HK1081669B - Image-forming device - Google Patents

Description

Image forming apparatus with a plurality of image forming units

Technical Field

The present invention relates to an image forming apparatus for forming an image on a recording medium, and more particularly, to an image forming apparatus equipped with a plurality of scanning units and process units, and also equipped with an endless belt for image formation that conveys a developer image or a recording medium.

Background

There has been proposed an image forming apparatus provided with: an endless belt for conveying a developer image or a recording medium; a plurality of process units provided with a plurality of photosensitive drums corresponding to a plurality of colors, each photosensitive drum facing the belt; a plurality of scanning units each for exposing and scanning a surface of a corresponding photosensitive drum to form an electrostatic latent image, the electrostatic latent image being developed by a corresponding process unit by using a developer of a corresponding color; and a transfer unit for transferring the developer image formed on the surface of each photosensitive drum onto a recording medium conveyed by the endless belt or onto the endless belt itself.

U.S. patent application publication No. us2003/0147678a1 has proposed a type of image forming apparatus in which an endless belt supports an intermediate transfer belt with developer. This type of image forming apparatus performs an image forming process in the following manner.

When the scanning unit exposes and scans a corresponding photosensitive drum of one color according to image data to form an electrostatic latent image, the corresponding process unit develops the electrostatic latent image by using the developer of the color. The developer image is transferred to the intermediate transfer belt by the transfer roller. Once the developer images of all colors are superimposed thereon, these developer images are transferred onto a recording medium.

Another type of image forming apparatus has been proposed in japanese patent laid-open No. 7-234622, in which an endless belt is a conveyor belt that conveys a recording medium. In this type of image forming apparatus, the developer image is directly superimposed on the recording medium, and the recording medium is conveyed by a conveyor belt to form a superimposed image on the recording medium.

Disclosure of Invention

An object of the present invention is to provide an image forming apparatus which can be easily made compact and has excellent maintainability for a process unit therein.

In order to attain the above and other objects, the present invention provides an image forming apparatus including: a housing; an endless belt; a plurality of processing units; a plurality of scanning units; a transfer portion; and a cartridge accommodating the recording medium. The endless belt is mounted in the casing and conveys either one of the developer image and the recording medium. A plurality of process units are mounted in the casing in one-to-one correspondence with the plurality of colors, the plurality of process units respectively including a plurality of photosensitive drums, each photosensitive drum facing the endless belt. A plurality of scanning units are mounted in the casing, and one scanning unit is provided for each photosensitive drum, each scanning unit scans the surface of the corresponding photosensitive drum with light to form an electrostatic latent image, and each process unit develops the electrostatic latent image with developer of a corresponding color. The transfer portion is installed in the casing and transfers the developer image formed on each photosensitive drum onto either the endless belt or the recording medium conveyed by the endless belt. A cartridge containing a recording medium is detachably mounted in the housing at a position below the endless belt. The scanning unit and the processing unit are alternately disposed in a horizontal direction. Each scanning unit and each processing unit are tilted with respect to the vertical direction. At least a portion of each processing unit is inserted into or removed from the housing in an inclined orientation. The endless belt is arranged such that its height increases in a direction in which the cartridge is pushed out of the housing.

Due to such a structure, the image forming apparatus can be made compact, and at least a part of the process unit can be easily attached to or detached from the image forming apparatus.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments when read in conjunction with the accompanying drawings, in which:

fig. 1 is a side sectional view of the overall structure of a color laser printer according to a first embodiment of the present invention;

fig. 2 illustrates how to replace the process cartridge in the color laser printer of fig. 1;

fig. 3 is a side sectional view showing a modified overall structure of the sheet discharge tray of fig. 1;

fig. 4 illustrates a state of the image forming portion from which the process cartridge is removed to adjust the orientation of the scanning unit by using a screwdriver;

FIG. 5 is a perspective view of the scanner unit mounted on the scanner support frame;

FIG. 6 is a plan view showing the interior of the scanner unit as viewed from one side of the scanner support frame;

FIG. 7(A) is a plan view showing the exterior of the scanning unit fixed to the scanner supporting frame in FIG. 5; FIG. 7(B) is a side cross-sectional view of the scan unit secured to the scanner support frame taken along line VIIB-VIIB in FIG. 7 (A);

FIG. 8 is an enlarged cross-sectional side view illustrating how the protrusions of the scanner unit are disposed on the depressions of the scanner support frame;

fig. 9 is a side sectional view of a modified overall structure of the color laser printer of fig. 1;

fig. 10 is a perspective view of a scanning unit mounted to a scanner support frame according to a second embodiment and corresponds to fig. 5 of the first embodiment;

fig. 11(a) is a plan view showing the outside of the scanning unit fixed to the scanner support frame shown in fig. 10 and corresponds to fig. 7 (a);

FIG. 11(B) is a cross-sectional view of the scanner unit secured to the scanner support frame taken at line XIB-XIB in FIG. 11(A) and corresponds to FIG. 7 (B);

FIG. 12 is an enlarged cross-sectional side view illustrating how the rotational axis of the scanner unit is mounted to the bearing portion of the scanner support frame;

fig. 13 is a side sectional view of a color laser printer according to a third embodiment;

FIG. 14 is a side sectional view showing a state where the sheet feeding cassette is ejected from the color printer of FIG. 13;

FIG. 15 is a side sectional view showing a state where the sheet supply cassette and the tape unit are ejected from the color printer of FIG. 13;

FIG. 16 is a side sectional view of the state in which the belt and the belt cleaning device are removed from the belt unit of FIG. 15;

FIG. 17 is an elevational, cross-sectional view of the color laser printer of FIG. 13 taken at line XVII-XVII;

FIG. 18 is a bottom view of the belt unit;

FIG. 19 is a perspective view of a shaft end portion of the transfer roller shown in FIG. 18;

FIG. 20 is a perspective view of the connection between the neutral bias line and the neutral comb shown in FIG. 18; and

fig. 21 is a modified side sectional view of the third embodiment.

Detailed Description

An image forming apparatus according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings, in which like parts and components are denoted by like reference numerals to avoid repetitive description.

< first embodiment >

First, a color laser printer 1 according to a first embodiment will be described with reference to fig. 1 to 8.

In the following description, expressions such as "front", "rear", "upper", "lower", "right", "left" and the like are used to define the respective portions when the laser printer 1 is set to its orientation in which it is used.

The laser printer 1 is of a horizontal tandem type in which a plurality of image forming sections 17 are arranged in a line in a horizontal direction. The laser printer 1 has a main casing 2 in which a paper supply section 4, an image forming section 5 and a paper discharge section 6 are provided.

The paper feed section 4 is for feeding a sheet of paper P as a recording medium. The image forming section 5 is for forming an image on the sheet P supplied from the sheet supply section 4. The sheet discharging section 6 is for discharging the sheet P on which the image forming section 5 forms an image.

The main casing 2 serves as a housing of the color laser printer 1. The main casing 2 has a box shape, and an upper opening thereof is covered with the sheet discharge tray 52. Therefore, the sheet discharge tray 52 functions as a top cover. The sheet discharge tray 52 is rotatably supported to the main casing 2 by a hinge 52a, and is openable and closable with respect to the main casing 2.

The paper supply section 4 is located at a lower portion of the main casing 2, and includes: a paper tray 9, a support plate 3c, a separation pad 3a, a spring 3b, a pair of paper feed rollers 10 and 11; a paper feed cassette frame 71; a pair of conveying rollers 13 (a front conveying roller 13a and a rear conveying roller 13 b); a paper-feeding-side U-shaped path 12; and a pair of registration rollers 14. The sheet tray 9, the support plate 3c, the separation pad 3a, the spring 3b and the front conveying roller 13a are mounted on a sheet feed cassette frame 71 and enter the sheet feed cassette 70 as an integral unit. The sheet feeding section 4 further includes a sheet feeding port 42 a.

The imaging section 5 includes: four image forming portions 17(17M, 17Y, 17C, 17K); a transfer portion 18; and a fixing section 19.

Image forming section 17M is for forming a magenta toner image, image forming section 17Y is for forming a yellow toner image, image forming section 17C is for forming a cyan toner image, and image forming section 17K is for forming a black toner image. The image forming sections 17M, 17Y, 17C, and 17K are disposed slightly higher than the center of the main casing 2 in the vertical direction.

Each image forming section 17 has a scanner unit 20 and a process cartridge 30. The scanner unit 20 is supported on a scanner support frame 260, which in turn is fastened to the main housing 2. As described below, the orientation of the scanner unit 20 relative to the scanner support 260 is adjustable.

The transfer section 18 is provided above the paper supply section 4 and below the image forming section 17 in the main casing 2, and extends in the front-rear direction. The transfer portion 18 includes: a driving roller 36, a driven roller 37, a conveying belt 38, a plurality of transfer rollers 39, and a belt cleaning unit 40. The conveyor belt 38 is disposed below the four image forming sections 17 and faces the four image forming sections 17.

The fixing portion 19 is disposed behind the transfer portion 18. The fixing section 19 includes a heat roller 48 and a pressure roller 49.

The sheet discharging section 6 has a discharge-side U-shaped path 50, a pair of sheet discharging rollers 51, and a sheet discharging tray 52.

< paper feeding section >

The paper feed section 4 will be described in more detail below.

In the sheet feeding section 4, a sheet feeding cassette 70 is detachably mounted in the main casing 2. The paper feed cassette 70 can be ejected from the storage position shown by the solid line in fig. 1 to the ejection position shown by the two-dot chain line in fig. 1, and in the ejected state, the recording paper P can be replenished appropriately. Thus, the paper supply cassette 70 can be horizontally inserted and removed at the front of the main casing 2.

The sheet feeding cassette 70 has a sheet tray 9. The support plate 3c is mounted on the sheet tray 9. The support plate 3c is urged upward by a spring (not shown) which is also mounted on the sheet tray 9.

Note that, in addition to the front conveying roller 13a, respective rollers are rotatably provided at predetermined positions of the main casing 2 and are driven by a drive source (not shown) for driving the image forming sections 17M, 17Y, 17C, and 17K.

The separation pad 3a and the spring 3b are installed in the paper supply cassette 70.

A pair of sheet feed rollers 10 and 11 are mounted in the main casing 2 at a position above the support plate 3 c.

When the sheet feeding cassette 70 is mounted to a predetermined position of the main casing 2, the separation pad 3a is pressed into contact with the sheet feeding roller 11 by the elastic force of the spring 3 b.

The paper feed rollers 10 and 11 separate the recording sheets P stacked on the support plate 3c one at a time and supply the separated sheet in a direction toward the conveying roller 13. More specifically, the paper feed roller 10 located on the rear side of the pair of paper feed rollers 10 and 11 conveys the uppermost sheet of the recording paper P stacked on the support plate 3c to the paper feed roller 11. The sheet feed roller 11 on the front side is pressed against the separation pad 3a, and separates and conveys one recording sheet P at a time. The paper feed roller 10 serves as a pickup roller.

Of the pair of conveying rollers 13, a front conveying roller 13a is mounted in the sheet feeding cassette 70, and a rear conveying roller 13b is mounted in the main casing 2. The pair of conveying rollers 13 cooperatively convey the recording sheet P.

A pair of conveying rollers 13 and a pair of registration rollers 14 are arranged in order along the paper feed side U-shaped path 12 along which the recording paper P is conveyed from the paper feed roller 11 to the image forming portion 17. Before the image forming portion 17 starts its image forming operation, the registration rollers 14 temporarily stop conveying the recording sheet P, align the orientation of the recording sheet P by nipping its leading edge, and convey the recording sheet P to the image forming portion 17.

The paper feed side U-shaped path 12 serves as a U-shaped conveying path that conveys the paper length. The paper feed side U-shaped path 12 extends from its upstream side edge to its downstream side edge through its middle.

In this embodiment, the paper-feed-side U-shaped path 12 is located at its upstream side edge adjacent to the paper feed roller 11, and conveys the paper forward at the upstream side edge. The conveying roller 13 is located in the middle of the paper-feeding-side U-shaped path 12. The paper feed side U-shaped path 12 is located at its downstream side edge adjacent to the registration roller 14, and conveys the paper sheet rearward.

Therefore, the recording sheet P is first conveyed in the forward direction at the upstream side edge of the paper feed side U-shaped path 12, and then conveyed by the conveying roller 13 at the center of the paper feed side U-shaped path 12. When the sheet P is conveyed by the conveying roller 13 in the middle of the paper feed side U-shaped path 12, the conveying direction of the sheet P is reversed. After being aligned by the registration rollers 14, the sheet P is conveyed out in a backward direction from the sheet-feed-side U-shaped path 12.

The paper feed port 42a is used for manually feeding the recording paper P to the color printer 1. The paper feed port 42a is located at a lower portion of the front side of the main casing 2 where the paper feed cassette 70 is pulled out. The recording sheet P supplied from the sheet feed port 42a is conveyed to a nip portion between the registration rollers 14 by a sheet feed roller 42b, wherein the sheet P is adjusted in its orientation before being sent to the image forming portion 17.

< imaging section 5>

Next, the imaging section 5 will be described in more detail.

In the image forming section 5, four image forming sections 17M, 17Y, 17C, and 17K are arranged in this order from front to back in the front-back direction. In each image forming section 17, a corresponding scanner unit 20 and a corresponding process cartridge 30 are mounted in the main casing 2. The scanning unit 20 is fixedly installed in the main casing 2, and its orientation can be adjusted. The process cartridge 30 is detachably mounted in the main casing 2. When the process cartridges 30 are mounted in all the image forming sections 17, the scanner units 20 and the process cartridges 30 are alternately arranged in the front-to-rear direction.

The scanning unit 20 is disposed to form an angle with its forwardly inclined upper end. When the process cartridge 30 is mounted in the image forming section 17, the process cartridge 30 is also set to form an angle with its forwardly inclined upper end. The process cartridge is inclined at substantially the same angle as the inclination angle of the scanner unit 20 with respect to the front-rear (horizontal) direction.

