中文摘要：

少自由度并联机构应用于机床上时要求具有很高的刚度，而少自由度并联机器人的刚度和机器人雅可比矩阵有很密切的关系。采用螺旋理论方法求出了4-RUC4自由度并联机构的雅可比矩阵，推导出4自由度并联机器人的刚度计算公式和条件指数计算公式，分析了少自由度并联机器人在某一位置时（z=0）最大和最小刚度所在的方向，给出了这种4自由度并联机器人的最大和最小刚度曲线，通过曲线可以评价出此并联机构在各个方向上刚度大小，为这种机器人的应用和开发提供了有力的依据。

英文摘要：

The high stiffness is required when the lower DOF parallel manipulator is used in the machine tool. The stiffness matrix of lower DOF ara manipulator depends 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 minmum stiffness when the parallel manipulator lies in fixed place is described. The stiffness curves show the maximal and minimal stiffness of parallel manipulator when the parallel manipulator lies in z = 0. The stiffness in the fixed direction offers the evidence for the use of parallel manipulator.