JPH07151516A - Speckle displacement gauge - Google Patents

Abstract

PURPOSE:To provide a speckle displacement gauge, by which high speed phenomenon can be caught without increasing the processing speed of a circuit for calculating the cross correlation of signal processing, without wasting optical information which enters each channel of a one-dimensional image sensor, and without lowering the average signal intensity. CONSTITUTION:In a device which is adapted to receive reflected light obtained by applying laser light to a sample W by a one-dimensional image sensor 2, guide the photoelectric transfer output to an arithmetic circuit 3 to obtain the travel of a speckle pattern, and obtain the displacement of the sample W, the scanning period of the one-dimensional image sensor 2 is made shorter than the scanning period of one frame determined by the number of channels and the transfer clock frequency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is capable of non-contact measurement of displacement, strain, etc. of a sample from the amount of movement of a speckle pattern of reflected light from the sample to be measured.
The present invention relates to a so-called speckle displacement meter.

[0002]

2. Description of the Related Art It has long been known that minute displacements or deformations of an object can be measured by using a speckle pattern obtained when a surface of an object is irradiated with light having good coherence such as laser light. Has been.

A method for measuring the amount of distortion or movement of an object in a desired direction by using such a speckle pattern in a non-contact manner and in almost real time has already been proposed (for example, Japanese Patent Publication No. 59-52963). No. 61-27681).

In these proposed methods, basically, a reflected light obtained by irradiating a measured portion of an object with a laser beam is photoelectrically converted by a one-dimensional image sensor and an electric signal corresponding to a speckle pattern is obtained. Is obtained, before and after the deformation of the object, in other words, by obtaining the cross-correlation function of the signal for each predetermined minute time, the momentary movement amount of the speckle pattern is obtained, and with this, the measured portion of the object is measured. The amount of displacement is used. Further, two laser beams are irradiated to the same point of the object at an angle symmetrical to each other with the surface normal therebetween, and the difference in the movement amount of the speckle pattern formed by each beam is obtained, or By irradiating a single laser beam on the above and observing the reflected light in two directions, and obtaining the difference in the movement amount of the speckle pattern obtained in the same manner at each observation point, the distortion amount of the object or The amount of deformation can be calculated.

[0005]

By the way, in a measurement of this kind, if an attempt is made to capture a higher speed phenomenon,
It is necessary to increase the scan rate of the three-dimensional image sensor, that is, to shorten the scanning cycle. On the other hand, in this type of measurement, real-time measurement is indispensable, so the output signal from the image sensor must be used immediately for correlation calculation processing, and in order to grasp high-speed phenomena, the signal correlation must be calculated. It is also necessary to increase the processing speed of the circuit to be processed, for example, a computer system including an AD converter.

Therefore, even if the scan rate of the image sensor is increased to catch a high-speed phenomenon, there is a limit in the circuit for calculating the correlation of the signal, and when the scan rate of the image sensor is increased beyond the limit, processing is performed. It becomes necessary to reduce the number of channels of the image sensor used for. In this case, scanning all channels and using only part of the data not only discards the information that has entered other channels, but also shortens the exposure time and thus reduces the average signal strength. There is a problem that it will end up.

That is, the one-dimensional image sensor has n pixels and an n-bit analog shift register which is a transfer unit corresponding to the number of pixels, where n is the number of channels, and a start pulse causes a pixel to shift from each pixel. After the photoelectric conversion signals are temporarily stored in the corresponding registers, the information in the n-bit shift register is taken out serially by the transfer clock. Normally, n times are generated during the generation period of the start pulse, that is, the scanning period. A transfer clock is generated, and photoelectric conversion signals for all channels, that is, data for one frame are taken out. That is,
In the n-channel one-dimensional image sensor, in order to extract the data of all the channels, when the transfer clock cycle is t (the transfer clock frequency is 1 / t), the scanning cycle T is n × t.

