JP2014019553A - Sheet conveying device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet conveying device capable of eliminating double feeding while minimizing reduction in productivity.SOLUTION: In this sheet conveying device, a pair of first conveying rollers 42a are reversely rotated to convey a sheet P detected at a double sheet feeding detection position P1 at an estimated time when a preceding sheet Pa is passed in a reverse direction to a sheet conveying direction. If a distance between the double sheet feeding detection position P1 and a rear end position of the preceding sheet Pa is more than a predetermined distance, the normal rotation of the conveying rollers is immediately restarted. And while, if the distance between the double sheet feeding detection position P1 and the rear end position of the preceding sheet Pa is less than the predetermined distance, the rotation is stopped until the distance between the double sheet feeding detection position P1 and the rear end position of the preceding sheet Pa reaches the predetermined distance and the normal rotation is restarted after the distance between the double sheet feeding detection position P1 and the rear end position of the preceding sheet Pa has reached the predetermined distance.

Description

  The present invention relates to a sheet conveying device and an image forming apparatus.

  An image forming apparatus that prints and outputs an image on a sheet includes a paper feed cassette that stores the paper, an image forming unit that transfers a toner image to the paper supplied from the paper feed cassette, and a toner image that is transferred to the paper. A fixing unit to be discharged, a paper discharge tray from which paper is discharged, and the like. In such an image forming apparatus, a paper conveyance path is provided from the paper feed cassette to the paper discharge tray via the image forming unit and the fixing unit.

  Usually, a plurality of transport rollers for transporting paper along the paper transport path are installed in the paper transport path. In addition, a plurality of paper detection sensors for detecting the arrival and passage of the paper are installed in the paper transport path in order to grasp whether or not the paper is normally transported. The control unit that controls the sheet conveyance detects the occurrence of a paper jam in the sheet conveyance path or the occurrence of double feeding based on the output of the sheet detection sensor. For example, in Patent Document 1, when a plurality of sheets are continuously conveyed in a sheet conveying apparatus, double feeding occurs in which subsequent sheets are conveyed in succession to preceding sheets based on the output of the sheet detection sensor. A technique for detecting whether or not the image is detected is disclosed.

  In Patent Document 1, at least two pairs of conveyance rollers are installed along the sheet conveyance path, and a sheet detection sensor is installed between these two pairs of conveyance rollers. Hereinafter, for convenience, the upstream conveyance roller pair in the paper conveyance direction is referred to as a first conveyance roller pair, and the downstream conveyance roller pair in the paper conveyance direction is referred to as a second conveyance roller pair.

  In this Patent Document 1, when a plurality of sheets are continuously conveyed, the presence / absence of a sheet is detected at the position where the sheet detection sensor is installed at the timing when the trailing edge of the preceding sheet passes through the position where the sheet detection sensor is installed. When the presence of the sheet is detected at the position where the sheet detection sensor is installed, it is determined that a double feed in which the succeeding sheet is conveyed in succession to the preceding sheet is generated, and the rotation of the first conveying roller pair is stopped. The second conveying roller pair is rotated as it is.

  At this time, if only the preceding sheet has reached the installation position of the second conveying roller pair, the preceding sheet is conveyed in the sheet conveying direction by the second conveying roller pair, but the succeeding sheet stays without being conveyed. Thereby, the overlap between the preceding sheet and the succeeding sheet is eliminated.

JP 2006-82889 A

  As described above, in Patent Document 1, when the presence of paper is detected at the location where the paper detection sensor is installed at the timing when the trailing edge of the preceding paper has passed through the location where the paper detection sensor is installed (when occurrence of double feeding is detected). The double feed is eliminated by stopping the rotation of the first transport roller pair while rotating the second transport roller pair as it is. Thereafter, the rotation of the first conveyance roller pair is resumed, whereby conveyance of the subsequent sheet in the sheet conveyance direction is resumed.

  At this time, in order to prevent the subsequent sheet from being conveyed in the sheet conveyance direction while the preceding sheet and the subsequent sheet overlap, the first conveyance roller pair is determined in advance after the occurrence of the double feed is detected. The rotation is resumed after the fixed time has elapsed (returning of the succeeding paper in the paper transport direction is resumed). However, the amount of overlap between the preceding sheet and the succeeding sheet at the time of detecting the occurrence of double feed varies. For example, the succeeding sheet may overlap most of the preceding sheets, or the succeeding sheet may overlap only the trailing end portion of the preceding sheet. For this reason, if the time point at which the rotation of the first transport roller pair is resumed after the occurrence of double feed is fixed, only the preceding sheet is transported even after the interval between the preceding sheet and the succeeding sheet reaches an appropriate interval. When the distance between the preceding sheet and the succeeding sheet becomes larger than necessary, the rotation of the first conveying roller pair is resumed (conveying the succeeding sheet in the sheet conveying direction is resumed). There is a case. In this case, the productivity (the time required to transport the required number of sheets) decreases.

  The present invention has been made to solve the above-described problems, and can eliminate double feeding while minimizing a decrease in productivity (time required to transport a required number of sheets). It is an object of the present invention to provide a sheet conveying device and an image forming apparatus.

