JPH09274386A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve speedy switching between development and nondevelopment (switching of color) in color image forming device without affecting images being formed. SOLUTION: An entire developing unit 2C comes into contact with and moves apart from a photoreceptive drum 1 by means of an eccentric cam 3 quickly. The developing unit 2C incorporates screws 5 and 6, a developing roller 4C, and a carrying roller 7. During development, developer circulated, mixed, and stirred by the screws 5 and 6 is drawn up and carried by the carrying roller 7, and is transferred to the developing roller 4C in an opposite area D. After the thickness of the developer is regulated by a doctor 10, the developer is brought into contact with a photoreceptive drum 1 to be subjected to development. The developer is carried into the unit again, and is caused to fall onto the screws 5 and 6 by means of gravity, centrifugal force, and so on in an area E where a material force is relatively weak.

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 such as a color copying machine or a color printer using an electrophotographic method, and more particularly to an improved developing apparatus thereof.

[0002]

2. Description of the Related Art A color image forming apparatus of this type has a black (B) color around a photosensitive drum.
k), cyan (C), magenta (M), yellow (Y)
4 developing devices are arranged, the latent images on the photoconductor drums are developed by developing devices of predetermined colors, respectively, and sequentially transferred to transfer paper or an intermediate transfer member to obtain a four-color superimposed image. However, it is necessary to prevent the color mixture by deactivating the other developing device while one developing storage device is operating. For example, JP-A-55-3707, JP-B-7-21673, and JP-A-6-6
JP-A No. 2-15562 discloses a technique of preventing color mixture by having a contacting / separating mechanism of a developing device and retracting the photosensitive member from the photoconductor during non-developing. However, in these technologies, the developer on the portion of the developing roller that faces the photoconductor remains in a spiked state as during development,
A considerable distance has to be moved and retracted until the non-developed state is reached, and it takes time to switch between development and non-development, which in turn requires time to switch colors, making it impossible to speed up copying or printing. Also, there is a problem that space cannot be saved because a space to save is also required. It is possible to deal with this by increasing the moving speed of the developing device at the time of switching, but there is a problem that there is a concern that the influence of vibration or the like on the image may occur.

Further, in JP-A-63-186275, JP-A-1-254978, and JP-A-2-302768, there is provided a contacting / separating mechanism of a developing device, and the developing roller is stopped at the time of retreat and slightly rotated. , A technique for adjusting the spikes is disclosed. These techniques are disclosed in the above-mentioned JP-A-55-3707.
Although it is an improvement over the technology of No. etc., if the developing roller is slightly rotated at the time of non-developing switching, it only stops to prepare the spikes, and there is a problem that it takes some time for color switching. It remains.

Further, Japanese Patent Publication No. 58-10748 and Japanese Patent Laid-Open No. 58-34469 have a developer scraping member which can be brought into contact with and separated from the surface of the developing roller, and the scraping member is provided on the developing roller during non-developing. A technique is disclosed in which the agent on the developing roller is removed by bringing them into contact with each other to prevent color mixture. In these techniques, it takes a certain amount of time to sufficiently scrape off the developer on the developing roller until a non-developed state is reached, and there is a problem that the color switching time is shortened and the speed map for copying and printing is disadvantageous. Further, in order to efficiently scrape off the developer, the scraping member must be brought into contact with the roller, and in addition, the roller surface is generally provided with a groove or blasted due to developer transport performance. Since it has been processed, both the scraping member and the roller member have a problem in durability.

Further, Japanese Patent Laid-Open No. 63-229466 has a carrying roller for supplying a developer to the developing roller.
A technique is disclosed in which color mixing is prevented by stopping the feeding roller during non-developing and cutting off the supply of the agent to the developing roller. With this technology, even if the auxiliary magnet roll is stopped and the supply of the developer to the main magnet roll is stopped, there is some agent that remains, so it takes time to reach a completely non-developed state, and the development on the photoreceptor is After that, in order to prevent the developer that has been transported by the main magnet roll and returned into the developing device from being supplied again (to prevent the developer from rotating with the developer), there are restrictions on the magnetic force distribution characteristics and layout of the magnet roller. However, there is a problem in that it is disadvantageous in cost because it is necessary to have a plurality of magnet rollers.

