JP2012030931A - Sheet feeding device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeding device that can stabilize a position of end of a sheet because a registration roller by catching the sheet without rotating itself when the sheet contacts with the registration roller.SOLUTION: The sheet feeding device 10 includes: the registration roller 11 disposed along a sheet feeding path S; a roller gear 11g that is fixed to a rotation shaft 11s of the registration roller 11; a drive gear 12 coupled with the roller gear 11g; and a drive means 13 that rotates forwardly and reversely the drive gear 12. The drive means 13 stops the drive gear 12 after rotating it in a reverse direction where the sheet is fed when the sheet is fed.

Description

  The present invention relates to a sheet conveying apparatus, and also relates to an image forming apparatus including the sheet conveying apparatus.

  2. Description of the Related Art Conventionally, in an apparatus for forming an image on a sheet such as a copying machine, a multifunction machine, a printer, and a facsimile, the position of the image is adjusted with respect to the sheet immediately before the image is formed. Specifically, after the sheet is fed to the nip portion of the registration roller that conveys the sheet to the image forming unit until the sheet is bent, the registration roller is rotated so as to synchronize with the image forming unit.

  FIGS. 11A and 11B are explanatory views showing the sheet conveying operation in the conventional image forming apparatus, wherein FIG. 11A is a side view showing the main part of the image forming apparatus, and FIG. It is an enlarged view which shows the part which a roller gear meshes with.

  In the conventional image forming apparatus, the registration roller 21 includes a driving roller 21a in which a roller gear 21g is fixed to a rotating shaft 21s, and a driven roller 21b arranged to face the driving roller 21a. The driven roller 21b is supported on the rotating shaft 21m so as to rotate in accordance with the rotation of the driving roller 21a. The driving roller 21a and the driven roller 21b are configured to rotate with the paper P interposed therebetween. The roller gear 21g is meshed with the drive gear 22, and the drive gear 22 is connected to drive means (not shown) that rotates the drive gear 22.

  When transporting the paper P, the roller gear 21g rotates as the drive gear 22 rotates. When the transport of the paper P is completed, the drive gear 22 is stopped. The position of the roller gear 21g when the drive gear 22 is stopped is shown as a two-dot chain line in FIG. When the drive gear 22 is stopped, the teeth of the roller gear 21g and the teeth of the drive gear 22 are in contact with each other, and a backlash BL occurs in the direction in which the paper P of the roller gear 21g is conveyed.

  In the conventional image forming apparatus, when the paper P is fed to the registration roller 21, the leading edge of the paper P is temporarily stopped at the nip portion NP. (The leading edge of the sheet P coincides with the auxiliary line L1 shown in FIG. 11A.) When the sheet P is further fed and bent, the thrust F that rotates the driving roller 21a (roller gear 21g) is generated. The thrust F acts in the direction of conveying the paper P, and the backlash BL exists in the direction of conveying the paper P. Therefore, the roller gear 21g can be easily rotated until the teeth of the roller gear 21g contact the teeth of the drive gear 22. Can do. As a result, the registration roller 21 rotates and the leading edge of the paper P may penetrate the nip portion NP, which makes it difficult to align the leading edge of the paper.

  Furthermore, since the thrust F varies depending on the type, temperature, humidity, and the like of the paper, there is a problem that the position of the front end of the paper is not constant.

  In order to solve the above-mentioned problem, a technique is considered in which the paper is fed to the nip portion of the registration roller, and then the registration roller is rotated forward and backward to align the leading edge of the paper (for example, see Patent Document 1). ).

Japanese Patent Laid-Open No. 9-255192

  As described above, the conventional image forming apparatus has a problem that it is difficult to align the leading edge of the paper.

  In the paper transport device described in Patent Document 1, the registration roller is rotated forward and backward to move the paper back and forth with respect to the nip portion. By this operation, alignment is performed so that the leading edge of the sheet is at a fixed position. In the paper conveyance device described in Patent Document 1, there is a problem that extra time is required because an operation for conveying the paper in the reverse direction is performed. As a result, the processing speed is reduced, and the first copy time from when the image formation is instructed to when the image-formed paper is discharged is increased.

  The present invention has been made to solve the above-described problem, and when the paper comes into contact with the registration roller, the registration roller receives the paper without rotating, thereby making the position of the front end of the paper constant. It is an object of the present invention to provide a paper transport device that can perform printing.

