Practical control systems generally are systems that consist of multiple control algorithms; so called multi-controllers. Each control algorithm is designed to fulfill a particular task. Designing such systems requires engineering skills not discussed by control theory. These skills are structuring the control problem and organizing the individual solutions. This thesis deals with design aspects related to these two skills and presents theory and tools to support them. In order to investigate the relevant aspects of structuring control problems and organizing individual solutions, a model of complex control problems has been formulated. This model describes complex control problems in terms of partial control problems and their interdependencies. It will appear that structuring control problems requires the identification of a ¿part-of¿ hierarchy of partial control problems, as well as the identification of the type of coupling between the partial control problems. The particular type of coupling between partial control problems determines how to integrate the obtained individual solutions. To integrate multiple control algorithms, insight from the field of control engineering is needed. The Multiple Model Approach (Johansen and Murray-Smith, 1997) is a general design method for multi-controllers that consists of local controllers; i.e. control algorithms that are operational only in some limited part of the overall operating regime of the plant. While designing a multi-controller, the designer has to deal with particular integration aspects, such as deciding when to (in)activate a local controller, initializing and finalizing state variables of the local controller and combining control actions of several local controllers. The Multiple Model Approach relies on a supervisor to integrate the local controllers and deals with the integration aspects in a central way. In contrast with this, in this thesis a decentralized integration method is developed, based on the concepts of an agent and a multi-agent system. The result is an open design environment for multicontroller systems, such that individual local controllers can be added, modified or removed from the overall multi-controller without redesigning the remaining system. Combining the concepts of a local controller and an agent has resulted in a so called controller-agent. A controller-agent is a local controller that is responsible for the initialization and finalization of its state variables, has knowledge about its operating regime and has an interface to coordinate its behavior with other controller-agents. Controller-agents can be combined into groups by using coordination objects, which solves dependencies between controller-agents. As a result, the multi-controller system is structured as a ¿part-of¿ hierarchy, which in general reflects the decomposition of the complex control problem. An implementation framework has been developed to realize an agent-based multi-controller. This framework is called the Multi-Agent Controller Implementation Framework (MACIF). This framework contains six functionally different software components, which can be connected to each other. These components can be specified by using the specification language MACSL (Multi-Agent Controller Specification Language), which was developed during this research. Two real-world control problems are described to illustrate the proposed agentbased design framework. These problems are: 1) the design of an ¿intelligent¿ room thermostat 2) the design and implementation of a controller for the placement module of the Philips Fast Component Mounter (FCM), an industrial pickand-place machine. These applications demonstrate the utility of the framework and the power of the design method.
|Award date||18 May 2001|
|Place of Publication||Enschede, The Netherlands|
|Print ISBNs||90 365 15955|
|Publication status||Published - 18 May 2001|