Abstract: A kind of posture alignment system of large rigid bodies based on 3-coordinate posts is studied. The system can be equivalent to a 6-DOF over-actuated parallel mechanism and the init and final posture of the movable-platform are given while the moving time and path are uncertain. In order to make the movement of the posts stable and to improve the precision of alignment, an optimal time trajectory planning algorithm with the actuating force and velocity restrains of the joints in the engineering is presented. Firstly, kinematics as well as dynamics models of the system are established with the analyzing method for over-actuated parallel mechanisms, and the minimum norm solution of the actuating force of the joints is obtained through Moore-Penrose pseudoinverse matrix. Then, the posture variety of the body is fitted by quintic polynomial while the aligning time is parameterized. At last, the optimal aligning time for the system subjected to the joint space restrains is calculated by the bisection method and the corresponding trajectory is generated. The simulation result shows that only a few times of iteration are needed to generate the trajectory with the algorithm. In conclusion, the planning method is feasible.

Key words: Dynamics, Kinematics, Optimal time, Parallel mechanism, Posture alignment