JPH08271231A - Non-contac displacement gage - Google Patents

Abstract

PURPOSE: To provide a non-contact displacement gage wherein the accumulation of error that follows updating of reference data is significantly reduced, even if the frequency in update of the reference data increases, in the case of repeated displacement of one area instead of displacement in a single direction. CONSTITUTION: Multiple reference data are stored in a storage means 7, and, when moving amount of speckle pattern calculated by a calculation means 6 reaches specified amount so that the updating of reference data is needed, such reference data among the past reference data in the storage means 7 as is close to current sampling data is selected and taken again as reference data, thus the error that follows updating of reference is not accumulated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement meter for obtaining displacement information of a sample to be measured without contact by using a speckle pattern obtained by irradiating the surface of the sample to be measured with laser light. . The displacement information referred to in the present invention means, in addition to displacement information at one point of the measured sample, elongation based on the amount of displacement at two points of the measured sample, such as elongation of a test piece in a material testing machine or the like. Including the amount of shrinkage.

[0002]

2. Description of the Related Art There is known a method of measuring displacement information 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.

When the displacement information is obtained by using such a speckle pattern, basically, the scattered light of the laser light from the surface to be measured of the sample to be measured is photoelectrically converted by an image sensor to obtain the speckle pattern. , And the cross-correlation function of the signals is obtained, so that the movement amount of the speckle pattern is obtained, and the displacement information of the measured sample is obtained from the movement amount of the speckle pattern. Further, by using such a principle, the amount of movement of the speckle pattern at two points of the sample to be measured is individually calculated and the difference between them is calculated.
The amount of elongation or contraction of the sample to be measured between the two points can be obtained, and can be used for measuring the elongation of the test piece of the material testing machine.

By the way, in this type of displacement meter, the calculation of the cross-correlation function is specifically performed by using the speckle pattern data sampled at a certain time as reference data and the reference data and every moment thereafter. The cross-correlation function with the speckle pattern data is calculated. From the change in the peak position of each cross-correlation function,
The amount of movement of each subsequent speckle pattern with respect to the speckle pattern used as the reference data is obtained. Therefore,
The amount of movement of each speckle pattern serves as information indicating the amount of displacement of the measured sample that occurs between the reference data sampling time point and each subsequent data sampling time point.

Here, the peak intensity of the cross-correlation function becomes lower as the amount of movement of the speckle pattern at the present time with respect to the reference data increases, and when the speckle pattern moves beyond a certain limit, the cross-correlation is increased. It becomes impossible to search the peak position of the function. Therefore, conventionally, when the movement amount of the speckle pattern calculated based on the reference data reaches a specified amount, instead of the reference data until then, the data at that time is newly stored as reference data, A so-called reference data update operation is performed, and thereafter, an operation using the updated reference data is performed. In this case, of course, each time the reference data is updated, the mutual positional relationship between the reference data before and after the update is added as the displacement information of the measured sample.

[0006]

When updating the reference data, when the positional relationship between the reference data before and after the updating is added to the displacement information of the sample to be measured, the resolution of the positional relationship is, of course, this displacement meter. Therefore, it cannot be denied that some errors are theoretically accumulated every time the reference data is updated.

Such an error caused by updating the reference data does not cause any problem when the number of updates is small, such as elongation measurement in a tensile test of a metal material or the like. When measuring the displacement information of the test piece in the test, the measurement time will be longer than in the normal tensile test, and if it is necessary to update the reference data many times during that time, update the reference data. Accumulation of error due to cannot be ignored.

For example, when the displacement information of the fatigue test piece is obtained by using a non-contact displacement meter that needs to update the reference data every time the displacement amount of the sample to be measured becomes 0.5 mm, the test piece under repeated load is used. The amplitude of ± is ±
It is not necessary to update the reference data within the range of 0.5 mm, but if the amplitude exceeds it, as shown by the black circles in the same figure (B), four times for each cycle of repeated load. It is necessary to update the reference data. In this case, even if an error of, for example, 1 μm at maximum occurs each time the reference data is updated, if the number of load repetitions required for the test is 10 ⁶ , the reference data update frequency is 4 × 10 ⁶ , and the cumulative error is The amount cannot be ignored.

