Conservative Error Space Estimation of 3-DoF Planar Parallel Mechanisms

This article develops a geometric method to estimate the error space of 3-DoF planar mechanisms with the Minimum Volume Ellipsoid Enclosing (MVEE) approach. Both the joint clearance and input uncertainty are considered in this method. Three typical planar parallel mechanisms are used to demonstrate. Error spaces of their serial limbs are analyzed, respectively. Thereafter, limb-error-space-constrained mobility of manipulator, namely, the manipulator error space is analyzed. MVEE method has been applied to simplify the constraint modeling. A closed-form expression for the manipulator error space is derived. The volume of the manipulator error space is numerically estimated. The study approached in this paper develops a geometric error analysis method of parallel mechanisms with clear algebraic expressions. Moreover, far fewer forward kinematics computations have been performed in the proposed method than in the widely used interval analysis method. Although the estimated error space is larger than that in practice, due to the enclosing ellipses enlarge the regions of limb error space, the method has attractive advantage of high computational efficiency.