JP2010137974A - Sheet carrying device and image forming device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet carrying device and an image forming device, capable of approaching the size of a clearance between sheets to zero, when continuously carrying a plurality of sheets. <P>SOLUTION: This sheet carrying device 35 is used for the image forming device 1 having a printing part for printing an image on paper. A carrier roller 19 carries the paper at a speed Va. A timing roller 20 carries the paper carried by the carrier roller 19 at a speed Vb to the printing part. Sensors Se1-Se5 are arranged between the carrier roller 19 and the timing roller 20, and detect the clearance between preceding paper and succeeding paper at a plurality of detecting positions when the preceding paper is carried by the timing roller 20 and the succeeding paper is carried by the carrier roller 19. A control part 30 controls the carrier roller 19 so that the speed Va becomes larger than the speed Vb when the sensors Se1-Se5 detect the clearance. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus, and more particularly, to a sheet conveying apparatus that continuously conveys sheets serving as print media and an image forming apparatus including the sheet conveying apparatus.

  In the sheet conveying apparatus, it is desirable that the size of the gap between the sheets is zero when conveying a plurality of sheets continuously for the following reasons. More specifically, when the size of the gap between the sheets is not zero, the conveyance roller, the transfer belt, and the like rotate even during the period in which the gap between the sheets passes. Therefore, when the size of the gap between the sheets is not zero, the travel distance of the conveyance roller, the transfer belt, etc. becomes longer compared to the case where the size of the gap between the sheets is zero. The belt is likely to deteriorate. Further, when the size of the gap between the sheets is not zero, the productivity becomes lower than when the size of the gap between the sheets is zero. Therefore, when conveying a plurality of sheets continuously, it is desirable that the size of the gap between the sheets is zero.

  Incidentally, as a conventional sheet conveying apparatus, for example, a sheet feeding apparatus described in Patent Document 1 is known. In the sheet feeding apparatus, when two sheets are sequentially fed sequentially, if the detecting means detects that the interval between the preceding sheet and the succeeding sheet is lower than a predetermined value, the succeeding sheet The control unit controls the feeding means so that the sheet conveyance speed is decreased. As a result, a plurality of sheets can be continuously fed while maintaining the size of the gap between the predetermined sheets.

However, in the sheet feeding device described in Patent Document 1, the size of the gap between the sheets is merely maintained at a predetermined size. For this reason, Patent Document 1 does not mention bringing the size of the gap between the sheets close to zero.
JP 2006-232475 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a sheet conveying apparatus capable of bringing the size of the gap between the sheets close to zero when conveying a plurality of sheets continuously, and an image forming apparatus including the sheet conveying apparatus. is there.

  A sheet conveying apparatus according to an aspect of the present invention is a sheet conveying apparatus used in an image forming apparatus including a printing unit that prints an image on a sheet. The first conveying unit conveys the sheet at a first speed. A second conveying means for conveying the sheet conveyed by the first conveying means to the printing section at a second speed, and between the first conveying means and the second conveying means. Detecting means provided in the first and second sheets when the first sheet is conveyed by the second conveying means and the second sheet is conveyed by the first conveying means. A plurality of detection means for detecting a gap with the second sheet at a plurality of detection positions, and when the detection means detects the gap, the first speed is greater than the second speed. As described above, the first conveying means or the second conveying means By comprising control means for controlling the feeding means, and characterized.

  An image forming apparatus according to an aspect of the present invention includes the sheet conveying device.

  Hereinafter, a sheet conveying apparatus and an image forming apparatus according to an embodiment of the present invention will be described.

(Configuration of image forming apparatus)
Hereinafter, an image forming apparatus including a sheet conveying apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of the image forming apparatus 1.

  The image forming apparatus 1 is an electrophotographic color printer and is configured to synthesize images of four colors (Y: yellow, M: magenta, C: cyan, K: black) in a so-called tandem system. is there. The image forming apparatus 1 has a function of forming an image on a sheet (sheet) P based on image data, and includes a printing unit 2, a sheet feeding unit 15, a sheet conveying device 35, a fixing device 22, and a paper discharge tray 23. It has.

  The paper supply unit 15 serves to supply the paper P one by one, and includes a paper tray 16, a paper supply roller 17, and a separating roller 18. A plurality of sheets of paper P in a state before printing are stacked on the paper tray 16. The paper feed roller 17 takes out the paper P placed on the paper tray 16 one by one. The separating roller 18 separates the sheets P picked up by the sheet feeding roller 17 one by one and conveys the single sheet P.

  FIG. 2 is an enlarged view of the sheet conveying device 35. As shown in FIG. 2, the sheet conveying device 35 includes a conveying roller 19, a timing roller 20, a control unit 30, a driving unit 31, a storage unit 32, an overlap prevention mechanism 40, a path R, and sensors Se1 to Se5. The transport roller 19 is driven to rotate by the drive unit 31 to transport the paper P at a speed Va. The drive unit 31 is configured by a motor, for example. The conveyance roller 19 and the drive unit 31 constitute a conveyance unit. The timing roller 20 is rotationally driven by a drive unit (not shown) and transports the paper P transported by the transport roller 19 to the printing unit 2 at a speed Vb. The timing roller 20 and a driving unit (not shown) constitute a conveying unit. The path R is formed between the conveying roller 19 and the timing roller 20 and is a sheet passing path through which the paper P passes.

