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.
This paper describes the design of an optical metrology system for fiber positioners. The system can be used for accurate calibration and verification of fiber positioners with SCARA-like RR planar kinematics. It is capable of measuring accurately the absolute position and tilt of the fiber tip over the whole workspace of the positioner. The metrology system works by back illuminating the optical fiber of the positioner with a laser. The position and tilt of the exiting cone at the tip of the fiber is measured with two optical cameras.
One of the big research topics in modern cosmology is the mystery of dark Energy. To unveil the secret, cosmologists want to measure precisely the evolution of large scale structures in the universe. One way of doing so is to measure the 3D location of a high number of galaxies. By measuring the redshift of a galaxy, it is possible to find its distance. In order to measure a high number of galaxies in a practical amount of time, we need to observe multiple objects in parallel. Instead of a spectrograph, thousands of optical fibres are placed in the focal plane of a telescope. They will transmit the light of many objects to a spectrograph. Each fibre has to be positioned to several μm precision in the focal plane of a telescope for each exposure. Each fibre is positioned by a 2-axis fibre positioner. In this paper such a fibre positioner with 24-mm diameter is presented. It is driven by two brushless DC motors in combination with a backlash free gearbox. The positioner has an optimal central fibre path and improved angular alignment. The fibre runs through the centre of the positioner and is only bent at the top to reach its target position. In this way, the flexion and torsion of the fibre are minimal. In addition to the high positioning accuracy, the design is optimized to allow a minimal tilt error of the fibre. This is demonstrated using a novel optical tilt measurement system.