JPH10300421A - Distance measuring device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To change the polarization direction of reflected light to 90 like a reflector.
Provided is an optical heterodyne type distance capable of measuring both the distance of an object to be rotated by degrees and the distance of an object which does not rotate the polarization direction of reflected light such as a cat's eye. SOLUTION: A laser beam LB is separated into a signal beam LS and a reference beam LR by a polarization beam splitter 5, a quarter-wave plate 6 and a mirror 7 are arranged on an optical path of the reference beam LR, and the laser beam LB is disposed on an optical path of the signal beam. A polarization direction changing device 10 and a scan mirror 8 are provided. When the object is a reflector, when the quarter-wave plate 11 of the polarization direction conversion device 10 is inserted into the optical path, both the signal light and the reference light are guided in the same direction by the polarization beam splitter 5. When the object is a cat's eye, when the quarter-wave plate 11 of the polarization direction conversion device 10 is removed out of the optical path, both the signal light and the reference light are guided in the same direction by the polarization beam splitter 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a distance measuring device. More specifically, the present invention relates to a distance measuring device for measuring a distance to an object based on a principle of optical heterodyne ranging.

[0002]

2. Description of the Related Art In a conventional optical heterodyne type distance measuring apparatus used for a vehicle or the like, a laser beam LB emitted from a light projecting section 2 is applied to a polarizing beam splitter 5 as shown in FIG. The laser beam LB is made to enter, and a part (S-polarized light component) of the laser light LB is transmitted through the polarization beam splitter 5 as the signal light LS and emitted forward, and the remaining (P-polarized light component) laser light LB is used as the reference light LR as a polarization beam splitter. 5 is reflected. Then, the signal light LS transmitted through the polarization beam splitter 5 is made incident on the scan mirror 8, and the scan mirror 8 scans the signal light LS toward the detection area of the object. When the object 9 is a reflector (a reflecting plate having a number of pyramid-shaped reflecting portions [corner cubes] and reflecting light in the original direction by reflecting incident light twice),
Since the plane of polarization of the linearly polarized light reflected by the reflector is rotated by 90 degrees between before and after the reflection, the signal light LS (P-polarized component) reflected by the object 9 and returned is reflected by the scan mirror 8 and polarized. When the light enters the beam splitter 5, it is reflected by the polarization beam splitter 5.

On the other hand, the reference light LR (P-polarized light) reflected by the polarization beam splitter 5 becomes circularly polarized when transmitted through the quarter-wave plate 6, reflected by the fixed mirror 7, and transmitted again through the quarter-wave plate 6. Then, the light is changed from circularly polarized light to S-polarized light and transmitted through the polarization beam splitter 5.

Accordingly, the signal light LS reflected by the polarization beam splitter 5 and the reference light LR transmitted through the polarization beam splitter 5 are transmitted through the half-wave plate 15, thereby causing the signal light LS and the reference light LR to interfere with each other and beat. A signal is generated, and the distance to the object 9 can be measured based on the beat signal.

However, in the optical heterodyne type distance measuring apparatus having such a structure, when the object 9 is a cat's eye (for example, a flat reflective sign provided on a vehicle or a road), , The signal light LS is the object 9
Since the polarization direction does not rotate when the light is reflected by the polarization beam splitter, the signal light LS (S-polarized light) incident on the polarization beam splitter 5 passes through the polarization beam splitter 5 as shown by a two-dot chain line in FIG. There is a problem that the object 9 such as a cat's eye cannot measure the distance because the LS and the reference light LR do not interfere with each other.

Therefore, in order to make it possible to detect an object 9 such as a cat's eye, as shown in FIG. 10, a quarter-wave plate 51 must be inserted in the light projecting light path and the light receiving light path of the signal light LS. Can be considered. In this distance measuring device, the signal light LS that has passed through the polarizing beam splitter 5 and has become S-polarized light has become circularly polarized light by passing through the quarter-wave plate 51, and has been reflected by the object 9 such as a cat's eye. Since the reflected signal light LS changes from circularly polarized light to P-polarized light by the 板 wavelength plate 51, it is reflected by the polarization beam splitter 5 and becomes the reference light LR.
And the distance can be measured.

