Date of Award

2024

Degree Name

Mechanical Engineering

College

College of Engineering and Computer Sciences

Type of Degree

M.S.M.E.

Document Type

Thesis

First Advisor

Dr. Yousef Sardahi, Committee Chairperson

Second Advisor

Dr. Asad Salem

Third Advisor

Dr. Mohammed Ferdjallah

Abstract

This work presents two objectives for the use of robust sliding mode controller (SMC) in optimal and multi-objective settings to regulate the position of the knee joint angle for patients suffering from knee injuries. The controller imitates the role of active orthoses that produce the joint torques required to overcome gravity and loading forces and regain natural human movements. The first objective is to focus only on the knee, for which a mathematical model of the shank, the lower part of the leg, is derived first and then used for the control system design and computer simulations. Four objectives are considered: minimization of the control effort and tracking error; and maximization of the control signal smoothness and closed-loop system's speed of response. The second objective is to include a knee exoskeleton in the dynamic equations, for which a mathematical model, which includes the shank and exoskeleton, was derived, and also add a disturbance observer to the system to allow for accurate tracking despite external disturbances that may occur in normal walking motion. There are again four objectives: minimization of the control effort, tracking error, and the square-sum of the observer’s gains; and maximization closed-loop system's speed of response. Optimal solutions in terms of the Pareto set and its image, the Pareto front, are obtained. The results show that there are trade-offs among the design objectives and many optimal solutions from which the decision-maker can choose to implement. Also, computer simulations conducted at different points from the Pareto set and assuming knee squat movement demonstrate competing relationships among the design goals. In addition, the proposed control algorithm shows robustness in tracking a standard gait signal when accounting for uncertainty in the shank's parameters. However, the disturbance observer developed in this work only partially estimated the human torque and will need to be improved in future work.

Subject(s)

Mechanical engineering.

Knee -- Wounds and Injuries -- Rehabilitation.

Orthopedic apparatus.

Algorithms.

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