  It is another object of the present invention to provide an image forming apparatus capable of forming an image at a certain position on a sheet by including a sheet conveying device that makes the position of the leading end of the sheet constant.

  A sheet conveying apparatus according to the present invention includes a registration roller disposed along a sheet conveying path, a roller gear fixed to a rotation shaft of the registration roller, a driving gear combined with the roller gear, and a driving gear. A sheet conveying device including a driving unit configured to rotate in a reverse direction, wherein when the sheet is conveyed, the driving unit rotates the driving gear in a direction opposite to a direction in which the sheet is conveyed and then stops the driving gear. It is characterized by leaving.

  According to this configuration, it is possible to prevent the roller gear from rotating in the forward direction by reducing backlash in the direction in which the roller gear transports the paper (forward direction). Therefore, when the sheet comes into contact with the registration roller, the registration roller receives the sheet without rotating in the forward rotation direction, so that the position of the leading end of the sheet can be made constant.

  The sheet conveying apparatus according to the present invention includes a detecting unit that detects the sheet conveyed to the registration roller, and the driving unit rotates the driving gear in the reverse direction when the detecting unit detects the sheet. It is characterized by that.

  According to this configuration, the drive unit can be operated before the sheet reaches the registration roller by detecting the sheet with the detection unit.

  The sheet conveying device according to the present invention is characterized in that when the drive gear is rotated in the reverse direction, teeth of the drive gear are in contact with teeth of the roller gear.

  According to this configuration, since the backlash in the forward rotation direction of the roller gear can be eliminated, it is possible to reliably prevent the registration roller from rotating in the forward rotation direction.

  An image forming apparatus according to the present invention includes the sheet conveying apparatus according to the present invention and an image forming unit that forms an image on a sheet.

  According to this configuration, it is possible to form an image at a certain position on the sheet by providing the sheet conveying device that makes the position of the leading end of the sheet constant.

  The image forming apparatus according to the present invention includes a rotation amount instruction unit that instructs the drive unit to rotate the drive gear, and the rotation amount instruction unit conveys the sheet from the registration roller to the image forming unit. In this case, the rotation amount set in advance is instructed based on the distance from the registration roller to the image forming means and the distance of the gap between the teeth of the drive gear and the teeth of the roller gear.

  According to this configuration, it is possible to prevent the positional deviation of the image with respect to the paper by correcting the positional deviation that occurs when the gear rotation direction changes.

  In the image forming apparatus according to the present invention, the rotation amount instruction means is set corresponding to a distance of a gap between the teeth of the drive gear and the teeth of the roller gear when the drive gear is rotated in the reverse direction. A rotation amount based on the distance is indicated.

  According to this configuration, when the drive gear is rotated in the reverse direction, the teeth of the drive gear and the teeth of the roller gear can be reliably in contact with each other.

  According to the present invention, it is possible to suppress the rotation of the roller gear in the forward rotation direction by reducing the backlash of the roller gear in the paper conveyance direction (forward rotation direction). Therefore, when the sheet comes into contact with the registration roller, the registration roller receives the sheet without rotating in the forward rotation direction, so that the position of the leading end of the sheet can be made constant.

1 is a side view illustrating a schematic configuration of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention. 1 is a perspective view schematically showing a sheet conveying device according to an embodiment of the present invention. It is a top view of FIG. 2A. FIG. 2 is an explanatory diagram schematically enlarging a portion of the sheet conveying device in FIG. 1. FIG. 3 is a schematic configuration diagram of a portion related to a rotation amount instruction unit of the image forming apparatus according to the embodiment of the present invention. 2A and 2B are explanatory views showing the operation of a sheet conveying device (particularly, a registration roller), in which FIG. 2A is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is an enlarged view which shows the part which engages. 2A and 2B are explanatory views showing the operation of a sheet conveying device (particularly, a registration roller), in which FIG. 2A is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is an enlarged view which shows the part which engages. 2A and 2B are explanatory views showing the operation of a sheet conveying device (particularly, a registration roller), in which FIG. 2A is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is an enlarged view which shows the part which engages. 2A and 2B are explanatory views showing the operation of a sheet conveying device (particularly, a registration roller), in which FIG. 2A is a cross-sectional view taken along the line AA in FIG. 2A, and FIG. It is an enlarged view which shows the part which engages. It is a time chart which shows operation | movement of a drive gear and a roller gear with progress of time. It is another time chart which shows operation | movement of a drive gear and a roller gear with progress of time. It is explanatory drawing which shows the operation | movement of paper conveyance in the conventional image forming apparatus, Comprising: (a) is a side view which shows the principal part of an image forming apparatus, (b) meshes with the drive gear and roller gear of (a). It is an enlarged view which shows a part.

