Fig. 1. Experimental setup for on-machine measurement system

Fig. 2. System hardware-software framework diagram

Fig. 3. Schematic of point autofocus sensor. (a) Structure diagram; (b) defocus-voltage curves of the sensor^[21]

Fig. 4. Temperature correlation verification. (a) Schematic of the experimental process; (b) 3D measurement result of optical plane; (c) spectrum analysis results for 2D profile averaged along the scanning direction and temperature

Fig. 5. Schematic of coordinate system for origin calibration of the measurement system

Fig. 6. Temperature compensation algorithm verification. (a) Original surface topography; (b) surface topography after temperature compensation; (c) comparison of mean topography along scanning direction before and after temperature compensation; (d) mean topography spectrum analysis before and after temperature compensation

Fig. 7. Measurement results of Fresnel structure. (a) Comparison of surface topography measured by conventional confocal sensor and point autofocus sensor; (b) cause analysis of central defect; (c) light intensity curve received by the equipment at the draft surface

Fig. 8. Schematic of spherical Fresnel workpiece and error evaluation. (a) Spherical Fresnel microstructure workpiece; (b) spherical Fresnel error evaluation process

Fig. 9. Error of Fresnel structure under different measuring equipments. (a) Offline white light interferometer; (b) offline point autofocus instrument; (c) on-machine point autofocus instrument without temperature compensation; (d) on-machine point autofocus instrument with temperature compensation

Table 1. Parameters for temperature correlation verification

Table 2. Parameters for probe calibration

Table 3. Optimization initial value and corresponding results for original optimization equation

Table 4. Optimization initial value and corresponding results for optimization equation proposed in this work