Dynamic Power and Energy Capabilities of Commercially-Available Electro-Active Induced-Strain Actuators

A method has been developed to predict the apparent material constants, the input and output power and energy, and the electro-mechanical energy conversion efficiency of electro-active induced-strain actuators under full-stroke, quasi-linear dynamic operation. The effect of the piezo-electric counter electro-motive force on the apparent input admittance is included. The non-symmetric expansion-retraction behavior of the electro-active material under full-stroke dynamic operation is symmetrized using a bias-voltage component and a superposed dynamic voltage amplitude that produce, in the actuator, a static position and a dynamic stroke amplitude, respectively. It is shown that the presence of the bias-voltage operation increases significantly the reactive power amplitude, and a simple formula for estimating this increase is provided. Reaction power values up to three times larger than those for unbiased operation were found. The secant linearization method and vendor data were used to evaluate the full-stroke piezoelectric strain coefficient, d, elastic compliance, s, electrical permittivity, ∈, and electro-mechanical coupling coefficient, x, of the electro-active actuator. Consistency with the basic active-material values was checked, and correction of the actuator full-stroke electro-mechanical coupling coefficient was applied, when required. Maximum power and energy delivery under optimal dynamic conditions (dynamic stiffness match) was studied, and the dynamic energy output capability of several commercially-available actuators were computed. Output energy densities per unit volume, mass, and cost were also calculated. The best electro-mechanical conversion efficiency, which was shown to take place at stiffness ratios slightly different from the dynamic stiffness match, was also computed.