Computer numerical control: Difference between revisions

Revision as of 03:34, 13 May 2005

Revision as of 05:00, 13 May 2005

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Numerical control (NC) is the precursor of computer numerical control (CNC), which controls the automation of machine tools and the inherent tool processes for which they are designed. The CNC machine tool is the [[servo]] [[actuator]] of the CAD/CAM (Computer Assisted Design/Computer Assisted Manufacturing) technology both literally and figuratively.

CNC inherits from NC the essential character of by-the-numbers interpolation of transition points in the work envelope (orthe "Machine Coordinate System") of a mult-axis motion platform, based on the separation of programming from operations. The set of instructions, (or "program) -" (usually an ASCII text file in which, in its simplest form, a line of text specifies the axial coordinates of a point in the Machine Coordinate System -) is prepared from a blueprint or CAD file and transferred to the memory of the CNC via floppy drive, serial data interface or a network connection. Once stored in the CNC memory and selected, forthe execution,program is executed by pressing the appropriate key on the machine operator panel causes the CNC to execute the program.

==Historical notes==

The need of the U.S. Air Force for templates more precise than could be obtained by methods which were representative of the state 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 in machining be put under servo control with position data generated by a computer (in order to have many more points that would defy the practicability 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.

His project was taken over by the Servo Mechanisms Laboratory of the Massachusetts Institute of Technology and redefined as interpolated position control that has the cutting tool traverse a straight line between points at a prescribed rate of travel. Thus, the tool would be constantly on the programmed contour and not spending most of its time making non-cutting moves.