New method of best-fitting on curved surface

With the coordinates measuring machine the measured points are obtained as a series of points consist of the original feature and the deviations caused by misalignment i. e. translated deviation and angular deviation. To evaluate the form deviation accurately it is required to best-fit the measured feature to the ideal feature. Conventional best-fitting has been done to minimize the sum of squares of deviations between measured feature and ideal feature by translating and rotating the measured feature. It is possible for the curved line but too difficult for the curved surface. This paper gives a new method of best-fitting using datums which minimize the sum of squares in its normal direction. The datum is defined as straight line for the curved line and plane for the curved surface. When the datum of measured feature is coincided with that of the ideal feature the deviations caused by misslignment are eliminated. In order to confirm the reliability of this method computer simulations and practical measurements were made. Then close agreement was obtained. Key words: coordinate measuring machine best-fitting curved surface datum method of least-squares form deviation software on the measurement accuracy y C) - Measured feature . /Ideal feature -I. Fig. 1 Conventional bestfitting method Ideal Measured feature feature eviation a) curved line Fig. 2 Designation of form deviation 54 / SPIE Vol. 2101 Measurement Technology and Intelligent Instruments (1993) b) curved surface