John T. Parsons
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John T. Parsons (Detroit, October 13, 1913) pioneered numerical control for machine tools in the 1940s.
This developments were done in collaboration with his employee Frank L. Stulen, who Parsons hired when he was head of the Rotary Wing Branch of the Propeller Lab at Wright-Patterson Air Force Base, in April 1946. Together, they were the first to use computer methods to solve machining problems, more in particular, the accurate interpolation of the curves describing helicopter blades. In 1946, "computer" still meant a punch-card operated calculation machine. In 1948, Parsons' company, "Parsons Corporation" of Traverse City, Michigan, was awarded a contract to make the innovative and challenging tapered wings for military aircraft; they won the contract because they developed the computer support to do the difficult three-dimensional interpolation for the complex shapes, as well as the 800 steps long production cycle for the wing manufacturing. IBM was one of the subcontractors, as was MIT, which took care of the servomechanisms. The latter lab boosted the developments of CNC machining in the following decades, by developing reliable servo control in 1952 and the APT (Automatic Programmed Tool) programming language for CNC machines. It was only after the servos were also steered by computers that real "numerical control" was realised. The initial developments of Parsons and Stulen were only about the calculations, and not the control: the results of the calculations were given to human operators that turned the wheels on the machine tool to generate the desired tool paths.
Parsons, however, quickly saw the potential of connecting computers to the machine motors. On January 14th, 1958, he received a patent for a Motor Controlled Apparatus for Positioning Machine Tool (patent number 2,820,187, filed on May 5th, 1952).
The initial developments of NC machines, however, had been so expensive, that Parsons was fired from his own company, because the funding of the MIT developments was too much for the company. Parsons was reinstated as president of the company, after royalties on the patent had generated significant amounts of money. (Bendix Corporation was an initial license taker of the patent, in 1955, and eventually bought all the rights to it.)
In 1985, Parsons and Stulen received the National Medal of Technology. In 1993, Parsons (but not Stulen) was inducted into the National Inventors Hall of Fame for inventing numerical control. In 1988 he received an honorary Doctor of Engineering degree from the University of Michigan.
