3D FINITE ELEMENT SIMULATION OF A SHAPE MEMORY MICROGRIPPER

摘要

A shape memory alloy (SMA) microgripper is presented, which is made of a monolithic SMA device of 2 x 5.8 x 0.1 mm~3 size comprising various integrated functional units like two microactuators for active closing and opening, gripping jaws and an optical slit for position sensing. The mechanical and thermal properties of the microgripper are investigated by coupled finite element simulations and force-displacement measurements. For simulation of the shape memory effect, a two-phase macromodel is used. Mechanical tests reveal spring constants in austenitic condition in the order of 4500 N/m and nonlinear force-displacement characteristics in R-phase condition, which are confirmed by the simulations. The maximum stroke of the gripping jaws is 300 μm. The maximum gripping force is determined to 35 mN. Typical heat transfer times upon heating are between 40 and 110 ms depending on the applied power. The cooling times are about a factor of two longer. These results are in quantitative agreement with experimentally determined time constants.