JPH01320489A - Method and instrument for measuring distance - Google Patents

Abstract

PURPOSE:To highly accurately measure a distance without disturbance by obtaining polarized light rays having orthogonally polarized components only from semiconductor laser light rays modulated to triangular waves and mutually changing the optical path lengths of both light rays, and then, obtaining the beat signal frequency corresponding to the difference between both optical path lengths. CONSTITUTION:Linearly polarized light rays LA2 and LA3 are led to a non-polarizing beam splitter 7 where they are respectively divided into two parts and become linearly polarized light rays LA21 and LA22 and LA31 and LA32 after they are respectively reflected by prisms 6a and 6b. The light rays LA21 and LA31, the polarized directions of which intersect each other at right angles, are emitted in the direction parallel to laser light LA1 and, at the same time, the light rays LA22 and LA32, the polarized directions of which intersect each other at right angles, are emitted in the direction perpendicular to the laser light LA1. The light rays LA21 and 31 are reflected by an object 9 to be measured after passing through a condenser lens system 8 and led to a polarizing element group 10 after again passing through the lens system 8. At the element group 10, the light rays LA21 advance straight and the other light rays LA31 are branched in the normal direction. Then the light rays LA21 and LA31 are led to a non-polarizing beam splitter 11 and the interference light rays between the LA21 and LA22 and between the LA31 and LA32 are respectively emitted in directions intersecting each other at right angles in a state where they are divided into two parts.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a distance measuring method and an apparatus thereof, and more specifically, the present invention relates to a distance measuring method and an apparatus thereof, and more specifically, the present invention relates to a distance measuring method and an apparatus thereof, and more specifically, to a distance measuring method and an apparatus thereof. The present invention relates to a novel distance measuring method and apparatus for obtaining polarized light having only two components, making the optical path lengths of both polarized lights different, and measuring the distance to a measurement target based on the interference signal obtained for each polarized light.

<Prior Art> Conventionally, devices with various configurations have been provided for measuring the distance to an object to be measured. Specifically, there are those that apply the principle of triangle 711H1 and those that apply the principle that the interference of light, ultrasonic waves, etc. changes based on the difference in distance, but there are applications that require high measurement accuracy. In this case, it is preferable to use a laser beam as the measurement light, which is not easily affected by external conditions.

Conventionally, as a distance measuring device that uses the above laser beam as a measuring beam, the laser beam is divided into two parts, the - side is irradiated on all fixed objects, and the other side is irradiated on a reference reflector whose distance is known. However, it is known to obtain a beat signal by interfering the reflected light from the measuring object and the reflected light from the reference reflector, and calculate the distance to the measuring object based on the frequency of the beat signal.

Specifically, the optical path length on the measurement target side is L1, the optical path length on the reference reflector side is LO1, the speed of light is 01, and the semiconductor laser (hereinafter referred to as LD) is
fI111 The frequency of the beat signal is fb The maximum oscillation frequency deviation due to SLD modulation is δ
Then, there is a relationship of L-LD-C-fb/4 f+a ・δ, and since LO1C% fn+Sfb and δ are known, L can be calculated, and the distance to the object to be measured can be calculated. It can be calculated.

However, the maximum oscillation frequency deviation δ of the LD varies greatly depending on the LD drive current and temperature (for example, if the drive current changes by 1a+A, it changes by about 3 to 8GH2), and
Since the LD differs considerably between different LDs, it becomes extremely difficult to accurately fix the value of the maximum oscillation frequency deviation δ, and as a result, the accuracy and reproducibility of distance measurement are significantly reduced. have.

In consideration of these problems, two reference reflectors with known optical path lengths and different lengths are prepared in addition to the reference reflector, and the reflected light from the measurement object is reflected from each reference reflector. By interfering with the light reflected from the reflector and by interfering with the light reflected from two reference reflectors, 28 types of beat signals are obtained, eliminating the influence of the maximum oscillation frequency deviation δ of the LD, and achieving accuracy. A distance 'DI determination device has been provided which performs accurate distance measurement (see Japanese Patent Laid-Open No. 61-223577).