  Hereinafter, an image forming apparatus including a sheet conveying device according to an embodiment of the invention will be described with reference to the drawings.

  FIG. 1 is a side view illustrating a schematic configuration of an image forming apparatus including a sheet conveying device according to an embodiment of the present invention.

  The image forming apparatus 100 is, for example, a color copying machine that forms multicolor and single color images on a predetermined sheet (original) in accordance with image data transmitted from the outside. The automatic document processing apparatus 120 is configured.

  The apparatus main body 110 includes an exposure unit 1, a developing device 2, a photosensitive drum 3, a cleaner unit 4, a charger 5, an intermediate transfer belt unit 6, and a fixing unit 7.

  In addition to the above-described configuration, the image forming apparatus 100 includes a document reading device 90 that reads an image of a document, a document placing table 92 on which a document is placed, and an automatic document processing device 120.

  The document reading device 90 is provided on the upper portion of the apparatus main body 110.

  The document placing table 92 is made of transparent glass and is provided on the upper side of the document reading device 90.

  The automatic document processing device 120 is attached to the upper side of the document placement table 92 and automatically conveys the document onto the document placement table 92. Further, the automatic document processing device 120 is configured to be rotatable around a pivot shaft along the document conveyance direction, and the document can be placed manually by opening the document table 92. ing.

  The image data handled in this image forming apparatus corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Accordingly, the developing device 2, the photosensitive drum 3, the charging device 5, the cleaner unit 4 and the intermediate transfer roller 64 are provided in four each so as to form four types of images corresponding to the respective colors. Magenta and yellow are set, and these constitute four image stations.

  The charger 5 is a charging unit for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. The charger 5 may be a charger type as shown in FIG. 1 or a contact type charger (for example, a roller type or a brush type).

  The exposure unit 1 has a function of exposing the charged surface of the photosensitive drum 3 according to input image data and forming an electrostatic latent image according to the image data on the surface of the photosensitive drum 3. Is. Specifically, the exposure unit 1 includes a polygon mirror that scans a laser beam and optical elements such as a lens and a mirror for guiding the laser beam reflected by the polygon mirror to the photosensitive drum 3.

  As the exposure unit 1, a laser scanning unit (LSU) provided with a laser emitting part, a reflection mirror, and the like, and a writing device (for example, a writing head) in which light emitting elements such as EL and LED are arranged in an array can be used.

  The developing device 2 visualizes the electrostatic latent image formed on the surface of each photosensitive drum 3 with toner of four colors (YMCK).

  The cleaner unit 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt unit 6 is disposed above the photosensitive drum 3 and includes an intermediate transfer belt 61, an intermediate transfer belt driving roller 62, an intermediate transfer belt driven roller 63, an intermediate transfer roller 64, and an intermediate transfer belt cleaning unit 65. ing.

  The intermediate transfer belt driving roller 62, the intermediate transfer belt driven roller 63, and the intermediate transfer roller 64 stretch and support the intermediate transfer belt 61, and the surface of the intermediate transfer belt 61 is directed in a predetermined direction (the arrow D direction in the figure). It is configured to move.

  The intermediate transfer belt 61 is provided so as to be in contact with the respective photosensitive drums 3, and the toner images of the respective colors formed on the photosensitive drums 3 are sequentially transferred to the intermediate transfer belt 61 so as to be transferred. It has a function of forming a color toner image (multicolor toner image) on the belt 61. The intermediate transfer belt 61 is formed in an endless shape using, for example, a film having a thickness of about 100 μm to 150 μm.

  The intermediate transfer roller 64 provides a transfer bias for transferring the toner image on the photosensitive drum 3 to the intermediate transfer belt 61. The intermediate transfer roller 64 is rotatably supported on the side opposite to the photosensitive drum 3 with the intermediate transfer belt 61 interposed therebetween. A high-voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 64 in order to transfer the toner image.

