JPH08261730A - Non-contact displacement meter - Google Patents

Abstract

PURPOSE: To provide a low-cost non-contact displacement meter which can irradiate a sample to be measured with a laser beam having a uniform intensity in a wide range with a simple structure without increasing the number of laser beam sources without reducing the utilization efficiency of the laser beam and has high performance with a wide measuring range. CONSTITUTION: A beam attenuation filter 5 having a reverse space light transmittance to a space intensity distribution of a laser beam via an optical system 2 is interposed between the system 2 for broadening the beam and a sample W to be measured to provide a uniform intensity distribution in the beam directed toward the sample W to be measured, and the output of an image sensor 3 for receiving the scattered light from the sample W to be measured is set to the signal for representing a speckle pattern based on sufficient contrast in all channels.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement meter which obtains displacement information of a sample to be measured without contact by using a speckle pattern obtained by irradiating the sample to be measured with laser light. The displacement information referred to in the present invention means 1 of the measured sample.
In addition to the displacement information at the points, for example, the elongation and contraction amount based on the displacement amount of the measured sample at two points, such as the elongation of the test piece in a material testing machine, and the strain distribution information based on the displacement amount at multiple points are also included. Including.

[0002]

2. Description of the Related Art There is known a method of measuring displacement information (displacement or elongation) of a sample to be measured without contact using a speckle pattern obtained by irradiating the surface of the sample to be measured with laser light. Has been.

When the displacement information is obtained using this speckle pattern, basically, the scattered light of the laser light from the surface of the sample to be measured is photoelectrically converted by an image sensor to generate an electric signal corresponding to the speckle pattern. The movement amount of the speckle pattern is obtained by obtaining the cross-correlation function of the signals every moment, and the displacement information of the sample is obtained from the movement amount of the speckle pattern.

Further, by using the principle of measurement using the speckle pattern, the movement amount of the speckle pattern at two points of the sample to be measured is calculated and the difference between them is calculated, and the elongation of the sample to be measured between the two points is calculated. Alternatively, the amount of shrinkage can be obtained, and it can be applied to, for example, measurement of elongation of a test piece of a material testing machine.

By the way, in the case of measuring the elongation of a test piece in a material testing machine as in the above application example, "elongation" means the distance between two gage marks initially set on the test piece. Since it is a rate that shows how it changes afterwards or with the progress of the test, when measuring elongation, the two observation points (gauge points) initially set on the test piece should be adjusted according to the deformation of the test piece. Need to be tracked. As a method for tracking such a control point, the present invention has already changed each irradiation position of the laser light stepwise based on the measurement result of the movement amount of each observation point (control point), The laser light from the laser light source is expanded one-dimensionally in the extension direction of the test piece using an optical system such as a cylindrical lens, and the sample laser beam is irradiated with the linear laser beam and the linear irradiation area The scattered light from the sensor is received by the one-dimensional image sensor, and among the outputs of each channel of the image sensor, the output of each of the plurality of channels corresponding to two positions separated by a predetermined distance from each other on the surface of the test piece is used as an observation point (marker). Channel that is adopted as observation point (mark) data based on the measurement result of the amount of movement of each observation point (mark) based on each observation point (mark) data We have proposed a method that will be changed in steps.

Of the above proposals, the latter proposal is
Since the observation point (gauge point) is tracked in the calculation of data without tracking the irradiation position of the laser light, a mechanism for changing the irradiation position of the laser light is unnecessary compared to the former proposal. Therefore, there is an advantage in cost, and there is an advantage that a measurement error caused by an error in the operation of the tracking mechanism does not occur.

[0007]

By the way, as in the above-described example, when the irradiation area of the laser beam on the surface of the sample to be measured is not a spot shape but a line shape or a surface shape, the laser is not used. It is necessary to spread the output light from the light source into a desired beam cross-sectional shape by an optical system such as a lens. In this case, since the output light from the laser generally has a Gaussian distribution centered on the optical axis, the beam expanded by the optical system also has a spatial intensity distribution according to this. This difference in intensity becomes more remarkable as the beam is expanded.

FIG. 6 shows the irradiation when the output light from the semiconductor laser 61 is linearly spread by the beam expander 63 composed of the collimator lens 62 and the two cylindrical lenses 63a and 63b to irradiate the surface of the sample W to be measured. In the explanatory diagram of the light intensity distribution, the spatial intensity distribution of the irradiation light is a Gaussian distribution centered on the optical axis according to the intensity distribution of the output light from the semiconductor laser 61, and the irradiation light intensity is uniform over a wide area. Can't get for that reason,
The light scattered by the surface of the sample W to be measured also has a distribution according to the intensity distribution of the irradiation light, and the speckle pattern contained therein also does not have a uniform intensity distribution. When such scattered light is detected by the one-dimensional image sensor, the output of the one-dimensional image sensor, when the irradiation light intensity is set so as to obtain a certain degree of contrast in the signal of the end channel, as shown in FIG. In the channel, the incident light intensity is too strong and saturated, and if the saturation of the central part is to be eliminated, the signal at the end part becomes weak and good speckle pattern data cannot be obtained.

