JPH10221164A - Miscellaneous light eliminating method in laser light detection and laser sensor equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate influence of miscellaneous lights under light environment having vibration, by installing a light receiving element adjacently to another light receiving element when intensity of a laser light is detected, receiving miscellaneous lights except the laser light with both of the elements, and eliminating the miscellaneous lights by operating intensity difference of the miscellaneous lights. SOLUTION: A second light receiving element D2 is arranged adjacently to a first light receiving element D1 for receiving a laser light. A differential circuit A obtains and outputs the intensity difference of the lights which the elements D1 and D2 receive. An amplifier A1 is connected with the element D1 . An amplifier A2 is connected with the element D2 . The outputs of both of the amplifiers A1 , A2 are inputted in a differential amplifier A3 and subjected to differential amplification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for removing noise in laser light detection in which laser light is received by a light receiving element and the intensity is detected.

[Prior art]

2. Description of the Related Art Generally, a laser sensor device detects the intensity of a laser beam by receiving a laser beam with a light receiving element, and is used for various industrial measurements. Devices used for measurement have been studied.
In this case, accuracy and reliability are the most important. In the basic research stage in an ideal environment on a completely dark room and a vibration-free surface plate, even if it may deviate from the initial purpose, when using it in the field, , The accuracy and reliability always decrease. In particular, when measuring the number of weft yarns in a weaving factory, measurement is required in an environment that is very bright and has a lot of vibration. Therefore, in the past, in order to remove the influence of such noise, use something like a camera hood, modulate the laser light, and further reduce the light to prevent the light from entering the light receiving element as much as possible. A method of applying a signal filter to the element has been considered.

[0003]

However, in such a method of removing light, none of these methods can completely remove the influence of the vibration of the light. However, there is a problem that the light removal is insufficient. The present invention has been made in view of such a problem, and a method and a method for laser light detection in laser light detection capable of positively completely removing the influence of light interference even in a bright and vibrating environment. It is an object to provide a sensor device.

[0004]

In order to achieve the above object, the present invention provides a method for removing miscellaneous light in laser light detection, comprising the steps of: receiving a laser beam by a light receiving element and detecting the intensity of the laser beam; In addition to the light receiving element, another light receiving element is provided close to the light receiving element, and light other than laser light is received by both light receiving elements, and is removed by calculating a difference in intensity of the received light. In addition, the laser sensor device of the present invention includes a first light receiving element that receives laser light, and a light receiving element that is provided close to the first light receiving element and receives light other than laser light together with the first light receiving element. It is configured to include a second light receiving element and a differential circuit that outputs the difference in intensity between the light received by the first and second light receiving elements.

The basic principle of the present invention is as shown in FIG.
Two light receiving elements of a required standard are used at close positions, and a laser beam as a signal is applied to only one of the light receiving elements to take out a difference output between the two elements. FIG. 2 shows the entire measurement system. Light-receiving element D _1, D ₂ noisy light intensity incident to the respective N _1, N _2, the current I ₁ of the laser beam intensity incident only on the light receiving elements D ₁ and the L ₁ occurs in the light receiving element D ₁ is I ₁ = _{k 1 (L 1 + N 1} ), the current I ₂ generated in the light-receiving element D ₂ is the _{I 2 = k 2 · N 2} . Here, k ₁ and k ₂ are coefficients representing the combined light receiving sensitivity of both light receiving elements D ₁ and D ₂ , and ideally k ₁ = k ₂ ≡k. Since both light receiving elements D ₁ and D ₂ are arranged close to each other, it can be considered that N ₁ = N ₂ ≡N.

[0006]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a laser light detecting method according to an embodiment of the present invention; Since the method for removing noise is realized in the laser sensor device, the operation of the laser sensor device will be described. As shown in FIG. 2, the laser sensor device according to the embodiment includes a first light receiving element D ₁ for receiving laser light, and a first light receiving element D provided near the first light receiving element D _{1. 1} with a second light-receiving element D ₂ that receives the noisy light other than the laser beam, the first and second light receiving elements D _1, D ₂ to take the intensity differences of the received light and outputs the differential circuit a And In the differential circuit A, A ₁ is an amplifier connected to the first light receiving element D ₁ , A ₂ is an amplifier connected to the second light receiving element D ₂ , A
Reference numeral ₃ denotes an amplifier to which the outputs of both amplifiers A ₁ and A ₂ are input and differentially amplifies, and R ₁ and R ₂ are resistors connected to the amplifier A ₃ .

According to this laser sensor device, since the outputs from the light receiving elements D ₁ and D ₂ are differentially connected as shown in the figure, the signal I to the differential circuit A is I = I ₁ −I ₂ = kL
It becomes ₁ and it becomes only the signal of the laser beam which is not affected by the interference light. In case of noisy light N ₁ and N ₂ in an environment is different to a degree that can not be ignored, adjusting either the amplification degree light receiving elements D _1, D or amplifiers A ₁ to devise mounting method _2, A ₂ To approximately N ₁ = N ₂ .

