JPH05232230A - Optical wave distance meter - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy by obtaining an attenuation vibration waveform having large output amplitude by constituting the light source part of an optical wave distance meter so as to emit a plurality of pulses made synchronous by a synchronizing amplifier. CONSTITUTION:A light pulse emitted from a laser diode 1 passes through an optical system to be converted to an electric signal of a current pulse train by an APD 71 and a synchronizing amplifier 160 converts the current pulse train to a voltage signal and also converts the voltage signal to an attenuation vibration waveform and performs reversal amplification. The attenuation vibration waveform is supplied to a receiving timing detection circuit 170 and a peak holding circuit 190 and the detection circuit 170 supplies a receiving timing signal to a sample holding S/H and a counter 180. A CPU 500 receives the signal from a level judging circuit 200 and employs the count value from the counter 180 and the data from an A/D converter 300 only when the quantity of light of a received light pulse train is a proper value. Since a light source part emits a plurality of pulses made synchronous by a synchronizing amplifier circuit, a large attenuation vibration waveform wherein output amplitude is about several times can be obtained and a measuring distance limit is extended to enhance measuring accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightwave rangefinder provided with a converting means for converting an input pulse signal into a damped oscillation waveform, and more particularly to a plurality of light source sections tuned to a tuning amplifier circuit. The present invention relates to an optical distance meter capable of performing highly accurate measurement with a long measurement limit distance by emitting a pulse and causing a tuning amplifier circuit to generate a damped oscillation waveform having a large output amplitude.

[0002]

2. Description of the Related Art In a conventional pulse type optical distance meter, an external distance measuring optical path and an internal reference optical path are switched by an optical chopper. When the optical chopper selects the external distance measuring optical path, the light emitting pulse emitted from the light emitting source is reflected by the corner cube of the object to be measured and is received as a light receiving pulse by the light receiving element in the optical distance meter. That is, the emission pulse shown in FIG. 7A is reflected by the corner cube,
The light is received as the light receiving pulse shown in (b). Then, the conventional optical distance meter converts the electric signal converted by the light receiving element into a damped oscillation waveform shown in FIG. 7C by the tuning amplifier, detects the cross point X with respect to 0 V by using the comparator, and It is configured to obtain the light reception timing signal shown in FIG. The measurement distance in the external distance measuring optical path is
The time T ₂ from the light emission of the light emitting diode to the light receiving timing signal shown in FIG. 7D is shown in FIG.
The rough measurement using the reference clock shown in (1) and the precision measurement by the precision interpolation means were used for the measurement, and the measurement was performed by combining the rough measurement and the precision measurement.

When the internal reference optical path is selected by the optical chopper, the light emitting pulse emitted from the light emitting source passes through the internal reference optical path and is then received by the light receiving element as the light receiving pulse shown in FIG. 7 (e). Then, the electric signal converted by the light receiving element is converted by the tuning amplifier into the damped oscillation waveform shown in FIG. 7F, and the light reception timing signal shown in FIG. 7G can be obtained. Then, from the light emission of the light emitting diode, FIG.
The time T ₁ until the light receiving timing signal shown in (g) is obtained. The distance in the internal reference light path was also obtained by performing the same processing as in the external reference light path, and the distance from the optical rangefinder to the corner cube was obtained by subtracting the distance in the internal distance measurement light path from the external distance measurement light path. ..

There is air fluctuation between the light distance meter and the corner cube, and the pulse received by the light distance meter fluctuates from a1 to a2, as shown in FIG. 8 (a). Along with this, the damping vibration waveform from the tuning amplifier is
As shown in FIG. 8B, it changes from b1 to b2. However, the cross point X between the damped vibration waveform and 0V
Is constant regardless of the peak value of the damped oscillation waveform. Therefore, the method of converting the received pulse into the damped oscillation waveform by the tuning amplifier is not affected by the fluctuation of the received light pulse. Therefore, as shown in FIG. 8C, if the comparator output C having the cross point X as the reception time is used as the reception timing signal, it is possible to provide the optical distance meter which is not affected by the fluctuation of the received light pulse.

