Saturday, February 26, 2011

PLC Simulation for Automated Manufacturing System

Industrial production lines are generally dynamic systems whose states change according to the occurrence of various events, thus exhibiting the characteristics of a discrete event system. If manufacturers remain competitive in a continuously changing marketplace, they have not to only continue to improve their products, but also strive to improve production systems continuously.

Thus, an efficient prototyping environment is crucial for production systems. A modern production line is a highly integrated system composed of automated workstations such as a hardware handling system and storage system, robots with tool- changing capabilities, and a computer control system that controls the operations of the entire system. The production line implementation requires much investment, and decisions at the design stage have to be made very carefully to ensure that a highly automated manufacturing system will successfully achieve the intended benefits.

It is necessary to create a much more detailed simulation model that can forecast not only the production capability of the system but also the physical validity and efficiency of co-working machines and control programs for a detailed design (virtual prototyping) of a production line. Various machines that operate in an industrial manufacturing system simultaneously are usually controlled by PLCs (Programmable Logic Controllers) emulates, currently the most suitable and widely employed industrial control technology. A PLC behavior is an electric ladder diagram. To emulate the workings of parallel circuits that respond instantaneously, PLCs use an input/output image table and a scanning cycle as they are sequential machines. When a program is being run in a PLC it is executing continuously a scanning cycle. The program scan solves the Boolean logic related to the information in the input table with that in output and internal relay tables. The information in the output and internal relay tables is updated during the program scan. This Boolean logic is typically represented using a graphical language known as a ladder diagram in a PLC.

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