Linear drive

An apparatus for producing linear motion comprising:

• an elongate rod of circular cross-section arranged to be continuously rotated in a first direction about an elongate axis;
• and
• a carriage arranged to mounted on the rod so as to permit axial movement of the carriage along the length of the rod;
• wherein the carriage comprises:
• at least one first roller member arranged to contact the rod such that an axis of rotation of said roller member is at a first angle to the axis of rotation of the rod;
• said apparatus being characterized by further comprising:
• at least one first piezo-electric actuator means arranged to carry the first roller member for pressing the first roller member against the rod to cause rotation of the roller member, said piezo-electric actuator means comprising a first substantially flat resilient leg member and a second substantially flat resilient leg member, said first and said second leg members being connected by a substantially stiff bight portion, said leg members being arranged to lie substantially parallel with opposite surfaces of each leg member in mutual engagement along a substantial length of each leg member, other surfaces of each leg member being provided with piezo-electric layers arranged to deflect each leg member away from the other respective leg member;
• wherein the rotation of the roller member generates at least one axial vector in a first axial direction along said rod whereby to cause movement of the carriage along the rod in said first axial direction.