JPH0465691A - Distance measuring instrument - Google Patents

Abstract

PURPOSE:To prevent a decrease in measurement accuracy due to a crosstalk signal and to make a measurement distance long by using a light pulse signal, which is intensity-modulated with a specific duty ratio, as a light projection signal. CONSTITUTION:An LD 1a for light projection is intensity-modulated and driven with the specific-duty-ratio pulse oscillation signal from an oscillator 3 so that the light emission intensity is in a rectangular wave shape. A photodiode (PD) 2a for photodetection near by the LD1a photodetects the projection laser light of the LD 1a. The PD 2b for photodetection photodetects reflected light from a body to be measured. Then a gate generation part 11 outputs a gate signal G corresponding to a phase difference corresponding to the distance between reference binary signals R and S based on photodetected light beams and a phase difference counting part 13 outputs distance measurement data. The constitution which uses the pulse signal is small in crosstalk between light emission and light reception as compared with a case where a sign signal is used, a decrease in distance measurement accuracy is prevented, and the measured distance can be made long.

Description

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

[Prior Art] Fig. 4 is a schematic block diagram showing the functional configuration of a conventional distance measuring device, which is configured to measure the distance to an object to be measured using the intensity modulation phase difference method. .

In the figure, the distance measuring device includes an oscillator 14 on the light emitting side, a laser diode (LD) lb1, a photodiode (PD) 2c provided near the LD1b, and an amplifier A.
P3 is included, and on the light receiving side there is a PD2d for light receiving and an amplifier AP.
4, and further includes a local oscillator 15, light emitting side and light receiving side beat generators 16 and 19, and light emitting side and light receiving side BP.
F (band pass filter) 17 and 20, AG
C (Auto Ga1n Control) circuit 2
1. Light emitting side and light receiving side comparators 18 and 22,
It includes a gate application-2□3, a clock generation section 24, and a phase difference counting section 25.

The oscillator 14 and local oscillator 15 are, for example, crystal oscillators, and oscillate at specific frequency levels. Further, the oscillator 14 oscillates at an intensity modulation frequency fffi for modulating the emission intensity of the LDlb connected to its output stage, and the local oscillator 15 oscillates at a local oscillation frequency f.
It has L1 and oscillates.

The LDlb provided on the light projecting side receives an intensity modulation frequency f given from the oscillator 14 connected to the front stage thereof. The light emission is controlled so that the light emission intensity is modulated according to the frequency level of the light.

Note that the light emitting element provided on the light projecting side is not limited to a laser diode, and may be an LED (light emitting diode).

The PD2c, which is installed near the LD1b and receives the light emitted from the LD1b, performs photoelectric conversion according to the light emission intensity, and outputs an electric signal, transmits the output signal to an amplifier A connected to the next stage.
Give to P3.

□Also, the intensity-modulated light emitted from the LD 1b is irradiated onto the object to be measured and reflected by the irradiation surface.

This reflected light enters the light-receiving surface of PD2d provided on the light-receiving side, is photoelectrically converted, and the light-receiving signal is given to an amplifier AP4 connected to the next stage.

Amplifiers AP3 and AP4 amplify the applied signal with a predetermined gain so as to facilitate subsequent signal processing, amplifier AP3 outputs reference signal r1, and amplifier AP3 outputs a reference signal r1.
4 receives the light reception signal S1.

Emitter side beat generator 16 and light receiver beat generator 19
inputs the reference signal r1 and the light reception signal s1, respectively, and generates a beat using the oscillation signal (local oscillation frequency fLt) output from the local oscillator 15. As a result, the reference signal r1 and the received light signal S1 are subjected to frequency modulation, respectively, and the reference beat signal rbl and the received light beat signal sbl are outputted, respectively.

The light-emitting side BPF 17 and the light-receiving side BPF 20 respectively input the reference beat signal rbl and the light-receiving beat signal Sb1, pass only their band components, and provide them to the next stage circuit.

The AGC circuit 21 provided on the light receiving side inputs a preset reference signal VB, and performs gain adjustment of the band-limited light receiving beat signal sbl provided from the light receiving side BPF 20 connected at the previous stage. That is, the gain is adjusted based on the reference signals V and B so that the received light signal has a predetermined amplitude.

Emitter side comparator 18 and light receiver side comparator 22
performs binarization processing on the signals provided from the circuits connected to the previous stage, respectively, and outputs a reference binary signal R1 and a received light binary signal S1.

The gate generator 23 inputs the reference binary signal R1 and the received light binary signal S1 at the same time, and accordingly converts both signals into a phase difference.
In other words, the gate signal G is detected by detecting the difference between the input periods of both signals.
Outputs 1.

The clock generating section 24 generates clock pulses with a predetermined period, and this clock signal is given to the phase difference counting section 25 connected to the next stage.

The phase difference counting section 25 counts the signal input period of the gate signal G1 based on the clock pulse, and outputs the count value n0 to the outside of the apparatus as data regarding the distance to the object to be measured.

As described above, the intensity-modulated laser light emitted from the laser diode provided on the light projection side is irradiated onto the surface of the object to be measured, and is reflected by the irradiated surface. The reflected light is received by the PD 2d provided on the light receiving side. PD2 for light reception
The phase component of the received light signal obtained by receiving the light at d and photoelectrically converting it according to the received light intensity includes a predetermined phase delay with respect to the laser light emitted from the light projecting side.

This phase delay corresponds to the distance between the distance measuring device and the object to be measured.
is extracted as The details will be described later.

Next, the operation of measuring the distance between the distance measuring device shown in FIG. 4 and the object to be measured will be explained.

The oscillator 14 provided on the light projection side starts oscillating at the intensity modulation frequency f0. This oscillation signal is given to the light projecting LDlb as a light emission drive signal.

Accordingly, LDlb has a given intensity modulation frequency f. A laser beam is irradiated onto the object to be measured while modulating the emission intensity according to the frequency level.

The intensity-modulated laser beam by this LDlb is received by the PD2c provided nearby, photoelectrically converted according to the intensity of the received light, and the obtained electrical signal is given to the next stage amplifier AP3. The amplifier AP3 amplifies the applied signal to facilitate subsequent signal processing, and then provides it as a reference signal r1 to the light projection side beat generation section 16 connected to the next stage.

As described above, when the laser light emitted from the LDlb on the light projection side is irradiated onto the surface of the object to be measured, it is reflected by the irradiation surface. The reflected light is transmitted to the PD2 installed on the light receiving side.
The light is received at the light receiving surface d, where it undergoes so-called photoelectric conversion, and an electric signal corresponding to the received light intensity is given to the next stage amplifier AP4. The amplifier AP4 amplifies the applied light reception signal so as to facilitate subsequent signal processing, and then supplies it as a light reception signal to the light reception side beat generating section 19 connected at the next stage.

As described above, the reference signal r1 having the intensity modulation frequency f1 is provided to the light-emitting side beat generator 16, and the light-receiving signal S1 is similarly provided to the light-receiving-side beat generator 19. At this time, the local oscillator 15 has a local oscillation frequency fL
1, and this oscillation signal is given to the light-emitting side and light-receiving side beat generators 16 and 19 at the same time. Therefore, in the light projection side beat generation section 16, the intensity modulation frequency f
The reference signal r1 having □ and the local oscillation signal having the local oscillation frequency fLt are mixed and processed to produce a beat.
is generated. That is, so-called heterodyne conversion processing is performed to perform frequency modulation on the reference signal r1 and output the reference beat signal rbl.

Similarly, in the light-receiving side beat generating section 19, the intensity variation-frequency 1. a + received light signal S1 and local oscillation frequency f'
A beat is generated by mixing with the local oscillation signal having L1. That is, the above-mentioned hetero gain conversion processing is performed, and the received light signal S1 is subjected to ceramic frequency modulation to output the received light beat signal Sb1.

゛It should be noted that the beat signals rb1 and s' generated in the light emitting side and light receiving side beat generating sections 16 and 19
bl' is the beat frequency fb.

Assume that

Next, the reference beat signal r"b'l outputted from the ζ emitter-side peat generating section 16 is given to the emitter-side BPFi 7, the noise component in the signal is removed, and the band component is transferred to the emitter-side BPFi 7. ``Given to comparator 18.

The light emitting side comparator 18 uses the light emitting side BPF 17 connected to the previous stage □ at a preset signal □ level as a boundary.
The signal given from R is binarized and the reference binary signal R is
1 is given to the gate generating section 23.

