JPH03120490A - Range finder - Google Patents

Abstract

PURPOSE:To improve the measurement performance without limiting the setting of oscillation frequency and to shorten the measurement time by controlling the oscillation of local oscillation frequency so that a reference signal generated by dividing the frequency of a clock output is equal to the frequency of a light-emission side beat signal. CONSTITUTION:A light-emission side beat generation part 7 is supplied with the refer ence signal Ref of intensity modulation frequency fm and a light-reception side beat generation part 13 is supplied with a light reception signal Si of frequency fm. At this time, a voltage-controlled local oscillator (VCO) 20a which receives a control voltage from a phase comparator 19a oscillates at the frequency fm and noise components are removed 8 and 14 from beat signals which are generated 7 and 13 as a result to send binary-coded signals REF and SIG to a gate generation part 16. At this time, a signal REF is inputted to a comparator 19a. The generation part 16 generates a gate signal GATE corresponding to the phase difference between the signals REF and SIG, a phase difference counting part 17a counts the input period of the signal GATE in synchronism with clock pulses which are N times as high as the beat frequency from the clock 11, and a trailing-stage microcomputer calculates the distance from the counted value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a distance measuring device, and particularly to a distance measuring device using an intensity modulation phase difference method.

[Conventional Example] Hereinafter, as a conventional example of a distance measuring device, a light wave distance measuring device using light will be described using two examples.

FIG. 2 is a schematic block diagram showing the functional configuration of a first example of a conventional optical distance measuring device, which is configured to measure distance using an intensity modulation phase difference method.

In the figure, the optical distance measuring device includes an oscillator 1 on the light emitting side,
It includes a modulation section 2, a light emitting section 3, a light receiving section 4, an amplifying section 5 on the light receiving side, a local oscillator 6, a beat generating section 7 and 13 on the light emitting side and the light receiving side, filters 8 and 14 on the light emitting side and the light receiving side, Light emitting side and light receiving side comparators 9 and 15, period counting section 10, clock 11, phase detecting section 12, gate generating section 16 and phase difference counting section 17
Contains b.

Oscillator 1 and local oscillator 6 are, for example, crystal oscillators, and oscillate at specific frequency levels. The oscillator 1 has an intensity modulation frequency f1. The local oscillator 6 has a local oscillation frequency fLl.

The modulating section 2 controls the light emission of the next stage light emitting section 3 so as to modulate the light emission intensity according to the frequency level of the applied intensity modulation frequency fl11.

The intensity-modulated light emitted from the light emitting section 3 is reflected by the object, and the reflected light is detected by the light receiving section 4. Light receiving section 4
The phase delay of the reflected light received at
The details will be described later. As mentioned above,
The device measures the distance to the object from the phase lag of the detected reflected light relative to the emitted light.

Next, the distance measuring operation of the light wave distance measuring device shown in FIG. 2 will be explained.

The oscillator 1 oscillates at an intensity modulation frequency fm, and this oscillation signal is given to the modulator 2 and the light-emitting beat generator 7 at the same time. The modulating section 2 controls the light emitting section 3 to emit light so as to modulate the emitted light intensity according to the frequency level of the applied intensity modulation frequency f.

As mentioned above, when the light emitted from the light emitting section 3 is reflected by an object, the reflected light is first received by the light receiving section 4,
Here, the light is subjected to so-called photoelectric conversion, and an electric signal corresponding to the received light level is given to the next stage amplifying section 5. The amplification section 5 amplifies the input signal, and the amplified light reception signal is given to the light reception side beat generation section 13.

As described above, the reference signal ReF having the intensity modulation frequency fllll is given to the light-emitting side beat generation section 7, and the light reception signal Sig is similarly given to the light-receiving side beat generation section 13. At this time, the local oscillator 6 oscillates at the local oscillation frequency fL1, and this output signal is given in parallel to the beat generators 7 and 13 on the light emitting side and the light receiving side. Therefore, the light-emitting side beat generator 7 mixes the reference signal ReF having the intensity modulation frequency fIll and the local oscillation output signal having the local oscillation frequency fLI, and operates to generate beats. Similarly, the light-receiving side beat generating section 13 operates to mix the light-receiving signal S1g having the intensity modulation frequency fm and the local oscillation output signal having the local oscillation frequency fLl to generate beats. It is assumed that the generated beat signal has a beat frequency fl)l.

