Patent Publication Number: US-2017355546-A1

Title: Sheet conveyance device and image forming apparatus

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a sheet conveyance device configured to convey a sheet, and to an image forming apparatus. 
     Description of the Related Art 
     Some printers, copiers, facsimile machines, and automatic document feeders: ADFs include a registration roller pair that corrects the skew of a sheet conveyed thereto. In the case of correcting the skew of a sheet by using the registration roller pair, a pre-registration roller pair disposed upstream of the registration roller pair in a sheet conveyance direction causes the sheet to form a loop by causing the sheet to abut a nip of the registration roller pair whose rotation is stopped. A force generated by the loop rotates the sheet such that a leading end of the sheet is aligned with the registration roller pair, and thus the skew is corrected. Then, the sheet whose skew has been corrected is conveyed by rotating the registration roller pair. 
     The registration roller pair is constituted by a registration driving roller driven by a motor and a registration driven roller that rotates along with the registration driving roller, and the registration driving roller is configured such that a driving force is transmitted from the motor via a gear system such as a gear train. Therefore, there is a risk that, when the sheet abuts the registration roller pair, the skew is not sufficiently corrected as a result of the registration roller pair being slightly rotated due to a backlash of the gear system and thus the leading end of the sheet being nipped by the registration roller pair and the rotation of the sheet being hindered. In consideration of this risk, Japanese Patent Laid-Open No. 2012-30931 proposes a configuration in which the registration driving roller is stopped after being driven against the direction in which the sheet is conveyed. That is, the configuration disclosed in Japanese Patent Laid-Open No. 2012-30931 is made so as to prevent the rotation of the registration roller pair caused by the backlash when the sheet abuts the registration roller pair such that the skew correction does not become insufficient. 
     In recent years, improvement in productivity in successive printing, successive reading, and the like, that is, acceleration of the speed in these operations is desired. In order to improve the productivity, it is required to shorten the intervals between sheets conveyed successively. However, in the case where the intervals are shortened in such a system as disclosed in Japanese Patent Laid-Open No. 2012-30931 described above in which the registration driving roller is rotated in a reverse rotation direction before the sheet abuts the registration roller pair, sufficient time for reverse rotation is not ensured in the shortened intervals, and thus the rotation caused by the backlash is not sufficiently prevented. Therefore, a problem that the skew correction of the sheet becomes insufficient arises. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, a sheet conveyance device includes a registration roller pair including a first roller and a second roller, configured to form a nip by the first roller and the second roller, and configured to correct a skew of a sheet conveyed thereto by allowing the sheet to abut the nip. The first roller includes an outer peripheral surface with a groove portion, the groove portion being formed in a region in which a corner portion of a sheet abuts the outer peripheral surface, and causing a part of the outer peripheral surface to be concave and another part of the outer peripheral surface to be convex in an axial direction. 
     According to a second aspect of the present invention, a sheet conveyance device including a registration roller pair including a first roller and a second roller, configured to form a nip by the first roller and the second roller, and configured to correct a skew of a sheet conveyed thereto by allowing the sheet to abut the nip. The first roller comprises plural grooves arranged in an axial direction. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of an image forming apparatus according to an exemplary embodiment illustrating a configuration thereof. 
         FIG. 2  is a perspective view of a registration roller pair according to the exemplary embodiment. 
         FIG. 3  is a section view of the registration roller pair according to the exemplary embodiment illustrating the shape thereof. 
         FIG. 4  is a schematic diagram illustrating a state in which a sheet is nipped by the registration roller pair according to the exemplary embodiment. 
         FIG. 5  is a schematic diagram illustrating a state in which a sheet is nipped by a registration roller pair having smooth outer peripheral surfaces. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An exemplary embodiment will be described below with reference to  FIGS. 1 to 4 .  FIG. 1  is a section view of an image forming apparatus according to the present exemplary embodiment illustrating a configuration thereof.  FIG. 2  is a perspective view of a registration roller pair according to the present exemplary embodiment.  FIG. 3  is a section view of the registration roller pair according to the present exemplary embodiment illustrating the shape thereof.  FIG. 4  is a schematic diagram illustrating a state in which a sheet is nipped by the registration roller pair according to the present exemplary embodiment. 
