Sheet transport device and image forming apparatus

A sheet transport device includes a shaft member that extends in an axial direction orthogonal to a sheet transport direction, and a roller that includes plural components which are assembled together so as to surround the shaft member. The components have a shape such that a joint between the components is formed on an outer peripheral surface of the roller which is formed by assembling the components together. The joint extends from one end to another end of the outer peripheral surface in the axial direction while bending or curving at least at a portion in the middle thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-109564 filed May 11, 2012.

BACKGROUND

1. Technical Field

The present invention relates to a sheet transport device and an image forming apparatus.

According to a first aspect of the invention, there is provided a sheet transport device including a shaft member that extends in an axial direction orthogonal to a sheet transport direction, and a roller that includes plural components which are assembled together so as to surround the shaft member, wherein the components have a shape such that a joint between the components is formed on an outer peripheral surface of the roller which is formed by assembling the components together, the joint extending from one end to another end of the outer peripheral surface in the axial direction while bending or curving at least at a portion in the middle thereof.

DETAILED DESCRIPTION

FIG. 1is a schematic configuration diagram of a copying machine1according to an exemplary embodiment of the present invention.

In the copying machine1illustrated inFIG. 1, an image forming apparatus according to an exemplary embodiment of the present invention and a sheet transport device according to an exemplary embodiment of the present invention are incorporated.

This copying machine1includes a document reading apparatus10and an image forming apparatus20. The document reading apparatus10is installed on the image forming apparatus20. A frame30is interposed between the document reading apparatus10and the image forming apparatus20so as to form a gap therebetween.

The document reading apparatus10includes a document sheet tray11on which documents S are stacked. The documents S on the document sheet tray11are sent one by one so as to be transported through a transport path (not shown) in the document reading apparatus10. In the course of transportation, a document reading optical system13reads text and images recorded on the document S being transported. The document reading optical system13is provided below a document reading plate12that is made of transparent glass. After the text and images are read, the document S is transported through the transport path so as to be discharged onto a document discharge table14.

The document reading apparatus10includes a hinge that extends in the depth direction ofFIG. 1at the right side ofFIG. 1. The document sheet tray11and the document discharge table14are configured to rotate upward together about the hinge. When the document sheet tray11and the document discharge table14are rotated upward, the document reading plate12appears.

In the document reading apparatus10, instead of placing documents on the document sheet tray11, a single document may be placed face down on the document reading plate12. In this case, the document reading optical system13moves from the far side to the near side ofFIG. 1so as to read text and images on the document placed on the document reading plate12.

Further, the document reading apparatus10includes an operation panel15at the left side ofFIG. 1. The user operates the operation panel15so as to input various settings such as the image output form (e.g., double-sided printing and single-sided printing) and the number of copies. A setting signal indicating the settings that are input from the operation panel15is output from the document reading apparatus10to the image forming apparatus20.

Also, an image signal is generated on the basis of the read text and images of the document that are read by the document reading optical system13, and is output from the document reading apparatus10to the image forming apparatus20.

The image forming apparatus20forms an image on the basis of the received image signal in the following manner.

The image forming apparatus20includes a controller21that controls operations of the components of the image forming apparatus20. The setting signal and the image signal received from the document reading apparatus10are input to the controller21of the image forming apparatus20. Then, the image forming apparatus20forms an image on the basis of the received setting signal and image signal under the control of the controller21.

Two sheet trays31are accommodated at the bottom of the image forming apparatus20. Each of the sheet trays31stores stacked sheets P. The size of the sheets P may differ between the two sheet trays31. The sheet trays31can be pulled out and pushed in for refilling sheets.

From one of the two sheet trays31(e.g., the sheet tray31storing the sheets P corresponding to the size of the document or corresponding to the size specified by the setting signal), some of the sheets P are sent by a corresponding one of pickup rollers32. The sent sheets P are separated one by one by separation rollers33, and one of the separated sheets P is transported upward such that the leading edge of the sheet P reaches standby rollers34. The standby rollers34serve to send the sheet P such that the timing of the subsequent transport process is adjusted. Thus, the sheet P having reached the standby rollers34is further transported by the standby rollers34such that the subsequent transport process is adjusted.

