Oscillatory drive unit

A drive unit for driving a passive element relative to an active element, wherein the active element comprises:

• a resonator and at least one excitation means for exciting oscillations in the resonator,
• the resonator comprising at least two arms extending from a connection region of the resonator at a same side of the connection region,
• the resonator and the at least two arms extending in parallel to a reference plane,
• each of the at least two arms comprising, at an outer end thereof, a contact
• element that is movable by oscillating movements of an associated one of the at least two arms,
• the passive element being arranged to be driven and moved relative to the active element by said oscillating movements;
• the passive element comprises contact areas, each contact area being arranged to be in contact with a respective contact element;
• wherein
• a pre-stress element is arranged to exert a relative force between the active element and passive element, whereby each contact area is pressed against the respective contact element with a pre-stress force that has a component that is normal to the reference plane.