Showing papers on "Job shop scheduling published in 1989"

Force-directed scheduling for the behavioral synthesis of ASICs

Abstract: A general scheduling methodology is presented that can be integrated into specialized or general-purpose high-level synthesis systems. An initial version of the force-directed scheduling algorithm at the heart of this methodology was originally presented by the authors in 1987. The latest implementation of the logarithm introduced here reduces the number of functional units, storage units, and buses required by balancing the concurrency of operations assigned to them. The algorithm supports a comprehensive set of constraint types and scheduling modes. These include multicycle and chained operations; mutually exclusive operations; scheduling under fixed global timing constraints with minimization of functional unit costs, minimization of register costs, and minimization of global interconnect requirements; scheduling with local time constraints (on operation pairs); scheduling under fixed hardware resource constraints; functional pipelining; and structural pipeline (use of pipeline functional units). Examples from current literature, one of which was chosen as a benchmark for the 1988 High-Level Synthesis Workshop, are used to illustrate the effectiveness of the approach. >

An algorithm for solving the job-shop problem

Abstract: In this paper, we propose a branch and bound method for solving the job-shop problem. It is based on one-machine scheduling problems and is made more efficient by several propositions which limit the search tree by using immediate selections. It solved for the first time the famous 10 × 10 job-shop problem proposed by Muth and Thompson in 1963.

A Survey of Priority Rule-Based Scheduling

Abstract: In this paper, we survey the literature on heuristic priority rule-based job shop scheduling. Priority rules have been intensively investigated over the last 30 years by means of simulation experiments. They are also used in Shop Floor Control software systems. We present a classification, a characterization, and an evaluation of elementary priority rules. Some priority rule-related model extensions are discussed.

Some Results of the Earliest Deadline Scheduling Algorithm

Abstract: Abmw&-Task scheduling is an important issue in the design of a renl-timc computer system because tasks have execution deadlines that must be met, otherwise the system fails with severe consequences upon the environment. In this paper, we study the problem of scheduling periodic time critical tasks on a monoprocessor system. A periodic time critkal task consists of an infinite number of -quests, each of whieh has a prescribed deadline. Tasks are assumed to meet their timing requirements when scheduled by the Earliest Deadline algorithm and preemptions are allowed. We report results from some investigations into the problem of making optimum use of the remaining processor idle time in scheduling perlodk tasks either as soon as possible M as late as possible. The major results consist of the statement and proof of properties relating to bcdhtion and duration of idle time intervals and enable us to provide an elRcient algorlthm lor determining maximum quantity of total idle time available between any two instants. We describe how these results can be applied, Brst to the decision problem that arises when a sporadic time critical task occurs and requires to be run at an unpredictable time and second, to the scheduling problem that arises in a fault tolerant system using the deadline mechanism for which each task implements primary and alternate algorithms. Index Terms-Deadline mechanism, idle time, preemptive schedul

Implementation of a Lagrangian relaxation based unit commitment problem

Abstract: The unit commitment problem in a power system involves determining a start-up and shut-down schedule of units to be used to meet the forecasted demand, over a future short term (24-168 hour) period. In solving the unit commitment problem, generally two basic decisions are involved. The "unit commitment" decision involves determining which generating units are to be running during each hour of the planning horizon, considering system capacity requirements including reserve, and the constraints on the start up and shut down of units. The related "economic dispatch" decision involves the allocation of system demand and spinning reserve capacity among the operating units during each specific hour of operation. As these two decisions are interrelated, the unit commitment problem generally embraces both these decisions, and the objective is to obtain an overall least cost solution for operating the power system over the scheduling horizon. The unit commitment problem belongs to the class of complex combinatorial optimization problems. During the past decade a new approach named "Lagrangian Relaxation" has been evolving for generating efficient solutions for this class of problems. It derives its name from the well-known mathematical technique of using Lagrange multipliers for solving constrained optimization problems, but is really a decomposition technique for the solution of large scale mathematical programming problems. The Lagrangian relaxation methodology generates easy subproblems for deciding commitment and generation schedules for single units over the planning horizon, independent of the commitment of other units.

Job scheduling system

Abstract: An improved job scheduling system provides for scheduling of a variety of jobs without special purpose coding by the use of time maps to maintain current data, including the preferred path through the shop, as well as scheduling jobs around bottleneck shop resources in a dynamic manner.

