Date of Award

5-2019

Document Type

Thesis - Open Access

Degree Name

Master of Science in Aerospace Engineering

Department

Graduate Studies

Committee Chair

Dr. Bogdan Udrea

First Committee Member

Dr. Hever Moncayo

Second Committee Member

Dr. Richard Prazenica

Abstract

The existence of backlash in mechanical systems provides significant challenges when attempting to control these systems to a high degree of precision. The imperfect meshing of gear or belt teeth deteriorates the performance of position controllers and tracking of small commands, producing unacceptable steady-state offsets, increased rise and settling times. Agile spacecraft often use control moment gyroscopes (CMGs) equipped with gear trains to efficiently provide torque for the fine attitude adjustments used in docking and precision stabilization maneuvers. A theoretical examination and a practical model is developed to study the effectiveness of both proportional-integral (PI) and model referencing adaptive controllers (MRAC) in overcoming the non-linearity introduced by gear lash. A Lyapunov analysis of the system’s equations of motion provides knowledge of its convergence, the tracking of ideal trajectories, and the rejections of disturbances. The objective is to create an adaptive control law that rejects the non-linearity and maintains acceptable performance with small torque commands. This control law is then validated in Simulink using a discontinuous backlash model.

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