JP2009282124A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus of a tandem type, in which a photoreceptor drum, other than a black image forming part and an intermediate transfer belt are separated from each other in a monochromatic mode, restraining the vibration of the intermediate transfer belt during image formation due to separation between the photoreceptor drum and the intermediate transfer belt so as to obtain an image of high image quality, without uneven pitch. <P>SOLUTION: In the case of a monochromatic mode, the respective primary transfer rollers 30Y, 30M, 30C of an yellow image forming part 2Y, a magenta image forming part 2M, a cyan image forming part 2C are separated from the photoreceptor drums 21Y, 21M, 21C, and shutter members 6Y, 6M, 6C are set in closing positions and are brought into contact with the intermediate transfer belt 11, to restrain vibration of the intermediate transfer belt 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a so-called tandem type color image forming apparatus in which a plurality of image forming units for forming toner images of different colors are arranged along an intermediate transfer member.

  In recent years, there has been a demand for high-speed full-color image output in image forming apparatuses, and so-called tandem type images in which image forming units containing toners of cyan, magenta, yellow, and black are arranged side by side along an intermediate transfer belt. Forming devices are being widely used.

  In this type of image forming apparatus, the intermediate transfer belt is pressed against the photosensitive drum of each image forming unit by a primary transfer roller. On the other hand, a secondary transfer roller is in pressure contact with the intermediate transfer belt, and a sheet as a recording medium is supplied between the intermediate transfer belt and the secondary transfer roller. The toner images of different colors respectively formed by the respective image forming units are primarily transferred and superimposed on the intermediate transfer belt, and then the superimposed toner images are secondarily transferred onto the paper. When the sheet on which the toner image has been transferred passes through the fixing unit, the toner image is heated and pressurized to be melted and fixed on the sheet, and the sheet is discharged onto a sheet discharge tray.

  In the image forming apparatus having such a mechanism, in order to extend the lifespan of the photosensitive drum and the intermediate transfer belt, the photosensitive drum in the image forming unit other than the black image forming unit is separated from the intermediate transfer belt during black and white image formation. An apparatus has been proposed and has already been commercialized.

  However, if the photosensitive drum of the image forming unit other than the black image forming unit is separated from the intermediate transfer belt, the intermediate transfer belt is likely to bend and vibrate, and density unevenness occurs at a constant period on the image. Problems such as unevenness may occur.

Accordingly, various techniques for separating and contacting the photosensitive drum and the intermediate transfer belt have been proposed. For example, Patent Document 1 proposes a technique for bringing the primary transfer roller into and out of contact with the photosensitive drum using the axis of the backup roller that stabilizes the nip of the primary transfer roller as the rotation axis. Patent Document 2 proposes a separation / contact technique that prevents the intermediate transfer belt from contacting all the photosensitive drums at once.
JP 2005-62642 A JP 2007-79571 A

  However, the former proposed technique has a configuration in which only the backup roller disposed on the transfer roller side is in contact with the intermediate transfer belt, and thus the effect of suppressing the vibration of the intermediate transfer belt is low. The latter proposed technique is intended to suppress vibration generated when the primary transfer roller contacts the intermediate transfer belt, and is intended to suppress vibration of the intermediate transfer belt during image formation. Not what you want.

  The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a photosensitive drum other than a black image forming unit in a monochrome mode in a so-called tandem type image forming apparatus. The intermediate transfer belt is separated from the intermediate transfer belt to extend the life of the photosensitive drum, and at the same time, the vibration of the intermediate transfer belt during image formation caused by separating the photosensitive drum from the intermediate transfer belt is suppressed, and the pitch is reduced. The purpose is to obtain a uniform high-quality image.

  According to the present invention, a plurality of toner images of different colors are formed, each comprising an electrostatic latent image carrier and a developing unit that visualizes the latent image formed on the electrostatic latent image carrier with toner. An image forming portion, an intermediate transfer member that rotates while contacting or separating from the surface of each electrostatic latent image carrier, and a position facing each electrostatic latent image carrier across the intermediate transfer member And a primary transfer means for transferring the toner image formed on the surface of each electrostatic latent image carrier to the intermediate transfer body, wherein one of the plurality of image forming sections develops a black color. In the image forming apparatus that is an image forming unit, at least the electrostatic latent image carrier other than the black image forming unit and the intermediate transfer member are relatively movable to a contact position and a separation position, and A latent image carrier and the intermediate transfer member are brought into contact with each other to form a color image. Only the electrostatic latent image carrier of the color mode and the black image forming unit is brought into contact with the intermediate transfer member, and the electrostatic latent image carrier of the other image forming unit is separated from the intermediate transfer member, so that the monochrome image Can be switched to the monochrome mode that forms the image, and at least one image forming unit positioned upstream of the black image forming unit in the rotation direction of the intermediate transfer member has external light incident on the electrostatic latent image carrier. A light-shielding member that is openable and closable, and the light-shielding member is in an open position when the electrostatic latent image carrier and the intermediate transfer member are in contact with each other. When the electrostatic latent image carrier and the intermediate transfer member are in the separated position, the closed position prevents the external light from entering the electrostatic latent image carrier, and the intermediate transfer member To suppress vibration when the intermediate transfer member rotates. An image forming apparatus is provided.

