Patent Application
20140361483
The present invention relates to a sheet conveying apparatus configured to correct a skew feed of a sheet being conveyed, and an image forming apparatus including the sheet conveying apparatus.
In general, in an image forming apparatus, accuracy of a recording position (hereinafter referred to as “recording accuracy”) of an image with respect to a sheet is one of the important factors from the viewpoint of keeping the image quality. Therefore, for example, when a sheet being conveyed is skewed in an image formation, it is necessary to correct the skewed sheet to form an image in an appropriate position on the sheet. As described above, various sheet conveying apparatus having a skew feed correction function are proposed to improve the recording accuracy in the conventional image forming apparatus.
For example, the sheet conveying apparatus described in Patent Literature 1 includes a plurality of conveying roller pairs configured to convey a sheet to an image forming portion, which are arranged on an upstream side in a sheet conveying direction so as to be closest to the image forming portion (hereinafter simply referred to as “upstream side”), and a locking member rotatable about a rotary shaft for one roller of the conveying roller pairs. The locking member has an abutment surface against which the sheet abuts, and is urged by an urging spring so that the abutment surface is located at a home position (position at which a leading edge of a skewed sheet is brought into abutment with the abutment surface so that skew feed is corrected). When a leading edge of the conveyed sheet abuts against the abutment surface of the locking member, the sheet is locked by an urging force applied to the locking member, and the locked sheet is deflected to be curved to form a loop. The loop thus formed causes the leading edge portion of the sheet to be aligned with a width direction orthogonal to the sheet conveying direction, to thereby correct the skew feed. After that, when the locking member is pushed and rotated by stiffness of the sheet, the sheet is nipped by nips of the conveying roller pairs with the leading edge of the sheet being aligned in the width direction, and conveyed to a downstream side by the conveying roller pairs.
By the way, in recent years, much higher throughput (number of sheets subjected to image formation per unit time) of an image forming apparatus has been demanded. In order to meet this demand, it has been required to convey sheets at a higher speed, and reduce a distance between a trailing edge of a preceding sheet and a leading edge of a succeeding sheet (hereinafter referred to as “sheet-to-sheet distance”). In accordance therewith, it is necessary to return the locking member to its home position within a short sheet-to-sheet distance.
In this context,
In this case, a requisite minimum sheet-to-sheet distance is equal to a total distance of a distance D1 from a position at which a trailing edge of a preceding sheet S passes the abutment surface 170a of the locking member 170 to the home position HP at which the skew feed of the sheet S is corrected, and a distance D2 required for conveying a succeeding sheet S to the home position HP while the preceding sheet S is moved by the distance D1. The locking member 170 performs reciprocating rotation, and hence the distance D1 is generated so as to return the locking member 170 to the home position HP after the sheet S passes through the nip N, and the locking member 170 takes a time ΔT for moving the distance D1. On the other hand, the distance D2 is a distance (ΔT×V) obtained by multiplying the time LT during which the locking member 170 moves the distance D1 by a conveying speed V of the sheet S. As the conveying speed V of the sheet S becomes higher, the distance becomes longer. Therefore, in the conventional sheet conveying apparatus, when the conveying speed V of the sheet S is increased, the sheet-to-sheet distance needs to be set longer, and hence further enhancement of the throughput is practically impossible.
Thus, in the sheet conveying apparatus in which skew feed of sheets is corrected by using the locking member, enhancement of throughput of the sheet conveyance has been limited due to a time period for returning the locking member.
In view of the circumstances, the present invention provides a sheet conveying apparatus configured to enhance throughput, and an image forming apparatus including the sheet conveying apparatus.
According to the present invention, there is provided a sheet conveying apparatus, including: a sheet conveying path through which a sheet is conveyed; a locking member having an abutment surface against which a leading edge of the sheet conveyed through the sheet conveying path abuts so that a skew feed of the sheet is corrected; a holding member configured to hold the locking member, the holding member being rotated integrally with the locking member from a waiting position when the locking member is pushed by the leading edge of the sheet being conveyed; a roller pair configured to nip the sheet of which the leading edge is in abutment against the abutment surface of the locking member; a first urging portion configured to urge the holding member so as to move the holding member to the waiting position after the sheet is nipped between the roller pair; a movable support portion configured to support the locking member in a manner that the locking member is movable with respect to the holding member so that the locking member is located in a retracted position in which the locking member is brought into contact with a surface of the sheet being conveyed by the roller pair and allows the sheet to pass in a state in which the holding member is located in the waiting position; and a second urging portion configured to urge the locking member in a manner that the locking member is moved from the retracted position to a position in which the abutment surface abuts against a leading edge of a succeeding sheet as a trailing edge of the sheet being conveyed by the roller pair passes the locking member.
