JP3819410B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a transfer apparatus used in an image forming apparatus, and more particularly to an apparatus for satisfactorily transferring an image formed on a recording medium to a sheet which is a transfer material being conveyed. The present invention relates to an image forming apparatus including a plurality of transfer units and a transport device that transports a sheet to these transfer units.

  In an image forming apparatus using an electrophotographic system or the like, a desired image is formed with a toner as a colorant on a photoconductor as a recording medium, and this is transferred to a sheet as a transfer material which is appropriately conveyed. I try to transcribe it. Therefore, a color image can be obtained by using a plurality of colors of toner.

  In recent years, the color orientation of offices has become stronger, and color image forming apparatuses have been widely used. One method for forming this color image is to form a toner image for each color on a photoconductor and sequentially superimpose it on a sheet to obtain a color image of a desired color. In this case, the sheet is repeatedly conveyed to a position where it comes into contact with the photosensitive member a plurality of times. For this reason, in forming a color image, it takes 3 or 4 times as compared to the case of a single color because an image is formed using toner of three or four colors.

  Therefore, a color image is obtained at the same speed as the monochrome image formation speed by providing a photoreceptor corresponding to each color and sequentially transporting the sheet of toner images formed on the photoreceptor along the transport path. There are three or four tandem photosensitive drums that can be used. This is because, for example, four photosensitive drums are arranged side by side at regular intervals, and toner images are formed on the respective photosensitive drums using yellow, magenta, cyan, and black toners. The toner images formed sequentially are transferred at respective transfer positions to obtain a color image.

  For example, in the quadruple tandem system, a sheet is held on a conveyance belt, and the toner image is transferred by feeding the sheet to the transfer position of each photoconductor drum so as to be in contact with the photoconductor.

  In addition to forming a color image, for example, image formation with black toner is desired. That is, in the case of a monochromatic image, an image with black toner that makes it very easy to recognize the image in terms of contrast and the like is desired compared to an image with other color toners. Therefore, at the time of such monochromatic image formation, toner images are not formed on the other three photosensitive drums of yellow, magenta and cyan, but a toner image in black is formed and transferred onto the sheet, and the black toner image is formed. I have an image.

  Also in the formation of the monochrome image, the sheet is conveyed while being held on the conveying belt so as to face each transfer position of the four photosensitive drums. For this reason, the surface of the conveyor belt always remains dirty with toner or the like.

  Contamination of the conveying belt may cause contamination on the back surface opposite to the image forming surface of the sheet or transfer unevenness when transferring a toner image from the surface of the photosensitive drum to the surface of the sheet. The contamination on the surface of the conveyor belt is mostly due to toner adhesion. If roughly classified, the toner scattered from the developing means, that is, the developer containing the developer, is disposed on the conveyor belt so as to face the photosensitive drum. And the toner deposited on the surface of the photosensitive drum is transferred and adhered to the surface of the conveying belt.

  In the toner adhesion on the surface of the conveyance belt, the most serious stain is that when a sheet conveyance failure occurs, the untransferred sheet remaining on the surface of the photosensitive drum is removed after removing the sheet having the conveyance failure on the conveyance belt. That is, the toner image adheres to the surface of the conveyance belt.

  Therefore, in the image forming apparatus described in Japanese Patent Laid-Open No. 3-288173, at the time of black image formation, the conveyor belt is separated from the photosensitive drum of the remaining image forming unit not involved in image formation to prevent toner contamination. Like to do. The configuration described in this publication will be described with reference to FIG.

  FIG. 7 shows a color image forming apparatus using a laser beam printer, which employs a photoconductor quadruple tandem system. In this image forming apparatus, four image forming units having a developing device and the like are provided around the photosensitive drum, and a toner image formed on each image forming unit is transferred to each photosensitive member. It is configured to be transferred onto a sheet that is held and conveyed on an endless conveyance belt that moves and passes so as to contact the body drum.

  In the figure, photosensitive drums 101M, 101C, 101Y, and 101K are arranged in image forming portions Pm, Pc, Py, and Pk that form images of magenta, cyan, yellow, and black, respectively. The body drum is rotatable in the direction of the arrow. Further, around each photosensitive drum 101M, 101C, 101Y and 101K, chargers 102M, 102C, 102Y and 102K, scanning optical devices 103M, 103C, 103Y and 103K, and developing devices 104M, 104C, 104Y and 104K, Cleaners 105M, 105C, 105Y and 105K are sequentially arranged along the rotation direction of the photosensitive drum. Further, transfer units 106M, 106C, 106Y, and 106K are arranged to face each other below the photosensitive drums 101M, 101C, 101Y, and 101K.

  A driving roller 108 and a driven roller arranged at intervals covering the arrangement distance of the photosensitive drums 101M to 101K so that an endless conveying belt 107 moves and passes between the photosensitive drums and the transfer units. It is stretched between 109. The transport belt 107 is driven to travel in the direction of the arrow by the rotational drive of the drive roller 108.

  On the right side of the transport belt 107, a paper feed cassette 110 for feeding the sheet P to the transport belt 107 is disposed. Therefore, when an image forming operation is started, when a color image is formed, the image forming operation is executed by the first magenta image forming unit Pm, and the magenta toner image formed on the photosensitive drum 101M is transferred to the transfer position. In synchronization with the arrival timing, the sheet P fed from the paper feed cassette 110 is held on the transport belt 107 and sent to the transfer unit 106M which is the first transfer position.

