JPH0814887A - Optical displacement gauge - Google Patents

Abstract

PURPOSE:To precisely measure a distance to an object to be measured even though the object has a concave or convex surface which carries out a slight regular refection. CONSTITUTION:In an optical displacement gauge in which a position of an object to be measured is obtained from a light receiving position on a position detecting element 5 which receives light reflected from the object to be measured, an optical noise filter 6 on which several microareas having phase differences delta=1/2lambda where lambda is the wavelength of used wave is located in the light receiving optical path. The light receiving distribution over the position detecting element exhibits a smooth curve with the regular reflecting components being restrained, thereby it is possible to reduce the displacement of the gravitational center.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement meter that optically detects displacement of a measuring object.

[0002]

2. Description of the Related Art An example of an optical displacement gauge is shown in FIG. Light emitted from a light source 1 such as a laser light source illuminates a measuring object 3 with a light projecting lens 2. And this reflected light is
It is condensed on the position detecting element 5 by the light receiving lens 4.
At this time, the current I flowing through the electrodes at both ends of the position detecting element 5 respectively
1 and I2 differ depending on the condensing position, so when the measurement object 3 moves from the distance R by ΔR, this ΔR
Is the baseline length BL, the angle θ, the distance R, and the currents I1, I
It can be calculated from 2. 13 and 14 show examples of processing circuits for this purpose. In the figure, 50 is a current-voltage conversion amplifier, 51 is an AC amplifier, 52 is an addition / subtraction amplifier,
Reference numeral 53 is a division amplifier, 54 is a logarithmic compression amplifier, and 55 is a differential amplifier.

By the way, the output of the position detecting element 5 is shown in FIG. 15 (b) even when the reflected light distribution focused on the position detecting element 5 has a gentle distribution as shown in FIG. 15 (a). )
Even in the case of a sharp distribution as shown in (1), since it is determined by the center of gravity, it is the same if the center of gravity is the same. On the other hand, the reflected light distribution characteristic of the surface of the measurement object 3 is shown in FIG.
In the case of the diffusive one as shown in (a), the condensing distribution on the position detecting element 5 has a gentle distribution as shown in (b) of the figure, but it has a glossy surface, that is, a specular reflection component. When the reflected light distribution characteristic is as shown in FIG. 17 (a),
The light distribution on the position detection element 5 may be as shown in FIG. 17 (b). At this time, since the movement m of the center of gravity occurs, it appears as an error. Figure 1 shows the ground metal surface
As shown in FIG. 8, since specular reflection due to minute unevenness exists, if the surface of the measurement object has such a reflection distribution, as the measurement object moves, the condensing distribution will be as shown in FIG. As shown in the figure, it changes, and the center of gravity moves so strongly that accurate displacement measurement cannot be expected.

[0004]

For this reason, Japanese Unexamined Patent Publication No.
No. 0-135714 discloses that a part of the light receiving lens is masked, and JP-A No. 62-115315 discloses that the angle between the light projecting axis and the light receiving optical system axis is limited. ing. However, in the former case, the reflected light is less likely to enter due to the mask, and since it is incident on the part without the mask, improvement cannot be expected so much. Since only the light receiving system is provided, it is useless for a measurement object having a specular reflection component even within this angle.

On the other hand, there is also a specular reflection type laser displacement meter in which the angle formed by the optical axes of the light projecting system and the light receiving system receives specularly reflected light, but this avoids the above influence. Therefore, the spots on the optical system and the position detection element are made small.Therefore, compared to the type that uses diffuse reflection, the distance measuring range is smaller and the distance to the measurement object is also smaller. It has a problem that it cannot be taken for a long time.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical displacement meter capable of accurately measuring a distance even if there is a concave-convex surface that makes a minute specular reflection. To provide.