[0005]

However, in the above-mentioned pulse type optical distance meter, since the rough measuring distance and the fine measuring distance are measured at the same time, the pulsed light is reflected from the corner cube which is the object to be measured, and the optical distance meter is measured. There was a problem that the next pulse could not be emitted until it returned to the main body. That is, as shown in FIG. 9A, if the light emission pulse is repeatedly emitted as P1, P2, ..., The light wave distance of the pulse reflected from the corner cube placed at the distance L ₁ The received light pulse of the meter is shown in Fig. 9 (b)
FP1 shown in FIG. Although the distance L ₁ can be uniquely obtained by using the rough measurement distance and the fine measurement distance at this time, when the corner cube is further away from the position of L ₂ , the light receiving pulse of the lightwave rangefinder is 9C, there is a problem that it is not possible to determine whether the light receiving pulse FP2 is the reflected light of the light emitting pulse P1 or the reflected light of the light emitting pulse P2.

That is, when the received light pulse is FP2, it cannot be determined whether the distance to the corner cube is L ₂ or L ₂ dash. For this reason, the pulse-type optical distance meter has a limitation that the interval of the light emission pulse must be longer than the time interval at which the pulsed light travels back and forth over the measurable limit distance of the optical distance meter.

Since the measurable distance of an ordinary pulse type optical distance meter is about 20 km, the repetition frequency fp of the light emission pulse is

Fp = 2 * (20 Km / C) (H
z) However, C = speed of light = 7.5 KHz

[0009] Therefore, the repetition frequency of the light-emission pulse of a general pulse-type light distance meter is selected to be about several hundred Hz to 5 KHz.

In order to avoid the limitation of the repetition frequency of the light emission pulse, a method of changing the light emission interval of the light emission pulse at the time of the coarse measurement distance observation and at the time of the precise measurement distance observation and measuring separately can be considered. In addition, there is a problem that it takes a long time to measure, and when the corner cube is moving, an error occurs when the coarse measurement distance observation value and the precise measurement distance observation value are combined, which is not practical.

From the viewpoint of improving the precision of the precision measurement value, it is desirable that the pulse width of the light emission pulse is narrow. However, the pulse laser diode used as the light source can be used only with a very small light emission duty. Generally, the emission pulse width is about 10 nSEC due to the limitation of the frequency characteristics of the tuning amplifier. If the repetition frequency of the light emission pulse is 5 KHz, the light emission duty Dp is

Dp = 10 nSEC / (1/5 KHz) = 0.005%

[0013]

It is possible to use a narrower pulse in order to improve the measurement accuracy, but the light emission duty is further reduced. However, the maximum rating of the emission duty of the pulse laser diode is about 0.1%.

Under a condition of a small light emission duty, the peak power of the light emission pulsed light may exceed the absolute maximum rating in some cases.

“Peak emission power” * “pulse width” = constant

Most of the pulse laser diodes do not satisfy the above relationship, and the improvement of the emission peak power cannot be expected so much.

That is, it is difficult for the conventional pulse type optical distance meter to raise the light emitting frequency of the light emitting pulse to enhance the averaging effect by repetition to improve the accuracy, and the width of the light emitting pulse must be narrowed. There is a problem in that the emission characteristics of the pulse laser diode used as the light source cannot be effectively used because of the restriction that it does not occur.

[0019]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned problems, and includes a light source section which emits light in a pulsed manner and an optical element for sending light from the light source section to an object to be measured. Means, light receiving means for receiving the reflected light from the object to be measured and converting it into a received pulse of an electric signal, and tuning amplification means for converting the received pulse converted by the light receiving means into a damped oscillation waveform And a reception timing detection means for forming a reception timing signal from the damped oscillation waveform converted by the tuning amplification means, and a distance from the object to be measured by a time difference from the light emission of the light source unit to the reception timing signal. In the lightwave rangefinder, the light source unit is configured to emit a plurality of pulses tuned by the tuning amplifier circuit.