Next, the beat signal output by the light-emitting side beat generator 7 is as follows:
The signal is applied to a light-emitting filter 8, noise components in the signal are removed, and the signal is input to a light-emitting comparator 9. The light emitting side comparator 9 binarizes the input light emitting side beat signal at a certain level, and outputs a binary signal REF to the gate generating section 16 and the period counting section 10.

Similarly, the light-receiving-side beat signal generated by the light-receiving-side beat generator 13 is filtered to remove noise components from the signal by a light-receiving filter 14, and then converted into a binary signal SIG by a light-receiving side comparator 15 at a certain level. The signal is converted and provided to the gate generator 16.

The gate generating section 16 generates a gate signal GATE and outputs it to the phase difference counting section 17b. This gate generating section 16
The operation of generating the gate signal GATE will be explained with reference to FIG.

FIG. 3 is a diagram for explaining the output processing of the gate signal GATE of the gate generator 16 of the optical distance measuring device shown in FIG. 2 and FIG. 4, which will be described later.

FIG. 3(1) and FIG. 3(b) show the binarized signal REF
and SIG, and the gate signal GATE obtained from both the binary signals.

The gate generator 16 generates a binary signal REF as shown in the figure.
According to the timing of the rise of the gate signal GA,
Changes TE to signal level “HI GH” and outputs it,
Immediately after, the gate signal GATE is set to the signal level "LO" according to the signal rise timing of the binary signal SIG, which is manually input.
W" and outputs it. Therefore,
The gate signal GATE is a signal indicating the phase difference between the binary signals REF and SIG, that is, the phase delay of the light reception signal with respect to the light emission signal.

Here, a description will be given of the method of calculating the measured distance in this device.

As described above, light is emitted toward the object while modulating the emission intensity using the intensity modulation frequency flIl. Accordingly,
The reflected light from the target object enters the device, and if we assume that the phase difference between the reference signal Ref on the light emitting side and the received light signal Sig on the light receiving side is φ(d e g), The distance @L is L-1/2Xφ/360 x c/
It can be calculated as f m (C: speed of light) (1).

By the way, the light emitting side and light receiving side beat generating sections 7 and 1
The beat frequency rb+ that 3 oscillates is the intensity modulation frequency f
From lll and local oscillation frequency fLI, fb+=lfm
fL+l...(2) is obtained. However, the intensity modulation frequency f and the local oscillation frequency fL
Even if a crystal oscillator is used for the oscillator 1 and the local oscillator 6, l has a variation of about ±1100 pp, and the oscillation frequency level is not stable. That is, if the intensity modulation frequencies fl and l are 10 MHz, the intensity modulation frequency flll and the local oscillation frequency fLl are ±1 kHz.
Since there is an error of 2, the beat frequency fl) from equation (2)
It can be seen that a variation of ±2 kHz occurs in I.

Therefore, as shown in FIG.
In Figure (b), although variations in the beat signal occur and the beat frequency is different, the gate signal GAT
A situation occurs in which the H signal widths are the same. therefore,
It can be seen that the phase difference φ in equation (1) cannot be determined only from the signal width of the gate signal GATE. In order to improve this problem, conventional measures have been taken as follows.

First, the gate signal GA output from the gate generator 16
TE is given to the next stage phase difference counting section 17b.

Accordingly, the phase difference counting section 17b outputs the gate signal GA in synchronization with the clock pulse given by the clock 11.
The signal input period of TH is counted, and the counted number n is given to the phase detection section 12 at the next stage.

In addition, the period counting section 10 to which the binary signal REF is given from the light-emitting side comparator 9 outputs a binary signal, which is a beat signal, in synchronization with the clock pulse given from the clock 11, similarly to the phase difference counting section 17b described above. One period of REF is counted and the counted number N is given to the phase detection section 12.

