STUDY SUMMARY - IPMU

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<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) 1.0 0.9 Optical Coupling 0.8 COUPLING EFFICIENCY 0.7 0.6 0.5 0.4 Complete Coverage with Positioners 35% Coverage with Positioners 0.3 0.2 Nominal Field Edge 0.1 0.0 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900 FOCAL PLANE SEMI-FIELD (Degrees) Figure 3.10-3: Optical coupling efficiency versus distance from the center of the field of view. The plot shows the field coverage of the positioner array. Coupling includes the optical performance of the WFC and the numerical aperture of the fiber, but does not include seeing or WFC internal flexure. The actuators are controlled in an open-loop mode with position information obtained after the fiber field is moved. Their positions are verified by back illuminating the optical fibers and measuring its location using a CCD metrology camera. The key to achieving rapid and accurate target acquisition are the Cobra Fiber Positioners, Figure 3.10-4. Cobra’s small size, high speed, and high resolution make it a key component of WFMOS. The critical technology is a new class of rotary motors, called Rotary Squiggle Motors, which were developed specifically for WFMOS by a small team of engineers at JPL and New Scale Technologies (NST). These motors set new benchmarks for small size and resolution performance which has not been achieved in electromagnetic motors. This simple, robust rotary piezo tube motor has been scaled to 3.3 mm diameter, without significant loss of power efficiency. JPL’s experience in high reliability spaceflight mechanisms combined with New Scale Technologies existing linear motor design and analysis skills as well as mass production capabilities is the perfect teaming relationship for the needs of WFMOS. The teams collaborated in a rapid 8 month development of the Cobra Positioner that successfully surpassed the requirements for positioning accuracy and speed. 37
<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) Figure 3.10-4: The Prototype Cobra Fiber Positioner The motive force of the Rotary Squiggle Motor is provided by two pairs of piezo plates mounted on a flexible tube that are actuated in a coordinated “hula” fashion to produce rotary motion (Figure 3.10-5). The Cobra Positioner is made up of a 2.4-mm motor and a 4.6-mm motor, which match the sizes required to ensure the WFMOS survey speed. Figure 3.10-5: Rotary Squiggle Motor Motive Force Schematic The Cobra unit is a 7.7-mm diameter, theta-phi style, 2-axis fiber positioner, with the dependant axis offset from the independent axis, enabling the optical fiber to be placed anywhere in a 9.5-mm patrol region, as shown in Figure 3.10-6. 38
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STUDY SUMMARY - IPMU

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