However, even if the optical heterodyne type distance measuring apparatus is improved in this way, when the object 9 is a reflector, the polarization direction of the signal light LS is rotated by 90 degrees when reflected by the object 9. Therefore, the signal light LS transmitted through the polarization beam splitter 5 returns from circularly polarized light to S-polarized light.
As indicated by a two-dot chain line at 0, the signal light LS (S-polarized light) incident on the polarization beam splitter 5 passes through the polarization beam splitter 5, so that the signal light LS and the reference light LR do not interfere with each other, and There was a problem that such an object 9 could not be measured.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the prior art, and has as its object to reduce the distance between different objects such as a reflector and a cat's eye. An object of the present invention is to provide a distance measuring device capable of measuring a distance.

[0009]

DISCLOSURE OF THE INVENTION A distance measuring apparatus according to the present invention divides a light beam into signal light and reference light having different polarization directions, and based on a beat signal generated by combining the signal light reflected by the object and the reference light. A distance measuring device for measuring a distance to a target object by using a polarization direction rotating means for rotating the polarization direction of linearly polarized light by 90 degrees while the signal light passes through a light projecting light path and a light receiving light path. It is provided on at least one of an optical path and a light receiving optical path, and the polarization direction rotating means can be switched between an operating state and a non-operating state.

Here, as the polarization direction rotating means for rotating the polarization direction of the linearly polarized light by 90 degrees while the signal light passes through the light projecting light path and the light receiving light path, a 波長 wavelength plate and an applied voltage are controlled. The phase of light in one polarization direction is 4
An element using the Kerr effect or the Bockels effect that delays by one-half wavelength, an optical rotatory substance that rotates the polarization direction by 90 degrees or 45 degrees, an element using the Faraday effect, and the like can be used.

In the above distance measuring device, there is provided a polarization direction rotating means for rotating the polarization direction of the linearly polarized light by 90 degrees while the signal light passes through the light projecting light path and the light receiving light path.
By switching the polarization direction rotating means between the active state and the inactive state, the polarization direction of the signal light returning to the light receiving optical path can be made different by 90 degrees. Therefore, even when the polarization directions of the signal light reflected by the object such as the reflector and the object such as the cat's eye are different by 90 degrees, the polarization beam can be turned on or off by operating the polarization direction rotating means. Signal light and reference light can be guided in the same direction and interfere with each other by a light combining means such as a splitter.

More specifically, the light beam is separated into signal light and reference light by a polarization splitting means, and an element for rotating the polarization direction by 90 degrees and a light reflector are arranged in the optical path of the reference light, and the signal light is reflected. In the case of a distance measuring apparatus provided with a polarization direction rotating means for rotating the polarization direction of the signal light by 90 degrees in the optical path and an optical scanning means for scanning the signal light toward the detection area, for example, the object may be a reflector. For example, the polarization direction rotating means on the optical path side of the signal light is deactivated. At this time, the signal beam and the reference beam are separated into, for example, an S-polarized component and a P-polarized component by the polarization beam splitter, respectively. When the reference light is reflected by the mirror and enters the polarization beam splitter, it is converted into S-polarized light. When the signal light is reflected by the object, the polarization direction is rotated by 90 degrees, so that the signal light is converted into P-polarized light when entering the polarization beam splitter. Therefore, the signal light and the reference light are combined by the polarization beam splitter, and the distance can be measured.

For example, if the object is a cat's eye, the polarization direction rotating means on the optical path side of the signal light is activated. In this case, when the signal light is reflected by the object, the polarization direction is not rotated, and the polarization direction is rotated by the polarization direction rotating means.
The signal light is converted to S-polarized light when entering the polarization beam splitter because the signal light is rotated by degrees. Therefore, the signal light and the reference light are combined by the polarization beam splitter, and the distance can be measured.

Therefore, according to the distance measuring device of the present invention,
It is possible to measure an object such as a reflector whose polarization direction is rotated by 90 degrees at the time of reflection and an object such as a cat's eye whose polarization direction is not rotated at the time of reflection.

If the polarization direction rotating means is switched between an operating state and a non-operating state at predetermined intervals, an object such as a reflector and an object such as a cat's eye can be detected alternately. Can also be measured.

