JPH0550710B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical distance measuring device that measures distance using, for example, laser or LED light.

[Technical Background of the Invention and Problems Therewith] In recent years, in distance measurement using light such as a laser beam, a distance measuring device using a so-called modulated wave telemetry method based on a modulated light signal has been proposed.

The basic principle of this distance measuring device using modulated wave telemetry is to measure the phase difference between modulated signals of transmitted and received light, and to determine distance using the wavelength of the modulated wave as a reference.

The basic configuration of a distance measuring device using this method is:
As shown in FIG. 3, a modulation signal source 21, a light source 12
5. It consists of a light wave distance meter 101 having a light receiving section 129, a phase difference detecting section 33, and a display section 37, and a corner cube 5. The basic operation of the device with this configuration is that, on the one hand, modulated light is projected from the light source 125 onto the corner cube 5 by the modulated signal 121 emitted from the modulated signal source 21, and the reflected light is sent to the light receiving section 1.
29 performs photoelectric conversion and inputs it to the phase difference detection unit 33 as an electric signal 131, and at the same time, the modulated signal 1
21 is input to the phase difference detection section 33, and the distance is measured by detecting the phase difference between these two input signals using this as a reference.

In the configuration shown in FIG. 3, the light emitted from the light source 125 is split into a measurement optical path 159 and an internal reference optical path 165 by a chopper beam splitter 123, and the light is received by a light receiving section 129. . This includes a semiconductor laser commonly used as the light source 125, a light receiving element of the light receiving section 129,
The amplifier etc. have a delay element, and the measurement optical path 1
59 includes this delay time, it is conceivable that the phase difference includes this delay time and the distance measurement accuracy deteriorates. Therefore, by using the chopper beam splitter 123, the measuring optical path 15 is
9 and an internal reference optical path 165.
Compensation is performed by not including the delay time of the delay element in the phase difference between the two, which is the output of No. 29.

By the way, if the device cannot be installed at the measurement location due to reasons such as the measurement environment, remote measurement will be performed. A conceivable configuration is such that the light emitting/receiving optical system 103 is separated from the light emitting optical fiber 101 and connected through the light emitting optical fiber 107 and the light receiving optical fiber 111.

However, the optical path length of this optical fiber is not constant, and is caused by temperature changes in the silicone resin and nylon coating surrounding the optical fiber. For example, in the case of an optical fiber with an optical path length of about 100 meters, temperature changes of several tens of degrees , a change in optical path length of several tens of millimeters occurs. Therefore, when compensating for this optical path length change using the chopper beam splitter 123, the chopper beam splitter 123 is placed in the light emitting/receiving optical system 103 to separate the measurement optical path and the internal reference optical path. is the optical path passing through the light emitting optical fiber 107 and the light receiving optical fiber 111, the distance is determined by detecting the phase difference between the two, and the change in the optical path length of the optical fiber is compensated for.

However, this small beam splitter 1
Since 23 is a mechanical mechanism and has electrical energy such as a power source, it is a relatively large scale device, and the chopper beam splitter 123 cannot be installed due to physical constraints of the location to be measured. A situation may arise. Furthermore, especially when the environment of the place to be measured does not favor electrical energy, such as an explosive gas atmosphere, the chopper beam splitter 123 cannot be installed in the light emitting/receiving optical system 103. Therefore, it is not possible to compensate for changes in the optical path length of the optical fiber, and as a result, there is a problem in that highly accurate measurement cannot be performed.

[Object of the Invention] The present invention has been made in view of the above, and its object is to accurately compensate for the delay time of the delay element of the device and the change in the optical path length of the optical fiber, thereby achieving highly accurate distance measurement. An object of the present invention is to provide an optical distance measuring device that can perform distance measuring regardless of the environment of the place.