Therefore, the phase detection unit 12 is simultaneously given the count number N obtained from one cycle of the beat signal and the count number n obtained from the gate signal GATE, and calculates the phase difference φ. In other words, the phase difference φ can be obtained from the following equation (3).

φ-n/NX360 − (3) Thereafter, the distance can be determined by giving the above equation (1), each constant, and the phase difference φ obtained from equation (3) to a microcomputer or the like.

As described above, in the conventional optical distance measuring device of the first example shown in FIG. Then, the distance is measured.

Next, a second example of the conventional optical wave distance 11i1 measuring device will be described.

In the first conventional example described above, it is necessary to count both one cycle period of the beat signal and the signal width of the gate signal GATH. However, in the second example below, the distance is measured by counting only the signal width of the gate signal GATH.

FIG. 4 is a schematic block diagram showing the functional configuration of a second example of a conventional optical distance measuring device, which is a device that multiplies a beat signal to obtain a pulse signal for counting the signal width of a gate signal GATE. The structure is as follows.

In the figure, the light wave distance measurement value is calculated from the oscillator 1 as in Figure 2.
, a modulation section 2, a light emitting section 3, a light receiving section 4, an amplifying section 5, a local oscillator 6, a light emitting side and a light receiving side beat generating section 7 and 13,
It includes light emitting side and light receiving side filters 8 and 14, light emitting side and light receiving side comparators 9 and 15, a phase difference counting section 17c, and a gate generating section 16. In addition, oscillator 1
has an intensity modulation frequency flll, and the local oscillator 6 has a local oscillation frequency fLl. Further, the generated beat signal has a beat frequency fbl.

Further, this device includes a frequency divider 18b1, a phase comparator 19b, and a VCO (abbreviation for voltage controlled oscillator) 20 in order to provide a pulse signal for counting operation to the phase difference counting section 17c.
Contains b.

Next, the distance measuring operation of the light wave distance measuring device shown in FIG. 4 will be explained. Incidentally, parts that operate in the same manner as the apparatus shown in FIG. 2 will be briefly explained.

As in the device shown in FIG. Further, the light receiving side also generates a binary signal SIG from the obtained beat signal and supplies it to the gate generator 16. Accordingly, the gate generator 16 generates binary signals REF and SIG.
The gate signal GATE is generated from the phase difference counting section 1.
Give to 7c. At this time, the phase comparator 19b is given the light-emitting side binary signal REF.

Next, the counting processing operation of the phase difference counting section 17c will be explained.

As shown in FIG. 4, the phase comparator 19b is
A control signal is applied to the VCO 20b, and the output signal of the VCO 20b generated in response is applied to the phase difference counting section 17C. Further, the output signal of the vCO 20b is given to the phase comparator 19b via the divider 18b.

Now, if the VCO 20b is controlled to generate a pulse with a frequency N times the frequency of the beat signal generated by the light-emitting beat generator 7, then
The distance per pulse is always constant.

The frequency divider 18b receives a pulse from the VCO 20b,
Accordingly, the frequency of this pulse is divided by 1/N, and the phase comparator 1
Give to 9b.

The phase comparator 19b connects the binarized signal REF and the frequency divider 18b.
A control voltage is generated according to the frequency and phase difference of both signals, and is output to the VCO 20b. Accordingly, the VCO 20b operates so as to always oscillate at a frequency N times that of the beat signal while adjusting its oscillation operation using the applied control voltage. Therefore, the phase difference counting section 17
Since c is given a pulse having a frequency N times that of the gate signal GATE and the beat signal, the gate signal GA
The signal input period of TH can be counted in synchronization with the given pulse. It also outputs the counted value to the next stage microcomputer. Therefore, the distance to the object can be easily determined from the distance M (constant) per pulse outputted by the vC020b and the count value of the phase difference counting section 17C.

[Problems to be Solved by the Invention] However, the distance measuring device using the conventional intensity modulation phase difference method described above has the following problems.

(1) It is necessary to use an oscillator that generates a beat frequency that facilitates processing, and there are restrictions on the configuration of the device.

(2) Due to the restriction in (1) above, the intensity modulation frequency is also restricted.