     Configuration of Image Forming Apparatus 
     As illustrated in  FIG. 1 , a printer  100  includes a printer body  101  including an image forming portion  102 , a sheet conveyance device  105 , and so forth. An image reading device  2  that reads a document automatically conveyed by an automatic document conveyance device  3  is provided above the printer body  101 . In addition, a sheet feeding device  104  is provided in a lower portion of the printer body  101 . A sheet fed by the sheet feeding device  104  is conveyed to the image forming portion  102  by the sheet conveyance device  105 , subjected to image formation at the image forming portion  102 , and then conveyed to a sheet discharge roller pair  41 . Then, the sheet on which an image has been formed is discharged onto a sheet discharge tray  50  by the sheet discharge roller pair  41 . 
     The image forming portion  102  is of a four-drum full-color type, and includes a laser scanner  13  and four process cartridges  10  that respectively form toner images of four colors of yellow, magenta, cyan, and black. Correspondence to yellow, magenta, cyan, and black will be hereinafter respectively indicated by letters Y, M, C, and K. The process cartridges  10  each include a photosensitive drum  11 , a charging roller  12 , a developing unit  14 , and a cleaner  15 . The charging roller  12  serving as a charging portion, and the developing unit  14  serving as a developing portion. In addition, the image forming portion  102  includes toner cartridges  19  and an intermediate transfer unit  106 . The intermediate transfer unit  106  is disposed above the process cartridges  10 . 
     The intermediate transfer unit  106  includes an intermediate transfer belt  31  that rotates in a state of being looped over a secondary transfer inner roller  34 , a tension roller  34   a , and so forth. In addition, the intermediate transfer unit  106  includes primary transfer rollers  17  that are disposed on the inner peripheral surface side of the intermediate transfer belt  31  and are in contact with the intermediate transfer belt  31  at positions opposing respective photosensitive drums  11 . 
     By applying a transfer bias of a positive polarity to the intermediate transfer belt  31  via the primary transfer rollers  17 , toner images of respective colors having a negative polarity on the photosensitive drums  11  are sequentially transferred onto the intermediate transfer belt  31  so as to be superimposed on one another. In addition, a secondary transfer outer roller  35  is disposed at a position opposing the secondary transfer inner roller  34  in the intermediate transfer unit  106 . The secondary transfer outer roller  35  constitutes a secondary transfer portion at which a color image formed on the intermediate transfer belt  31  is transferred onto a sheet. 
     The sheet feeding device  104  includes a feed cassette  20  and a feed roller  5 . Sheets P accommodated in the feed cassette  20  are fed one by one from the feed cassette  20  by the feed roller  5  by being separated from one another by a separation portion that is not illustrated. The sheet conveyance device  105  includes a pre-registration roller pair  22 , registration roller pair  23  of a registration unit  21 , and so forth. The pre-registration roller pair  22  serves as an example of a conveyance roller pair. A sheet P separated and conveyed by the sheet feeding device  104  is nipped and conveyed by the pre-registration roller pair  22  disposed upstream of the registration roller pair  23 . Then, the skew of the sheet P nipped and conveyed by the pre-registration roller pair  22  is corrected by the registration roller pair  23 , which is disposed downstream of the pre-registration roller pair  22  in a sheet conveyance direction, and the sheet P is further conveyed by the registration roller pair  23 . That is, a corner portion of a leading end of the sheet P nipped and conveyed by the pre-registration roller pair  22  is caused to abut a nip N 1  of the registration roller pair  23  of the registration unit  21  whose rotation is stopped. Then, the skew of the sheet P nipped and conveyed by the pre-registration roller pair  22  is corrected by causing the leading end of the sheet P to align with the nip N 1  and the sheet P to form a loop. Afterwards, the registration roller pair  23  is driven to rotate, and the sheet P whose skew has been corrected is nipped and conveyed by the registration roller pair  23 . 