  The sensors Se1 to Se5 are provided on the path R and detect the gap g between the sheets P1 and P2 when the two sheets P1 and P2 are continuously conveyed as shown in FIG. More specifically, the sensors Se <b> 1 to Se <b> 5 indicate a gap between the rear end of the paper P <b> 1 and the front end of the paper P <b> 2 when the paper P <b> 1 is transported by the timing roller 20 and the paper P <b> 2 is transported by the transport roller 19. g (hereinafter simply referred to as a gap g between the sheets P1 and P2) is detected at a plurality of detection positions on the path R. Each of the sensors Se1 to Se5 includes a light emitting section Se1-1 to Se5-1 and a light receiving section Se1-2 to Se5-2 as shown in the enlarged view in FIG. 2 (in the enlarged view, the light emitting section Se3). -1 and the light receiving unit Se3-2 only). The light emitting units Se1-1 to Se5-1 emit light. The light receiving units Se1-2 to Se5-2 constitute detection positions, receive light emitted by the light emitting units Se1-1 to Se5-1, and output signals Sig1 to Sig5 according to the light amount to the control unit 30. Output. Specifically, when the light receiving units Se1-2 to Se5-2 receive a relatively large amount of light, the light receiving units Se1-2 to Se5-2 output the relatively high voltage output signals Sig1 to Sig5, and the relatively small amount of light. Output light signals Sig1 to Sig5 having a relatively low voltage. Further, the light receiving portions Se1-2 to Se5-2 have a width l in the conveyance direction of the paper P as shown in the enlarged view in FIG. In this embodiment, the distance between adjacent sensors is set wider than the gap g between the sheets P1 and P2 in the initial stage of conveyance, and the gap g does not straddle a plurality of sensors.

  When the sensors Se <b> 1 to Se <b> 5 detect the gap g, the control unit 30 controls the driving unit 31 and the transport roller 19 so that the speed Va is larger than the speed Vb. More specifically, the storage unit 32 is configured by, for example, a hard disk or a memory, and stores the table shown in Table 1. The table is a table showing the relationship between the size L of the gap g and the speed Va.

  The control unit 30 detects the size L of the gap g based on the output signals Sig1 to Sig5 output from the sensors Se1 to Se5, and determines the speed Va based on the table. Here, in Table 1, the relationship of L1 <L2 <L3 and the relationship of V1 <V2 <V3 <V4 <V5 are established, and V1 is the same as the velocity Vb. That is, the speed Va always has a magnitude greater than or equal to the speed Vb. Therefore, when the gap g exists (when the size L of the gap g> 0), the control unit 30 moves toward the sensors Se1 to Se5 located on the downstream side in the conveyance direction of the paper P. The drive unit 31 and the conveyance roller 19 are controlled so as to be small. On the other hand, when the sensor Se no longer detects the gap g (when the size L of the gap g becomes 0), the control unit 30 sets the speed Va to V1, which is equal to the speed Vb, as shown in the table. Thus, the drive unit 31 and the transport roller 19 are controlled.

  The overlap prevention mechanism 40 functions as a release unit that releases the overlap between the paper P1 and the paper P2. More specifically, as shown in FIGS. 1 and 2, the overlap prevention mechanism 40 is provided on the downstream side of the path R (near the timing roller 20), and has a cross-sectional structure in which a part of a circular shape is raised. It is. FIG. 3 is a diagram illustrating the operation of the overlap prevention mechanism 40. As shown in FIG. 3A, when the paper P <b> 1 and the paper P <b> 2 reach the overlap prevention mechanism 40 in an overlapped state, the leading end of the paper P <b> 2 is caught by the raised portion of the overlap prevention mechanism 40. Then, as shown in FIG. 3B, the paper P2 is pushed up by the driving force of the transport roller 19 and rotates the overlap prevention mechanism 40. When the overlap prevention mechanism 40 rotates by a predetermined amount, as shown in FIG. 3C, the catch between the leading edge of the paper P2 and the overlap prevention mechanism 40 is released, and the paper P2 moves upward in the drawing. Be transported. Thereafter, the overlap prevention mechanism 40 further rotates and returns to the state of FIG. With the above operation, the sheet P2 is decelerated. On the other hand, between FIG. 3A to FIG. 3C, the sheet P1 is conveyed upward without being decelerated. As a result, the overlap between the paper P1 and the paper P2 is released.

