On Object Oriented Nondeterministic Supervisory Control

Implementation of complex discrete event fabrication processes can be considerably simplified by use of general reusable software modules representing the physical components. At the same time, construction of the control system can be facilitated by applying the supervisory control theory for the automatic generation of control laws. These two aspects can be joined into a general concept with object-oriented modeling and control law synthesis as foundations. The goal is to allow an operator to specify operation lists describing the required sequences of operations for the manufacturing of the product, independently of constraints given by a specific plant. With a suitable model of the capabilities and constraints of the resources of that plant, a product route can be automatically generated from the operation list. Such a product route describes all available paths through the system, for each type of product, irrespective of any other type of product that may be simultaneously present within the production system. Given a set of product routes and a model of the plant, control laws guaranteeing production according to those product specifications can be synthesized. Based on the supervisory control theory, using interleaved product routes as specification, we show how such control laws can be synthesized. An added complexity is that the specification becomes non-deterministic, in the sense that the same string of events can lead to different system states. We show that the supervisory control theory can be used with non-deterministic specifications assuming certain properties. An algorithm for synthesis of a non-deterministic supervisor is presented. We also describe an object-oriented modeling approach to discrete event fabrication processes. It is shown that the properties that have been defined as necessary for the non-deterministic supervisory approach are immediate by the modeling approach. Thus, we show that the approach to non-deterministic supervisory control can be combined with object-oriented modeling techniques, and so we have a powerful framework for implementing control of large and complex discrete event fabrication processes

An Iterative Approach for Collision Feee Routing and Scheduling in Multirobot Stations

This work is inspired by the problem of planning sequences of operations, as welding, in car manufacturing stations where multiple industrial robots cooperate. The goal is to minimize the station cycle time, \emph{i.e.} the time it takes for the last robot to finish its cycle. This is done by dispatching the tasks among the robots, and by routing and scheduling the robots in a collision-free way, such that they perform all predefined tasks. We propose an iterative and decoupled approach in order to cope with the high complexity of the problem. First, collisions among robots are neglected, leading to a min-max Multiple Generalized Traveling Salesman Problem (MGTSP). Then, when the sets of robot loads have been obtained and fixed, we sequence and schedule their tasks, with the aim to avoid conflicts. The first problem (min-max MGTSP) is solved by an exact branch and bound method, where different lower bounds are presented by combining the solutions of a min-max set partitioning problem and of a Generalized Traveling Salesman Problem (GTSP). The second problem is approached by assuming that robots move synchronously: a novel transformation of this synchronous problem into a GTSP is presented. Eventually, in order to provide complete robot solutions, we include path planning functionalities, allowing the robots to avoid collisions with the static environment and among themselves. These steps are iterated until a satisfying solution is obtained. Experimental results are shown for both problems and for their combination. We even show the results of the iterative method, applied to an industrial test case adapted from a stud welding station in a car manufacturing line

