JPH0458580B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of the Invention This invention targets a moving continuous solid object.
This invention relates to a laser speckle velocimeter used for non-contact speed measurement.

(b) Prior art and its problems Generally, when an object is irradiated with laser light, the light transmitted or reflected by the object becomes diffused light and spreads in space. This diffused light exhibits a clear speckle pattern of brightness and darkness due to the coherence lens property of the laser beam, and when the target object moves, the speckle pattern also moves at the same time.

A method of measuring the speed of a moving object by applying this property is published in the magazine "Laser Research" (published by the Laser Society of Japan).
Volume 8, No. 2 (March 1980), pages 37 to 37
Up to page 45, and Volume 8, No. 3 of the same magazine (May 1980)
It is described on pages 3 to 10 of the month).

According to this description, as shown in FIG. 1, a moving object 2 is irradiated with a laser beam 1, and the transmitted light is received by light receiving elements 3 and 4 arranged in parallel in the moving direction of the object 2. Then, the time delay τd of the cross-correlation peak of the speckle pattern intensity detected at these two points has a correlation with the moving object v as shown in the following equation.

|v|=x/τd・σ/(Δx ² /ω ² +σ ² ) σ=R/ρ+1 However, x: distance between light receiving elements 3 and 4, ω: illumination area curvature, Δx: speckle size, ρ : Illumination light curvature, R: Distance from the target object to the light receiving element.

Here, x, Δx, ρ, and R become constant once the optical system is determined. Therefore, it can be seen that the speed of a moving object can be measured by finding the time delay τd of the cross-correlation peak.

However, with this speed measuring method using the cross-correlation method, if the moving direction of the object is uncertain, direction detection cannot be performed, and therefore the correct moving speed of the object cannot be measured.

In addition, since the laser beam from the laser light source is directly irradiated onto a moving object, there is a limit to the range that can be measured.For example, when the object to be measured is inside a cylinder or inside a liquid such as water or lubricating oil, , could not be measured.

(c) Purpose of the Invention In view of the above, the purpose of the present invention is to provide a laser that can measure the direction and speed of movement even when the direction of movement is undefined, has a wide measurable range, and can perform measurements under various conditions. An object of the present invention is to provide a speckle velocimeter.

(d) Structure and Effects of the Invention In order to achieve the above object, the laser speckle velocimeter of the present invention is equipped with means for stabilizing the temperature of the operating environment and means for stabilizing the emission intensity, and generates coherent light. a first optical fiber that guides the coherent light from the light source to the object to be measured, each of which is arranged in pairs so that the distance between the incident ends of each pair is equal and the directions are different;
A plurality of second optical fibers are provided corresponding to the plurality of second optical fibers, and each of the second optical fibers is provided correspondingly to A plurality of photoelectric conversion elements that convert changes in speckle patterns into electrical signals, and receiving output signals from these photoelectric conversion elements, and calculating a cross-correlation function of signals corresponding to each pair of second optical fibers. storage means for storing the correlation peak value and its time delay in association with the corresponding second optical fiber pair if a correlation peak exists in the calculated cross-correlation function; means for searching for the maximum value of correlation peak values in means and extracting the second optical fiber pair corresponding to the maximum correlation peak; the position of the extracted second optical fiber pair and the time of the correlation peak; and means for calculating the moving direction and moving speed of the object to be measured based on the delay.

According to the laser speckle velocimeter of this invention,
In addition to being able to measure speed even if the direction of movement is uncertain, optical fibers are used to irradiate the object to be measured with coherent light and derive the speckle pattern from the object to the signal processing unit, so it is possible to measure the speed even when the direction of movement is uncertain. It can be easily measured in places where lens optical systems cannot measure, underwater, lubricating oil, etc.

Furthermore, since optical fibers have low loss and are not affected by induced noise, signals with low noise can be obtained even if the distance between the laser light source, photoelectric conversion element, and the object to be measured is increased. Therefore, since the distance between the laser light source, etc. and the object to be measured can be increased, the laser light source and the photoelectric conversion element can be incorporated into the apparatus main body, and the apparatus configuration is simplified. Furthermore, there is an advantage that the laser light source and the photoelectric conversion element can be protected even under a poor environment at the site where the object to be measured is placed.

Furthermore, by increasing the number of sets of two light-receiving fibers (second fibers), the accuracy of measuring the moving direction and speed of the object to be measured can be increased by the increased number. Furthermore, since the light source is equipped with a means for stabilizing the temperature of the operating environment and a means for stabilizing the emission intensity, stable coherent light can be emitted even if the operating environment of the light source, such as the ambient temperature, changes. From this point of view as well, the measurement accuracy in speed measurement is high.

(e) Description of Examples The present invention will be explained in more detail below with reference to Examples.

