تجزیه و تحلیل از قوانین اعزام پویا برای یک سیستم تولید انعطاف پذیر

This paper presents a simulation model of a flexible manufacturing system (FMS) which subjects to minimization three performance criteria simultaneously such as mean flow time, mean tardiness, and mean earliness. The dispatching rule will be changed at a frequency that is varied by the number of outputs produced by the system. Therefore, the dynamic nature is event-triggered rather than changing the rule at a regular time interval, which is passive. Three indexes are calculated to represent the three criteria under monitoring and the indexes are ranked in descending order: the greater the index, the worse is the situation of the criterion in the system. Thus, an appropriate rule will be selected for the next operation in order to tackle that criterion with the largest index. This mechanism is so called pre-emptive method. Furthermore, the indexes can be biased so that particular criterion can have a greater weighting as set by the decision-maker. Results show that a solution (range of frequency) can always be determined to change the dispatching rule so that the system is better than just using fixed FMS scheduling rule.

Flexible manufacturing systems (FMSs) have received increasing attention in recent decades. The development in robot design over the past 20 years has enabled automation in more complicated electromechanical assembly. In addition, with the aids of new microprocessor technologies, the concept of flexibility in manufacturing has become a key consideration in the design, operation, and management of manufacturing systems. An FMS is able to assemble a variety of product types in small-to-medium sized batches at the same time and at high rate comparable to that of traditional assembly lines designed for high volume/low variety manufacture. An FMS might be simply defined as follows: “A manufacturing system is flexible if it is able to process a number of different tasks automatically and in any order”. In fact, an FMS is a computer directed collection of CNC machines linked by an automated material handling system. The automated material handling system usually refers to automated guided vehicles (AGVs), which use embedded floor wires to direct driverless vehicles to various locations in the plant, and delivering materials [1]. Since FMSs are designed to combine the efficiency of a mass production line and the flexibility of a job shop to best suit the batch production of a mid-volume and mid-variety of products, it requires more management to function efficiently and effectively [2].

This research successfully developed an algorithm, using pre-emptive approach, for real-time dynamic scheduling of an FMS. It has been proven that the system’s performance when using dynamic scheduling could be improved by changing the corresponding dispatching rule at a correct frequency as discussed in Section 4. In addition, the algorithm is found to be useful even the performance criteria used for comparison are made to be biased on purpose. This conclusive remark indicates that the decision-maker can vary the weighting factor to each performance criterion according to his/her preference. Further research is recommended to ensure that this proposed algorithm is robust and ready for implementation in industrial application. Some of the major issues are described as follows: 1. In this paper, only the machine dispatching rule is varied. Other important operation rules, such as AGV dispatching, the machine selection rule, etc., are not considered. It is expected that the system’s performance will become better if more operation rules can be considered. 2. The “check-point” is triggered by a defined number of outputs produced by the system. In addition to this event, other triggering methods can be used to test the algorithm, such as machine break down, or rush jobs entering the system.