Image formation apparatus and photoreceptor cartridge Number:7,395,008 from the United States Patent and Trademark Office (PTO) owispatent

Title: Image formation apparatus and photoreceptor cartridge

Abstract: An image forming apparatus, includes: a mainframe; a photoreceptor; an exposing unit that exposes a surface of the photoreceptor to form an electrostatic latent image; and a developing unit that develops the electrostatic latent image by supplying a charged developer on the surface of the photoreceptor having the electrostatic latent image formed thereon. The photoreceptor is loadable in and unloadable from the mainframe separately from the developing unit.

Patent Number: 7,395,008 Issued on 07/01/2008 to Sato,   et al.

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Inventors:	Sato; Shougo (Seto, JP), Ishii; Makoto (Nagoya, JP), Okabe; Yasushi (Nagoya, JP)
Assignee:	Brother Kogyo Kabushiki Kaisha (Nagoya, JP)
Appl. No.:	10/782,973
Filed:	February 23, 2004

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Foreign Application Priority Data

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Feb 24, 2003 [JP]			2003-046435
Mar 13, 2003 [JP]			2003-068200
Mar 18, 2003 [JP]			2003-074072

Current U.S. Class:	399/116 ; 399/110; 399/119
Current International Class:	G03G 15/02 (20060101); G03G 15/04 (20060101)
Field of Search:	399/107,110,111,112,113,114,116,117,299,302,119

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References Cited [Referenced By]

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U.S. Patent Documents

6381428	April 2002	Yamamoto et al.
6453135	September 2002	Sameshima et al.
6463234	October 2002	Arimitsu et al.
6483527	November 2002	Kaneko et al.
6501925	December 2002	Yamamoto et al.
6608981	August 2003	Mae
6681088	January 2004	Kanno et al.
6697586	February 2004	Yamamoto et al.
6708011	March 2004	Nomura et al.
6799011	September 2004	Abe et al.

Foreign Patent Documents

	1311460		Sep., 2001		CN
	1369750		Sep., 2002		CN
	A-7-281579		Oct., 1995		JP
	A-7-295315		Nov., 1995		JP
	A-8-15948		Jan., 1996		JP
	A-8-137366		May., 1996		JP
	A-8-137367		May., 1996		JP
	A 10-48898		Feb., 1998		JP
	A 10-48901		Feb., 1998		JP
	A-10-149078		Jun., 1998		JP
	A-10-186851		Jul., 1998		JP
	A 10-307439		Nov., 1998		JP
	A 2000-267380		Sep., 2000		JP
	A 2000-321843		Nov., 2000		JP
	A-2001-34021		Feb., 2001		JP
	A-2001-134042		May., 2001		JP
	A-2001-142378		May., 2001		JP
	A 2001-166555		Jun., 2001		JP
	A-2001-175122		Jun., 2001		JP
	A-2001-255804		Sep., 2001		JP
	A-2001-255806		Sep., 2001		JP
	A 2001-281952		Oct., 2001		JP
	A-2001-356548		Dec., 2001		JP
	A-2002-72618		Mar., 2002		JP
	A-2002-108049		Apr., 2002		JP
	A-2002-304032		Oct., 2002		JP
	A-2003-15378		Jan., 2003		JP

Primary Examiner: Ngo; Hoang
Attorney, Agent or Firm: Oliff & Berridge, PLC

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Claims

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What is claimed is:

1. An image forming apparatus, comprising: a mainframe; a photoreceptor; an exposing unit that exposes a surface of the photoreceptor to form an electrostatic latent image; a developing unit that develops the electrostatic latent image by supplying a charged developer on the surface of the photoreceptor having the electrostatic latent image formed thereon; a cover that is capable of being opened and is structured to allow the photoreceptor to be loaded in and unloaded from the mainframe; and an evacuation mechanism that is linked to the cover and evacuates the developing unit from a moving path of the photoreceptor by moving the developing unit along a direction away from the photoreceptor when the cover is opened, wherein the photoreceptor is loadable in and unloadable from the mainframe separately from the developing unit.

2. The image forming apparatus as claimed in claim 1, further comprising: a photoreceptor cartridge that retains the photoreceptor and is loadable in and unloadable from the mainframe while being separated from the developing unit.

3. The image forming apparatus as claimed in claim 2, wherein the photoreceptor includes a plurality of photoreceptors for a plurality of colors; and the photoreceptor cartridge integrally retains the plurality of photoreceptors.

4. The image forming apparatus as claimed in claim 3, wherein the plurality of photoreceptors includes a photoreceptor corresponding to black color and being exchangeable separately from the other photoreceptors.

5. The image forming apparatus as claimed in claim 2, wherein the photoreceptor cartridge is loadable in and unloadable from the mainframe by moving the photoreceptor along a direction that is exactly parallel to or substantially parallel to a conveying direction of a transfer medium, the transfer medium being a medium onto which the charged developer is transferred from the photoreceptor.

6. The image forming apparatus as claimed in claim 2, wherein the photoreceptor cartridge includes a charger that uniformly charges the surface of the photoreceptor prior to formation of the electrostatic latent image.

7. The image forming apparatus as claimed in claim 2, wherein the mainframe includes a guide part that guides movement of the photoreceptor cartridge at the time of loading and unloading; and the photoreceptor cartridge includes a guided part guided by the guide part.

8. The image forming apparatus as claimed in claim 2, wherein the developing unit is loadable in and unloadable from the mainframe by moving the developing unit along a direction that crosses a conveying direction of a transfer medium and is substantially perpendicular to or exactly perpendicular to a longitudinal direction of the photoreceptor, the transfer medium being a medium onto which the developer is transferred from the photoreceptor.

9. The image forming apparatus as claimed in claim 1, wherein the developing unit is loadable in and unloadable from the mainframe by moving the developing unit along a direction different from the direction along which the photoreceptor is moved to be loaded and unloaded.

10. The image forming apparatus as claimed in claim 9, wherein the developing unit is loadable in and unloadable from the mainframe by moving the developing unit along a direction that is substantially opposite or exactly opposite to the direction in which the photoreceptor is moved to be loaded and unloaded.

11. The image forming apparatus as claimed in claim 1, wherein the photoreceptor faces the transfer unit at a transferring position; the exposing unit is disposed on a side of the photoreceptor opposite to the transferring position; and the exposing unit overlaps with the photoreceptor in a substantially horizontal or an exactly horizontal direction.

