Showing papers on "Flow shop scheduling published in 1986"

A Tactical Planning Model for a Job Shop

Abstract: We propose and develop a discrete-time, continuous-flow model for studying the operation of a job shop that sees a stationary input mix of job types. We are not concerned with issues of detailed scheduling, but rather hope to develop a tactical planning tool for a job-shop operation. With the model, we are able to characterize the operational behavior of each work center in the job shop for a given control policy. The control rule sets the production rate at a work center as a fixed proportion of its queue level in each time period, and is consistent with the assignment of a planned lead time to each work center. For these control rules, the model gives the steady-state distribution of the production levels at each work center, as well as the distribution of queue lengths. We show how to use the model not only to evaluate a choice of the controls but also to find a good specification that results in acceptable shop behavior. An example for a factory that produces grinding machines illustrates the use of the model.

Job-shop scheduling using automated reasoning: a case study of the car-sequencing problem

Abstract: The ‘job-shop scheduling problem’ is known to be NP-complete. The version of interest in this paper concerns an assembly line designed to produce various cars, each of which requires a (possibly different) set of options. The combinatorics of the problem preclude seeking a maximal solution. Nevertheless, because of the underlying economic considerations, an approach that yields a ‘good’ sequence of cars, given the specific required options for each, would be most valuable. In this paper, we focus on an environment for seeking, studying, and evaluating approaches for yielding good sequences. The environment we discuss relies on the automated reasoning program ITP. Automated reasoning programs of this type offer a wide variety of ways to reason, strategies for controlling the reasoning, and auxiliary procedures that contribute to the effective study of problems of this kind. We view the study presented in this paper as a prototype of what can be accomplished with the assistance of an automated reasoning program.

A simulation comparison of group technology with traditional job shop manufacturing

Abstract: A simulation model of an actual job shop was used to compare group technology with traditional job shop manufacturing. The experiment compared shops which had four different layouts, designed to emphasize different features of traditional job shops and group technology shops, and four distributions of demand for end items. The group technology shops exhibited superior performance in terms of average move time and average set-up time. The traditional job shops had superior performance in queue related variables (average queue length, average waiting time, work-in-process inventory, etc.). This was caused by group technology's dedication of machines. The effects of the queue related variables outweighed the effects of average move time and average set-up time: the average flow time was shorter in the traditional job shop than in the group technology shops.

Performance of real-time bus scheduling algorithms

Abstract: When periodic tasks with hard deadlines communicate over a bus, the problem of hard real-time bus scheduling arises This paper addresses several problems of hard real-time bus scheduling, including the evaluation of scheduling algorithms and the issues of message packet pacing, preemption, priority granularity and buffering

A Mixed-Integer Goal-Programming Formulation of the Standard Flow-Shop Scheduling Problem

Abstract: Until recently, the majority of models used to find an optimal sequence for the standard flow-shop problem were based on a single objective, typically makespan. In many applications, the practitioner may also want to consider other criteria simultaneously, such as mean flow-time or throughput time. As makespan and flow-time are equivalent criteria for optimizing machine idle-time and job idle-time, respectively, these additional criteria could be inherently considered as well. The effect of job idle-time, measuring in-process inventory, could be of particular importance.

On Johnson's two-machine flow shop with random processing times

Abstract: A set of n jobs is to be processed by two machines in series that are separated by an infinite waiting room; each job requires a known fixed amount of processing from each machine. In a classic paper, Johnson gave a simple rule for ordering of the set of jobs to minimize the time until the system becomes empty, i.e., the makespan. This paper studies a stochastic generalization of this problem in which job processing times are independent random variables. Our main result is a sufficient condition on the processing time distributions that implies that the makespan becomes stochastically smaller when two adjacent jobs in a given job sequence are interchanged. We also give an extension of the main result to job shops.

Decision-aid in job shop scheduling: A knowledge based approach

Abstract: This paper deals with operation scheduling on machines in a job shop. The jobs which consist of a set of related operations are supposed to be constrained by limit times (earliest starting times and due dates). The approach aims at generating restrictions on local scheduling decisions by only considering limit times and resource availability constraints (constraint based analysis). This is achieved through an inference process which is defined from generic knowledge arising in scheduling problems : limit times associated with each operation, logical sequencing conditions between operations, inference rules relating to limit times and sequencing conditions. A software implementation in PROLOG of a constraint-based analysis module is presented. Such a module may be used either in a static way in order to generate a plan over a certain horizon or in a dynamic way in order to help in making real time decisions. In this last case it can be held to act the part of a flexible planning function.

