JP2010222070A - Paper conveying device and image forming device equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper conveying device conveying paper without delay, even if the paper is thick. <P>SOLUTION: A paper feeding sensor 74 for detecting a rear end of recording paper is provided on a paper conveying direction upstream side of a paper feeding roller 71 and in the vicinity of the paper feeding roller 71. The paper feeding roller 71 and a pickup roller 19 are rotated and driven until the rear end of the recording paper is detected by the paper feeding sensor 74, conveying of the recording paper by each roller 71, 19 is continued, and each roller 71, 19 is stopped just after the detection of the rear end of the recording paper by the paper feeding sensor 74. The conveying of the recording paper by each roller 71, 19 is continued, therefore, until the rear end of the recording paper is detected by the paper feeding sensor 74, even in the recording paper of the first sheet, conveying force of the recording paper is improved, and contact between each roller 71, 19 and the recording paper does not become paper conveying resistance. As a result, delay is not generated in conveying of the recording paper, even when the recording paper is thick. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet such as a recording sheet or an original sheet, and an image forming apparatus including the sheet conveying apparatus.

  In an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of an image carrier such as a photosensitive drum, and the electrostatic latent image on the surface of the image carrier is developed with a developer to The toner image is transferred from the image carrier to the paper while the toner image is formed, and the paper such as plain paper or OHP is sandwiched and conveyed in the nip portion between the image carrier and the transfer member, and the paper is heated and heated. To fix the toner image on the paper. In some cases, the toner image is once transferred from the image bearing member to the intermediate transfer member, and then the toner image on the intermediate transfer member is transferred from the intermediate transfer member to the sheet to fix the toner image on the sheet.

  In such an image forming apparatus, a paper transport device is incorporated, and the paper is pulled out from a paper feed tray or the like by the paper transport device and transported and supplied. In the conveyance path of the sheet conveying apparatus, a pair of registration rollers (on the upstream side in the sheet conveying direction with respect to the nip portion between the image carrier and the transfer member or the nip portion between the intermediate transfer member and the transfer member) PS (Paper Stop) roller pair) is also provided, and the leading edge of the paper is abutted against the nip area of the resist roller pair in the stopped state, the paper is bent, and the leading edge of the paper is registered by the elastic force of this paper. After aligning in parallel with the roller pair, the sheet is conveyed to the nip portion by the registration roller pair. Accordingly, the sheet is prevented from passing through the nip portion at an angle, and the toner image is not transferred at an angle to the sheet.

  By the way, when the paper is thick and its rigidity is high, when the paper is abutted against the registration roller pair and bends, the paper shape is restored by the elastic force of the paper, and the leading edge of the paper projects the registration roller pair. In some cases, the leading edges of the sheets cannot be aligned. For this reason, in Patent Document 1, a paper selection key that is operated when a paper thicker than normal plain paper such as a postcard is used is provided, and a paper feed roller (pickup) is provided in response to the operation of the paper selection key. (Also referred to as a roller), the paper conveyance time is changed, the conveyance distance of the paper from the paper feed roller to the registration roller pair is shortened, the amount of deflection of the paper hitting the registration roller pair is reduced, and the leading edge of the paper is the registration This prevents the phenomenon that the roller pair is pushed out.

Japanese Patent Laid-Open No. 2-221047

  However, when the sheet is thick, not only the leading edge of the sheet protrudes from the registration roller pair as described above, but also a conveyance delay of the sheet may occur.

  A pickup roller is pressed against the paper on the paper feed tray, and the paper is drawn out and conveyed by the pickup roller. A one-way clutch is provided between the pickup roller and the rotational driving force transmission mechanism. The one-way clutch transmits the rotational driving force in the rotational direction for pulling out the paper to the pickup roller, and the pickup roller in the same rotational direction. Enables the following rotation (idling). Further, the pickup roller is intermittently rotated to draw out the respective sheets on the sheet tray at intervals, and the pickup roller is repeatedly driven and stopped. When the pickup roller is stopped, the sheet reaches the roller pair on the downstream side in the sheet conveyance direction with respect to the pickup roller, the sheet is conveyed by the roller pair and pulled out from the pickup roller, and the pickup roller is driven to rotate. However, the paper transport resistance increases due to the driven rotation of the pickup roller.

  Further, when the sheet is conveyed along the curved conveyance path, the sheet is slidably contacted with the inner wall of the conveyance path while being curved, so that the sheet conveyance resistance is increased.