  Here, from the viewpoint of further suppressing the vibration of the intermediate transfer member, the light-shielding member is provided so as to be freely opened and closed in all of the image forming units located upstream of the black image forming unit in the rotation direction of the intermediate transfer member. preferable.

  Further, according to the present invention, the electrostatic latent image carrier, the developing unit that visualizes the latent image formed on the electrostatic latent image carrier with toner, and the formed toner image are transferred. Cleaning means for cleaning the surface of the subsequent electrostatic latent image carrier, and a plurality of image forming units for forming toner images of different colors, and contacting or separating from the surface of each electrostatic latent image carrier. An intermediate transfer member that rotates while being positioned at a position facing each electrostatic latent image carrier with the intermediate transfer member interposed therebetween, and a toner image formed on the surface of each electrostatic latent image carrier is transferred to the intermediate transfer member. In an image forming apparatus having a primary transfer means for transferring to a transfer body, and one of the plurality of image forming units is a black image forming unit that develops a black color, at least electrostatic other than the black image forming unit The latent image carrier and the intermediate transfer member are in contact and separated positions. And at least one of the developing unit and the cleaning unit in the at least one image forming unit located upstream of the black image forming unit in the rotation direction of the intermediate transfer member A full color mode in which each electrostatic latent image carrier and the intermediate transfer body are brought into contact with each other to be moved relative to a position in contact with the transfer body and a separated position, and a black image is formed. Only the electrostatic latent image carrier of the part is brought into contact with the intermediate transfer member, and the electrostatic latent image carrier of the other image forming unit is separated from the intermediate transfer member and switched to the monochrome mode for forming a monochrome image. In the monochrome mode, the developing unit and the cleaning unit in at least one image forming unit located upstream of the black image forming unit in the rotation direction of the intermediate transfer member. As a position one or the both in contact with the intermediate transfer member, the image forming apparatus is provided, characterized in that to suppress the vibration at the time of rotation of the intermediate transfer body.

  The contact positions of one or both of the developing unit and the cleaning unit with the intermediate transfer member may be non-image forming regions at both ends in the width direction of the intermediate transfer member.

  Further, in order to keep the rubbing with the intermediate transfer member low, a low friction member is attached to a contact portion with one or both of the developing unit and the cleaning unit with the intermediate transfer member, or a rotating member is provided. You may make it attach.

  Further, from the viewpoint of shortening the time from the input of the image signal to the output of the image, it is preferable that the black image forming unit is arranged at the most downstream in the intermediate transfer member rotation direction.

  In the image forming apparatus according to the first invention, the light-shielding member is brought into contact with the intermediate transfer member in the monochrome mode, and in the image forming apparatus according to the second invention, one or both of the developing means and the cleaning means are provided. Since the vibration due to the rotation of the intermediate transfer member is suppressed by bringing it into contact with the intermediate transfer member, a high-quality image without pitch unevenness can be obtained. In addition, the light shielding member, the developing unit, and the cleaning unit that are brought into contact with each other to suppress the vibration of the intermediate transfer member are conventionally provided in the image forming apparatus. In the image forming apparatus of the present invention, the intermediate transfer member is provided. Therefore, a new member for suppressing the vibration is not required, and the apparatus can be reduced in size and weight.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in more detail, this invention is not limited to these examples at all.

  FIG. 1 is a schematic diagram showing an example of an image forming apparatus according to the present invention. The image forming apparatus in FIG. 1 is a tandem digital color printer (hereinafter, simply referred to as “printer”). Of course, in addition to a printer, the present invention can also be applied to a copying machine having a scanner, a facsimile, or a multi-function machine having these functions combined.

  First, a schematic configuration of the printer 1 will be described. The printer 1 includes an intermediate transfer belt (intermediate transfer member) 11 at a substantially central portion inside thereof. The intermediate transfer belt 11 is wound around the outer periphery of the roller 12, the tension roller 13, and the guide rollers 14 and 15, and is driven to rotate counterclockwise. The tension roller 13 is slidably attached to the outside and is urged by the pressing spring S from the inside to the outside of the intermediate transfer belt 11. Thus, the intermediate transfer belt 11 is always in a tensioned state.

