JP2005320093A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem wherein, in a conventional image formation device, arrival timing of an image and paper cannot be adjusted at an image transfer part if detection action by a sensor is not completed prior to writing the image on an image carrier body, when tab paper is conveyed to a resist roller with the tab part directed downstream in a conveying direction. <P>SOLUTION: The image formation device is provided with the resist roller 9 for feeding the paper to the image transferring part 10 for transferring the image to the paper at a predetermined conveying speed; a plurality of detection sensors 31, 32 for detecting passing of a distal end of the paper in an upstream side in the conveying direction of the resist roller 9 and at a different position of a direction perpendicular to the conveying direction; and a control part for controlling a conveying speed of the paper by the resist roller 9 based on the timing when passing of the distal end of the paper is detected by the plurality of detection sensors 31, 32 when the paper becoming an object of image formation is the paper with a tab and the paper with the tab is conveyed to the resist roller while directing a part of the tab to the downstream side in the conveying direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine.

  2. Description of the Related Art Image forming apparatuses such as copying machines and printers incorporate a paper transport device that transports paper along a predetermined path. In the paper transport device, a plurality of transport rollers are disposed along the paper transport path. Each transport roller is rotationally driven using a motor or the like as a drive source, whereby the paper is transported from the upstream side to the downstream side in the transport direction.

  In such an image forming apparatus, for example, when a sheet being conveyed is skewed toward an image transfer unit that actually transfers an image to the sheet, and the sheet is fed to the image transfer unit while being skewed, On the other hand, the image is transferred in a shifted state. Therefore, in order to prevent image misalignment, it is necessary to correct the skew of the paper and then send the paper to the image transfer unit.

  In the image transfer unit, it is necessary to match the arrival timing of the image (toner image) carried on the image carrier such as the photosensitive drum or the intermediate transfer belt with the arrival timing of the paper conveyed by the paper conveyance device. . Therefore, in the conventional image forming apparatus, a registration roller is provided on the upstream side of the image transfer unit, and the arrival timing when the sheet is fed to the image transfer unit by the registration roller is controlled. Further, it is well known that the skew of the sheet is corrected by abutting and bending the leading end of the sheet against the registration roller in a state where the rotation is stopped. In the present specification, the end of the preceding sheet in the transport direction is referred to as “the front end of the sheet”, and the end of the opposite sheet is referred to as “the rear end of the sheet”.

  Also, in conventional image forming apparatuses, double-sided printing that forms an image on both sides of the paper by reversing the paper on which the image is formed on one side in the image transfer unit and transporting it again to the image transfer unit Some are equipped with functions. As a method for reversing the front and back of the paper, a switchback method for reversing the traveling direction of the paper during conveyance is employed. In this type of image forming apparatus, for example, when tabbed paper (hereinafter also referred to as tab paper) is transported by a paper transport apparatus and an image is formed on both sides of the tab paper using the double-sided printing function, First, an image is formed on the first surface of the tab sheet by transporting the tab sheet to the image transfer unit with the tab portion positioned on the rear end side of the sheet (upstream in the transport direction). Next, after the tab paper is turned upside down by the switchback method in the paper reversing section provided in the middle of the conveyance path, the tab paper is conveyed again to the image transfer section, so that the second side of the tab paper is Form an image. At this time, in order to form an image on the second surface of the tab paper, the tab portion is transported to the image transfer section with the tab portion facing toward the leading edge of the paper (a state toward the downstream side in the transport direction). Become.

  In such a case, in the case where skew correction is performed by abutting against the registration roller as described above, the tab portion is preceded when the leading edge of the sheet is abutted against the registration roller when forming an image on the second surface of the sheet. Then it hits the registration roller. For this reason, the skew of the sheet is not properly corrected, and there is a possibility that the skew is promoted. Therefore, in Patent Document 1 and Patent Document 2 listed below, when a tab sheet is conveyed with the tab portion at the leading end side of the sheet, the sheet is transferred to the image transfer unit without performing skew correction by abutting against the registration roller. The technology to send to is described.

  When skew correction is performed using a registration roller, the sheet is temporarily stopped by abutting against the registration roller, and the registration roller is rotated in accordance with the arrival timing of the image to the image transfer unit (the sheet to the image transfer unit). The timing at which the paper reaches the image transfer unit is adjusted by starting the (feeding operation). Therefore, when the skew correction by the abutment with the registration roller is not performed, it is necessary to separately control the image transfer unit to match (synchronize) the arrival timing of the image and the paper. With respect to this point, Japanese Patent Application Laid-Open No. 2004-228561 provides a line sensor on the upstream side of the registration roller, and corrects the image data stored in the image memory based on the position and outer shape of the paper read by the line sensor. Is described. Further, in Patent Document 2 below, a plurality of sensors are arranged on a line orthogonal to the conveyance direction, and image writing corresponding to the tab portion is image-bearing based on the information of the sensor that detects the leading edge of the paper late. It is described to start on the body.

JP 2003-122223 A JP 2003-226448 A

  However, in the techniques described in Patent Document 1 and Patent Document 2, image transfer is performed by correcting image data written on the image carrier or controlling the start timing of image writing on the image carrier. In this case, before writing the image on the image carrier, the detection operation by the sensor and the control operation based on this (correction of image data, start timing of image writing) Setting).

  Accordingly, when the image transfer distance from the image writing start position on the image carrier to the image transfer unit is long, such as in a color image forming apparatus using an intermediate transfer member, image transfer is performed according to the transfer distance. It is necessary to secure a long conveyance path on the upstream side of the image forming section and to perform the sensor detection operation at a position substantially in front of the image transfer section. Therefore, after the sheet is detected by the sensor, the degree of advancement of the sheet varies depending on various factors (slip of the conveyance roller, etc.) from when the sheet reaches the image transfer unit, and the image transfer unit reaches the image transfer unit. There is a risk that the timing will be out of order. In addition, a long conveyance path must be secured on the upstream side of the image transfer unit, which hinders space saving.

