Abstract: A control system for a color copier which sets up an adequate color copying time for any particular size of paper sheets. A color document is repeatedly scanned to sequentially expose a single photoconductive drum, which is rotated at a constant speed, to a plurality of separated color components. Each of the latent images is developed by toner complementary in color to the color component associated with the latent image, and sequentially transferred to a paper sheet. The control system includes a paper size setting circuit, a scanning sensor for sensing the start of a scanning, and a home sensor for sensing an instantaneous angular position of the transfer drum.

Abstract: A toner mixture comprising ferromagnetic carrier particles and non-magnetic toner particles are caused to flow through a conduit for measuring the toner density which is the ratio of toner particles to carrier particles in the mixture. The effective inductance of an electromagnetic coil disposed in the conduit varies in accordance with toner density. The coil is designed so that the magnetic lines of force thereof are substantially confined within the conduit and are not influenced by external bodies.

Abstract: A flash tube is utilized as an imaging light source for a moving photoconductive belt or the like. A capacitor connected across the flash tube is charged from a power source. The flash tube is triggered when the voltage across the capacitor reaches a sufficient level to discharge the capacitor through the tube thereby firing the tube which emits an intense and brief flash of light for illuminating a document and imaging the photoconductive belt. A failure sensor produces a failure signal in response to a sheet jam or the like. A voltage comparator produces an enable signal when the voltage across the capacitor is sufficient to fire the flash tube. A trigger signal generator triggers the flash tube and shuts down the apparatus in response to the failure and enable signals in coincidence to discharge the capacitor and the photoconductive belt.