An approach to task coordination for hyperflexible robotic workcells

2014 - 2015The manufacturing industry is very diverse and covers a wide range of specific processes ranging from extracting minerals to assembly of very complex products such as planes or computers, with all intermediate processing steps in a long chain of industrial suppliers and customers. It is well know that the introduction of robots in manufacturing industries has many advantages. Basically, in relation to human labor, robots work to a constant level of quality. For example, waste, scrap and rework are minimized. Furthermore they can work in areas that are hazardous or unpleasant to humans. Robots are advantageous where strength is required, and in many applications they are also faster than humans. Also, in relation to special-purpose dedicated equipment, robots are more easily reprogrammed to cope with new products or changes in the design of existing ones. In the last 30-40 years, large enterprises in high-volume markets have managed to remain competitive and maintain qualified jobs by increasing their productivity with the incremental adoption and use of advanced ICT and robotics technologies. In the 70s, robots have been introduced for the automation of a wide spectrum of tasks such as: assembly of cars, white goods, electronic devices, machining of metal and plastic parts, and handling of workpieces and objects of all kinds. Robotics has thus soon become a synonym for competitive manufacturing and a key contributing technology for strengthening the economic base of Europe . So far, the automotive and electronics industries and their supply chains are the main users of robot systems and are accounting for more than 60% of the total annual robot sales. Robotic technologies have thus mainly been driven by the needs of these high-volume market industries. The degree of automation in the automotive industries is expected to increase in the future as robots will push the limits towards flexibility regarding faster change-over-times of different product types (through rapid programming generation schemes), capabilities to deal with tolerances (through an extensive use of sensors) and costs (by reducing customized work-cell installations and reuse of manufacturing equipment). There are numerous new fields of applications in which robot technology is not widespread today due to its lack of flexibility and high costs involved when dealing with varying lot sizes and variable product geometries. In such cases, hyper-flexible robotic work cells can help in providing flexibility to the system and making it adaptable to the different dynamic production requirements. Hyper-flexible robotic work cells, in fact, can be composed of sets of industrial robotic manipulators that cooperate to achieve the production step that characterize the work cell; they can be programmed and re-programmed to achieve a wide class of operations and they may result versatile to perform different kind of tasks Related key technology challenges for pursuing successful long-term industrial robot automation are introduced at three levels: basic technologies, robot components and systems integration. On a systems integration level, the main challenges lie in the development of methods and tools for instructing and synchronising the operation of a group of cooperative robots at the shop-floor. Furthermore, the development of the concept of hyper flexible manufacturing systems implies soon the availability of: consistent middleware for automation modules to seamlessly connect robots, peripheral devices and industrial IT systems without reprogramming everything (”plug-and-play”) . In this thesis both innovative and traditional industrial robot applications will be analyzed from the point of view of task coordination. In the modeling environment, contribution of this dissertation consists in presenting a new methodology to obtain a model oriented to the control the sequencing of the activities of a robotic hyperflexible cell. First a formal model using the Colored Modified Hybrid Petri Nets (CMHPN) is presented. An algorithm is provided to obtain an automatic synthesis of the CMHPN of a robotic cell with detail attention to aircraft industry. It is important to notice that the CMHPN is used to model the cell behaviour at a high level of abstraction. It models the activities of each cell component and its coordination by a supervisory system. As more, an object oriented approach and supervisory control are proposed to implement industrial automation control systems (based on Programmable Logic Controllers) to meet the new challenges of this field capability to implement applications involving widely distributed devices and high reuse of software components. Hence a method is proposed to implement both controllers and supervisors designed by Petri Nets on Programmable Logic Controllers (PLCs) using Object Oriented Programming (OOP). Finally preliminary results about a novel cyber-physical approach to the design of automated warehouse systems is presented. [edited by author]XIV n.s

System simulation and modeling of electronics demanufacturing facilities

Over the last decade, pressure on the electronic industry has been increasing as concerns for product take-back, product stewardship and global warming have continued to grow. Various end-of-life management options are being expanded including recycling to recapture values from basic materials through reengineering and recovery of subassemblies and individual components for remanufacturing. While progress has been reported on life cycle assessment (LCA), disassembly planning, design for disassembly, and design for environment (DFE), very little research has been focused on demanufacturing from a systems perspective. The objective of this thesis is to build an interface between the user who knows the demanufacturing operation and a software engine, which performs the simulation, collects detailed operational data, and displays results. This thesis bridges the gap between the requirement of hard core simulation knowledge and demanufacturing terminology to present a computerized software tool. Arena, a commercially available discrete event simulation software, acts as an engine for performing these simulations. The developed software tool for demanufacturing contains objects necessary for facility layout, systematic workflow and simulation of the facility. Each object refers to a specific demanufacturing activity and uses detailed simulation logic behind its design to perform that activity. The user selects and locates these objects to layout the facility for a graphical representation of the demanufacturing operation. Objects provide a user screen to input necessary data for the complete description of the activity and its operational characteristics. By simulating the facility for various scenarios, the demanufacturer can compare different options for improving operations, resource utilization, equipment and layout changes. To examine improvement options from an economic perspective a first-order model of demanufacturing costs has been developed and integrated with the simulation software. An activity based unit cost model is used to identify fixed and variable costs associated with each product demanufactured. A small electronics demanufacturing facility was observed and evaluated to validate the simulation modeling and operational logic. The application illustrates the usefulness of demanufacturing system simulation tool to manage and improve the overall efficiency of facilities for economical operation. In summary, a computer-base tool for simulating demanufacturing facility from a systems perspective has been developed and validated. An activity based cost model has been integrated with the simulation to give demanufacturers the ability to examine the full operational and economic trade-offs associated with the business

Resource selection and route generation in discrete manufacturing environment

When put to various sources, the question of which sequence of operations and machines is best for producing a particular component will often receive a wide range of answers. When the factors of optimum cutting conditions, minimum time, minimum cost, and uniform equipment utilisation are added to the equation, the range of answers becomes even more extensive. Many of these answers will be 'correct', however only one can be the best or optimum solution. When a process planner chooses a route and the accompanying machining conditions for a job, he will often rely on his experience to make the choice. Clearly, a manual generation of routes does not take all the important considerations into account. The planner may not be aware of all the factors and routes available to him. A large workshop might have hundreds of possible routes, even if he did know it all', he will never be able to go through all the routes and calculate accurately which is the most suitable for each process - to do this, something faster is required. This thesis describes the design and implementation of an Intelligent Route Generator. The aim is to provide the planner with accurate calculations of all possible production routes m a factory. This will lead up to the selection of an optimum solution according to minimum cost and time. The ultimate goal will be the generation of fast decisions based on expert information. Background knowledge of machining processes and machine tools was initially required, followed by an identification of the role of the knowledge base and the database within the system. An expert system builder. Crystal, and a database software package, DBase III Plus, were chosen for the project. Recommendations for possible expansion of and improvements to the expert system have been suggested for future development