[0007]

SUMMARY OF THE INVENTION However, the present invention is an optical system that collects reflected light from a measuring object on a position detecting element and detects the position of the measuring object from the converging position on the position detecting element. In the displacement meter, phase difference δ = 1 /
The first feature is that the optical noise filter having a large number of small regions of 2λ arranged at random is arranged in the light receiving optical path, and a spatial filter formed by randomly forming a large number of small apertures on the light shielding plate is formed. It has a second feature in that it is arranged in the light receiving optical path, and has a third feature in that it has a birefringent plate on the position detecting element, and further has a lenticular lens on the position detecting element. The fourth thing that we are arranging
It has the characteristics of

[0008]

According to the present invention, any of the optical noise filter, the spatial filter, the birefringent plate, and the lenticular lens is configured to change the center of gravity by making the light distribution on the position detecting element gentle with the regular reflection component suppressed. Make it smaller.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the illustrated embodiments. For a displacement meter composed of a light source 1, a light projecting lens 2, a light receiving lens 4 and a position detecting element 5 similar to the conventional example, The optical noise filter 6 is transparent to the used wavelength and has an area where the phase difference δ = 0 and an innumerable small area 60 that gives the phase difference δ = ½λ.
It is arranged near the measurement object 3 side. The regions 60 in the optical noise filter 6 are randomly present, and the total area of the regions 60 is approximately ½ of the area in the pupil. Regarding such an optical noise filter 6, "Applied Physics Vol. 27, 10"
No. (1958) ”for a theoretical explanation.

The optical noise filter 6
2 is inserted in the optical path, the spatial frequency of the light receiving system is
As shown in (a) at (a), the high frequency is cut off as shown at (b). Therefore, the condensing distribution on the position detection element 5 also changes from the sharp one shown in (a) in FIG. It becomes a gentle one as shown in (b). In other words, even if the specularly reflected light from the uneven surface that performs minute specular reflection is directed toward the light receiving lens,
By passing through the optical noise filter 6, the state is buried in a gentle distribution due to the diffuse reflection of the whole, so that the center of gravity hardly moves and accurate distance measurement can be performed. Since the optical filter 6 is a phase filter, basically no attenuation of the light amount occurs. Further, when the filter 6 is arranged on the measurement object 3 side of the light receiving lens 4, the size of the phase area can be increased as compared with the case where the phase area is arranged on the image plane side, which facilitates preparation. The distribution of the width of the filter 6 to be acted upon is determined by the size φ of the region 60 obtained by the following equation.

Φ = s1 × λ × 1 / (2a) s1; distance between the measuring object and the light-receiving lens a; condensed spot size on the measuring object λ; wavelength used Note that the size φ depends on the surface condition of the measuring object 3. The value may be about 1 to 2 which is a fraction of the calculation result.

As shown in FIG. 3, the optical filter 6 can be provided on the surface of the light receiving lens 4 to obtain the same effect. As shown in FIG. 4 or FIG. 6, it may be arranged on the position detecting element 5 side of the light receiving lens 4, and in this case,
The distribution of the width of the filter 6 to be acted upon is determined by the size φ of the region 60 obtained by the following equation.

Φ = s2 × λ × 1 / (2b) s2; distance between the position detecting element and the light receiving lens b; condensed spot size on the position detecting element λ; used wavelength region 60 to reduce the size It can be considered that the effect is easily exerted on the laser displacement meter, which tends to have a small light receiving optical system. This is because it is easy to halve the total area of the phase regions. Even in this case,
The size φ may be a value of about 1 to 2 which is a fraction of the calculation result, depending on the surface state of the measurement object 3.

