Metrology, calibration, integration and testing of the WEAVE fibre positioner

This thesis is about a pick-and-place fibre positioner for WEAVE, a new fibre-fed multi-object spectrograph for the 4.2 m William Herschel Telescope with a multiplex of 960. First light is expected sometime in 2020. The research presented in this thesis has been a major step in ensuring that the fibre positioner will be able to perform to the design specifications, and meet WEAVE's scientific requirements. The first piece of work presented in this thesis concerns the full positioner build, and the errors that are propagated by stacking components of the positioner. The guide to building a positioner shows that these errors can be measured and tracked, and ultimately compensated for. The tumbler assembly can be built to a high precision, but as long as the robot positioners do not move accurately, it is impossible to position fibres in the correct places on the field plate. One reason why this movement can be inaccurate, is that the coordinate systems of the targets, the robots, and the field plates are not expressed in each other correctly. Another is that the positioning structure itself changes under external influences such as temperature and gravity. A novel algorithm ensures that the positioning structure can be recalibrated periodically, removing these kinds of effects. Lastly, if the robot gantries cannot make repeatable accurate movements, this is a show-stopping problem too. Test procedures developed during this DPhil have shown that the X- and Y-gantries perform as expected, but the Z-gantry introduces unwanted movements in the x,y-plane when moving in the vertical direction. Because of the test procedures this design flaw was discovered and rectified by a new Z-gantry with a different internal structure. With these changes, the positioner robots are found to be repeatable to within the design specifications.