  In particular, when the paper is thick, the resistance between the paper and the pickup roller and the resistance between the paper and the inner wall of the transport path increase, causing slippage between the paper and the roller pair, resulting in a paper transport delay, which occurs on the paper. Cause printing misalignment.

  For this reason, it has been desired to prevent a paper conveyance delay regardless of the thickness of the paper.

  For example, in the above-mentioned Patent Document 1, the paper conveyance time to the registration roller pair is changed, but this is performed to adjust the amount of deflection of the paper abutted against the registration roller pair. Such a paper conveyance delay cannot be eliminated.

  Accordingly, the present invention has been made to solve the above-described problems, and provides a paper transport device that does not cause a paper transport delay even when the paper is thick, and an image forming apparatus including the same. Objective.

  In order to solve the above-described problems, the paper transport device of the present invention is intermittently driven to rotate so as to pull out the paper tray on which the paper is placed and each paper on the paper tray at intervals. In a paper conveying apparatus comprising a pickup roller and a roller pair for conveying a paper drawn by the pickup roller, a paper detecting means for detecting the presence or absence of the paper drawn by the pickup roller, and a paper by the roller pair When the paper is detected, the pickup roller is rotated while the paper is detected by the paper detection means, and the papers on the paper tray are spaced apart from each other while the paper is not detected by the paper detection means. And a control means for intermittently driving the pickup roller for pulling out.

  Further, the control means rotates the pickup roller while the paper is detected by the paper detection means, and when the leading edge of the paper passes the registration roller pair on the downstream side in the paper transport direction from the roller pair, Regardless of the detection result of the paper detection means, the rotation of the pickup roller is stopped.

  On the other hand, an image forming apparatus according to the present invention includes the above-described sheet conveying device according to the present invention.

  In the paper transport device of the present invention, the presence or absence of the paper drawn by the pickup roller is detected, and the pickup roller is driven to rotate while the paper is detected. If the pick-up roller continues to rotate when there is paper pulled out by the pick-up roller, the paper will be transported not only by the roller pair but also by the pick-up roller, improving the paper transport force and pick-up. There is no sheet conveyance resistance due to roller dragging, and there is no delay in sheet conveyance by the roller pair. Further, while the sheet is not detected, the pickup roller is intermittently driven to pull out the sheets on the sheet tray at intervals. For this reason, the paper on the paper tray can be pulled out with a gap between the paper trays by the pickup roller while eliminating the paper conveyance delay.

  Further, when the leading edge of the sheet passes through the registration roller pair, the rotation of the pickup roller is stopped regardless of the detection result of the presence or absence of the sheet pulled out by the pickup roller. When the leading edge of the sheet passes through the registration roller pair, the conveyance of the sheet can be surely performed. Therefore, the rotational driving of the pickup roller may be stopped.

  On the other hand, since the image forming apparatus according to the present invention includes the above-described sheet conveying apparatus according to the present invention, the same effects can be obtained.

1 is a cross-sectional view showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is an enlarged cross-sectional view illustrating a part of a sheet conveyance path in the image forming apparatus of FIG. 1. FIG. 2 is a block diagram illustrating a control system of the image forming apparatus in FIG. 1. (A), (b) is a figure which shows the conveyance state of the paper in the paper conveyance path | route in the image forming apparatus of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a cross-sectional view showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus 100 records and forms a document image read by the document reading apparatus 101 or an image received from the outside in color or single color on a recording sheet.

  The document reading device 101 reads the document image conveyed by the document conveying unit 42. In the document conveying section 42, when a document is set on the document set tray 41, the document pickup roller 44 is pressed against the document surface and rotated, the document is pulled out from the document set tray 41, and the document is pulled out from the suction roller 45 and the separation pad 46. After passing between the sheets, the sheets are separated one by one and then conveyed to the conveyance path 47.

  In this conveyance path 47, the leading edge of the document comes into contact with the document registration roller pair 49, the leading edge of the document is aligned in parallel with the document registration roller pair 49, and then the document is conveyed by the document registration roller pair 49 and read guide. It passes between 51 and the reading glass 52. Further, the document is conveyed by a pair of conveyance rollers 57 and is discharged to a discharge tray 59 via a discharge roller 58.

  In the document reading device 101, when the document passes between the reading guide 51 and the reading glass 52, the light from the light source of the first scanning unit 53 is irradiated on the surface of the document through the reading glass 52, and the reflected light thereof is read glass 52. The reflected light is reflected by the mirrors of the first and second scanning units 53 and 54 and guided to the imaging lens 55, and the image of the original is converted by the imaging lens 55. An image is formed on a CCD (Charge Coupled Device) 56. The CCD 56 reads a document image and outputs image data indicating the document image.

