عملکرد انعطاف پذیری: مطالعه روش تاگوچی سیستم های فیزیکی و کنترل عملیات پارامترهای FMS

In present manufacturing environment, the manufacturing flexibility has become one of the strategic competitive tools. Flexibility refers to the availability of alternative resources. These resources may have varied parameters, particularly related to physical and operating system. These physical and operating parameters of alternative resources may influence the system's performance with the changing levels of flexibility and operational control parameters such as scheduling rules. Is increase in a flexibility level provides desired improved performance output? If yes, than under what conditions of physical and operating parameters and under which control strategy (CS)? Is improved performance is present at all increasing levels of flexibility? Flexible manufacturing system (FMS) being consist of numerous physical and operating parameters and complex in nature, the solution to these questions can provide an understanding of the productive levels of flexibility for a given physical and operating parameters of an FMS. This paper establishes the need of modelling of the physical and operating parameters of flexible manufacturing system along with flexibility and presents a simulation study under Taguchi's method analysis of these parameters. The paper contributes an approach to study the impact of variations in physical and operating parameters of an FMS and to identify the level of these variations that do not restrict the advantages of flexibility. The results show that the expected benefits from increasing the levels of flexibility and a superior CS may not be achieved if the physical and operating parameters of alternative machines have variations. Taguchi's method analysis indicates that relative percentage contribution of variations in physical and operating parameters of alternative resources should be negligible or minimum in the performance of FMS. Their increasing relative contribution may restrict the advantages of flexibility. If these variations are higher than increase in flexibility level may be counter productive.

Evolving manufacturing environment offers new pressures to be confronted by the manufacturing systems, such as customised product (increasing variety) with delivery on time along with underline traditional requirements of quality and competitive cost. The manufacturing environment is changing and is quite different to the needs of the mass production period. The era of mass customization is emerging, leading to a need to manufacture a changing product and volume mix effectively. A manufacturing environment of increasing variety in products inspired by the vast capabilities of flexible manufacturing system (FMS) is evolving. In this environment the focus is on manufacturing flexibility rather than the system efficiencies. Rajput and Bennett [1] emphasise the need of greater flexibility, shorter cycle times and reduced inventory levels for present manufacturing environment. According to Wadhwa and Browne [2], flexibility offers opportunities to the control on flow of entities (material, resources and information, etc.) in a desirable direction among the available alternatives. However, first it is important to know whether this change in flow of entities provides expected benefits. The FMSs which are considered to be efficient with increasing variety of products and time-based delivery performance measure, the flexibility present in the system provides this capability to become most suitable in this manufacturing environment.

This paper presents an insight on the performance behaviour of an FMS with varying RF levels and control strategies when variations in physical and operating parameters are present on the alternative machines. Paper identifies the necessity of modelling physical and operating parameters of an FMS along with flexibility. The variations in physical and operating parameters of alternative machines may influence the performance of a given FMS. The results of simulation study show that expected benefits may not be present when RF levels are increased with presence of the variations in physical and operating parameters. The increase in RF level may even become counter productive under such environment when variations are above certain limits. It may be useful for decision maker to distinguish the level of flexibility upto which it can be gainfully increased under the presence of variations. At higher level of RF, the impacts of these variations are more significant as compare to lower level of flexibility. It may be judicious to operate with lower level of RF when the magnitudes of variations in physical and operating parameters are not known. The performance of control strategies are also influenced by the presence of variations in physical and operating parameters. At lower RF levels, the CS may help in improving the performance. However, the performance of control strategies change with level of RF and level of variations in physical and operating parameters. Decision maker should identify a suitable CS for a given level of flexibility and variations in these parameters.