A methodology for mechanical products assembly design defect identification was presented based on assembly constraint verification tree (ACVT). An identification system framework, which consists of verification tree constructors, modifier, monitor and identification analyzer, was proposed. Modified design parameters were stored into modifier, monitor was employed to supervise design parameters variation in modifier and renew design parameters information in verification tree, identification analyzer decided the start or stop of verification according to stack information in monitor. A prototype system based on above identification system framework was developed, assembly design defects identification results for driving leg of parallel manipulators demonstrate that not only can it enhance identification efficiency for assembly design defects effectively, but also can implement dynamic relating identification for assembly design defects of mechanical products.
Final assembly deviations of mechanical products are determined by accumulation, coupling and propagation of all parts tolerances in the assembly system, whether the final assembly meets the design specification or not can only be obtained after the assembly is completed. The verifiable design model in this paper took object-oriented Petri net as logic lever carrier, and embedded deviation in form of matrix to Petri net, and then analyzed and calculated the assembly deviation from the logical and numerical lever synchronically, after that the final cumulative deviation is obtained. If the cumulative deviation exceeded precision limit, key influence factors to the cumulative deviation could be analyzed. The assembly design defect is identified and located in the design process, and the synchronization of design and verification is achieved. This model has some excellent characteristics, such as modularization, reusability, and capability to describe structural logical relationships.
In this paper some fundamental formulae are derived for tetrahedron-based variable geometry truss manipulator which is composed of a series of tetrahedrons stacked upon each other such that one link in each cell is made variable on length. Analytical model for dynamics of the manipulator is established, and expressions in numeric-symbolic form of model matrices are derived. An example is given for illustration.
In order to identify design defects in mechanical product quickly and accurately, geometric constraints relationships between mechanical parts are formulated as critical functions, assembly constraint relationship (ACR) matrix is established based on encoding of geometric constraints between mechanical parts. Directed graph is employed to describe constraint relationship of ACR matrix, the node in directed graph denotes parts number, data structure of node stores the design parameters of mechanical parts, weights of directed graph arcs represents geometric constraint type. Weights of directed graph arcs are treated as antigen, design defects for mechanical parts are treated as antibody, mutation rules such as trimming, splicing and replacement is employed to identify design defects of antigen gene. Identification example of spherical mechanism demonstrates effectiveness and accuracy of above methodologies.
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