     Then, the registration roller pair  23  conveys the sheet P to a position between the intermediate transfer belt  31  and the secondary transfer outer roller  35  in a manner synchronized with conveyance of the toner image on the outer peripheral surface of the intermediate transfer belt  31 . The color toner image on the outer peripheral surface of the intermediate transfer belt  31  is subjected to a predetermined pressurizing force and electrostatic load bias voltage at a nip N 2  between the secondary transfer outer roller  35  and the secondary transfer inner roller  34  disposed on the inner peripheral surface side of the intermediate transfer belt  31  so as to oppose the secondary transfer outer roller  35 . According to this, the toner image on the outer peripheral surface of the intermediate transfer belt  31  is transferred onto the sheet P. Toner remaining on the intermediate transfer belt  31  after the transfer is removed and collected by a transfer cleaner  36  for preparation for next image formation. 
     The sheet P onto which the toner image has been transferred is conveyed to a fixing portion  40 , and, when the sheet P passes through the fixing portion  40 , the transferred toner image is heated and pressurized and is thus fixed onto the sheet P. Then, the sheet P onto which the toner image has been fixed is discharged by the sheet discharge roller pair  41  onto the sheet discharge tray  50 , which is an upper surface of the printer body  101 . 
     Configuration of Registration Unit 
     The configuration of the registration unit  21  will be described next. As illustrated in  FIG. 2 , the registration unit  21  includes the registration roller pair  23 , a motor  26 , and a gear train  27 . The motor  26  serves as an example of a rotational drive source. The registration roller pair  23  includes a registration driving roller  24  and a registration driven roller  25  rotationally disposed parallel to the registration driving roller  24 . Rotational drive is transmitted to the registration driving roller  24  via the gear train  27  configured to transmit the rotational drive output from the motor  26 . The registration driven roller  25  is disposed so as to oppose the registration driving roller  24 , is urged toward the registration driving roller  24  by an urging member that is not illustrated, and rotates along with the rotation of the registration driving roller  24 . The registration driving roller  24  includes a metal shaft  24   a  and two rubber rollers  24   b . The rubber rollers  24   b  are disposed at positions symmetrical in an axial direction, i.e., a shaft direction, with respect to a conveyance center line CT illustrated in  FIG. 3  and are fixed to the metal shaft  24   a  so as to be relatively unrotatable with respect to the metal shaft  24   a . The metal shaft  24   a  serves as an example of a first rotation shaft, and the rubber rollers  24   b  serve as an example of plural first rollers. In addition, the registration driven roller  25  includes a metal shaft  25   a  and two plastic rollers  25   b . The plastic rollers  25   b  are disposed at positions symmetrical in the axial direction with respect to the conveyance center line CT illustrated in  FIG. 3  and are fixed to the metal shaft  25   a  so as to be relatively unrotatable with respect to the metal shaft  25   a . The metal shaft  25   a  serves as an example of a second rotation shaft, and the plastic rollers  25   b  serve as an example of plural second rollers. That is, the rubber rollers  24   b  and the plastic rollers  25   b  are disposed at such positions that the rubber rollers  24   b  oppose and are in contact with the plastic rollers  25   b , and the nip N 2  illustrated in  FIG. 1  is formed by these rollers. That is, the rubber rollers  24   b  included in the registration driving roller  24  and the plastic rollers  25   b  included in the registration driven roller  25  constitute, by forming the nip N 2 , plural sheet contact portions that come into contact with and convey a sheet whose skew has been corrected. Moreover, in the present exemplary embodiment, plural groove portions  24   c  are defined in parts of outer peripheral surfaces  24   s  of the rubber rollers  24   b  of the registration driving roller  24 . 
