JPH06174844A - Laser distance measuring apparatus - Google Patents

Abstract

PURPOSE:To provide a laser distance measuring apparatus which can prevent errors in measurement due to changes in ambient temperature, reduce optical parts, be integrated and miniaturized, facilitates optical adjustment and has high measuring accuracy. CONSTITUTION:Light emitted from a laser 101 of a periodically modulated frequency is split by a light splitting and combining means 103 into reference light 1, 2 and measuring light 3, 4. The measuring light 4 is applied to a subject 108 for measurement and reflected there while the reference light 1 is reflected by a reflector 104, to obtain a beat signal from both light. Also, the measuring light 3 is reflected by a reflector 105 (of known optical distance) while the reference light 2 is reflected by the reflector 104 so as to obtain a beat signal from the difference in optical path between both light. Each pair of light is allowed to pass through the beam splitter 103 again and is combined together and impinges on a light detector 106. Errors resulting from changes in the amount of modulation of frequencies are prevented by a reference optical system. Optical parts are used in common so that miniaturization and reduction in the number of part items are made possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser distance measuring device used for FA (factory automation) or the like.

[0002]

2. Description of the Related Art Conventionally, as a laser distance measuring method, a laser light whose frequency is periodically modulated is divided into a measuring light and a reference light, and each light has a known optical distance from an object to be measured. There is known a method of irradiating a placed reflector with the obtained reflected light and performing coherent heterodyne detection to measure the distance to an object to be measured. In the laser distance measuring method as described above, the beat signal is obtained from the frequency difference caused by the optical path difference between the measurement light applied to the measurement object and the reference light applied to the reflector, and the beat signal is measured from the beat signal. The separation distance to the object can be calculated.

FIG. 9 shows the basic structure and principle of a laser distance measuring apparatus used in the above laser distance measuring method. This laser distance measuring apparatus is provided with a laser 901 which periodically FM-modulates the frequency of laser light into a triangular wave shape or a sawtooth wave shape and emits the FM light. As a method of modulating the frequency in this way, for example, a method of changing the amount of current injected into the semiconductor laser to change the oscillation wavelength generated is used. The laser light emitted from the laser 901 and having the frequency periodically modulated is collimated by the collimator lens 902 and split by the beam splitter 903. One is a reflector 904 placed so that the optical distance is known as reference light.
Is reflected by the measurement target 90 as the measurement light.
7 is irradiated and reflected or scattered. The respective lights are combined again by the beam splitter 903, are incident on the photodetector 905, and are subjected to coherent heterodyne detection. At this time, an interference fringe is generated in the photodetector 905, and the interference fringe temporally changes according to the frequency difference due to the optical path difference between the measurement light and the reference light. Then, a beat signal is output as the output of the photodetector 905. This beat signal is measured by the counter 906.

The frequency of the beat signal is given by the following equation (1).

[0005]

[Equation 1]

Here, fb is the beat signal frequency, τ is the time delay between the measurement light and the reference light, fm is the modulation frequency, and Δν
(GHz / mA) is the frequency modulation amount of the laser, R is the optical path length of the reference light, L is the separation distance to the measurement object, and c is the speed of light.

Further, the time interval T of the frequency sweep of the laser
The phase displacement (integral value) of the beat signal that occurs during (= 1 / fm) is given by the following equation (2).

[0008]

[Equation 2]

Here, the wave number of the beat signal N = (φ / 2
π), the following formula (3) is obtained.

[0010]

[Equation 3]

Therefore, the distance measurement information can be obtained by measuring the wave number of the beat signal and the phase change amount of the wave number.

The above laser distance measuring method has the advantages that the measurement dynamic range is wide and the measurement accuracy is high.

In the above laser distance measuring method, when a laser distance measuring device as shown in FIG. 9 is used, the frequency modulation amount Δν of the laser is accurately adjusted so as to increase the distance measuring accuracy. Need to control. But in reality,
The frequency modulation amount Δν of the laser changes due to changes in the ambient temperature, etc., which causes a measurement error.

