JP6124838B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a tandem type image forming apparatus.

  In general, a tandem type image forming apparatus including a plurality of image forming units arranged at positions along a rotating endless intermediate transfer belt is known. In the tandem-type image forming apparatus, each of the image forming units includes a drum-shaped image carrier (photoconductor) and a charging unit, a developing unit, a primary transfer unit, a charge eliminating unit, and a cleaning disposed around the image bearing unit. . Each of the image forming units sequentially forms images (toner images) of different colors on the surface of the intermediate transfer belt.

  Hereinafter, in the tandem type image forming apparatus, a direction in which the intermediate transfer belt rotates along the arrangement direction of the plurality of image forming units is referred to as a belt rotation direction.

  In the tandem type image forming apparatus, the state of the image forming unit is switched between a multi-color mode in which all the image forming units operate and a single color mode in which only the image forming unit on the most downstream side in the belt rotation direction operates. It is possible.

  Further, in the tandem type image forming apparatus, it is known that the charge eliminating unit of each of the image forming units has both a function of irradiating post-transfer charge removal light and a function of irradiating pre-transfer charge removal light (for example, Patent Document 1).

  The post-transfer charge removal light is a charge removal light that is applied to a position after image transfer on the image carrier from between the transfer portion and the cleaning portion in each of the image forming portions. Further, the pre-transfer charge removal light is a charge removal light applied to an image carrier of an image forming unit adjacent to the downstream side in the belt rotation direction from between the transfer unit and the cleaning unit in a certain image forming unit.

JP 2011-221405 A

  By the way, when the neutralization mode of the second image forming unit from the most downstream side in the belt rotation direction emits light in the situation where the single color mode is selected, the second image forming unit is stopped. The image carrier may be adversely affected.

  On the other hand, when the single color mode is selected and the charge eliminating portion of the second image forming portion from the most downstream side in the belt rotation direction is turned off, the image formation on the most downstream side in the belt rotation direction is performed. Static elimination before transfer is not performed at the part. In this case, there is a risk of image quality failure due to the transfer memory during image formation in the single color mode.

  The object of the present invention is that, when the charge eliminating portion of each of the plurality of image forming portions also functions as post-transfer charge removal and pre-transfer charge removal, post-transfer charge removal light from the charge removal portion adversely affects the image carrier, and An object of the present invention is to provide an image forming apparatus capable of preventing image quality defects caused by turning off a charge eliminating portion.

  An image forming apparatus according to an aspect of the present invention includes a plurality of image forming units, a mode switching unit, and a static elimination exposure switching unit. The plurality of image forming units are respectively arranged at positions along the rotating endless intermediate transfer belt. Each of the image forming units includes an image carrier, a developing unit that develops an electrostatic latent image on the surface of the image carrier, a primary transfer unit that transfers an image to the intermediate transfer belt, and a cleaning unit that cleans the surface of the image carrier. And a static elimination unit. Each of the image forming units forms images of different colors on the surface of the intermediate transfer belt. The neutralization unit provided in each of the image forming units includes a first neutralization light that travels between the primary transfer unit and the cleaning unit toward the upstream side in the rotational direction of the intermediate transfer belt and the rotational direction of the intermediate transfer belt. 2nd discharge light which goes to the downstream side. The mode switching unit changes the state of the image forming unit between a first mode in which all the image forming units operate and a part of the plurality of image forming units located downstream in the rotation direction of the intermediate transfer belt. A plurality of operation states including the second mode in which only the first image forming unit operates can be selectively switched. The static elimination exposure switching unit is configured to select the first mode when the first mode is selected in a second image forming unit located next to the first image forming unit on the upstream side in the rotation direction of the intermediate transfer belt. The neutralization light is applied to the image carrier and the second static elimination light is applied to the image carrier of the first image forming unit. Further, the static elimination exposure switching unit is configured to prevent the first static elimination light from being applied to the image carrier when the second mode is selected, and the second static elimination light to be applied to the image carrier of the first image forming unit. The body is irradiated.

