JPS6382365A - Motion measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain sufficient quantity of light to measure kinetic characteristic, by admitting a speckle pattern into a plate with openings arranged at random. CONSTITUTION:Light from a laser light source 10 is scattered by a moving object 12 to be incident into a measuring device. A measuring surface of the measuring device has a mask plate 15 with an opening at the center and a random pattern plate 14 in which fine openings are arranged closely in a random pattern 14'. The movement of a speckle pattern 13 in the measuring surface is detected with a photo detector 17 as timewise changes in the light intensity through the plate 14, after amplified with an amplifier 18, it is inputted into an analyzing section 20 cleared of an undesired frequency component with a filter 19 and the speed of the moving object 12 is displayed. Thus, measured light is made incident into the photo detector 17 through the random plate 14 thereby assuring sufficient quantity of light for measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a motion measuring device, and particularly to a motion measuring device for measuring motion characteristics such as the moving speed and moving state of an object to be measured.

[Prior Art] Various measuring devices using laser light have been known. In particular, in the field of measuring speed among the motion characteristics of objects, speed measuring devices that utilize speckle patterns created by scattered laser light are known.

Generally, laser light that is irradiated onto an object, reflected from the object, or transmitted through the object forms a so-called speckle pattern, which is a pattern of bright and dark spots, as a result of random interference of coherent light. Furthermore, when the target object being irradiated moves, the speckle pattern also moves at the same time. The speed measuring device determines the moving speed of the object in a non-contact manner by measuring the moving speed of this speckle pattern.

FIG. 11 shows the general configuration of a conventional motion measurement device.
A moving object 2 is irradiated with a laser beam 1, and a speckle pattern formed by the transmitted light is detected by a detection aperture 3 arranged on a detection surface. The light that has passed through the aperture is incident on the photodetector 4, and the amount of light is measured. The movement of the speckle pattern is detected as a temporal change in the light intensity seen through the detection aperture.

[Problems to be Solved by the Invention] In order to accurately detect changes in the light intensity of the speckle pattern, the diameter of the detection aperture should be determined by adjusting the diameter of the detection aperture to the individual speckles (corresponding to bright and dark spots) of the speckle pattern. It is desirable that the diameter of the detection aperture 3 be equal to or smaller than the diameter of the detection aperture 3. Therefore, in such applications, a pinhole is mainly used as the detection aperture 3.

However, if the speckle size becomes small due to the transmission characteristics of the object to be measured or other conditions, there is a problem that it is not possible to obtain a sufficient amount of light to be detected by the detector 4, and the output signal deteriorates or measurement becomes impossible. was there.

In addition, the speckle pattern is moving in a certain direction,
If the direction is known in advance, a spatial filter 5 such as a lattice having a row of slits arranged along a direction perpendicular to the moving direction of the speckle pattern may be used instead of the detection aperture 3 in FIG. You can also do it. According to this method, movement of the speckle pattern can be detected with sufficient light intensity, but it cannot be applied when the movement direction of the speckle pattern is not constant or does not match the slit arrangement direction of the spatial filter. This method can be used in the case of boiling speckles, where the speckle pattern does not move even when the object moves, and only bright and dark spots deform and fluctuate, or when the object to be measured is a fine particle that moves randomly. A fluctuation-like motion that is formed and does not have a fixed direction of motion cannot be detected.

Means for Solving Problem c] In order to solve the above problems, the present invention provides a laser light source for irradiating a moving object with laser light, and a laser light source scattered by the object to form a laser light source. A random pattern plate having randomly arranged openings into which the speckle pattern is incident, a photodetector that receives light passing through the random pattern plate and forms a detection signal according to the light intensity, and this photodetector. A configuration is adopted in which means is provided for analyzing the motion characteristics of the moving object from the movement state of the speckle pattern reflected in the characteristics of the output signal.

[Function] According to the above configuration, it is possible to detect a speckle pattern with a sufficient amount of light using a random pattern consisting of a plurality of apertures randomly arranged two-dimensionally, and it is also possible to detect a speckle pattern with a sufficient amount of light. Since no mask means is used, even movements with inconsistent directionality can be reliably measured.

[Example] Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows the configuration of a motion measuring device using the present invention. In FIG. 1, reference numeral 10 is a laser light source that generates a laser beam. The light emitted from the laser light source illuminates the measurement area of the moving object 12.

The irradiated laser light is scattered by the moving object 12,
The transmitted and scattered light enters the measuring device on the right side of the figure. In this embodiment, the measuring surface of the measuring device has a mask plate 15 with an opening in the center and a large number of random apertures closely spaced on this mask plate 15. A random pattern board 14 is arranged. m
The movement of the speckle pattern 13 formed on a constant plane is detected as a temporal change in light intensity via the random pattern plate 14 by a photodetector 17 composed of a phototransistor, a photomultiplier, and other elements.

A mask plate 15 with a finite aperture has a random pattern 14
The size of the opening in the mask plate 15 is determined depending on the area of the detection surface of the photodetector 17 for detection.

