JP5760838B2 - Primary transfer roller lifting mechanism and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a primary transfer roller elevating mechanism that switches between a non-image forming mode, a monochrome mode, and a color mode with a simple configuration, and an image forming apparatus including the same.

  Conventionally, a toner image is formed on a photoreceptor by electrophotography using toner, the toner image is primarily transferred to a belt, the primary transfer image is secondarily transferred to a sheet, and the transferred toner image is transferred by a fixing device. An image forming apparatus that forms a monochrome or full-color image by fixing on a sheet is known.

  Generally, in the monochrome mode, a primary transfer roller corresponding to a photosensitive drum that develops and carries a toner image of black toner is brought into contact with the transfer belt, and the remaining yellow, magenta, and cyan toner images are supported. The three primary transfer rollers are separated from the transfer belt.

  In the color mode, three primary transfer rollers corresponding to yellow, magenta, and cyan toners are further brought into contact with the transfer belt while the primary transfer roller corresponding to the black toner is in contact with the transfer belt.

  In the non-image forming mode when the operation is stopped, the four primary transfer rollers corresponding to all the toners of black, yellow, magenta, and cyan are separated from the transfer belt. Corresponding to these three types of modes, a mechanism for separating and contacting each primary transfer roller to the transfer belt is required.

  Conventionally, for example, a primary transfer roller for black toner (hereinafter referred to as K-compatible transfer roller) and a primary transfer roller for yellow, magenta, and cyan toner (hereinafter referred to as YMC-compatible transfer roller) are individually linked. A method has been proposed in which a mechanism is provided so that each primary transfer roller is separated from and contacted with a transfer belt. (For example, refer to Patent Document 1.)

  In addition, a method has been proposed in which a guide member and a trigger linked to a driving source are arranged on each primary transfer roller, and the K-compatible transfer roller and the YMC-compatible transfer roller are individually moved to be in contact with and separated from the transfer belt. Yes. (For example, see Patent Document 2.)

  A method of switching between the monochrome mode and the color mode by driving the link member of the K-compatible transfer roller and the link member of the YMC-compatible transfer roller by the movement of one rotating cam has been proposed. (For example, refer to Patent Document 3.)

Japanese Patent Laid-Open No. 2004-163795 JP 2001-318508 A JP 2003-057911 A

  However, in each of the above Patent Documents 1 to 3, the link unit that moves the YMC-compatible transfer roller that engages with one or two cams and the link unit that moves the K-compatible transfer roller are configured by separate component configurations. Has been. For this reason, the number of parts is large, which hinders downsizing of the apparatus main body and increases the cost.

  SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and provides a primary transfer roller elevating mechanism that switches between a non-image forming mode, a monochrome mode, and a color mode with a simple configuration, and an image forming apparatus including the same. With the goal.

  In order to solve the above-described problem, the primary transfer roller lifting mechanism of the present invention includes a plurality of photosensitive drums arranged side by side and a plurality of supporting rollers wound around the plurality of photosensitive drums. A transfer belt that primarily transfers a toner image formed on a predetermined photosensitive drum, and secondarily transfers the primary transferred toner image to an image forming medium being conveyed in a secondary transfer unit; and the photosensitive drum; A plurality of primary transfer rollers corresponding to the plurality of photosensitive drums and arranged to be movable up and down on the opposite side across the transfer belt in order to contact the transfer belt, and each of the plurality of primary transfer rollers A rack member having an engaging portion selectively engaging with both ends of the transfer roller and a gear portion and movable in the parallel direction, and a biasing member for biasing the rack member in one of the moving directions And the rack above A tooth missing gear that meshes with the gear portion of the material, and a rotation drive control of the tooth missing gear, and based on the movement of the rack member accompanying the rotation drive control, all of the plurality of photosensitive drums are connected to the intermediate transfer belt. A first position for contact, a second position for contacting one of the plurality of photosensitive drums with the intermediate transfer belt, and a contact between the plurality of photosensitive drums and the intermediate transfer belt. And a drive control unit that selectively moves each of the plurality of primary transfer rollers at a third position.

  In order to solve the above problems, an image forming apparatus according to the present invention includes the primary transfer roller lifting mechanism.

  The present invention can provide a primary transfer roller elevating mechanism that switches between a non-image forming mode, a monochrome mode, and a color mode with a simple configuration, and an image forming apparatus including the same.

