Awantha Jayasiri

Behavior Coordination of Mobile Robotics Using Supervisory Control of Fuzzy Discrete Event Systems

In order to incorporate the uncertainty and impreciseness present in real-world event-driven asynchronous systems, fuzzy discrete event systems (DESs) (FDESs) have been proposed as an extension to crisp DESs. In this paper, first, we propose an extension to the supervisory control theory of FDES by redefining fuzzy controllable and uncontrollable events. The proposed supervisor is capable of enabling feasible uncontrollable and controllable events with different possibilities. Then, the extended supervisory control framework of FDES is employed to model and control several navigational tasks of a mobile robot using the behavior-based approach. The robot has limited sensory capabilities, and the navigations have been performed in several unmodeled environments. The reactive and deliberative behaviors of the mobile robotic system are weighted through fuzzy uncontrollable and controllable events, respectively. By employing the proposed supervisory controller, a command-fusion-type behavior coordination is achieved. The observability of fuzzy events is incorporated to represent the sensory imprecision. As a systematic analysis of the system, a fuzzy-state-based controllability measure is introduced. The approach is implemented in both simulation and real time. A performance evaluation is performed to quantitatively estimate the validity of the proposed approach over its counterparts.

Modular Supervisory Control and Hierarchical Supervisory Control of Fuzzy Discrete-Event Systems

This paper establishes modular and hierarchical supervisory control theories of Fuzzy Discrete-Event Systems (FDES). It aims to resolve the horizontal and vertical complexities present in large-scale event-driven systems, which are affected by uncertainties in their event and state representations. The modular supervisory control architecture composed of a set of noncommunicating local supervisors, in which one supervisor is assigned for each module having its own sensing and acting capabilities. The notion of separability for languages in FDES is introduced and the property of a language specification of FDES, termed as separably-controllable-observability, is proposed to determine the existence of modular supervisors to the control problem. The hierarchical supervisory control architecture consists of multilevel supervisors assigned to detailed low-level and abstract high-level models of the plant. The notion of output-control-consistency is introduced for languages in FDES. Then, the property called strictly-output-control-consistency is defined for FDES in order to maintain the hierarchical consistency between low-level and high-level FDES modules. The property of H-fuzzy observability is introduced to ensure the hierarchical consistency under the partial observation of low-level FDES. Finally, using the established hierarchical supervisory control theory of FDES, a behavior-based mobile robot navigation example is discussed.

Generalizing the Decentralized Control of Fuzzy Discrete Event Systems

The main objective of this paper is to establish a general architecture for decentralized supervision of fuzzy discrete event systems (FDES). First, two different types of decentralized supervisory control architectures of FDES are presented, which fuse the locally enabled degrees of fuzzy events using the fuzzy-intersection operator and the fuzzy-union operator, respectively. Both of these architectures possess limitations in information association. Second, to overcome the aforementioned drawbacks, a general architecture for decentralized supervisory control of FDES is introduced, in which the decisions of local supervisors are fused by using both fuzzy-union and fuzzy-intersection operators. The proposed general architecture is then implemented to control a tightly coupled multirobot object manipulation task in simulation. A performance evaluation is performed to quantitatively estimate the validity of the proposed architecture compared with centralized FDES-based and decentralized crisp DES-based approaches.

Mobile robot behavior coordination using supervisory control of Fuzzy Discrete Event Systems

This paper presents a novel approach to behavior based control of mobile robots using supervisory control of Fuzzy Discrete Event Systems (FDES). Fuzzy events are triggered by the sensor readings and the inference occurs through a fuzzy rule base system. The supervisor can activate and control fuzzy controllable events simultaneously with fuzzy uncontrollable events to achieve the planned objectives. The fuzzy observability concept is incorporated to represent sensor uncertainties. Fuzzy state based controllability and observability measures are also discussed. The proposed theoretical development is then extended to discuss an application with behavior based control of mobile robots.

