotates until the trailing edge of the sheet P2 passes through the fixing nip. It will be in the state shown in. At this time, since the large-diameter portion 28b1 is in a position where the sheet is pushed down, the sheet P2 can be reliably waved.

  Next, when the trailing edge of the sheet passes through the fixing nip, the sheet P2 just after passing is in a state where it is conveyed only by the conveying force of the paper discharge roller 28a and the conveyance load is large (FIG. 2). Enter (see). For this reason, the inclination (biting amount) of the paper discharge roller 19 increases, and the paper discharge conveying force decreases accordingly.

  However, at this time, as shown in FIG. 6B, the small-diameter portion 28b2 of the seating ring 28b has moved to the position where the seat is pushed down, so that the sheet P2 is bent as shown in FIG. 6A. The amount, that is, the amount pushed down by the waist ring 28b decreases.

  Along with this, the amount of biting into the roller rubber portion 28a (sheet P2) of the paper discharge roller 19 decreases, and the conveying force increases. As the sheet conveying force increases as described above, the paper discharge roller 28 can overcome the maximum conveyance load state and convey the thick sheet P2.

  After that, when the paper discharge roller 28 rotates by a certain amount, the waist ring 28b enters the region of the large diameter portion 28b1 again, so that the conveying force decreases. However, since the maximum transport load region is a very narrow region as described above, the trailing edge of the sheet P2 can pass through the maximum transport load region when the paper discharge roller 28 rotates once or several times. Then, after passing through the maximum conveyance load region in this way, the inclination (biting amount) of the sheet discharge roller 19 is reduced thereafter, so that the sheet P2 can be discharged normally.

  In the case of the thin sheet P1, similarly, the amount of seating changes in one roller cycle, so that the region where the amount of seating necessary for maintaining good discharge stackability is reduced by a certain amount. However, even when the seating amount decreases at the small diameter portion 28b2 of the seating ring 28b, the seating amount recovers until the seating amount becomes a sufficient amount again when the paper discharge roller 28 rotates by a certain amount. Is hardly changed, and has little influence on the stacking ability of the discharged paper.

  Note that the diameters Ra and Rb of the large-diameter portion 28b1 and the small-diameter portion 28b2 of the waist ring 28b can obtain a sufficient conveying force with respect to the maximum conveying load and can stably discharge and stack the thin sheet P1. Is set to be

  In this way, by forming the small-diameter portion 28b2 on the waist ring 28b and reducing the pressing force by the waist ring 28b, the seating amount when discharging the sheet is not greatly affected. It becomes possible to cope with a local increase in the conveyance load. Thereby, a thick sheet can be discharged without increasing the roller pressure. As a result, it is possible to ensure the sheet discharge conveying force and to prevent the sheet from having roller marks.

  In the description so far, the waist ring 28b may be provided on the sheet discharge roller 28 side, and a seat ring for seating on the sheet may be provided on the sheet discharge roller 19 side.

  Next, a second embodiment of the present invention will be described.

  FIG. 7 is a diagram illustrating the configuration of the sheet discharge device according to the present embodiment. 7, the same reference numerals as those in FIG. 3 indicate the same or corresponding parts.

  In FIG. 7, 38 is a paper discharge roller, 38a is a roller rubber portion provided coaxially with a roller shaft 38c of the paper discharge roller 38, and 38b is a waist ring. 7A is a view of the state of the sheet discharge device 105 when discharging the thin sheet P1 as viewed from the sheet discharge direction L shown in FIG. 1, and FIG. 7B is a seating ring 38b. It is the figure which looked at from the side.

  In the present embodiment, a plurality of waisting rings 38b are provided coaxially with the roller shaft 38c. The tip shape of the inner waist ring 38bb among the plurality of waist rings 38b is formed in a shape along the imaginary line of the thin sheet P1 in the large diameter portion 38b1. Further, in the present embodiment, the plurality of waisting rings 38b are disposed at the center of the two roller rubber portions 38a in the sheet width direction.

