Hexapod load and range of motion analysis for expanding optomechanical applications at NASA Marshall’s X-ray and Cryogenic Facility

Positioning systems for optical metrology applications are continuously challenged to maintain high resolution, accuracy, and repeatability over ever-expanding ranges of motion and payload masses due to the need for larger optical apertures and sensor field of regard. To address these demands, new facility capabilities have been developed for the X-Ray & Cryogenic Facility (XRCF) at the NASA Marshall Space Flight Center. These upgrades included re-purposing the center of curvature optical bench (CoCOB) hexapod, originally designed for James Webb Space Telescope program testing, to provide precision positioning of large test articles. To maximize the potential range of test article sizes, and ultimately the utility of the facility, studies were undertaken to evaluate the maximum payload capacity and simultaneous range of motion combinations of the CoCOB hexapod without requiring significant hardware modifications. The analytical tools developed to assess and display the possible range of motion combinations for various center of rotation locations are discussed along with the results of the study. A hexapod load study was also completed to determine maximum allowable payload mass across a wide array of possible hexapod poses. Modeling was used to assess unmeasured deflections as a function of the displacement away from the hexapod’s null position and the associated impact on accuracy performance. The methodologies and results of each of these studies are presented in detail. Software techniques to prevent collisions between internal hexapod geometry and avoid overtravel of both actuator stroke and end-joint angular travel ranges are also discussed.