JP2002304032A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus constituted so that a transfer belt unit may not interrupt the work inside the device and a developing unit can be attached/detached without attaching/detaching the transfer belt unit to/from the apparatus body. SOLUTION: As for the typical constitution of the image forming apparatus, the apparatus is provided with an image carrier and a transfer material carrier unit equipped with a transfer material carrier for carrying the transfer material, and for transferring the image formed on the image carrier to the transfer material carried by the transfer carrier, the transfer material carrier unit is constituted so that it can be rocked around a rocking shaft arranged on one end side in the rotary shaft direction of the transfer material carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a color copying machine or a color printer adopting an electrophotographic system, and more particularly to an improvement in maintainability.

[0002]

2. Description of the Related Art Conventionally, an in-line type image forming apparatus in which a plurality of image carriers are arranged in series has been proposed.
Such image forming apparatuses are roughly classified into a horizontal arrangement in which a plurality of image carriers are arranged in a horizontal direction, and a vertical arrangement in which a plurality of image carriers are arranged in a vertical direction. The respective features are that the horizontal arrangement has a small height but a large installation area, and the vertical arrangement has a small installation area but a high height. When a configuration as a desktop printer in recent years is considered, a vertical configuration having a small installation area is advantageous, and the number of manufacturers providing the configuration is increasing.

Referring to FIG. 5, a conventional image forming apparatus having a vertical arrangement will be described. The image forming apparatus shown in the figure has developing units 100a to 100d (100a is not shown) as four image forming units arranged in a vertical direction, and each of the photosensitive drums 101a to 101d is an image carrier. (101a is not shown). Scanner units 103a to 103d are arranged at horizontal positions of the respective photosensitive drums 101, and are configured to irradiate a laser to the photosensitive drum 101 through the inside of the developing unit 100 to form a latent image. ing. Each developing unit 100 includes developing means 102a to 102d.
(102a is not shown), and the photosensitive drum 101 is provided.
The latent image formed above is developed with toner of each color to form a toner image.

At the lower part of the apparatus, there is provided a feeding means 104 for storing and feeding the transfer material. The feeding means 104 separates and feeds the transfer material one by one and sends it to an electrostatic transfer belt 105 as a transfer material carrier. The electrostatic transfer belt 105 contacts all of the plurality of photosensitive drums 101 and rotates while adsorbing a transfer material. When the transfer material conveyed by suction is passed through each photoreceptor drum 101, a toner image of each color carried on each is superimposedly transferred, and is heated and pressed by a fixing unit 106 to form a color image. After that, the sheet is discharged and stacked on a discharge tray 107 provided at the upper part of the apparatus, and the image formation is completed.

[0005] As shown in the figure, the electrostatic transfer belt 105 is configured to be openable and closable about a lower rotating shaft 105a, and is configured to remove a transfer material having a jam.
Further, the developing unit 100 is configured to be detachable with respect to the apparatus main body, and detachable with the electrostatic transfer belt 105 opened,
It can be replaced and toner can be supplied.

[0006]

The image forming apparatus having the above-described vertical arrangement has a feature that, although the installation area is reduced as described above, the apparatus main body becomes vertically long. Therefore, when replacing the developing unit 100 installed on the back side of the electrostatic transfer belt 105, it is necessary to work at a distance equal to the height of the electrostatic transfer belt 105, and extremely unstable work is required. There is a problem that must be done.

There has also been proposed a configuration in which the electrostatic transfer belt 105 is detachable from the apparatus main body. In such a configuration, the above-mentioned problem is solved in the operation on the developing unit 100, but the operation itself of attaching and detaching the electrostatic transfer belt 105 and the handling of the removed electrostatic transfer belt 105 are inconvenient.

Accordingly, the present invention provides an image forming apparatus capable of attaching and detaching a developing unit without the transfer belt unit obstructing the operation inside the apparatus and without attaching and detaching the transfer belt unit from the apparatus main body. It is intended to be.

[0009]

In order to solve the above-mentioned problems, a typical configuration of an image forming apparatus according to the present invention comprises an image carrier and a transfer material carrier having a transfer material carrier for carrying a transfer material. And an image forming apparatus for transferring an image on the image carrier to a transfer material carried on the transfer material carrier, wherein the transfer material carrier unit rotates the transfer material carrier. It is characterized by being capable of swinging about a swing shaft provided at one end in the axial direction.