1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (printer) including a primary transfer roller lifting mechanism according to Embodiment 1 of the present invention. (a) is an external perspective view of a printer provided with a primary transfer roller raising / lowering mechanism according to the first embodiment, and (b) is a developing device of the image forming unit, a reserve tank and a toner cartridge of a toner supply unit in an easy-to-understand manner. FIG. 2 is a perspective view schematically showing only the transfer belt together with the transfer belt. 2 is a circuit block diagram including a control device of a printer including a primary transfer roller lifting mechanism according to Embodiment 1. FIG. (a), (b), (c), (d) is a diagram for explaining the lifting operation of the primary transfer roller in the non-image forming mode, the monochrome mode, and the color mode in the primary transfer roller lifting mechanism according to the first embodiment. is there. FIG. 10 is a diagram schematically illustrating an internal configuration of a printer including a primary transfer roller lifting mechanism according to a second embodiment. FIG. 10 is a diagram illustrating the lifting and lowering operation of the primary transfer roller in the non-image forming mode, the monochrome mode, and the color mode in the primary transfer roller lifting mechanism according to the second embodiment.

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

  FIG. 1 is a cross-sectional view illustrating an internal configuration of a full-color image forming apparatus (hereinafter simply referred to as a printer) provided with a primary transfer roller lifting mechanism according to Embodiment 1 of the present invention.

  A printer 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, a transfer belt unit 3, a toner supply unit 4, a paper feeding unit 5, and a belt type fixing device. It comprises a unit 6 and a transport unit 7 for duplex printing.

  The image forming unit 2 is in contact with the lower running surface 8a of the transfer belt 8 of the transfer belt unit 3 and has four developing devices 9 (9k, 9c, 9m, 9y) arranged in a multistage manner from right to left in FIG. Configured. The image forming unit 2 is held by a frame of the printer 1 main body so as to be movable up and down from a printing execution position shown in FIG. 1 to a maintenance position below it.

  Of the four developing devices 9, three developing devices 9c, 9m, and 9y on the upstream side (the left side in the figure) are cyan (C), magenta (M), and yellow (Y), which are subtractive three primary colors, respectively. A mono-color image is formed with the color toner, and the developing device 9k forms a monochrome image mainly with black (K) toner used for characters and dark portions of the image.

  Each of the developing devices 9 has the same configuration except for the color of the toner that develops the image. Therefore, the configuration of the developing device 9y for yellow (Y) toner will be described below as an example.

  The developing device 9 includes a photosensitive drum 10 at the top. The photosensitive drum 10 has a peripheral surface made of, for example, an organic photoconductive material. A cleaner 11, a charging roller 12, an optical writing head 13, and a developing roller 15 of the developing device 14 are disposed in contact with or around the periphery of the photosensitive drum 10.

  The developing device 14 includes a housing 16 that covers the outside, a partition wall 17 provided inside, a developing roller 15, a first stirring and conveying screw 18, and a second stirring and conveying screw 19. Although not specifically shown, the first and second agitating and conveying screws 18 and 19 include a screw shaft and a fin that is integrally formed with the screw shaft and rotates.

  The developing unit 14 includes any one of black (K), cyan (C), magenta (M), and yellow (Y) indicated by K, C, M, and Y in FIG. The toner is supplied.

  The transfer belt unit 3 has an endless transfer belt 8 that extends in the shape of a flat loop in the left-right direction in the figure at approximately the center of the main unit, and the transfer belt 8 is stretched over the transfer belt 8. A driving roller 21 and a driven roller 22 are provided to circulate and move counterclockwise as indicated by an arrow a in the figure.

  The transfer belt unit 3 further includes a secondary transfer backup roller 23 over which the transfer belt 8 is stretched above the drive roller 21. A secondary transfer roller 24 is pressed against the secondary transfer backup roller 23 via the transfer belt 8 to form a secondary transfer portion.

  The transfer belt 8 includes a primary transfer roller 25 integrated with the unit. The primary transfer roller 25 is disposed so as to sandwich the transfer belt 8 at a position slightly shifted to the downstream side in the circulation movement direction of the transfer belt 8 with respect to the photosensitive drum 10.

  The primary transfer roller 25 directly transfers (primary transfer) the toner image to the belt surface that circulates below. The transfer belt 8 conveys the toner image to a secondary transfer portion where the secondary transfer roller 24 is pressed against the secondary transfer backup roller 23 via the transfer belt 8 in order to further transfer (secondary transfer) the toner image to a sheet.

  The image forming processing mode of the printer 1 of this example includes three types of processing modes: a non-image forming mode, a monochrome mode, and a color mode. The non-image forming mode is a processing mode when the operation of the apparatus main body is paused or stopped. At this time, all four primary transfer rollers are separated from the transfer belt 8.

  The monochrome mode is a processing mode for forming only a monochrome image using black (K) toner. At this time, only the developing device 9k is driven, the primary transfer roller 25 corresponding to the developing device 9k is lowered, and the transfer belt 8 is brought into contact with the photosensitive drum 10 of the developing device 9k.

  At this time, the remaining other developing devices 9y, 9m, and 9c are at rest, and the three primary transfer rollers 25 corresponding to these photosensitive drums 10 are in the raised position, and the transfer belt 8 is moved to the developing devices 9y, 9m. , 9c are separated from the photosensitive drum 10.

