JP5279612B2 - Sheet conveying apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet carrying device that carries sheets without causing skew or jam, nor lowering the productivity, and to provide an image forming device. <P>SOLUTION: A driving force transmitting part 5B, arranged between a reversely rotatable switch-back roller 53 and an energy storing spring 85 which elastically stores reverse-rotation driving force for reversely rotating the switch-back roller 53 in accordance with the forward-rotation driving amount of the switch-back roller 53, transmits the forward-rotation driving amount of the switch-back roller 53 to the energy storing spring 85 while the switch-back roller 53 rotates forward, and transmits the reverse-rotation driving force stored in the energy storing spring 85 to the switch-back roller 53 while the switch-back roller 53 is reversely rotated. This driving force transmitting part 5B is constituted to keep a predetermined amount of reverse-rotation driving force stored in the energy storing spring 85, after the energy storing spring 85 has stored the predetermined amount of reverse-rotation driving force during the forward rotation of the switch-back roller 53. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus, and more particularly to an apparatus having a reversing unit that pulls in a sheet and conveys the sheet by reversing the front-rear direction.

  2. Description of the Related Art Conventionally, in image forming apparatuses such as copying machines, printers, and facsimiles, for example, double-sided printing or double-sided copying is performed, and a sheet with an image formed on one side is conveyed again to the image forming unit with the front and back sides reversed. There is something like that. Further, some conventional image forming apparatuses include a sheet conveying device that conveys a sheet so that the sheet is reversed in order to reverse the front and back when discharging an image-formed sheet. Note that such a sheet conveying apparatus includes a reversing unit for reversing the front and back of the sheet. In such a reversing unit, for example, a so-called switchback conveying system in which the sheet is once pulled by a reversing roller, and then the front and back sides or the front and rear directions are reversed and conveyed in the opposite direction. Is used.

  By the way, in the conventional reversing unit, in order to rotate the reversing roller forward and backward, for example, a stepper motor that rotates bidirectionally is used as the driving source of the reversing roller, or two transmission paths from the driving source can be switched. Etc. are taken. However, such a method has a problem that it is expensive or it takes time to switch the rotation direction of the reverse roller. Therefore, conventionally, a unidirectional rotating motor is used as a driving source and the driving force of the motor is stored as a spring pressure so that the rotation direction of the reversing roller can be switched in a short time. Some have a power storage unit (see Patent Document 1).

  In such a reversing unit, during the normal rotation of the unidirectional rotating motor, the driving force for reversing the reversing roller in the power accumulation unit is stored as a spring pressure, and the reversing roller is reversed by releasing the stored force. I have to. In this way, by using a unidirectionally rotating motor as the driving source for the reversing roller, the driving source can be shared with other mechanism units, and an inexpensive configuration can be achieved as the overall configuration of the apparatus. Further, since the accumulated force due to the normal rotation of the reverse roller and the reverse rotation due to the release of the accumulated force have little time loss of the mechanism operation, the rotation direction of the reverse roller can be switched in a short time. For this reason, when conveying a sheet | seat continuously, the distance between sheets of a preceding sheet and a succeeding sheet can be shortened, and productivity as an image forming apparatus can be improved.

Japanese Utility Model Publication No. 62-18594

  However, in the conventional sheet conveying apparatus including the reversing unit configured as described above and the image forming apparatus including the reversing unit, the amount of accumulated force for reversing the reversing roller is proportional to the normal rotation driving amount of the reversing roller. Increase. For this reason, if the amount of forward rotation of the reversing roller exceeds the limit of the accumulated force on the mechanism, the mechanism may be damaged. Therefore, in order to prevent such damage to the mechanism, for example, the reverse roller has a non-circular shape having a notch, and after obtaining a certain amount of accumulated power, the reverse roller faces the notch to the driven roller. It is stopped at the position and the nip is released. Alternatively, the reverse roller is provided so as to be separated from the driven roller, and after obtaining a certain amount of accumulated power, the reverse roller is separated to release the nip.

  By the way, when comprised in this way, the amount of power stored as a spring pressure becomes fixed. Here, for example, when the amount of accumulated power is set so that the reversal amount of the reversing roller is an optimum amount for conveying a short sheet, when conveying a long sheet, conveyance of the difference in sheet length is performed. Is performed with the nip of the reversing roller released. In this case, when conveying a long sheet, the conveyance of the difference in length from the short sheet is performed by a conveyance roller upstream of the reversing roller. Therefore, there is a risk of causing skew or conveyance jam due to sheet conveyance resistance. Will increase. On the contrary, when the amount of accumulated power is set so that the reversal amount of the reversing roller is the optimum amount for conveying a long sheet, the sheet having a shorter length than the long sheet in continuous conveyance of the sheet However, it is necessary to adjust the sheet conveyance pitch to the long sheet conveyance pitch. For this reason, when a sheet having a short length is used, the sheet cannot be conveyed to the reversing roller until the reversing of the reversing roller is completed, and the productivity is lowered.

  Accordingly, the present invention has been made in view of such a current situation, and is a sheet conveying apparatus capable of reversing and conveying a sheet without causing skewing or jamming and without reducing productivity. An object of the present invention is to provide an image forming apparatus.

The present invention provides a sheet conveying apparatus having a reversing unit that pulls in a sheet and reverses the front-rear direction, and the reversing unit pulls the sheet to a reversing position where the sheet is reversed by normal rotation, A sheet reversing / conveying member capable of reversing and conveying the sheet reversing direction, and for reversing the sheet reversing / conveying member in accordance with the normal rotation driving amount of the sheet reversing / conveying member when the sheet reversing / conveying member is normally rotated. The reversing drive force is elastically stored between the sheet reversing and conveying member and the force accumulating member, and when the sheet reversing and conveying member is normally rotated, the normal rotation driving amount of the sheet reversing and conveying member is set. A driving force for transmitting the reverse driving force stored in the energy storage member to the sheet reversing conveyance member when the sheet reversing conveyance member is reversely transmitted to the energy accumulation member. Comprising a reach portion, wherein the driving force transmitting section, during forward rotation of the sheet reversing conveying member, where said energy storing member after accumulated the reverse drive force of a predetermined amount, stored in the energy storing member It is configured to maintain a fixed reverse driving force.

  As in the present invention, during normal rotation of the sheet reversal conveying member, after the energy storage member has accumulated a predetermined amount of reverse driving force, the stored reverse driving force is maintained so that skewing and jamming can be performed. The sheet can be reversed and conveyed without being generated and without reducing productivity.

1 is a perspective view of a color laser printer that is an example of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a configuration diagram inside a printer main body of the color laser printer. FIG. 3 is a perspective view illustrating a configuration of a reversing unit of a sheet conveying device provided in the color laser printer. The figure explaining operation | movement of the said inversion part. The control block diagram of the said inversion part. The figure which shows the other structure of the said inversion part. The figure which shows the structure of the inversion part provided in the sheet conveying apparatus which concerns on the 2nd Embodiment of this invention. The figure which shows the structure of the inversion part provided in the sheet conveying apparatus which concerns on the 3rd Embodiment of this invention.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view of a color laser printer which is an example of an image forming apparatus according to a first embodiment of the present invention. In FIG. 1, reference numeral 200 denotes a color laser printer. The color laser printer 200 includes a color laser printer main body (hereinafter referred to as a printer main body) 201 having an image forming unit and an image reading unit provided on the printer main body 201. 201A.

  Then, the printer main body 201 is fed from an image forming unit 202 that forms an image on a sheet, a feeding unit 203 that feeds the sheet to the image forming unit 202, and a feeding unit 203 as shown in FIG. A sheet conveying unit 204 that conveys the received sheet to the image forming unit 202. Further, a fixing device 6 for fixing an image formed on the sheet is provided. The image forming unit 202 includes a photosensitive drum 21 (21a to 21d) that is arranged in the vertical direction and is an image carrier that carries toner images of four colors of yellow, magenta, cyan, and black. The photosensitive drum 21 is rotated counterclockwise by a rotating means (not shown).

  Further, a charging device 23 (23a to 23d) that is arranged around the photosensitive drum along the rotation direction and uniformly charges the surface of the photosensitive drum, and the photosensitive drum is irradiated with a laser beam based on image information. A scanner unit (not shown) for forming an electrostatic latent image is provided thereon. Furthermore, toner of each color of yellow, cyan, magenta, and black is attached to the electrostatic latent image so as to be visualized as a toner image, and toner remaining on the surface of the photosensitive drum after the transfer is transferred to the developing device 22 (22a to 22d). A cleaning means (not shown) for removal is provided. In the present embodiment, the photosensitive drum 21, the charging device 23, the developing device 22, and the cleaning unit are integrally formed into a cartridge to form a process cartridge 24 (24a to 24d).

  In addition, transfer rollers 34 (34a to 34d) that sandwich the transfer conveyance belt 35 together with the four photosensitive drums 21 (21a to 21d) are respectively disposed inside an endless transfer conveyance belt 35 that conveys a sheet to be described later. It is attached. These transfer rollers 34 are connected to a power supply for transfer bias (not shown), and positive charges are applied to the sheet from the transfer roller 34 via the transfer conveyance belt 35. By thus applying the transfer bias, the negative color toner images on the photosensitive drum are sequentially transferred to the sheet in contact with the photosensitive drum 21 to form a multicolor image.

