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Robotics and Automation, IEEE Transactions on

Issue 2 • Date Apr 1994

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Displaying Results 1 - 15 of 15
  • Transient analysis of manufacturing systems performance

    Page(s): 230 - 244
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    We present several situations in manufacturing systems where transient analysis is very important. Manufacturing systems and models in which such situations arise include: systems with failure states and deadlocks, unstable queueing systems, and systems with fluctuating or nonstationary workloads. Even in systems where equilibrium exists, transient analysis is important in studying issues such as accumulated performance rewards over finite intervals, first passage times, sensitivity analysis, settling time computation, and deriving the behavior of queueing models as they approach equilibrium. In this paper, we focus on transient analysis of Markovian models of manufacturing systems. After presenting several illustrative manufacturing situations where transient analysis has significance, we discuss two problems for demonstrating the importance of transient analysis. The first problem is concerned with the computation of distribution of time to absorption in Markov models of manufacturing systems with deadlocks or failures, and the second problem shows the relevance of transient analysis to a multiclass manufacturing system with significant setup times. We also discuss briefly computational aspects of transient analysis View full abstract»

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  • A temporal framework for assembly sequence representation and analysis

    Page(s): 220 - 229
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    A unifying temporal logic framework is proposed for modelling, specifying, and analyzing mechanical assembly sequences. Propositional temporal logic of Manna and Pneuli is the assertion language used for representing and analyzing all constraints or conditions that assembly sequences must satisfy. The generalization of the existing representations through the proposed framework is demonstrated. A new concept of reverse-equivalence, relating assembly and disassembly forms of knowledge, is introduced. It is shown that existing and new assembly sequence properties can be formulated and rigorously proved via mechanical theorem proving based on two assembly process-axioms, and the language inference rules and theorems. Comparison of the proposed framework with the existing representation schemes highlights the main strengths of the proposed framework, viz., temporal expressiveness, strong mechanical manipulation capability and precise formalism. The implementation of the framework on an IPC SUN SPARC workstation using Quintus Prolog for automatic generation of assembly sequences is described. A simple example illustrates the use of the proposed framework for representation, evaluation and selection of feasible assembly sequences View full abstract»

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  • Distributed scheduling of flexible manufacturing systems: stability and performance

    Page(s): 133 - 141
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    We consider a manufacturing system producing several part-types on several machines. Raw parts are input to the system. Each unit of a given part-type requires a predetermined processing time at each of several machines, in a given order. A setup time is required whenever a machine switches from processing one part-type to another. For a single machine system with constant demand rates, we present a class of generalized round-robin scheduling policies for which the buffer level trajectory of each part-type converges to a steady state level. Furthermore, for all small initial conditions, we show that these policies can be Pareto-efficient with respect to the buffer sizes required. Allowing the input streams to have some burstiness, we derive upper bounds on the buffer levels for small initial conditions. For non-acyclic systems, we consider a class of policies which are stable for all inputs with bounded burstiness. We show how to employ system elements, called regulators, to stabilize systems. Using the bounds for the single machine case, we analyze the performance of regulated systems implementing generalized round-robin scheduling policies View full abstract»

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  • Production planning and scheduling using a fuzzy decision system

    Page(s): 160 - 168
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    In this paper short-range planning and scheduling problems are addressed using a nonclassical approach supported by fuzzy theory. The proposed methodology uses a hierarchical structure which includes three decision levels (higher, middle, lower), each responsible for a different production problem with a different time scale. The methodology approaches the tasks associated with each level using a heuristic formulation and solves the short-range planning and scheduling problems with a nonstationary policy. The higher decision level determines safety stock levels used to compensate for future resource failures. At the middle level, loading rates are computed. This is accomplished through a fuzzy controller that tends to minimize the error between the cumulative production and the cumulative demand while keeping the work in process below acceptable values. Finally, the lower level controls the flow of parts among the resources, using a modified version of the Yager's fuzzy decision method. This method has the ability to use several criteria to generate a decision. Simulation results reveal that the proposed system exhibits good performance, in terms of a high production percentage and a low WIP, under resource failures and demand variations View full abstract»

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  • Composite performance-dependability analysis of cellular manufacturing systems

