(57) A registration error is detected by reading register marks printed on a printing
medium in the preceding unit and the succeeding unit of a multi-color rotary press
and in response to a detected registration error, gains Kp and Ko in PD control are optimized based on (1) a pass length between the plate cylinders,
(2) pass length between a plate cylinder and a position at which a register mark is
detected, (3) the radius of a plate cylinder and (4) either of the displacement velocity
of a compensator roller or the printing speed to that the position of the shaft of
the compensator roller which is interposed between the adjacent units is displaced,
whereby register marks are registered with respect to each other.
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