ABSTRACT
In Figure 5.1, I show a somewhat schematic sketch of a piezoelectrically driven rotation stage from Mad City Labs.‡ This is a rotational positioner but it uses a translational piezo actuator acting at a lever arm to produce the desired rotary motion. Figure 5.2§ shows how six translational actuators
can be combined in a so-called hexapod confi guration to provide 6-degreeof freedom (3 translations and 3 rotations) motion control of a mechanical load such as a telescope mirror. Rotary piezoelectric motors are available in several forms. Figure 5.3* shows two Picomotors™ from New Focus, Inc., being used to control the angular attitude of a lens mount. These motors use translational piezo actuators to drive the rotation of a fi ne-pitch screw in a stepwise manner. That is, the screw is driven through a small and fi xed step rotation, slowly in the desired direction by frictional torque in a piezoelectrically actuated clamp. The actuator is then driven rapidly in the reverse direction, so fast that the screw inertia torque exceeds the friction torque and the friction coupling slips, allowing the piezo actuator to return to its neutral position, but the screw stays in its advanced location. Each pulse advances the screw about 20 nm and pulses can be applied as fast as 1000/s. In this way, full-scale motions of several inches can be controlled, far beyond the range of conventional translation actuator. Another form† of piezoelectric motor uses high-frequency wave motion to produce rotary or translational motion.