  The intermediate transfer roller 64 is based on a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm, and the surface is covered with a conductive elastic material (for example, EPDM, urethane foam, or the like). With this conductive elastic material, a high voltage can be uniformly applied to the intermediate transfer belt 61. In this embodiment, a roller-shaped transfer electrode is used, but a brush-shaped electrode or the like can also be used.

  As described above, the toner image visualized with the toner of each color on the photosensitive drum 3 is laminated on the intermediate transfer belt 61. The stacked toner images of the respective colors are moved by the rotation of the intermediate transfer belt 61, and are transferred onto the paper P by the transfer roller 8 arranged at the contact position between the paper P and the intermediate transfer belt 61.

  The intermediate transfer belt 61 and the transfer roller 8 are pressed against each other to form a nip region. A voltage for transferring the toner image on the intermediate transfer belt 61 to the paper P is applied to the transfer roller 8 (a high voltage having a polarity (+) opposite to the toner charging polarity (−)). Further, in order to obtain a nip area constantly, either the transfer roller 8 or the intermediate transfer belt driving roller 62 is made of a hard material (metal or the like), and the other is a soft material such as an elastic roller (elastic rubber roller or Foaming resin roller, etc.).

  Incidentally, the toner image on the intermediate transfer belt 61 may not be completely transferred onto the paper P, and the toner may remain on the intermediate transfer belt 61. This residual toner causes toner color mixing in the next step.

  For this reason, the intermediate transfer belt cleaning unit 65 is configured to remove and collect the remaining toner. For example, the intermediate transfer belt cleaning unit 65 includes a cleaning blade that contacts the intermediate transfer belt 61 as a cleaning member. The cleaning blade is supported on the back side of the intermediate transfer belt 61 (that is, the side opposite to the driven roller 63 of the intermediate transfer belt 61) at a position facing the intermediate transfer belt driven roller 63.

  The image forming apparatus 100 further includes a paper feed cassette 81, a manual paper feed cassette 82, and a discharge tray 91.

  The paper feed cassette 81 is a tray for storing paper P used for image formation, and is provided below the exposure unit 1. Further, paper used for image formation can also be placed in the manual paper feed cassette 82.

  The discharge tray 91 is provided above the apparatus main body 110 and is a tray for collecting printed sheets P face down.

  The apparatus main body 110 is provided with a substantially vertical sheet conveyance path S for sending the sheets of the sheet feeding cassette 81 and the manual sheet feeding cassette 82 to the sheet discharge tray 91 via the transfer roller 8 and the fixing unit 7. ing. Pickup rollers 71 a and 71 b, a plurality of transport rollers 72 a to 72 d, a transfer roller 8, and a fixing unit 7 are disposed in the vicinity of the paper transport path S from the paper feed cassette 81 and the manual paper feed cassette 82 to the paper discharge tray 91. Has been.

  The transport rollers 72 a to 72 d are small rollers for promoting and assisting the transport of the paper P, and a plurality of the transport rollers 72 a to 72 d are provided along the paper transport path S.

  The pickup roller 71 a is a drawing roller that is provided near the ends of the paper feed cassette 81 and the manual paper feed cassette 82 and supplies the paper P from the paper feed cassette 81 to the paper transport path S one by one.

  The fixing unit 7 heats and melts an unfixed toner image formed on the paper P and fixes it on the paper P.

  In the paper transport path S, a paper transport device 10 (see FIG. 2A) including a registration roller 11 that feeds the paper P to the transfer roller 8 is disposed. The paper transport device 10 will be described in detail later.

  The registration roller 11 temporarily stops the paper P conveyed from the paper feed cassette 81 and aligns the leading edge of the paper P.

  In the image forming apparatus 100 described above, the paper P transported from the paper feed cassette 81 or the manual paper feed cassette 82 is transported to the registration roller 11 by the transport roller 72a during image formation. Next, the registration roller 11 conveys the paper P to the transfer site in synchronization with the toner image on the intermediate transfer belt 61. The toner image on the intermediate transfer belt 61 is transferred onto the paper P conveyed to the transfer site by the transfer roller 8. When the sheet P passes through the fixing unit 7, the unfixed toner transferred onto the sheet P receives heat and pressure, is melted and fixed, and is fixed on the sheet P. The paper P on which the toner image is fixed is discharged to the discharge tray 91 through the transport roller 72b.

