JPH0719087B2 - Color image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention supports a transfer material on an endlessly rotating transfer material carrying means such as a drum or an endless belt, and is used in a photosensitive drum, an insulating drum, or the like. The present invention relates to a color image forming apparatus that obtains a color image on a transfer material by sequentially superimposing and transferring a plurality of developed images formed on the image carrier on the transfer material. The color image forming apparatus according to the present invention is embodied in, for example, a color electrophotographic copying machine, a color printer having a computer output section, and various other color printing machines. Although the present invention is described herein in the context of a color electrophotographic copying machine, the invention is not so limited.

[Background technology]

Conventionally, as a method for obtaining a color image by superposing and transferring development images of a plurality of colors onto the same transfer material as in an electrophotographic color image forming apparatus, particularly a color electrophotographic copying apparatus, the configuration shown in FIG. This color copying machine is generally used.

The color copying apparatus will be briefly described with reference to FIG. 5. The photosensitive drum 1, which is an image carrier, rotates in the direction of the arrow.
A corona discharger 2, an exposure optical system 3, a developing device 4, a transfer material carrying means 5 serving as a transfer drum, and a cleaner 6 are arranged around the corona discharger 2. The optical system 3 has a document scanning section 3a and a color separation filter section 3b. The developing device 4 includes a yellow developing device 4Y having yellow toner, a magenta developing device 4M having magenta toner, and a cyan developing device 4C having cyan toner.
The rotary developing device integrally includes a black developing device 4BK having black toner, and each developing device includes a support 4a.
And is rotated about the central axis 4b to replace the developing device with respect to the developing position D. In the figure, 41, 42,
Designated by 43 and 44 are developing sleeves in the developing devices.

On the other hand, the transfer drum 5 has a cylinder 5a and a transfer corona discharger 5b provided inside thereof, as will be better understood with reference to FIG. Cylinder 5a has an open area
A transfer material carrying sheet 5d composed of a sheet such as a film or a screen mesh is stretched on 5c, and a plurality of grippers for gripping the transfer material are attached to the cylinder as described later.
5e is provided in the longitudinal direction.

The formation of a full-color image is as follows. First, a blue color separation electrostatic latent image is formed on the photosensitive drum 1, and the yellow developing device 4Y
To develop. On the other hand, the transfer drum 5 grips the front end of the transfer material P fed from the paper feeding device 7 with the gripper 5e, winds the transfer material P on the carrier sheet 5d, and then transfers the transfer corona discharger 5b.
As a result, the toner image on the photosensitive drum 1 is transferred onto the transfer material P and the transfer material P is electrostatically adsorbed onto the carrier sheet 5d.
Next, a green color-separated latent image is formed and developed by the magenta developing device 4M, and the obtained toner image is transferred onto the transfer material P while being aligned with the previously transferred toner image. Similarly, red color separation latent image formation, development and transfer by the cyan developing device 4c, latent image formation by white light exposure, and development and transfer by the black developing device 4BK are performed. When the transfer of the four color toner images is completed in this way, the transfer material P is separated from the transfer drum 5 by the separating means 8, and the toner image on the transfer material P is fixed via the heat roller fixing device 9, and then is transferred to the tray 10. Is discharged.

However, when the developing device is set to the developing position in the apparatus as described above, or when the developing device is removed from the developing position to replace the next developing device after completing the developing operation at the developing position. The phenomenon that the developer on the developing sleeve comes into contact with the photosensitive drum and a part of the developer adheres to the photosensitive drum in a band shape occurs.

The developer attached on the photosensitive drum is carried to the transfer area as the photosensitive drum rotates, and the transfer material carrying sheet of the transfer drum is significantly soiled. Further, when the transfer material is carried on the transfer drum, that is, when the color image is repeatedly formed on the transfer material to form a color image on the transfer material, the developer attached to the photosensitive drum directly It adheres to the transfer material, which causes the deterioration of image quality.

[Object of the Invention]

The present invention has been made in view of the above-mentioned drawbacks of the related art, and a purpose thereof is to prevent the developer unnecessarily adhered to the image carrier when the developing means is attached to or detached from the developing position. It is an object of the present invention to provide a color image forming apparatus in which the transfer material on the transfer material holding means is not contaminated.

