JPH0835821A - Non-contact displacement or strain gauge - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a non-contact displacement or strain gauge capable of performing accurate measurement by suppressing an increase in the background level of an optical sensor even when measuring a high temperature sample. [Structure] An optical system 1 for irradiating a measured sample W in a spot shape, an optical sensor 2 for injecting reflected light of the spot irradiation light by the measured sample W, and an output of the optical sensor 2 for measured sample In a device provided with a calculation unit 3 for calculating the displacement or strain of W, a condenser lens 4 for condensing the reflected light of the irradiated light from the measured sample W between the measured sample W and the optical sensor. By providing the light-shielding plate 5 with the pinhole 51 formed therein, arranging the pinhole 51 on the spot image forming surface of the light reflected by the condenser lens 4 and making the hole diameter equivalent to the spot image, Radiation light or the like from the surface of the sample W to be measured excluding the irradiation position is prevented from entering the optical sensor 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called non-contact type displacement or strain gauge for measuring displacement or strain of a sample by using light such as laser light in a non-contact manner. The present invention relates to a non-contact type displacement or strain gauge suitable for measuring the amount of expansion and contraction of a test piece.

[0002]

2. Description of the Related Art A device for irradiating a sample to be measured with light such as laser light and measuring the reflected light with a one-dimensional image sensor or the like to measure the displacement or strain of the sample to be measured in a non-contact manner. It is known to use a speckle pattern.

The measurement principle of the displacement or strain gauge using such a speckle pattern is as follows. As shown in FIG. 6, when the surface of the sample W to be measured is irradiated with laser light, the light field observed at any one point on the observation surface is a large number of light waves reflected from different locations on the sample surface. Are caused by interference with each other. Since the phases of these light waves are random, reflecting the irregularities of the irregularities on the sample surface, the intensity distribution of light on the observation surface, which is the result of interference, is also random. This pattern is called a speckle pattern. When, for example, a one-dimensional image sensor is placed on the observation surface, the output from each pixel has a spatially random pattern, and when the sample surface moves or deforms, the pattern moves or deforms over time. It is possible to obtain the movement amount of the speckle pattern every moment by taking the photoelectric conversion signal of the speckle pattern obtained by placing the image sensor on the observation surface with time and obtaining the correlation function every moment. From the amount of movement of the speckle pattern, the amount of deformation or strain of the sample to be measured at the laser beam irradiation site can be calculated (for example, Japanese Patent Publication No. 59-52963).

Further, the inventor of the present invention utilizes such a speckle pattern to measure the displacement at two points in the strain direction of the sample to be measured, and from the respective measurement results, the two of the sample to be measured are measured.
We have proposed a device that calculates the amount of strain (elongation or contraction) between points to obtain the amount of elongation or contraction between the gauge marks of the test piece of the material testing machine. In this proposal, in order to measure at two points in the strain direction of the sample to be measured individually, the two points are irradiated with laser light having different wavelengths, and each reflected light is provided correspondingly. Corresponds to the vicinity of the incident surface of each image sensor to prevent the reflected light from one irradiation position from entering the image sensor for measuring the reflected light from the other irradiation position when the light is received by the sensor. The configuration is such that a bandpass filter that transmits light of the wavelength is provided.

[0005]

By the way, when a high temperature sample is measured by using the non-contact type displacement or strain gauge utilizing the speckle pattern as described above, the radiation of the sample itself causes the band pass, for example. Even if a filter is interposed, the background level of the image sensor rises, making measurement difficult.

That is, as shown in FIG. 7, in the image sensor on the observation surface, not only the reflected light of the spot-shaped laser light (shown by the solid line) but also the other of the sample W to be measured as shown by the broken line is measured. Light such as radiation from the position also arrives. Although such light does not interfere with the laser light, the background level of the image sensor greatly increases when the sample W to be measured is heated to a high temperature. Further, in a material test in which a sample is heated using an infrared heating furnace, a lamp light source for heating raises the background level.

When the background level of the sensor rises, the average output level of the sensor rises, and eventually the upper limit of the dynamic range of the sensor is reached and measurement becomes impossible.

In order to deal with such a problem, it is effective to narrow the band width of the bandpass filter provided in the preceding stage of the image sensor, but not only the filter becomes expensive, but also the oscillation wavelength of the laser and the bandpass filter. Since it is necessary to match the center wavelength of the filter, more precise wavelength control is required. Furthermore, depending on the heating temperature of the sample, no matter how narrow the bandwidth of the bandpass filter, the wavelength of the radiation from the sample surface The wavelengths of the laser beams may overlap, and in the end, the background level may not decrease.

