Tool radius compensation system

An apparatus for tool radius compensation in three-dimensional machining of a workpiece where a tool is offset from a commanded tool path by a distance commensurate with the radius of the tool, comprising:

• command means for producing command signals in first, second and third dimensions, with a workpiece contour being commanded in first and second dimensions as a tool path in a prescribed plane sectioning the workpiece;
• means for providing tool radius and inclination of a machined surface of the workpiece;
• means for computing a first tool offset quantity in the prescribed plane and a second tool offset quantity in a direction at right angles to the prescribed plane, based on the radius of the tool and the inclination of the machined surface;
• two-dimensional tool radius compensation means which receives the first and second dimension command signals from said command means for effecting tool radius compensation in the prescribed plane by correcting the first and second dimension command signals based on first tool offset quantity, and for outputting the corrected first and second dimension command signals;
• third dimension tool radius compensation means for correcting tool position in a direction at right angles to the prescribed plane by correcting the third dimension command signal from said command means based on the second tool offset quantity, and for outputting a corrected third dimension command signal;
• and
• means for machining the workpiece in three dimensions based on the corrected first and second dimension signals from said two-dimensional tool radius compensation means and the corrected third dimension signal from said third dimension tool radius compensation means.