Abstract

By investigation of movement of the Assur groups in normal connecting condition, and by inspection of the kinematic pair concept, the conclusions were found that #x201C;The freedom of Assur group is zero#x201D; in the Planar Mechanism Composition Principle conflicts with the fact that Assur group can move, and the external kinematic pairs of Assur group are inconsistent with the kinematic pair concept. Proposals were put forward then that the motion characteristics of Assur group should be studied in normal connecting conditions, Grade I Linkage Group should be introduced, and the PPP Type Linkage Group existence as an example was provided. Some new views were put forward in discussion of Planar Mechanism Composition Principle. And then an example of mechanism analysis was given to show that the correct statement of the Mechanism Composition Principle is helpful to solve mechanism analysis problems.