  Below the lower horizontal portion of the intermediate transfer belt 11, four image forming portions 2Y, 2M, 2C, and 2B respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (B) colors. Are arranged in this order along the intermediate transfer belt 11. Each image forming unit 2Y, 2M, 2C, 2B has a photosensitive drum (electrostatic latent image carrier) 21Y, 21M, 21C, 21B, respectively. Around each of the photosensitive drums 21Y, 21M, 21C, and 21B, the chargers 22Y, 22M, 22C, and 22B, the print head portions 23Y, 23M, 23C, and 23B, and the developing device (in the order along the rotation direction). Developing means) 24Y, 24M, 24C, 24B and cleaners (cleaning means) 25Y, 25M, 25C, 25B are arranged, respectively. The print head portions 23Y, 23M, 23C, and 23B are composed of a large number of LEDs arranged in the main scanning direction parallel to the axial direction of the photosensitive drum.

  Further, primary transfer rollers (primary transfer means) 30Y, 30M, 30C, and 30B are provided at positions facing the respective photosensitive drums 21Y, 21M, 21C, and 21B with the intermediate transfer belt 11 interposed therebetween. A secondary transfer roller 16 is pressed against a portion of the intermediate transfer belt 11 supported by the roller 12. A nip portion between the secondary transfer roller 16 and the intermediate transfer belt 11 becomes a secondary transfer region 17. The toner image formed on the intermediate transfer belt 11 in the secondary transfer region 17 is transferred to the conveyed paper P.

  A paper feed cassette 91 is detachably disposed at the bottom of the printer 1. The sheets P stacked and housed in the sheet feeding cassette 91 are pulled out one by one from the uppermost one by the rotation of the sheet feeding roller 92 and sent out to the transport path 93. The conveyance path 93 extends from the paper feed cassette 91 to the paper discharge tray 98 through the nip portion of the timing roller pair 94, the secondary transfer region 17, and the fixing unit 95. The paper P sent out from the paper feed cassette 91 is conveyed to the timing roller pair 94 and is sent out to the secondary transfer region 17 at a predetermined timing.

  The fixing unit 95 has a hollow cylindrical shape, and includes a fixing roller 96 having a halogen heater H therein, and a pressure roller 97 that is pressed against the fixing roller 96 and rotates. A nip portion between the fixing roller 96 and the pressure roller 97 through which the paper P onto which the toner image has been secondarily transferred passes is a fixing region.

  A schematic operation of the printer 1 having such a configuration will be described. First, in the full color mode for outputting a color image, when an image signal is input from an external device (for example, a personal computer) to an image signal processing unit (not shown) of the printer 1, the image signal processing unit converts the image signal to yellow, A digital image signal color-converted to cyan, magenta, and black is created, and this signal is transmitted to the LED drive circuit for the print head. This drive circuit performs exposure by causing the print head units 23Y, 23M, 23C, and 23B of the image forming units 2Y, 2M, 2C, and 2B to emit light based on the input digital signals. This exposure is performed with a time difference in the order of the print head portions 23Y, 23M, 23C, and 23B. Thereby, electrostatic latent images for the respective colors are formed on the surfaces of the respective photosensitive drums 21Y, 21M, 21C, and 21B.

  The electrostatic latent images formed on the photosensitive drums 21Y, 21M, 21C, and 21B are developed by the developing units 24Y, 24M, 24C, and 24B, respectively, and become toner images of the respective colors. The toner images of the respective colors are sequentially primary-transferred and superimposed on the intermediate transfer belt 11 that rotates counterclockwise in the drawing by the action of the primary transfer rollers 30Y, 30M, 30C, and 30B.

  The toner image formed on the intermediate transfer belt 11 in this way reaches the secondary transfer region 17 as the intermediate transfer belt 11 moves. In the secondary transfer region 17, the superimposed color toner images are collectively delivered to the paper P supplied from the paper feed cassette 91 to the transport path 93 and supplied by the timing roller pair 94 by the action of the secondary transfer roller 16. Second transfer is performed. The toner remaining on the intermediate transfer belt 11 after the secondary transfer is collected by a belt cleaner (not shown).

  The sheet P onto which the toner image has been secondarily transferred is sent to the fixing unit 95 through the conveyance path 93, where the toner image is fixed on the sheet P by passing through the fixing region. Then, the paper P is discharged to the paper discharge tray 98.

