Bias device for a copying machine

Claim 2

A bias device for a copying machine having a developing electrode confronting a photo-sensitive member, to which electrode a voltage is applied during development, which bias device comprises: memory means for storing the potential of the surface of said photo-sensitive member; voltage generating means for providing a voltage obtained by superposing a predetermined potential on said potential stored in said memory means; means for allowing the potential of the surface of said photo-sensitive member to be stored in said memory means in a non-image period which occurs with said photo-sensitive member; and switch circuit means for applying said voltage provided by said voltage generating means to said electrode in an image period.

Claim 3

A bias device as claimed in claim 1, in which in said non-image period, when said switch means is in off state, a negative bias period is provided for said electrode, and when said switch means is in on state, a positive bias period is provided for said electrode.

Claim 4

A bias device as claimed in claim 1, in which upon completion of a copying operation, the contents of said memory means are cleared.

Claim 5

A bias device as claimed in claim 1, in which said memory means is a capacitor.

Claim 6

A bias device as claimed in claim 2, in which said memory means is a capacitor.

Claim 7

A bias device as claimed in claim 3, in which said memory means is a capacitor.

Claim 8

In a copying machine having an electrode confronting a photo-sensitive member, to which electrode a voltage is applied during development, a bias device which comprises: memory means for storing the potential of the surface of said photo-sensitive member; voltage generating means for providing a bias voltage obtained by superposing a predetermined potential on the potential stored in said memory means; potential detecting switch means for allowing the potential of the surface of said photo-sensitive member to be stored in said memory means; bias voltage applying switch means for selectively applying a positive bias voltage and a negative bias voltage to said electrode; and change-over switch means for switching said positive bias voltage or negative bias voltage to be applied to said bias voltage applying switch, and in which a non-image period occurs when said photo-sensitive member is divided into a negative bias period and an electrode potential detection period; in said negative bias period said bias voltage applying switch means is turned on while an armature of said change-over switch means is tripped to a negative bias contact thereof; in said electrode potential detection period said bias voltage applying switch means is turned off while said potential detecting switch means is turned on; and in the period of said development the armature of said change-over switch means is tripped over to a positive bias contact while said bias voltage applying switch means is turned on.

Claim 9

In a copying machine having an electrode confronting a photo-sensitive member, to which electrode a voltage is applied during development, a bias device which comprises: memory means for storing the potential of the surface of said photo-sensitive member; voltage generating means for providing a bias voltage obtained by superposing a predetermined potential on the potential stored in said memory means; potential detecting switch means for allowing the potential of the surface of said photo-sensitive member to be stored in said memory means; bias voltage applying switch means for selectively applying a positive bias voltage and a negative bias voltage to said electrode; and change-over switch means for switching said positive bias voltage or negative bias voltage to be applied to said bias voltage applying switch, and in which a non-image period occurs when said photo-sensitive member is divided into a negative bias period and an electrode potential detection period; in said negative bias period said bias voltage applying switch means is turned on while an armature of said change-over switch means is tripped to a negative bias contact thereof; in said electrode potential detection period said bias voltage applying switch means is turned off while said potential detecting switch means is turned on; and in the period of said development the armature of said change-over switch means is tripped over to a positive bias contact while said bias voltage applying switch means is turned on.