Design and Analysis of Networked Controllers for

Mechanical Systems

Professor Dawn Tilbury

Mechanical Engineering Department

University of Michigan

As computers and computer networks continue to decline in price, distributed control systems are becoming more common. Each module of a mechanical system can have its own control system, with local I/O, computing power, and control algorithm. The mechanical modules interact physically while the control modules communicate through a network. This distributed architecture allows subsystems to be designed and tested independently. A distributed architecture is also more fault-tolerant---if one controller fails, the rest of the system may continue working in a degraded fashion. The subsystems may also be re-used in other systems, such as in reconfigurable manufacturing systems. However, most standard control designs are based on a centralized strategy, with one control algorithm supervising the entire system, and point-to-point connections between the sensors and actuators.

There are several challenges that must be addressed when building a networked control system. In this talk, we will present an overview of our work in this area. It is well-known that the network communication induces an unavoidable time delay in the control system, which can degrade the performance or even destabilize the system. We will present a formal characterization of the time delays that can be expected in a control system using standard networks. We will also present a methodology for designing a networked control system implementation architecture given the expected communication and computation delays. As the scale of a distributed system increases, the communication load on the network may result in intolerable time delays for the control system. We will discuss some results on reducing the amount of communication required by using local estimators. The talk will conclude with a discussion of future work in this area.

Friday, February 9, 2001

3:30 - 5:00 p.m.

1500 EECS