Condition monitoring of production lines using event-time observers
Michael J. Gazarik, Edward W. Kamen · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1996
Fault detection or condition monitoring is critical to the safe and reliable operation of today's complex automatic production systems. This paper describes an approach which performs condition monitoring of production lines based on a max-plus model of the event-time dynamics. In particular, this work pertains to discrete part manufacturing systems such as automotive assembly lines or electronic circuit board lines where the dynamics are governed by the action of certain events, e.g., the processing of a part by a machine or the departure of a part from a buffer. A state model of the event-time dynamics, based in the max-plus algebra, is used to emulate the nominal operation of a production line. The machine completion times are taken as the states of the model. Since only output measurements of the production line are available, an observer is needed to provide estimates of the machine completion times. Because of the nature of the max-plus algebra, a recursive state observer is not obtainable; instead, a block-form state observer is used to update the model state on a periodic basis. A timing residual is formed using the outputs of the model and the output measurements of the plant. The residual is then analyzed using standard statistical process control techniques to detect failures. Simulation results for a simple production line illustrate the approach. The novelties of this approach are the introduction of an event- time observer and the application of the observer to the problem of condition monitoring.