What are the stages in the Organization of NC Machine?

Organization of NC Machine

There are four significant stages in the Organization of NC machines.

(a) First Generation. The control system of  the first generation numerically control machines was built with vacuum tube and associated devices. The system was bulky, consumed lot of power and reliability was poor.

(b) Second Generation. Second Generation machines were built with transistors. The size of the control elements was reduced. However, all the functions had to be realized through electronic circuits. The number of printed circuits boards was large. Since there were thousands of components and connections involved, the reliability was again poor.

(c) Third Generation. Third generation NC machines were built with integrated circuits (IC). The IC's with medium scale integration improved the reliability of the system. Drive technology also made considerable progress. Thyristor (a type of transistor) controlled DC drive become popular during this period. Reliable and compact DC controllers were developed both for main drives and for the control of servomotors for axes feed drive. The various logic functions in the early NC systems (during 50's and 60's) were realized through fixed circuitry and hence were called hard wired systems. The integration of minicomputers with NC machines that led to the development of CNC machine tools was one of the two major significant development during mid 60's.Initially minicomputers were interfaced with NC machine tools. This development helped to introduce the much needed flexibility. From the totally hardwired design, the design of the NC machine tools became soft wired. Instead of reading and executing programs block by block it was possible to store the program in the computer memory and execute it. Several limitations of the NC systems could also be overcome by CNC systems. Program editing became much easier. The other development was the evolution the concept of Direct Numerical Control (DNC) technique by which several NC machine tools could be controlled from a single computer.

(d) Fourth Generation. Towards the end of 70's the computer design underwent changes and microprocessor came to be used as the CPU of computers. This change also affected the design of NC Machine tools. The designers started developing NC systems around microprocessors. This simplified the logic and control and design and instead of several PCB's in the case of NC machines, the entire control could be implemented with just one PCB for CNC machines. Initially 8 and 16 bit microprocessors were used. Later control systems with several processors (Multi- Processing Systems) were introduced. The reliability of the system was considerably improved. The developments in CNC systems still continue. Today many CNC systems are based on 32 bit microprocessors. A few personal computer based CNC systems are also available in the market.