Computer numerical control: Difference between revisions

Revision as of 01:04, 20 May 2005

Revision as of 01:18, 20 May 2005

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In the M.I.T. scheme, a contour of constantly changing curvature was represented as a poly-line with the intersections between line segments being points on the curve, and the axial coordinates of these points were listed for execution in sequential order in the part program (much like the figure which results from connecting-the-dots in an activity book). The shorter the line segments the more accurately the poly-line would approximate the actual curve. Thus, M.I.T. retained separation of programming from operations while redefining the servo control as interpolative, rather than discretionary, 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 reminiscent of a musician playing on a piano that has been modified to record his keystrokes on a paper chart which can be read by a player piano to reproduce the music. The popular novel, "The Player Piano", was 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 than numerical control in that the program is produced by the machinist in the process of making the first part.

Record/playback is different than 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/playback because 1} the latter put the machinists who were union members in charge of program production, thus union strikes could result in unacceptable delays in military production, and 2) numerical control demonstrated the capability of producing complex parts that were not possible by the conventional manual methods used in the record/playback technique. The Air Force used its deep pockets to get its way and while American manufacturing may have been better served by the simpler Parsons concept or by record/playback, today this is a moot issue.

==Today==