Computer numerical control: Difference between revisions

Revision as of 02:06, 14 May 2005

Revision as of 06:18, 15 May 2005

Line 8:

==Historical notes==

The need of the U.S. Air Force for templates more precise than could be obtained by methods which were representative state-of -the-art statemethods of the art in the late 1940s inspired a gentlemen by the name of John Parsons, President of the Parsons Works of Traverse City, Michigan, to propose that a by-the-numbers technique (commonly used inby machining[[machinist]]s of that era) be putplaced under servo control with positionpositional data generated by a computer, (in order tothereby haveproviding manymuch more pointsdata thatthan would defybe thepractical practicabilityby means of hand calculations). His concept was to machine to setpoints as guides for subsequent manual finishing, that is, to speed up a manual process so more points could be included.

Mr. Parsons' project was enjoined by the Servo Mechanisms Laboratory of the Massachusetts Institute of Technology and redefined as interpolatedinterpolative positionpositional control that caused the cutting tool to traverse a series of straight linelines between defined points at a prescribed rate of travel. Thus, the cutting tool waswould be constantly on the programmed contour and spentwould spend very little of its time making non-cutting moves.

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 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.