STEP/XML based macro data representation for parametric CAD model exchange

Abstract

There is tremendous need in collaborative design today for the integration of heterogeneous CAx systems. This general practice has serious shortcomings like design discontinuity, limited parallelisation, loss of information, and conversion errors. To overcome these shortcomings, macro-parametric approach (MPA), which is a history-based method of parametric CAD model exchange, has been proposed. The macro-parametric approach is a way to achieve compatible CAD model exchange amongst a variety of mutually incompatible CAD systems. CAD models can be exchanged in the form of a macro file that comprises a sequence of modeling commands. A standard macro file that contains a set of event-driven commands can transfer the designer intent such as parameters, features and constraints. Currently, STEP (STandard for the Exchange of Product model data) as an international standard (ISO-10303, Industrial automation systems and integration - Product data representation and exchange) for the computer-interpretable representation and the exchange of product model data is widely used. STEP is becoming the 'lingua franca' in the area of modelling and exchanging product data. One remaining problem of the using STEP as a neutral format is that it does not retain parametric information such as the designer intent but only the pure boundary representation (B-rep) of the CAD model. The B-rep model without parametric information presents difficulties for engineering changes and it may also lead to an unexpected distortion of shape. This research aims to investigate an exchange method that uses STEP/XML (extensible mark-up) technology to express a set of standard modeling commands extracted from CAD models created by Autodesk InventorTM, to enable the same CAD models are readable and shareable with other CAD application systems.