     As illustrated in  FIG. 3 , the groove portions  24   c  are arrayed in the axial direction such that the groove direction thereof is parallel to a plane perpendicular to the axial direction, that is, the groove direction is parallel to the conveyance center line CT of a sheet. The groove portions  24   c  form a shape including recesses and projections in the axial direction, in other words, in a thrust direction, on the outer peripheral surfaces  24   s  of the registration driving roller  24 . That is, the first roller  24  comprises an outer peripheral surface  24   s  with a groove portion  24   c , the groove portion  24   c  being formed in a region in which a corner portion of a sheet abuts the outer peripheral surface, and causing a part of the outer peripheral surface to be concave and another part of the outer peripheral surface to be convex in an axial direction. In the present exemplary embodiment, plural grooves continuous in the circumferential direction are arranged in the axial direction. However, the shape including recesses and projections in the axial direction may be formed by one continuous spiral groove. Intervals between the groove portions  24   c , that is, the pitch of the shape including recesses and projections in the axial direction, which is the distance between centers of adjacent recesses in the present exemplary embodiment, are preferably 0.5 mm or larger and 5 mm or smaller. In the present exemplary embodiment, the pitch is set to 3 mm. Widths of the projections in the outer peripheral surfaces  24   s  constituting the shape including recesses and projections are preferably 0.2 mm or larger and 4 mm or smaller. In the present exemplary embodiment, the width of each projection is set to 1 mm. 
     Plural projection portions are formed in the parts of the outer peripheral surfaces  24   s  of the registration driving roller  24  in which the plural groove portions  24   c  are formed. The parts including the groove portions  24   c  of the registration driving roller  24  are constituted by the rubber rollers  24   b , and parts of the registration driving roller opposing the parts including the groove portions  24   c  are constituted by the plastic rollers  25   b . That is, since the rubber rollers  24   b  have a smaller rigidity than the plastic rollers  25   b , the sheet nipped and conveyed by the registration roller pair  23  is not damaged. 
     The plural groove portions  24   c , that is, the shape including recesses and projections in the outer peripheral surfaces  24   s , are defined in two regions  24   d  provided at positions to be in contact with corner portions of the leading end of a sheet in the axial direction of the registration driving roller  24 . The two regions  24   d  serve as an example of plural regions. That is, since the direction in which the sheet conveyed to the registration roller pair  23  is inclined with respect to the conveyance direction is not constant, either one of the two corner portions of the leading end of the sheet abuts the registration driving roller  24  earlier than the other. Therefore, the regions  24   d  in which the plural groove portions  24   c  are provided are disposed so as to be symmetrical with each other with respect to the sheet conveyance center line CT, that is, the center in the axial direction, of the registration driving roller  24 . In other words, the region in which a corner portion of a sheet abuts the outer peripheral surface includes first and second regions disposed at positions symmetrical in the axial direction with respect to the conveyance center line of the sheet conveyed to the registration roller pair and the first and second regions are provided with first and second groove portions, respectively. It is noted that the first region is located on the first contact portion and the second region is located on the second contact portion which is formed separately from the first contact portion. 
     In addition, even in the case where the dimension, or, the size, of the sheet conveyed to the registration roller pair  23  is the same in the axial direction, the position in the axial direction at which the sheet abuts the registration roller pair  23  may vary. Therefore, the plural groove portions  24   c  are defined in positions determined in consideration of a margin of error such that the positions at which corner portions of the leading end of the sheet abuts are in the regions  24   d , in which the plural groove portions  24   c  are defined, even in the case where the position of the conveyed sheet varies in the axial direction. The sheet whose skew has been corrected is nipped by the plastic rollers  25   b  and parts of the outer peripheral surfaces  24   s  of the rubber rollers  24   b  of the registration driving roller  24  in which the plural groove portions  24   c  are not provided. 
     Sheets of various dimensions, that is, sheets of plural different sizes, can be used in the printer  100 , and thus the dimensions of sheets conveyed to the registration roller pair  23  are not uniform in the axial direction. However, how easily the skew of a sheet can be corrected varies depending on the dimension of the sheet. A sheet of a smaller dimension in the axial direction generates a smaller rotational force, and thus it is more difficult to correct the skew of a sheet of a smaller dimension. Therefore, the regions  24   d  corresponding to positions in the axial direction at which the plural groove portions  24   c  are defined are set at such positions that at least corner portions of the leading end of a sheet of the smallest dimension in the axial direction among plural types of sheets having different dimensions that are preset to be conveyable in the printer  100  abut the regions  24   d . In this way, both of nip-conveyance performance for sheets of large sizes and skew-correction performance for sheets of small sizes can be achieved at the same time. As a matter of course, regions of the plural groove portions  24   c  may be set for dimensions of all types of sheets in correspondence with positions at which corner portions of leading ends of the sheets abut as long as a sufficient nip-conveyance performance for the sheets is secured. 