(3) In addition, in the first conventional example, division processing is required to calculate the phase difference between the signal output from the device to the target object and the signal reflected by the target object and input to the device, so the device configuration is It becomes complicated.

(4) Furthermore, due to variations in beat frequency,
A phase shift occurs in the filter.

To further explain the above (1) and (2), among general-purpose crystal oscillators, there are, for example, the following combinations of frequencies of crystal oscillators whose oscillation frequencies are close. 4 MHz and 3.9936 MHz
(beat frequency -6,4kHz), 8MHz and 7
．． 9872MHz (beat frequency -12,8kHz
), 16 MHz, and 15°9744 MHz (beat frequency -22.6 kHz), and the beat frequency is uniquely determined depending on the combination of oscillators and is subject to limitations.

Regarding (4) above, further explanation will be added with reference to FIG.

FIG. 5 is a diagram showing an example of characteristics of a bandpass filter.

Figure 5(a) shows the amplitude-frequency characteristics, and Figure 5(b)
indicates the phase-frequency characteristic. In addition, Fig. 5(a) and (
b) In both cases, the frequency is shown on the horizontal axis.

As mentioned above, the beat frequency is uniquely determined and varies depending on the frequency of the oscillator applied to the device. For example, as shown in FIG. 5, if the beat frequency varies within the beat frequency change range, the obtained amplitude will also vary accordingly.

It can also be seen that a phase shift also occurs. In particular, Figure 5 (
As shown in b), it can be seen that the phase shift caused by a change in the beat frequency is much larger than the 9 phase shift caused by a temperature change.

Therefore, an object of the present invention is to provide a distance measuring device that is not limited by the setting of the oscillation frequency of the device, and that can improve the measurement performance of the device and shorten the measurement time.

[Means for Solving the Problems] A distance measuring device according to the present invention includes an oscillation means that outputs an oscillation signal of a predetermined frequency, and a target at a distance to be measured in response to the oscillation output signal of the oscillation means. a signal transmitting means for transmitting an intensity-modulated signal to the voltage-controlled local oscillating means; a voltage-controlled local oscillating means responsive to an oscillation output signal from the oscillating means; and a local oscillating output signal from the voltage-controlled local oscillating means. a first beat generating means for generating a first beat;
a receiving means for receiving an intensity-modulated signal reflected from the object and converting it into an electrical signal; and a receiving means responsive to the electrical signal from the receiving means and a local oscillation output signal from the local oscillating means. , detecting a phase difference based on a second beat generation means for generating a second beat, a first beat signal from the first beat generation means, and a second beat signal from the second beat generation means. a clock generating means; a means for counting clocks generated by the clock generating means during a period corresponding to the phase difference detected by the phase difference detecting means and outputting distance data; and the clock generating means. a frequency dividing means for frequency dividing the clock output of the frequency dividing means, the divided output frequency of the frequency dividing means and the first beat signal frequency from the first beat generating means are compared, and the comparison output is transmitted to the voltage controlled local and means for applying to the oscillation means.

[Function] Since the distance measuring device according to the present invention is configured as described above, the combination of signal frequencies of the oscillation output signal and the local oscillation output signal can be arbitrarily selected, and the beat signal frequency can be selected as desired. Can always be controlled at a constant level.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Although the distance measuring device according to the present invention can be applied to a device using sound waves, infrared rays, etc., a light wave distance measuring device using light is given as an example.

FIG. 1 is a schematic block diagram showing the functional configuration of a light wave distance a-1 determining device according to an embodiment of the present invention, which measures distance by an intensity modulation phase difference method.

In the figure, the optical distance measuring device includes an oscillator 1, a modulator 2,
The VCO 20a1 includes a light emitting section 3, a light receiving section 4, an amplifying section 5, beat generating sections 7 and 13 on the light emitting side and the light receiving side of the VCO 20a1, filters 8 and 14 on the light emitting side and the light receiving side, and comparators 9 and 15 on the light emitting side and the light receiving side. The device further includes a gate generator 16, a clock 11, a phase difference counter 17a1, a frequency divider 18a, and a phase comparator 19a. It is assumed that the oscillator 1 oscillates at the intensity modulation frequency flll, the VC020g oscillates at the local oscillation frequency fLO, and the light-emitting and light-receiving side beat generators 7 and 13 oscillate at the beat frequency fbO.

