JP4474999B2 - Paper conveying apparatus and image forming apparatus - Google Patents

Description

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

  Some image forming apparatuses such as copying machines and printers can handle tabbed paper (hereinafter referred to as tab paper) in addition to normal rectangular paper (hereinafter referred to as plain paper). . Tab paper is paper in which tabs partially protrude from the edge of the paper. Since the tab position on the tab sheet is not constant, when a character image such as a heading is formed on the tab part, in addition to determining whether the sheet on which the image is to be formed is a tab sheet, It is necessary to recognize the position.

  Therefore, in Patent Document 1 below, a tab detection unit is arranged on the paper conveyance path before the registration roll (upstream in the paper conveyance direction), and the tab detection sensor provided in the tab detection unit is defined as the paper conveyance direction. It describes what can be moved in an orthogonal direction and performs tab detection by movement of a tab detection sensor. Further, in Patent Document 2 below, a plurality of sensors are arranged in accordance with tab positions on a conveyance path on which paper (including tab paper) is conveyed, and based on timing and detection time when the plurality of sensors detect the paper. That detect tabs.

Japanese Patent Laid-Open No. 2001-13823 JP 2003-192144 A

  However, in the above-described Patent Documents 1 and 2, the tab detection sensor is provided on the upstream side (front side) of the position (image forming position) where the image is actually formed on the paper in the paper conveyance path. It is configured to detect tabs. Therefore, before feeding the sheet to the image forming position, the tab sheet is conveyed so that the tab portion passes through the detection position of the sensor. Therefore, it is necessary to secure the length of the transport path corresponding to the length of the tab sheet in the sheet transport direction on the upstream side of the image forming position. As a result, the length of the conveyance path between the paper feeding unit where the paper is fed and the image forming position becomes long, which hinders space saving. Further, the tab detection cannot be applied to an image forming apparatus having a short distance between the paper feeding unit and the image forming position.

  SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a sheet feeding unit having a function of detecting a tab of a sheet and an image forming apparatus including the sheet conveying unit. In other words, the length of the conveyance path between the image forming position and the image forming position is shortened to save space.

A paper transport device according to the present invention includes a paper storage unit capable of storing a tab sheet having a tab protruding from an edge of the paper, and a paper feeding unit that feeds the paper stored in the paper storage unit toward the transport path. A conveying unit that conveys the sheet fed by the sheet feeding unit along a conveying path; a pulling unit that pulls the sheet stored in the sheet storing unit in a direction opposite to the sheet feeding direction by the sheet feeding unit; Detecting means for detecting the tab of the paper drawn by the means , the paper storage portion stores the tab paper with the tab portion facing in the direction opposite to the paper feeding direction, and the drawing means is the paper storage When the paper contained in the paper is tab paper, the paper is pulled in the direction opposite to the paper feed direction. Retraction, sensing means, in a state in which retracted the paper only amount retraction mechanism retraction, which detects the tabs of the sheet. Further, an image forming apparatus according to the present invention includes the paper transport device having the above-described configuration.

  In the paper transport device and the image forming apparatus including the same according to the present invention, the paper stored in the paper storage unit is pulled in the direction opposite to the paper feeding direction by the pulling means, and the tab of the pulled paper is detected by the detecting means. By doing so, it is possible to perform tab detection even if the paper is not fed into the transport path and transported.

  According to the present invention, when detecting a tab of a sheet, it is not necessary to send the sheet to the conveyance path for conveyance, and therefore, the conveyance path length between the sheet feeding unit and the image forming position is shortened to save space. Can be achieved.

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

  FIG. 1 is a schematic front view 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. The individual paper storage cassettes 2,... Have basically the same configuration, although the size of the entire cassette differs depending on the size and type of paper 3 to be stored.

  A paper stacking plate (tray) 4 is provided inside the 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 lifted by driving the lifting mechanism while maintaining the horizontal state.