  According to the present invention, when the neutralization unit of each of the plurality of image forming units also functions as post-transfer neutralization and pre-transfer neutralization, post-transfer neutralization light from the neutralization unit adversely affects the image carrier, and It is possible to provide an image forming apparatus that can prevent the occurrence of image quality defects caused by turning off the charge removal unit.

FIG. 1 is a configuration diagram of an image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic plan view of the static elimination unit in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a schematic side view of the image forming unit and the light shielding switching unit in the color mode in the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a front view of the light shielding switching unit and its periphery in the color mode in the image forming apparatus according to the first embodiment of the present invention. FIG. 5 is a schematic side view of the image forming unit and the light shielding switching unit in the monochrome mode in the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is a front view of the light shielding switching unit and its periphery in the monochrome mode in the image forming apparatus according to the first embodiment of the present invention. FIG. 7 is a front view of the light shielding switching portion and its periphery in the image forming apparatus according to the second embodiment of the present invention. FIG. 8 is a front view of the light shielding switching unit and its surroundings in the color mode in the image forming apparatus according to the third embodiment of the present invention. FIG. 9 is a schematic front view of the light-shielding switching unit and its periphery in the monochrome mode in the image forming apparatus according to the third embodiment of the present invention. FIG. 10 is a schematic plan view of the charge removal portion in the image forming apparatus according to the fourth embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: It does not have the character which limits the technical scope of this invention.

  First Embodiment First, the image forming apparatus 10 according to a first embodiment of the present invention will be described with reference to FIGS. The image forming apparatus 10 according to the first embodiment of the present invention is an electrophotographic tandem type image forming apparatus. In the example shown in FIG. 1, the image forming apparatus 10 is a color printer. Other examples of the image forming apparatus 10 are a color copier, a color facsimile, or a multifunction machine having a color image forming function.

  [Schematic Configuration of Image Forming Apparatus 10] As shown in FIG. 1, the image forming apparatus 10 includes a sheet supply unit 2, a sheet conveying unit 3, a plurality of developer containers 40, and a plurality of image forming units in a housing 100. 4, an optical scanning unit 5, a fixing unit 6, an intermediate transfer belt 71, a secondary transfer unit 72, an operation display unit 80, a control unit 8, and the like. 3 and 5, the image forming apparatus 10 also includes a displacement mechanism 75 and a light shielding switching unit 77. 3 and 5 are schematic side views of all of the image forming unit 4 and the intermediate transfer belt 71 in the image forming apparatus 10.

  The sheet supply unit 2 includes a sheet cassette 21 that can be attached to and detached from the housing 100, and a sheet delivery unit 22 that sends out the recording sheet 9 accommodated in the sheet cassette 21 to the image forming unit 4. The recording sheet 9 is a sheet-like image forming medium such as paper, coated paper, postcard, envelope, and OHP sheet.

  The sheet delivery unit 22 includes a pickup roller 221 and a delivery roller 222. The sheet feeding unit 22 picks up the recording sheets 9 one by one from the sheet cassette 21 and further sends the recording sheets 9 to the sheet conveying path 300 of the sheet conveying unit 3.

  The sheet conveyance unit 3 includes a registration roller 31, a conveyance roller 32, a discharge roller 33, and the like. The registration roller 31 and the conveyance roller 32 convey the recording sheet 9 along the sheet conveyance path 300. Further, the discharge roller 33 discharges the recording sheet 9 on which an image has been formed in the middle of the sheet conveyance path 300 from the discharge port of the sheet conveyance path 300 onto the discharge tray 101.

  The developer container 40 and the image forming unit 4 are provided for each color of the developer (toner). The symbols Y, C, M, and K in the figure represent the corresponding developer colors (yellow, cyan, magenta, and black), respectively. The developer of each color is supplied to each of the image forming units 4 from each of the developer containers 40 that can be attached to and detached from the casing 100.