  In order to achieve the above object, the paper transport apparatus of the present invention is capable of forward and reverse rotation, and the first transport roller that transports the paper in the paper transport direction by rotating forward and the paper transport direction of the first transport roller A paper detection unit that includes a first paper detection sensor for detecting paper at a first downstream position, and detects the presence or absence of paper at the first position based on the output of the first paper detection sensor. . When a plurality of sheets are continuously conveyed in the sheet conveyance direction, the sheet detection unit detects the preceding sheet at the first position at the time when the trailing edge of the preceding sheet is scheduled to pass through the first position. By detecting the presence / absence of paper, double feed detection is performed to determine whether or not a double feed in which a succeeding paper is fed in succession to the preceding paper is generated. When the paper detection unit detects the presence of paper at the first position, the double feed canceling operation is carried out so that the paper detected at the first position at the time when the preceding paper passes is transported in the direction opposite to the paper transport direction by rotating backward. And when the paper detection unit detects the absence of paper at the first position after the double feed canceling operation is started, a predetermined interval is set between the first position and the trailing edge position of the preceding paper. If it is above, immediately positive While the rotation is resumed, if the interval between the first position and the trailing edge position of the preceding sheet is less than the predetermined interval, the rotation is performed until the interval between the first position and the trailing edge position of the preceding sheet reaches the predetermined interval. The rotation is stopped, and the normal rotation is resumed after the interval between the first position and the rear end position of the preceding sheet reaches a predetermined interval.

  According to the configuration of the present invention, when a plurality of sheets are continuously conveyed in the sheet conveyance direction, the sheet detection unit is configured to perform a preceding sheet passage scheduled time, which is a scheduled time when the trailing edge of the preceding sheet completely passes the first position. In addition, by detecting the presence or absence of paper at the first position, double feed detection is performed to determine whether or not a double feed in which a succeeding paper is fed to the preceding paper is generated. In addition, when the paper detection unit detects the presence of paper at the first position at the time when the preceding paper is scheduled to pass, the first transport roller rotates the reverse to rotate the paper detected at the first position when the preceding paper is scheduled to pass. The double feed elimination operation for transporting in the direction opposite to the paper transport direction is started. Here, if a double feed occurs in which the succeeding sheet is sent in succession to the preceding sheet, the sheet detecting unit detects the succeeding sheet at the first position when the preceding sheet is scheduled to pass. That is, when the paper detection unit detects the presence of paper in the first position at the time when the preceding paper is scheduled to pass, the paper detected at the first position at the time when the previous paper is scheduled to pass by the first transport roller that rotates in reverse is the paper transport direction. Are conveyed in the opposite direction, but the sheet conveyed in the opposite direction to the sheet conveying direction at this time is the succeeding sheet. As a result, even if a double feed occurs in which the succeeding sheet is sent in succession to the preceding sheet, the succeeding sheet can be quickly separated from the preceding sheet (the preceding sheet and the succeeding sheet are separated from each other). Overlap can be quickly resolved).

  The first transport roller determines the interval between the first position and the trailing edge position of the preceding sheet in advance when the sheet detection unit detects the absence of the sheet at the first position after the start of the double feed canceling operation. If the distance between the first position and the preceding paper is less than the predetermined distance, the forward rotation is immediately resumed. The rotation is stopped until the interval with the end position reaches a predetermined interval, and the normal rotation is resumed after the interval between the first position and the rear end position of the preceding sheet reaches the predetermined interval. Here, when the paper detection unit detects the absence of paper at the first position after the first transport roller starts the double feed canceling operation, it means that the succeeding paper is advanced in the direction opposite to the paper transport direction. This is when the leading edge has passed the first position, and the distance between the first position and the trailing edge position of the preceding sheet at this time corresponds to the spacing (between sheets) between the preceding sheet and the succeeding sheet. In other words, after the start of the double feed canceling operation, the time when the conveyance of the succeeding sheet in the sheet conveying direction is resumed when the sheet detection unit detects the absence of the sheet at the first position. It fluctuates according to the interval with the paper. Specifically, after the double feed canceling operation is started, the interval between the preceding sheet and the succeeding sheet when the sheet detecting unit detects the absence of the sheet at the first position is already equal to or greater than the predetermined interval. In this case, the conveyance of the subsequent sheet in the sheet conveyance direction is immediately resumed. If the interval between the preceding sheet and the succeeding sheet when the sheet detecting unit detects no sheet at the first position after the start of the double feed canceling operation is less than the predetermined interval, the succeeding sheet The transport in the direction opposite to the paper transport direction is stopped, and the transport of the succeeding paper in the paper transport direction is resumed after a predetermined interval (the interval between the preceding paper and the succeeding paper is necessary) The conveyance of the succeeding sheet in the sheet conveyance direction is resumed before it becomes larger).

  As a result, if a double feed occurs in which the preceding paper and the following paper are sent in succession, the productivity (required number of papers) ) Can be minimized.

  As described above, according to the present invention, a sheet conveying apparatus and an image forming apparatus capable of eliminating double feeding while minimizing a decrease in productivity (time required for conveying a necessary number of sheets). The device can be easily obtained.