  Then, the sheet P is sequentially conveyed by the conveying belt 107, and a toner image formed in the order of the image image forming portions Pc, Py, Pk is superimposed on the sheet every time it passes the transfer position. The sheet P that has passed all these transfer steps is separated from the conveying belt 107 and fed to the fixing device 111 via the guide belt 112. In the fixing device 111, the toner images superimposed on the sheet P are simultaneously heat-fixed, and a desired color image is formed on the sheet.

  The above is an image forming operation using a full-color image. However, in the case of forming an image using a single color, particularly black toner, the conveyance belt 107 is provided on a support table 113, and the support table 113 is rotationally eccentric. It is supported by cams 114a and 114b. In particular, the support table 113 is provided so as to be rotatable about the rotation shaft of the drive roller 108 or the rotation shaft of the driven roller 109 for driving the transport belt 107.

Therefore, when image formation is performed using the image forming unit Pk, the eccentric cam 114b on the side opposite to the drive roller 108 is rotated in the Q direction, so that the support base 112 is rotated in the R direction. In the state where the photosensitive drum is separated from the conveyor belt 107, image formation with black toner is performed. That is, the photosensitive drum 101K is brought into contact with the transport belt 107, and the formed toner image is transferred onto the transported sheet P held by the transport belt 107, so that an image with black toner can be obtained.
JP-A-3-288173 (published on December 18, 1991)

  As described above, by providing a conveyance belt for conveying a sheet, which is a transfer material having a configuration described in JP-A-3-288173, provided in a conventional image forming apparatus to each transfer position, toner on the belt is provided. Dirt caused by can be reduced.

  However, since all the photosensitive drums in the image forming unit cannot be separated from the conveyance belt, toner contamination on the conveyance belt cannot be prevented in the image forming unit at the time of standby or correction for copying.

  When handling a sheet with a conveyance failure by the conveyance belt, it is difficult to remove the sheet because the sheet is partially sandwiched between the photosensitive drum and the transfer belt when the sheet with the conveyance defect is removed from the inside of the apparatus. Thus, if the sheet is forcibly removed, the transport belt and the surface of the photoreceptor may be damaged. Further, the sheet is torn and a part of the torn sheet remains, which hinders the conveyance of the sheet at the next image formation.

  In view of the above-described problems, the present invention enables a conveyance belt that sequentially conveys sheets to a plurality of image forming units arranged in parallel to be separated from a photoreceptor of the image forming unit by simple means. This makes it easy to remove the sheet.

  In order to solve the above problems, an image forming apparatus according to the present invention is provided with a plurality of image forming portions for forming a toner image on the surface of the photoreceptor side by side, and the toner on the surface of the photoreceptor of these image forming portions. In order to transfer the image onto the transfer material, a transfer portion is provided opposite to each image forming portion, and one transfer material is sequentially transferred to each transfer position formed by each image forming portion and each transfer portion. In the image forming apparatus provided with the conveying belt for conveying, a first rotating member that is disposed on the conveying material transfer side on the conveying belt and is provided to be rotatable in one direction around the first axis. And a second rotating member that is disposed on the transfer belt on the conveying belt and is provided so as to be rotatable in one direction around the second axis. The first rotating member includes A plurality of the transfer portions for transferring the color toner image are provided, and the second rotating member is black. The transfer unit for transferring the toner image is provided, the first shaft is provided on the carry-out side of the first rotating member, and the first rotating member is rotated in one direction around the first axis. Thus, the transfer unit provided on the first rotating member is rotated together with the first rotating member, and the first rotating member side portion of the conveying belt is separated from the image forming unit. It is characterized by being possible.

  In addition, the image forming apparatus of the present invention is provided with a plurality of image forming portions that form toner images on the surface of the photoreceptor in parallel, and the toner images on the surface of the photoreceptor of the image forming portions are transferred onto a transfer material. In order to achieve this, a transfer unit is provided opposite to each image forming unit, and a transfer belt that sequentially transfers one transfer material to each transfer position formed by each image forming unit and each transfer unit is provided. In the image forming apparatus, the transfer member is disposed on the conveying belt on the carry-in side, and is provided so as to be capable of rotating in one direction around the first axis while supporting the plurality of transfer units that transfer the color toner images. The first rotation member and the transfer member on the conveying belt are disposed on the carry-out side of the transfer belt, and support the transfer unit for transferring the black toner image so as to be rotatable in one direction around the second axis. A second rotating member provided, and the first shaft carries the first rotating member. The second shaft is provided at a position different from the first shaft, and the first rotation member is rotated in one direction around the first shaft, whereby the first rotation is performed. The plurality of transfer portions provided on the member are rotated together with the first rotating member so that the conveying belt can be separated from the photosensitive member forming the color toner image, and the second rotating member is set to the second rotating member. By rotating in one direction around the axis, the transfer portion provided on the second rotating member is rotated together with the second rotating member, and the conveying belt forms the black toner image. It is characterized by being able to be separated from the body.