  In the image forming apparatus according to the present invention, in the full color mode, all the photosensitive drums 21Y, 21M, 21C, and 21B and the primary transfer rollers 30Y, 30M, 30C, and 30B are pressed against each other with the intermediate transfer belt 11 interposed therebetween. To do. On the other hand, in the monochrome mode, only the photosensitive drum 21B of the black image forming unit 2B and the primary transfer roller 30B are pressed against each other with the intermediate transfer belt 11 interposed therebetween, and the other image forming units 2Y, 2M, and 2C have photoconductors. The drums 21Y, 21M, and 21C are separated from the primary transfer rollers 30Y, 30M, and 30C.

  Here, in the image forming apparatus according to the first invention, the shutter members 6Y, 6M, and 6C (shown in FIG. 2) in the image forming portions 2Y, 2M, and 2C where the photosensitive drum and the intermediate transfer belt are separated from each other. Is in the closed position and contacts the intermediate transfer belt 11. Hereinafter, the contact / separation mechanism between the photosensitive drums 21Y, 21M, 21C, and 21B and the primary transfer rollers 30Y, 30M, 30C, and 30B, and the opening and closing of shutter members (light shielding members) 6Y, 6M, 6C, and 6B (shown in FIG. 2). The mechanism will be described.

  First, an example of the separation / contact mechanism of the primary transfer roller will be described. As shown in FIG. 2, primary transfer rollers 30 </ b> Y, 30 </ b> M, 30 </ b> C, and 30 </ b> B (hereinafter, may be collectively referred to as “primary transfer roller 30”) are disposed inside the intermediate transfer belt 11. The primary transfer roller 30 is rotatably supported on the support 31. The support 31 is slidably fitted into the frame 33, and a spring 34 is interposed between the frame 33 and the support 31. As a result, the primary transfer roller 30 is urged in the direction of the photosensitive drums 21Y, 21M, 21C, and 21B (hereinafter may be collectively referred to as “photosensitive drum 21”), and the intermediate transfer belt 11 is sandwiched therebetween. The body drum 21 is pressed. A protrusion 32 is formed on the side surface of the support 31, and one end of each of the substantially L-shaped levers 35 </ b> Y, 35 </ b> M, 35 </ b> C, 35 </ b> B that rotates about the shaft 36 is formed on the lower surface of the protrusion 32. It is in contact.

  Between the primary transfer rollers 30Y and 30M, a cam shaft 40 is attached between the frames 44 (partially shown in FIG. 3) on both sides, and two pairs of cams 41 and 42 are fixed in the vicinity of both ends of the cam shaft 40. ing. In FIG. 2, the two pairs of cams 41, 42 and the slide plates 51, 52 attached to the cam shaft 40 are moved up and down in order to facilitate understanding of the separation mechanism of the primary transfer roller 30 by rotation of the cams 41, 42. It is shown separately. Further, in order to make the rotational positions of the cams 41 and 42 easy to understand, black dots are marked on the outer edges of the cams 41 and 42.

  As shown in FIG. 3, slide plates 51 and 52 are slidably attached to both sides of the frame 44. Cams 41 and 42 are attached to the camshaft 40, and a gear 46 is fixed to one end protruding outward from the frame 44. The gear 46 meshes with a drive gear (not shown) on the apparatus main body side and is rotationally driven. As understood from FIGS. 2 and 3, the slide plate 51 includes projections 513, 514, 515 with which the upper ends of the levers 35 Y, 35 M, 35 C abut, a projection 511 with which the cam 41 abuts, and a cam An opening 512 from which one end of 41 can protrude is formed. On the other hand, on the slide plate 52, a protruding piece 522 that contacts the upper end of the lever 35B and a protruding piece 521 that contacts the cam 42 are formed at both ends.

  Next, the shutter members 6Y, 6M, 6C, and 6B (hereinafter, may be collectively referred to as “shutter member 6”) will be described. The shutter member 6 is originally intended to prevent external light from entering the photosensitive drum 21 when the image forming unit including the photosensitive drum 21 is detached from the apparatus main body. In addition to this role, the photosensitive drum 21 and the intermediate transfer belt 11 are closed when they are separated from each other and contact the intermediate transfer belt 11 to suppress the vibration of the intermediate transfer belt 11. . That is, as shown in FIG. 2, the shutter member 6 opens and closes in accordance with the separation and contact between the primary transfer roller 30 and the photosensitive drum 21.

