Induced-Strain Actuators

The induced-strain active-material actuators are the enabling technology for a number of micromechatronics applications involving micropositioning, vibration control, etc. In this chapter, we will describe the principles and applications of induced-strain active-material actuators. The chapter will start with some generic concepts about induced-strain activematerial actuators in comparison with the more conventional electromechanical and hydraulic actuators. Next, the construction details of piezoelectric, electrostrictive, and magnetostrictive induced-strain actuators will be examined. The modeling of induced-strain actuators will be developed from first principles. The typical performance of commercially available induced-strain actuators will be examined. A linearized model for the electromechanical behaviorwill be derived. Theprinciples of induced-strain actuation (ISA) of a compliant structurewill be analyzed. The displacement analysis and the electric responsewill be derived for both static and dynamic applications. Displacement-amplified induced-strain actuators will be introduced, and their analysis will be discussed. The electrical power and energy flow in ISA applications will be studied. The analysis of mechanical power and energy extraction will be followed by the analysis of the electrical power and energy demands. The power and energy conversion efficiency will be examined. Criteria for optimal energy conversion will be derived. A comparative study of commercially available induced-strain actuators will be presented. The efficient design of ISA applications will be studied. Guidelines for the effective design and construction of ISA solutions will be provided. Electric power supplies for energizing induced-strain actuators will be briefly discussed. The last part of the chapter will deal with shape memory alloy (SMA) actuators. The presentation of the shape memory effect and the superplasticity behavior of certain materials (e.g., nickel-titanium alloy Nitinol) will be followed by a development of the basic analytical principles for estimation of the SMA actuator behavior under loadwhen heat activated. The chapter will finish with summary and conclusions, followed by a bibliography and a list of commercial suppliers of induced-strain actuators. The chapter contains a number of worked out examples inserted in the text, and a number of problems and exercises grouped at the end of the chapter.