Further, according to the present invention, a light source section which emits light in a pulsed manner, an optical means for sending light from the light source section to an object to be measured, and a reflected light from the object to be measured are received, Light receiving means for converting an electric signal into a received pulse, tuning amplifying means for converting the received pulse converted by the light receiving means into a damping vibration waveform, and a threshold of the damping vibration waveform converted by the tuning amplifying means. Reception timing detecting means for detecting a cross point with respect to the level and forming a reception timing signal, and distance measuring means for measuring the distance to the object to be measured from the time difference of the reception timing signal from the light emission from the light source section. In the lightwave rangefinder consisting of, the reception timing detection means,
Of the plurality of crosspoints detected from the damped oscillation waveform, at least two or more crosspoints are configured to be reception timing signals, and the light source unit outputs a plurality of pulses tuned by the tuning amplifier circuit. It is configured to emit light.

Further, in the present invention, when the time when the light source section which emits light in a pulsed manner emits light is T, and the time when no light source existing between the light sources emits light is T ₂ ,

T ₂ = (2n + 1) T (n is an integer)

It is also possible to configure the relationship as follows.

Furthermore, the present invention may be configured such that the time when the light source emits light and the time when the light source existing between the light sources does not emit light are the same time T.

[0025]

According to the present invention configured as described above, the light source section emits a plurality of pulses tuned to the tuning amplifier circuit, and the optical means sends the light from the light source section to the object to be measured. The light receiving means receives the reflected light from the measuring object and converts it into a received pulse of an electric signal. The tuning amplification means converts the reception pulse converted by the light receiving means into a damped oscillation waveform, and the reception timing detection means forms a reception timing signal. Further, the distance measuring means measures the distance to the object to be measured from the time difference from the light emission of the light source unit to the reception timing signal.

Further, according to the present invention, the reception timing detecting means detects a cross point with respect to the threshold level of the damped oscillation waveform converted by the tuning and amplifying means, and at least two or more cross points among the detected plurality of cross points are detected. The point is used as a reception timing signal.

In the present invention, the time for which the light source emits light is T
And T ₂ is the time during which the light source existing between the light sources emits no light.

T ₂ = (2n + 1) T (n is an integer)

Due to the above relation, the light source section may emit light in a pulsed manner.

The light source section may emit light in a pulsed manner in the relationship of T = T ₂ .

[0031]

【Example】

An embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the optical distance meter of this embodiment is provided with a laser diode 1, a condenser lens 2, a condenser lens 3 and a pair of split prisms 41, 42.
, Optical path switching chopper 5, internal optical path 6, and APD
71, an optical fiber 8, a prism 9, and an objective lens 10. And corner cube 11
Corresponds to an object to be measured arranged at a position away from the main body of the optical distance meter, and has a function of reflecting an optical pulse.

Laser diode 1 and condenser lens 2
1, 22 and the light emitting side optical fiber 81 and the split prism 41
The prism 9 and the objective lens 10 correspond to optical means.

The laser diode 1 corresponds to a light source section, and the laser diode 1 of this embodiment is a pulse laser diode, which has a relatively large peak power and a duty ratio of about 0.01%. Can generate waves. The optical path switching chopper 5 switches the luminous flux. The light receiving element 7 corresponds to a light receiving means, and may be any element that can receive the pulsed light beam emitted from the laser diode 1.

The split prism 41 is composed of a first half mirror 411 and a second half mirror 412, and the split prism 42 is composed of a first half mirror 421 and a second half mirror 422. There is. The optical fiber 8 is composed of a light emitting side optical fiber 81 and a light receiving side optical fiber 82.