[Summary of the invention] In order to achieve the above object, the present invention
a light emitting section, a second light emitting section, a first light receiving section, and a second light emitting section.
The first light emitting part has a first optical fiber, the second light emitting part has a second optical fiber, and a first light receiving part.
The light receiving section of is connected to a third optical fiber, the second light receiving section is connected to a fourth optical fiber, and each optical fiber is connected to a light emitting and receiving optical system, and this light emitting and receiving optical system is The light outputted from each light emitting section via the first or second optical fiber is projected onto the object to be measured, and the reflected light is sent to each of the light receiving sections via the third or fourth optical fiber. and a measurement path through which the light outputted from each of the light emitting units via the first or second optical fibers is transmitted through the third or fourth optical fibers without being projected onto the object to be measured. A branching means is provided for branching into an internal reference optical path input to each of the light receiving sections, and the first light output from the first light emitting section is
The light is branched by the first optical fiber and the branching means of the light emitting/receiving optical system, and is received by the first and second light receivers via the measurement path and the internal reference optical path, respectively, and by this light reception, both light receivers a first phase difference calculating means for calculating a phase difference between the two optical signals from the optical signals respectively output from the second light emitting section; and a second light output from the second light emitting section.
The light is branched by the second optical fiber and the branching means of the light emitting/receiving optical system, and is received by the second and first light receivers via the measurement path and the internal reference optical path, respectively, and by this light reception, both light receivers a second phase difference calculation means for calculating the phase difference between the two optical signals from the optical signals respectively outputted from the optical signals; and a difference between the calculation result of the first phase difference calculation means and the second phase difference calculation means. and a distance calculation means for calculating the distance to the object to be measured based on the difference.

[Embodiments of the Invention] Examples of the invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an optical distance measuring device according to an embodiment of the present invention. The configuration in the figure assumes remote distance. In FIG. 1, for example, the first optical fiber is shown as an optical fiber (1), and the second optical fiber is shown as an optical fiber (2). The same applies to the light emitting section and the coupler.

The optical distance measuring device of this embodiment includes a light wave range meter 1, a light emitting and receiving optical system 3 installed remotely to the light wave range finder 1, and a light wave distance meter 1 and the light emitting and receiving optical system 3. The system to be measured includes a first optical fiber 7, a second optical fiber 9, a third optical fiber 11, and a fourth optical fiber 13, which are optically connected. The object to be measured is provided with a corner cube 5 that reflects and returns the light projected therethrough.

The optical distance meter 1 includes, as a light emitting system, a modulation signal source 21 that generates a modulation signal, a switch 23, and a modulation signal source 21 that inputs the modulated optical signal via the switch 23 to generate modulated light (the first type described in the claims). light) is the first
A first light emitting section 25 outputs the modulated light to the optical fiber 7, and a second light emitting section 25 inputs the modulated signal through the switch 23 to output the modulated light (second light described in the claims).
It has a second light emitting section 27 that outputs to the optical fiber 9.

Further, the light wave distance meter 1, as a light receiving system, inputs the modulated light transmitted through the third optical fiber 11,
a first light receiving section 29 that converts into an electrical signal and outputs it;
A second light receiving section 3 receives the modulated light transmitted through the fourth optical fiber 13, converts it into an electrical signal, and outputs it.
1.

Furthermore, the light wave distance meter 1 has the above-mentioned 2 as a processing system.
a phase difference detection section 33 that detects the phase difference between the electrical signals from the two light receiving sections 29 and 31 with reference to the modulation signal of the modulation signal source 21; A memory calculation processing unit 35 that performs
and a display section 37 for displaying the results of the arithmetic processing of step 5.

The light emitting/receiving optical system 3 includes four couplers (a first coupler 4) serving as a directional coupler in an optical transmission system.
1, second coupler 43, third coupler 45, and fourth coupler 47), and one mirror 49 that reflects light.
and ten optical fibers (fifth optical fiber 51, sixth optical fiber 53, seventh optical fiber 55, eighth optical fiber 57, ninth optical fiber 5) that transmit light.
9, 10th optical fiber 61, 11th optical fiber 63,
12th optical fiber 65, 13th optical fiber 67 and
It is composed of 14 optical fibers (69) and has no electrical components, so it can be installed regardless of the environment of the place to be measured.

