Developing Micro DC-Brushless Motor Driver and Position Control for Fiber Positioners

TL;DR

This paper presents a compact electronic control system for micro brushless DC motors used in fiber positioners for the DESI telescope, integrating power and control functions to improve space efficiency and reliability.

Contribution

It introduces a two-layer electronic control board that combines power management and control tasks for two brushless motors in a compact form.

Findings

Successful integration of power and control in a compact board

Effective diagnostics for motor and sensor failures

Capability to detect robot collisions through load sensing

Abstract

In the large-scale, Dark Energy Spectroscopic Instrument (DESI), thousands of fiber positioners will be used. Those are robotic positioners, with two axis, and having the size of a pen. They are tightly packed on the focal plane of the telescope. Dedicated micro-robots have been developed and they use 4mm brushless DC motors. To simplify the implementation and reduce the space occupancy, each actuator will integrate its own electronic control board. This board will be used to communicate with the central trajectory generator, manage low level control tasks and motor current feeding. In this context, we present a solution for a highly compact electronic. This electronic is composed of two layers. The first is the power stage that can drive simultaneously two brushless motors. The second one consists of a fast microcontroller and deals with different control tasks: communication, acquisition of the hall sensor signals, commutation of the motors phases, and performing position and current regulation. A set of diagnostic functions are also implemented to detect failure in the motors or the sensors, and to sense abnormal load change that may be the result of two robots colliding.