The random pattern plate 14 has a random pattern 14° formed by two-dimensionally arranging a plurality of minute openings at random above a predetermined large area, and has no specific directionality in the opening arrangement. As an example of the pattern board 14,
A conceivable example is a film in which a speckle pattern is formed by irradiating the assembly with laser light in a separate optical system and then photographed.

Here, it is desirable that the size of each opening of the random pattern plate 14 is approximately equal to or larger than the average diameter of the individual speckles on the speckle pattern 13. If the aperture is larger than the random aperture, one speckle 16 will be detected across multiple micro apertures 14a at the same time, as shown in FIG. This is because you will be exposed.

Furthermore, it is desirable that the average spacing between the minute openings in the random pattern of the random pattern plate 14 be approximately the same as the diameter of the openings.This means that if the average spacing is smaller than the opening diameter, adjacent openings will be close This is because the image of the speckle pattern is almost always observed through one of the apertures, and the detection signal does not change sufficiently in intensity as the speckle pattern moves.

On the other hand, if the average interval between micro-apertures becomes larger than the aperture diameter, the intensity changes in the amount of light detected from each aperture lose their correlation with each other, resulting in averaging of the detection signal and the overall result obtained from the photodetector. This is because information regarding the movement of the speckle pattern is lost from the signal, and in extreme cases, the output signal becomes almost only a DC component.

The light that has passed through the random pattern plate 14 is received by a photodetector 17 and converted into an electrical signal. The size of the light-receiving surface of the photodetector 17 is selected so that it can receive all the amount of light that has passed through the random pattern plate 14. The detection signal from the photodetector 17 is amplified by an amplifier 18 and input to a filter 19 to remove unnecessary frequency components such as noise and low frequency fluctuation components.
is input.

As shown in FIG. 3, the analysis unit 20 includes a signal processing unit 20a that performs signal processing as described below, an arithmetic unit 20b that includes a microcomputer that calculates the speed of a moving object, and a liquid crystal display SCR, T display. It is composed of a display section 20c consisting of, etc. The signal processing section 20a and the calculation section 20b calculate the speed of the moving object 12 from the output signal of the photodetector 17 as described below, and display it on the display section 20c.

Now, when the moving object 12 in FIG. 1 moves at a certain speed, the speckle pattern 13 also moves on the random pattern plate 14 across its minute opening. Since the openings of the random pattern plate 14 are randomly arranged as described above, the amount of light passing through the random pattern plate 14 changes randomly on the time axis according to the movement of the speckle butter 713. Therefore, the signal output from the photodetector 17 also changes randomly over time as shown in FIG.

Although the change in the output signal of the photodetector 17 does not have a constant periodicity, the faster the speckle pattern 13 moves, the faster the random fluctuation of the signal becomes, and the degree of random fluctuation and the moving speed of the moving object 12 There is a certain correlation between them.

Here, as a method for evaluating the degree of random fluctuation in the output signal of the photodetector 17, a method of examining the distribution of the power spectrum will be exemplified.

In this case, the signal processing section 20a is composed of a circuit that measures the power distribution for each frequency. The power spectrum calculated by the signal processing section has a distribution as indicated by symbols p and q in FIG. 5, depending on the moving speed of the moving object 12. In FIG. 5, the horizontal axis is frequency, and the vertical axis is signal strength in dB. If the moving speed of the moving object 12 is slow, a power distribution like p is obtained, and if the moving speed is fast, a power distribution like q is obtained. Therefore, if the degree of attenuation changes according to the moving speed of the moving object 12, the higher the zero frequency attenuates, the moving speed of the moving object 12 will be slow; The movement speed will be fast.

In order to measure the degree of attenuation, the calculation section 20b may perform the following analysis.

In each power spectrum distribution in FIG. 5, frequencies at which the power is attenuated by 10 dB and 20 dB are read based on the power value at frequency zero, and these are designated as fα and fβ. If this is plotted as shown in the graph of FIG. 6, with fα and fβ plotted on the horizontal axis and the object speed on the vertical axis, a certain proportional relationship will be obtained.

Therefore, considering various conditions such as the illumination area diameter of the optical system of the measuring device, the illumination beam curvature, the distance from the object to the random pattern plate 14, the speckle pattern diameter, and the aperture diameter of the random pattern plate 14, By calibrating the slopes of fα and fβ in advance, the object speed can be detected from the values of fα and fβ. fα to obtain a predetermined amount of attenuation
Or fβ can determine the speed with either one, so
Usually, it is sufficient to measure only either fα or fβ. However, by using both fα and fβ, there is an advantage that measurement accuracy can be greatly improved.

The speed of the moving object 12 calculated as described above is displayed on a display 20c such as a liquid crystal display or a CRT.