Optimal due-date assignment in a job shop†

Abstract: SUMMARY This paper presents an analytical model for determining the optimal processing-time and number of operations multiples for the TWK and TWK + NOP due-date assignment methods in a dynamic job shop subject to restrictive assumptions on queue discipline and processing time distribution. The analytical results are compared with the experimental results obtained from simulation of a hypothetical job shop under various shop conditions. The close agreement of the results reveals the validity of the analytical model. In addition, the results show that the TWK + NOP method is more effective in minimizing the missed due-date cost in a job shop.

A SLAM II simulation study of a simplified flow shop

Abstract: Control of jobs being processed in a flow shop is important to management. Shop performance is affected by shop congestion, processing time variation, and the dispatching rule used to load the jobs. Most previous research has concentrated on the effects of varying these parameters in a job shop setting. A SLAM II net work model and simulation analysis of these parameter varia tions was applied in a two-work center flow shop. Performance of the flow shop was tested using combinations of 5 dispatching rules, 3 shop load levels, and 2 levels of processing time varia tion. Based on a series of performance measures, the shop using the shortest processing time dispatching rule in one work center and the due data based rule in the other compares favorably with the shop that used the shortest processing time rule in both work centers. Results indicate that shop congestion and process ing time variation affect the performance of the flow shop as well. Performances between the flow shop and job shop are com pared, ...

A LISP-based heuristic scheduler for automatic insertion in electronics assembly

Abstract: SUMMARY Computer solutions have not made a very significant impact on scheduling problems. This reflects the fact that algorithmic solutions are often not appropriate for scheduling problems. Scheduling problems are more amenable to heuristic solution techniques. This paper describes a heuristic system for job scheduling in printed circuit board assembly. The main part of the system is written in Common LISP.

A job scheduling model for a flexible manufacturing machine

Abstract: The problems addressed in this paper arise in industry when flexible, automated machines are used to manufacture parts (jobs). These machines include numerically controlled (N/C) tools, robots,...etc. The goal is to avoid unnecessary set-up operations in order to effectively utilize the michines. In this paper we focus on developing a job scheduling model that considers the tool requirement of each job in an explicit fashion.

One-machine scheduling problems with resource constraints

Abstract: One-machines scheduling problems with maximum lateness and maximum tardiness criteria are generalized on the case with allocation of continuously-divisible constrained nonrenewable resource. Models of operation are assumed to be duration versus resource amount linear functions. For the problems with maximum lateness and the maximum tardiness criteria under equal release dates (i.e. moments at which operations are available for processing) polynomial-time algorithms are found. It is shown that the problem with maximum lateness criterion under unequal release dates is NP-hard. For this problem a branch-and-bound algorithm (utilizing properties shown) is outlined.

Inequalities for stochastic flow shops and job shops

Abstract: Consider an m-machine flow shop with n jobs. The processing time of job j, j = 1,…, n, on each one of the m machines is equal to the random variable Xj and is distributed according to Fj. We show that, under certain conditions, more homogeneous distributions F1,…, Fn result in a smaller expected makespan. We also study the effect of the variability of distribution Fj on the expected waiting costs of the n jobs and on the job sequencing which minimizes this total expected waiting cost. We show that the smallest (largest) variance first rule minimizes the total expected waiting cost on a single machine when the waiting cost function is increasing convex (concave). We also show that the smallest variance first rule minimizes, under given conditions, the total expected waiting cost in an m machine flow shop when the waiting cost function is increasing convex. Similar results are also obtained for the two-machine job shop. Similar results cannot be obtained when the processing times of job j on the various machines are i.i.d. and distributed according to Fj.

Stochastic scheduling and set-ups in flexible manufacturing systems

Abstract: : This paper describes an approach for the incorporation of set-up times into a stochastic scheduling algorithm for a FMS. Set-up changes should not be performed too often because of the resulting reduction of capacity. They should not be performed too infrequently, because of the resulting increases of inventories and delays. The goal of the analysis reported here is to calculate the long-term average frequencies of set-ups and the fraction of time the system should be set up for each part type or family of part types. Keywords: Integer programming. (Author)

Scheduling and labour-assignment policies for a dual-constrained repair shop†

Abstract: SUMMARY Priority-scheduling rules and labour-assignment policies are presented for a repair shop which supports a multiple-item repairable-inventory system with a hierarchical product structure Results from earlier research are extended to machine- and labour-limited environments Several scheduling rules, combined with two labour-assignment policies and two levels of labour-transfer control, are evaluated using a simulation model The results indicate that the better priority scheduling rules in the machine-limited situation are also good in the dual-constrained situation In addition, the better labour-assignment policy is shown to be a function of how often workers are available for reassignment

