JP4556718B2 - Positioning mechanism - Google Patents

Description

  The present invention relates to a positioning mechanism in which an image forming unit can be easily attached and detached and a member disposition space can be made as small as possible.

  Conventionally, there is an electrophotographic image forming apparatus. Particularly in recent years, tandem that performs full-color printing (including printing or image formation, and so on) on paper (sheet-like image forming medium, and so on) using toners of four colors, cyan, magenta, yellow, and black. Type page printers have been put into practical use.

  Usually, in an electrophotographic image forming apparatus, a photoreceptor kit and a developing kit are integrated into an image forming unit, and an optical writing head (also simply referred to as an optical head) is further assembled to the image forming unit. Thus, an image forming unit is configured.

The image formed by the image forming unit is transferred to a sheet fed from a sheet feeding device, is carried into a fixing unit, and is fixed on the sheet by heat and pressure, and is discharged outside the apparatus.
By the way, when a paper jam or image formation failure occurs, maintenance must be performed to recover from the failure. Also, when replacing old and new kits or units, replacement maintenance must be performed in the same manner.

  In such a case, instead of taking out the optical writing head, photoconductor kit, developing kit, etc. from the image forming apparatus main body and disassembling them separately, it is necessary to separate them separately so that they can be taken out separately. The work becomes troublesome and cumbersome.

For this purpose, the lid on the upper surface of the apparatus main body is opened, and the optical writing head attached to the back surface of the lid via a support member is lifted to the outside along with the rotation of the lid. There is a configuration in which the kits left inside can be taken out to the outside. (For example, see Reference Document 1.)
Also, the upper part of the main body of the apparatus is configured to be able to move largely upward, and the kits are configured to be supported on the upper part via a support member, where the kits can be pulled out to the outside. is there. (For example, see Reference 2.)
JP 09-160333 A ([Summary], FIG. 1) Japanese Patent Laying-Open No. 2001-242663 ([Summary], FIG. 5)

  However, in the method of performing maintenance by opening the upper body (a group of optical writing heads attached to the back surface of the lid via a support member) as in Patent Document 1, the lid on the upper surface is opened in a single manner around the hinge. However, the top cover also serves as a paper discharge tray. Therefore, the upper body cannot be opened without removing the image-formed paper placed on the top surface of the cover that also serves as the paper discharge tray. There is a trouble.

  In this case, as shown in Patent Document 1, there is a type in which the kit is left at the lower part of the apparatus main body and a type in which the kit is lifted upward together with the upper body, although not particularly shown. The former type that leaves the kit in the lower part of the main body can lighten the upper part of the rotating machine body. However, for the recovery processing of paper jam that occurs in the transport path below the kit, the kit must be used. Furthermore, the trouble of taking it out is attached.

  In addition, the latter type that lifts multiple kits together with the upper body, such as the latter, has a preferable structure in which excessive weight is added to the mechanism that rotates around the hinge, and fatigue over time occurs in the entire maintenance mechanism at an early stage. It was hard to say that there was.

  In Cited Document 2, since the trouble of removing the paper is eliminated and the problem of excessive load on only a part of the mechanism is solved, the operability is improved and the life of the maintenance mechanism is extended. Has been made.

However, there remains a problem that the link mechanism is complicated and the apparatus is enlarged in order to prevent the kit from being tilted using the parallel link and to support the weight of the kit.
In view of the above-described conventional situation, an object of the present invention is to be provided in an image forming unit that can be easily attached / detached and can easily perform a maintenance operation such as a kit operation or a paper jam restoration process, and a member arrangement space as much as possible. It is an object to provide a positioning mechanism that can be made small.