     Operation in Skew Correction 
     Next, an operation in skew correction by the registration roller pair  23  in the present exemplary embodiment will be described with reference to  FIG. 4 .  FIG. 5  is a schematic diagram illustrating a state in which a sheet is nipped by a registration roller pair having smooth outer peripheral surfaces. In other words,  FIG. 5  is a schematic diagram illustrating a case where groove portions are not formed on the registration driving roller  24  of the registration roller pair  23  as a comparative embodiment. 
     In the printer  100  according to the present exemplary embodiment, in the case of successively conveying sheets, intervals between the sheets are set to be small so as to improve the productivity in successive printing, and there is not enough time to rotate the registration roller pair  23  in a reverse rotation direction. Accordingly, in the printer  100 , control for rotating the registration roller pair  23  in the reverse rotation direction is not performed. Therefore, when a corner portion of the leading end of the sheet P abuts the registration roller pair  23 , the registration roller pair  23  rotates by an amount corresponding to the backlash of the gear train  27  and slightly pinches the corner portion of the leading end of the sheet P. 
     In the case where the groove portions  24   c  are not defined on the registration driving roller  24  as in the comparative embodiment illustrated in  FIG. 5 , a corner portion of the leading end of the sheet P is nipped by the registration roller pair  23  that has rotated by the amount corresponding to the backlash, and the area of a nipped portion of the sheet P is “area Sb”. In contrast, in the case where the plural groove portions  24   c  are defined on the registration driving roller  24  as in the present exemplary embodiment illustrated in  FIG. 4 , portions of the sheet P corresponding to the groove portions  24   c  are not nipped even though the registration roller pair  23  is rotated by the amount corresponding to the backlash. Therefore, only the projections contribute to nipping of the sheet P in the regions  24   d , and thus the area of the portion of the sheet P nipped by the outer peripheral surfaces  24   s  of the registration driving roller  24  is “area Sa”, which is smaller than the area Sb described above. That is, Sb&gt;Sa holds. As a matter of course, if the amount of the backlash of the gear train  27  is the same, the amount of rotation of the registration driving roller  24  rotated due to abutting of the sheet P is also the same. 
     In this way, in the case where the area of the portion of the corner portion of the leading end of the sheet P nipped by the registration roller pair  23  is smaller, the portion is more likely to behave as a point, and thus the sheet P can be rotated in the direction of an arrow illustrated in  FIG. 4  more easily about the corner portion of the leading end of the sheet P nipped by the registration roller pair  23 . Therefore, when the sheet P forms a loop by being kept conveyed by the pre-registration roller pair  22 , the sheet P is more likely to rotate, that is, the skew of the sheet P can be more easily corrected. 
     In addition, as described above, the rubber rollers  24   b  are fixed to the metal shaft  24   a  of the registration driving roller  24 , and the plastic rollers  25   b  are fixed to the metal shaft  25   a  of the registration driven roller  25 . Although the rubber rollers  24   b  have a larger frictional resistance than the plastic rollers  25   b , the rubber rollers  24   b  have a smaller contact area with the sheet P than the plastic roller  25   b  due to the plural groove portions  24   c . Therefore, the frictional force applied to the corner portion of the leading end of the sheet P nipped by the registration roller pair  23  by the rubber rollers  24   b  is reduced due to the smaller contact area, and thus the sheet P is more likely to rotate and the skew of the sheet P can be more easily corrected. 
     To be noted, as described above, the rubber rollers  24   b  have a smaller rigidity than the plastic rollers  25   b . Thus, in the case where, for example, groove portions are defined on the plastic rollers  25   b , there is a risk that the sheet P is damaged when the sheet P is rotated. However, in the present exemplary embodiment, since the groove portions  24   c  are provided on the rubber rollers  24   b , which have a smaller rigidity, the sheet P is not damaged when the sheet P is rotated. 
