Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1989-02-08
1990-09-25
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318574, 318573, 36447429, 36447431, G05B 19445
Patent
active
049595970
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a numerical control apparatus for interpolatory control of a tool along the shape of a workpiece to be machined.
2. Description of the Related Art
If a workpiece formed into a predetermined shape is to be milled by a tool of radius r, the path along which the center of the tool is to pass must be set as a path spaced away from the contour of the workpiece by the distance r when an ordinary machining program is created. Spacing the tool a certain distance away from the contour in this manner is referred to as "offsetting" the tool. An ordinary numerical control apparatus has a tool diameter compensating function for forming such an offset path.
Besides being required for linear and circular interpolation, this tool diameter compensation is also required when performing interpolation based on an involute curve in order to cut a gear or the vanes of a pump by a machine tool. The applicant has already filed an application for an invention regarding an interpolating system in which an involute curve can be simply interpolated within a numerical control apparatus (U.S. application Ser. No. 07/309,644). In accordance with this system, problems in terms of a pulse distribution relating to tool velocity possessed by conventional involute interpolation are solved and it is possible to perform high-speed interpolatory computations by circular interpolation.
In a numerical control apparatus having such a tool diameter compensating function, high-speed computation which will not restrict the tool traveling velocity is required in order to perform an offset computation for approximating the involute curve by a circular arc and to control the machine tool so that the workpiece is machined according to the shape along the involute curve.
SUMMARY OF THE INVENTION
The present invention has been devised in order to solve this problem of the prior art. The object of the present invention is to provide a numerical control apparatus in which a designated involute curve is approximated by a circular arc and an offset value corresponding to a tool diameter is computed at high speed to effect interpolatory control of the tool.
According to the present invention, there is provided a numerical control apparatus having a tool control function for machining a workpiece into a shape along an involute curve, comprising setting means for setting an approximation circle approximating the involute curve in accordance with an intersection angle at a command point commanding the start of machining along the involute curve, arithmetic means for computing an offset vector at the command point from the set approximation circle and an offset vector of a tool trajectory up to the command point, and interpolating means for interpolating an involute curve offset by a tool diameter based on the offset vector of the tool.
Accordingly, the numerical control apparatus of the present invention is such that when a tool path is computed from point sequence data designating an involute curve, an approximation circle is set in dependence upon the intersection angle at the command point, and an offset vector is computed from the approximation circle and the tool trajectory up to the command point. As a result, a tool diameter offset computation can be performed at high speed.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an embodiment of the present invention;
FIG. 2 is a flowchart illustrating computation steps;
FIG. 3 is a diagram illustrating an example of an involute curve; and
FIGS. 4 through 6 are diagrams for describing methods of setting approximation circles.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described in detail with reference to the drawings.
FIG. 3 illustrates an example of an involute curve. Here the involute curve is defined as the trajectory of a point at which the length of a tangent line becomes equal to the length of an arc P.sub.0 P, the tangent line of the circle being
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Fujibayashi Kentaro
Kawamura Hideaki
Otsuki Toshiaki
Fanuc Ltd
Ip Paul
Shoop Jr. William M.
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