More specifically, the main casing 2 has a front inner wall 2a and a rear inner wall 2b, both extending obliquely forward and upward. Four scanner support frames 260 are provided between the front inner wall 2a and the rear inner wall 2b, and also each extend obliquely forward and upward. The scanner support frame 260, the front inner wall 2a and the rear inner wall 2b extend substantially parallel to each other. The scanner unit 20 is mounted on the scanner support frame 260 to extend along the scanner support frame 260.

When the process cartridges 30 of all colors are mounted in the main casing 2, the process cartridge 30 of black is located between the scanner unit 20 of black and the scanner support frame 260 of cyan to extend along the scanner support frame 260 of cyan, the process cartridge 30 of cyan is located between the scanner unit 20 of cyan and the scanner support frame 260 of yellow to extend along the scanner support frame 260 of yellow, the process cartridge 30 of yellow is located between the scanner unit 20 of yellow and the scanner support frame 260 of magenta to extend along the scanner support frame 260 of magenta, and the process cartridge 30 of magenta is located between the scanner unit 20 of magenta and the front inner wall 2a to extend along the front inner wall 2 a.

Next, the imaging section 17 will be described in more detail. The image forming portions 17(17M, 17Y, 17C, and 17K) have mutually the same structure.

Each process cartridge 30 is mounted with: providing a roller 31; a developing roller 32; a photosensitive drum 33; a gated corona charging device 34; and a toner cartridge 35.

The photosensitive drum 33 is rotatably supported at a lower end inside the process cartridge 30.

The photosensitive drum 33 includes: a main drum body 33b having a cylindrical shape; a drum shaft 33a extending in the axial direction thereof along the axial center of the main drum body 33 b. The process cartridge 30 is mounted in the host/object 2, and a drum shaft (rotation shaft) 33a extends in the width direction of the main casing 2. The main drum body 33b has a photosensitive layer formed of polycarbonate or the like having a forward charging property on the outer surface thereof. The drum shafts 33a are fastened to two widthwise side plates (right and left side plates) constituting the process cartridge 30. The drum shaft 33a cannot rotate relative to the side plates. The main drum body 33b is rotatably supported on the drum shaft 33 a. Thus, the photosensitive drum 33 is rotatably supported within the process cartridge 30.

During image formation, the photosensitive drum 33 is driven to rotate in the clockwise direction in the drawing, and therefore the photosensitive drum 33 moves in the same direction as the conveying belt 38 at the position where it contacts the conveying belt 38.

The scorotron charging device 34 is of the positive charging type, having a charging wire and a grid for generating a corona discharge. A scorotron charging device 34 is provided at the rear of the photosensitive drum 33. The scorotron charging device 34 is opposite the photosensitive drum 33 but is spaced apart from the photosensitive drum 33 without contacting it.

The developing roller 32 is disposed above and opposite to the photosensitive drum 33. The developing roller 32 is pressed against the photosensitive drum 33. The developing roller 32 has a metal roller shaft 32a covered by a roller body 32b, and the roller body 32b is made of an elastic material, specifically, a conductive rubber material. More specifically, the roller body portion 32b of the developing roller 32 has a two-layer structure including: an elastic roller body part made of conductive urethane rubber, silicone rubber or EPDM rubber and containing carbon powder; and a coating layer mainly made of urethane rubber, urethane resin or polyimide resin. The roller shaft 32a is rotatably supported by a pair of width-direction side plates of the process cartridge 30.

The supply roller 31 is disposed above and opposite to the developing roller 32. The supply roller 31 has a metal roller shaft 31a covered by a roller body 31b, and the roller body 31b is made of a conductive foam material. The roller shaft 31a is rotatably supported by a pair of width-direction side walls of the process cartridge 30.

The toner cartridge 35 is defined in the upper portion of the supply roller 31 in the process cartridge 30. The toner cartridge 35 in the process cartridge 30 of the image forming section 17M stores magenta toner therein. The toner cartridge 35 in the process cartridge 30 of the image forming portion 17Y stores therein yellow powder. The toner cartridge 35 in the process cartridge 30 of the image forming section 17C stores therein cyan toner. The toner cartridge 35 in the process cartridge 30 of the image forming portion 17K stores therein black toner. The toner is a non-magnetic single component polymeric toner having a positive charging capability.

In this embodiment, the toner of each color is a polymer toner having substantially spherical particles.

The polymeric toner powder includes a binder resin as their main component. Each of the binder resins is prepared by copolymerizing monomers by a known polymerization method such as suspension polymerization. Examples of the polymerizable monomer include: styrene monomers such as styrene, acrylic monomers such as acrylic acid, alkyl (C1-C4) acrylates, alkyl (C1-C4) methacrylates.

The primary toner particles are formed by adding a coloring agent, a charge regulator and paraffin to the binder resin. In this example, the colorants are yellow, magenta, cyan, and black colorants. Examples of the charge control agent that can be used include charge control resins obtained by copolymerizing ionic monomers and copolymerizable monomers. In this case, the ionic monomer may be an ammonium salt or other monomer having an ionic functional group. The copolymerizable monomer may be copolymerized with the ionic monomer, and may be a styrene monomer, an acrylic monomer, or other monomer having an ionic functional group.

An external additive such as silica is added to the primary toner particles to increase the fluidity of the toner. Various inorganic substance powders may be used as the external additive. For example, powders of metal oxides, carbides, metal salts may be used as external additives. Metal oxide powders that may be used as external additives include silica, aluminum oxides (aluminates), titanium oxides, strontium titanates, cerium oxides, magnesium oxides.

The scanning unit includes 20: a scanner housing 26; and various optical components mounted in the scanner housing 26. The optical element includes: a laser diode (not shown) that emits a laser beam L; a polygon mirror 22 that reflects the laser beam L in a scanning direction perpendicular to the sheet of fig. 1; an f θ lens 24 that transmits the laser beam L from the polygon mirror 22; a folding mirror 23 that receives the laser beam L reflected by the polygon mirror 22 and reflects the laser beam L back toward the photosensitive drum 33 of the corresponding process cartridge 30, and a cylindrical lens 25 that transmits the laser beam L reflected from the folding mirror 23.

Note that the scanner housing 26 is formed with one exposure hole 26a at one side of the corresponding process cartridge 30. An optical element such as a protective mirror is provided on the scanner housing 26 to cover the exposure hole 26 a.

The folding mirror 23 is disposed in the vicinity of the upper end of the process cartridge 30, and an angle α of about 15 degrees is formed between the optical path of the laser beam L between the f θ lens 24 and the folding mirror 23 and the optical path of the laser beam L between the folding mirror 23 and the cylindrical lens 25 along an imaginary plane (a plane parallel to the drawing sheet) perpendicular to the scanning direction.

This ensures that the scanner unit 20 is disposed in close proximity to the process cartridge 30, making the entire apparatus 1 compact. The length of the optical path of the laser beam L required to expose the photosensitive drum 33 from the vicinity of the upper end of the scanner unit 20 to the photosensitive drum 33 in the vicinity of the lower end of the process cartridge 30 can be sufficiently secured. The elements such as the f θ lens 24 can be made compact, and the entire apparatus 1 can be made compact.

Moreover, since the laser beam L is reflected near the upper end of the scanner unit 20, the exposure hole 26a can be disposed above the vertical center of the scanner unit 20 so as to be sufficiently distant from the position of the photosensitive drum 33 located at the lower end of the process cartridge 30. The protective mirror covering the exposure hole 26a can prevent contamination by toner.

In each image forming section 17, during image formation, a laser beam L is emitted from a laser diode (not shown in the figure) according to image data and reflected by a polygon mirror 22, and reflected by a fold mirror 23. The laser beam L then exits the scanner unit 20 through the exposure hole 26a and reaches the photosensitive drum 33.

The toner stored in the toner cartridge 35 is supplied to the supply roller 31. Due to the rotation of the supply roller 31, the toner is supplied to the developing roller 32. When toner is supplied from the supply roller 31 to the developing roller 32, the toner is positively charged due to friction between the supply roller 31 and the developing roller 32 to which the developing bias is applied.

The scorotron charging device 34 is applied with a charging bias to generate corona discharge, thereby positively charging the surface of the photosensitive drum 33 uniformly. Due to the rotation of the photosensitive drum 33, the surface of the photosensitive drum 33, which is positively charged, is exposed to the high-speed scanning of the laser beam emitted from the scanner unit 20. As a result, an electrostatic latent image corresponding to an image to be formed on the sheet is formed on the surface of the photosensitive drum 33.

With further rotation of the photosensitive drum 33, the positively charged toner carried on the surface of the developing roller 32 is brought into contact with the photosensitive drum 33. At this time, the toner on the developing roller 32 is supplied to the low potential region of the electrostatic latent image on the photosensitive drum 33 exposed by the laser beam. As a result, toner is selectively carried on the photosensitive drum 33 so that the electrostatic latent image is developed into a visible toner image.

Each process cartridge 30 is mounted in the main casing 2 and is inclined forward at a position higher than the rear side thereof adjacent to the process cartridge 30. More specifically, the mounting position of each process cartridge 30 is shifted by a predetermined number higher than the adjacent process cartridge 30 on the rear side thereof.

More specifically, the deviation between the mounting position of the process cartridge 30 in the black image forming portion 17K and the mounting position of the process cartridge 30 in the cyan image forming portion 17C, the deviation between the mounting position of the process cartridge 30 in the cyan image forming portion 17C and the mounting position of the process cartridge 30 in the yellow image forming portion 17Y, and the deviation between the mounting position of the process cartridge 30 in the yellow image forming portion 17Y and the mounting position of the process cartridge 30 in the magenta image forming portion 17M are all equal to the preset value.

This ensures that when the process cartridges 30 of all colors are mounted in the image forming section 5 in the main casing 2, the photosensitive drums 33 in the process cartridges 30 are aligned such that the straight lines connecting the lower sides of the respective photosensitive drums 33 extend forward and upward at a predetermined angle with respect to the horizontal direction. Therefore, the space defined below the image forming portion 5 and above the paper feed cassette 70 has a tapered profile in which the height in the vertical direction becomes narrower rearward when viewed from one side. The transfer portion 18 is disposed in the space of this tapered profile.

Next, the transfer portion 18 will be described in detail.

The driving roller 36 is disposed behind the photosensitive drum 33 in the process cartridge 30 mounted in the black image forming portion 17K. The drive roller 36 is disposed at a position displaced in the vertical direction from the entirety of the photosensitive drum 33. During image formation, the driving roller 36 is driven to rotate in the opposite direction (counterclockwise in the drawing) to the photosensitive drum 33.

The driven roller 37 is disposed in front of the photosensitive drum 33 of the process cartridge 30 mounted in the magenta image forming portion 17M. The driven roller 37 is disposed at a position higher than the drive roller 36. When the drive roller 36 rotates, the driven roller 37 also rotates (counterclockwise in the drawing), and its portion in contact with the conveyor belt 38 moves in the same direction as the moving direction of the conveyor belt 38.

Each process cartridge 30 is mounted such that the axial direction of the photosensitive drum 33 is substantially parallel to the axial directions of the drive roller 36 and the driven roller 37.

The conveyor belt 38 is an endless belt formed of a resin such as conductive polycarbonate or polyimide in which conductive particles such as carbon particles are dispersed. The conveyor belt 38 is wound around the drive roller 36 and the driven roller 37. The conveyor belt 38 has: an upper portion 38a provided on the upper side of the drive roller 36 and the driven roller 37; and a lower portion 38b provided on the lower side of the drive roller 36 and the driven roller 37. Both the upper portion 38a and the lower portion 38b extend along a flat slope or an inclination that increases in height as one proceeds. When each process cartridge 30 is mounted in the main casing 2, the upper side portion 38a of the conveyor belt 38 comes into contact with the photosensitive drum 33 of the process cartridge 30 from below. The contact portion between the photosensitive drum 33 and the upper side portion 38a of the conveyor belt 38 will be referred to as an image transfer position hereinafter.

Note that the driven roller 37 is disposed on the upstream side in the moving direction of the upper portion 38a of the conveying belt 38, while the driving roller 36 is on the downstream side. On the other hand, the driven roller 37 is disposed on the downstream side in the moving direction of the lower portion 38b of the conveying belt 38, and the driving roller 36 is disposed on the upstream side.

When the drive roller 36 rotates in the counterclockwise direction, the conveying belt 38 rotates in the counterclockwise direction around the drive roller 36 and the driven roller 37, and the upper side portion 38a moves in the same direction as the photosensitive drum 33 at its image transfer position. The driving roller 36 is disposed on the downstream side of the upper portion 38a of the conveying belt 38 in the moving direction of the image transfer position, and the driven roller 37 is disposed on the upstream side. Therefore, slack in the upper side portion 38a of the conveyor belt 38 can be prevented. For this reason, the paper P can be conveyed accurately by the upper side portion 38a of the conveyor belt 38.

Four transfer rollers 39 are disposed between the upper portion 38a and the lower portion 38b of the conveyor belt 38. The transfer roller 39 is located at an image transfer position where the upper portion 38a of the conveying belt 38 contacts the photosensitive drum 33. Each transfer roller 39 faces the corresponding photosensitive drum 33 with the upper side portion 38a sandwiched therebetween.

Each transfer roller 39 has a metal roller shaft 39a, and is covered with a roller body portion 39b made of an elastic substrate substance such as a conductive rubber material. Both end portions of the roller shaft 39a of each transfer roller 39 are rotatably supported in the main casing 2 by bearings and compression springs (not shown in the drawings).

The transfer roller 39 is pressed upward by a compression spring (not shown in the figure), thereby pressing the conveying belt 38 against the photosensitive drum 33 at each image transfer position. At each image transfer position, a nip is formed between the photosensitive drum 33 and the conveying belt 38.