FIG. 2 is a schematic diagram of a laser speckle velocimeter showing one embodiment of the present invention. In the same figure,
Reference numeral 10 denotes a laser diode that generates a laser beam, and is mounted in a temperature control block 11 to keep temperature conditions constant and perform stable laser oscillation. The temperature control block 11 is provided with a Peltier element that maintains the ambient temperature of the laser diode 10 constant by absorbing and absorbing heat. 12 is a temperature sensor that detects the ambient temperature of the laser diode 10, and 13 is a temperature control circuit. Temperature control circuit 1
3 controls the heat absorption and absorption of the Peltier element in the temperature control block 11 according to the temperature detected by the temperature sensor 12, and keeps the ambient temperature of the laser diode 10 constant.

14 is an automatic power control (APC) circuit for stabilizing the emission intensity of the laser diode 10.

15 is an object to be measured, and 16 is an optical fiber bundle. The optical fiber bundle 16 includes one light emitting optical fiber 17 and n light receiving optical fibers 18a, 1.
8b, 18c...18n.
19a, 19b, 19c...19n are photodiodes provided corresponding to the optical fibers 18a, 18b, 18c...18n, and 20 is a signal processing section.

An optical fiber 17 for light projection is arranged near the laser diode 10 and the object to be measured 15, and is adapted to guide and irradiate the coherent light from the laser diode 10 to the object to be measured 15. Also,
Near the object to be measured 15 and the photodiode 19a,
Optical fibers 18a, 18b, 18c...18n for receiving light are arranged between 19b, 19c...19n, and diffuse reflected light from the surface of the object to be measured 15 forms a speckle pattern and is incident thereon. The photodiodes 19a, 19b, 19c...19n
It's designed to lead you up to the point. These light-receiving optical fibers 18a, 18b, 18c, . . . , 18n are arranged in parallel so that the pattern of the light incident end face is concentric as shown in FIG.

Photodiodes 19a, 19b, 19c...1
9n converts the speckle pattern into an electrical signal and provides a fluctuation signal of the converted speckle pattern to the signal processing section 20.

As shown in FIG. 4, the signal processing section 20 has input terminals 21a, 21b, 21c...2 corresponding to the photodiodes 19a, 19b, 19c...19n.
1n, sample and hold circuit 22a,
22b, 22c...22n, A/D converter 23
a, 23b, 23c...23, a CPU (central processing unit) 24, and an output circuit 25, and the CPU 24 includes a microprocessor, a memory for storing waveform data, and the like.

Next, the operation of the laser speckle velocimeter configured as described above will be explained.

When the power is turned on, coherent (laser) light is output from the laser diode 10, but the temperature is kept constant by the temperature control block 11, and the power is controlled by the automatic power control circuit 14. , stable coherent light is always output.

Coherent light from the laser diode 10 is transmitted to the moving object 15 via the optical fiber 17.
irradiated onto the surface of The diffusely reflected light generated from the surface of the object to be measured 15 forms a speckle pattern, a part of which is reflected by the optical fibers 18a, 18b, 18.
c...18n, photodiode 19
a, 19b, 19c... up to 19n are sent. And photodiodes 19a, 19b, 19c...
19n converts the light intensity distribution of the speckle pattern into an electrical signal and inputs it to the signal processing section 20.

The signal processing unit 20 has input terminals 21a, 21b,
The signals given to 21c...21n are sample-and-hold circuits 22a, 22b, 22
c...22n, converted into digital signals by A/D converters 23a, 23b, 23c...23n, and input to the CPU 24.

The CPU 24 stores the input digital data of the intensity waveform of each speckle pattern in the memory. Then, from these data, a pair of optical fibers located on the diameter of each optical fiber arranged concentrically is selected, and a cross-correlation function is determined. There are 16 optical fibers 18a, 18b, 18c...18n, and if these 16 optical fibers are expressed as F1, F1' and F2, F2'...F8, F8', the third
As shown in the figure, F1, F1', which are arranged diametrically,
A cross-correlation function is obtained for each pair of F2 and F2'...F8 and F8'. Since a correlation peak value appears in the signals from a pair of optical fibers located in the direction of movement of the object, the peak value is extracted from the cross-correlation function of each pair, and the direction of movement is determined from the corresponding pair of optical fibers. Furthermore, since the time delay of the correlation peak value is inversely proportional to the magnitude of the velocity of the object to be measured 15, the moving speed can be determined from the time delay of the correlation peak value.

FIG. 5 shows a measurement flow of the correlation peak value and the time delay of the correlation peak value in the CPU 24.

When the digital data of the intensity waveform of each speckle pattern is stored in the memory in step ST (hereinafter abbreviated as ST) 1, the last data number (if there are 8 pairs of photodiodes) is then stored in the counter NEND.
NEND=8) is stored (ST2). and
A P area for storing the magnitude of the cross-correlation peak and a T area for storing the time delay of the correlation peak are prepared in each of the NEND (eight) array storage areas (ST3).