According to the present invention, the throughput can be enhanced.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
In the following, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. The image forming apparatus according to the embodiment is an image forming apparatus, such as a copier, a printer, a facsimile machine, and a multifunction peripheral combining those machines, including a sheet conveying portion serving as a sheet conveying apparatus, which includes a skew feed correcting portion configured to correct a skew feed of a sheet being conveyed. In the following embodiments, the image forming apparatus will be described, taking an electrophotographic color image forming apparatus (hereinafter simply referred to as “image forming apparatus”) 1 configured to form toner images of four colors as an example.
The image forming apparatus 1 according to a first embodiment of the present invention will be described with reference to
As illustrated in
The sheet feeding portion 2 is arranged in a lower portion of the image forming apparatus 1, and includes a detachably mountable sheet containing portion 21 configured to contain the sheets S and a pick-up roller 22 configured to send the sheets S contained in the sheet containing portion 21. The sheet feeding portion 2 includes a separating portion 23 configured to separate one by one the sheets S sent by the pick-up roller 22. The sheet conveying portion 3 is arranged on a downstream side of the sheet feeding portion 2 in a sheet feeding direction (hereinafter simply referred to as “downstream side”), and includes a skew feed correcting portion 7 configured to correct a skew feed of the sheet S. Note that, the sheet conveying portion 3 will be described in detail later.
The image forming portion 4 is arranged on the downstream side with respect to the sheet conveying portion 3, and includes photosensitive drums 41a, 41b, 41c, and 41d on which toner images of yellow, magenta, cyan, and black are respectively formed, and exposure devices 43a, 43b, 43c, and 43d configured to form electrostatic latent images respectively on surfaces of the photosensitive drums 41a to 41d. Further, the image forming portion 4 includes process cartridges 42a, 42b, 42c, and 42d configured to respectively develop the electrostatic latent images formed by the exposure devices 43a to 43d into toner images, transfer portions 44a, 44b, 44c, and 44d configured to respectively transfer the toner images onto the sheet S, and a transfer belt 45 configured to convey the sheet S. The photosensitive drums 41a to 41d are arranged to be rotatable by motors (not shown). The process cartridges 42a to 42d each is made into a unit integrally including a charger, a developing device, and a cleaner, which are arranged around a corresponding one of the photosensitive drums 41a to 41d. The transfer portions 44a to 44d are arranged on an inside of the transfer belt 45 while opposing to the photosensitive drums 41a to 41d, respectively. The transfer belt 45 is arranged so that the rotation of the transfer belt 45 moves the sheets S sequentially to the transfer portions 44a to 44d.
The fixing portion 5 is arranged downstream of the image forming portion 4, and includes a fixing roller 51 provided with a built-in heater and a pressure roller 52 which is pressed against the fixing roller 51. The delivery portion 6 is arranged downstream of the fixing portion 5, and includes a delivery roller pair 61 configured to deliver the sheets S to an outside of the image forming apparatus, and a delivery tray 62 configured to stack the sheets S delivered to the outside of the image forming apparatus.
Next, an image forming process of the image forming apparatus 1 according to the first embodiment structured as described above will be described. When an image forming operation is started, based on image information input from a personal computer (not shown), first, the exposure device 43a emits a laser beam according to an image signal of a yellow color component of an original to the photosensitive drum 41a uniformly charged by the charger of the process cartridge 42a. In this way, a yellow electrostatic latent image is formed on the photosensitive drum 41a. Next, the yellow electrostatic latent image is developed with a yellow toner contained in the developing device of the process cartridge 42a. In this way, the yellow electrostatic latent image is visualized as a yellow toner image. In the same manner as described above, the electrostatic latent images of magenta, cyan, and black are formed respectively on the surfaces of the photosensitive drums 41b to 41d, and those electrostatic latent images are visualized respectively as a magenta toner image, a cyan toner image, and a black toner image.
Along with the above-mentioned toner image forming operation, the sheets S contained in the sheet containing portion 21 are sent to the sheet conveying portion 3 located on the downstream side while being separated one by one by the pick-up roller 22 and the separating portion 23. The sheet S sent to the sheet conveying portion 3 is subjected to skew feed correction by the skew feed correcting portion 7 in the sheet conveying portion 3, and then conveyed to the transfer portion 44a of the image forming portion 4 at a predetermined timing by a registration roller pair 11 located downstream of to the sheet conveying portion 3.