The present invention has been made in view of the above circumstances, and even if the frequency of updating the reference data is extremely high, especially when the displacement information of the test piece in the fatigue test is obtained, the frequency of updating the reference data increases accordingly. The purpose of the present invention is to provide a non-contact displacement meter that can significantly reduce the accumulated error amount.

[0010]

A structure for achieving the above object will be described with reference to FIG. 1 which is an embodiment drawing. In the non-contact displacement meter of the present invention, a sample W to be measured is irradiated with a laser beam. And a laser light irradiation optical system 1 for irradiating the laser light, an image sensor 2 for receiving the scattered light of the laser light by the surface of the sample W to be measured, and detecting a speckle pattern included in the scattered light, and an image sensor thereof. The output of 2 is used to calculate the cross-correlation function between the speckle pattern data detected at a predetermined time and the speckle pattern data detected at another time, thereby moving the speckle pattern during that time. The speckle pattern used as reference data when the amount of movement of the speckle pattern reaches the specified amount while obtaining the displacement information of the measured sample by obtaining the amount. In displacement meter having an arithmetic means 6 for updating over data, provided with a storage unit (reference data memory) 7 for storing a plurality of reference data, calculating means 6
Is configured to select, from the plurality of reference data stored in the storage means 7, data close to the latest speckle pattern when updating the reference data, and use the selected data as subsequent reference data. It is characterized by

[0011]

The calculating means 6 updates the reference data used up to that point at the time when the movement amount of the speckle pattern reaches the specified amount, which is the same as the conventional method. , Instead of simply using the latest speckle pattern data as the reference data, a plurality of reference data stored in the storage means 7 is searched for data close to the latest speckle pattern, and the data is newly referenced. Adopt as data.

That is, when the sample W to be measured does not monotonically displace in one direction, but when the sample W to be measured vibrates within a certain range like a test piece in a fatigue test,
In a state in which the speckle pattern data at some positions within the range are stored in the storage means 7, when the reference data needs to be updated, some of them are close to the sampling data. If the operation of selecting such data and adopting it as reference data is repeated, the accumulated amount of error due to the update of reference data is significantly larger than that when the latest speckle pattern data is newly captured as reference data. Less.

[0013]

FIG. 1 is a schematic diagram showing the overall construction of an embodiment of the present invention. The laser light irradiation optical system 1 includes a semiconductor laser 1a,
A state in which the output laser light from the semiconductor laser 1a is linearly extended in the vertical direction in the figure, which is the displacement measurement direction, is configured by a beam expander including a collimator lens 1b and two cylindrical lenses 1c and 1d. Then, the surface of the sample W to be measured is irradiated.

The scattered light of the irradiation laser light from the surface of the sample W to be measured is imaged on the light receiving surface of the image sensor 2 by the condenser lens 2a. The image sensor 2 has a plurality of pixels, for example, 2000 pixels, which are arranged in a line.
In the 0-channel 1-dimensional image sensor, the pixels are arranged in the vertical direction, which is the displacement measurement direction.

The output of the one-dimensional image sensor 2 is amplified by the amplifier 3 and then digitized by the A / D converter 4, and the data for one frame, that is, the data for all channels is temporarily stored at a predetermined frame rate. It is stored in the sampling data memory 5.

The calculation unit 6 includes a sampling data memory 5
Each time the frame data is stored in, the data of a part of the data of each channel for a preset number of consecutive channels is used as the observation area data, and the initial one is used as the initial reference. Then, based on the program described later, the cross-correlation function with the observation area data (hereinafter, this data will be referred to as sampling data) that is sampled at every moment is calculated to calculate the amount of movement of the speckle pattern at every moment. Then, the reference data is updated by a method which will be described in detail later every time the movement amount of the speckle pattern reaches a specified amount and the correlation strength decreases.

The reference data used for the calculation of the cross-correlation function by the calculation unit 6 is stored in the reference data memory 7,
An area for storing a plurality of reference data is set in the reference data memory 7, and as shown below, each time the latest sampling data is newly set as reference data, the reference data is stored together with position information. Further, each of the stored reference data is adapted to be used as the reference data again when the reference data is updated if there is data satisfying a certain condition.