  The printing unit 2 forms a toner image on the paper P conveyed from the timing roller 20, and as shown in FIG. 1, the image forming units 24Y, 24M, 24C, 24K, the primary transfer rollers 8Y, 8M, 8C, 8K, an intermediate transfer belt 11, a driving roller 12, a driven roller 13, a secondary transfer roller 14, and a cleaning device 21 are included. The image forming units 24Y, 24M, 24C, and 24K include photosensitive drums 4Y, 4M, 4C, and 4K, chargers 5Y, 5M, 5C, and 5K, exposure devices 6Y, 6M, 6C, and 6K, and developing devices 7Y and 7M. , 7C, 7K and cleaners 9Y, 9M, 9C, 9K. In the following description, when the photosensitive drum, the charger, the exposure device, the developing device, the primary transfer roller, the cleaner, and the image forming unit are collectively referred to, the photosensitive drum 4, the charger 5, The exposure device 6, the developing device 7, the primary transfer roller 8, the cleaner 9, and the image forming unit 24 are described as individual photosensitive drums, chargers, exposure devices, developing devices, primary transfer rollers, cleaners, and When the image forming unit is indicated, the photosensitive drums 4Y, 4M, 4C, and 4K, the chargers 5Y, 5M, 5C, and 5K, the exposure devices 6Y, 6M, 6C, and 6K, and the developing devices 7Y, 7M, 7C, and 7K are used. The primary transfer rollers 8Y, 8M, 8C, and 8K, the cleaners 9Y, 9M, 9C, and 9K, and the image forming units 24Y, 24M, 24C, and 24K are described.

  The charger 5 charges the peripheral surface of the photosensitive drum 4. The exposure apparatus 6 irradiates a laser under the control of an exposure control unit (not shown in FIG. 1). As a result, an electrostatic latent image is formed on the peripheral surface of the photosensitive drum 4. That is, the charger 5 and the exposure device 6 serve as an electrostatic latent image forming unit that forms an electrostatic latent image on the peripheral surface of the photosensitive drum 4.

  The developing device 7 serves as a developing unit that applies toner to the photosensitive drum 4 and forms toner images on the peripheral surfaces of the plurality of photosensitive drums 4. More specifically, the developing device 7 contains toner and is negatively charged by stirring the toner. Then, the developing device 7 conveys the toner to the vicinity of the photosensitive drum 4 by the developing roller. At this time, the negatively charged toner moves from the developing roller to the photosensitive drum 4 under the influence of the electric field due to the electrostatic latent image. As a result, a toner image is formed on the peripheral surface of the photosensitive drum 4.

  The intermediate transfer belt 11 is stretched between the driving roller 12 and the driven roller 13, and the toner image formed on the photosensitive drum 4 is primarily transferred. The primary transfer roller 8 is disposed so as to be in contact with the inner peripheral surface of the intermediate transfer belt 11, and a toner formed on the photosensitive drum 4 by applying a primary transfer voltage from a voltage application unit (not shown). It plays the role of primary transfer of the image to the intermediate transfer belt 11. The cleaner 9 serves to collect the toner remaining on the peripheral surface of the photosensitive drum 4 after the primary transfer. The driving roller 12 is driven by the intermediate transfer belt 11 by being rotated by an intermediate transfer belt driving unit (not shown in FIG. 1). As a result, the intermediate transfer belt 11 conveys the toner image to the secondary transfer roller 14.

  The secondary transfer roller 14 forms a nip portion N by facing the intermediate transfer belt 11, and the toner image conveyed by the intermediate transfer belt 11 is conveyed from the timing roller 20 and passes through the nip portion N. Secondary transfer is performed on the paper P. The cleaning device 21 removes the toner remaining on the intermediate transfer belt 11 after the secondary transfer of the toner image onto the paper P.

  The sheet P on which the toner image is secondarily transferred is conveyed to the fixing device 22. The fixing device 22 fixes the toner image on the paper P by performing heat treatment and pressure treatment on the paper P. A printed paper P is placed on the paper discharge tray 23.

(Operation of image forming apparatus)
An operation of the image forming apparatus 1 including the sheet conveying device 35 configured as described above will be described below with reference to the drawings. FIG. 4 is a flowchart illustrating an operation performed by the control unit 30 when the paper P1 and the paper P2 are continuously conveyed. FIG. 5 is a graph showing waveforms of output signals Sig1 to Sig5 from the sensors Se1 to Se5. FIGS. 6 to 8 are diagrams illustrating how the sheets P1 and P2 pass through the light receiving unit Sen-2 (n is an integer of 1 to 5).

  First, an outline of the operation of the image forming apparatus 10 will be described with reference to FIGS. When the light receiving units Se1-2 to Se5-2 receive a relatively large amount of light, they output relatively high voltage output signals Sig1 to Sig5 and receive a relatively small amount of light. In this case, output signals Sig1 to Sig5 having relatively low voltages are output. Therefore, in FIG. 5, during the period when the voltages of the output signals Sig1 to Sig5 are high (the period from time 0 to t3 in the figure), the gap g between the sheets P1 and P2 becomes light receiving portions Se1-2 to Se5-. Passing in front of 2. The size L of the gap g between the sheets P1 and P2 corresponds to a period during which the voltages of the output signals Sig1 to Sig5 are high. Therefore, in the image forming apparatus 10, the control unit 30 measures this period, calculates the size L of the gap g between the sheets P1 and P2, and controls the size of the speed Va.

