Multi-domain modelling, simulation, and control

For the design of large industrial systems, usually many different modelling languages are required. Currently, different projects aim at the development of standards that enable interaction between simulation models written in different languages. The Chi project aims at providing one language suited to modelling, simulation and control of systems from different application domains. Models may range from pure continuous-time models to pure discrete-event models, and any combination of the two. Due to the orthogonal design of the Chi language and careful selection of the language primitives, the core of the language is small. At the same time, the high-level data modelling constructs and high-level behaviour modelling constructs provide the modeller with expressive power. Verification of Chi models is currently limited to discrete-event models. The Chi language and simulator have proved themselves in many industrial projects involving discrete-event modelling and simulation. For continuous-time and hybrid systems, the current simulator provides time-event and state-event handling, root location, initial state calculation, handling of discrete-event sub-phases, and index 1 DAE solving. For real-time control, Chi models can be compiled to run on real-time operating systems such as VxWorks

RRR-robot design : basic outlines, servo sizing, and control

The RRR-robot project aims at a manipulator-like system (with three rotational degrees of freedom), to test a variety of advanced nonlinear control strategies. Since for high-speed tracking of complex trajectories, Coriolis and centrifugal torques form an essential part of the occurring nonlinear effects, the main requirement of this robot is to highlight these velocity dependent torques. In this paper the outlines of the manipulator design are discussed. By exploring the main requirements two important features of the RRR-robot are introduced: unconstrained rotation in each link (e.g., by using sliprings) and the use of direct-drive servos. Several types of direct-drive servos are discussed and a choice is made to use brushless DC motors. The iterative dynamic optimization problem of choosing appropriate servos is solved by using a rigid-robot model implemented in a symbolic manipulation program. This program is also used for simulation and evaluation of both open and closed loop behavio

Integrating Continuous-Time and Discrete-Event Concepts in Process Modelling, Simulation and Control

Currently, modelling of systems in the process industry requires the use of different specification languages for the specification of the discrete-event and continuous-time subsystems. In this way, models are restricted to individual subsystems of either a continuous-time or discrete-event nature. It is our aim to integrate such models, by using one language for the specification of complete plants or production units. For this purpose, we introduce the language Chi in this paper. This language integrates a small number of orthogonal continuous-time and discrete-event concepts. The continuous-time part of Chi 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 plant for the biochemical production of ethanol. The production takes place in a number of fermentors in a fed-batch fashion. The fermentation process and the control system, which controls the various valves and pumps and schedules the different batches, are both specified in Chi.. The example illustrates the relevance of integrating continuous-time and discrete-event concepts

Supervisor for toner error handling : a case study in supervisory control of Océ printers

The purpose of this report is to demonstrate the viability of supervisory control synthesis approach by presenting the formulation and a preliminary solution of a real-life control problem in Oce printers. In a nutshell, supervisory control synthesis is a procedure for automatic generation of control algorithms based on the formal model of the underlying system (plant) and of the requirements the controlled system has to satisfy. The underlying theory guarantees that the generated control algorithm will indeed force the system to meet the specified requirements, provided that the model of the system and of the requirements are accurate enough. The viability of the approach is demonstrated by applying it to a particular use-case of Oce, the toner error-handling problem. The presence of continuous-time behavior in the current use-case compelled us to use supervisory control theory in a novel way. Usually, when applying supervisory control theory, the plant is modeled as an automaton and this automaton is constructed manually. Instead, here we generate the finite-state automaton model by a computer program, which takes as inputs the value of a number of physical parameters.The reason for choosing to generate the model by a program is that the model is obtained by discretizing a hybrid model in time. In turn, the time-step used in the discretization of the hybrid model is one of the parameters of the computer program. By generating the model automatically, we are able to experiment with supervisors for different discretization time steps and different values of physical parameters

Improving evolvability of a patient communication control system using state-based supervisory control synthesis

Supervisory control theory enables control system designers to specify a model of the uncontrolled system in combination with control requirements, and subsequently use a synthesis algorithm for automatic controller generation. The use of supervisory control synthesis can significantly reduce development time of supervisory controllers as a result of unambiguous specification of control requirements, and synthesis of controllers that by definition are nonblocking and satisfy the control requirements. This is especially important for evolving systems, where requirements change frequently. For successful industrial application, the specification formalism should be expressive and intuitive enough to be used by domain experts, who define control requirements, and software experts, who implement control requirements and synthesize controllers. This paper defines such a supervisory control specification formalism that consists of automata, synchronizing actions, guards, updates, invariants, independent and dependent variables, where the values of the dependent variables can be defined in terms of functions on the independent variables. We also show how the language enables systematic, compositional specification of a control system for a patient communication system of an MRI scanner. We show that our specification formalism can deal with both event-based and state-based interfaces. To support systematic, modular specification of models for supervisory control synthesis, we introduce state trackers that record sequences of events in terms of states. The synthesized supervisor has been successfully validated by means of interactive user guided simulation

Partially-supervised plants : embedding control requirements in plant components

Supervisory control deals with automated synthesis of controllers based on models of the uncontrolled system and the control requirements. In this paper we share the lessons learned from synthesizing controllers for a patient support system of an MRI scanner regarding the specification of the control requirements. We learned that strictly following the philosophy of supervisory control, which partitions specifications in an uncontrolled plant and control requirements, may lead to unnecessarily complex specifications and duplication of information. In such cases, the specification can be substantially simplified by embedding part of the control requirements in so-called partially-supervised plants. To formalize the new concepts, we apply a recently developed process-theoretic approach to supervisory control. The new method for analysis of the models provides a better insight into their underlying behavior, which is demonstrated by revisiting the models of the industrial study

Hybrid Modeling and Simulation of plant/controller Combinations

In order to design controllers, models of the system to be controlled (the plant), and models of the controller are developed, and the performance of thecontrolled system is evaluated by means of, for instance, simulation. The plant and controller can be modeled in the continuous-time domain, the discrete-event domain, or in a combination of these two domains, the so-called hybrid domain. It is very convenient to have all these combinations available in one single formalism. In this paper, the hybrid Chi formalism is introduced and used to model a simple manufacturing system consisting of a production machinethat is controlled by a PI controller with anti-windup. The plant is modeled in the continuous-time domain as well as in the discrete-event domain. Likewise, the controller is modeled in both domains. Then, several (hybrid)plant/controller combinations are made. It is shown that the Chi language facilitates modeling of these combinations, because the individual plant and controller specifications remain unchanged. The Chi simulator is used to obtain the respective simulation results

Supervisory control synthesis for a patient support system

\u3cp\u3eSupervisory control theory (SCT) provides a formal approach to supervisory controller synthesis. In this paper, SCT is used to design a supervisory controller for a patient support system. This system is used to position a patient in a Magnetic Resonance Imaging (MRI) scanner. To improve the evolvability of the design, the uncontrolled system and the control requirements are modeled independently, using small, loosely coupled and minimally restrictive automata. An implementation of the synthesized supervisor is realized by means of a transformation to an automaton in the Compositional Interchange Format (CIF). The supervisor is validated by means of hardware-in-the-loop simulation, using the real patient support table.\u3c/p\u3

A control problem for hybrid systems with discrete inputs and outputs

We address the control synthesis of hybrid systems with discrete inputs and outputs. The control objective is to ensure that the events of the closed-loop system belong to the language of the control requirements. The controller is sampling-based and it is representable by a finite-state machine. We formalize the control problem and provide a theoretically sound solution based on finite-state abstractions of the symbolic behavior of the plant. In addition, we identify classes of hybrid systems for which a suitable finite-state abstraction can be computed and we sketch the corresponding algorithms

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