  The color mode is a processing mode in which a full-color image is formed using black (K) toner and four-color toners of cyan (C), magenta (M), and yellow (Y). At this time, the primary transfer rollers 25 corresponding to the four photosensitive drums 10 of the developing devices 9k, 9c, 9m, and 9y are lowered, and the transfer belt 8 is moved to the four photosensitive devices of the developing devices 9k, 9c, 9m, and 9y. The body drum 10 is brought into contact with the body drum 10.

  The four primary transfer rollers are moved up and down in accordance with the three types of processing modes, the non-image forming mode, the monochrome mode, and the color mode, by controlling a primary transfer lifting mechanism described later.

  Further, a belt cleaner 26 is disposed on the transfer belt 8 so as to abut on the surface of the driven roller 22. Below the belt cleaner 26, a waste toner collecting container 27 for storing waste toner removed from the transfer belt 8 by the belt cleaner 26 is detachably disposed.

  The toner supply unit 4 includes the above-described four reserve tanks 20 disposed above the upper running surface of the transfer belt 8 and toner replenishment toners detachably disposed on the reserve tanks 20. The cartridge 28 is configured.

  The four toner cartridges 28 respectively store black (K), cyan (C), magenta (M), and yellow (Y) toner, and the four reserve tanks 20 are respectively mounted on the toner. The toner is replenished from the cartridge 28.

  These four reserve tanks 20 are connected to the corresponding developing device 14 of the developing device 9 by a toner supply path (not shown in FIG. 1 hidden behind the transfer belt unit 3).

  Although not particularly shown, the toner supply unit 4 is held on the frame of the printer 1 main body so as to be able to be raised and lowered from the printing execution position shown in FIG. 1 to a maintenance position above it.

  On the left side of the toner supply unit 4, two electrical parts 29 are disposed from the left side of the belt cleaner 26 to above the driven roller 22. A circuit board on which a control device composed of a plurality of electronic components is mounted is mounted on the electrical component 29.

  The paper feed unit 5 includes two paper feed cassettes 31 (31a, 31b) arranged in two upper and lower stages. A paper take-out roller 32, a feed roller 33, a separating roller 34, and a standby conveyance roller pair 35 are arranged in the vicinity of the paper feed opening (right side in the drawing) of the two paper feed cassettes 31, respectively.

  The secondary transfer portion described above is formed in the paper conveyance direction (vertical upward direction in the drawing) of the standby conveyance roller pair 35. A belt-type heat fixing unit 6 is disposed downstream (upward in the drawing) of the secondary transfer portion.

  On the further downstream side of the belt-type heat fixing unit 6, a pair of carry-out rollers 36 for carrying out the fixed paper from the belt-type heat fixing unit 6, and a paper discharge tray 37 formed on the upper surface of the apparatus. A paper discharge roller pair 38 for paper discharge is provided.

  The conveyance unit 7 for double-sided printing also serves as an opening / closing member whose outer surface (right outer surface in the drawing) opens or shields the inside of the printer 1 from the side surface to the outside.

  This duplex printing transport unit 7 has a start return path 39a that branches rightward in the figure from just before the paper discharge roller pair 38, an intermediate return path 39b that bends downward, and further turns leftward to finally return. A return path 39 having an end return path 39c for reversing the paper is provided.

  In the middle of the return path 39, five pairs of return rollers 41 (41a, 41b, 41c, 41d, 41e) are arranged. The exit of the end return path 39 c joins the conveyance path to the pair of standby conveyance rollers 35 corresponding to the sheet feeding cassette 31 b below the sheet feeding unit 5.

  FIG. 2A is an external perspective view of the printer 1, and FIG. 2B is an easy-to-understand one each of the developing device 9 of the image forming unit 2, the reserve tank 20 of the toner supply unit 4, and the toner cartridge 28. FIG. 6 is a perspective view schematically showing only the transfer belt 8 together. 2A and 2B, the same components as those in FIG. 1 are given the same reference numerals as those in FIG.

  As shown in FIG. 2 (a), the printer 1 is provided with a front door 42 at the front, and an opening / closing member 44 with a handle 43 at the top on the right side. The double-sided printing conveyance unit 7 shown in FIG.

  As shown in FIG. 1, the printer 1 does not directly transfer a toner image onto a sheet, but instead passes a transfer belt 8 to a sheet that is vertically conveyed to a secondary transfer unit by a standby conveyance roller pair 35. The toner image is transferred.

  Accordingly, troubles such as paper jams do not occur in the arrangement portion of the kits, so the operation of attaching / detaching consumables such as kits concentrated on the left side of FIG. 1 opens the front door 42 shown in FIG. The kits are configured to be exchanged in the longitudinal direction (front door direction).