Next, in ST4, set the data No. to N=1, and set No.1 to
No. 1' waveform data, that is, optical fibers F1, F
The cross-correlation function is obtained from the waveform data of 1' (ST5), and the presence or absence of a peak in the cross-correlation function is determined (ST6). If there is no cross-correlation function peak, the process moves to ST7, but if there is a cross-correlation function peak, the peak value is stored in the P1 area and the delay time of the peak value is stored in the T1 area in ST9, and the process moves to ST7.
In ST7, it is judged whether “N≧NEND”, but initially the judgment is NO, and then it moves to ST8 and “N≧N+1”
(N=2) and returns to ST5. In ST5,
Next, the cross-correlation function is determined using the waveform data for the pair of optical fibers F2 and F2', and if there is a peak in the cross-correlation function, the peak value is set to P2 in ST9.
The delay time of the peak value is stored in the T2 area, and the process moves to ST7.

In the above manner, until the data number reaches 8
The processes of ST5 to ST9 are repeated, and the peak values of the cross-correlation numbers are stored in the P1 to P8 areas, and the delays of the mutual peaks are stored in the T1 to T8 areas, respectively.

When the data number becomes N=8, the judgment of ST7 is
YES and move on to ST10. Then, with reference to areas P1 to P8, the data number having the maximum cross-correlation function value is stored in area M (ST10). followed by P
The time delay TM between the correlation peak value PM in the (M) region and the correlation peak value in the T(M) region is read out (ST11).
Then, the velocity v is calculated from the time delay TM of this correlation peak value, and the moving direction of the object is determined from the data NoM and the sign/minus of the velocity (ST12). For example, in the case of M=3, the optical fiber F3/
One of the arrows F3' is the moving direction of the object.
Which one it is is determined by the sign of the speed.

The output circuit 25 converts the velocity of the object to be measured calculated by the CPU 24 into a signal of a required format, such as a display signal or an analog signal, and outputs the signal.

In addition, in the above embodiment, each cross-correlation function is calculated by the following algorithm. That is, a pair of input signals f(g) and g(k) sampled by a pair of sample-and-hold circuits.
are processed by FET (fast Fourier transform) to obtain frequency spectra F(n) and G(n), respectively, and further,
The product Φ of these frequency spectra F(n) and G(n)
By obtaining (n) and performing inverse FET on these,
Obtain the cross-correlation function φgk(l)= _N-1 〓 ^k-1 g(k)f(k-l).

In addition, in the above embodiment, the optical fibers 18a,
The arrangement of 18b, 18c...18n is circular as shown in Fig. 3, but as shown in Fig. 6, one optical fiber for receiving light is also arranged at the center of the circle. A pair of data may be obtained by combining an optical fiber and each optical fiber arranged in a circular shape.

Furthermore, the arrangement of the end face of the optical fiber is
As shown in the figure, a pair of data is obtained by combining one optical fiber at the center of the circle and optical fibers arranged in a semicircle around the circle, and the cross-correlation function is determined in both directions. For example, the same effect as shown in FIG. 6 can be obtained by halving the amount of data to be captured.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the measurement principle that is the premise of this invention, Fig. 2 is a schematic diagram of a laser speckle velocimeter showing one embodiment of the invention, and Fig. 3 is a diagram of the same laser speckle velocimeter. Fig. 4 is a block diagram specifically showing the signal processing section of the laser speckle velocimeter, and Fig. 5 shows the operation of the signal processing section. Flowcharts for explanation, FIGS. 6 and 7 are diagrams showing other examples of arrangement patterns of optical fibers in the laser speckle velocimeter of the above embodiment. 10... Laser diode, 15... Object to be measured, 17... Optical fiber for light projection, 18a, 18
b, 18c...18n... optical fiber for light reception,
19a, 19b, 19c...19n...photodiode, 22a, 22b, 22c...22n...
Sample and hold circuit, 24...
CPU.

Claims (1)

[Claims] 1. A light source that generates coherent light and is equipped with a means for constantizing the temperature of the operating environment and a means for stabilizing the emission intensity, and a first optical fiber that guides the coherent light from this light source to the object to be measured. 2
A plurality of second lights are arranged such that the distance between the incident ends of each pair is equal and the directions are different, and each pair is arranged so that the distance between the incident ends is equal and the direction is different, and each pair is irradiated onto the object to be measured to derive diffuse reflected light that forms a speckle pattern. an optical fiber, a plurality of photoelectric conversion elements provided corresponding to these plurality of second optical fibers, each converting a change in a speckle pattern into an electrical signal, and an output signal from these photoelectric conversion elements. receiving, said second
means for calculating a cross-correlation function of a signal corresponding to a pair of optical fibers; and if a correlation peak exists in the calculated cross-correlation function, the correlation peak value and its time delay are storage means for storing the second optical fiber pair in association with the second optical fiber pair; and means for searching for the maximum value of the correlation peak value in the storage means and extracting the second optical fiber pair corresponding to the maximum correlation peak; Based on the extracted position of the second optical fiber pair and the time delay of the correlation peak,
A laser speckle velocimeter, comprising means for calculating the moving direction and moving speed of an object to be measured.