1 is a schematic view of an image forming apparatus (paper transport unit) according to an embodiment of the present invention. FIG. 2 is a block diagram for explaining a hardware configuration of the image forming apparatus shown in FIG. FIG. 2 is a block diagram for explaining a hardware configuration of a paper transport unit of the image forming apparatus shown in FIG. The figure for demonstrating the installation position of the 1st paper detection sensor installed in the paper conveyance part of the image forming apparatus shown in FIG. FIG. 3 is a diagram for explaining an operation when double feeding occurs in the image forming apparatus shown in FIG. 1. FIG. 3 is a diagram for explaining an operation when double feeding occurs in the image forming apparatus shown in FIG. 1. FIG. 3 is a diagram for explaining an operation when double feeding occurs in the image forming apparatus shown in FIG. 1. FIG. 3 is a diagram for explaining an operation when double feeding occurs in the image forming apparatus shown in FIG. 1. FIG. 3 is a diagram for explaining the installation positions of a first paper detection sensor and a second paper detection sensor installed in a paper conveyance unit of the image forming apparatus shown in FIG. 1. Flowchart for explaining the operation when double feeding occurs in the image forming apparatus shown in FIG. Flowchart for explaining the operation when double feeding occurs in the image forming apparatus shown in FIG.

(Overall configuration of image forming apparatus)
First, an overall configuration of an image forming apparatus provided with a sheet conveying device will be described by taking an image forming apparatus (multifunction machine) capable of executing a plurality of types of jobs such as copying, scanning, and faxing as an example.

  As shown in FIG. 1, an image forming apparatus 100 according to the present embodiment includes an operation panel 101, an image reading unit 102, a paper feeding unit 103, a paper transport unit 104 (corresponding to the “paper transport device” of the present invention), and image formation. A unit 105 and a fixing unit 106 are provided.

  The operation panel 101 includes a liquid crystal display unit 11 whose display surface is covered with a touch panel. The liquid crystal display unit 11 displays setting keys (soft keys) for accepting various settings, and also displays a message indicating the device status. The operation panel 101 is also provided with a numeric keypad 12 for accepting numerical input, a start key 13 for accepting the start of execution of various jobs, and the like as hard keys.

  The image reading unit 102 reads a document and generates image data of an image to be formed. Although not shown, the image reading unit 102 is provided with optical system members such as an exposure lamp, a mirror, a lens, and an image sensor. Then, the image reading unit 102 irradiates the document placed on the placement reading contact glass 21 with light, and performs A / D conversion on the output value of the image sensor that receives the reflected light from the document. Generate image data. Thus, printing can be performed based on the image data obtained by the document reading operation (scanning) by the image reading unit 102. It is also possible to store image data obtained by scanning. The image reading unit 102 may be provided with a document presser 22 for pressing a document placed on the placement reading contact glass 21.

  The paper feed unit 103 includes a cassette 31 that stores paper P, and supplies the paper P in the cassette 31 to the paper transport unit 104 (paper transport path 104a). The paper feed unit 103 supplies the paper P in the cassette 31 to the paper transport unit 104 (paper transport path 104a) one by one, so that the pickup roller 32 for pulling out the paper P in the cassette 31 and the paper P A separation roller pair 33 and the like are provided to suppress double feeding of the toner.

  The paper transport unit 104 transports the paper P along the paper transport path 104a inside the apparatus. Specifically, the paper P supplied from the paper supply unit 103 is advanced by the paper transport unit 104 in the direction of arrow A (paper transport direction) in the drawing. That is, the paper P supplied from the paper supply unit 103 passes through the image forming unit 105 and the fixing unit 106 in this order, and is guided to the discharge tray 41.

  The paper transport unit 104 includes a plurality of transport roller pairs 42 installed along the paper transport path 104a. Of the plurality of transport roller pairs 42, the interval between the one transport roller pair 42 and the other transport roller pair 42 that are adjacent to each other without passing through a mechanism unit such as the image forming unit 105 or the fixing unit 106 is the sheet P to be transported. Is smaller than the minimum length (length in the paper transport direction). Further, the paper transport unit 104 includes a registration roller pair 43 installed at a position upstream of the image forming unit 105 in the paper transport direction (a position immediately before reaching the image forming unit 105). The registration roller pair 43 waits for the paper P immediately before the image forming unit 105 and sends the paper P to the image forming unit 105 in time.

  Further, the paper transport unit 104 includes a motor 44 (see FIG. 3) for rotating the plurality of transport roller pairs 42. The plurality of transport roller pairs 42 rotate by transmitting the driving force of the motor 44 and transport the paper P in the paper transport direction. Hereinafter, the rotation direction of the transport roller pair 42 when transporting the paper P in the paper transport direction is referred to as forward rotation.

  Further, the paper transport unit 104 includes a plurality of paper detection sensors 45 installed along the paper transport path 104a. For example, the paper detection sensor 45 is an optical sensor having a light emitting unit (not shown) that emits light toward the paper conveyance path 104a and a light receiving unit (not shown) that receives reflected light. The output is varied depending on whether or not the sheet P is present at the location where the sensor 45 is installed. For example, when the leading edge of the paper P reaches the installation location of the paper detection sensor 45, the output value of the paper detection sensor 45 rises, and when the trailing edge of the paper P passes through the installation location of the paper detection sensor 45, the paper detection sensor 45. The output value of falls.

  Alternatively, as the paper detection sensor 45, an optical sensor having an actuator (not shown) that rotates between the light emitting unit and the light receiving unit and protrudes to the paper conveyance path 104a may be used. In this case, when the paper P traveling on the paper conveyance path 104a reaches the installation location of the paper detection sensor 45, the paper P comes into contact with the actuator (the actuator rotates), whereby the optical path between the light emitting unit and the light receiving unit is established. When the paper P is completely passed through the installation position of the paper detection sensor 45 by being blocked (or opened) by the actuator, the optical path between the light emitting part and the light receiving part is opened (or cut off) by returning the actuator to the original position. ) As a result, the output of the paper detection sensor 45 varies depending on whether or not the paper P is present at the location where the paper detection sensor 45 is installed.

