the walking beam assembly of the forging presses operates in several movement phases including a lifting movement , advance movement , lowering movement , opening movement , return movement , and closing movement . step motors control driving members which perform individual moving processes in the individual movement phases . in turn , driving member processors drive the step motors by frequencies changing with time . when the velocity or frequency of the step motors are plotted on the ordinate of a graph and time along the abscissa of the graph , a trapezoidal graph form is produced along the time line of the graph for each of the movement phases . each trapezoidal form includes a rising flank and a falling flank with some of the flanks for adjacent driving member phase movement overlapping in time . the opening and return movement phases form a fixed cycle having a length predetermined and constant for all cycle lengths . the remaining phases form a varicycle having a length that changes with the length of the cycle time . during the fixed cycle , the walking beam assembly or manipulator does not move any workpieces . the varicycle can be adjusted to the respected mass of the workpieces . for workpieces having a large mass , the times for acceleration and delay are reduced .