In order to prevent the measurement error due to the frequency modulation amount, Japanese Patent Laid-Open No. 61-223577 (Distance measuring method using laser beam Kobayashi Takao) and IEICE Technical Report (OQE87-153, Semiconductor A laser range finder as shown in FIG. 10 has been proposed by FM heterodyne length measuring device using laser.

In this laser distance measuring device, the laser 10
The laser light emitted from 01 is collimator lens 10
And collimated light through the beam splitter 1003.
Is split through. One of them enters the reference optical system having a stable reference optical path difference as reference light. The reference optical system is provided with a beam splitter 1007 that splits the incident light into a reference light and a measurement light. Each light has a reflector 1008 placed so that its optical distance is known.
It is reflected at 1009. Then, the respective lights are combined again by the beam splitter 1007 and are incident on the photodetector 1010 to obtain a beat signal. The other light split by the beam splitter 1003 is incident on the distance measuring optical system. The distance measuring optical system also has the same configuration as the reference optical system. The incident light is split by a beam splitter 1004, the reference light is reflected by a reflector 1005 placed so that the optical distance is known, and the measurement light is measured object 10
Reflected or scattered by 06. Then, the respective lights are combined again by the beam splitter 1004,
It is incident on the photodetector 1011 and a beat signal is obtained. The beat signal obtained from each of the photodetectors 1010 and 1011 is amplified by the amplifier 1012, and the counter 10
The distance to the object to be measured is calculated by the computer 1014.

In the laser distance measuring method using the above laser distance measuring device, the distance L to the object to be measured is given by the following equation (4).

[0017]

[Equation 4]

Here, Ns is the wave number of the beat signal obtained by the distance measuring optical system, Nr is the wave number of the beat signal obtained by the reference optical system, Rr is the optical path length of the reference light of the reference optical system, and Lr is the reference. It is the optical path length of the measurement light of the optical system.

As can be understood from the above equation (4), in the laser distance measuring device provided with the reference optical system as described above, the calculated value of the distance L to the object to be measured is determined by the frequency modulation amount Δν of the laser. It will not be affected. Therefore, it is possible to obtain a laser distance measuring device with high measurement accuracy that does not cause an error due to the frequency modulation amount.

[0020]

However, in the laser distance measuring device as described above, the reference optical system is provided in addition to the distance measuring optical system. Since the size is doubled, it is difficult to reduce the size. In addition, the number of components such as the beam splitter and the reflector increases, resulting in cost increase, and the need for optical adjustment in optical components also increases, making adjustment difficult.

The present invention has been made to solve the above problems, and an object thereof is to reduce the number of optical components.
An object of the present invention is to provide a laser range finder that can be integrated and miniaturized, has easy optical adjustment, and has high measurement accuracy.

[0022]

A laser range finder according to the present invention comprises a light source for emitting a laser beam whose frequency is periodically modulated, a laser beam emitted from the light source for measuring light for a reference optical system, and a reference. The light is divided into the measuring light for distance measuring optical system and the reference light, the measuring light for distance measuring optical system is emitted toward the object to be measured, and the returning measuring light for distance measuring optical system and the reference light are returned. Light splitting / combining means for combining, and one or more reference optics having a known optical distance from the light dividing / combining means on the optical path of the reference optical system measurement light emitted from the light dividing / combining means. A known optical distance from the external light splitting / combining means is provided on the optical paths of the system reflector and the distance measuring optical system reference light and the reference optical system reference light emitted from the light splitting / combining means. Alternatively, it receives two or more reference light reflectors and the light combined by the light splitting means. And having a detector based on the received light to detect a distance to the measurement object, the above-described object can be achieved.

A plurality of the reference optical system reflectors are provided with different optical distances with respect to the light splitting / combining means, and a plurality of them are provided with an optical medium therebetween, and each optical medium has a coefficient of thermal expansion. It may consist of different things.