The image forming apparatus20includes a photoconductor22above the standby rollers34. The photoconductor22rotates in the direction of the arrow A. A charging unit23, an exposure unit24, a developing unit25, a transfer unit26, and a cleaner27are provided around the photoconductor22.

The photoconductor22has a cylindrical shape. The photoconductor22stores an electric charge when charged, and releases the electrical charge when subjected to exposure. Thus, an electrostatic latent image is formed on the surface of the photoconductor22.

The charging unit23charges the surface of the photoconductor22to a specific charge potential.

The exposure unit24receives, from the controller21, the image signal that is obtained by the document reading apparatus10as described above. Then, the exposure unit24outputs exposure light modulated in accordance with the image signal. The photoconductor22is exposed to the exposure light, so that an electrostatic latent image is formed on the surface of the photoconductor22.

After the electrostatic latent image is formed on the surface of the photoconductor22by exposure of the exposure light, the electrostatic latent image is developed by the developing unit25. The developing unit25includes a toner storage25a, a toner supply path25b, and a developing roller25c. In the developing unit25, the toner stored in the toner storage25ais sent to an area in the vicinity of the developing roller25cthrough the toner supply path25b. Then, the toner is supplied to the photoconductor22by the developing roller25c, so that the electrostatic latent image is developed. Thus, a toner image is formed on the surface of the photoconductor22.

The standby rollers34send the sheet P such that the sheet P reaches a position facing the transfer unit26at the timing when the toner image on the photoconductor22reaches that position. The toner image of the photoconductor22is transferred to the sent sheet P by the transfer unit26.

The toner remaining on the photoconductor22is removed from the photoconductor22by the cleaner27.

The photoconductor22, the charging unit23, the exposure unit24, the developing unit25, the transfer unit26, and the cleaner27together correspond to an example of an image forming unit according to an exemplary embodiment of the present invention.

The sheet P with the toner image transferred thereto further advances in the direction of the arrow B. The sheet P is heated and pressed by a fixing unit100, so that an image as a fixed toner image is formed on the sheet P.

The sheet P having passed through the fixing unit100advances to a discharge unit200in the direction of the arrow C, is further sent by the discharge unit200in the direction of the arrow D, and is discharged onto a sheet discharge table28.

The image forming apparatus20is capable of forming images on both sides of the sheet P. In the case of forming images on both sides of the sheet P, after an image is formed on a first side of the sheet P as described above, the sheet P is transported to a reverse position in the direction of the arrows C and D by the discharge unit200. At the reverse position, the trailing edge of the sheet P is inserted into the discharge unit200. Subsequently, the discharge unit200reverses the sheet transport direction to the direction of the arrow E opposite to the direction of the arrow D, so that the sheet P is drawn in the direction of the arrow E. Then the drawn sheet P advances in the direction of the arrow F, and is further transported by transport rollers35in the direction of the arrow G and the arrow H so as to reach the standby rollers34again. By the time the sheet P reaches the standby rollers34, the sheet P has been turned over. Then, the standby rollers34send the sheet P such that a second side of the sheet P opposite to the first side on which the image has been formed faces the photoconductor22. Then, an image is formed on the second side in the same manner as in the case of the first side. After images are formed on both sides of the sheet P in this way, the sheet P is discharged onto the sheet discharge table28.

The image forming apparatus20is configured such that a rear panel29, which covers the fixing unit100and the discharge unit200, is opened by being rotated in the direction of the arrow I about a support point29a. In the case where the sheet P is jammed between the fixing unit100and the discharge unit200, the user may open the rear panel29. When the rear panel29is opened, an opening appears. Then, the user removes the jammed sheet P by inserting the hand into the opening from the lower side of the document reading apparatus10.

