// Showcase
Six concepts for one tilt stage, assessed in three parallel evaluations. The winner had three documented arguments against it, and all three were answered afterwards, one at a time.
An optical module needed to be tilted around two axes to measure its wavefront at different points. That sounds simple, but it is not: the tilt axis has to run exactly through the pupil of the module, otherwise tilting shifts the very reference the measurement relies on, and the analysis reads that as an error that is not actually there. On top of that comes a repeatability of 5 arcseconds at loads of up to 25 kg, verified per ISO 230-2.
Six concepts, three parallel evaluations from mechanics, controls and manufacturing. In the end a commercial six-axis positioner came out on top, even though three things spoke against it: too expensive, travel range tight, pivot accuracy unclear. Instead of scrapping the concept, we tackled each point one by one: recalculated the travel range actually needed, turned the pivot point into a software question via coordinate transformation, and weighed the cost against the effort of four complete custom builds.
All four delivered units passed acceptance testing per ISO 230-2 at 200 kg load with clear margin: 0.10 to 0.39 µm translational repeatability against the required 0.5 µm, and 0.76 to 2.08 µrad rotational against 2.5 µrad. Of all things, the point that gave us the most headaches, pivot accuracy, ended up being the safest. The customer gets a measurement system with real buffer instead of a design cutting it close.
Four identical tilt stages, each mounted on a granite base with a rotation axis. For every module variant we mapped the optical pupil into the coordinate system of the positioner platform via coordinate transformation, in two mounting orientations. Whatever is left over goes into correction tables instead of tighter tolerances. Every unit ships with a full acceptance report per ISO 230-2.
A mechanical development job turned into an integration job. The effort shifted from bearings and kinematics to coordinate systems, correction tables and calibration routines. And it all carries over to other module variants with a different pupil location, with no new mechanics needed.
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