Part or all of the standard optical system reflector and the reference light reflector may be adhered to the outer surface of the light splitting / combining means directly or via an optical medium. .

[0025]

In the laser distance measuring apparatus of the present invention, the reference optical system reflector is provided on the optical path of the reference optical system measurement light.
Since the reference optical system is provided, it is possible to prevent an error caused by a change in the frequency modulation amount. Then, the reference optical system and the distance measuring optical system share the optical parts or use the respective parts of the same optical parts. For this reason,
It is possible to downsize the device and reduce the number of parts. Further, each reflector can be integrated with the light splitting / combining means, which facilitates adjustment of the optical components. Furthermore, a plurality of reference optical system reflectors may be provided, and the optical distance from each of the reference optical system reflectors to the light splitting / combining means and the thermal expansion amount of the optical medium may be different. Therefore, it is possible to correct the thermal expansion amount of each optical component to provide a laser distance measuring device with higher measurement accuracy.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1A shows an embodiment of the laser distance measuring apparatus of the present invention.

This laser distance measuring device drives the injection current of the laser 101 in a triangular wave shape or a sawtooth wave shape,
The frequency of laser light is modulated in a triangular wave shape or a sawtooth wave shape. This laser light is made into parallel light through the collimator lens 102 and guided to the optical system of the Michelson interference system. Then, the laser light is split by the beam splitter 103 into the measurement light and the reference light for the ranging optical system and the measurement light and the reference light for the standard optical system.

The measuring light for the distance measuring optical system (light ray 4) is irradiated onto the object to be measured 108 and reflected or scattered, and the reference light for the distance measuring optical system (light ray 1) has a known optical distance. Each light is reflected by the reflector 104 placed on the beam splitter 103 and is combined again through the beam splitter 103, and the light detector 10
6 is incident on.

The measuring light for the reference optical system (light ray 3) is reflected by the reflector 105 placed so that the optical distance is known, and the reference light for the reference optical system (light ray 2) has an optical distance of Reflected by a reflector 104 placed as is known, each light is again combined through the beam splitter 103,
The light is received by the photodetector 106.

The photodetector 106 detects a beat signal (f2) as shown in FIG. 1 (b) due to a frequency difference due to the optical path difference between the light ray 4 and the light ray 1, and the optical path between the light ray 2 and the light ray 3 is detected. A frequency difference is generated from the difference, and the beat signal (f1) is detected. From these two beat signals, the separation distance to the measurement object is calculated using the above equation (4).

In this embodiment, since the reference optical system and the distance measuring optical system are provided, it is possible to prevent an error caused by a change in the frequency modulation amount. Further, the reflector 104 is shared as the reference optical system reflector and the distance measuring optical system reflector, and the beam splitter 10 is used as the light splitting / combining means.
Since each part of 3 is used, it is possible to downsize and reduce the number of parts.

(Embodiment 2) FIG. 2 shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser range finder, a reflecting mirror 204, which serves as a reflector for reflecting the reference beam for the ranging optical system (light ray 1) and the reference beam for the standard optical system (light ray 2), is provided on the end face of the beam splitter 203. It is provided. Further, an optical medium 206 having a reflecting mirror 205 that reflects the reference optical system measurement light (light ray 3) is attached to or integrated with the other end surface of the beam splitter 203. Other configurations can be similar to those of the first embodiment.

In this embodiment, since the respective reflectors are integrated with the beam splitter which is the light splitting / combining means, the adjustment of the optical parts is easy.

As the reflector, the reflecting mirrors 204, 20
Not limited to 5, a corner cube mirror or a triangular prism may be used. In that case, since the subtle angle adjustment required for the reflecting mirror is not necessary, it becomes easier to adjust the optical components.

