JPH06249960A - Electro-optical distance measurement system - Google Patents

Abstract

PURPOSE:To realize highly accurate quick measurement of distance by removing noise components from an electric signal using a variable pass band filter for capturing an electric signal, obtained through optoelectric conversion of a received optical signal, over a wide band and making a switch to a narrow band. CONSTITUTION:Distance measurement light reflected on an object is converted through a light receiver 10 into a second electric signal which is fed to one input of a mixer 12. A frequency divider 23 feeds the other input of the mixer 12 with a fifth electric signal having a reference frequency shifted by an amount, corresponding to the frequency of a third electric signal being fed to a phase comparator 20, from the frequency of a first electric signal generated from an oscillator 2. The mixer 12 mixes the frequencies of the second and fith electric signals and feeds an amplifier 14 with a fourth electric signal obtained by subjecting the second electric signal to frequency conversion. The amplified fourth electric signal is fed to a variable pass band filter 16 which removes noise components from the side band of the fourth electric signal to produce only the distance information component.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light wave distance measuring device for measuring a distance to an object to be measured by using a light wave.

[0002]

2. Description of the Related Art A conventional device of this type emits distance-measuring light amplitude-modulated by a first electric signal of a predetermined frequency to a measuring object and receives distance-measuring light reflected from the measuring object. Phase difference between the third electric signal obtained by performing the predetermined processing on the first electric signal and the fourth electric signal obtained by performing the predetermined processing on the second electric signal. And the distance to the object to be measured is measured based on this phase difference.

However, due to the influence of noise due to atmospheric fluctuations in the optical path between the optical distance measuring device and the object to be measured,
Since the phase and the amplitude of the second electric signal are changed, sufficient distance measurement accuracy cannot be obtained by one measurement. Therefore, in the conventional distance measuring device, the phase value of the second electric signal is averaged by software processing to improve the distance measuring accuracy.

[0004]

As described above, in the conventional optical distance measuring apparatus, the accuracy of distance measurement is improved only by averaging the phase values by software, but this averaging processing is, for example, 10000. Since it has to be performed for measured values of about once, there is a problem that the work load of the software is heavy and the distance measurement time becomes long.

Further, conventionally, in the path for processing the second electric signal to obtain the fourth electric signal, the fifth reference frequency deviated from the frequency of the first electric signal by the frequency of the third electric signal. A band pass filter is provided in a stage subsequent to the mixer for frequency mixing the electric signal and the second electric signal.
Although it has been proposed to increase the S / N ratio, this method can remove the noise of the frequency component sufficiently distant from the center frequency, but the noise due to atmospheric fluctuation is noise near the center frequency. Since it passes through the filter as it is, it is difficult to improve the measurement accuracy by this method.

An object of the present invention is to obtain high distance measuring accuracy in a short measuring time.

[0007]

SUMMARY OF THE INVENTION An optical wave distance measuring apparatus according to the present invention includes a light emitting section for emitting distance measuring light amplitude-modulated by a first electric signal having a predetermined frequency to a measuring object, and a measuring object. A light receiving unit that receives the reflected distance measuring light and converts it into a second electric signal, a first electric signal generation unit that performs a predetermined process on the first electric signal, and outputs a third electric signal, and a second electric signal A second electric signal generator that outputs a fourth electric signal by subjecting the third electric signal to a predetermined difference, and a phase difference between the third electric signal and the fourth electric signal, and based on the phase difference, the distance to the measurement object is calculated. A lightwave distance measuring device comprising a signal processing unit for measuring,
In the path between the second electric signal generation unit and the signal processing unit, a band thereof is captured by capturing the second electrical signal in a wide band and switching the captured second electrical signal to a narrow band with the center frequency as a center frequency. A variable band pass filter (for example, the variable band pass filter 16 in FIG. 1) that removes noise components due to fluctuations in the atmosphere included in the two electrical signals is provided.

The second electric signal generating section frequency-mixes a fifth electric signal and a second electric signal having a reference frequency deviated from the frequency of the first electric signal by the frequency of the third electric signal (for example, as shown in FIG. It is preferable that the variable band pass filter is provided between the mixer and the signal processing unit.

The variable band pass filter includes a PLL circuit (for example, the PLL circuit 30 in FIG. 2) and a gate circuit (for example, for outputting an output signal of the PLL circuit).
The gate circuit 40) of FIG.
A phase comparator (for example, the phase comparator 32 in FIG. 2) that outputs the phase difference between the input signal and the output signal of the LL circuit, and a variable low-pass filter that passes the low-frequency component of the output signal of this phase comparator. Filter (eg, variable low-pass filter 34)
And PL the frequency signal based on the output of this filter.
A voltage-controlled oscillator (voltage-controlled oscillator 36) generated as an output signal of the L circuit, and when the phase of the output signal of the PLL circuit matches the phase of the input signal, the variable low-pass filter is switched from the wide band. It is preferable to switch to a narrow band and output the output signal of the PLL circuit via the gate circuit.

