D.A. van Beek

LANGUAGES AND APPLICATIONS IN HYBRID MODELLING AND SIMULATION: POSITIONING OF CHI

A widely used classification of modelling languages distinguishes the categories continuous time (CT), discrete event (DE), discrete time (DT), and hybrid. For a better insight into the many different hybrid languages, a classification of five categories (CT, CT+, DE, DE+, and CT/DE) is proposed. Each category is explained, together with many of the included languages, simulators, and the associated application fields. Special interest is given to the Chi language used for specification, simulation and real-time control of industrial systems. Its CT part is based on (conditional) DAEs, its DE part on Communicating Sequential Processes. The suitability of the language for DE, CT, and CT/DE modelling is illustrated by two cases.

Coordination of Resources using Generalized State-Based Requirements

Abstract Control and coordination is an important aspect of the development of complex machines due to an ever increasing demand for better functionality, quality, and performance. We develop a coordinator for maintenance procedures for a high-tech Oce printer that eliminates undesired behavior which stems from unrestricted interaction of its distributed components. To this end, we extend and employ a model-based engineering framework for supervisory controller synthesis. We generalize standard state-based control requirements to increase modeling convenience. We model the use case with 23 generalized state-based requirements, which translate to 500+ requirements in the original form.

MODELLING AND CONTROL OF PROCESS INDUSTRY BATCH PRODUCTION SYSTEMS

Abstract Many models of process industry batch production systems are of a continuous-time/discrete-event (CT/DE) nature: physical processes are modelled using CT specifications, operating procedures are modelled using DE specifications. For scheduling of batch production systems, special purpose tools are available. The Chi language is a CT/DE language with high level DE language elements. This makes it possible to model physical processes using CT and/or DE specifications. It also makes it possible to solve scheduling problems in Chi, and to integrate the scheduler with the model of the batch production systems. The advantages of this approach are illustrated by means of four case studies.

A state-based framework for supervisory control synthesis and verification

We extend an existing model-based framework for supervisory control synthesis with generalized control and verification state-based requirements. The former stem from the need for intuitive specification of the control requirements, whereas the latter are employed for liveness verification in order to ensure that the supervisor does not disable desired functionalities of the plant. First, we introduce generalized control requirements and show them provably equivalent to the standard state-based control requirements. In the process, we identify a class of state-based liveness requirements, which can be efficiently verified and employed in the supervisor synthesis framework to provide early feedback to the modeler.

New Concepts in the Abstract Format of the Compositional Interchange Format

Abstract The compositional interchange format for hybrid systems (CIF) supports inter-operability of a wide range of tools by means of model transformations to and from the CIF. Work on the CIF takes place in the FP7 Multiform project, and in several other European projects. The CIF consists of an abstract and a concrete format, used for defining a formal semantics and for modeling, respectively. This paper discusses the results of a redesign of the abstract format as previously published, leading to the following main changes: variables are introduced using scoping operators; the abstract language is made more orthogonal by providing an operator for each concept in the language; parallel composition has been defined in such a way that compositional verification (assume/guarantee reasoning) is supported; and the concept of urgent actions has been properly defined. As a result, the expressivity and semantics of the abstract language have been considerably improved.

Chaos in discrete production systems

Abstract In the literature, several cases are reported of models of discrete nonstochastic production systems that show irregular, apparently chaotic behavior. In this paper, a number of these cases are analyzed, and the irregular behavior is attributed to: (1) chaotic behavior in hybrid models, (2) chaotic behavior in discrete-event models that use a chaotic map, or (3) periodic behavior with a period longer than the observation window. The irregular behavior of a discrete-event model of a two-machine production system is analyzed by means of nonlinear time-series analysis and sensitivity analysis. This case reveals the possibilities and limitations of the application of chaos theory to discrete-event models of production systems. Also, a new method for determining the sensitivity of discrete-event models to truly small changes is introduced. Realistic, non-artificial discrete-event models of discrete production systems that show chaotic behavior were not found in this study.

Integrating Continuous-Time and Discrete-Event Concepts in Modelling and Simulation of Manufacturing Machines

Abstract Using simulation models for the development and testing of control systems can have significant advantages over using real machines. This paper demonstrates the suitability of the χ language for modelling, simulation and control of manufacturing machines. The language integrates a small number of powerful orthogonal continuous-time and discrete-event concepts. The continuous-time part of χ is based on DAEs; the discrete-event part is based on a CSP-like concurrent programming language. Models are specified in a symbolic mathematical notation. A case study is presented of a transport system consisting of conveyor belts.

Concrete Syntax and Semantics of the Compositional Interchange Format for Hybrid Systems

Abstract The compositional interchange format for hybrid systems is syntactically and semantically defined in terms of an interchange automaton in an abstract format, allowing among others differential algebraic equations, variables that can be internal or external, operators for parallel composition, action hiding, variable hiding and urgent actions, synchronization by means of shared labels, and communication by means of shared variables and CSP channels. A concrete format is defined for modeling. Its semantics is defined in terms of a mapping to the abstract format. The concrete format adds inputs, outputs and open and closed scopes to enable modular and hierarchical specifications. The concrete format is illustrated by means of a bottle filling line example.

Formal Semantics of Hybrid Chi

The verification formalism / modeling and simulation language hybrid Chi is defined. The semantics of hybrid Chi is formally specified using Structured Operational Semantics (SOS) and a number of associated functions. The χ syntax and semantics can also deal with local scoping of variables and/or channels, implicit differential algebraic equations, such as higher index systems, and they are very well suited for specification of pure discrete event systems.

Application of Supervisory Control Synthesis to a Patient Support Table of a Magnetic Resonance Imaging Scanner

In this paper, we present a case-study on application of Ramadge-Wonham supervisory control theory (abbreviated by SCT in the sequel) to a patient support system of a magnetic resonance imaging (MRI) scanner. We discuss the whole developmental cycle, starting from the mathematical models of the uncontrolled system and of the control requirements, and ending with the implementation of the obtained controller on the actual hardware. The obtained controller was tested on the physical system. In this case study, we attempted to build the models in a modular way, in order to decrease the computational complexity of the controller synthesis and to improve the adaptability of the models. An important advantage of SCT is that it allows automatic generation of the controller, and that it can thus improve adaptability of the control software. We also briefly discuss our experience on the adaptability of the control software, obtained in the course of this case study.