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Cutter Compensation in Numerical Control

IP.com Disclosure Number: IPCOM000090716D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Wortzman, D: AUTHOR

Abstract

A significant source of error in numerically controlled machined parts is the dimensional inaccuracy of the cutting tool. The processor of a computer, programmed to compute machine tool paths, calculates the center path of a tool on the basis of the path of the tool's cutting edge and its planned diameter. However, errors result if the tools are not their planned or normal size. Deviation from nominal diameter occurs due to too large a tolerance or to regrinding of used tools. This problem is solved by including cutter-diameter compensation as a function of the controller operating on the output of the processor.

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Cutter Compensation in Numerical Control

A significant source of error in numerically controlled machined parts is the dimensional inaccuracy of the cutting tool. The processor of a computer, programmed to compute machine tool paths, calculates the center path of a tool on the basis of the path of the tool's cutting edge and its planned diameter. However, errors result if the tools are not their planned or normal size. Deviation from nominal diameter occurs due to too large a tolerance or to regrinding of used tools. This problem is solved by including cutter-diameter compensation as a function of the controller operating on the output of the processor.

The correct center path is one that is parallel to the original center path, offset by the error in radius. However, the new path is either longer or shorter than the original path. Two corrections must be made. One offsets the cutter perpendicular to the direction of travel by the amount of error in the radius. Another adjusts the length of the center path of the tool.

This technique applies to more dimensions than two. In a multitool operation the system can store the correction values for all cutters to be used. The correct tolerance can be selected automatically as the tools are indexed, instead of the cutters coming to a halt each time one is to be changed in order that the correction for that particular tool can be inserted. The algorithm is incorporated in the basic program capability of the computer system. The algorithm supplies two cutter-compensation formulas. One is for linear segments and one is for formulas. One is for linear segments and one is for circular arcs.

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Linear cut vectors with compensation have one of three orientations L, R or C with respect to cutter compensation. L signifies cutter compensation to the left,
i.e., the tolerance to be held is to the left of the cutter as it moves. R signifies cutter compensation to the right. C signifies no compensation. The rules for generating the unit correction vector vary, depending on the sequence of the L, R, and C cuts. If an L (R) cut follows an L (R) cut, the unit correction vector has to be on the bisector of the junction angle alpha. in the direction of the tolerance to be held. An L (R) cut vector that has zero components in the plane of compensation is assumed to have the same direction in the plane of compensation as the previous cut. If an uncorrected C cut joins a left L or right R cut, the unit correction vector of their junction has to be normal to the L or R linear segment in the direction of the tolerance to be held. At the end of a C cut the correction has to be the null vector. An L and an R is always separated by a C cut.

In order that normalization not lead to an error of a pulse, at least one bit, preferably more, to the right of the decimal point...