ALMA Nutator Design and Preliminary Performance

TL;DR

This paper details the recent design improvements and initial performance results of the ALMA nutator, including structural, electronic, and software upgrades aimed at enhancing precision and reliability.

Contribution

It introduces new structural, electronic, and software modifications to the ALMA nutator, demonstrating advancements over previous designs.

Findings

Reduced flexing with carbon fiber structure

Improved stow position accuracy and repeatability

Preliminary performance shows promising results

Abstract

We report the past two years of collaboration between the different actors on the ALMA nutator. Building on previous developments, the nutator has seen changes in much of the design. A high-modulus carbon fiber structure has been added on the back of the mirror in order to transfer the voice coils forces with less deformation, thus reducing delay problems due to flexing. The controller is now an off-the-shelf National Instrument NI-cRIO, and the amplifier a class D servo drive from Advanced Motion Controls, with high peak power able to drive the coils at 300 Volts DC. The stow mechanism has been totally redesigned to improve on the repeatability and precision of the stow position, which is also the reference for the 26 bits Heidenhain encoders. This also improves on the accuracy of the stow position with wind loading. Finally, the software, written largely with National Instrument's LabView, has been developed. We will discuss these changes and the preliminary performances achieved to date. Keywords: ALMA, nutator, class D, high-modulus carbon fiber.