Pragmatic approach for modular control synthesis and implementation

Abstract

Abstract:Within the framework of Supervisory Control Theory, synthesis algorithms enable automatic generation of control rules from behavioural models of the process to be controlled and of goals to be achieved. This paper talks about a pragmatic use of these algorithms within an automation engineering context and focuses on two key issues: process and goals modelling and supervisory controller implementation. In this way, the approach presented in this paper combines the synthesis techniques and algorithms with an object-oriented automation method that supplies guidelines for the analysis, the design and the implementation of a modular control system. This pragmatic approach is applied to the synthesis and implementation of the control of an assembly station. It highlights the difficulties of the modelling step and its great influence on the synthesis result itself but also demonstrates the feasibility of our synthesis approach through a successful implementation in conformance with the IEC 61131-3 standard.

Reactive control system design using the Supervisory Control Theory: Evaluation of possibilities and limits

“…This problem has been faced in different ways in the literature (a survey is present in [5]). For the choice between uncontrollable and controllable events a solution often proposed is to give the priority to the uncontrollable events [6][7] [8], while in [9] the Supervisor is rejected if it is does not correspond to a Controller. The SCT is purposely reinterpreted in [10] to let the Supervisor acting like an events trigger.…”

“…The SCT is purposely reinterpreted in [10] to let the Supervisor acting like an events trigger. For the choice between controllable events [6] proposes the association of different priority levels or the manual intervention of the designer. In this work we propose to extract the Controller from the Supervisor selecting the path which minimizes the number of times that the PLC changes its outputs.…”

Supervisory synthesis for product-driven automation and its application to a flexible assembly cell

“…Modularity criteria are not only driven by state-space explosion issues (De Queiroz & Cury 2002), but must be justified by the structure of the physical process itself (Gouyon et al 2004).…”

“…The same approach is used for the specification of the vacuum system (8 states, 25 transitions). Note that these specifications are not natural at all and can be considered as a major difficulty of the synthesis process as further discussed in (Gouyon et al 2004).…”

“…The robustness of the synthesis algorithms is questionable (Gouyon et al 2004); indeed, on the one hand, the resulting supervisor strongly depends on the way the plant and specifications have been modelled; on the other hand, human based modelling activities can give rise to a wide range of models that more or less cover the initial needs. Consequently, the modelling phase remains a major difficulty for the synthesis, especially when using finite state machines.…”