The configuration of the positioning mechanism according to the present invention will be described below.
The positioning mechanism of the present invention has an image forming unit that has at least a photosensitive drum on which an electrostatic latent image is formed and is detachable in the drum axial direction with respect to the image forming apparatus main body, and is attached to the image forming apparatus main body. The image forming unit is disposed opposite to the surface of the photosensitive drum, and is disposed at a predetermined proximity position for optical writing on the surface of the photosensitive drum and a separation position that is separated from the proximity position with respect to the surface. In a positioning mechanism for positioning a position in two directions, the drum axis direction and a direction orthogonal to the drum axis direction, with respect to an optical head that is detachably provided, the optical head is pulled out in the drum axis direction The front side engaging portion provided on the front side in the direction, the back side engaging portion provided on the back side in the pulling direction in the drum axis direction, and the front side engaging portion of the optical head. A unit engaging portion provided along the drum axis direction of the image forming unit, and a back side engaging portion of the optical head provided on the back side of the mounting portion of the image forming unit of the image forming apparatus main body. The apparatus main body engaging part which can be engaged with a joint part is comprised.

  In this positioning mechanism, for example, the front engaging portion of the optical head is an engaging hole, and the unit engaging portion is connected to the photosensitive drum on the front side in the pulling-out direction in the drum axis direction in the image forming unit. In addition, for example, the back side engaging portion of the optical head is an engaging hole or an engaging convex portion, and the image forming apparatus main body is configured to be an engaging convex portion formed on the engaging portion. The apparatus main body engaging portion provided on the back side of the mounting portion is configured to be an engaging convex portion or an engaging hole.

  According to the present invention, the other-side engaging portion of the positioning engagement portion on the front side and the back side in the drum axis direction of the optical head with respect to the photosensitive drum of the image forming unit is used as the frame of the image forming unit and the image. Since it is provided separately in two different functions with respect to the frame on the forming apparatus main body side, the engaging portion corresponding to the positioning engaging portion on the rear side in the pull-out direction of the drum axis direction of the optical head is provided in the image forming unit. There is no need to provide the rear side of the drum kit in the attaching / detaching direction, and therefore there is no part competing with the optical head part on the inner side of the attaching / detaching direction of the photosensitive drum kit, thereby separating the optical head at a small distance from the photosensitive drum. This allows the entire photosensitive drum kit or image forming unit to be freely inserted into and removed from the mounting portion of the image forming apparatus main body, and the image forming unit can be easily attached and detached. One positioning mechanism between member disposing space to be configured as small as possible and it is possible to provide a.

Embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1)
FIG. 1 is a cross-sectional view illustrating an internal configuration of a secondary transfer image forming apparatus (hereinafter simply referred to as a printer) in Embodiment 1 of the present invention. A printer 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, which includes four image forming units 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a conveyance for duplex printing. The unit 5 is configured.

  The four image forming units 2 have a configuration in which four image forming units 6 (6M, 6C, 6Y, 6K) are arranged side by side in a multistage manner from right to left in FIG. Of the four image forming units 6, three image forming units 6M, 6C, and 6Y on the upstream side (right side in the figure) are magenta (M), cyan (C), yellow (subtractive three primary colors), respectively. A mono-color image is formed with the color toner of Y), and the image forming unit 6K forms a monochrome image with black (K) toner mainly used for dark portions of characters and images.

  Each of the image forming units 6 has the same configuration except for the color of the toner stored in the toner container. Accordingly, the configuration of the black (K) image forming unit 6K will be described below as an example.

  The image forming unit 6 includes a photosensitive drum 7 at the bottom. The peripheral surface of the photosensitive drum 7 is made of, for example, an organic photoconductive material. A cleaner 8, a charging roller 9, an optical head 11, and a developing roller 13 of the developing device 12 are disposed around the periphery of the photosensitive drum 7.

  The developing device 12 puts one of magenta (M), cyan (C), yellow (Y), and black (K) toners in the upper toner container as indicated by M, C, Y, and K in the drawing. The intermediate portion is provided with a toner replenishing mechanism for the lower portion, the lower portion is provided with the above-described developing roller 13 at the side opening, the toner stirring member inside, the toner supply roller for supplying toner to the developing roller 13, and the developing A doctor blade or the like for regulating the toner layer on the roller 13 to a constant layer thickness is provided.