  In addition, it is possible to read a document placed on the platen glass 61. The document transport unit 42 is pivotally supported on the back side of the document reader 101 so that the document table glass 61 is released when the document transport unit 42 is opened, and the document is placed on the document table glass 61. Can be placed. When the document is placed and the document transport unit 42 is closed, the first and second scanning units 53 and 54 are moved in the sub-scanning direction, and the first scanning unit 53 moves the document surface on the document table glass 61. After the exposure, the reflected light from the document surface is guided to the imaging lens 55 by the first and second scanning units 53 and 54, and the image of the document is formed on the CCD 56 by the imaging lens 55. At this time, the first and second scanning units 53 and 54 are moved while maintaining a predetermined speed relationship with each other, and reflection of the document surface → the first and second scanning units 53 and 54 → the imaging lens 55 → the CCD 56 is performed. The positional relationship between the first and second scanning units 53 and 54 is maintained so that the length of the optical path of the light does not change, and thereby the focus of the original image on the CCD 56 is always accurately maintained.

  The entire image of the original read in this way is transmitted as image data to the laser exposure apparatus 1 of the image forming apparatus 100, and the image forming apparatus 100 records the image on a recording sheet.

  On the other hand, the image forming apparatus 100 includes a laser exposure device 1, a developing device 2, a photosensitive drum 3, a charger 5, a cleaner device 4, an intermediate transfer belt device 8, a fixing device 12, a paper transport path S of the paper transport device 81, The paper feed tray 10 and the paper discharge tray 15 are configured.

  The image data handled in the image forming apparatus 100 uses data corresponding to a color image using each color of black (K), cyan (C), magenta (M), yellow (Y), or a single color (for example, black). This is in accordance with the monochrome image. Accordingly, four each of the developing device 2, the photosensitive drum 3, the charger 5, and the cleaner device 4 are provided so as to form four types of latent images corresponding to the respective colors, and black, cyan, magenta, and yellow are respectively provided. Four image stations Pa, Pb, Pc, and Pd are configured in association with each other.

  The photoconductor drum 3 is disposed at substantially the center of the image forming apparatus 100.

  The charger 5 is a charging means for uniformly charging the surface of the photosensitive drum 3 to a predetermined potential. In addition to a contact type roller type or brush type charger, a charger type charger is used. .

  The laser exposure apparatus 1 is a laser scanning unit (LSU) provided with a laser diode and a reflection mirror, and exposes the surface of a charged photosensitive drum 3 according to image data, and the surface of the photosensitive drum 3 corresponds to image data. An electrostatic latent image is formed.

  The developing device 2 develops the electrostatic latent image formed on the photosensitive drum 3 with black, cyan, magenta, and yellow toners. The cleaner device 4 removes and collects toner remaining on the surface of the photosensitive drum 3 after development and image transfer.

  The intermediate transfer belt device 8 disposed above the photosensitive drum 3 includes an intermediate transfer belt 7, an intermediate transfer belt drive roller 21, a driven roller 22, an intermediate transfer roller 6, and an intermediate transfer belt cleaning device 9. .

  The intermediate transfer belt drive roller 21, the intermediate transfer roller 6, the driven roller 22, etc. stretch and support the intermediate transfer belt 7, and move the intermediate transfer belt 7 in the direction of arrow C.

  The intermediate transfer roller 6 is rotatably supported in the vicinity of the intermediate transfer belt 7, is pressed against the photosensitive drum 3 via the intermediate transfer belt 7, and transfers the toner image on the photosensitive drum 3 to the intermediate transfer belt 7. A transfer bias is applied.

  The intermediate transfer belt 7 is provided so as to be in contact with each photoconductive drum 3, and a color toner image (each color is transferred by sequentially superimposing and transferring the toner image on the surface of each photoconductive drum 3 onto the intermediate transfer belt 7. Toner image). This transfer belt is formed in an endless belt shape using a film having a thickness of about 100 μm to 150 μm.

  The transfer of the toner image from the photosensitive drum 3 to the intermediate transfer belt 7 is performed by the intermediate transfer roller 6 that is in pressure contact with the back surface of the intermediate transfer belt 7. A high voltage transfer bias (a high voltage having a polarity (+) opposite to the toner charging polarity (−)) is applied to the intermediate transfer roller 6 in order to transfer the toner image. The intermediate transfer roller 6 is a roller whose base is a metal (for example, stainless steel) shaft having a diameter of 8 to 10 mm and whose 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 recording paper.