  An image forming apparatus according to the present invention includes a registration roller that feeds a sheet at a predetermined conveyance speed to an image transfer unit that transfers an image to the sheet, and a direction upstream of the registration roller in the conveyance direction and perpendicular to the conveyance direction. A plurality of detection sensors that detect the passage of the leading edge of the paper at different positions, and the paper to be image-formed is a paper with a tab, and the paper with the tab is registered with the tab portion facing the downstream side in the transport direction. And a control unit that controls the sheet conveyance speed by the registration rollers based on the timing at which the plurality of detection sensors detect passage of the leading edge of the sheet when the sheet is conveyed to the roller.

  In the image forming apparatus according to the present invention, the sheet on which the image is to be formed is a tabbed sheet, and the tabbed sheet is transported to the registration roller with the tab portion directed downstream in the transport direction. In this case, even if the paper is not temporarily stopped by being abutted against the registration roller, the image transfer can be performed by controlling the paper conveyance speed by the registration roller based on the timing when the detection of the leading edge of the paper is detected by a plurality of detection sensors. It is possible to match the arrival timing of the image and the paper in the section.

  According to the present invention, when a tabbed sheet is conveyed to the registration roller with the tab portion directed downstream in the conveyance direction, the plurality of detection sensors detect the sheet on the upstream side (front side) in the conveyance direction of the registration roller. By detecting the passage of the leading edge and controlling the sheet conveyance speed by the registration rollers by the control means based on the detection timing, it is possible to match the arrival timing of the image and the sheet at the image transfer unit. As a result, it is not necessary to complete the detection operation by the sensor before the image forming apparatus writes an image on the image carrier, so that the image transfer distance from the image writing start position on the image carrier to the image transfer unit is reduced. Even in a long color image forming apparatus or the like, it is possible to detect the passage of the leading edge of a sheet near the image transfer unit with a detection sensor and control the feeding of the sheet to the image transfer unit. As a result, it is possible to reduce the deviation in the arrival timing of the image and the paper at the image transfer unit, and it is easy to cope with space saving.

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

  FIG. 1 is a schematic diagram showing a configuration example of an image forming apparatus to which the present invention is applied. The illustrated image forming apparatus has a sheet conveying device. This sheet conveying apparatus is incorporated in the apparatus main body 1 of the image forming apparatus. That is, a plurality of (four in the illustrated example) sheet storage cassettes 2... Having a multistage structure are incorporated in the apparatus main body 1 with casters. Each of the paper storage cassettes 2,... Stores the paper 3 to be image-formed in a stacked state, and is detachably incorporated in the apparatus main body 1. These sheet storage cassettes 2,... Have basically the same configuration, although the size and shape of the entire cassette differ depending on the size and type of the sheet 3 to be stored.

  A paper stacking plate (tray) 4 is provided inside each paper storage cassette 2. The sheet stacking plate 4 is supported by an elevating mechanism (not shown) so as to be movable up and down. A sheet storage cassette 2 having the sheet stacking plate 4 can store a plurality of sheets (multiple sheets) 3 in a stacked state. When the paper storage cassette 2 is mounted in the apparatus main body 1, among the papers 3 stacked on the paper stacking plate 4, the height of the uppermost paper 3 is set to a predetermined (constant) height. Thus, the sheet stacking plate 4 is raised by driving the lifting mechanism while maintaining the horizontal state.

  The uppermost paper storage cassette 2 can store a plurality of tab sheets in a stacked state, and the other paper storage cassettes 2 can store plain papers of different sizes in a stacked state. It has become. The “tab paper” described here refers to a paper (tabbed paper) provided with a convex tab on one side of a rectangular paper, and “plain paper” is not provided with a tab. Normal rectangular paper. In the uppermost sheet storage cassette 2, the tab sheet is placed in a state where the tab portion (convex shape) protruding from one side of the sheet is directed to the side opposite to the sheet feeding direction by the pickup roller 5 (right side in FIG. 1). It is to be accommodated.

  The pickup roller 5 and the separating roller 6 feed the paper 3 stored in the paper storage cassette 2 toward the conveyance path. Among these, the pickup roller 5 is provided so as to be able to contact and separate from the uppermost sheet 3 arranged at the predetermined height. A solenoid can be used as a drive source for moving the pickup roller 5 in and out of contact. The pickup roller 5 sends out the paper 3 stored in the paper storage cassette 2 toward the first transport path R1. When the paper is sent out, the pickup roller 5 is pressed against the uppermost paper 3 loaded on the paper stacking plate 4 with a predetermined pressure. The paper is fed in the direction of the arrow in order from the upper paper 3.

  The separating roller 6 is arranged in the paper feeding direction by the pickup roller 5. In order to prevent a plurality of sheets 3 stored in the sheet storage cassette 2 from being overlapped and conveyed (multi-feed), the separation roller 6 is configured to separate the sheets 3 fed by the pickup roller 5 one by one. (Separated) to send out. The paper rollers 3 sequentially feed out the papers 3 from each paper storage cassette 2 in a form separated from each paper storage cassette 2. Further, the sheet 3 sent out in this way is conveyed inside the apparatus main body 1 by respective rollers (described later) appropriately disposed on the sheet conveyance paths R1 to R6. Incidentally, the pick-up roller 5 and the separating roller 6 are provided in a 1: 1 correspondence with the respective paper storage cassettes 2.

  A conveying roller 7 is disposed in the paper feeding direction by the separating roller 6. A plurality of transport rollers 7 are provided at predetermined intervals on a first transport path R1 formed substantially vertically. The plurality of transport rollers 7 transports the paper 3 sent out by the roller 6 corresponding to each paper storage cassette 2 upward along the first transport path R1.