Decentralized modular control of concurrent Fuzzy Discrete Event Systems

In order to analyze the event driven complex systems with uncertainties in their events and state transitions, Fuzzy Discrete Event Systems (FDES) has been proposed as an extension to the formal Discrete Event Systems theory (DES). In this paper we investigate the decentralized modular supervisory control problem of FDES with partial observation for systems which are composed of concurrently operating, multiple interacting modules with uncertainties in their events and states. The modular decentralized fuzzy supervisor consists of set of local fuzzy supervisors, one for each module and each with its own sensing and acting capabilities. Moreover, the communication is not allowed between the local fuzzy supervisors. The notion of separability for fuzzy languages is introduced and the property of a fuzzy language specification which is called separably - controllable - observable that is required for verifying the existence of modular fuzzy supervisors is defined. Some examples are presented to realize the theoretical developments.

Tightly-coupled multi robot coordination using decentralized supervisory control of Fuzzy Discrete Event Systems

In this paper, we address the multi robot coordination problem of tightly-coupled task execution, using a formal decentralized supervisory control approach. A general architecture for decentralized supervisory control of Fuzzy Discrete Event Systems (FDES), which is capable of modeling asynchronous event driven systems with inherited uncertainties, is developed. This architecture is then incorporated for controlling behavior-based mobile robots moving in unstructured environments while maintaining a fixed distance between each other, which resembles a tightly-coupled multi robot object manipulation task. The proposed approach is then successfully implemented in simulation with two mobile robots and a performance evaluation is also performed to investigate the validity of the proposed approach over the centralized and crisp Discrete Event System (DES) based approaches.

AUV-Based Plume Tracking

This paper presents a simulation study of an autonomous underwater vehicle AUV navigation system operating in a GPS-denied environment. The AUV navigation method makes use of underwater transponder positioning and requires only one transponder. A multirate unscented Kalman filter is used to determine the AUV orientation and position by fusing high-rate sensor data and low-rate information. The paper also proposes a gradient-based, efficient, and adaptive novel algorithm for plume boundary tracking missions. The algorithm follows a centralized approach and it includes path optimization features based on gradient information. The proposed algorithm is implemented in simulation on the AUV-based navigation system and successful boundary tracking results are obtained.

Dynamic Positioning of Vessels Using a UKF-Based Observer and an NMPC-Based Controller

This paper presents a solution to the problem of dynamic positioning (DP) of vessels in ice-infested environments using a nonlinear observer and a finite-horizon optimal control-based approach. An unscented Kalman filter-based nonlinear observer is developed to estimate both the vessel states and the unknown inputs, such as the ice load. To perform better control and disturbance rejection, a nonlinear model predictive controller is employed for DP. The developed modules are integrated with a commercial vessel maneuvering software, and promising real-time results are generated.Note to Practitioners—Accurate dynamic positioning (DP) of vessels in the presence of environmental disturbances is very important for Arctic explorations. This paper proposes a tightly coupled approach to estimate the unknown forces acting on a vessel and the vessel states. Also, an optimum control-based solution is proposed for robust DP.

Simulation of aided AUV navigation and adaptive plume tracking

This paper presents a simulation study of an Autonomous Underwater Vehicle (AUV), which is used for detecting a plume trajectory in a GPS-denied environment. Also. it proposes a novel algorithm for generating an adaptive search path to plume boundary detection. The algorithm is implemented in the navigation system and successful boundary tracking results are obtained.

A general architecture for decentralized supervisory control of Fuzzy Discrete Event Systems

In this paper, a general decentralized supervisory control architecture of Fuzzy Discrete Event Systems (FDES) is established. The proposed architecture is capable of fusing the decisions of each local supervisor using both union and intersection of the enabled degrees of the active fuzzy events. Moreover, the proposed architecture is implemented in both simulation and real-time for behavior coordination of a decentralized multi robot system, employed in a cooperative object manipulation task. A performance evaluation is carried out to compare the performance of the proposed approach against the centralized FDES and decentralized crisp Discrete Event Systems (DES) based supervisory control architectures.