JP2011121652A - Printing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent sheets from being contaminated with ink adhered to a carriage roller that constitutes a carrying means, in a printing device provided with the carrying means carrying sheets from a first printing means to a second printing means. <P>SOLUTION: The printing device 1 includes: the first printing means 3; the second printing means 5; and the carrying means carrying the sheets P from the first printing means 3 to the second printing means 5. The carrying means includes: a first carriage roller 82 comprising a pair of nip rollers; and a second carriage roller 83 arranged on the downstream side in the paper carrying direction with a distance less than the sheet length from this first carriage roller 82. The first carriage roller 82 drives, starting from the moment when the forefront of the sheet P bumps against the second carriage roller 83 while the second carriage roller 83 is stopped, until the sheet P has a slack, and stops. Thereafter, the second carriage roller 83 starts driving, and the first carriage roller 82 drives for assisting not later than the time when the slack is resolved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus, and more particularly, to a printing apparatus configured to print once on a printing sheet such as a double-sided printing apparatus and then print again on the sheet.

  In recent years, it has been desired to reduce the amount of paper used for printing from the viewpoint of environmental problems, and for this reason, double-sided printing, in which printing is performed on the front and back surfaces of paper, has been actively performed. As a double-sided printing apparatus for performing double-sided printing, for example, a double-sided stencil printing apparatus for performing stencil printing has been proposed. As an example of this apparatus, a cylindrical first drum in which perforated stencil paper is wound around an outer peripheral surface. And the second drum are arranged adjacent to each other, the first drum performs printing on the front surface of the paper, the paper on which the front surface is printed is conveyed to the second drum, and the second drum performs printing on the back surface of the paper. The device is known.

  In the double-sided printing apparatus as described above, a conveying means is provided between the first drum and the second drum for conveying the sheet printed on the surface of the first drum toward the second drum. . In many cases, this type of conveying apparatus is configured to include a conveying roller including a pair of nip rollers that sandwich a sheet, and Patent Document 1 shows an example of a double-sided printing apparatus that includes this type of conveying roller. ing. In many cases, two (two pairs) or more of such conveying rollers are arranged along the sheet conveying path. In this case, the distance between two adjacent conveying rollers is the sheet length, that is, the sheet conveying direction. It is set shorter than the size of.

  By the way, in the paper conveying means including two conveying rollers, the driving of the conveying rollers may be controlled so as to correct the meandering of the paper. In this control, the first transport roller is the second transport roller when the first transport roller is the upstream transport direction and the second transport roller is the downstream transport roller. In the period during which the paper is stopped, the sheet is driven until it sags after the leading edge of the sheet hits the second conveying roller, and then the second conveying roller is driven. In this way, when the leading edge of the sheet comes into contact with the second transport roller, the leading edge is aligned in parallel with the roller shaft, so even if the sheet meanders before that, The meandering will be corrected.

JP 2009-012216 A

  In the double-sided printing apparatus as described above, when the paper printed on one surface by the first drum is transported toward the second drum by the transporting means, the ink that has not completely dried adheres to the transporting roller. Sometimes. Thus, the ink adhering to the transport roller may be transferred to the paper and soil the paper when the transport roller subsequently transports the paper. This problem is not limited to the double-sided printing device, and other printing devices such as a multicolor printing device configured to transport the paper after printing by one printing unit to another printing device by the transporting unit. Can occur in the same way.

  This problem arises when the sheet conveying means includes first and second conveying rollers each consisting of a nip roller, and their drive is controlled to generate a temporary slack in the sheet as described above. It is recognized that it is particularly likely to occur.

  The present invention has been made in view of the above circumstances. In a printing apparatus in which the driving of the first and second conveyance rollers constituting the sheet conveyance unit is controlled so as to generate a temporary sag in the sheet. An object of the present invention is to prevent the paper from being soiled by the ink adhering to the roller.

  In the printing apparatus according to the present invention, when the paper is transported by the second transport roller after the slack is generated in the paper, the first transport roller is also assisted to drive between the transport rollers when the slack is eliminated. The speed difference is reduced.

That is, the printing apparatus according to the present invention is more specifically,
First printing means for printing on one surface of the paper;
Second printing means for printing on one surface or the other surface of the paper;
Conveying means for conveying the paper printed on the one surface to the second printing means;
A first conveying roller comprising a pair of nip rollers; and a second conveying roller disposed downstream of the first conveying roller at a distance less than the sheet length in the sheet conveying direction. In a printing apparatus configured to include:
The first conveying roller is driven and stopped until a slack occurs in the paper after the leading edge of the paper hits the second conveying roller during a period in which the second conveying roller is stopped,
Thereafter, the second conveying roller starts to drive,
At least when the slack is eliminated, the first conveying roller is configured to be driven to assist.

  In the printing apparatus according to the present invention, both the first and second transport rollers are arranged so that the slack is eliminated during the period when both the first transport roller and the second transport roller are transporting the paper at a constant speed. It is desirable that the drive is controlled.

