Objectives
The most important objective of simulation in manufacturing is the understanding of the change to the whole system because of some local changes. It is easy to understand the difference made by changes in the local system but it is very difficult or impossible to assess the impact of this change in the overall system. Simulation gives us some measure of this impact. Measures which can be obtained by a simulation analysis are: * Parts produced per unit time * Time spent in system by parts * Time spent by parts in queue * Time spent during transportation from one place to another * In time deliveries made * Build up of the inventory * Inventory in process * Percent utilization of machines and workers.Methods
In the past, manufacturing simulation tools were classified as languages or simulators. Languages were very flexible tools, but rather complicated to use by managers and too time consuming. Simulators were more user friendly but they came with rather rigid templates that didn’t adapt well enough to the rapidly changing manufacturing techniques. Nowadays, there is software available that combines the flexibility and user friendliness of both, but still some authors have reported that the use of this simulation to design and optimize manufacturing processes is relatively low. One of the most used techniques by manufacturing system designers is the discrete event simulation. This type of simulation allows to assess the system’s performance by statistically and probabilistically reproducing the interactions of all its components during a determined period of time. In some cases, manufacturing systems modelling needs a continuous simulation approach. These are the cases where the states of the system change continuously, like, for example, in the movement of liquids in oil refineries or chemical plants. As continuous simulation cannot be modeled by digital computers, it is done by taking small discrete steps. This is a useful feature, since there are many cases where both, continuous and discrete simulation, have to be combined. This is called hybrid simulation, which is needed in many industries, for example, the food industry. A framework to evaluate different manufacturing simulation tools was developed by Benedettini & Tjahjono (2009) using the ISO 9241 definition of usability: “the extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency, and satisfaction in a specified context of use.” This framework considered effectiveness, efficiency and user satisfaction as the three main performance criterion as follow: The following is a list of popular simulation techniques: # Discrete event simulation (DES) # System dynamics (SD) # Agent-based modelling (ABM) # Intelligent simulation: based on an integration of simulation and artificial intelligence (AI) techniques # Petri net # Monte Carlo simulation (MCS) # Virtual simulation: allows the user to model the system in a 3D immersive environment # Hybrid techniques: combination of different simulation techniques.Applications
References
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