Bias voltage control for electrophotocopier magnetic brush

Claim 1

In an electrophotocopying machine utilizing a two component developer material and having a reciprocating carriage for carrying an original document across the illuminating means, an endless re-usable photoconductor, said photoconductor rotating through two cycles for each copy produced of an original document and having a seam across the width thereof and having a total length less than the length to be imaged plus the length required for the physical location of all the photocopying process elements other than the transfer apparatus, a corona device for discharging electrical charge that might remain on the photoconductor after the developed image plus been transferred from the photoconductor, a magnetic brush developing device for developing the latent image on the photoconductor and removing untransferred developer material from the photoconductor, and a common source of internally generated voltage for both the discharging corona and the magnetic brush developing bias voltage, wherein the bias voltage for the magnetic brush developing device is terminated when the voltage to the discharging corona is terminated, an improvement for reducing the non-uniformity of charge deposited on the photoconductor to thereby increase photoconductor life while substantially maintaining the bias voltage during interruption of voltage to the discharging corona, said improvement comprising: a switch on the input to the common source of internally generated voltage, said switch being opened simultaneously with the disengagement of the clutch controlling the photoconductor motion ot thereby terminate the common source of internally generated voltage; means operatively connected to the common source of internally generated voltage for providing the bias voltage; a charge retaining element connected in parallel to the means providing the bias voltage; and a one way electrical valve operatively connected to the input for the charge retaining element and the bias voltage means, said charge retaining element substantially maintaining the bias voltage when the common source of voltage is terminated.