Design and performance of "R-FLEX", a flexure-based fiber positioning robot for spectroscopic cosmology

TL;DR

The paper introduces R-FLEX, a compact, high-precision fiber positioning robot for astronomical spectroscopic instruments, capable of mass production and suitable for next-generation cosmology surveys.

Contribution

It presents the design, fabrication, and testing of R-FLEX, a novel flexure-based fiber robot with improved size, accuracy, and durability for large-scale astronomical applications.

Findings

Achieves ≤5 μm positioning accuracy over 4 mm travel

Enables 6.2 mm pitch mounting with patrol coverage

Designed for 1 million cycle lifetime in harsh environments

Abstract

We present the design, fabrication, and testing of R-FLEX, a novel flexure mechanism for next-generation fiber-fed astronomical instruments. As the current Dark Energy Spectroscopic Instrument (DESI) revolutionizes cosmology with over 56 million collected spectra using 5,000 robotic fiber positioners at 10.4 mm pitch, we project that future instruments will require 2.5-3x smaller fiber robots by area. R-FLEX enables precision radial motion for fiber robots mountable at 6.2 mm pitch, delivering repeatable positioning accuracy $\leq$ 5 $\mu$m over a 4 mm travel range. The travel range extends outside the robot's mechanical envelope, providing complete patrol coverage of the focal surface. The R-FLEX design must meet challenging requirements for parasitic motion < 30 $\mu$m, angular misalignment < 0.3{\deg}, 1 million cycle lifetime, operating in a mountaintop telescope environment, and is suitable for mass production of $\sim$30,000 units.