  A conveyance roller 8 and a registration roller 9 are sequentially arranged in the conveyance direction of the sheet by the conveyance roller 7. The transport roller 8 and the registration roller 9 are provided in a positional relationship adjacent to each other in the paper transport direction on a second transport path R2 formed continuously from the first transport path R1. The conveyance rollers 8 convey the paper 3 conveyed by the respective conveyance rollers 7 toward the registration rollers 9. The registration roller 9 conveys the sheet 3 conveyed by the conveyance roller 8 from the upstream side toward the image transfer unit 10.

  As shown in FIG. 2, sensors 31 and 32 are arranged on the second conveyance path R2 between the conveyance roller 8 and the registration roller 9 while being shifted in the sheet conveyance direction. The sensor 31 is arranged in the vicinity of the conveyance roller 8 on the downstream side of the conveyance roller 8, and the sensor 32 is arranged in the vicinity of the registration roller 9 on the upstream side of the registration roller 9. Each of the sensors 31 and 32 is composed of, for example, a reflection type photosensor, and detects passage of a sheet (passing the leading edge and passing the trailing edge) on the second conveying path R2 from the conveying roller 8 to the registration roller 9. .

  For example, the output signals (detection signals) of the sensors 31 and 32 are turned on when a sheet is present at the detection position of the sensors 31 and 32, and are turned off when the sheet is not present. Therefore, when the paper passes through the detection positions of the sensors 31 and 32, the sensor output signal is switched from the OFF state to the ON state at the timing when the leading edge of the paper passes the sensor detection position, and then the trailing edge of the paper. The sensor output signal switches from the on state to the off state at the timing when the sensor passes the sensor detection position. The output signals of these sensors 31 and 32 are used to control the rotation operation of the transport roller 8 and the registration roller 9 in addition to detection of a paper jam (jam) during the transport.

  One of the sensors 31, 32, preferably the sensor 32 in the vicinity of the registration roller 9, is composed of two sensors 32A, 32B as shown in FIG. These two sensors 32A and 32B are arranged at a predetermined interval on the same straight line orthogonal to the paper transport direction. Each sensor 32A, 32B is arranged in a state straddling the tab position set at the center of the tab sheet in the direction orthogonal to the sheet conveyance direction. In addition, the interval between the sensors 32A and 32B is the center of a tab sheet of the type in which there are three tabs 3A when a plurality of (three or more) tab sheets having different tab positions are stacked as shown in the figure. The length is set to be longer than the tab length in the direction orthogonal to the transport direction and shorter than the minimum sheet width in the same direction so as to straddle the tab position set in the section. By arranging the sensors 32A and 32B in such a positional relationship, even when handling tab sheets with two or more tab sheets, at least one sensor 32A or 32B covers a portion other than the tabs. The detection unit can detect the passage of the leading edge of the sheet. The detected portion refers to the end portion of the paper that is actually detected by the sensor when the paper passes through the detection position of the sensor.

  The image transfer unit 10 is a part that transfers an image to the sheet 3 conveyed by the registration roller 9, and the image is transferred to the sheet 3 by feeding the sheet 3 to the image transfer unit 10. . In the image transfer unit 10, an intermediate transfer belt 11 serving as an image carrier is supported by a support roller 12, and a transfer pressure roller 13 is held in pressure contact with a belt winding portion of the support roller 12. Further, in the image transfer unit 10, an image is transferred from the intermediate transfer belt 11 to the paper 3 when passing through a pressure contact portion between the support roller 12 and the pressure roller 13 sandwiching the intermediate transfer belt 11. .

  The intermediate transfer belt 11 carries a visualized toner image and transfers the toner image to the image transfer unit 10 by rotation of the belt. As a specific example, the intermediate transfer belt 11 includes a plurality of photosensitive drums 101, 102, corresponding to each color component of yellow (Y), magenta (M), cyan (C), and black (K) as shown in FIG. The toner images formed on the surfaces 103 and 104 are primarily transferred, and the primarily transferred toner images are sent to the image transfer unit 10 by the rotation of the intermediate transfer belt 11 and are secondarily transferred (collectively transferred) to the paper. The

  The intermediate transfer belt 11 is an endless belt member and is stretched using a plurality of support rollers. Further, around each of the photosensitive drums 101, 102, 103, and 104, a charger, a laser writing device, a developing device, a transfer roller, a cleaner, a static eliminator, and the like are disposed. If the image forming apparatus is a copying machine, toner images are formed on the respective photosensitive drums 101, 102, 103, and 104 based on an image signal read by an image reading apparatus (not shown). If it is an apparatus, it is performed based on an image signal received via a communication means or network means (not shown).

  On the downstream side of the image transfer unit 10, a vacuum conveyance unit 14, an image fixing unit 15, a conveyance roller 16 and a discharge roller 17 are sequentially arranged. The second conveyance path R2 described above refers to a conveyance path from the conveyance roller 8 to the discharge roller 17 via the image transfer unit 10. On the second transport path R2, the vacuum transport unit 14 sucks the back surface of the paper 3 on which the image (toner image) is transferred by the image transfer unit 10 (the surface opposite to the surface on which the image is transferred) in a vacuum manner. Meanwhile, the paper 3 is conveyed to the image fixing unit 15. The image fixing unit 15 fixes the image transferred onto the paper 3 by pressing and heating. The transport roller 16 transports the paper 3 on which the image has been fixed by the image fixing unit 15, and the discharge roller 17 discharges the paper 3 transported by the transport roller 16 to the discharge tray 18. .

  On the downstream side of the transport roller 16, a third transport path R3 branches obliquely downward from the second transport path R2. A conveyance roller 19 is disposed on the third conveyance path R. The conveyance roller 19 conveys the sheet 3 sent to the third conveyance path R3 by the conveyance roller 16 to the sheet reversing unit 20.