The variable band pass filter further comprises:
A quadrature detector (for example, quadrature detector 50 in FIG. 2) that receives an input signal and an output signal of the PLL circuit as input signals and performs quadrature detection, and passes a low-frequency component of the output signal of this detector. Low-pass filter (see, for example, FIG.
Low pass filter 60) and a level detector (for example, the level detector 70 in FIG. 2) for detecting the level of the output of this filter, and the phase of the output signal of the PLL circuit becomes the phase of the input signal. When they match, the level detector detects that the output signal of the quadrature detector received through the low-pass filter has reached a predetermined level, which causes the variable low-pass filter to switch from wide band to narrow band. , P
The output signal of the LL circuit is preferably output via the gate circuit.

[0011]

In the light wave distance measuring apparatus of the present invention, the variable band pass filter removes the noise component due to fluctuation in the atmosphere contained in the second electric signal. Therefore, it is possible to eliminate or reduce the averaging process by software as in the prior art, and it is possible to perform highly accurate distance measurement in a short time.

When the variable band pass filter is provided between the mixer and the signal processing section, the variable band pass filter removes not only noise components due to fluctuations in the atmosphere but also spurious components. be able to.

When the variable band pass filter includes a PLL circuit and a gate circuit that selectively outputs the output signal of the PLL circuit, the phase of the output signal of the PLL circuit becomes the phase of the input signal. When they match, the variable low-pass filter is switched from the wide band to the narrow band, and the PL
The output signal of the L circuit is output via the gate circuit.
Therefore, even if there is fluctuation in the atmosphere, the second electric signal including the distance information can be reliably captured, and after capturing, only the distance information component in the second electrical signal is passed and the noise component is removed. Therefore, the distance can be measured quickly and accurately.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the lightwave distance measuring apparatus of the present invention. The oscillator 2 generates a rectangular-wave first electric signal having a constant frequency. This first electric signal is applied to the band pass filter 4
Is supplied to the light emission driver 6 via. Light emission driver 6
Performs amplitude modulation of the light source of the light emitter 8 based on the supplied first electric signal, and emits distance measuring light toward the measurement object.

The distance-measuring light reflected from the object to be measured is converted into a second electric signal by the photodetector 10, and the mixer 12
Is supplied to one of the inputs. The frequency divider 23 generates a fifth electric signal having a reference frequency, which is deviated from the frequency of the first electric signal generated from the oscillator 2 by the frequency of the third electric signal supplied to the phase comparator 20 described later, from the mixer 12. Supply to the other input. The mixer 12 frequency-mixes the fifth electric signal and the second electric signal, and supplies the amplifier 14 with a fourth electric signal obtained by frequency-converting the second electric signal.

The fourth electric signal amplified by the amplifier 14 is supplied to the variable band pass filter 16. The phase and amplitude of the second electric signal output by the photodetector 10, that is, the fourth electric signal output by the amplifier 14, are fluctuated due to the influence of noise caused by atmospheric fluctuations between the optical distance measuring device and the object to be measured. As shown in FIG. 3B, the frequency spectrum is a signal in which the sideband is widened due to the noise component centering on the distance information component. In addition,
FIG. 3A shows the first electric signal input to the light emitter 10.

When the sideband noise component is removed from the fourth electric signal by the variable bandpass filter 16, only the distance information component remains, so that the S / N ratio of the received signal can be improved and the ranging accuracy can be improved. Can be increased. Also,
The tunable bandpass filter 16 is set to a wide band first in order to speed up the response time, and captures the fourth electric signal including the distance information component and the noise component, that is, the input signal of the tunable bandpass filter 16 is input. After the phase matches the phase of the output signal, the band is switched to the narrow band.

By providing the variable band pass filter 16 after the mixer 12, not only the noise component due to fluctuations in the atmosphere but also the spurious component can be removed. The variable band pass filter 16 is provided after the amplifier 14 because it is preferable to remove the noise component after the signal including the distance information is stabilized.

The fourth electric signal having only the distance information component output from the variable band pass filter 16 is binarized, that is, digitized by the level converter 18, and is input to one of the phase comparators 20. Phase comparator 2
A signal obtained by dividing the first electric signal output from the oscillator 2 by the frequency divider 22 is supplied to the other input of 0.
The phase comparator 20 compares the phases of both input signals and outputs a phase difference, and the counter 24 counts the phase difference.