[Outline of Invention]

That is, according to the present invention which achieves the above object, a color separation latent image formed on a moving image carrier is developed by a developing device, and the developed image is transferred onto a transfer material carried on a transfer material carrying means at a transfer position. In a color image forming apparatus that forms a color image on the transfer material by superimposing and transferring a plurality of images,
The developing device has a plurality of developing means selectively movable with respect to a developing position for developing the latent image, and any one of the plurality of developing means enters the developing position and The image carrier and the transfer material carrying means are separated from each other when the area of the image carrier at the developing position moves to the transfer position when the image carrier is separated from the developing position. Is.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. still,
Since the present invention can be applied to the color image forming apparatus having the configuration shown in FIG. 5, the description will be given below on the premise of the apparatus configuration shown in FIG.

FIG. 4A shows the position from the developing position D of the developing device as the developing means with respect to the time t in the embodiment of the present invention. When θ = 0 °, the developing device is located at the developing position D, and θ =
At -90 °, the developing unit is the magenta developing unit 4M in Fig. 5.
And the developing device is located at the position of the black developing device 4BK in FIG. 5 when θ = 90 °. On the other hand, the 4th
FIG. 6B shows the on / off timing of the rotational drive of the developing sleeve with respect to the time t in the embodiment of the present invention. In FIGS. 4A and 4B, t ₁ indicates the time when the developing device is set to the developing position, t ₂ indicates the time when the rotational driving of the developing sleeve is started, and t ₃ indicates the rotational driving of the developing sleeve. Is stopped, t ₄ is a time when the developing device is separated from the developing position, and t ′ ₁ is a time when the developer layer on the developing sleeve and the surface of the photosensitive drum as an image carrier start contact. shows, t _'4 indicates a point when the contact between the developer layer and the image bearing member photosensitive drum surface on the developing sleeve is cut off.

As is clear from FIGS. 4A and 4B, the time during which the developer layer on the developing sleeve is in contact with the surface of the photosensitive drum while the rotation of the developing sleeve is stopped, that is, t ₂ −t ′ ₁
And t ′ ₄ −t ₃ . In the meantime, as described above, the phenomenon that the developer on the developing sleeve adheres to the photosensitive drum occurs. That is, band-shaped fog occurs on the photosensitive drum. (Note that the fog referred to here is a phenomenon different from white background fog which is generated when developing a latent image forming area, that is, so-called background fog.) Especially, the above-mentioned phenomenon is caused by the developer layer (spike) on the developing sleeve. ) And the surface of the photosensitive drum until the developing unit enters the developing position, that is, the area of t ₁ -t ′ _{1 in} FIG. until adhesive layer is separated from the photosensitive drum surface, that is significant in the region of t ₄ '-t _4.

Therefore, in the present invention, when the area of the photosensitive drum at the developing position moves to the transfer position when the arbitrary developing device enters the developing position and when the arbitrary developing device separates from the developing position, the transfer is performed with the photosensitive drum. Since the developer is attached to the photosensitive drum as described above due to the rotation of the photosensitive drum due to the separation from the drum, the developer does not contact the transfer drum or the transfer material. To do so.

Hereinafter, a configuration in which the transfer drum is separated from the photosensitive drum will be described.

FIG. 1 and FIG. 2 show only a photosensitive drum as an image carrier and a transfer drum as a transfer material carrying means.

In this embodiment, the transfer material carrying means is a transfer drum 5 similar to that shown in FIG. 6, and has a cylinder 5a, and the cylinder 5a has a transfer material carrying sheet 5d stretched over a peripheral opening area 5c. ,
Also, a plurality of grippers 5e are provided in the longitudinal direction.

As best shown in FIG. 2, grooves 5f are formed at both ends of the cylinder 5a of the transfer drum 5, and side plates are formed in the grooves 5f.
Rolls supported by 514,514 '511,512,513;511', 512 ', 5
13 'abuts, whereby the transfer drum 5 is rotatably supported. Further, the transfer drum 5 is provided with abutting members 522, 52 made of an elastic body provided on the outer peripheral surfaces of both ends of the cylinder 5a.
The transfer drum 5 is pressed against the photosensitive drum 1 via 2 '. Therefore, the transfer drum gear 523 integrated with the cylinder 5a meshes with the photosensitive drum gear 524, and the external drive source M
The drive is transmitted from the photosensitive drum 1 driven in (FIG. 6).