  FIG. 2A is a perspective view schematically showing a sheet conveying apparatus according to the embodiment of the present invention, and FIG. 2B is a plan view of FIG. 2A.

  The sheet conveying apparatus 10 according to the embodiment of the present invention is combined with a registration roller 11 disposed along the sheet conveying path S, a roller gear 11g fixed to a rotation shaft 11s of the registration roller 11, and a roller gear 11g. A drive gear 12 and drive means 13 for rotating the drive gear 12 forward and backward are provided. When the sheet is transported, the driving unit 13 rotates the drive gear 12 in advance in the direction opposite to the direction in which the sheet is transported, and then stops. In the following description, for the sake of explanation, the rotation direction corresponding to the direction in which the paper is conveyed is referred to as a normal rotation direction, and the rotation direction opposite to the normal rotation direction is referred to as a reverse direction.

  According to this configuration, it is possible to prevent the roller gear 11g from rotating in the forward direction by reducing backlash in the direction (forward direction) in which the paper P is conveyed by the roller gear 11g. Therefore, when the paper P comes into contact with the registration roller 11, the registration roller 11 receives the paper P without rotating in the forward rotation direction, so that the position of the leading edge of the paper P can be made constant.

  The registration roller 11 includes a driving roller 11a having a roller gear 11g fixed to a rotating shaft 11s, and a driven roller 11b disposed to face the driving roller 11a. The driven roller 11b is supported on the rotating shaft 11m so as to rotate in accordance with the rotation of the driving roller 11a. The driving roller 11a and the driven roller 11b are configured to rotate with the paper P interposed therebetween.

  The drive means 13 is, for example, a stepping motor or a DC motor. In the present embodiment, the driving means 13 and the driving gear 12 are directly connected. However, the present invention is not limited to this, and for example, the driving means 13 and the driving gear 12 are connected via a plurality of gears. It does not matter. That is, the drive means 12 may be rotated by the drive means 13 and the drive roller 11a may be rotated. Further, by exciting the motor that is the driving means 13, it is possible to suppress the driving gear 12 from rotating due to an external force.

  FIG. 3 is an explanatory diagram schematically enlarging a portion of the sheet conveying device in FIG. Note that components having substantially the same functions and configurations as those in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.

  The image forming apparatus 100 includes a detection unit 14 that detects the paper P conveyed to the registration rollers 11. When the detection unit 14 detects the paper P, the drive unit 13 rotates the drive gear 12 in the reverse direction. According to this configuration, by detecting the paper P by the detection unit 14, the driving unit 13 can be operated before the paper P reaches the registration roller 11.

  The detection unit 14 is disposed along the sheet conveyance path S between the conveyance roller 72 a and the registration roller 11. The detection means 14 is, for example, an actuator or an optical sensor that detects the paper P on the paper transport path S.

  The registration roller 11 is arranged apart from the transfer roller 8 by a predetermined distance L.

  As described above, the image forming apparatus 100 includes the sheet conveying device 10 and the image forming unit that forms an image on a sheet. The image forming means is the apparatus main body 110 and particularly corresponds to the transfer roller 8. According to this configuration, it is possible to form an image at a certain position on the sheet by including the sheet conveying device 10 that makes the position of the leading end of the sheet constant.

  In the image forming apparatus 100, the paper P is transported from the transport roller 72 a to the registration roller 11, and the position of the leading edge of the paper P is adjusted by the registration roller 11. Then, the paper P is conveyed from the registration roller 11 to the transfer roller 8, and the toner image on the intermediate transfer belt 61 is transferred to the paper P.

  FIG. 4 is a schematic configuration diagram of a portion related to the rotation amount instruction unit of the image forming apparatus according to the embodiment of the present invention.