  According to the image forming apparatus of the present invention, when a plurality of image forming units are arranged side by side, when a toner image is transferred onto a transfer material, when the image formation is performed using the individual image forming unit, the transfer material The conveying belt for conveying the toner can be easily contacted and separated from the image forming portion, the toner can be removed, and the jammed transfer material can be easily removed.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the entire image forming apparatus according to the present invention.

  First, referring to FIG. 1, an image forming apparatus according to the present invention will be described. Although FIG. 1 shows an image forming apparatus using a laser beam printer, the present invention is not limited thereto. For example, the present invention can be applied to a digital color copying machine and a normal analog color copying machine.

  In the figure, the image forming apparatus 1 is provided with image forming portions Pa, Pb, Pc, Pd corresponding to at least four colors. The number of the image forming units is four in the following embodiment of the present invention, but the present invention can be applied when at least two or more image forming units are arranged in parallel.

  In addition, a paper feeding device 2 is provided on one side, that is, the right side of the image forming apparatus 1, and a discharge unit 3 for discharging a sheet as a transfer material is provided on the opposite side. A fixing device 4 for heating and fixing an unfixed toner image transferred on the sheet is provided adjacent to the discharge unit 3, particularly on the upstream side in the sheet conveyance direction.

  Between the paper feeding device 2 and the fixing device 4, the sheet P fed from the paper feeding device 2 passes through the transfer positions of the image forming portions Pa, Pb, Pc, Pd described above. As described above, a conveying unit 5 that holds and conveys the sheet P is disposed.

  The sheet feeding device 2 has a conventionally well-known configuration. For example, a large number of sheets P are accommodated in a sheet feeding cassette 20 that is detachably provided on the main body of the image forming apparatus 1. The sheets in the sheet feeding cassette 20 are fed one by one by the sheet feeding rollers 21 arranged to face each other. The fed sheet P is stopped at the position of the registration roller 22 disposed between the paper feed roller and the transport unit 5, and the first sheet P is conveyed through the transport unit 5 so as to be synchronized with the image forming operation. It is sent to the transfer position of the image forming portion Pa.

  Further, the discharge unit 3 includes a discharge roller 30 provided at a discharge port corresponding to the roller pair constituting the fixing device 4, and a discharge tray 31 for receiving the sheet P sent via the discharge roller 30 is provided. ing.

  The fixing device 4 is well known in the art, and its structure will be briefly described. A heat roller 41 whose surface is held at a temperature at which fixing is possible by a heater (not shown), and an appropriate pressure on the heat roller 41. And a pressure roller 42 that is press-contacted with the pressure roller.

  On the other hand, the image forming portions Pa, Pb, Pc, and Pd have substantially the same configuration, and only the color of the formed image is different. The image forming portions Pa, Pb, Pc, and Pd are means for forming toner images of, for example, magenta, cyan, yellow, and black. In the figure, the same parts are denoted by the same reference numerals, and the differences depending on the colors are distinguished by a, b, c and d.

  In view of the configuration of the image forming unit Pa, the image forming unit Pa includes a photoconductive drum 10a that is rotationally driven in the direction of arrow F. A charger 11a for uniformly charging the photosensitive surface of the drum, a developing device 12a for developing the electrostatic latent image formed on the surface of the photosensitive member, a transfer unit 13a for transferring the developed toner image to the sheet P described above, A cleaning device 14a for removing toner remaining on the surface of the photoconductor after the transfer is sequentially disposed in the rotational direction of the photoconductor drum.

  Further, an imaging lens 15a and a laser beam scanner 16a are provided above the photosensitive drum 10a. The laser beam scanner 16a has a conventionally known structure. In particular, the laser beam scanner 16a is for forming an image by magenta. The semiconductor laser is ON / OFF driven and controlled according to image data corresponding to the magenta, and is deflected through a rotating mirror (polygon mirror) or the like. Further, the photosensitive drum 10a is scanned in the rotation axis direction via an fθ lens or the like.

  In the image forming portions Pa, Pb, Pc, and Pd having the above-described configuration, the developing devices 12a, 12b, 12c, and 12d contain magenta, cyan, yellow, and black toners, respectively. In 16a, 16b, 16c and 16d, images of the respective color components, particularly latent images, are formed on the photosensitive member and developed.

  On the other hand, the sheet conveying means 5 for transferring the toner images formed by the image forming portions Pa, Pb, Pc, and Pd onto the sheet includes the sheet feeding device 2, particularly the registration roller 22 and the fixing device 4. And an endless sheet conveying belt 52 stretched between a driving roller 50 and a driven roller 51 provided so as to correspond to the above. The sheet conveying belt 52 is further provided with a driven roller 53 for stabilizing the belt conveyance and movable in the direction of the arrow X, and is further urged in that direction to apply an appropriate tension to the belt 52. It has a tension roller 54 having a compression spring 55 that acts to cause it to move.

  The sheet conveying belt 52 has a position corresponding to the driven roller 51 facing the sheet fed via the registration roller 22 in order to hold and convey the sheet P fed on the surface thereof. In addition, a sheet suction charger 56 is provided. Therefore, the conveyed sheet P is electrostatically attracted to and conveyed by the sheet conveying belt 52 by the action of the adsorption charger 56.