  The intermediate transfer belt unit 3 has an endless transfer belt 14 extending in a flat loop shape from substantially the left and right sides of the figure at the approximate center of the main unit, and the transfer belt 14 is stretched over the transfer belt 14. A driving roller 15 and a driven roller 16 are provided to circulate and move the belt 14 counterclockwise in the drawing.

  The transfer belt 14 transfers the toner image directly onto the belt surface (primary transfer) and conveys the toner image to the transfer position to the paper for further transfer (secondary transfer). The whole is called an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 17 in the loop of the flat loop-shaped transfer belt 14. The belt position control mechanism 17 includes a primary transfer roller 18 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 7 via the transfer belt 14.

  The belt position control mechanism 17 has three primary transfer rollers 18 corresponding to the three image forming units 6M, 6C, and 6Y of magenta (M), cyan (C), and yellow (Y) as vertical support shafts. The image is transferred to the center at the same cycle, and the one primary transfer roller 18 corresponding to the black (K) image forming unit 6K is rotated at a rotation cycle different from the cycle of the three primary transfer rollers 18 for transfer. The belt 14 is moved away from the photosensitive drum 7, and the full color mode (all four primary transfer rollers 18 are in contact with the transfer belt 14) and the monochrome mode (only the primary transfer roller 18 corresponding to the image forming unit 6K is the transfer belt). 14) and all non-transfer mode (all four primary transfer rollers 18 are separated from the transfer belt 14).

  In the intermediate transfer belt unit 3, a belt cleaner unit is disposed further upstream of the uppermost image forming unit 6M on the upstream side in the belt movement direction, and is flat and thin so as to be substantially along the entire lower surface. The waste toner collection container 19 is detachably disposed.

  The paper feed unit 4 includes two paper feed cassettes 21 arranged in two upper and lower stages, and in the vicinity of the paper feed opening (right side in the figure) of the two paper feed cassettes 21, respectively, A feeding roller 23, a separating roller 24, and a standby conveying roller pair 25 are disposed. In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 25, a secondary transfer roller 26 that is in pressure contact with the driven roller 16 via the transfer belt 14 is disposed, and the secondary transfer portion to the paper is arranged. Forming.

  A belt-type heat fixing device 27 is disposed downstream (upward in the drawing) of the secondary transfer portion, and the sheet after fixing is fixed to the belt-type heat fixing device 27 further downstream of the belt-type heat fixing device 27. A pair of carry-out rollers 28 for carrying out the paper and a pair of paper discharge rollers 31 for discharging the carried paper to a paper discharge tray 29 formed on the upper surface of the apparatus are disposed.

  The duplex printing conveyance unit 5 includes a start return path 32a branched from the intermediate conveyance path between the carry-out roller pair 28 and the discharge roller pair 31 to the right side in the figure, and then an intermediate return path 32b bent downward. A terminal return path 32c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and four return roller pairs 33a, 33b, 33c, and 33d arranged in the middle of these return paths. ing. The exit of the end return path 32 c communicates with a conveyance path to the pair of standby conveyance rollers 25 corresponding to the sheet feeding cassette 21 below the sheet feeding unit 4.

  In this example, a cleaning unit 35 and a take-in roller 36 are disposed on the upper surface of the intermediate transfer belt unit 3. The cleaning unit 35 comes into contact with the upper surface of the transfer belt 14 and scrapes and removes the waste toner. The take-in roller 36 takes over the waste toner removed by the cleaning unit 35 and is not shown in the drawing, and is temporarily stored in the belt cleaner unit. The accumulated waste toner is conveyed to the upper part in the dropping cylinder by a conveying screw and sent to the waste toner collecting container 19 through the dropping cylinder.

  Further, in order to bring the cleaning unit 35 into pressure contact with the transfer belt 14 with an appropriate pressure, a pressure roller 37 is provided on the intermediate transfer belt unit 3 side to press the transfer belt 14 toward the cleaning unit 35 from below. ing.