  One of the plurality of paper detection sensors 45 is used for a double feed canceling operation described later, and corresponds to a “first paper detection sensor” of the present invention. Hereinafter, the paper detection sensor 45 used for the double feed canceling operation is referred to as a first paper detection sensor 45a.

  The image forming unit 105 forms a toner image based on the image data of the image to be formed, and transfers the toner image onto the paper P. The image forming unit 105 includes a photosensitive drum 51, a charging device 52, an exposure device 53, a developing device 54, a transfer roller 55, and a cleaning device 56.

  As a toner image forming process and a toner image transfer process, first, the photosensitive drum 51 is rotationally driven, and the charging device 52 charges the surface of the photosensitive drum 51 to a predetermined potential. The exposure device 53 outputs a light beam L based on the image data to be formed, and scans and exposes the surface of the photosensitive drum 51. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 51. The developing device 54 receives toner from the toner container TC, supplies the toner to the electrostatic latent image formed on the surface of the photosensitive drum 51, and develops it.

  The transfer roller 55 can rotate while being pressed against the surface of the photosensitive drum 51. Then, the registration roller pair 43 measures the timing and causes the paper P to enter between the transfer roller 55 and the photosensitive drum 51. At this time, a predetermined voltage is applied to the transfer roller 55. As a result, the toner image on the surface of the photosensitive drum 51 is transferred to the paper P. When the toner image transfer process is finished, the cleaning device 56 removes the toner remaining on the surface of the photosensitive drum 51.

  The fixing unit 106 heats and presses the toner image transferred onto the paper P to fix it. The fixing unit 106 includes a heating roller 61 and a pressure roller 62. The heating roller 61 incorporates a heater 63. The pressure roller 62 is in pressure contact with the heating roller 61. The paper P on which the toner image is transferred is heated and pressurized by passing between the heating roller 61 and the pressure roller 62. As a result, the toner image is fixed on the paper P and printing is completed. Thereafter, the printed paper P is sent to the discharge tray 41 by the transport roller pair 42.

(Hardware configuration of image forming apparatus)
Next, the hardware configuration of the image forming apparatus 100 will be described.

  As shown in FIG. 2, the image forming apparatus 100 includes a main control unit 110. The main control unit 110 includes a CPU 111 that is a central processing unit, an image processing unit 112, and a storage unit 113. The image processing unit 112 includes an ASIC dedicated to image processing, a memory, and the like, and performs various types of image processing (enlargement / reduction, density conversion, data format conversion, etc.) on the image data. The storage unit 113 includes a ROM, a RAM, an HDD, and the like. For example, programs and data necessary for job execution are stored in the ROM, and the programs and data are expanded in the RAM.

  The main control unit 110 is connected to the operation panel 101, the image reading unit 102, the paper feeding unit 103, the paper conveying unit 104, the image forming unit 105, and the fixing unit 106. The main control unit 110 performs overall control, image processing control, display control, motor drive control for rotating various rotating bodies, detection based on outputs from various sensors, and the like based on programs and data stored in the storage unit 113. I do.

  For example, as shown in FIG. 3, the main control unit 110 controls driving of the motor 44 for rotating the conveyance roller pair 42 of the paper conveyance unit 104. Further, the main control unit 110 receives the output of the paper detection sensor 45 and detects the presence or absence of the paper P at the place where the paper detection sensor 45 is installed based on the output of the paper detection sensor 45. In this configuration, the main control unit 110 corresponds to the “paper detection unit” of the present invention.

  Here, there are two types of motors 44 for rotating the transport roller pair 42, and for rotating a predetermined transport roller pair 42 (hereinafter referred to as a first transport roller pair 42a) of the plurality of transport roller pairs 42. The first motor 44a and the second motor 44b for rotating the transport roller pair 42 different from the first transport roller pair 42a are classified.

  The first motor 44a switches between forward and reverse rotation according to the conveyance state during the conveyance of the paper. That is, the first transport roller pair 42a can be rotated forward and backward, and is basically forward rotated during the paper transport to transport the paper P in the paper transport direction, but is rotated backward during the paper transport. The paper P may be transported in the direction opposite to the paper transport direction.

  On the other hand, the second motor 44b does not switch between forward and reverse rotation during paper conveyance. That is, the conveyance roller pair 42 that is rotated by the driving force transmitted from the second motor 44b rotates in the forward direction during sheet conveyance to convey the sheet P only in the sheet conveyance direction and reversely rotates during sheet conveyance. There is no.

  Note that which of the plurality of transport roller pairs 42 can be rotated forward and backward is not particularly limited. For example, the first transport roller pair 42 installed immediately after the sheet feeding unit 103 can rotate forward and backward. The transport roller pair 42a is used.

  Then, the main control unit 110 switches the forward / reverse rotation of the first transport roller pair 42a based on the output of the first paper detection sensor 45a, and controls the double feed canceling operation. The double feed canceling operation will be described in detail later.

  Returning to FIG. 2, the main control unit 110 is connected to the communication unit 120. Communication unit 120 is communicably connected to external computer 200 via network NT. Thus, printing can be performed based on the image data transmitted from the computer 200, and the image data obtained by scanning can be transmitted to the computer 200. Further, the communication unit 120 has a built-in modem, whereby it is possible to perform fax communication with the external fax machine 300 via the network NT such as a telephone line.