  Similarly, the printer 1 transfers the toner image to a sheet conveyed in the vertical direction to the secondary transfer unit via the transfer belt 8, and further conveys the sheet in the vertical direction to fix the transferred toner image on the sheet. It is a method to do.

  Therefore, at the time of maintenance processing for recovering from a problem such as a paper jam occurring in the paper transport path, as shown in FIG. 2 (a), it is possible to cope with it simply by opening the right opening / closing member 44.

  The toner cartridge 28 shown in FIG. 2 (b) is attached to and detached from the reserve tank 20 in the front direction with respect to the printer 1 main body shown in FIG. 2 (a), that is, as shown by the double-directional arrow b in FIG. 2 (b). It is free. Similarly, the transfer belt unit 3 is also detachable from the printer 1 body in the front direction.

  Although it is not visible between the toner cartridge 28 and the reserve tank 20 in FIG. 2B, when the toner cartridge 28 is attached to the reserve tank 20, it communicates with the reserve tank 20 and becomes reserved. A toner replenishing port for replenishing toner is formed.

  A cartridge motor 45 is engaged with the screw shaft of the toner cartridge 28 from the outside, and a reserve tank motor 46 is engaged with the screw shaft of the reserve tank 20 from the outside. A toner replenishing mechanism including a screw shaft and fins of the toner cartridge 28 conveys the internal toner to the toner replenishing port.

  The toner replenishing mechanism comprising the screw shaft and fins of the reserve tank 20 conveys the toner replenished from the toner cartridge 28 via the toner replenishing port to the upper end opening of the toner replenishment path 47 connecting the reserve tank 20 and the developing device 14. To do. The toner replenishment path 47 is disposed so as to wrap around the back of the transfer belt unit 3 and is connected to the developing device 14.

  FIG. 3 is a circuit block diagram including the control device of the printer 1 including the primary transfer roller lifting mechanism corresponding to the above-described three types of processing modes, the non-image forming mode, the monochrome mode, and the color mode.

  As shown in FIG. 3, the circuit block has a central processing unit (CPU) 50 as a center, and an interface controller (I / F_CONT) 51 and a printer controller (PR_CONT) 52 are connected to the CPU 50 via a data bus. ing. A printer printing unit 53 is connected to the PR_CONT 52.

  Also connected to the CPU 50 are a ROM (read only memory) 54, an EEPROM (electrically erasable programmable ROM) 55, an operation panel 56 of the main body operation unit, and a sensor unit 57 to which outputs from sensors arranged in each unit are input. Has been. A system program is stored in the ROM 54, and the CPU 50 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, first, the I / F_CONT 51 converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 58.

  In the frame memory 58, a storage area is set for each of black (K), cyan (C), magenta (M), and yellow (Y), and data of each color is developed in a corresponding area. The expanded data is output to PR_CONT 52, and is output from PR_CONT 52 to printer printing unit 53.

  The printer printing unit 53 is an engine unit, and under the control of the PR_CONT 52, controls the driving output to the belt driving unit 58 that performs rotational driving of the transfer belt 8 of the transfer belt unit 3 shown in FIG.

  Further, the printer printing unit 53 is connected to a conveyance mechanism driving unit 59 that drives a conveyance mechanism including rotationally driven parts such as a paper take-out roller 32 to a discharge roller pair 38, the photosensitive drum 10, and a heating roller of the fixing device 6. Controls drive output.

  Further, the printer printing unit 53 applies a voltage to a process load of an image forming unit having a driven unit such as the charging roller 12, the optical writing head 13, and the primary transfer roller 25, and a rotational driving system including the secondary transfer roller 24. The output of the applied voltage output unit 61 is controlled.

  Further, the printer printing unit 53 controls the drive output to the toothless gear driving unit 62 that drives the toothless gear of the primary transfer lifting mechanism corresponding to the three types of processing modes of the non-image forming mode, the monochrome mode, and the color mode. To do.

  The print data for each color of black (K), cyan (C), magenta (M), and yellow (Y) output from the PR_CONT 52 is sent from the printer printing unit 53 to the corresponding optical writing head shown in FIG. 13 is supplied.

  The optical writing head 13 performs optical writing on the photosensitive drum 10 based on the print data to form an electrostatic latent image, and the developing roller 15 develops the toner image (toner image). The developed toner image is primarily transferred to the transfer belt 8 by the primary transfer roller 25.

  The toner image primarily transferred to the transfer belt 8 is transferred to the paper at the secondary transfer portion. The toner image transferred to the paper is fixed on the paper by applying heat and pressure in the belt-type fixing unit 6. The paper on which the toner image has been fixed is discharged to a paper discharge tray 37.

  4 (a), (b), (c), and (d) show three types of processing modes, a non-image forming mode, a monochrome mode, and a color mode, in the primary transfer roller lifting mechanism of the printer 1 having the above-described configuration. FIG. 6 is a diagram for explaining a lifting operation of a corresponding primary transfer roller 25.

