Round-robin measurements of toroidal window

Abstract

We have performed a round-robin study of surface irregularity measurements of a free-form toroidal window. The measurement tools were a Leitz scanning CMM at Optimax Systems, Inc., an UltraSurf, a non-contact measuring system at OptiPro Systems, a Zeiss scanning CMM at OptiPro Systems, a F25 micro-CMM at Carl Zeiss Industrial Metrology, and an ASI(Q) TM at QED Technologies. Each instrument resulted in a 2.5D surface error map. The measurements were compared with multiple analysis settings. The different analysis settings removed some low frequency height errors, which varied amongst the measurements. This highlights the need for more study to determine the reasons for the differences in the low frequency errors. With the low frequency errors removed, the measurements compared very well, to within 0.2 µm rms.

Calibration and verification of areal surface texture measuring instruments

“…There have been no formal comparisons of areal surface texture measurement, although some comparisons of optical instruments have shown predictable variations [130,150] as do comparisons of AFM and optical instruments [131].…”

Freeform optical manufacturing and testing processes for IR conformal window and domes

“…The CMM has a touch trigger probe that scans surface and outputs the deviation of the measured surface from the nominal shape. We have participated in a round-robin study 6 of a freeform toroid window which showed that the CMM is accurate to about 1 µm peak-to-valley or 0.2 µm rms, Figure 4. To move beyond the precision provided by the CMM, we are using two methods.…”

“…Left: the CMM used for measuring freeform optics; middle: touch trigger probe used in the CMM measurements; right: the standard deviation of a set of round robin measurements of a toroid window6 indicating the accuracy of the CMM is near 0.2 µm.…”

Fabricating and Testing Freeform Optics: Current Capabilities, Lessons Learned and Future Opportunities

“…The area of freeform metrology is currently under investigation by a number of different research groups. [7][8][9][10] Achievable surface form error of freeform surfaces is a function of the complexity of the shape and the uncertainty of the measurement method. A typical scanning probe coordinate measuring machine is limited to approximately ±1 µm PV form error.…”

“…A typical scanning probe coordinate measuring machine is limited to approximately ±1 µm PV form error. [10] Surface smoothing may or may not be necessary based on the application and the severity of resulting midspatial frequency errors on the surface. Smoothing can be done implementing the VIBE smoothing process.…”