JP2881320B2 - Laser speckle speed detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser speckle speed detecting device for detecting a moving speed of a web or the like.

[Conventional technology]

The laser speckle velocity detection method is known, for example, from the report of “Laser Research”, Vol. 8, No. 2, page 379 et seq. The basic idea is that the object to be detected has some irregularities. The moving speed of the detection target is measured by detecting the movement of the detection target uneven portion at a position separated by a predetermined distance.

This can be summarized by referring to FIG. 1. When an object to be detected such as a web 1 is moving rightward, a laser beam from a laser light source 2 such as He-Ne is projected on the surface of the object via a projection lens 3. And irradiate. The transmitted light or reflected light of the laser light on the web 1 is detected by light receiving sensors 4A and 4B juxtaposed in the direction of speckle translation, and the time shift amount of the detected optical signal is detected by the correlation processor 5. The speed of the web 1 is detected by performing a correlation process.

Now, the moving speed of the web 1 is V, the translation magnification is σ, the moving speed of speckle on the light receiving sensor surface is v, the separation distance between the light receiving sensors 4A and 4B is X, and the distance between the light projecting lens 3 and the web 1 is The distance between the beam waist 6 and the web 1 is Z,
Assuming that the separation distance between the web 1 and the light receiving sensors 4A and 4B is R, the time shift amount τd of the signals detected by the light receiving sensors 4A and 4B is given by the following equation.

 v = σV σ = 1 + R / Z τd = X / v = X / σV Here, X and σ are known.

Also, as shown in FIG. 2, the light receiving sensor 4B shows a similar light receiving signal waveform with a time shift τd with respect to the light receiving signal waveform at the light receiving sensor 4A, so that the time shift τd can be measured. , The moving speed V of the target web 1 can be known. However, since the time shift amount τd can be measured through the above-described correlation processing, the moving speed of the web 1 can be measured after all.

[Problems to be solved by the invention]

However, in this kind of conventional moving speed detecting device, the parallel movement of the speckle pattern is directly detected by the light receiving sensor although the transmitted light or the reflected light may be reflected by the mirror.

However, in such a conventional method, the speed resolution is poor and the detection accuracy is not very high, as will be shown in the examples described later.

Therefore, the main object of the present invention is to achieve high speed resolution,
Accordingly, it is an object of the present invention to provide a speed detecting device having excellent detection accuracy.

[Means for solving the problem]

The above object is to irradiate the object to be detected with a laser beam and receive a light amount variation of the parallel movement of the reflected or transmitted speckle pattern with at least two light receiving sensors spaced in the direction of the speckle movement, In a device for determining a time shift amount of a signal from these light receiving sensors by a cross-correlation process and detecting a moving speed of an object to be detected, a speckle component of an optical signal taken into the light receiving sensor is compared with a speckle component. Narrowing means for narrowing the translation direction is provided, and the distance between the two light receiving sensors in the speckle translation direction is larger than the distance between the speckle translation directions of the transmitted lights narrowed by the narrowing means. Two light-receiving sensors are arranged, and a light-transmitting light between the narrowing means and the light-receiving sensor is incident on each of the corresponding light-receiving sensors. Provided a light separation guiding means, it can be solved by.

Along with the narrowing means, an expanding means for expanding in a direction orthogonal to the speckle translation direction is also provided.

[Action]

The speckle velocity detection method according to the present invention is based on the premise that an object to be detected is usually not a specular body but an optical diffuser, and detects diffused light from the object to be detected. Therefore, the amount of the received light is weak because it is the diffused light. The present inventors have found that the measurement accuracy is not high because this weak light amount is detected and used as a reference for measuring the moving speed.

However, according to the present invention, when a narrowing means for narrowing the translational movement direction of the speckle is provided for the speckle component of the optical signal captured by the light receiving sensor, the light receiving sensor can emit light only in a narrow area in the translation direction. Is detected, a steep change in the amount of light can be detected, thereby increasing the speed resolution. As a result, the detection accuracy increases.

On the other hand, in the direction orthogonal to the speckle translation direction, if an expanding means for expanding is provided, a target signal with respect to noise can be accurately detected, that is, the S / N ratio can be increased.

Further, by using this enlargement means, it is possible to receive light in a wider range than the light receiving area defined by the light receiving area of the light receiving sensor itself, so that the setting positioning of the light receiving sensor in the direction orthogonal to the speckle translation direction becomes easy. .

Furthermore, when a slit is used as the narrowing means, for example, when the size of each light receiving sensor is increased to increase the amount of received light, or when the slit interval is narrower than the sensor size, the specifications are reduced. In order to improve the translational performance and the detection accuracy, the center interval between the two light receiving sensors may be larger than the slit interval. In this case, the transmitted light from the other slit enters one sensor. As a result, the detection accuracy is reduced.

On the other hand, if the transmitted light sorting guide means for making each transmitted light incident on the corresponding light receiving sensor is provided between the narrowing means and the light receiving sensor, the influence of the transmitted light on the other slit can be prevented. Can receive light. Further, it is possible to realize a slit interval narrower than the sensor size, thereby improving speckle translation and detecting accuracy.