The optical distance measuring device shown in FIG. 1 uses a crystal oscillator as the oscillator 1, and uses a VCO 20a as a local oscillator.

The clock 11 generates a constant clock pulse and supplies it to the phase difference counting section 17a and the frequency divider 18a. Note that the clock pulse generated by the clock 11 has a frequency N times that of the beat signal generated by the light-emitting side beat generation section 7. The frequency divider 18a provides a reference signal obtained by dividing the clock pulse given from the clock 11 by 1/N times to the phase comparator 19a. The phase comparator 19a receives the binary signal REF from the light emitting side and the reference signal from the frequency divider 18a, generates a control voltage according to the frequency and phase difference between the two, and operates to supply it to the VC020a. do. Therefore, the VC020a is controlled to oscillate so that the image frequencies of the reference signal created by dividing the clock pulse and the beat signal match, and are controlled to oscillate at the local oscillation frequency fLO.

Next, the distance measuring operation of the light wave distance measuring device shown in FIG. 1 will be explained.

The oscillator 1 oscillates at an intensity modulation frequency flLl, and this oscillation signal is given to the modulator 2 and the light-emitting beat generator 7. The modulator 2 receives the applied intensity modulation frequency fl
The light emitting unit 3 is controlled to emit light so that the light emission intensity is modulated by Il.

On the other hand, when the light emitted from the light emitting section 3 is reflected by an object, the reflected light is received by the light receiving section 4, where it is subjected to so-called photoelectric conversion. The electric signal corresponding to the light reception level is amplified by the next-stage amplification section 5, and a light reception signal Sig is given to the light reception side beat generation section 13.

As described above, the reference signal ReF having the intensity modulation frequency fffl is given to the light emitting side beat generating section 7, and the light receiving signal Sig having the intensity modulating frequency fm is similarly given to the light receiving side beat generating section 13.

At this time, the VC020g oscillates at a frequency fLo, and transmits this oscillation signal to the beat generators 7 and 1 on the light emitting side and the light receiving side.
3, the light-emitting side beat generating section 7 mixes the local oscillation signal of the reference signal Ref and the local oscillation frequency fLO, and operates to generate beats. Similarly, the light-receiving side beat generation section 13 mixes the light-receiving signal Sig and the local oscillation signal of the local oscillation frequency fLO to generate the beat frequency f. It operates to generate a beat having a zero.

Next, the beat signal generated by the light-emitting beat generating section 7 is passed through a light-emitting filter 8 to remove noise components from the signal, and then provided to a light-emitting comparator 9 .

The light-emitting side comparator 9 binarizes the applied beat signal at a certain level, and provides a binarized signal REF to the gate generator 16 and the phase comparator 19a.

Similarly, the beat signal generated by the light-receiving-side beat generator 13 is subjected to a light-receiving-side filter 14 in which noise components are removed from the signal, and then provided to the light-receiving-side comparator 15 . The light-receiving side comparator 15 binarizes the applied beat signal at a certain level, and provides a binarized signal SIG to the gate generator 16.

From the applied binary signals REF and SIG, the gate generation section 16 generates a gate signal GATE corresponding to the phase difference between the two signals as shown in FIG.
Give to 7a.

The phase difference counting section 17a counts the input period of the gate signal GATH in synchronization with a clock pulse N times the beat frequency fbO given by the clock 11.

The count value of the phase difference counting section 17a is given to a next-stage microcomputer, etc., to obtain a measured distance. In other words, since the distance corresponding to one clock pulse output by the clock 11 is always constant, depending on the number of clock pulses counted during the input period of the gate signal GATE,
The measurement distance can be easily determined.