  The feeding unit 203 stores a plurality of sheets P, the sheet feeding cassette 11 loaded on the bottom of the printer main body, the pickup roller 9 that feeds the sheet P stored in the sheet feeding cassette 11, and one sheet P. It consists of a separation unit (not shown) that separates each one. At the time of image formation, the sheet P is separated and fed one by one from the paper feed cassette 11 by the pickup roller 9, and then the sheet P is conveyed to the sheet conveying unit 204 by the registration roller pair 12 at a predetermined timing. The

  The sheet conveying unit 204 is provided with a transfer conveying belt 35 as a sheet carrier that is stretched over the driving roller 37 and the driven roller 33 and arranged to face all the photosensitive drums 21. The transfer conveyance belt 35 electrostatically attracts the sheet to the outer peripheral surface facing the photosensitive drum 21, and is circulated and moved clockwise by a driving roller 37 so as to bring the sheet into contact with the photosensitive drum 21. Then, the sheet P is conveyed to the transfer position T by the transfer conveyance belt 35 by being electrostatically attracted to the transfer conveyance belt 35 that circulates in this way, and the toner image on the photosensitive drum 21 is transferred.

  A suction roller 36 is disposed at the most upstream position of the transfer conveyance belt 35 and is in pressure contact with the driven roller 33 via the transfer conveyance belt 35. The suction roller 36 brings the sheet P into pressure contact with the outer periphery of the transfer conveyance belt 35 and applies a voltage to the transfer conveyance belt 35 to electrostatically adsorb the sheet P to the transfer conveyance belt 35. The color laser printer 200 draws the sheet, reverses the front-rear direction, and discharges the sheet to the sheet discharge tray 58. In addition, the sheet conveying device 5 that conveys the sheet so as to pull the sheet in this way, reverse the direction, and discharge the sheet to the sheet discharge tray 58 is provided.

  Next, an image forming operation of the color laser printer 200 configured as described above will be described. First, each process cartridge 24 is sequentially driven in accordance with the print timing, and the photosensitive drum 21 is driven to rotate counterclockwise in accordance with the drive. Further, the scanner units corresponding to the respective process cartridges 24 are sequentially driven. By this driving, the charging device 23 applies a uniform charge to the peripheral surface of the photosensitive drum 21, and the scanner unit outputs an image signal corresponding to the document image read by the image reading unit 201 </ b> A on the peripheral surface of the photosensitive drum 21. In accordance with the exposure, an electrostatic latent image is formed on the circumferential surface of the photosensitive drum. Further, the latent image is developed by the developing device 22 to form toner images of four colors of yellow, magenta, cyan, and black on the surface of the photosensitive drum.

  In parallel with this toner image forming operation, the sheets P stored in the paper feed cassette 11 are picked up by the pickup roller 9 and separated and fed one by one by the separation unit. Thereafter, the sheet P hits the registration roller pair 12 that has stopped rotating to form a loop, and the skew of the sheet P is corrected by forming the loop in this way. Thereafter, at the timing when the leading edge of the toner image on the most upstream photosensitive drum 21d is rotated and conveyed to the contact point (transfer position) T with the transfer conveyance belt 35, the printing of the sheet P is performed at the contact point. The registration roller pair 33 starts to rotate so that the start positions coincide. As the registration roller pair 33 rotates, the sheet P is conveyed to the nip between the suction roller 36 and the transfer conveyance belt 35. At this time, the sheet P is attracted to the transfer conveyance belt 35 by the adsorption roller 36 and transferred to the photosensitive drum 21. The sheet is conveyed to a transfer portion where the conveyance belt 35 is in pressure contact.

  Next, the toner images of the respective colors on the photosensitive drum 21 are formed on the photosensitive drum 21 by the action of the transfer roller 34 which is disposed in each transfer unit and applied with a voltage having a polarity opposite to that of the toner. The images are sequentially superimposed and transferred on the sheet. Next, the sheet P on which the four color toner images are transferred in this way is separated from the transfer conveyance belt 35 by the curvature of the driving roller 37 and is carried into the fixing device 6. Thereafter, the toner image is fixed on the sheet P in the fixing device 6, and the sheet P on which the toner image is fixed is conveyed to the sheet conveying device 5 by the fixing roller 61 and the intermediate roller 51. Then, after the sheet is once pulled in the direction opposite to the sheet discharge tray 58 by the sheet conveying device 5, the front and rear directions are reversed, and the sheet is discharged to the sheet discharge tray 58 with the image forming surface facing down. The color laser printer 200 can form a double-sided image, and the sheet P is conveyed to the double-sided conveyance path 110 by switching the switching member 71 when the double-sided image is formed. Thereafter, the sheet P is fed again to the registration roller pair 12 by the double-sided roller 72, and a toner image is formed by the above-described image forming operation in the same manner as the image formation on the first side.

  By the way, the sheet conveying apparatus 5 is a second conveying path 102 that is a sheet discharging path for discharging a sheet to the sheet discharging tray 58, and a sheet conveying path that is a sheet conveying path for conveying a sheet on which an image is formed to the second conveying path 102. One transport path 101 is provided. Further, a reversing path 103 that is a reversing path that pulls in the sheet that has passed through the first transport path 101, reverses the front-rear direction, and sends the sheet to the second transport path 102 is provided. Further, the reverse path 103 is provided with a switchback roller 53 as a sheet reverse conveyance member capable of forward and reverse rotation. The switchback roller 53 conveys the sheet by forward and reverse rotation of a drive motor 90 as a drive source. The direction can be switched.

