Compositional synthesis of maximally permissive supervisors using supervision equivalence

This paper presents a general framework for efficient synthesis of supervisors for discrete event systems. The approach is based on compositional minimisation, using concepts of process equivalence. In this context, a large number of ways are suggested how a finite-state automaton can be simplified such that the results of supervisor synthesis are preserved. The proposed approach yields a compact representation of a least restrictive supervisor that ensures controllability and nonblocking. The method is demonstrated on a simple manufacturing example to significantly reduce the number of states constructed for supervisor synthesis

Supremica – An integrated environment for verification, synthesis and simulation of discrete event systems

An integrated environment, Supremica, for verification, synthesis and simulation of discrete event systems is presented. The basic model in Supremica is finite automata where the transitions have an associated event together with a guard condition and an action function that updates automata variables. Supremica uses two main approaches to handle large state-spaces. The first approach exploits modularity in order to divide the original problem into many smaller problems that together solve the original problem. The second approach uses an efficient data structure, a binary decision diagram, to symbolically represent the reachable states. Models in Supremica may be simulated in the environment. It is also possible to generate code that implements the behavior of the model using both the IEC 61131 and the IEC 61499 standard

Supremica-An Efficient Tool for Large-Scale Discrete Event Systems

Supremica is a tool for the modelling and analysis of discrete-event control functions based on state machine models of the uncontrolled plant and specification of the desired closed-loop behaviour. The modelling framework in Supremica is based on finite-state machines extended with variables, guard conditions, and action functions. In order to handle large-scale problems of industrially interesting size, Supremica uses advanced model checking techniques such as symbolic representations and compositional abstraction. Supremica has been used in several industrial research projects to verify and synthesise control functions for embedded controllers, industrial robots, and flexible manufacturing systems, and to verify program code for autonomous vehicles. This paper gives an overview of the modelling features of Supremica, shows the verification and synthesis facilities and their performance for large problems, and presents some of the industrial applications where Supremica has been used

Nonblocking and safe control of discrete-event systems modeled as extended finite automata

Extended Finite Automata (EFA), i.e., finite automata extended with variables, are a suitable modeling framework for discrete event systems owing to their compactness, resulting from the use of variables. In this paper, we propose a symbolic algorithm that efficiently synthesizes a supervisor for a plant modeled by an EFA and a specification defined by another EFA. The principle of the algorithm is to iteratively strengthen the guards of the plant EFA so that forbidden or blocking states become unreachable in the controlled plant. As a consequence of the algorithm, the controlled behavior is modeled by an EFA having the same structure as the plant EFA, having stronger guards and is shown to be maximally permissive. We illustrate our algorithm via a simple manufacturing example

Supervisory Control for State-Vector Transition Models - A Unified Approach

A generic state-vector transition (SVT) model is suggested, including a flexible synchronous composition involving both shared variables and events. This model is analyzed, focusing on properties that are important for supervisor synthesis. A synthesis procedure is then developed for the SVT model, where supervisor guards are generated that guarantee a controllable, nonblocking and maximally permissive supervisor. Novel conditions are introduced, such that more flexible specifications can be applied than earlier suggested for related models. Since the SVT model includes automata and (colored) Petri nets, optionally extended with variables, guards and actions, as special cases, the suggested synthesis approach unifies supervisor synthesis for the main discrete event model classes. Finally, the SVT model is naturally represented and efficiently computed based on binary decision diagrams, and the resulting supervisor guards are easily implemented in industrial control systems

Imaging Chronic Pain and Inflammation : Positron Emission Tomography Studies of Whiplash Associated Disorder

This thesis is on chronic neck pain after a rear impact car injury, so called whiplash associated disorder (WAD). Three empirical studies using positron emission tomography (PET) with different radioligands have been performed. The first study evaluated resting state regional cerebral blood flow (rCBF) in WAD patients and in healthy, pain-free controls, by use of oxygen-15 labeled water. Patients had heightened resting rCBF bilaterally in the posterior parahippocampal and the posterior cingulate gyri, in the right thalamus and in the right medial prefrontal gyrus. Attenuated tempero-occipital blood flow was also observed in the patient group as compared to healthy controls. Alterations in rCBF were related to patients’ neck disability ratings. Study I suggests an involvement of the posterior cingulate, the parahippocampal and the medial prefrontal gyri in WAD. This altered resting state neural activity may be linked to an increased self-relevant evaluation of pain and stress. The second study evaluated central expression of the neurokinin-1 (NK1) receptor in WAD patients and healthy controls. Using a carbon-11 labeled specific NK1 antagonist, the receptor availability was measured. Patients displayed lowered NK1 receptor availability in the insula, anterior cingulate, frontal lobe, hippocampus, amygdala and in the periaqueductal gray matter, consistent with results from animal models of chronic pain. NK1 receptor availability was most reduced in the ventromedial orbitofrontal cortex, where attenuations were linearly related to patients fear and avoidance of movement. Thirdly, carbon-11 labeled D-deprenyl was used to investigate the presence of locally inflamed soft tissue in the cervical neck in WAD patients. Although the retention mechanism of [11C]D-deprenyl is not known, the results suggest that WAD patients have chronic inflammatory processes in the neck, most commonly in the adipose tissue at the spineous process of the second vertebra. In summary, this thesis provides evidence for altered central blood flow and receptor characteristics in WAD patients. Further, WAD patients may also have signs of persistent peripheral tissue damage. Both central and peripheral pain mechanisms have been demonstrated and visualized in patients with whiplash associated disorder