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.