  By rotating the switchback roller 53 in the forward direction, the sheet that has passed through the first conveyance path 101 is pulled to the reversal position 100 where the sheet is reversed. In addition, after the sheet is pulled to the reversal position 100 in this way, the switchback roller 53 is reversed to reverse the front and back direction and send the sheet to the second conveyance path 102. Here, the drive motor 90 is a motor that always rotates in one direction. For this reason, in addition to driving the switchback roller 53, it is also possible to serve as driving of the fixing roller 61, the intermediate roller 51, the intermediate roller 56, and the paper discharge roller 57. The intermediate roller 56 is located downstream of the switchback roller 53 in the sheet feeding direction (downstream of the sheet conveyance direction), and the sheet fed with the front and rear direction reversed by the switchback roller 53 together with the switchback roller 53. It is a sheet conveying member to convey.

  In FIG. 2, 54 is arranged at substantially the same position as the sheet reversing position 100, and indicates the leading edge of the sheet P conveyed from the first conveying path 101 and the trailing edge of the sheet conveyed by the normal rotation of the switchback roller 53. It is a sheet | seat detection sensor which is a rear-end detection part to detect. The detection signal from the sheet detection sensor 54 is input to the control unit 250 that controls the drive of the drive motor 90. The control unit 250 detects the leading edge and the trailing edge of the sheet P passing through the first conveyance path 101 based on information from the sheet detection sensor 54. Further, the control unit 250 drives the drive motor 90 based on the leading edge detection information of the sheet P obtained by the sheet detection sensor 54 to cause the switchback roller 53 to rotate normally. Thereafter, after the sheet is pulled to the reversal position 100 by forward rotation of the switchback roller 53, the drive transmission of the drive motor 90 is interrupted (cut) based on the rear end detection information so as to reversely rotate the switchback roller 53. Control to do.

  Reference numeral 55 denotes a branch member provided at the junction of the first transport path 101 and the reverse path 103, and the branch member 55 causes the sheet that is switched back and transported by the switchback roller 53 to return to the first transport path 101. It can be prevented from being sent. In other words, the branch member 55 serves as a check valve for preventing the sheet from being fed back to the first conveyance path 101 when the sheet is switched back, and a swing plate, a sheet, or the like is used. Yes. Depending on the type of sheet to be transported and the transport conditions, the branch member 55 can be used only by the shape of the joining portion of the first transport path 101 and the reversing path 103 to avoid reverse sheet feeding to the first transport path 101. It is not always necessary.

  Next, a sheet conveyance (discharge) operation in the case of double-sided image formation by the sheet conveyance device 5 configured as described above will be described. When the sheet P on which image formation has been completed is conveyed from the first conveyance path 101 to the switchback roller 53 by the intermediate roller 51, the sheet P is first drawn into the reversal path 103 by the normal rotation of the switchback roller 53. Next, when the rear end of the sheet passes the branch member 55 and then reaches the reversal position 100, the switchback roller 53 is reversed and the sheet P is conveyed to the second conveyance path 102. Note that the reverse rotation of the switchback roller 53 at the reverse position 100 is performed based on the information on the trailing edge of the sheet obtained by the sheet detection sensor 54 as described above. Next, by switching of the switching member 71, the sheet P is conveyed from the second conveyance path 102 to the double-sided conveyance path 110 and is transferred to the registration roller pair 12 by the double-sided roller 72. Thereafter, the sheet P follows the same conveyance path as in the case of single-sided printing, an image is formed on the second side of the sheet P, and is discharged and stacked on the discharge tray 58 in page order.

  Incidentally, as shown in FIG. 3, the switchback roller 53 is rotated in one direction by the rotation of the drive motor 90 transmitted through the motor gear 91, the first swing gear 81, and the drive gear 92 fixed to the roller shaft 53a. The sheet rotates in the sheet discharge direction indicated by the arrow. The first oscillating gear 81 includes a first gear 81a that meshes with the motor gear 91, a second gear 81b that meshes with the first gear 81a and the drive gear 92, and the first and second gears 81a and 81b are rotatable. The holder 81c to hold | maintain is provided. The holder 81c is provided coaxially with the first gear 81a so as to be swingable, and is normally held at a position where the second gear 81b does not mesh with the drive gear 92 by a spring 81d. . Thereby, even if the drive motor 90 is in a rotating state, the drive of the drive motor 90 is not transmitted to the switchback roller 53.

  The holder 81c is provided between the switchback roller 53 and the drive motor 90, and is a solenoid that is a drive transmission switching member that selectively transmits the drive of the drive motor 90 to the switchback roller 53 when the sheet is pulled. 82 are connected. Here, when the solenoid 82 is turned on, the holder 81 c swings upward, and the second gear 81 b meshes with the drive gear 92 that is a drive gear that rotates integrally with the switchback roller 53. When the second gear 81 b meshes with the drive gear 92 in this way, the drive of the drive motor 90 is transmitted to the switchback roller 53. It should be noted that such transmission disconnection and connection of the drive motor 90 may be performed using an electromagnetic clutch or the like other than the solenoid 82.