Here, the functions of the four couplers 41 to 47 will be explained.

The first coupler 41 is a 2×2 directional coupler, and connects the light from the first light emitting unit 25 input via the first optical fiber 7 and the fifth optical fiber 51 to the first optical fiber 7 and the fifth optical fiber 51.
It is output to the mirror 49 via the optical fiber 63 and to the fourth coupler 4 via the twelfth optical fiber 65.
7, while the light from the mirror 49 input via the 11th optical fiber 63 is transmitted to the 9th optical fiber 5.
9 to the fourth coupler 47.

The second coupler 43 is also a 2×2 directional coupler, and mirrors the light from the second light emitting section 27 inputted via the second optical fiber 9 and the sixth optical fiber 53 via the thirteenth optical fiber 67. 49 and the third coupler 45 via the fourteenth optical fiber 69.
On the other hand, the light from the mirror 49 input via the 13th optical fiber 67 is output to the 10th optical fiber 61.
It is output to the third coupler 45 via.

The third coupler 45 is a 2×1 directional coupler, and includes light from the second coupler 43 inputted via the tenth optical fiber 61 and light from the second coupler 43 inputted via the fourteenth optical fiber 69. The light is outputted to the seventh optical fiber 55 and transmitted to the first light receiving section 29 via the third optical fiber 11.

The fourth coupler 47 is also a 2×1 directional coupler, and the light from the first coupler 41 is input via the ninth optical fiber 59 and the light from the first coupler 41 is input via the twelfth optical fiber 65. The light is outputted to the eighth optical fiber 57 and transmitted to the second light receiving section 31 via the fourth optical fiber 13.

Next, the operation of this embodiment will be explained.

In this distance measuring device, a modulation signal is given to the first light emitting section 25 or the second light emitting section 27 by switching the switch 23, and modulated light is output from each light emitting section 25, 27 in conjunction with the switching of the switch 23. There is.

First, modulated light output from the first light emitting section 25 is transmitted via the first optical fiber 7 and the fifth optical fiber 51 and reaches the first coupler 41. This modulated light is branched by the first coupler 41 and reaches the first light receiving section 29 and the second light receiving section 31. That is, 11th optical fiber 63 → reflection by mirror 49 → lens 7
0 → Reflection by corner cube 5 → Lens 70 →
Reflection by mirror 49 → 13th optical fiber 67 → 2nd coupler 43 → 10th optical fiber 61 → 3rd coupler 45 → 7th optical fiber 55 → 3rd optical fiber 11
→Measurement optical path called first light receiving section 29 and 12th optical fiber 65 →4th coupler 47 →8th optical fiber 57
It is branched into an internal reference optical path of →fourth optical fiber 13→second light receiving section 31.

On the other hand, the modulated light output from the second light emitting section 27 is transmitted via the second optical fiber 9 and the sixth optical fiber 53 and reaches the second coupler 43. This modulated light is branched by the second coupler 43 and reaches the first light receiving section 29 and the second light receiving section 31. That is, 13th optical fiber 67 → reflection by mirror 49 → lens 7
0 → Reflection by corner cube 5 → Lens 70 →
Reflection by mirror 49 → 11th optical fiber 63 → 1st coupler 41 → 9th optical fiber 59 → 4th coupler 47 → 8th optical fiber 57 → 4th optical fiber 1
3. A measurement optical path called the second light receiving section 31 and the 14th optical fiber 69 → the third coupler 45 and the seventh optical fiber 5
5→third optical fiber 11→first light receiving section 29, which is an internal reference optical path.

Next, the operation of the processing system of the optical distance meter 1 will be explained.