  The pick-up roll 5 and the separating roll 6 constitute a paper feeding means for feeding the paper 3 stored in the paper storage cassette 2 toward the transport path. Among these, the pick-up roll 5 is provided so as to be able to contact and separate from the uppermost sheet 3 disposed at the predetermined height. A solenoid can be used as a drive source for moving the pickup roll 5 in and out of contact. The pickup roll 5 feeds the paper 3 stored in the paper storage cassette 2 toward the first transport path R1. When the paper is fed, the pickup roll 5 is pressed against the uppermost paper 3 loaded on the paper stacking plate 4 with a predetermined pressure, and in this state, the pickup roll 5 rotates in the clockwise direction in FIG. The sheets are fed in the direction of the arrow in order from the upper sheet 3.

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

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

  A second transport roll 8 and a resist roll 9 are sequentially arranged in the paper transport direction by the first transport roll 7. The 2nd conveyance roll 8 and the resist roll 9 are provided on 2nd conveyance path R2 formed continuously from 1st conveyance path R1. The second transport roll 8 transports the paper 3 transported by the first transport roll 7 toward the registration roll 9. The registration roll 9 conveys the sheet 3 conveyed by the second conveyance roll 8 toward the image transfer unit 10.

  The image transfer unit 10 is a part that transfers an image to the paper 3 conveyed by the registration roll 9, and an image is formed on the paper 3 by feeding the paper 3 into 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 roll 12, and a transfer pressure roll 13 is held in pressure contact with a belt winding portion of the support roll 12. Further, in the image transfer unit 10, an image is formed (transferred) from the intermediate transfer belt 11 to the sheet 3 when passing through the pressure contact portion between the support roll 12 and the pressure roll 13 sandwiching the intermediate transfer belt 11. It has become.

  The intermediate transfer belt 11 carries the visualized toner image and transfers the toner image to the image transfer unit 10 by the rotation of the belt. As a specific example, a toner image formed on the surface of a photoreceptor (not shown) is primarily transferred to the intermediate transfer belt 11, and the primary transferred toner image is sent to the image transfer unit 10 by the rotation of the intermediate transfer belt 11. . At that time, the toner image is formed on the surface of the photosensitive member based on an image signal read by an image reading device (scanner or the like) (not shown) if the image forming device is a copying machine. If there is, 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 third conveyance roll 16 and a discharge roll 17 are sequentially arranged. The above-described second transport path R2 refers to a transport path from the second transport roll 8 to the discharge roll 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 third transport roll 16 transports the paper 3 on which the image has been fixed by the image fixing unit 15, and the discharge roll 17 discharges the paper 3 transported by the third transport roll 16 to the discharge tray 18. To do.

  On the downstream side of the third transport roll 16, the third transport path R3 branches obliquely downward from the second transport path R2. A fourth transport roll 19 is disposed on the third transport path R. The fourth transport roll 19 transports the paper 3 sent to the third transport path R3 by the third transport roll 16 to the paper 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 provided on one side of the apparatus main body 1 adjacent to the cassette storage space (see FIG. 1) with respect to the cassette storage space secured for mounting the plurality of paper storage cassettes 2. Is formed substantially perpendicularly to the left side). A fourth transport path R4 is formed in the sheet reversing unit 20 along the vertical direction. A first reversing roll 21 and a second reversing roll 22 are disposed on the fourth transport path R4 with a predetermined interval in the vertical direction. The first reversing roll 21 is disposed in the vicinity of the entrance of the fourth transport path 4 (the upper end of the sheet reversing unit 20), which is the position for taking in the paper into the sheet reversing unit 20. The 2nd inversion roll 22 is arrange | positioned in the substantially intermediate part of 4th conveyance path R4 along a perpendicular direction.

  A lower end portion of the sheet reversing unit 20 is connected to the sheet drawing-in accommodating unit 23. The paper pull-in storage unit 23 is a part for temporarily storing the paper 3 drawn downward by the first reverse roll 21 and the second reverse roll 22 in the paper reverse unit 20. This paper drawing-in storage section 23 is the lowermost part in the apparatus main body 1 that is lower than the cassette storage space, that is, the paper storage cassette 2 arranged at the lowest stage among the plurality of paper storage cassettes 2 having a multistage structure. It is formed almost horizontally just below.