12. The image forming apparatus as claimed in claim 11, wherein the exposing unit includes a laser scanner.

13. The image forming apparatus as claimed in claim 12, wherein: the laser scanner includes a plurality of laser scanners each having a casing; the developing units and the laser scanners are arranged alternately with each other in a substantially vertical or an exactly vertical direction; and the developing units are loadable in and unloadable from the mainframe along surfaces of the casings of the laser scanners.

14. The image forming apparatus as claimed in claim 13, wherein the mainframe includes a guide member that guides the developing unit being loaded therein and unloaded therefrom; and the developing unit includes an engaging part that engages with the guide member.

15. The image forming apparatus as claimed in claim 11, wherein the exposing unit includes an LED array.

16. The image forming apparatus as claimed in claim 1, wherein the developing unit includes a developer carrying member that carries a developer; and the developer remaining on the photoreceptor after the transfer unit transferring the developer image onto the transfer medium is recovered by the developer carrying member.

17. The image forming apparatus as claimed in claim 1, wherein the developing unit and the photoreceptor are independently loadable in and unloadable from the mainframe.

18. The image forming apparatus as claimed in claim 17, wherein the developing unit includes a first grab handle; and the photoreceptor is accommodated in a photoreceptor unit having a second grab handle.

19. The image forming apparatus as claimed in claim 18, wherein the developing unit includes a developer carrying member; the first grab handle is provided on the developing unit at both ends in an axial direction of the developer carrying member; and the second grab handle is provided on the photoreceptor unit at both ends in an axial direction of the photoreceptor.

20. The image forming apparatus as claimed in claim 1, wherein the exposing unit includes an LED array.

21. The image forming apparatus as claimed in claim 17, wherein the developing unit includes a developer carrying member that carries a developer; and the developer remaining on the photoreceptor after the transfer unit transferring the developer image onto the transfer medium is recovered by the developer carrying member.

22. The image forming apparatus as claimed in claim 1, wherein the developing unit includes a plurality of developer carrying members; the photoreceptor includes a plurality of photoreceptors; and the developer carrying members and the photoreceptors are alternately arranged in a conveying direction of the transfer medium.

23. The image forming apparatus as claimed in claim 1, wherein the developing unit includes a developer carrying member; the photoreceptor includes a photoreceptor drum; the photoreceptor drum opposes to the developer carrying member at a developing position; the photoreceptor drum opposes to the transfer medium at a transfer position; and a line passing through a rotation center of the photoreceptor drum and the developing position is substantially perpendicular to a line passing through the rotation center of the photoreceptor drum and the transferring position.

24. The image forming apparatus as claimed in claim 1, wherein the photoreceptor is accomodated in a photoreceptor unit loadable in and unloadable from the mainframe; the mainframe includes a guide part that guides the photoreceptor unit being loaded therein and unloaded therefrom; the photoreceptor includes an engaging part that engages with the guide part; and the guide part includes a positioning member that positions the photoreceptor unit at a deepest part thereof.

25. The image forming apparatus as claimed in claim 24, wherein the developing unit includes a developer carrying member; and the mainframe includes an urging part that urges the photoreceptor unit positioned by the positioning member to the developer carrying member.

26. The image forming apparatus according to claim 1, wherein: the photoreceptor is configured to be unloadable by moving the photoreceptor along a direction that is substantially perpendicular or exactly perpendicular to a longitudinal direction of the photoreceptor with the longitudinal direction being a direction along a rotational axis of the photoreceptor, and the developing unit is configured to be unloadable by moving the developing unit along a direction that is substantially perpendicular or exactly perpendicular to a longitudinal direction of the developing unit.

27. The image forming apparatus according to claim 1, wherein the developing unit and the photoreceptor are in contact with each other when developing the electrostatic latent image formed on the photoreceptor.

28. An image forming apparatus, comprising: a mainframe; a photoreceptor; an exposing unit that exposes a surface of the photoreceptor to form an electrostatic latent image; a developing unit that develops the electrostatic latent image by supplying a charged developer on the surface of the photoreceptor having the electrostatic latent image formed thereon; a cover that is capable of being opened and is structured to allow the photoreceptor to be loaded in and unloaded from the mainframe; and an evacuation mechanism that is linked to the cover and evacuates the developing unit from a moving path of the photoreceptor by moving the developing unit along a direction away from the photoreceptor when the cover is opened; wherein: the photoreceptor is configured to be unloadable from the mainframe by moving the photoreceptor along a direction that is substantially perpendicular or exactly perpendicular to a longitudinal direction of the photoreceptor with the longitudinal direction being a direction along a rotational axis of the photoreceptor, the developing unit is configured to be unloadable from the mainframe by moving the developing unit along a direction that is substantially perpendicular or exactly perpendicular to a longitudinal direction of the developing unit, the photoreceptor and the developing unit are loadable in and unloadable from the mainframe independently of each other, a belt that contacts with the photoreceptor is provided in the mainframe, and during unloading, the photoreceptor is moved from the mainframe along a direction that is towards the belt provided in the mainframe.

29. The image forming apparatus as claimed in claim 28, further comprising: a photoreceptor cartridge that retains the photoreceptor and is loadable in and unloadable from the mainframe while being separated from the developing unit.

30. The image forming apparatus as claimed in claim 29, wherein the photoreceptor includes a plurality of photoreceptors for a plurality of colors; and the photoreceptor cartridge integrally retains the plurality of photoreceptors.

31. The image forming apparatus as claimed in claim 30, wherein the plurality of photoreceptors includes a photoreceptor corresponding to black color and being exchangeable separately from the other photoreceptors.

32. The image forming apparatus as claimed in claim 28, wherein the developing unit is loadable in and unloadable from the mainframe by being moved along a direction different from the direction in which the photoreceptor is moved during loading and unloading.

33. The image forming apparatus as claimed in claim 29, wherein the photoreceptor cartridge includes a charger that uniformly charges the surface of the photoreceptor prior to formation of the electrostatic latent image.

34. The image forming apparatus as claimed in claim 29, wherein the mainframe includes a guide part that guides movement of the photoreceptor cartridge at the time of loading and unloading; and the photoreceptor cartridge includes a guided part guided by the guide part.

35. The image forming apparatus as claimed in claim 32, wherein the developing unit is loadable in and unloadable from the mainframe by moving the developing unit along a direction substantially opposite or exactly opposite to the direction along which the photoreceptor is moved to be loaded and unloaded.

