JPH09185210A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a color image forming device which forms an image of high image quality. SOLUTION: A developing roller 23Y is so disposed as to rotate in the same direction as a moving direction of photoreceptor at a specific peripheral speed ratio with the photoreceptor belt 1. A color developing device 6 rotates round a center O, it is arranged downstream side of an optical writing position 5A in the direction of the rotation of the photoreceptor belt 1 and upstream side of a black developing unit and, further, in such a position that a distance from the optical writing position 5A is shorter than a distance obtained by subtracting the distance of the movement of the photoreceptor belt 1 during the color switch of the color developing device 6 from the distance of non-image formation obtained by subtracting the length of the maximum transfer paper, which can be outputted, from the length of the periphery of an intermediate transfer belt. By such arrangement and operation, the color developing device 6 can be rotated when an exposure process is not carried out, therefore it does not exert effect on the drive of the photoreceptor belt 1, and trouble, such a lateral streak, does not occur on an image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus, and more particularly to an electrophotographic color image forming apparatus for forming a color toner image.

[0002]

2. Description of the Related Art Conventionally, a color image forming apparatus generally applies electrophotography to enable multicolor reproduction. In these color image forming apparatuses, a latent image carrier is exposed with a color separation light image, each latent image formed is developed with a toner having a complementary color of the color separation light, and a plurality of toner images obtained are identical. An image forming apparatus such as a full-color copying machine that superimposes and transfers it on a transfer paper, or images to be reproduced in different colors are separately exposed on the latent image carrier and developed with developers of different colors. There is known a multicolor image forming apparatus or the like that transfers a plurality of toner images by superimposing them on the same transfer paper. Specific examples of Conventional Example 1 based on this method are listed below.

In the "multicolor electrophotographic apparatus" of Japanese Patent Publication No. 59-26954, a developing apparatus corresponding to each color component red, green, and blue is selectively moved to a first developing position provided on a moving path of an electrophotographic photosensitive member. And a black developing device provided corresponding to a second developing position different from the first developing position for developing the electrostatic latent image developed by the black developer, and a moving device for forming the electrostatic latent image to be developed with the black developer. And a transfer means for transferring the developed image onto a transfer material.

In the "color image forming apparatus" of Japanese Patent Application Laid-Open No. 62-85266, a primary latent image is formed on a photoconductor and a static image corresponding to one of the color separations is formed from the primary latent image for each rotation of the photoconductor. Development switching means comprising an electrostatic latent image forming means for developing an electric image and a plurality of developing devices which are switched for each rotation of the photosensitive member to occupy a development position and develop with toner of a color corresponding to the electrostatic image. And a transfer means for transferring the color image formed on the photoconductor by being developed a plurality of times onto the transfer material, and a removable cleaning means for cleaning the photoconductor after the transfer.

In the "image forming apparatus" of Japanese Unexamined Patent Publication No. 61-231572, one or a plurality of developing devices are provided, and each developing device moves from a developing operation position to a developing non-operation position and does not develop. The movement from the operating position to the developing operating position is performed except during the image exposure process or the transfer process.

The image forming apparatus of the prior art example 1 requires a plurality of developing devices, but if each developing device is constructed separately and arranged in parallel around the latent image carrier, the size of the device becomes large. There is a problem. Therefore, the specific examples of Conventional Example 2 are JP-A-60-254063 and JP-A-63-153.
In No. 258 or the like, a rotating body is arranged so as to be close to the latent image carrier, a plurality of developing devices are supported at the predetermined position on the rotating body, and each developing device is sequentially rotated and conveyed to the developing area. As a result, a rotary developing device using a one-component developer and a two-component developer for developing the latent image on the latent image carrier with each color toner has been developed and put into practical use.

In the developing device of the conventional example 2, although the black monochromatic image is generally most frequently formed, the black, cyan, magenta, and yellow developing devices must all be moved even in that case. In addition, it is unnecessary to add extra load to the transportation means. In addition, there are problems that toner is likely to be scattered during movement and that black toner easily mixes with other color developing devices. In order to solve the problem of the conventional example 2, the Japanese Patent Publication No. 59-59, which is a specific example of the conventional example 3.
No. 26954 and JP-A-62-85266,
An image forming device in which a developing device that develops with black toner is not included in the rotary developing device but is separately provided separately so that the other color toner developing devices are not moved when a black monochromatic image is formed. A device has been proposed.