  As shown in FIG. 1, the image forming apparatus 1 does not directly transfer a toner image to a conventional sheet, but an intermediate transfer belt on a sheet that is vertically conveyed to a secondary transfer unit by a pair of standby conveying rollers 25. 14 is a method of transferring a toner image through the image forming apparatus 14.

Therefore, it is possible to cope with a maintenance process for recovering from a problem such as a paper jam occurring in the paper transport path by simply opening the right side of FIG.
In addition, since troubles such as paper jams do not occur in the arrangement section of the kits, the operation for attaching and detaching consumables such as kits concentrated on the left side of FIG. 1 may be a small space that can be replaced in the longitudinal direction. It is configured as follows.

  Thereby, the dimension between kits is reduced as much as possible, and size reduction of the whole apparatus main body is achieved. In addition, the optical head itself is also miniaturized and has a configuration closer to the photosensitive drum.

  FIG. 2 is a perspective view showing the state in which the four optical heads thus miniaturized are respectively housed in the head holder and collectively held by the holder base. .

  FIG. 2 shows the optical head 11, the head holder 38, and the holder base 39. In addition, a photosensitive drum 7 positioned directly below the optical head 11 via the head cover is also shown.

  The photosensitive drum 7 is a constituent member of the image forming unit, and the optical head 11 is a constituent member of the head unit. That is, the members are incorporated in separate units. These are integrally shown in the figure for reference showing the mutual positional relationship.

  3 is a cross-sectional view taken along the line AA ′ of FIG. FIG. 3 shows the optical head 11, the head holder 38, the holder base 39, and the photosensitive drum 7, and further, the release rod 41, the head spring 42, and a spacer 43 described later in detail.

  4A is a cross-sectional view taken along the line BB ′ of FIG. 2, and FIG. 4B is a partially enlarged view thereof. FIG. 4A shows the optical head 11, the head holder 38, the holder base 39, the release rod 41, the photosensitive drum 7, the release lever 44, the front lifter 45, the rear lifter 46, and the front head pin 47. , And the rear head pin 48.

  4B shows the optical head 11, the release rod 41, the spacer 43, the front positioning member 49 for focusing the optical writing by the optical head 11, and the front outside of the photosensitive drum 7. A drum cover 51 that supports and protects the end is shown.

  5 (a) and 5 (c) are perspective views in which the head holder 38 and the holder base 39 are removed from the configuration shown in FIG. 4, and FIGS. 5 (b) and 5 (d) are FIGS. , (c) is a perspective view as seen from the left side.

  5A and 5B, the optical head 11 disposed opposite to the surface of the photosensitive drum 7 as shown in FIG. 4 has a predetermined proximity to the surface of the photosensitive drum 7 for optical writing. The state located in the position is shown.

5 (c) and 5 (d) show a state where the optical head 11 is located at a separation position that is separated from the surface of the photosensitive drum 7 rather than the proximity position.
5A to 5D, a front lifter 45 is connected to the release lever 44, and a rear lifter 46 is disposed on the front lifter 45 via a release rod 41 so as to be interlocked.

  The release rod 41 is supported by a support member 52 (not shown in FIGS. 5 (b) and 5 (d)) so that the center portion of the U-shape can be rotated. The lower lifter 46 is rotatably engaged with the lower part.

  The proximity shown in FIGS. 5A and 5B and the separation shown in FIGS. 5C and 5D with respect to the surface of the photosensitive drum 7 by the optical head 11 are shown in FIGS. 5A and 5B. This is because the release lever 44 when it is in the proximity position shown is pulled upward by the operator's hand as shown by the arrow a in FIGS.

  When the release lever 44 is pulled upward, the front lifter 45 connected to the release engagement member 44 rises as shown by the arrow b in FIG. 5C, and simultaneously engages with the front lifter 45. The front end of the release rod 41 rises and rotates the entire release rod 41 as indicated by an arrow c, and a rear lifter 46 that engages with the rear end of the release rod 41 in conjunction with this rotation is indicated by an arrow d. As shown, it rises the same distance as the front lifter 45.

