New Parallel Structure Based on Pseudo-Elastic Flexure Hinges for 2D-Orientation

'A new parallel structure for the orientation of a platform in two dimensions is presented. The new structure bases on two kinematic chains performing a closed loop. The structure consists of two interlaced cardan joints with identical axis of rotation. The main advantage of this structure is that both drives are fixed to the frame. This allows a very compact and light construction and a high dynamic behaviour because of the low moved masses. Additionally the orientation accuracy will be higher with less constructive and economic effort in comparison to a serial structure because the degrees of freedom are decoupled. Possible applications are e.g. laser deflection units, active orientation units for different tools (e.g. lacquering, laser), active support (e.g. to compensate out-of-balances), inclinometer, active cardanic shaft coupling. A patent is applied for this structure and applications. A typical problem of parallel structures is the high number of joints resulting in decreasing precision because of their backlash, friction and slip-stick-effects. To overcome these problems flexure hinges are used instead of conventional rotational joints. In order to achieve high angular deflections of the platform the flexure hinges are realised with a pseudo-elastic material. A single crystal CuAlNiFe material is used which surpasses other shape memory materials in its possible elastic strains. FEM simulations for different geometries of the hinges have been made to calculate the possible maximal angular deflections which are restricted to elastic strain rates up to 15%. Investigations are made to characterise the fatigue failure behaviour of this special material. Because of its single crystal structure leading to anisotropic properties tests have been made to determine dependencies between the orientation of the notch relative to the lattice and the mechanical fatigue of the hinges. '