  Each of the image forming portions 4 provided for each color of the developer is disposed at a position along the rotating endless intermediate transfer belt 71. Each of the image forming units 4 forms images (toner images) of different colors on the surface of the rotating intermediate transfer belt 71 so as to overlap each other.

  Each of the image forming units 4 includes a drum-shaped photoconductor 41, a charging unit 42, a developing unit 43, a primary transfer unit 45, a charge eliminating unit 46, a primary cleaning unit 47, and the like. The photoreceptor 41 is an example of an image carrier.

  The intermediate transfer belt 71 is an endless belt-like member formed in an annular shape. The intermediate transfer belt 71 rotates in a state of being spanned between the driving roller 73 and the driven roller 74. In the following description, a direction in which the intermediate transfer belt 71 rotates (moves) along the arrangement direction of the plurality of image forming units 4 is referred to as a belt rotation direction R1.

  In each of the image forming units 4, the photoreceptor 41 rotates at a peripheral speed corresponding to the peripheral speed (moving speed) of the intermediate transfer belt 71, and the charging unit 42 uniformly charges the surface of the photoreceptor 41. Let

  Further, an electrostatic latent image is written on the surface of the photosensitive member 41 charged by the optical scanning unit 5 having a laser light source (not shown), the polygon mirror 51, and the deflecting optical device 52 by scanning the laser beam. Further, the developing unit 43 supplies the toner (developer) to the photoconductor 41 to develop the electrostatic latent image into a toner image. The optical scanning unit 5 is generally called a laser scanning unit (LSU).

  Further, the primary transfer unit 45 transfers the toner image on the photoreceptor 41 onto the surface of the intermediate transfer belt 71. Further, the primary cleaning unit 47 cleans the surface of the photoreceptor 41 by removing the toner remaining on the surface of the photoreceptor 41.

  The charge removal unit 46 provided in each of the image forming units 4 is provided between the primary transfer unit 45 and the primary cleaning unit 47. For example, the charge removal unit 46 is fixed to a surface of the primary cleaning unit 47 on the primary transfer unit 45 side.

  The charge removal unit 46 is a device that outputs light (charge removal light) for discharging the photoreceptor 41. The static elimination unit 46 outputs a first static elimination light L1 and a second static elimination light L2.

  The first charge removal light L1 is charge removal light that travels between the primary transfer portion 45 and the primary cleaning portion 47 toward the upstream side in the belt rotation direction R1. On the other hand, the second charge removal light L2 is charge removal light that travels between the primary transfer portion 45 and the primary cleaning portion 47 toward the downstream side in the belt rotation direction R1.

  In the example shown in FIG. 2, the static elimination unit 46 includes a light source 461 and an optical branching device 462 mounted on a substrate 460, and the optical branching unit 462 removes the emitted light (static elimination light) from the light source 461. The electric light L1 and the second charge eliminating light L2 are branched. In this case, the light source 461 of the first charge removal light L1 also serves as the light source of the second charge removal light L2. The light source 461 is, for example, a light emitting diode.

  In each of the image forming units 4, the first charge removal light L 1 is a post-transfer removal that is irradiated between a portion of the photoconductor 41 facing the primary transfer unit 45 and a portion corresponding to the primary cleaning unit 47. It is lightning.

  On the other hand, in each of the image forming units 4, the second charge-removing light L <b> 2 has a location corresponding to the developing unit 43 in the image forming unit 4 adjacent to the image forming unit 4 on the downstream side in the belt rotation direction R <b> 1. This is a pre-transfer charge eliminating light that is irradiated between a portion corresponding to the primary transfer portion 45.

  In this embodiment, the black image forming unit 4K, the magenta image forming unit 4M, the cyan image forming unit 4C, and the yellow image forming unit 4Y are arranged in order from the downstream side to the upstream side in the belt rotation direction R1. Has been placed.

