JP2012131610A - Method of detecting front end of paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect the front end of subsequent paper even when the rear end of preceding paper and the front end of the subsequent paper are carried partially overlapped with each other.SOLUTION: When the rear end of paper P1 reaches a space 51 formed at a part of a carrying path 5 facing a sensor S, the rear end of the paper P1 moves in the space 51 in a direction separating from the sensor S by the bent carrying path 5 and stiffness of the paper P1. Thereby, the sensor S comes into an off-state from an on-state. Next, when the front end of subsequent paper P2 reaches the sensor S, the sensor S comes into the on-state from the off-state. Thereby, the front end position of the paper P2 is detected.

Description

  The present invention relates to a sheet leading edge detection method, and more specifically, even when a sheet is conveyed in a state where a trailing edge of a preceding sheet and a leading edge of a succeeding sheet partially overlap each other. The present invention relates to a method for detecting the leading edge of a sheet.

  For example, in an image forming apparatus such as a facsimile, a printer, and a copying machine, a plurality of sheet feeding cassettes that store sheets are provided with sheet feeding means such as an FRR (Feed and Reverse Roller) sheet feeding method and an air suction belt sheet feeding method. Thus, the sheets are fed one by one from the uppermost sheet of the sheet feeding cassette to the image forming unit.

  In recent years, the image forming speed has been increased, and the distance between sheets fed out from the sheet feeding cassette (hereinafter, sometimes referred to as “sheet spacing”) has been shortened. For this reason, if the paper feeding speed is different due to insufficient separation of the paper by the paper feeding means or due to variations in the roller diameter of the pair of paper transport rollers, the leading edge of the preceding paper and the following paper Inconveniences that are transported with the rear end partly overlapping.

  Therefore, in the prior art document 1, a sensor is provided in the middle of the paper conveyance path, and after the paper is fed, the time for the trailing edge of the paper to pass the sensor is calculated and predicted, and the trailing edge of the paper is detected at the predicted time. If it is not detected, it is determined that the preceding paper and the following paper are partially overlapped and are transported, and the paper transport speed on the upstream side in the paper transport direction is slowed to ensure the formation of the gap between the papers. Has been proposed.

JP 2005-306503 A

  However, with the proposed technique, it can be detected that the preceding sheet and the succeeding sheet are partially overlapped, but it is not possible to clearly grasp how much the overlapping amount is. Therefore, in order to reliably form the gap between the sheets, it is necessary to unnecessarily increase the time for slowing the sheet conveyance speed of the conveyance roller on the upstream side in the sheet conveyance direction. For this reason, the gap between sheets becomes longer than necessary, and as a result, a predetermined image forming speed may not be obtained.

  The present invention has been made in view of such conventional problems, and its purpose is to reliably detect the leading edge of the succeeding sheet even if the preceding sheet and the succeeding sheet are partially overlapped and conveyed. The purpose is to ensure a predetermined gap between sheets.

  It is another object of the present invention to provide an image forming apparatus that can reliably obtain a predetermined image forming speed without causing a positional shift in image formation.

  A paper leading edge detection method according to a first aspect of the present invention that achieves the above object is a method for detecting the leading edge of a paper being transported, wherein the curved transport path between two pairs of transport rollers is curved, A paper detection unit is provided on the conveyance surface on the inner peripheral side of the conveyance path, and a space is provided on the outer conveyance surface facing the paper detection unit so that the rear end of the sheet can move in a direction away from the paper detection unit. Even when the paper is being transported with the trailing edge of the preceding paper partially overlapping the leading edge of the succeeding paper, the trailing edge of the preceding paper is moved to the space and the trailing The leading edge of the sheet to be detected is detected by the sheet detecting means.