(Double feed cancellation operation)
As shown in FIG. 4, the first paper detection sensor 45a used for the double feed canceling operation is a position P1 on the downstream side in the paper transport direction of the first transport roller pair 42a that can rotate forward and backward (the “first position” of the present invention). It is installed so that the paper can be detected. The downstream conveying roller pair 42 in the sheet conveying direction of the first conveying roller pair 42a corresponds to the “second conveying roller” of the present invention, and the interval between the first conveying roller pair 42a and the first conveying roller pair 42a is conveyed. It is installed to be smaller than the minimum length. Hereinafter, the transport roller pair 42 is referred to as a second transport roller pair 42b.

  When the main control unit 110 continuously conveys a plurality of sheets P in the sheet conveyance direction, the main control unit 110 changes the preceding sheet P (hereinafter referred to as the preceding sheet Pa) based on the output of the first sheet detection sensor 45a. A double feed detection is performed as to whether or not a double feed is performed in which a row of paper P (hereinafter referred to as a subsequent paper Pb) is continuously conveyed. That is, the position P1 is a double feed detection position, and in the following description, the position P1 is referred to as a double feed detection position P1.

  Specifically, when the main control unit 110 continuously conveys a plurality of sheets P in the sheet conveyance direction, the main control unit 110 passes the preceding sheet, which is a scheduled time when the trailing edge of the preceding sheet Pa passes through the double feed detection position P1. When the scheduled time is reached, the presence or absence of the paper P at the double feed detection position P1 is detected based on the output of the first paper detection sensor 45a. For example, the main control unit 110 requires the trailing edge of the preceding paper Pa to pass through the double feed detection position P1 after the leading edge of the preceding paper Pa reaches the double feed detection position P1 based on the conveyance speed and the paper size. Time is calculated and the estimated time of passing the preceding paper is calculated.

  Here, in the state where double feeding has occurred, when the preceding paper passage scheduled time point is reached, as shown in FIG. 5, the trailing edge of the preceding paper Pa has completely passed the double feed detection position P1, but the preceding paper has passed. Since the succeeding sheet Pb continues to the sheet Pa, the succeeding sheet Pb is conveyed to the double feed detection position P1. For this reason, it is possible to determine whether or not a double feed has occurred by detecting the presence or absence of the paper P at the double feed detection position P1 at the scheduled time for passing the preceding paper. That is, when no paper is detected at the double feed detection position P1 at the time when the preceding paper is scheduled to pass (in the state shown in FIG. 4), no double feed has occurred (the preceding paper Pa and the following paper Pb). If there is a sheet detected at the double feed detection position P1 at the time when the preceding paper is scheduled to pass (in the state shown in FIG. 5), double feed occurs. (The succeeding paper Pb is continuous with the preceding paper Pa).

  When the main control unit 110 detects the absence of paper at the double feed detection position P1 at the time when the preceding paper is scheduled to pass (in the case shown in FIG. 4), the main control unit 110 determines that double feed has not occurred, and The conveyance roller pair 42a and the second conveyance roller pair 42b are continuously rotated as they are (normal paper conveyance operation is continued).

  On the other hand, when the main control unit 110 detects the presence of paper at the multi-feed detection position P1 at the scheduled time for passing the preceding paper (in the state shown in FIG. 5), it determines that multi-feed has occurred. Then, the first conveying roller pair 42a is rotated in the reverse direction (double feed canceling operation is performed). At this time, the main control unit 110 continues to rotate the second transport roller pair 42b as it is (continues normal paper transport operation).

  When the double feed canceling operation by the first transport roller pair 42a is started, as shown in FIG. 6, the first transport roller pair 42a rotating in the reverse direction is detected at the multi-feed detection position P1 at the scheduled time for passing the preceding paper. The paper P (following paper Pb) is transported in the direction opposite to the paper transport direction. At this time, the second transport roller pair 42b continues to transport the preceding paper Pa in the paper transport direction by rotating forward. As a result, the preceding paper Pa is conveyed in the sheet conveying direction and the succeeding sheet Pb is conveyed in the direction opposite to the sheet conveying direction, so that the overlap between the preceding sheet Pa and the following sheet Pb is eliminated.

  The main control unit 110 continues the double feed cancellation operation by the first transport roller pair 42a until the absence of paper is detected at the double feed detection position P1 (until the state shown in FIG. 7 is reached). When the main control unit 110 detects the absence of paper at the double feed detection position P1 after the start of the double feed cancellation operation, that is, the leading edge of the succeeding paper Pb that travels in the direction opposite to the paper transport direction is detected. Whether or not the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa is equal to or greater than a predetermined interval when the paper passes through the position P1 (the space between the preceding paper Pa and the succeeding paper Pb) Whether or not is more than the appropriate paper interval). For example, the main control unit 110 obtains the trailing edge position of the preceding paper Pa based on the elapsed time from the time when the leading edge of the preceding paper Pa is detected at the double feed detection position P1, the conveyance speed, and the paper size, and performs the double feed canceling operation. After the start, the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa when no paper is detected at the double feed detection position P1 is calculated.

  If the interval between the double feed detection position P1 and the trailing edge position of the preceding sheet Pa is equal to or greater than a predetermined interval, the main control unit 110 immediately rotates the first conveying roller pair 42a in the forward direction (the sheet conveying direction of the subsequent sheet Pb). To resume transport immediately). As a result, as shown in FIG. 8, the preceding paper Pa and the succeeding paper Pb are transported in the paper transport direction in a state where the overlap between the preceding paper Pa and the following paper Pb is eliminated.