First, when the switch 23 is at the a side contact,
The first light receiving section 29 outputs the modulated light emitted from the first light emitting section 25 via the measurement optical path through photoelectric conversion, and the second light receiving section 31 outputs the modulated light emitted from the first light emitting section 25 via the internal reference optical path. The modulated light is photoelectrically converted and output. The phase difference detection section 33 detects the phase difference between these two electrical signals using the modulation signal output from the modulation signal source 21 as a reference, and outputs it to the storage calculation processing section 35 . The storage calculation processing unit 35 temporarily stores this. Next, when the switch 23 is switched to the b-side contact, the modulated light emitted from the second light emitting section 27 via the internal reference optical path is photoelectrically converted and output from the first light receiving section 29, and the second light receiving section 3
1, the modulated light emitted from the second light emitting section 27 via the measurement optical path is photoelectrically converted and output. Similarly, the phase difference detection unit 33 detects the phase difference between these two electrical signals and outputs it to the storage calculation processing unit 35. The storage calculation processing unit 35 temporarily stores this, subtracts this phase difference from the previously temporarily stored phase difference, performs correction based on this subtraction result, and displays the display unit 3.
Output to 7. The display section 37 displays this value as a measurement result.

Next, the series of processes described above will be described quantitatively using FIG.

FIG. 2 is a diagram for explaining the principle of operation of FIG. 1. Here, the delay time due to the delay element of the light emitting section is Δφ _Si (i=1, 2), the delay time due to the delay element of the light receiving section is Δφ _Ri (i=1, 2), and the delay time due to the delay element of the light receiving section is Δφ Ri (i=1, 2). The delay time of the four optical fibers 13 is △T _j (j
= 1 to 4), one-way delay time of the measured system (distance from lens 70 to corner cube 5) △T _x
It is said that That is, as follows.

Delay time of first light emitting unit 25……△φ _S1 Delay time of second light emitting unit 27……△φ _S2 Delay time of first light receiving unit 29……△φ _R1 Delay time of second light receiving unit 31 ………△φ _R2 Delay time of the first optical fiber 7……△T ₁ Delay time of the second optical fiber 9……△T ₂ Delay time of the third optical fiber 11…△T ₃ Delay time of the fourth optical fiber 13 Delay time...△T ₄ Delay time of measured system ( _one way)...△T
- Regarding the fourteenth optical fiber 69, the optical path length is very short compared to those of the first optical fiber 7 to the fourth optical fiber 13, and changes in the optical path length can be ignored, so this optical path length should be measured in advance. It is sufficient to treat it as a constant and correct the final measurement result, and it is not considered here.

Now, the total delay time △ of the output signal V ₁ ← ₁ of the first light receiving section 29 when the first light emitting section 25 outputs modulated light
As shown in FIG. 2, T ₁ ← ₁ is expressed as the following equation.

△T ₁ ← ₁ = △φ _S1 +△T ₁ +△T ₃ +△φ _R1 +2△T _x ...Formula At that time, the total delay time ΔT ₂ ← ₁ of the output signal V ₂ ← ₁ of the second light receiving section 31 is , as shown in the following equation.

△T ₂ ← ₁ = △φ _S1 + △T ₁ + △T ₄ + △φ _R2 ... Formula From the formula, the delay time difference between the two φ ⁽¹⁾ _V1-V2 can be obtained by the following formula.

φ ⁽¹⁾ _V1-V2 =△T ₃ +△φ _R1 −△T ₄ −△φ _R2 +2△T _x =△L+2△T _x … Formula Here, △L=△T ₃ +△φ _R1 −△ T ₄ −△φ _R2 Similarly, the total delay time △T ₁ ← ₂ of the output signal V ₁ ← ₂ of the first light receiving unit 29 when the second light emitting unit 27 outputs modulated light, The total delay time ΔT ₂ ← ₂ of the output signal V ₂ ← ₂ is expressed by the following equation, as shown in FIG.

△T ₁ ← ₂ = △φ _S2 +△T ₂ +△T ₃ +△φ _R1 …formula △T ₂ ← ₂ =△φ _S2 +△T ₂ +△T ₄ +△φ _R2 +2△T _x …formula , from the equation, the delay time φ ⁽²⁾ _V1-V2 between the two can be obtained by the following equation.