To explain in more detail, as shown in FIG.
The laser beam output from (31) is split into two by the beam splitter (32), and one of the beams is sent to the beam splitter (33).
), the light is further divided into two and irradiated onto reference reflectors (34) and (35) each having a different optical path length, the reflected lights are interfered with each other, and the interference light is received by a light receiving element (36) to obtain a beat signal. That's what I do. Then, the other light is further split into two by a beam splitter (37) and the reference reflector (
38) and the object to be measured (39), the reflected lights are caused to interfere with each other by a beam splitter (37), and the interference light is received by a light receiving element (30) to obtain a beat signal. Furthermore, the light receiving element (3B) (
It has a calculation section (41) that receives the beat signal obtained by step 30) and performs a predetermined calculation to calculate the distance to the object to be measured (39).

Note that (42) is a DC power supply, and (43) is a modulator for controlling the drive current.

That is, if the above configuration is adopted, both reference reflectors (34)
Since the optical path lengths of (35) are known, by measuring the frequency of the beat signal based on the reflected light from these,
The maximum oscillation frequency deviation δ of the LD can be calculated.

Therefore, based on the calculated maximum oscillation frequency deviation δ and the frequency of the beat signal based on the reflected light from the reference reflector 38) and the measurement object (39),
) can be accurately calculated.

<Problems to be Solved by the Invention> In the distance DI determination device described in the above-mentioned Japanese Patent Application Laid-Open No. 81-223577, the laser beam output from the LD (31) is divided into two parts by the beam splitter (32). After that, each light is further transmitted to a beam splitter (33) (
37), each laser beam passes through a different atmosphere. As a result, each laser beam is affected by disturbances such as atmospheric fluctuations, and each interference signal frequency is significantly affected compared to the case where it is not affected by disturbances. Even if the influence of the maximum oscillation frequency deviation δ can be eliminated, there is a problem in that it becomes impossible to calculate the distance to the measurement object (39) with very high accuracy.

Furthermore, in consideration of the above problems, a pair of LDs that emit laser beams of different wavelengths are used, and the laser beams emitted from both LDs are guided to the same optical path, so that each laser beam of each wavelength is It is conceivable to obtain an interference signal, eliminate the influence of disturbance based on both interference signals, and measure the distance to the measurement target with high precision, but this would not only increase the number of LDs but also require the use of both laser beams. There is a problem in that a means for guiding the light to the same optical path is required, and the overall configuration becomes extremely complicated.

<Object of the invention> This invention was made in view of the above problems,
It is an object of the present invention to provide a distance measuring method and a device thereof that can eliminate the influence of disturbance without increasing LD and measure the distance to a measurement target with high precision.

<Means for Solving the Problems> In order to achieve the above object, the distance measuring method of the present invention obtains a laser beam whose frequency is modulated in a triangular wave form by triangular wave modulating a semiconductor laser. Obtain polarized light having only mutually orthogonal polarized components based on the light,
While guiding both polarized lights to almost the same optical path, the optical path length of each polarized light is mutually changed in the middle of the optical path, and a signal corresponding to the interference signal frequency based on the polarized light with the same polarization direction in the rising and falling parts of the triangular wave is generated. In this method, the beat signal frequency corresponding to the optical path length difference is obtained based on the signals corresponding to both interference signal frequencies.

To achieve the above object, the distance measuring device of the present invention has a modulation means for modulating a semiconductor laser with ≦angular waves, and only mutually orthogonal polarization components based on a triangular wave frequency modulated laser beam. A polarized light generating means for obtaining polarized light, an optical interference system that guides both polarized lights to substantially the same optical path, and an optical path length adjusting means for mutually changing the optical path length of each polarized light in the middle of the optical path.
A pair of interference signal extraction means for obtaining a signal corresponding to an interference signal frequency based on polarization having the same polarization direction in the rising and falling portions of a triangular wave, and a pair of interference signal extraction means for obtaining a signal corresponding to an interference signal frequency based on polarization having the same polarization direction in the rising and falling portions of the triangular wave, and corresponding to the optical path length difference based on the signal corresponding to both interference signal frequencies. and a beat frequency calculation means for obtaining a beat signal frequency.

However, the polarized light generation means is a polarized beam splitter, and the optical interference system divides each polarized light generated by the polarized beam splitter into two, and divides the polarized light having only mutually orthogonal polarized components into different polarized lights. Preferably, it has a non-polarizing beam splitter that leads to two optical paths.

Further, when the measurement object reflects linearly polarized light as elliptically polarized light, the polarization generating means may be disposed in the optical path of the laser beam branched from the laser beam directed toward the measurement object. preferable.

Further, it is preferable that the optical path length adjusting means selects different optical paths depending on the type of polarized light, and is disposed on one of the optical path of the reflected light from the object to be measured and the reference optical path.

In the distance measurement method described above, the laser beam output from the triangular wave modulated semiconductor laser is divided into two parts, one of which is irradiated onto the object to be measured, and the other is placed on a reference optical path with a known optical path length. When the reflected light from the object to be measured and the light guided to the reference optical path are interfered to obtain an interference signal and distance data is obtained based on the interference signal, only mutually orthogonal polarization components based on the laser beam are used. Since polarized light having the same polarization component is obtained, interference signals can be obtained only between polarized light having the same polarization component.

Since the optical path length of each polarized light is changed in the middle of the optical path, the interference signal based on each polarized light has a frequency corresponding to the optical path length difference of each polarized light, the maximum oscillation frequency shift, and the disturbance. Become. Furthermore, the maximum oscillation frequency shift has the same absolute value and opposite signs in the rising and falling parts of the triangular wave.

Therefore, the beat signal frequency corresponding to the difference between the optical path length including the measurement target and the reference optical path length can be obtained based on the signal corresponding to the interference signal frequency based on each of the polarizations, and based on the beat signal frequency. The distance to the object to be measured can be measured with high precision.

With the distance measuring device having the above configuration, by triangular wave modulating the semiconductor laser using the modulation means, it is possible to emit a laser beam frequency modulated in a triangular wave shape. By guiding the laser beam to the polarization generating means before or after it is split into two, polarized light having only mutually orthogonal polarization components can be obtained, and both polarized lights are guided to almost the same optical path in the optical interference system. It will be destroyed. Therefore, the light reflected from the measurement object and the light guided to the reference optical path are
Both of them have polarized lights whose polarization directions are orthogonal to each other, and two interference signals are obtained when the polarized lights of the same polarization direction finally interfere with each other.

However, since the light guided to either optical path is guided to the optical path length adjustment means, the optical path lengths of the polarized lights with different polarization directions are different, and the two interference signals mentioned above are different from each other. This corresponds to the difference in optical path length.

Then, by the pair of interference signal extraction means, it is possible to obtain a signal corresponding to the interference signal frequency based on the polarization having the same polarization direction in the rising and falling parts of the triangular wave, and the signal corresponding to the interference signal frequency corresponding to both obtained interference signal frequencies can be obtained. By supplying the signal to the beat frequency calculation means, it is possible to eliminate the influence of the maximum oscillation frequency shift and the influence of disturbance, and obtain the beat signal frequency corresponding to the optical path length difference.

Therefore, the distance to the object to be measured can be calculated with high accuracy based on the obtained beat signal frequency and optical path length difference.

And the polarization generating means is a polarization beam splitter,
The optical interference system has a non-polarizing beam splitter that divides each polarized light generated by the polarizing beam splitter into two and guides the polarized light having only mutually orthogonal polarized components to two mutually different optical paths. In some cases, it is possible to obtain polarized light whose polarization directions are orthogonal to each other by a polarizing beam splitter, and by supplying these polarized lights to a non-polarizing beam splitter, each polarized light is divided into two, and each polarized light is divided into two. It can be guided to the same optical path as the separated light.

Therefore, the distance to the object to be measured can be calculated with high accuracy in the same manner as described above by guiding the light including both polarized lights to separate optical paths.

In addition, if the object to be measured reflects linearly polarized light as elliptically polarized light and the polarization generating means is placed in the optical path of the laser beam branched from the laser beam directed toward the object to be measured, It is sufficient to simply guide the laser beam to the object to be measured, and no configuration is required to align the optical path of the laser beam, so the configuration can be simplified and distance measurement can be performed with high precision. can.

Furthermore, when the optical path length adjustment means selects different optical paths depending on the type of polarized light, and is arranged on one of the optical path of the reflected light from the measurement object and the reference optical path, the optical path length adjustment means The configuration of the adjusting means can be simplified, and there is no need to provide an extra optical member for aligning both polarized lights, and the optical system as a whole can be simplified.