    Page(s): 245 - 258
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    This paper deals with the transient analysis of manufacturing systems in the presence of failures and repairs. The exact model is decomposed into: 1) a structure state process, modeling the failure and repair events which occur at a slower time scale; and 2) a performance model, modeling the part processing and material movement events occurring at a faster time scale. The solutions of these two models are combined to yield the mean and standard deviation of cumulative production over an interval. Such studies, called combined performance-dependability studies, are important in the manufacturing context. We define combined performance and dependability (performability) measures in the manufacturing context, and provide a mathematical formulation. Detailed performability studies are carried out for cellular manufacturing systems, in particular for a flexible manufacturing cell and a two-cell manufacturing system featuring blocking and prioritized, centralized repair. We also present several numerical examples View full abstract»

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  • Optimal robot selection and workstation assignment for a CIM system

    Page(s): 210 - 219
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    In this paper, a mathematical program and solution algorithm is developed for optimal robot selection and workstation assignment for a CIM system. In specific, our model considers selection of a proper mix of multiple-type robots such that operational requirements from a given number of work- stations are satisfied at minimal system cost. Each robot is characterized by its fixed charge, and subject to limits on machine time and work envelope. Each workstation has known demands on both robot machine time and work space. The model is formulated as a pure 0-1 mathematical program and is shown harder than two-dimensional bin packing, a well-known NP-hard problem. A three-phase optimization algorithm is implemented and tested by solving 450 randomly generated problems. Computational results indicate the solution algorithm is effective in solving problems of a practical size (i.e., 50 workstations and a maximum of 20 robots) within acceptable computational times View full abstract»

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  • Scheduling products with bills of materials using an improved Lagrangian relaxation technique

    Page(s): 99 - 111
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    A bill of materials specifies the sequence in which parts are to be processed and assembled in order to manufacture a deliverable product. In practice, a bill of materials may be quite complex, involving hundreds of parts to be processed on a number of limited resources, making scheduling difficult. This has forced many practitioners to turn to Material Requirements Planning (MRP) and heuristic rules to perform scheduling. These methods are seldom integrated, resulting in unreliable completion times for products and, hence, low customer satisfaction. This paper addresses the issue of integrally scheduling parts that are related through a bill of materials for the purpose of improving the on-time performance of products as well as reducing work-in-process (WIP) inventory. The technique presented here is based on an existing Lagrangian relaxation (LR) approach for the scheduling of independent parts in a job shop. An auxiliary problem formulation with a modified subgradient method is adopted to improve the computation time of the existing LR approach. This improved LR approach allows the bill of material constraints to be considered directly in the problem formulation View full abstract»

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  • Approximate solutions for large-scale piecewise deterministic control systems arising in manufacturing flow control models

    Page(s): 142 - 152
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    We propose a numerical technique for approximately solving large-scale piecewise deterministic control systems that are typically related to manufacturing flow control problems in unreliable production systems. The method consists of reformulating the stochastic control problem under study into a Markov decision process. Then we exploit the associated dynamic programming conditions and we propose an “approximate” policy iteration algorithm. This will be based on an approximation of the Bellman functions by a combination of a set of base functions, using a specific decomposition technique. The numerical method is applicable whenever a turnpike property holds for some associated infinite horizon deterministic control problem. To illustrate the approach, we solve an example and compare this new approximation method with a more classical approximation-by-decomposition technique View full abstract»

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  • Scheduling semiconductor lines using a fluid network model

    Page(s): 88 - 98
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    We present a novel method for “what's next” scheduling of semiconductor manufacturing lines based on the deterministic fluid network model of Chen and Yao. By “what's next” scheduling we mean specifying the order in which jobs are processed at each tool group. The approach we take here is first to determine how to allocate tool capacity among competing job types by solving a series of linear and quadratic programming problems related to the fluid model and then to specify a “what's next” scheduling algorithm designed to track these capacity allocations. The primary advantage of our approach is that it gives rise to a dynamic schedule which is based on global rather than local state information and which is responsive to stochastic changes in the line including tool incapacitation events and operator unavailability. This is in contrast to many other scheduling rules, such as first come first served and closest to completion which are essentially static rules based on local information. We also present some theoretical results about the fluid model that have important implications in the context of semiconductor manufacturing as well as some preliminary simulation results comparing the fluid model to other scheduling policies View full abstract»

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  • Petri net structural analysis for supervisory control

    Page(s): 185 - 195
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    The primary motivation for this research is to show how Petri nets may be efficiently used within the framework of supervisory control. In particular, the paper discusses how integer programming techniques for Petri net models may be used to validate supervisors for the control of discrete event systems. We consider a class of place/transition nets, called elementary composed state machines. The reachability problem for this class can be solved by a modification of classical incidence matrix analysis. In fact it is possible to derive a set of linear inequalities that exactly defines the set of reachable markings. Finally, we show how important properties of discrete event systems, such as the absence of blocking states or controllability, may be analyzed by integer programming techniques View full abstract»

