Module E (1) : Computer Numeric Control of Machine Tools
An Overview Of CNC Machines


( 1 ) Historical Perspective

The word NC which stands for numerical control refer to control of a machine or a process using symbolic codes consisting of characters and numerals. The word CNC came into existence in seventies when microprocessors and microcomputers replaced integrated circuit IC based controls used for NC machines. The development of numerical control owes much to the United States air force. The concept of NC was proposed in the late 1940s by John Parsons who recommended a method of automatic machine control that would guide a milling cutter to produce a curvilinear motion in order to generate smooth profiles on the work-pieces. In 1949, the U.S Air Force awarded Parsons a contract to develop new type of machine tool that would be able to speed up production methods.
Parsons sub-contracted the Massachusetts Institute of Technology (MIT) to develop a practical implementation of his concept. Scientists and engineers at M.I.T built a control system for a two axis milling machine that used a perforated paper tape as the input media. This prototype was produced by retrofitting a conventional tracer mill with numerical control servomechanisms for the three axes of the machine. By 1955, these machines were available to industries with some small modifications.
The machine tool builders gradually began developing their own projects to introduce commercial NC units. Also, certain industry users, especially airframe builders, worked to devise numerical control machines to satisfy their own particular production needs. The Air force continued its encouragement of NC development by sponsoring additional research at MIT to design a part programming language that could be used in controlling N.C. machines.
In a short period of time, all the major machine tool manufacturers were producing some machines with NC, but it was not until late 1970s that computer-based NC became widely used. NC matured as an automation technology when electronics industry developed new products. At first, miniature electronic tubes were developed, but the controls were big, bulky, and not very reliable. Then solid-state circuitry and eventually modular or integrated circuits were developed. The control unit became smaller, more reliable, and less expensive.
Prof.Madhusudan Rao