Research On Neutral File And Its Application To Reverse Engineering

Reverse Engineering (RE) is a technology of creating a digital model from an existing physical part so that subsequent manufacturing processes may be implemented. There are many measurement methods in RE, and the measurement data are different from each other in format so that several different kinds of CAD software are necessary for data processing. How to share the measurement data among different CAD systems is a very pressing problem in RE research. In this paper, the STEP neutral file and its topology structure are researched, and an interface based on neutral file is developed, which implements data sharing by transforming CMM (Coordinate Measurement Machine) data to neutral file in application.Firstly, the present status and application of STEP are introduced, the EXPRESS language is illuminated, the way to describe entities in neutral file is discussed, the method to define the simple feature in neutral file is summarized, and the structure of neutral exchange file is described.Secondly, the topology information model in neutral file is analyzed, the way to describe the topology information among entities is researched, and the topology model trees of sphere, parallelepiped, cylinder, and pipes are established.Thirdly, the data transform interface based on neutral file is developed, the DFC (data flow chart) is given, the program arithmetic is introduced from several aspects, such as reading data, calculating parameters, changing data format, outputting neutral file and so on. The interface function is implemented by a VC program.Finally, the application of interface in RE is illuminated, which is applied to reconstruct pipes model, B-spline surface model and complicated shape part model. A comparison in efficiency and precision is given between normal reconstruction way and the using interface way.