Numerical Control:
It is defined as a method of automation in which various functions of machine tools are controlled by letters, numbers and symbol.
Computer Numerical Control:
It is an NC system, that utilizes a dedicated, stored program computer to perform some or all of the basic numerical control functions.
Direct Numerical Control:
It is defined as a manufacturing system in which a number of machines are controlled by a computer (central mainframe computer) through direct connections and in real time.
Developments and improvements in NC, CNC and DNC applications:
- In NC, numbers from a program of instructions designed for a particular work part or job. When the job changes, the program of instructions is changed. This capability to change the program for each new job is what gives NC its flexibility.
- The program of instructions is the detailed step-by-step set of directions which tell the machine: tool what to do. The most common input medium is 1-inch wide punched tape. Out of two methods, the first method of input to the NC system is called manual data input, and is appropriate only for relatively simple jobs. The second method of input is by means of a direct link with a computer. In computer assisted part programming much of the tedious computational work required in manual part programming is transferred to the computer. This is appropriate for complex workpiece geometries and jobs with many machining steps. The use of computers provided significant improvements in part programming procedures. The control of NC machinery has also been dramatically enhanced through computer technology.
- Computer numerical control (CNC) uses the part program tape and tape reader only once to enter the program into computer memory. This results in improved reliability since the tape reader is commonly considered the least reliable component of a conventional NC. The NC tape can be corrected and even optimized. One of the most significant advantages of CNC over conventional NC is its flexibility, which provides the opportunity to introduce new control options with relative ease at low cost.
- In DNC, the punched tapes and tape readers are eliminated. In some DNC systems, the hard wired control unit is also eliminated and replaced by a special machine control unit designed to be more compatible with DNC operation. Because the computational and data processing function are implemented with software rather than with hard wired devices, there exists the flexibility to alter and improve the method by which these functions are carried out. Examples of there functions include circular interpolation and part programming packages with convenient editing and diagnostic features. The combination of CNC and DNC provides the opportunity to add new capability and refine existing capabilities in the computerised manufacturing systems.