JP2001125393A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device made small in size as a whole by miniaturizing a transfer unit. SOLUTION: By turning a cam 37 and rocking a rocking arm 36 centering a supporting shaft 38, transfer rollers 22Y, 22M and 22C are moved up and down, and the carrying belt 21 of the transfer unit 20A laid over a driving roller 31, a driven roller 32 and a tension roller 33 and circularly moving in a transfer material carrying direction contacts with and separates from photoreceptor drums 10Y, 10C, 10M and 10BK, whereby a toner image is transferred to transfer material 100 carried by the belt 21. The center of the rocking of the arm 36 is positioned more outward in the transfer material carrying direction than the drum 10BK arranged at the end. Thus, the rocking angle of the arm 36 is made small and the unit 20A is miniaturized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a transfer belt for transferring a transfer material circulating with respect to a plurality of image carriers arranged in parallel. A tandem-type image forming apparatus for transferring a single-color image or a multicolor image selected by bringing an endless belt such as a transfer belt into or out of contact with the endless belt or a transfer material conveyed by the endless belt It is.

[0002]

2. Description of the Related Art As this type of tandem type image forming apparatus, for example, as shown in FIGS. 5 (a) and 5 (b), four photosensitive drums (image carriers) 41a and 41b arranged side by side are used. ,
41c, 42, a plurality of toner image forming means for individually forming a predetermined color toner image on the photoconductor drum, and a transfer material adsorbed on the outer peripheral surface to contact the transfer material with at least one photoconductor drum. A transfer belt (conveyor belt) 43 that circulates in the direction of arrow H to transfer, and a transfer brush 44 as a transfer unit that forms a transfer unit corresponding to the four photosensitive drums
a, 44b, 44c, and 44d, and a driving rotary roller 46 and a driven rotary roller 47 that hang the conveyor belt,
The transfer belt 43 is held so that the transfer material always comes into contact with the photosensitive drum 42 closest to the driving rotary roller 46 in the same posture, and the transfer belt 43 can be transferred or transferred to the other photosensitive drums. 2. Description of the Related Art An image forming apparatus is known which includes a belt moving unit for moving a material to a non-transferable position separated from a photosensitive drum so as to be in non-contact, and a control unit for selectively controlling the belt moving unit. JP 9
146383).

When full-color printing is performed by the image forming apparatus, as shown in FIG. 5A, a cam 63 rotates counterclockwise by 90 degrees, and a movable arm 55 rotates around a support shaft of a fixed support roller 56. Swing upward about 59. As a result, the movable support roller 57 of the movable arm 55 moves upward, and the transport belt 43 comes into contact with all four photosensitive drums 41a, 41b, 41c, 42. Then, each of the photosensitive drums 41a, 41
At the timing when the leading ends of the toner images formed on the transfer belts 43, 42c, and 42 are conveyed to the point facing the conveyance belt 43, the conveyance belt 43 is moved so that the printing start position of the transfer material coincides with the point. The transfer material is conveyed by the circulating movement, and the toner image on each photosensitive drum is sequentially transferred onto the transfer material by an electric field formed between each photosensitive drum and each transfer brush 44a, 44b, 44c, 44d.

On the other hand, when monochrome printing of only black is performed by the image forming apparatus, as shown in FIG. 5B, the cam 63 rotates clockwise by 90 degrees, and the movable arm 55 swings downward. Move. As a result, the movable support roller 57 moves downward and separates from the transport belt 43, and the transport belt 43
Maintains the contact state between the driving rotation roller 46 and the fixed support roller 56 with the photosensitive drum 42, and separates the fixed support roller 56 and the driven rotation roller 47 from the other photosensitive drums 41a, 41b, 41c. I do. At the timing when the leading end of the toner image formed only on the photosensitive drum 42 by the toner image forming means is rotated and conveyed to a point opposed to the conveyor belt 43, the printing start position of the transfer material is set at the opposed point. The transfer material is transported by the circulating movement of the transport belt 43 so that the toner images on the photosensitive drum 42 are transferred onto the transfer material by an electric field formed between the photosensitive drum 42 and the transfer brush 44d so as to coincide with each other. You.