  Accordingly, the second charge removal light L2 (the charge removal light before transfer) is transferred from the charge removal section 46 of the yellow image formation section 4Y to the photoreceptor 41 of the cyan image formation section 4C, one downstream side. The image forming section 4C for cyan is one downstream from the charge eliminating section 46 to the photoconductor 41 of the magenta image forming section 4M, and the one downstream from the charge eliminating section 46 of the magenta image forming section 4M. The photosensitive member 41 of the black image forming unit 4K is irradiated with the light.

  When the three photosensitive members 41 corresponding to three colors (black, magenta, and cyan) that are relatively conspicuous are irradiated with the second charge removal light L2 in addition to the first charge removal light L1, the primary transfer portion 45 is used. The transfer voltage can be kept relatively low. As a result, image memory problems are less likely to occur.

  Since the yellow image is not conspicuous, the problem of the image memory is not easily revealed even when the second charge removal light L2 (pre-transfer charge removal light) is not applied to the photoconductor 41 of the yellow image forming unit 4Y.

  The roller-shaped secondary transfer unit 72 transfers the image (toner image) transferred to the surface of the intermediate transfer belt 71 to the recording sheet 9 moving on the sheet conveyance path 300.

  The fixing unit 6 sandwiches the recording sheet 9 on which the toner image is formed between a fixing roller 61 including a heater 610 such as a halogen heater and a pressure roller 62, and sends the recording sheet 9 to a subsequent process. Thus, the fixing unit 6 heats the toner image (image) on the recording sheet 9 and fixes the image on the recording sheet 9.

  The control unit 8 displays an operation menu or the like on the operation display unit 80, and based on input information input through the operation display unit 80 and detection information of various sensors (not shown), Control electrical equipment.

  For example, the control unit 8 includes a microprocessor unit (MPU) and a storage unit. The MPU executes various arithmetic processes by executing a control program recorded in advance in the storage unit. Thereby, the control unit 8 controls the image forming apparatus 10 in an integrated manner.

  The displacement mechanism 75 shown in FIGS. 3 and 5 is a mechanism that changes the positional relationship between the intermediate transfer belt 71 and the photoreceptor 41 (image carrier). The displacement mechanism 75 can selectively switch the operation states of the plurality of image forming units 4 to a plurality of operation modes including the first mode and the second mode by changing the positional relationship. The displacement mechanism 75 is an example of the mode switching unit.

  In the present embodiment, the displacement mechanism 75 can selectively switch the operation state between a color mode corresponding to the first mode and a monochrome mode which is an example of the second mode. The color mode is a mode in which the photoconductors 41 of all the image forming units 4 operate in contact with the intermediate transfer belt 71. On the other hand, the monochrome mode is a mode in which only the photosensitive member 41 of the black image forming unit 4K located on the most downstream side in the belt rotation direction R1 is in contact with the intermediate transfer belt 71.

  For example, the displacement mechanism 75 rotates a support frame 76 that supports the primary transfer unit 45 of the remaining image forming units 4 (4Y, 4C, 4M) excluding the driven roller 74 and the black image forming unit 4K. It is a mechanism to move. In this case, the displacement mechanism 75 rotates the support frame 76 around the primary transfer portion 45 of the black image forming portion 4K, for example. The displacement mechanism 75 is, for example, a solenoid actuator.

  When the color mode is selected, the control unit 8 turns on the charge removal unit 46 of the image forming unit 4 for all four colors. On the other hand, when the monochrome mode is selected, the control unit 8 controls the neutralization unit 46 of the black image forming unit 4K operating in the monochrome mode and the magenta adjacent to the upstream side of the belt rotation direction R1. The charge removing unit 46 of the image forming unit 4M is turned on, and the other charge removing units 46 are turned off.

  As described above, in the image forming apparatus 10, the static elimination unit 46 of each of the image forming units 4 also functions as post-transfer static elimination and pre-transfer static elimination. In such an image forming apparatus 10, a case where the image forming apparatus 10 does not include the light shielding switching unit 77 will be considered. In this case, when the monochrome mode (single color mode) is selected, when the neutralization unit 46 of the second magenta image forming unit 4M from the most downstream side in the belt rotation direction R1 emits light, There is a possibility that the 1 static elimination light L1 may adversely affect the stopped photoconductor 41 in the magenta image forming unit 4M.