  4 (a), (b), (c), and (d), the same components as those in FIGS. 1 and 2 are given the same numbers as those in FIGS. . For easy understanding of the configuration, the photosensitive drum 10 and the primary transfer roller 25 corresponding to the developing devices 9y, 9m, 9c, and 9k are respectively 10y, 10m, 10c, 10k, and 25y, 25m, 25c, and 25k. Show.

  FIG. 4A shows a plurality (four in this example) of photosensitive drums 10 (10y, 10m, 10c, 10k) arranged side by side and a plurality of support rollers (of the configuration shown in FIG. 1). A transfer belt 8 wound around a driving roller 21, a driven roller 22, and a secondary transfer backup roller 23) is shown.

  The transfer belt 8 is disposed along the four photosensitive drums 10, and a toner image formed on the predetermined photosensitive drum 10 is transferred to a lower portion by a primary transfer roller 25 corresponding to the predetermined photosensitive drum 10. Primary transfer is performed on the running surface 8a.

  As described above, the toner image primarily transferred to the transfer belt 8 is transferred to the paper by the secondary transfer unit, and the transferred toner image is fixed to the paper by the belt-type fixing unit 6 to fix the toner image. Is discharged to the paper discharge tray 37.

  In this processing step, the four primary transfer rollers 25 move up and down on the opposite side of the transfer belt 8 corresponding to the four photosensitive drums 10 in order to bring the photosensitive drum 10 and the transfer belt 8 into contact with each other. Arranged freely.

  At both ends of these four primary transfer rollers 25, as shown in FIGS. 4B, 4C, and 4D, engaging portions 63 that selectively engage with both ends of the predetermined primary transfer roller 25 are provided. 2 rack members 64 (only one is shown in the front side of the drawing in FIGS. 4B, 4C, and 4D) are disposed.

  The teeth 66a of the toothless pinion 66 mesh with the teeth 65 of the rack member 64, or the toothless portion (toothless portion) 66b slides. FIG. 4B shows a state in which the tooth notch portion 66 b of the tooth notch pinion 66 is in sliding contact with the tooth 65 of the rack member 64.

  The rack member 64 is engaged with a push spiral spring 67 as a biasing means for biasing the rack member 64 in one direction of movement (rightward in FIGS. 4B, 4C, and 4D). Yes.

  As shown in FIG. 4B, in a state where the tooth 66a of the toothless pinion 66 is detached from the tooth 65 of the rack member 64 and the toothed portion 66b is in sliding contact with the tooth 65, the rack member 64 is pushed and spiraled. The spring 67 is moved to the rightmost position by the urging force of the spring 67 and is stopped by contacting a stopper (not shown).

  The upper surface 64 a on which the engaging portion 63 of the rack member 64 is formed is set at a position slightly lower than the uppermost portion of the photosensitive drum 10. The front surface of the engaging portion 63 that is urged and faces the direction of movement forms an inclined surface 63a, and the rear side following the inclined surface 63a forms a horizontal surface 63b of a predetermined length.

  When the rack member 64 is moved to the rightmost end as shown in FIG. 4B, all of the four primary transfer rollers 25 ride on the horizontal surface 63b of the four engaging portions 63. That is, the transfer belt 8 is separated from the back surface 8b of the lower running surface 8a.

  Accordingly, the lower running surface 8a of the transfer belt 8 is also separated from the four photosensitive drums 10 shown in FIG. This state is a setting state of the primary transfer roller 25 in the non-image forming mode.

  From this state, the toothless gear drive unit 62 of the control device drives the toothless pinion 66 to rotate at a predetermined angle in the counterclockwise direction as shown by an arrow c, as shown in FIG. As a result, first, the teeth 66 a of the toothless pinion 66 mesh with the teeth 65 of the rack member 64.

  Further, when the toothless pinion 66 is rotated to a predetermined angle, the rack member 64 is moved through the teeth 65 of the rack member 64 against the urging force of the push spiral spring 67 in the left direction in the figure with an arrow d. As shown by, it is moved by a predetermined distance.

  As a result, both ends of the primary transfer roller 25k slide rightward on the horizontal surface 63b of the engaging portion 63 and further slide downward on the inclined surface 63a to disengage from the engaging portion 63.

  Since the upper surface 64a of the rack member 64 on which the engaging portion 63 is formed is set at a position lower than the uppermost portion of the photosensitive drum 10, the primary transfer roller 25k that is disengaged from the engaging portion 63 is shown in FIG. As shown in c), the transfer belt 8 is pressed against the back surface 8b of the lower running surface 8a.

  At this time, the size of the horizontal surface 63b is set in advance so that both ends of the remaining primary transfer rollers 25y, 25m, and 25c are all placed on the horizontal surface 63b of the engaging portion 63 of the rack member 64. Yes. This state is a setting state of the primary transfer roller 25 in the monochrome mode.