[0005]

The tandem type image forming apparatus has a smaller number of units than an image forming apparatus (color copying machine) called a one-drum type in which an image carrier (photosensitive drum) and an optical system are one. It has many advantages, such as a high image formation speed per contact, the ability to use thick transfer materials, and a large degree of freedom in transfer paper size. However, in this tandem-type image forming apparatus, a plurality of image forming units as toner image forming means including a charger, an optical system, a developing device, and a cleaning device are provided around a plurality of photosensitive drums arranged in parallel. Since a large number of units such as a transfer unit including a transfer belt, a transfer unit, and a belt moving unit are arranged, the entire apparatus becomes large, and miniaturization thereof is one of the major technical problems.

Here, the belt moving means is also one of the factors for increasing the size of the entire apparatus. That is, in the tandem-type image forming apparatus, when performing single-color printing, as shown in FIG. 5B, it is necessary to avoid unnecessary deterioration of the photosensitive drums 41a, 41b, and 41c unrelated to single-color printing. For this reason, the transfer belts 44a, 44b, 44c and the transfer belt 43 are separated from the photosensitive drums 41a, 41b, 41c by the belt moving means. The amount of belt displacement during the separation operation of the conveyance belt 43 is determined by the fixed support roller 56 so that the separation operation of the conveyance belt 43 ensures a sufficient separation distance between the photosensitive drum 41c and the conveyance belt 43.
It is determined by setting the arrangement positions of and the driven rotary roller 47.

Therefore, in order to sufficiently separate the conveyor belt 43 from the photosensitive drum 41c, the swing center of the movable arm (swing member) 55 as the belt moving means (the fixed supporting roller is used in the illustrated belt moving means). 56 spindles 59
The center of the driven roller 47 needs to be shifted downward from the position shown in FIG. 5B as the position of the driven rotary roller 47 approaches the photosensitive drum 41c. Further, when the disposition position of the driven rotary roller 47 is shifted downward, it is necessary to increase the displacement amount of the movable support roller 57, so that the swing angle of the movable arm 55 must be increased. . In order to increase the swing angle of the movable arm 55, a space in the inner peripheral portion of the transport belt 43 for disposing the movable arm 55 is enlarged, and a cam for swinging the movable arm 55 is provided. It is necessary to shift the arrangement position of 63 to a lower side than the position shown in FIG.

Therefore, in this type of image forming apparatus, the swing center of the movable arm 55 as the belt moving means approaches the photosensitive drum 41c side and the movable arm 5
The larger the swing angle of 5, the larger the transfer unit becomes, and the larger the whole apparatus becomes. SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and an object of the present invention is to provide an image forming apparatus capable of reducing the size of a transfer unit and making the entire apparatus compact.

[0009]

In order to achieve the above object, an object of the present invention is to provide a method for forming a plurality of image carriers arranged in parallel and individually forming images on the plurality of image carriers. Image forming means, an endless belt circulating around a plurality of rollers so as to be in contact with the image carrier at least at one end, and an image carrier other than the image carrier at the end A belt pressing member that presses the back surface of the endless belt to move the endless belt toward and away from the image carrier, and moves the belt pressing member toward and away from the back surface of the endless belt by rocking. Transfer for transferring the image onto the endless belt or a transfer material conveyed by the endless belt in a state where the endless belt is in contact with the image carrier on which the image is formed, with the swing member. The swing unit The swing center of, and is characterized in that is positioned outward from the image bearing member disposed on said end.

