JPS63191169A - Color image forming device - Google Patents

Abstract

PURPOSE:To prevent a developer from being stuck to a transfer material or a transfer material carrying means at the time of replacing developing device by separating an image carrier from the transfer material carrying means in accordance with the loading/unloading of the developing device to/from a developing position. CONSTITUTION:The developing device 4Y (4M, 4C) enters a developing position from a home position and then developing sleeves 41-44 are rotated to start developing operation. In order to prevent the setting of the developing device 4Y (4M, 4C) on the developing position and the transfer of fogging toner generated from the stopped states of the sleeves 41-44 during the period up to the rotation of the sleeves 41-44, a transfer drum 5 is separated from a photosensitive drum 1 in accordance with the rotation of a rotational movement type developing device. The transfer drum 5 is pressed against the photosensitive drum 5 at the timing delayed from the start of rotation of the sleeves 41-44 by a prescribed time.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to carrying a transfer material on an endlessly rotating transfer material carrying means such as a drum or an endless belt. The present invention relates to a color image forming apparatus in which a plurality of developed images sequentially formed on an image carrier are sequentially superimposed and transferred onto the transfer material to obtain a color image 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 with a computer output section, and various other color printing machines. Although the invention is described herein in connection with a color electrophotographic reproduction apparatus, the invention is not so limited.

(Background Art) Conventionally, as in an electrophotographic color image forming apparatus, particularly a color electrophotographic copying apparatus, a method of obtaining a color image by superimposing and transferring developed images of multiple colors onto the same transfer material is shown in FIG. A color copying apparatus having the configuration shown in the figure is common.

To briefly explain such a color copying apparatus with reference to FIG. 5, the photosensitive drum 1, which is an image carrier, rotates in the direction of the arrow.
Around it are a corona discharger 2° exposure optical system 3. Developing device 4. A transfer material carrying means 5, which is a transfer drum, and a cleaner 6 are provided. The optical system 3 includes a document scanning section 3a and a color separation filter portion 3b. The developing device 4 is a rotary developing device which integrally includes a yellow developing device 4Y having yellow toner, a magenta developing device 4M having magenta toner, a cyan developing device 4c having cyan toner, and a black developing device 48k having black toner. is,
Each developing device is held by a support 4a, and by rotating around a central axis 4b, the developing device can be replaced with respect to the developing position. In the figure, 41, 42, 43, and 44 are developing sleeves in each of the above-mentioned developing devices.

On the other hand, the transfer drum 5 has a cylinder 5a and a transfer corona discharger 5b provided inside the cylinder 5a, as will be better understood with reference to FIG. The cylinder 5a has a peripheral opening area 5c stretched with a transfer material carrying sheet 5d made of a sheet such as a film or a screen mesh, and the cylinder also has a plurality of grippers for gripping the transfer material as described later. 5e are provided in the longitudinal direction.

Formation of a full color image is as follows. First, a blue color-separated electrostatic latent image is formed on the photosensitive drum 1, and then the yellow developing device 4
Develop with Y. On the other hand, the transfer drum 5 grips the leading end of the transfer material P fed from the paper feeder 7 with a gripper 5e, wraps the transfer material P around a carrier sheet 5d, and then transfers the transfer material P onto the photosensitive drum 1 using a transfer corona discharger 5b. The toner image is transferred onto the transfer material P, and the transfer material P is electrostatically attracted onto the carrier sheet 5d. Next, a green color-separated latent image is formed and developed by the magenta developing device 4M, and the resulting toner image is transferred onto the transfer material P in alignment with the previously transferred toner image. Similarly, formation of a red color separation latent image, development and transfer by the cyan developer 4c.

Furthermore, latent image formation by white light exposure, black developer 48k
Development and transfer are performed using When the transfer of the four-color toner image is completed in this way, the transfer material P is separated from the transfer drum 5 by the separating means 8, and transferred to the heat roller fixing device 9.
After the upper toner image is fixed, it is discharged onto the tray 10.

However, in the above-mentioned apparatus, when the developing device is set at the developing position, and furthermore, when the developing device is removed from the developing position to be replaced with the next developing device after completing the developing operation at the developing position, A phenomenon occurred in which the developer on the developing sleeve came into contact with the photosensitive drum, and a portion of the developer adhered to the photosensitive drum in the form of a band.

