Control design and performance evaluation of a hybrid flexure bearing for precision pointing applications

Weir, Nathan Andrew

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https://hdl.handle.net/2142/117768 Copy

Description

Title

Control design and performance evaluation of a hybrid flexure bearing for precision pointing applications

Author(s)

Weir, Nathan Andrew

Issue Date

2022-11-23

Director of Research (if dissertation) or Advisor (if thesis)

Alleyne, Andrew

Doctoral Committee Chair(s)

Alleyne, Andrew

Committee Member(s)

• Salapaka, Srinivasa
• Sreenivas, Ramavarapu
• Messner, William

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• control design
• dual-stage
• coarse-fine
• dynamic friction
• precision pointing
• gimbaled pointing systems
• flexure bearing
• plant/controller alignment

Abstract

Gimbaled pointing systems are commonly used to aim and stabilize sensitive instrument payloads such as lasers, radars, cameras, and other electro-optical/infrared (EO/IR) sensors for a variety of commercial, scientific, and military applications. For precision imaging systems, overall performance is tied directly to the pointing system's ability to accurately point toward a target in inertial space and to reject disturbances that cause undesirable line of sight (LOS) motion. Any residual or uncompensated LOS motion, known as jitter, can degrade the quality of the captured images. The jitter requirements for future systems grow even more demanding as image sensor performance and resolution continue to improve, resulting in smaller pixel size and higher pixel densities. Thus, there is a critical need for improved jitter reduction techniques to enable the deployment of future higher-resolution imaging systems. This research effort is motivated by a hybrid flexure bearing concept which was developed to reduce the effects of friction that degrade performance in precision pointing systems with conventional ball bearing joints. The hybrid flexure bearing concept combines the large travel advantage of a conventional ball bearing joint with the smooth, repeatable, and frictionless motion of a rotational flexure. This research seeks to advance the state-of-the-art in precision pointing through modeling, control design, and experimental evaluation of the hybrid flexure bearing concept. A significant challenge associated with the development of precision motion control systems is the identification and modeling of friction. An accurate friction model is crucial for assessing the impact of bearing friction on pointing performance. A data-based dynamic friction model is proposed, which significantly improves friction model accuracy in both the time and frequency domains. Key friction model features are identified to better match frictional behavior observed in experiments. Simulation results are validated with measured friction data collected from the experimental testbed. The closed-loop properties of general two-input single-output (TISO) feedback systems are described using the concepts of plant/controller alignment. In general, we show that it is desirable to design a controller that is well aligned with the plant in order to minimize the size of the closed-loop sensitivity functions and closed-loop interactions. A new graphical controller design approach is proposed which exploits the concept of plant/controller alignment using alignment contours on the conventional Bode plot. The utility of the approach is shown through its application to the hybrid flexure bearing system. The performance of a well-aligned and poorly aligned controller are evaluated in simulation and validated with an experimental testbed under a variety of base motion disturbances. Lastly, model-based friction compensation techniques are investigated using the data-based friction model. The overall pointing performance is improved by using a well-aligned controller and the data-based friction compensation approach, reducing both jitter and control energy usage.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Nathan Andrew Weir

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