  Here, when the thin sheet P1 is discharged, since the waist of the sheet P1 is weak, the sheet P1 is pushed down by the ring 38b without being pushed back without being pushed back. It passes through the paper discharge nip constituted by

  Accordingly, the sheet P1 is discharged at the discharge nip in a state (posture) indicated by a straight line connecting the end of the discharge nip and the ridgeline of the waist ring 38b as shown in FIG. In the present embodiment, the waist ring 38b has a ridge line R of about 0.5 mm at the end, thereby preventing a roller mark from being attached to the sheet P1 when the sheet P1 is seated. It is out.

  8A is a view of the state of the sheet discharge device 105 when discharging the thick sheet P2 as viewed from the discharge direction L shown in FIG. 1, and FIG. 8B is a seating ring 38b. It is the figure which looked at from the side.

  Here, when the thick sheet P2 is discharged while being seated, the urging pressure F of the sheet discharge roller 19 is lost by the waist of the sheet P2, and a part of the sheet discharge roller 19 is on the waist ring side of the roller rubber portion 38a. Tilt while biting into the opposite end.

  However, since the inner waist ring 38bb has a D-cut shape having a large diameter portion 38b1 having a large diameter Ra and a small diameter portion 38b2 having a small diameter Rb, the large diameter portion 38b1 is formed as shown in FIG. When the sheet is in a position where the sheet is pushed down, the sheet is pushed down with a large force.

  On the other hand, as shown in FIG. 9, when the small diameter portion 38b2 is in a position to push down the sheet, the sheet P is pushed down with a small force, and accordingly, the amount of biting into the roller rubber portion 38a (sheet P2) of the paper discharge roller 19 is reduced. Decrease and increase the conveying force. As the sheet conveying force increases as described above, the paper discharge roller 38 can overcome the maximum conveying load state and convey the thick sheet P2.

  By the way, in the present embodiment, among the plurality of waist rings 38b, the waist ring 38ba closest to the roller rubber 38a (hereinafter referred to as the roller rubber side waist ring) has a perfect circle shape. The roller rubber side support ring 38ba rotates while always contacting the sheet P1 as shown in FIG. 7A when discharging the thin sheet P1.

  This roller rubber side waist ring 38ba is as shown in FIG. 8 (a) when the large diameter portion 28b1 of the inner waist ring 38bb is in a position to push down the sheet when discharging the thick sheet P2. It is in a state of being separated from the virtual posture line of the sheet P2.

  Next, a sheet discharge operation of the sheet discharge apparatus 105 including the waist ring 38b having such a shape will be described.

  When a thick sheet P2 is discharged, the shape of the discharge nip is approximately ½ of the area where the discharge roller 38 rotates until the trailing edge of the sheet P2 passes through the fixing nip. It will be in the state shown in. At this time, the large diameter portion 38b1 of the inner waist ring 38bb is in a position where the sheet is pushed down, and the roller rubber side waist ring 38ba is in contact with the sheet P2, so that the sheet P2 can be reliably waved.

  Next, when the trailing edge of the sheet passes through the fixing nip, the sheet P2 just after passing is in a state where it is conveyed only by the conveying force of the paper discharge roller 28a and the conveyance load is large (FIG. 2). Enter (see). For this reason, the inclination (biting amount) of the paper discharge roller 19 increases, and the paper discharge conveying force decreases accordingly.

  However, at this time, as shown in FIG. 9B, the small-diameter portion 38b2 of the inner waist ring 38bb has moved to the position where the sheet is pushed down, so that the sheet P2 as shown in FIG. The amount of flexure decreases.

  Along with this, the amount of biting into the roller rubber portion 28a (sheet P2) of the paper discharge roller 19 decreases, and the conveying force increases. As the sheet conveying force increases as described above, the paper discharge roller 38 can overcome the maximum conveying load state and convey the thick sheet P2.

  After that, when the paper discharge roller 38 rotates by a certain amount, the waist ring 38b enters the region of the large diameter portion 38b1 again, so that the conveying force decreases. However, since the maximum transport load area is a very narrow area as described above, the trailing edge of the sheet P2 can pass through the maximum transport load area when the paper discharge roller 38 rotates once or several times. Then, after passing through the maximum conveyance load region in this way, the inclination (biting amount) of the sheet discharge roller 19 is reduced thereafter, so that the sheet P2 can be discharged normally.