  In addition, when the monochrome mode is selected and the neutralization unit 46 of the second magenta image forming unit 4M from the most downstream side in the belt rotation direction R1 is turned off, the most downstream side for black The image forming unit 4K does not perform static elimination before transfer. In this case, there is a risk of image quality failure due to the transfer memory during image formation in the monochrome mode.

  On the other hand, if the image forming apparatus 10 including the light-shielding switching unit 77 is employed, as will be described below, the charge removal unit 46 is used when the charge removal unit 46 functions as both post-transfer charge removal and pre-transfer charge removal. It is possible to prevent the first static elimination light L1 from 46 from adversely affecting the photosensitive member 41 and the occurrence of image quality defects due to the static elimination unit 46 being extinguished.

  The light shielding switching unit 77 outputs the first charge removal light L1 in the magenta image forming unit 4M located adjacent to the upstream side of the belt rotation direction R1 with respect to the black image forming unit 4K operating in the monochrome mode. It is possible to block.

  More specifically, when the color mode is selected, the light shielding switching unit 77 does not block the first static elimination light L1 toward the photoconductor 41 in the magenta image forming unit 4M. On the other hand, when the monochrome mode is selected, the light shielding switching unit 77 shields the first charge removal light L1 toward the photoconductor 41 in the magenta image forming unit 4M.

  4 and 6 are front views of the light shielding switching unit 77 and its surroundings in the color mode and the monochrome mode, respectively. The light shielding switching unit 77 in this embodiment includes a light shielding member 771 that shields light and a connecting portion 772 that couples the light shielding member 771 to the support frame 76.

  4 and 6 and FIGS. 7 to 9 described later also show the cross section of the intermediate transfer belt 71 and the support frame 76 and the primary transfer portion 45 drawn by a virtual line (two-dot chain line). ing.

  The light shielding member 771 is displaced in conjunction with the movement of the displacement mechanism 75 by being supported by the support frame 76 via the connecting portion 772. More specifically, the light blocking member 771 is interlocked with the movement of the displacement mechanism 75 to block the optical path of the first charge removal light L1 in the magenta image forming unit 4M and the first charge removal light L1. It is displaced between the position where the optical path is not blocked.

  3 and 4 show a state in which the light shielding member 771 is present at a retreat position where the light path of the first static elimination light L1 is not blocked. On the other hand, FIGS. 5 and 6 show a state in which the light blocking member 771 exists at a blocking position that blocks the optical path of the first static elimination light L1.

  Therefore, when the color mode is selected in the second image forming unit 4 (4M) from the most downstream side in the belt rotation direction R1, the light shielding switching unit 77 receives the first charge removal light L1. The photosensitive member 41 is irradiated and the second charge eliminating light L2 is irradiated to the photosensitive member 41 of the image forming unit 4 (4K) on the most downstream side.

  Further, the light shielding switching unit 77 is configured to output the first charge removal light L1 when the monochrome mode is selected in the second image forming unit 4 (4M) from the most downstream side in the belt rotation direction R1. The photosensitive member 41 is not irradiated and the second charge eliminating light L2 is irradiated to the photosensitive member 41 of the image forming unit 4 (4K) on the most downstream side. The light shielding switching unit 77 is an example of the static elimination exposure switching unit.

  As described above, when the image forming apparatus 10 is employed, the neutralization unit 46 of the magenta image forming unit 4M is lit in a state where the monochrome mode is selected. The black image forming unit 4K performs static elimination before transfer. For this reason, it is possible to prevent image quality defects due to the transfer memory during image formation in the monochrome mode.

  Further, in the magenta image forming unit 4M when the monochrome mode is selected, the first charge removal light L1 from the charge removal unit 46 is interrupted on the way to the photoconductor 41. For this reason, it is possible to prevent the first charge eliminating light L1 from adversely affecting the stopped photoconductor 41 in the magenta image forming unit 4M.