Further, for the purpose of reducing the average output level of the sensor, an ND filter is arranged on the incident surface of the sensor to reduce the total amount of light incident on the sensor and prevent its output from being saturated. However, in this case, the signal strength is also attenuated,
Accurate measurement will not be possible.

The present invention has been made in view of the above circumstances, and a non-contact displacement or strain gauge capable of performing accurate measurement by suppressing an increase in the background level of the image sensor even when measuring a high temperature sample. The purpose is to provide.

[0011]

In order to achieve the above object, the non-contact displacement or strain gauge of the present invention irradiates a sample W to be measured in a spot shape as shown in FIG. An optical system 1, an optical sensor 2 that receives reflected light of the spot irradiation light from the measured sample, and an arithmetic unit 3 that calculates the displacement or strain of the measured sample W using the output of the optical sensor 2 are provided. In the device, the sample W to be measured and the optical sensor 2
And the light-shielding plate 5 in which the pinhole 51 is formed and the condenser lens 4 that condenses the reflected light of the irradiation light from the sample W to be measured are arranged. It is characterized in that it is placed on the spot image plane of the reflected light by and has a hole diameter equivalent to that of the spot image.

[0012]

As shown in FIG. 2, the spot light from the irradiation optical system 1 is reflected by the sample W to be measured, is condensed by the condenser lens 4, and is once imaged at a position corresponding to the focal length of the lens 4. To be done. By providing a pinhole 51 having a hole diameter equivalent to that of the focused spot image on the imaging surface, and guiding only the light passing through the pinhole 51 to the sensor 2, the sample surface other than the laser spot irradiation position Light from does not reach the sensor 2. That is, the measured sample W
Only the radiation within the laser spot is incident on the sensor 2, and the background level can be reduced without attenuating the signal of the speckle pattern.

[0013]

FIG. 1 is a schematic diagram showing the overall structure of an embodiment in which the present invention is applied to a displacement meter.

The sample W to be measured is irradiated with spot-like laser light from the irradiation optical system 1 including the semiconductor laser 11 and the lens 12. The reflected light of the laser light from the surface of the measured sample W is received by the one-dimensional image sensor 2 for obtaining a signal according to the speckle pattern. Then, the output from the one-dimensional image sensor 2, that is, the speckle pattern data, is taken into the arithmetic unit 3 every moment. The calculation unit 3 obtains the amount of movement of the speckle pattern by obtaining the cross-correlation function of the speckle pattern data from the one-dimensional image sensor 2 with time, and the measured amount at the laser light irradiation position by a known method. Calculate the displacement of the sample.

Between the one-dimensional image sensor 2 and the sample W to be measured, a condenser lens 4 for collecting the laser light reflected by the sample W to be measured, and a pinhole 51.
The light-shielding plate 5 having the is arranged. The position where the pinhole 51 is provided is the image forming position of the spot-shaped laser light reflected from the surface of the sample W to be measured, and the hole diameter is the same as the size of the imaged spot image.

According to the above-described embodiment of the present invention, the light incident on the one-dimensional image sensor 2 is only the light from the surface irradiated with the laser spot from the irradiation optical system 1.
That is, as shown in FIG. 2 which is an explanatory view of the operation of the optical system in FIG. 1, after the laser light from the irradiation optical system 1 is irradiated in spots on the surface of the sample W to be measured as shown by the solid line in the figure. , Is reflected by the surface of the sample W and enters the condenser lens 4. The distance between the surface of the sample W to be measured and the condenser lens 4 is A
And the focal length of the condenser lens 4 is f, the laser light reflected by the sample W to be measured enters the condenser lens 4 and then the distance B = fA / (A−f) from the condenser lens 4.
Connect the spot image to the position. A pinhole 51 having a hole diameter equivalent to that of the spot image is formed at the position where the spot image is formed.
Are arranged, the one-dimensional image sensor 2
All of the laser spot image and light (radiation light or the like) from the surface of the measured sample W at the irradiation position of the laser spot are incident. On the other hand, the light emitted from the surface of the measured sample W other than the laser spot irradiation position does not pass through the pinhole 51 but is shielded from light, although a part of the light is incident on the condenser lens 4 as shown by the broken line in the figure. It is blocked by the plate 5 and does not enter the one-dimensional image sensor 2.