In this image forming apparatus, the span from the swing center of the swing member to the belt pressing member is:
Because it is larger than that of the conventional image forming apparatus,
Slight swinging of the swinging member can greatly displace the belt pressing member. This makes it possible to reduce the swing angle of the swing member, reduce the space of the inner peripheral portion of the transfer unit, and use the means for swinging the swing member (the cam 63 in FIG. 5). ) Can be shifted to the transfer material transport path side (upper side in FIG. 5).

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the swing center of the swing member is passed over the endless belt provided on the side of the image carrier located at the end. And the center of rotation of the rollers.

In this image forming apparatus, since the support shaft of the roller can be used also as the support shaft of the swinging member, the transfer unit is simplified.

According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the belt pressing member and the transfer unit are formed of the same member.

In this image forming apparatus, the transfer unit is simplified because the belt pressing member and the transfer unit are formed of the same member.

According to a fourth aspect of the present invention, in the image forming apparatus of the first, second or third aspect, a plurality of the transfer means are provided so as to individually correspond to the plurality of image carriers, and The transfer means corresponding to an image carrier other than the image carrier located in the portion is provided on the swing member.

In this image forming apparatus, since the transfer means corresponding to the image carrier other than the image carrier located at the end is provided on the swinging member, the transfer means is provided. No transfer frame is required, and the transfer unit is further simplified.

According to a fifth aspect of the present invention, in the image forming apparatus of the first, second, third or fourth aspect, the transfer means comprises a transfer roller disposed opposite to the image carrier with the endless belt interposed therebetween. It is characterized by the following.

In this image forming apparatus, an endless belt is formed by the transfer roller without using a backup roller, which is essential when a fixed transfer member such as a transfer brush or a mylar is used as the transfer means. Since a stable transfer nip can be formed at a contact portion with the image carrier, the configuration is simplified as compared with a case where a fixed transfer member is used. In this image forming apparatus, for example, the image forming apparatus is wound around a transfer roller (located downstream of the backup roller) facing an image carrier located at the most downstream portion in the transfer material transport direction. In this state, the endless belt is moved toward and away from the other image carrier, and the inclination of the transfer material conveying surface when the endless belt is separated from the other endless belt is endless while the endless belt is wound around the backup roller. The size of the transfer unit is smaller than when the belt is moved toward and away from the unit, and the swing angle of the swing member is also small, so that the transfer unit is further downsized (details will be described later).

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a color electrophotographic copying machine (hereinafter simply referred to as "copier") which is an electrophotographic image forming apparatus will be described below. First, the overall configuration of the copying machine according to the present embodiment will be described. As shown in FIG. 1, the copying machine includes an image reading unit (hereinafter, referred to as “scanner unit”) 1 and an image forming unit (hereinafter, referred to as “printer unit”) 2.

The scanner section 1 forms an image of an original 4 placed on a contact glass 3 on a CCD 7 via an illuminating lamp, a mirror group 5 and a lens 6 (not shown), and outputs color image information of the original. For example, it is read as blue (hereinafter, referred to as “B”), Green (hereinafter, referred to as “G”), Red (hereinafter, referred to as “R”) color separation light, and converted into an electric image signal. The B, G, and R image signals thus obtained are subjected to color conversion processing by an image processing unit (not shown) based on the intensity levels. By this color conversion processing, color image data of yellow (hereinafter, referred to as “Y”), cyan (hereinafter, referred to as “C”), magenta (hereinafter, referred to as “M”), and black (hereinafter, referred to as “Bk”) Become.