  The image forming apparatus 100 includes a paper transport device 10 and a rotation amount instruction unit 131 that instructs the drive unit 13 to rotate the drive gear 12. When the sheet P is conveyed from the registration roller 11 to the image forming unit (transfer roller 8), the rotation amount calculating unit 131 determines the distance L from the registration roller 11 to the image forming unit (transfer roller 8) and the teeth of the drive gear 12. And a rotation amount set in advance based on the distance between the teeth of the roller gear 11g and the teeth of the roller gear 11g (backlash BLb, see FIG. 7 described later). According to this configuration, it is possible to prevent the positional deviation of the image with respect to the paper by correcting the positional deviation that occurs when the gear rotation direction changes. The rotation amount is, for example, the number of times or time for rotating the drive gear 12, and a plurality of rotation amounts are stored in the memory in advance. When the drive gear 12 is rotated, the rotation amount instruction unit 131 appropriately selects the rotation amount and instructs the drive unit 12.

  The rotation amount instruction unit 131 is realized by a computer program (computer) incorporated in advance in the CPU 130 (central processing unit) of the image forming apparatus 100.

  Next, the operation of transporting the paper P in the paper transport device 10 will be described in detail.

  5 to 8 are explanatory views showing the operation of the sheet conveying device (particularly, the registration roller), in which (a) is a cross-sectional view taken along the line AA in FIG. 2A, and (b) is ( It is an enlarged view which shows the part which the drive gear and roller gear of a) mesh.

  FIG. 5 shows a state after the paper P is conveyed. Here, in order to convey the paper P, the drive means 13 stops the drive gear 12 by rotating the drive gear 12 in the forward rotation direction (the arrow A direction in the figure). As the drive gear 12 rotates in the forward direction, backlash BLa (play in the rotational direction) occurs in the forward direction of the roller gear 11g. When the rotation of the drive gear 12 in the forward direction stops, the roller gear 11g also stops.

  FIG. 6 shows a state where the drive gear 12 is rotated in the reverse direction (the arrow B direction in the figure). When the drive gear 12 rotates in the reverse direction and the teeth of the drive gear 12 come into contact with the teeth of the roller gear 11g, backlash BLb occurs in the reverse direction of the roller gear 11g. The drive means 13 rotates the drive gear 12 by a certain amount and then stops the drive gear 12.

  FIG. 7 shows a state when a new sheet P reaches the registration roller 11. As the sheet P bites into the registration roller 11, a thrust F that rotates the driving roller 11a and the roller gear 11g in the normal rotation direction is applied to the driving roller 11a. Here, since there is no backlash in the forward rotation direction of the roller gear 11g, the roller gear 11g does not rotate in the forward rotation direction. That is, since the teeth of the drive gear 12 and the teeth of the roller gear 11g are in contact, the rotation of the roller gear 11g in the forward rotation direction is suppressed by the drive gear 12. Since the drive gear 12 and the roller gear 11g are not rotating, backlash BLb is generated in the reverse direction of the roller gear 11g.

  FIG. 8 shows a state where a new sheet P is being conveyed. The drive means 13 rotates the drive gear 12 in the forward rotation direction (the direction of arrow A in the figure) and conveys the paper P. By rotating the drive gear 12 in the forward direction, backlash BLa occurs again in the forward direction of the roller gear 11g.

  FIG. 9 is a time chart showing the operation of the drive gear and the roller gear over time.

  FIG. 9 shows whether the drive gear 12 and the registration roller 11 are rotating in the forward rotation direction, stopped, or rotating in the reverse direction. FIG. 9 also shows the state of the sensor. The sensor is turned on when the detection unit 14 is detecting the paper and is turned off when the detection unit 14 is not detecting the paper.

  In the present embodiment, the operation is started when the sheet P is being conveyed (see FIG. 5), and the drive gear 12 and the roller gear 11g are rotating in the forward rotation direction. At this time, since the paper P is outside the detection range of the detection means 14, the sensor is off. When the conveyance of the paper P is completed, the roller gear 11g is also stopped by stopping the drive gear 12.

  Next, the driving unit 13 rotates the driving gear 12 in the reverse direction before the new paper P reaches the registration roller 11 (see FIG. 6). Note that the time from when the drive gear 12 is stopped to when it is rotated in the reverse direction may be set as appropriate.

  When the drive gear 12 is rotated in the reverse direction, the rotation amount of the drive gear 12 may be appropriately indicated, but it is desirable to rotate the teeth of the drive gear 12 so as to contact the teeth of the roller gear 11g. According to this configuration, the backlash in the forward rotation direction of the roller gear 11g can be eliminated, so that the rotation of the registration roller 11 in the forward rotation direction can be reliably prevented.