A transfer bias voltage is applied to each transfer roller 39. Each transfer roller 39 rotates in the counterclockwise direction in the drawing, and thus moves in the same direction as the conveying belt 38 at the image transfer position.

The sheet P supplied from the sheet feeding section 4 is conveyed from front to rear by the conveying belt 38 which is driven by the driving roller 36 and moved by the driven roller 37 to make a circulating motion, successively passing through the image transfer position between the conveying belt 38 and the photosensitive drum 33 of the image forming section 17. During the conveyance, the toner images of each color carried by the respective photosensitive drums 33 of each image forming portion 17 are successively transferred onto the sheet P, so that images of a plurality of colors are formed on the sheet P.

In other words, images of a plurality of colors can be formed on the paper P by first transferring the magenta toner image carried on the surface of the photosensitive drum 33 of the magenta image forming section 17M onto the paper P, then by transferring the yellow toner image carried on the surface of the photosensitive drum 33 of the yellow image forming section 17Y onto the magenta toner image already transferred onto the paper P, and similarly transferring the cyan toner image carried on the surface of the photosensitive drum 33 of the cyan image forming section 17C and the black toner image carried on the surface of the photosensitive drum 33 of the black image forming section 17B onto the previous image on the paper P.

The belt cleaning device 40 is provided below the conveying belt 38 in a relatively large space formed in the vicinity of the driven roller 37 side, that is, in a space larger than the space formed in the vicinity of the drive roller 36 side.

The belt cleaning device 40 has a cleaning cartridge 46 and a cleaning roller 47.

The cleaning box 46 has a box-like outline, and is formed with a hole at its portion facing the lower side portion 38b of the conveyor belt 38. The inner space of the cleaning cartridge 46 is formed as a collecting portion that collects the substances attached to the conveyor belt 38 and removed from the conveyor belt 38 by the cleaning roller 47.

The cleaning roller 47 is a metal roller rotatably supported at a hole portion in the cleaning cartridge 46, and is in contact with the lower side surface of the lower side portion 38b of the conveyor belt 38. During the cleaning operation, a cleaning bias voltage is applied to the cleaning roller 47. The cleaning roller 47 is driven to rotate in the counterclockwise direction in the drawing. Therefore, the cleaning roller 47 moves in a direction opposite to the moving direction of the conveyor belt 38 at its portion contacting the conveyor belt 38.

Note here that the toner adheres to the conveying belt 38 when the conveying belt 38 is in contact with the photosensitive drum 33. Paper dust adheres to the conveyor belt 38 when the paper P comes into contact with the conveyor belt 38. Substances such as toner and paper dust are captured by the cleaning roller 47 by electrostatic force when the conveyor belt 38 brings the substances to a position opposed to the cleaning roller 47. The thus-captured matter is removed from the cleaning roller 47 and collected in a collecting portion of the cleaning cartridge 46.

By such a method, when the cleaning roller 47 is in contact with the outer surface or the lower surface of the lower side portion 38a of the conveying belt 38, the cleaning roller 47 recovers the toner adhering to the surface of the conveying belt 38 when the toner is scattered from the photosensitive drum 33 and the paper dust adhering to the surface of the conveying belt 38 when the paper is conveyed on the conveying belt 38.

The fixing section 19 will be described below.

The heating roller 48 is composed of a metal pipe having a release layer formed on the surface thereof. The heating roller 48 accommodates therein a halogen lamp extending in the axial direction of the heating roller 48. The halogen lamp heats the surface of the heating roller 48 to a fixing temperature. The pressure roller 49 is in pressure contact with the heating roller 48.

In this fixing section 19, the recording paper P with the toner image thereon is sandwiched between a heating roller 48 and a pressure roller 49, and the toner image is thermally fixed on the paper P by pressure.

< paper discharge section 6>

The paper discharge side U-shaped path 50 is formed as a conveyance path of the paper P of a substantially U-shaped profile extending upward from an upstream end portion thereof to a downstream end portion thereof. The upstream end portion of the paper discharge-side U-shaped path 50 is in the vicinity of the fixing portion 19 and conveys the paper P rearward. The downstream end portion of the discharge-side U-shaped path 50 is in the vicinity of the discharge tray 52 and conveys the sheet P forward.

The paper discharge rollers 51 are provided in pairs at the downstream-side ends of the paper discharge-side U-shaped path 50.

The sheet discharge tray 52 defines an upper surface of the main casing 2 as an inclined wall inclined rearward from the front.

The sheet conveyed from the fixing section 19 is fed backward at an upstream end portion of the discharge-side U-shaped path 50, reverses its conveying direction in the discharge-side U-shaped path 50, and is conveyed forward by the discharge roller 51 onto the sheet discharge tray 52.

The sheet discharge tray 52 is configured such that the entire tray can rotate about the center of a hinge 52a provided below the sheet discharge roller 51. Each process cartridge 30 can be removed from the main casing 2 by rotating this discharge tray 52 opening device upward, as shown in fig. 2.

As described above, according to the present embodiment, the color laser printer 1 is a tandem type in which a plurality of process cartridges 30 (one for each color) are respectively provided in a plurality of image forming portions 17. Accordingly, the formation of the image of each color is performed at substantially the same speed as the monochrome image, making it possible to form the images of a plurality of colors quickly. For this reason, images of a plurality of colors can be formed, and the compactness of the apparatus is maintained.

More specifically, the photosensitive drum 33 is rotatably supported in each process cartridge 30 near the lower end of the process cartridge 30. The scorotron charging device 34 charges the surface of the photosensitive drum 33. The toner cartridge 35 is disposed at a position above the photosensitive drum 33. The supply roller 31 and the developing roller 32 are disposed at positions below the toner cartridge 35. Toner is supplied onto the surface of the photosensitive drum 33 by the operation of the supply roller 31 and the developing roller 32. An electrostatic latent image is formed on the surface of the photosensitive drum 33 by the laser beam L emitted from the scanner unit 20, and thereafter the electrostatic latent image is developed by the developing roller 32 supplying toner to the surface of the photosensitive drum 33. The photosensitive drum 33 faces the transfer roller 39 with the conveying belt 38 sandwiched therebetween. A transfer bias voltage is applied to the transfer roller 39. Accordingly, the toner that develops the electrostatic latent image on the photosensitive drum 33 is transferred onto the recording paper P conveyed on the conveying belt 38. This results in that magenta, yellow, cyan, and black color images are sequentially formed on the recording paper P. The recording paper P passing under each image forming portion 17 is then supplied to a fixing portion 19. The recording sheet P on which the image is then fixed by the fixing portion 19 is conveyed by a pair of discharge rollers 51 and is discharged onto a discharge tray 52 on the top of the main casing 2.

As shown in fig. 2, in each image forming section 17, the process cartridge 30 is inserted or removed in a direction D which is inclined in both the horizontal direction (front-rear direction) and the vertical direction (thickness direction of the sheet P), in other words, in a forward-upward direction. It is possible to improve the ease of operation of inserting or removing the process cartridge 30.

Also, a plurality of process cartridges 30 and a corresponding plurality of scanner units 20 are alternately arranged in the front-rear direction of the color printer 1. Such an efficient arrangement enables the device to be more compact.

More specifically, the scanner unit 20 and the process cartridges 30 are alternately arranged in the direction in which the sheet P is conveyed by the scanner unit 20 and the conveyor belts 38 under the process cartridges 30 at the image transfer position. Therefore, the scanner unit 20 and the process cartridge 30 can be efficiently arranged in the color laser printer 1, making the color laser printer 1 compact.

The scanner unit 20 and the process cartridge 30 are inclined with their upper ends facing upward and forward. This enables the height of the apparatus to be reduced to be more compact than in the comparative example in which the scanner unit 20 and the process cartridge 30 are not inclined but vertically erected.

Note here that although the scanner unit 20 and the process cartridge 30 are disposed at an angle in the color laser printer 1, the depth dimension (front-rear dimension) of the color laser printer 1 is not greatly increased relative to the comparative example. This is because the paper supply cassette 70 is inserted and removed in the depth direction, and since the depth dimension of the printer of the comparative example is larger than the entire depth dimension of all the vertically upright scanner units 20 and the process cartridges 30 by the length of the interval provided between the next scanner unit 20 in the depth direction in the main casing 2 and the process cartridge 30 to receive other components such as various rollers mounted therein.

Further, each process cartridge 30 is inserted or removed in a forward tilting direction (direction indicated by arrow D in fig. 2) which is tilted forward in a direction parallel to the front inner wall 2a and the rear inner wall 2 b.

In other words, each process cartridge 30 is inserted or removed in a direction inclined with respect to the direction in which the sheet P is conveyed at its image transfer position below its associated process cartridge 30 and the thickness direction of the sheet orthogonal to the conveying direction. Thereby facilitating insertion or removal of the process cartridge.

Moreover, since the operation of replenishing the recording paper P in the paper feed cassette 70 and the operation of removing the recording paper P from the paper output tray 52 are performed from the front in a similar manner to the insertion or removal of each process cartridge 30, the present embodiment ensures that the operation of the apparatus is greatly improved.

With this embodiment, the conveyor belt 38 is disposed at an incline so that its front face is higher than its rear face. In other words, the conveyor belt 38 descends downward on the downstream side in the toner transfer direction. For this reason, a wide space is formed below the front side of the conveyor belt 38, enabling components such as the paper feed rollers 10 and 11 to be mounted below the front side of the conveyor belt 38.

Since the conveyor belt 38 is inclined, the depth dimension of the apparatus can be reduced. The whole device can be more compact.

The direction in which the conveying belt 38 is inclined and the direction in which the process cartridge 30 is inclined form a space on the downstream side of each photosensitive drum 33 in the rotational direction thereof. This enables a relatively large scorotron charging device 34 to be disposed on the downstream side of each photosensitive drum 33 in its rotational direction without increasing the size of the apparatus 1.

Moreover, the apparatus 1 can be made more compact by ensuring that the height of the scanning unit matches the height of the process cartridge 30.

More specifically, a straight line connecting the scanner unit 20 and the upper end of the process cartridge 30 extends at a predetermined angle with respect to the horizontal direction to be inclined upward and forward. A straight line connecting the upper end surface of the scanner unit 20 and the upper end surface of the process cartridge 30 is parallel to the inclination direction of the conveyor belt 38. The device 1 can therefore be more compact.

The sheet discharge tray 52 is provided along the upper ends of the scanner unit 20 and the process cartridge 30. The sheet discharge tray 52 extends in a direction substantially parallel to the conveyor belt 38. Therefore, a fixed-width air flow is generated on the lower side of the tray 52, that is, between the sheet discharge tray 52 and the scanner unit 20 and the process cartridge 30. For this reason, the apparatus 1 can be made relatively compact while ensuring ventilation near the upper end of the process cartridge 30. This can facilitate heat dissipation.

A fold mirror 23 is located near the top of each scanning unit 20. The photosensitive drum 33 is near the lower end of the process cartridge 30. Therefore, before the exposure scanning of the photosensitive drum 33 is performed, the laser light is emitted from the vicinity of the upper end of the scanner unit 20 to the vicinity of the lower end of the process cartridge 30. Therefore, a longer length of the exposure light path can be maintained and the scanning unit 20 can be made compact by reducing the size of the lens mounted therein.

Moreover, since exposure scanning is performed from a position at a distance from the photosensitive drum 33, toner contamination of optical components mounted in the scanner unit 20 can be prevented. The device can be more compact and can form a clearer image.

The upper end of the scanner housing 26 is made narrower in the backward direction. The upper end of each toner cartridge 35 is enlarged in the rearward direction by the same amount to protrude toward the upper end of the scanner housing 26 which is narrowed.

More specifically, each scanner housing 26 has: an upper portion extending from an upper end 26U to a middle portion of the scanner housing 26; and a lower portion extending from a middle portion of the scanner housing 26 to a lower end 26D. Each of the process cartridges 30 has: an upper portion extending from an upper end 30U of the process cartridge 30 to the middle; and a lower portion extending from the middle portion to the lower end 30D of the process cartridge 30. In the lower portion, the scanner housing 26 has a uniform depth (width in the front-rear direction) from the lower end 26D to the middle portion. Also, in the lower portion of the process cartridge 30, the process cartridge 30 has a uniform depth (width in the front-rear direction) from the lower end 30D to the middle portion. In contrast, the upper portion of each scanner housing 26 has a depth (width in the front-rear direction) that decreases from the middle portion toward the upper end 26U by narrowing in the rear direction toward the upper end 26U. The upper portion of each process cartridge 30 has a depth (width in the front-rear direction) that increases from the middle portion to the upper end 30U by protruding in the rear direction toward the upper end.

By such a method, the depth of each scanning unit 20 (the width of each scanning unit 20 in the direction in which the scanning unit 20 and the process cartridge 30 are alternately arranged) becomes narrower near the upper end of the scanning unit 20, and the depth of each process cartridge 30 (the width of each process cartridge 30 in the same direction) becomes wider near the upper end of the process cartridge 30 to match or complement the narrowed portion of the scanning unit 20. Therefore, the sum of the depth of the scanning unit 20 and the depth of the processing unit 31 is uniform from the lower end to the upper end thereof.

Therefore, the amount of toner that can be stored in the toner cartridge 35 can be increased without making the apparatus 1 large, reducing the frequency of replacement and improving maintainability. Thereby enabling the color laser printer 1 to be relatively compact and improving maintainability thereof.

In the color laser printer 1, the paper P is guided forward by the pickup roller 10 in the paper feed section 4, the paper P is conveyed backward at the image transfer position, and the paper P is conveyed forward by the discharge roller 51 in the discharge section 6. The apparatus can be made compact while ensuring the conveyance path of the sheet P.

