Abstract: A controller for controlling a bias power source associated with, for example, a developing unit of an electrophotographic copier such that a bias voltage to be applied to the developing unit for the adjustment of image density is variable in level. The controller includes a central processing unit in which a timer/event counter is built in for delivering a trigger pulse signal to trigger the power source. In order to produce a bias voltage associated with a desired density level, the trigger pulse signal is subjected to pulse width modulation control at a period which is far shorter than an output time consant of the power source.

Abstract: A copier with a toner supply device which includes a toner cartridge. Toner is supplied from the toner cartridge to a hopper section of a developing unit of the copier and from the toner hopper section to a developing section which includes a developing sleeve. The end of toner in the toner hopper is sensed by a toner end sensing mechanism. A switching device is provided which performs an on-off operation as an operation for supplying toner from a new or full toner cartridge proceeds. A controller controls the developing unit, toner end sensing mechanism and switching device to insure good reproductions even before or immediately after the supply of toner.

Abstract: A copying machine which takes copies of a draft sheet by slit exposure while it is being conveyed. This copying machine includes a draft correction apparatus. This draft correction apparatus is provided with holding bars attached to a copying machine body so as to turn round the center line of a convey way for the draft, a pair of curved guide plates leaving therebetween a distance sufficient for forming a curved convey way constituting a part of said convey way, at least a pair of solenoids which are attached to the copying machine body on both sides of the draft convey way for turning said holding bars, draft sensors which are provided corresponding to said solenoids on both sides of the center line of the draft convey way this side of the solenoids, and a control means which inputs detection signals from the draft sensors and outputs working signals corresponding thereto against solenoids.