JPS6360391B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrophotographic apparatus.

In an electrophotographic apparatus that has a photoreceptor drum for image formation and a transfer drum that is in pressure contact with the photoreceptor drum, the so-called transfer methods have conventionally been (a) a corona transfer method, and (b) a bias transfer method. There are some known methods. For example, the first
The figure shows a color electrophotographic apparatus employing a corona transfer method. In the figure, reference numeral 1 indicates a photosensitive drum, and reference numeral 2 indicates a transfer drum.

The transfer drum 2 has a cylindrical shape and is rotatably supported by three pairs of supporting rollers 3, 4, and 5.
The main part of the circumferential surface, excluding the part where the clamper 7 is disposed, is composed only of a dielectric film wound into a cylindrical shape. A transfer charger 6 is disposed within the transfer drum 2 corresponding to the pressure contact portion of both drums. A clamper 7 for gripping the transfer paper is provided on the outer periphery of the transfer drum 2, and is adapted to clamp the leading edge of the transfer paper S fed by the pair of rollers 8.

In the figure, reference numeral 9 indicates exposure light, reference numeral 10 an electrostatic charger, reference numeral 11 an antistatic charger, reference numeral 12 a cleaning brush, further reference numeral 13 a transfer paper separation claw, and reference numeral 14 a pair of heat rollers for fixing. .

Now, the outline of the process in this electrophotographic apparatus is as follows: As the process progresses, the yellow, magenta, and cyan developing devices 15A, 15B,
The color toner images developed by C are sequentially transferred from the photosensitive drum 1 onto the transfer paper S by the electric force applied by the transfer charger 6, thereby creating a color copy.

Next, there is a color electrophotographic device that uses the bias transfer method mentioned in (b) above, but in this case, a transfer drum made of conductive rubber is used instead of the transfer drum 2 shown in FIG. During transfer, a transfer bias voltage is applied to the transfer drum made of conductive rubber.
In this method as well, as in the example shown in FIG. 1, a clamper for gripping the transfer paper is provided on the peripheral surface of the transfer drum.

By the way, in such an electrophotographic device,
In order to transfer the image to as wide a surface as possible, covering almost the entire surface of the transfer paper S, it is necessary to press the photosensitive drum as close as possible to the portion of the transfer paper gripped by the clamper. However, doing so may cause the following troubles.

(1) The photoreceptor 16 (so-called Se-based or OPC-based photoreceptor) covers the circumferential surface of the photoreceptor drum 1 so that the clamper 7 directly interferes with the photoreceptor drum 1.
(See Figure 2).

(2) Since the clamper directly interferes with the photoreceptor drum, the clamper is damaged or soiled by developer.

(3) The clamper 7 is usually provided on a rigid part 17 that is part of the outer periphery of the transfer drum 2, and the rest of the outer periphery is provided with a dielectric film 18.
However, when the remaining liquid of the developer in the rigid part solidifies, this solid material will damage the photoreceptor when both the photoreceptor drum and the transfer drum are in pressure contact (see Figure 2). . In addition,
In this case, solidification of toner in a portion other than the rigid portion (dielectric film portion) generally does not occur, and even if it occurs, the solidification of the toner does not occur in the dielectric film 18.
The light escapes elastically, so it does not damage the photoreceptor. Therefore, as the rigid body portion 17 and the photosensitive drum come into pressure contact with each other, there is a problem in that the photosensitive drum may be damaged by the solid material.

An object of the present invention is to provide an electrophotographic apparatus that can eliminate the problems described in (1) to (3) above.

The present invention will be explained in detail below.

The present invention provides an electrophotographic apparatus having a photoreceptor drum for image formation and a transfer drum that is in pressure contact with the photoreceptor drum, in which a predetermined non-image area on the photoreceptor drum or the transfer drum is a pressure contact portion of both drums. From the time it turned to
The present invention is characterized in that the copying process is performed with both drums in a non-contact state by interposing a spacer between both drums until the non-image area comes off the pressure contact portion.

Here, the predetermined non-image area is a part that is not directly involved in image formation, and specifically corresponds to a part where it is necessary to carry out the present invention, such as the clamper 7 part and the rigid body 17 part in the transfer drum. In addition, in the photoreceptor drum 1, if the photoreceptor coating itself is of a type other than seamless, the joint portion (this portion does not directly participate in image formation) is called a non-image area. If this area is brought into direct pressure contact with the transfer drum, it may cause problems such as damaging the drum surface, and in that case, it is treated as a predetermined non-image area and the two drums are separated.

Next, an embodiment will be explained with reference to the drawings. In FIG. 3, reference numeral 18 indicates a photosensitive drum, the shaft 18a of which is pivotally supported by a stationary member not shown. A gear 18g is formed integrally with the photosensitive drum 18 at the right end of the photosensitive drum 18. This gear 18g meshes with a drive gear (not shown) and rotates in the direction of arrow P by power transmission from the drive gear. This photosensitive drum 18
A photoreceptor is wrapped around the circumferential surface of the photoreceptor. In this invention, the photosensitive drum 18 is a pressure-contact drum, and the transfer drum 18 is fixedly set (the position of the drum itself does not change).
Alternatively, the configuration may be such that the transfer drum 19 is brought into pressure contact with the pressure-contact drum by swinging, or the transfer drum 19 is used as the pressure-contact drum and the photosensitive drum 18 is moved against the transfer drum 19 which is fixedly set. A configuration may also be adopted in which the drum is brought into pressure contact with the pressure-contact drum by singing.