  As described above, the toner images on the surfaces of the respective photosensitive drums 3 are stacked on the intermediate transfer belt 7 and become a color toner image indicated by the image data. The toner images of the respective colors stacked in this way are transported together with the intermediate transfer belt 7 and transferred onto the recording paper by the transfer roller 11a of the secondary transfer device 11 that is in contact with the intermediate transfer belt 7.

  The intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11 are pressed against each other to form a nip region. Further, the transfer roller 11a of the secondary transfer device 11 has a voltage for transferring the toner image of each color on the intermediate transfer belt 7 onto a recording sheet (high polarity (+) opposite to the toner charge polarity (-)). Voltage) is applied. Further, in order to constantly obtain the nip region, either the transfer roller 11a of the secondary transfer device 11 or the intermediate transfer belt drive roller 21 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, foaming resin roller, etc.).

  In addition, the toner image on the intermediate transfer belt 7 may not be completely transferred onto the recording paper by the secondary transfer device 11, and the toner may remain on the intermediate transfer belt 7. Causes color mixing. Therefore, the residual toner is removed and collected by the intermediate transfer belt cleaning device 9. The intermediate transfer belt cleaning device 9 is provided with, for example, a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 7 to remove residual toner, and the intermediate transfer belt is driven by a driven roller 22 at a portion where the cleaning blade comes into contact. 7 The back side is supported.

  The paper feed tray 10 is a tray for storing recording paper, and is provided below the image forming unit of the image forming apparatus 100 to supply the recording paper in the tray. The manual feed tray 17 is a tray on which recording paper is placed, and is provided on the side wall of the image forming apparatus 100 to supply the recording paper in the tray.

  The paper transport device 81 pulls out the recording paper from the paper feed tray 10 or the manual feed tray 17 and transports the recording paper along the paper transport path S. The recording paper is transferred to the secondary transfer device 11, the fixing device 12, and the paper. It is sent out to the discharge tray 15. A pre-registration roller pair 18, a registration roller pair 14, a fixing device 12, and a conveyance roller pair 20 for conveying a recording sheet are arranged along the sheet conveyance path S.

  A pickup roller 16 is provided at the end of the paper feed tray 10, and the recording paper is pulled out from the paper feed tray 10 one by one by the pickup roller 16 and sent out to the paper transport path S. Further, a pickup roller 19 is provided at the end of the manual feed tray 17, and the recording paper is pulled out from the manual feed tray 17 one by one by the pickup roller 19 and sent out to the paper transport path S. The pre-registration roller pair 18 and the plurality of pairs of transport rollers transport the recording paper along the paper transport path S.

  The registration roller pair 14 temporarily stops the recording paper that has been conveyed, aligns the leading edge of the recording paper, and is positioned on the intermediate transfer belt 7 in the nip region between the intermediate transfer belt 7 and the transfer roller 11 a of the secondary transfer device 11. The recording paper is conveyed in a timely manner in accordance with the rotation of the photosensitive drum 3 and the intermediate transfer belt 7 so that the color toner image is transferred onto the recording paper.

  For example, the registration roller pair 14 is based on the detection output of a pre-registration sensor (not shown), and the front end of the color toner image on the intermediate transfer belt 7 in the nip region between the intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11. The recording paper is transported so that is aligned with the tip of the image forming area of the recording paper.

  The fixing device 12 includes a heating roller 31, a pressure roller 32, and the like. The heating roller 31 and the pressure roller 32 sandwich and convey the recording paper that has passed through the nip region between the intermediate transfer belt 7 and the transfer roller 11a of the secondary transfer device 11.

  The heating roller 31 is controlled so as to reach a predetermined fixing temperature based on the detection output of a temperature detector (not shown), and the toner transferred onto the recording paper by thermocompression bonding with the pressure roller 32. It has a function of fusing, mixing, and pressing an image to thermally fix the image on a recording sheet.

  The recording paper after fixing the toner images of the respective colors is discharged face down onto the paper discharge tray 15 by a pair of conveying rollers.

  FIG. 2 is an enlarged cross-sectional view illustrating a part of the sheet conveyance path S from the pickup roller 19 of the manual feed tray 17 to the transfer roller 11a of the transfer device 11.