  Here, as shown in FIG. 5, the output signals Sig1 to Sig5 have three types of waveforms. More specifically, the output signals Sig1 and Sig2 have a trapezoidal waveform, the output signal Sig3 has a square waveform with the trapezoidal top and bottom inclined, and the output signal Sig4 has a triangular waveform. ing. The output signal Sig5 has a constant waveform that does not change because the gap g between the sheets P1 and P2 is eliminated.

  As described above, the reason why the waveforms are different like the output signals Sig1 to Sig5 is that the size of the gap g is different. Specifically, as shown in FIG. 6, when the size L of the gap g is larger than the light receiving unit Sen-2, the output signal Sign has a waveform like the output signals Sig1 and Sig2 in FIG. . As shown in FIG. 7, when the size L of the gap g is smaller than the light receiving unit Sen-2, the output signal Sign has a waveform like the output signal Sig3 in FIG. Further, as shown in FIG. 8, when the size L of the gap g becomes zero during the passage of the light receiving unit Sen-2, the output signal Sign has a waveform like the output signal Sig4 of FIG. . This will be described in more detail below with reference to FIGS.

  When the size L of the gap g is larger than the width l of the light receiving unit Sen-2, first, as shown in FIG. 6A, the rear end of the sheet P1 passes through the light receiving unit Sen-2. At this time, since the area where the light receiving unit Sen-2 is covered with the paper P1 decreases, the voltage of the output signal Sign increases as shown by the output signals Sig1 and Sig2 in FIG. Next, as shown in FIG. 6B, when the rear end of the sheet P1 has passed through the light receiving unit Sen-2, the light receiving unit Sen-2 is not covered with the sheets P1 and P2. Therefore, the voltage of the output signal Sign is constant at a relatively high voltage as indicated by the output signals Sig1 and Sig2 in FIG. Next, as shown in FIG. 6C, the leading edge of the sheet P2 passes through the light receiving unit Sen-2. At this time, since the area where the light receiving unit Sen-2 is covered with the paper P2 increases, the voltage of the output signal Sign decreases as shown by the output signals Sig1 and Sig2 in FIG. Finally, as shown in FIG. 6D, when the leading edge of the paper P2 has passed through the light receiving unit Sen-2, the light receiving unit Sen-2 is covered with the paper P2. Therefore, the voltage of the output signal Sign becomes constant at a relatively low voltage as indicated by the output signals Sig1 and Sig2 in FIG.

  Next, when the size L of the gap g is smaller than the width l of the light receiving unit Sen-2, first, as shown in FIG. 7A, the rear end of the sheet P1 passes through the light receiving unit Sen-2. To do. At this time, since the area where the light receiving unit Sen-2 is covered with the paper P1 decreases, the voltage of the output signal Sign increases as shown by the output signal Sig3 in FIG. Next, as shown in FIG. 7B, the leading edge of the sheet P2 passes through the light receiving unit Sen-2. Here, since the speed Va is larger than the speed Vb, the area where the light receiving unit Sen-2 is covered with the paper P2 gradually increases. Therefore, the voltage of the output signal Sign gradually decreases as shown by the output signal Sig3 in FIG. Next, as shown in FIG. 7C, when the rear end of the paper P1 has passed through the light receiving unit Sen-2, only the front end of the paper P2 passes through the light receiving unit Sen-2. The voltage rapidly decreases as shown by the output signal Sig3 in FIG. Finally, as shown in FIG. 6D, when the leading edge of the paper P2 has passed through the light receiving unit Sen-2, the light receiving unit Sen-2 is covered with the paper P2. Therefore, the voltage of the output signal Sign is constant at a relatively low voltage as shown by the output signal Sig3 in FIG. As described above, when the size L of the gap g is smaller than the width l of the light receiving unit Sen-2, the front end of the paper P2 receives light before the rear end of the paper P1 finishes passing through the light receiving unit Sen-2. The passage of the part Sen-2 is started. Therefore, during the period from time t1 to time t2, the voltage of the output signal Sign is not constant but gradually decreases.

  Next, when the size L of the gap g becomes zero during the passage of the light receiving unit Sen-2, first, as shown in FIG. 8A, the rear end of the sheet P1 passes the light receiving unit Sen-2. pass. At this time, since the area where the light receiving unit Sen-2 is covered with the paper P1 decreases, the voltage of the output signal Sign increases as shown by the output signal Sig4 in FIG. Next, as shown in FIG. 8B, the leading edge of the sheet P2 passes through the light receiving unit Sen-2. Here, since the speed Va is larger than the speed Vb, the area where the light receiving unit Sen-2 is covered with the paper P2 gradually increases. Therefore, the voltage of the output signal Sign gradually decreases as shown by the output signal Sig4 in FIG. Next, as shown in FIG. 8C, the leading edge of the paper P2 catches up with the trailing edge of the paper P1. As a result, the light receiving unit Sen-2 is covered with the sheets P1 and P2. Therefore, the voltage of the output signal Sign is constant at a relatively low voltage as indicated by the output signal Sig4 in FIG.

