Local annealing of complex mechanical devices: a new approach for developing monolithic micro-devices

The concept of monolithic shape memory alloys (SMA) micro-devices is to int egrate all device functions within the same piece of material. This is very interesting in the field of micro-systems, because assembly is avoided. In such devices, the main problem is to create a reversible motion. Recently, the use of the two-way shape memory effect has been investigated. A simple r solution could be to integrate a pullback spring within the monolithic st ructure. This implies introducing shape memory properties only in some pred efined parts of the material. In this paper, an approach based on local ann ealing of the material is proposed. The annealed parts will exhibit a shape memory effect and the remaining non-annealed parts will have an elastic be havior. Two methods of local annealing have been investigated. The first on e is done by an electrical current, which needs a special design of the ele ctrical path. The second one is done by local laser heating, which allows c omplete freedom in choosing the 'memory regions' of the material. With thes e tools, complex mechanical devices with active and passive parts can be de signed. To illustrate this idea, two mechanical structures containing local ly annealed parts are presented. (C) 1999 Elsevier Science S.A. All rights reserved.