Construction of High Quality Cad Model from Rough Physical Model

This paper deals with data processing technology to easily construct a computer model (a CAD model) with high quality surfaces from the shape data of a roughly created physical model. The position vectors and the unit normal vectors of discrete points on the rough physical model are obtained as measured data and are processed with the least square method based on quadratic surface approximation. The discrete points are then classified and grouped onto surfaces constructing the model according to the histogram (frequency distribution) of curvature. The position vectors and the unit normal vectors of the points classified on each surface are further adjusted by the least square method based on quadratic surface approximation. Finally, the computer model is constructed by combining the improved surfaces. INTRODUCTION In the recent aesthetic design of products, free-form surfaces are plentifully used to make the outer shape of a product in order to distinguish with other products. However, the currently used CAD systems do not have sufficient performance to directly design the product shape from thinking of an aesthetic designer. As shown in Fig. 1, in the current aesthetic design processes, industrial designers first draw sketches imaged by the product concept and create the precise physical models of clay, wood, or polystyrene according to the sketches because sketching is one of the easiest means for representation of designer’s idea. In this case, the computer model (CAD model) is constructed from measurement data of the physical model; this technology is called “Reverse Engineering”. Therefore, the physical model in reverse engineering should be created with deliberate attention so that it takes much time and cost. The positions of discrete points on the physical model are obtained as the measurement data in the current measurement technology. However it is hard to construct the computer model with high quality from the discrete position data because discrete positions are not enough data for restricting the shape. A designer represents a product shape by a sketch or a physical model according to the idea imaged by the product concept because currently used CAD systems are not suitable for representing designer’s idea of a shape. A precise physical model needs much time for creating. However, there is not such a problem in case of creating a rough physical model and a virtual clay model. An aesthetic design system based on a sketch, a virtual clay model, or a rough physical model is then desired for the practical use. In this study, a new method to easily construct a computer model with high quality shape from a roughly created model is proposed in order to reduce lead-time and cost in aesthetic design processes, and an original system based on the method is developed. PROPOSED DESIGN METHOD Figure 2 shows the procedures of the proposed aesthetic design processes. A rough computer model will be constructed from a sketch, a virtual clay model, or a rough physical model that are created by designer’s art work, and the computer model with high quality will be re-constructed by computer processing from the rough computer model. As shown in Fig. 3, a rough computer model is constructed from an image sketch, a virtual clay model, a rough physical model. The constructing system of a rough computer model from a sketch is under the developing course in the study of the authors. The virtual clay modeling system of which the development is also the author’s research project can create a rough computer clay model in the virtual world as if an operator creates a physical clay model in the real world. The author made it clear that the positions and the normal directions of discrete points are effective information for restricting the model shape and constructing the high quality computer model. A system 4 to autonomously measure the positions and the normal directions of discrete points on a physical model has been developed and a system to automatically construct the computer model from the positions and the normal directions of discrete points has been developed. Designer or Engineer Concept