If the polarization direction rotating means can be switched between an operating state and a non-operating state by operating a switch, a mode in which an object such as a reflector can be detected by operating the switch and an object such as a cat's eye can be detected. The mode can be switched to a mode in which an object can be detected.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(Optical System) FIG. 1 is a view showing an optical system 1 of an optical heterodyne type distance measuring apparatus according to an embodiment of the present invention. First, the optical system 1 will be described. The light projecting unit 2 includes a laser diode (LD) 3 that generates a laser beam LB.
And the laser light L emitted from the laser diode 3
And a collimating lens 4 for collimating B. A first polarizing beam splitter (PBS) is provided in front of the light emitting section 2
The collimated laser beam LB emitted from the light projecting unit 2 is separated by the first polarizing beam splitter 5 into a signal beam LS and a reference beam LR. Since the first polarization beam splitter 5 transmits the S polarization component and reflects the P polarization component, the signal light LS passes through the first polarization beam splitter 5 to become light of the S polarization component, and the reference light LR is the first polarization light. The light is reflected by the beam splitter 5 and becomes P-polarized light.

On the reflection side of the first polarizing beam splitter 5, a quarter-wave plate 6 and a fixed mirror 7 are arranged, and the reference light LR of the P-polarized light component reflected by the first polarizing beam splitter 5 is one. The light is converted into circularly polarized light by passing through the 波長 wavelength plate 6. The circularly polarized reference light LR is reflected by the fixed mirror 7 and again passes through the quarter-wave plate 6, and the reference light LR is returned from the circularly-polarized light to the linearly-polarized light by the quarter-wave plate 6. At this time, since the polarization direction of the linearly polarized light is rotated by 90 degrees from the original direction, the linearly polarized light is converted from the original P-polarized light component to the S-polarized light component, and is incident on the first polarization beam splitter 5 again. Since the first polarization beam splitter 5 transmits S-polarized light, the reference light LR transmits through the first polarization beam splitter 5.

On the other hand, the signal light LS of the S polarization component transmitted through the first polarization beam splitter 5 is reflected by the scan mirror 8 of the optical scanner disposed on the transmission side of the first polarization beam splitter 5, and Or scanning towards the sensing area. Here, a polarization direction conversion device 10 as shown in FIGS. 2A and 2B is arranged between the first polarization beam splitter 5 and the scan mirror 8.

FIG. 2A shows the polarization direction changing device 10.
As shown in (b), each divided region is divided into four (in the figure, divided into four, but may be divided into two, six, etc.).
A rotating plate 13 provided with four wavelength (λ / 4) plates 11 and glass plates 12 alternately is rotated at a constant speed or intermittently by a pulse step motor 14. Depending on the angle, the signal light LS is
Or through the quarter-wave plate 11. The pulse step motor 14 is controlled by a signal from the control calculation unit 25. The rotation speed of the rotary plate 13 is such that one area of the rotary plate 13 passes through the optical path of the signal light LS during two scans by the scan mirror 8. It is defined as follows. Therefore, when the rotating plate 13 includes n quarter-wave plate regions and n glass plate regions, the rotating plate 13 is
While rotating, the signal light LS is scanned 4n times.

Now, assuming that the area of the quarter-wave plate 11 of the rotating plate 13 is on the optical path of the signal light LS, the signal light LS of the S-polarized component transmitted through the first polarizing beam splitter 5 is 1
The light is converted into circularly polarized light by passing through the 波長 wavelength plate 11. The circularly polarized signal light LS is reflected by the scan mirror 8 and is scanned on the object 9. The signal light LS reflected by the object 9 passes through the scan mirror 8 and the 波長 wavelength plate 11 again, is returned from the circularly polarized light to the linearly polarized light again by the １ ／ wavelength plate 11, and is returned to the first polarization beam splitter 5. Incident on. At this time, when the object 9 does not rotate the polarization direction at the time of reflection, such as a cat's eye, the polarization direction rotates 90 degrees when the signal light LS passes through the quarter-wave plate 11. , The signal light LS is converted from the original S-polarized light component to the P-polarized light component, and
And is reflected by the first polarizing beam splitter 5.
As a result, the signal light LS of the P polarization component and the reference light LR of the S polarization component are guided in the same direction, that is, toward the light receiving unit.

On the other hand, when the object 9 rotates the polarization direction by 90 degrees at the time of reflection like a reflector, the signal light LS
Is reflected by the object 9, the polarization direction is rotated by 90 degrees, and further, it is rotated by 90 degrees when passing through the quarter-wave plate 11, so that the polarization direction is eventually rotated by 180 degrees. As a result, the signal light LS is converted again from the original S-polarized light component to the S-polarized light component, enters the first polarization beam splitter 5, and passes through the first polarization beam splitter 5. Therefore, in this case, the signal light LS of the S polarization component is not guided to the light receiving unit side.