  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 roll 21 and the second reverse roll 22. On the fifth transport path R5, a plurality (six in the illustrated example) of transport rolls 25,... Are arranged at predetermined intervals, and a re-transport section 26 is formed by the plurality of transport rolls 25,. The re-conveying unit 26 is a part for conveying the paper 3 on which the image is transferred on one side by the image transfer unit 10 to the image transfer unit 10 again for double-sided printing, double-sided copying, and the like. The fifth conveyance path R5 is formed in a state connecting the fourth conveyance path R4 and the second conveyance path R2 between the sheet reversing unit 20 and the second conveyance roll 8.

  On the other hand, a sixth transport path R <b> 6 is branched from the first reversing roll 21 of the paper reversing unit 20 toward the discharge roll 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 transport paths R1 to R6 described above, the direction in which the paper advances is appropriately switched by a gate member (not shown).

  Next, a basic operation of the image forming apparatus having the above configuration will be described. First, the user inputs desired image forming conditions (for example, density and number of copies for image formation, designation of double-sided recording, etc.) using an operation panel (not shown) of the image forming apparatus, and then a start button in the operation panel. Press. At this time, if, for example, the lowermost sheet storage cassette 2 is selected by the user's input operation using the operation panel, the pickup roll 5 and the rolling roll 6 corresponding to the lowermost sheet storage cassette 2 rotate. Thus, the uppermost sheet 3 is sent out in the direction of the arrow (left direction) in the figure.

  Thus, the sheet 3 sent out from the sheet storage cassette 2 is transported upward along the first transport path R <b> 1 by the rotation of the transport roll 7, and is delivered to the second transport roll 8. Further, the sheet 3 is conveyed to the registration roll 9 side along the second conveyance path R <b> 2 by the rotation of the second conveyance roll 8. Thereafter, the sheet 3 is skew-corrected by abutting the leading end of the sheet against the nip portion of the resist roll 9 and bending in a loop shape. After the sheet 3 is stopped in this state, the sheet 3 is matched with the arrival timing of the image at the image transfer unit 10. The resist roll 9 is rotated and fed to the image transfer unit 10. In the image transfer unit 10, the toner image carried on the intermediate transfer belt 11 is transferred from the surface of the intermediate transfer belt 11 to the first surface of the sheet 3 at the pressure contact portion between the belt support roll 12 and the pressure roll 13. .

  The sheet 3 having the image transferred thereon is sent to the image fixing unit 15 by the vacuum conveyance unit 14. In the image fixing unit 15, an image is fixed on the surface of the paper 3 by a pressurizing action and a heating action applied between the pair of rolls while the paper 3 is sandwiched between the pair of rolls. If the sheet 3 is for single-sided recording, the sheet 3 sent from the image fixing unit 15 is transferred to the discharge roll 17 by the rotation of the third transport roll 16, and further discharged by the rotation of the discharge roll 17. Is discharged.

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

  In the paper reversing unit 20, the paper 3 sent by the fourth conveying roll 19 is sequentially sandwiched between the first reversing roll 21 and the second reversing roll 22, and the first reversing roll 21 and the second reversing roll 22 rotate. Thus, the sheet 3 is transported downward along the fourth transport path R4. At this time, the sheet 3 is drawn downward until the rear end of the sheet 3 passes through the branching portion between the fourth transport path R4 and the fifth transport path R5 after passing through the first reverse roll 21. Then, before the rear end of the sheet 3 reaches the second reverse roll 22, the rotation of the second reverse roll 22 is temporarily stopped.

  Thereafter, the second reversing roll 22 starts (restarts) rotation in the opposite direction to the timing at which the image arrives at the image transfer unit 10 in time. Then, in the sheet reversing unit 20, the sheet 3 held between the second reversing rolls 22 moves upward in the fourth conveying path R <b> 4 so as to switch back, and then is guided by a gate member (not shown) to perform the fourth conveying. It is guided from the path R4 to the fifth transport path R5. In the fifth transport path R <b> 5, the paper 3 is sequentially delivered to each transport roll 25 forming the re-transport unit 26, and the paper 3 is delivered to the second transport roll 8 by the last transport roll 25.