  The paper reversing unit 20 is a part for reversing the front and back of the paper 3 when the paper 3 is conveyed again to the image transfer unit 10 or discharged to the discharge tray 18. The sheet reversing unit 20 is formed on one side of the apparatus main body 1 adjacent to the cassette storage space with respect to the cassette storage space secured for mounting the plurality of paper storage cassettes 2. ing. A fourth transport path R4 is formed in the sheet reversing unit 20 almost vertically. A first reverse roller 21 and a second reverse roller 22 are arranged on the fourth transport path R4 at a predetermined interval in the transport direction (vertical direction). The first reversing roller 21 is disposed in the vicinity of the entrance of the fourth transport path 4 (upper end portion of the paper reversing unit 20), which is a position for taking in the paper into the paper reversing unit 20. The 2nd inversion roller 22 is arrange | positioned in the substantially intermediate part of 4th conveyance path R4 along a perpendicular direction.

  Further, in the sheet reversing unit 20, a fifth transport path R <b> 5 is branched obliquely upward from the fourth transport path R <b> 4 between the first reverse roller 21 and the second reverse roller 22. On the fifth transport path R5, a plurality of (six in the illustrated example) transport rollers 25,... Are arranged at predetermined intervals, and a re-transport section 26 is formed using the plurality of transport rollers 25,. Yes.

  The re-conveying unit 26 conveys the paper 3 on which the image is transferred on one side (first side) by the image transfer unit 10 to the image transfer unit 10 again for double-sided printing, and the conveyance roller 8 on the second conveyance path R2. The sheet 3 is conveyed toward the registration roller 9. The fifth transport path R5 is formed between the paper reversing unit 20 and the transport roller 8 so as to connect the fourth transport path R4 and the second transport path R2.

  On the other hand, a sixth conveyance path R <b> 6 is branched from the first reverse roller 21 of the paper reversing unit 20 toward the discharge roller 17. The sixth transport path R6 is a transport path for reversing the paper 3 taken into the paper reversing unit 20 through the third transport path R3 and discharging it to the discharge tray 18. Incidentally, at the branch portions of the conveyance paths R1 to R6 described above, the traveling direction of the sheet is appropriately switched by a gate member (not shown).

  FIG. 4 is a block diagram showing, in particular, the configuration of the control system for controlling the rotation operations of the transport roller 8 and the registration roller 9 as the configuration of the paper transport control system of the image forming apparatus according to the embodiment of the present invention. In the figure, the control unit 27 controls driving of the carry motors 28 and 29 based on the output signals of the sensors 31 and 32 (32A and 32B) described above. The transport motor 28 is a drive source for rotating the transport roller 8, and the transport motor 29 is a drive source for rotating the registration roller 9. Each of the transport motors 28 and 29 is configured using, for example, a pulse motor. By using this pulse motor, when driving signals (pulse signals) are individually supplied from the control unit 27 to the conveyance motors 28 and 29, the rollers 8 and 9 are rotated and stopped, and further, the rotation direction and the rotation amount. It is possible to easily perform the control.

Next, the operation of the image forming apparatus according to the embodiment of the present invention will be described. First, the user inputs desired image forming conditions (for example, image forming density and number of copies, designation of duplex printing, etc.) using an operation panel (not shown) of the image forming apparatus, and then a start button in the operation panel. push. At this time, if the uppermost sheet storage cassette 2 is selected by the user's input operation using the operation panel, the pickup roller 5 and the separation roller 6 corresponding to the uppermost sheet storage cassette 2 rotate. The uppermost sheet 3 is sent out in the direction of the arrow in the figure. In this case, since the tab sheet is stored in the uppermost sheet storage cassette 2, the sheet 3 fed out from the sheet storage cassette 2 is a tab sheet. In such a case, the conveyance operation of the paper 3 in the image forming apparatus is controlled as follows by a conveyance control unit (not shown).

  First, the sheet 3 sent out from the sheet storage cassette 2 is conveyed upward along the first conveyance path R <b> 1 by the rotation of the conveyance roller 7, and delivered to the conveyance roller 8. Further, the sheet 3 is conveyed to the registration roller 9 side along the second conveyance path R2 by the rotation of the conveyance roller 8 with the tab directed toward the upstream side in the conveyance direction. At this time, the output signals (on and off states) of the sensors 31 and 32 are switched at the timing when the leading edge and the trailing edge of the sheet 3 pass through the detection positions of the sensors 31 and 32. Therefore, the control unit 27 grasps the position of the sheet on the second transport path R2 based on the detection signals obtained from the respective sensors 31 and 32. Further, in the control unit 27, the conveyance when the sheet 3 sent from the first conveyance path R <b> 1 to the second conveyance path R <b> 2 reaches the registration roller 9 and the sheet is fed to the image transfer unit 10 by the registration roller 9. Control conditions are set according to the processing flow of FIG.

  First, it is determined whether or not the sheet 3 to be image formed is a tab sheet (step S1). Whether or not the sheet 3 to be image-formed is a tab sheet can be determined when the sheet storage cassette 2 is selected by the user's input operation. That is, when the uppermost sheet storage cassette 3 is selected by the user's input operation using the operation panel as described above, and the fact is notified from the operation panel to the control unit 27, the image forming target is selected. When the sheet 3 to be formed is determined to be a tab sheet, and the other sheet storage cassette 3 is selected, it is determined that the sheet 3 to be image-formed is a plain sheet. Here, the paper type (tab paper, plain paper) is determined according to the cassette selection information by the user. However, in addition to this, the paper type can also be determined using a sensor.

  Next, it is determined whether or not the image forming mode is set to the duplex mode (step S2). The duplex mode is a mode in which images are formed on both sides of a sheet. In this case, if double-sided printing is specified by the user's input operation, it is determined that the duplex mode is set, and if double-sided printing is not specified, it is determined that the duplex mode is not set.