  As a result, the optical head 11 whose front and rear ends are supported by the front lifter 45 and the rear lifter 46 moves upward against the pressing force of the head spring 42 shown in FIG. That is, the optical head 11 is separated to a separation position with respect to the surface of the photosensitive drum 7.

  At this time, as shown in FIGS. 4A and 4B, the front head pin 47 and the rear head pin 48 engaged with the lower surface of the optical head 11 are respectively engaged with the optical head 11 in FIG. , (d) as shown.

6 (a) is a side sectional view of the central portion of FIGS. 5 (a) and 5 (b), and FIG. 6 (b) is an enlarged view of the portion surrounded by a circle B in FIG. 6 (c) is an enlarged view of a portion surrounded by a circle C in FIG.
6A, 6B, and 6C show a state in which the optical head 11 is located at a predetermined proximity position for optical writing with respect to the surface of the photosensitive drum 7. FIG. .

  In this state, as shown in FIG. 6B, the image forming unit 6 is inserted into the front head engaging hole 53 as a front engaging portion formed on the front side in the pulling direction of the optical head 11 in the drum axis direction. A front head pin 47 protruding integrally with the drum cover 51 of the photosensitive drum 7 as a unit engaging portion provided along the drum axis direction of the optical head 11 and the XY between the optical head 11 and the image forming unit 6 is inserted. Positioning in the direction (main scanning direction and sub-scanning direction) is performed.

  At this time, the front positioning member 49 is brought into contact with the peripheral surface of the front end portion of the photosensitive drum 7 via the spacer 43, so that the position in the Z direction by the optical head 11 (the optical writing focus position by the optical head 11). Is positioned.

  Further, in the state shown in FIG. 6 (a), as shown in FIG. 6 (c), the rear head engagement as a back side engaging portion formed on the back side in the pull-out direction of the optical head 11 in the drum axis direction. A rear head pin as an apparatus main body engaging portion that is provided in the hole 54 on the back side of the mounting portion of the image forming unit 6 of the image forming apparatus (printer 1) main body and can be engaged with the rear head engaging hole 54 of the optical head 11. 48 is inserted to indirectly position the optical head 11 and the image forming unit 6 in the X and Y directions.

  The rear head pin 48 has an engagement convex portion fixed integrally with the main body frame 55 at the end of the main body frame 55 bent slightly inside the mounting portion of the image forming unit 6 of the printer 1 main body. Forming.

  On the other hand, a rear end portion of the photosensitive drum 7 is formed with an engaging portion 61 with a driving system on the printer 1 main body side, which will be described later, and the engaging portion 61 is a photosensitive member of the driving system on the main body side of the printer 1. By being engaged with the drum driving unit, the positioning is automatically performed with respect to the main body frame 55.

Accordingly, the positioning between the optical head 11 and the image forming unit 6 is indirectly performed through the main body frame 55 and the photosensitive drum 7.
In other words, the above-described positioning with respect to the optical head 11 is provided with an engaging portion for positioning with respect to the optical head 11 on the image forming unit 6 and the image forming apparatus main body 1 side to construct a function separation type positioning mechanism. It can be said that.

In FIG. 6C as well, the position in the Z direction is positioned by the rear positioning member 56 coming into contact with the peripheral surface of the rear end portion of the photosensitive drum 7 via another spacer 43.
From the state where the optical head 11 is located at a predetermined proximity position for optical writing with respect to the surface of the photosensitive drum 7 shown in FIGS. 6 (a), 6 (b) and 6 (c), FIG. When separated to the separation positions shown in c) and (d), the front head pin 47 shown in FIGS. 6B and 6C comes out of the front head engagement hole 53 and engages with the front head engagement hole 53. At the same time, the rear head pin 48 comes out of the rear head engagement hole 54 and is disengaged from the rear head engagement hole 54.