In the printer section 2, the scanner section 1
An image is formed based on the color image data obtained in step (1). In the present embodiment, four photoconductor drums 10Y, 10C, 10M, and 10Bk are provided as image carriers, and each photoconductor drum corresponding to Y, C, M, and Bk from the paper feeding unit 15 side is substantially provided. They are arranged in parallel on the same plane.
Each photosensitive drum 10Y, 10C, 10M, 10Bk is
The charging devices 11Y, 11C, 11M, and 11Bk serving as charging means provided for the respective components uniformly charge the surface, for example, to a negative polarity. Each of the charged photosensitive drums 10Y, 10C, 10M, and 10Bk is
Optical writing is performed by optical writing units 12Y, 12C, 12M, and 12Bk provided for each of the photosensitive drums. As a result, an electrostatic latent image corresponding to each image data is formed on each photosensitive drum. The electrostatic latent images are developed by developing devices 13Y, 13C, 13M, 13B as developing means provided for each of the photosensitive drums.
By k, reverse development is performed with each color toner charged to the negative polarity, and a toner image of each color is formed on each photosensitive drum.

Next, the registration roller 1 is
6, the transfer material 100 is transferred to each transfer area of the transfer material transport path formed between each photosensitive drum and the transfer unit 20.
Is fed. As the transfer material 100, ordinary copy paper, an OHP sheet, or the like can be used. The transfer unit 20 has a transport belt 21 that is wrapped around a plurality of drive rollers 31, a driven roller 32, and a tension roller 33 and circulates in a transfer material transport direction.
The transfer belt 21 is formed of a dielectric material such as a polyester film, and is charged with a charge for electrostatically attracting the transfer material 100 to a surface thereof by a charging brush 35 as a charging unit.

As a result, the transfer material 100 fed from the paper feed unit 15 is electrostatically attracted to the transfer belt 21 and is conveyed toward the left in FIG. Is done. At this time, the printing start position of the transfer material 100 is set at the timing when the leading end of each color toner image formed on each photosensitive drum is rotated and conveyed to each transfer area which is a point facing the conveyance belt 21. It is transported so as to coincide with the opposing point. Then, each photosensitive drum 10Y, 1
The toner images of the respective colors formed on 0C, 10M, and 10Bk are respectively transferred by transfer rollers 22Y, 22C, 22M, and 22Bk as transfer means disposed on the back side of the transfer belt 21 so as to face the respective photosensitive drums. Sequentially
The image is superimposed and transferred onto the transfer material 100. Specifically, the transfer belt 21 is charged by the transfer rollers 22Y, 22C, 22M, and 22Bk to a polarity (here, a positive polarity) opposite to the polarity of the toner, so that a negative polarity on each photosensitive drum is formed. The toner is attracted to the transfer belt 21 by electrostatic force and is transferred to the transfer material 100.

The transfer material 100 onto which the toner images of the respective colors have been transferred in this manner is separated from the transfer belt 21 by a separating device 23 as a separating device disposed at an end of the fixing device 26 as a fixing device. . Then, the transfer material 100 separated from the transfer belt 21 is conveyed to a fixing device 26, and after the toner image transferred onto the transfer material is fixed, the paper 100 is discharged outside the machine as a color image copy by a paper discharge roller 27. Is discharged. The charge accumulated on the transfer belt 21 is neutralized and neutralized by a belt neutralization device 24 as a neutralization unit after the transfer material 100 is separated. Further, scattered toner, paper dust, and the like adhering to the transfer belt 21 in the toner image transfer step and the like are removed by the cleaning blade 2
5a.

On the other hand, after the transfer of the toner image to the transfer material 100, each of the photosensitive drums 10Y, 10C, 10M, 10B
The transfer residual toner remaining on k is removed by cleaning blades of cleaning devices 14Y, 14C, 14M and 14Bk as cleaning means provided for each photosensitive drum. Each of the photosensitive drums thus cleaned is supplied to its own charging device 11Y,
It is charged again by 11C, 11M, and 11Bk, and the process proceeds to the next image forming step.

Next, the configuration of the transfer unit 20, which is a feature of the present invention, will be described. The transfer unit 20A shown in FIGS.
In addition to the transfer rollers 22Y, 22M, 22C, and 22Bk, a belt pressing member, which corresponds to a belt moving unit of the conventional transfer unit shown in FIGS. And a swing member that swings toward and away from the rear surface of the transport belt 21 by swing. The transport belt 21 of the transfer unit 20A is always in contact with the photosensitive drum 10Bk located at the left end in FIG.
The driving roller 31, the driven roller 32, and the tension roller 33 are wound around.