36. The image forming apparatus as claimed in claim 28, wherein the photoreceptor faces the transfer unit at a transferring position; the exposing unit is disposed on a side of the photoreceptor opposite to the transferring position; and the exposing unit overlaps with the photoreceptor in a substantially horizontal or an exactly horizontal direction.

37. The image forming apparatus as claimed in claim 36, wherein the exposing unit includes a laser scanner.

38. The image forming apparatus as claimed in claim 37, wherein the developing unit includes a plurality of developing units; the laser scanner includes a plurality of laser scanners each having a casing; the developing units and the laser scanners are arranged alternately with each other in a substantially vertical direction; and the developing units are loadable in and unloadable from the mainframe along surfaces of the casings of the laser scanners.

39. The image forming apparatus as claimed in claim 38, wherein the mainframe includes a guide member that guides the developing unit being loaded therein and unloaded therefrom; and the developing unit includes an engaging part that engages with the guide member.

40. The image forming apparatus as claimed in claim 36, wherein the exposing unit includes an LED array.

41. The image forming apparatus as claimed in claim 28, wherein the developing unit includes a developer carrying member that carries a developer; and the developer remaining on the photoreceptor after the transfer unit transferring the developer image onto the transfer medium is recovered by the developer carrying member.

42. The image forming apparatus as claimed in claim 28, wherein the exposing unit includes an LED array.

43. The image forming apparatus as claimed in claim 28, wherein the developing unit includes a plurality of developer carrying members; the photoreceptor includes a photoreceptors; and the developer carrying members and the photoreceptors are alternately arranged in a conveying direction of the transfer medium.

44. The image forming apparatus as claimed in claim 28, wherein the developing unit includes a developer carrying member; the photoreceptor includes a photoreceptor drum; the photoreceptor drum opposes to the developer carrying member at a developing position; the photoreceptor drum opposes to the transfer medium at a transfer position; and a line passing through a rotation center of the photoreceptor drum and the developing position is substantially perpendicular to a line passing through the rotation center of the photoreceptor drum and the transferring position.

45. The image forming apparatus as claimed in claim 28, wherein the developing unit includes a first grab handle; and the photoreceptor is accommodated in a photoreceptor unit having a second grab handle.

46. The image forming apparatus as claimed in claim 45, wherein the developing unit includes a developer carrying member; the first grab handle is provided on the developing unit at both ends in an axial direction of the developer carrying member; and the second grab handle is provided on the photoreceptor unit at both ends in an axial direction of the photoreceptor.

47. The image forming apparatus as claimed in claim 28, wherein the photoreceptor is accommodated in a photoreceptor unit loadable in and unloadable from the mainframe; the mainframe includes a guide part that guides the photoreceptor unit being loaded therein and unloaded therefrom; the photoreceptor includes an engaging part that engages with the guide part; and the guide part includes a positioning member that positions the photoreceptor unit at a deepest part thereof.

48. The image forming apparatus as claimed in claim 47, wherein the developing unit includes a developer carrying member; and the mainframe includes an urging part that urges the photoreceptor unit positioned by the positioning member to the developer carrying member.

49. The image forming apparatus as claimed in claim 28, wherein the developing unit includes a developer carrying member that carries a developer; and the developer remaining on the photoreceptor after the transfer unit transferring the developer image onto the transfer medium is recovered by the developer carrying member.

50. The image forming apparatus according to claim 28, wherein the belt is an intermediate belt.

51. The image forming apparatus according to claim 28, wherein the belt is a transfer belt.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for forming an image, such as a color laser printer.

2. Background Art

As an apparatus for forming a multicolor image, such as a four-color image, on a recording medium, such as recording paper, a tandem type apparatus has been known, which has, for each of colors, a photoreceptor, an exposing unit for exposing the photoreceptor to form an electrostatic latent image on the surface thereof, and a developing unit for developing the electrostatic latent image by attaching a charged developer on the surface of the photoreceptor having the electrostatic latent image formed thereon. A four-cycle type apparatus has also been known, which has one pair of an exposing unit and a photoreceptor, and plural developing unit for the respective colors arranged around the photoreceptor.

The four-cycle type apparatus is not suitable for speeding up the image formation because the exposing and developing steps of the photoreceptor are sequentially carried out with changing colors. In the tandem type apparatus, on the other hand, the exposing and developing steps of the photoreceptors can be simultaneously carried out for the colors, and a multicolor image can be formed by sequentially transferring the developers attached on the photoreceptors corresponding to the respective colors on a recording medium. Therefore, the tandem type apparatus for forming a multicolor image exhibits a color image forming speed equivalent to the case of a monochrome image, and is suitable for high-speed image formation.

SUMMARY OF THE INVENTION

In the apparatus for forming an image, the photoreceptor and the developing unit should be replaced as needed. In the tandem type apparatus for forming a multicolor image, plural pairs of a exposing unit and a photoreceptor are provided corresponding to the respective colors, and therefore, it is necessary to prevent the photoreceptor and the developing unit (which are, in some cases, integrally configured as an exchangeable process cartridge) from interfering with the exposing unit upon replacement. Under the circumstances, it has been proposed that the exposing unit is evacuated to prevent from interfering upon replacement of the process cartridge (as described, for example, in JP-A-2001-166555).

In the case where the exposing unit is evacuated upon replacement of the process cartridge, the relative positions of the exposing unit of the respective colors are slightly deviated to cause a possibility of color drift. However, it is difficult in the configuration of the conventional apparatus for forming a multicolor image that the process cartridge is replaced without evacuation of the exposing unit. In particular, it is significantly difficult that the photoreceptor is replaced without evacuation of the exposing unit because the photoreceptor is disposed in the back of the apparatus for forming a multicolor image as viewed from the user.

Further, the photoreceptor drums of the tandem type color laser printer are required to have an extremely high dimensional accuracy for preventing color drift because images of the respective colors are transferred from the four different photoreceptor drums onto the single transfer medium. Therefore, the processing of the photoreceptor drums brings about high cost.

As described, for example, in JP-A-10-48898, a tandem type color laser printer may have image forming units for each of colors, which integrally retains a toner cartridge, a photoreceptor drum and a developing roller, and the whole of the image forming unit is replaced in the case where the toner is emptied out.