Now, for example, as shown in FIG.
Using a 00-channel one-dimensional image sensor, and assuming that the transfer clock cycle is 1 μsec, the start pulse cycle T is 2 msec and the frame rate is 500 Hz.
Becomes If the processing speed of the circuit for calculating the correlation is the limit in this state, the frame of the transfer clock cycle t is set to 0.5 μsec as shown in FIG. 4B for the purpose of catching a higher speed phenomenon. Rate 1 kHz
When doubled, due to the limitation of the processing speed of the circuit for correlation calculation, only 1000 points of data can be processed out of 2000 points of data obtained from the image sensor, and the remaining 1000 points of data can be processed. Since it is necessary to discard it, and the exposure time of each pixel of the image sensor is halved, the average intensity of the signal is halved. Set the frame rate to 2 to catch even higher speed phenomena.
When the frequency is set to kHz, the cycle t of the transfer clock is 0.25 μsec and the cycle T of the start pulse is 500 μsec, as shown in FIG. 4C. With this alone, the data of 1500 points is discarded, and the average intensity of the signal is reduced to 1/4.

The present invention has been made in view of the above circumstances, and does not increase the processing speed of the circuit for calculating the cross-correlation of signals, and wastes optical information in each channel of the one-dimensional image sensor. It is an object of the present invention to provide a speckle displacement gage capable of catching a higher speed phenomenon without reducing the average signal intensity.

[0010]

In order to achieve the above-mentioned object, a speckle displacement meter of the present invention comprises an irradiation optical system 1 for irradiating a sample W to be measured with laser light, and a sample W to be measured of the light.
The one-dimensional image sensor 2 having a predetermined number of channels for receiving the reflected light by the moment, and the arithmetic circuit 3 for obtaining the movement amount of the speckle pattern using the output of the image sensor 2.
A one-dimensional image sensor 2 in a displacement meter that is provided with: and obtains the amount of displacement of the sample to be measured from the amount of movement of the speckle pattern.
Is characterized in that the scanning is performed with a period τ shorter than the scanning period T of one frame determined by the number of channels n of the one-dimensional image sensor 2 and the transfer clock frequency 1 / t.

[0011]

As described above, the scanning cycle of t × n = T is required to retrieve the data for all channels of the n-channel one-dimensional image sensor 2, that is, the data for one frame. Then, as shown in FIG. 2, the scanning period τ of the one-dimensional image sensor 2 is, for example, T / 2. In this case, the next frame data is accumulated in the shift register before half of the data for n channels accumulated in the shift register of the one-dimensional image sensor 2 has been transferred, and the latter half of the data in the previous scanning ( C ₄ ~
C ₁ ) and the first half data (C ₈ ~
C ₅ ) will be added.

When the image sensor is used for knowing the shape of an object or the like, the images cannot overlap in such a way because the images overlap each other. However, when the one-dimensional image sensor 2 is used to obtain the movement amount of the speckle pattern, the speckle pattern is a random pattern, and thus the data after addition (for example, C ₄ + C ₈ ) is random + random. Therefore, the property that the speckle pattern moves in parallel with the movement of the sample W to be measured is preserved as it is, and the amount of movement of the speckle pattern can be sufficiently calculated by calculating the cross-correlation of such data. .

In this case, if it is assumed that the processing speed of the arithmetic circuit 3 for calculating the correlation has a limit of T to process the data of n pieces, the n pieces of optical information incident on each channel are between τ. For example, as C ₄ + C ₈ is taken out as n / 2 pieces of data, it is possible to perform calculation processing using the data of all channels during T / 2, and no data is discarded.

Further, by setting τ to T / 2, the exposure time of the pixel of each channel is halved, but since the data is taken out as the added value of the exposures of two times, the average intensity of the signal also decreases. There is nothing to do.

[0015]

FIG. 1 is a schematic diagram showing the overall construction of an embodiment of the present invention. The laser light source 1a is placed on the measured portion of the measured sample W.
The laser light from the irradiation optical system 1 including the lens 1b is irradiated. The reflected light of the laser light from the measured sample W is observed by the n-channel one-dimensional image sensor 2. The output of the one-dimensional image sensor 2 is included in an arithmetic circuit 3 including an A / D converter and mainly composed of a computer, and the cross-correlation between signals at respective time points is calculated by a known arithmetic operation. The amount of movement of the pattern, that is, the amount of displacement of the measured sample W at the measured portion is obtained.