[0008]

However, in the image forming apparatus of the conventional example 3, unless the arrangement of the black developing device and the color developing device and the order of operation are proper, the operation is wasteful and the print speed becomes slow. I have to do it.
Furthermore, the peripheral length of the transfer member is increased to increase the moving time of the developing device, or the rotary developing device such as a color developing device is rotated during optical writing. There is a problem that the driving of the image carrier is affected and defects such as horizontal stripes occur on the image. It is an object of the present invention to provide a color image forming apparatus that forms a high quality image.

[0009]

In order to achieve the above object, the color image forming apparatus according to the invention of claim 1 blackens the electrostatic image formed on the electrostatic image carrier around the electrostatic image carrier. A first developing device that develops with a developer and a plurality of developing devices that sequentially move to a developing position different from the developing position of the first developing device to develop an electrostatic image with a colored developer corresponding to the electrostatic image. A color image forming apparatus including a second developing device having a developing device, wherein the developing position of the second developing device is on the downstream side of the optical writing position on the electrostatic image carrier and at the first position. It is arranged on the upstream side of the phenomenon position of the developing device, and the distance from the optical writing position on the electrostatic image carrier to the developing position of the second developing device is from the non-imaging distance to the color switching of the second developing device. It is characterized in that it is shorter than the remaining distance minus the distance that the electrostatic image carrier moves.

A color image forming apparatus according to the invention of claim 2 is
A first developing device that develops an electrostatic image formed on the electrostatic image bearing member around the electrostatic image bearing member with a black developer, and a developing position different from the developing position of the first developing device. Move
A color image forming apparatus having a second developing device having a plurality of developing devices for developing an electrostatic image with a color developer corresponding to the electrostatic image, wherein the developing position of the second developing device is It is arranged on the downstream side of the optical writing position on the electrophotographic image carrier and on the upstream side of the phenomenon position of the first developing device, and the color switching time of the second developing device is changed from the non-imaging time to the electrostatic image. It is characterized in that it is shorter than the remaining time after subtracting the moving time of the electrostatic image carrier from the optical writing position on the carrier to the developing position of the second developing device.

The color image forming apparatus according to the invention of claim 3 is
A first developing device that develops an electrostatic image formed on the electrostatic image bearing member around the electrostatic image bearing member with a black developer, and a developing position different from the developing position of the first developing device. Move
A color image forming apparatus having a second developing device having a plurality of developing devices for developing an electrostatic image with a color developer corresponding to the electrostatic image, wherein the color switching operation of the second developing device is performed. It is characterized in that it is carried out other than during the developing operation of the first developing device.

The color image forming apparatus according to the invention of claim 4 is
A first developing device that develops an electrostatic image formed on the electrostatic image bearing member around the electrostatic image bearing member with a black developer, and a developing position different from the developing position of the first developing device. Move
A second developing device having a plurality of developing devices for developing an electrostatic image with a colored developer corresponding to the electrostatic image is provided, and toner images of a plurality of colors are formed on the electrostatic image carrier. Is a color image forming apparatus having an intermediate transfer member that sequentially transfers and transfers the images, and an image forming apparatus having a plurality of marks on the intermediate transfer member.
The developing operation of the second developing device is arranged downstream of the optical writing position on the electrostatic image carrier and upstream of the developing position of the first developing device, and the developing operation of the second developing device is performed more than the developing operation of the first developing device. It is characterized in that the reference mark on the intermediate transfer member is delayed for each print during continuous printing, and one print is output for each distance between marks added to four rotations of the intermediate transfer member.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a color image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown an embodiment of a color image forming apparatus of the present invention.