Similarly, the light-receiving beat signal sbl generated by the light-receiving-side beat generator 19 has noise components removed from the signal at the light-receiving side BPF-20, and its band components are provided to the AGC circuit 21 at the next stage. In the AGC circuit 21, the gain of the signal provided from the light receiving side BPF 20 connected to the previous stage is adjusted based on the reference signal VB. In other words, the gain is adjusted so that the amplitude (received light intensity) of the received light signal is always kept constant. Thereafter, the gain-adjusted signal is given to the light receiving side comparator 22.

In the light-receiving side comparator 22, in the same way as the light-emitting side comparator 18 described above, the applied signal is binarized with a preset signal level as the boundary, and the light-receiving binary signal S1 is sent to the gate generator 23. give to

The gate generating section 23 generates a gate signal G1 based on the applied signals R1 and Sl, and the phase difference counting section 25 generates a gate signal G1.
give a force to Gate signal G generated by this gate generator 23
The operation of generating 1 will be explained below.

FIGS. 5(a) to 5(e) are schematic diagrams showing waveforms of input and output signals of each circuit of the distance measuring device shown in FIG. 4 above.

FIG. 5(a) is a schematic diagram showing the waveform of the reference signal r1 shown in FIG. 4 above.

FIG. 5(b) is a schematic diagram showing the waveform of the light reception signal S1 shown in FIG. 4 above.

FIG. 5(C) shows the reference binary signal R shown in FIG. 4 above.
FIG. 1 is a schematic diagram showing a waveform of No. 1;

FIG. 5(d) shows the received light binary signal S shown in FIG. 4 above.
FIG. 1 is a schematic diagram showing a waveform of No. 1;

FIG. 5(e) shows the gate signal G1 shown in FIG. 4 above.
FIG.

In each figure, the vertical axis represents the signal level, and the horizontal axis represents the passage of time on the same scale.

As shown in FIGS. 5(a) and (b), the reference signal r1 and the received light signal S1 are sinusoidal signals having the same frequency (fl), and the received light signal S1 has a predetermined phase than the reference signal r1. It can be seen that there is a delay by the difference. This phase difference corresponds to the time required for the projected light to travel the distance of the object to be measured and be received.

Furthermore, reference 2 shown in FIGS. 5(C) and (d)
The value signal R1 and the received light binary signal S1 are binary signals obtained by binarizing the amplitudes of the reference signal r1 and the received light signal s1 described above based on a predetermined signal level.

The gate signal G1 shown in FIG. 5(e) is a signal output from the gate generator 23. In other words, gate generation section 2
3, the reference binary signal R1 and the received light binary signal S1 are applied simultaneously. Therefore, by activating its output in accordance with the rising timing of the reference binary signal R1, the signal level of the gate signal G1 is set to "HIG".
The signal level of the gate signal G1 is changed to LOW and output by setting the gate signal G1 to LOW by making the output negative according to the signal rise timing of the received light binary signal S1 that is input immediately after. It is working as it should. Therefore, the gate signal G1 becomes a signal component indicating the phase difference between the binary signals R1 and Sl, that is, the phase delay of the received light signal $1 with respect to the reference signal r1.

Here, a description will be given of the method of calculating the measured distance using the distance measuring device shown in FIG.

As mentioned above, the light emitting side LDlb has an intensity modulation frequency f
, n, the laser beam is irradiated onto the object to be measured while modulating the intensity of the emitted light. The reflected light from the object to be measured generated in response to this light irradiation is transmitted through a P
It is incident on D2d. At this time, assuming that the phase difference between the reference signal r1 on the light emitting side and the light receiving signal sl on the light receiving side is φ(d e g), the distance to the object to be measured is L = 1/2 x φ/360 °X c/f m(
However, C: speed of light) can be calculated as (1).

As described above, the distance to be measured is determined by the above equation (1). Therefore, the gate signal G1 outputted from the gate generating section 23 is applied to the phase difference counting section 25 connected to the next stage. As a result, the phase difference counting section 25 counts the signal input period of the gate signal G1 in synchronization with the clock pulse of a predetermined period given from the clock generating section 24, and outputs the counted count value n0 as data corresponding to the distance. Output to.

Therefore, for example, the beat signal rbl or sb
Assuming that the count value synchronized with the clock pulse of the clock generator 24 obtained from one cycle period of l is N,
The phase difference φ can be easily calculated from the count value nQ obtained from the gate signal G1. In other words, the phase difference φ is expressed by the following formula (
2) It can be obtained from

φ = no / N x 360° - (2) After that, if you give the phase difference φ found by equation (1), each constant, and equation (2) to a microcomputer, etc., you can easily find the distance to be measured. be able to.

