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'''Numerical control''' or '''numerically controlled''' ('''NC''') [[machine tool]]s are machines that are automatically operated based on commands that are fed into them. NC machines were first developed soon after [[World War II]] and made it possible for
[[de:Numerische Steuerung]]
[[ja:NC加工]]
Numerical control (NC) is the precursor of computer numerical control (CNC)
CNC inherits from NC its essential character of by-the-numbers interpolation of transition points in the work envelope of a motion platform based on the separation of programming from operations. The program
==Historical notes==
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In the M.I.T. scheme, a contour of constantly changing curvature (that is, a spline) is represented as a poly-line with the intersections between line segments being points on the curve and these points were listed in sequential order in the part program (like a child connecting the dots of a workbook to display a figure). The shorter the line segments the more closely the poly-line approximated the original curve. Thus, M.I.T. retained separation of programming from operations while redefining the servo control as interpolation rather than discrete positioning. M.I.T. demonstrated the first ever NC machine tool to a select group from the military, the aerospace industry, the machine tool industry and the technical media in September, 1952.
At the time when M.I.T. was developing numerical control, engineers at General Motors were putting position transducers on the lead screws of a conventional engine [[lathe]] and recording the motion of the axes as the machinist put the machine through its paces to make a workpiece. The machine was also fitted with a servo system that took data from the recording to reproduce the same sequence of motion to produce a second, third and more parts. This technique is called record/playback and it is reminicent of a musician making music on a piano that has been modified to record his keystrokes on a paper chart to be read by a player piano to reproduce the music. The popular novel, "The Player Piano", is inspired by this machine. The author [[Kurt Vonnegut]] was exposed to the machine when he worked as a publicist for General Electric. Record/playback is different from numerical control in that the program is produced by the machinist in the process of making the first part.
The Air Force wanted numerical control and not record feedback because the latter put the machinist in charge of program production. This was the same machinist who was a union member; thus union strikes could result in delays in military production. Also, numerical control demonstrated the ability to produce parts that were not possible by conventional, manual means. The Air Force used its deep pockets to get its way and while American manufacturing may have been better served with the simpler Parson concept or with record/playback, today this is a mute issue.
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