  In the case of the thin sheet P1, similarly, the amount of seating changes in one roller cycle, so that the region where the amount of seating necessary for maintaining good discharge stackability is reduced by a certain amount. However, even if the seating amount decreases at the small diameter portion 38b2 of the inner seating ring 38bb, the seating amount recovers until the seating amount reaches a sufficient amount again when the paper discharge roller 38 rotates by a certain amount. The position hardly changes and hardly affects the paper discharge stackability.

  By the way, in the present embodiment, as shown in FIG. 7A, when the thin sheet P1 is discharged, the roller rubber side waist ring 38ba is the inner waist ring 38bb. Even in such a position (phase), it is always in contact with the sheet P1. Thus, the sheet discharge performance can be stabilized by contacting the sheet regardless of the phase of the inner waist ring 38bb.

1 is a diagram illustrating a schematic configuration of a laser beam printer which is an example of an image forming apparatus including a sheet discharge device according to a first embodiment of the present invention. The figure explaining the detail of the said sheet discharge apparatus. The figure explaining the state when discharging the thin sheet of the said sheet discharge apparatus. FIG. 4 is a first diagram illustrating a state when a thick sheet is discharged by the sheet discharge device. The figure explaining the shape of the waist ring provided in the said sheet | seat discharge apparatus. FIG. 7 is a second diagram illustrating a state when a thick sheet is discharged by the sheet discharge device. The figure explaining the state when discharging the thin sheet | seat of the sheet discharge apparatus which concerns on the 2nd Embodiment of this invention. FIG. 4 is a first diagram illustrating a state when a thick sheet is discharged by the sheet discharge device. FIG. 7 is a second diagram illustrating a state when a thick sheet is discharged by the sheet discharge device. 1 is a diagram illustrating a schematic configuration of a conventional image forming apparatus. FIG. 9 is a schematic view of a sheet discharge unit of an image forming apparatus showing a conventional configuration when a thin sheet is passed (viewed from a sheet discharge direction). FIG. 10 is a schematic view of a sheet discharge unit of an image forming apparatus showing a conventional configuration when a thick sheet is passed (viewed from a sheet discharge direction). FIG. 9 is a detailed view of a sheet discharge unit of an image forming apparatus showing a conventional configuration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Laser beam printer 101 Image forming part 104 Fixing part 105 Sheet discharge apparatus 14 Separation guide 19 Paper discharge roller 22 Paper discharge roller spring 28 Paper discharge roller 28a Roller rubber part 28b Seat ring 28b1 Large diameter part 28b2 Small diameter part 28c Roller shaft 38 Paper discharge Roller 38a Roller rubber part 38b Waist ring 38b1 Large diameter part 38b2 Small diameter part 38ba Roller rubber side waist ring 38bb Inner waist ring 38c Roller shaft P1 Thin sheet P2 Thick sheet

Claims (4)

In a sheet discharge device that discharges a sheet on which an image is formed with a waist,
A paper discharge roller having a roller shaft and a plurality of roller bodies provided coaxially with the roller shaft;
A plurality of driven rollers that are in pressure contact with the plurality of roller bodies, respectively;
A waisting means having a diameter larger than that of the roller body, which is provided coaxially with the plurality of roller bodies and between the roller bodies and seats on the sheet held and conveyed by the roller bodies and the driven rollers. With
A sheet discharging apparatus characterized in that a small-diameter portion is formed in the seating means so as to reduce the seating force by the seating means.   A plurality of waisting means having a larger diameter than the roller body are coaxially provided between the roller bodies, and among the plurality of waisting means, a waisting means closer to the roller body than the diameter of the centering waisting means is provided. 2. The sheet discharging apparatus according to claim 1, wherein the diameter is reduced.   Between the lowering means formed with the small-diameter portion and the roller body, the roller body is larger in diameter than the roller body that is supported by the roller body and the driven roller, and has a perfect circle shape. The sheet discharging apparatus according to claim 2, further comprising: An image forming apparatus comprising: an image forming unit; and the sheet discharging device according to any one of claims 1 to 3, which discharges a sheet on which an image is formed by the image forming unit.

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