When the sheet S is conveyed to the transfer portion 44a, the yellow toner image formed on the surface of the photosensitive drum 41a is transferred onto the sheet S by transfer bias applied to a transfer charger (not shown). After the yellow toner image is transferred onto the sheet S, the magenta toner image, the cyan toner image, and the black toner image are sequentially transferred in a superimposed manner onto the yellow toner image while the sheet S is conveyed by the transfer belt 45 in the same manner as described above. In this way, a full-color toner image is formed on the sheet S.
The sheet S on which the full-color toner image is transferred is conveyed to the fixing portion 5, and the toners are fused and mixed while being heated and pressurized by the fixing roller 51 and the pressure roller 52. In this way, the full-color toner image is fixed as a full-color image. After that, the sheet S on which the full-color image is fixed is delivered by the delivery roller pair 61 provided downstream of the fixing portion 5 onto the delivery tray 62 arranged in an upper portion of the image forming apparatus 1. With this, the image forming process is completed.
Note that, duplex printing is performed as follows. After an image is fixed to a first side of the sheet S in the fixing portion 5, the delivery roller pair 61 is reversely rotated so that the sheet S is not delivered onto the delivery tray 62 by the delivery roller pair 61 but conveyed into a duplex conveying path 12 with the front side and the back side of the sheet S being reversed. The sheet S conveyed into the duplex conveying path 12 is re-conveyed to the sheet conveying portion 3 by oblique-feed roller pairs 13 and a U-turn roller pair 14 so that the sheet S is subjected to the skew feed correction at the skew feed correcting portion 7 of the sheet conveying portion 3. Then, the sheet S is conveyed to the image forming portion 4 so that an image is fixed to a second side of the sheet S by the image forming portion 4.
Next, the sheet conveying portion 3 of the image forming apparatus 1 according to the first embodiment will be described with reference to
As illustrated in
The feeding frame 33 includes a guide portion 33a configured to guide the sheet S together with a guide frame 15 to the nips N, the guide portion 33a being provided upstream of the nips N formed by the plurality of conveying rotatable members 32 and the plurality of conveying rollers 31. In cooperation with the guide frame 15, the guide portion 33a regulates both sides in a thickness direction of the sheet S on the upstream side of the nips N, and guides the sheet S to the nips N. Further, the guide portion 33a and the guide frame 15 form a loop forming portion 34 in which the sheet S is curved by abutting against abutment surfaces 70a of locking members 70 described below so as to form a loop. Skew feed of the sheet S conveyed to the sheet conveying portion 3 is corrected through formation of the loop in the loop forming portion 34. Note that, in this embodiment, although the guide frame 15 configured to guide the sheet S to the nips N together with the guide portion 33a is additionally provided, a guide portion configured to guide the sheet S to the nips N together with the guide portion 33a may be provided on the feeding frame 33.
The skew feed correcting portion 7 includes a holding member 72 supported by to the feeding frame 33 so as to be rotatable, a first urging spring 73 as a first urging portion configured to urge the holding member 72, and the plurality of locking members 70 supported by the holding member 72 so as to be rotatable. Further, the skew feed correcting portion 7 includes a plurality of second urging springs 71 as second urging portions configured to respectively urge the plurality of locking members 70.
