JPH073329B2 - Three-dimensional free curved surface measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a three-dimensional free-form surface measuring apparatus, and more specifically, it separates a frequency-modulated laser beam into two laser beams, and thereafter The present invention relates to a three-dimensional free curved surface measuring device for measuring the surface condition of an object to be measured by causing both laser beams to interfere with each other.

<Prior Art> Conventionally, as the three-dimensional free-form curved surface measuring apparatus, the one having the configuration shown in FIG. 3 has been provided.

That is, the current source (32) is controlled by the modulation source (31) to control the injection current into the semiconductor laser (33), and the frequency-modulated laser light (34) is output. This laser light (34) is guided through a lens (35) to a beam splitter (36) composed of a half mirror, and is separated into two laser beams (34a) and (34b) which are oriented at right angles to each other.
One laser beam (34a) is applied to the mirror (37), and the other laser beam (34b) is applied to the measured object (39) through the lens (38).
Each of the laser beams (34a) and (34b) is reflected by the mirror (37) and the object to be measured (39), guided to the beam splitter (36) again, and detected in the interfered state. To the vessel (40).

In the case of the three-dimensional free-form curved surface measuring device having the above-mentioned configuration, the beam splitter (36) is re-corresponded to the distance from the beam splitter (36) to the mirror (37) and the distance to the object to be measured (39). ), The laser beam in the state of being interfered with is guided to the detector (40). Therefore, by detecting the beat caused by the temporal change of the phase difference between both laser beams (34a) (34b), The difference in distance can be detected.

Further, since the distance to the mirror (37) is set to a predetermined reference distance, an accurate distance can be detected by adding or subtracting the difference of the above distance to the reference predetermined distance. it can.

<Problems to be Solved by the Invention> In the above three-dimensional free-form curved surface measuring apparatus, the laser source (3
Laser light output from 3) is beam splitter (36)
Two laser beams (34
a) and (34b), which are respectively guided to the mirror (37) and the object to be measured (39), and then reflected and again guided to the beam splitter (36). (34a) and (34b) are likely to have significantly different atmospheres, and are affected by suspended matter, etc., and are affected by temperature-induced level fluctuations. However, there is a problem that an accurate measurement cannot be performed. In particular, when the measurement is performed with the accuracy of the μm order, there is a problem that the above-mentioned influence and the error due to the difference in the level fluctuation become too large, and the measurement accuracy of the μm order cannot be guaranteed. Moreover, in the above atmosphere, the refractive index changes when a temperature difference occurs, and the refractive index changes corresponding to the temperature difference, so that there is a problem that the measurement accuracy cannot be guaranteed in this respect as well.

In addition, it is separated by the beam splitter (36) 2
Since the laser beams (34a) (34b) of the book are directed at right angles to each other, a considerable distance in the direction of both laser beams (34a) (34b) (the distance to the mirror (37) and the object to be measured ( The distance up to 39) is required, and there is a problem that the three-dimensional free-form curved surface measuring device becomes large as a whole.

<Objects of the Invention> The present invention has been made in view of the above problems,
It is an object of the present invention to provide a three-dimensional free-form curved surface measuring apparatus that can measure an object to be measured with high accuracy without being affected by an atmosphere through which a laser beam passes.

<Means for Solving Problems> A three-dimensional free-form curved surface measuring apparatus according to the present invention for achieving the above object includes a laser light source that outputs a frequency-modulated laser light, and a laser light source that outputs the laser light. A polarizing element that separates the laser beam into one book and a mirror that reflects one laser beam, and one laser beam reflected by the mirror and the other laser beam reflected by the measuring object are polarized by the polarizing element. To obtain a measured value corresponding to the state of the surface of the object to be measured based on the detection result of the detector that receives the interfered laser beam,
As the polarizing element, one that separates the laser light into two laser beams that are deviated from each other by a minute angle is adopted, and the optical path of each laser beam between the polarizing element and the mirror and the object to be measured is spatially defined. They are set so that they are close to each other.

However, the polarization element may be a Wollaston prism.

Further, the laser light source is a semiconductor laser, and a collimator is arranged between the semiconductor laser and the polarizing element, and the laser beam spot system is kept small over a wide range between the polarizing element and the object to be measured. A condensing optical system may be provided.