Further, in Japanese Patent Publication No. 25880/1994, the developing roller is rotated in the direction opposite to that at the time of non-developing so that the portion of the developing roller on which no agent is adhered faces the photoconductor. Therefore, a technique for preventing color mixture is disclosed. In this technology, magnetic poles of the same magnet are arranged adjacent to each other,
Although the area where the developer does not adhere is set, in general, the magnetic force is not zero in this area, and the virtual poles S'1, S'2, N'1 which are repulsive magnetic fields as in the example shown in FIG. Exists. The magnetic force of these virtual poles is small compared to the magnetic force of the pole in which the magnetic pole is arranged, and it is possible to set the magnetic force so that the developer does not adhere, but the magnetic pole is not arranged and the portion is There are many restrictions to control.
Further, the developer does not adhere to the magnetic pole S1 or S2 at the same time.
It is necessary to reliably separate the agent that has been conveyed up to the roller by gravity or centrifugal force, and there is a restriction on the layout of the roller itself. Further, as described above, in order to set the area where the developer does not adhere to such a degree that it is in the completely non-developed state, there are restrictions on the magnetic force distribution specification of the developing roller and the arrangement of the developing roller, and the arrangement of other components. There is a problem.

The present invention has been made in view of the above-mentioned conventional problems, and it is possible to switch between development and non-development at high speed without adversely affecting images and the like, and it is possible to perform color switching at a high speed, thereby achieving a high-speed color image. It is an object of the present invention to provide a color image forming apparatus that can be formed, has a high degree of freedom in designing layout, magnetic force distribution specifications, and the like, and has excellent durability of parts.

[0008]

A color image forming apparatus according to a first aspect of the present invention has a plurality of developing devices arranged around a photoconductor, and each developing device is arranged on the photoconductor during development. In a color image forming apparatus having a contacting / separating unit that moves close to and retracts from the photoconductor during non-development, the developing roller of each of the developing devices has a plurality of magnetic poles and includes the magnetic pole of the magnetic pole facing the photoconductor. A magnet roller in which a magnetic pole center angle between adjacent magnetic poles arranged on the downstream side in the rotation direction during development and on the upstream side of the magnetic pole facing the developer storage portion is wider than that between other adjacent magnetic poles. And a sleeve fitted to the outer periphery of the magnet roller so as to be able to rotate in the forward and reverse directions. When the non-developing mode is switched, the sleeve is rotated in the direction opposite to the direction for developing to remove the developer. And it features.

According to a second aspect of the present invention, the developing roller of each of the developing devices comprises a magnet roller having a plurality of magnetic poles inside and a sleeve rotatably fitted to the outer circumference of the magnet roller. A developer removing unit which is provided so as to be able to come into contact with and separate from the developing roller, and which comes close to the developing roller at a predetermined interval when switching the non-developing, and removes the developer on the developing roller. To do.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a sectional view showing a main part of an embodiment of the color image forming apparatus according to the present invention. The photosensitive drum 1 rotates in the direction of the arrow in the figure, and four developing units 2B, 2C, 2M, and 2Y of black (Bk), cyan (C), magenta (M), and yellow (Y) are arranged around the photosensitive drum 1. It is arranged. The latent image on the photosensitive drum 1 is developed by any one of the developing units 2B to 2Y of a predetermined color and sequentially transferred to a transfer paper or an intermediate transfer member to obtain a four-color superimposed image. .

Each color developing unit 2B, 2C, 2M, 2Y
Are arranged so that they are brought into contact with and separated from the photosensitive drum 1 by the eccentric cams 3, respectively, whereby the developing roller 4 incorporated in each of the color developing units 2B to 2Y.
The positions of B, 4C, 4M, and 4Y come into contact with and separate from the photosensitive drum 1. That is, the developing rollers 4B to 4Y are close to the photosensitive drum 1 at a predetermined distance during development, and are also separated by a predetermined distance during non-developing. Color switching is performed by sequentially performing this operation by each of the color developing units 2B to 2Y. In FIG. 2, only the cyan (C) developing unit 2C is in the developing state, and the others are in the non-developing state. During development, the surface of the photosensitive drum 1 and the developing roller 4B
The distance of 4Y is, for example, 0.6 mm, and when not developed, it is, for example, 2.0 mm.

Next, the structure and operation of each color developing unit 2B to 2Y will be described. Below, cyan (C) in FIG.
The developing unit 2C will be described. The other units are omitted because they have the same configuration and operation. A pair of screws 5 and 6 are arranged in parallel at the bottom inside the developing unit 2C, and together with the periphery thereof form a developer storage section.
The screws 5 and 6 are set in the rotation direction and the screw winding direction so as to convey the developer in the opposite directions in the longitudinal direction.

