JPS6315881Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a developing device for a dry type electrophotographic copying machine.

FIG. 1 shows an example of a dry type electrophotographic copying machine. 1 is a drum-shaped photoreceptor, a is an image area, and b is a non-image area. A developing device 2 includes two magnetic brushes 3a and 3b and a lifting roller 4. Developer 5 in the developing device 2
is pumped up by the rotation of the pumping roller 4 and sequentially supplied to the magnetic brushes 3a and 3b. The magnetic brushes 3a and 3b supply the developer 5 to the circumferential surface of the photoreceptor 1, and cause the toner to be attracted to the electrostatic latent image on the photoreceptor 1, thereby performing development. This development is performed using the magnetic brush 3a,
This is carried out while applying a bias voltage to 3b. When the magnetic brushes 3a and 3b face the image area a on the photoconductor 1, the bias voltage is applied, but the bias voltage is maintained even when the magnetic brushes 3a and 3b face the non-image area b. Then, the carrier of the developer 5 adheres to the non-image area b, which may cause a problem. In this case, it is necessary to reduce the bias voltage for that period. Further, contrary to the above, adhesion of toner to the non-image area b may become a problem. In this case, it is necessary to increase the bias voltage for that period.

By the way, a plurality of magnetic brushes 3 as described above
In the case where a and 3b are used, the bias voltage cannot be switched smoothly. FIG. 2 shows this situation, and shows an example in which the bias voltage is switched in order to prevent carriers from adhering to the non-image area b. In the state shown in Fig. a, both magnetic brushes 3a and 3b face the image area a, and are therefore connected to a bias power source E via a changeover switch S. In the state shown in Figure b, the upstream magnetic brush 3a faces the non-image area b, but the downstream magnetic brush 3b faces the final image area a, so it is difficult to reduce the bias voltage. Can not. Therefore, the magnetic brush 3a causes the carrier to adhere to the non-image area b. The bias voltage applied to both magnetic brushes 3a and 3b can be reduced only after they both come to face the non-image area b, as shown in Figure c. When the upstream magnetic brush 3a comes to face the next image area a as shown in Figure d, the downstream magnetic brush 3b moves towards the next non-image area b.
The bias voltage must be returned to its normal value even though it is facing the opposite direction. Therefore,
Carrier adhesion also occurs here.

The present invention aims to solve the above-mentioned problems, and FIG. 3 shows an embodiment thereof. This example is for preventing carrier adhesion.

The upstream magnetic brush 3a remains directly connected to the bias power supply E, and the downstream magnetic brush 3b is switched and connected to the bias power supply E and ground via the changeover switch S.

When both the magnetic brushes 3a and 3b are facing the image area a as shown in figure a, the changeover switch S is switched to the bias power supply E side, so both the magnetic brushes 3a and 3b are A bias voltage is being applied, and the developing operation is normal. As shown in figure b, the upstream magnetic brush 3
Even if only a comes to face the non-image area b,
Since the output selector switch S remains switched to the bias power supply E side, the application of the bias voltage remains unchanged. Therefore, there is no problem in developing the image area a, but the carrier c adheres to the non-image area b. As shown in figure c, both magnetic brushes 3a,
3b both come to face the non-image area b,
The changeover switch S is switched to the ground side. As a result, the bias voltage of the magnetic brush 3b on the downstream side is lowered, so that the carrier does not adhere to the non-image area b. Not only that, but the magnetic brush 3 on the upstream side
The carrier c that a has attached to the non-image area b is attracted and recovered by the magnetic attraction force of the magnetic brush 3b. In this way, the upstream magnetic brush 3a
Since a regular bias voltage is always applied to the image area, the carrier c is attached to the non-image area b.
However, after that, the magnetic brush 3 on the downstream side
b collects the carrier c. The bias voltage to the downstream magnetic brush 3b continues to decrease even when the upstream magnetic brush 3a comes to face the image area a, as shown in figure d, and decreases in both bias voltages as shown in figure e. When both the magnetic brushes 3a and 3b come to face the image area a, the bias voltage is returned to the normal bias voltage.

The same applies to the switching of the bias voltage to prevent toner adhesion; the upstream side magnetic brush 3a is always applied with the regular bias voltage, and the downstream side magnetic brush 3b is set so that it faces the non-image area b. A high bias voltage is applied only during this period. Further, in the above embodiment,
Although a device using two magnetic brushes is shown, the present invention can also be implemented in a device using three or more magnetic brushes. In that case, it is sufficient to switch the bias voltage only for the most downstream magnetic brush.

As described above, since the present invention only switches the bias voltage for the most downstream of the plurality of magnetic brushes, the operation is simple, and moreover, ,
It can prevent carrier or toner from adhering.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional front view showing an example of an electrophotographic copying machine, and FIGS. 2 a to 2 d are front views for explaining the operation of a magnetic brush. FIGS. 3a to 3e are front views illustrating the operation of the embodiment of the present invention. 1...Photoreceptor, 2...Developing device, 3a...Upstream magnetic brush, 3b...Downstream magnetic brush,
a...image section, b...non-image section, c...carrier, E...bias power supply, S...changeover switch.

Claims (1)

[Scope of utility model registration request] In an apparatus in which development is performed by applying a developing bias voltage using a plurality of magnetic brushes arranged in the moving direction of the photoreceptor, for preventing toner or carrier from adhering to the non-image area of the photoreceptor,
A developing device for a dry type electrophotographic copying machine in which application of a developing bias voltage or switching of grounding is performed only to the most downstream magnetic brush.