Investigation of active materials as driving elements of a hydraulic hybrid actuator

In recent years, there have been growing applications of active materials, such as piezoelectrics and magnetostrictives, as actuators in the aerospace and automotive fields. Although these materials have high force and large bandwidth capabilities, their use has been limited due to their small stroke. The use of hydraulic amplification in conjunction with motion rectification is an effective way to overcome this problem and to develop a high force, large stroke actuator. In the hydraulic hybrid actuator concept, a hydraulic pump actuated by an active material is coupled to a conventional hydraulic cylinder, from which output work can be extracted. This actuation concept requires a high bandwidth active material with a moderate stroke. Both piezoelectrics, and magnetostrictives such as Terfenol-D and Galfenol are well suited as driving elements for this application, however, each material has its drawbacks. This paper presents a comparison of the performance of a piezoelectric, Terfenol-D and Galfenol element as the driving material in a hydraulic hybrid actuator. The performance of the actuator with each driving element is measured through systematic testing and the driving elements are compared based on input power required and actuator mass. For a pumping chamber of diameter 1” and a driving element of length 2”, the maximum output power was measured to be 2.5 W for the Terfenol-D hybrid actuator and 1.75 W for the piezoelectric hybrid actuator.