In the transfer unit 20A, as shown in FIGS. 2A and 2B, transfer rollers 22Y, 22M, 22C and 22Bk as transfer means are provided.
It is configured to also be used as the belt pressing member. Thereby, each transfer roller 22Y, 22M, 22
C, 22Bk and the belt pressing member are formed of the same member, and the transfer unit 20A is simplified. Further, the transfer rollers 22Y and 22Y as the transfer means and the belt pressing member corresponding to the respective photosensitive drums 10Y, 10C and 10M other than the photosensitive drum 10Bk located at the end.
M and 22C are provided integrally with a swing arm 36 as the swing member. Accordingly, a frame for disposing the transfer rollers 22Y, 22M, and 22C is not required, and the transfer unit 20A is further simplified.

When color printing is performed by using the transfer unit 20A, as shown in FIG. 2A, the cam 3 serving as a swing means for swinging the swing arm 36 is used.
7 rotates, and the swing arm 36 swings upward about the support shaft 38. Thereby, each of the transfer rollers 22Y, 22M, 2
2C moves upward, and the back surface of the conveyor belt 21 is pressed by the transfer rollers 22Y, 22M, 22C, and the conveyor belt 21 is moved to all the photosensitive drums 10Y, 10C, 10C.
M, 10Bk. Then, as described in FIG. 1, the transfer material 10 conveyed by the conveyance belt 21
The toner images of the respective colors are sequentially transferred onto 0.

On the other hand, when performing monochrome printing using only the photosensitive drum 10Bk, as shown in FIG. 2B, the cam 37 rotates about 180 degrees from the state shown in FIG. 2A. The swing arm 36 swings downward about the support shaft 38. As a result, the transfer rollers 22Y, 22M, and 22C move downward together with the swing arm 36, and the transfer rollers 22Y, 22M, and 22C move from the back of the transport belt 21.
Is separated from the photosensitive drum 10B
Contact only k. Then, the photosensitive drum 10Bk
Is transferred onto the transfer material 100 conveyed by the conveyance belt 21 only.

Here, the support shaft 38 of the swing arm 36
As shown in FIGS. 2A and 2B, the swing arm 3
6 is located at the end of the photosensitive drum 1
It is disposed so as to be located outside of the transfer material transfer direction from 0Bk. Thus, the transfer rollers 22Y and 22Y as the belt pressing members are moved from the swing center of the swing arm 36 to the transfer rollers 22Y and 22Y.
The span up to 22M and 22C is larger than that of the conventional image forming apparatus shown in FIGS. 5A and 5B. Therefore, in the transfer unit 20A, the transfer rollers 22Y, 22M, and 22C as the belt pressing members can be largely displaced by the slight swing of the swing arm 36. Thus, the swing angle of the swing arm 36 can be reduced, and the transfer unit 20A can be made compact.

FIG. 3 shows a schematic configuration of a transfer unit 20B used in a copying machine according to another embodiment of the present invention. The transfer unit 20B includes a roller (not shown) for swinging the swinging center of the swinging arm 36 as the swinging member over the transport belt 21 provided on the photosensitive drum 10Bk located at the end. Here, it is characterized in that it is made to coincide with the rotation center of the driving roller 31). In the transfer unit 20B, since the support shaft 31a of the drive roller 31 is also used as the support shaft of the swing arm 36, the transfer unit 20B is further simplified. Further, in the transfer unit 20B, the span from the swing center of the swing arm 36 to each of the transfer rollers 22Y, 22M, and 22C is the transfer unit 20A shown in FIGS. 2A and 2B.
Larger than that of. Therefore, this transfer unit 2
In the case of 0B, the swing angle of the swing arm 36 can be further reduced, and the transfer unit 20A can be made smaller.