FIG. 2is a cross-sectional diagram illustrating the fixing unit100and the discharge unit200of the copying machine1ofFIG. 1. The fixing unit100includes a heating roller101and a pressure roller102. The heating roller101has a cylindrical shape and has a heat source101atherein. The pressure roller102also has a cylindrical shape. The peripheral surface of the pressure roller102is pressed against the peripheral surface of the heating roller101. The sheet having advanced in the direction of the arrow B and reached the fixing unit100is guided by a sheet guide103to a contact point between the heating roller101and the pressing roller102. The sheet is nipped by the heating roller101and the pressure roller102at the contact point.

The heating roller101and the pressure roller102are rotated in the direction of the arrow J while being in contact with each other. Therefore, the sheet having guided to the contact point is nipped by the heating roller101and the pressure roller102at the contact point, and advances toward the discharge unit200. At this point, the sheet is heated by the heating roller101and is pressed by the pressure roller102, so that an image as a fixed toner image is formed on the sheet.

The fixing unit100further includes a frame100athat rotatably supports the heating roller101and the pressure roller102, and a cover104that covers the contact point between the heating roller101and the pressure roller102. The cover104is attached to the frame100aso as to be rotatable about a support point104a. The cover104is closed so as to be in contact with an extending portion100a_1of the frame100a, which extends above the pressure roller102, and to cover the upper side of a first transport path20a. When the sheet passes, an end of the cover104is lifted by the sheet. Further, the fixing unit100includes fixing-unit-side guide ribs100a_2that guides the sheet in the first transport path20ato the discharge unit200. The plural fixing-unit-side guide ribs100a_2are arranged in a sheet width direction (a direction perpendicular to the paper surface ofFIG. 2). When the above-described cover104is in the closed position, the end opposite to an end at the support point104aside is disposed between the fixing-unit-side guide ribs100a_2.

The discharge unit200includes a lower frame201that serves as a lower guide in a second transport path20bin the discharge unit200, an upper frame202that serves as an upper guide, and a discharge member203that sends the sheet. The discharge unit200further includes a detector300that detects the sheet having been transported.

The detector300includes a shaft311that is rotatable and extends in a direction perpendicular to the paper surface ofFIG. 2, and a detection claw312fixed to the shaft311. When the leading edge of the sheet reaches the detector300, the detection claw312is rotated together with the shaft311in the upward direction by the leading edge of the sheet, so that the rotation of the shaft311is photoelectrically detected. In this way, the detector300detects whether the sheet has reached the detector300.

The detector300monitors whether the sheet reaches the detector300at the timing when the sheet is supposed to reach the detector300, thereby serving to check whether this apparatus is operating properly. The sheet detection result obtained by the detector300is reported to the controller21(seeFIG. 1). If the sheet does not reach the detector300at the timing when the sheet is supposed to reach the detector300, an error such as paper jam is determined to have occurred. Then, the controller21stops operations of the apparatus and notifies the user of the error.

The image forming apparatus20has a single-sided printing mode for forming an image only on one side of the sheet, and a double-sided printing mode for printing images on both sides of the sheet. The single-sided mode or the double-sided mode is selected on the operation panel15ofFIG. 1, and the selection is reported to the controller21(seeFIG. 1) in the form of a setting signal. When the double-sided printing mode is selected, the discharge member203reverses a rotational direction thereof while transporting the sheet in the direction of the arrow D direction, and thus transports the sheet in the direction of the arrow E. The detector300also serves to determine the timing of reversing the rotation. More specifically, the detector300counts the time elapsed from the detection of the leading edge of the sheet, and reverses the rotation when the trailing edge of the sheet reaches a branch point20dand thus the above-described cover104is closed again.

The discharge unit200has a pressing piece204. The pressing piece204presses, from above, the sheet having been discharged onto the sheet discharge table28so as to prevent the sheet from being lifted and interfering with the discharge of the following sheet.

The pressing piece204is rotatable about an upper end thereof. When the sheet being discharged by the discharge member203pushes the pressing piece204, the pressing piece204rotates so as to open the path of the sheet. Then, when the trailing edge of the sheet passes the discharge member203, the pressing piece204is returned to the position shown inFIG. 2so as to press the trailing edge of the sheet downward. Thus, a discharge path for the following sheet is secured.

The following description is focused on transport of the sheet.

