A shape-memory actuator for surface geometry control

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 $\mu$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

Iterative Complex Phase Resonance Analysis.

Experimental modal analysis has proved to be of increasing importance in many structural engineering fields. It is used more and more often, particularly as an important prerequisite for the refinement and updating of structural mathematical models on which the dynamic qualification of modern aerospace structures is based. Complete identification of structures with weak damping coupling, in the form of their normal frequencies, real modes, damping coefficients and generalized masses, is successfully performed by means of the conventional phase resonance approach. In this method, the optimal exciter locations as well as the exciter frequency and force amplitudes are chosen by means of the Mode Indicator Functions (MIF) in order to excite only one mode of the system at a time. In contrast, complete characterization of structures with strong damping coupling requires knowledge of a full modal damping matrix among the other parameters. Such knowledge can be obtained only theoretically from results of the classical phase resonance approach, while the high degree of accuracy and complexity necessary of the measurements made any effort up to now unsuccessful. The new approach presented here allows for phase resonance tests to be performed on structures with strong damping coupling and high damping for the first time, obtaining a complete identification as a result, also in characterizing damping properties. As compared to the classic methods, some new features of the approach make it interesting when applied to structures with weak damping coupling as well

High Precision Form Measurement through the Use of Adaptive Structures Technology

A smart solution to vibration suppression in form measuring machines is presented in which the machine's vibrations are counteracted actively. For this purpose, the machine was equipped with a sensing system, an active interface, and a special controller. This new concept has been successfully tested on a real form measuring machine