The developing unit 2C includes a developing roller 4C.
In addition to the above, a transport roller 7 is provided, which has a fixed magnet roller 8 therein, and a sleeve 9 around the outer circumference of which rotates in the direction of the arrow. It is designed to be conveyed by rotation. During development, the screws 5 and 6 circulate,
The mixed and agitated developer is drawn up by the carrying roller 7 and carried, and is delivered to the developing roller 4C at a portion D in the figure. Further, the developer is conveyed by the rotation of the developing roller 4C, the thickness thereof is regulated by the doctor 10, and then the developer is brought into contact with the photosensitive drum 1 for development, and the developer is conveyed again into the unit, and the magnetic force is set to be relatively weak. At the portion E in the inside, it is separated from the developing roller 4C by gravity, centrifugal force or the like and dropped onto the screws 5 and 6.

The timing of switching between the series of developing operations and the non-developing state is shown in FIG. After the image on the black (Bk) photosensitive drum 1 in the previous step has passed through the C developing portion, the rotation of the developing roller 4C and the proximity operation of the developing unit 2C to the photosensitive drum 1 are started, and the cyan (C) It will be in a stable state by the time the latent image arrives. The transport roller 7 starts its operation prior to this, and the rise time is shortened. When switching to non-development, after the C development is completed (after the C latent image has passed), the separation operation is started with a margin time. Prior to this, the transport roller 7 stops its operation and stops the supply of the developer to the developing roller 4C. The developing roller 4C finally stops its operation in order to peel off the agent accumulated in the agent transfer section or the like on the roller. The switching stop time can be shortened by setting the operation stop timing of the transport roller 7 to a forward position so as not to affect the developing operation.

In this embodiment, since the developing roller 4C is separated from the photosensitive drum 1 during non-developing as compared with during developing, there is a margin for the amount of residual agent on the developing roller 4C due to rotation of the agent. Therefore, there is a margin for variations in the magnetic force distribution of the developing roller 4C, etc., and the reliability is high. Further, since the moving drive is performed by the eccentric cam 3, the retreat distance is short, the time required for the development switching operation is short, the layout is relaxed, the space can be used efficiently, and the space can be saved. .

FIG. 4 shows an example of the developing unit according to the second embodiment of the present invention. In the developing unit 2C, the pair of screws 5 and 6 and the developing roller 4C each have a larger diameter than that of the example of FIG. 3, and the conveying roller is not provided. The operation and the like are similar to those in FIG.

The magnetic force distribution of the developing roller 4C in this example is shown in FIG.
Shown in In the magnetic force distribution shown in the figure, basically, a magnet with five poles is arranged, and the angle θ between the magnetic pole centers of the magnetic poles P2 and P6 is
Is set wider than the center angle interval between other magnetic poles. The center of the magnetic pole means the center of the angle of 1/2 of the maximum magnetic flux density on the magnetic force distribution waveform as shown in FIG. 5 (B). In addition, although the magnetic poles are arranged with five poles, magnetic poles P3, 4, 5 (virtual poles) that are repulsive magnetic fields are generated in the magnetic force distribution, and the number of poles is eight.

The operation of the developing unit 2C of this example will be described. During development, the developer near the screws 5 and 6 is mainly
The magnetic force of 6 poles draws it up to the developing roller 4C, conveys it along with the rotation of the sleeve 9 in the direction of the arrow, regulates its thickness by the doctor 10, and contacts the photoconductor drum 1 to develop the latent image on the photoconductor drum 1. To do. Then, the developing roller 4C is rotated again to convey the agent, and the agent is separated from the developing roller 4C at the portions of the virtual poles P3, 4 and 5 having a lower magnetic force than the other poles and dropped onto the screws 5 and 6. Let At this time, mainly if the magnetic forces of the virtual poles P3, 4, 5 are sufficiently low, the agent will leave without leaving. However, if the magnetic force becomes high to some extent due to variations or the like, some of them will not leave and some will be adsorbed on the developing roller 4C. I will go around with it. If the amount of the entrained agent is too large, it is used again for development without being stirred and mixed as it is, and problems such as uneven density occur.However, a small amount has no effect on development, so The magnetic force may be set in consideration of.

FIG. 7B shows the timing of switching between the series of developing operations and the non-developing state. Development unit 2C
The timing of contact and separation with respect to the photosensitive drum 1 is the same as in the previous example. The developing roller 4C starts a rotation operation in the rotation direction (normal rotation) at the time of development almost at the same time as the unit proximity operation at the start of development, and the proximity operation enters a stable state by the time the latent image reaches. When switching to non-development, after completion of cyan (C) development,
The reverse rotation operation is started with a margin, and the operation is stopped after a predetermined time (or a predetermined angle or a predetermined revolution reverse rotation). By this reverse rotation operation, the agent is not conveyed at the virtual poles P3, P4 and P5 and is sifted off as in the case of normal rotation. For this reason, the agent does not exist on the portion of the developing roller 4C facing the photoconductor drum 1, or the agent is very small even if it exists.