FIG. 1 is a diagram showing a full-color printer which is an example of the image forming apparatus of the present invention. In the printer of FIG. 1, a belt-shaped photosensitive member (latent image carrier) 1 is uniformly charged by a charging charger 4 and then scanned and exposed by a laser optical device 5 based on image information to electrostatically charge the surface. A latent image is formed. Here, the image information to be exposed is monochromatic image information in which a desired full-color image is decomposed into yellow, magenta, cyan, and black color information. The formed electrostatic latent image contains three developing means containing yellow, magenta, and cyan color toners, that is, a rotary type color developing device 6, and a black toner provided separately from the color developing device 6. By the black developing device 7 which is the developing means, the development is performed with predetermined yellow, magenta, cyan, and black toners, respectively, and each color image is formed on the photoconductor 1.

The color developing device 6 and the black developing device 7 described above.
Is provided with each developing roller which comes in close proximity to or in contact with the photoconductor belt 1 at a predetermined position, and has a function of visualizing the latent image on the photoconductor belt 1 by non-contact development or contact development. Reference numeral 10 denotes an intermediate transfer belt which is an intermediate transfer member. The intermediate transfer belt 10 is installed between rotating rollers 11 and 12 and is rotated by driving the rotating rollers 11 and 12.

The photoconductor belt 1 is installed between rotating rollers 2 and 3, and is driven by the rotating rollers 2 and 3 to form an arrow A in the figure.
Rotate in the direction. The intermediate transfer belt 10 in contact with the photoconductor belt 1 rotates in the direction of arrow B in the figure in synchronization with the photoconductor belt 1. As a result, each color image formed on the photoconductor belt 1 is applied with an appropriate voltage to the primary transfer bias brush 13 provided in the intermediate transfer belt 10, so that yellow, magenta, cyan, and black images are formed. For each single color,
The images are successively transferred and transferred onto the intermediate transfer belt 10.

The yellow, magenta, cyan, and black images superposed on the intermediate transfer belt 10 are transferred onto a transfer paper which is conveyed from a paper feed cassette (not shown) to a transfer unit via a paper feed roller and a registration roller. It is collectively transferred by 14. After the transfer is completed, the transfer paper is fixed by the fixing device 18 to complete a full-color image.

Reference numeral 15 is a waste toner collecting container including the cleaning blade 15A of the photosensitive belt 1, and 16 is a cleaning device for the intermediate transfer belt 10. The cleaning blade 16A of the cleaning device 16 is for cleaning the intermediate transfer belt 10 during image formation. Kept in a position away from the surface,
As shown in the drawing, the toner image is pressed against the surface of the intermediate transfer belt 10 only during cleaning after the transfer of the toner image onto the paper.

FIG. 2 shows an embodiment of a developing device relating to the image forming apparatus of the present invention. A rotary type (also referred to as a revolver type or a rotary type) color developing device 6 as a color developing device according to this embodiment, and a black developing device provided separately from the color developing device 6 in the vicinity of the photoconductor belt 1 described above. The container 7 is arranged. In this rotary type color developing device 6, a casing 20 forming a rotating body.
Is rotatably provided about a rotation center ◯ and is rotated in the direction of arrow C by a drive mechanism (not shown). Further, the casing 20 has a shape that divides the developing device into three parts, and thereby developing devices of respective colors 22Y, 22M, and 22C are formed.

FIG. 3 shows a state in which one developing device 22Y in the color developing device 6 is in the developing position. Each of the developing devices 22Y, 22M, 22C is provided with a cylindrical developing roller 23Y, 23M, 23C as a developer carrying member. The developing rollers 23Y, 23M and 23C are
The casing 20 is arranged so that a part thereof is exposed to the outside through an opening provided in the casing 20, and rotates in the direction of arrow C in the drawing in synchronization with color information to develop a corresponding electrostatic latent image.

The developing device of this embodiment is a developing device using a non-magnetic one-component developer. Each unit stores yellow, magenta, and cyan toners, and selectively rotates around the center of rotation ◯. Rotate to the developing position, and sequentially rotate the photoreceptor belt 1
A full-color image is formed by developing the electrostatic latent image formed above and superposing each developed image on the intermediate transfer belt 10 and the transfer paper as described above.