<Operation> In the case of the three-dimensional free-form curved surface measuring device having the above configuration, when the frequency-modulated laser light from the laser light source is guided to the polarizing element, two laser beams, an ordinary ray and an extraordinary ray, are emitted. Since the laser beams are separated from each other and the displacement angle between the two laser beams is very small, it is possible to irradiate a predetermined position close to each other, that is, a mirror arranged in substantially the same atmosphere, and an object to be measured. . The both laser beams are reflected by the mirror and the object to be measured, guided again to the polarization element, and interfered with each other. Therefore, the interfered laser beams are received by the detector to be measured. It is possible to output a measurement value corresponding to the state of the surface of the object.

Further, if the polarizing element is a Wollaston prism,
The deviation angle between the two laser beams can be about 5 degrees.

Further, the laser light source is a semiconductor laser, a collimator is arranged between the semiconductor laser and the polarizing element, and the laser beam spot diameter is kept small over a wide range between the polarizing element and the object to be measured. If a condensing optical system is provided, a laser beam having an anisotropic spread is converted into a laser beam having an isotropic spread by a collimator, and this laser light is collected. It is possible to irradiate the object to be measured with the system having a small spot diameter over a wide range.

<Example> Hereinafter, detailed description will be given with reference to the accompanying drawings illustrating an example.

FIG. 1 is a schematic view showing an embodiment of the three-dimensional free-form surface measuring device of the present invention.

An injection current is supplied by a current source (2) to a semiconductor laser (1) that outputs a laser beam for measurement, and a modulation signal is supplied by a modulation source (3) to the current source (2).

Laser light (4) output from the semiconductor laser (1)
Is guided to the beam splitter (6) through the lens (5), a part of which is reflected at a right angle and is irradiated to the output monitor section (7), and the rest goes straight to the Wollaston prism (8) as a polarizing element. Is irradiated. The Wollaston prism (8) separates the irradiated laser beam (4) into an ordinary ray and an extraordinary ray, and irradiates the mirror (9) and the object to be measured (10) arranged at predetermined positions, respectively. To do. However, since the ordinary ray and the extraordinary ray are emitted at an angle of about 5 degrees with respect to each other, the mirror (9) and the object to be measured (10) are arranged relatively close to each other. There is.

Incidentally, (11) is a lens arranged between the Wollaston prism (8) and the object to be measured (10), and (12) is arranged on the opposite side of the beam splitter (6). It is the detected detector. Although not shown, the intensity change of the output laser light (4) can be suppressed by feeding back the output signal from the output monitor section (7) to the semiconductor laser drive system.

The operation of the three-dimensional free-form surface measuring device having the above configuration is as follows.

An injection current responsive to a signal from the modulation source (3) is supplied from the current source (2) to the semiconductor laser (1), so that the semiconductor laser (1) emits a laser beam (4) that is frequency-modulated. Output.

This laser light (4) is guided to a Wollaston prism (8) through a lens (5) and is separated into an ordinary ray and an extraordinary ray having a deviation angle of about 5 degrees, one of which is a reference light (4a). Is directly irradiated onto the mirror (9), and the other is irradiated onto the object to be measured (10) through the lens (11) as probe light (4b). After that, both lights (4a) and (4b) are reflected, guided through the same path as above to the Wollaston prism (8), and emitted in an interference state with each other. The laser light (4c) in the interference state is reflected by the beam splitter (6) and is applied to the detector (12).

In the detector (12), the laser light (4
The difference between the distance to the mirror (9) and the distance to the object to be measured (10) can be detected by detecting the beat included in c) due to the temporal change of the phase difference. . In this case, the optical path from the Wollaston prism (8) to the mirror (9) and the optical path to the object to be measured (10) have a deviation angle of about 5 degrees and are very close to each other. Since they are passing through almost the same atmosphere, it is possible to accurately detect only the beats corresponding to the difference in distance by being affected by the floating substances and the like to the same extent.

Therefore, by measuring a minute distance change on the surface of the object to be measured (10), it can be used as a surface roughness meter, a scratch inspection device, etc. Measurement when applied to such an application As for accuracy, the accuracy on the order of μm was achieved.