In FIG. 1, a side plate 514 supporting the rollers 511, 512, 513.
Has an arm 514a protruding outward, and the arm 514a is rotatably supported by a fixed shaft 515. Therefore, the transfer drum 5 can swing about the shaft 515. Further, a lever 514b protruding outward is provided at a portion of the side plate 514 facing the arm 514a in a substantially diametrical direction.

The side plate 514 'is also formed in the same manner as the side plate 514, and the levers 514b and 514b' on both side plates are connected by a plate 516. The connecting plate 516
Has tension springs 517 and 517 'connected to one side,
The transfer drum 5 is biased toward the photosensitive drum 1, and the transfer drum 5 is pressed against the photosensitive drum 1 with an appropriate pressure contact force.
It should be noted that stoppers 518 and 518 'for restricting the movement of the connecting plate 516 are provided so that an excessive pressure contact force is not applied between the two drums. The solenoid 520 is connected to the other side of the connecting plate 516 via a tension spring 519. When the solenoid 520 is energized, that is, when it is turned on, the transfer drum 5 causes the springs 517 and 51.
It is separated from the photosensitive drum 1 against the force of 7 ', and its movement amount is adjusted by stoppers 521, 521'. This separation distance is such that the photosensitive drum gear 524 and the transfer drum gear 523 are not disengaged from each other, and therefore the driving force from the photosensitive drum 1 to the transfer drum 5 is continuously transmitted. As a result, the synchronous rotary motion is always maintained between the photosensitive drum and the transfer drum.

In the above configuration, when transferring the toner image on the photosensitive drum, the solenoid is turned off and the photosensitive drum and the transfer drum are in pressure contact with each other.When the developing device enters and leaves the developing position, the solenoid is turned on. Sequence control is performed so that the photosensitive drum and the transfer drum are separated from each other.

It should be noted that this separation distance is preferably at least 0.5 mm or more in order to obtain the effect of offset prevention (prevention of developer adhesion). By providing such a slight separation distance, the transfer material held by the transfer drum and the photosensitive drum are brought into a non-contact state. In order to obtain a more reliable effect, it is necessary to increase the separation distance, but if it is about 0.7 to 1.0 mm, a sufficient effect can be obtained. Further, if the distance is about this range, even if general gears are used as the photosensitive drum gear 524 and the transfer drum gear 523, the synchronous rotation drive can be easily performed while maintaining the meshed state of both.

Next, the sequence control of the color electrophotographic copying machine in this embodiment will be briefly described.

FIG. 3 shows the color electrophotographic copying apparatus as shown in FIG. 5 in which the photosensitive drum 1 has a diameter of 80 mm and the transfer drum 5 has a diameter of 160 mm (that is, photosensitive drum diameter: transfer drum diameter 1: 2). 2 shows an example of the time sequence of the color electrophotographic copying apparatus described above. In the illustrated example, the image exposure time with respect to the rotation speed of the photosensitive drum and the transfer drum
The rotational drive time of the developing sleeve, the transfer charging time by the transfer corona discharger, the rotational movement time of the rotary developing device, and the separation time of the transfer drum are shown for transfer sizes A4 and A3, respectively. Incidentally, the transfer charging is shown to be turned on / off in order to make it easy to understand the transfer timing due to the difference in the size of the transfer material in FIG.
It does not have to be turned off.

As is clear from FIG. 3, the case of A4 size transfer material
The sequence is different from that of A3 size transfer material. This is due to the return time to the start position after scanning of the original scanning optical system or the moving time of the developing device accompanying the replacement of the developing device.
It cannot be done with the same transfer drum speed as A4 size.

That is, in the case of copying A3 size transfer material, about 1 transfer drum
It is necessary to perform idle rotation corresponding to the rotation, and after the transfer of the toner image of the first color until the transfer of the toner image of the second color, the transfer of the toner image of the second color and the transfer of the toner image of the third color. Until the above, and before the transfer of the toner image of the fourth color and the transfer of the toner image of the fourth color, the step of contacting the transfer material with the photosensitive drum on which the toner image is not formed is required.