  As the opening / closing mechanism of the shutter member 6, a conventionally known mechanism can be used. For example, the above-described separation / contact mechanism of the primary transfer roller 30 can be diverted. A specific example is shown in FIG. FIGS. 2A to 2C are state diagrams corresponding to FIGS. 2A to 2C, respectively. A cam shaft 43 is attached between the yellow photosensitive drum 21M and the magenta photosensitive drum 21M, and two pairs of cams 44 and 45 are fixed in the vicinity of both ends of the cam shaft 43. In FIG. 4, as in FIG. 2, two pairs of cams 44, 45 attached to the cam shaft 43 and a slide plate 53 are provided to facilitate understanding of the opening / closing mechanism of the shutter member 6 by the rotation of the cams 44, 45. , 54 are divided into upper and lower parts. Further, in order to make the rotational positions of the cams 44 and 45 easy to understand, black dots are marked on the outer edge portions of the cams.

  As shown in FIG. 4, on the slide plate 53, the protruding pieces 533, 534, 535 with which the shutter members 6Y, 6M, 6C abut, the protruding piece 531 with which the cam 44 abuts, and one end of the cam 44 can project. An opening 532 is formed. On the other hand, the slide plate 54 is formed with a projecting piece 543 with which the shutter member 6B abuts, a projecting piece 541 with which the cam 45 abuts, and an opening 542 from which one end of the cam 45 can project. The shutter members 6Y, 6M, 6C, and 6B are urged clockwise by urging means (not shown).

  In such a configuration, in the full color mode, each of the primary transfer rollers 30Y, 30M, 30C, and 30B is moved through the intermediate transfer belt 11 by the biasing force of the spring 34, as shown in FIG. 21Y, 21M, 21C, and 21B are press-contacted. In addition, as shown in FIG. 4A, the shutter members 6Y, 6M, 6C, and 6B have the long diameter portions of the cams 44 and 45 in contact with the projecting pieces 531 and 541, respectively, and the projecting pieces of the slide plates 44 and 45. By 535,543, an open position is maintained against the urging | biasing force of an urging means (not shown).

  Next, in the monochrome mode, as shown in FIG. 2B, the cam shaft 40 is rotated 90 ° clockwise by a driving means (not shown), and the cam 41 contacts the projecting piece 511 of the slide plate 51. The part changes from the short diameter part to the long diameter part. As a result, the slide plate 51 moves to the right in FIG. Then, the end portions of the levers 35Y, 35M, and 35C are pressed by the projecting pieces 513, 514, and 515 of the slide plate 51, and the levers 35Y, 35M, and 35C rotate clockwise about the shaft 36, and the levers 35Y, 35M , 35C pushes the support 31 upward through the protrusion 32 against the urging force of the spring 34. Accordingly, the primary transfer rollers 30Y, 30M, and 30C of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C are separated from the photosensitive drums 21Y, 21M, and 21C. Further, since the intermediate transfer belt 11 is always tensioned by the tension roller 13 (shown in FIG. 1), it is separated from the photosensitive drums 21Y, 21M, and 21C together with the primary transfer rollers 30Y, 30M, and 30C. On the other hand, as in the full color mode, the short diameter portion of the cam 42 is in contact with the protruding piece 521 of the slide plate 52, so the slide plate 52 does not move, and the primary transfer roller 30B of the black image forming portion 2B is Then, the state in pressure contact with the photosensitive drum 21B is maintained.

  In the monochrome mode, as shown in FIG. 4B, the cam shaft 43 is also rotated 90 ° clockwise, and the contact portion of the cam 44 with the protruding piece 531 of the slide plate 53 is changed from the long diameter portion to the short diameter portion. Part. As a result, the slide plate 53 is slidable in the right direction in the figure, and the shutter members 6Y, 6M, and 6C of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C are urging means ( At the same time, the shutter members 6Y, 6M, and 6C press the projecting pieces 533, 534, and 535 of the slide member 53 to the right by the urging force (not shown) and the slide plate 53 Move to the right in the figure. On the other hand, even if the cam 45 is rotated by 90 °, the contact portion with the protruding piece 541 of the slide plate 54 remains the long diameter portion, so that the shutter member 6B of the black image forming portion 2B maintains the open position.

