Abstract: During the semi-physical simulation experiment of unmanned vehicle, taking into account the features of high precision requirement to motion simulation system, a modified three degrees of freedom parallel manipulator based on the 3-RPS parallel manipulator is proposed. In comparison with the 3-RPS parallel manipulator, because the forces along the spinning shafts of the actuators in 3-RPS parallel manipulator are undertaken by the passive constraints of the modified parallel manipulator, the mechanical properties of the actuators are improved. The kinematic equations are established according to the structure of this parallel manipulator. The dynamic equations of the moving platform are formulated based on the Newton-Euler method. In the light of the principle of moment equilibrium, a force which is perpendicular to the actuator and its spinning shaft is worked out, and a force which is perpendicular to the upper part of the passive constraint and its spinning shaft is also worked out. According to the principle of power balance, a force along the upper part of the passive constraint is calculated. The driving forces of the actuators and the forces along the spinning shafts of the passive constraints can be obtained finally. This calculation method sheds light on dynamics calculation of lower mobility parallel manipulators.

Key words: Dynamic analysis, Kinematic analysis, Passive constraint, Power balance