However, in the case where the whole of the image forming unit is replaced, the expensive photoreceptor drum is also replaced when the toner is emptied out, so as to increase the running cost and to increase the amount of industrial waste.

According to an aspect of the invention, an image forming apparatus may include: a mainframe; a photoreceptor; an exposing unit that exposes a surface of the photoreceptor to form an electrostatic latent image; and a developing unit that develops the electrostatic latent image by supplying a charged developer on the surface of the photoreceptor having the electrostatic latent image formed thereon. The photoreceptor is loadable in and unloadable from the mainframe separately from the developing unit.

According to this aspect, the surface of the photoreceptor is exposed with the exposing unit to form an electrostatic latent image, and the latent image is developed by attaching the charged developer to the surface of the photoreceptor with the developing unit. The developers thus developing the electrostatic latent image on the surface of the photoreceptor provided is transferred to the recording medium to form an image on the recording medium. The apparatus of this aspect can be easily subjected to speeding up owing to the tandem type system.

The invention may provide a photoreceptor cartridge to be loaded in an image forming apparatus, wherein the image forming apparatus includes a developing unit that develops an electrostatic latent image by supplying a charged developer. The photoreceptor cartridge includes a photoreceptor having a surface on which the electrostatic latent image is formed to be developed by the developing unit. The photoreceptor cartridge is loadable in and unloadable from a mainframe of the image forming apparatus while being separated from the developing unit.

Preferably, the photoreceptor includes a plurality of photoreceptors for a plurality of colors, which are integrally retained. According to this configuration, the photoreceptor cartridge integrally retains the photoreceptors for each of colors, and is detachable from the mainframe as being separately from the developing unit. Due to this, the photoreceptors can be detached without interference with the exposing unit of the image forming apparatus as being separated from the developing unit. Therefore, the photoreceptor can be easily replaced without movement of the exposing unit, and thus, occurrence of color drift in the image forming apparatus can be fairly prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more readily described with reference to the accompanying drawings:

FIG. 1 is a schematic cross sectional view showing a laser color printer according to an embodiment of the invention.

FIGS. 2A and 2B are a side view and a perspective view, respectively, showing a configuration of a supporting member of the printer.

FIG. 3 is an elevational view showing a configuration of a photoreceptor cartridge of the printer.

FIGS. 4A and 4B are perspective views showing a detailed configuration of the supporting member.

FIG. 5 is an elevational view showing the photoreceptor cartridge before mounting.

FIG. 6 is an elevational view showing a modified embodiment of the photoreceptor cartridge.

FIG. 7 is a cross sectional view showing another embodiment of a color laser printer as the apparatus for forming an image.

FIG. 8 is a cross sectional view showing the color laser printer shown in FIG. 7 in a state where a front cover thereof is opened.

FIG. 9 is a cross sectional view showing the color laser printer shown in FIG. 7 in a state where a rear cover thereof is opened.

FIG. 10 is an enlarged cross sectional view showing a process part of the laser color printer shown in FIG. 7 (in a state where drum cartridges corresponding to a yellow developing cartridge and a magenta developing cartridge are mounted).

FIG. 11 is a cross sectional view showing another embodiment of a color laser printer as the apparatus for forming an image.

FIG. 12 is a cross sectional view showing another embodiment of a color laser printer as the apparatus for forming an image.

FIG. 13 is a cross sectional view showing another embodiment of the color laser printer shown in FIG. 12 in a state where an openable cover thereof is opened.

FIG. 14 is an enlarged cross sectional view showing a process part of the laser color printer shown in FIG. 12 (in a state where only a drum cartridge corresponding to a black developing cartridge is mounted).

FIG. 15 is a schematic side view showing a positional relationship of photoreceptor drums, developing rollers and transfer rollers.

FIG. 16 is a cross sectional view showing another embodiment of a color laser printer as the apparatus for forming an image.

FIG. 17 is a cross sectional view showing the color laser printer shown in FIG. 16 in a state where an openable cover thereof is opened.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The First Preferred Embodiment

Embodiments of the invention will be described with reference to the drawings. FIG. 1 is a schematic cross sectional view showing a color laser printer 1 as an apparatus for forming a multicolor image, to which the invention is applied. The color laser printer 1 shown in FIG. 1 has a visual image forming part 4, an intermediate transfer material in a belt form 5, a fixing part 8, a paper feeding part 9 and a paper delivery tray 10b.

The visual image forming part 4 has, for each of visual image forming steps with respective toners of magenta (M), cyan (C), yellow (Y) and black (Bk), developing devices 51M, 51C, 51Y and 51Bk as a developing unit, photoreceptor drums 3M, 3C, 3Y and 3Bk as a photoreceptor, cleaning rollers 70M, 70C, 70Y and 70Bk as a cleaning unit, charging devices 71M, 71C, 71Y and 71Bk as a charging unit, and exposing unit 72M, 72C, 72Y and 72Bk.

These configurational elements will be described in more detail below. The developing devices 51M, 51C, 51Y and 51Bk have developing rollers 52M, 52C, 52Y and 52Bk, respectively. The developing rollers 52M, 52C, 52Y and 52Bk each is configured in the form of a cylinder with electroconductive silicone rubber as a base material having formed on the surface thereof a coated layer of a resin or rubber material containing fluorine. The developing rollers 52M, 52C, 52Y and 52Bk may not be configured with electroconductive silicone rubber but may be configured with electroconductive urethane rubber. The ten-point average roughness (Rz) of the surface thereof is from 3 to 5 .mu.m, which is smaller than 9 .mu.m, the average particle diameter of the toner.

The developing devices 51M, 51C, 51Y and 51Bk have feeding rollers 53M, 53C, 53Y and 53Bk, respectively. The feeding rollers 53M, 53C, 53Y and 53Bk are electroconductive sponge rollers, which are in contact with the developing rollers 52M, 52C, 52Y and 52Bk, respectively, under pressure with an elastic force of sponge. The feeding rollers 53M, 53C, 53Y and 53Bk may be configured with a foamed body of a suitable material, such as electroconductive silicone rubber, EPDM and urethane rubber.

