Hexapods are finding increased use in telescope applications for positioning large payloads. Engineers from The University of Texas at Austin have been working with engineers from ADS International to develop large, high force, highly precise and controllable hexapod actuators for use on the Wide Field Upgrade (WFU) as part of the Hobby Eberly Telescope Dark Energy Experiment ( These actuators are installed in a hexapod arrangement, supporting the 3000+ kg instrument payload which includes the Wide Field Corrector (WFC), support structure, and other optical/electronic components. In addition to force capability, the actuators need to meet the tracking speed (pointing) requirements for accuracy and the slewing speed (rewind) requirements, allowing as many observations in one night as possible. The hexapod actuator stroke (retraction and extension) was very closely monitored during the design phase to make sure all the science requirements could be met, while minimizing the risk of damaging the WFC optical hardware in the unlikely event of a hexapod actuator or controller failure.

The paper, “The Development of high-precision hexapod actuators for the Hobby-Eberly Telescope Wide Field Upgrade,” coauthored by Joseph Zierer,

Jason Mock, and Joseph Beno (UTCEM), John Good and John Booth (UT McDonald Observatory), and Paolo Lazzarini, Pierluigi Fumi, and Enzo Anaclerio (ADS International) and presented at the SPIE Astronomical Telescopes and Instrumentation 2010, San Diego, California, 27 June-2 July 2010, discusses the design trade-offs between stiffness, safety, back-drivability, and accuracy, leading to selection of the motor, high ratio worm gear, roller screw, coupling, end mounts, and other key components.

For more information please contact Joseph Zierer.

prototype actuator

Prototype actuator installed in the partially assembled laboratory test stand.

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