As described above, according to the present embodiment, the color laser printer 1 has the scanner unit 20 and the process cartridges 30 which are alternately disposed in the front-rear direction with their upper ends inclined forward at an angle. Since the scanner unit 20 and the process cartridge 30 are inclined, the height of the apparatus 1 can be reduced and the apparatus 1 can be made more compact, as compared with a comparative example in which the process cartridge 30 stands vertically above the conveyor belt 38.

Since each process cartridge 30 can be inserted and removed in a direction inclined with respect to the forward direction, the insertion and removal of the process cartridge 30 is easier compared to a comparative example in which the process cartridge 30 stands vertically and must be pulled out in the vertical direction.

Furthermore, the conveyor belt 38 is disposed at an angle such that its front end is higher than its rear end, so that the apparatus 1 can be more compact.

< modification of paper output tray >

In the above description, the sheet discharge tray 52 is provided to cover all the image forming portions 17M to 17K. Alternatively, as shown in fig. 3, a plurality of sheet discharge trays 152 may be provided to cover the image forming portions 17M to 17K, respectively. Each of the sheet discharge trays 152 can be independently opened or closed by its hinge 152 a.

In this modification, only one sheet discharge tray 152 corresponding to the process cartridge 30 requiring maintenance needs to be opened or closed. The operation becomes simplified.

< details of the scanning unit >

The construction of the scanner support 260 and the scanner unit 20 will be described in more detail with reference to fig. 4-8.

As shown in fig. 4, 4 support frames 260 corresponding to magenta, yellow, cyan, and black are fixedly installed in the main casing 2 in parallel with the front and rear inner side walls 2a and 2b (fig. 1). The scanning unit 20 is mounted on each of the supporting frames 260.

As shown in fig. 5, the support frame 260 has a substantially rectangular bottom plate 260 a. The bottom plate 260a has an inner surface 260aa and an outer surface 260ab facing each other. The support bracket 260 also has a sidewall 260b disposed around the periphery of the base plate 260 a. Sidewall 260b is upstanding perpendicularly from inner surface 260aa around inner surface 260aa of base plate 260 a. The support frame 260 is fixedly installed in the main casing 2, and the bottom plate 260a extends obliquely forward and upward with the inner surface 260aa facing in the forward and downward direction.

As shown in fig. 4 to 6, the scanner housing 26 of the scanner unit 20 has a bottom plate 26b formed with an exposure hole 26 a. The bottom plate 26b has a flat portion 26bf and an inclined portion 26 bs. The flat portion 26bf extends from the lower edge 26D of the scanner housing 26 to the middle of the scanner housing 26, while the inclined portion 26bs extends from the middle of the scanner housing 26 to the upper edge 26U of the scanner housing. The inclined portion 26bs is inclined with respect to the flat portion 26 bf. The bottom plate 26b has an inner surface 26b1 and an outer surface 26b2 facing each other. The scanner housing 26 also has a side wall 26c disposed around the periphery of the bottom plate 26 b. The sidewall 26c is upstanding perpendicularly from the inner surface 26b1 around the inner surface 26b 1. The side wall 26c has a top end surface 26 ce. As shown in fig. 4, the height of a portion of the side wall 26c upstanding from the flat portion 26bf of the bottom plate 26 is substantially uniform throughout the flat portion 26bf, while the height of the remaining portion of the side wall 26c upstanding from the inclined portion 26bs of the bottom plate 26b decreases toward the upper end 26U.

The scanning unit 20 is mounted on the supporting frame 260, and the inner surface 26b1 of the bottom plate 26b and the top end surface 26ce of the side wall 26c face the inner surface 260aa of the supporting frame 260. Note that the right and left ends 26R and 26L of the scanning unit 20 face the right and left directions in the main casing 2. The upper end 26U and the lower end 26D of the scanner unit 20 face up and down in the main casing 2.

As shown in FIG. 6, the polygon mirror 22, the f θ lens 24, and the cylindrical lens 25 are mounted on the inner surface 26b1 of the bottom plate 26 b. Further, a collimating lens 255, a slot device 256, a cylindrical lens 257, mirrors 258a, 258b, and 258c, and a BD sensor 259 are mounted on the inner surface 26b1 of the bottom plate 26 b. The laser diode 254 is attached to the side wall 26c on the lower edge 26D of the scanner housing 26. The fold back mirror 13 is attached to a side wall 26C on the upper edge 26U of the scanner housing 26.

The laser diode 254 emits a laser beam L. After passing through the collimating lens 255, the slit device 256, and the cylindrical lens 257, the laser beam L is reflected by a reflecting mirror 258a before reaching the polygon mirror 22. The polygon mirror 22 reflects the laser beam L in the scanning direction, i.e., from left to right. The laser beam L passes through the f θ lens 24 before reaching the folding mirror 23. The laser beam L is reflected by the folding mirror 23 to be directed to the hole 26a through the cylindrical lens 25. The laser beam L reaches the photosensitive drum 33 after passing through the hole 26 a.

The positions of the polygon mirror 22, the f θ lens 24, the fold mirror 23, the cylindrical lens 25, and the exposure hole 26a, and the orientations of the mirror surfaces of the fold mirror are set such that the optical path extending from the fold mirror 23 through the cylindrical lens 25 to the exposure hole 26a is offset by an angle α (15 degrees in this example) from the optical path from the polygon mirror 22 through the f θ lens 24 to the fold mirror 23 along an imaginary plane perpendicular to the scanning direction.

When the laser beam L is scanned by the polygon mirror 22, the laser beam L from the f θ lens 24 reaches the folding mirror 23 or the reflection mirror 258b disposed adjacent to the folding mirror 23. When the laser beam L reaches the mirror 258b, the laser beam L is reflected by the mirror 258b and the mirror 258c before being incident on the BD sensor 259.

The rotation period and the rotation time of the polygon mirror 22 are set to ensure that when the laser beam L is incident on the reflection mirror 258b, the corner edge of the polygon mirror 22 is not on the optical path of the laser beam L between the reflection mirror 258c and the BD sensor 259 as shown by the solid line in fig. 6.

The laser diode 254 is controlled to be turned on and off at a timing synchronized with the rotation of the polygon mirror 22 according to image data. The position in the scanning direction where the image starts to be written on the photosensitive drum 33 is appropriately fixed by controlling this on/off time depending on the time when the laser beam L is incident on the BD sensor 259.

Next, how to mount the scanner unit 20 on the support frame 260 attached to the main casing 2 will be described.

As shown in fig. 6 and 7(B), the scanner housing 26 has a right extension 26e extending rightward from the side wall 26c at the right end 26R and thinner than the side wall 26 c. The right extension 26e has: a surface 26e1 facing an inner surface 260aa of the bottom plate 260a of the scanner support bracket 260; and another surface 26e2 opposite surface 26e 1. The surface 26e1 is continuous with the top end surface 26ce of the side wall 26 c.

A pair of protrusions 27 are formed on the surface 26e1 of the right extension 26 e. The pair of projections 27 are disposed along a straight line extending perpendicularly to the scanning direction (right-left direction).

As shown in fig. 8, each of the protrusions 27 has a substantially semicircular profile in a cross section thereof along an imaginary plane extending in parallel to the scanning direction (left-right direction) and perpendicular to the directions of the surfaces 26e1 and 26e 2.

The leaf spring 261 is fixed at one end thereof to the inner surface 260aa of the scanner support frame 260 by a bolt 267. The other end of the leaf spring 261 presses the surface 26e2 of the right extension 26e in a direction towards the bottom plate 260 a. Therefore, the pair of protrusions 27 are pressed against the bottom plate 260a by the leaf spring 261.

A pair of recesses 262 are formed on an inner surface 260aa of bottom plate 260 a. Each recess 262 is positioned to face the corresponding protrusion 27, as shown in fig. 8. The recess 262 has a V-shaped profile in a cross section along an imaginary plane extending parallel to the scanning direction (left-right direction) and perpendicular to the inner surface 260 aa.

The projection 27 is placed at the center of the recess 262 by the urging force of the leaf spring 261. The depth of the depression 262 is sufficiently small that the top end surface 26ce of the side wall 26c and the surface 26e1 of the right extension 26e do not contact the inner surface 260aa of the bottom plate 260a when the projection 27 is placed in the center of the depression 262.

As shown in fig. 6-7 (B), a flange portion 26d protrudes leftward from the side wall 26c at the left side end 26L of the scanner housing 26. The flange portion 26d has: surface 26d1 facing inner surface 260aa of bottom plate 260 a; and another surface 26d2 opposite surface 26e 1. The steel plate 28 is secured to the surface 26d1 of the flange portion 26 d.

Bolt 263 passes through bottom plate 260a with its bolt head 263a on the side of outer surface 260ab and its tip 263b on the side of inner surface 260 aa. Thus, the bolt 263 is engaged with the base plate 260 a.

The leaf spring 264 is disposed near the bolt 263. That is, the leaf spring 264 is fixed at one end thereof to the outer surface 260ab of the scanner support frame 260 by a bolt 266. The other end of the leaf spring 264 presses the surface 26d2 of the flange portion 26d in a direction toward the bottom plate 260 a. Accordingly, the leaf spring 264 presses the flange portion 26d in a direction toward the bottom plate 260a to bring the tip end 263b of the bolt 263 into contact with the steel plate 28.

With the above-described structure, when the engagement amount of the bolts 263 is adjusted to change the distance between the bottom plate 260a and the flange portion 26d, the scanner unit 20 swings about the contact between the protrusion 27 and the recess 262. Accordingly, the orientation of the scanning unit 20 with respect to the supporting frame 260 can be adjusted in the left-right direction.

When the adjustment of the engagement amount of the bolt 263 is completed, when the scanner unit 20 is supported by three points (the bolt 263 and the pair of protrusions 27), the scanner unit 20 is fastened to the support frame 260 in the adjusted orientation.

The scanning unit 20 has a relatively long and flat structure in the left and right directions in which the light beams are scanned. The scanning unit 20 is supported at both end portions 26R and 26L in its longitudinal direction by a combination of the projection 27 and the recess 262 and a combination of the bolt 263 and the leaf spring 264, respectively. Since the distance between the scanner unit 20 and the support frame 260 at the left end 26L is determined by the adjusting bolt 263, the assembly of the scanner unit 20 and the support frame 260 is extremely stable after the distance is adjusted. No further fixing operation is required after the distance adjustment is completed.

As shown in fig. 5 and 7(a), a through hole 265 is formed through the bottom plate 260a at a position close to the leaf spring 264. The through hole 265 facilitates adjustment of the engagement amount of the bolt 263.

More specifically, as shown in fig. 4, the orientation adjustment of each scanning unit 20 can be performed when the process cartridge 30 is removed from the main casing 2, and a sensor such as a CCD is provided on the conveyor belt 38.

The orientation of each scanning unit 20 can be adjusted by inserting a screwdriver into the through-hole 265 as shown by the broken line in fig. 4, even when a plurality of scanning units 20 are mounted in the main casing 2.

In this example, only the through hole 265 for adjusting the engagement amount of the bolt 263 is provided on the scanner support frame 260. However, another through hole 265 can be additionally formed through the scanner support bracket 260 so that the engagement amount of the bolt 266 fixing the leaf spring 264 can be adjusted.

Therefore, according to the present embodiment, the scanner support frame 260 is provided in parallel in multiple stages in the main casing 2. The optical scanning units 20 each having the scanner housing 26 are mounted on the scanner support frame 260. A through hole 265 is formed on each support bracket 260 to allow insertion of a screwdriver to make adjustment of the engagement amount of the bolt 263 in the next scanning unit 20 of the belonging scanning unit 20 in the forward direction.

It is to be noted here that, since the color laser printer 1 is of a tandem type, a plurality of scanning units 20 are arranged in parallel to each other in multiple stages. In this type of device, the orientation of each scanning unit 20 must be adjusted. According to the present embodiment, the orientation of each scanner unit 20 can be adjusted by adjusting the engagement amount of the bolt 263.

Also, a through hole 265 is formed in the support frame 260 of each stage to insert a screwdriver to adjust the engagement amount of the bolt 263 of the adjacent scanning unit 20. The orientation of the scanner housing 26 of each scanner unit 20 can be adjusted without moving the other scanner units 20 mounted in the main housing 2. The orientation of each scanning unit 20 can thus be adjusted in an extremely simple manner without disturbing the other scanning units 20, even if the scanning units 20 are arranged in multiple levels in parallel.

As described above, according to the present embodiment, the leaf spring 261 presses the protrusion 27 formed on the surface 26e1 of the right extension 26e from the opposite side 26e2 in the direction toward the bottom plate 260a of the support bracket 260, thereby bringing the protrusion 27 into contact with the depression 262 formed on the bottom plate 260 a. Bolt 263 passes through base plate 260a from outer surface 260ab to inner surface 260aa such that its top end 263b faces flange portion 26d of scanner unit 20. Thus, the bolt 263 is engaged with the base plate 260 a. A leaf spring 264 is fixedly mounted on the base plate 260a near the bolt 263 to press the flange portion 26d in a direction toward the base plate 260 a. The orientation of the scanner unit 20 with respect to the support bracket 260 can be adjusted by adjusting the engagement amount of the bolts 263. Therefore, the ease of the operation of attaching the scanning unit 20 to the supporting bracket 260 can be improved.

The combination of the projection 27 and the recess 262 adjusts the position of the scanner housing 26 relative to the scanner support bracket 260 by bringing the projection 27 and the recess 262 into contact with each other, thereby maintaining a certain amount of spacing between the scanner housing 26 and the scanner support bracket 260. The scanner housing 26 is held such that a gap is formed between the scanner housing 26 and the support bracket 260.