  And when the drive of both the conveyance rollers is controlled in this way, when the first conveyance roller is driven to assist, the sheet conveyance speed is 70 to 90% of the sheet conveyance speed of the second conveyance roller. It is desirable that the driving of both the transport rollers is controlled so that the slack is eliminated under the condition of being in the range.

  In the printing apparatus according to the present invention, it is desirable that the paper feed amount by the assist drive of the first transport roller can be adjusted according to the type of paper.

  Further, it is particularly desirable that the assist driving of the first conveying roller is performed at the same start timing and the same acceleration as the driving of the second conveying roller.

  Further, the conveying means in the printing apparatus of the present invention reverses the orientation of the paper printed on one surface by the first printing means so that the second printing means can print on the other surface. It is desirable that the reversing unit to be included is included.

  According to the research of the present inventor, as described above, when the driving of the two conveying rollers is controlled so as to correct the meandering of the paper, the paper smear is particularly likely to occur for the following reason. I understood that.

  Even if some undried ink adheres to the transport roller to some extent, it is difficult to transfer the ink to the transport roller side as long as the sheet is transported at a speed that matches the peripheral speed of the transport roller. However, if only the first transport roller is driven to generate the above-described sag in the paper, and then the paper is transported by the second transport roller while the first transport roller is stopped, the sag is eliminated. At this moment, a force against the conveyance, so-called back tension, acts on the second conveyance roller because the first conveyance roller composed of a nip roller holds the sheet therebetween. Then, slipping and rubbing occur between the second transport roller and the paper, so that the ink attached to the peripheral surface of the second transport roller can be easily transferred to the paper. The ink stain is caused by the difference in the conveyance speed between the second conveyance roller and the first conveyance roller (if the first conveyance roller is stopped, the conveyance speed of the second conveyance roller remains unchanged. It was also found that the larger the difference in speed), the darker it appears.

  Based on the above knowledge, in the printing apparatus of the present invention, since the second conveying roller starts driving, the first conveying roller is configured to be driven at least when the sheet slack is eliminated. The difference in transport speed between the two transport rollers at the moment when the slack is eliminated is smaller than when the first transport roller is kept stopped. Therefore, since the above-described back tension is reduced, slippage and rubbing between the second conveyance roller and the sheet are less likely to occur, and as a result, sheet contamination due to ink transfer from the second conveyance roller is prevented. The

  In the printing apparatus according to the present invention, both the transport rollers are driven so that the slack of the paper is eliminated particularly during the period in which both the first transport roller and the second transport roller transport the paper at a constant speed. Is controlled, the effect of preventing paper smearing can be stably obtained. In other words, for example, when both the transport rollers are accelerating, the speeds of both the transport rollers are likely to become unstable due to characteristic variations of the drive motor. Therefore, if the sag is eliminated under such a condition, the sag may be eliminated when the speed difference between the two conveying rollers is large. In this case, the paper is likely to be stained. Considering this point, if the drive is controlled so that the slack is eliminated under the condition that both the transport rollers are stably driven at a constant speed, the speed difference between the two transport rollers is inadvertently large. Since it is possible to prevent the sagging from being eliminated, the effect of preventing paper smearing can be stably obtained.

  At this time, the two conveying rollers are driven so that the slack is eliminated under the condition that the sheet conveying speed of the first conveying roller is in the range of 70 to 90% of the sheet conveying speed of the second conveying roller. If is controlled, the effect of preventing paper stains can be obtained more stably. The reason will be described in detail later in accordance with the embodiment.

  Further, in the printing apparatus of the present invention, in particular, when the paper feed amount by the assist drive of the first transport roller is adjustable according to the paper type, even if the sag generation amount changes according to the paper type, Correspondingly, it is possible to eliminate sheet sag during a preferable period in which both the first conveyance roller and the second conveyance roller are conveying the sheet at a constant speed.

1 is a side view showing a schematic configuration of a printing apparatus according to an embodiment of the present invention. The partially broken side view which shows the principal part of the said printing apparatus Exploded perspective view showing a paper carry-out device used in the printing apparatus FIG. 3 is an exploded perspective view showing a state different from FIG. 3 of the paper carry-out device. Schematic explaining the dirt on the paper Time chart showing the operating state (1) of the conveying roller in the printing apparatus and the operating state (2) of the conveying roller in the conventional apparatus The flowchart which shows the flow of the printing process in the said printing apparatus. The flowchart which shows a part of subroutine processing in the processing of FIG. The figure explaining the look-up table used for the subroutine process of FIG. The flowchart which shows another subroutine process in the process of FIG. Time chart showing another operating state (1) of the transport roller and an operating state (2) of the paper carry-out device Timing chart showing timing relationship between operation of conveyance roller and operation of paper detection sensor in the printing apparatus

