Geometrical instruments – Gauge – Coordinate movable probe or machine
Patent
1992-03-25
1994-09-13
Cuchlinski, Jr., William A.
Geometrical instruments
Gauge
Coordinate movable probe or machine
33546, 33551, 356376, G01B 1124
Patent
active
053456874
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This Invention relates to a noncontact tracing control device, and more particularly, to a device of this kind in which a distance detector is always positioned in such a manner that a measurement axis thereof is perpendicular to a model surface, to thereby improve the tracing accuracy.
BACKGROUND ART
Noncontact tracing control devices are known in which, while an optical distance detector mounted to a tracer head Is moved along a model surface, a distance to the model surface is detected in a noncontact fashion, and the operation of a machine tool is controlled in accordance with the result of distance detection representing the model shape. This type of control device is advantageous in that the model surface is not damaged when the model surface is traced. If the ankle of inclination of the model surface is large, however, the measurement axis of the optical distance detector becomes almost parallel to the model surface, and the spot on the model surface is enlarged to an ellipsoid, thus lowering the tracing accuracy. Particularly when using a trigonometric type distance detector, measurement sometimes becomes impossible due to an interference between the optical axis and the model surface.
SUMMARY OF THE INVENTION
An object of this invention is to provide a noncontact tracing control device in which the orientation of a noncontact distance detector is controlled in accordance with an angle of inclination of a model surface in such a manner that the measurement axis of the detector is exactly or nearly perpendicular to the model surface, to thereby improve the tracing accuracy.
To achieve the above object, a noncontact tracing control device according to this invention comprises: a first detector arranged to be rotatable around a rotary axis and movable relative to a model in a direction perpendicular to the rotary axis, having a measurement axis extending obliquely with respect to the rotary axis, for measuring a distance therefrom to a point on a surface of the model in a noncontact fashion; a second detector arranged to be movable together with the first detector and having a measurement axis extending obliquely with respect to the rotary axis and shifted from the measurement axis of the first detector in a direction perpendicular to the rotary axis, for measuring a distance therefrom to another point on the surface of the model in a noncontact fashion; calculating means for calculating a normal vector of the surface of the model based on four measured distance values, which include first two values and second two values successively measured by the first and second detectors, respectively, at predetermined time intervals, while the first and second detectors are moved relative to the model, and calculating an angular position of a projection of the normal vector on a plane perpendicular to the rotary axis; and positioning means for positioning the first and second detectors at the angular position thus calculated.
As described above, according to this invention, while the first and second detectors for detecting the distances therefrom to respective different points on the model surface are moved relative to the model, a normal vector of the model surface is calculated based on four measured distance values successively measured by the first and second detectors, an angular position of a projection of the normal vector on the plane perpendicular to the common rotary axis of the two detectors is calculated, and the detectors are positioned at the calculated angular position. As a result, the detectors can be always oriented exactly or nearly perpendicular to the model surface, whereby the distances to the model surface can be accurately measured and the tracing accuracy is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating a noncontact tracing control device according to an embodiment of this invention and a tracing machine tool;
FIG. 2 is an enlarged perspective view showing in detail a tracer head and a noncontact distance detector appea
REFERENCES:
patent: 4905158 (1990-02-01), Seki et al.
patent: 5071252 (1991-12-01), Matsuura
Matsumoto Eiji
Matsuura Hitoshi
Cuchlinski Jr. William A.
Fanuc Ltd.
Wirthlin Alvin
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