  As described above, when the size L of the gap g changes, the order in which the trailing edge of the paper P1 and the leading edge of the paper P2 pass changes. Therefore, the control unit 30 identifies the passage of the rear end of the paper P1 and the passage of the front end of the paper P2 based on the waveform of the output signal Sign from the light receiving unit Sen-2. Hereinafter, the operation of the image forming apparatus 10 will be described with reference to FIG.

  The control unit 30 sets n to 1 (step S1). Step 1 is performed, for example, triggered by the fact that the leading edge of the paper P1 is detected by the sensor Se5 located on the most downstream side of the path R.

  Next, in order to determine whether or not the gap g exists between the sheets P1 and P2, the control unit 30 assumes that the sensor Sen (n is an integer of 1 to 5) reaches the rear end of the sheet P1. It is determined whether or not the trailing edge of the paper P1 is detected during a predetermined timing (step S2). When the rear end of the sheet P1 passes in front of the light receiving unit Sen-2, the area where the light receiving unit Sen-2 is covered with the sheet P1 decreases. Therefore, the amount of light received by the light receiving unit Sen-2 gradually increases. As a result, the voltage of the output signal Sign of the light receiving unit Sen-2 gradually increases. Therefore, the control unit 30 determines the moment when the output signal Sign rises as the moment when the trailing edge of the paper P1 is detected. Thereafter, the process proceeds to step S4. On the other hand, when the trailing edge of the paper P1 is not detected, the control unit 30 determines that there is no gap g between the papers P1 and P2. Then, the process proceeds to step S3.

  When the trailing edge of the paper P1 is not detected, the control unit 30 sets the speed Va to V1 (step S3). In this process, the control unit 30 determines that there is no gap g between the sheets P1 and P2, and therefore determines that it is not necessary to adjust the speed Va. Therefore, the control unit 30 sets the speed Va to the same V1 as the speed Vb. Thereafter, the process proceeds to step S18.

  When the trailing edge of the paper P1 is detected, the control unit 30 starts time measurement (step S4). As shown in FIG. 5, the control unit 30 starts time measurement with the moment when the output signal Sign rises as t = 0. Next, the control unit 30 determines whether or not the increase in the voltage of the output signal Sign has been stopped (step S5). As shown in FIG. 6B, when the rear end of the paper P1 has finished passing through the light receiving unit Sen-2, the light receiving unit Sen-2 is not covered with the paper P1, so that the light receiving unit Sen-2 is not covered. The increase in the amount of received light stops, and the increase in the voltage of the output signal Sign also stops. Similarly, as shown in FIGS. 7B and 8B, when the leading edge of the paper P2 reaches the light receiving unit Sen-2, the light receiving unit Sen-2 starts to be covered with the paper P2. The increase in the amount of light received by the light receiving unit Sen-2 stops, and the increase in the voltage of the output signal Sign also stops. However, at the stage of step S5, the control unit 30 cannot distinguish whether the trailing edge of the paper P1 has finished passing through the light receiving unit Sen-2 or whether the leading edge of the paper P2 has reached the light receiving unit Sen-2. This distinction is made in step S7 described later. When the increase in the voltage of the output signal Sign stops, the process proceeds to step S6. If the increase in the voltage of the output signal Sign has not stopped, the process returns to step S5. And step S5 is repeated until the increase in the voltage of the output signal Sign stops.

  When the increase in the voltage of the output signal Sign stops, the control unit 30 acquires a time t1 (see FIG. 5) at which the increase in the voltage of the output signal Sign stops (Step S6).

  Next, the control unit 30 determines whether or not time t1 is equal to time ta (step S7). The time ta is a value obtained by dividing the width l of the light receiving unit Sen-2 by the speed Vb, and is the time taken for the trailing edge of the paper P1 to pass through the light receiving unit Sen-2. Since the speed Vb is a constant value, it is a value that the control unit 30 recognizes in advance. In step S7, it is determined whether or not time t1 and time ta are equal. The cause of the increase in the output signal Sign being stopped is that the rear end of the sheet P1 is the light receiving unit Sen-2 as shown in FIG. Or the end of the sheet P2 has reached the light receiving unit Sen-2 as shown in FIGS. That is, the control unit 30 determines which of the output signals Sig1 to Sig4 in FIG. 5 is the waveform of the output signal Sign. When the time t1 is equal to the time ta, the control unit 30 determines that the increase in the voltage of the output signal Sign has stopped because the rear end of the paper P1 has finished passing through the light receiving unit Sen-2 (FIG. 5). (See the waveforms of the output signals Sig1, Sig2). Thereafter, the process proceeds to step S8. On the other hand, when the time t1 and the time ta are not equal, the control unit 30 determines that the increase of the output signal Sign has stopped because the leading edge of the paper P2 has reached the light receiving unit Sen-2 (the output of FIG. 5). (See waveforms of signals Sig3 and Sig4). Thereafter, the process proceeds to step S10.

