Modeling for supervisor synthesis – a lock-bridge combination case study

Abstract

Designing supervisory controllers for high-tech systems is becoming increasingly complex due to demands for verified safety, higher quality and availability, and extending functionality. Supervisor synthesis is a method to automatically derive a supervisor from a model of the plant and a model of the control requirements. While supervisor synthesis is an active research topic, only a few reports exist on industrial applications. One of the reasons for this is the lack of acquaintance of control engineers with modeling and specifying in the framework of automata. In addition to this, there are no clear guidelines for obtaining the necessary models for synthesis. In this paper, we describe a general way of modeling for the plant and the requirements in order to contribute towards the acceptance of supervisor synthesis in industry. This way of modeling is illustrated with an industrial case study in which a supervisory controller is synthesized for the Algera complex. The Algera complex consists of a waterway lock and a movable bascule bridge. The supervisor has to control 80 actuators based on the observations from 96 discrete sensors, in response to 63 control commands available from the operator. We show how to model the plant as a collection of extended finite-state automata, how to model the requirement as a collection of event conditions, how to synthesize the monolithic supervisor, and how to validate the resulting supervisor using continuous-time simulation.

Efficiently enforcing mutual state exclusion requirements in symbolic supervisor synthesis

“…Consequently, this type of requirement specification was sometimes avoided when modeling larger systems. This can be observed in, e.g., the model in [4].…”

“…With these inputs, a supervisory controller can be computed algorithmically (synthesized) so that it restricts the plant's behavior in accordance with the specification. Some examples where supervisory control theory is applied to controller design are; Theme park vehicles in [2], a patient support table of a magnetic resonance imaging scanner in [3], and a waterway lock and movable bridge combination in [4]. Despite the advantages of applying this technique, and the examples thereof shown in case studies, industrial acceptance is scarce.…”

Supervisory controller synthesis and implementation for safety PLCs

“…Each component can be modeled separately. This way of modeling has proven to be useful for modeling the plant for supervisor synthesis, as shown in Kovács et al (2012), Huang et al (2015), and Reijnen et al (2020b). In Goorden et al (2019), modeling guidelines are proposed that help in obtaining the necessary models.…”

“…This entails that component models do not share events or refer to variables local to other EFAs. For infrastructural systems, it has been shown in Reijnen et al (2020b) that a realistic plant model can be created by composing asynchronous component models consisting of 2 to 4 states each.…”

“…Using the input-output perspective offers two advantages. Firstly, textual control requirements formulated by engineers can be more easily translated into event-condition models, as the states of actuators and sensors are directly available in the plant model (as demonstrated in Reijnen et al (2020b). Secondly, for implementation the component models can easily be coupled to the available sensors and actuators as there exist dedicated component models for these.…”