  The rotation amount instruction means 131 is based on a distance set corresponding to the distance between the teeth of the drive gear 12 and the teeth of the roller gear 11g when the drive gear 12 is rotated in the reverse direction (reverse direction). It is desirable to indicate the amount of rotation. According to this configuration, when the drive gear 12 is rotated in the reverse direction, the teeth of the drive gear 12 and the teeth of the roller gear 11g can be reliably in contact with each other.

  In the present embodiment, the time for rotating the drive gear 12 in the reverse direction from the rotation amount based on the backlash BLa is set as the reverse time Tr. The roller gear 11g starts to rotate with a delay time Td after the driving gear 12 starts to rotate. Further, when the rotation of the drive gear 12 in the reverse direction stops, the roller gear 11g also stops.

  Next, the paper P is transported from the transport roller 12a, the detection means 14 detects the paper P at time t1, and the sensor is turned on. After the conveyance time Tc has elapsed from time t1, the paper P reaches the registration roller 11 at time t2 (see FIG. 7).

  After the preparation time Tp has elapsed from time t2, the drive gear 12 is rotated in the forward direction. Here, since the backlash BLb (refer to FIG. 7) exists in the reverse direction of the roller gear 11g (corresponding to the forward rotation direction in the drive gear 12), the roller gear 11g is rotated after the drive gear 12 starts to rotate. There is a delay by the delay time Td. Therefore, after the delay time Td has elapsed, the roller gear 11g starts to rotate (see FIG. 8), and the paper P is conveyed from the registration roller 11 to the transfer roller 8.

  As described above, in the present embodiment, the sheet P is conveyed by repeating the operations shown in FIGS.

  FIG. 10 is another time chart showing the operation of the drive gear and the roller gear over time.

  In FIG. 10, instead of the operation shown in FIG. 9, the drive gear 12 starts to rotate in the reverse direction from the time t <b> 1 when the detection unit 14 detects the paper P, and the other operations are the same as in FIG. 9. In this case, the inversion time Tr is preferably shorter than the transport time Tc.

  In the paper conveying apparatus 10 according to the present embodiment, when the paper P reaches the registration roller 11, it does not require time for adjusting the position of the leading edge of the paper P, so that the processing speed for paper conveyance is improved. Can do. That is, the first copy time can be shortened.

DESCRIPTION OF SYMBOLS 10 Paper conveying apparatus 11 Registration roller 11a Drive roller 11b Driven roller 11g Roller gear 11s Rotating shaft 12 Drive gear 13 Drive means 14 Detection means

Claims (6)

A sheet comprising a registration roller disposed along a sheet conveyance path, a roller gear fixed to a rotation shaft of the registration roller, a driving gear combined with the roller gear, and a driving means for rotating the driving gear forward and backward. A conveying device,
The paper transporting apparatus, wherein when the paper is transported, the drive means rotates the drive gear in a direction opposite to the paper transport direction and then stops the drive gear. The sheet conveying device according to claim 1,
A detecting means for detecting a sheet conveyed to the registration roller;
The paper conveying device, wherein the driving means rotates the driving gear in the reverse direction when the detecting means detects a paper. The sheet conveying device according to claim 1 or 2,
The sheet conveying device according to claim 1, wherein when the driving gear is rotated in the reverse direction, teeth of the driving gear are in contact with teeth of the roller gear.   An image forming apparatus comprising: the sheet conveying device according to any one of claims 1 to 3; and an image forming unit that forms an image on the sheet. The image forming apparatus according to claim 4,
A rotation amount instruction means for instructing the drive means of a rotation amount for rotating the drive gear;
The rotation amount instruction means, when conveying the paper from the registration roller to the image forming means, the distance from the registration roller to the image forming means, and the distance of the gap between the teeth of the drive gear and the teeth of the roller gear An image forming apparatus characterized by instructing a preset rotation amount based on the above. The image forming apparatus according to claim 5, wherein
The rotation amount instruction means instructs a rotation amount based on a distance set corresponding to a distance of a gap between the teeth of the drive gear and the teeth of the roller gear when rotating the drive gear in the reverse direction. An image forming apparatus characterized by that.

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