rotatably supported in a rotary or rotational bearing 23 this rotary bearing 23 is guided for selective movement as a unit in the direction of the double headed arrow c of fig2 in a stationary slide mounting not shown but cannot be lifted off its guide structure the perforated suction drum or suction drum 4 is driven by a suitable drive motor 27 fixed to a housing portion or part 26 the counter roll or drum 24 is driven for instance by an elastic belt or belt member 28 or equivalent drive or power transmitting element stretched or trained around the perforated suction drum 4 and the counter roll or drum 24 at any suitable location a guide element 29 is secured to the rotation or rotary bearing 23 in order to control the movements of the counter roll or drum 24 in one or the other of the directions indicated by the double headed arrow c the guide element 29 bears by means of a slide or ramp surface 30 on a cam or cam member 31 or equivalent structure this cam 31 is pivotably supported in a fixedly mounted rotary or rotational bearing 32 and is connected by means of a joint or hinge connection 33 with a stationary adjusting or positioning motor 34 a compression or pressure spring 35 is fixedly arranged between the rotary bearing 23 and a fixed housing portion.