Contactless profiling method

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

Patent

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Details

318572, 318577, 364513, 36447408, 356375, 356376, G01B 1100, G05B 1900, B23Q 3528

Patent

active

049490249

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a contactless profiling method and, more particularly, to a contactless profiling method for performing profiling while tilting a distance measuring probe.


DESCRIPTION OF THE RELATED ART

A contactless profiling method is available in which the surface of a model is traced by a probe sensor (a distance measuring probe), such as a laser distance measuring probe, that is capable of measuring distance contactlessly, whereby either profiling machining is performed in accordance with the model or the model surface data is digitized.
In general, the distance measuring probe used in such contactless profiling possesses a reference distance L.sub.0, and it is arranged so that the difference between an actual measured distance L and the reference distance L.sub.0 can be outputted as an error .sub..DELTA. L.
FIG. 9 is a view for describing contactless profiling. Assume that a model MDL is to be profiled, and that points A, B, C are suitably selected sampling points. When a distance L.sub.1 (=L.sub.0 +.sub..DELTA. L.sub.1) at point A is measured, an error quantity of .sub..DELTA. L.sub.1 in comparison with the reference distance L.sub.0 is produced. The probe is then directed to the next sampling point B while a corrective operation is applied along the measurement axis (along the optic axis) in an amount corresponding to the error quantity. An error quantity .sub..DELTA. L.sub.2 is then obtained at the point B and the probe is directed to point C so as to similarly apply a correction operation corresponding to the error quantity .sub..DELTA. L.sub.2. By subsequently repeating identical processing, the model surface is traced contactlessly.
An optical triangular measurement method, by way of example, can be employed with a contactless distance measuring probe. With such a probe, a laser beam emitted by a light-emitting element (semiconductor laser) is projected onto the model surface via a projecting lens, and a part of the diffusely reflected light beam forms a spot on a position detecting element via a light-receiving lens. Distance is measured by changing the spot position in dependence upon the distance to the model surface. Accurate measurement of distance cannot be performed unless the a sufficient amount of light enters the light-receiving lens. Consequently, there is a limitation upon the range of distance that can be measured accurately by a distance meausuring probe PB. In FIG. 10, a range equivalent to the reference distance L.sub.0 .+-.l is a measurable range MSR. In addition, the distance measuring probe PB has a limit value in terms of a model surface inclination angle .theta. (see FIG. 11) which is capable of being accurately measured; distance to a surface having an inclination angle greater than this limit angle cannot be measured. Hence, the with precision.
As a result, if the model MDL has a wall WAL (irrespective of whether it is ascending or descending) defining nearly a right angle, as shown in FIG. 12, the distance cannot be measured at a corner portion P when the, distance measuring probe PB is moved from point A to point B. The prior art is such that when distance measurement becomes impossible, the probe PB is returned to point A by being moved in the opposite direction, speed is drastically reduced, the probe is again moved in the direction of point B while being raised and lowered to search for a position at which measurement becomes possible. When this position is found, ordinary contactless profiling is resumed from the position.
Thus, when distance measurement becomes impossible while using a prior-art contactless profiling method, a considerable period of time is required for normal contactless profiling to resume. As a result, neither high-speed contactless profiling machining nor digitizing of data by high-speed contactless profiling can be carried out.
Another problem with the prior-art method is that there is a large range in which exists distance cannot be measured, or in other words, a large range exists in which contactless pro

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