A guideline for the selection of coordinate measuring techniques in reproduction of a wide range of sculptured surfaces

Student thesis: Master's Thesis

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  • Chi Cheun HOU


Awarding Institution
  • Wai Lam Ralph IP (Supervisor)
Award date28 Dec 1998


Three different sculptured surface reproduction approaches, namely Surface machining from touch probe measurement, Range Image Machining (RIM), and Shaded Image Machining (SIM) were investigated. The process in each approach is based on the surface coordinate measuring techniques, surface modelling and computerized numerically controlled (CNC) machining. In the approach of surface machining from touch probe measurement, the object surface was measured using a coordinate measuring machine (CMM). The acquired data points were used to reconstruct a surface using non-uniform rational Bspline (NURBS) surface model. The information of the modelled surface were used to Produce the surface on a CNC machining centre. The surface modeling and surface machining techniques were similar in all approaches, but the surface coordinate measuring techniques were significantly different In the RIM approach, the range data of the object surfaces were measured by laser scanners. Two laser scanning systems were used, one was a commercial sq stem and another was a tailor-made prototype system. SIM employed the photographic method to acquire the surface coordinates. In this approach, the coordinates of the surface profile were recovered using the principles of shape from shading model. The profile of the surface is recovered from multiple monochrome images. The used optical reflective properties in the approach were empirically assigned to the Phong reflection model. The surface coordinates of the surface are calculated by successive integration of the recovered surface normals using a reflectance map. The capability of the three approaches was examined by machining trials. A press handle was measured by a Mitutoyo CMM and a Kreon laser scanning system separately. The tailor-made prototype laser scanning system was used to digitize the face profile of a patient who suffered from Nasopharyngeal Carcinoma. A plastic mask used for external radiotherapy was produced from the scanned data. An experiment was performed to reproduce the surface profile of a computer mouse by the SIM approach. The results of the investigation show that the three different surface coordinate measuring techniques are suitable for a limited range of surfaces. For example, the surfaces with rigid and continuous features can be measured by direct touching method on a CMM. Soft and deformable surfaces are required to be measured either by RIM and SIM approaches. However, the former method provides a higher resolution measurement, and the later method is specially designed for some huge size and unreachable objects, such as mountains and planets. A selection method for the three types of coordinate measurement is found, and the measuring speed, accuracy and resolution of each type of measurement is also suggested.

    Research areas

  • Coordinate measuring machines, Surfaces (Technology), Measurement