Recent advances and applications of NASA's new ultrahigh-sensitivity absolute optical pattern recognition encoders

NASA's new optical encoders use pattern recognition for images of encoder scales to encode both rotary and linear, absolute, mechanical position with ultra-high sensitivity. These encoders have advanced beyond prototype stage and are now being used in a variety of demanding applications both in the laboratory and in optical ground support equipment for space flight instrumentation. Rotary versions of these new pattern recognition encoders have sensitivity down to 0.01 arcseconds while linear models have demonstrated sensitivity of 10 nm (0.01 micrometer) with higher sensitivities achievable in both formats. The means for encoding is a radical departure from that for conventional optical encoders and offers advantages of absolute operation, very low cost, compact form, considerable immunity to scale-damage-induced dropouts of position information, an order of magnitude or more higher sensitivity over commercially available encoders, demonstrated applicability in cryostatic and vacuum environments, and suitability for space flight. Operational details of the encoder are given. Representative sensitivity performance is presented along with several examples of uses to date. Planned future development is also discussed.