The developer deposited on the photosensitive drum is carried to the transfer area as the photosensitive drum rotates, thereby significantly staining the transfer material carrying sheet of the transfer drum. Furthermore, when the transfer material is carried on the transfer drum, that is, when the image is repeatedly transferred onto the transfer material to form a color image on the transfer material, the developer attached to the photosensitive drum is directly It adheres to the transfer material, causing a reduction in image quality.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned drawbacks of the conventional art, and its purpose is to prevent the developer from unnecessarily adhering to the image carrier when the developing device is attached to and detached from the developing position from the transfer material carrying means. It is an object of the present invention to provide a color image forming apparatus in which a transfer material on a transfer material carrying means is not soiled.

(Summary of the Invention) That is, the present invention that achieves the above object maintains synchronous movement of the image carrier and the transfer material carrying means in response to the movement of the developing device when it enters and leaves the developing position. The transfer material carrying means and the image carrier are separated from each other within a range.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. still,
Since the present invention is applicable to the color image forming apparatus having the configuration as shown in FIG. 5, the following description will be given assuming the apparatus configuration as shown in FIG.

FIG. 4A shows the position of the developing device from the developing position with respect to time t in the embodiment of the present invention. When θ=0°, the developing device is located at the developing position, and when θ=−90°, the developing device is located at the developing position. The developing device is located at the position of the magenta developing device 4M in FIG. 5, and when θ=90°, the developing device is located at the position of the black developing device 48 in FIG. On the other hand, FIG. 4B shows the timing of turning on and off the rotational drive of the developing sleeve with respect to time t in the embodiment of the present invention. In FIGS. 4A and 4B, tl indicates the time when the developing device is set at the developing position, t2 indicates the time when the rotational drive of the developing sleeve starts, and t indicates the time when the rotational drive of the developing sleeve stops. t4 indicates the point in time when the developing device leaves the developing position, t'1 indicates the point in time when the developer layer on the developing sleeve and the surface of the photosensitive drum serving as the image bearing member start contacting each other, and t4 indicates the point in time when the developing device leaves the developing position. '4 indicates the point in time when the contact between the developer layer on the developing sleeve and the surface of the photosensitive drum serving as the image carrier is broken.

As is clear from FIGS. 4A and 4B, the time period during which the developer layer on the developing sleeve contacts the surface of the photosensitive drum when the rotation of the developing sleeve is stopped, that is, t2-
t', and t'4-t3 occur. During this time, as described above, a phenomenon occurs in which the developer on the developing sleeve adheres to the photosensitive drum and is carried away. In other words, band-shaped fogging occurs on the photosensitive drum. (The fog referred to here is a phenomenon different from white background fog, so-called background fog, which occurs when developing the latent image forming area.) In particular, the above-mentioned phenomenon is caused by the developer layer on the developing sleeve ( )
The developer is in contact with the surface of the photosensitive drum until the developer enters the developing position, that is, in the areas t, -t,' in FIG. This is noticeable until the layer separates from the photosensitive drum surface, that is, in the region t4'-t4.

Therefore, in the present invention, when any developing device enters the developing position or when any developing device leaves the developing position,
By slightly separating the transfer drum from the photosensitive drum in response to the movement of the photosensitive drum (however, within a range that maintains synchronous movement between the transfer drum and the photosensitive drum), as the photosensitive drum rotates, the transfer drum is moved as described above. Even if the developer attached to the photosensitive drum reaches the transfer position, the developer is prevented from coming into contact with the transfer drum or the transfer material.

A configuration for separating the transfer drum from the photosensitive drum will be described below.

1 and 2 only show the photosensitive drum, which is an image carrier, and the transfer drum, which is 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 1-5d stretched over its peripheral opening area 5C. A plurality of grippers 5e are provided in the longitudinal direction.

