Abstract
Parts must be measured to evaluate the manufacturing accuracy in order to check whether their dimension is in expected tolerance. In engineering, parts with free-form surfaces are generally measured by high-precision coordinate-measuring machines. The measurement accuracy is usually improved by increasing the density of measurement points, which is time-consuming and costly. In this article, a novel sampling method of measurement points for free-form surface inspection is proposed. First, surface inspection is simplified into the inspection of a number of section curves of the surface. Second, B-spline curves constructed with an iterative method are employed to approximate these section curves. Subsequently, data points necessary to construct the B-spline curves are taken as the measurement points. Finally, the proposed method is compared with other two sampling methods. The results indicate that the proposed method greatly reduced the number of measurement points without decreasing the precision of surface modeling.
Highlights
With the rapid development of computer-aided design/ computer-aided manufacturing (CAD/CAM) technology, free-form surfaces are widely used in the field of industry, especially in the area of aviation, aerospace, shipbuilding, and automobile
In order to improve the inspection efficiency of the freeform surfaces, a novel measurement point sampling method is proposed in this article
B-spline curves are adopted to approximate the section curves of the inspected free-form surface. They are iteratively constructed under the constraint of a certain allowable approximation error based on the shape information of the section curves
Summary
With the rapid development of computer-aided design/ computer-aided manufacturing (CAD/CAM) technology, free-form surfaces are widely used in the field of industry, especially in the area of aviation, aerospace, shipbuilding, and automobile. The number and positions of measurement points are planned in real time during the measurement process In this aspect, Edgeworth and Wilhelm[10] proposed an adaptive inspection method based on an error surface model which interpolated by the measurement points. In the second category of the previous researches, the position and number of measurement points are determined based on the nominal CAD model In this aspect, ElKott and Veldhuis[16] developed a sampling method aiming to inspection of trimmed sculptured features. Measurement point sampling for free-form surface inspection can be described as the mathematical model in equation (1). The key issue of the B-spline curve construction becomes determining the knot vector, positions of measurement points, and their corresponding parameters. Two strategies are given as follows to acquire a better approximation of surface section curves with the Bspline curves
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