(Embodiment 3) FIG. 3 shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser distance measuring device, the end faces of the beam splitter 303 are provided with reflectors 304, 304 for reflecting the reference light for the distance measuring optical system (light ray 1) and the reference light for the standard optical system (light ray 2). The optical medium 306 is laminated or integrated. Reflectors 304, 3
04 are provided at different positions so that an optical path difference occurs between the reference optical system and the distance measuring optical system. A reflector 305 that reflects the reference optical system measurement light (light ray 3) is provided on the other end surface of the beam splitter 303. Other configurations can be similar to those of the first embodiment.

In this embodiment, as in the second embodiment,
Since the respective reflectors are integrated with the beam splitter which is the light splitting / combining means, the adjustment of the optical parts becomes easy.

(Embodiment 4) FIG. 4 shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser range finder, a triangular prism 403 is provided as a light splitting / combining means. In this triangular prism 403, a single layer film or a multilayer film 407 that divides the incident light at an arbitrary division ratio is formed on the slope. A reflector 404 that reflects the reference light for the ranging optical system (light ray 1) and the reference light for the reference optical system (light ray 2) is provided on the end surface of the triangular prism 403. An optical medium 406 having a reflector 405 that reflects the measurement light for the reference optical system is attached to or integrated with the inclined surface of the triangular prism 403. Other configurations can be similar to those of the first embodiment.

In this embodiment, since the triangular prism is used as the light splitting / combining means, the internal multiple reflection due to the two parallel end faces of the beam splitter unlike the case of using the cubic beam splitter does not occur. .
Therefore, the measurement error due to the multiple beat signals does not occur, and the measurement accuracy can be further improved.

(Embodiment 5) FIG. 5 shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser range finder, a polarization beam splitter 503 is provided as a light splitting / combining means. The polarization beam splitter 503 is provided with λ / 4 polarizing plates 504 and 505 on its end faces. Then, the polarization plane of the laser light is adjusted by the polarization beam splitter 503 so as to be split at an appropriate split ratio,
It is incident on the polarization beam splitter 503.

The reference light for the ranging optical system (ray 1) and the reference light for the reference optical system (ray 2) reflected by the polarization beam splitter 503 are polarized into P waves. Each light polarized into the P wave passes through the λ / 4 polarizing plate 504, becomes circularly polarized light, and is reflected by the reflector 506. Each reflected light is again transmitted through the λ / 4 polarizing plate 504, is polarized into an S wave, and is transmitted through the beam splitter 503.

The measuring light for the distance measuring optical system (light ray 4) and the measuring light for the reference optical system (light ray 3) transmitted through the polarization beam splitter 503 are polarized into S waves, and the λ / 4 polarizing plate 5 is used.
The light is transmitted through 05 to become circularly polarized light. The light beam 4 is the measurement object 51.
2 and the ray 3 is reflected by the reflector 507. Each reflected light is again transmitted through the λ / 4 polarizing plate 505, is polarized into a P wave, and is reflected by the beam splitter 503.

Each light is circularly polarized by the λ / 4 polarizing plate 509 and received by the photodetector 510. In the photodetector 510, a frequency difference is generated from the optical path difference between the light ray 4 and the light ray 1, and a beat signal is detected, and a frequency difference is generated from the optical path difference between the light ray 2 and the light ray 3, and a beat signal is detected. From these two beat signals, the separation distance to the measurement object is calculated using the above equation (4).

In this embodiment, since the polarization beam splitter is used as the light splitting / combining means, when the reflected light of the measurement light is reflected by the beam splitter by 90 degrees, as when the non-polarization beam splitter is used. It is not lost as transmitted light. Further, the reflected light of the reference light is not lost as 90-degree reflected light when passing through the beam splitter. Therefore, the intensity of the laser light can be effectively used.

(Embodiment 6) FIG. 6A shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser range finder, a reflecting mirror 604, which serves as a reflector for reflecting the reference beam for the ranging optical system (light ray 1) and the reference beam for the standard optical system (light ray 2), is provided on the end face of the beam splitter 603. It is provided. An optical medium 606 having a reflecting mirror 605 that reflects the reference optical system measurement light (light ray 3) is attached to or integrated with the other end surface of the beam splitter 603. Other configurations can be similar to those of the first embodiment.

