Mechanisms in the GMT acquisition guiding and wavefront sensing system

The Giant Magellan Telescope’s Acquisition, Guiding, and Wavefront Sensing System (AGWS) is comprised of four identical probes, each containing 11 axes of precision control. The largest of the mechanisms carries a mass of nearly 500kg. The mechanisms are diverse in type, including a voice coil actuated tip-tilt mirror, a rotary harmonic drive, high accuracy and precision lenslet rotation stages and ballscrew driven linear stages. To meet image quality, positioning, and tracking requirements, these mechanisms and their EtherCATcontrolled servos are designed for stiffness. Employing inductive tape encoders, they must position and track to 10um precision with minimal backlash, over velocities ranging from ~10mm/sec to essentially zero, where stiction becomes significant. We will present the designs of the mechanisms, highlighting key features, design trades, and preliminary prototyping results.