Velocity- and pointing-error measurements of a 300 000 r/min self-bearing permanent-magnet motor for optical applications

TL;DR

This paper reports the first measurements of velocity and pointing errors in a high-speed (up to 5 kHz) self-bearing permanent-magnet motor, providing crucial data for optical applications requiring high precision.

Contribution

It presents novel measurements of velocity and pointing errors at multi-kHz speeds, filling a gap in existing high-speed motor performance data.

Findings

Velocity fluctuations up to 3.4 ns (RMS) observed

Pointing errors of 12 μrad (RMS) at 5 kHz

First measurement at multi-kHz rotation frequencies

Abstract

Compact, ultra-high-speed self-bearing permanent-magnet motors enable a wide scope of applications including an increasing number of optical ones. For implementation in an optical setup the rotors have to satisfy high demands regarding their velocity and pointing errors. Only a restricted number of measurements of these parameters exist and only at relatively low velocities. This manuscript presents the measurement of the velocity and pointing errors at rotation frequencies up to 5 kHz. The acquired data allows to identify the rotor drive as the main source of velocity variations with fast fluctuations of up to 3.4 ns (RMS) and slow drifts of 23 ns (RMS) over ~120 revolutions at 5 kHz in vacuum. At the same rotation frequency the pointing fluctuated by 12 $\mu$rad (RMS) and 33 $\mu$rad (peak-to-peak) over ~10000 roundtrips. To our best knowledge this states the first measurement of velocity and pointing errors at multi-kHz rotation frequencies and will allow potential adopters to evaluate the feasibility of such rotor drives for their application.