André B. Leal

Supervisory control theory applied to swarm robotics

Currently, the control software of swarm robotics systems is created by ad hoc development. This makes it hard to deploy these systems in real-world scenarios. In particular, it is difficult to maintain, analyse, or verify the systems. Formal methods can contribute to overcome these problems. However, they usually do not guarantee that the implementation matches the specification, because the system’s control code is typically generated manually. Also, there is cultural resistance to apply formal methods; they may be perceived as an additional step that does not add value to the final product. To address these problems, we propose supervisory control theory for the domain of swarm robotics. The advantages of supervisory control theory, and its associated tools, are a reduction in the amount of ad hoc development, the automatic generation of control code from modelled specifications, proofs of properties over generated control code, and the reusability of formally designed controllers between different robotic platforms. These advantages are demonstrated in four case studies using the e-puck and Kilobot robot platforms. Experiments with up to 600 physical robots are reported, which show that supervisory control theory can be used to formally develop state-of-the-art solutions to a range of problems in swarm robotics.

A Method for PLC Implementation of Supervisory Control of Discrete Event Systems

This paper faces the problem of coordinating equipment operation in a flexible manufacturing system consisting of several subsystems including robots, assembling machines, CNC lathes, and mills. There are two main problems in such a system. The first is controlling each individual subsystem considering its own sensors, actuators, and specialized controller to perform a certain sequence of activities. Due to their expertise and/or application of formal methods, programmable logic controller (PLC) practitioners and equipment manufacturers develop efficient and safe solutions to address this problem. The second problem is coordinating the concurrent operation of these subsystems with the goal of producing what is requested as efficiently as possible and guaranteeing the integrity and safety of the system. Supervisory control theory (SCT) is particularly suited to this problem. This paper presents a method that allows a designer to systematically convert SCTs results into a PLC application program. The resulting program conforms to IEC 61131-3 and preserves the natural modularity of the system to be controlled and control specifications. An extension of this method allows a designer to reuse existing PLC hardware and application programs designed for the control of equipment by easily integrating with the code corresponding to the SCT solution. A major portion of this code may even be automatically generated, reducing development time and minimizing editing errors.

Application of Supervisory Control Theory to Swarms of e-puck and Kilobot Robots

At present, most of the source code controlling swarm robotic systems is developed in an ad-hoc manner. This can make it difficult to maintain these systems and to guarantee that they will accomplish the desired behaviour. Formal approaches can help to solve these issues. However, they do not usually guarantee that the final source code will match the modelled specification. To address this problem, our research explores the application of formal approaches to both synthesise high-level controllers and automatically generate control software for a swarm of robots. The formal approach used in this paper is supervisory control theory. The approach is successfully validated in two experiments using up to 42 Kilobot robots and up to 26 e-puck robots.

Supervisory control implementation into Programmable Logic Controllers

This paper deals with the implementation of supervisory control of discrete event systems into Programmable Logic Controllers (PLCs). It discusses the problems that arise in this type of implementation and presents an implementation methodology that solves these problems. The local modular approach is used to synthesize the supervisors and a case study problem is presented as an example.

PLC-Based Implementation of Local Modular Supervisory Control for Manufacturing Systems

Developing and implementing control logic for automated manufacturing systems is not a trivial task. Industrial production lines should be able to produce many types of products that go through a growing number of processes given the needs of the market, and there is an ever growing flexibility demand because of it. To keep up with it a faster way to develop control logic automation for the production lines is required. And this should be done in such a way to easy development and to guarantee that the control is correct in terms of making the system to behave as it should. To this end, the use of formal modelling tools seems to help raise the abstraction level of specifying systems’ behaviour at the same time that it provides ways to test the resulting model.

Smooth Trajectory Tracking Interpolation on a Robot Simulator

When there is the need of a robotic manipulator to follow a certain smooth and continuous trajectory, it involves the specification of the curve to be followed and the way the gripper should behave alongside it. This work aims to identify and analyze a technique to be used in a 3D virtual robotic simulator that executes smooth and continuous movements. It also aims to develop a method for trajectory programming using a solution that covers the main problems of trajectory tracking (smoothness of path and gripper approach). An efficient and flexible method to embed trajectory tracking was indentified and implemented which allows its integration with existing standard (linear or circular) movements.

Modular supervision of hybrid systems: a DES approach

Abstract This paper presents the formulation and solution of a modular supervisory control problem for a class of hybrid systems in which threshold-crossing events in the continuous state space force discrete state transitions. The continuous dynamics are determined by a discrete condition, which depends on the current discrete state of the system. The problem is to construct modular supervisors, each to satisfy a particular specification given in terms of sequences of threshold events, in such a way that the joint action of these supervisors results in an optimal control action. The supervisors for the hybrid system are obtained using the theory of supervisor synthesis for discrete event systems. A condition under which the proposed approach can be applied is given and an illustrative example is presented.

Finite Automata as an Information Model for Manufacturing Execution System and Supervisory Control Integration

Abstract The use of MES (Manufacturing Execution System) is an alternative to link the ERP (Enterprise Resource Planning) to the activities at the shop floor. Due to the difference between the transactional feature of the ERP systems and the real-time features of the operations of the shop floor, MES becomes an important tool. SCADA (Supervisory Control And Data Acquisition) are responsible for monitoring the behaviour of shop floor and can interfere or alert in case of failures. The SCT (Supervisory Control Theory) is a formal methodology for modelling and control synthesis of DES (Discrete Event Systems). SCT appears to be an appropriate tool for this task, ensuring an optimal control logic that is minimally restrictive and non-blocking. The simultaneous use of MES, SCADA, ERP and controllers synthesized by SCT requires the creation of an interface between them. This creation requires development time, delays the project, being inflexible to change and is subject to failure. One of the formal models for the synthesis of DES controllers in the SCT is the DFA (Deterministic Finite Automaton). DFA is one of the computational models within the theory of automata. This paper shows the use of the DFA models to build the DES controller to interface SCADA and MES to save development time and to deal with flexibility and failure-tolerant issues.

Implementation of Supervisory Control systems based on state machines

This paper presents a new methodology for the implementation of discrete event-based control systems. An algorithm is proposed to transform an automata-based supervisor obtained from the supervisory control theory (SCT) in a Mealy finite state machine. This machine may be simplified in order to have a reduced number of state transitions. The machine simplification represents a formal method for a discrete event control system to be implemented in a controller. It is presented an example of a manufacturing system to illustrate such procedure. The implementation of the control for this system is performed in Ladder, a useful language for programmable logic controllers (PLCs). The methodology may be expanded to other programming languages and controller types as well.

Towards automatic code generation for UAV mission planning using decision sensors

The planning of an autonomous mission for UAVs requires more than the description of the points to be visited along the trajectory by which a certain task must be performed. However, the way in which such missions are planned does not provide conditions for the aircraft or the ground control system to find alternative ways of carrying out the mission, in the event of a risk or other situation different from what was initially planned. In this sense, this paper makes use of a complementary description of the trajectory of a UAV, specifying it through the Discrete Events Systems (DES) framework. Furthermore, it makes use of sensor information to identify situations of risk and, from this, to systematically carry out changes in the mission initially programmed in the aircraft in order to avoid undesired situations.