JPH0635921B2 - Speckle length meter - Google Patents

Description

The present invention relates to a speckle length measuring instrument for measuring an amount of movement of an object using a speckle pattern generated by diffused light from the surface of an object irradiated with laser light. It is about.

(Prior Art) Conventionally, a method of measuring a minute deformation amount of an object by applying a speckle pattern has been proposed (Japanese Patent Publication No. 59-52963).

The measuring method irradiates the surface of a deformed object to be measured with a laser beam, arranges an image sensor in the diffuse reflection light, and based on an image signal output from the sensor, before and after the object deformation. The cross-correlation function of the output signal is calculated, and the object movement amount is measured in such a manner that the peak position of the cross-correlation function corresponds to the movement amount of the speckle pattern.

(Problems to be Solved) However, in the above measurement method, the cross-correlation function is calculated by directly A / D converting the waveform of the image signal that fluctuates drastically as shown in FIG. The number of samplings was extremely large, and it took a long time to perform a calculation process for obtaining a cross-correlation function from these sampling data, which made real-time measurement difficult.

Therefore, it has been proposed that the image signal is once binarized at a predetermined threshold level and the so-called polarity correlation is taken to reduce the calculation processing time (for example, “Corona Inc.“ Needs and Seeds for Optical Measurement ”). "Page 40).

However, when the polarity correlation by binarization is adopted, the correlation function does not have a continuous distribution as shown in FIGS. 5 (a) to 5 (e), and it depends on the resolution of the image sensor (for example, CCD array pitch). It is obtained as a set of a plurality of discrete correlation value data.

Therefore, if the target object is the pixel array pitch (for example, 13 μm)
When moving within a smaller range, the cross-correlation function of the speckle pattern before and after the movement shows a correlation as shown in, for example, FIGS. 5 (a) and 5 (b) even if the moving distance differs within the range. The peak position Pp of the value data is the same.

That is, the conventional speckle prompt sizing instrument cannot obtain a resolution higher than that of the image sensor, and there is a limit in measurement accuracy.

An object of the present invention is to provide a speckle length measuring instrument that can obtain a measurement resolution exceeding that of a one-dimensional image sensor.

Another object of the present invention is to provide a speckle length measuring instrument capable of executing a process for calculating a moving distance at high speed.

(Means for Solving the Problem) A speckle length measuring instrument according to the present invention is a laser generator for emitting a laser beam toward the surface of a moving object to be measured, and a laser irradiation surface of the object. An image sensor (13) for converting the speckle pattern appearing on the facing observation surface into an image signal, and the image sensor (1
3) Binarization circuit that binarizes the image signal output from
(4) and the cross-correlation function of the speckle pattern at the reference position of the target object and the speckle pattern at the subsequent moving position on the basis of the output data of the binarization circuit (4), a plurality of correlation value data (C _1, C _2, ... correlator for calculating a discrete distribution from Cn) and (5), the correlation value data output from the correlator (C _1, C _2, ... calculate the moving distance of the object based on Cn) It has an information processing circuit and a display (9) for displaying the calculation result of the circuit.

The information processing circuit includes first means for searching a peak position from a set of the correlation value data (C ₁ , C ₂ , ... Cn), correlation value data Cp of the peak position and two correlation value data before and after the correlation value data. Second means for determining a logical peak position when the cross-correlation function is approximated as a continuous distribution from Cf and Ca, and calculating an object movement amount based on the logical peak position.

The second means of the information processing circuit is provided with a difference (Cp-
Cf) and (Cp-Ca) first calculating means, and the actual peak position of the correlation value data at the address defined by the two difference data (Cp-Cf) and (Cp-Ca). And a memory means in which correction data corresponding to the difference between the logical peak position and the logical peak position is stored in advance, and data read from the memory means is controlled based on the difference data (Cp-Cf) and (Cp-Ca). The control unit may include a control unit and a second calculation unit that calculates the moving distance of the target object based on the actual peak position and the correction data.

(Working) One-dimensional image sensor (13) as the target object moves
The image signal photoelectrically converted by the image sensor (13) changes at a cycle corresponding to the scanning cycle of the speckle pattern by the image sensor (13), and a binarization circuit is provided for each speckle pattern.
It is sent to (4) and binarized.