FIG. 6 shows an example of a developing unit according to the third embodiment of the present invention. The developing unit 2C includes a scraper 11 inside the doctor 10. The scraper 11 is provided so as to be movable between a developing position (G) separated from the developing roller 4C and a position (H) having a predetermined distance and close to the developing roller 4C. The timing for switching between development and non-development in this example is shown in FIG.
The contact / separation timing of the developing unit 2C with respect to the photosensitive drum 1 is the same as in the previous example. At the time of development, the scraper 11 is at the position G, and immediately after the completion of the predetermined developing process, the scraper 11 moves to the position H to scrape off the developer on the developing roller 4C. The developing roller 4C rotates for a predetermined time and enters a stop operation, and after the developing roller 4C stops, the scraper 1 moves to the position G to prepare for the next developing operation. This scraper 11 is the developing roller 4
The scraper 11 and the developing roller 4C in the state of being close to C and the scraper 11 and the developing roller 4C in the state of the developing unit 2C (developing roller 4C) being separated from the photosensitive drum 1 can be scraped off completely by the scraper 11. Instead, each value is set to such an extent that the latent image on the photosensitive drum 1 is not developed depending on the amount of the developer remaining on the portion on the developing roller 4C facing the photosensitive drum 1.

[0021]

The color image forming apparatus according to the first aspect of the present invention is
As described above, when the developing roller is retracted from the photoconductor to put it in the non-development state, the developer on the developing roller which is a part of the powder facing the photoconductor is removed. Since the distance is short, the switching time can be shortened without causing an adverse effect such as an increase in load and vibration due to increasing the retracting speed in order to reduce the switching time. It is possible to reduce the gap between them, speed up copying and printing, and increase the number of images to be formed.Also, widen the gap between the magnetic poles facing the photoconductor drum during development compared to other parts. Therefore, it is possible to stably and sufficiently remove the remaining agent not used for development, and develop the latent image or image of another color with the developer remaining on the developing roller. There is an effect that defects etc. is less likely to occur.

In the color image forming apparatus according to the second aspect, since the removing means for peeling off the developer on the developing roller is provided in non-contact with the developing roller, in addition to the above-mentioned common effects, the durability of the developing roller member is high. Has the effect of improving.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a magnetic pole arrangement of a conventional developing roller.

FIG. 2 is a sectional view showing a main part of an embodiment of a color image forming apparatus according to the present invention.

FIG. 3 is an enlarged cross-sectional view showing a cyan (C) developing unit of the embodiment of FIG.

FIG. 4 is an enlarged sectional view showing a cyan (C) developing unit of another embodiment of the color image forming apparatus according to the present invention.

5A and 5B are a conceptual diagram (A) showing the magnetic pole arrangement of the developing roller of the developing unit of FIG. 4 and an explanatory diagram (B) showing the magnetic pole center.

FIG. 6 is an enlarged sectional view showing a cyan (C) developing unit of still another embodiment of the color image forming apparatus according to the present invention.

FIG. 7 is a diagram showing a timing of switching between a series of developing operations and a non-developing state in each embodiment.

[Explanation of symbols]

 1 Photoconductor drum 2B, 2C, 2M, 2Y Developing unit 3 Eccentric cam 4B, 4C, 4M, 4Y Developing roller 5, 6 Screw 7 Conveying roller 8 Magnet roller 9 Sleeve 10 Doctor 11 Scraper

Claims (2)

[Claims] 1. A plurality of developing devices are arranged around a photoconductor,
In a color image forming apparatus in which each of the developing devices has a contacting / separating unit that is brought closer to the photoconductor during development and retracted from the photoconductor during non-development, the developing roller of each of the development devices has a plurality of magnetic poles. The magnetic pole center angle between the adjacent magnetic poles arranged on the downstream side of the magnetic poles facing the photoconductor in the rotation direction during development including the magnetic poles and on the upstream side including the magnetic poles facing the developer storage unit is A magnet roller that is arranged in a wider pole than between the adjacent magnetic poles of
A color image forming apparatus comprising a sleeve fitted to the outer periphery of the magnet roller so as to be rotatable in the forward and reverse directions, and the developer is removed by rotating the sleeve in a direction opposite to that at the time of developing when switching to non-developing. . 2. The developing roller of each of the developing devices comprises a magnet roller having a plurality of magnetic poles inside and a sleeve rotatably fitted to the outer circumference of the magnet roller, and can be brought into contact with and separated from the developing roller. 2. The color image according to claim 1, further comprising: a developer removing unit which is provided in the developing roller and comes close to the developing roller at a predetermined interval when the non-developing mode is switched, and removes the developer on the developing roller. Forming equipment.