  As shown in FIG. 2, from the pickup roller 19 to the transfer roller 11a, from the upstream side to the downstream side in the paper conveyance direction, the pickup roller 19, paper feed roller 71 and suction roller 72, conveyance roller pair 20, and pre-registration roller pair 18, a pair of registration rollers 14 and a transfer roller 11a are sequentially arranged.

  The shaft 71 a of the paper feed roller 71 is positioned at a fixed position and connected to a rotation drive mechanism (not shown) of the paper feed roller 71. The arm 73 is pivotally supported by the shaft 71 a, and the shaft 19 a of the pickup roller 19 is pivotally supported on the distal end side of the arm 73.

  A rotation transmission mechanism (not shown) for transmitting the rotational driving force of the paper feed roller 71 to the pickup roller 19 is provided between the paper feed roller 71 and the pickup roller 19, and the paper feed roller 71 rotates clockwise. The pickup roller 19 is rotationally driven in the same direction as the paper feed roller 71. At the same time, as the paper feed roller 71 rotates clockwise, a clockwise moment about the axis 71a is generated in the arm 73, the arm 73 rotates clockwise, and the pickup roller 19 moves to the manual feed tray 17. The recording paper in the manual feed tray 17 is pulled out by the pick-up roller 19 and is pressed against the uppermost recording paper, and the recording paper is conveyed between the paper feed roller 71 and the suction roller 72 to the conveying roller pair 20.

  A one-way clutch (not shown) is provided on the shaft 71 a of the paper feed roller 71. The one-way clutch transmits a rotational driving force in the rotational direction for pulling out the paper to the paper feeding roller 71 and the pickup roller 19 to rotationally drive the paper feeding roller 71 and the pickup roller 19, and also feeds the paper in the same rotational direction. 71 and the pickup roller 19 can be driven to rotate (idling).

  Here, the paper feed roller 71 and the pickup roller 19 are driven to rotate intermittently so that the recording sheets in the manual feed tray 17 are pulled out with a space therebetween. While these rollers 71 and 19 are rotationally driven, a sheet of recording paper is pulled out from the manual feed tray 17 by each of the rollers 71 and 19 and conveyed to the conveying roller pair 20 and the pre-registration roller pair 18. Further, the length of the recording paper on the manual feed tray 17 is detected by a sensor of the manual feed tray 17, and based on the length of the recording paper detected by this sensor, the recording paper drawing start timing and the drawing speed by the pickup roller 19. Thus, the timing immediately before the trailing edge of the recording sheet passes through the pickup roller 19 is obtained, and the rotation of the rollers 71 and 19 is continued until the timing immediately before the passage. Stopped. Thus, the recording paper is continuously pulled out and conveyed by the rollers 71 and 19 until the trailing edge of the recording paper passes through the pickup roller 19.

  When the paper feed roller 71 and the pickup roller 19 are stopped, the rollers 71 and 19 are dragged by the recording paper and rotated (idled), and the recording paper is pulled out from the rollers 71 and 19 and then picked up. The roller 19 stops. Therefore, the next recording sheet is not pulled out immediately, and the next recording sheet is pulled out when the rollers 71 and 19 are driven to rotate again.

  The recording sheet pulled out in this way is conveyed to the registration roller pair 14 via the conveyance roller pair 20 and the pre-registration roller pair 18. At this time, the registration roller pair 14 is temporarily stopped, the leading edge of the recording paper hits the registration roller pair 14, the recording paper bends, and the leading edge of the recording paper is caused by the elastic force of the recording paper. Aligned in parallel. Thereafter, when the rotational driving of the registration roller pair 14 is started, the recording paper is conveyed to the transfer device 11 without being skewed.

  Note that the drive motor for the paper feed roller 71 and the pickup roller 19, the drive motor for the transport roller pair 20 and the pre-registration roller pair 18, and the drive motor for the registration roller pair 14 are provided independently of each other. . For this reason, the paper feeding roller 71 and the pickup roller 19, the conveying roller pair 20, the pre-registration roller pair 18, and the registration roller pair 14 can be separately rotated and stopped.

  Incidentally, the recording sheets placed on the manual feed tray 17 have various sizes, and the lengths thereof are not constant. For this reason, as described above, the length of the recording paper is detected by the sensor of the manual feed tray 17, and the timing immediately before the trailing edge of the recording paper passes through the pickup roller 19 is obtained. The rollers 71 and 19 are continuously driven to convey the recording paper.

