Performance Tradeoffs Posed by Moving Magnet Actuators in Flexure-Based Nanopositioning

Abstract

Moving magnet actuators (MMAs) are direct-drive, single-phase electromagnetic linear actuators that provide frictionless and backlash-free motion over a range of several millimeters. This paper investigates the feasibility of using MMAs to simultaneously achieve large range, high speed, and high motion quality in flexure-based nanopositioning systems. Component and system level design challenges and associated tradeoffs in meeting the aforementioned nanopositioning performance are discussed and derived. In particular, it is shown that even as the overall size of a traditional MMA is varied, the actuation force remains directly proportional to the square root of the actuator's moving magnet mass and the square root of power consumed. This proportionality constant, identified as the dynamic actuator constant, serves as a figure of merit for MMAs. When an MMA is employed in a flexure-based nanopositioning system, this constant directly impacts the system-level positioning performance in terms of range, resolution, speed, and temperature rise. This quantitative determination highlights the significance of incorporating a thermal management system for heat dissipation, minimizing noise and harmonic distortion in the current driver, and improving the force-stroke uniformity of the actuator. Based on this understanding, a single-axis nanopositioning system, which simultaneously achieves 10 mm range, 4 nm resolution, open-loop natural frequency of 25 Hz, and temperature rise of less than 0.5 °C, is designed, fabricated, and tested. Preliminary controller design and closed-loop operation highlight the potential and limitations of MMAs in large-range, high-speed nanopositioning.