[0008]

Next, an embodiment will be described. The light receiving elements D ₁ and D _{2 according} to this embodiment are both S2281 series photodiodes (HAMAMATSU), and the amplifiers A ₁ and A ₂ are both
C2719 photosensor amplifier (HAMAMATSU), final-stage amplifier A ₃ used was fabricated in the laboratory. Next, the following test was performed using the laser sensor device according to this example to examine the usefulness of the present method. Fluorescent lamps were used as the light source for the purpose of use in the field. In the test, a shield cover C capable of covering both light receiving elements D ₁ and D ₂ was used as shown in FIG.
If the light receiving elements D ₁ and D ₂ are mounted on the same support system, the vibrations received by the light receiving elements D ₁ and D ₂ become completely the same, so that errors due to the vibration can be eliminated.

First, an output of only a fluorescent lamp having a normal brightness when one light receiving element is shielded from light was obtained. FIG. 3 shows the output result. Further, an output of only the laser beam when one of the light receiving elements was shielded was obtained. FIG. 4 shows the output result. Further, when one of the light receiving elements was shielded from light, an output voltage E ₀ (a total output in which a DC component and an AC component were superimposed) was obtained when both were incident simultaneously. FIG. 5 shows the output result.
The respective output voltages are 2.92 V, 6.58 V and 9.50 V, and the sum of the output values shown in FIGS. 3 and 4 is completely the output value shown in FIG.

Next, in order to confirm the usefulness of the present method,
The same experiment as above was operated differentially. 6 to 8 show the results.
Shown in That is, the results shown in FIG.
The results shown in FIG. 8 are the output voltages when only the laser beam was applied, and the results shown in FIG. The output voltages are 18.85 mV, 0.94 mVm, and 20.25 mV, respectively, and the sum of the output values shown in FIGS. 6 and 7 is almost the output value shown in FIG.
From the results shown in the figure, the change in the intensity of the laser light is completely negligible, and the slight noise component of about 20 mV is considered to be a change in the amount of light of the fluorescent lamp incident on both light receiving elements. However, a fluorescent light output of 2.92 V of normal brightness, which is a miscellaneous light component,
(See FIG. 3), which is reduced to about 0.6%.
In this experiment, the laser light was attenuated and was directly incident on the light receiving element. However, since a reflected or scattered or transmitted light is usually used, a large voltage as shown in FIG. 4 is not always generated. However, simple experiments show that even relatively small amounts of scattered light
Since a laser light output of about V was obtained, the signal-to-noise ratio was 100 when the signal intensity was used as the signal intensity.

FIG. 9 shows the noise voltage of the light receiving element and the amplifier itself. It is about 3 mV, but this stray voltage is also negligible for this purpose. In the above example, the amplifier directly connected to both light receiving elements is of the same standard, but is not necessarily limited to this.
By using a variable amplification factor, even if different amounts of light are incident on both light-receiving elements, the influence of the light can be further reduced by finely adjusting them to almost the error of the element itself. It may be changed appropriately.

[0012]

As described above, according to the laser light detection method and the laser sensor device of the present invention, two identical light-receiving elements are differentially connected, and only one of the light-receiving elements is connected to the laser light. So that the so-called active light removal is performed as a difference output signal, so that the light component in the field of normal brightness can be reduced, the signal-to-noise ratio can be improved at least 100 times or more, and bright light can be obtained. In addition, even under a vibrating environment, the influence of noise can be positively almost completely removed, and accurate detection can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a basic principle of the present invention.

FIG. 2 is a diagram showing a laser sensor device according to an embodiment of the present invention.

FIG. 3 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 4 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 5 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 6 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 7 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 8 is a graph showing experimental results of the laser sensor device according to the example of the present invention.

FIG. 9 is a graph showing a noise voltage of the light receiving element and the amplifier itself of the laser sensor device according to the embodiment of the present invention.

[Explanation of symbols]

L ₁ Laser light intensity N ₁ , N ₂ Miscellaneous light intensity D ₁ First light receiving element D ₂ Second light receiving element A Differential circuit A ₁ , A ₂ , A ₃ Amplifier R ₁ , R ₂ resistance C Shield cover

Claims (2)

[Claims] When detecting the intensity of a laser beam by receiving a laser beam with a photodetector, another photodetector is provided in close proximity to the photodetector in addition to the aforementioned photodetector, so that light other than the laser beam is received by both photodetectors. And removing the received light by calculation of the intensity difference of the received light. 2. A first light receiving element for receiving a laser beam,
A second light receiving element that is provided near the first light receiving element and receives miscellaneous light other than laser light together with the first light receiving element; and a light receiving element that receives the light received by the first and second light receiving elements. A laser sensor device comprising: a differential circuit that outputs an intensity difference.