  Next, from the state of FIG. 4 (c), the toothless gear drive unit 62 of the control device moves the toothless pinion 66 in the counterclockwise direction as shown by the arrow e as shown in FIG. 4 (d). Are rotated by a predetermined angle.

  In response to the rotation of the tooth 66a of the toothless pinion 66 by a predetermined angle, the rack member 64 is further moved in the left direction in the figure against the pushing biasing force of the pushing spiral spring 67 as indicated by an arrow f. Move a predetermined distance.

  As a result, both ends of the primary transfer rollers 25y, 25m, and 25c slide rightward on the horizontal surface 63b of the engaging portion 63, and further slide downward on the inclined surface 63a to disengage from the engaging portion 63. As shown in d), the transfer belt 8 is pressed against the back surface 8b of the lower running surface 8a.

  At this time, the primary transfer roller 25k that has already been in pressure contact with the back surface 8b of the transfer belt 8 remains in the same position. Accordingly, the four primary transfer rollers 25y, 25m, 25c, and 25k are all in pressure contact with the back surface 8b of the transfer belt 8. This state is a setting state of the primary transfer roller 25 in the color mode.

  If the toothless pinion 66 is sequentially rotated in the direction opposite to the arrow e in FIG. 4D and the direction opposite to the arrow c in FIG. It goes without saying that it is possible to easily shift from the color mode 4 (d) to the monochrome mode shown in FIG. 4 (c) and further to the non-image forming mode shown in FIG. 4 (b).

  In this manner, the rack member 64 is configured to be movable in the direction in which the photosensitive drums 10 are arranged in parallel by the rotation of the toothless pinion 66, and the four primary transfer rollers 25 can be moved up and down by the engaging portion 63. .

  That is, the three positions of the primary transfer roller, that is, the non-image forming position (total separation position), the monochrome position, and the color position, can be switched by a configuration with a small number of parts such as the rack member 64 and the toothless pinion 66.

  The amount of movement of the rack member 64 may be determined by the relationship between the drive pulse of the drive motor of the drive control unit and the rotation angle of the toothless pinion 66, and the position of the rack member 64 may be detected by a position detector such as a photosensor. May be detected and determined.

  FIG. 5 is a diagram schematically illustrating an internal configuration of a printer including the primary transfer roller lifting mechanism according to the second embodiment. In the printer 70 shown in FIG. 5, the transfer belt 73 stretched between the driving roller 71 and the driven roller 72 circulates in the counterclockwise direction as indicated by an arrow g.

  Four image forming units 74 (74k, 74c, 74m, 74y) are arranged above the upper running surface 73a in which the transfer belt 73 is circulated, and these photosensitive drums 75 are arranged in the direction in which the transfer belt 73 circulates. Along the line.

  Corresponding to these photosensitive drums 75, a primary transfer roller 76 is disposed so as to be movable up and down on the opposite side across the transfer belt 73.

  The printer 70 is a printer of a so-called top transfer system that primarily transfers a toner image onto the upper running surface 73a of the transfer belt 73, and the primary transfer roller 76 is raised during image formation and lowered during non-image formation. It has become.

  FIGS. 6A and 6B are diagrams for explaining the raising / lowering operation of the primary transfer roller 76 in the non-image forming mode, the monochrome mode, and the color mode in the primary transfer roller raising / lowering mechanism of the printer of the present example having the above-described configuration. .

  Note that the primary transfer roller lifting mechanism 77 shown in FIGS. 6A and 6B is disposed between the upper traveling portion and the lower traveling portion of the transfer belt 73 of the printer 70. FIGS. 6A and 6B show the primary transfer rollers 76 corresponding to the image forming units 74 (74k, 74c, 74m, and 74y) shown in FIG. 7 as 76k, 76c, 76m, and 76y, respectively. ing.

  The front and rear rack members 78 (78a, 78b) are similar in operation except that the moving direction and the direction of the engaging portion are opposite to each other. The description will proceed below.

  The rack member 78a includes an engaging portion 81 (81k, 81c, 81m, 81y) with the primary transfer roller 76 on the upper surface 79. Side teeth are formed on the inner side surface 82 of the rack member 78a, although it is not clearly seen in the figure. A helical spring 83 having a pressing force is engaged with the rear end portion of the rack member 78a in the moving direction.

  A large-diameter tooth missing gear 84 is disposed between the front and rear rack members 78 (78a, 78b). On the circumferential portion of the tooth missing gear 84, teeth 84a and tooth missing portions (toothless portions) 84b are formed at predetermined intervals.

  In FIG. 6A, the tooth missing gear 84 rotates the clockwise direction indicated by the arrow h with the tooth 84a meshed with the side teeth of the rack member 78 (78a, 78b), and the rack member 78 is indicated by the arrow i. It is a figure which shows the state moved to the moving direction (right side in a figure) fully.

