Fathi Ghorbel - US grants

Abstract:
Closed kinematic chain mechanical systems promise advantages over open chains in terms of less moving inertia, faster and stiffer motion, and much better force-to-weight ratio. However, derivation of dynamic equations of motion for closed chain mechanisms suitable for controller design is still a challenge because of the complexity of the kinematics, dynamics, and control analyses. This research identifies the central difficulties in the modeling and control of these systems and provides an analytical framework to derive dynamics models appropriate for advanced model-based control laws. Two modeling-for-control approaches are investigated. In the first approach, a formulation of the dynamics equations of closed chain mechanisms in terms of independent generalized coordinates (reduced model) is developed. Methods to extend the wealth of control laws of open chains to closed chains while taking into consideration the local and implicit nature of the reduced model are considered. The second approach is to transform the Differential Algebraic Equations (DAE) describing closed kinematic chains into a singularly perturbed differential equation system with asymptotically stable fast dynamics. It follows that when a proper control design is made for the singularly perturbed system, then for a small value of an artificially introduced small parameter, the response of the controlled singularly perturbed system would be quite close to that of the controlled DAE system (closed chain mechanism). The techniques developed in this research potentially have applications to many other systems described by DAE.
The educational objective of this research is to help introduce dynamic modeling and control of complex closed chain dynamical systems in the traditional dynamics and control courses and laboratories. In particular, a robotic device will be made accessible for control experimentation over the World Wide Web for a more effective dissemination of the results of this research and integration in control education.

9819869
Ghorbel

Description: This award is to support a US-Tunisia research project to study the fundamental issues in modeling, analysis, and real-time implementation of nonlinear control laws for electromechanical systems with Harmonic Drives (H-D). The Principal Investigator is Dr. Fathi Ghorbel, Assistant Professor of Mechanical Engineering, Rice University, Houston, Texas. The Tunisian collaborator is Dr. Rached Dhaouadi, Assistant Professor of Electrical Engineering at Ecole Polytechnique de Tunisie, La Marsa, Tunisia. They plan to develop methodologies to quantify the hysteresis effect in the dynamic torque-displacement relationship, exhibited in experimental work on a harmonic drive system. They first will formulate mathematical models for the H-D system. These models must lead to mathematically well posed differential equations when coupled with the equations of motion of the overall system. The second phase will investigate the integration of these models into a complete drive system and the development of nonlinear control strategies to compensate for the nonlinear effects on the overall system performance. The singular perturbation technique will be investigated to elaborate a control methodology for the model reduction, the control design and the stability analysis. Numerical simulation and experiments will be used to test these drive control concepts.

Scope: This project deals with an important topic in high performance industrial and instrumentation servo systems. The two scientists plan to collaborate in the development of the mathematical model to be carried out at Rice University. They will also collaborate in the following phases of model parameter identification, numerical simulation, and the experimental investigation and model validation. This proposal meets the INT objective of supporting joint research in areas of mutual interest. This project is co-funded by the Division of International Programs and by the Division of Civil and Mechanical Systems.

0613016
Ghorbal
This planning-visit award allows Dr. Fathi H. Ghorbel, Department of Mechanical Engineering, Rice University, Houston, Texas to work with Dr. Lotfi Romdhane, Ecole Nationale de Ingenieurs de Monastir, Monastir, Tunisia, to plan a joint project on the locomotion and path planning of in-pipe robots.

Intellectual Merit: Recently, robots that move inside pipes started to gain importance within the research community. For example, robots moving inside petrochemical and energy pipes represent a new means of in-pipe inspection that will revolutionize the health monitoring and inspection of this critical industry infrastructure. In-pipe robotic locomotion and path planning is crucial in the advancement of this robotic technology. This visit will allow Dr. Ghorbel and Dr. Romdhane to make their robotic experiences in use to formulate the problem of the kinematics and path planning of this type of robots. The visit will allow taking this interaction to a research project formulation level.

Broad Impact: Aside from the intellectual exchanges, the visit will set the stage to future collaboration leading to broader impacts in the area of student exchanges, development of new robotic coursework material, and the involvement of females and minorities in the project. The work on the project, if successful, can have significant impacts on industries that utilize long pipelines.