Considering the area difference, from the above literature, if δ = 1 / 2λ, then RB = (S0-S1) ² S0; area ratio of phase δ = 0 S1; area of phase δ = 1 / 2λ Ratio RB; Response of spatial frequency If δ = 1 / 2λ and S0 = S1 = 0.5, the response can be RB = 0 at the cutoff spatial frequency. If S0 = 0.6 and S1 = 0.4, RB
Since it is 0.04, it can be said that the influence of the area is small. (See FIG. 5) The shape of the area to which the phase is applied is not limited to the circular shape as shown in the figure, but may be a directional shape such as a rectangular shape. In particular, the rectangular shape is preferable when it is desired to have a difference in the influence (spatial frequency) between the moving direction of the spot and the direction perpendicular thereto. And, such an optical noise filter 6 is
It can be obtained by vapor-depositing a transparent thin film which gives a phase difference of 1 / 2λ on one surface of a plane-parallel glass in a desired pattern. Specifically, a mask having a desired pattern is prepared, the mask is arranged on the glass surface, and a thin film is vapor-deposited on the mask. It can also be obtained by vapor-depositing a thin film on the glass surface and then etching the desired pattern by photolithography. In addition, cover the glass surface with a mask with the desired design, create a thin film by vapor deposition (CVD) or chemical plating, or create a thin film by CVD or chemical plating, and etch the desired pattern by photolithography. Can also be obtained by It may be appropriately selected depending on the cost and quantity. Also when it is formed on the surface of the light receiving lens 4, it can be formed by the above method. The thickness d of the thin film at this time is: d = λ / 2 × 1 / n n; Any material may be used as the material of the thin film as long as it is transparent to the wavelength used, but as an optically used material, Al ₂ O ₃ , CaF ₃ , CeF ₃ , CeO ₂ , MgF ₂ , La
₂ O ₃ , SiO ₂ , TiO _{2 and the} like. Of course, it may be a multilayer film made of these materials.

FIG. 7 shows another embodiment. Here, a spatial filter 7 in which a myriad of microscopic apertures 70 are randomly arranged so that the total area of the apertures 70 is half the pupil area is arranged in the optical path on a plate that is opaque to the light of the used wavelength. are doing. In this case, although the amount of light reaching the position detection element 5 is reduced, it is possible to eliminate the unnecessary movement of the center of gravity by smoothing the light distribution as in the case of the optical noise filter which is the phase filter. Further, since the spatial filter 7 can be obtained simply by making a hole in a thin metal plate with a die, a laser, a drill, etc., low cost and quick response can be achieved. The equivalent can also be obtained by forming a light shielding part on the transparent plate.

In the embodiment shown in FIGS. 8 and 9, the birefringent plate 8 is arranged immediately before the position detecting element 5. As the birefringent plate 8, a plate having a thickness d such that the amount of deviation z of the light beam is about a fraction of the received light spot size to about 1 time is used. Since the deviation z between the ordinary ray C and the extraordinary ray D compliments the unevenness of the distribution of each other, the synthetic distribution becomes gentle.

In the embodiment shown in FIGS. 10 and 11, the lenticular lens 9 which is an array of cylindrical lenses is arranged in front of the position detecting element 5. The distance w between the position detecting element 5 and the lenticular lens 9, the focal length f of the lenticular lens 9 and the lens pitch P are used to control the amount of blurring y, thereby blurring the light spot on the position detecting element 5 to distribute the light. Is to be gentle. 10B shows the case where the lenticular lens 9 is provided, and F shows the case where the lenticular lens is not provided. The array direction is the same as the moving direction of the light spot due to the distance change of the measurement object 3. The blur amount y given by the lenticular lens is y = Pw / f
Can be obtained by

[0018]

As described above, according to the present invention, an optical noise filter randomly provided with a large number of minute regions having a phase difference δ = 1 / 2λ with respect to a used wavelength λ, or a large number of minute apertures in a light shielding plate. Spatial filters that are randomly formed are arranged in the light receiving optical path, and because a birefringent plate and a lenticular lens are arranged on the position detection element, these optical noise filters, spatial filters, birefringent plates, and lenticular lenses are provided. In both cases, the condensing distribution on the position detection element is made gentle with the regular reflection component suppressed, and in order to reduce the movement of the center of gravity, even if there is an uneven surface that makes a minute regular reflection on the measured object, it is accurate. It can measure distance.