  Further, transfer units 13a, 13b, 13c, and 13d constituting the image forming units Pa, Pb, Pc, and Pd described above are arranged in the sheet conveying belt 52. It is provided in the support body 57 which is a 1st rotation member, and the support body 58 which is a 2nd rotation member. The first support member 57 particularly supports the transfer portions 13a, 13b, and 13c, and the second support member 58 supports the transfer portion 13d.

  The first support 57 is pivotally supported by a pivot shaft 59 provided on the side corresponding to the image forming portion Pc, particularly on the side opposite to the carry-in side to which the sheet P is fed. The second support 58 is pivotally supported by a rotation shaft 60 so that the side corresponding to the image forming unit Pd, particularly the side carried out from the sheet image forming unit Pd, can rotate. The first support 57 is supported by the circumferential surface (cam surface) of the eccentric cam 61 at a position opposite to the rotating shaft 59 side on the surface opposite to the supported transfer portion. Also in the second support body 58, the surface opposite to the similarly supported transfer portion is supported by the peripheral surface (cam surface) of the eccentric cam 62 at a position opposite to the rotation shaft 60. ing.

  In the eccentric cams 61 and 62, the transfer drums 13a, 13b, 13c and 13d are in the photosensitive drums 10a and 10b of the image forming portions Pa, Pb, Pc and Pd when the distance from the rotation shaft to the cam surface is the longest. , 10c and 10d, the sheet conveying belt 52 is brought into contact with a certain width so that it can be positioned in a transferable state.

  The transfer units 13a, 13b, 13c, and 13d may be configured by two cylindrical rollers, and transfer may be performed by applying a transfer voltage to the two rollers. Further, the roller may be provided simply for bringing the belt into contact with the photosensitive drum, and a transfer device for performing corona discharge (not shown) may be separately provided therebetween.

(Description of image forming operation)
The image forming apparatus according to the present invention is configured as described above, and the image forming operation will be described below. When forming a full-color image including black toner, the eccentric cams 61 and 62 are maintained in the state shown in FIG. 1, and the transfer portions 13a, 13b, 13c supported by the first and second supports 57, 58 are maintained. And 13d are positioned at the transfer position.

  In this state, the sheet P is rotated by the rotation of the paper feed roller 21 when the image forming operation is started, and one sheet is fed from the paper feed cassette 20. If the fed sheet leading edge is detected by a sheet leading edge detecting means (not shown), the photosensitive drums 10a, 10b, 10c and 10d of the image forming portions Pa, Pb, Pc and Pd are rotated by the signal. Start. The front end of the fed sheet P waits at the position of the registration roller 22 and is stopped.

  Upon receiving the detection signal, the driving roller 50 in the sheet conveying means 5 also rotates, and the sheet conveying belt 52 travels in the direction of arrow Z. As a result, the sheet conveying belt 52 sequentially passes through the image forming portions Pa, Pb, Pc, and Pd. Then, image forming operations for the photosensitive drums 10a, 10b, 10c, and 10d are sequentially started at a predetermined timing as the driving base point of the registration roller 22, that is, the conveyance start base point of the sheet P. First, an image of magenta toner is formed on the photosensitive drum 10a which is the first image forming unit Pa, and then an image of cyan toner is formed on the photosensitive drum 10b of the second image forming unit Pb. Then, the yellow toner image is assigned to the photosensitive drum 10c of the third image forming portion Pc, and the black toner image is finally assigned to the photosensitive drum 10d of the fourth image forming portion Pd. It is formed by shifting.

  Here, the deviation in the timing of image formation for each color is set equal to the time required for the sheet conveying belt 52 to move from the transfer unit 13a to the next transfer unit 13b. In this case, the transfer portions 13a, 13b, 13c, and 13d are arranged at equal intervals.

  Then, the sheet P is adsorbed on the surface of the sheet conveying belt 52 by the action of the adsorption charger 56 and is sent to the first image forming portion Pa. At the timing when the leading edge of the sheet is fed to the transfer position facing the transfer portion 13a, the leading edge of the magenta toner image formed on the photosensitive drum 10a reaches, and the transfer of the toner image is started. Thereafter, the sheet P conveyed in the same manner by the sheet conveying belt 52 sequentially passes through the transfer portions of the second, third and fourth image forming portions Pb, Pc and Pd, so that the toner images of the respective colors are sequentially obtained. It is transferred and superimposed. Then, when the sheet P passes through the transfer portion of the final fourth image forming portion Pd, the electrostatic adsorption state is released from the sheet sheet transport belt 52 by an AC static eliminator (not shown) and separated from the belt. Then, it is sent to the fixing device 4.

  The sheet P fed to the fixing device 4 has the toner images of the respective colors sequentially transferred onto the upper surface of the sheet P, which is heated and fixed, and a color image is synthesized. The sheet P after the fixing is sent to the discharge tray 31 via the discharge roller 30 at the discharge port.

(Description according to one embodiment of the present invention)
Next, in the image forming apparatus having the above-described configuration according to the present invention, the operation in the embodiment of the mechanism for contacting and separating the image forming portions Pa, Pb, Pc and Pd by the sheet conveying belt 52, That is, a mechanism and its operation for contacting and separating the photosensitive drums 10a, 10b, 10c and 10d of each image forming unit will be described.

