A state dependent heuristic method of job shop scheduling

• Main Author: El-Kilani, Mohamad Abdullah
• Published: University of Edinburgh 1992
• Subjects: 670
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.649943

The main object of this work is to develop a 'Fair Delivery and Shop State Dependent Scheduling dispatching rule' (FDSSD) in a job shop environment. The fairness principle could be defined by saying that the customers who came first be given a higher priority than those who came afterwards. The basic principle behind the FDSSD rule is fairness towards customers. This is to some extent taken into account by the First Received First Served and Earliest Due Date scheduling rules. The FDSSD rule, however, takes into account both the order in which orders have been received and related delivery dates. Techniques which do not consider both of these criteria can produce unnecessary anomalies. These anomalies can often be overcome by human judgement in a relatively simple situation where results produced by logical scheduling may be immediately seen as unfair. The FDSSD rule introduces this moral element into logical scheduling. Because of this, many more anomalies which could adversely affect customers can be thrown out. The unecessary unfairness within the schedule may not be apparent to management until too much work has been done to change things. Owing to the moral principles introduced within the FDSSD rule, a direct comparison (one to one) with other scheduling rules does not exhibit the complete performance of the FDSSD rule. However, some comparisons based on tardiness criteria are made. Towards this end, a computer simulation model has been developed. The computer model is named herein as 'Job Shop Scheduling Simulation Model' (JSSM). The model has been used in improving the procedure of In-Process scheduling of the FDSSD rule. In contrast to the currently available scheduling rules which tend to be used, the FDSSD rule achieves a balance between the three main objectives of a production system. The objectives are: (i) to meet delivery dates,: (ii) to decrease Work-In-Process (WIP), and (iii) to increase machine utilisation. This balance compromises the Fairness Principle. The FDSSD rule uses First Received First Served rule (FRFS), delivery date consideration and state in the shop. The FDSSD rule offers a very close result if not better than some other known rules such as FRFS, FCFS and EDD rules.