  Next, it is determined whether or not the second side of the paper is to be printed (step S3). When executing the duplex mode (double-sided printing), the image transfer unit 10 forms an image on the first side of the paper, and then the paper is turned upside down and sent to the image transfer unit 10 again, so that the second paper is printed. An image is formed on the surface. Therefore, when the paper is first fed to the image transfer unit 10, it is determined that the first side of the paper is the printing target, and when the paper is fed again to the image transfer unit 10 after that, the second side of the paper is the printing target. It is determined that

  In the above three determination processes, when it is determined that the sheet 3 to be imaged is a tab sheet, the image forming mode is set to the duplex mode, and the second side of the sheet is set as the printing target Then, the conveyance control condition suitable for the presence of the tab is set (step S4), and all other conditions are set to the conveyance control condition suitable for the absence of the tab (step S5). The conveyance control condition suitable for the presence of a tab is a conveyance control condition set so as to be adapted when a sheet with a tab is conveyed to the registration roller 9 with the tab portion directed downstream in the conveyance direction. In addition, the conveyance control conditions suitable for the absence of tabs include a case where plain paper is conveyed to the registration roller 9 and a sheet with tabs is conveyed to the registration roller 9 with the tab portion directed upstream in the conveyance direction. This is a transport control condition set so as to be adapted to the case.

  In the above processing flow, if the sheet 3 sent from the first transport path R1 to the second transport path R2 is a tab sheet and set to the duplex mode, both “Yes” in steps S1 and S2. However, since the first surface of this sheet is the printing target, “No” is determined in step S3. If the paper on which image formation is to be performed is plain paper, “No” is determined in step S1, and if the paper on which image formation is to be performed is tab paper, the duplex mode is not set. It is determined as “No” in S2. For this reason, in any case, the conveyance control conditions suitable for the absence of tabs are set, and the conveyance of the paper is controlled based on the conveyance control conditions.

  The conveyance control of the paper based on the conveyance control condition adapted without tabs is performed by the control unit 27 as follows. First, the control unit 27 rotates the conveyance roller 8 by driving the conveyance motor 28 in a state where the rotation of the registration roller 9 is stopped by stopping the conveyance motor 29, so that the sheet 3 is rotated according to the rotation of the conveyance roller 8. Is fed to the registration roller 9. Then, the leading edge of the sheet 3 (the side of the sheet 3 opposite to the tab) is abutted against the pressure contact portion (the portion where the sheet is nipped) of the registration roller 9 in the rotation stopped state, and is bent in a loop shape. Correct skew. At that time, the loop of the sheet 3 is formed in a bulging portion (not shown) provided in the second conveyance path R2 before (upstream side) the registration roller 9.

  Next, the control unit 27 stops driving the conveyance motor 28 and temporarily stops the rotation of the conveyance roller 8, and then simultaneously drives the conveyance rollers 28 and 19 in accordance with the arrival timing of the image at the image transfer unit 10. By doing so, the conveyance roller 8 and the registration roller 9 are rotated. As a result, the sheet 3 is fed into the image transfer unit 10 according to the rotation of the transport roller 8 and the registration roller 9. In the image transfer unit 10, the toner image carried on the intermediate transfer belt 11 is pressed between the belt support roller 12 and the pressure roller 13 from the surface of the intermediate transfer belt 11 to the first surface (tab portion) of the sheet 3. ).

  FIG. 6 shows a conveyance method in the case where the control unit 27 controls the conveyance of the sheet according to the conveyance control condition suitable for the absence of the tab. In the drawing, the vertical axis indicates the position in the conveyance direction, and the horizontal axis indicates the time. . In the drawing, when the leading edge of the sheet 3 passes the sensor position (the position of the sensor 32 in this example), the sheet conveyance speed is set to the first conveyance speed V1. When the leading edge of the sheet 3 hits the registration roller 9, the sheet 3 is temporarily stopped, and then the sheet conveyance speed is set to the second conveyance speed V2 that is lower than the first conveyance speed V1. By starting the conveyance of the sheet by the registration roller 9, the leading edge of the sheet 3 is sent to the image transfer unit 10 in accordance with the arrival timing of the image to the image transfer unit 10.

  The sheet 3 on which the image is formed on the first side is sent to the image fixing unit 15 by the vacuum conveyance unit 14. In the image fixing unit 15, the image 3 is fixed on the surface of the paper 3 by a pressurizing action and a heating action applied between the pair of rollers while the paper 3 is nipped between the pair of rollers. The sheet 3 sent out from the image fixing unit 15 is transferred to the discharge roller 17 by the rotation of the conveying roller 16 and further to the discharge tray 18 by the rotation of the discharge roller 17 if the sheet 3 is for single-sided printing. Discharged.

  If the sheet 3 sent out from the image fixing unit 15 is designated for double-sided printing, the sheet 3 is moved from the second conveyance path 2 to the third by the rotation of the conveyance roller 16 and the switching operation of a gate member (not shown). Guided to the transport path R3. The sheet 3 guided to the third transport path R3 is sent to the sheet reversing unit 20 by the rotation of the transport roller 19.

  In the sheet reversing unit 20, the sheet 3 sent by the transport roller 19 is nipped in turn by the first reversing roller 21 and the second reversing roller 22, and by the rotation of the first reversing roller 21 and the second reversing roller 22, The sheet 3 is conveyed downward along the fourth conveyance path R4. Then, when the rear end of the sheet 3 passes through the branch portion of the fourth transport path R4 and the fifth transport path R5, the rotation direction of the second reversing roller 22 is reversed. As a result, the sheet 3 is conveyed upward in accordance with the rotation (reverse rotation) of the second reversing roller 22, and is guided by a gate member (not shown) and sent from the fourth conveyance path R4 to the fifth conveyance path R5.