  The sheet conveying belt 52 constituting the sheet conveying means 5 is stretched between a driving roller 50 and a driven roller 51 disposed on both sides. Further, moderate tension is applied by the driven roller 53 and the tension roller 54, and normal conveyance in the direction of the arrow Z, that is, traveling driving is performed by the driving roller 50.

  The driving roller 50 and the driven rollers 51 and 53 are rotatably supported by a support base (not shown in FIG. 1) provided so as to be able to be pulled out from the main body of the image forming apparatus 1 although not shown. Only the drive roller 50 is provided so as to be connectable to a drive unit on the image forming apparatus 1 main body side. The tension roller 54 is supported so as to be movable in the arrow X direction with respect to the support base, and is always supported by a compression spring 55 interposed between the support base-side fixing portion 55-1 and the roller 54 (not shown). A biasing force in the Y direction is applied. As a result, an appropriate tension is applied to the sheet conveying belt 52, and the contact state with the driving roller 50 is kept good.

  On the other hand, the transfer portions 13a, 13b, 13c, and 13d of the image forming portions Pa, Pb, Pc, and Pd are divided into color transfer and black transfer, respectively, and the first support 57 and the second transfer respectively. A support 58 is divided and held. That is, the transfer portions 13a, 13b, and 13c held by the first support 57 are configured as a color transfer unit, and the transfer portion 13d held by the second support 58 is a black transfer unit.

  On the surface opposite to the transfer portion holding surface of the first support member 57 that is the color transfer unit and the second support member 58 that is the black transfer unit, an eccentricity that is rotationally driven for contacting and separating the sheet conveying belt 52. Cams 61 and 62 are provided. Accordingly, since the first and second support members 57 and 58 are rotatably supported by the shaft portions 59 and 60, the difference in the distance from the rotation shaft to the cam surface is caused by the rotation of the eccentric cams 61 and 62. It will be rotated by.

  In the full color image forming mode including normal black toner, the rotational positions of the eccentric cams 61 and 62 are maintained in the state shown in FIG. That is, the first and second supports 57 and 58 are supported and positioned by the cam surface having the longest distance from the rotation shaft of each eccentric cam 61 and 62. As a result, the sheet conveying belt 52 contacts the photosensitive drums 10a, 10b, 10c, and 10d of the image forming portions Pa, Pb, Pc, and Pd with a certain width at the transfer portions 13a, 13b, 13c, and 13d. In this state, a full color image forming operation is performed.

  When the monochrome image formation mode, that is, the black image formation mode is selected from the color image formation mode described above, the eccentric cam 61 is driven to rotate in the direction of arrow S, and the smallest cam surface from the rotation axis is the first cam surface. The support body 57 is rotated to a position where it is supported. That is, the eccentric cam 61 is rotated by 180 ° and stopped. Thereby, as shown in FIG. 1, the first support member 57 is rotated about the rotation shaft 59 in the direction of arrow T, and as shown in FIG. 2, the transfer portions 13a, 13b, 13c, which are color transfer units, are moved. Separated from the photosensitive drums 10a, 10b, and 10c. Therefore, the sheet conveying belt 52 is separated from the photosensitive drums 10a, 10b, and 10c.

  At this time, the tension roller 54 is moved in the direction of the arrow X by the action of the compression spring 55, applies a biasing force in the Y direction to the sheet conveying belt 52, and maintains a good tension state.

  In this case, the fixing portion 55-1 that fixes (locks) one end of the compression spring 55 may be provided on the first support body 57 side without being fixed to a support base (not shown). At the same time, the fixing portion 55-1 is rotated, whereby the tension of the sheet conveying belt 52 by the tension roller 54 can be maintained in a better tension state, particularly in the color image forming mode.

  In the state where the color transfer unit is separated by the above operation, an image forming operation in a single color, that is, black is performed. In this case, the sheet P is attracted to and conveyed by the sheet conveying belt 52 under exactly the same conditions as the color image forming operation by the adsorption charger 56 facing the unchanged driven roller 51. In the black image forming portion Pd, since the transfer portion 13d is maintained in contact with the photosensitive drum 10d under a certain condition, stable image formation can be performed without any change in the conditions.

  Next, a color image forming mode using color toners that is different from the single color image forming mode using black and different from the full color image forming mode including black will be described. In this case, in FIG. 1, the three colors magenta, cyan, and yellow are formed as colors. However, the present invention is not limited to this, and when a single color image is formed with one color, the image is formed with a color toner corresponding to one color. Any one of the parts Pa, Pb, and Pc is provided.

  Therefore, in forming a color image including a single color image using color toner in FIG. 1, the eccentric cam 62 is driven to rotate 180 ° in the direction of the arrow Q, and the second support 58 is moved by the shortest cam surface from the rotation axis. To support. As a result, the second support 58 is rotated in the direction of the arrow R, and the sheet conveying belt 52 is separated from the photosensitive drum 10d of the image forming unit Pd as shown in FIG. The looseness of the sheet conveying belt 52 during the separation is alleviated by the tension roller 54.

  Accordingly, the sheet conveying belt 52 is stretched with an appropriate tension by the action of the tension roller 54, contacts the photosensitive drums 10a, 10b, and 10c of the image forming portions Pa, Pb, and Pc, and an image of a necessary color is displayed. It will be ready to form. Even in this case, since the contact state between the sheet conveying belt 52 and the photosensitive drums 10a, 10b, 10c and the like is maintained constant, the transfer conditions and the like do not change.