  Thereafter, the sheet 3 is sent to the image transfer unit 10 by the second transport roll 8 and the resist roll 9 in the same procedure as described above, and the image is transferred to the second surface of the sheet 3 and the sheet 3 is vacuum transported. The image is transferred from the section 14 to the third transport roll 16 via the image fixing section 15. In this case, the sheet 3 is guided again to the third transport path 3 by the rotation of the third transport roll 16 and the switching operation of the gate member (not shown). Similarly to the above, the sheet 3 is fed into the sheet reversing unit 20 by the rotation of the fourth transport roll 19. However, in this case, the rotation direction of the first reversing roll 21 and the second reversing roll 22 when the rear end of the sheet 3 passes through the third conveying path R3 and the branching section with the sixth conveying path R6. Is reversed. Then, the sheet 3 moves upward in the fourth conveyance path R4 in a form of being switched back by the sheet reversing unit 20. At this time, the sheet 3 is guided by a gate member (not shown), guided from the fourth transport path R4 to the sixth transport path R6, and is discharged to the discharge tray 18 through the discharge roll 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 sheet 3 on which the image is formed on the first side is reversed and turned upside down by the switchback at the sheet reversing unit 20 and discharged to the discharge tray 18.

  Here, among the plurality of sheet storage cassettes 2... Having a multistage structure as described above, the uppermost sheet storage cassette 2 can store a plurality of tab sheets in a stacked state. In the uppermost sheet storage cassette 2, tab sheets are stored in a state where the tab portion protruding from the edge of the sheet is directed to the opposite side (right side in FIG. 1) of the sheet feeding direction by the pickup roll 5. It has come to be. The pickup roll 5 that feeds the paper (tab paper) 3 stored in the uppermost paper storage cassette 2 toward the first transport path R1 is, for example, a motor that rotates the direction of a drive motor that rotationally drives the pickup roll 5. By switching control (reversing) by the control circuit, it is possible to rotate in both the clockwise direction (paper feeding direction) and the counterclockwise direction (paper drawing direction) in the figure.

  On the other hand, tabs as shown in FIGS. 2 and 3 are provided near the uppermost sheet storage cassette 2 and on the side opposite to the sheet feeding side on which the separating roll 6 is disposed (the side on which the tab sheet tab is disposed). A detection unit 27 is provided. The tab detection unit 27 detects the tab of the paper stored in the uppermost paper storage cassette 2.

  The tab detection unit 27 is roughly guided by a tab detection sensor 28, a drive motor 29 as a drive source for moving the sensor 28, and the sensor 29 so as to be movable in a direction orthogonal to the paper feeding direction. The guide mechanism 30 is supported, and a power transmission mechanism 31 that transmits the driving force of the drive motor 29 to the guide mechanism 30.

  The sensor 28 is configured using, for example, a reflection type photosensor having a light emitting element and a light receiving element integrally. The detection surface of the sensor 28 (the light emitting surface and the light receiving surface in the case of a reflection type photosensor) is arranged upward. In addition, the detection surface of the sensor 28 is the uppermost one of the sheets (stacked sheets) 3 stored in the uppermost sheet storage cassette 2 and disposed at a predetermined (constant) height by the rising of the sheet stacking plate 4. It is arranged slightly lower than the paper 3.

  The drive motor 29 is configured using, for example, a pulse motor that can easily control the rotation direction and the rotation amount.

  The guide mechanism 30 includes a sensor support bracket 32, a pair of guide shafts 33, and a moving member 34. The sensor support bracket 32 is a substantially L-shaped plate-like member having a sensor attachment portion that is arranged substantially horizontally and a belt attachment portion that stands up substantially vertically from an end side of the sensor attachment portion. The sensor 28 described above is fixed to the sensor mounting portion of the sensor support bracket 32 by screwing, bonding, or the like.

  The pair of guide shafts 33 are round shafts each having a circular cross section, and are arranged in parallel to each other along a direction orthogonal to the sheet feeding direction. Further, both end portions of each guide shaft 33 are fixed in a fitted state to shaft support portions 35 </ b> A and 35 </ b> B formed integrally with the plate-like base member 35.

  The moving member 34 is substantially U-shaped in a plan view, and is movably guided and supported by the pair of guide shafts 33 with the opposing portions fitted to the pair of guide shafts 33, respectively. Further, the lower end portion of the moving member 34 is attached to the sensor attachment portion of the sensor support bracket 32 together with the sensor 28 in a fixed state.

