Actor-Oriented Control System Design

Jie Liu, Johan Eker, Xiaojun Liu, John Reekie, and Edward A. Lee

IEEE Transactions on Control System Technology, special issue on Computer Automated Multi-Paradigm Modeling, March, 2002.

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Complex control systems are heterogeneous, in the sense of discrete computer-based controllers interacting with continuous physical plants, regular data sampling interleaving with usually irregular communication and user interaction, and multilayer and multimode control laws. This heterogeneity imposes great challenges for control system design technologies in terms of end-to-end control performance modeling and simulation, traceable refinements from algorithms to software/hardware implementation, and component reuse. This paper presents an actor-oriented design methodology that tames these issues by separating the data-centric computational components (a.k.a. actors) and the control-flow-centric scheduling and activation mechanisms (a.k.a. frameworks). The underlying principle of frameworks is to use formal models of computation to manage the interactions among actors. Semantically different frameworks can be composed hierarchically to manage heterogeneity, improve understandability, and achieve actor and framework reusability. This methodology is implemented through the Ptolemy II software environment. As an example, the methodology and the Ptolemy II software have been applied to the design of a pendulum inversion and stabilization system.