Kinematic Analysis Based On Assembly Geometry Model

In a mechanical assembly model, the motions of its parts are determined by their configuration relations in the assembly. However, kinematic models for an assembly are still built manually by users after constructing the assembling relations between the parts in most current commercial CAD systems. This not only leads to low efficiency, but also can't ensure consistency between the kinematic model and the original assembly structure. This paper proposes an instantaneous kinematic analysis approach based on geometry information and space configuration of the parts in assembly after analyzing and summarizing previous related research work, and the result of the kinematic analysis can be used for improving the design of original assembly models.The first work of this thesis is presented for automatically generating assembly features according to space locations of parts. In this method, by comparing geometry equations and boundaries of part faces, face-face contact types and relations between two parts are extracted and assembly features are created, according to which, a part adjacency matrix is also generated for representing the global relationships among parts in the assembly.The second work of this paper is to develop an approach for generating a model of assembly mobility. In this method, face-face mobility is defined by means of screw theory according to its contact type specified in its assembly feature. After that, the mathematical model of part mobility along an assembly feature is generated using screw intersection operations in Konkar algorithm. For common assembly feature, this model is just the twist representation of a motion joint.Finally, this thesis presents an approach for analyzing part mobility and driving relationships in assemblies. In this method, a spanning tree is generated from the part relation graph represented by the part adjacency matrix first. Then, by comparing the spanning tree with the part adjacency graph, independent closed loops in the graph are identified, from which, a circuit matrix is generated according to Kirchhoff's Circulation Law. Based on the circuit matrix, mechanism constraints in the assembly are created and its solutions are used to generate the motion twists between two disjoint parts. At last, after giving a condition for checking drivable relations between two parts, the matrix of driving relations is generated.Based on the work mentioned above, a prototype system for instantaneous kinematic analysis of assembly models has been developed to validate the ideas and methods proposed in this thesis. In the environment of UG NX3.0, using Visual C++6.0, Matlab 6.5 and UG Open/API, three sub-modules, including extraction of geometry information, generation of the joint's mathematical model and assembly mobility analysis, are developed. A practical example is used to validate the correctness and effectiveness of the research results. In the end of the thesis, some conclusions have been drawn and the future directions in the filed are given.