Hybrid struts with smart piezoactuators for high-dynamic parallel kinematics

The structural advantages of parallel kinematic mechanisms for highly dynamic motions are undisputed. The mass values to be moved are essentially determined by the structure of the end effector platform. The accuracy of machines with parallel kinematic drive concepts is decisively defined by the joint and feed unit assemblies. Statical (except in hexapods) and dynamical bending and torsional loads limit the shape of the strut geometry. As a rule, an increase in volume to enhance stiffness at the same times results in an increase in weight and thus worse dynamic characteristics. Active compensation and damping elements provide an alternative to passively increasing stiffness by geometries fitted to load. An active compensation of torsion is aimed at achieving a high "virtual" torsional stiffness of the whole drive unit by means of a compensation drive which is based on piezoelectric actuators. The compensation drive works autonomously and measures and corrects the appearing torsional deformation in a self-controlled manner, independent of the end effector platform' s position in the working space adjusting feed units.