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

  FIG. 1 is a schematic configuration diagram of a double-sided stencil printing apparatus 1 according to an embodiment of the present invention, and FIG. 2 is a side view showing an enlarged main part thereof. As shown in FIG. 1, the double-sided stencil printing apparatus 1 is provided on an apparatus housing 10 and one side surface of the apparatus housing 10, that is, the left side surface in the figure, and stacks a plurality of sheets P as printing media. A paper feed tray 2 to be held, a first stencil printing unit (first printing means) 3 for printing on one surface of paper P fed from the paper feed tray 2, and a paper printed on one surface A storage section 4 for temporarily storing a plurality of P sheets, a second stencil printing section (second printing means) 5 for printing on the other surface of the paper P stored in the storage section 4, and an apparatus housing 10 It is provided on the other side surface, that is, the right side surface in the drawing, and includes a paper discharge tray 6 that stacks and holds sheets P on both sides, that is, one surface and the other surface.

  Further, the double-sided stencil printing apparatus 1 includes a paper feeding unit 7 that feeds the paper P from the paper feeding table 2 to the first stencil printing unit 3, and a paper P that is fed from the first stencil printing unit 3 into the storage unit 4. A first intermediate transport unit 8A that transports the sheet P, a second intermediate transport unit 8B that transports the paper P from the inside of the storage unit 4 to the second stencil printing unit 5, and a discharge tray 6 from the second stencil printing unit 5 And a paper discharge unit 9 for conveying the paper P to the top.

  The paper feed unit 7 has a pickup roller 71 disposed so as to be positioned above the paper P stacked on the paper feed tray 2, and the paper P picked up by the pickup roller 71 at a first timing at a first timing. A timing roller 72 that feeds the stencil printing unit 3 is schematically configured. The timing roller 72 includes a pair of nip rollers. When the timing roller 72 is stopped, the paper feeding to the first stencil printing unit 3 is stopped.

  The first intermediate transport unit 8A reverses the sheet P printed on one surface (the upper surface in FIGS. 1 and 2) by the first stencil printing unit 3 along an arcuate trajectory. Is generally configured by a reversing device 73 that turns the paper P downward and a carry-in device 74 that carries the paper P reversed by the reversing device 73 into the storage unit 4. The first intermediate transport unit 8A constitutes a sheet reversing unit together with a second intermediate transport unit 8B and a storage unit 4 described later.

  The second intermediate transport unit 8B includes a carry-out device 81 that carries out the paper P stored in the storage unit 4, a pickup roller 82 that picks up the paper P carried out by the carry-out device 81, and the pickup roller 82. And a timing roller 83 that sequentially conveys the paper P picked up by the above to the second stencil printing unit 5 at a predetermined timing. The pickup roller 82 and the timing roller 83 are each composed of a pair of nip rollers driven by motors M1 and M2.

  A first sensor S1 that detects the leading edge of the sheet P to be conveyed is disposed slightly downstream of the pickup roller 82 in the sheet conveyance direction, and is similarly conveyed in the sheet conveyance direction slightly downstream of the timing roller 83. A second sensor S2 that detects the leading edge of the paper P is provided.

  On the other hand, the paper discharge unit 9 is composed of a discharge device 84 that carries out the paper P, on which the other surface has been printed by the second stencil printing unit 5 and the double-sided printing has been completed, toward the paper discharge table 6.

  The carry-in device 74, the carry-out device 81, and the discharge device 84 are spanned around a pair of pulleys 74a, 81a, and 84a arranged at predetermined intervals, and the outer periphery of the pair of pulleys 74a, 81a, and 84a. Are provided with annular conveying belts 74b, 81b, and 84b that move as the pulleys 74a, 81a, and 84a rotate, and suction fans 74c, 81c, and 84c, respectively.

  Since these carry-in device 74, carry-out device 81, and discharge device 84 have the same basic configuration except for one point that will be described later, the carry-out device 81 is taken as an example, and its exploded perspective view is shown in FIG. Details will be described with reference to FIG. The conveyor belt 81b has a plurality of holes 81d formed on the surface thereof, and the conveyor belt 81b is arranged in a case 81g (not shown in FIG. 1) with the stretched portion facing the paper P side exposed to the outside. It is installed. While the double-sided stencil printing apparatus 1 is in operation, the fan 81c is basically always driven together with the transport belt 81b to suck air in the case 81g, and then sucks air from the hole 81d of the transport belt 81b. A suction force is generated on the conveyance surface of the conveyance belt 81b.

  A shutter unit 81e is disposed between the conveyance belt 81b and the fan 81c. The shutter unit 81e is provided with a plurality of shutter blades 81f that rotate like, for example, a lens shutter of a camera. The shutter blades 81f rotate so that the conveyance belt 81b and the fan 81c The air flow path between them can be selectively opened and closed.