  On the other hand, the drive gear 92 of the switchback roller 53 is connected to a power accumulation gear 84 for reversing the switchback roller 53 via a second swing gear 83 that is a transmission gear. Here, the second oscillating gear 83 is urged by an urging means (not shown) in a direction to mesh with the drive gear 92 and the accumulator gear 84 when the switchback roller 53 is rotating forward. . As a result, the forward rotation of the switchback roller 53 is transmitted to the force accumulation gear 84 that is a force accumulation gear that transmits the amount of forward rotation to the energy accumulation spring 85 via the second swing gear 83.

  As will be described later, when the switchback roller 53 rotates in the reverse direction, the second swing gear 83 is pressed by the switchback roller 53 and can move in a direction to disengage the drive gear 92 and the accumulator gear 84. It has become. Then, the second oscillating gear 83 moves in a direction in which the engagement of the drive gear 92 and the accumulator gear 84 is disengaged as described above, whereby the drive transmission to the accumulator gear 84 via the second oscillating gear 83 is achieved. Is disconnected.

  The power accumulation gear 84 is used to prevent the switchback roller 53 from rotating even if the switchback roller 53 continues normal rotation after the power accumulation spring 85 stores a predetermined amount of reverse drive force during normal rotation of the switchback roller 53. In this embodiment, a missing gear (fan gear) is used. Here, the force accumulation gear 84 has the number of teeth necessary to obtain a rotation amount of the switchback roller 53 sufficient to convey the sheet P from the sheet reverse position 100 to the intermediate roller 56 by the reverse rotation of the switchback roller 53. have.

  In this embodiment, the sheet conveyance distance from the sheet reversal position 100 to the nip position of the intermediate roller 56 is 30 mm, and the roller diameter of the switchback roller 53 is φ16 mm. Accordingly, the sheet conveyance amount for one rotation of the switchback roller 53 is about 50 mm, which is sufficient for conveying the sheet P from the sheet reversal position 100 to the intermediate roller 56. For this reason, in the present embodiment, the accumulator gear 84 is provided with the number of teeth required to rotate the switchback roller 53 by approximately one rotation.

  The accumulator gear 84 is provided with an accumulator spring 85 that stores a spring force (elastic force) for urging the accumulator gear 84 to reversely rotate the switchback roller 53. Then, as shown in FIG. 4, the force accumulation gear 84 rotates in the direction of the arrow as the switchback roller 53 rotates forward, and the force accumulation spring 85 follows the phase of the force accumulation gear 84 that changes accordingly. The spring pressure of the spring 85 is increased. Note that the spring pressure of the force accumulation spring 85, which is a force accumulation member that elastically accumulates the reverse driving force to reversely rotate the switchback roller 53, is necessary for the switchback roller 53 to convey the sheet P in the reverse direction. It is set to a sufficient pressure against the torque. That is, the accumulation force of the accumulation spring 85 includes the operation amount of the accumulation gear 84 with respect to the conveyance amount necessary for rotating the switchback roller 53 and conveying the sheet P from the sheet reverse position 100 to the intermediate roller 56. Is set to

  The switchback roller 53, the drive gear 92, the force accumulation gear 84, the force accumulation spring 85, the second swing gear 83, the solenoid 82, the drive motor 90, and the like pull the seat and reverse the front-rear direction. The reversing unit 5A for conveying is configured. Reference numeral 5B denotes a driving force transmission unit that is disposed between the switchback roller 53 and the power storage spring 85, and transmits the normal driving amount of the switchback roller 53 to the power storage spring 85 when the switchback roller 53 rotates forward. is there. In addition, when the switchback roller 53 is reversely rotated, the driving force transmission unit 5B transmits the reverse driving force stored in the accumulator spring 85 to the switchback roller 53. The drive gear 92, the accumulator A gear 84 and a second swing gear 83 are included.

  Next, the switchback discharge (conveyance) operation of the sheet by the reversing unit 5A configured as described above will be described. The sheet P on which image formation has been completed is conveyed from the first conveyance path 101 to the switchback roller 53 by the intermediate roller 51 shown in FIG. At this time, the arrival of the leading edge of the sheet P is detected by the sheet detection sensor 54 arranged at substantially the same position as the sheet reversal position 100, and the control unit 250 drives via the driver 251 shown in FIG. The motor 90 is driven. Further, the control unit 250 supplies power to the solenoid 82 via the driver 251 to turn on the solenoid 82.