  When the fixing portion 55-1 at one end of the compression spring 55 is provided on the first support 57 side, the tension roller 54 moves in the X direction, so that a constant tension state is always maintained. It cannot act on the sheet conveying belt 52. However, when the sheet conveying belt 52 is separated from only the photosensitive drum 10d of the image forming unit Pd using black toner, the amount of movement of the sheet conveying belt 52 is larger than the case where the preceding color unit is separated. Small and the belt tension state does not change much. Therefore, even if the position of the spring 55 is rotated in the Q direction of the rotary cam 62 and does not change, the sheet conveying belt 52 is in a certain tension state within a predetermined range.

  The tension state of the sheet conveying belt 52 will be described in detail in the description of another embodiment.

  As described above, by setting the image forming mode using color toner, only the image forming portion Pd using black toner is set to a non-image forming state. Image formation, for example, red image formation by magenta and yellow, green image formation by cyan and yellow, and the like are performed. Further, it is possible to perform color image formation excluding black toner as necessary.

  Finally, an operation during standby of the image forming apparatus, aging, or occurrence of a sheet jam trouble, particularly a state of separation of the sheet conveying belt 52 from the photosensitive drum will be described.

  In this case, the rotating cam 61 and the rotating cam 62 are rotated in the directions of arrows S and Q in FIG. That is, the sheet conveying belt 52 is rotated so as to be separated from the image forming portions Pa, Pb, Pc, and Pd. As a result, the first and second supports 57 and 58 are rotated as shown in FIG. 3, and the sheet conveying belt 52 is separated from the photosensitive drums 10a, 10b, 10c and 10d.

  In this state, correction aging is performed, and toner contamination from the photosensitive drum of the sheet conveying belt 52 is prevented. Further, in the case of sheet jam trouble, since the belt 52 is completely separated from the photosensitive drum, the sheet removing process is simplified, and there is no risk of damaging the sheet or damaging the surface of the sheet conveying belt or the photosensitive drum. .

(Another embodiment of applying tension)
Next, another embodiment of tension application according to the present invention will be described below. In this embodiment, the tension state of the sheet conveying belt 52 can be maintained constant in each image forming mode.

  In the example described in the previous embodiment, the looseness of the sheet conveying belt 52 is reduced by the action of the spring 55 of the tension roller 54, and the belt 52 is maintained so as to act at a constant tension. Further, a fixing portion at one end of the spring 55 is provided on the first support 57 side, and the fixing portion 55-1 is similarly moved in the X direction in association with the rotation of the first support 57, and the spring 55 The tension length was kept constant, and the tension state was kept constant.

  Separately from this, as shown in FIG. 4, a fixing portion 55-1 in which one end of the spring 55 is fixed to a support base (not shown in FIG. 4) that supports the sheet conveying belt 52. The fixed portion 55-1 is provided so as to be movable in the X direction. The fixed portion 55-1 is moved in the X direction using the cam surface of the rotational eccentric cam 61 as shown in FIG. I am trying to move. As a result, the length of the compression spring 55 between the tension roller 54 and the fixed portion 55-1 is constant in a state where the sheet conveying belt 52 is separated from the image forming portions Pa, Pb, and Pc and in a contact state. Therefore, the tension state acting on the sheet conveying belt 52 can be kept constant.

  Further, the cam surface of the rotation eccentric cam 61 is used to move the fixed portion 55-1 of the spring 55 in conjunction with each other, but the second rotation that rotates in conjunction with the rotation shaft 63 of the rotation cam 61 is performed. An eccentric cam or the like may be provided, and the fixed portion 55-1 may be moved in the X direction on the surface of the second rotational eccentric cam.

  When configured in this manner, a third rotational eccentric cam is provided which is interlocked with the rotation of the rotational eccentric cam 62 that supports the second support 58, and the third rotational eccentric cam also includes the fixing portion 55-. 1 can also be moved in the X direction.

  In addition, since the distance that the sheet conveying belt 52 is separated from the photoconductive drum 10d of the image forming unit Pd is short in the rotation by the rotating cam 62, the fixing unit 55- The cam surface of the third rotational eccentric cam is formed so that the distance by which 1 is moved in the X direction is shortened. In such a configuration, the tension state of the sheet conveying belt 52 can be kept constant even in the color image forming mode.

  Here, when the single color unit and the color unit are separated from the image forming portions Pa, Pb, Pc and Pd, the fixed portion 55-1 is naturally moved by the second rotational eccentric cam. That is, the second rotational eccentric cam and the third rotational eccentric cam rotate in conjunction with each other, but the distance over which the fixed portion 55-1 is moved by the second rotational cam is substantially larger. In this case, since it is not directly related to image formation, there is no problem even if the tension state of the sheet conveying belt 52 is slightly changed, and the sheet conveying belt 52 maintains an appropriate tension action.

(Embodiment according to the present invention)
Next, an embodiment according to the present invention, that is, a pull-out mechanism of a support base that supports the sheet conveying belt 52 will be described. In particular, the entire sheet conveying belt 52 can be pulled out only when the sheet conveying belt 52 is separated from the image forming portions Pa, Pb, Pc, and Pd, and cannot be pulled out when any of them is in contact. It is comprised so that it may become.