In order to solve such a problem, for example, as shown in FIG. 8, of the output light from the semiconductor laser 81, only the light centered on the optical axis and having a small intensity distribution is used for the irradiation light. Alternatively, as shown in FIG. 9, a plurality of semiconductor lasers 91 and a dedicated optical system 92 are arranged in the direction in which the irradiation light spreads so that the output light of each semiconductor laser is not expanded so much. It suffices to combine the output lights and irradiate the measured sample as a long linear beam as a whole. However, in the former method, the utilization efficiency of the laser light is poor, a higher power semiconductor laser is required to obtain the desired scattered light intensity, and there is a problem in safety and cost, and in the latter method, There is a problem that the cost increases as the number of semiconductor lasers and optical elements associated therewith increases.

The present invention has been made in view of such circumstances, and particularly, without deteriorating the utilization efficiency of laser light,
Further, it is possible to irradiate the sample to be measured with a laser beam having a uniform intensity over a wide range without increasing the number of laser light sources, which is inexpensive, and is a high-performance non-contact displacement meter having a wide measurement range. To provide.

[0011]

A structure for achieving the above-mentioned object will be described with reference to FIG. 1 which is an embodiment drawing, and a non-contact displacement meter of the present invention comprises an output light from a laser light source 1. Optical system 2 for irradiating the surface of the sample W to be measured with a predetermined spread, and an image sensor 3 for receiving scattered light of the laser light from the surface of the sample W to be measured.
And an output of the image sensor 3 is used to calculate the amount of movement of the speckle pattern contained in the scattered light every moment, and the displacement meter is provided with a calculation means 4 for obtaining displacement information of the sample to be measured. It is characterized in that a neutral density filter 5 having a spatial light transmittance distribution opposite to the spatial intensity distribution of light passing through the optical system 2 is provided between the system 2 and the surface of the sample W to be measured.

[0012]

According to the present invention, the spatial intensity distribution of the light radiated to the sample W to be measured through the optical system 2, which is generated mainly due to the spatial intensity distribution of the output light from the laser light source 1, is used as the transmittance. This is to be solved by passing through the neutral density filter 5 having a spatial distribution.

That is, as shown in FIG. 3, between the optical system 2 and the surface of the sample W to be measured, there is a spatial transmittance distribution opposite to the spatial intensity distribution of the laser light passing through the optical system 2. By interposing the neutral density filter 5, the high intensity portion near the optical axis is transmitted with low transmittance, and the peripheral low intensity portion is transmitted with high transmittance. The laser light directed to the measurement sample W can be made to have a uniform intensity.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the structure of an embodiment of the present invention. The output light from the semiconductor laser 1, which is a laser light source, is
An optical system 2 including a collimator lens 21 and a beam expander 22 composed of two cylindrical lenses 22a and 22b is used to spread the light in a one-dimensional manner in the vertical direction in the drawing, which is the displacement direction to be measured, and The surface of the measurement sample W is irradiated in a line shape. The scattered light from the surface of the sample W to be measured of the irradiation light of the one-dimensional image sensor 3 of a plurality of channels in which each channel is arranged by the condenser lens 3a along the up-down direction which is also the displacement direction to be measured. An image is formed on the light receiving surface. Note that, in FIG. 1, the image sensor 3 is shown in a tilted manner for the sake of simplification of description.
Is parallel to the surface of the sample W to be measured, and each channel thereof extends in the displacement direction to be measured, and is arranged at a predetermined angle with respect to the irradiation light in the direction orthogonal to the drawing.

Outputs from the respective channels of the image sensor 3 are taken into the arithmetic unit 4 including an AD converter and mainly composed of a computer every moment. In the calculation unit 4,
Of the output from each channel of the image sensor 3, each of a plurality of channels corresponding to two observation point regions preset on the surface of the sample W to be measured with a predetermined distance in the displacement (stretching) direction to be measured. The amount of movement of the speckle pattern at each observation point is calculated by calculating the cross-correlation function of the data from each observation point using the data of 1. The elongation between the observation points of the measurement sample W is calculated. In addition, during such a measurement operation, each time the observation point is calculated by sequentially shifting the channel used as the observation point in the movement direction each time the movement amount of the speckle pattern at each observation point reaches a specified amount. When the tracking is performed and the tracking is performed, the tracking amount is also used for the elongation calculation together with the movement amount of the speckle pattern at each observation point.

The feature of the embodiment of the present invention is that the final stage of the optical system 2 is a cylindrical lens 22.
The point is that a neutral density filter 5 whose transmittance changes depending on the position is provided between b and the sample to be measured W as described below.