To explain in more detail, the noise Nω(1) due to disturbances such as atmospheric fluctuations is multiplicative noise, and the interference signal I ac (t) considering this noise is Iac(t) =
A cos (ωb t+Nω(t)+φ)...■ (where I ac (t) is the alternating current component of the heterodyne interference signal by triangular wave modulation, A is the amplitude intensity, ωb is the beat frequency, and φ is the phase). That is, the interference signal frequency is affected by the disturbance and has a value different from the original beat frequency ωb.

It has long been known that it is impossible to know the frequency components of this disturbance, and for this reason, conventional methods have been to calculate the distance to the measurement target based on the interference signal frequency that is still affected by the disturbance. Was.

As a result of intensive research, the inventor of the present invention found that although it is impossible to know the frequency of disturbance, unless under a particularly bad environment, the frequency of disturbance is below several 10I (Z), and is usually as low as 1OH2 or below. If the frequency component is found to be a high frequency component, and if there is only such a low frequency component, by obtaining the interference signal frequency using two interference systems, the influence of disturbance can be significantly eliminated, and a highly accurate beat frequency can be obtained. We found that it is possible to calculate

To explain in detail, the interference frequency must be measured within half a period of the triangular wave that is the modulated wave, and the normal measurement time is set to several m5ec or less.

In this way, in a time that is significantly shorter than the frequency change of the disturbance, Nω(t)' and ωNt (however, ωN is a collection of low frequencies), so the above equation 20 becomes Iac(t)', A cos ((ωb +(LIN
) t+φ)...■ It can be approximated as follows.

Also, since the beat frequency is proportional to the frequency deviation amount δ,
The absolute value of the frequency shift is the same in the rising and falling parts of the triangular wave, and only the signs are opposite. Therefore, the alternating current component of the interference signal corresponding to the above image part is I ac (rise) : A cos ((ωb + ω
N ) t+φ)...■ Iac (falling) ′, A cos ((ωb −CL
)N ) t+φ)...■. As a result, the interference signal frequencies (ωb + ωN) and (ωb - ωN) are obtained from Equation 10 above, respectively,
It is possible to calculate the beat frequency ωb from which the influence of disturbance has been removed based on the image frequency.

However, the beat frequency ωb calculated as above
Immediately calculate the distance to the object based on
Since the beat frequency is affected by the amount of frequency deviation,
The calculated distance becomes inaccurate.

Focusing on this point, laser beam LIS that does not interfere with each other
If L2 is guided to almost the same optical path and both optical path lengths JO are set to predetermined values in advance, the frequency ω11ω2 of each laser beam L1 and L2 will be ω1−ωb1+ωN (rising)
...■ or ωl-ωbl-ωN (falling) ...■
ω2■ωb2+ωN (rising) ・・・■
Or ω2-ωb2-ωN (falling)...■
(However, ωbl and ωb2 are laser beams Ll, respectively.

L2 beat frequency) becomes.

Therefore, if the above equation (10 or (10) is selected and calculated depending on whether the optical path length of the laser beam Ll is long or not, the distance J to the object to be measured can be calculated as follows:
ωb2) / (ωbl-ωb2)-11JO/2+J
L (where JL is the distance between the separator that divides the laser beam into two and the reference reflector), and not only the influence of disturbance but also the influence of frequency deviation are eliminated, and the distance to the 'DI constant target is This means that the distance can be calculated accurately.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

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

For t, o (1) that outputs the laser beam for measurement, the output signal from the DC power supply and the modulator (3
) are added together by an adder (4) and then supplied. Then, by periodically changing the output signal from the modulator (3) in the form of a triangular wave,
L D (1) outputs a laser beam whose frequency changes in a triangular wave pattern.

A collimator lens (5) and a polarizing beam splitter (
6) are arranged in this order, and the non-polarizing beam splitter (7) is arranged so that the light branching surface is located on an extension of the light branching surface of the polarizing beam splitter (6). Prisms (8a) and (6b) are arranged to guide both of the lights split into two by the polarizing beam splitter (6) to the non-polarizing beam splitter σ).

A condensing lens system (8) is arranged between one exit surface of the non-polarizing beam splitter (7) and the object to be measured (9). Furthermore, two polarizing beam splitters (10a) (f
ob) and one polarizing beam splitter (10a) to the other polarizing beam splitter (10a).
b) Two polarizing beam splitters (10c) (l
A polarizing element group (10) consisting of a polarizing element group (10) is arranged, and a polarizing element group (10) consisting of a polarizing element group (10) is arranged, and a polarizing element group (10) consisting of Polarizing beam splitter (11
) are placed. A polarizing plate (
12a) (12b) and light receiving elements (18a) (13
b) are arranged respectively. Further, the interference signals output from both the light receiving elements (13a) and (13b) are supplied to a signal processing section (14).

Note that the n1 constant object (9) may be any material as long as it reflects light without changing its polarization characteristics, such as metal.

The operation of the distance Δ-1 constant device having the above configuration is as follows.

The laser beam LAI output from the LD (1) is collimated by the collimator lens (5) and then enters the polarizing beam splitter (6), thereby forming linearly polarized beams LA2 and LA3 in mutually orthogonal directions. is generated, and the linearly polarized light LA2 is emitted in the extension direction of the laser beam LAI, and the linearly polarized light LA3 is emitted in the direction perpendicular to the linearly polarized light LA2. And both linearly polarized lights LA2, LA3
are reflected by the prism (Ba) (6b) and guided to the non-polarizing beam splitter (7), so
Each of the linearly polarized lights LA2 and LA3 is divided into two to become linearly polarized lights LA21, LA22, LA31, and LA32, and the linearly polarized lights LA21 and LA31 whose polarization directions are orthogonal to each other
is emitted in a direction parallel to the laser beam LA1, and linearly polarized lights LA22 and LA3 whose polarization directions are orthogonal to each other are emitted.
2 is emitted in a direction perpendicular to the laser beam LAI.

The linearly polarized lights LA21 and LA31 are condensing lens systems (8)
After being guided to the surface of the object to be measured (9) and reflected, the polarizing element group (10
). In the polarizing element group (10), the linearly polarized light LA21 is made to travel straight in the polarizing beam splitter (10a), and the linearly polarized light LA31 is split in orthogonal directions. The linearly polarized light LA31 is guided to the polarized beam splitter (10b) by changing its traveling direction by 90'' by the polarizing beam splitters (10e) and (10d), and the linearly polarized light LA21
The light continues straight and is guided to the polarizing beam splitter (TAB), so it is emitted in the same direction again. However, as is clear from the above description, the optical path length of the linearly polarized light LA31 is longer than the optical path length of the linearly polarized light LA21.

Linearly polarized light LA with a difference in optical path length as described above
21. Since LA31 is guided to the non-polarized beam splitter (11), and the linearly polarized lights LA22 and LA32 are also guided to the non-polarized beam splitter (1'1), the linearly polarized lights LA21 and SLA22 are caused to interfere, and the linear The polarized lights LA31 and LA32 are caused to interfere, and both interference lights are emitted in two halves in directions perpendicular to each other. Then, one of the emitted lights LA4 is guided to the polarizing plate (12a), so that the linearly polarized lights LA21. Only the interference light LA41 caused by LA22 is extracted, and the light receiving element (13a
) is converted into an electrical signal by Also, the other output light L
By guiding A5 to the polarizing plate (12b), linearly polarized light LA31. Only the interference light LA51 caused by LA32 is extracted and converted into an electrical signal by the light receiving element (13b).

Thereafter, by supplying the electrical signals output from both light receiving elements (13a) (RAB) to the signal processing unit (14), the influence of disturbance and the influence of frequency deviation can be eliminated and the signal to be measured can be detected. Accurate distance can be calculated.

FIG. 2 is a block diagram showing an example of the electrical configuration of the signal processing section, in which the waveform shaper (1
5a) (15b) and both waveform shapers (15a) (1
a multiplier (16) inputting the output signal from 5b);
Bandpass filters (17a) (17b) that receive the output signal from the multiplier (16) as inputs, and amplifiers (18a) (16b) that receive the output signals from each of the bandpass filters (17a) (17b) as inputs. , each amplifier (18a)
a comparator (19a) (tab) which uses the output signal from (16b) as a comparison input signal; a gate pulse generator (20) which generates a pair of gate pulses Gl and G2 having mutually different levels; A counter (21a) (2) whose operation is controlled by the pulse Gl and which inputs the comparison result signal from each comparator (19a) (19b).
lb), a counter (21c) whose operation is controlled by the gate pulse G2 and receives the comparison result signal from the comparator (19a), and the counter (21a).
) (21b) It has an arithmetic unit (22) which inputs the count signal from (21c), and a display device (23) which inputs the output signal from the arithmetic unit (22).