  Thereby, the first and second gears 81a and 81b of the motor gear 91 and the first swing gear 81 shown in FIG. 3 rotate, and the holder 81c swings upward. Along with this, the second gear 81b of the first swing gear 81 meshes with the drive gear 92, and the switchback roller 53 starts to rotate in the forward rotation direction indicated by the arrow. Further, in conjunction with the rotation of the switchback roller 53, the second rocking gear 83 and the power storage gear 84 start to rotate, and when the switchback roller 53 makes one rotation, the power storage gear 84 is moved as shown in FIG. In this state, the spring pressure of the accumulator spring 85 is maintained in a phased state. In addition, since the accumulating gear 84 is a toothless gear, after the switchback roller 53 rotates approximately once, the accumulating force is not increased and the accumulated force is not released.

  By such rotation of the switchback roller 53, the sheet P is conveyed in the direction of receiving from the first conveyance path 101 by the switchback roller 53, and the passage of the rear end is detected by the sheet detection sensor 54. As described above, when the sheet detection sensor 54 detects the trailing edge of the conveyed sheet P, the control unit 250 turns off the solenoid 82. As a result, the holder 81c swings downward, the meshing between the second gear 81b of the first swing gear 81 and the drive gear 92 is released, and the drive transmission from the drive motor 90 to the drive gear 92 is cut off.

  Here, at the moment when the engagement of the first swing gear 81 with the second gear 81 b is released, the switchback roller 53 becomes free, so that the rotational torque becomes smaller than the rotational torque due to the spring pressure of the accumulator spring 85. The spring pressure of the accumulation spring 85 is released. As a result, the switchback roller 53 is rotated in the reverse direction by one rotation by the spring pressure stored by the accumulating spring 85, and the sheet P is conveyed in the reverse direction to the second conveyance path 102. And transferred to the intermediate roller 56. As described above, when the spring pressure of the accumulator spring 85 is released, the sheet P is conveyed by the conveyance of the intermediate roller 56 while being nipped by both the reverse switchback roller 53 and the intermediate roller 56. .

  In this way, when the sheet P is reversed and conveyed, the sheet P is conveyed together with the intermediate roller 56 while being nipped by the switchback roller 53, so that various skews and jams due to sheet conveyance resistance are not generated. A sheet having a length can be conveyed. After releasing the spring pressure of the accumulating spring 85, that is, after releasing the accumulating force (after releasing the reverse driving force), the switchback roller 53 is in the direction opposite to the arrow shown in FIG. 3 by the sheet P conveyed by the intermediate roller 56. Followed rotation. When the switchback roller 53 rotates in the reverse direction in this way, the second swing gear 83 moves upward, and thereby the drive transmission from the switchback roller 53 to the power storage gear 84 is cut off.

  As described above, in this embodiment, after the predetermined amount of reverse driving force is stored in the power storage spring 85, the reverse driving force is kept constant even if the switchback roller 53 continues to rotate forward. I am doing so. Accordingly, the switchback roller 53 can always nip the sheet regardless of the length of the sheet being conveyed, and sheet skew and conveyance jam due to sheet conveyance resistance can be prevented. In addition, since the forward drive amount of the switchback roller necessary to store the reverse drive force can be set according to the shortest sheet to be conveyed, even when the sheets are conveyed continuously, It becomes possible to obtain an optimum conveyance pitch for each sheet length. Thereby, it is possible to optimize productivity as an image forming apparatus.

  As described above, in the present embodiment, during the forward rotation of the switchback roller 53, after the accumulator spring 85 stores a predetermined amount of reverse driving force, the stored predetermined amount of reverse driving force is maintained. I am doing so. As a result, the sheet can be reversed and conveyed without causing skewing or jamming and without reducing productivity. In this embodiment, the swinging gear 83 is used to prevent the driven rotation of the switchback roller 53 from being transmitted to the accumulator gear 84 when the switchback roller 53 is driven to rotate. A one-way rotation mechanism may be used instead of the gear 83. In the above description, the reversing unit using the power accumulation gear 84 has been described as an example. However, the same effect can be obtained by using the rack 86 as shown in FIG. be able to.

  Next, a second embodiment of the present invention will be described. FIG. 7 is a diagram illustrating a configuration of a reversing unit provided in the sheet conveying apparatus according to the present embodiment. In FIG. 7, the same reference numerals as those in FIG. 3 described above indicate the same or corresponding parts. In FIG. 7, reference numeral 87 denotes an accumulative full-circumference gear that is an all-round gear without missing teeth that meshes with the switchback roller 53, and 88 denotes an accumulator full-circumference gear 87 so as to reversely rotate the switchback roller 53. It is an accumulator torsion spring as an example of the elastic member to be urged. Here, a plurality of locking pieces 87 a that lock one end of the power storage torsion spring 88 are concentrically provided on the side surface of the power storage circumferential gear 87.

  Then, one end is locked to one of the locking pieces 87a, and the force accumulation torsion spring 88 is attached in a direction to reverse the switchback roller 53 with the other end fixed to a fixing portion (not shown). It is attached to the shaft 87b of the accumulator full-circumference gear 87 in such a direction that it is energized. Note that the spring pressure of the accumulator torsion spring 88 is set to a pressure sufficient for the torque required for the switchback roller 53 to convey the sheet P in the reverse direction.