Production Scheduling

Generally speaking, scheduling is the procedure of mapping a set of tasks or jobs (studied objects) to a set of target resources efficiently. More specifically, as a part of a larger planning and scheduling process, production scheduling is essential for the proper functioning of a manufacturing enterprise. This book presents ten chapters divided into five sections. Section 1 discusses rescheduling strategies, policies, and methods for production scheduling. Section 2 presents two chapters about flow shop scheduling. Section 3 describes heuristic and metaheuristic methods for treating the scheduling problem in an efficient manner. In addition, two test cases are presented in Section 4. The first uses simulation, while the second shows a real implementation of a production scheduling system. Finally, Section 5 presents some modeling strategies for building production scheduling systems. This book will be of interest to those working in the decision-making branches of production, in various operational research areas, as well as computational methods design. People from a diverse background ranging from academia and research to those working in industry, can take advantage of this volume

Engineering framework for service-oriented automation systems

Tese de doutoramento. Engenharia Informática. Universidade do Porto. Faculdade de Engenharia. 201

On the decidability of problems in liveness of controlled Discrete Event Systems modeled by Petri Nets

A Discrete Event System (DES) is a discrete-state system, where the state changes at discrete-time instants due to the occurrence of events. Informally, a liveness property stipulates that a 'good thing' happens during the evolution of a system. Some examples of liveness properties include starvation freedom -- where the 'good thing' is the process making progress; termination -- in which the good thing is for an evolution to not run forever; and guaranteed service -- such as in resource allocation systems, when every request for resource is satisfied eventually. In this thesis, we consider supervisory policies for DESs that, when they exist, enforce a liveness property by appropriately disabling a subset of preventable events at certain states in the evolution of DES. One of the main contributions of this thesis is the development of a system-theoretic framework for the analysis of Liveness Enforcing Supervisory Policies (LESPs) for DESs. We model uncertainties in the forward- and feedback-path, and present necessary and sufficient conditions for the existence of Liveness Enforcing Supervisory Policies (LESPs) for a general model of DESs in this framework. The existence of an LESP reduces to the membership of the initial state to an appropriately defined set. The membership problem is undecidable. For characterizing decidable instances of this membership problem, we consider a modeling paradigm of DESs known as Petri Nets, which have applications in modeling concurrent systems, software design, manufacturing systems, etc. Petri Net (PN) models are inherently monotonic in the sense that if a transition (which loosely represents an event of the DES) can fire from a marking (a non-negative integer-valued vector that represents the state of the DES being modeled), then it can also fire from any larger marking. The monotonicity creates a possibility of representing an infinite-state system using what can be called a "finite basis" that can lead to decidability. However, we prove that several problems of our interest are still undecidable for arbitrary PN models. That is, informally, a general PN model is still too powerful for the analysis that we are interested in. Much of the thesis is devoted to the characterization of decidable instances of the existence of LESPs for arbitrary PN models within the system-theoretic framework introduced in the thesis. The philosophical implication of the results in this thesis is the existence of what can be called a "finite basis" of an infinite state system under supervision, on which the membership tests can be performed in finite time; hence resulting in the decidability of problems and finite-time termination of algorithms. The thesis discusses various scenarios where such a finite basis exists and how to find them

A Capacity Planning Simulation Model for Reconfigurable Manufacturing Systems

Important objectives and challenges in today’s manufacturing environment include the introduction of new products and the designing and developing of reconfigurable manufacturing systems. The objective of this research is to investigate and support the reconfigurability of a manufacturing system in terms of scalability by applying a discrete-event simulation modelling technique integrated with flexible capacity control functions and communication rules for re-scaling process. Moreover, the possible extension of integrating the discrete-event simulation with an agent-based model is presented as a framework. The benefits of this framework are collaborative decision making using agents for flexible reaction to system changes and system performance improvement. AnyLogic multi-method simulation modelling platform is utilized to design and create different simulation modelling scenarios. The developed capacity planning simulation model results are demonstrated in terms of a case study using the configurable assembly Learning Factory (iFactory) in the Intelligent Manufacturing Systems (IMS) Center at the University of Windsor. The main benefit of developed capacity planning simulation in comparison to traditional discrete-event simulation is, with a single simulation run, the recommended capacity for manufacturing system will be determined instead of running several discrete-event simulation models to find the needed capacity