     Summary of Present Exemplary Embodiment 
     As described above, according to the printer  100  of the present exemplary embodiment, the registration roller pair  23  is slightly rotated by, for example, the backlash of the gear train  27 , and a corner portion of the leading end of a sheet is nipped by the registration roller pair  23 . In this case, since the plural groove portions  24   c  are defined on the registration driving roller  24 , the area of the portion of the leading end of the sheet nipped by the registration roller pair  23  can be reduced. Therefore, the sheet can be more easily rotated about the nipped portion of the leading end of the sheet. Accordingly, it can be attempted to prevent the occurrence of insufficient skew correction even in the case where the intervals of sheets successively conveyed is reduced in order to improve the productivity. 
     In addition, the plural groove portions  24   c  are defined in the regions  24   d  at which corner portions of the leading end of a sheet abut the registration driving roller  24 . Therefore, the sheet can be more easily rotated about a corner portion of the leading end of the sheet nipped by the registration roller pair  23 . 
     In addition, the regions  24   d  in which the plural groove portions  24   c  correspond to regions in which corner portions of a sheet of the minimum size in the width direction, among sheets of sizes preset to be conveyable in the printer  100 , abut the registration roller pair  23 . According to this, it becomes possible to, for example, achieve both of nip-conveyance performance for sheets of larger than the minimum size and skew-correction performance for the sheet of the minimum size at the same time. 
     Further, the regions  24   d  in which the plural groove portions  24   c  are defined are plural regions disposed at positions symmetrical in the axial direction with respect to the conveyance center line of a conveyed sheet. According to this, skew correction of a sheet can be performed sufficiently even in the case where the direction in which the sheet is inclined with respect to the conveyance direction is not constant. 
     In addition, the plural groove portions  24   c  are defined not on the plastic rollers  25   b  but on the rubber rollers  24   b . Thus, the frictional force is reduced and the sheet is more likely to rotate. Further, it can be attempted to prevent a damage to the sheet. 
     OTHER EMBODIMENTS 
     Although a configuration in which the groove portions  24   c  are provided on the registration driving roller  24  of the registration roller pair  23  has been described in the present exemplary embodiment, groove portions may be provided on the registration driven roller  25 . Further, groove portions may be provided on both of the registration driving roller  24  and the registration driven roller  25 . In addition, in the case of providing groove portions on the registration driven roller  25 , the registration driven roller  25  may be constituted by a rubber roller. In this case, the registration driving roller  24  may be constituted by a plastic roller. In addition, groove portions may be provided on the plastic roller, and, in this case, corners of projections formed between groove portions may be rounded such that the sheet is not damaged by the projections. 
     In addition, although a configuration in which the registration roller pair  23  is not caused to rotate in the reverse rotation direction before the sheet comes into contact therewith has been described in the present exemplary embodiment, the registration roller pair  23  may be caused to rotate in the reverse rotation direction for a possible period of time in order to reduce the area of the nipped portion of the sheet even if the reverse rotation does not fully cancel the backlash. 
     In addition, a configuration in which the groove portions  24   c  are defined in correspondence with a sheet of the minimum size among sheets of sizes preset to be conveyable in the printer  100  has been described in the present exemplary embodiment. However, the configuration is not limited to this, and the regions in which the groove portions  24   c  are defined may be set in the axial direction in correspondence with a sheet of the second smallest size, a sheet of the third smallest size, or the like. That is, the regions in which groove portions are defined may be set such that nip-conveyance performance for sheets of large sizes and skew-correction performance for sheets of small sizes can be achieved at the same time. 
     In addition, although a configuration in which the registration roller pair  23  is included in the sheet conveyance device  105  in the printer body  101  has been described in the present exemplary embodiment, groove portions may be defined on a registration roller pair of a sheet conveyance device in the automatic document conveyance device  3 . In this case, it can be attempted to achieve a high speed and a high skew correction performance in successive reading of documents serving as an example of sheets. 
     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. 2016-114407, filed Jun. 8, 2016, which is hereby incorporated by reference wherein in its entirety.