The holding member 72 is supported by the feeding frame 33 so as to be rotatable, about a rotary shaft 72b parallel to the roller shaft 31a, between a first position illustrated in
The locking member 70 is formed into a substantially L-shape, and includes the abutment surface 70a configured to abut against a downstream leading edge (hereinafter simply referred to as “leading edge”) of the sheet S on the sheet conveying path, a striking surface 70b configured to strike against the regulating portion 72a, and a rotary shaft 70c parallel to the rotary shaft 72b. The locking member 70 has one end provided with the abutment surface 70a and the other end provided with the striking surface 70b. The locking member 70 is held by the holding member 72 so as to be movable (rotatable) so that the abutment surface 70a and the striking surface 70b are rotated about the rotary shaft 70c. A movable support portion provided on the holding member 72 rotatably supports the rotary shaft 70c, and hence the locking member 70 is movably held by the holding member 72. The holding member 72 and the locking member 70 are movable (rotatable) integrally with each other. When the holding member 72 is located in the first position, the locking member 70 is movable to a protruding position in which the abutment surface 70a protrudes on the sheet conveying path upstream of the nip N and to a retracted position in which the abutment surface 70a is retracted toward the holding member 72. The striking surface 70b strikes against the regulating portion 72a so as to regulate the rotation of the locking member 70 urged by the second urging spring 71 toward the protruding position (in the direction indicated by the arrow K1 in
Next, how the skew feed correction of the sheet S is performed by the skew feed correcting portion 7 according to the first embodiment will be described with reference to
As illustrated in
First, as illustrated in
When the sheet S enters the sheet conveying portion 3 in the skewed state of the sheet S with respect to the sheet conveying direction X, first, a preceding leading edge of the sheet S abuts against the abutment surface 70a of one of the plurality of locking members 70 (for example, locking member 70H illustrated in
In this process, as illustrated in
When the sheet S forms a predetermined loop, a pressing force of moving the holding member 72 and the locking members 70 in a direction (rotational direction) indicated by the arrow Z1 in
In this context, skew feed correction performance of the skew feed correcting portion 7 becomes greater in proportion to a size of the loop formed inside the loop forming portion 34 formed by the guide portion 33a and the guide frame 15. In other words, as illustrated in
As illustrated in
Further, in accordance with elimination of the pressing force from the sheet S, the holding member 72 starts to be rotated in the direction indicated by the arrow Z2 in
As described above, in the image forming apparatus 1 according to the first embodiment, the sheet S is brought into abutment against the abutment surfaces 70a of the locking members 70 so that skew feed of the sheet S is corrected. Then, the holding member 72 moves to the second position together with the locking members 70. After that, when the leading edge of the sheet S is disengaged from the abutment surfaces 70a at the second position, the holding member 72 returns to the first position and the locking members 70 wait at the retracted position until the sheet S has gone past the nips N. Thus, immediately after the sheet S passes through (has gone past) the nips N, the locking members 70 can be returned to the protruding position at which the leading edge of the succeeding sheet S can be brought into abutment against the abutment surfaces 70a, and the skew feed correcting portion 7 can be returned to the home position. With this, a time period between a time when the sheet S passes through (has gone past) the nips N and a time when the locking members 70 return to the home position can be reduced. As a result, a sheet-to-sheet distance is prevented from increasing even at a higher sheet conveying speed, and hence higher throughput can be obtained.
Further, when the width of the sheet S is relatively large (sheet S indicated by the solid line in
Further, in order to obtain skew feed correction performance which enables more accurate correction of the skew feed of the sheet S, it is preferred that the plurality of locking members 70 corresponding to various widths of the sheets S be arranged at as large intervals as possible and substantially symmetrically with respect to a center of the width of the sheet S. This is because the purpose of reducing correction angle errors of the leading edge of the sheet S with respect to a direction of the rotary shafts of the conveying rollers 31 and the conveying rotatable members 32. Thus, the locking members 70 are arranged in the vicinities of both the end portions of the sheet S to be conveyed. However, it is preferred to arrange the locking member 70 also in a vicinity of a conveying central portion C of the sheet S so that the sheet S having a relatively small width is also subjected to skew feed correction.
Further, at this time, it is preferred to set an interval between the two locking members 70F and 70G on both sides near the conveying central portion C of the sheet conveying path of the sheet S to be smaller than a minimum width of the sheet S. In that case, it is preferred to arrange the abutment surfaces 70a of the locking members 70F and 70G, which abut against the leading edge of the sheet S, slightly more downstream in the sheet conveying direction than the abutment surfaces 70a of the locking members 70E and 70H. With this, even when correcting skew feed of the sheet S having a large width, none of the locking members 70F and 70G abuts against the leading edge of the sheet S. Thus, the correction angle errors can be reduced.
Further, a distance between the abutment surfaces 70a and the nips N between the conveying rollers 31 and the conveying rotatable members 32 is reduced. With this, the sheet S is conveyed while being nipped by the nips N between the conveying rollers 31 and the conveying rotatable members 32 immediately after the locking members 70 correct a skew feed of the sheet S. Thus, an effect of the skew feed correction of the sheet S can be maintained. Further, the plurality of abutment surfaces 70a of the locking members 70, which abut against the leading edge of the sheet S, are provided substantially symmetrically with respect to the center of the sheet width in the sheet width direction Y orthogonal to the sheet conveying direction X. With this, it is possible to obtain higher skew feed correction performance which enables more accurate skew feed correction of the sheet S. Further, local imprints can be prevented from being formed even through abutment of the sheet S against the locking members 70.