[0010]

[First Embodiment] A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is an external perspective view of an image forming apparatus according to the present embodiment, and FIG. 2 is an overall configuration diagram of the image forming apparatus. The image forming apparatus according to the present embodiment is an in-line type color image forming apparatus in which a plurality of image carriers are vertically arranged.

First, the overall configuration of the apparatus will be described with reference to FIG. The color image forming apparatus shown in FIG. 1 includes four photosensitive drums 1a to 1
d. Each photosensitive drum 1 is driven to rotate counterclockwise in the figure by a driving unit (not shown). Charging means 2a to 2d for uniformly charging the surface of each photoconductor drum 1 in order according to the rotation direction around each photoconductor drum 1,
Scanner units 3a to 3a to form a latent image on each photosensitive drum 1 by irradiating a laser beam based on image information
d, developing devices 4a to 4d as developing means for developing toner as a toner image by attaching toner to the latent image, and an electrostatic transfer roller 5a for transferring the toner image on each photosensitive drum 1 to the transfer material S
And cleaning devices 6a to 6d for removing transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer. Here, each photosensitive drum 1, charging means 2, developing device 4, and cleaning device 6 are integrally formed as a cartridge, and a process cartridge 7a is formed as an image carrier unit.
To d.

The photosensitive drum 1 has an organic photoconductor layer (OPC photosensitive member) on the outer peripheral surface of an aluminum cylinder having a diameter of, for example, 30 mm.
Is applied. The photosensitive drum 1 is rotatably supported at both ends by support members.
When a driving force from a driving unit (not shown) is transmitted to one end, the end is rotated counterclockwise in the drawing.

As the charging means 2, a contact charging type is used. The charging member is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photoconductor drum 1 and a charging bias voltage is applied to the roller to make the surface of the photoconductor drum 1 uniform. It is charged.

The scanner units 3a to 3d are arranged substantially in the horizontal direction of the photosensitive drums 1a to 1d, emit image light corresponding to image signals by a laser diode (not shown), and rotate at high speed by a scanner motor (not shown). The light is applied to mirrors 8a to 8d. The image light reflected by each polygon mirror 8 selectively exposes the surface of the charged photosensitive drum 1 via the imaging lenses 9a to 9d to form a latent image.

The developing devices 4a to 4d are respectively yellow,
It is composed of a developing device in which magenta, cyan and black toners are stored. Each developing device has developing rollers 10a to 10d, and forms toner images of each color on each photosensitive drum 1 by transferring toner to a low potential portion of a latent image on the photosensitive drum 1 (development). I do.

The electrostatic transfer belt 11, which is a transfer material carrier,
It is arranged so as to be in contact with all the photosensitive drums 1a to 1d. The electrostatic transfer belt 11 is constituted by a film-shaped belt member having a peripheral length of about 780 mm and a thickness of about 150 μm having a volume specific resistance of 1011 to 1014 Ωcm, and a belt driving roller 12, a driven roller 13 a in a vertical direction, 13b, tension roller 14
The transfer material S is electrostatically attracted to the outer peripheral surface on the left side in the figure and circulates clockwise in the figure so that the transfer material S comes into contact with the photosensitive drums 1a to 1d. Thus, the transfer material S is conveyed from the driven roller 13a side (lower side) to the belt driving roller 12 side (upper side). Also, electrostatic transfer belt
Reference numeral 11 is stored in an electrostatic transfer belt unit 25 which is a transfer material carrier unit described later.

The photosensitive drum 1a inside the electrostatic transfer belt 11
The electrostatic transfer rollers 5a to 5d are disposed at positions facing to the transfer material S through the electrostatic transfer belt 11 from the electrostatic transfer rollers 5. Due to the electric field generated by the electric charges, the negative toner image on the photosensitive drum 1 is superimposedly transferred onto the transfer material S in contact with the photosensitive drum 1.