  Next, the switchback discharge (conveyance) operation of the sheet by the reversing unit 50A provided with such an accumulating all-around gear 87, an accumulating torsion spring 88, and the like will be described. When the switchback roller 53 rotates in the direction indicated by the arrow, the accumulator full-circumference gear 87 starts to rotate via the second oscillating gear 83 in conjunction with the normal rotation. Winding in the winding direction increases the spring pressure of the accumulator torsion spring 88. Here, since the force-accumulating torsion spring 88 is attached to the shaft 87b of the force-accumulating full-circumference gear 87, when one end is wound in the spring winding direction with the rotation of the force-accumulating full-circumference gear 87, As the angle between the one end and the other end widens, the length from the rotation center to the spring end becomes shorter.

  Then, when the accumulator full circumference gear 87 is rotated by an amount capable of rotating the switchback roller 53 substantially once, the end of the accumulator torsion spring 88 is disengaged from the locking piece 87a of the accumulator full circumference gear 87, It moves to the locking piece 87a on the downstream side in the next rotation direction. This operation is continuously performed while the accumulator full circumference gear 87 continues to rotate. That is, after the accumulating torsion spring 88 has accumulated a predetermined amount of reverse driving force, one end of the accumulating torsion spring 88 is rotated in the rotational direction of the accumulating circumferential gear 87 along with the rotation of the accumulating circumferential gear 87. Are sequentially locked to different locking pieces while moving in the opposite direction. Thus, even if the switchback roller 53 continues to rotate forward after the accumulated reverse driving force reaches a predetermined amount, both ends of the accumulating torsion spring 88 regardless of the amount of rotation of the accumulating full circumference gear 87. The supporting positions of the parts are kept constant with respect to each other. As a result, the accumulated force torsion spring 88 is maintained in a state in which the stored reverse drive force does not increase and the reverse drive force is not released.

  As described above, in the present embodiment, during the forward rotation of the switchback roller 53, after the accumulating torsion spring 88 stores a predetermined amount of reverse driving force, the angle formed by the one end and the other end is determined. The switchback roller 53 is configured to be constant even if it continues normal rotation. As a result, a predetermined amount of reverse driving force stored can be maintained, and the sheet can be reversed and conveyed without causing skewing or jamming and without reducing productivity. In the above description, the accumulator torsion spring 88 is used as the elastic member, but a mainspring spring may be used.

  Next, a third embodiment of the present invention will be described. FIG. 8 is a diagram illustrating a configuration of a reversing unit provided in the sheet conveying apparatus according to the present embodiment. In FIG. 8, the same reference numerals as those in FIG. 7 described above indicate the same or corresponding parts. In FIG. 8, reference numeral 120 denotes a torque limiter that is provided on the rotating shaft of the accumulator omnidirectional gear 89 and is connected to the accumulator omnidirectional gear 89. One end of the accumulator torsion spring 88 is connected to the driven side of the torque limiter 120. A receiving piece 121 is provided. Here, the torque limiter 120 is set such that slip occurs when the accumulated force by the accumulated force torsion spring 88 reaches a torque necessary to reversely rotate the switchback roller 53.

  Next, the switchback discharge (conveyance) operation of the sheet by the reversing unit 50A including such a torque limiter 120 will be described. When the switchback roller 53 normally rotates in the direction indicated by the arrow, the accumulator full-circumference gear 87 starts to rotate via the second swing gear 83 in conjunction with the normal rotation. Then, when the accumulator full circumference gear 89 starts to rotate in this way, the connected torque limiter 120 starts to rotate without slipping, and the end of the accumulator torsion spring 88 is wound in the winding direction of the spring, and the spring pressure is increased. To increase. Thereafter, when the accumulated force by the torsion spring 88 reaches a predetermined amount, the torque limiter 120 slips, and thereafter the support positions of both ends of the accumulated force torsion spring 88 regardless of the rotation amount of the accumulated force circumferential gear 89. Are kept in a fixed position relative to each other.

  In this way, by using the torque limiter 120, the reverse drive force increases even if the switchback roller 53 continues to rotate forward after the reverse drive force stored in the force accumulation torsion spring 88 reaches a predetermined amount. Without being reversed, and the reverse driving force is maintained in an unreleased state. Note that, by using the torque limiter 120 as in the present embodiment, the one end of the accumulator torsion spring 88 does not move, so that it is possible to prevent the occurrence of collision noise.