The correlator (5) calculates the cross-correlation function of the binarized data of the speckle pattern at the reference position and the binarized data of the speckle pattern after the object movement based on the binarized data D. . The cross-correlation function is obtained as a discrete distribution composed of a plurality of correlation value data (C ₁ , C ₂ , ... Cn) (see FIG. 5).

The calculated correlation value data is sent to the information processing circuit, and the first means of the circuit outputs the correlation value data (C ₁ , C ₂ , ... Cn).
The actual peak position Pp that takes the maximum value is searched from among.

Here, assuming a theoretical cross-correlation function when the resolution of the one-dimensional image sensor approaches zero as much as possible, the correlation value data C of the actual peak position and its front and rear positions
Since p, Cf, and Ca are considered to be plotted on the distribution of the above-mentioned logical cross-correlation function, the peak position of the theoretical cross-correlation function is based on these data.
(Theoretical peak position) can be determined.

The second means of the information processing circuit determines the theoretical peak position by a predetermined method, and further calculates the object moving distance based on the theoretical peak position.

The calculated moving distance is displayed on the display (9) in real time.

Further, when the second means of the information processing circuit is composed of the first and second arithmetic means, the memory means and the read control means,
The memory means stores the difference (Cp-C) between the correlation value data Cp and Cf.
f) and the correction data, which is addressed by the difference between the correlation value data Cp and Ca (Cp-Ca) and is preset in the memory means, is called instantaneously. Then, the actual peak position is corrected by the correction data to determine the logical peak position.

(Effects of the Invention) According to the speckle length meter according to the present invention, a measurement resolution exceeding the resolution of the one-dimensional image sensor can be obtained, and highly accurate length measurement is possible.

Further, the use of the memory in which the correction data is registered in advance speeds up the calculation process for calculating the moving distance.

(Example) Hereinafter, a specific configuration of the speckle length measuring instrument according to the present invention will be described with reference to the drawings. It should be noted that the examples are for explaining the present invention and should not be understood as limiting the invention described in the claims or reducing the scope.

As shown in Fig. 1, the measuring head of the speckle length measuring instrument (1)
Is a semiconductor laser (11) in a closed casing having a beam emission window (10), and a collimator lens (1) for shaping laser light from the semiconductor laser (11) into a parallel laser beam (17).
2), a one-dimensional image sensor (13) composed of a CCD for photoelectrically converting a speckle pattern formed by being diffusely reflected by the target object (18) and the like are arranged.

FIG. 2 shows an example of the configuration of a measuring circuit for connecting to the measuring head (1), calculating the amount of movement of the object based on the image signal from the one-dimensional image sensor (13), and displaying it. ing.

As is well known, the one-dimensional image sensor (13) repeats scanning in the CCD array direction at regular intervals by a reset signal, a start signal and a shift signal sent from the buffer amplifier (14). The output signal of the sensor (13) is the first stage amplifier.
It is connected to the sample and hold circuit (2) via (15), which removes the noise peculiar to the CCD.

The output signal of the sample and hold circuit (2) is sent to the binarization circuit (4) via the gain control amplifier (3), whereby the image signal S as shown in FIG.
The digitized data D is sent to the correlator (5), the cross-correlation function of the speckle pattern that changes with the movement of the target object is repeatedly calculated as described later, and the calculation result is sent to the microcomputer (7). To be

The microcomputer (7) comprises a ROM (8) which is addressed by two address data of upper 8 bits and lower 8 bits as an external storage device, and is registered in advance in the peak position of the cross-correlation function and the ROM (8). The moving distance of the object is calculated from the table of the correction data described later, and the result is digitally displayed on the display (65).

Also, the buffer amplifier (14) and the sample and hold circuit
(2) The operations of the binarization circuit (4) and the correlator (5) are controlled by the timing signals supplied from the timing generator (6).

