Sensory-based Distributed Control Schemes for Mobile Robots


Faculty

Distributed Sensory Control for Mobile Robot Navigation

In any closed-loop control system, sensors are used to provide the feedback information that represents the current status of the system and the environmental uncertainties. The sensors used in most control systems are considered to be passive elements that provide raw data to a central controller. The central controller computes the next command based on the required task and the sensor readings. The disadvantage of this scheme is that the central controller may become a bottleneck when the number of sensors increases which may lead to longer response time. In some applications the required response time may vary according to the required task and the environment status. For example, in an autonomous mobile robot with the task of reaching a destination position while avoiding unknown obstacles, the time to reach to the required position may not be important, however, the response time for avoiding obstacles is critical and requires fast response. Fast response can be achieved by allowing sensors to send commands directly to the physical system when quick attention is required.

In this work, several controllers (clients) are working in parallel, competing for the server. The server selects the command to be executed based on a dynamically configured priority scheme. Each of these clients has a certain task, and may use the sensor readings to achieve its goal. A special client with the task of avoiding obstacles is assigned the highest priority. The clients may also aquire the current state of the system and the command history to update their control strategy.

The logical sensor approach, which we used to model the sensory system, allows flexible and modular design of the controllers. It also provides several levels of data abstraction and tolerance analysis based on the sensor type and the required task. This approach is used to build high-level requests which may be used by the application programs.

Any sensory system can be viewed as a passive or dumb element which provides raw data. It can also be viewed as an intelligent element which returns ``analyzed'' information. Finally, it can be viewed as a commanding element which sends commands to the physical system. Each of these views is used in different situations and for different tasks. Commanding sensors are an extension to the logical sensor approach in which a mapping from events to actions is added to the sensor model.

We propose a sensor-based distributed control scheme for mobile robots. The application of this scheme to control a real mobile robot is discussed. A server-client model is used to implement this scheme where the server is a process that carries out the commands to be executed, and each client is a process with a certain task. The logical sensor approach is used to model the sensory system which provides different levels of data representation with tolerance measures and analysis.

Selected Publications:

Books and Book Chapters:

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T. M. Sobh, M. Dekhil, and A. A. Efros, ``Sensing Under Uncertainty for Mobile Robots,'' in ASME Series on Robotics and Advanced Manufacturing, Volume 3, 1996.

Journal Papers

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T. M. Sobh, ``Hybrid and Distributed Control in Robotics and Automation.'' Submitted to the International Journal of Science and Technology, Special Issue on Automation and Robotics, December 1995.

Conference Papers

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M. Dekhil and T. M. Sobh, ``Embedded Tolerance Analysis for Sonar Sensors.'' Invited paper to the special session of the 1997 Measurement Science Conference: Measuring Sensed Data for Robotics and Automation, Pasadena, California, January 1997.

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M. Dekhil, T. M. Sobh, and A. A. Efros, ``Commanding Sensors and Controlling Indoor Autonomous Mobile Robots,'' in proccedings of the IEEE International Conference on Control Applications, Dearborn, Michigan, September 1996.

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T. M. Sobh, M. Dekhil, and A. A. Efros, ``Sensing Under Uncertainty for Mobile Robots,'' Presented in the Second World Automation Congress, First International Symposium on Intelligent Automation and Control (ISIAC 96), Montpellier, France, May 1996.

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M. Dekhil, T. M. Sobh, and A. A. Efros, ``Sensor-based Distributed Control Scheme for Mobile Robots,'' Invited paper, IEEE International Symposium on Intelligent Control (ISIC 95), Monterey, California, August 1995.

Technical Reports

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M. Dekhil and T. M. Sobh, ``Embedded Tolerance Analysis for Sonar Sensors,'' Technical Report UBCSE-96-005, Department of Computer Science and Engineering, University of Bridgeport, December 1996.

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M. Dekhil, T. M. Sobh, and A. A. Efros, ``Commanding Sensors and Controlling Indoor Autonomous Mobile Robots,'' Technical Report UBCSE-95-003, Department of Computer Science and Engineering, University of Bridgeport, October 1995.

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T. M. Sobh, M. Dekhil, and A. A. Efros, ``Logical Control for Mobile Robots,'' Technical Report UBCSE-95-002, Department of Computer Science and Engineering, University of Bridgeport, October 1995.

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T. M. Sobh, M. Dekhil, and A. A. Efros, ``Sensing Under Uncertainty for Mobile Robots,'' Technical Report UBCSE-95-001, Department of Computer Science and Engineering, University of Bridgeport, September 1995.

Snap shots of the experiments


sobh@bridgeport.edu