  On the other hand, if the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa is less than a predetermined interval, the main control unit 110 determines that the interval between the double feeding detection position P1 and the trailing edge position of the preceding paper Pa is small. The rotation of the first conveyance roller pair 42a is stopped until the predetermined interval is reached, and the first rotation of the first conveyance roller pair 42a is rotated when the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa reaches the predetermined interval. (Resuming transport of the succeeding paper Pb in the paper transport direction).

  By the way, as shown in FIG. 9, the first sheet detection is performed so that the sheet can be detected at the downstream position P2 (corresponding to the “second position” in the present invention) of the second conveyance roller pair 42b in the sheet conveyance direction. There is a case where a paper detection sensor 45 different from the sensor 45a is installed. The paper detection sensor 45 for detecting the paper at the position P2 corresponds to the “second paper detection sensor” of the present invention, and is referred to as a second paper detection sensor 45b in the following description.

  In this case, based on the transport speed and the paper size, the time required for the trailing edge of the preceding paper Pa to pass through the double feed detection position P1 after the leading edge of the preceding paper Pa reaches the position P2 is obtained. It is also possible to calculate the scheduled passage time of the preceding paper. Further, the trailing end position of the preceding sheet Pa is obtained based on the elapsed time from the time when the leading end of the preceding sheet Pa is detected at the position P2, the transport speed, and the sheet size, and the double feed detection position P1 and the trailing end position of the preceding sheet Pa are obtained. You may calculate the space | interval.

  Hereinafter, a flow when the double feed canceling operation is performed based on the output of the first paper detection sensor 45a will be described along the flowcharts shown in FIGS.

  The flowchart shown in FIG. 10 is started when an instruction to execute a job for continuously printing a plurality of sheets of paper P is received and paper feeding from the paper feed unit 103 to the paper transport unit 104 (paper transport path 104a) is started. To do.

  In step S1, the main control unit 110 determines whether or not the leading edge of the preceding paper Pa has reached the double feed detection position P1 based on the output of the first paper detection sensor 45a. As a result of the determination, if the leading edge of the preceding paper Pa has reached the double feed detection position P1, the process proceeds to step S2. If the leading edge of the preceding paper Pa has not reached the double feed detection position P1, the determination in step S1 is made. repeat.

  In step S2, the main control unit 110 calculates a preceding paper passage scheduled time point, which is a scheduled time point when the trailing edge of the preceding paper Pa passes through the double feed detection position P1. For example, the main control unit 110 requires the trailing edge of the preceding paper Pa to pass through the double feed detection position P1 after the leading edge of the preceding paper Pa reaches the double feed detection position P1 based on the conveyance speed and the paper size. By calculating the time, the scheduled passage time of the preceding paper is calculated. In step S <b> 3, the main control unit 110 determines whether or not the scheduled passage time of the preceding sheet has been reached. As a result of the determination, if the preceding paper passage scheduled time has been reached, the process proceeds to step S4. If the preceding paper passage scheduled time has not been reached, the determination in step S3 is repeated.

  In step S4, the main control unit 110 determines whether or not there is the paper P at the double feed detection position P1 based on the output of the first paper detection sensor 45a (the weight of the preceding paper Pa and the succeeding paper Pb being conveyed continuously). Whether or not transmission has occurred is detected. As a result, when the presence of paper is detected (when the succeeding paper Pb is detected), the process proceeds to step S5. In step S5, the main control unit 110 reversely rotates the first transport roller pair 42a (makes the first transport roller pair 42a perform the double feed canceling operation). That is, the first transport roller pair 42a transports the paper P (following paper Pb) detected at the double feed detection position P1 at the scheduled time for passing the preceding paper in the direction opposite to the paper transport direction.

  In step S6, the main control unit 110 detects the presence or absence of the paper P at the double feed detection position P1 based on the output of the first paper detection sensor 45a, and moves to step S7 if it detects the absence of paper.

  In step S7, the main control unit 110 determines whether or not the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa is equal to or greater than a predetermined interval (the interval between the preceding paper Pa and the succeeding paper Pb). Whether or not is more than the appropriate paper interval). For example, the main control unit 110 obtains the trailing edge position of the preceding paper Pa based on the elapsed time from the time when the leading edge of the preceding paper Pa is detected at the double feeding detection position P1, the conveyance speed, and the paper size. The interval between the position P1 and the trailing edge position of the preceding paper Pa is calculated. As a result of the determination, if the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa is equal to or greater than a predetermined interval, the process proceeds to step S8, and the interval between the double feeding detection position P1 and the trailing edge position of the preceding paper Pa. If is not greater than or equal to the predetermined interval (if less than the predetermined interval), the process proceeds to step S9.

  If transfering it to step S8, the main control part 110 will immediately rotate the 1st conveyance roller pair 42a forward. On the other hand, if it transfers to step S9, the main control part 110 will stop rotation of the 1st conveyance roller pair 42a, and will return to step S7. That is, the first conveyance roller pair 42a stops rotating until the interval between the multifeed detection position P1 and the trailing edge position of the preceding paper Pa reaches a predetermined interval, and the double feeding detection position P1 and the trailing edge position of the preceding paper Pa are stopped. The forward rotation is resumed after the interval between and reaches a predetermined interval. Thereafter, the process proceeds to step S10. In step S4, when the absence of paper is detected (when the succeeding paper Pb is not detected), the process proceeds to step S10.

