Control system for color copier

Abstract

A control device for a color copier which sets up an adequate color copying time for any particular size of transfer papers. A color document is repeatedly scanned by a scanning optical system 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 electrostatically formed on the drum is developed by a toner which is supplied from a developing device and complementary in color to the color component associated with the latent image, the resulting toner images being sequentially transferred to a transfer paper which is held on and rotated together with a transfer drum. The control device includes a paper size setting circuit for setting the size of a transfer paper to be used before a copying operation, a scanning sensor for sensing the start of a scanning performed by the optical system, and a home sensor for sensing the instantaneous angular position of the transfer drum. A control circuit is constructed to determine a transfer start time and a transfer end time in response to a paper size signal outputted by the paper size setting circuit, an ouput signal of the scanning sensor, and an output of the home sensor, and to variably control the rotation speed of the transfer drum during the interval between the transfer start and transfer end times so as to align the leading end of a transfer paper loaded on the transfer drum and the leading end of each of the toner images formed on the photoconductive drum and different in color from each other.