A shape-memory actuator for surface geometry control

Abstract
A compact actuator based on the constrained recovery effect is presented in the paper. Initially designed for airfoil shape adaptation, the so-called fish-mouth actuator can be used everywhere high stroke-to-thickness ratio is needed. The fish-mouth actuator consists essentially of a composite flexible structure coupled with a coil of NiTi-wires. Some additional components like special brass connection blocks and a silicone rubber filling were added in the course of development for performance improvement. In its final design, the actuator is composed of 14 parts, assembled separately. The fish-mouth actuator is designed and tested for a maximum stroke of 2 mm and a maximum force of 200 N. Its thickness (in activation direction) amounts to 7.8 mm. If used with a feedback control system, it can reach a displacement precision tolerance of less than 1 m. The paper opens with the description of the actuator's concept as well as of the dimensioning procedure. Then the main development steps are explained, some mechanical, thermal and manufacturing problems are addressed and the corresponding solutions discussed. Finally, some significant experimental results are discussed and a method for fine adjustment of the performance curve is sketched.