As described above, in the conventional distance measuring device shown in FIG. 4, the phase delay (phase difference (φ) period) of the received light signal s1 with respect to the reference signal r1 on the light emitting side is counted by a clock pulse of a constant period. Then, the distance to be measured is measured based on the count value.

[Problems to be Solved by the Invention] However, in the conventional distance measuring device as described above, since the signal waveform for driving the light emitted from the light emitting side by intensity modulation is sinusoidal, it is difficult to use the signal waveform for this modulation. There is a problem in that the oscillated drive signal leaks into the circuit system on the light receiving side as a crosstalk signal, causing a phase shift in the light receiving signal. This will be explained in detail with reference to the drawings.

FIG. 6 is a diagram illustrating the influence of black and stalk signals on the conventional distance measuring device shown in FIG. 4 above.

In FIG. 6, the solid line indicates the approximate waveform of the original received light signal.The dotted line indicates the approximate waveform of the crosstalk signal leaking inside the circuit.Furthermore, the dashed line indicates that the original received light signal is This shows a signal waveform when a phase shift occurs due to a crosstalk signal.

As mentioned above, the phase component of the received light signal originally contains only the phase lag component corresponding to the distance to the object to be measured (phase lag compared to the light emitting signal from the light emitting side). The distance is measured. However, according to the conventional distance measuring device shown in FIG. 4, the received light signal includes an additional phase shift as shown in FIG. 6 due to the crosstalk signal component leaking into the circuit due to the oscillation signal. Therefore, an error occurs in the phase delay corresponding to the distance to be measured. Therefore, there is a problem that the accuracy of distance measurement decreases.

In addition, as mentioned above, conventional distance measuring devices similarly perform frequency modulation processing (heterodyne conversion processing) on the light emitting signal on the light emitting side and the light receiving signal on the light receiving side, making subsequent signal processing easier. A beat signal is generated so that the

However, this beat signal particularly has a proportional relationship of [amplitude of light-receiving signal on the light-receiving side - beat signal amplitude], and a gain adjustment section such as an AGC circuit is essential for the light-receiving signal.

Therefore, there was a problem in that the circuit configuration inevitably became complicated. In other words, it was necessary to maintain the received light intensity on the light receiving side constant (independent of the intensity of reflected light from the object to be measured).

Therefore, 1 and 2 objects of the present invention are to prevent a decrease in measurement accuracy due to leakage of other signal components (crosstalk signals) within a circuit, and to increase the intensity of light emitted so that the distance to be measured can be measured over long distances. The object of the present invention is to provide a distance measuring device that can be used to

[Means for Solving the Problems] A distance measuring device according to the present invention is a distance measuring device that measures the distance to an object to be measured. Specifically, a light projecting means for projecting an intensity-modulated optical signal having a predetermined duty ratio onto the object to be measured; a first light-receiving means for photoelectrically converting the received light intensity and outputting a light-receiving signal; a local oscillation means for oscillating at a predetermined frequency; a second modulation means for frequency modulating the received light signal according to an oscillation signal by the oscillation means, a first modulation signal by the first modulation means, and a second modulation by the second modulation means. It is configured to include a phase difference detection means for detecting a phase difference with a signal, and a conversion means for converting the phase difference detected by the phase difference detection means into distance data with respect to the object to be measured. Ru.

[Function] Since the distance measuring device according to the present invention is configured as described above, by irradiating the object to be measured with pulsed light by the light projecting means, the light reception signal obtained by the light reception means also becomes a pulse signal. It is said that

Therefore, it is possible to prevent a decrease in measurement accuracy caused by signal leakage (crosstalk) on the light emitting side into the circuit on the light receiving side.

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

The distance measuring device according to this embodiment measures distance using the intensity modulation phase difference method. Specifically, a light emitting element provided on the light projecting side is driven so that its light emission is modulated in a pulsed manner. In addition, since the amplification systems for each signal provided on the light emitting side and the light receiving side are amplified by switching operation, there is no need for linear amplification), the oscillation signal of the local oscillator is made into a sine wave shape, This prevents deterioration in measurement accuracy due to signal leakage (crosstalk) from the light emitting side to the received light signal, and also increases the distance to be measured by increasing the light emitting intensity.