The far-field pattern of a semiconductor laser usually has an elliptical light intensity distribution. A (Numerical Aperture
When collimated light is obtained using a collimator lens having a large numerical aperture, a light intensity distribution as shown in FIG. 6B is obtained.
Usually, a portion of the ellipse having a high light intensity is beam-shaped by a prism lens or the like to obtain parallel light having a uniform light intensity. In this embodiment, a reflector 605 as shown in FIG. 6C is provided so that the weak light intensity portion shown in FIG. 6B can be used for the reference optical system. This makes it possible to effectively use light and reduce the number of parts such as a prism lens. In this method, since the part with weak light intensity is used for the reference optical system,
The problem is that the light intensity is weak. However, in this embodiment, the optical distance to the optical medium 606 is shortened, and a total reflection body is used as the reflection body 605 to prevent scattering loss. Therefore, it is possible to obtain a sufficient amount of light to obtain the beat signal.

(Embodiment 7) FIG. 7A shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser distance measuring apparatus, a reflector for reflecting the reference light for the distance measuring optical system (light ray 2) and the two reference light for the reference optical system (light ray 1 and light ray 3) is provided on the end face of the beam splitter 703. A reflecting mirror 704 is provided. Further, on the other end face of the beam splitter 703, an optical medium 706 having a reflecting mirror 705a for reflecting one reference optical system measuring light (light ray 4) and another reference optical system measuring light (light ray 6). 705b that reflects light
And an optical medium 707 having the above are bonded or integrated. The optical media 706 and 707 have different thermal expansion coefficients. Further, the optical distances to the reflecting mirrors 705a and 705b are made different. Other configurations can be similar to those of the first embodiment.

The photodetector 708 detects a beat signal (f3) as shown in FIG. 7B due to a frequency difference due to the optical path difference between the light ray 5 and the light ray 2, and the optical path between the light ray 3 and the light ray 4 is detected. The beat signal (f1) is detected due to the frequency difference from the difference, and the beat signal (f) is detected from the frequency difference between the light rays 1 and 6.
2) is detected. The frequency ratio f1 / f2 of the two beat signals is determined by the optical distance between the two reference optical systems and is not influenced by the frequency modulation amount Δν of the laser.

In this embodiment, the optical medium 706,
As 707, those having different thermal expansion coefficients are used. Therefore, when the environmental temperature of the laser range finder changes and the optical component thermally expands, the beat signal frequency ratio f1 / f2 changes as shown in FIG. 6C. The thermal expansion amount of each optical medium 706, 707 can be calculated from the beat signal frequency ratio f1 / f2 to correct the thermal expansion amount. Therefore, the laser distance measuring device can be provided with higher measurement accuracy without being affected by the environmental temperature of the laser distance measuring device.

(Embodiment 8) FIG. 8 shows another embodiment of the laser distance measuring apparatus of the present invention.

In this laser distance measuring apparatus, a photodetector 808 and a counter 811 for coherently heterodyne detecting the measuring light (light ray 4) and the reference light (light ray 1) for the distance measuring optical system, and the measuring light for the reference optical system ( A light detector 809 and a counter 812 for coherent heterodyne detection of the light ray 3) and the reference light (light ray 2) are separately provided. Other configurations can be similar to those of the fourth embodiment.

In this embodiment, since two beat detectors can detect each beat signal and two counters can detect the frequency of each beat signal, it is necessary to use an expensive frequency measuring device. Therefore, the cost of the device can be reduced.