The feeding section 15 is arranged at the lower part of the apparatus,
Are stacked and stored, and are fed and conveyed. At the time of image formation, the feed roller 17 and the retard roller pair 18 using a half-moon roller are driven and rotated in accordance with the image forming operation, and separate and feed the transfer materials S in the feed cassette 16 one by one. The fed transfer material S abuts the leading edge against the pair of registration rollers 19 and temporarily stops, forms a loop, corrects skew, and adjusts the position. Then, the registration roller pair 19 rotates again in synchronization with the rotation of the electrostatic transfer belt 11 and the image writing position, and feeds the transfer material S to the electrostatic transfer belt 11. That is, when the leading end of the toner image on the peripheral surface of the photosensitive drum 1a at the most upstream position is rotated and conveyed to a point opposed to the electrostatic transfer belt 11, the recording of the transfer material S is started at the opposed point. The paper is transported so that the positions match.

The transfer material S is sandwiched between the electrostatic attraction roller 22 and the electrostatic transfer belt 11 so that the electrostatic transfer belt 11
By pressing against the outer periphery of the electrostatic transfer belt 11 and applying a voltage between the electrostatic transfer belt 11 and the electrostatic attraction roller 22, electric charges are transferred to the transfer material S, which is a dielectric, and the dielectric layer of the electrostatic transfer belt 11. The transfer member is induced to electrostatically attract the transfer material to the outer periphery of the electrostatic transfer belt 11. As a result, the transfer material S is stably adsorbed on the electrostatic transfer belt 11, and is conveyed to the most downstream photosensitive drum 1d while transferring toner images of each color from the photosensitive drums 1a to 1d. Thereafter, the transfer material S is separated from the electrostatic transfer belt 11 by a curvature according to the curvature of the belt driving roller 12, and is conveyed to the fixing unit 20.

The fixing section 20 fixes the toner images of a plurality of colors transferred to the transfer material S. The fixing section 20 has a rotating heating roller 21a and a pressurizing member which presses the rotating heating roller 21a to apply heat and pressure to the transfer material S. A fixing roller pair 21 including a roller 21b is provided. That is, when the transfer material S on which the toner image on the photosensitive drum 1 is transferred passes through the fixing unit 20, heat and pressure are applied by the fixing roller pair 21, and the toner image is permanently fixed on the surface of the transfer material S. . Thereafter, the transfer material S is discharged to the discharge tray 24 with the image surface down by the discharge roller pair 23.

Next, an electrostatic transfer belt unit 25 including the electrostatic transfer belt 11 will be described with reference to FIG. The electrostatic transfer belt 11 includes a belt drive roller 12, a driven roller 13,
a, 13b and wound around the tension roller 14 are supported by a support frame 26. Bearings 27a to 27d are rotatably supported at both ends of the belt drive roller 12 and the driven roller 13a, and are respectively supported by the support frame 26 with the outer peripheral portions exposed.

A rotating shaft is provided at a side end of the support frame 26.
28a and 28b are provided. On the other hand, rotary bearings 29a and 29b for receiving the rotary shaft are provided on the apparatus body side.
It is pivotally supported rotatably with slight play with respect to 28a and 28b. That is, the electrostatic transfer belt 11 is supported by the apparatus main body so as to be rotatable laterally in the rotation direction.

At the positions corresponding to the bearings 27a to 27d supported by the belt drive roller 12 and the driven roller 13a, bending portions 30a to 30d (30c and 30d are not shown) of the side plate of the main body and guides are provided.
31a to 31d are formed. When the electrostatic transfer belt unit 25 is moved closer to the apparatus main body, the shaft ends of the belt drive roller 12 and the driven roller 13a are guided by guides 31a to 31d (31c, 31d
(Not shown) is urged by urging means (not shown) while being positioned by positioning each bearing 27 against each bent portion 30 of the main body side plate. A grip portion 32 is formed on the support frame 26, and serves as a clue for opening / closing and attaching / detaching the electrostatic transfer belt unit 25.

With the above configuration, it is possible to attach / detach the process cartridge 7 only by opening / closing operation without attaching / detaching the electrostatic transfer belt unit 25 from / to the main unit. In addition, since the electrostatic transfer belt 11 is configured to be rotatable in the lateral direction with respect to the rotation direction, the electrostatic transfer belt 11 can be opened in the lateral direction, so that the electrostatic transfer belt 11 is sufficiently close to the main body when the process cartridge 7 is replaced. The work can be easily and safely performed.

