Abstract: A coupling (12) to be operated between a platen (16) and a sheet separating arrangement (18) may be triggered by the reversal of the direction of rotation of the platen (16) in order to produce a driving connection from the platen (16) to the separating arrangement (18). The drive at the same time takes place as a result of a reverse rotation through a predetermined rotational angle and a subsequent forward rotation. In order, however, to make possible also a backward rotation of the platen without any triggering of the couling, said coupling has camming discs (40, 44) one of which serves for the production of the driving connection by engagement of one driver and the other for the prevention of an engagement of the driver, whenever the platen is turned backward beyond the predetermined angle of rotation. The prevention of coupling which is caused thereby, produces the freedom of rotating the platen forward and backward for the production of a graphic presentation on the sheet.