Therefore, when the sample W to be measured is heated at a high temperature, even if a large amount of energy is radiated from the surface of the sample W to be measured, of the radiation from the surface of the sample W to be measured, a laser spot is generated. Since the light is blocked by the light shielding plate 5 except for the light from the irradiation position of 1 and does not enter the one-dimensional image sensor 2, the background level hardly rises and the reflected light of the laser light as the signal light can be attenuated. Absent.

Here, the irradiation optical system 1 and the detection optical system including the one-dimensional image sensor 2 can be housed and used in a common housing 10 as illustrated in FIG. 3, for example. , Between the condenser lens 4 and the sample W to be measured,
It is also possible to interpose a bandpass filter 9 that selectively passes the output wavelength of the semiconductor laser 11.

In the above embodiment, the reflected light of the laser light from the irradiation optical system 1 was observed by one image sensor 2 at one location to obtain the displacement. It goes without saying that the present invention can also be applied to a device for obtaining the amount of distortion at the laser spot irradiation position of.
That is, the reflected light from the sample to be measured W is observed at two points and the difference in the movement amount of the speckle pattern at each observation position is obtained, or the surface normal is sandwiched with respect to the same point of the sample to be measured W. By irradiating two laser beams at mutually symmetric angles with each other and obtaining the difference in the movement amount of the speckle pattern formed by each beam, the strain amount of the sample W to be measured is extracted from the movement amount of the speckle pattern. be able to. Even when measuring such distortion amount, the background level is lowered by interposing a condenser lens and a light shielding plate having a pinhole as shown in FIG. 1 in front of the image sensor for detecting the speckle pattern. As a result, accurate measurement is possible even in measurement at high temperature.

Further, according to the present invention, not only the displacement or strain at one point of the sample W to be measured as described above, but also an extensometer for measuring the elongation between two points of the sample W to be measured (between two points) is measured. It can also be applied to measurement of strain amount).

FIG. 4 is a schematic diagram showing the overall structure.
In this example, two sets of the irradiation optical system and the detection optical system which are exactly the same as those in the example of FIG.
Calculate the amount of movement of the speckle pattern at the location,
The difference between the two points of the measured sample W is calculated from the difference.

Both ends of the sample to be measured W are fixed to, for example, a grip of a material testing machine, and a vertical tensile load is applied. The sample W to be measured is irradiated with laser light having wavelengths different from each other at two positions separated by a predetermined distance in the acting direction of the load. That is, the semiconductor laser 11a having the output wavelength λ _1, the lens 12a, and the mirror 13a.
Is provided, and a second irradiation optical system 1b including a semiconductor laser 11b having an output wavelength λ _2, a lens 12b, and a mirror 13b is provided, and a spot laser beam from these is measured. The surface of the sample W is irradiated at positions vertically separated from each other by a distance L.

Reflected light of each of the laser lights of λ ₁ and λ ₂ by the sample W to be measured is provided in a corresponding manner.
Individually measured by a set of detection optics. Each of the detection optical systems is equivalent to that of the example of FIG. 1, and includes a condenser lens 4a or 4b and a pinhole 51a or 51b.
Light-shielding plate 5a or 5b provided with 1 placed behind it
It consists of a three-dimensional image sensor 2a or 2b,
In this embodiment, filters 6a and 6b for selectively passing light of wavelength λ ₁ or λ ₂ between the condenser lenses 4a and 4b and the mirrors 13a and 13b.
Is arranged. Due to the presence of the filters 6a and 6b, the laser light from the one irradiation optical system corresponding thereto is selectively incident on one detection optical system,
The influence of the laser light from the other irradiation optical system does not affect, and it becomes possible to detect the speckle pattern from each irradiation position independently.

Outputs from the respective one-dimensional image sensors 2a and 2b are respectively provided to the A / D converter 31a.
And digitized by 31b, the correlation functions are obtained by the respective correlators 32a and 32b, respectively, whereby the movement amount of the speckle pattern at the irradiation position of each laser beam is obtained. The outputs of the correlators 32a and 32b are input to the calculator 33. The calculator 33 calculates the difference between the movement amounts of the speckle patterns calculated by the correlators 32a and 32b. When the difference in the amount of movement of each speckle pattern is taken, the information regarding the amount of strain of the sample W to be measured included in each amount of movement is substantially canceled, and the sample W to be measured between the irradiation positions of the laser beams. The amount of elongation can be calculated.

