The fiber positioner for 4MOST: exploration of an alternative R-θ design

We present a new type of R-θ fiber actuator named PotsPos for multi-object astronomical spectroscopy. It was initially intended to use as an alternative positioner design for the 4-meter Multi-Object Spectroscopic Telescope (4MOST). Although another tilting spine technology developed by the Australian Astronomical Observatory (AAO) is currently chosen for the 4MOST, PotsPos design has some technical advantages over other positioning technologies and might therefore be an attractive choice for future spectrographs. The design would be similar in positioning capabilities to the tilting spine design but would not suffer from telecentricity and defocus errors. The mechanical design, suitable motors, computational results from dynamic simulations and finite element analyses are presented.