  3 and 4 show a state where the shutter unit 81e opens and closes the air flow path, respectively. Here, the case 81g is shown partially broken. In these figures, the schematic flow paths of air in each state are indicated by arrows in the figure. As can be seen from this, in the former state, air is sucked from the holes 81d of the transport belt 81b and sucked into the transport surface. A force is generated, and this suction force is not generated in the latter state. Therefore, by opening and closing the shutter blade 81f during the driving period of the transport belt 81b, the transport belt 81b can be switched appropriately between the state of sucking and holding the paper P and the state of not transporting the paper P. Will be described in detail later.

  Hereinafter, the description will be made with reference to FIGS. 1 and 2 again. The devices 74, 81, and 84 configured as described above rotate the pulleys 74a, 81a, and 84a by a motor (not shown) to move the conveyor belts 74b, 81b, and 84b, and rotate the fans 74c, 81c, and 84c. By generating the aforementioned suction force, the paper P is conveyed while being sucked and held. The carry-in device 74 and the discharge device 84 do not have means similar to the shutter unit 81e described above, and are different from the carry-out device 81 only in this one point.

  The carry-in device 74 may be provided with a plurality of conveyance belts 74b and fans 74c that are stretched around the outer periphery of the pair of pulleys 74a in parallel so that a single sheet P can be sucked and held and conveyed. . The same applies to the carry-out device 81 and the discharge device 84.

  As shown in FIG. 2, the reversing device 73 has four pulleys 73a arranged along an arcuate locus, and is wound around the outer circumferences of the four pulleys 73a and moves as the pulleys 73a rotate. An annular conveyor belt 73b and a suction fan 73c are provided and operate in substantially the same manner as the devices 74, 81, 84.

  On the other hand, the first stencil printing unit 3 includes a first drum 31 and a first press roller 32. As shown in FIG. 2, a stripping claw 33 for stripping the paper P from the first drum 31 is provided on the downstream side of the first drum 31 in the paper transport direction. The first drum 31 has an ink cartridge (not shown) inside, and stencil paper (not shown) is wound around the outer peripheral surface of the first drum 31. This stencil sheet is made by thermal perforation based on input image data in a plate making unit (not shown). The sheet P is fed between the first drum 31 and the press roller 32 by the timing roller 72 that is driven synchronously with the rotation of the first drum 31, and one surface thereof is pressed against the stencil sheet by the press roller 32. Stencil printing is performed on the one surface.

  Similar to the first stencil printing unit 3, the second stencil printing unit 5 includes a second drum 51 and a second press roller 52. Further, on the downstream side of the second drum 51 in the paper conveyance direction, a peeling claw 53 for peeling the paper P from the second drum 51 is provided. The second drum 51 has an ink cartridge (not shown) inside, and stencil paper is wound around the outer peripheral surface of the second drum 51. This stencil sheet was also made by heat-sensitive perforation based on image data in the same manner as described above. The sheet P is fed between the second drum 51 and the second press roller 52 by the timing roller 83 that is driven synchronously with the rotation of the second drum 51, and the other surface is pressed against the stencil sheet by the press roller 52. Thus, stencil printing is performed on the other surface.

  The storage unit 4 temporarily stores a plurality of sheets of paper P printed on one surface by the first stencil printing unit 3 before sending it to the second stencil printing unit 5. The paper P is held in a box-shaped case 40 in a state where the paper P is stacked.

  Next, the operation of the double-sided stencil printing apparatus 1 of the present embodiment configured as described above will be described. Each operation is performed based on an instruction from a control unit (not shown) provided in the apparatus housing 10.

  When performing double-sided stencil printing, first, the pickup roller 71 sequentially picks up the paper P stacked on the paper feed tray 2 at a predetermined time interval and sends it to the timing roller 72. The timing roller 72 conveys the paper P to the first stencil printing unit 3. The first stencil printing unit 3 prints an image on one surface of the conveyed paper P as described above.

  Next, the reversing device 73 sends the paper P with one printed surface facing upward, along the arc-shaped locus while sucking the other surface, so that one surface faces downward. Then, it is conveyed toward the inside of the storage unit 4 while being reversed. The paper P thus sequentially conveyed is carried into the storage unit 4 while the carry-in device 74 sucks and holds the upper surface, that is, the other surface.

  After the paper P is temporarily stored in the storage unit 4, the carry-out device 81 carries out the paper P from the storage unit 4. The pick-up roller 82 sequentially picks up the paper P thus carried out and conveys it to the timing roller 83. The timing roller 83 sequentially conveys the paper P at a predetermined timing and sends it to the second stencil printing unit 5.

  The second stencil printing unit 5 prints an image on the upper surface, that is, the other surface of the conveyed paper P as described above. Subsequently, the discharge device 84 conveys the paper P with the other printed surface facing upward to the discharge table 6 while sucking and holding the one surface. As described above, the paper P on which double-sided printing has been completed is sequentially stacked on the paper discharge tray 6.