  All four primary transfer rollers 76 are moved down from all four engaging portions 81 of the rack member 78a and supported by the upper surface 79 of the rack member 78a. This state is a non-image forming mode state in which all four primary transfer rollers 76 are separated from the transfer belt 73.

  From this state, when the tooth missing gear 84 rotates by a predetermined angle in the direction opposite to the arrow h, that is, in the counterclockwise direction, the rack member 78a moves in the direction opposite to the arrow i by the distance B.

  By this movement, although not particularly shown, the primary transfer roller 76k corresponding to the black toner photosensitive drum 75 rides on the engaging portion 81k, and brings the transfer belt 73 into contact with the black toner photosensitive drum 75.

  At this time, the movement amount B of the rack member 78a is set to be slightly larger than the distance from the remaining three primary transfer rollers 76c, 76m, and 76y to the lower ends of the inclined surfaces of the engaging portions 81c, 81m, and 81y.

  Therefore, the remaining three primary transfer rollers 76c, 76m, and 76y are supported on the upper surface 79 of the rack member 78a without riding on the engaging portions 81c, 81m, and 81y. This state is the monochrome mode.

  From this state, the tooth missing gear 84 further rotates by a predetermined angle in the direction opposite to the arrow h, that is, in the arrow j direction (clockwise direction) in FIG. Correspondingly, the rack member 78a moves in the arrow k direction by the distance C.

  The moving distance C of the rack member 78a is a distance that the primary transfer rollers 76c, 76m, and 76y can ride on the horizontal plane from the lower end of the inclined surface of the rack member 78a, and the primary transfer roller 76k is first in the horizontal plane. This is the distance that does not drop off from the boarded position to the rear end side in the moving direction.

  As a result, as shown in FIG. 6B, all four primary transfer rollers 76k, 76c, 76m, and 76y contact the transfer belt 73 with the photosensitive drum 75 of black, cyan, magenta, and yellow toner, respectively. Make contact. This state is the color mode.

  In the toothless gear drive unit 62 of the control device, if the toothless gear 84 is driven and controlled in the reverse order of the explanation in FIG. 6A and the explanation in FIG. 6B, FIG. 6B. Needless to say, it is possible to easily shift from the color mode of () to the monochrome mode and further to the non-image forming mode of FIG.

  In the first or second embodiment described above, the position of the rack member in the monochrome mode and the color mode is determined by the position of meshing between the teeth of the rack member and the teeth of the toothless gear. You may make it position by providing a stopper member in a certain cover.

  In that case, the stopper is released by opening the cover, and the rack member is moved to the position of the rightmost end to set the non-image forming mode. When the cover is closed, the stopper comes into contact with the right end of the rack member, and the rack member is set to the monochromatic position.

  In this case, the teeth of the toothless gear remain detached from the teeth of the rack member and rotate only when the color mode is entered. That is, once the transfer belt unit is attached to the apparatus main body, the primary transfer roller lifting mechanism only switches between the monochrome position and the color position.

Although several embodiments of the present invention have been described, the present invention is included in the invention described in the claims and the equivalents thereof. Hereinafter, the invention described in the scope of claims of the present application will be appended.
[Appendix 1]

A plurality of photosensitive drums arranged side by side;
A toner image that is wound around a plurality of support rollers and disposed along the plurality of photosensitive drums and formed on the predetermined photosensitive drum is primarily transferred, and the primary transferred toner image is transferred to a secondary transfer portion. A transfer belt for secondary transfer to the image forming medium being conveyed in
A plurality of primary transfer rollers arranged to be movable up and down on the opposite side of the transfer belt in correspondence with the plurality of photosensitive drums so as to contact the photosensitive drum and the transfer belt;
A rack member that selectively engages both ends of each transfer roller of the plurality of primary transfer rollers, and a rack member that is movable in the juxtaposed direction;
A biasing member that biases the rack member in one of the moving directions;
A toothless gear meshing with a gear portion of the rack member;
A first position where all of the plurality of photosensitive drums are brought into contact with the intermediate transfer belt based on movement of the rack member accompanying rotation control of the tooth-missing gear, and the plurality of photosensitive members. A plurality of primary positions at a second position where one of the drums is in contact with the intermediate transfer belt and a third position where all of the plurality of photosensitive drums are not in contact with the intermediate transfer belt. A drive controller for selectively moving each of the transfer rollers;
A primary transfer roller raising / lowering mechanism comprising:
[Appendix 2]

The transfer belt is a transfer belt on which a toner image is primarily transferred onto a lower moving surface that circulates, and the tooth missing gear is a tooth missing pinion that engages with a gear portion of each rack member. The primary transfer roller lifting mechanism according to Supplementary Note 1.
[Appendix 3]

The transfer belt is a transfer belt on which a toner image is primarily transferred onto an upper moving surface that circulates, and the tooth-missing gear is engaged with a gear portion formed on a side surface of each rack member on an opposed peripheral surface in a diametrical direction. The primary transfer roller raising / lowering mechanism according to appendix 1, wherein the gear is a large-diameter gear with missing teeth.
[Appendix 4]

  An image forming apparatus comprising the primary transfer roller raising / lowering mechanism according to appendix 1, 2 or 3.

