Abstract: A drive mechanism for converting a rotational drive motion into a linear back and forth motion comprising driven member (21) for performing said back and forth motion, and a rotational drive member (33) for applying a driving force to the driven member. The drive member has a cam track (40, 43) cooperating with a cam follower (34, 35) of the driven member. The cam track has straight sections and motion direction reversing zones (41, 42) interconnecting the straight sections to provide an uninterrupted cam track. The cam track straight sections have back-tapered cam surfaces arranged in such a manner that the cam follower does not engage the respective cam surface which faces in a direction opposite to an instantaneous linear motion direction of the driven member, whereby the cam follower engages only cam surfaces facing in the instantaneous motion direction, except in said motion direction reversing zones.