Accordingly, the orientation of the scanner housing 26 can be adjusted in a simple manner by pivoting the scanner housing 26 about the contact portion between the projection 27 and the recess 262, while maintaining the spacing between the scanner housing 26 and the support bracket 260. In this case, adjustment of the bolt 263 pivots the scanner housing 26 about the contact portion to adjust the orientation of the scanner housing 26. Even with a simple structure of the projection 27 and the recess 262, the position of the pivot center does not shift, and therefore the orientation of the scanner housing 26 can be adjusted in a simple manner. Also, the scanner housing 26 can be more securely supported on the support bracket 260 after adjustment.

As described above, each scanner unit 20 of the color laser printer 1 can be adjusted in a simple manner by merely adjusting the engagement amount of the bolts 263 without the position of the scanner unit being shifted after the adjustment. The operation of fixing the scanner unit 20 to the scanner supporting frame 260 can be facilitated, so that the ease of operation can be improved.

The flange 26d of the left end 26L of the scanner housing 26 is sandwiched between the leaf spring 264 and the bolt 263. Therefore, the flange 26d can be firmly fixed to the scanner support frame 260 while adjusting the bolts 263, regardless of this simple structure. The scanning unit 20 can be stably supported on the supporting bracket 260 after adjustment.

Since the plurality of projections 27 are provided along a straight line in a direction perpendicular to the scanning direction of the laser beam L in each scanning unit 20, it is possible to prevent the scanning unit 20 from rotating about the center of the axis parallel to the scanning direction. This makes adjustment of the orientation of the scanning unit 20 simple.

The folding mirror 23 reflects the laser beam L in such a manner that an angle formed between the laser beam L before reflection and the laser beam L after reflection on an imaginary sectional plane perpendicular to the scanning direction is substantially 15 degrees. By adjusting the engagement amount of the bolts 263 to adjust the orientation of the scanner unit 20 in the scanning direction, the scanning direction (i.e., the direction of the scanning line formed on the photosensitive drum 33) can be adjusted to be parallel to the rotational axis of the photosensitive drum 33. The accuracy of image formation can be improved.

Note here that the angle α formed between the light beam before being reflected by the fold back mirror 23 and the light beam after being reflected by the fold back mirror 23 on an imaginary sectional plane perpendicular to the scanning direction may not be equal to 15 degrees. Preferably, the angle α satisfies the inequality 0< α <45 degrees. In this case, the degree of parallelism between the axis of the photosensitive drum 33, which most affects the image quality, and the scanning direction can be ensured by adjusting the orientation of the scanning unit 20 about the axis perpendicular to the scanning direction, and the quality of the image formed after the adjustment can be improved.

It is noted here that, as shown in dashed lines in fig. 6, a further protrusion 27' can additionally be provided on the surface 26e1 of the right extension 26 e. The additional protrusion 27' is located on the same straight line as the protrusion 27 in a direction perpendicular to the scanning direction of the laser beam L. The additional protrusions 27' extend continuously on the straight line on which the protrusions 27 are provided. The additional protrusions 27' have the same shape and size in cross-section as the protrusions 27, as shown in fig. 8.

In this case, although not shown in the drawings, another recess is additionally formed on the inner surface 260aa of the bottom plate 260a of the support bracket 260. The additional depression is located on the same line as the depression 262 in a direction perpendicular to the scanning direction of the laser beam L. The additional recesses are located at positions facing the additional protrusions 27 'and continuously extend in the same length as the additional protrusions 27' on a line on which the recesses 262 are provided. The additional recess has the same shape and size in cross-section as the recess 262, as shown in fig. 8. By adjusting the number of engagement of the bolts 263, it is possible to pivot the scanning unit 20 around the contact positions between the projection 27 and the depression 262 and between the additional projection 27' and the additional depression.

Note that when the additional elongated projection 27' is provided on the scanner housing 26 and the additional elongated recess is provided on the scanner support bracket 260, the projection 27 may be omitted from the scanner housing 26 and the recess 262 may be omitted from the scanner support bracket 260. In this case, the scanner housing 26 is supported on the scanner support frame 260 at two points, that is, a contact portion between the additional elongated protrusion 27' and the additional elongated recess and a contact portion between the flange 26d and the bolt 263.

Alternatively, the protrusions 27 and/or additional elongated protrusions 27' may be provided on the support bracket 260 and the recesses 262 and/or additional elongated recesses may be provided on the scanner housing 26.

(modification of the first embodiment)

In the first embodiment described above, toner is directly transferred from each photosensitive drum 33 onto the recording paper P conveyed by the conveying belt 38. However, in the present modification, the configuration is modified to the color laser printer 201 as shown in fig. 9, the conveying belt 38 is used as an intermediate transfer belt onto which toner is temporarily transferred before being transferred from the conveying belt 38 to the recording paper P.

More specifically, an additional transfer roller 139 is provided in the present modification so that the conveyance belt 38 is sandwiched between the additional transfer roller 139 and the driven roller 37. The additional transfer roller 139 is applied with a transfer bias.

All the four color toner images are superimposed one on another on the upper side portion 38a of the conveyor belt 38 while being conveyed in the backward direction. Then, the toner image is conveyed in the forward direction by the lower side portion 38b of the conveying belt 38 before finally reaching the nip portion between the conveying belt 38 and the additional transfer roller 139. The toner image and a sheet of recording paper P supplied from the conveying roller 13 pass through the nip portion simultaneously with each other, and the toner image is transferred onto the recording paper P.

In the present modification, although the conveyance path for conveying the recording paper is different from that in the first embodiment, the apparatus 201 can be made compact by arranging the conveyance belt 38 to incline upward toward the front side.

(second embodiment)

Next, a color laser printer 301 according to a second embodiment will be described with reference to fig. 1 and fig. 10 to 12.

The color laser printer 301 is the same as the color laser printer 1 except for the combination of the scanner unit 320 and the scanner holder 360 for each image forming section 17 instead of the combination of the scanner unit 20 and the scanner holder 260 in the first embodiment.

The scanner unit 320 is the same as the scanner unit 20 except that it has a scanner housing 326 in place of the scanner housing 26 in the first embodiment.

The scanner housing 326 is the same as the scanner housing 26 in the first embodiment except for the points described below.

The scanner housing 326 is shown without the projection 27, but instead has a rotational axis 329. The pivot shaft 329 protrudes from the scanner housing 326 at its lower end 326D. The rotating shaft 329 is located on the scanner housing 326 at a substantially central position in a light scanning path of the light beam L scanned by the polygon mirror 22. The rotation axis 329 extends in a direction perpendicular to the scanning direction of the laser beam L and substantially parallel to the top end surface 26ce of the side wall 26c of the scanner housing 326. As shown in fig. 12, the rotation shaft 329 has a substantially circular shape in its cross section along an imaginary plane extending parallel to the scanning direction (left-to-right direction) and perpendicular to the tip end surface 26 ce.

At the left end 326L, the scanner housing 326 is not formed with the flange portion 26d or the steel plate 28, but instead is formed with the flange portion 326d and the steel plate 328, which are smaller in size than the flange portion 26d and the steel plate 28 in the first embodiment. The flange portion 326d has surfaces 326d1 and 326d2 that face each other. The steel plate 328 is fixed to a surface 326d1 of the flange portion 326d facing the scanner support bracket 360.

Instead of the bolt 263 in the first embodiment, a bolt 363 penetrates the bottom plate 260a of the scanner support frame 360 from the outer surface 260aa of the bottom plate 260a to the inner surface 260ab of the bottom plate 260 a. The bolt 363 further passes through the steel plate 328 and the flange portion 326 d. Thus, the bolt head 363a of the bolt 363 is located on the outer surface 260ab side, and the bolt tip 363b of the bolt 363 is located on the surface 326d2 side. Thus, the scanner unit 320 engages the scanner support frame 360 at its left end 326L.

The support frame 360 is the same as the support frame 260 of the first embodiment except for the following points.

The support frame 360 is not formed with the recess 262, but instead is formed with a bearing portion 360d at its side wall 260b for receiving the rotation receiving shaft 329.

The support bracket 360 is not mounted with the leaf spring 264 or bolt 266 of the first embodiment.

The bearing portion 360d is opened in a V shape as shown in fig. 12, and thus has a V-shaped section along an imaginary plane extending parallel to the scanning direction (left-right direction) and the bottom plate 260 a.

The opening depth of the bearing portion 360d is sufficiently small that the tip end surface 26ce of the side wall 26c of the scanner housing 326 facing the bottom plate 260a does not contact the bottom plate 260a when the scanner unit 320 is supported on the support frame 360 with the rotation shaft 329 received in the bearing portion 360 d. This structure can adjust the orientation of the scanning unit 320 by pivoting the scanning unit 320 about the contact portion between the rotation shaft 329 and the bearing portion 360 d.

Also, the right end 326R of the housing 326 is urged in the direction toward the bottom plate 260a by the combination of the bolt 267 and the leaf spring 261 in the same manner as in the first embodiment. Accordingly, the orientation of the scanner unit 320 can be adjusted by adjusting the number of engagements of the screw 363 that engages the scanner unit 320 with the support bracket 360 near the left end 326L of the housing 326.

Also in the second embodiment, the orientation of the scanning unit 320 can be easily adjusted, and the scanning unit 320 can be fastened to the supporting bracket 360 while the adjustment is completed. For this reason, the operation of fixing each scanning unit 320 to the corresponding support frame 360 is simple, and the ease of operation can be improved.

Further, since the orientation of the scanning unit 320 is adjusted about the axis of the rotation shaft 329 perpendicular to the scanning direction, the scanning unit 320 is prevented from rotating about the center of the axis parallel to the scanning direction, making the above-mentioned orientation adjustment simpler.

Because the bearing portion 360d has the above-described structure, even with such a simple structure, the rotating shaft 329 can be held in a fixed position without being erroneously displaced from the position.

Because the rotation shaft 329 is perpendicular to the scanning direction, the scanning unit 320 is prevented from rotating about an axis parallel to the scanning direction, further simplifying the adjustment of the orientation of the scanning unit 320 and ensuring that the orientation of the scanning unit 320 is in the correct direction relative to the photosensitive drum 33.

Further, the right end portion 326R of the scanner housing 326 in the scanning direction is pushed toward the inner surface 260aa of the support frame 360 by the leaf spring 261, and the distance between the left end portion 326L of the support frame 360 and the surface 260aa is adjusted by the bolt 363. In this way, the scanning unit 320 may be securely fixed to the support frame 360 while the orientation of the scanning unit 320 is adjusted relative to the support frame 360. The scanning unit 320 may thus be stably supported on the support frame 360 after adjustment.

(third embodiment)

A color laser printer 401 of a third embodiment will be described with reference to fig. 13 to 20.

The color laser printer 401 is the same as the color laser printer 1 in the first embodiment except for the points to be described below.

In the first embodiment, the image forming portions 17K, 17C, 17Y, and 17M for four colors of black, cyan, yellow, and magenta are arranged in this order from the rear to the front. On the other hand, in the third embodiment, the image forming portions 17K, 17C, 17M, and 17Y for four colors of black, cyan, magenta, and yellow are arranged in this order from the rear to the front.

The belt unit 60 is constructed by loading the transfer portion 18 (driving roller 36, driven roller 37, conveying belt 38, transfer roller 39, and belt cleaning unit 40), pickup roller 10, sheet feeding roller 11, rear conveying roller 13b, and a pair of registration rollers 14 into a belt unit frame 61 and by integrating them into one unit. The belt unit 60 can be moved horizontally (in a front-to-rear direction) and can be inserted into and removed from the front side of the main casing 2.

When the belt unit 60 is mounted in the main casing 2 at its mounting position, as shown in fig. 13, the belt 38 is brought into contact with the photosensitive drum 33 in the same manner as in the first embodiment, and a terminal 91 (to be described later) on the belt unit 60 is brought into contact with an electrode 92 (to be described later) in the main casing 2. When the belt unit 60 moves in the forward direction to separate from the mounting position, the conveying belt 38 separates from the photosensitive drum 33, and thereafter the rear edge 91c of the terminal 91 separates from the electrode 92 to be described later.

Note that, as shown in fig. 15, similarly to the first embodiment, the vertical position of each process cartridge 30 is higher than the adjacent process cartridge 30 on the rear side thereof by a predetermined amount (which will be referred to as an amount "a" hereinafter). That is, the amount of shift between the vertical position of the process cartridge 30 in the black image forming portion 17K and the vertical position of the process cartridge 30 in the cyan image forming portion 17C, the amount of shift between the vertical position of the process cartridge 30 in the cyan image forming portion 17C and the vertical position of the process cartridge 30 in the magenta image forming portion 17M, and the amount of shift between the vertical position of the process cartridge 30 in the magenta image forming portion 17M and the vertical position of the process cartridge 30 in the yellow image forming portion 17Y are all equal to the preset amount a. Therefore, when the process cartridges 30 of all colors are mounted in the image forming section 17, the photosensitive drums 33 in the process cartridges 30 of different colors are disposed in such a manner that the straight line connecting the lower sides of the respective photosensitive drums 33 is higher on the upstream side in the mounting direction of the belt unit 60 and is inclined downward on the downstream side in the mounting direction of the belt unit 60.

Similarly to the first embodiment, the space below the image forming portion 5 and above the paper feed cassette 70 has a shape in which the height in the vertical direction becomes smaller toward the rear as viewed from the side. The belt unit 60 is installed in the space of the tapered shape, and thus the belt unit 60 is formed to have an overall shape, which becomes smaller toward the rear side in the vertical direction, corresponding to the taper of the installation space, as viewed from the side. That is, similarly to the first embodiment, the driven roller 37 is provided higher than the drive roller 36.

When the belt unit 60 is mounted in the mounting position of the main casing 2, the driven roller 37 is disposed from the front of the photosensitive drum 33 of the process cartridge 30 mounted in the yellow image forming portion 17Y.

The upper side portion 38a of the conveying belt 38 is inclined so as to form an angle between the moving direction of the upper side portion 38a caused by the driving of the driving roller 36 and the horizontal direction (the direction in which the tape unit 60 is drawn out from the color laser printer 1), the angle being such that the contact between the surface of the conveying belt 38 and each photosensitive drum 33 is simultaneously released when the tape unit 60 is moved in the forward direction from the mounting position so as to be removed from the main casing 2.