  As a result, in the monochrome mode, as shown in FIG. 2B, only transfer from the photosensitive drum 21B of the black image forming unit 2B to the intermediate transfer belt 11 is possible, and a monochrome image is formed. . At the same time, the shutter members 6Y, 6M, and 6C of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C come into contact with the intermediate transfer belt 11, and vibration of the intermediate transfer belt 11 is suppressed. The

  Next, when each image forming unit is detached from the apparatus main body, as shown in FIG. 2C, the cam shaft 40 further rotates about 90 ° clockwise. At this time, the primary transfer rollers 30Y, 30M, and 30C of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C are in contact with the protruding piece 511 of the slide plate 51 of the cam 41. Is still a long-diameter portion, so that it is kept away from the photosensitive drums 21Y, 21M, and 21C. On the other hand, for the primary transfer roller 30B of the black image forming unit 2B, the contact portion of the cam 42 with the protruding piece 521 of the slide plate 52 is changed from the short diameter portion to the long diameter portion, so that the slide plate 52 is shown in the drawing. The lever 35B is rotated clockwise by the protruding piece 522 of the slide plate 52, and the primary transfer roller 30B is separated from the photosensitive drum 21B.

  Further, as shown in FIG. 4C, the shutter members 6Y, 6M, and 6C of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C are arranged on the slide plate 53 of the cam 44. Since the contact portion with the protruding piece 531 is still the short diameter portion, the closed position is maintained. On the other hand, in the shutter member 6B of the black image forming portion 2B, the slide plate 54 slides in the right direction in the figure when the contact portion of the cam 45 with the slide plate 54 protruding piece 541 is changed from the long diameter portion to the short diameter portion. The shutter member 6B is rotated clockwise by a biasing force of a biasing means (not shown) to be in the closed position.

  In this way, in all the four image forming units, the primary transfer rollers 30Y, 30M, 30C, and 30B are separated from the photosensitive drums 21Y, 21M, 21C, and 21B, and the shutter members 6Y, 6M, 6C, and 6B are all in the closed position, and the image forming units 2Y, 2M,. 2C and 2B can be detached from the apparatus main body.

  In the embodiment described above, in the embodiment, the shutter members 6Y, 6M, and 6C are provided in all of the yellow image forming unit 2Y, the magenta image forming unit 2M, and the cyan image forming unit 2C, and in the monochrome mode. The shutter members 6Y, 6M, and 6C are all in contact with the intermediate transfer belt 11, but a shutter member is provided in at least one of the image forming portions upstream of the black image forming portion 2B in the rotation direction. At the same time, the shutter member may be brought into contact with the intermediate transfer belt 11.

  Next, an image forming apparatus according to the second invention will be described. In the image forming apparatus according to the second invention, in the full color mode, all the photosensitive drums 21Y, 21M, 21C, and 21B and the primary transfer rollers 30Y, 30M, 30C, and 30B sandwich the intermediate transfer belt 11. In the monochrome mode, only the photosensitive drum 21B of the black image forming unit 2B and the primary transfer roller 30B are in pressure contact with the intermediate transfer belt 11 interposed therebetween. In the other image forming units 2Y, 2M, and 2C, The photosensitive drums 21Y, 21M, and 21C and the primary transfer rollers 30Y, 30M, and 30C are separated from each other. However, these configuration examples are the same as those in the image forming apparatus according to the first aspect of the invention, and thus description thereof is omitted. To do.

  The image forming apparatus according to the second invention is significantly different from the image forming apparatus according to the first invention in that one or both of the developing means and the cleaning means are used instead of bringing the shutter member into contact with the intermediate transfer belt. This is in that the vibration of the intermediate transfer belt is suppressed by contacting the intermediate transfer belt. FIG. 5 is a perspective view showing an embodiment of the developing device 24 arranged in the image forming units 2Y, 2M, and 2C. The developing device 24 has a developing case 243 in which a developer (not shown) is built, a recess 244 is formed in a lower corner, and a developing sleeve 241 that is rotatably supported by the developing case 243. The developing device 24 is swingably attached to an apparatus main body (not shown) by shafts 242 provided on both side surfaces of the developing sleeve 241.

  On the other hand, a cam shaft 71 is disposed so as to pass through the recess 244 at the lower corner of the developing device 24, and a pair of cams 72 a and 72 b are fixed in the vicinity of both ends of the cam shaft 71. The gear 73 is fixed. The gear 73 rotates in mesh with a gear (not shown) on the apparatus main body side. As a result, the pair of cams 72a and 72b rotate to swing the developing device 24. FIG. 6 shows a specific state diagram of the developing device 24.

  FIG. 6A is a state diagram in the full color mode, in which the side surface of the concave portion 244 of the developing device 24 is pressed by the long diameter portions of the pair of cams 72 a and 72 b, and the developing device 24 is separated from the intermediate transfer belt 11. Maintained. Next, in the monochrome mode, as shown in FIG. 5B, the pair of cams 72 a and 72 b rotate about 90 ° counterclockwise, and the long diameter portions of the cams 72 a and 72 b are the concave portions 244 of the developing device 24. Press the top of the. Then, the developing device 24 rotates clockwise about the shaft 242, and the upper surface edge portion of the developing device 24 contacts substantially the entire width direction of the intermediate transfer belt 11. As a result, vibration associated with the rotation of the intermediate transfer belt 11 is effectively suppressed.