  The paper leading edge detection method according to the second invention is a method for detecting the leading edge of the paper being transported, and is provided on one transport surface of a transport path provided between two successive pairs of transport rollers. A detecting unit is provided, and a space where the trailing end of the sheet can move in a direction away from the sheet detecting unit is provided on the conveying surface side facing the sheet detecting unit, and further downstream in the sheet conveying direction than the sheet detecting unit. In the case where a sheet is transported in a state in which a blowing unit is provided for moving the sheet in a direction away from the detection unit, and the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped. Also, the trailing edge of the preceding sheet is moved to the space by the blowing means, and the leading edge of the succeeding sheet is detected by the sheet detecting means.

  Here, the paper detection means is preferably a contact type detection means.

  In addition, the image forming apparatus according to the third invention bends the conveyance path between two continuous conveyance roller pairs, and provides a sheet detection means on the conveyance surface on the inner peripheral side of the curved conveyance path, A space where the rear end of the sheet can move in a direction away from the sheet detecting unit is provided on the outer peripheral conveyance surface facing the sheet detecting unit, and the trailing end of the preceding sheet is moved to the space to follow. If the leading edge of the sheet is detected by the sheet detecting means and it is determined that the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped, the sheet is conveyed upstream in the sheet conveying direction. It is characterized in that the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is ensured by reducing the conveying speed of the roller pair.

  Furthermore, an image forming apparatus according to a fourth aspect of the invention is provided with a sheet detection unit on one conveyance surface of a conveyance path provided between two consecutive conveyance roller pairs, and a conveyance surface side facing the sheet detection unit And a blower means for moving the paper in a direction away from the detection means on the downstream side of the paper detection direction with respect to the paper detection means. And the trailing edge of the preceding sheet is moved to the space by the blowing means, the leading edge of the succeeding sheet is detected by the sheet detecting means, and the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are detected. Is determined to be partially overlapped, the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet by slowing the conveying speed of the conveying roller pair on the upstream side in the sheet conveying direction. Special to ensure To.

  According to the paper leading edge detection method of the present invention, the trailing edge of the preceding paper and the leading edge of the succeeding paper are separated by the curved conveyance path or the air blowing means, and the leading edge of the succeeding paper is detected by the paper detecting means. Therefore, the leading edge of the succeeding sheet can be reliably detected even when the preceding sheet and the succeeding sheet are conveyed partially overlapping.

  According to the image forming apparatus of the present invention, the leading edge of the succeeding sheet is detected by the sheet detecting means, and the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped and conveyed. If it is determined that there is a gap, the conveyance speed of the pair of conveyance rollers on the upstream side in the sheet conveyance direction is decreased to ensure a predetermined gap between the sheets. Can be definitely obtained.

1 is a schematic diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 2 is an enlarged configuration diagram of a conveyance path from a paper feed cassette to a conveyance roller pair 13 of the image forming apparatus of FIG. 1. It is explanatory drawing which shows an example of the sensor S used by this invention. FIG. 3 is a state diagram for detecting the leading edge of a succeeding paper P2 in the conveyance path shown in FIG. It is a schematic diagram which shows other embodiment of the paper front-end | tip detection method based on this invention. FIG. 10 is a schematic view showing still another embodiment of the paper leading edge detection method according to the present invention.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to these embodiments.

  FIG. 1 is a schematic view of a tandem type color image forming apparatus as an example of the image forming apparatus of the present invention. The image forming apparatus D shown in this figure includes a scanner unit 200 that reads an original image, a printer unit 300 that prints and reproduces the read image on a sheet material, and an operation for inputting print conditions and displaying the operation status of the apparatus. The display unit 400 is configured. The scanner unit 200 is a known unit that reads an image of a document placed on a not-illustrated document glass plate while moving the scanner. The read image data is converted into an electrical signal for each color by an image sensor, and the printer unit 300. Sent to. In addition, the image forming apparatus D includes a control unit 60 that controls the operation of the apparatus and stores image data, and is driven and controlled with specifications designed according to information from various sensors and instructions from the user.