  The power transmission mechanism 31 is configured using two large and small pulleys 36 and 37 and an endless belt 38. The large-diameter pulley 36 is fitted and fixed to the rotation shaft (drive shaft) of the drive motor 29 attached to the base member 35. The small-diameter pulley 37 is rotatably mounted on the base member 35 at a position away from the large-diameter pulley 36 by a predetermined distance. The belt 38 is stretched around the two pools 36 and 37 in a loop shape. A part of the belt 38 is fixed to the belt attaching portion of the sensor support bracket 32 by screwing, bonding, or the like.

  In the tab detection unit 27 configured as described above, when the pulley 36 on the large diameter side is rotated by driving the drive motor 29, the belt 38 travels using the pulley 36 as a drive pulley, and the small diameter side ( The pulley 37 on the driven side rotates. When the belt 38 travels, the belt support bracket 32 and the moving member 34 move accordingly. At this time, since the moving member 34 moves along the pair of guide shafts 33, the moving direction of the belt support bracket 32 is guided by the pair of guide shafts 33. Therefore, by arranging the pair of guide shafts 33 in a direction orthogonal to the paper feed direction, the sensor 28 on the belt support bracket 32 can be moved in a direction perpendicular to the paper feed direction. Further, by reversing the rotation direction of the drive motor 29 (forward rotation, reverse rotation), the sensor 28 can be moved in one direction and the other direction (reciprocal movement) in a direction orthogonal to the paper feed direction.

  The movement range of the sensor 28 is set according to the width of the sheet (tab sheet) 3 to be detected by the tab (the sheet size in the direction orthogonal to the sheet feeding direction). Specifically, as shown in FIG. 4, in the paper width direction (arrow direction) orthogonal to the paper feed direction, the movement start point P1 provided outside one side of the paper 3 and the other side of the paper The movement range L of the sensor 3 is set so that the sensor 3 can move at a substantially constant speed (except for the acceleration period and the deceleration period) between the movement end point P2 provided outside the side of Has been.

  Subsequently, a sheet conveying operation and an image forming operation when an image is formed on the tab portion of the tab sheet using the sheet conveying apparatus including the tab detection unit 27 as described above will be described. Note that the sheet conveyance operation is controlled by a sheet conveyance control unit (not shown), and the image forming operation is controlled by an image formation control unit (not shown).

  First, in a state where a plurality of sheets (tab sheets) 3 are stored (stacked) in the uppermost sheet storage cassette 2, the uppermost sheet storage cassette 2 is selected by, for example, a user input operation using an operation panel. Then, the pickup roll 5 corresponding to the uppermost sheet storage cassette 2 is displaced in the direction of the arrow in FIG. 2 and comes into contact (pressure contact) with the uppermost sheet 3. Next, the pick-up roll 5 rotates in a direction opposite to the direction in which the paper is fed out (counterclockwise direction in FIG. 2) prior to feeding the paper toward the first transport path R1. As a result, the uppermost sheet 3 is pulled in the direction opposite to the sheet feeding direction as the pickup roll 5 rotates. When the amount of paper drawn by the pickup roll 5 reaches a predetermined amount set in advance, the pickup roll 5 stops rotating at that time.

  At this time, if the paper 3 drawn by the pickup roll 5 is a tab paper, the tab portion is arranged at a position that can be detected by the sensor 28. The position that can be detected by the sensor 28 is a position that faces the detection surface of the sensor 28 during the movement of the sensor 28 when the sensor 28 is moved by driving the drive motor 29 as described above.

  Subsequently, the sensor 28 starts to move from the movement start point P1 to the movement end point P2 by driving the drive motor 29 in the tab detection unit 27, and a sensor output signal (tab detection signal) output from the sensor 28 during this movement. Is captured by the paper transport control unit. At this time, the sensor output signal takes one of an on state (Hi) and an off state (Low) depending on the electrical output level (voltage level or the like). Also, assuming that the sensor 28 is a reflection type photosensor, the sensor output signal is turned off when the tab portion of the sheet does not exist at a position facing the detection surface of the sensor 28, and when it exists, The sensor output signal is turned on.