The levels of the gate pulses Gl and G2 are changed in accordance with the rising and falling portions of the triangular wave.

The operation of the horizontal and vertical signal processing sections described above is as follows.

Since the light-receiving element (13a) outputs an electrical signal corresponding to the interference light LA41, the waveform shaper (15a) performs division to eliminate the influence of intensity modulation, thereby changing the COS (ωbs+ωN)t. A signal having frequency components can be obtained, and the light receiving element (1
Since the electrical signal corresponding to the interference light LA51 is output from 3b), the waveform shaper (15b) performs division to eliminate the influence of intensity modulation, thereby converting the frequency component of COS (ωbp+ωN)t. You can get a signal with

However, ωbs is the beat frequency of interference light LA41, ωbp
is the beat frequency of the interference light LA51, and ωN is the noise caused by disturbance.

Then, each frequency component cos (ωbs+ωN) t
.

The signal with cos (ωbp+ωN)t is sent to the multiplier (1
6) for multiplication, and then supplied to bandpass filters (17a) and (17b) to obtain mutually different frequency components COS (ωbs+ω
bp+2 ωN ) tSeO8(ωbs −ωbp)
Two signals with t are obtained. Next, both of the above signals are amplified by amplifiers (18a) and (16b), respectively, and compared with predetermined reference values in comparators (19a and 19b), thereby obtaining a pulse signal corresponding to the frequency of each signal. . Therefore, by counting the number of these pulse signals, the frequency of each of the above signals can be obtained. To explain in more detail, for a signal that does not have a frequency component caused by the above-mentioned noise, the counter (
21b), it is only necessary to count the number of pulse signals, and ω
A frequency of 3-ωbs-ωbp can be obtained. Furthermore, regarding the signal having a frequency component caused by the above-mentioned noise, the frequency of ωl-ωbs+ωbp+2ωN (third (see Figure C) can be obtained, and the gate pulse G2
The counter (21c
) by counting the number of pulse signals (L)2
Frequency of wa ωbs+ ωbp -2ωN (Fig. 3C
) can be obtained. Then, the image frequency ω1
By adding 1ω2, ωN is completely removed (see Figure 3C).

Therefore, each of the above counters (21a) (21b)
The frequencies ω1, ω3, and ω2 obtained by (21c) are supplied to the arithmetic unit (22) to calculate J−iL−+(ωl+ω2)/2ω3−1)ﾗ0/2, thereby reducing noise. It is possible to accurately calculate the distance to the n1 constant object (9) by eliminating the influence and also by eliminating the influence of the amount of frequency deviation. Thereafter, the calculated distance can be visually displayed on the display (23).

<Example 2> Fig. 4 is a schematic diagram showing the main parts of another example of the distance M measuring device, and the difference from the above example is that the polarizing element group (10)
A condensing lens system (8) and a non-polarizing beam splitter (11)
), but instead of being placed between the non-polarizing beam splitters (7) and (11), the configuration of the other parts is the same.

Therefore, in the case of this example, the measurement object (9)
The optical path length of the light irradiated to and reflected from the beam is equal for each polarization, but if there is no polarization beam splitter (7)
Since the polarizing element group (10) is arranged in the optical path of the light that is directly guided from the polarization beam to the non-polarizing beam splitter (11), the optical path length of each polarized light while passing through this optical path becomes a different value. .

As a result, the interference generated for each polarized light differs depending on the difference in optical path length, and as a result, the influence of the frequency caused by noise is eliminated based on the different interference frequencies, and the measurement target is The distance to object (9) can be calculated accurately.

<Embodiment 3> Fig. 5 is a schematic diagram showing the main parts of yet another embodiment of the distance 7111 fixing device. A non-polarizing beam splitter (24) is arranged between the polarizing beam splitter (6) and the non-polarizing beam splitter (7) for the optical path of the light split by the non-polarizing beam splitter (24). The point where the prism (Eia) (6b) is arranged and the measurement target (9) are not only made of a material that can reflect light without changing the modification characteristics as in Examples 1 and 2 above, but also The only difference is that it can be applied to materials that reflect elliptically polarized light when linearly polarized light is incident, such as paper and wood, and the configuration of other parts is the same.