FIG. 1 is a schematic diagram showing the functional configuration of a distance measuring device according to an embodiment of the present invention, and is configured to measure the distance to an object to be measured using an intensity modulation phase difference method.

In the figure, the distance measuring device includes an oscillator 3 on the light emitting side, a laser diode (LD) la, and is installed near the LD la. Diode (PD-)2
a, includes an amplifier API, and a PD2b for light reception on the light receiving side
, an amplifier AP2, and further includes a local oscillator 4, bead generators 5' and 8 on the light transmitting side and the light receiving side, band pass filters (BPF) 6 and 9 on the light transmitting side and the light receiving side,
It includes light emitting side and light receiving side comparators 7 and 10, a gate generating section 11, a clock generating section 12, and a phase difference counting section 13.

The oscillator 3 and the local oscillator 4 are composed of, for example, a crystal oscillator, and stably oscillate at a specific frequency level. In particular, the oscillator 3 oscillates in pulses at an intensity modulation frequency (with a predetermined duty ratio, for example 50%) for modulating the emission intensity of the LDla. This pulse oscillation signal drives the light emitting LDla connected to the next stage with intensity modulation so that the light emission intensity becomes a square wave. Further, the local oscillator 4 oscillates a sinusoidal signal having a predetermined local oscillation frequency.

The LDla provided on the light projecting side is driven to project light so that its emission intensity is modulated according to the frequency level of the applied intensity modulation frequency.

The light receiving PD 2a provided near the LD 1a is
An amplifier API that receives the light emitted from the LD1a, performs photoelectric conversion according to the intensity of the received light, and sends electrical and electrical signals to the next stage.
give to

The light receiving PD2b provided on the light receiving side is connected to the LD1a.
The device is provided so that the laser beam projected from the device is irradiated onto the irradiation surface of the object to be measured, and the device receives the reflected light accordingly.

A received light signal that is incident on the light receiving surface of this PD2b and is photoelectrically converted according to the received light intensity is given to an amplifier AP2 connected to the next stage.

Amplifiers API and AP2 amplify the applied signals with a predetermined gain so as to facilitate signal processing in subsequent stages. The reference signal r and the light reception signal S obtained by the amplification processing in this manner are respectively given to the light emitting side beat generating section 5 and the light receiving side beat generating section 8 connected at the next stage.

The light emitting side beat generating section 5 and the light receiving side beat generating section 8 are as follows:
The applied reference signal r and the received light signal S are subjected to so-called heterodyne conversion processing using the local oscillation signal outputted by the local oscillator 4, and a beat is generated for the reference signal r and the received light signal S to perform frequency modulation, respectively. Let's do it. The reference beat signal rb and the received light beat signal sb thus obtained are transmitted to the light emitting side B connected to the next stage.
It is given to PF6 and light receiving side BPF9, respectively.

The light projecting side BPF 6 and the light receiving side BPF 9 operate to pass only the band components of the applied reference beat signal rb and received light beat signal sb, respectively.

□Emitter side comparator 7 and light receiver side comparator 10
is the light emitting side BPF6 and the light receiving side BP connected to the previous stage.
Each signal given from F9 is binarized using a preset signal level, and a reference binary signal R is obtained.
and a received light binary signal S are output respectively.

The gate generator 11 generates the reference binary signal R and the light receiving unit 2.
A value signal S is input, and a gate signal G is output accordingly.

The clock generating section 12' oscillates clock pulses at a predetermined period, and the oscillated clock signal is given to the phase difference counting section 13 connected to the next stage.

The phase difference counting section 13 receives the clock pulse signal and the gate signal G at the same time, counts the input period of the gate signal G using the clock pulse signal, and calculates the count value n as data corresponding to the distance to be measured. It is output to the outside of the device as

As described above, according to the distance measuring device shown in FIG. reflected. The reflected light is transmitted to the PD2b installed on the light receiving side.
Light is received by the light-receiving surface of the sensor, and photoelectrically converted according to the level of the received light. The phase delay of the reflected light received by the PD 2b with respect to the projected light is generated by the gate generator 11 connected at the subsequent stage.
It is obtained as a pulsed gate signal G in .

In this way, the distance measuring device shown in FIG. 1 is configured to measure the distance to the object to be measured based on the phase delay of the received light signal with respect to the light emitting signal on the light emitting side. has been done.

