Developments in high-density Cobra fiber positioners for the Subaru Telescope's Prime Focus Spectrograph

TL;DR

This paper discusses the development and testing of a high-density fiber positioner system called Cobra for the Subaru Telescope's Prime Focus Spectrograph, enabling rapid and precise fiber placement for astronomical surveys.

Contribution

It introduces a novel high-density fiber positioning system with 2394 SCARA robot mechanisms, demonstrating high accuracy and efficiency for large-scale astronomical instrumentation.

Findings

Cobra can position fibers within 5μm of targets in 6 moves

Achieved a 95% success rate in fiber placement accuracy

Designed for rapid reconfiguration of over two thousand fibers

Abstract

The Prime Focus Spectrograph (PFS) is a fiber fed multi-object spectrometer for the Subaru Telescope that will conduct a variety of targeted surveys for studies of dark energy, galaxy evolution, and galactic archaeology. The key to the instrument is a high density array of fiber positioners placed at the prime focus of the Subaru Telescope. The system, nicknamed "Cobra", will be capable of rapidly reconfiguring the array of 2394 optical fibers to the image positions of astronomical targets in the focal plane with high accuracy. The system uses 2394 individual "SCARA robot" mechanisms that are 7.7mm in diameter and use 2 piezo-electric rotary motors to individually position each of the optical fibers within its patrol region. Testing demonstrates that the Cobra positioner can be moved to within 5{\mu}m of an astronomical target in 6 move iterations with a success rate of 95 per cent. The Cobra system is a key aspect of PFS that will enable its unprecedented combination of high-multiplex factor and observing efficiency on the Subaru telescope. The requirements, design, and prototyping efforts for the fiber positioner system for the PFS are described here as are the plans for modular construction, assembly, integration, functional testing, and performance validation.