FIG. 2 is a flow chart showing the contents of the arithmetic operation by the arithmetic unit 6, and FIG. 3 is a graph showing an example of the situation of displacement of the sample W to be measured with time which appears in a fatigue test or the like. The operation of the embodiment of the present invention will be described with reference to these drawings.

When a measurement start command is given, the sampling data at that time is stored in the reference data memory 7 as reference data of the origin (ST1). This reference data is indicated by A in FIG. Then, calculate the cross-correlation function of the sampling data and the reference data every moment,
The amount of movement of the speckle pattern in the observation area is obtained from the position of the correlation peak and used as displacement information (ST
2).

When the amount of displacement of the sample to be measured W reaches a prescribed amount and the correlation strength decreases, it is necessary to update the reference data (ST3). At the time of updating the reference data, the sampling data at the present time is used as the reference data. Or whether the data already stored in the reference data memory 7 is used again as the reference data (ST
4). If there is no close data, the sampling data at that time is adopted as reference data and stored as reference data in the reference data memory 7 together with its position information (ST5). If there is close data, the stored data is stored. Is adopted again as reference data (ST
6).

That is, since only the reference data corresponding to the origin is stored in the reference data memory 7 at the beginning of the measurement, when the reference data is updated for the first time, for example, as shown by B in FIG. The sampling data at that time is stored in the reference data memory 7 as new reference data. At this time, the position information L1 of the data is also stored (ST5). After the reference data is updated, the displacement amount of the sample W to be measured from the origin A calculated in ST2 is the movement amount of the speckle pattern obtained by the calculation of the cross-correlation function between the sampling data and the updated reference data. And the position information of the updated reference data. That is, in the state where the sampling data at the position indicated by B in FIG. 3 is used as the reference data, the displacement amount of the point indicated by C is the specification obtained by the cross-correlation function of the sampling data at C and the reference data. It is the sum of the movement amount L2 'of the pattern and the position information L1 of the reference data fetched in B. Here, assuming that the error of the position information of the new reference data is e1, the displacement amount of C is L1 + e1 + L2 '... (1).

The displacement of the sample W to be measured increases as shown by D in FIG. 3, and the moving amount of the speckle pattern with respect to the reference data in the sampling data in B reaches the specified amount again and the reference data needs to be updated. In this case as well, since there is no data close to this in the reference data memory 7 as in the above case, the sampling data at that time is stored as new reference data in the reference data memory 7 together with its position information L2. After that, the calculation using the reference data is performed. For example, when the sample W to be measured is displaced to a position indicated by E in FIG. 3, the displacement amount is the movement amount of the speckle pattern with respect to the reference data L3 ′,
When the position information of the reference data captured at the point D with respect to the point B is L2 and the error is e2, the actual displacement amount of the measured sample W at the point E is L1 + e1 + L2 + e2 + L3 '... (2).

By repeating the above calculation and the reference data updating operation, for example, when the sample W to be measured is displaced to G, the reference memory 7 stores A, B, D ,.
The data sampled at each point of F is stored as reference data together with the respective position information. If the reference data needs to be updated at this time, the reference data memory 7 stores the data at the point D, which is close to the sampling data at the point G at that time. Is adopted again as reference data.

In this case, the displacement amount at the H point is the actual displacement amount of the measured sample W at the H point when the movement amount of the speckle pattern using the sampling data at the D point as reference data is L3 ″. Becomes L1 + e1 + L2 + e2 + L3 ″ ... (3).

As described above, when it is determined that the reference data needs to be updated, if the data close to the sampling data at that time is not in the data stored in the reference data memory 7, the time is updated. Although the sampling data in 3 is newly adopted as the sampling data and stored in the reference data memory 7, if there are some of the past reference data in the reference data memory 7 that are close to the sampling data at that time, , The past reference data is used again as new reference data.