The image signal obtained from the gain control circuit (3) is the fourth
As shown in the figure, the period T _{0 of the} start signal sent from the timing generator (6) to the one-dimensional image sensor (13)
It generated every, image sensor (1 in the periodic T in the ₀
It corresponds to one scanning time of the speckle pattern by 3).

The image signal is sent to the binarization circuit (4) in FIG.
The average value (L in FIG. 4) of the occurrence period T is binarized as a threshold level. The binarized data D is further supplied to the correlator (5).

The correlator (5) can employ various well-known configurations, for example, the first
And a second shift register, a plurality of EX-OR circuits, an adder, etc., and calculates a cross-correlation function as follows based on the data D input one after another at the period T ₀ .

That is, a series of data D corresponding to one speckle pattern sent at the start of length measurement is set in the first shift register, and then a series of data D sent one after another as the object moves. Are sequentially set in the second shift register, and the cross-correlation function of the data set in both shift registers is calculated. The cross-correlation function is obtained as a discrete distribution composed of a plurality of correlation value data (C ₁ , C ₂ , ... Cn) (see FIG. 5). Then, when the peak value of the cross-correlation function falls below a predetermined level, the data in the second shift register at that time is transferred to the first shift register. After that,
Using the updated data in the first shift register as a reference, the cross-correlation function is repeatedly calculated as described above.

The calculated correlation value data is sent to the microcomputer (7) one after another, and the microcomputer (7) collects a group of correlation value data (C ₁ ,
The arithmetic processing means (FIG. 3) described below is executed for each of C ₂ , ... Cn).

Here, the measurement principle according to the present invention will be described with reference to FIG.

A group of correlation value data (C ₁ , C ₂ , ... Cn) corresponding to one speckle pattern obtained from the correlator (5) is a discrete value, and is one-dimensional as shown by a solid line in FIG. Image sensor resolution, ie CCD array pitch Q (eg 1
3 μm) can be drawn as a histogram with the horizontal axis pitch. Focusing on the data Cp of the actual peak position Pp which takes the maximum value among these correlation value data and the two data Cf and Ca before and after it, the logical cross-correlation in the case where the polar correlation by binarization is not taken It is considered that the distribution of the function changes continuously as shown by the chain line, and the above three data Cf, Cp and Ca are plotted on this continuous distribution. Then, it can be estimated that the theoretical peak position Z of the cross-correlation function as the continuous distribution is at a position deviated from the actual peak position X by the correction distance Y.

Therefore, the theoretical peak position Z can be determined from the actual peak position X of the correlation function and the correction distance Y, and the theoretical peak position Z has higher accuracy than the actual peak position. When the correlation data Cf and Ca before and after the peak have the same value, the actual peak position and the theoretical peak position match.

Various prediction methods or interpolation methods can be adopted as a method of obtaining the correction distance Y, but here, in consideration of simplification of data processing, only the above-mentioned three data Cf, Cp, and Ca are used as basic data, and further continuous The distribution of the cross-correlation function is approximated by the straight lines on the two right and left sides of the isosceles triangle whose apex is the theoretical peak position, and the correction amount is obtained by the interpolation method.

In this case, the ratio Y / Q between the correction distance Y and the CCD array pitch Q can be obtained by the following equation.

(I) When Cf <Ca (II) When Cf = Ca (III) When Cf> Ca 5 (a) to 5 (d), the peak position Pp does not change, but in FIG. 5 (e), the peak position Pp 'has moved by the CCD array pitch Q. The ratio Y / Q is calculated from the correlation value data having the position Pp 'as the new peak position.

Further, in this embodiment, in consideration of the overall efficiency of a series of arithmetic processing described later, the number of divisions M (for example, 16) when the CCD array pitch is further divided and interpolated and the ratio Y / Q are set. The product Vc = M × Y / Q (4) is used as the interpolation value Vc in the arithmetic processing.

Therefore, with the actual peak position Pp at the start of length measurement as the origin,
Immediately after that, the actual peak position Pp when the correlation value data Cf and Ca before and after the peak are the same is 1, and the actual peak position P when the correlation value data Cf and Ca are the same next time is P.
The value of the actual peak position Pp occurring at the interval of the CCD array pitch, where p is 2, ... Is an integer value. When the moving direction is reversed, Pp is expressed as a negative value, and the object moving distance R at an arbitrary time point is represented. Is represented by the following formula.