The start pulse and the transfer clock pulse are supplied from the driver 4 to the one-dimensional image sensor 2. In this example, the period τ of the start pulse is ½ of the normal one-frame scanning period T = t × n, which is determined by the frequency 1 / t of the transfer clock and the number of channels n.
Is. As a result, as for the output from the one-dimensional image sensor 2, only n / 2 of the outputs obtained by adding the outputs of the two channels are taken out during the period τ as shown below and supplied to the arithmetic circuit 3. Will be.

FIG. 2 is an explanatory diagram of the operation of the one-dimensional image sensor 2. The number n of channels of the one-dimensional image sensor 2 is actually about 2000, for example, but in this figure, n = 8 for simplification of description. Therefore, in this description, when the frequency of the transfer clock pulse is 1 / t (period t), the scanning period, that is, the generation period τ of the start pulse is 4t.

As shown in (A), when the first start pulse is supplied, the photoelectric conversion signals from the eight pixels S _{1 to} S ₈ which are photoelectric conversion units are transferred to the CC which is a transfer unit.
The data is transferred to each corresponding area of the D analog shift register 2a. When the photoelectric conversion signals (charge amounts) from the pixels S _{1 to} S ₈ are represented by C _{1 to} C ₈ , the electric charge as shown in (A) is stored in each area of the shift register 2a by the first start pulse generation. Will be done.

The transfer clock pulse is generated at the cycle t, and the data C _{1 to} C ₈ in the shift register 2a are shifted every time the transfer clock pulse is supplied, but after the first start pulse is generated. , At the time when four transfer clock pulses are supplied after the time 4t has passed,
As shown in (B), C _{5 to} C ₈ are exposed to the outside,
C ₁ -C ₄ is remaining state in the shift register 2a.

At the time when this 4t has passed, the next start pulse is supplied. By the supply of this second start pulse, the shift register 2a is moved to the area where the data C _{1 to} C ₄ transferred to the shift register 2a by the previous start pulse are left, as shown in (C). Data C _{5 to} C ₈ of each pixel are transferred, and in these areas, the sum of data of pixels different from each other transferred at the time of generation of two start pulses, that is, C
₁ + C ₅ , C ₂ + C _6, ... Are stored.

Each time a transfer clock pulse is supplied after the second start pulse is generated, as shown in (D), the shift register 2a outputs C ₄ + C ₈ and C ₃ + C ₇
The data is taken out in the order of ... And incorporated into the arithmetic circuit 3.

After the second start pulse is generated,
During the period from the time 4t to the generation of the third start pulse, n consisting of the sum of the above two data
/ 2 pieces of data are taken into the arithmetic circuit 3, and when the third start pulse is generated, the data is transferred to the shift register 2a again by the second start pulse to the half area as shown in (B). The generated data C _{1 to} C ₄ remain and are transferred to the shift register 2a by the previous scan as shown in (C) as in the case of the second case by the generation of the third start pulse. data C ₁ -C ₄ follows the space remaining data C ₅ -C ₈ is to be transferred.

By repeating the above-mentioned operation, after the second start pulse is supplied, the different pixels S which are always transferred from the shift register 2a to the shift register 2a by the previous and present start pulses. ₁ and S ₅ , S ₂ and S ₆ , S ₃ and S _7, and S ₄ and S
Sum of data from ₈ , namely C ₁ + C ₅ , C ₂ + C ₆ ...
・ Will be taken out.

According to the operation of the one-dimensional image sensor 2 as described above, 1/2 of the number of channels n is obtained during the scanning period τ.
Data is output, and these individual data are 2
It is the sum of the data from the two pixels obtained by one start pulse, so to speak, n pieces of data of n channels are aggregated into n / 2 pieces, and the number of data is n / 2, but the content is The data for all n channels are collected.

Therefore, since the number of data to be processed by the arithmetic circuit 3 is 1/2 as compared with the case of processing one frame of normal data, the scanning cycle τ of the one-dimensional image sensor 2 is Even if the scan rate is doubled from the normal T, that is, the correlation can be calculated based on the original processing speed even if the scan rate is doubled. Moreover, all of the optical information incident on the n pixels is used for the processing. Also,
Regarding the average intensity of the data, the average intensity of the signals (C ₁ , C ₂ ...) From the individual pixels is halved because the scanning period is halved. Since the signals are extracted in the form of sum, the arithmetic circuit 3 is supplied with a signal having the same average intensity as the original intensity.

