Stiffness analysis of four degrees parallel manipulator

The high stiffness is required when the lower DOF parallel manipulator is used in the machine tool. The stiffness matrix of lower DOF are manipulatordepends on the Jacobian matrix. The Jacobian matrix of 4-RUC parallel manipulator is derived by screw theory. According to the Jacobian matrix, the stiffness matrix and the condition of parallel manipulator can be founded. The direction of the maximum and minimumstiffness when the parallel manipulator lies in fixed place is described. The stiffness curves showthe maximal and minimal stiffness of parallelmanipulator when the parallel manipulatorlies in z=0. The stiffness in the fixed direction offers the evidence for the use of parallel manipulator.