JPH08233522A - Non-contact displacement gage - Google Patents

Abstract

PURPOSE: To obtain a displacement information with resolution finer than the arranging pitch of each element of an image sensor by synthesizing two frame data by using a plurality of the frame data obtained at every movement of the image sensor. CONSTITUTION: On the surface of a sample W to be measured, the laser light from an illuminating optical system 1 is cast. An image of the scattered light from this surface is formed on the light receiving surface of an image sensor 3 by a condenser lens 2. The output of the sensor 3 is transferred into an operating part 5 including A-D converter for every data of one frame. The operating part 5 accepts the transfers of the frame data four times at time t1 -t4 . The four frame data are used, and one frame data having the space resolution of 1/4 of the arranging pitch of the elements of the sensor 3 is synthesized. In the operating part 5, the frame data having the high resolution are used, and the mutual correlation for every data, wherein a constant interval is provided, is operated. The moving amount of a speckle pattern during this period is computed.

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 is not only displacement information at one point of the sample to be measured, but also displacement amount at two points of the sample to be measured, such as elongation of a test piece in a material testing machine or the like. It also includes the amount of expansion and contraction based on it.

[0003]

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 by 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 a one-dimensional image sensor and an electric signal corresponding to the speckle pattern is obtained. The amount of movement of the speckle pattern is obtained by obtaining the signal momentarily and the cross-correlation function of the momentary signal, and the displacement information of the sample is obtained from the amount of movement of the speckle pattern.

Here, in this type of measurement using a speckle pattern, the amount of displacement of the speckle pattern at one point of the sample to be measured gives the amount of displacement at that point, and also 2 The amount of expansion or contraction between the two points can be obtained from the difference in the movement amount of the speckle pattern at the points.
Further, two laser beams are applied to the same point of the sample to be measured at an angle symmetrical to each other with the surface normal therebetween, and the difference in the amount of movement of the speckle pattern formed by each beam is obtained, or By irradiating the measurement site with one laser beam, observing the scattered light in two directions, and obtaining the difference in the amount of movement of the speckle pattern obtained in the same way at each observation point, the sample to be measured is obtained. There are various deformations as specific measurement methods, such as the amount of distortion or the amount of deformation can be obtained.

[0006]

When the scattered light from the sample to be measured is received by the one-dimensional image sensor to obtain the speckle pattern data, the spatial resolution is determined by the arrangement pitch of the elements of the image sensor. Therefore, in a displacement meter that obtains displacement information from the amount of movement of a speckle pattern, if the output of the image sensor is used as it is, the spatial resolution of the obtained displacement information will not be finer than the array pitch of each element of the image sensor. Absent. Here, the resolution can be improved up to about 10 times by interpolating the output from each element of the image sensor using Gaussian approximation or the like, but there is a limit to that.

An object of the present invention is to obtain speckle pattern data having a resolution finer than the array pitch of the respective elements of the image sensor without using interpolation, and
It is an object of the present invention to provide a non-contact displacement meter that can obtain displacement information with significantly higher resolution than the conventional displacement meter using a speckle pattern by using the interpolation together.

[0008]

In order to achieve the above object, the non-contact displacement meter of the present invention comprises means for irradiating a sample to be measured with laser light and scattered light from the sample to be measured of the laser light. An image sensor composed of a plurality of light-receiving elements and an arithmetic means for obtaining displacement information of the sample to be measured by calculating the amount of movement of the speckle pattern contained in the scattered light using the output from the image sensor. In the provided displacement meter, each time the output of one frame of the image sensor is captured, the displacement sensor has means for moving the image sensor by a distance smaller than the array pitch of the elements in the displacement direction to be measured, and the arithmetic means includes: By combining one frame data using a plurality of frame data obtained at the position for each movement and using the combined result for calculation of the movement amount, It is marked.

