A Comparative Analysis of Job Scheduling for Optimum Performance of Parallel Machines by Considering the Energy Consumption

In this study, a comparative analysis of scheduling of machines and jobs was conducted by proposing a method, which aims to optimize the performance of the job-shop environment. A wide range of objective functions including make-span, maximum tardiness, total flow time, total tardiness, total weighted flow time, and total weighted tardiness, and energy consumption. The decision variables of a manufacturing company including the job’s weight, stating and completion time, due dates, releasing date, and processing time were considered as inputs of the optimization model. Then, subject to the defined technical constraints of the system, a comparative analysis on the basis of eight scheduling methods was conducted to assess the performance indicators of the job-shop system. Results of the analysis revealed variations of different objective functions based on the proposed methods. The optimum make-span varied from minimum of 210 days estimated by the Earliest Due Date (EDD) method, up to 222 days estimated by the Critical Ratio (CR) method. Further recommendations were also made for optimum values of the involved decision variables in the considered job-shop environment. Results revealed that the maximum tardiness was best optimized using the EDD method, whilst the Shortest Processing Time (SPT) led to the best optimum value for the total flow time. Analysis of the energy evaluation of the machines showed that the optimum overall energy consumption has been observed with the value of 7,934 kWh for the first operating machine under the effect of the Minimum Slack method, whilst the optimum energy consumption for the second machine was observed with the value of 7,968 kWh using the First Come First Served (FCFS). Last stage of study recommended the optimum planning schedules and resource allocations of the jobs in the machines considering each scheduling method during the operation of the designed job-shop.

New Solution Methods for Single Machine Bicriteria Scheduling Problems: Minimizing the Total Flowtime and Maximum Tardiness with Zero Release Dates

This paper considers the bicriteria scheduling problem of minimizing the maximum tardiness and total flowtime on single machine with zero release dates. The problem is NP hard, though Early Due Date (EDD) and Shortest Processing Time (SPT) rules yielded optimal solutions for maximum tardiness and total flowtime, respectively if each criterion were to be considered singly. Thus, the values of each of the criteria for the two proposed heuristics; AA and SA were compared to the optimal solution of the sub problems. Results of computational experiment on job sizes varies from 5-150 jobs showed that the SA heuristic is preferred over AA. This is because the heuristic SA yielded maximum tardiness and total flowtime not significantly different from the EDD and SPT results, respectively at 99% significant level. Though AA yielded optimal for total flowtime, the maximum tardiness results is significantly different from the EDD results.