Here, the arithmetic circuit 3 always takes in the data in the form of the sum of the optical information signals from the two pixels, and the optical signals incident on the two pixels become an overlapping image signal. These data are not used for imaging, but used for calculating the movement amount of the speckle pattern that is a random pattern. Since random + random = random, data for several pixels are stored. Even if the sum is used, there is no problem in its use.

By applying the embodiment of the present invention described above, for example, as shown in FIG. 3, the number of channels n of the one-dimensional image sensor 2 is 2000 and the period t of the transfer clock pulse is 1 μ.
In the case of sec, in the conventional operation method in which the data for one frame is individually used, the scanning cycle T is 2 as shown in (A).
However, in the above-described embodiment of the present invention, only the period τ of the start pulse is T / msec.
2, the signal of the same average intensity as in the case of (A) is obtained, and the data of all channels are used without waste.

Although the period τ of the start pulse is n × t / 2 in the above embodiments, the present invention is not limited to this, and τ is any period shorter than n × t = T, Preferably, it may be a cycle of an arbitrary integer fraction of n × t. For example, by setting τ = n × t / 4, it becomes possible to catch a phenomenon at a higher speed. In this case, the data is taken out from the shift register 2a in the form of the sum of the signals from the four pixels.
As shown in (C), the average intensity of the signal becomes equivalent to that in (A), and moreover, the data of substantially all channels are provided to the processing by the arithmetic circuit 3. However, when τ is significantly smaller than T, for example, when data is extracted in the form of the sum of signals from several tens of pixels, the difference between all data is small, which is not preferable.

Further, in the above embodiment, the displacement of the laser light irradiation portion was obtained by calculating the movement amount of one speckle pattern, but the reflected light obtained by the laser light irradiation is observed at two positions. Then, the amount of movement of each speckle pattern is obtained, and even if the amount of deformation or distortion of the sample to be measured is obtained by obtaining the difference between them, the present invention is not necessary when calculating the amount of movement of each speckle pattern. Of course, the same can be applied.

[0030]

As described above, according to the present invention,
Reflected light obtained by irradiating the sample to be measured with laser light is received by a one-dimensional image sensor with a predetermined number of channels,
In a displacement meter that obtains the amount of movement of the speckle pattern using the output of the image sensor and obtains the amount of displacement of the sample to be measured from the amount of movement, the scanning period of the one-dimensional image sensor is the number of channels of the one-dimensional image sensor. Since it is configured to scan at a cycle shorter than the scanning cycle of one frame determined by the transfer clock frequency, the cross-correlation of the output of the image sensor including the AD converter that digitizes the output from the image sensor is included. Even if the processing speed of the arithmetic circuit for calculation is constant, it is possible to capture a higher-speed phenomenon by using the optical information incident on all channels and without lowering the average intensity of the photoelectric conversion signal. Become.

Further, the correlation calculation processing circuit does not determine the limit of the speed of the displacement meter, but in the case where the image sensor determines the limit, the frame rate determined by the maximum allowable transfer clock frequency of the image sensor. The present invention is also effective when it is desired to collect a signal beyond the range.

[Brief description of drawings]

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

FIG. 2 is an operation explanatory diagram of the one-dimensional image sensor 2.

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

FIG. 4 is an explanatory diagram of measures for trying to catch a higher-speed phenomenon with a conventional speckle displacement meter and its problems.

[Explanation of symbols]

 1 Irradiation optical system 1a Laser light source 1b Lens 2 One-dimensional image sensor 2a CCD analog shift register 3 Arithmetic circuit 4 Driver

Claims (1)

[Claims] 1. An irradiation optical system for irradiating a sample to be measured with laser light, a one-dimensional image sensor having a predetermined number of channels for receiving the reflected light of the light from the sample to be measured, and the output of the image sensor are used. In a displacement meter that includes an arithmetic circuit that obtains the movement amount of the speckle pattern and obtains the displacement amount of the sample to be measured from the movement amount of the speckle pattern, the one-dimensional image sensor has the number of channels of the one-dimensional image sensor. Determined by transfer clock frequency 1
A speckle displacement meter characterized by being configured to scan at a cycle shorter than a frame scan cycle.