On the other hand, the column of the rotary developing device in FIG. 3 shows the moving state of the developing device, and 1 → 2 means that the developing device at the developing position D is from the yellow developing device of the first color to the second developing device. The color magenta developing device is replaced, 2 → 3 indicates that the second color magenta developing device is replaced by the third color cyan developing device, and 3 → 4 indicates the third color cyan developing It is shown that the developing device is replaced with a black color developing device of the fourth color. H.
P. means the home position of the rotary-moving type developing device, which is a position where neither developing device faces the photosensitive drum.

Here, the moving operation of the developing device and the separating operation of the transfer drum will be described in association with each other. First, the first color yellow developing device enters the developing position from the home position (HP), and then the developing sleeve rotates to start the developing operation. During this period, that is, until the developing sleeve rotates, the transfer drum 5 is separated as described above in order to avoid transfer of the fog toner generated due to the setting of the developing device to the developing position and the developing sleeve being stopped. To do. That is, the transfer drum is separated from the photosensitive drum in accordance with the rotation of the rotary movement type developing position.
Then, the transfer drum is pressed against the photosensitive drum at a timing delayed by a predetermined time from the time when the developing sleeve starts to rotate.

This predetermined time is the time required for the photosensitive drum to rotate from the developing position D to the transfer position T. In this embodiment, the photosensitive drum diameter is 80 mm and the process speed is 160 mm.
Since the angle between the developing position D and the transfer position T is about 100 ° / sec, the predetermined time is about 0.9 (S).

Next, the rotation of the developing sleeve of the first color yellow developing device is stopped, the yellow developing device moves away from the developing position, and the yellow developing device moves to the second color magenta developing device. Then, the developing sleeve of the magenta developing device rotates to start the developing operation. During this time, that is, after the predetermined time has elapsed after the developing sleeve of the first color yellow developing device has stopped, the transfer drum is separated from the developing sleeve of the second color magenta developing device for a predetermined time after starting to rotate. To do.

After that, when moving to the cyan developing device for the third color and the black developing device for the fourth color, the transfer drum is separated at the same timing.

In the present embodiment, as described in FIG. 4B, the developing device for attaching and detaching the developing device to the developing position with the developing sleeve stopped rotating has been described. The present invention can be applied to a developing device for performing either one of attachment and detachment, or a developing device in which the developing sleeve is constantly rotating.

Further, the apparatus described in the above embodiment shows the one in which a latent image is formed on the photosensitive drum by scanning the original, but the present invention is not limited to this, and for example, a laser scanner or an LED element that forms a latent image according to image information. It goes without saying that the exposure optical system can be applied.

〔The invention's effect〕

As described above, according to the present invention, when the area of the image carrier at the developing position moves to the transfer position when the developing unit enters and leaves the developing position, the image carrier and the transfer material are moved. Since it is separated from the carrying means, it is possible to prevent unnecessary developer, which adheres to the image carrier when the developing means is replaced, from adhering to the transfer agent or the transfer material carrying means at the transfer position.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a transfer device portion according to an embodiment of a color image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and is a structural explanatory view of the photosensitive drum in the axial direction. FIG. 3 is an explanatory view showing a part of a timing chart showing the sequence control of the color electrophotographic copying machine in this embodiment. FIG. 4A is a graph showing the position from the developing position of the developing device with respect to time in terms of angles. FIG. 4B shows that the developing sleeve rotation drive is turned on / off with time.
It is a graph which shows off timing. FIG. 5 is a cross-sectional view for explaining an essential part of the color electrophotographic copying machine. FIG. 6 is a perspective view showing the relationship between the photosensitive drum and the transfer drum of the apparatus shown in FIG. 1 ... Photosensitive drum (image bearing member) 4 ... Developing device 4Y ... Yellow developing device 4M ... Magenta developing device 4C ... Cyan developing device 4Bk ... Black developing device 5 ... Transfer drum (transfer material carrying means) 41,42,43,44 …… Developing sleeve D …… Developing position T …… Transfer position

Claims (1)

[Claims] 1. A color separation latent image formed on a moving image carrier is developed by a developing device, and a plurality of the developed images are superposed on a transfer material carried on a transfer material carrying means at a transfer position. In a color image forming apparatus for forming a color image on the transfer material by transferring, the developing device has a plurality of developing means selectively movable with respect to a developing position for developing the latent image, When any one of the plurality of developing means enters the developing position and separates from the developing position, when the area of the image carrier at the developing position moves to the transfer position, A color image forming apparatus characterized in that the image carrier and the transfer material carrier are separated from each other.