  However, there is a case where an object other than the recording paper is placed on the manual feed tray 17 or the mounting position of the recording paper is shifted, and the reliability of the length of the recording paper detected by the sensor of the manual feed tray 17 is low. . If the length of the recording paper detected by the sensor of the manual feed tray 17 is longer than the actual length of the recording paper, the length of the recording paper is detected by the sensor, and the trailing edge of the recording paper is the pickup roller. Even when the timing immediately before passing through the roller 19 is obtained, the trailing edge of the recording sheet passes through the rollers 71 and 19 at this timing, and before the rollers 71 and 19 are stopped by this timing, the rollers are stopped. The next recording sheet is pulled out by 71 and 19. In this case, two or more recording sheets are double-fed and a jam occurs.

  Therefore, conventionally, when the first recording sheet is pulled out from the manual feed tray 17, the length of the recording sheet is set to the minimum length regardless of the length of the recording sheet detected by the sensor of the manual feed tray 17. Therefore, at the timing when the recording sheet is sent to the conveying roller pair 20 or the pre-registration roller pair 18, the rotational driving of the rollers 71 and 19 is stopped, and the recording sheet is fed only by the conveying roller pair 20 and the pre-registration roller pair 18. The recording sheet is conveyed and pulled out from the rollers 71 and 19.

  However, when the recording paper is thick, the resistance between the recording paper and each of the rollers 71 and 19 increases, and therefore slip occurs between the recording paper and the transport roller pair 20 and the pre-registration roller pair 18 to delay the transport of the recording paper. Occurs. Further, since the recording sheet is conveyed along the curved conveying path, the recording sheet is slidably brought into sliding contact with the inner wall of the conveying path to increase the sheet conveying resistance. This causes a slip between the pre-registration roller pair 18 and causes a delay in conveyance of the recording paper. Then, printing misalignment or the like on the recording paper occurred due to such a conveyance delay of the recording paper.

  Therefore, in the present embodiment, a paper feed sensor 74 that detects the trailing edge of the recording paper is provided in the vicinity of the paper feed roller 71 and upstream of the paper feed roller 71 in the paper transport direction. Until the trailing edge of the recording sheet is detected, the sheet feeding roller 71 and the pickup roller 19 are rotationally driven to continue the conveyance of the recording sheet by the rollers 71 and 19, and the trailing edge of the recording sheet by the sheet feeding sensor 74 is detected. Immediately after detection, the rollers 71 and 19 are stopped. Therefore, even if it is the first recording sheet, until the recording sheet passes through the paper feed roller 71, the conveyance of the recording sheet by the rollers 71 and 19 is continued, and the conveying force of the recording sheet is improved. Further, there is no sheet conveyance resistance due to dragging of the rollers 71 and 19. For this reason, even if the recording paper is thick, there is no delay in the conveyance of the recording paper.

  FIG. 3 is a block diagram showing a control system for performing drive control of such a pickup roller. In FIG. 3, three drive motors 82, 83, and 84 are for driving the paper feed roller 71 and the pickup roller 19, the transport roller pair 20, the pre-registration roller pair 18, and the registration roller pair 14, respectively. It is.

  As described above, the paper feed sensor 74 is disposed upstream of the paper feed roller 71 in the paper transport direction and in the vicinity of the paper feed roller 71, and detects the trailing edge of the recording paper.

  The pre-registration sensor 85 is for detecting the leading edge of the recording paper that has passed the pre-registration roller pair 18.

  Further, the paper leading edge sensor 86 is for detecting the leading edge of the recording paper that has passed through the registration roller pair 14 on the upstream side of the registration roller pair 14 in the paper transport direction.

  The control unit 87 rotationally drives the drive motors 82, 83, and 84 based on the detection outputs of the sensors 74, 85, 86, etc., and controls the conveyance of the recording paper.

  In such a configuration, when the recording sheet on the manual feed tray 17 is detected by a sensor (not shown) of the manual feed tray 17, the control unit 87 controls the drive motor 82 to drive the paper feed roller 71. And the pickup roller 19 are rotated, the pickup roller 19 is rotated around the axis 71a of the paper feed roller 71, and the pickup roller 19 is brought into pressure contact with the uppermost recording paper in the manual feed tray 17. To pull out the recording paper. At the same time, the control unit 87 drives and controls the driving motor 83 to rotationally drive the conveyance roller pair 20 and the pre-registration roller pair 18. For this reason, the recording paper is conveyed to the conveyance roller pair 20 through the paper feed roller 71 and the suction roller 72, and further conveyed from the pre-registration roller pair 18 to the registration roller pair 14.

