Abstract: The mobility of the parallel mechanism calculated by using the screw theory tool is instantaneous, especially for the overconstrained parallel mechanism, not only the nature of the mobility may be changed, but also movement of some mobility could not realized at all, so whether the mobility is instantaneous or not must be checked. Since there have been very few investigations on the methods for distinguishing mobility’s instantaneity of the overconstrained parallel mechanism home and abroad, a simple method for distinguishing the mobility’s instantaneity of the overconstrained parallel mechanism is put forward based on the geometric constraint conditions of their own. For this method, the geometric constraint equations are established according to geometric constraint conditions of the different limbs of the overconstained parallel mechanism, and then whether the geometric constraint equations exist nonzero real solution is examined to determine the instantaneity of the mobility, and five overconstrained parallel mechanisms are taken as examples to elaborate the specific steps of the method. Then a simulation analysis method for distinguishing mobility’s instantaneity of the overconstrained parallel mechanism is proposed based on the simulation software ADAMS. And for this method, the extra degrees of freedom that are automatically added in the simulation model are firstly detected, then whether the extra degrees of freedom produce displacement is examined to judge the instantaneity of the mobility. Similarly, the above five overconstrained parallel mechanisms are analyzed by using this simulation analysis method. The results obtained by using these two kinds of distinguishing methods are consistent, which effectively verifies the correctness of the two distinguishing methods.

Key words: Geometric constraints, Instantaneity of mobility, Overconstrained parallel mechanism, Software ADAMS