  At this time, the front head pin 47 protrudes on the front end side of the photosensitive drum 7, but the rear head pin 48 protrudes on the main body frame 55, so that the front head pin 47 is positioned on the rear end side of the photosensitive drum 7. There is no projecting like 47.

  Accordingly, the photosensitive drum 7 on which the front head pin 47 protrudes is provided as long as a gap is formed between the optical head 11 and the photosensitive drum 7 so that the front head pin 47 is pulled out from the front head engaging hole 53. The front end portion of the photosensitive drum 7 not having the engaging convex portion as well as the rear end portion of the photosensitive drum 7 in front of the bottom surface of the optical head 11 does not conflict with the concave-convex configuration near the end portion of the optical head 11, so Can be removed.

In this way, a positioning mechanism is realized in which the image forming unit can be easily attached and detached and the member arrangement space can be made as small as possible.
Next, positioning in the Z direction between the optical head 11 and the photosensitive drum 7, that is, positioning of a focus out position for optical writing by the optical head 11, will be described below.

  As described with reference to FIGS. 5A to 5D, when the photosensitive drum 7 and the optical head 11 are relatively in contact with each other, the optical head 11 is in the normal position in the Z direction (the predetermined proximity described above). In general, a positioning device such as an abutment pin or a slide cam is often used for positioning. In this example, a spacer is used for positioning between the photosensitive drum 7 and the optical head 11.

  FIGS. 7A, 7B, and 7C are views showing the positions where the spacers are arranged on the photosensitive drum. In FIGS. 7A, 7B, and 7C, the spacer 43 is shown as a single unit for easy understanding of the position of the arrangement on the photosensitive drum 7. As shown in FIGS. 7A, 7B, and 7C, they are not arranged as a single unit, but, for example, are integrally attached to the bearing of the charging roller 9 or the like.

  As shown in FIG. 7A, the spacer 43 is disposed so as to be in sliding contact with the boundary portion 58 of the flange 57 (57a, 57b) at both ends of the photosensitive drum 7 with the drum portion 7-1. . As a result, as described with reference to FIGS. 6B and 6C, the distance between the photosensitive drum 7 and the optical head 11 is positioned.

  As shown in FIGS. 7B and 7C, a flange 57a at one end of the photoconductive drum 7 has a boundary portion 58 with the drum portion 7-1, a gear portion 59, and a main unit drive. It consists of an engaging part 61 with the system.

The flange 57b at the other end of the photosensitive drum 7 includes a boundary portion 58 with the drum portion 7-1 and a gear portion 62, as shown in FIG.
The engaging portion 61 is rotated by being engaged with the drive system of the main body apparatus, and is engaged with the rotation system of the image forming unit by the gear portions 59 and 62 at both ends, and is arranged in the image forming unit. The rotational drive is transmitted to the rotating member provided.

  8 (a) and 8 (b) are diagrams showing an actual assembled state of the spacer and its operating state. As described above, the spacer 43 of this example is integrally attached to the bearing of the charging roller 9, so that the operation of pressing and releasing the pressure roller 9 against the photosensitive drum 7 is performed in conjunction with the above operation. The spacer 43 is in contact with and away from both ends of the photosensitive drum 7, and the both ends of the optical head 11 are in contact with and away from the spacer 43.

  Since the spacer 43 is integrated with the bearing of the charging roller 9 as described above, the position does not fluctuate even when the photosensitive drum 7 and the optical head 11 are separated from each other, as shown in FIG. When the photosensitive drum 7 and the optical head 11 are in contact with each other, they are always inserted at the same position, so that the interval between the photosensitive drum 7 and the optical head 11 is always stably positioned. It has become so.

