Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1990-10-17
1992-03-31
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
31856815, 318574, 318570, G05B 1925
Patent
active
051011476
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of controlling a machining speed during an involute curve interpolation process, and more particularly to an involute interpolation speed control method which reduces a machining speed in the vicinity of a base circle for an involute curve.
BACKGROUND ART
Nonlinear interpolation, particularly involute interpolation, in numerical control systems is highly required for the machining of gears, pump vanes, or the like. Generally, an involute curve is interpolated by a computer or an NC program generator which is separate from a numerical control system, producing linear data on a tape, and a workpiece is machined by the numerical control system using the tape.
The applicants have filed Japanese Patent Application No. 62-157302 (Japanese Laid-Open Patent Publication No. 64-2106) on an involute interpolation speed control method. According to the disclosed method, an involute curve is simply interpolated in a numerical control system, and the speed in a tangential direction is held constant irrespective of the angle.
In the proposed involute interpolation speed method, the coordinates of a point on an involute curve are given by: to .theta.=(.theta.3-.theta.1) by an increment: according to the above equations, and the difference between the points is determined, thus interpolating the involute curve.
The speed in a tangential direction can be rendered constant by selecting the increment of .theta. to be of a value which is reduced in inverse proportion to the angle, i.e., a value of K/(R.multidot..theta.).
In the vicinity of the base circle for the involute curve, i.e., a region where the radius of curvature of the involute curve is relatively small, however, a cutter would be subjected to a large load, making the machined surface defective if the workpiece were machined at a feed speed commanded by the program.
DISCLOSURE OF THE INVENTION
The present invention has been made in view of the aforesaid drawbacks. It is an object of the present invention to provide an involute interpolation speed control method which reduces a machining speed in a region near a base circle, where the radius of curvature of an involute curve is relatively small, thereby producing a well machined surface.
To achieve the above object, there is provided in accordance with the present invention a method of controlling a machining speed during a numerical control machining process with involute curve interpolation, comprising the steps of determining a radius of curvature from equations of the involute curve, determining whether said radius of curvature is smaller than a predetermined value, and reducing the machining speed with an override value if the radius of curvature is smaller than the predetermined value.
In the vicinity of a base circle for the involute curve, since the radius of curvature is small, any well machined surface would not be produced at a given tangential speed. Therefore, the machining speed is reduced with the override value in the vicinity of the base circle.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart of a processing sequence of an involute interpolation speed control method according to the present invention;
FIG. 2 is a diagram showing an involute curve interpolated according to the present invention;
FIG. 3 is a diagram showing the correspondence between radii of curvature and override values; and
FIG. 4 is a schematic block diagram of a numerical control system in the embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will hereinafter be described with reference to the drawings.
FIG. 2 is a diagram showing an involute curve interpolated according to the present invention. The diagram illustrates an instance in which the involute curve is drawn by the end of a thread as it is unwound counterclockwise away a base circle C. The command for the involute curve is given by G03.1. Another involute curve includes a curve drawn by the end of a thread as it is wound clockw
REFERENCES:
patent: 4899096 (1990-02-01), Kawamura et al.
patent: 4926102 (1990-05-01), Kawamura et al.
patent: 4935681 (1990-06-01), Kawamura et al.
patent: 4959597 (1990-09-01), Kawamura et al.
Murakami Kunihiko
Sano Masafumi
Sasaki Takao
Bergmann Saul M.
Fanuc Ltd.
Shoop Jr. William M.
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