  Here, as shown in FIG. 4A, it is assumed that the length of the recording paper P is the same as or longer than the transport distance from the paper feed roller 71 to the registration roller pair 14. In this case, based on the detection output of the paper feed sensor 74, the control unit 87 determines that there is a recording sheet in the vicinity of the paper feed roller 71 on the downstream side in the paper transport direction, and rotates the paper feed roller 71 and the pickup roller 19. The drive is continued, and the conveyance of the recording paper by these rollers 71 and 19 is continued. Therefore, the recording sheet is conveyed by the paper feed roller 71 and the pickup roller 19, the conveying roller pair 20, and the pre-registration roller pair 18, and the leading edge of the recording sheet comes into contact with the registration roller pair 14. At this time, since the registration roller pair 14 is in a stopped state, the recording paper is bent, and the leading edge of the recording paper is aligned in parallel with the registration roller pair 14.

  The pre-registration sensor 85 is arranged at a predetermined distance from the registration roller pair 14 on the upstream side in the paper conveyance direction. Accordingly, after a predetermined time from the detection of the leading edge of the recording paper by the pre-registration sensor 85, the leading edge of the recording paper comes into contact with the registration roller pair 14 and the recording paper is bent, and the leading edge of the recording paper is parallel to the registration roller pair 14. Will be aligned. Based on the detection output of the pre-registration sensor 85, the control unit 87 determines the detection timing of the leading edge of the recording sheet by the pre-registration sensor 85, and when a certain time has elapsed from this detection timing, that is, when the leading edge of the recording sheet is aligned. Then, the drive motor 84 is driven and controlled, and the registration roller pair 14 is rotationally driven, and the conveyance of the recording paper by the registration roller pair 14 is started.

  Subsequently, the control unit 87 determines whether or not the leading end of the recording sheet has passed the registration roller pair 14 based on the detection output of the sheet leading end sensor 86. The motor 82 is stopped, and the rotational driving of the paper feed roller 71 and the pickup roller 19 is stopped. At this time, the paper feed roller 71 and the pickup roller 19 are dragged by the recording paper and rotated (idled).

  Further, when the trailing edge of the recording paper P passes through the detection position of the paper feed sensor 74, the control unit 87 sets the recording paper near the downstream side in the paper transport direction of the paper feed roller 71 based on the detection output of the paper feed sensor 74. The drive motor 82 is driven and controlled at a timing after a lapse of a certain time from this determination, and the recording paper on the manual feed tray 17 is pulled out by the paper feed roller 71 and the pickup roller 19. As a result, the drawing out of the recording sheets at intervals is resumed.

  That is, as shown in FIG. 4A, when the length of the recording paper P is equal to or longer than the transport distance from the paper feed roller 71 to the registration roller pair 14, the leading edge of the recording paper P is The recording paper P is continuously conveyed by the paper feed roller 71 and the pickup roller 19 until just before the registration roller pair 14 passes, and the paper feed roller 71 and the pickup roller 19 are not dragged and rotated by the recording paper P. The paper feed roller 71 and the pickup roller do not cause the conveyance resistance of the recording paper P. Therefore, the recording paper P does not slip in any of the transport roller pair 20 and the pre-registration roller pair 18, and the transport of the recording paper P to the registration roller pair 14 is normally performed.

  Further, when the leading edge of the recording paper P passes through the registration roller pair 14, the rotation driving of the paper feeding roller 71 and the pickup roller 19 is stopped, so that the paper feeding roller 71 and the pickup roller 19 are dragged by the recording paper P and driven. At this time, the conveying roller pair 20, the pre-registration roller pair 18, and the registration roller pair 14 are rotationally driven by the two drive motors 83 and 84, and the recording paper is recorded by these roller pairs 20, 18, and 14. Since P is conveyed, the conveyance force of the recording paper P is large, no slip occurs between the roller pairs 20, 18, and 14 and the recording paper P, and no conveyance delay of the recording paper P occurs.

  Next, it is assumed that the recording paper P is short as shown in FIG. In this case, when the trailing edge of the recording paper P passes the detection position of the paper feed sensor 74, the control unit 87 sets the recording paper near the downstream side of the paper feed roller 71 in the paper transport direction based on the detection output of the paper feed sensor 74. The drive motor 82 is stopped, and the rotational driving of the paper feed roller 71 and the pickup roller 19 is stopped.