Referring to FIG. 3, the transfer drum 19 is mainly composed of a drum frame 19a which is formed by cutting out a central part of a cylindrical body leaving a band shape in the axial direction, and has annular remaining thickness at both ends in the axial direction. A clamper 20 for gripping the transfer paper is provided on the band-shaped rigid body portion 19'a connecting the two. This clamper 20 is pivotally supported on a rigid portion 19'a via a shaft 20a. One end of this shaft 20a is bent into an L-shape, and as the transfer drum 19 rotates, the L-shaped bent portion engages with a control cam (not shown) to open and close the clamper 20. Further, a dielectric film 21 is wrapped around the drum frame 19a so as to sufficiently cover the central notch.

The transfer drum 19 is pivotally supported at both ends in the longitudinal direction of the shaft by transfer drum support arms (not shown). and the rotational behavior of the transfer drum support arm in one direction (given by the pressure spring).
As a result, the transfer drum 19 is elastically pressed against the photosensitive drum 18. Further, a gear 19g is provided at the right end of the transfer drum 19 substantially integrally with the drum 19.
is formed and meshes with the gear 18g. In this example, the pitch diameters of both gears, the outer diameters of the photosensitive drum 18, the transfer drum 19, etc. are all the same. Therefore, the transfer drum 19 rotates in the direction of arrow P' at the same peripheral speed as the photosensitive drum 18.

What should be further noted is that spacers 22 are provided on the annular remaining thickness portions at both ends of the drum frame 19a in the axial direction, corresponding to the clampers 20.
23 is provided. The thickness of these spacers 22 and 23 is set to be equal to or greater than the amount by which the clamper 20 protrudes outward from the outer peripheral surface of the transfer drum 19. Further, the lengths of these spacers 22 and 23 in the rotational direction of the transfer drum 19 are set to values that sufficiently cover the size of the clamper 20.

With this configuration, as shown in FIG. 6, as the copying process progresses, the clamper 2
0 comes into pressure contact with the photoreceptor drum 18, the photoreceptor drum 18 rides on the spacers 22 and 23, and the transfer drum 19 moves in the direction of the arrow Q.
, and both drums are separated. In this way, interference with the photosensitive drum 18 by the clamper 20 is avoided. In addition, in the figure, the reference numeral 24 indicates a transfer charger. This transfer charger 24
is arranged inside the transfer drum 19, and is set to face the pressure contact portion of both drums.

Now, as the rotation of both drums further progresses from the state shown in FIG. 6 above, the spacers 22 and 23 are removed from the pressure contact portions of both drums, as shown in FIG. 7, so that both drums come into direct pressure contact with each other. .

Thus, according to the present invention, a predetermined non-image area of the transfer drum can be automatically separated from the photoreceptor drum. Here, the separation distance is gear 1
8g, 19g is the limit that allows mutual engagement to be maintained. In other words, the gear specifications of the gears 18g and 19g are such that power transmission can be maintained even when the spacers 22 and 23 are separated, and the spacer portions are in pressure contact or from the pressure contact state. It is assumed that the value is set to such a level that vibration and impact force do not adversely affect transfer performance when released. In the example, when each module of the gears 18g and 19g is 1, the distance between the two drums by the spacer (thickness of the spacer) is set to 0.2 to 0.5 mm, and good results are obtained.

Further, in the embodiment, the spacer is provided only on the transfer drum side, but the spacer may be provided on the photoreceptor drum side, or may be provided on both the transfer drum and the photoreceptor drum, respectively. moreover,
It goes without saying that the present invention can be carried out even if the two drums have different outer diameters.

[Brief explanation of the drawing]

FIG. 1 is a side view of the main parts of a color electrophotographic apparatus that uses a corona transfer method, FIG. 2 is an enlarged side view of the clamper portion in the same figure, and FIG. 3 is a photosensitive drum illustrating an embodiment of the present invention. A perspective view of the transfer drum in pressure contact state, FIG. 4 is a cross-sectional view of the pressure contact portion of both drums in the above figure, and FIG. 5 is a Y-Y line in FIG. 3.
The sectional view, FIG. 6, and FIG. 7 are partial side views of the press-contact portion of both drums, respectively, illustrating the operating state of the present invention step by step. 18...Photosensitive drum, 19...Transfer drum,
22, 23...Spacer.

Claims (1)

[Scope of Claims] 1. A transfer drum that has a photosensitive drum for image formation and a clamper that grips the leading edge of transfer paper on a part of its circumferential surface, and that rotates while being in elastic pressure contact with the photosensitive drum. In an electrophotographic apparatus having the above, a spacer maintains both drums in a non-contact state from the time when the clamper mounting portion on the transfer drum rotates to the pressure contact portion with the photoreceptor drum until the time when the clamper attachment portion on the transfer drum comes out of the pressure contact portion. An electrophotographic apparatus characterized in that: is interposed between the two drums.