The developing devices 51C, 51Y, 51Y and 51Bk have squeezing blades 54M, 54C, 54Y and 54Bk, respectively. The squeezing blades 54M, 54C, 54Y and 54Bk are formed in a plate form having a stainless steel base end fixed to casings 55M, 55C, 55Y and 55Bk of the developing devices, and a tip end edge formed with insulating silicone rubber, insulating fluorine rubber or resin, or the like. The tip end edges of the squeezing blades 54M, 54C, 54Y and 54Bk are in contact with the developing rollers 52M, 52C, 52Y and 52Bk, respectively, under pressure from underneath of the developing rollers 52M, 52C, 52Y and 52Bk.

The toner housed in the casings 55M, 55C, 55Y and 55Bk of the developing devices is a positively charged non-magnetic one-component developer, which has toner mother particles having an average particle diameter of 9 .mu.m formed by adding a known coloring agent, such as carbon black, and a charge controlling agent, such as a quaternary ammonium salt, or a charge controlling resin to a styrene-acrylic resin formed into a spherical form by suspension polymerization. The toner contains silica as an external additive on the surface of the toner mother particles. The silica as the external additive has been subjected to a known hydrophobic treatment with a silane coupling agent, a silicone oil or the like, and has an average particle diameter of 10 nm. The addition amount of the silica is 0.6% by weight based on the amount of the toner mother particles. Magenta, cyan, yellow and black toners are housed in the casings 55M, 55C, 55Y and 55Bk of the developing devices, respectively.

The toner is excellent in flowability because the toner is a suspension polymerization toner having such a shape that is extremely close to sphere, and contains hydrophobic silica having an average particle diameter of 10 nm in an amount of 0.6% by weight. Therefore, a sufficient charge amount can be obtained through frictional charge. Furthermore, the toner does not have sharp corners, which are found in pulverized toners. Therefore, the toner is difficult to receive mechanical forces, is excellent in followability to an electric field, and exhibits good transfer efficiency.

The photoreceptor drums 3M, 3C, 3Y and 3Bk each is formed, for example, with an aluminum base material having formed thereon a positively charging photosensitive layer. The thickness of the photosensitive layer is 20 .mu.m or more, and the aluminum base material is used as a grounding layer. In this embodiment, a slight difference is provided between the velocities of the photoreceptor drums 3M, 3C, 3Y and 3Bk and an intermediate transfer material 5.

The cleaning rollers 70M, 70C, 70Y and 70Bk each is a roller formed with an elastic material, such as electroconductive sponge, and are in frictionally contact with the photoreceptor drums 3M, 3C, 3Y and 3Bk, respectively, from underneath of the photoreceptor drums 3M, 3C, 3Y and 3Bk. The cleaning rollers 70M, 70C, 70Y and 70Bk are applied with a negative voltage, which is contrary to the toners, with an electric power source not shown in the figure, and remove the remaining toners on the photoreceptor drums 3M, 3C, 3Y and 3Bk through actions of the frictional force to the photoreceptor drums 3M, 3C, 3Y and 3Bk and an electric field formed by the applied voltage. This embodiment employs a so-called cleaner-less developing system, in which the remaining toners thus removed with the cleaning rollers 70M, 70C, 70Y and 70Bk in the prescribed process step after completing the developing step are returned to the photoreceptor drums 3M, 3C, 3Y and 3Bk, and then recovered by the developing rollers 52M, 52C, 52Y and 52Bk into the developing devices 51M, 51C, 51Y and 51Bk of the corresponding colors.

The charging devices 71M, 71C, 71Y and 71Bk are scorotron charging devices and are disposed to face the photoreceptor drums 3M, 3C, 3Y and 3Bk in non-contact therewith from underneath of the photoreceptor drums 3M, 3C, 3Y and 3Bk on the downstream of the rotation direction of the photoreceptor drums 3M, 3C, 3Y, and 3Bk with respect to the cleaning rollers 70M, 70C, 70Y and 70Bk.

The exposing unit 72M, 72C, 72Y and 72Bk each is configured with a known laser scanner unit. The exposing unit 72M, 72C, 72Y and 72Bk are disposed to overlap in the vertical direction the developing devices 51M, 51C, 51Y and 51Bk of the visual image forming part 4, and to overlap in the horizontal direction the photoreceptor drums 3M, 3C, 3Y and 3Bk and the charging devices 71M, 71C, 71Y and 71Bk, and expose the surfaces of the photoreceptor drums 3M, 3C, 3Y and 3Bk with laser light on the downstream of the rotation direction of the photoreceptor drums 3M, 3C, 3Y and 3Bk with respect to the charging devices 71M, 71C, 71Y and 71Bk. The surfaces of the photoreceptor drums 3M, 3C, 3Y and 3Bk are exposed with laser light corresponding to image data by the exposing unit 72M, 72C, 72Y and 72Bk to form electrostatic latent images of each of colors on the surfaces of the photoreceptor drums 3M, 3C, 3Y and 3Bk.

The toners are positively charged, and then the toners are fed to the developing rollers 52M, 52C, 52Y and 52Bk through the feeding rollers 53M, 53C, 53Y and 53Bk and formed into thin layers with the squeezing blades 54M, 54C, 54Y and 54Bk. The toners thus positively charged develop negatively the electrostatic latent images thus positively charged on the photoreceptor drums 3M, 3C, 3Y and 3Bk in good conditions to form images with significantly high quality.

The intermediate transfer material 5 in a belt form (corresponding to the transfer medium) is formed with an electroconductive sheet, such as polycarbonate and polyimide, into a belt form. The intermediate transfer material 5 in a belt form is hung on two driving rollers 60 and 62, and intermediate transfer rollers 61M, 61C, 61Y and 61Bk are disposed in the vicinities of the positions facing the photoreceptor drums 3M, 3C, 3Y and 3Bk. The surface of the intermediate transfer material 5 facing the photoreceptor drums 3M, 3C, 3Y and 3Bk is conveyed from top down in the vertical direction, as shown in FIG. 1.

The intermediate transfer rollers 61M, 61C, 61Y and 61Bk are applied with a prescribed voltage to transfer the toner images formed on the photoreceptor drums 3M, 3C, 3Y and 3Bk onto the intermediate transfer material 5. A secondary transfer roller 63 is provided to face the roller 62 provided down below in the vertical direction of the intermediate transfer material 5, at which the toner images are transferred to paper P (corresponding to the recording medium), and the secondary transfer roller 63 is also applied with a prescribed voltage. As a result, the toner images of four colors carried on the intermediate transfer material 5 in a belt form are transferred to the paper P.

