<p>The recent burgeoning interest in massive multiobject spectroscopy has pushed the development of massive optical fiber positioning systems. These systems rely on precise fiber placement to detect the light spectra of many stars and galaxies. One successful approach is the use of robotic fiber positioners, which allow one to automate and scale up observations. However, due to the need for high precision and accuracy, each positioner must be calibrated and verified to comply with the requirements. The calibration measurements are nontrivial, and the large number of the robotic positioners up to thousands can lead to a prohibitively long time for calibration. We describe and validate an optical calibration setup and procedure for robotic fiber positioning systems. Based on the measurements results, we have developed models describing the behavior of the positioners and we introduce new performance metrics that allow one to verify the stringent positioner specifications and furthermore help to identify and analyze design and manufacturing flaws.</p>
The Dark Energy Spectroscopic Instrument (DESI) is under construction to determine the expansion history of the Universe using the Baryon Acoustic Oscillation technique. Over the life of the experiment DESI will measure the spectra of 35 million galaxies and quasars over 14,000 square degrees out to a redshift of 3.5. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5,000 robotic fiber positioners located at the prime focus. The fibers in turn will feed ten broad-band spectrographs covering the wavelength range from 360nm to 980 nm. Rapid and accurate targeting of the fibers is provided by precision theta-phi robotic fiber positioners. The fiber positioners are manufactured at the University of Michigan. Following assembly each positioner passes through a burn-in and verification sequence. We describe the testing of the positioners and discuss the performance achieved.