Research On Automatic Assembly Of Parallel Mechanism Base On Reverse CAD Assembly Technology

At present, there are a lot of researches of developing CAD softwares for two-dimensional mechanisms, and the relative theories of developing softwares for three-dimensional mechanisms have also been muture.We can see many standard parts, for instance gears and bearings, parameterized virture system for three-dimensional entity modeling. However, the researches of automatic assembly modeling secondary development for the three-dimensional entity is still at the beginning stage, and there are much fewer of parameterized automatic assembly system for parallel mechanisms. Among the developed automatic assembly system, in general, the structure type of parallel mechanisms and kinds of files of pair components are placed in a designed database.It not only increases the difficulty of developing, but also leads an obvious limitation of structure type and parts size,which is their greatest disadvantage. Therefore, based on macro technology and assembly precess reverse CAD method, a system which supports parallel mechanisms automatic assembly modeling is developed.In CAD softwares assembly environment, by analyzing CAD softwares API object model and the grammatical structure and parameters of their functions related assembly operation, the secondary development method of controlling virous of geometric reference entities and add mates to them is implemented; the problem that the instance number produced by calling a certain part for more than once affects the parameterized assembly result is solved; it allows user to assemble components to any leg simultaneously through controlling the leg parameters.The parameterized assembly process is realized.By analyzing the type of mates among the pair components in parallel mechanisms, various three-dimensional entities modeling is done in the form of lines, and a broad sense's and dynamic parts database based on series parts design table is established, beyond the database technology and relatived softwares. It is absolutely parameterized in the aspect of size of pair components.Using assembly precess reverse CAD method and CAD softwares API object and its functions,combining with Visual Basic 6.0 senior programming language, parallel mechanism assembly system is developed, which supports three legs, four legs,five legs and six legs parallel mechanisms automatic and parameterised assembly modeling. It is proved that assembly precess reverse CAD method is a good way to do assembly modeling secondary development to softwares for three-dimensional mechanisms and it can be used for developing large and serial assembly modeling parameterized systems.