As best illustrated in FIG. 2, grooves 5f are formed at both ends of the cylinder 5a of the transfer drum 5, and in the grooves 5f are rollers 511, 51 supported by side plates 514, 514'.
2,513; 511', 512', and 513' are in contact with each other, whereby the transfer drum 5 is rotatably supported. Further, the transfer drum 5 has abutment members 522 and 522' made of elastic bodies provided on the outer peripheral surface of both ends of the cylinder 5a.
Therefore, the transfer drum gear 523 integrated with the cylinder 5a meshes with the photosensitive drum gear 524, and the transfer drum 5 is driven by an external drive source M (FIG. 6). Drive is transmitted from the photosensitive drum 1.

In FIG. 1, a side plate 514 supporting the rollers 511, 512, 513 has an arm 514a projecting outward, and the arm 514a is rotatably supported by a fixed shaft 515. Therefore, the transfer drum 5 is allowed to swing around the shaft 515. Further, a lever 514b protruding outward is provided at a portion of the side plate 514 that is substantially diametrically opposed to the arm 514a.

Further, the side plate 514' is also formed in the same manner as the side plate 514, and the levers 514b and 514b' of both side plates are connected by a plate 516. Tension springs 517 and 517' are connected to one side of the connecting plate 516, which urges the transfer drum 5 toward the photosensitive drum 1 and presses the transfer drum 5 against the photosensitive drum 1 with an appropriate pressing force. There is. In addition, stoppers 518 and 518' are provided to restrict movement of the connecting plate 516 so that excessive pressure is not applied between both drums. Connecting plate 5
A solenoid 520 is connected to the other side of 16 via a tension spring 519.

When the solenoid 520 is energized, that is, turned on, the transfer tram 5 is separated from the photosensitive drum 1 against the force of the springs 517 and 517', and the amount of movement is determined by the stopper 521.
, 521'. This separation distance is set to such an extent that the photosensitive drum gear 524 and the transfer drum gear 523 are not disengaged from each other, so that the driving force from the photosensitive drum 1 to the transfer drum 5 is continuously transmitted. As a result, synchronous rotational movement is always maintained between the photosensitive drum and the transfer drum.

In the above configuration, when the toner image on the photosensitive drum is transferred, the solenoid is turned off and the photosensitive drum and the transfer drum are in pressure contact, and when the developing device enters or 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.

Note that this separation distance is preferably at least 0.5 mm or more in order to obtain the effect of preventing offset (preventing developer adhesion). By providing such a small distance, the transfer material held on 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 it is 0.7 to 1.0 mm.
A sufficient effect can be obtained. Also, if the distance is this much, the photosensitive drum gear 524 and the transfer drum gear 5
Even if a general gear is used as the gear 23, it is easy to drive the gears in synchronous rotation while maintaining the meshing state between the gears.

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

FIG. 3 shows a color electrophotographic copying apparatus as shown in FIG. 5, in which the diameter of the photosensitive drum 1 is 80 mm and the diameter of the transfer drum 5 is 160 mm (that is, the diameter of the photosensitive drum: the diameter of the transfer drum is 1:2). This figure shows an example of a time sequence of the above-mentioned color electrophotographic copying apparatus. The illustrated examples are the image exposure time and the rotation drive time of the developing sleeve with respect to the rotational speed of the photosensitive drum and transfer drum.

The transfer charging time by the transfer corona discharger, the rotational movement time of the developing device for one rotation, and the separation time of the transfer drum are shown for the cases of A4 and A3 transfer sizes, respectively. Although the transfer charging is shown to be turned on and off in FIG. 3 in order to make it easier to understand the timing of transfer depending on the size of the transfer material, it is not necessarily necessary to turn it off.

As is clear from FIG. 3, the sequence is different between the A4 size transfer material and the A3 size transfer material. This is due to the time it takes for the original scanning optical system to return to the starting position after scanning, or the moving time of the developing device when the developing device is replaced. I can't do that.

In other words, in the case of copying an A3 size transfer material, the transfer drum needs to idle for about one rotation, and after the first color toner image is transferred until the second color toner image is transferred, the second color toner image is transferred. During the period after the color toner image is transferred and before the third color toner image is transferred, and after the third color toner image is transferred and until the fourth color toner image is transferred, the transfer material This requires a step of contacting a photosensitive drum on which no surface is formed.

