New developments in robotic fibre positioning for astronomical multi-object spectroscopy

Thesis

This thesis presents two bodies of work, both related to automated optical fibre positioning in highly-multiplexed astronomical instrumentation.

Part one concerns the development and prototyping of a pick-and-place fibre positioner for WEAVE, a new 1000-fibre spectrograph for the 4.2 m William Herschel Telescope. This research has helped shape the positioner's final design and has included development of three novel techniques to enhance predicted performance: i) a scheme for automatically calibrating the fibre measurement system; ii) an algorithm for finding the centre of an imaged fibre with superior accuracy and speed; and iii) a robot motion control scheme to greatly reduce field reconfiguration time. Following these developments, and with rigorous testing of the proposed industrial robotic components, it is found that the performance of the positioner is likely to meet WEAVE's scientific requirements.

Part two of this thesis presents a new design of piezoelectric motor for 'tilting spine' fibre positioners. Tilting spine technology already allows simultaneous positioning of fibres in high-density fields, but has two significant drawbacks: i) fibres are tilted, resulting in optical losses; and ii) actuators require signal amplitudes of >100 V, placing performance-degrading limitations on the control system. The new motor has a more efficient mechanism and a drive voltage of just ±9 V, allowing new control approaches that vastly improve the technology's capabilities. Prototyping has shown a closed-loop positioning accuracy of <2.8 μm, lower than any other published technique. A 50% reduction in optical loss is shown to be feasible by trading some accuracy for a spine length increase. It follows that any survey using this motor would have a higher signal-to-noise ratio and/or would complete faster than with the existing technology.

Authors: Gilbert, J

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: astronomical instrumentation; pick-and-place positioning; fibre-fed spectroscopy; piezo actuators; micro-positioning; multiple-object spectroscopy; piezoelectric motors; massively-multiplexed
• Subjects: Astronomical instruments; Astronomy; Fiber optics; Optomechanics; Piezoelectric devices; Actuators; Robotics