  Therefore, as shown in FIG. 5, locking members 65 and 66 for drawer locks are attached to one end of the rotary shafts 63 and 64 of the rotary cams 61 and 62 on the back side. Fixing plates 67 and 68 provided on the main body side of the image forming apparatus 1 are provided so as to correspond to the locking members 65 and 66, and a locking mechanism is configured by the locking members and the fixing plate.

  The positional relationship between the locking members 65 and 66 and the fixing plates 67 and 68 is provided on the far side in the pull-out direction W as shown in FIG. FIG. 6 is a top view in which unnecessary portions in FIG. 5 are omitted, and the support base 69 is simply illustrated.

  In this figure, rotating shafts 63 and 64 of rotational eccentric cams 61 and 62 are rotatably supported on a support base 69, and locking members 65 and 66 are attached to one ends of the rotating shafts 63 and 64, respectively. Yes. The fixing plates 67 and 68 are fixed to the main body side of the image forming apparatus 1. Further, the locking members 65 and 66 and the fixing plates 67 and 68 are in a state where the sheet conveying belt 52 is in contact with the photosensitive drums 10a, 10b, 10c and 10d of the image forming portions Pa, Pb, Pc and Pd. In the state where the longest distances to the cam surfaces of the zygomatic rotation eccentric cams 61 and 62 are in contact with the first and second support members 57 and 58, they are positioned in opposing locking states.

  Therefore, when the sheet conveying belt 52 is in contact with the photosensitive drums 10a, 10b, and 10c and in the state of being in contact with the photosensitive drum 10d, both or one of the locking members 65 and 66 is fixed. It faces the plates 67 and 68, and the locked state is maintained as shown in FIGS. 6 (a) and 6 (b). Therefore, the support base 69 that supports the entire conveying unit including the sheet conveying belt 52 cannot be pulled out in the arrow W direction.

  That is, as shown in FIG. 3, when the sheet conveying belt 52 is separated from the photosensitive drums 10a, 10b, 10c, and 10d, the locking members 65 and 66 are opposed to the fixing plates 67 and 68. Thus, the support base 69 can be pulled out in the arrow W direction. In this case, since the sheet conveying belt 52 is separated from the photosensitive drums 10a, 10b, 10c, and 10d, the pulling operation is not hindered, and there is a risk of damage to the photosensitive drum and the sheet conveying belt. Absent.

  Note that all the members constituting the conveying means 5 are supported on the support base 69. That is, the driving roller 50, the driven rollers 51 and 53, the tension roller 54, the spring 55, the fixing portion 55-1, the first and second support members 57 and 58, and the rotating cam 61 for stretching the sheet conveying belt 52. And 62 are rotatable and movable, and are supported in a fixed state.

  As described above, according to the present invention, the sheet conveying belt 52 is provided in the image forming portions Pa, Pb, Pc, and Pd so as to be arbitrarily contactable and separable, and supports the sheet conveying belt 52. Since it is not necessary to provide the base 69 so as to be able to contact and separate, the mechanism and the configuration are very simple. Moreover, although the sheet conveying belt 52 is provided so as to be able to contact and separate, a tension roller 54 is provided so that the tension state at that time can be maintained constant, and the distance of the compression spring 55 for applying tension to the tension roller 54 is set. In this way, a constant state can always be maintained regardless of the image forming mode, and in particular, there is no change in transfer conditions.

  In the present invention, the rotation shafts 59 and 60 of the first and second support members 57 and 58 are provided to face each other in order to separate the sheet conveying belt 52 from the photosensitive drum. That is, the rotation shafts 59 and 60 are provided so as to be opposite to the driven roller 51 or the driving roller 50 side. By doing so, a large space is formed on the carry-in side and the carry-out side of the sheet, as shown in FIG. That is, when the rotation shaft 59 is provided on the driven roller 51 side, a large space on the sheet carry-in side cannot be obtained, and the removal of the jam sheet becomes troublesome. Further, if the rotation shaft 60 is provided on the drive roller 50 side, the spacing between the photosensitive drums 10a, 10b, 10c and 10d and the sheet conveying belt 52 becomes very short, and the sheet removing operation and the like are only troublesome. In addition, the contact state with the photosensitive drum cannot be completely separated, and it becomes impossible to prevent the toner from being contaminated.

  Such inconvenience can be eliminated in the configuration of the present invention. For example, as shown in FIG. 3, the sheet conveying belt 52 is largely opened to the sheet carry-in side and the carry-out side, so that the removal of the sheet is very simple. Become.

  Here, the rotation shafts 59 and 60 of the first and second support members 57 and 58 are individually provided, but these are made the same axis, and the first and second support members 57 are respectively arranged on this shaft. And 58 can be provided to be pivotable in opposite directions. This can be said to be a unique configuration of the present invention that can be adopted by providing the rotating shafts 59 and 60 on the side opposite to the driven roller 51 or the driving roller 50 side.