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  • A new approach to modular liveness analysis conceived for large logic controllers' design

    Page(s): 169 - 184
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    When dealing with complex automation systems, the development and maintenance of control software often is a delicate task and takes a long time. The paper illustrates a Petri nets-based model to design logic controllers in an incremental mode, in which liveness analysis can be easily carried out, based on the compressed information contained in a compact graph that can be associated to the Petri net. Moreover, the incremental liveness analysis allows the portion of a net specifically involved in a fault to be identified and suggests a number of possible, even complex, remedies according to the nature of the detected faults. A necessary and sufficient condition of liveness is stated and proved View full abstract»

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  • Discrete event modeling and optimization of unreliable production lines with random rates

    Page(s): 153 - 159
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    We consider a serial production system with unreliable machines maintained by a limited number of repairmen, and finite storage between machines. Processing times may be random variables with exponential or gamma distributions, or deterministic. We develop a continuous-flow model for such a system utilizing simulation and analysis. Random processing times are approximated by sums of deterministic variables using a simple probabilistic technique. The model observes a limited number of events which are sufficient to determine system performance and mean buffer levels. By appropriately reducing the rates of starved and blocked machines and using analysis to compute the times of next event at each machine and buffer, discrete part computations are avoided. It is demonstrated that this approximate model is highly accurate and faster by a factor of 3 or more when compared to conventional simulators. The paper addresses also optimal repair allocation to maximize the expected throughput of the system. Two different approaches are proposed: perturbation analysis and experimental evaluation of various nonpreemptive rules for assigning a repairman to failed machines View full abstract»

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  • Dispatching-driven deadlock avoidance controller synthesis for flexible manufacturing systems

    Page(s): 196 - 209
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    This paper develops a new method for synthesizing deadlock avoidance controllers (DACs) that realize job and machine dispatching policies of a flexible manufacturing system (FMS) into deadlock free control actions. Such controllers not only keep the FMS capable of repeating any of its operations, but also achieve a high resource utilization under any given dispatching policy. Our methodology is based on an untimed Petri net formalism. It consists of four ingredients: 1) a bottom-up approach for synthesizing a controlled production Petri net (CPPN) model of a FMS; 2) a necessary and sufficient liveness condition based on decomposition of the CPPN into controlled production subnets and the concept of minimal resource requirements; 3) a sufficient procedure to test whether the liveness condition is kept after a control action is executed; and 4) an algorithm that combines the test procedure with the given dispatching policy to generate valid and utilization maximizing control actions. We assess that this method is of polynomial time complexity and show that it results in a much larger class of controls than that of an existing deadlock avoidance scheme View full abstract»

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  • Scheduling flexible manufacturing systems using Petri nets and heuristic search

    Page(s): 123 - 132
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    Petri net modeling combined with heuristic search provides a new scheduling method for flexible manufacturing systems. The method formulates a scheduling problem with a Petri net model. Then, it generates and searches a partial reachability graph to find an optimal or near optimal feasible schedule in terms of the firing sequence of the transitions of the Petri net model. The method can handle features such as routing flexibility, shared resources, lot sizes and concurrency. By following the generated schedule, potential deadlocks in the Petri net model and the system can be avoided. Hence the analytical overhead to guarantee the liveness of the model and the system is eliminated. Some heuristic functions for efficient search are explored and the experimental results are presented View full abstract»

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  • Scheduling flexible flow shops with no setup effects

    Page(s): 112 - 122
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    This paper presents an efficient, optimization model-based approach for scheduling the production of discrete-part, make-to-order type of flexible flow shops, where setup effects are negligible. A nominal scheduling algorithm based on Lagrangian relaxation and minimum cost linear network flow is first developed for scheduling under nominal conditions. Fast rescheduling algorithms that exploit the economic interpretation of the Lagrange multipliers and the network structure of production flows are then proposed for timely adjusting the nominal schedule to cope with disturbances. Numerical results on realistic examples demonstrate that our methodology is quite effective; it generates near-optimal schedules, provides relatively smooth adjustment for small disturbances, and is computationally efficient View full abstract»

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Aims & Scope

This Transactions ceased production in 2004. The current retitled publications areIEEE Transactions on Automation Science and Engineering and IEEE Transactions on Robotics.

Full Aims & Scope