Preemptive scheduling under time and resource constraints

Abstract: We consider the problem of scheduling a set of n preemptable tasks in a system having r resources. Each task has an arbitrary, but known, worst case processing time and a deadline, and may request simultaneous use of a number of resources. A resource can be used either in shared mode or exclusive mode. In this paper, we develop and evaluate algorithms for determining whether or not a set of preemptive tasks is schedulable in such a real-time system, and if so, determining a schedule for it. This scheduling problem is known to be computationally intensive. In many real-time application environments, tasks are scheduled dynamically, and hence the scheduling algorithms used must have low run-time costs. To keep run-time costs low, we propose the use of suboptimal but practical algorithms that employ computationally simple heuristics. The computational complexity of our algorithms for scheduling n tasks in a system having r resources is O(rn2), which is very much lower than that of known optimal algorithms. We report on the results of simulation studies performed on such heuristic preemptive scheduling algorithms and the sensitivity of the performance of the algorithms with respect to various scheduling parameters. These studies show that due to the complexity of the problem, straightforward heuristics do not perform satisfactorily. However, an algorithm that uses combinations of such heuristics in conjunction with limited backtracks works very well.

The pinwheel: a real-time scheduling problem

Abstract: Some satellites transmit a piece of information for a set duration, then proceed with another piece of information. A ground station receiving from several such satellites and wishing to avoid data loss faces a real-time scheduling problem. The pinwheel is a formalization of this problem. Given a multiset A of integers=(a/sub 1/, a/sub 2/, . . ., a/sub n/), a successful schedule S is an infinite sequence over (1, 2, . . ., n) such that any subsequence of a/sub i/ (1 >

Schedule generation and reconfiguration for parallel machines

Abstract: A methodology for scheduling independent jobs with due dates on identical, parallel machines is presented. The jobs have different levels of importance and various processing times on the machines, and the objective is to minimize the total weighted job tardiness of the schedule. Since the problem is NP hard, the goal is not to obtain the optimal schedule. Rather, an efficient near-optimal algorithm based on Lagrangian relaxation is presented. This approach provides a lower bound on the cost, which can be used as a measure of suboptimality. According to an implementation for a work center at Pratt and Whitney, most schedules generated are within 1% of the optima with reasonable CPU times. Furthermore, the method provides valuable job interaction information, which shop floor management uses to answer 'what if' questions, to reconfigure the schedule to accommodate dynamic changes, and to schedule new jobs. >

A fault-tolerant scheduling problem

Abstract: A real-time system must be reliable if a failure to meet its timing specifications might endanger human life, damage equipment, or waste expensive resources. A deadline mechanism has been previously proposed to provide fault tolerance in real-time software systems. The mechanism trades the accuracy of the results of a service for timing precision. Two independent algorithms are provided for each service subject to a deadline. The primary algorithm produces a good quality service, although its real-time reliability may not be assured. The alternate algorithm is reliable and produces an acceptable response. An algorithm to generate an optimal schedule for the deadline mechanism is introduced, and a simple and efficient implementation is discussed. The schedule ensures the timely completion of the alternate algorithm despite a failure to complete the primary algorithm within real time.

Scheduling and Binding Algorithms for High-Level Synthesis

Abstract: New algorithms for high-level synthesis are presented. The first performs scheduling under hardware resource constraints and improves on commonly used list scheduling techniques by making use of a global priority function. A new design-space exploration technique, which combines this algorithm with an existing one based on time constraints, is also presented. A second algorithm is used for register and bus allocation to satisfy two criteria: the minimization of interconnect costs as well as the final register (bus) cost. A clique partitioning approach is used where the clique graph is pruned using interconnect affinities between register (bus) pairs. Examples from current literature were chosen to illustrate the algorithms and to compare them with four existing systems.

A branch and bound algorithm for the multiple depot vehicle scheduling problem

Abstract: This article describes analyses carried out to solve the scheduling problem for freight vehicles assigned to various different depots. The vehicle scheduling problem concerns the assigning of a set of time-tabled trips to vehicles so as to minimize a given cost function. We consider the np-hard multiple depot case in which, in addition, one has to assign vehicles to depots. Different lower bounds based on assignment relaxation and on connectivity constraints are presented and combined in an effective bounding procedure. A strong dominance procedure derived from new dominance criteria is also described. A branch and bound algorithm is finally proposed. Computational results are given.

Scheduling networks of queues: heavy traffic analysis of a simple open network

Abstract: We consider a queueing network with two single-server stations and two types of customers. Customers of type A require service only at station 1 and customers of type B require service first at station 1 and then at station 2. Each server has a different general service time distribution, and each customer type has a different general interarrival time distribution. The problem is to find a dynamic sequencing policy at station 1 that minimizes the long-run average expected number of customers in the system. The scheduling problem is approximated by a dynamic control problem involving Brownian motion. A reformulation of this control problem is solved, and the solution is interpreted in terms of the queueing system in order to obtain an effective sequencing policy. Also, a pathwise lower bound (for any sequencing policy) is obtained for the total number of customers in the network. We show via simulation that the relative difference between the performance of the proposed policy and the pathwise lower bound becomes small as the load on the network is increased toward the heavy traffic limit.