  In the conventional double-sided stencil printing apparatus having the basic configuration as described above, the undried ink attached to the paper P on which single-sided printing has been completed adheres to the timing roller 83, as indicated by G in FIG. In other words, a defect that is transferred to the paper P and becomes dirty is recognized. In FIG. 5, an area where the paper P is soiled by the ink G is indicated by an arrow H. That is, this example is a case where a plurality of timing rollers 83 are provided across the paper width direction.

  Hereinafter, a configuration for preventing such a problem will be described. The second intermediate transport unit 8B, together with the first intermediate transport unit 8A, constitutes a transport unit in the present invention. In the pickup roller 82 and the timing roller 83 included in the second intermediate conveyance unit 8B, the former constitutes the first conveyance roller in the present invention, and the latter constitutes the second conveyance roller in the present invention. Therefore, in the following description, they are referred to as a first conveyance roller 82 and a second conveyance roller 83, respectively.

  FIG. 6 (1) shows the operating states of the first and second transport rollers 82 and 83, where the horizontal axis represents time and the vertical axis represents their transport speed. FIG. 12 shows the timing relationship between the rotation ON / OFF of the transport rollers 82 and 83 and the paper detection ON / OFF of the first sensor S1 and the second sensor S2. In FIG. 12, the state where the conveying rollers 82 and 83 are rotating even a little is indicated as ON, and the state where the conveying rollers 82 and 83 are stopped are indicated as OFF. The period during which M1 and M2 are energized is shown. The periods indicated by T1 and T2 are periods in which the first conveying roller 82 shifts to a stopped state after the power supply to the motor M1 is cut off.

  First, as shown in FIG. 6 (1), the first conveying roller 82, which is shown in an operating state by a solid line, performs basic operation at a predetermined timing based on the above-described command from the control unit, that is, a normal sheet. The operation of conveying P is entered. At this time, the second transport roller 83 indicated by a broken line indicates the basic operation of transporting the previous sheet P. When the first conveying roller 82 is energized to the motor M1, the first conveying roller 82 accelerates at a constant acceleration and then conveys the paper P at a predetermined constant speed. When the leading edge of the sheet P is detected by the first sensor S1, the energization to the motor M1 is cut off by the command of the control unit based on the output of the first sensor S1, and the first conveying roller 82 is decelerated. To stop.

  Before the first transport roller 82 completely stops, the leading edge of the paper P abuts on the stopped second transport roller 83, so that a slack is generated in the paper P. This sagging continues to be generated during a period until the first conveying roller 82 is completely stopped, that is, a period indicated by hatching in FIG. By generating the slack in this way, the leading edge of the paper P becomes parallel to the axis of the second transport roller 83. If the paper P has meandered by then, the meandering is corrected.

  When a predetermined time (this is longer than the time until the first conveyance roller 82 completely stops) after the first sensor S1 detects the leading edge of the paper P, the motor M2 is energized and the first time. The second conveying roller 83 starts to drive. The time point at which this driving is started is indicated by a in FIG. As a result, the sheet P is now conveyed by the second conveyance roller 83. The operation of the second conveying roller 83 at this time is also a basic operation for normally conveying the paper P.

  When the second transport roller 83 is driven for a predetermined time, the energization to the motor M2 is cut off, and the second transport roller 83 starts to decelerate, but immediately after that, the leading edge of the sheet reaches the second drum 51, and thereafter The paper P is conveyed by the second drum 51 and the second press roller 52. In this state, the second transport roller 83 is rotated along with the transport of the paper P, and when the paper P is completely removed, the second transport roller 83 decelerates and stops (refer to the operation for the previous paper P shown on the left side of the figure). .

  As described above, when driving as the basic operation of the second transport roller 83 starts at the time point a, the first transport roller 82 also starts to be driven by energizing the motor M1. The driving of the first conveying roller 82 is assist driving for reducing the difference between the conveying speed (zero if not driven) and the conveying speed of the second conveying roller 83. The angle b shown in the figure indicates the acceleration of the first conveyance roller 82 and the second conveyance roller 83. As shown here, in this embodiment, the acceleration of the assist drive of the second conveyance roller 83 is shown. Is set to be the same as the driving acceleration as the basic operation of the second transport roller 83.

  In this way, both the transport rollers 82 and 83 are driven to transport the paper P. The arrival speed of the first transport roller 82, that is, the maximum speed that is constant, is that of the second transport roller 83 as shown in the figure. Since the value is set to be slightly lower than that, the sagging of the paper P is eliminated after a certain amount of time has elapsed. The speed difference between the conveying rollers 82 and 83 when the sheet slack is eliminated is a value indicated by c in the figure.

  For comparison, in FIG. 6B, in the case where the first conveyance roller 82 does not perform the assist driving, that is, the first conveyance roller 82 is simply rotated along with the conveyance of the sheet after the slack of the sheet is eliminated. The change in the speed of both the transport rollers 82 and 83 in the case of the above is shown. As shown here, if the first conveyance roller 82 is not driven to assist, the slack in the sheet is eliminated during acceleration when the second conveyance roller 83 starts to be driven. The speed difference between the rollers 82 and 83 is considerably larger than the speed difference c when assist driving is performed, as indicated by c ′ in the figure.