On the other hand, assuming that the area of the glass plate 12 of the rotating plate 13 is on the optical path of the signal light LS, the signal light LS of the S-polarized component transmitted through the first polarization beam splitter 5 is transmitted through the glass plate 12. And reflected by the scan mirror 8,
The object 9 is scanned. The signal light L reflected by the object 9
S again passes through the scan mirror 8 and the glass plate 12,
The light enters the first polarization beam splitter 5. At this time, when the object 9 rotates the polarization direction by 90 degrees when reflected like a reflector, the signal light LS reflected by the object 9 rotates the polarization direction by 90 degrees to become a P-polarized component. Therefore, the light is reflected by the first polarization beam splitter 5.
As a result, the signal light LS of the P polarization component and the reference light LR of the S polarization component are guided in the same direction, that is, toward the light receiving unit.

On the other hand, when the polarization direction is not rotated by 90 degrees when the object 9 is reflected like a cat's eye, the polarization direction does not rotate when the signal light LS is reflected by the object 9, so that the signal light LS is not reflected. After passing through the glass plate 12, the signal light LS eventually enters the first polarization beam splitter 5 while maintaining the original S-polarized component. As a result, the signal light LS passes through the first polarization beam splitter 5. Therefore, in this case,
The signal light LS of the S polarization component is not guided to the light receiving unit side.

When the rotating plate 13 of the polarization direction changing device 10 rotates, whether the object 9 is a reflector or a cat's eye, the P-polarized signal light LS and the S-polarized light Is simultaneously guided to the light receiving side. A 波長 wavelength (λ / 2) plate 15 and a second polarizing beam splitter 16 are disposed on the light receiving side of the first polarizing beam splitter 5, and are disposed on the transmitting side and the reflecting side of the second polarizing beam splitter 16. Are provided with light receiving elements 17, 18 such as photodiodes, respectively. The electrical principal axis direction of the half-wave plate 15 is inclined with respect to the P-polarization direction and the S-polarization direction of the signal light LS and the reference light LR. When the light LR passes through the half-wave plate 15, the polarization directions of the signal light LS and the reference light LR are rotated, and both the P-polarized light component and the S-polarized light are transmitted.
It has a polarization component. As a result, a part of the signal light LS and the reference light LR, that is, the light of the S-polarized component passes through the second polarization beam splitter 16 and the light-receiving element 1
7 is incident. Also, of the signal light LS and the reference light LR, P
The polarized light component is reflected by the second polarizing beam splitter 16 and enters the light receiving element 18. Thus, the signal light LS and the reference light LR that have entered the light receiving element 17 have a polarization direction (S
Since the (polarization components) match, a beat signal is generated in the light receiving element 17. Similarly, since the signal light LS and the reference light LR that have entered the light receiving element 18 have the same polarization direction (P polarization component), a beat signal is generated in the light receiving element 18.

Further, a photocurrent (beat signal) output from the light receiving element 17 and a photocurrent (beat signal) output from the light receiving element 18 are input to a differential amplifier 19, and an electric signal is output from the differential amplifier 19. Is output.

FIG. 3 is a schematic diagram for explaining the reason why a beat signal is generated at the light receiving elements 17 and 18 by the optical system 1 as described above (the differential amplifier 19 is omitted). Laser light LB emitted from light emitting unit 2
Is expressed as a ₀ · expj (2πνt). Here, a ₀ = √ (2P ₀ ) P ₀ : light intensity of the laser light LB emitted from the light projecting unit 2 j = √ (−1) ν: frequency of the laser light LB t: time. The reference light LR ignores the phase shift due to the optical path length to reach the light receiving element 17, the reference light intensity P _R
= When a _R ^2/2, the reference light LR enters the light receiving element 17, 18 is represented by a _R · expj (2πνt). Further, it is assumed that a frequency change of Δν occurs in the signal light LS due to a temporal change of an emission frequency of the laser diode 3 and a change in a relative speed with respect to the optical heterodyne type distance measuring device due to movement of the object 9,
When ^{_{P S = a S 2/2}} , the signal light LS incident on the light-receiving element 17, 18 is represented by _{a S · expj [2π (ν} + Δν) t]. Therefore, assuming that the conversion efficiency of the light receiving elements 17 and 18 is η, when receiving the signal light LS and the reference light LR, the photocurrent i flowing through the light receiving circuit including the light receiving elements 17 and 18 and the resistor R ₀ is expressed by the following equation. The beat signal becomes as shown. i = η | a _R · expj (2πνt) + a _S · expj [2π (ν + Δν) t] | ² = η [a _R ² + a _S ² + 2a _R · a _S · cos (2πΔνt)] Then, the photocurrent i When the DC component is removed by the band-pass filter 21, the photocurrent i becomes a beat signal i _F represented by the following equation. i _F = 2η · a _R · a _S · cos (2πΔνt)]

