Echidna: a multifiber positioner for the Subaru prime focus

摘要

The aim for a spectrograph feed from the Subaru prime focus is to have 400 fibers. Since the are of the field is only approximately 1/10 that of the 400 fiber two degree field system on the Anglo-Australian Telescope, placement of magnetic buttons by a robot, as done for 2df, was not considered applicable. Instead, a concept has been developed in which each fiber is held on a spine which can be tilted to position its tip anywhere within a circle. With targets randomly scattered over the field and the radial range for each spine equal to the spine pitch, the success rate in reaching targets is acceptably high. At the f/2 focus, a spine tilt of 1/20 radian is just acceptable and requires the spines be 140 mm long. Two basic mechanisms for tilting and holding such a spine have been investigated experimentally. The first uses three commercial miniature linear actuators set parallel and linked to the base of the spine through simple flexures. A prototype has been built and demonstrated to perform satisfactorily. Another approach is to mount the spine ona ball joint and drive it directly in tip and tilt using a bending piezo impact drive. A prototype of this from has been built; initial test are promising.