R = (Pp * M + Vc) * Q / M (5) Next, the contents of the ROM (8) shown in FIG. 2 will be described.

The ROM (8) stores the difference (Cp-
Cf) is the upper 8-bit address data AH, and the difference (Cp-Ca) between the correlation value data Cp and Ca is the lower 8-bit address data AL.
The interpolation value Vc obtained from the equations (1) to (4) is calculated and registered in advance for all possible difference data.

Therefore, by the address data AH and AL, RO
The interpolation value Vc can be instantly called from M (8), which shortens the calculation processing time.

Since the control of reading data from the ROM (8) by the microcomputer (7) is well known,
The description is omitted.

FIG. 3 shows the processing procedure of the microcomputer. First, a group of correlation value data (C ₁ , C ₂ , ... Cn) corresponding to one speckle pattern is taken in from the correlator,
The peak position Pp is searched from these data. Next, based on the correlation value data before and after the peak position, the difference data
(Cp-Cf) and (Cp-Ca) are calculated, and these are output to the ROM (8) as address data. Then, the interpolated value Vc of the corresponding address is read from the ROM (8), the object moving distance R is calculated from the value X of the peak position Pp and the interpolated value Vc based on the equation (5), and the result is displayed on the display. (9)
Output to.

The moving distance R is successively displayed in real time as the object moves on the display (9).

According to the speckle length measuring device, for example, the number of interpolation divisions M is
16. If the CCD resolution is 13 μm, the length measurement resolution is about 0.8 μm, and extremely high accuracy can be obtained.

Since the movement distance is measured by using the ROM table in which the interpolation value is registered in advance, the calculation processing is speeded up and the above-mentioned high resolution is exhibited even when the movement speed of the target object is high. Can be done.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic configuration of a speckle length measuring device, FIG. 2 is a block diagram of a measuring circuit, FIG. 3 is a flowchart showing a processing procedure of a microcomputer, FIG. 4 is a waveform diagram of an image signal, and FIG. 5 (a) to 5 (e) are a series of graphs showing changes in the distribution of correlation value data, and FIG. 6 is an explanatory diagram of the measurement principle of the present invention. (1) …… Measuring head, (11) …… Semiconductor laser (13) …… One-dimensional image sensor S …… Image signal (C ₁ , C ₂ ,… Cn)… Correlation value data

Claims (2)

[Claims] 1. A laser generator for emitting a laser beam toward the surface of a moving object to be measured, and a speckle pattern appearing on an observation surface facing the laser irradiation surface of the object as an image signal. An image sensor (13) for conversion, a binarization circuit (4) for binarizing an image signal output from the image sensor (13), and the binarization circuit
A correlator that calculates a cross-correlation function between the speckle pattern at the reference position of the target object and the speckle pattern at the subsequent moving position based on the output data of (4) (5)
And correlation value data (C ₁ , C ₂ ,
.. Cn), an information processing circuit for calculating the moving distance of the object, and a display device (9) for displaying the calculation result of the circuit, wherein the information processing circuit is provided with the correlation value data (C ₁ , C _{2. When} the cross-correlation function is approximated as a continuous distribution from the first means for searching the peak position from the set of Cn) and the correlation value data Cp of the peak position and the two correlation value data Cf and Ca before and after the peak value. And a second means for calculating an object movement amount based on the logical peak position. 2. The second means of the information processing circuit comprises a difference (Cp−Cp) between the three correlation value data Cp, Cf, Ca.
Cf) and (Cp-Ca) first calculating means, and the actual peak position of the correlation value data at the address defined by the two difference data (Cp-Cf) and (Cp-Ca). And a memory means in which correction data corresponding to the difference between the logical peak position and the logical peak position is stored in advance, and data read from the memory means is controlled based on the difference data (Cp-Cf) and (Cp-Ca). The speckle length measuring instrument according to claim 1, comprising control means and second calculation means for calculating a moving distance of the target object based on the actual peak position and correction data.