Here, in the configuration of FIG. 4, the respective condenser lenses 4a and 4b are provided for the purpose of improving the condenser efficiency.
When a lens having a large NA is used, the lens aperture becomes large and there is a risk of interference with an adjacent light receiving system. In such a case, as shown in FIG.
It is possible to adopt a configuration in which a condensing lens 40 common to the two detection optical systems is provided and both of the laser beams reflected from the respective irradiation positions are condensed by the condensing lens 40.
With this configuration, the reflected light of the irradiation light to the upper side of the measured sample W is imaged on the lower detection optical system, and the reflected light of the lower irradiation light is imaged on the upper detection optical system. In this case, the bandpass filters 6a and 6b are respectively provided with the light shielding plate 5a.
Alternatively, it may be interposed between 5b and the one-dimensional image sensor 2a or 2b.

As an embodiment of the present invention, a moving mechanism for displacing one or both of the condenser lens and the pinhole along the measurement optical axis is provided to change the distance between them. It is possible to adopt a configuration in which the control mechanism is provided to automatically change the distance so as to maximize the output of the one-dimensional image sensor.

That is, in all the embodiments of the present invention described above, a moving mechanism for changing one or both of the condenser lens and the pinhole along the measurement optical axis is provided, and the moving mechanism is a control mechanism. It is configured so that the distance between the two can be appropriately changed by controlling by. If the control mechanism operates so as to appropriately change the distance between the condenser lens and the pinhole (light-shielding plate) so that the output of the one-dimensional image sensor is maximized,
Even when the distance between the measurement optical system and the sample changes when the sample to be measured is attached, this can be automatically adjusted to perform measurement in the optimum state. That is, the output of the one-dimensional image sensor changes depending on the state of focus of the image on the pinhole, and the sensor output becomes maximum when the image is accurately formed on the pinhole. Therefore, if the output of the one-dimensional image sensor is monitored and the distance between the pinhole and the condenser lens is automatically adjusted so that the output is maximized, the sample position will always be slightly displaced for each measurement. Optimal measurement is possible. This technique can also be applied when assembling the device. In this case, the assembly and adjustment can be facilitated by appropriately adjusting the positions of the condenser lens and the pinhole with respect to the one-dimensional image sensor with the sample placed at the reference position.

Further, according to the present invention, the laser spot shape is not limited to a circular shape, but may be an elliptical shape, a rectangular shape or the like, and the same effect can be obtained by appropriately selecting the shape of the pinhole. be able to.

[0029]

As described above, according to the present invention,
The reflected light from the sample to be measured is once formed into a spot image by a condenser lens, and a pinhole having a hole diameter equivalent to that of the spot image is arranged at the spot of the spot image and passed through the pinhole. Since the light is guided to the sensor, only light (reflected light and radiated light) from the irradiation position of the spot light from the irradiation optical system is incident on the sensor, and light from other positions is incident on the sensor. No radiant light is incident. Therefore, even when the sample to be measured is heated to a high temperature, the background level caused by radiation from the sample to be measured or the heater for heating hardly increases, and the signal level is not particularly lowered. Accurate measurement is possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the overall configuration of an embodiment in which the present invention is applied to a displacement meter.

FIG. 2 is an explanatory diagram of the operation of the optical system.

FIG. 3 is an explanatory diagram of a specific configuration example of the optical system according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing an overall configuration of an embodiment in which the present invention is applied to an extensometer.

FIG. 5 is a schematic diagram showing a configuration of a main part of another embodiment in which the present invention is applied to an extensometer.

FIG. 6 is an explanatory diagram of the principle of a displacement or strain gauge using a speckle pattern.

FIG. 7 is an explanatory diagram of a problem that occurs when a sample to be measured is heated in a displacement or strain gauge using a speckle pattern.

[Explanation of symbols]

 1 Irradiation optical system 11 Semiconductor laser 12 Lens 2 1-dimensional image sensor 3 Calculation part 4 Condenser lens 5 Light-shielding plate 51 Pinhole W Measured sample

Claims (1)

[Claims] 1. An optical system for irradiating a sample to be measured in a spot shape, an optical sensor for injecting reflected light of the spot irradiation light by the sample to be measured, and displacement of the sample to be measured using the output of the optical sensor. In a device including a calculation unit for calculating the strain, a condenser lens that condenses the reflected light and a light shielding plate having a pinhole are arranged between the sample to be measured and the optical sensor, and The non-contact displacement or strain gauge is characterized in that the pinhole is provided on a spot image forming surface of the reflected light by the condenser lens and has a hole diameter equivalent to that of the spot image.