As shown in fig. 17, the belt unit frame 61 includes: a left side panel 65 and a right side panel 66; a base plate 62; and a paper guide member 64. The left side plate 65 and the right side plate 66 face each other with a certain separation distance in the width direction. The bottom panel 62 is suspended between a left side panel 65 and a right side panel 66. As shown in fig. 13, the sheet guide member 64 is placed between a left side plate 65 and a right side plate 66 on the front end of the bottom plate 62 to be suspended in a swingable manner for guiding the sheet P conveyed through the U-shaped path 12 on the sheet feeding side onto the conveyor belt 38.

The pickup roller 10, the sheet feeding roller 11, the rear conveying roller 13b, the pair of registration rollers 14, the driving roller 36, and the driven roller 37 are rotatably suspended between a left side plate 65 and a right side plate 66 in the belt unit frame 61.

The transfer rollers 39 are suspended between the left side plate 65 and the right side plate 66 so that each transfer roller 39 is rotatable about its axis and movable in the vertical direction.

As will be described later with reference to fig. 19, each transfer roller 39 is urged upward by a compression spring 44. Therefore, when the belt unit 60 is mounted at the mounting position in the main casing 2 as shown in fig. 13, the conveying belt 38 is sandwiched between each transfer roller 39 and the corresponding photosensitive drum 33.

More specifically, as will be described later in conjunction with fig. 18, the left-side end and the right-side end of the roller shaft 39a of each transfer roller 39 are rotatably supported by the left-side and right-side bearings 43, respectively. The bearing 43 is supported to be vertically movable in the belt unit frame 61. Left and right compression springs 44 are also installed in the belt unit frame 61 for urging the transfer roller 39 upward. Therefore, when the belt unit 60 is located in the mounting position as shown in fig. 13, the transfer roller 39 presses the conveying belt 38 against the photosensitive drum 33, forming a nip (image forming position) between the photosensitive drum 33 and the conveying belt 38.

As shown in fig. 13, the bottom plate 62 has a front region 62a and a middle-rear region 62b disposed in the front-rear direction. The front region 62a faces the driven roller 37 of the conveyor belt 38. The mid-rear region 62b is positioned lower than the front region 62a and thus defines a depression 103 therein, the depression 103 being depressed lower than the front region 62 a. The belt cleaning device 40 is disposed in a front portion of the recess 103.

As shown in fig. 13 and 18, a positioning groove 102 and a plurality of (6 in this example) terminal grooves 104 are formed in the rear edge of the bottom plate 62. As shown in fig. 13, each terminal slot 104 has a vertical wall 104a and a horizontal wall 104 b.

As shown in fig. 17, the lower end portion of each of the left side plate 65 and the right side plate 66 is bent inward in the width direction, forming a sheet cassette guide 67 for guiding insertion of the sheet cassette frame 71 of the sheet cassette 70 into the sheet cassette 70 or removal from the sheet cassette 70.

The sheet cassette frame 71 includes: a left side plate 72 and a right side plate 73; and a front plate 74 (see fig. 13). The left side plate 72 and the right side plate 73 are disposed to face each other in the width direction at a certain separation distance. The front plate 74 is suspended between the front end portions of the left and right side plates 72, 73. The sheet cassette frame 71 holds the sheet tray 9 between the left side plate 72 and the right side plate 73 at a position behind the front plate 74.

The left side plate 72 faces the left side plate 65 of the belt unit frame 61 with a predetermined interval therebetween, and the right side plate 73 faces the right side plate 66 of the belt unit frame 61 with a predetermined interval therebetween.

Each of the left side plate 72 and the right side plate 73 has an extended portion 75. The extension portion 75 extends from the upper end of the corresponding side plate 72 or 73 toward the outside in the width direction and extends in the front-to-rear direction. The extended portions 75 of the left and right side plates 72 and 73 are joined to the sheet feeding unit guide 67 of the belt unit frame 61 from above. The sheet-feed-cassette frame 71 is thus held on the tape unit frame 61 so that the sheet-feed-cassette frame 71 can slide horizontally along the sheet-feed-unit guide 67.

The main casing 2 has a left main casing side plate 81 and a right main casing side plate 82. When the belt unit 60 is mounted in the main casing 2, the left main casing side plate 81 faces the left side plate 65 with a predetermined interval therebetween, and the right main casing side plate 82 faces the right side plate 66 of the belt unit frame 61 with a predetermined interval therebetween.

Each of the left and right main housing side plates 81 and 82 has a band unit guide 83 formed at a lower end thereof. The belt unit guides 83 protrude inward in the width direction and extend in the front-rear direction over a length long enough to receive the entire length of the belt unit frame 61. Each tape unit guide 83 forms a guide portion 85. The guide portion 85 is a rectangular cutout formed on the upper edge of the tape unit guide 83, and extends along the inside of the tape unit guide 83 in the width direction along the entire length of the tape unit guide 83 in the length direction. When the lower ends of the left and right side plates 65, 66 are mounted on the guide portion 85, the belt unit frame 61 can slide horizontally along the guide portion 85 of the belt unit guide 83.

As shown in fig. 13, the main casing 2 is also provided with an electrode holder 86. When the belt unit 60 is mounted in the main casing 2, the electrode holder 86 is disposed at a position where the electrode holder 86 faces the rear edge of the belt unit frame 61. As shown in fig. 18, a plurality of (six in the present embodiment) electrodes 92 are supported on the electrode holder 86. The electrodes 92 are arranged in the width direction. Each electrode 92 extends forwardly.

As shown in fig. 18, a center portion of one positioning projection 101 in the width direction projects forward from the front surface of the electrode holder 86. The positioning projection 101 has a substantially rectangular shape as viewed from the bottom, as shown in fig. 18.

As shown in fig. 13 and 18, the terminals 81 are disposed in terminal slots 104 in the rear edge of the tape unit frame 61. The terminals 91 are used as power supply terminals, and the terminals 91 are brought into contact with the corresponding electrodes 92 when the band unit 60 is mounted in the main casing 2.

As shown in fig. 13, each terminal 91 has an L-shape, and has a vertically extending portion 91a and a horizontally extending portion 91 b. The vertically extending portion 91a extends vertically along the front-to-surface of the vertical wall 104a of the terminal groove 104. At the upper end of the vertically extending portion 91a, the terminal 91 is bent rearward so that the horizontally extending portion 91b projects outwardly from the inside of the belt unit frame 61 to the outside of the belt unit frame 61 via the vertical wall 104 a. The horizontally extending portion 91b extends horizontally (rearward) along the lower side surface of the horizontal wall 104b of the terminal groove 104. Thus, when the tape unit frame 61 is mounted in the main casing 2 as shown in fig. 13, the lower surface of the horizontally extending portion 91b of each terminal 91 can be brought into contact with the contact point 92a of the corresponding electrode 92.

The distance between the rear edge 91c of the terminal 91 and each transfer roller 39 is greater than or equal to the distance between the contact point 92a of the electrode 92 and the corresponding photosensitive drum 33. More specifically, the distance between the rear edge 91c and the black transfer roller 39 is greater than or equal to the distance between the contact point 92a and the black photosensitive drum 33. The distance between the rear edge 91c and the cyan transfer roller 39 is greater than or equal to the distance between the contact point 92a and the cyan photosensitive drum 33. The distance between the rear edge 91c and the magenta transfer roller 39 is greater than or equal to the distance between the contact point 92a and the magenta photosensitive drum 33. The distance between the rear edge 91c and the yellow transfer roller 39 is greater than or equal to the distance between the contact point 92a and the yellow photosensitive drum 33. Note that, in the front-rear direction, the distance between the black and cyan photosensitive drums 33, the distance between the cyan and magenta photosensitive drums 33, and the distance between the magenta and yellow photosensitive drums 33 are equal to the distance between the black and cyan transfer rollers 39, the distance between the cyan and magenta transfer rollers 39, and the distance between the magenta and yellow transfer rollers 39, respectively. Therefore, when the belt unit 60 is inserted into the main casing 2 from the front side thereof and moved rearward, the transfer rollers 39 reach positions below the respective photosensitive drums 33 as shown in fig. 13 accurately while or after the rear edge 91c of the terminal 91 comes into contact with the contact point 92a of the electrode 92. In other words, when the belt unit 60 is inserted into the main casing 2 and moved rearward, the belt unit 60 reaches the mounting position in fig. 13 where the conveyor belt 38 is in contact with the photosensitive drum 33, simultaneously with or after the rear edge 91c of the terminal 91 is in contact with the contact point 92a of the electrode 92.

As shown in fig. 18, when the belt unit frame 61 is mounted in the main casing 2, the positioning projections 101 are fitted into the positioning grooves 102. The belt unit frame 61 can be positioned in the width direction with respect to the main casing 2 by fitting the positioning projections 101 into the positioning grooves 102.

The erroneous positioning of the terminal 91 provided on the belt unit frame 61 in the width direction with respect to the electrode 92 supported on the electrode support 86 can be prevented by using the positioning projection 101 as a reference for positioning the belt unit frame 61 in the width direction with respect to the main casing 2. For this reason, it is possible to achieve reliable connection between the terminals 91 and the respective electrodes 92.

The belt unit frame 61 further supports therein: four transfer bias lines 93 for supplying a transfer bias to the four transfer rollers 39; a cleaning bias line 94 for supplying a cleaning bias to the cleaning roller 47; and a neutralization bias line 96 for supplying neutralization bias to the four neutralization combs 95. Each neutralization comb 95 is disposed along a respective transfer roller 39.

Note that each transfer roller 39 and each neutralization comb 95 are located between the upper side portion 38a and the lower side portion 38b of the endless belt 38 in the vertical direction. In this example, the conveyor belt 38 is constituted by a plurality of endless belt strips that are wound around the drive roller 36 and the driven roller 37 and are disposed adjacent to each other in the width direction. A small amount of widthwise gaps (inter-strip gaps) are formed between every two adjacent endless belt strips.

Each transfer bias line 93 has one end connected to one of the terminal ends 91, and the other end connected to the left-side end of the corresponding transfer roller 39. More specifically, the transfer bias line 93 extends forward from the terminal end 91, then bends upward so as to pass through an inter-strip gap between two adjacent endless belt strips into a space between the upper and lower side portions 38a and 38b of the conveyor belt 38, and then bends leftward before finally reaching the left end of the corresponding transfer roller 39.

Note that, as shown in fig. 18, the left-side end and the right-side end of the roller shaft 39a of each transfer roller 39 are rotatably supported by the left-side and right-side bearings 43, respectively. The left and right bearings 43 are electrically conductive and are mounted on left and right compression springs 44, respectively. The left and right compression springs 44 are also electrically conductive and are supported by left and right side plates 65 and 66, respectively. Fig. 19 shows how the left-side end of the roller shaft 39a is supported by the left-side bearing 43, and how the left-side bearing 43 is supported on the left-side compression spring 44. Each bearing 43 is urged upwardly by a respective compression spring 44. As shown in fig. 18, the left and right bearings 43 are guided by the left and right side plates 65 and 66, respectively, so that the bearings 43 can slide in the vertical direction along the left and right side plates 65 and 66. As shown in fig. 19, the transfer bias line 93 is connected to the left compression spring 44. The transfer bias line 93 is thus connected to the left end of the transfer roller 39 through the left compression spring 44 and the left bearing 43.

Thus, each transfer bias line 93 is connected to the compression spring 44 connected to the bearing 43 of the corresponding transfer roller 39. The transfer bias is thus applied from the corresponding transfer bias line 93 to each transfer roller 39 through the corresponding compression spring 44 and bearing 43.

The cleaning bias line 94 has one end connected to the corresponding terminal 91 and the other end connected to the right-side end of the cleaning roller 47. More specifically, the cleaning bias lines 94 extend forward from the respective terminal ends 91, and then are bent rightward and upward before finally reaching the right-side end of the cleaning roller 47.

The neutral bias line 96 has one end connected to the corresponding terminal 91. The neutralizing bias line 96 extends rearward from the terminal end 91, then bends upward through an inter-strip gap between two adjacent endless belt strips into a space between the upper and lower side portions 38a and 38b of the conveyor belt 38, and then bends so as to extend forward to be connected in turn with the neutralizing comb 95 for the image forming portions 17K, 17C, 17M and 17Y.

As shown in fig. 20, each of the neutralization combs 95 forms a through-hole through which a neutralization bias line 96 passes, and is connected to the neutralization bias line 96 by a conductive material 97 such as a solder material. The upper edge portion of each of the neutralization combs 95 is formed with a large number of mountain-shaped projections and is in contact with the lower surface of the upper side portion 38a of the conveyor belt 38.

According to the above-described structure, the belt unit 60 can be inserted into or removed from the main casing 2 by sliding the belt unit frame 61 along the guide portion 85 of the belt unit guide 83 along the linear insertion/removal path 100 extending horizontally from the front, as shown in fig. 15.

The sheet feed cassette 70 can also be inserted or removed horizontally from the front of the main casing 2 and the belt unit 60 by sliding the sheet feed cassette frame 71 along the sheet feed unit guide 67 as shown in fig. 14.

This ensures that the paper supply cassette 70 can be inserted into the main casing 2 alone or removed from the main casing 2, as shown in fig. 14.

Further, the tape unit 60 may be inserted into the main casing 2 or removed from the main casing 2 together with the paper supply cassette 70.