An embodiment of the developing device according to the present invention will be described below with reference to FIG. Color developing devices 22Y, 2
Since the 2M and 22C have the same form and the same operation, only the developing device 22Y for one color will be described here. In FIG. 4, the developing device 22Y is disposed below the photoconductor belt 1 serving as an electrostatic latent image carrier, and the electrostatic latent image formed on the photoconductor belt 1 above the developing device 22Y has a non-magnetic single component. Toner as a developer is supplied.

In the figure, reference numeral 22Y indicates (yellow).
The developing device is shown, and an opening is formed in the upper part of the developing device 22Y at the developing position. In this opening, a developing roller 23Y as a developer bearing member is arranged in the same direction as the photosensitive member moving direction (arrow D in the figure) at a predetermined peripheral speed ratio with the photosensitive member belt 1 so as to face the photosensitive member. It is arranged to rotate. Further, below the developing roller 23, a supply roller 31 as a toner supply member made of an elastic material such as foamed polyurethane slides on the developing roller 23 and slides on the developing roller 23 at a predetermined peripheral speed ratio. The developing roller 23 and the contact portion are provided so as to rotate in the same direction (arrow E in the figure).

On the downstream side of the supply roller 31 in the moving direction of the developing roller 23, a thin layer blade 32 made of an elastic body such as a stainless steel plate or urethane rubber having a thickness of about 0.1 mm is provided near one end of the opening. Developing roller 23 near the part
It is provided so as to contact with. Incidentally, reference numeral 33 in FIG. 4 denotes a screw-shaped first toner conveying member which will be described later, and conveys toner from the front side to the rear side in the drawing.

On the front side of the developing unit 22, the toner storage unit 3 is provided.
6 is provided (see FIG. 5 described later). The toner conveying member 33 is a screw-shaped first toner conveying member, and is arranged in parallel with the developing roller 23 and the supply roller 31 from the above-mentioned toner accommodating portion 36 to the other side plate of the developing device 6, Interlocks with the developing roller 23 and the supply roller 31 to convey the toner from the front side to the back side,
It is rotated at a predetermined peripheral speed ratio. The casing 20 is arranged so that a part thereof is in contact with the supply roller 31, and the developing roller 23, the supply roller 31, and the casing 20 form a toner carrying space 34 surrounding the toner carrying member 33.

FIG. 5 shows a cross section of the color developing device. FIG. 6 shows a perspective view of the entire color developing device. In these drawings, the screw-shaped first toner conveying member 33 is interlocked with the developing roller 23 and the supply roller 31 so as to convey the toner from the front side to the rear side in the drawing,
It is rotated at a predetermined peripheral speed ratio. By this rotation, the first toner transport member 33 transports the toner from the toner storage portion 36 into the toner transport space and supplies the toner onto the supply roller 31. The toner supplied onto the supply roller 31 is supplied from the supply roller 31 while being charged on the surface of the developing roller 23, and is carried on the surface of the developing roller 23. The toner carried on the surface of the developing roller 23 is made into a thin toner layer having a uniform thickness and a predetermined thickness by the blade 32.
The electrostatic latent image formed on the surface of the photosensitive belt 1 is developed by contact development.

By the way, the toner not used in the developing step is conveyed by the first toner conveying member 33 to the end portion of the developing device opposite to the toner accommodating portion 36. A space for toner circulation is provided outside the effective diameter portion of the developing roller 23 and the supply roller 31 in the axial direction. The toner carried by the first toner carrying member 33 to the end of the developing device drops to the lower part of the developing device 22 due to gravity.