Scheduling strategies for multiprocessor real-time DSP

Abstract: The authors explore the possibilities for automatic schedulers that result in low implementation cost and can target a broad class of DSP (digital signal processing) applications. They define four classes of scheduling strategies: (1) fully dynamic; (2) static assignment; (3) self-timed; and (4) fully static. Moving from (1) to (4), more scheduling activity is performed at compile time and less at run time. The authors argue that for most DSP applications, self-timed scheduling is the most attractive strategy. In this strategy, the assignment of actors to processors and the ordering of the firing of actors are determined by a compiler. Only the timing of the firing is determined at run time. The run-time cost of this determination is minimal. Furthermore, automatic scheduling techniques that fit this model are growing in generality and efficiency. >

Dynamic instabilities and stabilization methods in distributed real-time scheduling of manufacturing systems

Abstract: Manufacturing systems consisting of many machines and producing many types of parts are considered. Each part type requires processing for a specified length of time at each machine in a prescribed sequence of machines. Machines may require a setup time when changing between part types, and parts may incur a variable transportation delay when moving between machines. The goal is to schedule all the machines dynamically so that all the part types are produced at the desired rates while maintaining bounded buffer sizes at all machines. A previously open problem is resolved by exhibiting the instability of all clearing policies for some nonacyclic manufacturing systems. Surprisingly, such instabilities can occur even when all setup times are identically zero, and they are induced purely by starvation of machines. Sufficient conditions on the system topology and processing and demand rates which ensure the stability of distributed clear-a-fraction policies are shown. A general distributed supervisory mechanism which will stabilize any policy is studied. >

A new integer linear programming formulation for the scheduling problem in data path synthesis

Abstract: A novel approach is presented to the operation scheduling problem in a data path synthesis. After obtaining the start time and the require time of each operation by the ASAP (as soon as possible) and ALAP (as late as possible) methods, respectively, an integer linear programming (ILP) formulation is formed to solve the scheduling problem. The objective is to fully utilize the hardware resources, i.e. to minimize the requirement of function units under a given timing constraint. The formulation can be generalized to support multicycle operations, multiple operations per cycle, pipelined data paths, mutually exclusive operations, and variables' lifetime consideration in a data path. A fifth-order filter containing 26 addition and 8 multiplication operations can be scheduled optimally for the cases from 17 cycles to 21 cycles per minute on a VAX-11/8800. >

Time-critical database scheduling: a framework for integrating real-time scheduling and concurrency control

Abstract: A framework is presented for analysis of time-critical scheduling algorithms. The main assumptions are analyzed behind real-time scheduling and concurrency control algorithms, and a unified approach is proposed. Two main classes of schedulers are identified according to the availability of information about resource requirements and execution times: conflict-resolving schedulers resolve conflicts at run-time, and hence can only produce a sequence of operations satisfying task priorities and resource constraints; and conflict-avoiding schedulers determine resource requirements and expected execution times through offline transaction-class preanalysis and produce a complete time-critical schedule satisfying both timing and resource constraints. For the latter case, the resolution of overload is essential. Examples are given to illustrate the framework and the main classes of scheduling algorithms. >

Alternative Formulations of a Flow-shop Scheduling Problem

Abstract: This paper presents an alternative approach to an earlier model developed by other authors to formulate a problem of sequencing N jobs on M machines in a standard flow-shop. The objectives of the model are to minimize makespan and flow-time. The new formulation involves substantially fewer variables, at the expense of a rise in the number of constraints. Practical limitations of both approaches are discussed.

An efficient decision support systems for academic course scheduling

Abstract: This paper describes a network-based decision support system approach to the most general form of the academic course scheduling problem. The dimensions of faculty, subject, time, and room are considered by incorporating a penalty function into a network optimization approach. The approach, based on a network algorithm, is capable of solving very large problems. This methodology can be applied to other scheduling situations where there are competing objectives and multiple resources. Such situations include: scheduling of exams, times, and rooms in an academic setting, and scheduling of clients, times, and facilities for physicians, hospitals, dentists, counselors, and clinics. Common problems in such settings include the utilization of available space, and dissatisfaction with assigned times and locations. The proposed system results in more effective room utilization patterns, improved instructor satisfaction levels, and streamlines the tedious scheduling process. We describe the use of the model to sch...