DESCRIPTION OF SYMBOLS 5 ... Sheet conveying apparatus, 5A ... Reversing part, 5B ... Driving force transmission part, 53 ... Switchback roller, 54 ... Sheet detection sensor, 56 ... Intermediate roller, 81 ... First swing gear, 82 ... Solenoid, 83 ... First 2 oscillating gears, 84 ... accumulating gear, 85 ... accumulating spring, 86 ... rack, 87 ... accumulating all-around gear, 88 ... accumulating torsion spring, 87a ... locking piece, 90 ... driving motor, 92 ... driving Gear 120, torque limiter 200, color laser printer 202, image forming unit 250, control unit P, sheet

Claims (9)

In the sheet conveying apparatus having a reversing unit that pulls in the sheet and reverses the front-rear direction,
The inversion part is
A sheet reversing and conveying member capable of reversing forward and reverse to convey the sheet drawn back to the reversing position for reversing the sheet by normal rotation and reversing the front-rear direction;
A power accumulation member that elastically stores a reverse driving force for reversing the sheet reverse conveying member according to a normal driving amount of the sheet reverse conveying member during normal rotation of the sheet reverse conveying member;
The sheet reversing and conveying member is disposed between the sheet reversing and conveying member, and during normal rotation of the sheet reversing and conveying member, the normal rotation driving amount of the sheet reversing and conveying member is transmitted to the force storing member, and the sheet reversing and conveying member is A driving force transmission unit configured to transmit the reverse driving force stored in the power storage member to the sheet reverse conveyance member when reversely rotating;
The driving force transmission unit maintains a predetermined amount of reverse driving force stored in the power storage member after the power storage member stores a predetermined amount of reverse driving force during normal rotation of the sheet reverse conveying member. It is comprised so that the sheet conveying apparatus characterized by the above-mentioned. A drive source for normally rotating the sheet reversal conveying member;
A drive transmission switching member that is provided between the sheet reversal conveyance member and the drive source, and selectively transmits the drive of the drive source to the sheet reversal conveyance member when the sheet is pulled in;
A trailing edge detection unit that detects a trailing edge of the sheet conveyed by normal rotation of the sheet reversal conveying member,
When reversing the sheet reversing conveyance member, the sheet reversal by the drive transmission switching member is performed based on a signal from the rear end detection unit so as to release the reverse driving force stored in the power accumulation member. The sheet conveying apparatus according to claim 1, wherein the driving transmission of the driving source to the conveying member is cut off. The driving force transmission unit is
A drive gear that rotates integrally with the sheet reversal conveying member;
An accumulator gear that transmits a normal rotation drive amount to the accumulator member as the drive gear rotates;
Provided between the drive gear and the accumulator gear, and when the sheet reverse conveying member rotates in the forward direction, the normal rotation drive amount of the sheet reverse conveying member is transmitted to the force accumulation gear, and the sheet reverse conveying member is A transmission gear for transmitting the rotation of the force-accumulating gear by the reverse-rotation driving force stored in the energy-accumulating member to the driving gear when reversing,
Through the drive gear, the transmission gear, and the force accumulation gear, during the normal rotation of the sheet reverse conveyance member, the normal rotation drive amount of the sheet reverse conveyance member is transmitted to the force accumulation member, and the sheet reverse conveyance is performed. 3. The sheet conveying device according to claim 1, wherein when the member is rotated in reverse, the reverse driving force stored in the energy storing member is transmitted. The sheet reversing and conveying member is provided on the downstream side in the conveying direction after reversing the front and rear direction, and the sheet reversed and forwarded by the sheet reversing and conveying member is conveyed together with the sheet reversing and conveying member. A sheet conveying member,
When the sheet reverse conveying member continues to reverse by the sheet conveyed by the sheet conveying member after releasing the reverse driving force of the power accumulating member, the transmission gear transmits the force accumulation from the sheet reverse conveying member. 4. A sheet conveying apparatus according to claim 3, wherein said sheet conveying apparatus is provided so as to be movable to a position at which drive transmission to the gear is cut off. The power storage gear does not rotate when the sheet reversing conveyance member continues normal rotation after the power accumulation member stores a predetermined amount of reverse driving force during normal rotation of the sheet reversing conveyance member. 5. The sheet conveying apparatus according to claim 3 , wherein the sheet conveying apparatus is configured. One end of the power storage member is locked to the power storage gear and the other end is fixed, and the angle formed by the one end and the other end increases as the power storage gear rotates. Is an elastic member arranged as follows:
After the predetermined amount of reverse driving force is accumulated during normal rotation of the sheet reverse conveying member, the angle formed by the one end and the other end is determined so that the sheet reverse conveying member rotates forward. 6. The sheet conveying apparatus according to claim 3 , wherein the sheet conveying apparatus is configured to be constant even if continued. A plurality of locking pieces for locking one end of the elastic member to the power storage gear are provided concentrically,
After the elastic member stores a predetermined amount of reverse driving force, one end portion of the elastic member changes while moving in the direction opposite to the rotation direction of the power storage gear as the power storage gear rotates. The sheet conveying device according to claim 6, wherein the sheet conveying device is configured to be sequentially locked to the locking pieces.   A torque limiter is provided between the force-accumulating gear and the elastic member so that the angle formed by the one end and the other end is constant even if the sheet reversal conveying member continues to rotate forward. The sheet conveying apparatus according to claim 6.   An image forming unit, and the sheet conveying device according to any one of claims 1 to 8, wherein the sheet on which an image has been formed by the image forming unit is drawn and conveyed in a reverse direction. An image forming apparatus.

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