The patented design of the Picomotor actuator relies on the basic difference between dynamic and static friction. A graphic example of this is the tablecloth trick, in which a quick pull of the cloth leaves the dishes on the table (low dynamic friction), while a slow pull of the tablecloth ends up pulling the dishes off the table (high static friction and a big mess!). Our Picomotor actuator uses the same principle with a threaded jaw, similar to two halves of a split nut, clamped around a precision 80-pitch screw. One jaw is connected to one end of a piezoelectric transducer, and the other jaw is connected to the other end of the transducer. A slow electrical signal applied to the piezo slowly changes the length, causing the two jaws to slide in opposite directions. This slow sliding motion makes the screw turn (static friction). At the end of the transducer motion, a fast electrical signal quickly returns the jaws to their starting positions. Because of the screws inertia and low dynamic friction, it remains motionless, holding its position. Simply reversing the order of the fast and slow signals reverses the direction of rotation.
U.S. Patent #5,410,206