  In the fifth transport path R5, the paper 3 is sequentially delivered to the transport rollers 25 forming the re-transport section 26, and the paper 3 is transferred to the transport roller 8 on the second transport path R2 by the final transport roller 25. Is passed. Next, the sheet 3 is a registration roller along the second conveyance path R <b> 2 by the rotation of the conveyance roller 8 with the second surface on which the image is not formed facing upward (a state in which the tab is directed downstream in the conveyance direction). 9 is sent. At that time, in the control unit 27, before the sheet 3 sent from the fifth transport path R5 to the second transport path R2 reaches the registration roller 9, the registration roller 9 feeds the sheet to the image transfer unit 10. The conveyance control conditions are set according to the processing flow of FIG. As a result, if the sheet 3 fed from the fifth transport path R5 to the second transport path R2 is a tab sheet and is set to the double-side mode, “Yes” in steps S1, S2, and S3. Therefore, when the sheet 3 is sent to the image transfer unit 10 by the registration roller 9, the conveyance of the sheet is controlled by the control unit 27 as follows based on the conveyance control condition suitable for the presence of the tab.

  First, the controller 27 transports the paper 3 along the second transport path R2 by driving the transport motors 28 and 29 to rotate the transport roller 8 and the registration roller 9 together. When the leading edge of the sheet 3 passes through the detection positions of the sensors 31 and 32 during the conveyance, the output signals (on and off states) of the sensors 31 and 32 are switched accordingly. Therefore, the control unit 27 grasps the position of the sheet on the second transport path R2 based on the detection signals obtained from the respective sensors 31 and 32. Further, the control unit 27 obtains a deviation amount (time difference) of the timing at which the sensors 32A and 32B detect passage of the leading edge of the sheet, and compares the deviation amount with a predetermined amount set in advance to thereby detect each sensor 32A. , 32B, it is recognized whether or not the detected part of the paper that has detected the leading edge passage is a tab part. In that case, as shown in FIG. 3, the sensors 32A and 32B are arranged in a state crossing the tab position set at the center of the tabbed paper in the direction orthogonal to the paper transport direction, thereby providing the necessary maximum. It becomes possible to recognize the detected part by using two sensors which are a small number.

  More specifically, when the positional relationship between the tab 3A portion of the paper 3 and the sensors 32A and 32B is as shown in FIG. 7, the sensor 32A existing on the moving path of the tab 3A passes through the leading edge of the paper 3. Is detected and the sensor output signal is switched from the off state to the on state, and then the sensor 32B detects the passage of the leading edge of the paper 3 and the sensor output signal is switched from the off state to the on state. Then, the control unit 27 obtains a deviation amount ΔT between the timings T1 and T2 when the output signals of the sensors 32A and 32B are switched on. In this case, the shift amount ΔT between the detection timings T1 and T2 between the sensors 32A and 32B is larger than the predetermined amount. Therefore, in this case, in the control unit 27, the sensor 32A that detects the passage of the leading edge of the sheet 3 recognizes that the leading edge of the sheet 3 has been detected by using the tab 3A as the detected portion. The sensor 32B with the later timing of detecting the passage of the leading edge of the paper recognizes that the passage of the leading edge of the paper 3 has been detected using a portion other than the tab as a detected portion.

  Although not shown, even when the sensor 32B is present on the movement path of the tab 3A, the shift amount ΔT of the detection timings T1 and T2 between the sensors 32A and 32B is larger than the predetermined amount. Therefore, in the control unit 27, the sensor 32B having the earlier timing of detecting the passage of the leading edge of the paper 3 recognizes that the passage of the leading edge of the paper 3 is detected with the portion of the tab 3A as the detected portion, and the leading edge of the paper 3 is detected. The sensor 32A having the later timing of detecting passage recognizes that the passage of the leading edge of the paper 3 has been detected using a portion other than the tab as a detected portion.

  On the other hand, when the positional relationship between the tab 3A portion of the paper 3 and each of the sensors 32A and 32B is as shown in FIG. 8, since none of the sensors 32A and 32B exist on the movement path of the tab 3A, The output signals of the sensors 32A, 32B are switched from the OFF state to the ON state almost simultaneously (strictly speaking, a time difference corresponding to the skew of the paper is generated, so the predetermined amount is set in consideration of the time difference). . Then, the control unit 27 obtains the shift amount ΔT between the timings T1 and T2 when the output signals of the sensors 32A and 32B are switched to the ON state in the same manner as described above. In this case, the shift amount ΔT between the detection timings T1 and T2 between the sensors 32A and 32B is equal to or less than the predetermined amount. Therefore, in that case, the control unit 27 recognizes that any of the sensors 32A and 32B has detected passage of the leading edge of the paper 3 with a portion other than the tab as a detected portion.

  Next, the control unit 27 determines the leading edge passage detection timing of the sheet on the basis of the detection timing of the sensor that detects passage of the leading edge of the sheet 3 with a portion other than the tab as a detected portion. For example, in the case of FIG. 7, the detection timing T2 is determined as the leading edge passage detection timing of the sheet with reference to the timing T2 when the sensor 32B detects the leading edge passage of the sheet 3. In the case of FIG. 8, the timing T1 or T2 when the sensor 32A or 32B detects the passage of the leading edge of the paper 3 is used as a reference, and this timing T1 or T2 is determined as the leading edge passage detection timing of the paper. As a result, in the transport direction of the sheet 3 transported along the second transport path R2, in both cases of FIGS. 7 and 8, the sheet is traveling at the leading edge passage detection timing determined as described above. The paper position is the same.