As a result, the accumulation of errors associated with updating the reference data is greatly reduced. By the way, in the case where the reference data is the sampling data at that time each time the reference data needs to be updated as in the conventional case, the above H
For the actual displacement amount of the measured sample W at the point, the position information of the point F with respect to the point D which is the sampling position of the previous reference data is L3.
And the error due to the update of the reference data is e3, F
If the position information of the G point with respect to the point is L4 and the error due to the updating of the reference data is e4, then L1 + e1 + L2 + e2 + L3 + e3 + L4 + L3 ″ (4) 3, the data sampled at the point B is used as the reference data in the embodiment of the present invention, so that L1 + e1 + L2 ″. On the other hand, in the conventional example, since the sampling data at points B, D, E, F, G, and I are newly adopted as reference data, position information of a total of six reference data B to I is obtained. It can be clearly seen that the sum of the errors is the same as the above, and the cumulative error according to the embodiment of the present invention is small.

Here, in updating the reference data, it is determined whether or not the past reference data in the memory 7 is close to the current sampling data, that is, whether or not the past reference data is used. The method can be performed by, for example, determining whether the current position with respect to the past reference data is within a preset range. Further, when there are a plurality of data satisfying such conditions, it is reasonable to adopt the closest data.

At the positions indicated by K, L, and M in FIG. 3, since there is no data near the reference data memory 7 at the beginning of measurement, in this case, the sampling data at these positions are newly set as reference data. These are adopted, but these are the sample to be measured W due to repeated loading.
Will be used as reference data as it passes through these areas.

In addition, the surface state of the sample W to be measured may change during measurement, and when updating the reference data, sufficient correlation strength may not be obtained even if close one of the past reference data is adopted. There is. In such a case, the sampling data at that time may be used as new reference data. Even in such a case, it is expected that the change of the sample surface will occur sufficiently slowly.Therefore, it is necessary to update the reference data more than the conventional method in which the sampling data at that time is used as the reference data every time the reference data is updated. The amount of accumulated error is significantly reduced.

In the above embodiment, an example in which the displacement at one point of the sample W to be measured is measured based on the data from the channel corresponding to one observation point area has been shown. Two point areas are provided, and the data from the corresponding channels are individually used to measure the sample W to be measured.
By measuring the displacement at two points and finding the difference,
Elongation or contraction between two points of the sample W to be measured can be measured.

[0031]

As described above, according to the present invention,
When a storage means capable of storing a plurality of reference data is provided and the reference data needs to be updated, the data close to the sampling data at that time is selected from among the respective data in the storage means, and the past data is selected. Since the reference data of is used as the new reference data again, the accumulation of errors due to the update of the reference data is reduced. Especially, when the displacement information of the test piece in the fatigue test is obtained, the same area is repeated for a long time. In the case of the measurement of displacing, the accumulated amount of error becomes significantly smaller than that of the conventional method.

[Brief description of drawings]

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

FIG. 2 is a flowchart showing the operation of the calculation unit.

FIG. 3 is an operation explanatory view of an embodiment of the present invention based on a graph showing an example of a state of displacement of a measured sample W with time which appears in a fatigue test or the like.

FIG. 4 is an explanatory diagram of a situation of displacement of a test piece with time in a fatigue test, and an example in a case where updating of reference data is unnecessary (A)
And a graph showing an example (B) when it is also necessary

[Explanation of symbols]

 1 Laser Light Irradiation Optical System 2 Image Sensor 4 A-D Converter 5 Sampling Data Memory 6 Computing Unit 7 Reference Data Memory

Claims (1)

[Claims] 1. A laser light irradiation optical system for irradiating a sample to be measured with laser light, and light scattered by the surface of the sample to be measured of the laser light is received to detect a speckle pattern included in the scattered light. By using the image sensor and the output of the image sensor to calculate the cross-correlation function with the speckle pattern data detected at another time using the speckle pattern data detected at a predetermined time as reference data. In addition to obtaining the displacement information of the sample to be measured by obtaining the movement amount of the speckle pattern at, the calculation means for updating the speckle pattern data used as the reference data when the movement amount of the speckle pattern reaches the specified amount The displacement meter is provided with a storage unit for storing a plurality of reference data, and the arithmetic unit updates the reference data. At the time of new, a non-contact displacement meter characterized by being configured so that data closest to the latest speckle pattern is selected from the plurality of reference data, and the selected data is used as reference data thereafter.