  The printer unit 300 forms an image by an electrophotographic method, and the intermediate transfer unit 20 is installed at a substantially central portion thereof. The intermediate transfer unit 20 includes an intermediate transfer belt 21, a driving roller 23 that stretches the intermediate transfer belt 21, a driven roller 22, and a tension roller 24 that applies tension to the intermediate transfer belt 21 as main components. The intermediate transfer belt 21 rotates counterclockwise in the drawing. The drive roller 23 is rotationally driven by a drive motor 25. A cleaning blade 26 is in contact with the driven roller 22 with the intermediate transfer belt 21 interposed therebetween. The cleaning blade 26 removes residual toner that has not been transferred to the paper P from the surface of the intermediate transfer belt 21.

  Below the lower horizontal portion of the intermediate transfer belt 21, four image forming portions 30Y, 30M, 30C, and 30K corresponding to the colors yellow, magenta, cyan, and black are arranged side by side. In each image forming unit, the surface of the photosensitive member is uniformly charged, then exposed according to the image data converted into an electric signal to form an electrostatic latent image, and the formed electrostatic latent image is developed with toner. And visualized. Then, the toner images formed for the respective colors are primarily transferred to the intermediate transfer belt 21 and overlapped to form a full color toner image. The image forming units 30Y, 30M, 30C, and 30K are supplied with toner from the respective color toner containers 31Y, 31M, 31C, and 31K.

  The sheets P are stacked in the sheet feeding cassette 41, and are sequentially pulled out one by one from the uppermost sheet P by the pickup roller 11, and sent out to the conveyance path 5 by the pair of sheet feeding rollers 12. A sensor (paper detection means) S for detecting the paper P is provided on the downstream side of the paper feed roller pair 12 in the paper conveyance direction. The sheet P is fed by the conveying roller pair 13 to the nip portion (secondary transfer region) between the driving roller 23 and the transfer roller 42 in synchronization with the rotation of the intermediate transfer belt 21. Then, the toner image formed on the surface of the intermediate transfer belt 21 is transferred to the paper P. Thereafter, while the paper P passes through the fixing device 43, the toner image is heated and pressurized to be melted and fixed on the paper P, and the paper P is discharged to the paper discharge tray 45 by the discharge roller 44.

  FIG. 2 shows an enlarged cross-sectional view of the transport path 5 from the paper feed cassette 41 through the paper feed roller pair 12 to the transport roller pair 13. The conveyance path 5 between the paper feed roller pair 12 and the conveyance roller pair 13 is curved. A contact-type sensor S is provided on the inner peripheral conveyance surface of the curved conveyance path 5, and a space 51 is formed on the outer peripheral conveyance surface facing the sensor S.

  FIG. 3 shows an example of the sensor S. The sensor S shown in this figure blocks the optical path between the light emitting unit 711 and the light receiving unit (not shown), and the main body 71 provided with the light emitting unit 711 and the light receiving unit (not shown) facing each other. And a detection rod 72 which is provided so that the other end projects into the conveyance path 5 and is rotatable about a shaft 73. In this sensor S, the detection rod 72 is rotated counterclockwise by the conveyed paper P. Then, one end of the detection rod 72 that has blocked the optical path between the light emitting unit 711 and the light receiving unit (not shown) moves so that the light from the light emitting unit 711 is received by the light receiving unit (not shown). Become. The leading edge of the paper P is detected by the light detection signal. Note that the sensor S that can be used in the present invention is not limited to such a method, and any conventional sensor S can be used as long as it cannot be detected when the paper P passes a predetermined distance or more from the sensor S. A known sensor can be used.

  In the enlarged configuration diagram of FIG. 2, the drive sources of the paper feed roller pair 12 and the transport roller pair 13 are different, and the rotation speed of the paper feed roller pair 12 is variable. The pickup roller 11 is rotated by the same drive source as the paper feed roller pair 12 and is provided so as to be raised and lowered by a drive means (not shown).