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

First, the oscillator 3 oscillates pulses with a duty ratio of 50%, for example. The oscillation signal is given as a drive signal to the light projection LDla connected to the next stage, and the LDla is accordingly modulated and driven so that the light projection becomes a square wave. Further, the light emitted from this LDla is received by the PD2a provided in the vicinity thereof, and photoelectrically converted according to the intensity of the received light. The electrical signal obtained by this photoelectric conversion is given to the amplifier API connected to the next stage.

The amplifier API amplifies the applied signal so as to facilitate signal processing at the next stage and thereafter, and supplies the signal as a reference signal r to the light projection side beat generating section 5 at the next stage.

Now, an optical signal modulated into a rectangular waveform emitted from the LDla on the light projecting side is irradiated onto the surface of the object to be measured, and is accordingly reflected on the irradiated surface. The reflected light is transmitted to the PD on the receiving side.
2b, the light is photoelectrically converted according to the so-called intensity of the received light, and an electric signal corresponding to the level of the received light is given to the next stage amplifier AP2.゛The amplifier AP2 amplifies the received light signal to facilitate signal processing in the next stage and subsequent stages. The light reception signal S obtained through the amplification processing is given to the light reception side beat generation section 8.

As described above, the reference signal r having the intensity modulation frequency (duty ratio of 50%) of the oscillator 3 is given to the light emitting side beat generating section 5, and the reference signal r having the intensity modulation frequency of the oscillator 3 (duty ratio 50%) is similarly applied to the light receiving side beat generating section 8. A received light signal S having a modulation frequency (duty ratio of 50%) is provided. At this time, the local oscillator 4 is stably oscillating at a predetermined local oscillation frequency, and this sinusoidal oscillation signal is simultaneously given to the beat generating sections 5 and 8 on the light projecting side and the light receiving side. Therefore, in the light projecting side beat generating section 5, the square wave reference signal r having a duty ratio of 50% and the sinusoidal local oscillation signal are mixed to generate beats (beads). Similarly, in the light-receiving side beat generation section 8, - intensity modulation frequency (duty ratio 50%
) and a sinusoidal local oscillation signal having a local oscillation frequency are mixed to generate a beat. In other words, in the light-emitting side and light-receiving side beat generation units 5 and 8, so-called hetero gain conversion processing is performed to convert the reference signal r and the light-receiving signal S.
The signal is frequency modulated to facilitate signal processing in subsequent stages.

The reference beat signal rb and the light-receiving beat signal sb thus obtained are respectively given to the light-emitting side BPF 6 and the light-receiving side BPF 9.

Now, the light projecting side BPF 6 operates so as to remove the noise component in the applied signal and provide only the band component to the light projecting side comparator 7 at the next stage. The light projecting side comparator 7 binarizes the applied signal at a predetermined signal level, and outputs a reference binary signal R to the gate generator 11 at the next stage.

Similarly, the light-receiving beat signal sb generated by the light-receiving beat generator 8 has its noise components removed by the light-receiving side BPF 9, and only the band components are provided to the light-receiving side comparator 10 at the next stage. The light-receiving side comparator 10 binarizes the signal given at a predetermined signal level, and outputs the light-receiving binary signal S to the gate generator 11.

The gate generating section 11 generates a gate signal G based on the applied reference binary signal R and the received light binary signal S, and outputs this to the phase difference counting section 13 connected to the next stage. The operation of the gate signal G generation by the gate generation section 11 will be explained with reference to the drawings.

FIGS. 2(a) to 2(e) are schematic diagrams showing waveforms of input and output signals of each circuit of the distance measuring device shown in FIG. 1 above.

Solution 2 FIG. 2 (a) is a schematic diagram showing the waveform of the reference signal r shown in FIG. 1 above.

FIG. 2(b) is a schematic diagram showing the waveform of the light reception signal S shown in FIG. 1 above.

FIG. 2(C) shows the reference binary signal R shown in FIG. 1 above.
FIG.

FIG. 2(d) is a schematic diagram showing the waveform of the received light binary signal S shown in FIG. 1 above.

FIG. 2(e) is a schematic diagram showing the waveform of the gate signal G shown in FIG. 1 above.

In each figure, each signal level is plotted on the vertical axis, and the time course on the same scale is plotted on the horizontal axis.

As shown in FIGS. 2(a) and (b), the reference signal r and the received light signal S have the same frequency (duty ratio 50
%), and the received light signal S is expressed as a square wave with a reference signal r
It can be seen that the delay is delayed by a predetermined phase difference. This phase difference corresponds to the time it takes for the projected light to travel back and forth from the object to be measured until it is received.

