An 8-mm diameter fibre robot positioner for massive spectroscopy surveys

Abstract

Context. Massive spectroscopic survey are becoming trendy in astrophysics and cosmology, as they can address new fundamental knowledge such as Galactic Archaeology and probe the nature of the mysterious Dark Energy. To enable massive spectroscopic surveys, new technology are being developed to place thousands of optical fibers at a given position on a focal plane. These technology needs to be: 1) accurate, with micrometer positional accuracy; 2) fast to minimize overhead; 3) robust to minimize failure; and 4) low cost. In this paper we present the development of a new 8-mm in diameter fiber positionner robot using two 4mm DC-brushless gearmotors, developed in the context of the Dark Energy Spectroscopic Instrument. This development was conducted by a SpanishSwiss (ES-CH) team led by the Instituto de Física Teórica (UAM-CSIC) and the Laboratoire d'Astrophysique (EPFL), in collaboration with the AVS company in Spain and the Faulhaber group (MPS & FAULHABER-MINIMOTOR) in Switzerland. Aims. The meachanical concept, DC-brushless motor properties, and the final performance of a prototyped unit is presented. Methods. Performance and verification tests were conducted with a fiber view camera-based optical set-up and using an automatic algorithm. Results. The prototype build is mechanically robust and reliable, and its control electronics ensure a very firm system with an xy positional accuracy better than 5µm. Conclusions. In this paper, we validate the concept of our advanced 8-mm fiber robot positioner prototype, as well as demonstrate that it can meet the requirements of the DESI project. Such efficient gearmotor fiber positionner robotic system can be adapted to any future massive fiber-fed spectrograph instrument.

Comparison of communication architectures for a fiber-positioning spectrograph

“…The positioner's electronics and actuators are the main source of heat near the focal plate. Fahim et al 26 report an average power consumption of 600 mW per positioner during its action. The most powerdemanding solutions, the ones based on CAN bus, would increase this value by 30 mW (i.e., 5%).…”

“…An initial estimation has reported that a path of 16 coordinates or fewer is enough to avoid collisions. 26 One byte for this length of field would suffice. Therefore, the largest amount of data to be sent to a single positioner consists of the move instruction and its two parameters: the field specifying the number of coordinates and 16 coordinates.…”

The Robotic Multi-Object Focal Plane System of the Dark Energy Spectroscopic Instrument (DESI)

“…The design was developed at Lawrence Berkeley National Laboratory (LBNL) and Space Sciences Laboratory (SSL), and mass-produced by the University of Michigan (UM) and École Polytechnique Fédéral Lausanne (EPFL). To ensure the overall success of the project, alternative designs were developed in parallel and successfully tested by a Spanish-Swiss consortium of member institutions within the collaboration (Fahim et al 2015).…”

Precision control of miniature SCARA robots for multi-object spectrographs

“…In order to measure many targets in parallel, the number of fibers is maximized. The correct placement of the optical fibers can be achieved with miniature SCARA Robots [15][16][17][18][19][20][21][22][23][24][25] (Figures 2 and 3). These robots have two serially actuated rotation axes (a and b), which position the fibers with micrometer precision on the focal plane.…”