  In the embodiment shown in FIGS. 5 and 6, since the upper surface edge of the developing unit 24 and the intermediate transfer belt 11 are in contact with each other over substantially the entire width direction, wear or heat generation of both may occur depending on the material. obtain. Therefore, in the embodiment shown in FIGS. 7 and 8, the contact area and the contact resistance of the developing device 24 with the intermediate transfer belt 11 are reduced to suppress wear and heat generation. That is, in the embodiment shown in FIG. 7, a pair of low friction members 81 a and 81 b are attached to both ends in the width direction of the upper surface edge of the developing device 24. Thereby, the contact area between the intermediate transfer belt 11 and the developing device 24 is reduced, and the frictional resistance is reduced. In addition, if the low friction members 81a and 81b are brought into contact with the non-image forming area of the intermediate transfer belt 11, the intermediate transfer belt 11 is even stained or damaged due to contact with the low friction members 81a and 81b. However, the influence on the image quality can be kept small. Examples of the low friction members 81a and 81b that can be used here include a low friction sheet made of a fluorine-based resin typified by polytetrafluoroethylene.

  Further, in the embodiment shown in FIG. 8, a pair of rollers (rotators) 82a and 82b are rotatably attached instead of the low friction member. Even with such a configuration, the contact area between the intermediate transfer belt 11 and the developing device 24 is reduced and the frictional resistance is reduced as described above. If the pair of rollers 82a and 82b are brought into contact with the non-image forming area of the intermediate transfer belt 11, it is assumed that the intermediate transfer belt 11 is stained or damaged due to the contact with the pair of rollers 82a and 82b. However, the influence on the image quality is suppressed.

  In the embodiment of the image forming apparatus according to the second invention described above, the developer 24 is tilted and brought into contact with the intermediate transfer belt 11 in the monochrome mode. However, the cleaners 25Y, 25M, and 25C shown in FIG. At least one of these may be brought into contact with the intermediate transfer belt 11, or both the developing device 24 and the cleaner 25 may be brought into contact with the intermediate transfer belt 11. The developing device 24 and the cleaner 25 may be moved away from the intermediate transfer belt 11 by moving the developing device 24 and the cleaner 25 in a straight line by a power unit such as a solenoid.

  In the image forming apparatus shown in FIG. 1, the black image forming unit 2B is provided on the most downstream side in the rotation direction of the intermediate transfer belt 11. However, the present invention is not limited to this. Any position may be used. However, from the viewpoint of increasing the output time of the black and white image, the installation position on the most downstream side in the rotation direction shown in the embodiment is desirable. Each image forming unit may be unitized with the photosensitive drum 21, the charger 22, the print head unit 23, the developing unit 24, the cleaner 25, and the shutter member 6. Alternatively, these may be provided individually without integrating the constituent members. Further, an arbitrary combination, for example, the photosensitive drum 21 and the developing device 24 may be combined into one unit, or the charging unit 22 and the cleaner 25 may be combined into one unit. Further, the separation and contact between the photosensitive drum 21 and the intermediate transfer belt 11 is not limited to the mode in which the intermediate transfer belt 11 is moved by moving the primary transfer roller 30 as in the above-described actual mode, but also the photosensitive drum 21 is moved. Alternatively, both the photosensitive drum 21 and the intermediate transfer belt 11 may be moved.

1 is a schematic diagram illustrating an example of a printer (image forming apparatus) according to the present invention. It is a figure which shows the example of the separation / contact mechanism of a primary transfer roller and a photoconductive drum. It is a fragmentary perspective view which shows the arrangement | positioning relationship between a cam shaft, a cam, and a slide plate. It is a figure which shows the example of an opening-and-closing mechanism of a shutter member. It is a perspective view which shows one Embodiment of the developing device which concerns on 2nd invention. FIG. 6 is a diagram illustrating a state in which the developing unit of FIG. It is a perspective view which shows other embodiment of the developing device which concerns on 2nd invention. It is a perspective view which shows further another embodiment of the developing device based on 2nd invention.

