Pseudo-elastic flexure-hinges in robots for micro assembly

An increasing tendency of products towards miniaturization makes the substitution of conventional hinges to flexure hinges necessary, since they can be manufactured almost arbitrarily small. On account of their multiple advantages like no backlash, no slip-stick-effects and no friction, their application is especially reasonable in high-precision robots for micro assembly. Particular pseudo-elastic shape memory alloys offer themselves as material for flexure hinges. Since flexible joints gain their mobility exclusively via the elastic deformation of matter, the attainable angle of rotation is strongly limited when using conventional metallic materials with approximately 0.4% maximal elastic strain. Using pseudo-elastic materials, with up to 15% elastic strain, this serious disadvantage of flexure hinges can be avoided. A further problem of flexible joints is their kinematic behavior since they do not behave exactly like conventional rotational joints. In order to examine the kinematics of the hinges an experimental set-up was developed whereby good compliance with theoretical computed values could be achieved. A three (+1) degree of freedom parallel robot with integrated flexure hinges is investigated showing its cinematic deviations to its rigid body model. The data of the kinematic model of the flexible joint can then be implemented into the control of this compliant mechanism in order to gain not only a higher repeatability but also a good absolute accuracy over the entire working space.