  Therefore, the control unit 27 starts measuring time with a timer based on the leading edge detection timing of the paper determined as described above. When the measured value of the timer reaches a timer reference value set in advance corresponding to the conveyance control condition suitable for the presence of the tab, the rotation speed of the conveyance motor 29 is reduced at that time, thereby causing the registration roller 9 to The conveyance speed of the sheet 3 (the feeding speed of the sheet 3 to the image transfer unit 10) is set to a predetermined conveyance speed set in advance. The timer reference value defines the timing for changing the conveyance speed of the sheet 3 by the registration rollers 9 from the first conveyance speed to the second conveyance speed (predetermined conveyance speed) lower than the first conveyance speed. To do. This timer reference value is the same as when the paper 3 is stopped by abutting against the registration roller 9 at the same timing as when the paper 3 is controlled under a conveyance control condition suitable for the absence of a tab (tab portion). Is set in consideration of the progress of the paper 3 corresponding to the protruding dimension of the tab 3A. The predetermined transport speed is set to a speed substantially equal to the transport speed in accordance with the transport speed of the image (toner image) by the intermediate transfer belt 11.

  FIG. 9 shows a conveyance method in the case where the control unit 27 controls the conveyance of the sheet according to the conveyance control condition suitable for the presence of the tab. In the figure, the vertical axis indicates the position in the conveyance direction, and the horizontal axis indicates the time. . In the figure, when the leading edge of the sheet 3 passes the sensor position (the position of the sensor 32 in this example), the sheet conveyance speed is set to the first conveyance speed V1. Further, when a predetermined time elapses after the leading edge of the sheet 3 passes the sensor position (when the timer measurement value reaches the timer reference value), the sheet conveyance speed is changed from the first conveyance speed V1 to the second at that time. The transporting speed V2 of the paper 3 is changed, and the paper is transported by the registration rollers 9 according to the second transporting speed V2, so that the leading edge of the paper 3 (the leading edge of the tab) is synchronized with the arrival timing of the image on the image transfer unit 10. Is sent to the image transfer unit 10.

  In this way, the sheet 27 is fed to the image transfer unit 10 by the registration roller 9 while the conveyance of the sheet is controlled by the control unit 27, so that the image (toner image) is transferred to the second surface (tab portion) of the sheet 3. Is done. The sheet 3 on which the image is formed on the second side in this way is delivered from the vacuum conveyance unit 14 to the conveyance roller 16 via the image fixing unit 15. Then, the sheet 3 is guided again to the third transport path 3 by the rotation of the transport roller 16 and the switching operation of the gate member (not shown).

  Thereafter, the sheet 3 is sent to the sheet reversing unit 20 by the rotation of the transport roller 19. Next, when the rear end of the sheet 3 passes through the branching section with the sixth transport path R6 via the third transport path R3, the rotation directions of the first reverse roller 21 and the second reverse roller 22 are reversed. As a result, the sheet 3 moves upward in the fourth conveyance path R4 in a form of being switched back by the sheet reversing unit 20, and is guided by a gate member (not shown) from the fourth conveyance path R4 to the sixth conveyance path R6. And is discharged to the discharge tray 18 via the discharge roller 17 as it is.

  In the above description of the operation, the sheet 3 on which images are formed on both sides (the first side and the second side) is reversed and discharged to the discharge tray 18. In some cases, the paper 3 on which the image is formed on one side is reversed and turned upside down by the switchback at the paper reversing unit 20 and discharged to the discharge tray 18. Further, when forming an image on the second surface of the paper 3, if the paper 3 to be image-formed is a plain paper instead of a tab paper, it is the same as when forming an image on the first surface of the paper 3. The control unit 27 controls the conveyance of the sheet according to the conveyance control condition suitable for the absence of the tab, so that the skew of the sheet 3 is corrected by being abutted against the registration roller 9 and then the rotation of the registration roller 9 is performed. The image is transferred to the image transfer unit 10.

  Further, in the above-described embodiment, the sheet 3 is temporarily stopped by being abutted against the registration roller 9 when the conveyance of the sheet is controlled by the control unit 27 according to the conveyance control condition suitable for the absence of the tab. In addition to this, for example, as shown in FIG. 10, it is also possible to adopt a conveyance method in which the paper is not temporarily stopped. In FIG. 10, when the leading edge of the sheet 3 passes the sensor position (the position of the sensor 32 in this example), the sheet conveying speed is set to the first conveying speed V1, and the leading edge of the sheet 3 passes the sensor position. When a predetermined time has elapsed since then, the sheet conveyance speed is changed from the first conveyance speed V1 to the second conveyance speed V2. In this case, the time from when the leading edge of the sheet 3 passes the sensor position until the sheet conveyance speed is changed from the first conveyance speed V1 to the second conveyance speed V2 is the conveyance control adapted to the presence of the tab. It becomes longer than the case where the conveyance of the sheet is controlled according to the conditions.

  Further, in the above embodiment, the two sensors 32A and 32B are arranged on the same straight line orthogonal to the paper transport direction. However, other than this, for example, as shown in FIGS. 11 (A) and 11 (B). As described above, the configuration may be such that the passage of the leading edge of the paper is detected using the two sensors 31 and 32 that are arranged with the positions shifted in the paper conveyance direction. In this case, the positional relationship between the sensors 31 and 32 in the direction orthogonal to the paper conveyance direction is set under the same conditions as the positional relationship between the sensors 32A and 32B, so that at least one sensor 31 or 32 is not a tab. This part can be used as a detected part to detect passage of the leading edge of the paper.

  Here, as shown in FIG. 11A, when the sensor 31 exists on the moving path of the tab 3A, the upstream sensor 31 detects the passage of the leading edge of the sheet 3 (passing the leading edge of the tab portion). After ΔTa time elapses after the sensor output signal is switched from the OFF state to the ON state, the downstream sensor 32 detects passage of the leading edge of the paper 3 and the sensor output signal is switched from the OFF state to the ON state. Further, as shown in FIG. 11B, when the sensors 31 and 32 do not exist on the moving path of the tab 3A, the upstream sensor 31 detects the passage of the leading edge of the paper 3, and the sensor output signal is in the OFF state. After ΔTb time has elapsed since switching from the ON state to the ON state, the downstream sensor 32 detects passage of the leading edge of the sheet 3 and the sensor output signal is switched from the OFF state to the ON state. Although not shown, when the sensor 32 exists on the movement path of the tab 3A, the upstream sensor 31 detects the passage of the leading edge of the paper 3, and the sensor output signal is switched from the off state to the on state. After a predetermined time ΔTc has elapsed, the downstream sensor 32 detects passage of the leading edge of the sheet 3 (passing the leading edge of the tab portion), and the sensor output signal is switched from the off state to the on state. In this case, assuming that the conveyance speed of the sheet 3 conveyed by the conveyance roller 8 is constant, the deviations (time differences) ΔTa, ΔTb, and ΔTc of the timings at which the sensors 31 and 32 detect the passage of the leading edge of the sheet 3 are detected. Satisfies the relationship ΔTa> ΔTb> ΔTc.