  In step S10, the main control unit 110 determines whether or not the succeeding paper Pb subject to double feed detection is the final supply paper P. As a result of the determination, if it is the final supply paper P, the double feed detection is terminated. On the other hand, if it is not the final supply paper P, the process proceeds to step S1. In this case, the previous succeeding paper Pb becomes the preceding paper Pa, and the paper P following the previous succeeding paper Pb becomes the following paper Pb.

  By the way, if it is not detected in step S6 that no paper is detected, it means that the succeeding paper Pb remains (jam has occurred) (in step S5, the first transport roller pair 42a is moved). After reverse rotation for a predetermined time, the presence or absence of the paper P at the double feed detection position P1 is detected based on the output of the first paper detection sensor 45a. It may be determined that Pb remains retained). Therefore, in this case, the process proceeds to step S11 to forcibly discharge the preceding paper Pa. In step S12, the paper transport operation is stopped. At this time, for example, the operation panel 101 displays an error message to notify that a jam has occurred.

  When the double feed canceling operation is performed based on the outputs of both the first sheet detection sensor 45a and the second sheet detection sensor 45b (see FIG. 9), the preceding sheet is positioned at the position P2 in the flowcharts of FIGS. In response to the arrival of the tip of Pa, the process may proceed to step S2. In this case, in step S2, the time required for the trailing edge of the preceding paper Pa to pass through the double feed detection position P1 after the leading edge of the preceding paper Pa reaches the position P2 is determined based on the conveyance speed and the paper size. It may be obtained and the scheduled passage time of the preceding paper may be calculated. In step S7, the trailing edge position of the preceding sheet Pa is obtained based on the elapsed time from the time when the leading edge of the preceding sheet Pa is detected at the position P2, the transport speed, and the sheet size, and the double feed detection position P1 and the preceding sheet Pa are determined. You may obtain | require the space | interval with a rear-end position.

  In the present embodiment, as described above, when a plurality of sheets P are continuously conveyed in the sheet conveyance direction, the main control unit 110 (sheet detection unit) determines that the trailing edge of the preceding sheet Pa is at the double feed detection position P1. By detecting the presence or absence of the paper P at the multi-feed detection position P1 at the time when the preceding paper is scheduled to pass through (the first position), the multi-feed in which the succeeding paper Pb is continuously sent to the preceding paper Pa is performed. Double feed detection is performed to see if it has occurred. Further, the first transport roller pair 42a (first transport roller) rotates in the reverse direction when the main control unit 110 detects the presence of paper at the multifeed detection position P1 at the time when the preceding paper is scheduled to pass, thereby causing the preceding paper to pass through. Then, the double feed canceling operation for carrying the paper P detected at the double feed detection position P1 in the direction opposite to the paper carrying direction is started. Here, if a double feed in which the succeeding paper Pb is sent in succession to the preceding paper Pa is generated, the main control unit 110 detects the following paper Pb at the multifeed detection position P1 at the scheduled time of passing the preceding paper. become. That is, when the main control unit 110 detects the presence of paper at the multifeed detection position P1 at the time when the preceding paper is scheduled to pass, it is detected at the multifeed detection position P1 at the time when the preceding paper is scheduled to pass by the reversely rotating first transport roller pair 42a. The sheet P is conveyed in the direction opposite to the sheet conveyance direction. At this time, the sheet P conveyed in the direction opposite to the sheet conveyance direction becomes the subsequent sheet Pb. As a result, even if the double feeding in which the succeeding paper Pb is sent in succession to the preceding paper Pa occurs, the succeeding paper Pb can be quickly separated from the preceding paper Pa (the preceding paper Pa and the following paper Pb are separated from each other). Overlap can be quickly resolved).

  When the main control unit 110 detects that there is no paper at the double feed detection position P1 after starting the double feed canceling operation, the first transport roller pair 42a detects the trailing edge of the double feed detection position P1 and the preceding paper Pa. If the interval with the position is greater than or equal to a predetermined interval, the forward rotation is immediately resumed. On the other hand, if the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa is less than the predetermined interval, The rotation is stopped until the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa reaches a predetermined interval, and after the interval between the double feeding detection position P1 and the trailing edge position of the preceding paper Pa reaches the predetermined interval. Resume forward rotation. Here, when the main controller 110 detects the absence of paper at the double feed detection position P1 after the first transport roller pair 42a starts the double feed canceling operation, it proceeds in the direction opposite to the paper transport direction. This is the time when the leading edge of the succeeding paper Pb has completely passed the double feed detection position P1, and the interval between the double feed detection position P1 and the trailing edge position of the preceding paper Pa at this time is the distance between the preceding paper Pa and the following paper Pb. This corresponds to the interval (paper interval). That is, after the start of the double feed canceling operation, the time point at which the conveyance of the succeeding paper Pb in the paper conveyance direction is resumed from the preceding paper Pa when the main controller 110 detects the absence of paper at the double feed detection position P1. It fluctuates according to the interval with the succeeding paper Pb. Specifically, after the double feed canceling operation is started, the interval between the preceding paper Pa and the succeeding paper Pb when the main control unit 110 detects the absence of paper at the double feed detection position P1 is already greater than or equal to a predetermined interval. If so, the conveyance of the succeeding paper Pb in the paper conveyance direction is immediately resumed. If the interval between the preceding sheet Pa and the succeeding sheet Pb when the main control unit 110 detects the absence of sheet at the double-feed detection position P1 after the double-feed canceling operation is started is less than the predetermined interval, The conveyance of the line paper Pb in the direction opposite to the sheet conveyance direction is stopped, and the conveyance of the subsequent sheet Pb in the sheet conveyance direction is resumed after a predetermined interval (between the preceding sheet Pa and the subsequent sheet Pb). The conveyance of the succeeding paper Pb in the paper conveyance direction is resumed before the interval becomes larger than necessary).