Below the developing unit 22, a screw-shaped second toner conveying member 35 is arranged in parallel with the developing roller 23, the supply roller 31, and the first toner conveying member 33, and the first toner conveying member 33 is provided. The toner is rotated so as to convey the toner in the direction opposite to that of the toner conveying member 33, and the toner not used in the developing process is conveyed to the toner accommodating portion 36. First toner carrying member 33 and second toner carrying member 3
By appropriately setting the conveyance amount of No. 5, the toner can be supplied onto the supply roller 31 without detecting the toner amount in the developing device 22 and complicated supply amount control, the layout flexibility is large, and the cross section with respect to the photosensitive belt is large. It is possible to provide a small-sized developing device having a small occupation ratio. A toner cartridge 37 is removably mounted in the toner storage portion 36, and is mounted and replaced when the developing device 6 is newly mounted or when the toner is exhausted, so that the toner storage portion 36 always stores a required amount of toner. .

FIG. 7 shows a state in which the black developing device 7 is in the developing position. The black developing device 7 is a developing device of the type in which the black toner is contained in the developing container 41, and is a developing device integrally formed as a so-called developing cartridge whose life is replaced when the toner is out. Similarly to the developing device 22 of the color developing device 6, the developing roller 23 faces the photoconductor belt 1 so that the developing roller 23 rotates in the same direction as the moving direction of the photoconductor belt 1 at a predetermined linear velocity ratio. It is arranged.

Above the developing roller 23, a supply roller 31 made of an elastic material such as polyurethane foam slides on the developing roller 23 at a sliding portion and in the same direction as the developing roller 23 with a predetermined linear velocity ratio. It is provided to rotate. Further, a thin layer blade 32 made of a stainless thin plate having a thickness of about 0.1 mm or an elastic body such as urethane rubber.
However, one end thereof is provided so as to contact the developing roller 23.

In the developing container 41, a paddle 4 having a plurality of blade-shaped portions for stirring the toner in the vicinity of the thin layer blade 32.
2, the supply roller 31 and the developing roller 2 are provided.
A first agitator 43 and a second agitator 44 that convey and agitate the toner are provided on the third side.

The black developing device 7 is provided with a pressurizing means (not shown).
Pressure is applied in a direction away from the photosensitive belt 1, and the rotation of the cam 45 causes the developing roller 23 and the photosensitive belt 1 to rotate.
And are separated from each other.

Next, a more specific image forming apparatus of the first embodiment will be described with reference to FIG. As shown in the figure, the color developing device 6 is arranged on the downstream side of the optical writing position 5A and on the upstream side of the black developing device 7 with respect to the rotation direction of the photosensitive belt 1. Further, the color developing device 6 has a distance from the optical writing position from the non-image forming distance (intermediate transfer member peripheral length-maximum transferable paper length that can be output) to the photosensitive member during color switching of the color developing device 6. The belt 1 is arranged to be smaller than the remaining distance less the moving distance.

Specifically, the distance from the optical writing position on the photosensitive belt 1 to the developing position of the color developing device 6 is 24.
2 mm, the circumference of the intermediate transfer belt 10 is 393 mm, the maximum transfer paper that can be output is 297 mm in A4 length, and the distance that the photosensitive belt 1 moves during color change of the color developing device 6 is 3 mm.
It was set to 8.5 mm.

A timing chart showing this is shown in FIG. In FIG. 8, the vertical axis represents the position of each member arranged on the photoconductor belt 1, and the horizontal axis represents the actual movement distance. Also, the solid line indicates the operating state, and the broken line indicates the non-operating state. Also, the alternate long and short dash line indicates the synchronized position.

From this figure, the distance from the optical writing position on the photoconductor belt 1 to the developing position of the color developing device 6 (a in the figure) is from the non-image forming distance (b in the figure) of the color developing device 6. The optical writing position and the color developing device are arranged and operated so as to be smaller than the remaining distance obtained by subtracting the moving distance (c in the figure) of the photosensitive belt 1 during color switching.

By arranging and operating in this way, the rotation operation of the color developing device 6 can be performed during the non-exposure step, and horizontal stripes and the like are formed on the image without affecting the driving of the photosensitive belt 1. No problems will occur.

If the distance from the optical writing position on the photosensitive belt 1 to the developing position of the color developing device 6 (a in the figure) is
If the distance is greater than the remaining distance obtained by subtracting the distance (c in the figure) that the photosensitive belt 1 moves during the color switching of the color developing apparatus 6 from the non-image forming distance (b in the figure), rotation of the color developing apparatus 6 is performed. The exposure process is started during the operation, which affects the driving of the photoconductor belt 1 and causes defects such as horizontal stripes on the image.