Explanation of symbols

1 Printer (image forming device)
2, 2Y, 2M, 2C, 2B Image forming unit 6Y, 6M, 6C, 6B Shutter member (light shielding member)
11 Intermediate transfer belt (intermediate transfer member)
21, 21Y, 21M, 21C Photosensitive drum (electrostatic latent image carrier)
24, 24Y, 24M, 24C, 24B Developer (Developer)
30Y, 30M, 30C, 30B Primary transfer roller (primary transfer means)
81a, 81b Low friction member 82a, 82b Roller (rotary body)

Claims (7)

A plurality of image forming units for forming toner images of different colors, comprising: an electrostatic latent image carrier; and a developing unit that visualizes the latent image formed on the electrostatic latent image carrier with toner.
An intermediate transfer member that rotates while contacting or separating from the surface of each electrostatic latent image carrier;
Primary transfer means disposed at a position facing each electrostatic latent image carrier with the intermediate transfer member interposed therebetween, and transferring a toner image formed on the surface of each electrostatic latent image carrier to the intermediate transfer member In the image forming apparatus, wherein one of the plurality of image forming units is a black image forming unit that develops a black color.
At least the electrostatic latent image carrier other than the image forming unit for black and the intermediate transfer member are relatively movable to a contact position and a separation position,
Each electrostatic latent image carrier and the intermediate transfer member are brought into contact with each other, a full color mode for forming a color image, and only the electrostatic latent image carrier of the image forming unit for black is brought into contact with the intermediate transfer member, The electrostatic latent image carrier of the other image forming unit can be separated from the intermediate transfer member and switched to a monochrome mode for forming a monochrome image,
At least one image forming unit located upstream of the black image forming unit in the rotation direction of the intermediate transfer member is provided with a light-shielding member that can prevent external light from entering the electrostatic latent image carrier, and can be opened and closed. The light shielding member is in an open position when the electrostatic latent image carrier and the intermediate transfer member are in a contact position, and enables contact between the electrostatic latent image carrier and the intermediate transfer member. When the intermediate transfer member and the intermediate transfer member are separated from each other, the closed position is set to prevent external light from entering the electrostatic latent image carrier, and when the intermediate transfer member rotates while contacting the intermediate transfer member. An image forming apparatus that suppresses vibration of the image.   The image forming apparatus according to claim 1, wherein the light shielding member is provided so as to be openable and closable at all of the image forming units located upstream of the black image forming unit in the intermediate transfer member rotation direction. An electrostatic latent image carrier, a developing unit that visualizes the latent image formed on the electrostatic latent image carrier with toner, and the electrostatic latent image carrier after the formed toner image is transferred A plurality of image forming units that form toner images of different colors, and a cleaning unit that cleans the surface of the body,
An intermediate transfer member that rotates while contacting or separating from the surface of each electrostatic latent image carrier;
Primary transfer means disposed at a position facing each electrostatic latent image carrier with the intermediate transfer member interposed therebetween, and transferring a toner image formed on the surface of each electrostatic latent image carrier to the intermediate transfer member In the image forming apparatus, wherein one of the plurality of image forming units is a black image forming unit that develops a black color.
At least the electrostatic latent image carrier other than the black image forming unit and the intermediate transfer member can be moved relative to the contact position and the separation position, and further upstream of the black image forming unit in the rotation direction of the intermediate transfer member. One or both of the developing unit and the cleaning unit in at least one image forming unit located on the side are relatively movable between a position in contact with the intermediate transfer member and a position separated from the intermediate transfer member.
Each electrostatic latent image carrier and the intermediate transfer member are brought into contact with each other, a full color mode for forming a color image, and only the electrostatic latent image carrier of the image forming unit for black is brought into contact with the intermediate transfer member, The electrostatic latent image carrier of the other image forming unit can be separated from the intermediate transfer member and switched to a monochrome mode for forming a monochrome image,
In the monochrome mode, one or both of the developing unit and the cleaning unit are in contact with the intermediate transfer member in at least one image forming unit located upstream of the black image forming unit in the rotation direction of the intermediate transfer member. An image forming apparatus that suppresses vibration during rotation of the intermediate transfer member as a position to be rotated.   The image forming apparatus according to claim 3, wherein a contact position of one or both of the developing unit and the cleaning unit with the intermediate transfer member is a non-image forming region at both ends in the width direction of the intermediate transfer member.   5. The image forming apparatus according to claim 3, wherein a low friction member is attached to a contact portion of one or both of the developing unit and the cleaning unit with the intermediate transfer member.   The image forming apparatus according to claim 3, wherein a rotating body is attached to a contact portion of one or both of the developing unit and the cleaning unit with the intermediate transfer body.   The image forming apparatus according to claim 1, wherein the black image forming unit is arranged on the most downstream side in the rotation direction of the intermediate transfer member.