A dynamic analysis of parallel robots with consideration to friction of spherical joints

Abstract

This paper presents a dynamic analysis method for parallel robots with passive spherical joints having a friction torque. We applied the d'Alembert's principle to the dynamic analysis by modeling the friction torque of the joints as external moments. Dynamics of a Delta robot were formulated based on this method. On the other hand, an identification strategy of the friction torque at spherical joints from measured driving torques of the actuators was presented. As a result of numerical analysis using the presented method, step change was observed in the calculated driving torque at the time when the direction of relative angular velocity of paring elements of spherical joint significantly changed.