  When the slack in the sheet is eliminated when the speed difference between the transport rollers 82 and 83 is large, the sheet P transported by the second transport roller 83 is relatively large that resists transport. Power is added. For this reason, slipping and rubbing occur between the paper P and the second transport roller 83. If the ink has adhered to the peripheral surface of the second transport roller 83 during the previous transport operation, the ink Is transferred to the paper P and becomes dirty. It has been found by the inventor's research that the dirt G shown in FIG. 5 is generated in this way.

  On the other hand, if the second transport roller 83 is driven to assist as in the present embodiment and the speed difference c between the transport rollers 82 and 83 when the paper slack is eliminated is set to be small, Since slipping and rubbing between the sheet P and the second transport roller 83 are less likely to occur, the sheet P can be effectively prevented from being stained.

  After the paper sagging is eliminated as described above, when the leading edge of the paper P is detected by the second sensor S2, energization to the motor M1 is cut off by a command from the control unit based on the output of the second sensor S2. Then, the first conveyance roller 82 that has been driven by assist is decelerated and shifts to a stopped state.

  Here, the speed difference c will be described. In this embodiment, the slack is eliminated when both the first transport roller 82 and the second transport roller 83 are driven at a constant speed, but the first transport roller 82 at this time is eliminated. If there is a large speed difference c so that the transport speed of the second transport roller 83 is less than 70% of the transport speed of the second transport roller 83, the paper stains due to the slip and rubbing between the paper P and the second transport roller 83 described above Becomes more noticeable. Further, the stain becomes deeper as the speed difference c is larger.

  On the contrary, if the speed difference c is so small that the transport speed of the first transport roller 82 exceeds 90% of the transport speed of the second transport roller 83, it takes a long time to eliminate the sag. There is a high possibility that slack will not be resolved within a period during which both are driven at a constant speed. In other words, in this case, since the sag is eliminated after the first conveying roller 82 shifts to the stopped state, the sag is eliminated under the condition that the both conveying rollers 82 and 83 have a large speed difference. As a result, the above-mentioned slipping and rubbing that cause paper contamination are likely to occur. From the above, when the slack is eliminated when both the first transport roller 82 and the second transport roller 83 are driven at a constant speed, the paper transport speed of the first transport roller 82 Is preferably set in the range of 70 to 90% of the sheet conveying speed of the second conveying roller 83.

  The sagging of the paper P does not necessarily have to be made under the condition where both the first transport roller 82 and the second transport roller 83 are driven at a constant speed. However, for example, under the condition where both the transport rollers 82 and 83 are accelerating, there is a situation in which the speed of the transport rollers 82 and 83 is likely to become unstable due to characteristic variations of the motors M1 and M2. Therefore, if the sag is eliminated under such a condition, the sag may be eliminated when the speed difference between the two conveying rollers 82 and 83 is large. It becomes easy to do. In consideration of this point, it is desirable to control the driving of the two conveying rollers 82 and 83 so that the slack is eliminated under the condition that both of the conveying rollers 82 and 83 are stably driven at a constant speed.

  Further, in the present embodiment, the assist driving of the first conveying roller 82 performed from the point a in FIG. 6A is performed at the same start timing and the same acceleration as the driving of the second conveying roller 83 that performs the basic operation. However, this is not always necessary. That is, the drive start timing and acceleration of the first transport roller 82 and the second transport roller 83 may be different from each other. However, according to this embodiment, the design for eliminating the sag under a preferable condition in which both the conveying rollers 82 and 83 are both driven at a constant speed is facilitated.

  Note that the required sheet feed amount from the start of the assist driving of the first conveying roller 82 and the basic operation of the second conveying roller 83 to the elimination of the slack of the sheet P depends on the type of the sheet P. Are often different. That is, in general, even if the condition for generating the sag is constant, a larger sag occurs as the sheet P is thinner, and thus it is necessary to perform the assist driving of the first conveying roller 82 for a longer time. . Hereinafter, in consideration of this point, a description will be given of a control that reliably eliminates slack under the condition that both the transport rollers 82 and 83 are both driven at a constant speed. Here, since the basic configuration of the double-sided stencil printing apparatus 1 to which this control is performed is the same as that shown in FIGS. 1 to 4 above, the components of the apparatus that will be described below are shown in FIG. See ~ 4.

  FIG. 7 is a flowchart showing the flow of processing from paper feed to paper discharge in this case, FIGS. 8 and 10 are flowcharts showing the flow of subroutine processing in a part of this processing, and FIG. 9 is FIG. It is the schematic explaining the content of the look-up table (LUT) used for the process of.