The clock pulses generated by the clock 11 are passed through the frequency divider 18.
a, the frequency is divided by 1/N by a frequency divider 18a, and the resultant signal is applied to a phase/phase comparator 19a as a reference signal. The phase comparator 19a inputs the binary signal REF obtained from the beat signal on the light emitting side and the reference signal from the frequency divider 18a, and provides the VC020a with a control voltage based on the frequency and phase difference of both signals. . Therefore, VC020
a is controlled to oscillate at a frequency fLo such that the beat frequency fbo and the frequency of the reference signal match. Therefore, the beat frequency fl)0 is always kept constant,
Since variations are eliminated, phase shifts due to filters are less likely to occur.

In addition, in this embodiment, the reference frequency that locks the beat frequency fbo is set to the clock 11 and the frequency divider 18a.
However, another oscillator may be provided to obtain the reference frequency.

[Effects of the Invention] As described above, according to the present invention, a clock pulse is generated inside the device, and the clock pulse is divided by a predetermined frequency division number.
A desired reference frequency is created, and the oscillation operation of the voltage-controlled local oscillation means is controlled so that the reference frequency and the beat frequency are locked. Therefore, phase shifts in the filter due to frequency variations in the beat signal are less likely to occur. Furthermore, since only the intensity modulation frequency needs to be obtained from the crystal oscillator, a crystal oscillator with a wavelength suitable for the measurement distance can be selected as the oscillation means. For example, if the measurement distance is expected to be about 5 m, the wavelength can be arbitrarily selected such as an intensity modulation frequency (15 MHz) that gives a wavelength of 20 m.

Furthermore, since the beat frequency is obtained by locking to a desired reference frequency, the beat frequency can be set sufficiently high within the allowable range of frequencies that can be used as clock pulses. Therefore, the time required for the averaging process to obtain the measured distance can be shortened. For example, if the distance given by counting 64 clock pulses within the period corresponding to the phase difference is averaged and this is the measured distance, then if the beat frequency is 12.8kHz, the time required for the averaging process is 5m5ec, If the frequency is 20kHz2, the time required for the averaging process is 3.2m5ec.

Also, with the clock pulse constant, the beat frequency is set to 2.
If it is doubled, the distance corresponding to one clock pulse will be doubled, and the time required for the above-mentioned averaging process will be halved. Therefore, the reference frequency is changed by the frequency dividing number of the frequency dividing means,
If the filter characteristics are changed accordingly, it is possible to arbitrarily switch the function between high-speed processing (lower resolution) and high resolution (longer measurement time).

[Brief explanation of drawings]

FIG. 1 is a schematic block diagram showing the functional configuration of an optical distance measuring device according to an embodiment of the present invention. FIG. 2 is a schematic block diagram showing the functional configuration of a first example of a conventional optical distance measuring device. FIG. 3 is a diagram for explaining the gate signal output processing of the gate generation section of the optical distance measuring device. FIG. 4 is a schematic block diagram showing the functional configuration of a second example of a conventional optical distance measuring device. FIG. 5 is a diagram showing an example of characteristics of a bandpass filter. In the figure, 1 is an oscillator, 11 is a clock, 16 is a gate generator, 17a is a phase difference counter, 18a is a frequency divider, 19
a is a phase comparator, and 20a is a VCO. fln is the intensity modulation frequency, fLo is the local oscillation frequency, R
ef is the reference signal, SLg is the received light signal, REF and SI
G is a binary signal and GATE is a gate signal. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] Oscillator means for outputting an oscillation signal of a predetermined frequency; and a signal for transmitting an intensity-modulated signal to an object at a distance to be measured in response to the oscillation output signal of the oscillation means. transmitting means; voltage-controlled local oscillation means;
a first beat generating means for generating a beat of the target object; a receiving means for receiving an intensity-modulated signal reflected from the object and converting it into an electrical signal; a second beat generating means for generating a second beat in response to a local oscillation output signal from the means; a first beat signal from the first beat generating means; and a second beat signal from the second beat generating means. means for detecting a phase difference based on the 2-beat signal; a clock generating means; and counting a clock generated by the clock generating means for a period corresponding to the phase difference detected by the phase difference detecting means. means for outputting distance data; frequency dividing means for frequency dividing the clock output of the clock generating means; a divided output frequency of the frequency dividing means; and a first beat signal frequency from the first beat generating means. and means for comparing and providing a comparison output to the voltage controlled local oscillation means.