  If the time t1 is equal to the time ta, the control unit 30 determines whether the sensor Sen has detected the leading edge of the paper P2 (step S8). More specifically, when the leading edge of the paper P2 passes in front of the light receiving unit Sen-2, the light receiving unit Sen-2 covers the paper P2 as shown in FIGS. 6C and 6D. Increased area is increasing. Therefore, the amount of light received by the light receiving unit Sen-2 gradually decreases. As a result, the voltage of the output signal Sign of the light receiving unit Sen-2 also gradually decreases as shown by the output signals Sig1 and Sig2 in FIG. The control unit 30 determines that the control unit 30 detects the leading edge of the paper P2 at the moment when the output signal Sign falls. If the control unit 30 does not detect the leading edge of the paper P2, the process returns to step S8. In this case, step S8 is repeated until the control unit 30 detects the leading edge of the paper P2. On the other hand, when the control unit 30 detects the leading edge of the paper P2, the process proceeds to step S9.

  In step S7, when the time t1 and the time ta are not equal, the control unit 30 determines whether or not the time t1 is smaller than the time ta (step S10). The time ta is the time taken for the trailing edge of the paper P1 to cross the light receiving unit Sen-2. Therefore, even though the time t1 may be equal to the time ta, it does not become longer than the time ta. Therefore, the control unit 30 determines that an error has occurred when the time t1 is not smaller than the time ta. Therefore, this process ends. On the other hand, when the time t1 is smaller than the time ta, the process proceeds to step S11.

  Next, the control unit 30 determines whether or not the rear end of the sheet P1 has finished passing through the light receiving unit Sen-2 (step S11). When the rear end of the sheet P1 has finished passing through the light receiving unit Sen-2, as shown in FIG. 7C, the light receiving unit Sen-2 is covered only by the sheet P2. Since the sheet P2 is traveling so as to cover the light receiving unit Sen-2, the voltage of the output signal Sign decreases rapidly as indicated by the output signal Sig3 in FIG. Therefore, the control unit 30 determines whether or not the trailing edge of the sheet P1 has finished passing through the light receiving unit Sen-2 by determining whether or not the decrease rate of the output signal Sign has increased. If the trailing edge of the sheet P1 has finished passing through the light receiving unit Sen-2, the process proceeds to step S9. If the trailing edge of the sheet P1 has not finished passing through the light receiving unit Sen-2, the process proceeds to step S12.

  If the trailing edge of the paper P1 has not finished passing through the light receiving unit Sen-2, the control unit 30 determines whether or not the voltage of the output signal Sign has become 0 (step S12). In step S12, the control unit 30 determines whether or not the leading end of the sheet P2 has caught up with the trailing end of the sheet P1 in the light receiving unit Sen-2 as shown in the output signal Sig5 of FIG. 5 and FIG. Yes. When the voltage of the output signal Sign is 0, the control unit 30 determines that the leading edge of the paper P2 has caught up with the trailing edge of the paper P1. Thereafter, the process proceeds to step S13. On the other hand, when the voltage of the output signal Sign is not 0, the control unit 30 determines that the leading edge of the paper P2 has not caught up with the trailing edge of the paper P1. Thereafter, the process returns to step S11.

  When the voltage of the output signal Sign becomes 0, the control unit 30 determines that the size L of the gap g between the sheets P1 and P2 is 0 (step S13). Thereafter, the process proceeds to step S17.

  In step S9, the control unit 30 acquires time t2 (see FIG. 5) at which the voltage of the output signal Sign starts decreasing in steps S8 and S11 (step S9). Further, the control unit 30 determines whether or not the leading end of the paper P2 has finished passing through the light receiving unit Sen-2 (step S14). When the leading edge of the sheet P2 has finished passing through the light receiving unit Sen-2, the light receiving unit Sen-2 is covered with the sheet P2, so that the amount of light received by the light receiving unit Sen-2 becomes 0, and the voltage of the output signal Sign. Is also 0. Therefore, the control unit 30 determines whether or not the leading edge of the paper P2 has finished passing through the light receiving unit Sen-2 by determining whether or not the output signal Sign has become zero. When the leading edge of the paper P2 has finished passing through the light receiving unit Sen-2, the process proceeds to step S15. If the leading edge of the paper P2 has not finished passing through the light receiving unit Sen-2, the process returns to step S14. In this case, step S14 is repeated until the leading edge of the sheet P2 finishes passing through the light receiving unit Sen-2.

  When the leading edge of the paper P2 has finished passing through the light receiving unit Sen-2, the control unit 30 acquires time t3 (see FIG. 5) when the leading edge of the paper P2 has finished passing through the light receiving unit Sen-2 (see FIG. 5). Step S15).