The phase value counted by the counter 24 is
The phase value is converted into the distance by the calculator 26, and the display 28 displays the distance output from the calculator 26.

The phase value measurement uses not only a single-wavelength ranging signal but also a plurality of ranging signals of different wavelengths in order to remove an uncertain value of an integer wavelength. And the distance measurement procedure of the distance measuring device are controlled by the controller 100.

FIG. 2 shows the variable band pass filter 1 of FIG.
6 shows an example of the configuration. The variable band pass filter of this example includes a PLL circuit 30 and a gate circuit 40 that selectively outputs an output signal of the PLL circuit 30. P
The LL circuit 30 includes a phase comparator 32 that outputs a phase difference between an input signal and an output signal of the PLL circuit, and a variable low-pass filter 34 that passes a low-frequency component of the output signal of the phase comparator 32. And a voltage controlled oscillator 36 for generating a signal having a frequency based on the output of this filter as an output signal of the PLL circuit, and changing the characteristic of the variable low pass filter 34 makes it possible to change the pass band width of the signal. it can.

In order to change this pass band width, FIG.
The variable band pass filter of No. 1 receives the input signal and output signal of the PLL circuit 30 as input signals and performs quadrature phase detection, and a low-pass component that passes low-frequency components of the output signal of the detector 50. A bandpass filter 60 and a level detector 70 for detecting the level of the output of the filter 60 are provided, and when the phase of the output signal of the PLL circuit 30 matches the phase of the input signal, that is, the PLL circuit 30.
When the fourth electric signal containing the distance information component from the amplifier 14 is captured, the level detector 70 detects that the output signal of the quadrature detector received through the low pass filter has reached a predetermined level, As a result, the variable low pass filter 34 is switched from the wide band to the narrow band, and the PLL circuit 3
The output signal of 0 is output to the level converter 18 via the gate circuit 40.

When the PLL circuit 30 is switched to the narrow band, the voltage controlled oscillator 36 does not respond to the noise component of the side band in the fourth electric signal from the amplifier 14 and follows only the phase component indicating the distance information. To do. Therefore, highly accurate distance measurement can be performed in a short time.

The noise component due to fluctuations in the atmosphere has a relationship of frequency (f) and intensity (n) of n with the received signal as the center.
= 1 / f, and the frequency (f) width ranges from several Hz to several 100 Hz depending on the degree of fluctuation, but it is a frequency component very close to the center of the received signal. In addition, the received signal is the one that the transmission signal passed through the optical path and was reflected from the measurement object, so the original transmission due to fluctuations in the optical path due to fluctuations, movement of the measurement object, fluctuations in the distance measuring device from the time of transmission to the time of reception, etc. Not only the phase but also the center frequency fluctuates slightly from the signal.

Therefore, in order to remove a noise component due to fluctuations in the atmosphere, a narrow band filter having a frequency band of about several Hz and a very large Q (for example, about 10,000) is required, and the center frequency fluctuates slightly. It is necessary to track the center frequency of the filter so as not to remove the received signal that is being processed. The variable band pass filter using the PLL circuit of FIG. 2 can satisfy such two requirements. A conventional LC filter or active filter having a small central frequency and a fixed center frequency cannot remove noise components due to fluctuations in the atmosphere.

While the conventional LC filter and active filter work passively (unilaterally) on the input signal, FIG.
In the variable band pass filter using the PLL circuit 30 of FIG. 1, the voltage controlled oscillator 36 actively works by following the input signal.

Immediately after the signal is input to the PLL circuit 30, the input signal and the output signal of the voltage controlled oscillator 36 in the PLL circuit 30 are deviated in both frequency and phase, and the error component of the deviation is detected. Therefore, the variable low-pass filter 34 in the PLL circuit 30 has a wide band, and as a result, the entire PLL circuit 30 also operates in a wide band. Here, if the variable band pass filter 34 in the PLL circuit 30 is set to have a narrow band from the beginning, the above-mentioned error component is not detected or is difficult to be detected.
The whole doesn't work or it takes a very long time to work.

The voltage controlled oscillator 36 is controlled by the detected error component, and the voltage controlled oscillator 36 is synchronized with the input signal. When the synchronization is established, the error component becomes very small, and the variable band pass filter 34 in the PLL circuit 30 also needs a narrow band. Therefore, by switching the variable band pass filter 34 to a narrow band here, the noise component of the input signal can be further eliminated, and as a result, the entire PLL circuit 30 functions as a narrow band filter. When the input signal is interrupted for some reason, the voltage-controlled oscillator is out of the input signal, so it is necessary to return to wideband operation. Then, when the synchronization with the input signal is established again, the operation is switched to the narrow band operation.