More specifically, as shown in fig. 14 and 15, the tape unit 60 and the paper supply cassette 70 are disposed so as to partially overlap each other in the vertical direction. Therefore, as shown in fig. 15, when the belt unit 60 is desired to be removed from the main casing 2, by withdrawing the belt unit 60 forward, the lower front portion of the belt unit 60, i.e., for example, the rollers 13a and 11, pushes the paper supply cassette 70 forward, thereby enabling the belt unit 60 and the paper supply cassette 70 to be removed together from the main casing 2. When the tape unit 60 and the paper supply cassette 70 are intended to be mounted in the main casing 2, the integral unit of the tape unit 60 and the paper supply cassette 70 is moved rearward by pushing the front surface of the paper supply cassette 70 rearward, and as a result, the upper front portion of the paper supply cassette 70, i.e., for example, the roller 13b and the separation pad 3a, pushes the tape unit 60 rearward, thereby enabling the tape unit 60 and the paper supply cassette 70 to be mounted in the main casing 2 together. In this manner, the integral unit of the tape unit 60 and the paper supply cassette 70 is inserted into or removed from the main casing 2 in the same direction as the paper supply cassette 70 is inserted into or removed from the main casing 2 alone. For this reason, the tape unit 60 and the paper supply cassette 70 can be inserted or removed by a single operation. As a result, the ease of operation during insertion or removal of the tape unit 60 and the paper supply cassette 70 can be improved.

Further, when the belt unit 60 and the paper supply cassette 70 are withdrawn from the main casing 2 as shown in fig. 15, a large space is formed below the image forming portion 5. When the sheet P is jammed in, for example, the fixing section 19, the user can easily take out the sheet P from the inside of the main casing 2 by inserting a hand into this large space from the front.

With this color laser printer 401, the insertion/removal path 100 extends horizontally without being curved, and the tape unit 60 can move in a straight line from the start of the ejection of the main casing 2 to the completion of the ejection. Further, the belt unit 60 can be moved in a straight line along the insertion/removal path 100 with respect to the main casing 2 from the start to the end of the mounting. For this reason, the operation of inserting or removing the belt unit 60 with respect to the main casing 2 can be performed extremely easily.

After the belt unit 60 is withdrawn from the main casing 2 as shown in fig. 16, the belt 38 and the belt cleaning device 40 are lifted from the belt unit 60 by turning the paper guide member 64 upward, either together or separately, and the belt 38 and the belt cleaning device 40 are taken out of the belt unit frame 61. This may facilitate replacement or servicing of the conveyor belt 38 and belt cleaning device 40.

According to this embodiment, the belt units 60, including the conveyor belt 38, may be removed along a linear insertion/removal path 100. Further, an angle is formed between the direction in which the upper side portion 38a of the conveying belt 38 is driven to move by the driving roller 36 and the direction in which the belt unit 60 is ejected, so that the contact between the conveying belt 38 and the photosensitive drum 33 is released by ejecting the belt unit 60.

That is, the upper side portions 38a of the conveying belt 38 are inclined upward with respect to the forward direction (the exit direction of the belt unit 60), and the upper side portions 38a are brought into contact with the photosensitive drums 33 from their front lower ends. This ensures that the withdrawal or movement of the belt unit 60 in the forward direction releases the contact between the surface of the conveyor belt 38 and the photosensitive drum 33. Thus, when the belt unit 60 is withdrawn in the forward direction along the linear insertion/removal (horizontal) path 100, the contact between the surface of the conveying belt 38 and the photosensitive drum 33 is released along the course of the withdrawal. Therefore, no additional operation is required to move the belt unit 60 in the direction crossing the horizontal direction in order to separate the transfer belt 38 from the photosensitive drum 33, and this can improve the ease in the operation of ejecting the belt unit 60 from the main casing 2.

On the other hand, when the belt unit 60 is inserted into the main casing 2, mounting the belt unit 60 along the linear insertion/removal path 100 can ensure that the surface of the conveyor belt 38 comes into contact with the photosensitive drum 33 after the mounting of the belt unit 60 is completed. In this manner, the conveyor belt 38 comes into contact with the photosensitive drum 33 after the belt unit 60 completes the movement in the direction of the insertion/removal path. Therefore, an additional operation of moving the belt unit 60 in a direction across or across the horizontal direction is not required, and thus the ease in the operation of mounting the belt unit 60 to the main casing 2 can be improved.

In this manner, additional movement of the belt unit 60 across the direction of movement along the insertion/removal path 100 is not necessary during the operation of inserting or removing the belt unit 60 relative to the main housing 2. Therefore, the structure for guiding the belt unit 60 can be simplified, and the production cost can be reduced.

Since the direction in which the belt unit 60 is withdrawn is substantially horizontal, the belt unit 60 can be withdrawn from the main casing 2 in a simple manner. This means that the ease of the insertion or removal operation of the belt unit 60 can be improved.

Further, since the belt unit 60 is withdrawn in the direction perpendicular to the rotation shaft 33a of the photosensitive drum 33, the contact between the surface of the conveying belt 38 and the photosensitive drum 33 can be released immediately after the belt unit 60 starts moving in the direction of withdrawing from the mounting position of the belt unit 60. For this reason, sliding contact between the conveyor belt 38 and each photosensitive drum 33 can be prevented. This can prevent damage to the photosensitive drum 33 or the conveying belt 38 due to sliding contact between the conveying belt 38 and the photosensitive drum 33.

The photosensitive drum 33 is disposed along the moving direction of the conveying belt 38 of the belt unit 61. When the belt unit frame 61 starts moving in the withdrawal direction from the mounting position in fig. 13, the conveyor belts 38 are separated from the respective photosensitive drums 33 simultaneously with each other.

Since the movement of the belt unit 60 is guided by the belt unit guide 83, the belt unit 60 can be withdrawn from the main casing 2 in a simple manner. This can improve the ease of the insertion and removal operations of the belt unit 60.

As shown in fig. 13, the tape unit 60 and the paper feed cassette 70 are arranged so as to partially overlap each other in the ejection direction of the tape unit 60, i.e., in the horizontal direction, and the size of the color laser printer 1 in the horizontal direction can be reduced.

Further, as shown in fig. 15, the tape unit 60 and the paper feed cassette 70 are disposed so as to partially overlap each other in a direction perpendicular to the ejecting direction of the tape unit 60, i.e., in the perpendicular direction, and the size of the color laser printer 1 in the perpendicular direction can be reduced. Therefore, by moving the tape unit 60 in the removing direction, the lower front portion of the tape unit 60 pushes the paper supply cassette 70 forward, so that the tape unit 60 and the paper supply cassette 70 can be removed together from the main casing 2.

Further, since the terminal 91 is provided at the end on the downstream side in the mounting direction of the belt unit 60, the terminal 91 is not exposed until the belt unit 60 is completely removed from the main casing 2. In this way, the user is prevented from touching the terminal 91.

Further, since the electrodes 92 are provided on the downstream side of the mounting direction of the belt unit 60 thereof in the main casing 2, it is possible to prevent the user from touching the electrodes 92. Thus, the terminal 91 and the electrode 92 can be prevented from being contaminated.

Since the terminals 91 are arranged in a row in the width direction, when the tape unit 60 is mounted in the main casing 2, connections between the plurality of terminals 91 and the electrodes 92 can be achieved simultaneously.

The terminal 91 and the electrode 92 are disposed in such a positional relationship that the conveyor belt 38 is brought into contact with the photosensitive drum 33 at the same time as or after the connection between the terminal 91 and the electrode 92 is achieved in the process of mounting the belt unit 60 to the main casing 2. Therefore, after the conveyor belt 38 comes into contact with the photosensitive drum 33, it is not necessary to further move the belt unit 60 in the backward direction for making the connection between the terminal 91 and the electrode 92. Sliding contact between the conveyor belt 38 and the photosensitive drum 33 can be prevented. Thus, damage to the photosensitive drum 33 or the transmission belt 38 due to sliding contact between the transmission belt 38 and the photosensitive drum 33 can be prevented.

When the belt unit 60 is withdrawn from the main casing 2 and the nip of each photosensitive drum 33 and the conveying belt 38 is released, each transfer roller 39 is moved upward by the elastic force of the compression spring 44. As a result, the upper side portion 38a of the conveyor belt 38 moves upward as shown in fig. 15.

Note that the vertical position of each process cartridge 30 is higher by a predetermined amount a than the process cartridge 30 adjacent to the rear side thereof. When the belt unit 60 is mounted to the mounting position in the main casing 2 as shown in fig. 13, each transfer roller 39 is urged upward by a compression spring 44 (see fig. 19) and the conveying belt 38 is sandwiched between each transfer roller 39 and the corresponding photosensitive drum 33. The moving direction in which the belt unit 60 is withdrawn from the mounting position is the horizontal direction, and therefore is perpendicular to the direction in which the transfer roller 39 is urged by the compression spring 44. Therefore, when the belt unit 60 is moved forward from the mounting position to be withdrawn from the main casing 2, the transfer roller 39 is moved upward by an amount B due to the elastic force of the compression spring 44, so that the conveyor belt 38 is lifted upward, that is, in the direction in which the compression spring 44 acts, by an amount B.

According to the present embodiment, the amount of shift a between the vertical positions of the image forming sections 17 adjacent in the front-rear direction, that is, the amount of shift a between the lower edges of the adjacent photosensitive drums 33 has a value such that the value C obtained by subtracting the lifting amount B of the conveyor belt 38 from the amount of shift a is greater than 0. In other words, the offset amount a is larger than the lift amount B.

Thus, the belt unit 60 supports each transfer roller 39 in such a manner that the lifting amount B of the conveying belt 38 at the corresponding transfer roller 39, which occurs when the belt unit 60 moves in the forward direction from the mounting position, is smaller than the offset amount a between the vertical mounting positions of the image forming sections 17 disposed adjacent to each other in the front-rear direction.

For this reason, when the belt unit 60 is moved forward from the mounting position so as to be withdrawn from the main casing 2, it is possible to ensure that a gap is formed between the conveyor belt 38 and the lower edge of the photosensitive drum 33. The conveying belt 38 does not contact the lower edge of the photosensitive drum 33. Therefore, even in the case where the conveyor belt 38 is lifted, the sliding contact between the conveyor belt 38 and the photosensitive drum 33 can be reliably prevented. As a result, damage to the photosensitive drum 33 or the conveying belt 38 due to friction between the conveying belt 38 and the photosensitive drum 33 can be prevented.

According to the present embodiment, the plurality of photosensitive drums 33 are arranged along the moving direction of the conveying belt 38. By the movement of the belt unit 60 in the withdrawing direction, the contact between the conveying belt 38 and the plurality of photosensitive drums 33 is mutually simultaneously released. Therefore, an additional operation of moving the belt unit 60 in a direction crossing or crossing the moving direction is not required, and thus the ease of operation in removing the belt unit 60 from the main casing 2 can be improved.

< modification >

In the above-described embodiment, the transfer belt 38 is composed of a plurality of belt strips arranged in the width direction with an inter-strip gap therebetween. However, the conveyor belt 38 may be constituted by a single conveyor belt having no gap therebetween.

In this case, each bias line 93 is modified to first extend in the width direction from the terminal end 91 outward toward the width edge of the conveyor belt 38, and then to bend upward so as to pass through the gap between the width edge of the conveyor belt 38 and the left or right side plate 65 or 66 before finally reaching the left or right side end of the corresponding transfer roller 39. The bias line 96 may be modified similarly to the bias line 93.

The terminal 91 may further include a terminal for electrically grounding the belt unit frame 61.

Similarly to the color laser printer 201 according to the modification of the first embodiment, the configuration of the present embodiment may be modified to a color laser printer 501 as shown in fig. 21 such that the conveyor belt 38 serves as an intermediate transfer belt onto which toner is temporarily transferred before being transferred from the conveyor belt 38 to the recording paper P. In this case, an additional transfer roller 139 is installed in the belt unit 60.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit of the invention.

For example, in the above-described embodiment, images are formed using four colors of magenta, yellow, cyan, and black. However, it is also possible to form an image using only three colors of magenta, yellow, and cyan, using only two colors, or using only one color.

The present invention can be utilized to other various kinds of image forming apparatuses such as an image forming apparatus equipped with a facsimile function.

In the above-described embodiment, the photosensitive drum 33 and the toner cartridge 35 are replaced with the process cartridge 30 as a whole. However, this structure may be modified so that only the toner cartridge 35 may be replaced. More specifically, the process cartridge 30 may be constituted by a combination of one N developing cartridge and one drum cartridge. The developing cartridge may include the toner cartridge 35, the supply roller 31, and the developing roller 32, and the drum cartridge may include the photosensitive drum 33. The developing cartridge may be detachably engaged with the drum cartridge. The developing cartridge can be detached from the drum cartridge and removed from the main cartridge casing 2 while the drum cartridge is still mounted in the main casing 2.

In the first embodiment, the image forming sections 17 for black, cyan, yellow, and magenta are arranged in this order from the rear to the front. In the second embodiment, the image forming sections 17 for black, cyan, magenta, and yellow are arranged in this order from the rear to the front. However, the image forming portions of the four colors can be arranged in any order.

In the first embodiment, the combination of the protrusion 27 and the recess 262 is located at one end of the scanner housing 26 in the scanning direction to adjust one end of the scanner unit 20 not to contact the supporting bracket 260, and the bolt 263 is located at the other end of the scanner housing 26 in the scanning direction to adjust the distance between the left end of the scanner unit 20 and the supporting bracket 260. However, the combination of the protrusion 27 and the recess 262 may be located closer to one end in the scanning direction to the other end, and the bolt 263 may be located closer to the other end in the scanning direction to the one end.

Also, in the second embodiment, the leaf spring 261 is located at one end of the scanner housing 326 in the scanning direction, and the bolt 363 is located at the other end of the scanner housing 326 in the scanning direction. However, the leaf spring 261 may be located closer to one end of the scanner housing 326 in the scanning direction than the other end, and the bolt 363 may be located closer to the other end of the scanner housing 326 in the scanning direction.

