Abstract: Isotropy is an important index of performance evaluation for a six-dimensional force sensor, and the isotropic performance analysis is a key problem in the structural design of Stewart platform-based force sensor. In order to achieve the best isotropy performance, the static mathematical model of Stewart platform-based force sensor is built by using screw theory, and the isotropy indices of the sensor are studied systematically. By using the mathmatical analysis method, the performance analysis of the forward and backward isotropy is presented. The analytic expressions of the key structural parameters are derived when both forward force and torque isotropy are satisfied. It is proved to be impossible to realize the backward force and torque isotropy simultaneously, and the restrictive relationships of the four isotropy indices are obtained. By compromising all the four isotropy indices and solving the extreme of the comprehensive performance objective function, the best comprehensive isotropy index of Stewart platform-based force sensor is achieved and the corresponding analytic expressions of the key structural parameters are obtained. The results of the theoretical deduction are important to the performance evaluation and structure design of the six-dimensional force sensor.

Key words: Analytic method, Isotropy, Optimal design, Performance index, Six-dimensional force sensor, Stewart