φ ⁽²⁾ _V1 = △T ₃ +△φ _R1 −△T ₄ −△φ _R2 −2△T _x = △L−2△T _x …Formula φ ⁽¹⁾ _V1-V2 and φ ^{( 2)} _V1-V2 is the output of the phase difference detection section 33, and each value is temporarily stored in the storage calculation processing section 35, and the subtraction shown in the following equation is executed.

φ ⁽¹⁾ _V1-V2 −φ ⁽²⁾ _V1-V2 =4ΔT _x Formula A correction is made based on this subtraction result, and the correction result is displayed on the display section 37 as a measurement result. That is, as described above, the optical path lengths of the fifth optical fiber 51 to the fourteenth optical fiber 69 in the light emitting/receiving optical system 3 are much larger than those of the first optical fiber 7 to the fourth optical fiber 13. Since the optical path length is short and changes in the optical path length can be ignored, this optical path length is measured in advance and treated as a constant to correct the final measurement result.

Therefore, according to the distance measurement of this device, the delay time of the light emitting parts 25, 27, the light receiving parts 29, 31, and the optical fibers 7 to 13 does not appear in the measurement results; Each delay element of 29 and 31,
It is also possible to compensate for temperature changes in the optical path lengths of the optical fibers 7 to 13.

[Effects of the Invention] As explained above, according to the present invention, in an optical distance measuring device, it is possible to compensate for the delay element of the device and the change in optical path length, so that highly accurate distance measurement can be performed. This can be done regardless of the local environment.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an optical distance measuring device according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the principle of operation of the embodiment of Fig. 1, and Fig. 3 is a conventional optical distance measuring device. FIG. 4 is a block diagram showing an example of an optical distance measuring device for remote measurement. DESCRIPTION OF SYMBOLS 1...Lightwave distance meter, 3...Light emission/reception optical system, 5...Corner cube (object to be measured), 7...First optical fiber, 9...Second optical fiber, 11...Third optical fiber, 13...Fourth optical fiber , 21...modulation signal source,
23...Switch, 25...First light emitting section, 27...Second
Light-emitting section, 29...first light-receiving section, 31...second light-receiving section,
33... Phase difference detection section, 35... Memory calculation processing section, 3
7...Display section, 41...First coupler, 43...Second coupler, 45...Third coupler, 47...Fourth coupler.

Claims (1)

[Claims] 1. A first light emitting section, a second light emitting section, a first light receiving section, and a second light receiving section. The part is connected to a second optical fiber, the first light receiving part is connected to a third optical fiber, and the second light receiving part is connected to a fourth optical fiber,
Each optical fiber is connected to a light emitting and receiving optical system, and this light emitting and receiving optical system projects the light outputted from each of the light emitting sections through the first and second optical fibers onto the object to be measured. a measurement path for emitting light and inputting the reflected light to each of the light receiving sections via the third or fourth optical fibers; the third or fourth without projecting the light onto the object to be measured.
and a branching means for branching into an internal reference optical path that is input to each of the light receiving sections via an optical fiber, the first light output from the first light emitting section is
The light is branched by the first optical fiber and the branching means of the light emitting/receiving optical system, and is received by the first and second light receivers via the measurement path and the internal reference optical path, respectively, and by this light reception, both light receivers a first phase difference calculating means for calculating a phase difference between the two optical signals from the optical signals respectively output from the second light emitting section; and a second light output from the second light emitting section.
The light is branched by the second optical fiber and the branching means of the light emitting/receiving optical system, and is received by the second and first light receivers via the measurement path and the internal reference optical path, respectively, and by this light reception, both light receivers a second phase difference calculation means for calculating the phase difference between the two optical signals from the optical signals respectively outputted from the optical signals; and a difference between the calculation result of the first phase difference calculation means and the second phase difference calculation means. an optical distance measuring device comprising: a distance calculation means for calculating the distance to the object to be measured based on the difference;