Furthermore, as shown in FIGS. 2(C) and (d),
The reference binary signal R and the light-receiving binary signal S are binary signals obtained by binarizing the amplitudes of the reference signal r and the light-receiving signal S described above with reference to a predetermined level. therefore,
The gate generator 11 inputs the reference binary signal R and the received light binary signal S as shown in FIGS. 2(C) and 2(d) simultaneously, and generates a gate as shown in FIG. 2(e). I am using signal G. In other words, by activating the output of the reference binary signal R in accordance with the rising timing of the reference binary signal R, the gate signal G is set to the signal level "HIGH".
By making the output negative according to the timing of the rise of the received light binary signal S that is input immediately after, the gate signal G is set to the signal level "LOW".
Therefore, the gate signal G is a signal indicating the phase difference between the given binary signals R and S, that is, the phase delay of the received light signal S with respect to the reference signal. .

Referring to FIG. 1, a gate signal G (see FIG. 2(e)) output from gate generating section 11 is given to phase difference counting section 13 connected to the next stage.

The phase difference counting section 13 counts the signal input period of the gate signal G based on the clock pulse of a predetermined period given from the clock generating section 12, and calculates the count value n.
is output to the outside of the device. In other words, this count value n indicates data regarding the distance to the object to be measured.

By the way, assuming the phase difference φ(d e g) between the reference signal r obtained on the light emitting side and the light receiving signal S obtained on the light receiving side, the distance to the object to be measured is L=1/ 2Xφ/3
60°X c/F m (C-; speed of light, Fm
;frequency of oscillator 3)...(3) It can be calculated as follows.

Therefore, the gate signal G output from the gate generator 11
In the phase difference counting section 13 at the next stage, the signal input period of the gate signal G is obtained from, for example, one period period of the beat signal rb or Sb in synchronization with the clock pulse of a predetermined period given from the clock generating section 12. When the count value synchronized with the clock pulse of the clock generator 12 is assumed to be N, the phase difference φ is calculated from the count value n.
can be easily calculated. In other words, the phase difference φ can be obtained from the following equation (4).

φ=n/NX360°−(4) After that, the distance can be easily determined by giving the phase difference φ determined by equation (3), each constant, and equation (4) to a microcomputer or the like.

As described above, in the distance measuring device shown in FIG. The distance to be measured is measured based on the count value.

As described above, according to the distance measuring operation of the distance measuring device shown in FIG. L
Dla is lit in pulses. Therefore, this pulsed light emission is received by the monitoring PD 2a, photoelectrically converted there, and provided to the amplification API. In addition, the LD1
The pulsed light projected from a is irradiated onto the object to be measured, and the reflected light (pulsed light) from the irradiation surface is received by the PD 2b provided on the light receiving side and subjected to photoelectric conversion. This photoelectrically converted signal is given to amplifier AP2. In this way, since these light emitting signals and light receiving signals are pulse signals with a predetermined duty ratio, the amplifiers API and AP2 that perform amplification processing do not need to linearly amplify the applied signals, but rather It is only necessary to provide a function of performing signal amplification processing in a switching manner in synchronization with the signal. Therefore, the circuit configuration of amplifiers API and AP2 becomes simple.

Further, the pulse signals outputted from the amplifiers API and AP2 are subjected to heterodyne conversion processing using a sinusoidal local oscillation signal from the local oscillator 4 in the light emitting side beat generating section 5 and the light receiving side beat generating section 8. , frequency modulation processing is performed on the light emitting signal and the light receiving signal.

Thereafter, the gate signal G is obtained via the light emitting side BPF 6, the light receiving side BPF 9, the light emitting side comparator 7, the light receiving side comparator 10, and the gate generating section 11. In this way, the sinusoidal signal oscillated by the local oscillator 4 is stably oscillated so as to be kept at a nearly constant signal level, so there is no need to perform gain adjustment on the signal on the light receiving side.

In other words, the gain adjustment circuit can be removed from the signal processing circuit on the light receiving side. This is [the output level of the received light beat signal sb - the output level of the local oscillation signal of the local oscillator 4], and the output level of the received light beat signal sb is unrelated to the signal level of the received light signal S. This is due to this. However, the signal level of the light receiving signal S and the signal level of the reference signal r cause the diodes (not shown) of the multipliers provided in the light emitting side beat generating section 5 and the light receiving side beat generating section 8 to conduct (ON). The minimum required signal level is
I and AP2 output stages.