A cleaning device, 6 is provided on the side of the intermediate transfer material 5 opposite to the photoreceptor drums 3M, 3C, 3Y and 3Bk, as shown in FIG. 1. The cleaning device is configured with a scraping member 65 and a casing 66, and the toner remaining on the intermediate transfer material 5 is scraped with the scraping member 65 to house in the casing 66.

The fixing part 8 is configured with a first heating roller 81 and a second heating roller 82, and the paper P carrying the toner images of four colors is conveyed by holding between the first heating roller 81 and the second heating roller 82 under heat and pressure to fix the toner images on the paper P.

The paper feeding part 9 is provided at the bottom of the apparatus and is configured with a housing tray 91 housing paper P and a pickup roller 92 for delivering the paper P. The paper feeding part 9 feeds the paper P at a prescribed timing corresponding to the image forming step carried out by the exposing unit 72M, 72C, 72Y and 72Bk, the developing devices 51M, 51C, 51Y and 51Bk, the photoreceptor drums 3M, 3C, 3Y and 3Bk, and the intermediate transfer material 5.

An upper cover 10 is provided rotatably around an axis 10a on the top of the apparatus, and a part of the surface cover 10 configures a paper delivery tray 10b. The paper delivery tray 10b is provided on the paper delivery side of the fixing part 8 and houses the paper P thus delivered from the fixing part 8 and conveyed by pairs of rollers 101, 102 and 103.

In this embodiment as shown in FIG. 1, a front cover 20 is provided rotatably in the direction shown in FIG. 1 around an axis 20a. The developing devices 51M, 51C, 51Y and 51Bk can be replaced by opening the front cover 20. Spring members 21M, 21C, 21Y and 21Bk are provided on the front cover 20 at the positions facing the developing devices 51M, 51C, 51Y and 51Bk to press the developing devices 51M, 51C, 51Y and 51Bk to the rear (leftward in FIG. 1) upon closing the front cover 20.

As shown in FIG. 2A, a side view, and FIG. 2B, a perspective view, supporting members 31 for supporting the photoreceptor drums 3M, 3C, 3Y and 3Bk and the developing devices 51M, 51C, 51Y and 51Bk are fixed on side panels 30 on the right and left sides of the color laser printer 1. The supporting member 31 has formed therein a substantially vertical guide channel 32 for guiding axes 3aM, 3aC, 3aY and 3aBk of the photoreceptor drums 3M, 3C, 3Y and 3Bk, substantially horizontal guide channels 33M, 33C, 33Y and 33Bk for guiding axes 52aM, 52aC, 52aY and 52aBk of the developing rollers 52M, 52C, 52Y and 52Bk, and substantially horizontal guide channels 34M, 34C, 34Y and 34Bk for guiding projections 55aM, 55aC, 55aY and 55aBk provided on the casings 55M, 55C, 55Y and 55Bk of the developing devices.

The axes 52aM, 52aC, 52aY and 52aBk of the developing rollers 52M, 52C, 52Y and 52Bk are positioned at tip ends of the guide channels 33M, 33C, 33Y and 33Bk, respectively, by pressing the casings 55M, 55C, 55Y and 55Bk of the developing devices with the spring members 21M, 21C, 21Y and 21Bk upon closing the front cover 20.

The photoreceptor drums 3M, 3C, 3Y and 3Bk, are retained by a holder 35 and are integrally detachable upon opening the upper cover 10. As shown in FIG. 3, the holder 35 is formed to have a substantially horseshoe shape with an opening downward and retains the photoreceptor drums 3M, 3C, 3Y and 3Bk being in parallel to each other to configure a photoreceptor cartridge 37. The holder 35 also retains the charging devices 71M, 71C, 71Y and 71Bk. The holder 35 further retains the cleaning rollers 70M, 70C, 70Y and 70Bk, which are not shown in the figure.

As shown in FIG. 3, gears 3bM, 3bC, 3bY and 3bBk provided on the outer peripheries of the photoreceptor drums 3M, 3C, 3Y and 3Bk are exposed from the holder 35 and are engaged with gears of a driving system, which is not shown in the figure, upon mounting the photoreceptor cartridge 37 on the color laser printer 1 to enable driving of the photoreceptor drums 3M, 3C, 3Y and 3Bk. The lengths of the axes 3aM, 3aC, 3aY and 3aBk of the photoreceptor drums 3M, 3C, 3Y and 3Bk are sequentially decreased in this order (i.e., the lower axis is shorter). That is, the protruding lengths of the axes 3aM, 3aC, 3aY and 3aBk from the holder 35 are increased from the upstream to the downstream in the mounting direction of the photoreceptor cartridge 37 on the color laser printer 1. Corresponding to the configuration, step parts 32M, 32C, 32Y and 32Bk are formed in the guide channel 32, as shown in FIG. 2B, and the axes 3aM, 3aC, 3aY and 3aBk are engaged with the step parts 32M, 32C, 32Y and 32Bk, respectively, to position the photoreceptor drums 3M, 3C, 3Y and 3Bk.

A linking rod 41 is vertically provided on the supporting member 31, and the linking rod 41 moves vertically associated with closing and opening motion of the upper cover 10, whereby the developing devices 51M, 51C, 51Y and 51Bk move upon opening the upper cover 10 as described below.

FIG. 4A is a perspective view showing the configuration of the vicinity of the part of the supporting member 31 where the guide channels 33M and 34M, and FIG. 4B is a perspective view showing the configuration in the state where an inner panel 31a (the guide channels 33M and 34M are formed in the inner panel 31a) is removed from the supporting member 31. The vicinity of the guide channels 33C and 34C, the vicinity of the guide channels 33Y and 34Y, and the vicinity of the guide channels 33Bk and 34Bk are configured in the similar manner.

As shown in FIG. 4B, an upper end of the linking rod 41 is swingably connected to one end of a linking rod 42, the other end of which is swingably connected to the upper cover 10. According to the configuration, the movement of the upper cover 10 is transferred to the linking rod 41 through the linking rod 42, and the linking rod 41 moves vertically upon opening and closing the upper cover 10. The guide channel 34M has on the outside thereof (on the side of the side panel 30) a slider 43 capable of slidingly moving along the guide channel 34M, and one end of a linking rod 44 is swingably connected to the slider 43. The other end of the linking rod 44 is swingably connected to the linking rod 41. The slider 43 is disposed in front of the linking rod 41 (on the near side in FIGS. 4A and 4B), and the connecting part of the linking rod 44 and the slider 43 is disposed above the connecting part of the linking rod 44 and the linking rod 41. According to the configuration, upon opening the upper cover 10, the linking rod 44 falls down to the substantially horizontal position associated with ascent of the linking rod 41, whereby the slider 43 moves forward. Upon closing the upper cover 10, on the other hand, the slider 43 moves backward associated with descent of the linking rod 41.