The variable band pass filter 16 may be composed of various filters such as a digital filter instead of the structure of FIG.

Further, in the above embodiment, the rectangular wave electric signal is generated from the oscillator 2, but a sine wave electric signal may be generated.

In the above embodiment, the noise due to the fluctuation of the atmosphere is a problem, but the variable band pass filter 16 is used.
By providing, it is possible to remove noise due to background light such as sunlight.

[0033]

According to the optical distance measuring apparatus of the present invention, an electric signal obtained by photoelectrically converting an optical signal received by a light receiver is captured in a wide band, and the captured electric signal is used as a center frequency in a narrow band. By using a variable band-pass filter that can be switched, noise components due to fluctuations in the atmosphere contained in the electrical signal are removed, so even if there is fluctuation in the atmosphere, an electrical signal containing distance information can be reliably obtained. In addition to capturing the distance information component after capturing, the noise component can be removed and the distance measurement can be performed quickly and accurately. Further, since the averaging process by software as in the conventional case can be made unnecessary or slight, sufficient distance measuring accuracy can be achieved in a shorter time than in the conventional case. Further, if the averaging process is performed by software, for example, over the same distance measuring time as in the conventional case, the distance measuring accuracy can be further improved. Further, if the same distance measuring time and distance measuring accuracy as the conventional ones are sufficient, it is possible to reduce the size of the entire device by reducing the size of the objective lens to reduce the amount of received light.

Further, by providing the variable band pass filter in the latter stage of the mixer, it is possible to remove not only noise components due to fluctuations in the atmosphere but also spurious components by the variable band pass filter.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a configuration example of a variable band pass filter 16 shown in FIG.

FIG. 3 is a diagram showing an example of frequency spectra of a first electric signal input to a light emitter 8 and a second electric signal output from a light receiver 8 in the embodiment of FIG.

[Explanation of symbols]

 2 oscillator 4 band pass filter 6 light emission driver 8 light emitter 10 light receiver 12 mixer 14 amplifier 16 variable band pass filter 18 level converter 20 phase comparator 22 frequency divider 30 PLL circuit 32 phase comparator 34 variable low band Pass filter 36 Voltage controlled oscillator 40 Gate circuit 50 Quadrature detector 60 Low pass filter 70 Level detector

Claims (4)

[Claims] 1. A light emitting unit for emitting distance measuring light amplitude-modulated by a first electric signal of a predetermined frequency to a measuring object, and a second receiving unit for receiving the distance measuring light reflected from the measuring object. A light receiving unit for converting into an electric signal, a first electric signal generation unit for performing a predetermined process on the first electric signal and outputting a third electric signal, and a fourth electric signal for performing a predetermined process on the second electric signal. And a signal processing unit that obtains a phase difference between the third electric signal and the fourth electric signal and measures the distance to the measurement object based on the phase difference. In the optical distance measuring device, the second electric signal is captured in a wide band in the path between the second electric signal generation unit and the signal processing unit, and the captured second electric signal is acquired. By switching to a narrow band centered on the signal Optical distance measuring apparatus characterized by having a variable band pass filter to remove noise components caused by fluctuations in the air contained in the second electrical signal. 2. The second electric signal generation section frequency-mixes the fifth electric signal and the second electric signal having a reference frequency deviated from the frequency of the first electric signal by the frequency of the third electric signal. The optical distance measuring device according to claim 1, comprising a mixer, wherein the variable band-pass filter is provided between the mixer and the signal processing unit. 3. The variable bandpass filter is a PLL.
A circuit and a gate circuit that selectively outputs the output signal of the PLL circuit, the PLL circuit outputs a phase difference between the input signal and the output signal of the PLL circuit, and the phase comparator. And a voltage controlled oscillator that generates a signal of a frequency based on the output of this filter as an output signal of the PLL circuit. When the phase of the output signal of 1 matches the phase of the input signal, the variable low-pass filter is switched from the wide band to the narrow band, and the output signal of the PLL circuit is output via the gate circuit. The lightwave distance measuring device according to claim 1. 4. A quadrature phase detector, wherein the variable band pass filter further receives an input signal and an output signal of the PLL circuit as input signals and performs quadrature phase detection,
The detector is provided with a low-pass filter that passes the low-pass component of the output signal, and a level detector that detects the level of the output of this filter, and the phase of the output signal of the PLL circuit becomes the phase of the input signal. When they match, the level detector detects that the output signal of the quadrature detector received through the low pass filter has reached a predetermined level,
4. The optical distance measuring device according to claim 3, wherein the variable low pass filter is switched from a wide band to a narrow band, and the output signal of the PLL circuit is output via the gate circuit.