The difference between NC and CNC is one of age andcapability.
The earliest NC machines performed limited functionsand movements controlled by punched tape or punch.
As the technology evolved, the machines were equiped with increasingly powerful microprocessors (computers) with the addition of these computers, NC machinesbecome CNC machines.
CNC machines have far more capability than theirpredecessor.
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Numerical control has caused a virtual revolution in the discrete metal parts manufacturing industry. The success of NC has led to number of extensions of Numeric Control concepts and technology. Four of the important developments are the following:
Direct numerical control (DNC).
Computer numerical control (CNC).
Adaptive Control.
Industrial robots.
Direct Numerical Control(DNC)
There are number of problems inherent in conventional machiningwhich are motivated machine tool builders to seek imprivements in the basic NC system. Among the difficulties encountered in using conventional numerical control machine are the following Part programming mistakes,Punched tape, Tape reader, Controller, Management information.
DNC defined
It can be defined as a manufacturing system in which a number of machines are controlled by a computer through direct connection and in real time. The tape reader is omitted in DNC thus releiving the system of its least reliable component. Instead of using tape reader the part program is tranmitted to the machine tool directly from the computer memory. In principle,one computer can be used to control more than 100 seperate machines. Figure below illustrates the general DNC configuration
The system consists of four components.
1. Central computer
2. Bulk memory which stores the NC part programs.
3. Telecommunication lines.
4. Machine Tools.
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