In the transfer units A and B, the transfer rollers 22Y and 22Y, which also serve as the belt pressing members, are used.
The transfer units 22M, 22C, and 22Bk are used as transfer units. The transfer units include transfer brushes 28Y and 28B, such as a transfer unit 20C shown in FIGS. 4A and 4B.
A transfer member of a fixed system composed of M, 28C, 28Bk, Mylar or the like may be used. However, in the transfer unit 20C using such a fixed transfer member, as shown in FIGS. 4A and 4B, a backup roller 29Y is provided upstream of the transfer member in the transfer material transport direction. ,
29M, 29C and 29Bk are provided. For this reason, in the transfer unit 20C, there is a possibility that the number of components increases and the cost increases. On the other hand, in the transfer units A and B, the transfer rollers 22Y, 22M, 22
The cost of the transfer brushes C, 22Bk themselves is
Although it is higher than M, 28C and 28Bk, there is no need to use the above-mentioned backup roller, and as a result, the cost can be reduced as compared with the case of using a fixed transfer member.

In the case of this transfer unit 20C, another photosensitive drum is wound around a backup roller 29Bk facing the photosensitive drum 10Bk located at the most downstream part in the transfer material transport direction. 10M, 10C,
Since the transfer belt 21 is moved toward and away from the transfer belt 10Y, the inclination of the transfer material transfer surface when the transfer belt 21 is separated is adjusted by the transfer rollers 22Y, 22M, 22C, and 22C as the transfer means.
It is necessary to make it larger than the case where 22Bk is used. For this reason, in this transfer unit 20C, the swing angle of the swing arm 36 becomes larger than when the transfer roller is used as the transfer unit, and the transfer unit 20C becomes larger. On the other hand, when the transfer rollers 22Y, 22M, 22C, and 22Bk, which also serve as the belt pressing members, are used as the transfer unit, as in the transfer units A and B, the transfer unit is located at the most downstream portion in the transfer material transport direction. The transfer belt is wound around the transfer roller 22Bk, which is located downstream of the backup roller 29Bk and faces the photosensitive drum 10Bk, and is conveyed to the other photosensitive drums 10M, 10C, and 10Y. 21 are separated from each other. Therefore, in the transfer units A and B, the inclination of the transfer material transport surface when the transport belt 21 is separated is
Since the size of the transfer unit is smaller than that of the transfer unit 20C and the swing angle of the swing arm 36 is small, the size of the transfer unit is further reduced.

In this embodiment, the transfer unit provided with the transport belt 21 has been described. However, the present invention firstly transfers the image formed on the photosensitive drum to the intermediate transfer belt, and then transfers the image to the intermediate transfer belt. The present invention is also applicable to an image forming apparatus having a configuration in which an image primarily transferred to a belt is collectively transferred onto a transfer material. In this case, the size of the intermediate transfer belt unit including the intermediate transfer belt can be reduced.

[0035]

According to the first to fifth aspects of the present invention, it is possible to reduce the swing angle of the swing member, reduce the space of the inner peripheral portion of the transfer unit, and reduce the swing member. The arrangement position of the means for swinging can be shifted to the transfer material transport path side, so that there is an excellent effect that the transfer unit can be downsized and the entire apparatus can be downsized.

In particular, according to the second aspect of the present invention, the transfer unit can be simplified by using the support shaft of the roller for passing the conveyor belt as the support shaft of the swinging member. There is an excellent effect that cost can be reduced.

According to the third aspect of the present invention, since the belt pressing member and the transfer means are formed of the same member, the transfer unit can be further simplified, so that the apparatus can be formed at lower cost. There is an excellent effect.