  At this time, the leading edge of the recording sheet does not pass through the registration roller pair 14, and the recording sheet is conveyed only by the conveying roller pair 20 and the pre-registration roller pair 18. After passing through the pickup roller 19, the paper feeding roller 71 and the pickup roller 19 are not dragged by this recording paper, and the recording paper conveyance resistance is small, and the recording paper and conveyance roller pair 20 and pre-registration rollers No slip occurs between the pair 18, and no recording paper conveyance delay occurs.

  That is, when the recording paper P is short as shown in FIG. 4B, the feeding roller 71 and the pickup roller 19 rotate immediately after the trailing edge of the recording paper P passes the detection site of the paper feeding sensor 74. However, since the trailing edge of the recording paper P has passed through the paper feed roller 71 and the pickup roller 19, the conveyance resistance of the recording paper P is small, and the recording paper P and the conveyance roller pair 20 or the pre-registration roller pair No slip occurs between 18, and no conveyance delay of the recording paper P occurs.

  The recording paper P is also conveyed to the registration roller pair 14 via the conveyance roller pair 20 and the pre-registration roller pair 18, and the leading end thereof is brought into contact with the registration roller pair 14 and is further conveyed by the registration roller pair 14. Go.

  Further, when the control unit 87 determines that there is no recording sheet near the downstream side of the sheet feeding direction of the sheet feeding roller 71 based on the detection output of the sheet feeding sensor 74, the control unit 87 is driven at a timing after a certain time has elapsed from this determination. The drive motor 82 is driven and controlled, and the recording paper on the manual feed tray 17 is pulled out by the paper feed roller 71 and the pickup roller 19. As a result, the drawing out of the recording sheets at intervals is resumed.

  As described above, in this embodiment, since the paper feed roller 71 and the pickup roller 19 are rotationally driven until the trailing edge of the recording paper is detected by the paper feed sensor 74, the recording paper conveyance force is improved and the recording is performed. Even if the paper is thick, there is no delay in the conveyance of the recording paper. Further, after the trailing edge of the recording sheet is detected by the sheet feeding sensor 74, intermittent rotation driving of the sheet feeding roller 71 and the pickup roller 19 is started, so that each recording sheet is spaced apart from each other. The drawer can be resumed.

  In the image forming apparatus 100 of the present embodiment, the registration roller pair 14, the pre-registration roller pair 18, and the conveyance roller pair 20 are provided, but depending on the size and structure of the image forming apparatus, the pre-registration roller pair 18 and The conveyance roller pair 20 may be omitted. In this case as well, the same effect can be achieved by controlling the rotation and stop of the paper feed roller 71 and the pickup roller 19 based on the detection output of the paper feed sensor 74.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. It is understood.

DESCRIPTION OF SYMBOLS 1 Laser exposure apparatus 2 Developing apparatus 3 Photoconductor drum 4 Cleaner apparatus 5 Charging device 7 Intermediate transfer belt 8 Intermediate transfer belt apparatus 10 Paper feed tray 11 Secondary transfer apparatus 12 Fixing apparatus 14 Registration roller pair 18 Pre-registration roller pair 20 Conveyance roller Pair 15 Paper discharge tray 31 Heating roller 32 Pressure roller 41 Document set tray 42 Document transport section 44 Document pickup roller 53 First scanning section 54 Second scanning section 55 Imaging lens 56 CCD
71 Feed roller 72 Sabaki roller 73 Arm 74 Feed sensor 81 Paper transport device 82, 83, 84 Driving motor 85 Pre-registration sensor 86 Paper leading edge sensor 87 Control unit

Claims (3)

A paper tray on which paper is placed, a pickup roller that is intermittently driven to pull out the paper on the paper tray with a space between each other, and a paper that has been drawn out by the pickup roller is conveyed. In a paper transport device comprising a roller pair,
Paper detection means for detecting the presence or absence of paper pulled out by the pickup roller;
When the paper is conveyed by the roller pair, the pickup roller is rotated while the paper is detected by the paper detection means, and each paper on the paper tray is removed while the paper is not detected by the paper detection means. And a control means for intermittently driving the pick-up rollers for pulling them out with a space therebetween.   The control means rotates the pickup roller while the paper is detected by the paper detection means, and detects the paper when the leading edge of the paper passes the registration roller pair on the downstream side in the paper transport direction from the roller pair. 2. The paper conveying apparatus according to claim 1, wherein the pickup roller is stopped from rotating regardless of the detection result of the means.   An image forming apparatus comprising the sheet conveying device according to claim 1.

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