Multiloop Control of a Nanopositioning Mechanism for Ultraprecision Beam Steering

Published

January 1, 2004

Author(s)

Jason J. Gorman, Nicholas Dagalakis, B G. Boone

Abstract

Beam steering accuracy is critical to the successful operation of optical communications systems, especially those which take place over extreme length scales, such as for an interstellar spacecraft. In this paper, a novel beam steering mechanism and several control system approaches for ultra-precision beam steering are discussed. The beam steering mechanism is a nanopositioning device which utilizes a parallel cantilever configuration and a piezoelectric actuator to obtain extremely high positioning accuracy with minimal parasitic errors. An analytical model for this mechanism is discussed as well as its experimental verification. This model is then used to design a robust motion controller which is designed to compensate for modeling errors as well as the piezoelectric actuator's hysteretic behavior. This controller is intended for use with feedback from the nanopositioner's built-in capacitance probe. Due to the need to track the trajectory of the steered beam, two additional control approaches are presented which combine the robust motion controller with additional feedback from an optical sensor, such as a quad photocell, monitoring the actual path of the beam. The first controller design uses the optical sensor feedback in an outer feedback loop which provides robustness to errors in the modeled relation between nanopositioner motion and beam angle. The second controller adds an additional feedback loop to compensate for disturbances, such as structural vibrations, which are sensed in the beam motion. These multi-loop control approaches provide a level of robustness to thermal effects, vibrations and sensor noise which could not be obtained from a single sensor and feedback loop. Simulation results based on experimentally verified models are provided for each of the control designs and discussed with respect to future optical communications requirements for space exploration.

Proceedings Title

Free-Space Laser Communication and Active Laser Illumination, Conference | | Free-Space Laser Communication and Active Laser Illumination III | SPIE

Volume

5160

Conference Dates

August 1, 2003

Conference Location

Undefined

Conference Title

Proceedings of SPIE--the International Society for Optical Engineering

Pub Type

Conferences

Keywords

beam jitter, beam steering, multi-loop control, nanopositioner, optical communication

Citation

Gorman, J. , Dagalakis, N. and Boone, B. (2004), Multiloop Control of a Nanopositioning Mechanism for Ultraprecision Beam Steering, Free-Space Laser Communication and Active Laser Illumination, Conference | | Free-Space Laser Communication and Active Laser Illumination III | SPIE, Undefined (Accessed April 19, 2024)