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J. Eur. Opt. Society-Rapid Publ. 21, 12( 2025)
Figure
2. Visualization of kinematic properties for freeform grinding.
( A)
( B)
Figure
3. Closed-loop power control:( A) scheme of the working principle and( B) comparison of the measured temperature curve with PID control( blue) and without PID control( red), respectively.
DIAS Infrared Systems), which was attached to the PJ source body. A synchronous movement of PJ source and IR camera ensures that the measurement spot always coincides with the PJ-surface contact area. The principle of operation is shown in Figure 3( A).
The PJ source was moved by a 3-axis CNC-controlled motion system along an x-y-meandering toolpath. The z-direction was varied according to the surface contour along the toolpath maintaining a constant working distance( i. e. the distance between PJ nozzle and the sample surface). Figure 3( B) shows an example of temperature measurement during PJP. While the power was maintained at a constant value, resulting in the red curve, which indicates a significant temperature fluctuation, PID control was employed, resulting in the blue curve. At the end of each meander line, which corresponds to the edge of the workpiece, the power was set to a fixed lower value to prevent the temperature from exceeding the setpoint temperature.
In order to reduce internal residual stress caused by local surface heating, all samples underwent annealing following PJP in a chamber furnace( Carbolite GPC1200, Carbolite Gero GmbH & Co. KG). An individualized temperature cycle was programmed in accordance with the thermal properties of the utilized sample materials.
2.3 Sample surface geometry
A so-called Alvarez freeform lens [ 33 ] was chosen and designed as the experimental geometry. This is an adaptive optical component consisting of two identical workpieces for varying the focus. These two components can enable a variable focal length setting depending on their lateral displacement relative to each other, shown in Figure 4( B). In general, this type of geometry is described by the following mathematical formula: