中文摘要：

为研究一种三自由度支链嵌套并联机构的瞬时运动特性,对该机构的主螺旋进行了计算。在计算中首先利用虚拟机构法,建立了一阶影响系数矩阵。然后依据二次曲面分解理论并结合该机构自身特点识别了机构的主螺旋,进而以主螺旋为工具分析了机构的瞬时运动。结果表明：该机构在任意位型下的运动螺旋系皆为第五种特殊三系,且机构动平台可实现轴线沿z轴方向的360°旋转。

英文摘要：

To study the characteristics of instantaneous kinematics of a 3-DOF parallel with limbs of embedding structures, the principal screw of the mechanism is calculated. Firstly, the first-order influence coefficient matrix of the mechanism is established by the method of the imaginary mechanism. Secondly, the principal screw is identified according to quadricsurface degenerating theory and the characteristics of the mechanism. Then the instantaneous kinematics is analyzed by the principal screw. The results show that the motions of the mechanism in any configuration belong to the five special three-system, and the moving platform can achieve 360 degree rotation along the Z axis in the axis direction.