The amount of deformation on the surface is symmetrically distributed, and the amount of deformation is constantly changing as the probe moves continuously on the slope. When the probe is outside the positioning groove or at the bottom of the groove, the deformation of the probe is always fixed and the value does not change. In this way, the amount of deformation of the probe at the bottom of the positioning groove can be used as a basis for judgment. When the deformation of the probe at the lower slope is less than 厶1+0.1, the angle at this time is recorded. When the deformation of the probe on the upper slope is greater than 0.1, the angle at this time is recorded as a2, then the position of the centerline The detection of a (a|+a2) workpiece is mainly to determine the position of the center line of the positioning groove. If the position of the center line cannot meet the processing requirements, the machining error cannot be controlled. Since the sampling period of the data is relatively short, assuming that the change value of the deformation amount of the probe in each sampling period is AX, the angular error recorded by the two sections of the slope should be within two sampling periods, that is, at (AA+0.1-AX). Between the angles corresponding to (厶+0.1+AX), adjust the size of AX to make the position of the center line of the positioning groove meet the processing requirements.