The output data is coordinates of the probe sphere center when the curve or surface is measured by CMM (coordinate measuring machinc), so the radius compensation for the probe must be done. On the basis of summarizing the methods of the radius compensation for the probe at present, measurement of the free surface is classified into two modes as inspection and reconstruction according to the measurement purpose. The compensation is finished in different ways on measurement modes. In the inspection mode, it is done by comparing the distance from the measured points to the theoretical surface with the radius of the probe to judge the measured surface is qualified or not. In the reconstruction mode, it is done by fitting the surface of the probe radius center first, followed by searching for the equidistance surface to gain measured surface The methods for calculating the minimum distance from point to surface and equidistance surface are introduced%测量机测量曲线和曲面时获取的数据是测头中心坐标值.因此必须对测头半径进行补偿.在总结目前测头补偿方法的基础上,提出以达到测量目的为宗旨,将自由曲面测量分为检测模式和重构模式,根据测量模式采取不同方法对测头半径进行补偿.检测模式下通过比较测头半径与测点到被测曲面的距离大小来判断曲面是否合格,重构模式下通过求取测头球心面的等距面来获得被测曲面,从而实现测头半径补偿.对于点到曲面距离的算法、等距面计算进行了研究.
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