  Therefore, as shown in FIG. 4, if the sheet 3 drawn by the pickup roll 5 is a tab sheet having the tab 3 </ b> A, the sheet is positioned at a position facing the detection surface of the sensor 28 on the movement path of the sensor 28. The tab portion of (tab paper) 3 exists. Therefore, as shown in FIG. 5, the output signal of the sensor 28 is in an off state during a period until the elapsed time from the sensor movement start (detection start) to T1 (a period in which the sensor 28 detects a portion without a tab). However, the sensor 28 switches from the off state to the on state at the moment the tab 28 is detected. Thereafter, in the period T2 in which the sensor 28 detects the portion with the tab, the sensor output signal is maintained in the on state. When the sensor 28 detects the portion without the tab again, the sensor 28 switches from the on state to the off state.

  In view of this, in the paper transport control unit, when the sensor 28 is moved within the sensor movement range L, the sensor output signal output from the sensor 28 is continuously captured, whereby the captured sensor output signal (tab detection result). ) To determine whether the sheet 3 (the sheet conveyed for image formation) stored in the uppermost sheet storage cassette 2 is a tab sheet, and the determination result of the determination process When it is determined that the sheet 3 is a tab sheet, a recognition process for recognizing tab information including the tab position of the tab sheet is performed.

  More specifically, the paper transport control unit determines that the paper 3 to be transported is a tab paper when the sensor output signal is switched from the off state to the on state during the movement of the sensor 28 in the determination process. When the sensor output signal is always kept off from the start of movement of the sensor 28 to the end of movement, it is determined that the paper 3 to be transported is plain paper instead of tab paper. In the paper conveyance control unit, in the recognition process, the sensor output signal is maintained in the on state during the period T1 from the start of the movement of the sensor 28 (starting the tab detection) until the sensor output signal is switched on. The tab information is recognized based on the period T2. As tab information, it is possible to recognize the tab size in addition to the tab position of the tab sheet.

  The tab position of the tab paper is the direction along the edge of the tab paper from which the tab protrudes (the movement direction of the sensor 28) and indicates where the tab portion exists. Indicates the length of the tab in the direction along the edge of the tab sheet from which the tab protrudes. Therefore, when the tab position or tab size of the tab sheet changes, the on / off timing of the sensor output signal changes accordingly. That is, when the tab position changes, the period T1 until the sensor output signal switches from the off state to the on state changes, and when the tab size changes, the period T2 during which the sensor output signal is maintained in the on state changes. More specifically, when the tab position is shifted toward the sensor movement start point P1 in the movement direction of the sensor 28, the period T1 is shortened by that amount. Conversely, when the tab position is shifted toward the sensor movement end point P2, The period t2 becomes longer by the amount. Further, in the moving direction of the sensor 28, when the tab size is reduced, the period T2 is shortened accordingly, and when the tab size is increased, the period T2 is lengthened accordingly. Therefore, the sheet conveyance control unit can recognize the tab position and the tab size of the tab sheet based on the periods T1 and T2.

  When the series of processes related to tab detection as described above is completed, the pickup roll 5 rotates in the direction of feeding out the paper, contrary to the previous process. As a result, the uppermost sheet 3 for which the tab detection has been completed is fed in the sheet feeding direction according to the rotation of the pickup roll 5. When the paper feed amount by the pickup roll 5 reaches the predetermined amount, the pickup roll 5 stops rotating at that time. As a result, the uppermost sheet 3 is returned to the original position. Further, after the sensor 28 has moved to the movement end point P2 (after the end of the tab detection), the rotation of the drive motor 29 is temporarily stopped, and then the rotation direction of the drive motor 29 is reversed to move the sensor 28 to the movement start point P1. Return to.