The slider 43 has on the inner surface thereof a pair of projections 43a and 43b provided with a certain distance in the back and forth direction. According to the configuration, in the case where the projections 55aM, 55aC, 55aY and 55aBk are disposed between the corresponding projections 43a and 43b, the projections 43b push the projections 55aM, 55aC, 55aY and 55aBk forward against the biasing force of the spring members 21M, 21C, 21Y and 21Bk upon opening the upper cover 10, so as to move the developing devices 51M, 51C, 51Y and 51Bk forward (rightward in FIG. 1). Upon closing the upper cover 10, the projections 43a push the projections 55aM, 55aC, 55aY and 55aBk backward, so as to move the developing devices 51M, 51C, 51Y and 51Bk backward.

The back end of the moving range of the slider 43 is the position where the developing rollers 52M, 52C, 52Y and 52Bk are in substantially contact with the photoreceptor drums 3M, 3C, 3Y and 3Bk, respectively, and precise positioning can be attained by receiving the pressing force from the spring members 21M, 21C, 21Y and 21Bk as described in the foregoing. The front end of the moving range of the slider 43 is the position where the developing devices 51M, 51C, 51Y and 51Bk are certainly evacuated from the moving path for detaching the photoreceptor cartridge 37, and the developing devices 51M, 51C, 51Y and 51Bk can be easily replaced. The projections 55aM, 55aC, 55aY and 55aBk are temporarily retracted into the casings 55M, 55C, 55Y and 55Bk of the developing devices by operating a prescribed lever (or button), which is not shown in the figure, provided on the casings 55M, 55C, 55Y and 55Bk of the developing devices. According to the configuration, engagement of the projections 55aM, 55aC, 55aY and 55aBk and the projections 43a and 43b is released to enable replacement of the developing devices 51M, 51C, 51Y and 51Bk.

The front surface of the projection 43a on the near side forms a tapered surface, and the projections 55aM, 55aC, 55aY and 55aBk pressed from the front overstride the projection 43a by being retracted as described in the foregoing. According to the configuration, the developing devices 51M, 51C, 51Y and 51Bk can be mounted without operation of the lever or button. Furthermore, the pressing force necessary for the projections 55aM, 55aC, 55aY and 55aBk to overstride the projection 43a is smaller than the pressing force applied by the spring members 21M, 21C, 21Y and 21Bk. Therefore, the developing devices 51M, 51C, 51Y and 51Bk can be completely mounted by lightly inserting the developing devices 51M, 51C, 51Y and 51Bk, followed by closing the front cover 20.

The operation of the color laser printer 1 according to the embodiment will be described. The photosensitive layers of the photoreceptor drums 3M, 3C, 3Y and 3Bk are uniformly charged with the charging devices 71M, 71C, 71Y and 71Bk, respectively, and then the photosensitive layers are exposed corresponding to images of magenta color, cyan color, yellow color and black color, respectively. A magenta toner, a cyan toner, a yellow toner and a black toner are attached to electrostatic latent images formed on the photosensitive layers of the photoreceptor drums 3M, 3C, 3Y and 3Bk with the magenta developing device 51M, the cyan developing device 51C, the yellow developing device 51Y and the black developing device 51Bk, so as to effect development of magenta color, cyan color, yellow color and black color. The toner images of magenta color, cyan color, yellow color and black color thus formed are once transferred onto the intermediate transfer material 5.

The toners remaining on the photoreceptor drums 3M, 3C, 3Y and 3Bk after transferring are temporarily retained by the cleaning rollers 70M, 70C, 70Y and 70Bk. The toner images of the respective colors are formed with certain time differences among them corresponding to the moving velocity of the intermediate transfer material 5 and the positions of the photoreceptor drums 3M, 3C, 3Y and 3Bk, and the toner images of the colors are transferred to overlap on the intermediate transfer material 5.

The toner images of the four colors thus formed on the intermediate transfer material 5 are transferred onto the paper P fed from the paper feeding part 9 at the position where the secondary transfer roller 63 and the intermediate transfer material 5 are in contact with each other under pressure. The toner images are fixed on the paper P in the fixing part 8 and delivered to the paper delivery tray 10b. Thus, a four-color image is formed.

In the case where the photoreceptor drums 3M, 3C, 3Y and 3Bk are replaced, the upper cover 10 is opened, whereby the developing devices 51M, 51C, 51Y and 51Bk are evacuated from the moving path of the photoreceptor cartridge 37, and the photoreceptor drums 3M, 3C, 3Y and 3Bk can be taken out by withdrawing the photoreceptor cartridge 37 upward. In the case where a new one of a photoreceptor cartridge 37 is mounted, the upper cover 10 is left opening, and the photoreceptor cartridge 37 is brought down with the axes 3aM, 3aC, 3aY and 3aBk of the photoreceptor drums 3M, 3C, 3Y and 3Bk being engaged with the guide channel 32. The axes 3aM, 3aC, 3aY and 3aBk are then positioned at the step parts 32M, 32C, 32Y and 32Bk.

The new photoreceptor cartridge 37 is covered with a covering member 47 as shown in FIG. 5, and upon mounting the photoreceptor cartridge 37, the covering member 47 is removed. Accordingly, the photoreceptor drums 3M, 3C, 3Y and 3Bk are favorably prevented from being damaged until the photoreceptor cartridge 37 is mounted on the color laser printer 1. Upon opening the upper cover 10, the developing devices 52M, 51C, 51Y and 51Bk move to the front side, at which they can be easily taken out, and on this occasion, the developing devices 51M, 51C, 51Y and 51Bk can be replaced by opening the front cover 20. Thus, the maintenance property is improved.