Therefore, in the case of this example, the measurement object (9)
The laser beam irradiated on the laser beam remains the linearly polarized light emitted from the L D (1), but becomes elliptically polarized light by being reflected from the object to be measured (9), and then passes through the polarizing element group (
10) to obtain two polarized lights with different optical path lengths, and a polarizing beam splitter (6) based on the linearly polarized laser light split by the non-polarizing beam splitter (24).
Since the non-polarizing beam splitter (7) and the non-polarizing beam splitter (7) can obtain linearly polarized light in mutually orthogonal directions, the accurate distance to the measurement target (9) can be calculated by eliminating the influence of disturbances in the same way as in the above embodiment. can do.

In addition, (25) in Fig. 5 is a non-polarizing beam splitter (7).
This is a light-receiving element that receives polarized light in mutually orthogonal directions, and is used to monitor the intensity of laser light emitted from L D (1).

<Embodiment 4> Fig. 6 is a schematic diagram showing the main parts of yet another embodiment of the distance measuring device, and the difference from the embodiment shown in Fig. 5 is a polarizing beam splitter (6) and a non-polarizing beam splitter. (7),
The only difference is that the positions of the prisms (6a) and (6b) and the polarizing element group (10) are exchanged, and the configuration of other parts is the same.

Therefore, in the case of this example, the measurement object (9)
The optical path lengths are different based on the laser light that is not guided by the
In addition, it is possible to obtain linearly polarized light whose polarization directions are orthogonal to each other, and linearly polarized light whose optical path lengths are equal and whose polarization directions are orthogonal to each other based on the laser beam guided to the measurement object (9). Therefore, the accurate distance to the object to be measured (9) can be calculated by eliminating the influence of disturbances, as in the above embodiment.

Note that the present invention is not limited to the above-mentioned embodiments, and for example, a right-angle prism or a corner cube may be used in place of the polarizing beam splitters (10c) (10d) constituting the polarizing element group (10). In addition to being possible,
In place of the polarizing beam splitter (6), it is possible to use a non-polarizing beam splitter and a polarizing element that polarizes each of the lights divided into two by the non-polarizing beam splitter into polarized lights whose polarization directions are orthogonal to each other. Various design changes can be made without departing from the gist of the invention.

<Effects of the Invention> As described above, the first invention obtains linearly polarized light whose polarization directions are orthogonal to each other based on laser light emitted from one semiconductor laser, and eliminates the difference in optical path length between the two linearly polarized lights. Because it is made to have a
The influence of disturbances to which both linearly polarized lights are affected to the same extent can be eliminated based on the interference signal obtained by both linearly polarized lights, and the complexity of the configuration due to the use of two semiconductor lasers and the need for each optical system can be eliminated. By eliminating the need for high precision element placement,
This has the unique effect of being able to accurately measure the distance to the object to be measured.

The second invention obtains linearly polarized light whose polarization directions are orthogonal to each other based on laser light emitted from one semiconductor laser,
Since both linearly polarized lights are made to have a difference in optical path length and are guided to almost the same optical path, the influence of disturbances that both linearly polarized lights receive to the same extent can be absorbed by the interference obtained by both linearly polarized lights. This eliminates the complexity of the configuration associated with the use of two semiconductor lasers and the high precision of the placement of each optical element, allowing accurate distance to the object to be measured. [It has the unique effect of being able to perform 11 constants.

The third invention is that by simply setting the relative positional relationship between a polarizing beam splitter and a non-polarizing beam splitter, linearly polarized lights whose polarization directions are orthogonal to each other can be guided to the same optical path, and they can be mutually It can be divided into two parts in orthogonal directions, and has the unique effect of minimizing the complexity of the configuration.

In the fourth invention, it is sufficient to simply guide the laser light between the semiconductor laser and the object to be measured, and there is no need for a configuration for aligning the optical path of the laser beam, so the configuration can be simplified, and This has the unique effect of being able to perform highly accurate distance measurements.

