Non-contact tracer control device

Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems

Patent

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Details

318578, 318579, 318571, 36447408, 36447403, G01B 1100, G01B 1900

Patent

active

051402394

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to a non-contact tracer control device, and more particularly, to a non-contact tracer control device having an improved tracing accuracy.


BACKGROUND ART

Recently, non-contact tracer control devices for tracing a profile of a model by using a non-contact distance detector have been developed, and in this non-contact distance detector, an optical distance detector is used in such a way that it is fixed to the distal end of a tracer head and the distance of the model surface therefrom is detected to thereby provide a tracing. Accordingly, since there is no fear of damage to the model, models made of a soft material can be used, and thus a wider application of the profile machining is expected.
Nevertheless, conventional non-contact tracer control devices have a problem in that the tracing accuracy is lowered at a portion of a model where the angle of inclination is large. Namely, at such a portion, the measurement optical axis of the distance detector becomes almost parallel to the model surface and the spot on the model surface is enlarged and becomes an ellipsoidal shape, thus lowering the resolution of the distance detector and the tracing accuracy. Particularly, in triangulation type distance detectors, a problem sometimes arises in that the measurement optical axis interferes with the model surface, depending on the inclination angle, and thus the measurement becomes impossible.


DISCLOSURE OF THE INVENTION

This invention was created in view of the above circumstances, and an object thereof is to provide a non-contact tracer control device having an improved tracing accuracy.
To solve the above problems, this invention provides a non-contact tracer control device for carrying out a profile machining on a workpiece while tracing a profile of a model in a non-contact fashion, comprising first and second non-contact distance detectors mounted to a tracer head, which is controlled through a predetermined straight axis and a rotary axis rotatable about the straight axis, and inclined at a predetermined angle with respect to the straight axis, each detector individually measuring a distance of a surface of the model therefrom, sampling means for sampling measurement values obtained by the respective first and second non-contact distance detectors at predetermined sampling intervals, storage means for storing a first measurement value obtained by the first non-contact distance detector and a second measurement value obtained by the second non-contact distance detector, both sampled at a previous sampling time, vector calculating means for calculating a vector normal to the surface of the model, based on at least three of four measurement values including the first and second measurement values, a third measurement value obtained by the first non-contact distance detector sampled at a current sampling time, and a fourth measurement value obtained by the second non-contact distance detector sampled at the current sampling time, angle calculating means for calculating an angle of a projected vector obtained by projecting the normal vector onto a plane perpendicular to the straight axis, and rotary axis driving means for rotating the rotary axis in a direction of the angle.
Based on the values measured at the previous and current sampling times by the two non-contact distance detectors mounted to the tracer head, the coordinates of the four vertexes of a very small rectangle on the model surface are obtained, and the normal vector is obtained by using the coordinates of three required vertexes out of the four vertexes. The tracer head is rotated in the direction of a projected vector obtained by projecting the normal vector onto an X-Y plane. Accordingly, the measurement axes of the non-contact distance detectors are oriented in a direction as perpendicular as possible to the model surface, whereby a high-accuracy distance measurement can be carried out.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an arrangement of a non-contact tracer control

REFERENCES:
patent: 4396832 (1983-08-01), Henderson
patent: 4625104 (1986-11-01), Parker et al.
patent: 4694153 (1987-09-01), Bejczy et al.
patent: 4734572 (1988-03-01), Gorman
patent: 4933541 (1990-06-01), Dufour
patent: 4949024 (1990-08-01), Matsuura
patent: 4952772 (1990-08-01), Zana
patent: 4961155 (1990-10-01), Ozeki et al.
patent: 4999555 (1991-03-01), Yamazaki et al.
patent: 5067086 (1991-11-01), Yamazaki et al.

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