Abstract: Closed-loop mechanism is widely used in engineering practice, but when processing its dynamics analysis, the computation complexity is greatly enhanced due to the coupled constraints. The articulated-body (AB) algorithm which is efficient for the dynamics of a manipulator with a fixed base, the decoupled tree-structure (DTS) method which models the contact between the foot of robot and the ground and the hard-constraint method for treating the motion constraint problem are combined to process the dynamic analysis of the closed-loop mechanism. Meanwhile, a method which can select the Baumgert parameters dynamically is used to treat the violated constraint problem during the computational period. As a computational example, a hexapod using a closed-loop six-bar mechanism as its leg is developed based on the requirements of producing a small up-down change of the body when walking robot moves. The correctness of algorithm is validated by comparing the results of simulation of the hexapod in a program written by C++ based on the developed algorithm and ADAMS, meanwhile the motion displacement diagram shows that the hexapod satisfies the prescribed motion requirement.

Key words: AB/DTS algorithm, Dynamics, Kinematic constraint, Violated constraint, beating-up mechanism, conjugate cam, dynamic response, dynamics