The fifth invention is capable of simplifying the configuration of the optical path length adjustment means, eliminating the need to provide an extra optical member for aligning both polarized lights, and minimizing the complexity of the optical system. It has the unique effect of being able to.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the distance measuring device of the present invention, Fig. 2 is a block diagram showing an example of the electrical configuration of the signal processing section, and Fig. 3 shows the operation for removing frequency components caused by noise. A waveform diagram to be explained; FIG. 4 is a schematic diagram showing the main parts of another embodiment of the distance measuring device; FIGS. 5 and 6 each show the main parts of still other embodiments of the distance measuring device. Schematic diagram, FIG. 7 is a schematic diagram showing a conventional example. (1)...LD, (3)...Modulator,
(6)...Polarizing beam splitter, (7)(11)...Non-polarizing beam splitter, (9)
...Measurement object, (10)...Polarizing element group, (12a) (12b)--Polarizing plate, (13a) (13b)--Light receiving element, (14)...
Signal processing unit, (19a)... Comparator, (20)...
Gate pulse generator, (21a) (21c)--Counter, (LAI)-
...Laser light, (LA2)(LA3)(LA21)(LA22)(
L A 31) (L A 32)...Linearly polarized light patent applicant Daikin Industries, Ltd. Representative Patent attorney Tomo Tsugawa 3 Figures (A) Time (B) Time (C) Between n

Claims (1)

[Claims] 1. Laser light (LA) output from a semiconductor laser (1)
1) is divided into two parts, one is irradiated onto the measurement target (9), and the other is guided to a reference optical path with a known optical path length, and the reflected light from the measurement target and the light guided to the reference optical path are interfered. In the distance measuring method of obtaining an interference signal and obtaining distance data based on the interference signal, a semiconductor laser (1) is triangularly modulated to obtain a triangularly frequency-modulated laser beam (LA1). Polarized light (LA2) (LA3) having only mutually orthogonal polarization components is obtained based on the laser light (LA1), both polarized lights (LA2) (LA3) are guided to almost the same optical path, and each polarized light is separated in the middle of the optical path. By mutually changing the optical path lengths of (LA2) and (LA3), we obtain a signal corresponding to the interference signal frequency based on the polarization with the same polarization direction in the rising and falling parts of the triangular wave, and obtain a signal corresponding to both interference signal frequencies. A distance measuring method characterized in that a beat signal frequency corresponding to an optical path length difference is obtained based on the optical path length difference. 2. Laser light (LA) output from the semiconductor laser (1)
1) is divided into two parts, one is irradiated onto the measurement target (9), and the other is guided to a reference optical path with a known optical path length, and the reflected light from the measurement target and the light guided to the reference optical path are interfered. A distance measuring device that obtains an interference signal and obtains distance data based on the interference signal includes a modulation means (2) for modulating a semiconductor laser (1) in a triangular wave, and a laser beam frequency-modulated in a triangular wave (
a polarized light generating means (6) that obtains polarized light (LA2) (LA3) having only mutually orthogonal polarized light components based on LA1), and an optical interference system (6) that guides both polarized light (LA2) (LA3) to substantially the same optical path. 6a) (6b) (7), each polarized light (LA2
) (LA3), and a pair of interferometers for obtaining a signal corresponding to an interference signal frequency based on polarized light having the same polarization direction in the rising and falling parts of the triangular wave. Signal extraction means (14) (15a) (15b) (16) (17
a) (17b) (20) (21a) (21b) (21c
) and beat frequency calculation means (14) and (23) for obtaining a beat signal frequency corresponding to an optical path length difference based on signals corresponding to both interference signal frequencies. 3. The polarization generating means is a polarization beam splitter (6), and the optical interference system is a polarization beam splitter (6).
), each of the polarized lights (LA2) (LA3) generated by
2. The distance measuring device according to claim 2, further comprising a non-polarizing beam splitter (7) that guides the light source (7) to two different optical paths. 4. The object to be measured (9) reflects linearly polarized light as elliptically polarized light, and the polarized light generating means (6) generates a laser beam (LA1) directed toward the object to be measured (9).
2. The distance measuring device according to claim 2, wherein the distance measuring device is disposed in the optical path of the laser beam branched from the distance measuring device. 5. The optical path length adjustment means (10) is for selecting different optical paths depending on the type of polarized light, and is arranged on one of the optical path of the reflected light from the measurement object (9) and the reference optical path. A distance measuring device according to any one of claims 2 to 4 above.