  The present invention can be used for an image forming apparatus that switches between a non-image forming mode, a monochrome mode, and a color mode with a simple configuration.

1 Full-color image forming device (printer)
DESCRIPTION OF SYMBOLS 2 Image formation part 3 Transfer belt unit 4 Toner supply part 5 Paper feed part 6 Belt type fixing unit 7 Conveyance unit for double-sided printing 8 Transfer belt 8a Lower running surface 8b Back surface 9 (9y, 9m, 9c, 9k) Developing device 10 ( 10y, 10m, 10c, 10k) Photosensitive drum 11 Cleaner 12 Charging roller 13 Optical writing head 14 Developer 15 Developing roller 16 Housing 17 Partition 15 Developing roller 18 First stirring and conveying screw 19 Second agitating and conveying screw 20 Reserve tank 21 Drive roller 22 Driven roller 23 Secondary transfer backup roller 24 Secondary transfer roller 25 (25y, 25m, 25c, 25k) Primary transfer roller 26 Belt cleaner 27 Waste toner collection container 28 Toner cartridge 29 Electrical component 31 (31a, 31b) Paper cassette 3 2 Paper take-out roller 33 Feed roller 34 Rolling roller 35 Standby conveyance roller pair 36 Unload roller pair 37 Paper discharge tray 38 Paper discharge roller pair 39 Return path 39a Start return path 39b Intermediate return path 39c End return path 41 (41a, 41b, 41b) 41c, 41d, 41e) Return roller pair 42 Front door 43 Handle 44 Opening / closing member 45 Cartridge motor 46 Reserve tank motor 47 Toner supply path 50 CPU (central processing unit)
51 Interface Controller (I / F_CONT)
52 Printer Controller (PR_CONT)
53 Printer printing section 54 ROM (read only memory)
55 EEPROM (electrically erasable programmable ROM)
56 operation panel 57 sensor unit 58 belt drive unit 59 transport mechanism drive unit 61 applied voltage output unit 62 toothless gear drive unit 63 engagement unit 64 rack member 64a upper surface 65 teeth 66 toothless pinion 66a teeth 66b toothless portion (toothless) Part)
67 Pushing spiral spring 70 Printer 71 Drive roller 72 Driven roller 73 Transfer belt 74 (74k, 74c, 74m, 74y) Image forming unit 75 Photosensitive drum 76 Primary transfer roller 77 Primary transfer roller lifting mechanism 78 (78a, 78b) Rack member 79 Upper surface 81 (81k, 81c, 81m, 81y) Engaging portion 82 Inner side surface 83 Spiral spring 84 Tooth missing gear 84a Tooth 84b Tooth missing portion (toothless portion)

Claims (4)

A plurality of photosensitive drums arranged side by side;
A toner image that is wound around a plurality of support rollers and disposed along the plurality of photosensitive drums and formed on the predetermined photosensitive drum is primarily transferred, and the primary transferred toner image is transferred to a secondary transfer portion. A transfer belt for secondary transfer to the image forming medium being conveyed in
A plurality of primary transfer rollers arranged to be movable up and down on the opposite side of the transfer belt in correspondence with the plurality of photosensitive drums so as to contact the photosensitive drum and the transfer belt;
A rack member that selectively engages both ends of each transfer roller of the plurality of primary transfer rollers, and a rack member that is movable in the juxtaposed direction;
A biasing member that biases the rack member in one of the moving directions;
A toothless gear meshing with a gear portion of the rack member;
A first position where all of the plurality of photosensitive drums are brought into contact with the intermediate transfer belt based on movement of the rack member accompanying rotation control of the tooth-missing gear, and the plurality of photosensitive members. A plurality of primary positions at a second position where one of the drums is in contact with the intermediate transfer belt and a third position where all of the plurality of photosensitive drums are not in contact with the intermediate transfer belt. A drive controller for selectively moving each of the transfer rollers;
Equipped with a,
The primary transfer roller ascending / descending mechanism , wherein the tooth-missing gear engages with a gear portion formed on a side surface of each rack member on a diametrically opposed peripheral surface . The transfer belt, the transfer belt Ru der, primary transfer roller lifting mechanism according to claim 1, characterized in that it is primarily transferred toner image to the upper portion moving surface moves cyclically. The missing tooth gear is large, the primary transfer roller lifting mechanism according to claim 1 or 2, wherein the.   An image forming apparatus comprising the primary transfer roller lifting mechanism according to claim 1.