  When the paper P is fed from the paper feed cassette 41, the pickup roller 11 waiting in the raised position is lowered and simultaneously rotated counterclockwise, so that the uppermost paper P stored in the paper feed cassette 41 is moved. Pulled in the direction of the pair of paper feed rollers 12. Then, the leading edge of the paper P is sandwiched between the paper feed roller pair 12 and sent out to the conveyance path 5. When the leading edge of the paper P is detected by the sensor S, control such as the start of rotation of the transport roller pair 13 is started.

  Conventionally, when a plurality of sheets are continuously fed, the leading edge of each sheet can be detected by a sensor when there is a gap between sheets. When the continuous sheets are transported in a partially overlapped state, the leading edge of the succeeding sheet cannot be detected. On the other hand, in the detection method of the present invention, the leading edge of the succeeding sheet can be reliably detected even if the preceding sheet and the succeeding sheet are partially overlapped and conveyed.

  FIG. 4 shows a schematic diagram. When the leading edge of the preceding sheet P1 and the leading edge of the succeeding sheet P2 are transported (FIG. 4A), the sheet is formed in a portion of the transport path 5 facing the sensor S. When the trailing edge of the paper P1 reaches the space 51, the trailing edge of the paper P1 moves in a direction away from the sensor S due to the curved conveyance path 5 and the stiffness of the paper P1 (FIG. 4B). ). As a result, the sensor S changes from the on state to the off state. Next, when the leading edge of the succeeding paper P2 reaches the sensor S, the sensor S changes from the off state to the on state (FIG. 4C). Thereby, the leading end position of the paper P2 is detected. Then, for example, the overlap width of the paper P1 and the paper P2 is calculated from the elapsed time from when the leading edge of the paper P1 is detected by the sensor S until the leading edge of the paper P2 is detected and the length of the paper P1 in the transport direction. Then, the conveyance speed of the pair of paper feed rollers 12 is decreased or the conveyance is stopped so that a predetermined interval is formed between the rear end of the paper P1 and the front end of the paper P2.

  FIG. 5 shows another embodiment of the paper leading edge detection method according to the present invention. In the conveyance path 5 between the conveyance roller pair 14 and the conveyance roller pair 15, a curved portion is formed by shifting the middle of the conveyance path in a direction perpendicular to the sheet conveyance direction. In addition, a sensor S is provided on the inner conveyance surface of the curved conveyance path 5, and a space 51 is formed on the outer conveyance surface facing the sensor S. When the rear end portion of the preceding paper P1 reaches the curved portion, the rear end portion of the paper P1 moves away from the sensor S due to the curved conveyance path 5 and the stiffness of the paper P1 as in the above embodiment. Move to. As a result, the sensor S changes from the on state to the off state. Next, when the leading edge of the succeeding paper P2 reaches the sensor S, the sensor S changes from the off state to the on state, and the leading edge position of the paper P2 is detected. In the same manner as in the above-described embodiment, the paper P1 and the paper P2 are calculated based on the elapsed time from the detection of the leading edge of the paper P1 by the sensor S until the leading edge of the paper P2 is detected and the transport direction length of the paper P1. And the conveyance speed of the conveyance roller pair 14 is decreased or conveyance is stopped so that a predetermined interval is formed between the trailing edge of the sheet P1 and the leading edge of the sheet P2.

  FIG. 6 shows another embodiment of the paper leading edge detection method according to the present invention. In the conveyance path 5 between the conveyance roller pair 14 and the conveyance roller pair 15 shown in this figure, a space 51 partially expanded in the direction perpendicular to the sheet conveyance direction is formed on one conveyance surface in the middle of the conveyance path. Is formed. A blower fan (blower unit) 8 is provided in the vicinity of the other conveyance surface facing the space 51, and a sensor S is provided on the upstream side of the blower fan 8 in the sheet conveyance direction. In addition, a plurality of openings for allowing air to pass through are formed on the conveyance surface of the conveyance path 5 facing the blower fan 8.

