CNC Control - 2: Continuous Path
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The continuous-path control system is more commonly known as the contouring system. Its function is to synchronize the axes of motion to generate a predetermined path, generally a line or a circular arc. The contouring system has the capability of controlling its drive motors independently at various speeds as the tool moves towards the specified position. This involves simultaneous motion control of two or more axes which requires separate position and velocity loops.
The contouring capability of NC is one of the primary reasons it was invented. Prior to NC if a contour was to be machined it had to be machined from a pattern on a tracing mill. In some cases a pattern was used just for roughing purposes and then a very large set of X and Y coordinates were calculated that would represent the curve. Two machinists were then used to operate a milling machine, one machinist on each axis. They would move each axis in unison to the proper coordinate printed out on their axis sheet. This was quite an improvement in accuracy over the pattern tracers but extremely time consuming and expensive. R.S.
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