The sheet having passed through the fixing unit100, in which a toner image is fixed onto the first side of the sheet, passes through the first transport path20ain the direction of the arrow C while pushing up the end of the cover104, and then passes through the second transport path20bin the direction of the arrow D while pushing up the detection claw312. When the leading edge of the sheet reaches the discharge member203, the sheet is further transported in the direction of the arrow D by the discharge member203. In the case of the single-sided printing mode, the sheet is directly discharged onto the sheet discharge table28.

In the case of the double-sided printing mode, the sheet with an image formed only on the first side is transported in the direction of the arrow D by the discharge member203in the same manner as in the case of the single-sided printing mode. When the trailing edge of the sheet reaches the branch point20d, the rotation of the discharge member203is reversed. Then, the sheet advances in the direction of the arrow E. The cover104prevents the sheet from entering the first transport path20awhich the sheet has just passed through, so that the sheet is guided by the upper surface of the cover104so as to be transported through a third transport path20cin the direction of the arrow F. The third transport path20cextends to the standby rollers34(seeFIG. 1) so as to meet the first transport path20a. The sheet is turned over by passing through the third transport path20csuch that the second surface on which an image is to be formed faces the photoconductor22(seeFIG. 1). The sheet is sent by the standby rollers34in the same manner as in the case of the formation of an image on the first side. After that, an image is formed on the second side in the same manner as in the case of the formation of an image on the first side. When images are formed on both sides of the sheet in this way, the sheet is discharged onto the sheet discharge table28.

FIG. 3is a perspective view of the discharge unit200as viewed from a discharge member side.FIG. 4is a cross-sectional view of the discharge unit200taken along the line IV-IV inFIG. 3.FIG. 5is a perspective view of the lower frame201and the discharge member203of the discharge unit200with the upper frame202removed.FIG. 6is an enlarged view of the portion indicated by the circle VI inFIG. 5.

The discharge member203includes a driving member210and driven members220. A sheet (not shown) having passed through the second transport path20bofFIG. 4(see alsoFIG. 2) is held between the driving member210and the driven members220. Thus, the sheet is transported in the direction of the arrow D ofFIG. 3(see alsoFIG. 2), and is discharged onto the sheet discharge table28shown inFIGS. 1 and 2.

The driving member210includes a shaft member211, driving rollers212, and curve imparting rollers213. The shaft member211is a rod-shaped member that is rotated by a driving force from a motor (not shown). The driving rollers212are made of rubber, and are press-fitted onto the shaft member211from the axial direction. The driving rollers212transport the sheet by holding the sheet with driven rollers222aand222b. The curve imparting rollers213have a greater diameter than the driving rollers212, and are made of a material having a low coefficient of friction with respect to the sheet. The curve imparting rollers213serve to corrugate the sheet being transported by the driving rollers212, in the width direction of the sheet.

In the case where the sheet comes out flat without being corrugated in the width direction, the leading edge of the sheet being discharged drops onto the sheet discharge table28(seeFIGS. 1 and 2) so as to come into contact with a sheet that has already been discharged onto the sheet discharge table28and thus to push the already discharged sheet in the direction out of the sheet discharge table28. This might result in disordering the sheets stacked on the sheet discharge table28. On the other hand, in the case where the sheet comes out to the sheet discharge table28with a widthwise corrugated shape, the sheet is substantially linearly discharged in the discharge direction, so that the leading edge of the sheet is less likely to drop onto the sheet discharge table28. Thus, the sheet is placed onto the sheet discharge table28without disordering the sheets on the sheet discharge table28.

Each of the curve imparting rollers213of this exemplary embodiment includes plural (two in this exemplary embodiment) components made of resin. The curve imparting rollers213are attached, after the driving rollers212are press-fitted onto the shaft member211, to the shaft member211from a lateral direction orthogonal to the axial direction, instead of being attached to the shaft member211from the axial direction.