Furthermore, a method of examining an autocorrelation function may be considered as a process performed by the analysis unit 20 to determine the speed. Photodetector 17
When the autocorrelation function of the output signal is determined by the signal processing section 20a, a correlation as shown in FIG. 7 is obtained depending on the speed of the moving object 12. Figure 7 shows how the photodetector 17 changes over time.
shows the autocorrelation of the output. In FIG. 7, p is the autocorrelation when the speed of the moving object 12 is slow, and q is the autocorrelation when the speed of the moving object 12 is fast. This is because if the speed of the moving object 12 is slow, the autocorrelation of the output signal of the photodetector 17 is maintained over a long time range, and if the speed is fast, the autocorrelation does not persist.

In this method as well, the velocity can be calculated by performing the same analysis as the power spectrum method described above in the calculating section 20b. The autocorrelation function is 1/e, 1
The time at which it decays to /e2 is τα and τβ, respectively, and as shown in Figure 8, the horizontal axis represents the object velocity and the vertical axis represents 1/τ.
If α and 1/τβ are plotted, a certain proportional relationship can be obtained. Therefore, here too, if the slopes of l/τα and l/τβ are calibrated according to the conditions of the measurement system, τα and τβ
From the measurement of , the velocity of the moving object 12 can be determined. In this case, as in the case of the power spectrum method, τ
The speed can also be calculated by measuring only either α or τβ.

According to this embodiment, the moving object 12 is not limited to the case where the moving object 12 performs a relatively regular motion;
Good measurement results can also be obtained when the particles 2 move randomly like fine particles. Random pattern board 14
is not a spatial filter using slits or the like as described above, but is composed of a random open pattern, so even when the moving object 12 such as a particle moves randomly, the speckle pattern that reflects the movement will not fluctuate randomly. A detection output signal corresponding to the random motion can be obtained from the photodetector 17 according to the random motion. Therefore, the average moving speed of the moving object 12 or the activity level of the particles can be measured using the same analytical principle as described above.

In other words, when measuring microparticles, when the particles 30 do not move in a uniform direction as shown in Figure 9, but individually move in random directions completely independently as shown in Figure 1O. , the individual speckles of the speckle pattern formed along with this also move in random directions. Even in such a movement, if a random pattern plate 14 having a random opening pattern is used, a signal with sufficient intensity fluctuation can be obtained as each speckle crosses each aperture. Even in such a case, there is a certain correlation between the speed of random movement of individual speckles and the degree of intensity fluctuation of the output signal.

Therefore, by evaluating the output signal of the photodetector 17 using the above-mentioned analysis method, it is possible to obtain object velocities corresponding to fα, fβ, τα, and τβ, as shown in FIG. 6 or 8. However, in this case, the microparticles are moving randomly.

It is not possible to obtain a constant speed.

Therefore, here, the velocity obtained from Figure 8 can be treated as the degree of random movement of microparticles, or the degree of activity.The measurement results can be evaluated as the average value of the motion of a large number of microparticles, and the obtained The activity level can be interpreted as the average speed of movement.

[Effects] As is clear from the above, according to the present invention, a laser light source for irradiating a moving object with laser light and a random arrangement in which speckle patterns formed by laser scattered light scattered by the object are incident. a photodetector that receives the light that has passed through the random pattern plate and forms a detection signal according to the light intensity; Since the structure includes means for analyzing the motion characteristics of the moving object from the movement state of the speckle pattern, it is easier to measure speed and other motion characteristics than when using pinhole apertures as in the past. In addition, the measurement light is incident on the photodetector via a random opening pattern, which makes it possible to obtain sufficient light to measure It has an excellent effect in that it can also measure characteristics.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the configuration of a motion measuring device employing the present invention, FIG. 2 is a perspective view showing the configuration of the random pattern plate in FIG. 1, and FIG. 3 is an illustration of the analysis section in FIG. FIG. 4 is a block diagram showing the configuration, FIG. 4 is a diagram showing the output signal of the photodetector in FIG. 1, FIGS. 5 and 6 are diagrams showing the velocity analysis method according to the present invention, and FIG. 8 are a diagram showing different speed analysis methods according to the present invention, and an explanatory diagram showing a ninth configuration, respectively. 10... Laser light source 11... Lens 12...
Moving object 13...Speckle pattern 14...Random pattern plate 17...Photodetector 18...Amplifier 19...Filter 20...
-Analysis section 20a...Signal processing section 20b...
Arithmetic unit 20c...Display unit Fig. 4

Claims (1)

[Claims] 1) A laser light source for irradiating a moving object with laser light, and a random pattern plate having randomly arranged openings into which a speckle pattern formed by the laser scattered light scattered by the object enters. and a photodetector that receives the light that has passed through this random pattern plate and forms a detection signal according to the light intensity, and from the moving state of the speckle pattern reflected in the characteristics of the output signal of this photodetector. A motion measurement device characterized by comprising means for analyzing motion characteristics of the moving object. 2) The motion measurement device according to claim 1, wherein the analysis means calculates the speed of the moving object from a power spectrum distribution related to the frequency of the output signal of the photodetector. 3) The motion according to claim 1, wherein the analyzing means calculates the moving speed of the moving object from the time-related attenuation of the autocorrelation function of the output signal of the photodetector. measuring device.