In this embodiment having been described herein, the photoreceptor drums 3M, 3C, 3Y and 3Bk are integrally retained in the photoreceptor cartridge 37 and are detachable separately from the developing devices 51M, 51C, 51Y and 51Bk. Furthermore, the detaching direction thereof is the substantially vertical direction, which is substantially in parallel to the conveying direction of the intermediate transfer material 5 on the surface facing the photoreceptor drums 3M, 3C, 3Y and 3Bk and to the aligning direction of the photoreceptor drums 3M, 3C, 3Y and 3Bk. According to the configuration, the photoreceptor drums 3M, 3C, 3Y and 3Bk can be replaced without interference with the exposing unit 72M, 72C, 72Y and 72Bk to prevent favorably color drift from occurring.

Upon mounting the photoreceptor cartridge 37, the axes 3aM, 3aC, 3aY and 3aBk are positioned at the step parts 32M, 32C, 32Y and 32Bk, whereby the photoreceptor drums 3M, 3C, 3Y and 3Bk can be precisely positioned to prevent further favorably color drift from occurring. Upon opening the upper cover 10 for detaching the photoreceptor cartridge 37, the developing devices 51M, 51C, 51Y and 51Bk are automatically evacuated from the moving path of the photoreceptor cartridge 37, whereby the photoreceptor cartridge 37 can be easily detached.

In this embodiment, moreover, the charging devices 71M, 71C, 71Y and 71Bk are integrally retained in the photoreceptor cartridge 37 and can be replaced simultaneously with the photoreceptor drums 3M, 3C, 3Y and 3Bk, whereby the maintenance property of the color laser printer 1 is improved. The service life of the charging devices 71M, 71C, 71Y and 71Bk is longer than that of the developing devices 51M, 51C, 51Y and 51Bk and is equivalent to or longer than that of the photoreceptor drums 3M, 3C, 3Y and 3Bk. In this embodiment, therefore, the running cost of the color laser printer 1 can be further reduced in comparison to the case where the charging devices 71M, 71C, 71Y and 71Bk are replaced simultaneously with the developing devices 51M, 51C, 51Y and 51Bk.

In the case where the configuration of this embodiment is changed to dispose assemblies black (Bk), yellow (Y), cyan (C) and magenta (M) in this order from top down, it is possible that the photoreceptor cartridge is configured in the manner shown in FIG. 6, whereby the running cost can be further reduced. Specifically, in the photoreceptor cartridge 137 shown in FIG. 6, photoreceptor drums 3M, 3C and 3Y, cleaning rollers 70M, 70C and 70Y, and charging devices 71M, 71C and 71Y are retained by a holder 135 having a substantially horseshoe shape with an opening downward, and a photoreceptor drum 3Bk, a cleaning roller 70Bk and a charging device 71Bk are retained by a holder 136 having a substantially horseshoe shape with an opening downward and being capable of connecting to an upper part of the holder 135. A hook 136a is provided at the lower end of the holder 136 and is capable of being engaged with a female hook 135a provided at the upper end of the holder 135. The hook 136a temporarily moves outward by operating a lever (or button), which is not shown in the figure, provided in an upper part of the holder 136, so as to release the engagement with the female hook 135a.

In the case where the photoreceptor cartridge 137 thus configured is withdrawn upward without releasing the engagement, the photoreceptor drums 3M, 3C, 3Y and 3Bk, the cleaning rollers 70M, 70C, 70Y and 70Bk, and the charging devices 71M, 71C, 71Y and 71Bk can be integrally replaced as similar to the case of the photoreceptor cartridge 37. In the case where the engagement is released, on the other hand, only the photoreceptor drum 3Bk, the cleaning roller 70Bk and the charging device 71Bk can be replaced with the photoreceptor drums 3M, 3C and 3Y, the cleaning roller 70M, 70C and 70Y, and the charging devices 71M, 71C and 71Y being left remaining in the color laser printer 1.

Black color is frequently used in comparison to the other colors, and therefore, the service life of the photoreceptor 3Bk expires faster in comparison to the photoreceptor drums 3M, 3C and 3Y. In the photoreceptor cartridge 137, only the photoreceptor drum 3Bk can be replaced with the photoreceptor drums 3M, 3C and 3Y being left remaining, whereby the running cost of the color laser printer 1 can be further reduced. The photoreceptor cartridge 137 is also covered with a covering member similar to the covering member 47.

In the embodiments described in the foregoing, the photoreceptor cartridge 137 is detached in the direction, which is substantially perpendicular to the axes 3aM, 3aC, 3aY and 3aBk, whereby the configuration of the bearing part and the like can be simplified to reduce the production cost of the color laser printer 1, in comparison to the case where the photoreceptor cartridge is detached along the axes 3aM, 3aC, 3aY and 3aBk. In the embodiments, furthermore, the photoreceptor 3M, 3C, 3Y and 3Bk can be replaced as being separated from the developing devices 51M, 51C, 51Y and 51Bk, whereby the running cost of the color laser printer 1 can be further reduced in comparison to the case where they are integrally replaced.

In the embodiments described in the foregoing, the guide channel 32 corresponds to the guide part, the axes 3aM, 3aC, 3aY and 3aBk correspond to the guided part, and the linking rods 41, 42 and 43 and the slider 43 correspond to the evacuating unit. The invention is not limited to the embodiments and can be practiced with various embodiments as far as the gist of the invention is not deviated. For example, it is not necessary that the developing devices 51M, 51C, 51Y and 51Bk are automatically evacuated.

Furthermore, it is possible that the spring members 21M, 21C, 21Y and 21Bk are omitted, and the front cover 20 is provided apart from the developing devices 51M, 51C, 51Y and 51Bk. In this case, however, it is preferred that the developing rollers 52M, 52C, 52Y and 52Bk are positioned, for example, by such a manner that spring members for fixing the axes 52aM, 52aC, 52aY and 52aBk are provided at tip ends of the guide channels 33M, 33C, 33Y and 33Bk.

Moreover, while the toners are once transferred to the intermediate transfer material 5 and then further transferred to the paper P in the embodiment, the toners may be directly transferred to the paper P. In this case, the paper P corresponds to both the recording medium and the transfer medium. Still moreover, the guide part may be a rail instead of a channel.

The Second Preferred Embodiment

FIG. 7 is a cross sectional view showing a second embodiment of a color laser printer as an apparatus for forming an image. FIG. 8 is a cross sectional view showing the color laser printer shown in FIG. 7 in a state where a front cover thereof is opened. FIG. 9 is a cross sectional view showing the color laser printer shown in FIG. 7 in a state where a rear cover thereof is opened. FIG. 10 is an enlarged cross sectional view showing a process part of the laser co