That is, this neutral density filter 5 is shown in FIG.
As schematically shown in (A), for example, the metal vapor deposition film 5b is formed on one surface of the glass substrate 5a, and the metal vapor deposition film 5b is thicker toward the center and thinner toward both ends. The light transmittance of the neutral density filter 5 has a distribution such that it is lower at the center and higher at both ends, as shown in FIG. Then, the neutral density filter 5 having such a transmittance distribution is arranged so that its center is located on the optical axis of the optical system 2.

According to the embodiment of the present invention as described above, FIG.
In order to show the light intensity distribution in each part of the irradiation light shaping system and the transmittance distribution of the neutral density filter 5, the optical system 2 spreads the light in a line shape, and the optical axis is set in accordance with the output light distribution of the semiconductor laser 1. The laser light having a Gaussian distribution-like intensity distribution at the center is converted into a linear laser light having an almost uniform intensity by passing through the neutral density filter 5. As a result, the light scattered by the surface of the sample W to be measured also has a spatially substantially uniform intensity distribution, and the output of each channel of the image sensor 3 that receives this is the baseline as illustrated in FIG. Becomes almost uniform, and a signal representing a speckle pattern is obtained with good contrast over the entire area without causing saturation or the like.

The thickness of the metal vapor deposition film 5b of the neutral density filter 5 does not necessarily have to change smoothly as shown in FIG. 2, but changes stepwise as shown in FIG. 5 (A). In this case, the light transmittance distribution as shown in FIG. 7B is obtained. However, even with such a light transmittance distribution, the saturation of the output of the image sensor 3 is eliminated and all channels are used. The object of the present invention to obtain a signal representing a speckle pattern with sufficient contrast can be achieved. For example, as shown in FIG. 1C, the metal vapor deposition film having such a gradual thickness has a vapor deposition mask 100 separated from the glass substrate 5a by a predetermined distance with respect to the surface normal of the substrate 5a. The metal may be vapor-deposited from two directions inclined by a predetermined angle.

Further, in the above embodiment, the case where the sample W to be measured is irradiated with the laser beam expanded in a one-dimensional manner has been described. However, the present invention irradiates the laser light expanded in a two-dimensional manner. Needless to say, the same can be applied to the case.

[0021]

As described above, according to the present invention,
A displacement meter that irradiates the sample to be measured with the output light from the laser light source in a state where it has a predetermined spread by the optical system, and obtains displacement information of the sample to be measured from the movement amount of the speckle pattern included in the scattered light. In, by providing between the optical system and the sample to be measured, a neutral density filter having a spatial light transmittance distribution opposite to the spatial intensity distribution of the light passing through the optical system,
Since the spatial intensity distribution of the laser light after spreading is made uniform over almost the entire area, the output of the image sensor that receives scattered light becomes almost uniform, and the speckle pattern should be displayed with sufficient contrast over all channels. become. As a result, a high-performance non-contact displacement meter having a wide measurement range can be obtained with a simple and inexpensive structure.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of the neutral density filter 5 (A) and an explanatory diagram of a light transmittance distribution (B).

FIG. 3 is an explanatory view of the operation of the embodiment of the present invention.

FIG. 4 is a graph showing an output example of the image sensor 3 according to the embodiment of the present invention.

FIG. 5 is a schematic configuration diagram (A) of a neutral density filter of another embodiment of the present invention, an explanatory diagram of its light transmittance distribution (B), and an explanatory diagram of an example of its manufacturing method (C).

FIG. 6 is an explanatory view of a spatial intensity distribution of irradiation light when the output light of the semiconductor laser is linearly spread by an optical system by a conventional device.

7 is a graph showing an output example of the image sensor obtained by the configuration of FIG.

FIG. 8 is an explanatory diagram of a comparative example for obtaining irradiation light having a uniform spatial intensity distribution.

FIG. 9 is an explanatory view of another comparative example for obtaining irradiation light having a uniform spatial intensity distribution.

[Explanation of symbols]

 1 Semiconductor Laser 2 Optical System 21 Collimator Lens 22 Beam Expanders 22a, 22b Cylindrical Lens 3 Image Sensor 3a Condenser Lens 4 Calculation Section 5 Dark Filter 5a Glass Substrate 5b Metallized Film

Claims (1)

[Claims] 1. An optical system for irradiating a surface of a sample to be measured with an output light from a laser light source having a predetermined spread, and receiving scattered light of the laser light from the surface of the sample to be measured. In the displacement sensor provided with an image sensor and an arithmetic means for obtaining the displacement information of the sample to be measured by calculating the moving amount of the speckle pattern included in the scattered light every moment using the output from the image sensor, Non-contact displacement characterized in that a neutral density filter having a spatial light transmittance distribution opposite to the spatial intensity distribution of light passing through the optical system is provided between the optical system and the surface of the sample to be measured. Total.