the action pattern of the amount of web feeding by the lug folding flaps is made optimal in accordance with deviations of detection marks , such as specified printing patterns on the printing surface on web w , from the reference values when they are detected , and the pressing force applied onto web w by dancer roller 9 is stepwise or continuously adjusted according to the detection of the patterns . therefore , in comparison with the conventional examples , it is possible to widen the corrective range for the amount of web feeding . thus , the tolerance for printing errors on web w can be increased , and it is possible to operate the equipment without stopping . furthermore , it is possible to produce packaging containers with printing patterns applied at appointed positions , and faulty products are eliminated .