Performance characterization and control scheme derivation for "R-FLEX", flexure-based fiber positioner robot for Spec-S5 and future large-scale spectroscopic instruments*

The ”R-FLEX” positioner robot is a miniature high-precision fiber robot design for Spec-S5, intended

to improve upon the already massively successful DESI two-stage rotation robots. In this paper, we

take diagnostics of the robot through some preliminary testing, gathering precision and accuracy data.

We find root-mean-squared error (RMSE) at around 5 microns in both random-move ’cruise speed’

tests and small-step ’creep speed’ tests in the posive φ direction, but higher RMSE in the negative

φ. We use this information to set up correction-move scripts, which work exceptionally well with

over 95% of robots within 5 microns error after one correction. Through this, we derive the optimal

control scheme to be used during a future ’lifetime test’, the test to investigate how the robot performs

through many times its realistic lifetime. This will replicate the likely move pattern of Spec-S5 robots

in operation, and will be informative on whether this design can be pursued further in the R&D process.