Control Systems
CNC (Computer Numerical Control) is a versatile and specialized form of Soft Automation and its applications cover many kinds, although it was initially developed to control the motion and operation of machine tools.
The CNC control system is divided into two, they are:
Open loop systems do not have access to the real time data about the performance of the system and therefore no immediate corrective action can be taken in case of system disturbance. This system is only applied normally to the case where the output is almost constant and predictable. Therefore, an open loop system is unlikely to be used to control machine tools since the cutting force and loading of a machine tool is never a constant. The only exception is the wire cut machine for which some machine tool builders still prefer to use an open loop system because there is virtually no cutting force in wire cut machining.
Feed back devices closely monitor the output and any disturbance will be corrected in the first instance in a close loop system. Therefore high system accuracy is achievable. This close loop system is more powerful than the open loop system and can be applied to the case where the output is subjected to frequent change. Nowadays, almost all CNC machines use this control system.
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