FIG. 3 is a diagram illustrating the influence of crosstalk signals on the distance measuring device according to the embodiment of the present invention shown in FIG. 1 above.

In the figure, the solid line indicates the approximate waveform of the original light reception signal.

Furthermore, the dotted line indicates the approximate waveform of the crosstalk signal 9 leaking inside the circuit.

As shown in Figure 3, there is no phase shift caused by the crosstalk signal in the phase component of the received light signal (the zero point and loss point of the received light signal remain unchanged), and as shown in the figure, The crosstalk signal component affects the received light signal as only a slight noise.

Therefore, the phase component of the received light signal includes only the phase lag component (phase lag compared to the light emitting signal from the light emitting side) corresponding to the distance to be measured from the original object to be measured. This means that the distance can be measured. In other words, since the gate signal G obtained in the gate generation section 11 includes only the phase delay component, the phase difference counting section 13 synchronizes the input period of this gate signal G with the pulse signal of a predetermined period from the clock generation section 12. By counting, it is possible to obtain an accurate count value n corresponding to the distance to be measured.

[Effects of the Invention] According to the present invention, in a distance measuring device using an intensity modulation phase difference method, the light projection signal in the light projection means is a square wave signal having a predetermined duty ratio, and the light projection signal The light reception signal obtained by the light receiving means according to the above is also obtained as a square wave light reception signal having the predetermined duty ratio. Therefore, deterioration of measurement accuracy due to leakage (crosstalk) from the light emitting signal to the light receiving signal in the frequency modulation processing by the first and second modulation means can be prevented, and the light emitting intensity on the light emitting side can be increased. , it is possible to easily increase the distance to be measured.

Furthermore, as mentioned above, since the light emitting signal and the light receiving signal are each obtained as a square wave signal with a predetermined duty ratio1, the amplification circuit provided in the signal processing circuit can also have a simple circuit configuration that performs switching operation. There are advantages. Furthermore, there is no need for a gain adjustment circuit for adjusting the amplitude of the light-receiving signal on the light-receiving side circuit, and the circuit configuration of the device is further simplified.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the functional configuration of a distance measuring device according to an embodiment of the present invention. FIGS. 2(a) to 2(e) are schematic diagrams showing waveforms of input and output signals of each circuit of the distance measuring device shown in FIG. 1. FIG. 3 is a diagram illustrating the influence of crosstalk signals on the distance measuring device according to the embodiment of the present invention shown in FIG. 1. FIG. 4 is a schematic diagram showing the functional configuration of a conventional distance measuring device. Figure 5(a) to e) shows the fourth
FIG. 2 is a schematic diagram showing waveforms of input and output signals of each circuit of the distance measuring device shown in the figure. FIG. 6 is a diagram illustrating the influence of the ripstoke signal on the conventional distance measuring device shown in FIG. 4. In the figure, 1a is an LD (laser diode), 2a and 2b are PDs (photodiodes), 3 is an oscillator, 4 is a local oscillator, 5 and 8 are beat generators on the light emitting side and light receiving side, and 6 and 9 are on the light emitting side. and light receiving side BPF, 7 and 10 are light emitting side and light receiving side comparators, 11 is a gate generation section, 12 is a clock generation section, 13 is a phase difference counting section, r and S are reference and light reception signals, R and S are reference and a received light binary signal, G is a gate signal, and n is a count value. In each figure, the same reference numerals indicate the same or corresponding parts. yri 2 fig.

Claims (1)

[Scope of Claims] A distance measuring device for measuring a distance to an object to be measured, comprising: a light projecting means for projecting an intensity-modulated optical signal having a predetermined duty ratio onto the object to be measured; a light receiving means provided to receive the intensity modulated light reflected by the object to be measured, photoelectrically converting it according to the received light intensity and outputting a received light signal; a local oscillation means oscillating at a predetermined frequency; and the light emitting means. a first modulating means for frequency modulating a signal in accordance with an oscillation signal by the oscillating means; and a second modulating means for frequency modulating the received light signal in accordance with an oscillating signal by the oscillating means.
a phase difference detection means for detecting a phase difference between a first modulation signal by the first modulation means and a second modulation signal by the second modulation means; A distance measuring device comprising: conversion means for converting a phase difference into distance data with respect to the object to be measured.