A Parametric Design Method for Computer-aided Design of Electric Machinery

In this paper the basic ideas behind an original computer-aided design (CAD) system for designing electric machinery is described. The framework in which all modules are implemented is a powerful interactive graphics system. The user thus continuously maintains control over the entire design through graphical communication. Because the CAD system is essentially conceived as a closed loop process, it supports a flexible and progressive design, allowing many trials-and-errors. Basically, the CAD system comprises two nested loops. In the outer loop, the adaptive modelling process, the geometry of the machine is controlled. The resulting geometric model maintains a dual representation of the machine. The boundary representation accepts all graphical actions of the interactive drafting system and guarantees compatibility with external systems through standards. The material region representation, on the other hand, is required for the purpose of calculation. The geometric model is hierarchically organized. This property permits the design engineer to build up the geometry from the constituent items that are relevant for the design, yielding a simple and meaningful structure. Moreover, this geometric structure need not be defined more than once. Mere assignment of new values to the parameters directly results in a new machine of the same type. Finally, any physically measurable quantity may be treated as a parameter, allowing a flexible simulation of dynamics. The inner feedback loop of the CAD system is the calculation process. In this process two basic calculation tools are provided. The magnetic network tool permits the condense description of simple field patterns at a low cost. The more expensive finite element routine provides an accurate description of complex fields. A powerful feature of the calculation process is that it supports any combination of both tools. The calculation tools are assigned to distinct machine subregions in the discretization process. This discretization is performed upon the geometric model and thus allows re-discretieation while preserving the geometry. Conversely, once a satisfactory discretization is achieved, the resulting discretized model may be embedded within the geometric model.