(Processing Circuit) FIG. 4 is a block diagram showing a signal processing circuit 20 in the optical heterodyne type distance measuring apparatus. The signal processing circuit 20 includes a light receiving element 17,
It has a function of processing the signal from 18 to calculate the distance to the object 9 and controlling the driving of the light projecting unit 2 and the scan mirror 8.

The reception signal processing portion of the signal processing circuit 20
It comprises a band pass filter 21, a rectifier 22, an integrator 23, and an analog / digital (A / D) converter 24. Thus, the photocurrent (beat signal) i output from the light receiving elements 17 and 18 is output to the differential amplifier 19,
The differential output passes through the band pass filter 21. The band-pass filter 21 has a transmittance spectrum as shown in FIG. The maximum frequency ν _max is determined by the spectral width (coherent length) of the laser diode 3. For example, the coherent length of the laser diode 3 is ΔL = 10 m, and the light speed c (= 3 × 10 ⁻⁸ m / se).
Assuming c), from ν _max = c / ΔL, ν _max = 30 MH
z. Therefore, in the differential output signal of the photocurrent i, the DC component and the frequency components other than the band determined by the spectrum width of the laser diode 3 are removed. The AC component of the output signal (beat signal i _F ) that has passed through the band-pass filter 21 is rectified by the rectifier 22 and integrated by the integrator 23. Upon receiving the reset signal from the control operation unit (CPU) 25, the integrator 23 resets the integrated value to 0, integrates the signal output from the rectifier 22, and when a predetermined integration time T has elapsed, the integrated value is reset. A / D converter 24
Output to Upon receiving the integrator output converted to a digital signal by the A / D converter 24, the control operation unit 25 resets the integrator 23 again. The control calculation unit 25 calculates the distance to the object 9 based on the value of the output of the integrator as described later.

The laser diode drive circuit 26 causes the laser diode 3 to emit light based on a light emission control signal from the control operation unit 25. Laser diode drive circuit 2
Reference numeral 6 denotes a built-in modulation circuit that continuously switches the laser diode 3 at every integration time T in the integrator 23 based on a light emission control signal from the control calculation unit 25.
e) Emit light (FIG. 6A) or emit intensity modulated light with a duty ratio of 50% (FIG. 7A).

The optical scanner drive circuit 27 for driving the optical scanner rotates the scan mirror 8 based on the signal from the control operation unit 25 and scans the signal light LS at a constant period. The signal light LS is scanned twice while passing through the 波長 wavelength plate 11 of the polarization direction conversion device 10 and
Are scanned during the scanning, the laser diode 3 emits light continuously in one of the two scans, and the laser diode 3 emits intensity-modulated light in the remaining one scan.

Next, a method of obtaining the distance to the object 9 by the above-described signal processing circuit 20 will be described with reference to FIGS. The optical heterodyne type distance measuring device divides a scanning range where the signal light LS is scanned into a plurality of detection regions (for example, 80 regions), and measures the distance to the object 9 for each detection region. For this reason, the laser diode 3 is switched between continuous light emission and intensity modulated light emission for each detection area, and each time an integrated output is output from the integrator 23 to calculate the distance to the object 9.