Note that, as illustrated in
Next, an image forming apparatus 1A according to a second embodiment of the present invention will be described with reference to
First, an overall structure of the image forming apparatus 1A according to the second embodiment will be described with reference to
As illustrated in
Next, how the skew feed correcting portion 7A of the sheet conveying portion 3A of the image forming apparatus 1A according to the second embodiment corrects skew feed of the sheet S will be described with reference to
As illustrated in
As illustrated in
As described above, the image forming apparatus 1A according to the second embodiment includes the pressing portion 16 and the pressed portion 74. With this, when the locking members 70 are moved to the second position together with the holding member 72, the locking members 70 can be reliably rotated toward the retracted position.
Next, an image forming apparatus 1B according to a third embodiment of the present invention will be described with reference to
First, an overall structure of the image forming apparatus 1B according to the third embodiment will be described with reference to
As illustrated in
The detection lever 17 is connected coaxially to the rotary shaft 70c of the locking members 70, and moved in conjunction with the movement of the locking members 70. The detecting sensor 18 is an optical sensor (for example, photo sensor) forming an optical path with a light emitting element and a light receiving element, and is fixed to the feeding frame 33. The optical path of the detecting sensor 18 is blocked with the detection lever 17 when the holding member 72 and the locking members 70 are in the home position. The detecting sensor 18 produces a detection signal when blocking of the optical path with the detection lever 17 is cancelled. In other words, when the holding member 72 is moved to the second position together with the locking members 70, the leading edge of the sheet S is detected, and in response thereto, the detecting sensor 18 produces a detection signal.
Next, how the skew feed correcting portion 7B of the sheet conveying portion 3B of the image forming apparatus 1B according to the third embodiment corrects skew feed of the sheet S will be described with reference to
When the holding member 72 and the locking members 70 are located in the home position as illustrated in
When the detection signal produced by the detecting sensor 18 is received, the image forming portion 4 starts an operation of forming an image to be transferred onto the conveyed sheet S. After that, the same operation as that in the first embodiment is performed, and as illustrated in
As described above, the image forming apparatus 1B according to the third embodiment includes the detection lever 17 which interlocks with the locking members 70, and the detecting sensor 18. With this, in addition to skew feed correction of the sheet S with the locking members 70 and the holding member 72, the position of the leading edge of the sheet S can be detected. Specifically, the leading edge of the sheet S subjected to skew feed correction at the sheet conveying portion 3B is detected, and hence image formation can be performed by the image forming portion 4 at an appropriate timing based on the position of the sheet S. As a result, for example, it is no longer necessary to additionally provide a leading edge detecting portion configured to detect the position of the leading edge of the sheet S, and hence manufacturing cost can be suppressed.
Further, the detection lever 17 moves in the same way as that of the locking members 70. Thus, substantially simultaneously with completion of the passage of the trailing edge of the sheet S through the sheet conveying path, the detection lever 17 can come to and wait at the home position at which the leading edge of the succeeding sheet S is detected (position at which the optical path of the detecting sensor 18 is blocked). With this, even when a sheet-to-sheet distance is short under a high sheet conveying speed condition, the detection lever 17 can return to the home position so as to detect the leading edge of the succeeding sheet S. In this way, user's demands for higher throughput of the image forming apparatus can be met.
The embodiments of the present invention are described above, but the present invention is not limited to the embodiments described above. Further, the advantages described in the embodiments of the present invention are merely described as most preferred advantages to be achieved by the present invention. Thus, the advantages of the present invention are not limited to those described in the embodiments of the present invention.
For example, in the embodiments of the present invention, the locking members 70 are held by the holding member 72 so as to be rotatable between the protruding position and the retracting position.
However, the present invention is not limited thereto. For example, the locking members 70 may be supported by the holding member 72 so as to pop up and down (slidably move) between the protruding position and the retracted position.
Further, as described in the embodiments of the present invention, the urging springs are used as a first urging unit and a second urging unit, but the present invention is not limited thereto. The first urging unit and the second urging unit may include elastic members configured to urge a holding member and a locking member, respectively. Further, as described in the embodiments of the present invention, the conveying rollers 31 and the conveying rotatable members 32 are used as a sheet conveying unit, but the present invention is not limited thereto. For example, the sheet conveying unit is not particularly limited as long as the sheet S can be nipped and conveyed.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-025190, filed Feb. 8, 2012, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-025190 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2013/052779 | 1/31/2013 | WO | 00 | 6/16/2014 |