[Second Embodiment] Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 3 is an external perspective view of the image forming apparatus according to the present embodiment. Parts that are the same as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, the electrostatic transfer belt 11 is included in an electrostatic transfer belt unit 33, and a belt driving roller 12 around which the electrostatic transfer belt 11 is wound, a driven roller
13a, 13b and the tension roller 14 are supported by a support frame 34, respectively. Bearings 27a-d (27a, 27b) are provided at both ends of the belt drive roller 12 and the driven roller 13a.
(Not shown) are pivotally supported by the support frame 34 with the outer peripheral surface exposed.

Locking portions 35a and 35b are provided on the back surface of the support frame 34, that is, on the side opposite to the photosensitive drums 1a to 1d. On the other hand, door means 38 as an opening / closing part
And locking holes 36a and 36b are formed on the inner surface thereof, that is, on the electrostatic transfer belt unit 33 side. The locking holes 36a and 36b are engaged with the locking portions 35a and 35b with a slight play, thereby holding the electrostatic transfer belt unit 33.

The door means 38 is rotatably provided at the side end of the apparatus main body, and is configured to be rotatable on the side in the rotation direction of the electrostatic transfer belt 11. Therefore, by locking the electrostatic transfer belt unit 33 to the door means 38, it becomes possible to open the electrostatic transfer belt 11 in the lateral direction as the door means 38 opens and closes.

Bends 30a-d (30c, 30d are not shown) of the main body side plate and guides are provided at positions corresponding to the respective bearings 27a-d supported by the belt drive roller 12 and the driven roller 13a.
31a to 31d are formed. When the electrostatic transfer belt unit 25 is moved closer to the apparatus main body, the shaft ends of the belt driving roller 12 and the driven roller 13a are guided by guides 31a to 31d (31c, 31d).
(Not shown) is urged by urging means (not shown) while being positioned by positioning each bearing 27 against each bent portion 30 of the main body side plate. A gripping portion 37 is formed on the support frame 26, and serves as a clue when the electrostatic transfer belt unit 25 is opened and closed and when the electrostatic transfer belt unit 25 is attached and detached.

With the above configuration, the process cartridge 7 can be attached and detached only by opening and closing operations without attaching and detaching the electrostatic transfer belt unit 33 from the apparatus main body. In addition, by opening the door means 38, the electrostatic transfer belt 11 can be opened in the lateral direction, and when the process cartridge 7 is replaced, the electrostatic transfer belt 11 can be sufficiently close to the main body. Can be.

Further, the transfer belt unit (the entire transfer belt unit or the gripping portion of the transfer belt unit (the grip portion of the transfer belt unit) is not linked to the opening and closing door of the image forming apparatus, but is linked to the operation of opening and closing the door. The handle portion)) may be moved to a predetermined position in the opening / closing direction of the opening / closing door (upward in FIG. 3) by using an urging means (compression spring or the like). With such a configuration, usability at the time of maintenance can be improved.

[Third Embodiment] Next, a third embodiment of the image forming apparatus according to the present invention will be described. FIG. 4 is an overall configuration diagram of the image forming apparatus according to the present embodiment. The same reference numerals are given to the same parts as those in the above embodiments, and the description is omitted.

In each of the embodiments described above, the electrostatic transfer belt 11 as a transfer material carrier is described as the transfer belt unit. However, the images superimposedly transferred from the image carrier are collectively transferred to the transfer material. The present invention can also be applied to an image forming apparatus using an intermediate transfer member that transfers images by transfer.

In the figure, an intermediate transfer belt 40, which is an intermediate transfer member, is arranged so as to be in contact with all the photosensitive drums 1a to 1d, and includes a belt drive roller 12, driven rollers 13a and 13
b, wound around the tension roller 14. The intermediate transfer belt 40 circulates clockwise in the figure, and the toner images are superimposedly transferred from the photosensitive drums 1a to 1d by the electrostatic transfer rollers 5a to 5d.