First, at the same time as resetting the integrator 23, the laser diode 3 is caused to start continuous light emission.
When the integration time T has elapsed, light emission is stopped. Since the optical path length of the reference light LR is short and the delay time until the light is received by the light receiving elements 17 and 18 can be ignored, the light receiving elements 17 and 18 can be ignored.
FIG. 6 shows a signal (light projection signal) based on the reference light LR received by
This is shown in FIG. If the distance to the object 9 is R,
Since the signal light LS arrives at the light receiving elements 17 and 18 with a delay of 2R / c from the light projection timing, the light receiving elements 17 and 18
Signal (light receiving signal) by the signal light LS received at 18
Is represented in FIG. 6 (b). Accordingly, as shown in FIG. 6C, the beat signal generated by the interference between the light projection signal (reference light) and the light reception signal (signal light) is, as shown in FIG.
/ C to T). Assuming that the integration speed of the beat signal in the integrator 23 is α, the integrated output I ₀ of the integrator 23 after the integration time T is I ₀ = α (T−2R / c) as shown in FIG. Is represented by Here, the integration time T is equal to the delay time 2R /
Since it is sufficiently longer than c, it can be considered that T >> 2R / c. Therefore, I ₀ = αT. After the elapse of the integration time T, the integration output I ₀ of the integrator 23
Is output to the control operation unit 25 via the A / D converter 24.

Next, at the same time as resetting the integrator 23, the laser diode 3 is caused to emit light with intensity modulation at a duty ratio of 50% and a period of 1 / ν _CLK (where ν _CLK is an intensity modulation frequency), and the integration time T of the integrator 23 has elapsed. Sometimes stops emitting light. The reference light L received by the light receiving elements 17 and 18
FIG. 7A shows a signal (light projection signal) based on R. Since the signal (light receiving signal) by the signal light LS received by the light receiving elements 17 and 18 is delayed by 2R / c, FIG.
It is represented by (b). Therefore, the beat signal generated by the interference between the light-projected signal (reference light) and the light-receiving signal (signal light) is shown in FIG.
As shown in (c), the period has a length of 1 / (2ν _CLK ) − (2R / c) with a period of 1 / ν _CLK . Therefore, assuming that the integration speed of the beat signal in the integrator 23 is α, the integration process is performed intermittently in the integrator 23, and the integrated output I ₁ of the integrator 23 after the integration time T is as shown in FIG. I ₁ = α · [1 / (2ν _CLK ) − (2R / c)] × (T · ν _CLK ) After integration time T has elapsed, the integration output I ₁ of the integrator 23 is outputted to the control arithmetic unit 25 via the A / D converter 24, the integrator 23 is reset.

Upon obtaining the integrated output I ₀ of the integrator 23 by continuous light emission and the integrated output I ₁ by intensity-modulated light emission, the control operation unit 25 calculates the integrated output I ₀ and I ₁ to the object 9 based on both the integrated outputs I ₀ and I ₁ . The distance R is calculated. That is, when determining the ratio of the integrated output I ₁ for the integral output I _0, the above equation and _{Equation, I 1 / I 0 = ν} CLK [1 / (2ν CLK) - (2R / c)] = (1/2 ) − (2Rν _CLK / c). Accordingly, the distance R to the object 9 is represented by R = (c / 2ν _CLK ) × [1 / 2− (I ₁ / I ₀ )]. Therefore, it is possible to determine the ratio of the integration output I ₁ by the intensity modulation light emission for the integral output I ₀ by continuous emission, the distance from the intensity modulation frequency [nu _CLK to the object 9.

According to such a system, an inexpensive laser beam LB having a short coherent length can be used in the optical heterodyne system. Further, heterodyne detection can be performed without performing FM modulation. Furthermore, the S / N ratio becomes better than the pulse echo method,
The measurable distance also increases.

In the above embodiment, the rotating plate 1
The type of the target 9 (that is, the type of the target 9, that is, the one-third 波長 wavelength plate 11 or the glass plate 12 is generated on the optical path of the signal light LS when the beat signal is generated by the light receiving elements 17 and 18).
Reflector or cat's eye).

(Other Embodiments) FIG. 8 is a diagram showing a configuration of a polarization direction changing device 28 according to another embodiment of the present invention. The polarization direction changing device 28 is provided with the 波長 wavelength plate 11
Is moved on the optical path of the signal light LS or moved out of the optical path by sliding or rotating the actuator 29 in the vertical direction or the horizontal direction by the actuator 29. , The quarter-wave plate 11 is moved on the optical path of the signal light LS or out of the optical path at regular intervals.