[0009]

When the image sensor is moved, the incident position of scattered light on the image sensor changes before and after the movement according to the amount of movement. The moving distance is determined by the arrangement pitch d of the elements.
If the distance is smaller than that, for example, d / 4, scattered light at a position displaced on the light receiving surface by the distance d / 4 is incident on each element before and after the movement.

When such a minute distance d / 4 is moved every time one frame of data is fetched, each frame data is spatially shifted by d / 4. By using such four pieces of frame data, as schematically shown in FIG. 3, frame data having a spatial resolution of ¼ of the array pitch of the elements can be obtained.

Here, the moving interval of the image sensor, in other words, the frame rate of the image sensor,
By sufficiently increasing the displacement speed of the sample to be measured, the combined frame data is hardly influenced by the displacement of the sample to be measured.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing the structure of an embodiment of the present invention. The surface of the sample W to be measured is irradiated with laser light from the irradiation optical system 1 including the semiconductor laser 1a and the cylindrical lens 1b. The scattered light of the laser light from the surface of the measured sample W is imaged on the light receiving surface of the image sensor 3 by the condenser lens 2.

The image sensor 3 is, for example, a 2000-channel one-dimensional image sensor, and the array pitch of its elements is d. The image sensor 3 is operated by a start pulse and a transfer clock supplied from the sensor driver 4, and its output is A for each frame of data under a frame rate determined according to the cycle of the start pulse. The data is transferred to the arithmetic unit 5 which includes a -D converter and is mainly composed of a computer. here,
The frame rate of the image sensor 3 is sufficiently higher than the displacement speed of the sample W to be measured.

The image sensor 3 is supported on a pedestal 7 via a so-called Roberval mechanism 6 using, for example, parallel springs, and its displacement direction is restricted only to the vertical direction which is the displacement direction of the sample W to be measured. In addition, the lower surface of the image sensor 3 is in contact with the piezo actuator 8 which is vertically displaced. Then, the piezo actuator 8 is drive-controlled by a voltage signal from a piezo driver 9 which operates according to a command supplied from the arithmetic unit 5.

In the structure described above, the piezo actuator 8 is driven by the drive voltage from the piezo driver 9 as shown in FIG.
As shown in the time chart, the transfer timings t _1, t _2, t of the frame data of the image sensor 3 to the arithmetic unit 4 are shown.
_In synchronism with _3, t _4, ..., The element is displaced upward by a distance corresponding to 1/4 of the arrangement pitch d of the elements of the image sensor 3, and after the upward displacement is repeated three times, the distance 3
The operation of displacing downward by d / 4 is repeated. As a result, the image sensor 3 moves upward by the distance d / 4 three times every time frame data is transferred, and then moves downward by 3d / 4 when transferring the next frame data. It will be.

[0016] By the above operation, the calculation unit 5 time t ₁ ~
At t ₄ , the frame data is transferred four times, but the arithmetic unit 5 uses these four frame data to arrange the array pitch d of the elements of the image sensor 3.
One frame data having a spatial resolution of 1/4 is synthesized. That is, in each frame data transferred from t _{1 to} t ₄ , the position of each element of the image sensor 3 is d /
Since the data is shifted by 4, the data from each element is combined as shown in FIG. 3 by using these four frame data, so that the space of 1/4 of the array pitch d of each element is obtained. One frame data having a resolution can be obtained. Assuming that the number of channels of the image sensor 3 is 2000 as described above, frame data consisting of 8000 channels can be obtained by the above synthesis.

Then, the calculating unit 5 calculates the cross-correlation of each data with a certain interval by using the high resolution frame data by the above composition, and calculates the movement amount of the speckle pattern during this period. To do. This calculation result represents the displacement information of the irradiation position of the laser beam of the measured sample W. The displacement information thus obtained has a spatial resolution of d / 4, even though the array pitch of the elements of the image sensor 3 is d. Further, by further interpolating the frame data synthesized as described above, displacement information having a spatial resolution of about d / 40 can be obtained.

