(57) 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 by
scanning optics (58) to sequentially expose a single photoconductive drum (52), 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 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 paper sheet which is held on and rotated together with a transfer drum (66).
The control system includes a paper size setting circuit (44) for setting the size
of a paper sheet to be used before a copying operation, a scanning sensor (86) for
sensing the start of a scanning performed by the optics, and a home sensor (88) for
sensing an instantaneous angular position of the transfer drum. A control circuit
(98) is constructed to determine a transfer start and a transfer end time in response
to a paper size signal outputted by the paper size setting circuit (94), an output
signal of the scanning sensor (86), and an output signal of the home sensor (88),
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 register the leading end
of a paper sheet loaded on the transfer drum and that of each of the toner images
formed on the photocondutive drum and different in color from each other. The circumferential
length of one of the photoconductive and transfer drums is greater than that of the
other by a multiple other than integral multiples.
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