While performing the above operation, the semiconductor laser (1)
Part of the output laser light (4) from the semiconductor laser (1) passes through the beam splitter (6) and is emitted to the output monitor section (7). The change in the output laser light intensity can be known, and the output laser light intensity can be stabilized by controlling the temperature, injection current, etc. of the semiconductor laser (1) as necessary.

FIG. 2 is a schematic view showing another embodiment, which is different from the above embodiment in that a collimator (13) is interposed between the semiconductor laser (1) and the beam splitter (6), and It is only the point where a condensing optical system (14) consisting of three lenses is interposed between the Wollaston prism (8) and the object to be measured (10).

More specifically, the collimator (13) converts the laser light output from the semiconductor laser (1) having an anisotropic beam spread into a laser beam having an isotropic beam spread. It is to convert.

The condensing optical system (14) is composed of three lenses (15) (1) arranged in order from the Wollaston prism (8) side.
6) (17), the first lens (1
By condensing the laser light by 5), it is possible to form the region L having the same amplitude distribution as that inside the laser resonator. Second lens (1
6) is provided at the end of the area L, and the third lens (17) is provided at a position separated from the lens (16) by a predetermined distance D, and each has a focal point. The distances f ₁ and f ₂ are set.

The predetermined distance D and the focal length f2 are D ≦ (f _F / X _m ) ^1/2 , f ₂ = {1- (f _F / X _m -D ² ) ^1/2 / f _F } / D Is the distance represented.

However, f _F = πγ ₀ ² / λ, x _m = b (c ₁ c ₂ ) ^1/2 / c ₀ , c ₀ = c ₁ a ² + c ₂ (a + b) ² , γ ₀ is laser light , Λ is the wavelength of light, a is the working distance, b is the measurement interval, and c ₁ and c ₂ are the specific gravity of each term of the evaluation function.

By setting as described above, the laser light in the range of the measurement section b can be narrowed down into a small spot shape, and the distance to the object to be measured (10) can be accurately measured.

The present invention is not limited to the above-described embodiments, and, for example, it is possible to use a Ronschon prism in place of the Wollaston prism, and other various modifications are possible without departing from the scope of the invention. It is possible to change the design of.

<Effects of the Invention> As described above, the present invention separates the laser light into the reference light and the probe light having only a small angle by the changing element, and at the same time, the polarizing element, the mirror, and the object to be measured. Since the optical paths of the laser beams in between are set so as to be spatially close to each other, the reference light and the probe light are affected by the atmosphere to the same degree, and the above effects are caused by causing the reflected lights to interfere with each other. By eliminating this, it is possible to remarkably improve the measurement accuracy of the three-dimensional free-form surface, and it is possible to reduce the size as a whole.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the three-dimensional free-form curved surface measuring device of the present invention, FIG. 2 is a schematic view showing another embodiment, and FIG. 3 is a schematic view showing a conventional example. (1) ... Semiconductor laser, (2) ... Current source, (3) ... Modulation source, (4) ... Laser light, (8) ... Wollaston prism as polarizing element, (9) ... Mirror, (10) ... Object to be measured, (12) ... Detector, (13) ... Collimator, (14) ...
Condensing optical system, (15) (16) (17) ... Lens

Claims (3)

[Claims] 1. A mirror comprising: a laser light source for outputting frequency-modulated laser light; a polarizing element for separating the laser light into two laser beams; and a mirror for reflecting one laser beam. One laser beam reflected by and the other laser beam reflected by the measurement object are interfered by the polarizing element, and the measurement object based on the detection result of the detector that receives the interfered laser beam A three-dimensional free-form curved surface measuring apparatus for obtaining a measured value corresponding to a surface state, wherein the polarizing element is one that separates laser light into two laser beams that are deviated from each other by a minute angle, A three-dimensional free-form curved surface measuring apparatus characterized in that the optical paths of the respective laser beams between the mirror and the object to be measured are set to be spatially close to each other. 2. A three-dimensional free-form curved surface measuring apparatus according to claim 1, wherein the polarizing element is a Wollaston prism. 3. A laser light source is a semiconductor laser, a collimator is arranged between the semiconductor laser and a polarizing element, and a laser beam spot diameter is widened between the polarizing element and an object to be measured. The three-dimensional free-form curved surface measuring device according to claim 1, wherein a converging optical system for holding the device small is provided.