The present invention, in addition to the above-mentioned embodiments,
As an embodiment of means for moving the image sensor each time the output of one frame of the image sensor is captured, a displacement sensor for detecting displacement of the image sensor is separately provided, and a closed sensor using the output of the displacement sensor is provided. Under the loop control, a mode of controlling the movement of the image sensor, further, in place of the displacement sensor, among the channels of the image sensor, using an extra plurality of channels not used for receiving scattered light, Irradiate light from a fixed light source to these channels,
The output of each channel is interpolated to calculate the peak position of the irradiation light, and the movement of the image sensor is controlled based on the closed loop control using the calculation result as the detection result of the position of the image sensor. Aspects can be adopted.

By adopting such a closed loop control, the amount of movement of the image sensor can be made more accurate, and the displacement information of the measured sample W can be made more accurate.

FIG. 4 and FIG. 5 are schematic configuration diagrams of essential parts showing an example in which the movement of the image sensor 3 is controlled by the closed loop control. In the example of FIG. 4, the displacement sensor 10 is fixed to the gantry 7, the position of the image sensor 3 is detected by this displacement sensor 10, and the detection output is fed back to the piezo driver 9 via the amplifier 11. In this configuration, the resolution of the displacement sensor 10 is set sufficiently higher than the array pitch d of the elements of the image sensor 3 so that the image sensor 3 is a very small amount such as 1/10 of the array pitch d of the elements. It becomes possible to move accurately one by one, and the spatial resolution after combination is greatly improved.

The example of FIG. 5 is an example in which the image sensor 3 is moved under the closed loop control without providing a separate displacement sensor as described above. That is, of the channels of the image sensor 3, an extra tens of channels that are not used for receiving scattered light from the sample W to be measured are used as a channel group for displacement monitoring so as to straddle the plurality of channels. Light from a light source 12 such as a fixed LED or semiconductor laser is emitted. Then, the output of the channel group for displacement monitoring is calculated by the calculation unit 5
The light source 12
The peak position of the irradiation light from is calculated. Since this peak position can be detected by interpolation with a resolution of about 1/10 of the arrangement pitch d of the elements of the image sensor 3, the change in the peak position is detected by the piezo driver 9 as the displacement detection result of the image sensor 3. I have feedback.
With such a configuration, the amount of movement of the image sensor 9 can be made more accurate than in the case of open loop control.

In each of the above examples, the spatial resolution is improved by moving the image sensor by a small amount. In this case, the moving distance is set to the array pitch d of the elements.
When 1 / N is set, the combined frame data to be used in the calculation of the correlation function is obtained every time the actual frame data is sampled N times. This means that when the frame rate of the image sensor is constant, the time resolution is reduced to 1 / N as compared with the conventional displacement meter of this type which directly uses the actual frame data for the calculation of the correlation function. To do. It can be a problem when it is necessary to catch high-speed phenomena moment by moment.

Therefore, as an application of the technical idea of the present invention, scattered light to be incident on the image sensor is separated and guided by a beam splitter in a plurality of directions, and the separated scattered light is arranged in each direction. While receiving light with an individual image sensor, each image sensor is arranged with respect to each scattered light after separation, shifted by a distance smaller than the array pitch of each element in the displacement direction to be measured,
It is possible to adopt a configuration in which the frame data of each image sensor is combined in the same manner as in the above example, and is used to calculate the movement amount of the speckle pattern. FIG. 6 schematically shows a configuration example of the main part. In FIG. 6, the displacement direction of the sample W to be measured is a direction orthogonal to the paper surface, and the elements of the image sensors 3a to 3c are arranged in that direction.

The scattered light from the sample W to be measured is reflected by the lens 20.
After being converted into a substantially parallel light beam by the beam splitter 21, the beam splitter 21 splits the beam into a straight beam and a beam bent by 90 °. And the light flux that goes straight
Further, the beam splitter 22 splits the beam into a straight type and a 90 ° type. Then, the light fluxes thus divided into three are imaged on the light-receiving surfaces of the individual image sensors 3a, 3b, 3c of the same type by the condenser lenses 2a, 2b, 2c, respectively.