[Specific configuration of the invention]

 Hereinafter, the present invention will be described in more detail with reference to the drawings.

Although the measurement principle of the present invention is as described above, in reality,
For example, as shown in FIG. 4, the laser light from the laser light source 2 passes through the beam expanders 7 and 8, and then is condensed by the condensing lens 3, and the object to be detected, for example, the object to be detected via the plane mirror 9 After irradiating the photosensitive web 1 and transmitting it, the light receiving sensor 4
A, 4B (only one is shown in the figure). In addition, the moving direction of the web 1 and the speckle translation direction are directions penetrating the paper surface, and the numerals attached to f in FIGS. 3, 3 and 5 show examples of the focal length, and the numerals attached to Z and R. Indicates the above numerical example.

FIG. 3 shows a conventional example, whereas in the present invention,
Narrowing means is provided for narrowing the speckle translation direction with respect to the speckle component of the optical signal taken into the light receiving sensor. As an example of this narrowing means, as shown in FIG.
It can be configured by disposing a narrow slit 20 in the speckle translation direction in front of each of the light receiving sensors 4A and 4B.

Due to the presence of this slit 20, the light receiving area of the light receiving sensor 4A or 4B at a certain point in time is 4A * or 4A * in FIG.
If it is 4B *, a change in the amount of light with respect to the translation speed in the speckle translation direction can be detected sharply, as can be easily estimated from FIG.

Incidentally, in the embodiment according to FIG. 3 in which the slit 20 is not provided, a correlation signal as shown in FIG. 8 can be obtained from the signals of the respective light receiving sensors 4A and 4B in FIGS. Seventh
Comparing FIGS. A and b, it can be seen that the lowering peaks Pa and Pb are particularly similar. However, FIGS. 7 and 8
According to the figure, each waveform is also found to be dull.

In contrast, the slit according to the invention according to FIG.
In the embodiment provided with 20, the waveform is sharp and the obtained correlation signal is clear as shown in FIGS. 9a and 9b. Therefore, it can be seen that providing the slit 20 in front of the light receiving sensors 4A and 4B according to the present invention is more effective for improving the speed resolution than the conventional example.

In the present invention, more preferably, in addition to the narrowing means, for example, the slit 20, an expanding means for expanding in a direction orthogonal to the speckle translation direction is provided.

This expanding means can be constituted by disposing a cylindrical lens 30 in front of the slit 20 as shown in FIG. The cylindrical lens 30 receives light in a direction orthogonal to the speckle translation direction by the light receiving sensor 4A.
Or there is a function to focus on 4B. Further, as shown in FIG. 13, a converging device 40 in which optical fibers 40a are bundled so as to converge backward may be provided in front of the light receiving sensors 4A and 4B. The converging device 40 also has a narrowing means because the optical fibers 40a are bundled with a narrow width in the vertical direction, together with the expanding means.

FIG. 11 shows the signal waveforms of the light receiving sensors 4A and 4B according to the embodiment of FIG. 5, and FIG. 12 shows the correlation signals. 9 and 11, it can be seen that the level of the received light signal has increased, and when comparing FIG. 10 with the twelfth one, it is not very clear, but the S / N ratio has increased. You can see that

On the other hand, to increase the amount of received light,
It is preferable to increase the size of A and 4B. However, when the interval between the slits 20 and 20 is fixed, the center interval between the two light receiving sensors 4A and 4B is
In some cases, the distance may be larger than the interval. In this case, the transmitted light from the other slit enters one of the sensors, and as a result, the detection accuracy is reduced.

The same can be said for a case where the slit interval is narrower than the sensor size when the sensor size is constant, thereby improving the speckle translation and the detection accuracy.

In contrast, the slit 20 and the light receiving sensor 4A or 4B
Between the slits 20 and 20, there is provided a transmitted light sorting guide means for making the transmitted light of the corresponding light-receiving sensors 4A and 4B incident on the corresponding light receiving sensors 4A and 4B, for example, when a prism is provided as described below, the influence of the transmitted light on the other slit is Light can be received while preventing.

That is, in FIGS. 14a and 14b, a slit plate 200 as a narrowing means is provided on the back surface of the cylindrical lens 201, and a prism 20 as a transmitted light sorting guide means is provided behind the slit plate 200.
2, the light passing through each slit 200a, 200b is totally reflected by the reflecting surface 202a, 202b of the prism 202, and the light receiving sensors 4A, 4B in which the reflected light is arranged at intervals larger than the interval between the slits 200a, 200b. To be incident.

Thereby, the transmitted light transmitted through the slits 200a and 200b can be made incident on the corresponding light receiving sensors 4A and 4B. In addition, a large light receiving sensor 4A, 4B can be used, and the amount of received light can be increased, thereby increasing the detection accuracy. Conversely, a slit interval narrower than the sensor size can be realized, and detection accuracy can be improved.

