Discrete Event and Hybrid Systems in Robotics and Automation


Faculty

Students

An Environment and Applications for Discrete Event and Hybrid Systems in Robotics and Automation

Hybrid systems, in which digital and analogue devices and sensors interact over time, is attracting the attention of researchers. Representation of states and the physical system condition includes continuous and discrete numerics, in addition to symbols and logical parameters. Most of the current robotics, automation, and intelligent systems problems, as well as problems in other domains, fall within the description of hybrid systems. There are many issues that need to be resolved, among them, definitions for observability, stability and stabilizability, controllability in general, uncertainty of state transitions and identification of the system.

The underlying mathematical representation of complex computer-controlled systems is still insufficient to create a set of models which accurately captures the dynamics of the systems over the entire range of system operation. We remain in a situation where we must tradeoff the accuracy of our models with the manageability of the models. Closed-form solutions of mathematical models are almost exclusively limited to linear system models. Computer simulation of nonlinear and discrete-event models provide a means for off-line design of control systems. Guarantees of system performance are limited to those regions where the robustness conditions apply. These conditions may not apply during startup and shutdown or during periods of anomalous operation.

Recently, attempts have been made to model low and high-level system changes in automated and semi-automatic systems as discrete event dynamic systems (DEDS). Several attempts to improve the modeling capabilities are focused on mapping the continuous world into a discrete one. However, repeated results are available which indicate that large interactive systems evolve into states where minor events can lead to a catastrophe. Discrete event and hybrid system formulations have been used in many domains to model and control system state changes within a process. Some of the domains include: Manufacturing, Robotics, Autonomous Agent Modeling, Control Theory, Assembly and Planning, Concurrency Control, Distributed Systems, Hierarchical Control, Highway Traffic Control, Autonomous Observation Under Uncertainty, Operating Systems, Communication Protocols, Real-Time Systems, Scheduling, and Simulation.

A number of tools and modeling techniques are being used to model and control discrete event systems in the above domains. Some of the modeling strategies include: Timed, untimed and stochastic Petri Nets and State Automata, Markovian, Stochastic, and Perturbation models, State Machines, Hierarchical State Machines, Hybrid Systems Modeling, Probabilistic Modeling (Uncertainty Recovery and Representation), Queuing Theory, and Recursive Functions.

In our project we develop a graphical environment for simulating, analyzing, synthesizing, monitoring, and controlling complex discrete event and hybrid systems within the robotics, automation, and intelligent systems domain. We also attempt to apply the discrete event and hybrid system formulations in various problems within robotics and automation.

Some of the work in this project is done as a part of the activities of the IEEE Robotics and Automation Society, Technical Committee on Discrete Event Dynamic Systems, which is co-chaired by Professor Tarek Sobh, and Professor Beno Benhabib of the Department of Mechanical Engineering, University of Toronto.

Student Reports:

Selected Publications:

Books and Book Chapters:
-
T. M. Sobh, C. Jaynes, M. Dekhil, and T. C. Henderson, ``Automated Inspection and Reverse Engineering,'' in Intelligent Systems: Safety, Reliability, and Maintainability Issues, O. Kaynak, G. Honderd and E. Grant (Eds.), Springer-Verlag, Berlin, pp. 95-122, 1993.
-
T. M. Sobh and R. Bajcsy, ``Visual Observation of a Moving Agent,'' in Engineering Systems with Intelligence; Concepts, Tools, and Applications, Book Chapter, Kluwer Academic Publishers, 1991.

Journal Papers
-
T. M. Sobh, J. C. Owen, K. P. Valavanis, and D. Gracanin, ``A Subject-Indexed Bibliography of Discrete Event Dynamic Systems.'' In IEEE Magazine on Robotics and Automation, Vol. 1, No. 2, June 1994.
-
T. M. Sobh, J. C. Owen, and M. Dekhil, ``A Dynamic Recursive Approach for Autonomous Inspection and Reverse Engineering.'' In Journal of Robotics and Autonomous Systems, Special Issue on Discrete Event Systems in Robotics and Automation, October 1994.
-
T. M. Sobh, J. C. Owen, M. Dekhil, and T. C. Henderson, ``Industrial Inspection and Reverse Engineering'', Invited paper, Computer Vision, Graphics, and Image Processing (CVGIP), Image Understanding Journal, Special Issue on Model-Based Vision.
-
T. M. Sobh and R. Bajcsy, ``A Discrete Event Framework for Autonomous Observation Under Uncertainty.'' In the Journal of Intelligent and Robotic Systems, October 1996.

Invited Papers and Book Chapters:
-
T. M. Sobh and R. Bajcsy, ``Visual Observation as a Discrete Event Dynamic System''. Presented at the International Joint Conference on Artificial Intelligence (IJCAI), Workshop on Dynamic Scene Understanding, Sydney, Australia, August 1991.
-
T. M. Sobh, C. Jaynes, M. Dekhil, and T. C. Henderson, ``Automated Inspection and Reverse Engineering,'' in Intelligent Systems: Safety, Reliability, and Maintainability Issues, O. Kaynak, G. Honderd and E. Grant (Eds.), Springer-Verlag, Berlin, pp. 95-122, 1993.
-
T. M. Sobh, J. C. Owen, M. Dekhil, and T. C. Henderson, ``Industrial Inspection and Reverse Engineering'', Invited paper, Computer Vision, Graphics, and Image Processing (CVGIP), Image Understanding Journal, Special Issue on Model-Based Vision.

Conference Papers
-
T. M. Sobh, P. Sloan, and M. Dekhil, ``A Graphical Environment and Applications for Discrete Event and Hybrid Systems in Robotics and Automation''. Submitted to the IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS 95), Pittsburgh, August 1995.
-
T. M. Sobh, M. Dekhil, and J. C. Owen, ``Discrete Event Control for Inspection and Reverse Engineering.''. In proceedings of the IEEE International Conference on Robotics and Automation, San Diego, May 1994.
-
T. M. Sobh, J. C. Owen, M. Dekhil, C. Jaynes, and T. Henderson, ``Industrial Inspection and Reverse Engineering''. In Proceedings of 1993 IEEE CAD-Based Vision Workshop, Pittsburgh, February 1994.
-
T. M. Sobh, M. Dekhil, C. Jaynes, and T. Henderson, ``A Perception Framework for Inspection and Reverse Engineering''. In Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition (CVPR '93), New York City, June 1993.
-
T. M. Sobh, C. Jaynes, and T. Henderson, ``A Discrete Event Framework for Intelligent Inspection.''. In Proceedings of the IEEE International Conference on Robotics and Automation, Atlanta, May 1993.
-
T. M. Sobh, R. Bajcsy, and J. R. James,``Visual Observation for Hybrid Intelligent Control Implementation''. In Proceedings of the IEEE Conference on Decision and Control, Tucson, Arizona, December 1992. Invited Session on Hybrid Systems.
-
T. M. Sobh, C. Jaynes, and T. Henderson, ``Intelligent Inspection and Reverse Engineering''. NATO Advanced Research Workshop on Intelligent Systems, Izmir, Turkey, August 1992.

Snap shots of the environment


sobh@bridgeport.edu