  Further, (1) and (2) in FIG. 11 respectively show the operating state of the first conveying roller 82 and the operating state of the unloading device 81 (see FIG. 2) when this processing is performed. . Here, in (1) of the figure, the horizontal axis represents time, and the vertical axis represents the conveyance speed of the conveyance roller 82. Although only the operating state of the first conveying roller 82 is shown here, the second conveying roller 83 operates basically in the same manner as shown in FIG. In FIG. 11 (2), the horizontal axis indicates time, and the vertical axis indicates the suction state of the conveyor belt 81b based on opening and closing of the shutter blade 81f (see FIGS. 3 and 4).

  When the processing of FIG. 7 starts, first, paper is fed in step S10, and then in step S11, setting for setting the paper feed amount by the assist operation of the first transport roller 82 is performed. This setting is made by the subroutine processing shown in FIG. 8. First, in step S20, the paper feed conditions, that is, the size and thickness type of the paper P are confirmed. Next, in step S21, data for determining the paper feed amount by the assist operation is obtained from the LUT. To be acquired.

  As an example, the sheet feed amount is determined in the form of how much the length feed amount is extended with respect to a predetermined reference feed amount. The feed extension amount is determined with reference to the LUT shown in FIG. 9. In this example, the paper type is thick, and the standard type has a length of 0 (zero) regardless of the paper size. When the paper size is A3, A4, or B4, the extension amounts are 40 mm, 30 mm, and 35 mm, respectively. The data thus acquired from the LUT is transferred to a control unit (not shown) that controls the operation of the motor M1 (see FIG. 2) that drives the first transport roller 82 in step S22.

  Next, returning to the processing of FIG. 7, in step S12, the first printing unit 3 performs printing on one surface of the paper. Thereafter, in step S13, the printed paper P is stored (stocked) in the storage unit 4 constituting a part of the paper reversing unit. Next, in step S14, it is determined whether or not a predetermined time has elapsed since the start of processing. If it is determined that the predetermined time has elapsed, the flow of processing proceeds to the next step S15. If it is not determined that the predetermined time has elapsed, this determination processing is repeated.

  In the next step S15, paper is fed from the reversing unit to the second printing means 5, and then in step S16, printing is performed on the other surface of the paper by the second printing means 5, and finally the paper is discharged in step S17. Thus, a series of printing processes is completed. In the above description, the case of printing on one sheet of paper has been described. However, in the case of printing on a plurality of sheets of paper, printing on one surface of the sheet by the first printing unit 3, storing of sheets in the storage unit 4, Printing on the other surface of the paper by the second printing means 5 is performed in parallel.

  Here, the paper feed in step S15 is performed by a subroutine process shown in FIG. Here, when the process starts, first, in step S30, the opening / closing port of the shutter unit 81e shown in FIGS. 3 and 4, that is, the shutter blade 81f is set to the open state. Next, in step S31, the feeding operation (basic operation) of the motor M1, that is, the first conveying roller 82 is started, and then after a predetermined time, the shutter blade 81f is set in a closed state in step S32. . The opening / closing timing of the shutter blade 81f will be described in detail later. Further, the energization of the motor M1 is interrupted when the first sensor S1 detects the leading edge of the paper P, as in the case described above.

  When a predetermined time further elapses, in step S33, the assist operation of the motor M1, that is, the first transport roller 82 is started. Thereafter, in step S34, it is determined whether or not the timing for stopping the assist operation has come. This determination process is continued until it is determined that the stop timing has been reached. If it is determined that the stop timing has been reached, then in step S35, the power supply to the motor M1 is cut off, and the assist operation ends.

  Here, the processing in step S34 will be described in detail. In this process, the control unit that controls the driving of the motor M1 sets the sheet feed amount by the assist operation of the first transport roller 82 to a predetermined reference feed amount, which is indicated by the data acquired in step S21 of FIG. Determine by adding the amount of extension. That is, when only the reference feed amount is set (when the feed extension amount is zero), the control unit cuts off the power to the motor M1 when the second sensor S2 detects the leading edge of the paper P, and assist drive. The first conveyance roller 82 that is being moved is shifted to a stopped state.

  On the other hand, if the feed extension amount indicated by the data is not zero, the control unit delays by a time corresponding to the extension amount from the time when the second sensor S2 detects the leading edge of the paper P, and sends it to the motor M1. Turn off the power. Therefore, the assist driving time of the second transport roller 83 is extended as shown by broken lines e1 and e2 in FIG. 11A, and the sheet feeding amount by the assist driving is extended.

  As described above, the sag generated on the paper P is generally larger as the paper P is thinner, even if the generation conditions are constant. Therefore, as described above, if the assist drive is extended based on the LUT shown in FIG. 9, the longer the slack is generated, the longer the assist drive time is. Therefore, both the transport rollers 82 and 83 are driven at a constant speed. The slack is surely eliminated under the preferable condition.

