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Open-Loop & Closed-Loop Control

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What are Closed-Loop and Open-Loop Control?

This is a pretty easy explanation. In open-loop control, when the die cast machine runs, a variety of sensors monitor information about the shot. A human operator looks at this information after the shot is complete, and makes any adjustments required. Then another shot is done. This method has 2 main drawbacks: it demands a human operator with skill and judgement, and it can't help the current shot in any way - whatever information is picked up, there's nothing to be done about it until the next time the machine is run.

In closed-loop control, instead of having the sensors' information shown to a human operator, that information is fed back into the system (closing the loop, hence the name). A control system then acts on the data it is getting, making adjustments at that instant. With closed-loop systems, you don't need a human to make decisions at the end of each shot, and you don't have to wait until the next shot to improve things - if a shot starts to go poorly, that information is handled as it comes in, and corrections are made instantly. Another benefit is that there are many tiny variations that occur during any shot, too small and short-lived to be adjusted with the regular machine controls, but that can strongly affect the quality of the casting. With closed-loop control, the control systems can fine-tune shot variables many times a second, permitting very precise control and ensuring superior quality.

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