Modeling technology of tolerance zone in virtual environment

Tolerance zone modeling plays a fundamental role in error propagation analysis, assembly precision predicting and assembly simulation with geometric precision. By analyzing the shape, size and local coordinate systems of various tolerance zones corresponding with different tolerances, a synthetic tolerance zone model integrating size and position tolerances was presented, in which the representation of virtual boundary and its constraint to geometrical element were central part, besides mathematic equation groups were built to represent tolerance boundary and geometric constraints were characterized by direction vector and error vector. The model was applied to find the range of tolerance zone constrained geometric variation among cylinder, concentric cylinder and two parallel planes. A prototype system was developed by using ACIS geometric modeling tool to perform the construction and display of typical tolerance zones in virtual environment, and related models and algorithms were verified by examples.