High-authority telescoping actuators

A family of high authority actuators was developed at the Naval Research Laboratory. These actuators are based on displacement amplification within a compact, solid state, monolithic piezoelectric actuator, by using a telescoping tube design. In this design, concentric tubes are mechanically connected in series. This gives an effective actuator length that is equal to the sum of the lengths of the individual concentric elements. The high displacement output of this actuator permits efficient coupling of the actuator output into a load of similar impedance, and thereby much greater effective actuator output. Initial prototypes were made of commercially available PZT tubes of three different diameters and wall thickness. These tubes were pulsed through the thickness of the walls and the change in their lengths were used for actuation. Their actuation is therefore making use of the d31 piezoelectric coefficient. Alternatively, electrodes can be applied to the ends of the individual concentric tubes and their lengthwise displacement will subsequently be proportional to the d33 parameter of the material. The tubes were bonded at their ends to alumina plates using epoxy-based adhesive. The displacement obtained from the assembly is close to the sum of those of the three individual tubes at the same applied field. Other parameters such as blocking force and energy densities are also reported. These actuators have applications where high force and simultaneously large displacement are required and space is limited. Potential uses include high end aerospace as well as low tech commercial applications.