A new concept fiber positioner

Abstract

Large multi-object spectroscopy telescopes measure the light from millions of stars and galaxies for the use in astronomical studies. One part of these telescopes is the fiber positioner, where a few thousand of optical fibers need to be individually positioned very accurately. The problem with current fiber positioners is the small patrol area, the long production times and the light loss due to the incorrect movement of the tip. The goal of this research is to design a new type of positioner which solves the mentioned problems; large patrol area, fast production and reduction of light loss. The final design is an r-theta design with one rotating motor and a displacement mechanism to move the fiber horizontally over the focal plane. The design is based on the best suitable straight line mechanism from the Reuleaux collection: the Scott-Russell linkage. Flexures are used in the final design. This eliminates backlash and slip-stick effects in therefore improves the accuracy. An experiment with a scale model has been done to show that an exact horizontal positioning with the fiber exactly orthogonal is possible with this design. By adjusting two parameters in the design, the movement and the angle between the horizontal and the fiber can be adjusted. This means an exact movement can be finetuned in order to reduce light loss. The flexure based displacement system is monolithic and can be made by laser cutting. This reduces the production and assembly time of the system drastically. The design meets the patrol area requirement and shows large potential to increase this area up to an estimated 4 times the pitch. In order to validate the remaining requirements of this very promising design, additional experiments with a real scale fully functional prototype is needed.