  Next, the control unit 30 calculates the size L of the gap g between the sheets P1 and P2 based on the width l, the speed Vb of the light receiving unit Sen-2, and the time t3 (step S16). Specifically, the control unit 30 calculates the size L of the gap g based on the following formula (1).

L = t3 × Vb−1 (1)

  Next, the control unit 30 controls the driving unit 31 and the conveyance roller 19 so that the speed Va is increased based on the size L of the gap g. Specifically, the control unit 30 refers to the table in Table 1 and specifies the speed Va corresponding to the size L of the gap g (step S17). Further, the control unit 30 controls the driving unit 31 and the conveyance roller 19 so that the paper P2 is conveyed at the speed Va specified in step S17. Since V2 to V5 in Table 1 have a magnitude equal to or higher than the speed Vb, the gap g between the paper P1 and the paper P2 gradually decreases. Thereafter, the process proceeds to step S18.

  In step S18, the control unit 30 determines whether or not n = 5 (step S18). In step S18, it is determined whether or not the processing in steps S2 to S17 has been performed for all the sensors Se1 to Se5. If n = 5, this process ends. On the other hand, if n = 5 is not true, the process proceeds to step S19.

  If not n = 5, the control unit 30 resets the time measurement (step S19). Next, the control unit 30 increments n by one (step S20). Thereafter, the process returns to step S2.

  The control unit 30 performs the same process for the sensors Se2 to Se5. Above, description of operation | movement of the image forming apparatus 1 provided with the sheet conveying apparatus 35 is complete | finished. According to the operation of the image forming apparatus 1, as shown in FIG. 5, the size of the gap g decreases as it goes from the upstream sensor Se <b> 1 in the conveyance direction of the paper P to the downstream sensor Se <b> 5.

(effect)
According to the sheet conveying apparatus 35 configured as described above and the image forming apparatus 1 including the sheet conveying apparatus 35, the gap g between the sheets P1 and P2 is set to zero when the plurality of sheets P1 and P2 are continuously conveyed. You can get closer. More specifically, in the sheet conveying device 35, a plurality of sensors Se1 to Se5 are provided at a plurality of locations on the path R. Therefore, the control unit 30 can adjust the speed Va of the paper P2 being conveyed by the conveying roller 19 a plurality of times. Therefore, the sheet conveying device 35 can control the speed Va more precisely than the sheet feeding device described in Patent Document 1 that detects the gap between the sheets only once. As a result, the sheet conveying apparatus 35 and the image forming apparatus 1 including the sheet conveying apparatus 35 can bring the gap g between the sheets P1 and P2 closer to zero with higher accuracy than the sheet feeding apparatus described in Patent Document 1. . Therefore, the lifetimes of the transport roller 19 and the intermediate transfer belt 11 can be extended and productivity can be increased.

  Further, in the sheet conveying apparatus 35 and the image forming apparatus 1 including the sheet conveying apparatus 35, the gap g between the sheets P1 and P2 can be brought close to zero, so that productivity can be maintained even if the speeds Va and Vb are reduced. Can do. As described above, if the speeds Va and Vb are reduced, the speed at which the paper P passes through the fixing device 22 is also reduced, and the fixing temperature of the fixing device 22 can be lowered. As a result, the power consumption of the image forming apparatus 1 can be reduced.

  Further, according to the sheet conveying device 35 and the image forming apparatus 1 including the same, if the size of the gap g is relatively large, the speed Va is relatively increased, and the size of the gap g is relatively large. If it becomes smaller, the speed Va is made relatively smaller. Therefore, in the sheet conveying device 35 and the image forming apparatus 1 including the sheet conveying device 35, when the leading end of the sheet P2 is likely to catch up with the leading end of the sheet P1, the speed Va is decreased so that the sheet P1 and the sheet P2 are separated. Prevents overlapping.

  Further, since the sheet conveying device 35 and the image forming apparatus 1 including the same are provided with the overlap prevention mechanism 40, even if the sheets P1 and P2 overlap, the overlap prevention mechanism 40 causes the sheets P1 and P2 to be separated. Overlap is released.

(Modification)
The sheet conveying device 35 and the image forming apparatus 1 configured as described above are not limited to those shown in the above-described embodiment, and can be changed within the scope of the gist thereof. Hereinafter, modified examples of the sheet conveying device 35 and the image forming apparatus 1 including the sheet conveying device 35 will be described.

  FIG. 9 is a diagram illustrating a modification of the sensors Se <b> 1 to Se <b> 5 of the sheet conveying device 35. As shown in FIG. 9A, the light receiving unit corresponding to the light emitting units Se1-1 to Se5-1 may be configured by one light receiving unit Se1-2. Further, as shown in FIG. 9B, a camera C may be used instead of the sensors Se1 to Se5. In this case, as shown in FIG. 9C, it is desirable that the camera C is arranged so as to take an image around the vicinity of the timing roller 20. This is because the gap g is preferably 0 in the timing roller 20.