In the above-described embodiment, the polarization direction converting means 10 and 28 move the quarter-wave plate 11 from the optical path of the signal light LS to the optical path or from the optical path to the optical path at regular intervals. However, the 波長 wavelength plate 11 may be set on the optical path of the signal light LS or removed from the optical path of the signal light LS by manual operation of the operation switch. In this case, by operating the operation switch, the optical heterodyne type distance measuring device is switched to a mode in which an object such as a cat's eye can be distance-measured or a mode in which an object such as a reflector can be distance-measured. be able to.

Further, as the above-mentioned polarization direction conversion device, 1
Instead of the 波長 wavelength plate 11, an optical element utilizing the Pockels effect or the Kerr effect, which controls the applied voltage to delay the phase of the incident light by ４ wavelength, may be used (not shown).

Alternatively, an optical rotatory substance or a Faraday element for rotating the polarization direction by 90 degrees may be arranged on one of the light projecting light path and the light receiving light path of the signal light. Alternatively, the polarization direction is set to 45 for each of the light projecting optical path and the receiving optical path
An optically rotating substance or a Faraday element that is rotated by an angle may be arranged.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system of an optical heterodyne type distance measuring apparatus according to an embodiment of the present invention.

FIGS. 2A and 2B are a front view and a plan view showing the structure of a polarization direction changing means.

FIG. 3 is a schematic explanatory diagram illustrating a principle of generating a beat signal in a light receiving unit.

FIG. 4 is a block diagram showing a configuration of a signal processing circuit of the optical heterodyne type distance measuring apparatus according to the first embodiment;

FIG. 5 is a diagram showing a transmittance spectrum of a bandpass filter.

FIG. 6 is a waveform diagram of each part of the signal processing circuit during continuous light emission.

FIG. 7 is a waveform diagram of each part of the signal processing circuit during intensity-modulated light emission.

FIG. 8 is a schematic diagram showing another embodiment of the polarization direction conversion device.

FIG. 9 is a diagram showing a configuration of a conventional optical heterodyne type distance measuring apparatus.

FIG. 10 is a diagram showing an improved example of a conventional optical heterodyne type distance measuring apparatus.

[Explanation of symbols]

 Reference Signs List 3 laser diode 5 first polarization beam splitter 8 scan mirror 10 polarization direction conversion device 11 1/4 wavelength plate 12 glass plate 13 rotating plate 14 pulse step motor 17, 18 light receiving element 20 signal processing circuit LB laser light LS signal light LR Reference light

Continuation of front page (71) Applicant 597066429 1000 William Pitt Way Pittsburgh, PA 15238, U.S.A. S. A. (72) Inventor Yoshihiko Tamura William Pittway 1000, Pittsburgh, Pennsylvania, USA, within Optmation Inc.

Claims (6)

[Claims] 1. A light beam is divided into signal light and reference light having different polarization directions, and a distance to the object is measured based on a beat signal generated by combining the signal light reflected by the object and the reference light. In the distance measuring device, the polarization direction rotating means for rotating the polarization direction of linearly polarized light by 90 degrees while the signal light passes through the light projecting light path and the light receiving light path,
A distance measuring device provided on at least one of a light projecting optical path and a light receiving optical path of signal light, wherein the polarization direction rotating means can be switched between an operating state and a non-operating state. 2. A polarization separating means for separating a projection beam into a signal light and a reference light, an element and an optical reflector arranged in an optical path of the reference light for rotating the polarization direction of the reference light by 90 degrees, and a signal light. A polarization direction rotating means for rotating the polarization direction of the signal light by 90 degrees and an optical scanning means for scanning the signal light toward the detection area, wherein the reference light is reflected by the light reflector. And the signal light is reflected by the object to be measured again so as to be incident on the polarization separation means again. The polarization direction rotation means is activated and deactivated. The distance measurement device according to claim 1, wherein the distance measurement device can be switched between (1) and (2). 3. The distance measuring apparatus according to claim 1, wherein said polarization direction rotating means switches between an active state and a non-active state at predetermined intervals. 4. The distance measuring apparatus according to claim 1, wherein the polarization direction rotating means is switched between an operating state and a non-operating state by operating a switch. 5. The distance measuring apparatus according to claim 1, wherein said polarization direction rotating means is a quarter wave plate. 6. The polarization direction rotating means is an element for delaying the phase of light in one polarization direction by a quarter wavelength by controlling an applied voltage.
The distance measuring device according to claim 1.