  Note that the shutter blade 81f shown in FIGS. 3 and 4 is controlled to be opened and closed by a shutter control unit (not shown), whereby the suction state of the conveyor belt 81b is controlled as shown in FIG. 11 (2). The conveyance belt 81b is in a suction state for holding the paper P when the shutter blade 81f is opened, and is in a state in which no suction is performed when the shutter blade 81f is closed, that is, a state in which the paper P is released.

  The conveyance belt 81b is rotationally driven together with the first conveyance roller 82 by a motor M1 through a power transmission mechanism (not shown). That is, while the first conveyance roller 82 is driven including the assist drive period, the conveyance belt 81b is also continuously driven to rotate. The transport belt 81b is set in a suction state before the basic operation of the first transport roller 82 starts, and sucks and holds one sheet P at the bottom of the storage unit 4 to hold the first transport roller 82. To send. When the first sensor S1 detects the leading edge of the sheet, the shutter control unit closes the shutter blade 81f and sets the transport belt 81b to the released state.

  By doing so, even if the first conveying roller 82 is subsequently driven to assist and the conveying belt 81b is rotationally driven simultaneously during the assist driving period, the conveying belt 81b cannot adsorb the paper P. Then, the next paper P is not taken out from the storage unit 4. Therefore, it is possible to prevent the sheets from being double-fed during the assist drive period, or the sheet P from being sent to the second drum 51 at an improper timing and printing a shifted image on the sheet P.

  When the assist driving of the first transport roller 82 is finished, the shutter blade 81f is opened after a short time. Therefore, the conveyance belt 81b is set to the suction state, and the next sheet P can be taken out from the storage unit 4. The timing for opening the shutter blade 81f is also delayed in accordance with the extension of the assist of the first conveying roller 82, as indicated by broken lines e1 and e2 in FIG. By doing so, it is possible to prevent the problem of sheet double feeding or the like from occurring after the sheet suction holding of the conveyor belt 81b is resumed even though the assist driving of the first conveyor roller 82 continues. The

  The embodiment applied to the double-sided stencil printing apparatus 1 has been described above. However, the present invention is not limited thereto, and includes the first printing unit and the second printing unit, and the sheet is transferred from the first printing unit to the first printing unit. The present invention can also be applied to other printing apparatuses provided with a conveying means for conveying to the second printing means, for example, a multicolor printing apparatus that does not have a paper reversing unit, and in this case, the same effect as described above can be obtained. It is. That is, even in a printing apparatus having such a configuration, it is possible that undried ink may be transferred from a sheet printed by the first printing unit to a conveyance roller constituting the conveyance unit. When applied, it is possible to prevent such ink from being transferred to the paper and becoming dirty.

  Further, when the present invention is applied to a double-sided stencil printing apparatus, the printing apparatus is not limited to the apparatus of the above-described embodiment. A stencil making unit for perforating a stencil sheet based on the stencil image data generated based on the image data of the read document image may be provided.

DESCRIPTION OF SYMBOLS 1 Double-sided stencil printing apparatus 2 Paper feed stand 3 1st stencil printing part (1st printing means)
4 storage section 5 second stencil printing section (second printing means)
REFERENCE SIGNS LIST 6 Discharge stand 7 Paper feed unit 8A First intermediate transport unit 8B Second intermediate transport unit 9 Paper discharge unit 10 Device housing 73 Reversing device 74 Carry-in device 81 Carry-out device 81a Pulley 81b Conveyor belt 81c Fan 81e Shutter unit 81f Shutter blade 82 Pickup roller (first transport roller)
83 Timing roller (second transport roller)
84 Discharging device M1, M2 Motor P Paper S1 First sensor S2 Second sensor

Claims (5)

First printing means for printing on one surface of the paper;
Second printing means for printing on one surface or the other surface of the paper;
Conveying means for conveying the paper printed on the one surface to the second printing means;
A first conveying roller comprising a pair of nip rollers; and a second conveying roller disposed downstream of the first conveying roller at a distance less than the sheet length in the sheet conveying direction. In a printing apparatus configured to include:
The first conveying roller is driven and stopped until a slack occurs in the paper after the leading edge of the paper hits the second conveying roller during a period in which the second conveying roller is stopped,
Thereafter, the second conveying roller starts to drive,
The printing apparatus is configured so that the first transport roller is driven to assist at least when the slack is eliminated.   The drive of both the transport rollers is controlled so that the slack is eliminated during a period in which both the first transport roller and the second transport roller transport the paper at a constant speed. The printing apparatus according to claim 1.   The printing apparatus according to claim 1, wherein the sheet feeding amount by the assist driving of the first conveying roller is adjustable according to the type of the sheet.   4. The printing apparatus according to claim 1, wherein the assist driving of the first transport roller is performed at the same start timing and the same acceleration as the driving of the second transport roller. 5.   The transport means includes a reversing unit that reverses the direction of the paper printed on one surface by the first printing means so that the second printing means can print on the other surface. The printing apparatus according to claim 1, wherein:

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