Accuracy characteristics of the generalized cross-spring pivot

The cross-spring pivot, formed by crossing two leaves symmetrically at their midpoints, has been exploited extensively in a precision machine. However, the parasitic motions of this pivot are not small enough. The generalized cross-spring pivot improves the characteristics of center shift by changing the cross point to an arbitrary position along the leaf length. In this paper, a center shift model for the generalized cross-spring pivot is firstly developed without loss of generality. Then the characteristics of parasitic motions are investigated based on the model, and a pivot with small center shift is obtained by locating the cross point appropriately. Meanwhile, the influences of machining imperfections on design parameters are analyzed in order to evaluate the actual performance of the pivot, especially for parasitic motions. Furthermore, a compound generalized cross-spring pivot with large motion range but small parasitic motions is proposed. According to an equivalent model, the expressions for its center shift prediction are derived. Finally, the accuracy characteristics, revealed by the analysis model, are validated by finite element analysis (FEA). (C) 2010 Elsevier Ltd. All rights reserved.