The torque balance equations of a spherical 3-DOF manipulator was derived in closed forms by analyzing the relationship of its input and output torques

then the torque input stability evaluation index and the global torque input stability evaluation index were defined and discussed based on the torque balance equation in detail. Finally

using the physical model technique

the parameters of the spherical 3-DOF manipulator were optimized based upon the global torque input stability evaluation index. Moreover

the integrated design scheme of spherical 3-DOF manipulator was confirmed to provide theoretical base for the applications of the spherical 3-DOF manipulator when satisfied the assembly conditions. Experimental results show that the spherical 3-DOF manipulator can be used as the waist

wrist and the precision platform to meet the requirements for high stiffness

high accuracy and good technological efficiency.