Further, from this figure, if the color developing device 6 is arranged on the downstream side of the black developing device 7, for example, if the color developing device is arranged at the black developing position in the figure, the color developing device 6 is placed on the photosensitive belt 1. The distance from the optical writing position to the developing position of the color developing device 6 (a in the figure) increases. Therefore, in order to make it smaller than the remaining distance obtained by subtracting the distance (c in the figure) that the photosensitive belt 1 moves during color switching of the color developing device 6 from the non-image forming distance (b in the figure), the intermediate transfer is performed. It is necessary to increase the peripheral length of the belt 10 and increase the non-image forming distance (b in the figure), resulting in an increase in the size and cost of the entire image forming apparatus.

In the image forming apparatus of this embodiment, since the color developing device 6 is arranged on the upstream side of the black developing device 7, the peripheral length of the intermediate transfer belt 10 can be minimized, and as a result, the size of the entire image forming device can be reduced. Can be achieved.

Next, a more specific image forming apparatus of the second embodiment will be described with reference to FIG. In FIG. 9, the vertical axis represents the position of each member arranged on the photoconductor belt 1, and the horizontal axis represents the elapsed time. In this figure, the color switching time (d in the figure) of the color developing device is from the non-image forming time (e in the figure) to the photoconductor belt from the optical writing position on the photoconductor belt to the developing position of the color developing device. It is shown that the operation is performed so as to be shorter than the remaining time obtained by subtracting the moving time (f in the figure).

This is because the color developing device 6 is arranged on the downstream side of the optical writing position and on the upstream side of the black developing device 7 with respect to the rotation direction of the photosensitive belt 1, so that This is achieved because the distance from the optical writing position to the developing position of the color developing device can be reduced and the moving time (f in the figure) of the photosensitive belt during that time can be shortened.

By arranging and operating in this way, the color developing device 6 can be rotated during the non-exposure step, and horizontal stripes or the like are formed on the image without affecting the driving of the photosensitive belt 1. No problems will occur.

Further, in the image forming apparatus of the present embodiment, the color switching time (d in the figure) of the color developing device can be made longer, and as a result, the motor and gear for rotating the color developing device can be made smaller and lower. The cost can be reduced. Alternatively, since the non-image forming time (e in the figure) can be further shortened, the circumference of the intermediate transfer belt 10 can be minimized, and as a result, the overall size of the image forming apparatus can be reduced.

Next, a more specific image forming apparatus according to the third embodiment will be described with reference to FIG. 10 which is divided into three diagrams (a) to (c). FIG. 10 shows an outline of a timing chart of the image forming apparatus of this embodiment. The operation will be described. First, the photosensitive belt is driven, and at the same time, charging is performed by the charging charger. Next, prior to the exposure step, the color developing device is rotated by the rotation driving mechanism, and the cyan developing device is driven from the reference position so as to face the photoconductor belt. After that, an exposure process is performed to form a cyan electrostatic latent image on the photosensitive belt. When the electrostatic latent image moves to the developing position, it is developed by the cyan developing device. The toner image is transferred onto the intermediate transfer member by the primary transfer means. Next, the color developing device is rotated by the rotation driving mechanism, and the magenta developing device faces the developing position on the photosensitive belt. Further, a magenta electrostatic latent image is formed in synchronization with the toner image on the intermediate transfer member, and development is performed in synchronization with the movement of the electrostatic latent image to the developing position.

Next, similarly, yellow development is performed. After the yellow development, the color developing device is rotated by the rotation driving mechanism, and all the developing devices are stopped at the reference position where they do not face the photoconductor belt. Finally, a black electrostatic latent image is formed in synchronism with the toner image on the intermediate transfer member, and the black developing device moves to the cam in synchronization with the electrostatic latent image moving to the developing position. The rotation moves to the development position on the photoconductor belt, and black development is performed.