As the transmitted light sorting guide means, FIG.
As shown in FIG. 2B, a mirror 203 may be provided on one surface of the prism 204 to separate transmitted light.
Further, in addition to this, an example in which a mirror is simply provided at the place of the mirror 203 without providing the prism 204 may be used.

By the way, as described above, the transmitted light is
When sorting and changing direction by 202, each slit 200a, 2
00b transmitted light affects each other's transmitted light,
There is a concern about the effects of so-called traffic.

Therefore, to examine this point, as shown in FIG.
Using a mask 50, only the light incident on one slit 200a is blocked by the mask 50, and the difference in the output of one light receiving sensor 4B depending on the presence or absence of the mask is determined.

As a result, the light receiving sensors 4A and 4B without the mask
17a and 17b are output waveforms corresponding to FIG. 17, while when only the incident light to the slit 200a is masked, the output waveform of FIG.
Figures a and b are obtained. A comparison of the waveforms in FIG. 17b and FIG. 18b shows that there is almost no change. When the output level change of the light receiving sensor 4B at this time was examined, no difference was found in the output level.

From the above, it was determined that there was no influence of the wraparound of the light transmitted through the slit of the other party, and the effectiveness of the example in FIG. 14 was confirmed.

Further, the waveforms detected by the respective light-receiving sensors 4A and 4B and the correlation signals after the cross-correlation processing were examined in the mode shown in FIG. 19 in the embodiment shown in FIG. 19, and the light-receiving sensors shown in FIGS. Output waveforms of 4A and 4B were obtained, and correlation outputs as shown in FIG. 21 were obtained. As described above, it is clear that the correlation output clearly appears when the transmitted light sorting guide unit is provided.

As the light receiving sensor in the present invention, an appropriate one can be used. For example, a photodiode PD, an avalanche photodiode APD, a photodiode array P
DA, solid-state imaging device CCD, and the like can be given. In addition, the order of disposing the expanding means and the narrowing means may be either.

On the other hand, in order to increase the resolution and the amount of received light, it is important that the slit width is small and the slit length is long as the received light signal.For example, in the photodiode array PDA shown in FIG. hard. In this point, when the solid-state imaging device CCD is used, a slit that is sufficiently narrow and long can be obtained, but the response is low because the output is serial, which is a disadvantage.

In contrast, according to the present invention, a sufficiently narrow and long slit signal can be easily obtained.

〔The invention's effect〕

As described above, according to the present invention, a speed detection device having high speed resolution and thus excellent detection accuracy is provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of speckle velocity detection according to the present invention, FIG. 2 is a diagram illustrating waveforms and correlation signal waveforms at a light receiving sensor, FIG. 3 is a diagram illustrating an optical system of a conventional example, FIG. FIG. 6 is an explanatory view of an optical system according to the present invention, FIG. 6 is a layout diagram of slits, FIG. 7 and FIG.
FIGS. 12 to 14 are waveform diagrams according to the present invention, FIG. 13 is a perspective view of another example of the enlarging means, and FIGS. Changed illustration,
15a and 15b are explanatory views of another example in which the transmitted light sorting guide means is attached, in which the viewing direction is changed by 90 degrees, respectively, FIG. 16 is an explanatory view of a slit transmitted light wraparound experiment, FIGS. 17a and b and 18a and 18b are signal waveform diagrams of each light receiving sensor depending on the presence or absence of a mask, FIG. 19 is a configuration diagram of a speckle speed detecting device in an example provided with transmitted light sorting guide means, FIGS. 20a and b 19 is a signal waveform diagram of each light receiving sensor according to the example of FIG. 19, and FIG. 21 is a correlation output diagram. 1. Web (object to be detected) 2. Laser light source 4A,
4B: light receiving sensor, 5: correlation processor, 20: slit, 30, 201: cylindrical lens, 40: converging device, 200: slit plate, 200a, 200b: slit, 20
2,204 ... Prism (transmitted light sorting guide means).

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-173715 (JP, A) JP-A-61-189462 (JP, A) JP-A-1-172756 (JP, A) JP-A-1- 172758 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G01P 3/36 G01P 3/80

Claims (2)

(57) [Claims] 1. An object to be detected is irradiated with a laser beam, and a variation in the amount of parallel movement of a reflected or transmitted speckle pattern is received by at least two light-receiving sensors spaced in a moving direction of the speckle. In a device for determining the time shift amount of signals from these light receiving sensors by cross-correlation processing and detecting the moving speed of an object to be detected, the speckle component of an optical signal taken into the light receiving sensor is speckled. A narrowing means for narrowing the translational movement direction of the two light-receiving sensors in a state in which the distance between the speckle translational movement directions of the two light receiving sensors is larger than the distance between the speckle translational movement directions of the respective transmitted lights narrowed by the narrowing means. The two light-receiving sensors are arranged, and a light-transmitting light that causes each transmitted light to enter the corresponding light-receiving sensor between the narrowing unit and the light-receiving sensor. It provided a light separation guiding means, laser speckle velocity detecting apparatus characterized by. 2. An apparatus according to claim 1, further comprising an expanding means for expanding in a direction orthogonal to a speckle translation direction, together with said narrowing means.