When a light emitting pulse train is emitted from the laser diode 1, it is coupled to the input end 81a of the light emitting side optical fiber 81 by the condenser lenses 21 and 22. The light emission pulse train emitted from the output end 81b of the light emission side optical fiber 81 is sent to the split prism 41. The pulse train transmitted through the first half mirror 411 of the split prism 41 can be emitted to the external distance measuring optical path via the optical path switching chopper 5. It is reflected by the first half mirror 411 of the split prism 41, and is further reflected by the second half mirror 4
The pulse train reflected by 12 is the optical path switching chopper 5
Can be emitted to the internal distance measuring optical path 6 via. The optical path switching chopper 5 is for switching between the internal distance measuring optical path 6 and the external distance measuring optical path. Therefore, when the optical path switching chopper 5 selects the external distance measuring optical path, the pulse train is reflected by the prism 9 and then emitted to the outside by the objective lens 10.

The pulse train emitted from the objective lens 10 is reflected by the corner cube 11 and again the objective lens 1
The light is received at 0 and sent to the prism 9. The received pulse train is reflected by the prism 9 and sent to the split prism 42, and the received pulse light transmitted through the first half mirror 421 of the split prism 42 is coupled to the light receiving end 82 a of the light receiving side optical fiber 82.

When the optical path switching chopper 5 selects the internal distance measuring optical path 6, the emission pulse train is sent to the split prism 42 through the internal distance measuring optical path 6. Then, the optical pulse train is reflected by the first half mirror 421 and the second half mirror 422 incorporated in the split prism 42,
It is adapted to be coupled to the light receiving end 82a of the light receiving side optical fiber 82.

The exit end 8 of the light receiving side optical fiber 82
The optical pulse train emitted from 2b is the condenser lens 3
It is designed to bind to APD71 by 1, 32,
The light receiving element 7 converts the current pulse.

Next, the configuration of the electric circuit of this embodiment will be described in detail.

(First embodiment)

The first embodiment shown in FIG. 1 is a crystal oscillator 10
0, first frequency divider 110, synthesizer 120, second
Frequency divider 130, timing circuit 140, laser diode 1, laser diode driver 150, and APD7
1, a tuning amplifier 160, and a reception timing detection circuit 170
A counter 180, a peak hold circuit 190, a level determination circuit 200, a band pass filter 210, a sample hold (S / H) 220, a switch 230, an AD converter 300, a memory 400 and a CPU 500.

The crystal oscillator 100 is one of the reference signal generating means and generates a 15 MHz reference signal.
This reference signal is supplied to the first frequency divider 110, the synthesizer 130, the bandpass filter 210, and the counter 180. The reference signal supplied to the first frequency divider 110 is divided into 1/100 by the first frequency divider 110 and becomes 150 KHz, which is sent to the synthesizer 130. The synthesizer 130 creates 15.15 MHz from 150 KHz supplied from the first frequency divider 110 and 15 MHz supplied from the crystal oscillator 100, and sends it to the second frequency divider 130. Second frequency divider 13
0 is 15.15 supplied from synthesizer 130
The frequency is divided into 1/50 to generate 303 KHz and sent to the timing circuit 140. The first frequency divider 110, the second frequency divider 130, the synthesizer 12
The output signal of 0 is a binarized signal.

The timing circuit 140 sends a pulse laser emission timing signal to the laser diode driver 150, and the timing circuit 140 sends a reset signal to the peak hold circuit 190 of the damped oscillation waveform. There is. The capacitor charge signal, the pulse laser emission timing signal, and the reset signal for the peak hold circuit 190 are all 3
It is a signal repeated at 030 Hz.

The laser diode driver 150
Is to drive the laser diode 1 in a pulsed manner in accordance with the pulsed laser emission timing signal of the timing circuit 140.

Here, the laser diode driver 150
Will be described in detail. Here, the capacitor charge signal is CS, the reset signal for the peak hold circuit 190 is RS, and the pulse laser emission timing signal P
S.

First, the operation of the laser diode driver 150 for the reset signal RS, the capacitor charge signal CS, and the pulse laser emission timing signal PS for the peak hold circuit 190 will be described with reference to FIG.

