This paper presents the performances of recent high-tech hexapod positioning systems. Those devices with six degrees of freedom, are commonly used in Ground System Equipment (GSE) design, to qualify and conduct, for example, optical performance test activities. They are frequently used in vacuum environments. This is the case for example for EUCLID, CHIME, PLATO missions. They are also commonly used on large scientific instruments like Telescope or synchrotrons.
The latest innovations in terms of the performances, measurement technology, stability and control of those positioners are presented. The know-how the manufacturer has mastered to mature this technology and push the boundaries is on display. The characterization of the performance in terms of resolution, repeatability, accuracy, cross-coupling, backlash, and stiffness is clarified. The methods and measurement instruments used to characterize each specification are explained. Then, the most advanced performances of different hexapod positioners are described in detail. The goal of this step is to provide the current state of the art of hexapod technology and describe the most advanced system. Ongoing innovations that could push the boundaries are also featured.
Finally, we present how engineers can specify their positioners to be integrated into the next generation of Ground Support Equipment (GSE). This analysis will include key parameters such as the stiffness, duty cycle, thermal management but also the control requirements.
As part of the telescope completion plan, the Large Millimeter Telescope (LMT/GTM) project replaced the hexapod positioner for the secondary (M2) mirror. The new hexapod was provided by Symetrie of Nimes, France. The particular challenges for the LMT/GTM hexapod are that it is both large and precise. After completion of the fabrication and internal contractor verification of the system, the project conducted a series of characterization tests, both at the fabrication facility and at the telescope site. During the factory tests, the project team tested the hexapod in both vertical and horizontal positions, verifying the motion range, accuracy, repeatability, and velocity, all at the maximum operational payload. Additionally, the team performed verification checks on the stiffness of the hexapod. The results were excellent, with calibrated errors of less than 5 microns in the translation degrees of freedom and less than 1 arcsec in the rotations, which was at the limit of the metrology of the tests. Following the successful factory test, the system was transported to the telescope site and the tests were repeated. While the calibration step was not performed during the site tests, the raw results were comparable to the factory values, clearing the way for installation on the telescope. The new hexapod was installed, along with a new M2 mirror, in the Fall of 2017 in advance of the LMT/GTM’s first observing season as a 50 m telescope. This paper presents the test program, the metrology approach, the characterization tests, the calibration method, and the final factory acceptance test results.
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