Graduate Exam Abstract

Ashraf Bader

Ph.D. Preliminary
April 3, 2020, 9:00 am - 11:00 am
Design and Control of Kinematically Redundant Robots for Maximizing Failure-tolerant Workspaces

Abstract: Kinematically redundant robots have extra degrees of freedom so that they can tolerate a joint failure and still complete an assigned task. Previous work has defined the “failure-tolerant workspace” as the workspace that is guaranteed to be reachable both before and after an arbitrary locked-joint failure. One mechanism for maximizing this workspace is to employ optimal artificial joint limits prior to a failure. This work presents two techniques for determining these optimal artificial joint limits. The first technique is based on the gradient ascent method. The proposed technique is able to deal with the discontinuities of the gradient that are due to changes in the boundaries of the failure tolerant workspace. This technique is illustrated using two examples of three degree-of-freedom planar serial robots. The first example is an equal link length robot where the optimal artificial joint limits are computed exactly. In the second example, both the link lengths and artificial joint limits are determined, resulting in a robot design that has more than twice the failure-tolerant area of previously published locally optimal designs. Because of the difficulties of computing the gradients for robots with higher degrees of freedom operating in higher dimensional workspaces, the second technique proposed in this work is based on a genetic algorithm. The values of the artificial joint limits and kinematic parameters are encoded into a chromosome so that optimal values can be determined. The genetic algorithm approach has been verified using the results from the first technique, with new results for higher degrees of freedom robots to be presented.

Adviser: Anthony A. Maciejewski
Co-Adviser: N/A
Non-ECE Member: Juliana Oprea, Department of Mathematics
Member 3: Peter Young, Department of Electrical and Computer Engineering
Addional Members: Ali Pezeshki, Department of Electrical and Computer Engineering

A. M. Bader and A. A. Maciejewski, “Maximizing the failure-tolerant workspace area for planar redundant robots,” Mechanism and Machine Theory, vol. 143, p. 103635, 2020.

Program of Study:
ECE-481A2-001 Introduction to Robot Programming/Simulation
MATH-560-001 Linear Algebra
ECE-520-001 Optimization Methods-Control and Communication
ECE-555-001 Robot Motion Planning
ECE-611-001 Nonlinear Control Systems
ECE-666-001 Topics in Robotics
CIS-600-001 Information Technology and Project Management