  Second Embodiment Next, an image forming apparatus 10A according to a second embodiment of the present invention will be described with reference to FIG. Compared to the image forming apparatus 10, the image forming apparatus 10 </ b> A has a configuration in which the light shielding switching unit 77 is replaced with a light shielding switching unit 77 </ b> A.

  FIG. 7 is a front view of the light shielding switching unit 77A and its periphery in the image forming apparatus 10A. 7, the same components as those shown in FIGS. 1 to 6 are given the same reference numerals. Hereinafter, differences between the light shielding switching unit 77A of the image forming apparatus 10 and the light shielding switching unit 77 of the image forming apparatus 10A will be described.

  The light shielding switching unit 77A includes the light shielding member 771 that shields light and a displacement mechanism 772A that supports and displaces the light shielding member 771. The displacement mechanism 772A displaces the light shielding member 771 between the blocking position and the retracted position. FIG. 7 shows a state where the light shielding member 771 is present at the retracted position.

  For example, it is conceivable that the controller 8 controls the displacement mechanism 75 that displaces the support frame 76 and the displacement mechanism 772A that displaces the light shielding member 771 in synchronization. In this case, the control unit 8 controls the displacement mechanism 772A to position the light shielding member 771 at the retracted position when the displacement mechanism 75 is controlled to the color mode state. Further, the control unit 8 controls the displacement mechanism 772A to position the light shielding member 771 at the blocking position when controlling the displacement mechanism 75 to the monochrome mode.

  Even when the light shielding switching unit 77A is employed, it is possible to prevent the first static elimination light L1 from the static elimination unit 46 from adversely affecting the photoconductor 41 and image quality failure due to the extinguishing of the static elimination unit 46. it can.

  Third Embodiment Next, an image forming apparatus 10B according to a third embodiment of the present invention will be described with reference to FIGS. Compared with the image forming apparatus 10, the image forming apparatus 10 </ b> B has a configuration in which the light shielding switching unit 77 is replaced with a light shielding switching unit 77 </ b> B.

  8 and 9 are front views of the light shielding switching unit 77B and its surroundings in the image forming apparatus 10B. FIG. 8 shows a state when the color mode is selected, and FIG. 9 shows a state when the monochrome mode is selected. 8 and 9, the same components as those shown in FIGS. 1 to 7 are given the same reference numerals. Hereinafter, differences between the light shielding switching unit 77B of the image forming apparatus 10B and the light shielding switching unit 77 of the image forming apparatus 10 will be described.

  The light shielding switching unit 77B is an optical shutter fixed to the optical path of the first charge removal light L1 in the magenta image forming unit 4M. The light shielding switching unit 77B selectively allows the aperture unit 771B positioned in the optical path of the first charge removal light L1 to be in a transparent state where the first charge removal light L1 is allowed to pass and an opaque state where the first charge removal light L1 is blocked. It is possible to switch to. The light shielding switching unit 77B is, for example, a liquid crystal shutter.

  For example, it is conceivable that the control unit 8 performs control in synchronization with the displacement mechanism 75 that displaces the support frame 76 and the light shielding switching unit 77B (optical shutter). In this case, when the control unit 8 controls the displacement mechanism 75 to the color mode state, the control unit 8 sets the aperture unit 771B of the light shielding switching unit 77B to a transparent state. Further, when the control unit 8 controls the displacement mechanism 75 to the monochrome mode, the control unit 8 sets the aperture 771B of the light shielding switching unit 77B to an opaque state.

  Even when the light shielding switching unit 77B is employed, it is possible to prevent the first static elimination light L1 from the static elimination unit 46 from adversely affecting the photoconductor 41 and image quality failure due to the extinguishing of the static elimination unit 46. it can.

  In the same way as the light blocking switching unit 77, the light blocking switching units 77A and 77B both move toward the photoconductor 41 in the magenta image forming unit 4M in accordance with the selected state of the color mode and the monochrome mode. It has a configuration in which whether or not to block the 1 static elimination light L1 is switched to the selected enemy. The light shielding switching units 77A and 77B are also examples of the static elimination exposure switching unit.