  According to such a configuration, the apparatus for achieving the above-described object according to the present invention has a configuration in which the conveyance belt is individually brought into contact with and separated from the recording medium of the image forming unit. Since it is not necessary to provide a moving mechanism, the configuration is simple. Further, since the conveyance belt can be separated from all the image forming units, the operation of removing the jammed transfer material is simplified, and there is no possibility of damaging the conveyance belt. In the image forming apparatus having the above-described configuration, the conveyance unit including the conveyance belt and a mechanism for driving the conveyance belt is supported on a support base provided so as to be able to be pulled out from the image forming apparatus main body. A locking member that locks the drawer of the support base in conjunction with the rotation of the first and second rotating members, and a fixing plate that is provided on the image forming apparatus main body side and can be locked in correspondence with the locking member. And the locking member is in a locked state with the fixing plate in a state where the conveying belt is separated from each image forming unit by the first and second rotating members. It can be unraveled, so that the support can be pulled out. That is, in a state where the carry-out belt is separated from each image forming unit, the locked state is released, and the conveyance means including the conveyance belt and a mechanism for driving the conveyance belt can be easily pulled out. In this case, since the conveyance belt does not contact the image forming unit, the image forming unit side and the conveyance belt side are not damaged.

FIG. 3 is a cross-sectional view illustrating the entire structure of an image forming apparatus including a sheet conveying unit that is provided with a sheet conveying belt according to the present invention so as to be freely contactable with and separated from a plurality of image forming units. FIG. 2 is an explanatory diagram illustrating a state in which a conveyance belt is separated from one image forming unit in FIG. 1. FIG. 2 is an explanatory diagram illustrating a state in which a conveyance belt is separated from all image forming units in FIG. 1. It is a figure where it uses for structure and operation | movement of the part of the conveyance means for description concerning the provision of tension concerning this invention. It is a figure where it uses for the structure and operation | movement description including the locking mechanism which enables the conveyance means in this invention to be pulled out. FIG. 6 is a top view in a state where unnecessary portions in FIG. 5 are omitted. FIG. 10 is a cross-sectional view illustrating a structure of a conveying unit in which a conventional sheet conveying belt is provided so as to be able to contact and separate from a plurality of image forming units.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 2 Paper feeder 5 Sheet conveyance means 10 Photoconductor 11 Charger 12 Developing device 13 Transfer part 14 Cleaning device Pa, Pb, Pc, Pd Image forming part 22 for each color 22 Registration roller 50 Driving roller 51 Driven roller 52 Sheet Conveying Belt 57 First Support (First Rotating Member)
58 Second support (second rotating member)
59 Rotation axis (first axis)
60 Rotating axis (second axis)
61 Eccentric cam (contact / separation member)
62 Eccentric cam (contact / separation member)
63 Cam rotation shaft 64 Cam rotation shaft 65 Locking member (lock mechanism)
66 Locking member (locking mechanism)
67 Fixing plate (locking mechanism)
68 Fixing plate (locking mechanism)
69 Support stand

Claims (2)

A plurality of image forming portions for forming toner images are provided side by side on the surface of the photosensitive member, and each toner image on the surface of the photosensitive member of the image forming portion is opposed to each image forming portion in order to transfer it onto a transfer material. In the image forming apparatus provided with a transfer belt provided with a transfer belt that sequentially transfers one transfer material to each transfer position formed by each image forming unit and each transfer unit.
A first rotating member disposed on the transfer belt carrying-in side of the transfer belt and provided so as to be rotatable in one direction around a first axis; and on the transfer-material unloading side on the transfer belt. And a second rotating member that is disposed so as to be rotatable in one direction around the second axis,
The first rotation member is provided with a plurality of transfer portions for transferring a color toner image, and the second rotation member is provided with the transfer portion for transferring a black toner image.
The first shaft is provided on the carry-out side of the first rotating member,
By rotating the first rotating member in one direction around the first axis, the transfer unit provided on the first rotating member is rotated together with the first rotating member, and the conveyance is performed. An image forming apparatus characterized in that a portion of the belt on the first rotating member side can be separated from the image forming unit. A plurality of image forming portions for forming toner images are provided side by side on the surface of the photosensitive member, and each toner image on the surface of the photosensitive member of the image forming portion is opposed to each image forming portion in order to transfer it onto a transfer material. In the image forming apparatus provided with a transfer belt provided with a transfer belt that sequentially transfers one transfer material to each transfer position formed by each image forming unit and each transfer unit.
A first rotation is provided on the conveying belt on the transfer material carry-in side, and supports a plurality of transfer portions for transferring a color toner image, and is provided to be rotatable in one direction around a first axis. A moving member;
A second rotating member that is disposed on the transfer material transfer side on the conveyor belt and is provided to support the transfer portion for transferring the black toner image and to be rotatable in one direction around the second axis. And
The first shaft is provided on the carry-out side of the first rotating member,
The second axis is provided at a position different from the first axis,
By rotating the first rotating member in one direction around the first axis, the plurality of transfer portions provided on the first rotating member are rotated together with the first rotating member, The conveyor belt can be separated from the photoconductor for forming a color toner image,
By rotating the second rotating member in one direction around the second axis, the transfer portion provided on the second rotating member is rotated together with the second rotating member, and the transfer is performed. An image forming apparatus characterized in that a belt can be separated from the photosensitive member for forming a black toner image.

Images