The driving member210of this exemplary embodiment includes two curve imparting rollers213. In this exemplary embodiment, two of the driving rollers212are disposed at the center between the two curve imparting rollers213. Supposing that the curve imparting rollers213are designed to be attached to the shaft member211from the axial direction, the driving rollers212and the curve imparting rollers213that are made of different materials need to be alternately attached to the shaft member211. This makes it difficult to assemble the driving member210. On the other hand, each of the curve imparting rollers213of this exemplary embodiment includes two components, and may be attached, after the driving rollers212are press-fitted onto the shaft member211, to the shaft member211from the lateral direction in a manner such that the two components clamp the shaft member211therebetween. Thus, the driving member210is easily assembled.

Each of the driven members220includes a shaft221of the driven member220, and two driven rollers222aand222bdisposed on the opposite ends of the shaft221. The shaft221and the two driven rollers222aand222bare molded integrally from resin. As illustrated inFIG. 5, the two driven members220are arranged in the axial direction (the sheet width direction), and a total of four driven rollers222aand222bare disposed so as to face the respective four driving rollers212of the driving member210.

The shaft221of each driven member220is rotatably supported by bearings201a(seeFIG. 6) formed in the lower frame201. The bearings201ahave a fork shape.

Further, spring members241that press the shaft221of the driven member220toward the driving member210are provided in the vicinity of the respective bearings201a. The driven rollers222aand222bare pressed against the driving rollers212with the biasing force of the spring members241.

In the case where the curve imparting rollers213are provided on the driven members220, if a sheet that does not easily bend, such as a thick sheet, is used, the driven members220are pushed by the sheet so as to be moved away from the driving member210against the biasing force of the spring members241. That is, the driven rollers222aand222bare moved away from the driving rollers212, which might result in an insufficient driving force. In this exemplary embodiment, since the curve imparting rollers213are included in the driving member210, even if a sheet that does not easily bend is used, a sufficient driving force is constantly obtained.

In the following, the curve imparting rollers213will be described in greater detail.

FIGS. 7 and 8are perspective views of one of the curve imparting rollers213attached to the shaft member211of the driving member210as viewed from different angles.

The curve imparting roller213includes two components280made of resin. In this exemplary embodiment, these two components280have the same shape. The two components280of the same shape are oriented in the same direction with respect to the axial direction of the shaft member211, and are displaced from each other by 180 degrees in the rotational direction of the shaft member211, and are coupled together so as to clamp the shaft member211therebetween. Thus, the two components280form the curve imparting roller213.

A joint285between the two components280is formed in an outer peripheral surface286of the curve imparting roller213. This joint285has a so-called stepped shape, including a first portion285aextending in an axial direction (i.e., a direction in which the shaft member211extends) from an axial end280aof the outer peripheral surface286of the curve imparting roller213, a second portion285bcontinuous with the first portion285aand extending in a circumferential direction of the outer peripheral surface286, and a third portion285ccontinuous with the second portion285band extending to another axial end280b. The second portion285bof the joint285extending in the circumferential direction is formed at an inner side in a width direction of the sheet being transported.

Since the joint285is formed into a stepped shape as described above, and since the second portion285bis formed at an inner side in a width direction of the sheet being transported, a transport error due to the leading edge of the transported sheet entering the joint285may be prevented.

FIGS. 9 and 10are perspective views of one of the two components280of the curve imparting roller213attached to the shaft member211as viewed from different angles.FIGS. 11 and 12are perspective views of the other one of the two components280attached to the shaft member211as viewed from different angles.FIGS. 13 and 14are perspective views of a curve imparting roller attachment portion of the shaft member211as viewed from different angles.FIGS. 15 and 16are a plan view and a perspective view, respectively, of the curve imparting roller213as viewed from one side in the axial direction, wherein the two components280are coupled together.FIGS. 17 and 18are plan view and a perspective view, respectively, of the curve imparting roller213as viewed from the other side in the axial direction, wherein the two components280are coupled together.

Each component280includes a projection283that projects axially for engagement with the other component280(seeFIGS. 11 and 15), and a hole284(seeFIGS. 10 and 15) to receive the projection283of the other component280.