  [Fourth Embodiment] Next, an image forming apparatus 10C according to a fourth embodiment of the present invention will be described with reference to FIG. Compared with the image forming apparatus 10, the image forming apparatus 10 </ b> C has a configuration in which the light shielding switching unit 77 is omitted and the charge removing unit 46 is replaced with a charge removing unit 46 </ b> C.

  FIG. 10 is a schematic plan view of the charge removal unit 46C in the image forming apparatus 10C. 10, the same components as those shown in FIGS. 1 to 9 are given the same reference numerals. Hereinafter, differences between the charge removal unit 46C of the image forming apparatus 10B and the charge removal unit 46 of the image forming apparatus 10 will be described.

  The charge removal unit 46C includes a first light source 4611 for the first charge removal light L1 and a second light source 4612 for the second charge removal light L2 mounted on the substrate 460. The first light source 4611 outputs light toward the upstream side in the belt rotation direction R1, and the second light source 4612 outputs light toward the downstream side in the belt rotation direction R1. The first light source 4611 and the second light source 4612 can be turned on and off independently.

  For example, the control unit 8 may control the displacement mechanism 75 that displaces the support frame 76 in synchronization with the first light source 4611 and the second light source 4612. In this case, when the control unit 8 controls the displacement mechanism 75 to the color mode state, the control unit 8 and the first light source 4611 in the charge removal unit 46C of the black image forming unit 4K and the remaining three colors. The first light source 4611 and the second light source 4612 in the charge removal unit 46C of the image forming units 4M, 4C, 4Y are turned on.

  On the other hand, when the control unit 8 controls the displacement mechanism 75 to the monochrome mode, the first light source 4611 in the charge removal unit 46C of the black image forming unit 4K and the adjacent magenta The second light source 4612 in the charge removal unit 46C of the image forming unit 4M is turned on, and all the remaining light sources of the charge removal unit 46C are turned off.

  That is, when the color mode (first mode) is selected in the magenta image forming unit 4M (second image forming unit), the charge eliminating unit 46C and the control unit 8 perform the first charge eliminating light L1. Is applied to the photoconductor 41 and the second charge eliminating light L2 is applied to the photoconductor 41 of the black image forming unit 4K (first image forming unit). Further, the charge removal unit 46C and the control unit 8 are configured such that when the monochrome mode is selected, the first charge removal light L1 is not applied to the photoconductor 41, and the second charge removal light L2 is applied to the black image formation. The photosensitive member 41 of the part 4K is irradiated. The charge removal unit 46C and the control unit 8 are also examples of the charge removal exposure switching unit.

  Even when the image forming apparatus 10C is employed, the first static elimination light L1 from the static elimination unit 46C has an adverse effect on the photoconductor 41 and prevents image quality defects due to the static elimination unit 46C being turned off. it can.

  [Other Application Examples] In the image forming apparatuses 10, 10A, 10B, and 10C shown above, the positional relationship between the magenta image forming unit 4M and the cyan image forming unit 4C in the belt rotation direction R1 is reversed. It is also conceivable.

  Further, in the image forming apparatuses 10, 10A, 10B, and 10C, the first mode and the second mode, which are options of operation modes, are the color mode for all colors and the monochrome mode for only one color, respectively. It may be other than

  For example, the first mode is a mode in which the image forming units 4 of all colors operate, and the second mode is a mode in which two or three image forming units 4 operate from the most downstream side in the belt rotation direction R1. It is not unthinkable.

  The image forming apparatus according to the present invention can be freely combined with the above-described embodiments and application examples, or can be appropriately modified within the scope of the invention described in each claim. Alternatively, it may be configured by omitting a part.