The optical noise filter may be arranged not only between the light receiving lens and the measurement object but also between the light receiving lens and the position detecting element. In the latter case, in particular, in the area where the phase difference is produced, It is easy to make the total area approximately 1/2 of the most preferable value, the pupil area.
If the optical noise filter is formed on the surface of the light receiving lens, the cost can be reduced by reducing the number of parts.

In the case of a lenticular lens which can be formed by a spatial filter or plastic molding, it can be provided at a low cost, and in the case of a birefringent plate, it can be integrated with a position detecting element, which is easy to handle. In addition, the placement accuracy is not affected.

[Brief description of drawings]

1A is a schematic view of an embodiment, and FIG. 1B is a front view of an optical noise filter of the same.

FIG. 2A is a spatial frequency characteristic diagram by the optical noise filter of the above, and FIG. 2B is a distribution characteristic diagram.

3A is a schematic view of another embodiment, and FIG. 3B is a front view of the optical noise filter of the same.

4A is a schematic view of another embodiment, and FIG. 4B is a front view of the optical noise filter of the same.

FIG. 5 is a spatial frequency characteristic diagram based on the above area ratio.

FIG. 6A is a schematic view of another embodiment, and FIG. 6B is a front view of the optical noise filter of the same.

FIG. 7A is a schematic view of another embodiment, and FIG. 7B is a front view of the spatial filter of the above.

FIG. 8 is a schematic view of still another embodiment.

9A is an explanatory view of the action of the birefringent plate, FIG. 9B is an explanatory view of a condensed state, and FIG. 9C is an explanatory view of a condensed distribution.

FIG. 10 is a schematic view of yet another embodiment.

FIG. 11A is an explanatory view of the action of the lenticular lens,
(b) is an explanatory view of a light distribution and (c) is a perspective view of a lenticular lens.

FIG. 12 is a schematic view of an optical displacement meter.

FIG. 13 is a block diagram showing an example of a circuit block.

FIG. 14 is a block diagram showing another example of a circuit block.

15 (a) and 15 (b) are explanatory views of a light distribution and a center of gravity.

16A is a reflection light distribution characteristic diagram in the case of diffuse reflection, and FIG.
[Fig. 3] is an explanatory diagram of a light condensing distribution in the above case.

FIG. 17 (a) is a reflection light distribution characteristic diagram when there is regular reflection,
(b) is an explanatory view of a light distribution in the same case.

18 (a) is a schematic diagram of a state of a ground metal surface, and FIG. 18 (b) is a reflection light distribution characteristic diagram of the same.

19 (a), (b), (c), and (d) are explanatory views of the above-mentioned light distribution.

[Explanation of symbols]

 4 Light receiving lens 5 Position detector 6 Optical noise filter

Claims (7)

[Claims] 1. An optical displacement meter that collects the reflected light from a measurement object on a position detection element and detects the position of the measurement object from the focus position on the position detection element with respect to the wavelength λ used. An optical displacement meter characterized in that an optical noise filter randomly provided with a large number of minute regions with a phase difference δ = 1 / 2λ is arranged in a light receiving optical path. 2. The optical displacement meter according to claim 1, wherein an optical noise filter is arranged between the light receiving lens and the measurement object. 3. The optical displacement meter according to claim 1, wherein an optical noise filter is arranged between the light receiving lens and the position detecting element. 4. The optical displacement meter according to claim 2, wherein an optical noise filter is formed on the surface of the light receiving lens. 5. An optical displacement meter that collects the reflected light from a measurement object on a position detection element and detects the position of the measurement object from the focus position on the position detection element. An optical displacement meter characterized in that a spatial filter formed by randomly providing openings is arranged in a light receiving optical path. 6. An optical displacement meter, which collects the reflected light from a measuring object on a position detecting element and detects the position of the measuring object from the condensed position on the position detecting element. An optical displacement meter characterized by arranging a refraction plate. 7. An optical displacement meter that collects the reflected light from a measurement object on a position detection element and detects the position of the measurement object from the condensed position on the position detection element. A lenticular on the position detection element. An optical displacement meter characterized by arranging a lens.