The laser diode driver 150 includes a first transistor 1501 and a second transistor 15
02, the third transistor 1503, and the coil 150.
4, a first diode 1505, a second diode 1506, a first capacitor 1507, a second capacitor 1508, and a delay circuit 1510. Signals are input to the laser diode driver 150 in the order of the capacitor charge signal CS and the pulse laser emission timing signal PS.

The capacitor charge signal CS is H
The first transistor 1501 is turned on while it is high,
A current I _{L is} passed through the coil 1504. When the capacitor charge signal CS becomes LOW, the coil 15
The energy stored in 04 is stored as electric charge in the first capacitor 1507 via the first diode 1505 for rectification, and is also stored as electric charge in the second capacitor 1508 via the second diode 1506 in the same manner. ..
After that, the pulsed laser emission timing signal PS is sent to the second transistor 1502 and the delay circuit 1510. The second transistor 1502 and the third transistor 1503 are avalanche transistors. Second
The transistor 1502 receives the pulsed laser emission timing signal PS and causes the electric charge accumulated in the second capacitor 1508 to flow into the laser diode 1 to emit pulsed light. On the other hand, the delay circuit 1510
Is configured to delay the pulse laser emission timing signal PS by a fixed time and send the delayed pulse laser emission timing signal PS to the third transistor 1503. The third transistor 1503 is adapted to flow the electric charge accumulated in the first capacitor 1507 to the laser diode 1 to emit pulsed light when the delayed pulsed laser light emission timing signal PS is input.

In the delay circuit 1510, as shown in FIG. 3B, from the end of the first light emission pulse by the second transistor 1502 to the second by the third transistor 1503.
The light emission of the light emission pulse is delayed by the time T ₂ , and in this embodiment,

T ₁ = T ₂ = T ₃

It is set so that The light emission train of the two pulsed lights is repeated at 3030 Hz.

The light pulse emitted from the laser diode 1 passes through the optical system and is received by the APD 71. This APD 71 is one of the light receiving elements 7, and is a diode capable of obtaining a gain by applying a deep bias to the pn junction to induce a drooping multiplication. The APD 71 receives the optical pulse that has passed through the internal reference optical path and the optical pulse that has passed through the external distance measuring optical path. The optical pulse is converted into an electric signal of a current pulse train by the APD 71 and sent to the tuning amplifier 160.

The tuning amplifier 160 converts the current pulse train input from the APD 71 into a voltage signal, converts it into a damped oscillation waveform, and performs inverting amplification. The damped oscillation waveform formed by the tuning amplifier 160 is supplied to the reception timing detection circuit 170 and the peak poled circuit 190.

The tuning amplifier 160 has a center frequency f _0.
But

F ₀ = 1 / (T ₁ + T ₂ )

By setting Q of the tuning circuit to an appropriate value (for example, about Q = 5), a damping oscillation waveform as shown in FIG. 4B is obtained with respect to the single pulse of FIG. 4A. It is for output.

Further, with a pulse width as shown in FIG.
Have equal spacing

T ₁ = T ₂ = T ₃

With respect to the pulse train of (1), the output of the tuning amplifier 160 is the damping vibration waveform by the first pulse d1 (FIG. 4 (e)) and the damping vibration waveform by the second pulse d2 of the pulse train shown in FIG. 4 (d). (FIG. 4 (f))
The waveform shown in (g) is obtained, which is an excellent effect that a damping vibration waveform several times that of FIG. 4 (a) is obtained.

As shown in FIG. 1, the reception timing detection circuit 170 is composed of a first comparator 171, a second comparator 172, a one-shot vibrator 173, a rising edge detector 174 and a falling edge detector 175. There is. The first comparator 171 has a threshold level V _S1 , and confirms light reception by capturing the g1 portion of the damping vibration waveform of FIG. 4 (g), and the second comparator 172 having a threshold level 0V is operated for a certain period of time. It is supposed to be in an active state. Then, the second comparator 172 catches two points of g3 and g4 which are cross points with 0V of the damped oscillation waveform and has a width corresponding to the portion of g2 (FIG. 4 (h)).
Is output.

