Kinematic design of 3-URU pure rotational parallel mechanism to perform precise motion within a large workspace

We present an optimum design of lower-dof parallel mechanism, a 3-URU pure rotational parallel mechanism that reflects issues of workspace and the position error of the center of rotation of the platform. The uncompensatable error determined by position error of center of rotation was used as an evaluation index for the design. The uncompensatable error index, an index used in the optimum design, was proposed taking into account four sources of errors, representing errors between adjacent joints. Based on the application of the mechanism and the error index, the effect of the redundant platform orientation parameter was numerically investigated and the design flow of the mechanism was proposed. We made a kinematic design of a mechanism with a large workspace subject to minimization of platform’s position error of the center of rotation. A prototype of mechanism with a large inclination angle of the platform up to 1.3 rad was shown, and its characteristics are also discussed.