  Therefore, in the control unit 27, based on the distance between the sensors 31 and 32 in the sheet conveyance direction and the sheet conveyance speed by the conveyance roller 8, the conveyance time required to convey the sheet by the distance between the sensors is calculated as follows: The reference timing deviation amount ΔTr is set in advance. Then, a timing deviation amount ΔTs when the sensors 31 and 32 actually detect the passage of the leading edge of the sheet 3 is obtained, and the deviation amount ΔTs is compared with the reference timing deviation amount ΔTr. In this comparison result, when the difference between ΔTs and ΔTr is smaller than a predetermined value set in advance (in other words, when ΔTs≈ΔTr), each of the sensors 31 and 32 uses a portion other than the tab as a detected portion. It is recognized that the leading edge of the paper has been detected. Further, when the difference between ΔTs and ΔTr is equal to or greater than the predetermined value, it is determined whether or not the detected portion where each of the sensors 31 and 32 detects the passage of the tip is a tab portion according to the magnitude relationship. recognize. Specifically, if the magnitude relationship between ΔTs and ΔTr is ΔTs> ΔTr, the upstream sensor 31 detects passage of the leading edge of the sheet using the tab portion as a detected portion, and the downstream sensor 32 is a portion other than the tab. Is detected as having detected the passage of the leading edge of the paper. If the relationship between ΔTs and ΔTr is ΔTs <ΔTr, the upstream sensor 31 detects the passage of the leading edge of the sheet using a portion other than the tab as a detected portion, and the downstream sensor 32 detects the tab portion. It is recognized that the passage of the leading edge of the paper is detected as a part. This enables the control unit 27 to recognize whether or not the detected part of the paper that has detected passage of the leading edge by each sensor is a tab part without arranging a plurality of sensors on the same straight line. It becomes.

1 is a schematic diagram illustrating a configuration example of an image forming apparatus to which the present invention is applied. 1 is a schematic diagram illustrating a configuration example around an image transfer unit of an image forming apparatus according to an embodiment of the present invention. It is a figure explaining the arrangement | positioning state of a sensor. FIG. 2 is a diagram illustrating a configuration of a sheet conveyance control system of the image forming apparatus according to the first embodiment of the present invention. It is a figure which shows the setting processing flow of a conveyance control condition. FIG. 10 is a diagram illustrating an example of a conveyance method when the conveyance of a sheet is controlled in accordance with a conveyance control condition that does not include a tab. It is FIG. (1) explaining an example of a sensor detection operation | movement. It is FIG. (2) explaining an example of a sensor detection operation | movement. FIG. 10 is a diagram illustrating an example of a conveyance method when the conveyance of a sheet is controlled according to a conveyance control condition suitable for the presence of a tab. FIG. 10 is a diagram illustrating another example of a conveyance method when the conveyance of a sheet is controlled in accordance with a conveyance control condition that does not include a tab. It is a figure explaining other examples of sensor detection operation.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 3 ... Paper, 3A ... Tab, 9 ... Registration roller, 10 ... Image transfer part, 27 ... Control part, 28, 29 ... Conveyance motor, 31, 32, 32A, 32B ... Sensor

Claims (6)

A registration roller that feeds the paper at a predetermined conveyance speed to an image transfer unit that transfers an image to the paper;
A plurality of detection sensors for detecting the passage of the leading edge of the paper at different positions in the direction orthogonal to the conveyance direction upstream of the registration roller in the conveyance direction;
When the paper on which image formation is to be performed is a paper with a tab, and the paper with the tab is transported to the registration roller with the tab portion directed downstream in the transport direction, the plurality of detection sensors An image forming apparatus comprising: a control unit that controls a conveyance speed of the sheet by the registration roller based on a timing at which the leading edge of the sheet is detected. The control means recognizes whether or not the detected portion of the paper whose front end passage has been detected by the plurality of detection sensors is the tab portion, and the paper according to the front end passage detection timing of the paper based on the recognition result. The image forming apparatus according to claim 1, wherein the image forming apparatus controls a conveyance speed of the image forming apparatus. The image forming apparatus according to claim 1, wherein the plurality of detection sensors are arranged in a state straddling a tab position set in a central portion of the tabbed sheet in a direction orthogonal to the transport direction. . The control means determines the leading edge passage detection timing of the sheet with reference to a detection timing of a detection sensor that detects passage of the leading edge of the sheet with a portion other than the tab as the detected portion among the plurality of detection sensors. The image forming apparatus according to claim 2. When the plurality of detection sensors detect passage of the leading edge of the paper, the control means determines whether the detected portion is a portion of the tab based on a detection timing shift amount generated between the detection sensors. The image forming apparatus according to claim 2, wherein the image forming apparatus recognizes whether or not. A plurality of detection sensors for detecting passage of the leading edge of the paper at different positions in the direction orthogonal to the paper conveyance direction,
The plurality of detection sensors are arranged in a state straddling a tab position set in a central portion of the tabbed paper in a direction orthogonal to the transport direction, and the plurality of detection sensors detect the passage of the leading edge by the plurality of detection sensors. An image forming apparatus that recognizes whether or not the detected portion is a tab portion of a tabbed sheet.

Images