On the other hand, the column labeled "Rotary developing device" in FIG. 2-3 indicates that the second color magenta developer is replaced with the third color cyan developer, and 3→4 indicates that the third color cyan developer is replaced. This indicates that the developing device will be replaced with the fourth color black developing device. Sho H
, P means the home position of the rotationally movable 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 explained in relation to each other. First, the yellow developing device of the first color enters the developing position from the home position (H, P,), and then the developing sleeve rotates and starts the developing operation. During this time, that is, until the developing sleeve rotates, the transfer drum is separated as described above to avoid transferring the fog toner that occurs when the developing device is set at the developing position and the developing sleeve is stopped. . In other words, the transfer drum is separated from the photosensitive drum as the rotationally movable developing device rotates. Then, the transfer drum is brought into pressure contact with the photosensitive drum at a timing delayed by a predetermined time from the time when the developing sleeve starts rotating.

This predetermined time is the time it takes for the photosensitive drum to rotate from the development position to the transfer position T, and in the case of this embodiment, the diameter of the photosensitive drum is 80 mm and the process speed is 160 mm/see.

Since the angle between the development position and the transfer position T is approximately 100°, the predetermined time is approximately 0.9 (S).

Next, the rotation of the developing sleeve of the first color yellow developer stops, the yellow developer moves away from the developing position, and the yellow developer moves to the second color magenta developer. Thereafter, the developing sleeve of the magenta developing device rotates and begins a developing operation. During this period, that is, after the predetermined period of time has elapsed after the developing sleeve of the yellow developing device of the first color has stopped, and until the predetermined period of time has elapsed since the developing sleeve of the magenta developing device of the second color starts rotating, the transfer drum is not separated. conduct.

Thereafter, 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 this embodiment, the developing device is described in which the developing device is attached to and detached from the developing position while the rotation of the developing sleeve is stopped as shown in FIG. 4B. The present invention can also be applied to a developing device in which either loading or unloading is performed, or a developing device in which the developing sleeve is constantly rotating.

The apparatus briefly described in the above embodiments is one in which a latent image is formed on a photosensitive drum by scanning an original, but the apparatus is not limited to this, and may be used, for example, with a laser scanner, an LED element, etc., which forms a latent image according to image information. Of course, an exposure optical system can be applied.

(Effects of the Invention) As described above, according to the present invention, when the developing device enters the developing position or when the developing device leaves the developing position, the image carrier and the transfer material are moved in response to the movement. Since the image carrier is separated from the image carrier, unnecessary developer that adheres to the image carrier when replacing the developing device is prevented from adhering to the transfer material or the transfer material carrier at the transfer position. can.

Therefore, deterioration in image quality can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a transfer device portion of an embodiment of a color image forming apparatus according to the present invention. FIG. 2 is a sectional view taken along the line A--A in FIG. 1, and is an explanatory diagram of the structure of the photosensitive drum in the axial direction. FIG. 3 is an explanatory diagram showing a part of a timing chart showing sequence control of the color electrophotographic copying apparatus in this embodiment. FIG. 4A is a graph showing the position of the developing device from the developing position in terms of angle with respect to time. FIG. 4B is a graph showing the on/off timing of rotational drive of the developing sleeve with respect to time. FIG. 5 is a sectional view illustrating the main parts of the color electrophotographic copying apparatus. 6 is a perspective view showing the relationship between the photosensitive drum and the transfer drum of the apparatus shown in FIG. 5. FIG. 1 ----------One photosensitive drum (image carrier) 4 -One---Developing device 4Y------Yellow developing device 4M------Macenter developing device 4C--- --- One for cyan developer 48 --- One for black developer 5 --- One for transfer drum (transfer material carrying means) 41
, 42. 43. 44-11111 developing sleeve

Claims (1)

[Scope of Claims] A color separation latent image formed on an image carrier is developed by a developing device, and a plurality of the developed images are transferred in a superimposed manner onto a transfer material carried on a transfer material carrying means. , a color image forming apparatus that forms a color image on the transfer material, wherein the developing device has a plurality of developing means that are selectively movable with respect to a developing position for developing the latent image, and the plurality of developing means When any one of the developing means enters and leaves the developing position,
A color image forming apparatus characterized in that the transfer material carrying means and the image carrying member are separated from each other within a range in which the image carrying member and the transfer material carrying means maintain synchronous movement in response to the movement. .