Minimizing the expected weighted number of tardy jobs in stochastic flow shops

Abstract: This paper is devoted to two types of stochastic scheduling problems, one involving a single machine and the other involving a flow shop consisting of an arbitrary number of machines. In both problem types, all jobs to be processed have due dates, and the objective is to find a job sequence that minimizes the expected weighted number of tardy jobs. For the single-machine case, sufficient optimality conditions for job sequences are derived for various choices of due date and processing time distributions. For the case of a flow shop with an arbitrary number of machines and identically distributed due dates for all jobs, we prove the following intuitively appealing results: (i) when all jobs have the same processing time distributions, the expected weighted number of tardy jobs is minimized by sequencing the jobs in decreasing order of the weights, (ii) when all weights are equal, the jobs should be sequenced according to an increasing stochastic ordering of the processing time distributions.

The flow shop problem with time lags and separated setup times

Abstract: This paper generalizes Khurana-Bagga's flow-shop model which involves separated setup times and time lags where no restrictions are imposed on the processing and setup times as well as start and stop lags. It solves the two machine case and provides and approximate solution for the multimachine case. It also shows that Khurana-Bagga's algorithm is restricted to a special case of the two machine problem.

On Minimizing the Expected Makespan and Flow Time in Stochastic Flow Shops with Blocking

Abstract: Consider an m machine flow shop with no intermediate storage between any two successive machines and blocking. The processing time of job j, j = 1,..., n, on each one of the m machines is equal to the random variable Xj and is distributed according to Fj. We assume that the processing times are stochastically ordered in such a way that F1 ≤st... ≤stFn. We show that the sequence 1, 3, 5,..., n-1, n, n-2,..., 6, 4, 2 when n is even and the sequence 1, 3, 5,..., n-2, n, n-1,..., 6, 4, 2 when n is odd minimizes the expected makespan and that the sequence 1,..., n minimizes the expected flow time.

FMS scheduling: A crucial element in an expert system control structure

Abstract: In this paper a structure of the manufacturing expert system is presented. This system is to control three subsystems: process planning, programming of robots and machines and production planning. One of the basic elements of the production planning system is the production scheduling. A scheduling framework together with the heuristic scheduling algorithm are developed. The algorithm is illustrated on a numerical example.

Efficient Implementation of Johnson's Scheduling Algorithm

Abstract: An efficient implementation of Johnson's algorithm for n job two machine scheduling problem has been developed. Computational complexity of the proposed scheduling algorithm is O (nlogn).

An application of hierarchical planning and constraint-directed search to scheduling parallel processors

Abstract: This research investigated the applicability of Artificial Intelligence methods to the problem of scheduling and sequencing parallel processors subject to preference, sequencing, and buffer inventory constraints. Specifically, hierarchical planning and constraint-directed search were used to develop a prototype scheduling system for a case study problem. The prototype's planning structure included logic for dividing the scheduling period into sub-periods to allow parallel scheduling and handling of time-dependent constraints. The prototype system was tested using operational data from the case study and compared to schedules created by the human scheduler. The prototype system produced schedules very similar to the human scheduler, demonstrating the effectiveness of these methods in developing scheduling systems for parallel processors.

Scheduling of a manufacturing cell with simulation

Abstract: Overcoming the difficult problem of effectively scheduling batch production in individual machine cells may be paramount to the success of a group technology/machine cell application. Simulation of the cell can incorporate the constraints and characteristics of the system, without making restrictive assumptions, in order to evaluate system performance for any particular sequence of parts. The resulting output for decision criterion variables for several different sequences may be evaluated to yield an advantageous part sequence. This paper describes the development and successful use of a generalized simulation model for the shop floor scheduling of many similar cells.

Effectiveness of improved repair scheduling in the performance of bus transit maintenance (discussion and closure)

Abstract: Described in this paper is a computer simulation model that is used to investigate the efficiency improvements that are possible through the scheduling of bus maintenance repairs through a maintenance shop. The scheduling rules that are investigated rank repair jobs in priority order according to the length of time the bus has been waiting for repair and the length of time the job will take. It is found that scheduling, as opposed to not scheduling, can make dramatic improvements in the maintenance system's efficiency. Further, once scheduling policies are identified that result in superior performance, it is found that these same policies are superior under a variety of system conditions. The conditions varied include the number of spare buses carried, the fleet size, the failure distribution parameters, mechanic labor availability, and the maximum length of time a bus can wait for a repair.