In the first and third embodiments, the combination of the protrusion 27 and the recess 262 is used to adjust the distance between the scan unit 20 and the support frame 260, and the bolt 363 is used to adjust the distance between the scan unit 20 and the support frame 260. In the second embodiment, the combination of the rotation shaft 329 and the bearing portion 360d is used to adjust the scanning unit 320 not to contact the support frame 360, and the bolt 363 is used to adjust the distance between the scanning unit 320 and the support frame 360. However, there are many other configurations that can be used to adjust the distance between the scan unit and the support frame without contacting the scan unit with the support frame.

Claims (39)

1. An image forming apparatus, characterized by comprising:

a housing;

an endless belt mounted in the casing and conveying either one of the developer image and the recording medium;

a plurality of process units installed in the casing, corresponding to the plurality of colors one by one, the plurality of process units respectively including a plurality of photosensitive drums, each photosensitive drum facing the endless belt;

a plurality of scanning units mounted in the casing and provided one for each of the photosensitive drums, each scanning unit scanning a surface of a corresponding photosensitive drum with light to form an electrostatic latent image, each process unit developing the electrostatic latent image with a developer of a corresponding color; and

a transfer portion which is mounted in the casing and transfers the developer image formed on the surface of each photosensitive drum to any one of the endless belt and the recording medium conveyed by the endless belt; and

a cartridge containing a recording medium, the cartridge being detachably mounted in the casing at a position below the endless belt;

the scanning unit and the processing unit are alternately arranged in the horizontal direction;

each scanning unit and each processing unit are inclined to the vertical direction;

at least a portion of each processing unit is inserted into or removed from the housing in an inclined orientation,

the endless belt is arranged such that its height increases in a direction in which the cartridge is withdrawn from the housing.

2. The imaging apparatus of claim 1,

each of the scanning units and each of the process units are inclined to a direction in which the cartridge is detached from the housing.

3. The image forming apparatus as claimed in claim 1, further comprising a plurality of covers attached to the housing to cover the plurality of process units from above in one-to-one correspondence with each other, the plurality of covers being openable and closable independently of each other.

4. The image forming apparatus as claimed in claim 1, wherein the endless belt conveys the recording medium thereon in the conveying direction, the endless belt being disposed to be inclined with a portion thereof on a downstream side in the conveying direction being lower than a portion thereof on an upstream side in the conveying direction.

5. The image forming apparatus as claimed in claim 1, wherein a straight line connecting the upper end surface of the scanning unit and the upper end surface of the process unit is substantially parallel to the inclination direction of the endless belt.

6. The image forming apparatus as claimed in claim 1, further comprising a sheet discharge tray receiving the recording medium on which the image is formed, the sheet discharge tray being disposed above the scanning unit and the process unit, the sheet discharge tray being inclined in a direction substantially parallel to an inclined direction of the endless belt.

7. An image forming apparatus as claimed in claim 1, wherein each of the photosensitive drums is rotatably supported in the vicinity of a lower end thereof in the corresponding process unit, the photosensitive drum being scanned by a light beam emitted from the vicinity of an upper end of the corresponding scanning unit.

8. The image forming apparatus as claimed in claim 2, wherein the portion of each of the scanning units including at least the upper end thereof has a width in a direction in which the scanning units and the process units are alternately arranged, the at least a portion of each of the scanning units being narrowed toward the upper end in a direction opposite to a direction in which the cartridge is withdrawn from the main casing, the width being reduced toward the upper end of the scanning unit;

wherein at least the portion of each of the process units including the upper end thereof has a width in a direction in which the scanning unit and the process units are alternately arranged, the at least a portion of each of the process units protruding toward the upper end in a direction opposite to a direction in which the cartridge is withdrawn from the main casing, the width increasing toward the upper end of the process unit.

9. The imaging apparatus of claim 1, wherein each scanning unit comprises:

a scanner housing;

a light source mounted in the scanner housing; and

a deflection unit installed in the scanner housing and deflecting the light beam emitted from the light source to scan the surface of the corresponding photosensitive drum; and

further comprising:

a plurality of support brackets, each support bracket fixedly mounted within the housing and supporting a respective scanner housing thereon;

an adjusting unit for adjusting at least a portion of the scanner housing away from the support bracket; and

an adjustment unit for adjusting an orientation of the scanner housing relative to the support frame.

10. The imaging apparatus of claim 9, wherein:

the scanner housing has a scanner surface facing the support frame;

the support frame has a frame surface facing the scanner surface;

the adjustment unit has:

a protrusion protruding from one of the scanner surface and the frame surface;

a receiving portion formed at the other of the scanner surface and the frame surface to receive the protrusion; and

an adjusting unit that pivots the scanner housing about a contact portion between the protrusion and the receiving portion to adjust an orientation of the scanner housing.

11. The imaging apparatus of claim 10, wherein the receiving portion includes a recess having a V-shaped cross section formed in the other of the scanner surface and the frame surface.

12. The image forming apparatus as claimed in claim 10, wherein the adjusting unit includes an urging member that urges the projection and the receiving portion toward a direction in which they approach each other.

13. The image forming apparatus as claimed in claim 10, wherein the scanner surface has a first end portion and a second end portion in a direction in which the deflection unit scans the light beam;

any one of the projection and the receiving portion is formed on a side of the scanner surface, the side being spaced from the first end portion by a distance smaller than a distance from the second end portion; and

the adjusting unit includes a distance adjusting unit that is provided at the other side of the scanner surface, the other side being at a distance from the second end portion smaller than the first end portion, and adjusts a distance between the second end portion of the scanner surface and the frame surface.

14. The imaging apparatus of claim 13, wherein the scanner surface has a plurality of positions in a direction perpendicular to the scanning direction, the frame surface has a plurality of positions in one-to-one correspondence with the plurality of positions on the scanner surface,

any one of the projection and the receiving portion is formed at each of the plurality of positions on the surface of the scanner,

the other of the projection and the receiving portion is formed at a corresponding position on the surface of the frame.

15. The image forming apparatus as claimed in claim 13, wherein the projection and the receiving portion both extend continuously in a direction perpendicular to the scanning direction.

16. The imaging apparatus according to claim 13, wherein the distance adjusting unit includes:

a leaf spring urging the second end portion of the scanner surface toward the frame surface; and

a bolt for adjusting the position of the second end portion of the scanner surface relative to the frame surface against the urging force of the leaf spring.

17. The imaging apparatus of claim 9, wherein:

the scanner housing has a scanner surface positioned to face the support bracket;

the support frame has a frame surface positioned to face the scanner surface;

the adjusting unit includes:

a rotation axis provided in the scanner housing to extend in a direction of the scanner surface; and

a bearing portion projecting from the frame surface in a direction defined to extend from the frame surface toward the scanner surface, the bearing portion rotatably receiving the rotary shaft; and

and an adjusting unit pivoting the scanner housing about a contact portion between the rotation shaft and the bearing portion to adjust an orientation of the scanner housing with respect to the support frame.

18. The image forming apparatus as claimed in claim 17, wherein the bearing portion includes a projection whose front edge is opened in a V-shaped cross section.

19. The image forming apparatus as claimed in claim 17, wherein the rotation axis is located substantially at a central portion of a scanning path of the deflection unit for scanning the light beam, and extends perpendicular to the scanning direction;

the scanner surface has a first end portion and a second end portion in a scanning direction in which the deflection unit scans the light beam along the scanning path; and

the adjusting unit includes:

a leaf spring provided on a side of the scanner surface, the side being spaced from the first end portion by a distance smaller than a distance from the second end portion, and urging the first end portion toward the frame surface; and

and a bolt provided on the other side of the scanner surface, the other side being spaced from the second end portion by a distance smaller than the distance from the first end portion, and adjusting the distance between the second end portion of the scanner surface and the frame surface against the urging force of the leaf spring.

20. The image forming apparatus as claimed in claim 16, wherein the scanner housing further has a mirror receiving the light beam scanned by the deflection unit and reflecting the light beam toward the photosensitive drum; and the combination of (a) and (b),

an angle α formed along an imaginary plane perpendicular to the scanning direction between the light beam before being reflected by the mirror and the light beam after being reflected by the mirror satisfies an inequality of 0 degrees < α <45 degrees.

21. The imaging apparatus of claim 20, wherein the support frame is disposed in the housing in a plurality of stages in parallel,

a through hole is formed through each support bracket so that a screwdriver can be inserted through the through hole to adjust the engagement amount of a bolt provided on a scanner housing supported on the support bracket next to each support bracket.

22. The imaging apparatus of claim 1, further comprising:

a plurality of rollers supporting an endless belt capable of circulating around the plurality of rollers; and

supporting the plurality of rollers such that the endless belt and the plurality of rollers form a belt unit frame integrally as a belt unit,

said housing having walls defining a linear insertion/removal path along which the tape unit frame is movable for detachable mounting within said housing, a predetermined mounting position being defined within the housing along the linear insertion/removal path to which the tape unit frame is movable along the linear insertion/removal path in an insertion direction and is movable along the linear insertion/removal path in a removal direction from the predetermined mounting position,

when the belt unit is mounted at a mounting position in the casing, the surface of the endless belt is brought into contact with each photosensitive drum,

the withdrawal direction and the direction in which the endless belt moves at a position where its surface comes into contact with the respective photosensitive drums form an angle that releases the contact between the surface of the endless belt and each photosensitive drum when the belt unit starts moving in the withdrawal direction from the mounting position.

23. The imaging apparatus of claim 22, wherein the linear insertion/removal path extends in a substantially horizontal direction.

24. The image forming apparatus as claimed in claim 22, wherein each photosensitive drum is rotatable about an axis thereof, the axis of the photosensitive drum extending substantially parallel to the rotational axis of the roller; and

the withdrawal direction is substantially perpendicular to the axis of each photosensitive drum.

25. The imaging apparatus of claim 22, wherein said housing wall includes a guide member for guiding the belt unit frame along the insertion/removal path.

26. The image forming apparatus as claimed in claim 22, further comprising a cassette accommodating the recording medium and detachably mounted in the housing, the cassette being capable of being withdrawn from the housing in the same direction as the withdrawing direction of the tape unit.

27. The imaging apparatus of claim 26, wherein the belt unit and the cassette are removable together from the housing.

28. The image forming apparatus as claimed in claim 26, wherein a portion of the belt unit overlaps the cartridge in a direction in which the belt unit and the cartridge are withdrawn when the belt unit is mounted in the housing at the mounting position.

29. The image forming apparatus as claimed in claim 22, wherein the belt unit frame includes a power supply terminal for supplying power to a portion of the belt unit, the power supply terminal being located at an end portion of the belt unit frame, the end portion being located at a downstream end of the belt unit with respect to an insertion direction of the housing.

30. The image forming apparatus as claimed in claim 29, wherein the power supply terminal includes a plurality of power supply terminals arranged in an axial direction of the rotation axis of the roller.

31. The imaging apparatus of claim 30, wherein the housing includes a plurality of electrodes, the electrodes being connected to the power supply terminal when the belt unit is mounted in the housing in the mounting position;

when the belt unit is moved in the insertion direction to the mounting position within the housing, the endless belt contacts the photosensitive drum after the power supply terminal has been connected to the electrode.

32. The imaging apparatus of claim 29, wherein:

the transfer portion includes a plurality of transfer rollers in one-to-one correspondence with the plurality of photosensitive drums,

the belt unit frame further supports the plurality of transfer rollers,

the power supply terminal includes a transfer bias terminal that supplies a transfer bias to the transfer roller to transfer the developer image from each photosensitive drum in a direction toward the endless belt.

33. The imaging apparatus of claim 32, wherein:

the belt unit frame further supports a cleaning roller, which cleans the endless belt and the neutralizing unit of the neutralizing endless belt,

the power supply terminal further includes at least one of the following terminals:

a cleaning bias terminal for providing a cleaning bias to the cleaning roller to clean the endless belt;

a neutralizing bias terminal for supplying a neutralizing bias to the neutralizing unit to electrically neutralize the annulus;

and a ground terminal for grounding the belt unit frame.

34. The imaging apparatus of claim 22, wherein

A plurality of photosensitive drums arranged in a direction in which the endless belt moves; and

when the endless belt frame starts moving in the retreating direction from the mounting position, the endless belt and the plurality of photosensitive drums are separated from each other at the same time.

35. The imaging apparatus of claim 34,

wherein a position of each of the photosensitive drums in a vertical direction perpendicular to both the withdrawal direction and the rotation axis of the roller is offset by an offset amount from another photosensitive drum located on an upstream side of each of the photosensitive drums in the withdrawal direction, an

Wherein the belt unit frame further supports thereon a pushing unit that moves a contact portion of the endless belt, which is in contact with the photosensitive drum when the belt unit is located at the mounting position, by an amount of movement in a vertical direction, which is smaller than the offset amount, when the belt unit is moved from the mounting position in the removing direction.

36. The image forming apparatus as claimed in claim 22, wherein the endless belt conveys the recording medium thereon.

37. The imaging apparatus of claim 36, further comprising:

a supply unit that picks up the recording medium from the cassette and supplies the recording medium to the endless belt when the belt unit is mounted in the casing; and

a discharge unit that receives and discharges a recording medium, the recording medium being conveyed by an endless belt and a developer image being formed by a photoreceptor drum,

the process unit is disposed on a path along which the endless belt conveys the recording medium from the supply unit to the discharge unit, thereby sequentially forming developer images of respective colors on the recording medium,

the direction in which the supply unit picks up the recording medium from the cassette and the direction in which the discharge unit discharges the recording medium are opposite to the medium conveying direction in which the recording medium is conveyed endless to pass through the image forming position where the image is formed.

38. The image forming apparatus as claimed in claim 37, wherein the process unit is inserted or removed in a direction inclined with respect to the medium conveying direction and a thickness direction of the recording medium conveyed by the endless belt perpendicular to the medium conveying direction.

39. The imaging apparatus of claim 37, wherein the processing unit and the scanning unit are disposed alternately in the media transport direction.