  In the conveyance path having such a structure, when the rear end portion of the preceding paper P1 reaches the space 51, the blower fan 8 is driven, and the rear end portion of the paper P1 detects the space 51 by the air flow from the blower fan 8. Move away from S. As a result, the sensor S changes from the on state to the off state. Next, when the leading edge of the succeeding paper P2 reaches the sensor S, the sensor S changes from the off state to the on state, and the leading edge position of the paper P2 is detected. Control for ensuring the space between the paper P1 and the paper P2 after the leading edge of the paper P2 is detected is the same as in the above embodiment.

  Note that the attachment position of the blower fan 8 is not particularly limited as long as an air flow for moving the rear end portion of the paper P1 to the space 51 can be formed. For example, the blower fan 8 may be attached to the left side of the conveyance path 5 in FIG. Of course.

  The paper leading edge detection method according to the present invention is useful in that the leading edge of the succeeding sheet can be reliably detected even when the preceding sheet and the succeeding sheet are partially overlapped and conveyed.

5 Conveyance path 8 Blower fan (Blower unit)
S sensor (paper detection means)
51 Space 12 Paper feed roller pair (conveyance roller pair)
13 Transport roller pair 14, 15 Transport roller pair P1, P2 Paper

Claims (5)

A method for detecting the leading edge of a sheet being conveyed,
A conveyance path between two consecutive conveyance roller pairs is curved, and a sheet detection unit is provided on the conveyance surface on the inner peripheral side of the curved conveyance path, and a sheet is formed on the outer conveyance surface facing the sheet detection unit. Providing a space in which the rear end can move in a direction away from the paper detection means;
Even when the paper is being transported with the trailing edge of the preceding paper partially overlapping the leading edge of the succeeding paper, the trailing edge of the preceding paper is moved to the space and the trailing A method for detecting the leading edge of a sheet, wherein the leading edge of the sheet to be detected is detected by the sheet detecting means. A method for detecting the leading edge of a sheet being conveyed,
A direction in which a sheet detection unit is provided on one conveyance surface of a conveyance path provided between two consecutive conveyance roller pairs, and a rear end of the sheet is separated from the sheet detection unit on the conveyance surface side facing the sheet detection unit Provided with a movable space, and further provided with a blowing means for moving the paper in a direction away from the detection means on the downstream side of the paper detection direction with respect to the paper detection means,
Even when the paper is being conveyed with the trailing edge of the preceding paper partially overlapping the leading edge of the succeeding paper, the trailing edge of the preceding paper is moved to the space by the air blowing means. The leading edge of the succeeding sheet is detected by the sheet detecting means.   3. The paper leading edge detection method according to claim 1, wherein the paper detection means is a contact type detection means. A conveyance path between two consecutive conveyance roller pairs is curved, and a sheet detection unit is provided on the conveyance surface on the inner peripheral side of the curved conveyance path, and a sheet is formed on the outer conveyance surface facing the sheet detection unit. Providing a space in which the rear end can move in a direction away from the paper detection means;
The trailing edge of the preceding sheet is moved to the space, the leading edge of the succeeding sheet is detected by the sheet detecting means, and the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped and conveyed. If it is determined that the paper is transported, the transport speed of the transport roller pair on the upstream side in the paper transport direction is decreased to secure a distance between the trailing edge of the preceding paper and the leading edge of the succeeding paper. Image forming apparatus. A direction in which a sheet detection unit is provided on one conveyance surface of a conveyance path provided between two consecutive conveyance roller pairs, and a rear end of the sheet is separated from the sheet detection unit on the conveyance surface side facing the sheet detection unit Provided with a movable space, and further provided with a blowing means for moving the paper in a direction away from the detection means on the downstream side of the paper detection direction with respect to the paper detection means,
The trailing edge of the preceding sheet is moved to the space by the blowing means, the leading edge of the succeeding sheet is detected by the sheet detecting means, and the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are identical. If it is determined that the sheets are being conveyed in duplicate, the conveyance speed of the conveyance roller pair on the upstream side in the sheet conveyance direction is decreased to ensure the distance between the trailing edge of the preceding sheet and the leading edge of the following sheet. An image forming apparatus.