The image sensors 3a, 3b, 3c are arranged in the direction corresponding to the displacement direction of the sample W to be measured with respect to the incident light, that is, in the example shown in FIG. , 3b, 3c are arranged at intervals of ⅓ of the arrangement pitch d of the elements.

With the above arrangement, the scattered light from the sample W to be measured is simultaneously received by the three image sensors 3a, 3b and 3c, and the frame data simultaneously output from each of these image sensors is the image sensor. Since the positions of the respective elements 3a, 3b, 3c are data deviated by d / 3 in the direction corresponding to the displacement direction to be measured, based on the idea equivalent to the above-described combining method of FIG.
By combining these three frame data, one frame data having a spatial resolution of ⅓ of the arrangement pitch d of each element can be obtained. By providing the frame data synthesized in this way for the calculation of the correlation function, it is possible to obtain the same operational effect as the above-mentioned respective examples.

Moreover, a point to be noted in this configuration is that frame data whose positions are relatively displaced by a distance smaller than the arrangement pitch of the elements of the image sensor can be obtained at the same time. Therefore, according to this configuration, each time one actual frame data is transferred from each of the image sensors 3a to 3c, frame data having a resolution smaller than the array pitch of the elements can be combined, and the time resolution can be improved. There is an advantage that it does not decrease.

Although FIG. 6 shows an example in which scattered light is separated in three directions and received by three image sensors, the number of separated and image sensors is arbitrary, and the number of image sensors used is n. If the array pitch of the elements is d,
By relatively shifting these image sensors by d / n, it is possible to achieve the same effects as the above.

[0029]

As described above, according to the present invention,
The image sensor for receiving the scattered light from the sample to be measured and obtaining the speckle pattern data has a distance smaller than the array pitch of the elements in the displacement direction to be measured each time the output for one frame is taken into the calculation unit. By moving each one, and combining one frame data by using a plurality of frame data obtained at each position of movement, to obtain speckle pattern data having a spatial resolution higher than the array pitch of the elements and combine the data. Since the amount of movement of the speckle pattern is calculated using the subsequent data, it is possible to obtain displacement information with a resolution finer than the array pitch of each element of the image sensor, which is commonly used in conventional displacement gauges of this type. By using this together with the interpolation calculation, it is possible to obtain displacement information with significantly higher resolution than before.

[Brief description of drawings]

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

FIG. 2 is a time chart showing the operation timing of each part of the embodiment of the present invention.

FIG. 3 is a schematic explanatory view of a method of synthesizing frame data according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a main part of another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a main part configuration of still another embodiment of the present invention.

FIG. 6 is a schematic diagram showing a main part configuration of still another embodiment of the present invention.

[Explanation of symbols]

 1 Irradiation optical system 1a Semiconductor laser 1b Cylindrical lens 2 Condenser lens 3 Image sensor 4 Sensor driver 5 Calculation unit 6 Roberval mechanism 7 Stand 8 Piezo actuator 9 Piezo driver

Claims (1)

[Claims] 1. A means for irradiating a sample to be measured with a laser beam, an image sensor comprising a plurality of elements for receiving scattered light of the laser beam from the sample to be measured, and an output from the image sensor are used. In a displacement meter provided with a calculation means for obtaining displacement information of a sample to be measured by calculating the amount of movement of a speckle pattern contained in scattered light every moment,
Each time the output of one frame of the image sensor is fetched, the image sensor has means for moving in the displacement direction to be measured by a distance smaller than the array pitch of the elements, and the computing means has a function for each movement. A non-contact displacement meter, characterized in that a plurality of pieces of frame data obtained at a position are used to combine one piece of frame data and the combined result is used for calculating the movement amount.