[0059]

As is apparent from the above description, in the laser range finder of the present invention, since the reference optical system is provided, the frequency modulation amount Δν due to the change in the environmental temperature of the laser range finder, etc. It is possible to prevent an error due to the amount of change. By sharing the optical components such as the reflector and the light splitting / combining means between the reference optical system and the distance measuring optical system and using each part of the same optical component, it is possible to reduce the size and the number of components, and It becomes easy to adjust. Further, in the conventional laser distance measuring apparatus, since the light is split into the reference optical system and the distance measuring optical system, the light loss due to the light splitting / combining means is large, but the loss can be prevented. In the laser distance measuring apparatus of the present invention, the ratio of the measuring light for the distance measuring optical system to the measuring light for the reference optical system can be adjusted with an arbitrary beam area, so that the distance measuring optical system is compared with the reference optical system. It is possible to improve the measurable distance and the measurement accuracy by increasing the measurement light output of. Further, by providing a plurality of reference optical systems and making the optical distance and the thermal expansion amount of the optical medium in each reference optical system different, the thermal expansion amount of each optical component can be corrected, and further measurement can be performed. A highly accurate laser distance measuring device can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a laser distance measuring device according to the present invention.

FIG. 2 is a diagram showing another embodiment of the laser range finder of the present invention.

FIG. 3 is a diagram showing another embodiment of the laser distance measuring apparatus of the present invention.

FIG. 4 is a diagram showing another embodiment of the laser distance measuring device of the present invention.

FIG. 5 is a diagram showing another embodiment of the laser distance measuring device of the present invention.

FIG. 6 is a diagram showing another embodiment of the laser distance measuring apparatus of the present invention.

FIG. 7 is a diagram showing another embodiment of the laser distance measuring apparatus of the present invention.

FIG. 8 is a diagram showing another embodiment of the laser distance measuring apparatus of the present invention.

FIG. 9 is a diagram showing a basic configuration of a laser distance measuring device.

FIG. 10 is a diagram showing a conventional laser distance measuring device.

[Explanation of symbols]

101, 201, 301, 401, 501, 601, 7
01,801 Laser 102,202,302,402,502,602,7
02, 802 Collimator lens 103, 203, 303, 403, 503, 603, 7
03, 803 Optical division combining means 104, 105, 204, 205, 304, 305, 4
04, 405, 506, 507, 604, 605, 70
4, 705, 804, 805 Reflectors 106, 207, 307, 408, 510, 607, 7
08, 808, 809 Photodetectors 107, 208, 308, 409, 511, 608, 7
09, 811, 812 counters 108, 209, 309, 410, 512, 609, 7
10, 810 Measurement object 206, 306, 406, 508, 606, 706, 7
07,806 Optical medium 407,807 Multilayer film (single layer film) 504, 505, 509 λ / 4 polarizing plate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruhisa Takiguchi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (3)

[Claims] 1. A light source that emits a laser beam whose frequency is periodically modulated, and a laser beam emitted from the light source, which is a measuring beam and a reference beam for a standard optical system and a measuring beam and a reference beam for a ranging optical system. Divide into, and emit the measurement light for distance measurement optical system toward the object to be measured,
A light splitting / combining means for combining the measuring light for the distance-measuring optical system and the reference light, which has returned again, and an optical path of the measuring light for the reference optical system emitted from the light splitting / combining means, from the light splitting / combining means. On the optical path of the reference light for the ranging optical system and the reference light for the reference optical system emitted from the light splitting / combining means. , One or more reflectors for reference light provided with known optical distances from the external light splitting / combining means, and the light synthesized by the light splitting means, and the measurement target based on the received light A laser distance measuring device having a detector for detecting a separation distance to an object. 2. The reference optical system reflector is provided with a plurality of optical distances different from each other with respect to the light splitting / combining means, and a plurality of optical media are provided therebetween, and each optical medium has a coefficient of thermal expansion. The laser range finder according to claim 1, wherein the laser range finder is different. 3. A part or all of the standard optical system reflector and the reference light reflector are attached to the outer surface of the light splitting / combining means directly or between them via an optical medium. The laser range finder according to claim 1.