  Thereafter, when a paper transport command is issued from the image forming control unit, the pickup roll 5 rotates again in the direction of feeding the paper at a timing based on the transport command, and the uppermost paper 3 moves the roll 6 in accordance with this rotation. Via the first transport path R1. Thereafter, the sheet 3 is conveyed in accordance with the procedure described in “Basic operation of the image forming apparatus”. Further, when an image is formed on the tab portion of the tab sheet by the image transfer unit 10 during the sheet conveyance, the image writing position in the direction orthogonal to the sheet conveyance direction is the sheet conveyance control as described above. Control is based on tab information recognized by the section. For example, when the tab position recognized by the recognition processing of the paper transport control unit is located at the center in the paper width direction, the image formation control unit sets the image writing position so that an image is formed in accordance with the tab position. Be controlled. As a specific example, in an image forming apparatus of a type (electrophotographic method) in which an image (electrostatic latent image) is written by irradiating a photoconductor with a laser beam, an image by a laser beam is used according to the tab position recognized in the recognition process. By adjusting the writing start timing and adjusting the image writing period with the laser beam according to the tab size recognized in the above recognition process, the image writing position can be adjusted appropriately according to the tab position and tab size. Can be controlled.

  As described above, in the present embodiment, the sheet 3 stored in the uppermost sheet storage cassette 2 is a tab sheet, and the tab sheet is picked up when the tab sheet is sent out to the conveyance path and conveyed to the image transfer unit 10. Prior to the feeding of the sheet by the roll 5, the uppermost sheet 3 is pulled in the direction opposite to the feeding direction by the rotation of the pickup 5, and the tab of the pulled-in sheet can be detected by the tab detection unit 27. There is no need to detect tabs on the paper transport path as in the prior art. Therefore, it is possible to save space by shortening the conveyance path length between the paper feeding unit and the image forming position. Further, since the tab can be detected without conveying the sheet, the tab detection can be applied to an image forming apparatus having a short distance between the sheet feeding unit and the image forming position.

  In the above embodiment, the detection of the tab is performed by moving one sensor 28. However, the present invention is not limited to this, and the detection of the tab is performed using a plurality of sensors. Also good.

1 is a schematic front view illustrating a configuration example of an image forming apparatus to which the present invention is applied. It is a schematic side view which shows the structure of the tab detection unit which concerns on embodiment of this invention. It is a perspective view which shows the structure of the tab detection unit which concerns on embodiment of this invention. It is a top view which shows operation | movement of the tab detection unit which concerns on embodiment of this invention. It is a timing diagram which shows the state change of the sensor output signal by tab detection.

Explanation of symbols

  2 ... paper storage cassette, 5 ... pickup roll, 6 ... paper roll, 10 ... image transfer unit, 27 ... tab detection unit, 28 ... sensor, 29 ... drive motor, 30 ... guide mechanism, 31 ... power transmission mechanism, R1 R6 ... transport path

Claims (6)

A paper storage section capable of storing tab paper having tabs protruding from the edge of the paper;
A paper feeding means for feeding out the paper stored in the paper storage unit toward the conveyance path;
Conveying means for conveying the paper sent out by the paper feeding means along the conveying path;
Pull-in means for pulling the paper stored in the paper storage unit in a direction opposite to the paper feeding direction by the paper feeding means;
Detecting means for detecting a tab of the paper drawn by the drawing means ;
The paper storage unit stores the tab paper in a state where the tab portion is directed in a direction opposite to the paper feeding direction,
When the paper stored in the paper storage portion is a tab paper, the pull-in means is arranged such that the tab portion of the paper drawn in the direction opposite to the paper feed-out direction is arranged at a position where the detection means can detect. Pull in the paper by the preset pull-in amount,
The sheet conveying device , wherein the detecting unit detects a tab of the sheet in a state where the drawing unit has pulled the sheet by the amount of the drawing . The sheet conveying apparatus according to claim 1, wherein the detection unit includes a tab detection sensor that is movable in a direction orthogonal to a feeding direction of the sheet. The paper transport apparatus according to claim 1, further comprising: a determination unit that determines whether the paper stored in the paper storage unit is a tab sheet based on a detection result of the detection unit. 4. The paper transport according to claim 3, wherein the determination unit recognizes tab information including a tab position of the tab sheet when determining that the sheet stored in the sheet storage unit is a tab sheet. 5. apparatus. An image forming apparatus comprising the sheet conveying device according to claim 1. A sheet conveying device according to claim 4;
Control means for controlling an image writing position when an image is formed on the tab portion of the tab sheet fed by the paper feeding means and conveyed by the conveying means based on the tab information recognized by the determining means; An image forming apparatus comprising:

Images