Cobra: A two-degree of freedom fiber optic positioning mechanism

The Wide-Field Multi Object Spectrometer (WFMOS) along with corrective optics will mount in place of the Secondary Mirror of the Subaru telescope on Mauna Kea, Hawaii to allow simultaneous observations of cosmologic targets. It will conduct large scale Galactic Archeology and Dark Energy surveys to help unlock the secrets of the universe. The key enabler of the observations is an array of 2400 Cobra optic fiber positioners made from very small rotary motors which were developed for this purpose. Cobra is a two degree of freedom mechanism that can position an optical fiber in the prime focus of the telescope to a precision of 5 mum. It is a theta-phi style positioner containing two rotary piezo tube motors with one offset from the other, which enables 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 name Cobra was chosen because the positioner resembles a snake ready to strike.