SQUIGGLE® custom rotary piezoelectric motors
New Scale Technologies
The Wide-Field Multi Object Spectrometer (WFMOS) is a ground-based astronomical instrument that is scheduled to be commissioned on the Subaru Telescope on Mauna Kea, Hawaii in 2013. The WFMOS, along with corrective optics, will be mounted in place of the secondary mirror of the telescope. An array of NASA Jet Propulsion Laboratory’s Cobra fiber positioners will feed light from a 1.5-degree field of the sky to a visible spectrometer, for red shift observations of 2,400 cosmological targets simultaneously. The light will be transferred to the spectrograph using 2,400 f/2.4 fibers with 107 μm cores.
The array of 2,400 Cobra optic fiber positioners contains two SQUIGGLE custom rotary piezoelectric motors, which were developed specifically for this purpose by New Scale Technologies. Working with JPL’s design requirements, New Scale optimized the miniature rotary motor for high torque over 3.0 mN m and step size less than 0.065º. Each theta-phi style Cobra fiber positioner includes one 4.4 × 4.4 mm and one 2.5 × 2.5 mm SQUIGGLE motor, with one offset from the other, allowing the optic fiber to be placed anywhere in a small circular patrol region. The patrol diameter of the actuator is large enough to obtain 100% sky coverage of the close-packed hex array pattern of positioners.
The Cobra positioner was tested in a lab environment in a manner that simulates its use on the Subaru Telescope. The positioner was controlled in open loop, and used a CCD camera to image its optical fiber to determine its location. Over 100 simulated cosmological targets were tested using the Cobra positioner, which showed that it can converge on over 90% of its targets within 5 μm in six open-loop move iterations. The next phase of the project will include a high-fidelity design and test cycle. Characterization of performance versus lifetime at an environment that represents Mauna Kea will be conducted.
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