Research on laser confocal free-form surface measurement method based on adaptive ant colony algorithm

Free-form curved optical elements have problems such as high degree of freedom of the surface shape, large surface gradient changes, requiring precise sample position adjustment before the measurement, which limits the accurate measurement of the surface shape. In order to address these problems, this paper proposes a laser confocal free-form surface profile measurement method based on the Adaptive Ant Colony Algorithm. This method utilizes the fact that the peak of the laser confocal axial response curve corresponds to the focal point of the sensor and that the peak position is not affected by changes in the tilt angle of the surface to be measured, thus realizing high-precision measurements of the three-dimensional morphology of free-form surfaces with large tilting angles. This method establishes the matrix transformation relationship between the coordinate system of the freeform surface measurement system and the design equation, and realizes the in-situ preliminary pre-alignment of the free-form surface by constructing a nonlinear least squares objective function. Then, through the Adaptive Ant Colony Algorithm, the optimal solutions of the six parameters in the transformation relation are globally searched, and the high-precision tracking measurement of the measured free-form surface is achieved. We constructed a high-precision free-form surface measurement system, and experimentally verified the laser confocal free-form surface measurement method based on the Adaptive Ant Colony Algorithm proposed in this paper. The results of the aspheric surface measurement test show that the repeatable measurement accuracy of the asphere surface shape residual PV99 is better than 50nm, the repeatable measurement accuracy of the residual RMS is better than 15nm, demonstrating the high iterative alignment accuracy of the Adaptive Ant Colony Algorithm. Therefore, our method provides an effective means of high-precision measurements of free-form surfaces.