Large-amplitude rotary induced-strain (LARIS) actuator

Induced-strain materials can produce very large forces and, hence, large energy density, but small actual displacements. A new concept for obtaining large-amplitude rotary displacements from small linear displacements generated by induced-strain material stacks is proposed. The concept utilizes the theory of twist-warping coupling in thin-wall open tubes. The theory of the proposed solid-state axial-to-rotary converter-amplifier, together with the appropriate bibliographical references, is given. A simple formula is generated for estimating the axial-to-rotary conversion-amplification coefficient from the geometrical length, L, and enclosed area, A, of the open tube. A large-displacement induced-strain rotary (LARIS) actuator proof-of-concept demonstrator was built and tested to verify and validate the theoretical developments. The LARIS actuator consisted of a 28 mm diameter, 1.2 m length open tube and a 120 mu m, -1000 V PZT translator. The experimental set-up and the excitation and measuring equipment are fully described in the paper. A maximum rotary displacement of 8 degrees was measured, and the linear relationship between the rotation coefficient, the tube length, L, and the inverse of the enclosed area, A, was verified. An improved theoretical model, that accounts for the experimentally observed zero off-set, is also given. The theoretical developments and experimental tests presented in this paper show that the proposed LARIS actuator, based on a novel solid-state axial-to-rotary converter-amplifier utilizing the warping-torsion coupling of an open tube, is a viable design option, of great constructive simplicity and very low parts count. This concept can be successfully used in a series of aerospace and mechanical engineering applications, as for example in the actuation of adaptive control surfaces for aircraft wings and helicopter blades. The 8 degrees rotary displacement capabilities measured on the proof-of-concept demonstrator can be easily scaled to other values to meet the operation requirements of specific applications. For very large angles (40-50 degrees), conventional electro-mechanical actuators (e.g., stepper-motors and ball-screws assemblies) can be used.