According to the fourth aspect of the present invention, the transfer means corresponding to the image carrier other than the image carrier located at the end portion,
Since the transfer member is disposed integrally with the swinging member, a frame for disposing the transfer unit becomes unnecessary.
There is an excellent effect that the transfer unit can be further simplified and the apparatus can be configured at lower cost.

According to the fifth aspect of the present invention, a stable transfer nip can be formed at the contact portion between the transfer belt and the image carrier by the transfer roller without using a backup roller. The structure is simplified as compared with the case where a fixed transfer member is used as the means, and the transfer unit can be configured at low cost. Further, as compared with the case where a fixed transfer member is used as the transfer unit, the inclination of the transfer material transfer surface when the transfer belt is separated from the image carrier can be reduced, and the swing angle of the swing member can be reduced. Therefore, there is an excellent effect that an image forming apparatus having a smaller transfer unit can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2A is a schematic diagram illustrating an operation mode of a transfer unit when performing color printing by the image forming apparatus.
FIG. 3B is a schematic diagram illustrating an operation mode of the transfer unit when performing monochrome printing by the image forming apparatus.

FIG. 3 is a schematic configuration diagram of a transfer unit in an image forming apparatus according to another embodiment.

FIG. 4A is a schematic diagram illustrating an operation mode of a transfer unit when performing color printing by an image forming apparatus according to still another embodiment. FIG. 3B is a schematic diagram illustrating an operation mode of the transfer unit when performing monochrome printing by the image forming apparatus.

FIG. 5A is a schematic diagram illustrating an operation mode of a transfer unit when performing color printing by a conventional image forming apparatus.
FIG. 3B is a schematic diagram illustrating an operation mode of the transfer unit when performing monochrome printing by the image forming apparatus.

[Explanation of symbols]

2 Image forming unit (printer unit) 10Y, 10M, 10C, 10Bk Photoconductor drums 11Y, 11M, 11C, 11Bk Charging device 12Y, 12M, 12C, 12Bk Optical writing unit 13Y, 13M, 13C, 13Bk Developing device 14Y, 14M , 14C, 14Bk Cleaning device 15 Paper feed unit 16 Registration roller 20A, 20B, 20C Transfer unit 21 Conveyor belt 22Y, 22M, 22C, 22Bk Transfer roller 25 Cleaning unit 26 Fixing device 27 Discharge roller 28 Transfer brush 29 Backup roller 31 Drive Roller 32 Follower roller 33, 34 Tension roller 35 Charging brush 36 Swing arm 37 Cam 38 Shaft of swing arm

Claims (5)

[Claims] A plurality of image carriers arranged in parallel, image forming means for individually forming images on the plurality of image carriers, and an image carrier located at least at one end thereof Endless belt circulating around a plurality of rollers as described above, and the endless belt for moving the endless belt toward and away from an image carrier other than the image carrier located at the end. A belt pressing member for pressing the back surface of the belt, a swinging member for swinging the belt pressing member toward and away from the back surface of the endless belt, and an endless shape for an image carrier on which an image is formed. An image forming apparatus having a transfer unit for transferring the image onto the endless belt or a transfer material conveyed by the endless belt in a state where the belt is in contact with the belt, wherein the swing center of the swing member is Positioned outward from the image carrier disposed at the end An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein a center of the swing of the swing member is provided to the endless belt provided on the side of the image carrier positioned at the end. An image forming apparatus, wherein the image forming apparatus is matched with a rotation center. 3. An image forming apparatus according to claim 1, wherein said belt pressing member and said transfer means are constituted by the same member. 4. An image forming apparatus according to claim 1, wherein a plurality of said transfer means are provided so as to individually correspond to said plurality of image carriers, and said transfer means is located at said end. 4. The image forming apparatus according to claim 3, wherein transfer means corresponding to an image carrier other than the carrier is provided on the swing member. 5. An image forming apparatus according to claim 1, wherein said transfer means comprises a transfer roller disposed opposite to said image carrier with said endless belt interposed therebetween. Forming equipment.