In the shaft member211, recesses291and partial flat portions292are formed as illustrated inFIGS. 13 and 14. The recesses291are formed at positions in the shaft member211that are displaced from each other by 180 degrees. Similarly, the flat portions292are formed at positions that are displaced from each other by 180 degrees. On the other hand, each component280of the curve imparting roller213includes a protrusion281that protrudes toward the shaft member211so as to be inserted into the recess291of the shaft member211, and a flat portion282that comes into contact with the flat portion292of the shaft member211so as to be locked against rotation with respect to the shaft member211.

The two components280having the structure described above are coupled together so as to surround the shaft member211. Thus, the attitude of the curve imparting roller213with respect to the shaft member211and the position of the curve imparting roller213in the axial direction are fixed.

Since the curve imparting roller213has the structure described above, the curve imparting roller213may be attached to the shaft member211after the driving rollers212are press-fitted onto the shaft member211. Thus, the driving member210is easily assembled.

A roller material having the same structure as the curve imparting roller described above may be used not only as a curve imparting roller, but also as a transport roller that transports a sheet, such as the standby roller34and the transport roller35of the image forming apparatus20of the copying machine1shown inFIGS. 1 and 2.

FIG. 19is a perspective view of an example of a transport member500.

The transport member500includes a driving member510and two driven members520.

The driving member510includes a shaft member511that is rotated by a motor (not shown), and four driving rollers512that are made of rubber and are press-fitted onto the shaft member511from the axial direction.

Each of the two driven members520includes a shaft member521of the driven member520, and two driven rollers522attached to the shaft member521.

A total of four driven rollers522oppose the respective four driving rollers512, and are pressed against the opposing driving rollers512by spring members (not shown).

A sheet (not shown) is held between the driving rollers512and the driven rollers522so as to be transported by rotation of the driving member510.

Each of the driven rollers522of the driven member520includes two components having the same basic structure as the two components280of the above-described curve imparting roller213.

In the shaft member521of the driven member520ofFIG. 19, recesses and flat portions are formed that are similar to the recesses291and the flat portions292shown inFIGS. 13 and 14.

In the case where the shaft member521of the driven member520ofFIG. 19is supported by bearings similar to the bearings201aofFIGS. 4 and 5, for example, since the shaft member521slidably rotates on the bearings, the friction coefficient of the shaft member521may be made as small as possible. On the other hand, since the driven rollers522transport the sheet by holding the sheet with the driving rollers512, the driven rollers522may have a certain degree of high friction coefficient in order to transport the sheet with a sufficient force, without slipping on the sheet being transported. In the case where these conditions need to be satisfied, it is not possible to integrally mold the shaft member521and the driven rollers522of the driven member520from the same material. Therefore, the shaft member521and the driven rollers522may be molded separately and assembled together. In order to satisfy these conditions, the above-described roller of the type that is formed by assembling plural components may be used as a roller that transports a sheet by holding the sheet with another roller.

AlthoughFIG. 19illustrates an example in which the roller of the type that is formed by assembling plural components is used as the driven roller522, the roller of this type may be used as an roller on the driving member side.

In the above description, as depicted inFIGS. 7 and 8, the components are illustrated that form a joint which includes the first portion285aaxially extending from the axial end280aof the outer peripheral surface286of the roller213, the second portion285bextending in the circumferential direction of the outer peripheral surface286, and the third portion285caxially extending to the other axial end280b. However, a joint to be formed in the exemplary embodiment is not limited to the joint having such a shape. More specifically, the joint is not limited to one that extends linearly from one end to the other end in the axial direction, and may include those having a shape that extends from one end to the other end while bending or curving at least at a portion in the middle thereof. If the joint has such a shape, a transport error due to the leading edge of the transport sheet entering the joint may be prevented. In the case of the joint having such a shape, as in the case described above, at least a part of the bent or curved portion of the joint may be formed at an inner side in a width direction of the sheet being transported.

In the above description, the image forming apparatus that is shown inFIGS. 1 and 2and that forms a monochrome image is illustrated. However, the image forming apparatus according to the above-described exemplary embodiment may be implemented as an image forming apparatus that forms a color image. Further, the sheet transport device according to the above-described exemplary embodiment may be applied not only to image forming apparatuses, but also to other apparatuses having a mechanism that transports a sheet.