At this time, since the black developing device is on the downstream side of the color developing device and the developing operation of the color developing device is executed prior to the developing operation of the black developing device, the color developing device is operated before the black developing device is executed. The rotating operation of the developing device can be terminated, and the rotating operation of the color developing device does not affect the driving of the photoconductor belt during the black development, so that a defect such as a horizontal stripe does not occur on the image.

Conversely, if the developing operation of the black developing device is executed before the developing operation of the color developing device, the developing operation of the black developing device is completed because the black developing device is located downstream of the color developing device. After that, the time from the start of the developing operation of the color developing device becomes short, and the rotating operation of the color developing device must be performed during black development. As a result, the driving of the photoconductor belt is affected, and defects such as horizontal stripes occur on the image.

Next, during continuous printing, after the optical writing of the first black image information is completed, the reference mark on the intermediate transfer member is delayed by one and the second cyan image information is optically written. Try to do it. As a result, the time from the end of the developing operation of the first black developing device to the start of the developing operation (cyan) of the second color developing device can be increased accordingly.
The rotation operation of the second color developing device can be performed after the completion of the development operation of the first black developing device and before the second cyan development operation. Therefore, the rotation of the color developing device does not affect the driving of the photoconductor belt during black development, and a defect such as horizontal stripes does not occur on the image.

In the image forming apparatus of the present embodiment, the peripheral length of the intermediate transfer belt can be minimized by arranging and operating the developing devices as described above, and as a result, the overall size of the image forming apparatus can be reduced. Can be measured.

[0051]

As is apparent from the above description, claim 1
In the image forming apparatus described in (1), the developing position of the second developing device is arranged on the downstream side of the optical writing position of the electrostatic image carrier and on the upstream side of the developing position of the first developing device. The distance from the optical writing position on the electrophotographic image carrier to the developing position of the second developing device is the second image forming distance from the non-image forming distance (intermediate transfer member peripheral length-maximum transferable paper length that can be output). The distance is set to be shorter than the remaining distance less the moving distance of the electrostatic image carrier during color change of the developing device. Therefore, it is possible to drive the latent image carrier without slowing the print speed or increasing the circumference of the intermediate transfer member, and without rotating the rotary developing device that is a color developing device during optical writing. It does not affect and does not cause defects such as horizontal stripes on the image.

In the image forming apparatus of the second aspect, the developing position of the second developing device is located downstream of the optical writing position on the electrostatic image carrier and at the developing position of the first developing device. The electrostatic image carrier disposed on the upstream side, from the non-image forming time to the color switching time of the second developing device, from the optical writing position on the electrostatic image carrier to the developing position of the second developing device. It is set shorter than the remaining time after subtracting the travel time of. Therefore, it is possible to drive the latent image carrier without slowing the print speed or increasing the circumference of the intermediate transfer member, and without rotating the rotary developing device that is a color developing device during optical writing. It does not affect and does not cause defects such as horizontal stripes on the image.

In the image forming apparatus according to the third aspect, since the color switching operation of the second developing device is performed except during the developing operation of the first developing device, the driving of the latent image carrier is affected. No problems such as horizontal stripes appear on the image.

In the image forming apparatus according to the present invention, a plurality of marks are provided on the intermediate transfer member, and the developing position of the second developing device is located downstream of the optical writing position on the electrostatic image carrier. And the upstream side of the developing position of the first developing device, the developing operation of the second developing device is performed first by the developing operation of the first developing device, and during continuous printing, an intermediate operation is performed for each print. The reference mark on the transfer body is delayed by one, and one print is output every four rotations of the intermediate transfer body + mark distance. Therefore, the color switching operation of the second developing device is performed except during the developing operation of the first developing device without slowing down the printing speed or increasing the circumference of the intermediate transfer member. It does not affect the driving of the and does not cause a defect such as a horizontal stripe on the image.

[Brief description of the drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a vertical cross-sectional configuration diagram showing a configuration example of a developing device.

FIG. 3 is a vertical cross-sectional configuration diagram showing a configuration example of a developing device.

FIG. 4 is a vertical cross-sectional configuration diagram showing one developing device in the rotary developing device.

