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Thesis (M.S. in Computer Science)--Naval Postgraduate School, Sept. 2004. / Thesis Advisor(s): Cynthia E. Irvine, Deborah S. Shifflett. Includes bibliographical references (p. 73-75). Also available online.

Thesis (M.S.)--Ohio State University, 2005. / Includes bibliographical references (leaves 166-170). Available online via OhioLINK's ETD Center

The Flexible Manufacturing Cell (FMC) represents an important and widely utilized constituent of hierarchically structured automated manufacturing systems. The control of FMCs is therefore of great importance in automated manufacturing. However, there are few tools and methodologies available for specifying and developing the control logic. The few tools that do exist have proven to be impractical due to their equirements for compatibility by the constituent equipment. Therefore, this research focuses on the development of a solution to the control of FMCs through the development of a programming language that provides a methodology and capabilities for developing the supervisory control applications. Accordingly, a programming language was developed in which the control logic is specified in modules, each of which control an equipment or resource in the cell. These modules interact with each other according to well defined models of interaction to achieve the control. The language provides features to enable this modularity and the interaction between the modules. The process plan of the parts that are produced in the cell drive the control logic and are also the means of communication between the modules. Additionally, several features required for control such as the detection of deadlocks, part information and so on are also developed. In the proposed language, the communication problem is separated from the logic specification. Guidelines and requirements are developed for a language implementation system that will enable the communication with the cell devices and that works with the language structure. / Master of Engineering

In this thesis, we investigate the problem of fault tolerance in the framework of discrete-event systems (DES). We introduce our setting, and then provide a set of fault-tolerant definitions designed to capture different types of fault scenarios and to ensure that our system remains controllable and nonblocking in each scenario. This is a passive approach that relies upon inherent redundancy in the system being controlled, and focuses on the intermittent occurrence of faults. Our approach provides an easy method for users to add fault events to a system model and is based on user designed supervisors and verification. As synthesis algorithms have higher complexity than verification algorithms, our approach should be applicable to larger systems than existing active fault-recovery methods that are synthesis based. Also, modular supervisors are typically easier to understand and implement than the results of synthesis. Finally, our approach does not require expensive (in terms of algorithm complexity) fault diagnosers to work. Diagnosers are, however, required by existing methods to know when to switch to a recovery supervisor. As a result, the response time of diagnosers is not an issue for us. Our supervisors are designed to handle the original and the faulted system. In this thesis, we next present algorithms to verify these properties followed by complexity analyses and correctness proofs of the algorithms. Finally, examples are provided to illustrate our approach. In the above framework, permanent faults can be modelled, but the current method was onerous. To address this, we then introduce a new modeling approach for permanent faults that is easy to use, as well as a set of new permanent fault-tolerant definitions. These definitions are designed to capture several types of permanent fault scenarios and to ensure that our system remains controllable and nonblocking in each scenario. New definitions and scenarios were required as the previous ones were incompatible with the new permanent fault modeling approach. We then present algorithms to verify these properties followed by complexity analyses and correctness proofs of the algorithms. An example is then provided to illustrate our approach. Finally, we extend the above intermittent and permanent fault-tolerant approach to the timed DES setting. As before, we introduced new fault-tolerant properties and algorithms. We then provide complexity analyses and correctness proofs for the algorithms. An example is then provided to illustrate our approach. / Thesis / Doctor of Philosophy (PhD)

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Interruptions have negative effects on the task performance in modern work environments. These negative effects are not affordable in tasks in which decisions are time-critical and have a life-critical nature. Human-supervisory control (HSC) tasks in time-critical settings such as mission command and control and emergency response are especially vulnerable to the negative effects of interruptions since supervisors in these settings are prone to frequent interruptions which are valuable source of information and hence cannot be ignored and consequences of a wrong decision in these settings is very costly because of their life-critical nature. To address this issue, this thesis investigates an activity-centric design approach that aims to help team supervisors in a complex mission control operation to remain aware of the activities that most likely would affect their decisions, while minimizing disruption. An interruption recovery assistant (IRA) tool was designed to promote activity and situation awareness of a team of UAV operators in a representative task. Initial pilot studies showed a positive trend in effectiveness of the IRA tool on recovery time and decision accuracy. This thesis explores alternative design approaches to validate the effectiveness of an interruption recovery tool that enable mission commanders rapidly and effectively regain the situational awareness after an interruption occurs in the mission environment. This thesis overview these design approaches and present results from a series of formative evaluations of our prototype designs. These evaluations were conducted in an experimental platform designed to emulate futuristic semi-autonomous UAV team mission operations.

Interruptions have negative effects on the task performance in modern work environments. These negative effects are not affordable in tasks in which decisions are time-critical and have a life-critical nature. Human-supervisory control (HSC) tasks in time-critical settings such as mission command and control and emergency response are especially vulnerable to the negative effects of interruptions since supervisors in these settings are prone to frequent interruptions which are valuable source of information and hence cannot be ignored and consequences of a wrong decision in these settings is very costly because of their life-critical nature. To address this issue, this thesis investigates an activity-centric design approach that aims to help team supervisors in a complex mission control operation to remain aware of the activities that most likely would affect their decisions, while minimizing disruption. An interruption recovery assistant (IRA) tool was designed to promote activity and situation awareness of a team of UAV operators in a representative task. Initial pilot studies showed a positive trend in effectiveness of the IRA tool on recovery time and decision accuracy. This thesis explores alternative design approaches to validate the effectiveness of an interruption recovery tool that enable mission commanders rapidly and effectively regain the situational awareness after an interruption occurs in the mission environment. This thesis overview these design approaches and present results from a series of formative evaluations of our prototype designs. These evaluations were conducted in an experimental platform designed to emulate futuristic semi-autonomous UAV team mission operations.

We study the supervisory control of supply chain operation modelled by (timed) State Tree Structures (STS). We model each agent involved in a supply chain using holons. Three operational models, make-to-order, make-to-stock, and assemble-to-order are considered. A strong assumption on the original STS theory is weakened to allow events shared among agents to be located at different levels. A supervisor is synthesized for the example of a mattress supply chain with make-to-stock operation under certain specifications. Moreover, a new version of the Timed STS framework is developed to allow events to have an upper time bound i.e. deadline. With Timed STS framework, more specifications requiring time measurement can be modeled and a supervisory control is synthesized for the timed model of a supply chain. For a nonempty supervisory synthesis result, the maximum time for the inventory periodic review rate, and the minimum cycle time for customer order satisfaction are achieved.

We study the supervisory control of supply chain operation modelled by (timed) State Tree Structures (STS). We model each agent involved in a supply chain using holons. Three operational models, make-to-order, make-to-stock, and assemble-to-order are considered. A strong assumption on the original STS theory is weakened to allow events shared among agents to be located at different levels. A supervisor is synthesized for the example of a mattress supply chain with make-to-stock operation under certain specifications. Moreover, a new version of the Timed STS framework is developed to allow events to have an upper time bound i.e. deadline. With Timed STS framework, more specifications requiring time measurement can be modeled and a supervisory control is synthesized for the timed model of a supply chain. For a nonempty supervisory synthesis result, the maximum time for the inventory periodic review rate, and the minimum cycle time for customer order satisfaction are achieved.