2: Sheet feeding unit 3: Sheet conveying unit 4: Image forming unit 4C: Cyan image forming unit 4K: Black image forming unit 4M: Magenta image forming unit 4Y: Yellow image forming unit 5: Optical scanning unit 6: Fixing unit 8: Control unit 9: Recording sheets 10, 10A, 10B, 10C: Image forming apparatus 21: Sheet cassette 22: Sheet feeding unit 31: Registration roller 32: Conveying roller 33: Discharge roller 40: Developer container 41: Photosensitive Body 42: Charging unit 43: Developing unit 45: Primary transfer unit 46, 46C: Static elimination unit 47: Primary cleaning unit 51: Polygon mirror 52: Deflection optical device 61: Fixing roller 62: Pressure roller 71: Intermediate transfer belt 72 : Secondary transfer unit 73: driving roller 74: driven roller 75: displacement mechanism (mode switching unit)
76: Support frames 77, 77A, 77B: Shading switching part (static discharge exposure switching part)
80: Operation display unit 100: Housing 101: Ejection tray 221: Pickup roller 222: Delivery roller 300: Sheet conveyance path 460: Substrate 461: Light source 462: Optical branching device 610: Heater 771: Light shielding member 771B: Aperture unit 772: Connecting portion 772A: displacement mechanism 4611: first light source 4612: second light source L1: first charge removal light L2: second charge removal light R1: belt rotation direction

Claims (5)

An image carrier, a developing unit for developing an electrostatic latent image on the surface of the image carrier, a primary transfer unit for transferring an image to the intermediate transfer belt, and the image, which are respectively arranged at positions along the rotating endless intermediate transfer belt An image forming apparatus including a plurality of image forming units each including a cleaning unit for cleaning the surface of the carrier, and forming images of different colors on the surface of the intermediate transfer belt,
Provided in each of the image forming units, the first charge removal light traveling between the primary transfer unit and the cleaning unit toward the upstream side in the rotational direction of the intermediate transfer belt and the downstream side in the rotational direction of the intermediate transfer belt. A static elimination unit that outputs a second static elimination light;
The state of the image forming unit is changed to a first mode in which all the image forming units operate, and only a part of the first image forming units located on the downstream side in the rotation direction of the intermediate transfer belt among the plurality of image forming units. A mode switching unit capable of selectively switching to a plurality of operation states including a second mode in which
When the first mode is selected in the second image forming unit located next to the first image forming unit on the upstream side in the rotation direction of the intermediate transfer belt, the first charge eliminating light is emitted from the image carrier. When the second mode is selected, the first charge removal light is applied to the image carrier when the second mode is selected and the second charge removal light is applied to the image carrier of the first image forming unit. An image forming apparatus comprising: a charge removal exposure switching unit that causes the second charge eliminating light to be irradiated onto the image carrier of the first image forming unit.   The static elimination exposure switching unit does not block the first static elimination light toward the image carrier in the second image forming unit when the first mode is selected, and the second mode is selected. 2. The image forming apparatus according to claim 1, wherein the second image forming unit is a light blocking switching unit that blocks the first charge removal light toward the image carrier.   The said light shielding switching part contains the member displaced between the position which interrupts | blocks the optical path of the said 1st static elimination light in the said 2nd image formation part, and the position which does not interrupt | block the optical path of the said 1st static elimination light. The image forming apparatus described. The mode switching unit changes the positional relationship between the intermediate transfer belt and the image carrier to change the first mode in which the image carrier of all the image forming units and the intermediate transfer belt are in contact with each other. A displacement mechanism capable of switching to the second mode in which the image carrier of only one image forming unit and the intermediate transfer belt are in contact with each other;
The light shielding switching unit is configured to displace a member that is displaced between a position where the optical path of the first charge removal light in the second image forming unit is blocked and a position where it is not blocked in conjunction with the movement of the displacement mechanism of the mode switching unit. The image forming apparatus according to claim 3, comprising:   The light shielding switching unit is fixed to an optical path of the first charge removal light in the second image forming unit, and can be selectively switched between a state in which the first charge removal light is allowed to pass and a state in which the first charge removal light is blocked. The image forming apparatus according to claim 2, wherein the image forming apparatus is an optical shutter.

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