2 is a cross-sectional view illustrating an internal configuration of a secondary transfer image forming apparatus (printer) according to Embodiment 1. FIG. It is the perspective view which looked at the state where the head holder which accommodated four optical writing heads was collectively held by the holder base from the lower part. FIG. 3 is a cross-sectional view taken along the line AA ′ in FIG. 2. (a) is a BB 'cross-sectional arrow view of FIG. 2, (b) is the partially expanded view. (a), (c) is a perspective view showing the configuration shown in FIG. 4 with the head holder and holder base removed, and (b), (d) are perspective views of (a), (c) as seen from the left side, respectively. It is. (a) is a cross-sectional side view of the central portion of FIGS. 5 (a) and (b), (b) is an enlarged view of the portion surrounded by the circle B of (a), and (c) is a circle C of (a). It is an enlarged view of the part shown surrounded by. (a), (b), (c) is a figure which shows the arrangement | positioning position to the photoconductive drum of a spacer. (a), (b) is a figure which shows the actual installation state of a spacer, and its operation state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 2 Image formation part 3 Intermediate transfer belt unit 4 Paper feed part 5 Duplex printing conveyance unit 6 (6M, 6C, 6Y, 6K) Image formation unit 7 (7m, 7c, 7y, 7k) Photosensitive drum 7-1 Drum unit 8 Cleaner 9 Charging roller 11 Optical writing head (optical head)
DESCRIPTION OF SYMBOLS 12 Developing device 13 Developing roller 14 Transfer belt 15 Drive roller 16 Driven roller 17 Belt position control mechanism 18 Primary transfer roller 19 Waste toner collection container 21 Paper feed cassette 22 Paper take-out roller 23 Feeding roller 24 Rolling roller 25 Standby transport roller pair 26 Secondary transfer roller 27 Belt type heat fixing device 28 Unloading roller pair 29 Discharge tray 31 Discharge roller pair 32a Start return path 32b Intermediate return path 32c End return path 33a, 33b, 33c, 33d Return roller pair 35 Cleaning unit 36 Taking in Roller 37 Pressing roller 38 Head holder 39 Holder base 41 Release rod 42 Head spring 43 Spacer 44 Release lever 45 Front lifter 46 Rear lifter 47 Front head pin 48 Rear head pin 49 Front positioning member 51 Drum Cover 52 Support member 53 Front head engagement hole 54 Rear head engagement hole 55 Body frame 56 Rear positioning member 57 (57a, 57b) Flange 58 Boundary portion 59 Gear portion 61 Engagement portion 62 Gear portion

Claims (3)

An image forming unit having at least a photosensitive drum on which an electrostatic latent image is formed and detachable in the drum axis direction with respect to the image forming apparatus main body, and the photosensitive of the image forming unit mounted on the image forming apparatus main body It is disposed opposite to the surface of the body drum, and is provided so as to be freely contacted and separated at a predetermined proximity position for optical writing with respect to the surface of the photosensitive drum and a separation position separated from the surface from the proximity position. In a positioning mechanism that positions the optical head with respect to the two directions of the drum axis direction and the direction orthogonal to the drum axis direction,
A front side engaging part provided on the front side in the pulling direction of the optical axis of the optical head and a back side engaging part provided on the back side in the pulling direction of the drum axis direction;
A unit engaging portion provided along the drum axial direction of the image forming unit so as to be engageable with the front engaging portion of the optical head;
An apparatus main body engaging portion that is provided on the back side of the image forming unit mounting portion of the image forming apparatus main body and is engageable with the back side engaging portion of the optical head;
A positioning mechanism comprising:   The front engaging portion of the optical head is an engaging hole, and the unit engaging portion is formed in an engaging portion with the photosensitive drum on the front side in the pulling direction in the drum axis direction in the image forming unit. The positioning mechanism according to claim 1, wherein the positioning mechanism is an engaging convex portion.   The back side engaging portion of the optical head is an engaging hole or an engaging convex portion, and the apparatus main body engaging portion provided on the back side of the mounting portion of the image forming apparatus main body is an engaging convex portion or an engaging portion. The positioning mechanism according to claim 1, wherein the positioning mechanism is a hole.