FIG. 5 is a cross-sectional view showing a configuration example of a color developing device.

FIG. 6 is a perspective view of the entire color developing device.

FIG. 7 is a diagram showing a state in which the black developing device is in a developing position.

FIG. 8 is a timing chart showing an operation example 1.

FIG. 9 is a timing chart showing an operation example 2;

FIG. 10 is a timing chart showing an operation example 3;

[Explanation of symbols]

 1 Photosensitive Belt 2, 3 Photosensitive Belt Rotating Roller 4 Charging Charger 5 Laser Optical Device 5A Optical Writing Position 6 Rotary Type Developing Device 7 Black Developing Device 10 Intermediate Transfer Belt 11, 12 Intermediate Transfer Belt Rotating Roller 13 Primary Transfer bias brush 14 Transfer roller 15 Waste toner collecting container 15A Cleaning blade 16 Cleaning device 16A Cleaning blade 18 Fixing device 20 Casing 22 Developing device 23 Developing roller 31 Supplying roller 32 Thin layer blade 33 First toner conveying member 34 Toner conveying space 35 Second toner conveying member 36 Toner accommodating portion 37 Toner cartridge 41 Developing container 42 Paddle 43 First agitator 44 Second agitator 45 Cam

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Noriyuki Kimura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A first developing device for developing an electrostatic image formed on the electrostatic image bearing member around the electrostatic image bearing member with a black developer, and a developing position of the first developing device. A color image forming apparatus provided with a second developing device having a plurality of developing devices that sequentially move to different developing positions and develop an electrostatic image with a color developer corresponding to the electrostatic image, The developing position of the developing device is arranged on the downstream side of the optical writing position on the electrostatic image carrier and on the upstream side of the phenomenon position of the first developing device. The distance from the writing position to the developing position of the second developing device is shorter than the remaining distance less the non-imaging distance minus the distance that the electrostatic image carrier moves during color switching of the second developing device. A color image forming apparatus characterized by the above. 2. A first developing device for developing an electrostatic image formed on the electrostatic image bearing member on the electrostatic image bearing member with a black developer, and a developing position of the first developing device. In a color image forming apparatus provided with a second developing device having a plurality of developing devices that sequentially move to different developing positions and develop an electrostatic image with a color developer corresponding to the electrostatic image, The developing position of the developing device is arranged downstream of the optical writing position on the electrostatic image carrier and upstream of the phenomenon position of the first developing device, and the color switching time of the second developing device is set. However, from the non-imaging time,
A color image forming apparatus, which is shorter than the remaining time after subtracting the moving time of the electrostatic image carrier from the optical writing position on the electrostatic image carrier to the developing position of the second developing device. 3. A first developing device for developing an electrostatic image formed on the electrostatic image bearing member on the electrostatic image bearing member with a black developer, and a developing position of the first developing device. In a color image forming apparatus provided with a second developing device having a plurality of developing devices that sequentially move to different developing positions and develop an electrostatic image with a color developer corresponding to the electrostatic image, A color image forming apparatus, wherein the color switching operation of the developing device is performed except during the developing operation of the first developing device. 4. A first developing device for developing an electrostatic image formed on the electrostatic image bearing member around the electrostatic image bearing member with a black developer, and a developing position of the first developing device. A second developing device having a plurality of developing devices for sequentially moving to different developing positions and developing an electrostatic image with a color developer corresponding to the electrostatic image is provided and formed on the electrostatic image carrier. A color image forming apparatus having an intermediate transfer member that sequentially transfers the transferred toner images of a plurality of colors and carries the toner images in an overlapping manner, the image forming apparatus having a plurality of marks on the intermediate transfer member. The developing position of the second developing device is arranged downstream of the optical writing position on the electrostatic image carrier and upstream of the developing position of the first developing device, and the developing operation of the second developing device is performed. Is performed before the developing operation of the first developing device, and during continuous printing, the intermediate transfer member Delaying the reference mark, color image forming apparatus according to claim 1 to print output every distance between marks to be applied to the intermediate transfer member 4 rotates.