07/13/2022
By Sokny Long

The Francis College of Engineering, Department of Mechanical Engineering, invites you to attend a doctoral dissertation proposal defense by Amir Iqbal on “Modeling, Planning, and Control of Legged Locomotion on Dynamic Rigid Surfaces.”

Ph.D. Student: Amir Iqbal
Proposal Defense Date: Thursday, July 21, 2022
Time: 3 to 5 p.m. EDT
Location: This will be a hybrid defense via Zoom and in-person at Southwick 240. Those interested in attending should contact Amir_Iqbal@student.uml.edu and committee advisor, yan_gu@uml.edu, at least 24 hours prior to the defense to request access to the meeting.

Committee Chair (Advisor): Yan Gu, Ph. D., Assistant professor, Mechanical Engineering, UMass Lowell

Committee Members:

  • Christopher Niezrecki, Ph. D., Distinguished University Professor, Mechanical Engineering, UMass Lowell
  • Kshitij Jerath, Ph. D., Assistant Professor, Mechanical Engineering, UMass Lowell
  • Sushant Veer, Ph. D., Research Scientist, NVIDIA Research
  • Kelilah Wolkowicz, Ph. D., Assistant Professor, Mechanical Engineering, UMass Lowell

Brief Abstract:

Legged robots have the potential to navigate over challenging terrains and assist humans in performing demanding tasks in hazardous environments. However, the existing approaches do not explicitly address the challenges of legged locomotion on dynamic rigid surfaces (i.e., rigid surfaces that move in an inertial frame). This dissertation proposal aims to bridge the existing knowledge gap in the dynamic modeling and control of legged robot locomotion on dynamic rigid surfaces (DRSes). To achieve the overarching goal, this dissertation comprises the following four studies.

The first study of this dissertation utilizes a reduced-order spring-loaded inverted pendulum (SLIP) model to reveal the essential dynamic behaviors of the highly complex legged locomotion on a DRS. The study presents modeling, analysis, and control design for SLIP running on DRSes that are representative of real-world locomotion surfaces (e.g., harmonically excited platforms, suspended floors, and bridges). The effectiveness of the proposed control strategy in sustaining SLIP motion on DRS is validated through simulations. After gaining insight into the essential dynamic behaviors of locomotion on DRS using a reduced-order model, the following study focuses on deriving control laws that enable provably stable locomotion based on a full-order robot model.

The second study derives a full-order dynamic model of legged walking on DRS, proposes a provably stabilizing controller for walking on DRS with known periodic surface motion, and validates the framework in simulations and hardware experiments. The control approach is synthesized based on the formulation of the full-order robot model as a hybrid, time-varying system. The stability analysis of the closed-loop control system is performed through the construction of multiple Lyapunov functions. The validation results in simulations and hardware experiments confirm the effectiveness of the proposed control approach in guaranteeing the stability and robustness of a quadrupedal robot walking on a DRS. Still, this study relies on computationally expensive offline trajectory planning, which is unsuitable for real-world applications where the DRS may have changing motion profiles. To that end, the subsequent contributions aim to realize efficient trajectory planning for real-time applications.

The third study derives a reduced-order linear inverted pendulum (LIP) model for legged walking on a DRS and introduces an approximate analytical solution to the LIP model under a vertical sinusoidal DRS motion (e.g., ship motion in regular sea waves). Furthermore, the study designs a hierarchical planner that exploits the proposed analytical solution to enable real-time, physically feasible motion generation for locomotion on DRS. The validation results confirm the efficiency and accuracy of the proposed solution in simulations, as well as the efficiency and physical feasibility of the proposed planner through 3-D realistic simulations and hardware experiments. Yet, this framework only solves the real-time locomotion planning problem for a DRS with a sinusoidal vertical movement, which may not be suitable for DRSes with general motions. To overcome this limitation, the subsequent study focuses on legged locomotion on a DRS with a general motion.

The ongoing final study of this dissertation aims to solve the locomotion planning and control problem for DRSes with general motions. Towards effectively solving this problem, we plan to: (a) derive stability conditions for LIP locomotion on a DRS with general (periodic or aperiodic) motion based on the Lyapunov stability theory of hybrid systems; (b) utilize the derived stability condition to guide the design of a real-time, dynamically feasible planner; and (c) synthesize an optimization-based controller that explicitly ensures the feasibility of necessary locomotion constraints (e.g., ground contact constraints). Finally, we will validate the performance of the framework both through simulations and experimentally on Unitree’s quadrupedal robot and an instrumented treadmill emulating ship motions in regular sea waves.

All interested students and faculty members are invited to attend the online defense via remote access.