A secondary transfer roller 41 is urged against the driven roller 13a at the lower end of the intermediate transfer belt 40. The transfer material S conveyed from the registration roller pair 19 is transferred between the intermediate transfer belt 40 and the secondary transfer roller 41. The color toner images superimposed in the nip are collectively transferred. Thereafter, the transfer material S is fixed at the fixing unit.
The toner image is conveyed to the printer 20, heat and pressure are applied thereto, and after the toner image is permanently fixed, the toner image is discharged and stacked on a discharge tray 24 outside the apparatus.

Even in the image forming apparatus having the above-described configuration, the intermediate transfer belt 40 is configured to be opened and closed in the horizontal direction, similarly to the first embodiment, so that the intermediate transfer belt 40 can be removed from the main body without being detached. The attachment / detachment operation of the process cartridge 7 can be performed only by the opening / closing operation. Further, when the process cartridge 7 is replaced, it becomes possible to sufficiently approach the main body, so that the operation can be made easy and safe.

Further, similarly to the second embodiment, the intermediate transfer belt unit may be configured to be supported by the opening and closing door, and the intermediate transfer belt unit may be moved together with the opening and closing door to the outside of the image forming apparatus main body.

[0038]

As described above, in the image forming apparatus according to the present invention, the transfer material carrier unit is swung about a swing shaft provided at one end of the transfer material carrier in the rotation axis direction. With this configuration, the transfer belt unit can be opened and closed in the horizontal direction. Therefore, the image carrier unit can be attached / detached only by the opening / closing operation without attaching / detaching the transfer material carrier unit from / to the apparatus main body. Further, since the transfer material carrier unit can be opened in the lateral direction, it is possible to sufficiently approach the main body when replacing the image carrier unit, and the operation can be made easy and safe.

[Brief description of the drawings]

FIG. 1 is an external perspective view of an image forming apparatus according to a first embodiment.

FIG. 2 is an overall configuration diagram of the image forming apparatus.

FIG. 3 is an external perspective view of an image forming apparatus according to a second embodiment.

FIG. 4 is an overall configuration diagram of an image forming apparatus according to a third embodiment.

FIG. 5 is a diagram illustrating a conventional image forming apparatus having a vertical arrangement.

[Explanation of symbols]

 S ... transfer material 1 ... photosensitive drum 2 ... charging means 3 ... scanner unit 4 ... developing device 5 ... electrostatic transfer roller 6 ... cleaning device 7 ... process cartridge 8 ... polygon mirror 9 ... imaging lens 10 ... developing roller 11 ... Electrostatic transfer belt 12… Belt drive roller 13… Driving roller 14… Tension roller 15… Supply unit 16… Supply cassette 17… Supply roller 18… Retard roller pair 19… Registration roller pair 20… Fixing unit 21… Fixing roller Pair 21a Heating roller 21b Pressure roller 22 Electrostatic suction roller 23 Discharge roller pair 24 Discharge tray 25 Electrostatic transfer belt unit 26 Support frame 27 Bearing 28 Rotating shaft 29 Rotating bearing 30 … Bending part 31… Guide 32… Grip part 33… Electrostatic transfer belt unit 34… Support frame 35… Lock part 36… Lock hole 37… Grip part 38… Door means 40… Medium Transfer belt 41 ... secondary transfer roller

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AA06 AA07 AB02 AD05 AD16 BB01 BB22 BB42 BB43 BB46 BB71 2H071 BA03 BA13 BA14 BA16 BA23 BA24 DA02 DA08 DA09 DA15 DA21 EA18 2H200 FA12 FA17 GA12 GA23 GA33 GA44 GB41 HA01 HB12 JB10 JB13 JC03 LA38

Claims (24)