  As a result, even if the double feed cancellation operation for canceling the double feed occurs when the double feed in which the preceding paper Pa and the succeeding paper Pb are continuously sent occurs, the productivity (the required number of sheets of paper) It is possible to minimize a decrease in the time required for transporting P).

  In the present embodiment, as described above, the second transport roller pair 42b (second transport roller) is provided on the downstream side of the first transport roller pair 42a in the paper transport direction. Then, the second transport roller pair 42b transports the preceding paper Pa in the paper transport direction by rotating forward when the first transport roller pair 42a is performing the double feed canceling operation. Thus, when the double feed canceling operation is performed, the preceding paper Pa is transported in the paper transport direction by the second transport roller pair 42b that rotates in the forward direction, and the subsequent paper Pb is transported by the first transport roller pair 42a that rotates in the reverse direction. The paper is conveyed in the direction opposite to the paper conveyance direction. Therefore, when the double feeding in which the succeeding paper Pb is continuously sent to the preceding paper Pa occurs, the succeeding paper Pb can be reliably separated from the preceding paper Pa.

  Further, in the present embodiment, as described above, the main control unit 110 performs the following of the preceding paper Pa based on the elapsed time from the time when the leading edge of the preceding paper Pa is detected at the double feed detection position P1, the transport speed, and the paper size. By obtaining the end position, the interval between the double feed detection position P1 and the rear end position of the preceding paper Pa is calculated. As a result, the double feed canceling operation can be easily controlled only by the output of the first paper detection sensor 45a.

  In the modification of the present embodiment, the main control unit 110 includes a second paper detection sensor 45b for detecting paper at a position P2 (second position) on the downstream side in the paper conveyance direction of the second conveyance roller 42b. In addition. In this case, the double feed detection position P1 and the preceding paper Pa are obtained by obtaining the trailing edge position of the preceding paper Pa based on the elapsed time from the time when the leading edge of the preceding paper Pa is detected at the position P2, the transport speed, and the paper size. The distance from the rear end position can be calculated.

  It should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is shown not by the description of the above-described embodiment but by the scope of claims for patent, and further includes meanings equivalent to the scope of claims for patent and all modifications within the scope.

42a First transport roller pair (first transport roller)
42b Second transport roller pair (second transport roller)
45a First paper detection sensor 45b Second paper detection sensor 110 Main control unit (paper detection unit)
P Paper P1 Double feed detection position (first position)
P2 position (second position)

Claims (5)

A first transport roller that is capable of forward and reverse rotation and transports paper in the paper transport direction by rotating forward;
A first paper detection sensor for detecting paper at a first position downstream of the first transport roller in the paper transport direction, and whether or not paper is present at the first position based on an output of the first paper detection sensor; A paper detection unit for detecting
When continuously conveying a plurality of sheets in the sheet conveying direction,
The paper detection unit follows the preceding paper by detecting the presence or absence of the paper at the first position at a time when the preceding paper is scheduled to pass through, which is a time when the trailing edge of the preceding paper is scheduled to pass through the first position. Double feed detection is performed to determine whether or not multiple feeds are being sent.
The first transport roller is detected at the first position when the preceding paper is scheduled to pass by rotating in reverse when the paper detection unit detects the presence of paper at the first position at the time when the preceding paper is scheduled to pass. When the paper detection unit detects the absence of paper at the first position after starting the double feed cancellation operation to start the double feed cancellation operation of transporting the received paper in the direction opposite to the paper transport direction, If the interval between the first position and the trailing edge position of the preceding sheet is equal to or greater than a predetermined interval, the forward rotation is immediately resumed, while the first position and the trailing edge position of the preceding sheet are If the interval is less than the predetermined interval, the rotation is stopped until the interval between the first position and the trailing edge position of the preceding paper reaches the predetermined interval, and the trailing edge position of the first position and the preceding paper is reached. Whether the interval between and has reached the predetermined interval Sheet conveying apparatus characterized by resuming normal rotation. A second transport roller installed downstream of the first transport roller in the paper transport direction;
The said 2nd conveyance roller conveys a preceding sheet | seat in the said sheet | seat conveyance direction by carrying out normal rotation, when the said 1st conveyance roller is performing the said double feed cancellation operation | movement. Paper transport device.   The paper detection unit obtains the trailing edge position of the preceding paper based on the elapsed time from the time when the leading edge of the preceding paper was detected at the first position, the transport speed, and the paper size, and thereby determines the leading position of the preceding paper. 3. The sheet conveying apparatus according to claim 1, wherein an interval between the sheet and a rear end position of the sheet is calculated.   The paper detection unit further includes a second paper detection sensor for detecting paper at a second position downstream of the second transport roller in the paper transport direction, and the leading edge of the preceding paper is detected at the second position. The interval between the first position and the trailing edge position of the preceding sheet is calculated by obtaining the trailing edge position of the preceding sheet based on the elapsed time from the detected time, the conveyance speed, and the sheet size. The sheet conveying apparatus according to claim 2.   An image forming apparatus comprising the sheet conveying device according to claim 1.

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