  Note that the control unit 30 controls the magnitude of the speed Va by keeping the speed Vb constant, but may control the magnitude of the speed Vb to keep the speed Va constant. In this case, when detecting the gap g between the sheets P1 and P2, the control unit 30 controls the timing roller 20 and the driving unit of the timing roller 20 so that the speed Vb is smaller than the speed Va.

  Further, when the sensor Se1 located on the most upstream side in the transport direction of the paper P does not detect the gap g, the control unit 30 drives the transport roller 19 and the drive so that the speed Va becomes smaller than the speed Vb. The drive unit of the unit 31 or the timing roller 20 and the timing roller 20 may be controlled. If the sensor Se1 does not detect the gap g, the controller 30 determines that there is a possibility that the sheets P1 and P2 overlap, and then forms the gap g between the sheets P1 and P2, and then the sheets P1 and P2. Control is performed so as to eliminate the gap g between P2. As a result, it is possible to prevent the paper P1 and P2 from leaving the route R in a state where the papers P1 and P2 overlap. Even when the sensors Se2 to Se5 other than the sensor Se1 do not detect the gap g, the control unit 30 causes the transport roller 19 and the drive unit 31 or the timing roller 20 so that the speed Va is smaller than the speed Vb. In addition, the drive unit of the timing roller 20 may be controlled.

  Further, the overlap prevention mechanism 40 is not limited to that shown in FIG. FIG. 10 is a view showing an overlap prevention mechanism 40 ′ according to a modification. The overlap prevention mechanism 40 ′ is configured by bending a guide that configures the path R. As a result, the leading edge of the paper P2 is caught by the guide. As a result, the overlap of the sheets P1 and P2 is released.

1 is a diagram illustrating an overall configuration of an image forming apparatus according to an embodiment. It is an enlarged view of the sheet conveying apparatus in FIG. It is the figure which showed operation | movement of the overlap prevention mechanism. 6 is a flowchart illustrating an operation performed by a control unit when continuously transporting paper. It is the graph which showed the waveform of the output signal from a sensor. FIG. 6 is a diagram illustrating a state in which a sheet passes through a light receiving unit. FIG. 6 is a diagram illustrating a state in which a sheet passes through a light receiving unit. FIG. 6 is a diagram illustrating a state in which a sheet passes through a light receiving unit. It is the figure which showed the modification of the sensor of a conveying apparatus. It is the figure which showed the overlap prevention mechanism which concerns on a modification.

Explanation of symbols

P1, P2 Paper R path Se1 to Se5 Sensor Sig1 to Sig5 Output signal 1 Image forming apparatus 15 Paper feed unit 16 Paper tray 17 Paper feed roller 18 Rolling roller 19 Transport roller 20 Timing roller 30 Control unit 31 Drive unit 32 Storage unit 35 Sheet Transport device 40, 40 'Overlap prevention mechanism

Claims (8)

In a sheet conveying device used in an image forming apparatus provided with a printing unit that prints an image on a sheet,
First conveying means for conveying the sheet at a first speed;
Second conveying means for conveying the sheet conveyed by the first conveying means to the printing unit at a second speed;
A detection unit provided between the first conveyance unit and the second conveyance unit, wherein the first sheet is conveyed by the second conveyance unit and the second sheet is conveyed by the first conveyance unit. A plurality of detection means for detecting gaps between the first sheet and the second sheet at a plurality of detection positions when being conveyed by the means;
Control means for controlling the first conveying means or the second conveying means so that the first speed is higher than the second speed when the detecting means detects the gap; ,
Having
A sheet conveying apparatus characterized by the above. The control means controls the first conveying means or the second conveying means so that the gap becomes smaller as going to the detection position located downstream in the conveying direction of the sheet;
The sheet conveying apparatus according to claim 1. When the detection unit no longer detects the gap, the control unit sets the first transfer unit or the second transfer so that the first speed and the second speed are equal to each other. Controlling the means,
The sheet conveying apparatus according to claim 1, wherein: The control means is configured so that the first speed is smaller than the second speed when the detection means located on the most upstream side in the sheet conveyance direction does not detect the gap. Controlling the first conveying means or the second conveying means;
The sheet conveying apparatus according to any one of claims 1 to 3, wherein The detection position has a predetermined width,
The control means includes
The first speed is obtained based on the time required for the trailing edge of the first sheet to pass the detection position and the predetermined width, and the leading edge of the second sheet passes the detection position. And determining the second speed based on the time taken for and the predetermined width,
Based on the predetermined width, the second speed, and the time taken for the gap to pass through the detection position, the size of the gap is determined.
Controlling the first conveying means or the second conveying means based on the size of the gap so that the first speed is smaller than the second speed;
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. Release means for releasing the overlap between the first sheet and the second sheet;
More
The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is a sheet conveying apparatus. The first speed is constant;
The sheet conveying apparatus according to claim 1, wherein Comprising the sheet conveying device according to any one of claims 1 to 7,
An image forming apparatus.

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