[Claims] 1. An image forming apparatus comprising: an image carrier; and a transfer material carrier unit having a transfer material carrier for carrying a transfer material, wherein an image on the image carrier is carried by the transfer material carrier. An image forming apparatus for transferring to a material, wherein the transfer material carrier unit is capable of swinging about a swing shaft provided at one end side of the transfer material carrier in a rotation axis direction. . 2. The image forming apparatus according to claim 1, further comprising an image carrier unit including the image carrier, wherein the image carrier unit is moved relative to an image forming apparatus main body through a space formed after the transfer material carrier unit is swung. The image forming apparatus according to claim 1, wherein the image forming apparatus is removable. 3. The image forming apparatus according to claim 2, wherein the image carrier unit includes a developing unit that develops a latent image on the image carrier. 4. The image forming apparatus according to claim 1, wherein a plurality of the image carriers are provided, and the images on the respective image carriers are sequentially transferred to a transfer material carried on the transfer material carrier. Any of the image forming apparatuses. 5. An image forming apparatus having an image carrier unit having an image carrier and transferring an image on the image carrier to a transfer material, wherein the image carrier unit has a rotation axis of the image carrier. An image forming apparatus capable of swinging about a swing shaft provided at one end in the direction. 6. An image forming unit for forming an image on the image carrier, wherein the image forming unit is moved relative to an image forming apparatus main body through a space formed after the image carrier unit is swung. The image forming apparatus according to claim 5, wherein the image forming apparatus is detachable. 7. The image forming apparatus according to claim 6, wherein the image forming unit includes a photoconductor, and an image on the photoconductor is transferred to the image carrier. 8. The image forming apparatus according to claim 7, wherein the image forming unit includes a developing unit that develops a latent image on the photoconductor. 9. An image forming apparatus according to claim 7, wherein a plurality of said photoconductors are provided, and an image on each of said photoconductors is sequentially transferred to said image carrier. 10. The image forming apparatus according to claim 6, wherein the image forming unit includes a developing unit that develops a latent image on the image carrier. 11. The image forming apparatus according to claim 10, wherein a plurality of said developing units are provided, and each of said developing units sequentially develops a latent image on said image carrier. 12. A transfer device comprising: an image carrier; and a transfer material carrier unit having a transfer material carrier for carrying a transfer material, wherein an image on the image carrier is carried on the transfer material carrier. In the image forming apparatus for transferring to a material, an opening / closing unit that can be opened / closed to expose the inside of the image forming apparatus main body is provided, and the transfer material carrier unit is moved outside the image forming apparatus main body in conjunction with the operation of opening the open / close unit An image forming apparatus, wherein the image forming apparatus is moved. 13. The image according to claim 12, wherein the transfer material carrier unit is supported by the opening / closing unit, and the transfer material carrier unit is movable outside the image forming apparatus main body together with the opening / closing unit. Forming equipment. 14. The image forming apparatus further comprising an image carrier unit having the image carrier, wherein the image carrier unit is moved relative to an image forming apparatus main body through a space formed after the transfer material carrier unit is moved. 14. The image forming apparatus according to claim 12, wherein the image forming apparatus is detachable. 15. The image forming apparatus according to claim 14, wherein the image carrier unit includes a developing unit that develops a latent image on the image carrier. 16. The image carrier according to claim 12, wherein a plurality of said image carriers are provided, and the images on each of said image carriers are sequentially transferred to a transfer material carried on said transfer material carrier.
Any one of the image forming apparatuses. 17. An image forming apparatus having an image carrier unit having an image carrier and transferring an image on the image carrier to a transfer material, wherein the image forming apparatus is capable of opening and closing to expose the inside of the image forming apparatus main body. Wherein the image carrier unit is moved out of the image forming apparatus main body in conjunction with an operation of opening the opening / closing section. 18. The image forming apparatus according to claim 17, wherein the image carrier unit is supported by the opening / closing section, and the image carrier unit is movable together with the opening / closing section outside the image forming apparatus main body. . 19. An image forming unit for forming an image on the image carrier, wherein the image forming unit is moved relative to an image forming apparatus main body through a space formed after the image carrier unit is moved. 19. The image forming apparatus according to claim 17, wherein the image forming apparatus is detachable. 20. The image forming unit includes a photoconductor,
20. The image forming apparatus according to claim 19, wherein the image on the photoconductor is transferred to the image carrier. 21. The image forming apparatus according to claim 20, wherein the image forming unit includes a developing unit that develops a latent image on the photoconductor. 22. The image forming apparatus according to claim 20, wherein a plurality of said photoconductors are provided, and an image on each of said photoconductors is sequentially transferred to said image carrier. 23. The image forming apparatus according to claim 19, wherein said image forming unit includes a developing means for developing a latent image on said image carrier. 24. The image forming apparatus according to claim 23, wherein a plurality of said developing units are provided, and each of said developing units sequentially develops a latent image on said image carrier.