A review of scheduling rules in flexible manufacturing systems

Abstract: In this paper, the literature dealing with the parts scheduling problem in flexible manufacturing systems (FMS) has been reviewed. Although the parts scheduling problem is only part of much larger decision-making process, it has fundamental implications on the overall performance of the system: internally by affecting the utilization of expensive resources (e.g. machine tools and fixtures), and externally by affecting its responsiveness to meet the changing customer demands. This paper has two objectives: (1) to develop a framework within which to discuss the current literature on dispatching rules; and (-2) to compare the developed list of dispatching rules and performance criteria from the surveyed literature with that desired by the FMS operators. The research findings are critically reviewed and. analysed according to various two-dimensional classifications. The results from real-life case studies of FMSs are also discussed. Finally, the results are summarized to present suggestions for futur...

The effects of product structure and sequencing rule on assembly shop performance

Abstract: SUMMARY Single-stage job-shop scheduling has received a great deal of attention in the published literature. Significantly less research has been done in the area of assembly job shops. With the onslaught of MRP implementations designed to plan and control assembly job shops, practitioners have been confronted head-on with the need to improve dispatching procedures. This paper examines the effect of three different product structures on the performance of selected priority dispatching rules in a six-machine assembly job shop. Results indicate that significant relationships exist between the structure of the product bill of materials and the priority dispatching rule, and that specific rules are indeed better suited to certain product structures.

Single-machine scheduling to minimize absolute deviation of completion times from a common due date

Abstract: The article considers a single-machine n-job scheduling problem to minimize the sum of absolute lateness given a common due date. Two models are defined depending on whether the start time t0 of schedules is arbitrary or fixed. Conditions are provided when those two models coincide. The developed branch-and-bound procedure is tested on nine known examples from the literature (6 ⩽ n ⩽ 14) and 90 medium-size random problems (15 ⩽ n ⩽ 25) with a fixed t0.

Applying Stochastic Algorithms to a Locomotive Scheduling Problem

Abstract: This paper addresses a problem common to all railway networks Given a fixed train timetable and locomotives (or other forms of traction) of various types, each train must be allocated a locomotive This paper examines the use of stochastic algorithms for such a problem Two types of algorithm are used—a simple ‘local improvement’ method, performed successively from randomly chosen starting points, and a ‘simulated annealing’ approach Both are found to give considerably better results than a deterministic method in current use, and the annealing approach is probably the better stochastic method

Production planning of a flexible manufacturing system in a material requirements planning environment

Abstract: Early flexible manufacturing system (FMS) production planning models exhibited a variety of planning objectives; typically, these objectives were independent of the overall production environment. More recently, some researchers have proposed hierarchical production planning and scheduling models for FMS. In this article, we examine production planning of FMS in a material requirements planning (MRP) environment. We propose a hierarchical structure that integrates FMS production planning into a closed-loop MRP system. This structure gives rise to the FMS/MRP rough-cut capacity planning (FMRCP) problem, the FMS/MRP grouping and loading (FMGL) problem, and the FMS/MRP detailed scheduling problem. We examine the FMRCP and FMGL problems in detail and present mathematical programming models for each of these problems. In particular, the FMRCP problem is modeled as a generalized assignment problem (GAP), and a GAP-based heuristic procedure is defined for the problem. We define a two-phase heuristic for the FMGL problem and present computational experience with both heuristics. The FMRCP heuristic is shown to solve problems that exhibit a dependent-demand relation within the FMS and with FMS capacity utilization as high as 99 percent. The FMGL heuristic requires very little CPU time and obtains solutions to the test problems that are on average within 1.5 percent of a theoretical lower bound. This FMS/MRP production planning framework, together with the resulting models, constitutes an important step in the integration of FMS technology with MRP production planning. The hierarchical planning mechanism directly provides for system-level MRP planning priorities to induce appropriate production planning and control objectives on the FMS while simultaneously allowing for necessary feedback from the FMS. Moreover, by demonstrating the tractability of the FMRCP and FMGL problems, this research establishes the necessary groundwork upon which to explore systemwide issues pertaining to the coordination of the hierarchical structure.

Simultaneous Resource Scheduling to Minimize Weighted Flow Times

Abstract: Many scheduling problems in manufacturing and service firms involve tasks that require more than one resource to be used simultaneously to execute the task. Two formulations of this scheduling problem are given. We develop a Lagrangian relaxation for the problem that has an intuitive interpretation. The relaxation suggests heuristics and provides a lower bound on the optimal solution. Next a surrogate relaxation is developed that provides a second bound and a heuristic solution. An enumeration procedure to determine the optimal solution is described, and computational results on the effectiveness of the bounds and the heuristics are presented. The Lagrangian relaxation performs better on problems with a low degree of simultaneity, and the surrogate relaxation does better with a high degree of simultaneity.