The "fish-mouth" actuator: Design issues and test results

The so-called "fish-mouth actuator", developed at DLR in the framework of the Adaptive Wing project (ADIF), is a compact hybrid actuator based on the interaction of a shape memory material and a composite flexible mechanism. The actuator offers a high effective strain (ratio between actuator's stroke and mounting dimension in the activation direction) and is therefore particularly interesting for the shape control of thin surfaces. In the ADIF project, the actuator development was focused on the realization of a wind-tunnel model for an adaptive wing with transonic bump. The actuator is designed and tested for a maximum stroke of 2 mm and a maximum force of 200N. Its thickness (in activation direction) amounts to about 8 mm. If used with a feedback control system, it can reach a displacement precision of less than 1 mum. More than 400 single actuators were built and tested; 84 of them were integrated in the final system. In this paper, several design issues are discussed that are typical for such fully coupled hybrid systems. The design analysis and procedure used for the actuator development is described and a choice of experimental results is shown and discussed. The reported design philosophy and the related discussion include many concepts and solutions of general relevance which can be adopted for the development of similar hybrid actuators in the future.