Further, in the case of the damping vibration waveform of FIG. 4 (g), the amplitude of g2 to g5 is the maximum, so that the slope of g4 is the steepest and is less susceptible to the error factors. Therefore, the reception timing signal uses the trailing edge of the waveform shown in FIG. For waveforms after g5, the active state of the second comparator 172 has ended, and the comparator does not operate.

A rising edge detector 174 and a falling edge detector 175 are connected to the output side of the second comparator 172, and the output signal of the rising edge detector 174 is the first sample hold circuit 2
21 and the output signal of the falling edge detector 175 is sent to the second sample and hold circuit 222. It should be noted that two or more cross points of the damped vibration waveform with 0 V may be detected.

The reception timing detection circuit 170 supplies the reception timing signal to the sample hold (S / H) 220 and the counter 180. Counter 18
0 is reset by the reset signal from the timing circuit 140, and the time until the reception timing signal is counted by 15 MHz from the crystal oscillator 100. That is, the rising edge detector 174
Of the rising edge detector 17 is supplied to the counter 180.
Until the signal from 4 is input, 15 MHz from the crystal oscillator 100 is counted.

15 MHz sent from the crystal oscillator 100 to the bandpass filter 210 becomes a sine wave and is sent to the first sample hold circuit 221 and the second sample hold circuit 222. Then, the first sample hold circuit 221 performs sample hold by the output signal of the rising edge detector 174, and the second sample hold circuit 222 performs sample hold by the output signal of the falling edge detector 175. There is. The waveform signals sample-held by the sample-hold circuit 221 and the second sample-hold circuit 222 are switched by the switch 23.
0, and the switching unit 230 is switched according to the switching signal from the CPU 500. The waveform signal switched by the switch 230 is AD-converted by the AD converter 300, and the converted digital data is stored in the predetermined memory 400. When the AD conversion is completed, a conversion end signal is output to the CPU 500.

The damped oscillation waveform sent from the tuning amplifier 160 to the peak hold circuit 190 is peak-held by the peak hold circuit 190 and becomes a DC level signal according to the peak value of the damped oscillation waveform, and the level determination circuit 20
Sent to 0. The level determination circuit 200 receives the signal from the peak hold circuit 190, and the light quantity of the received light pulse train is A
The PD 71, the tuning amplifier 160, and the reception timing detection circuit 170 determine whether or not they are within the proper operating range, and send the result to the CPU 500. CPU4
The counter 31 receives the signal from the level determination circuit 200, and only when the light quantity of the received light pulse train is an appropriate value, the counter 18
The counter value from 0 and the data from the AD converter 300 are adopted.

Further, since the peak hold circuit 190 is reset each time the light emission pulse train is emitted by the reset signal from the timing circuit 140, it is possible to judge the light quantity for each light emission of the light emission pulse. Therefore, it is possible to minimize the adverse effect due to the fluctuation of the received light amount due to the fluctuation of the air between the lightwave distance device main body and the measurement object.

15 MH transmitted from the crystal oscillator 100
The sine wave obtained by passing z through the bandpass filter 210 and the emission frequency of 3030 Hz of the laser diode 1 are slightly shifted. Therefore, as shown in FIG. 5A, the phase relationship between the reception timing signal and the sine wave obtained by passing through the bandpass filter 210 is also slightly shifted. This phase shift amount is

(1/3030 Hz) / (1/15 MHz) = 4950 + (50/101)

And becomes “50/101”.

Each light emission pulse train and band pass filter 2
As shown in FIG. 5B, the phase relationship with the sine wave sine wave signal obtained through 10 is one cycle for 101 times.
It has the same phase relationship as the first time. For this reason,
The output signal of the sample hold (S / H) 220 is

F = 3030 Hz / 101 = 30 Hz

One cycle becomes, and a sine wave is not generated as shown in FIG. 5C, but by performing rearrangement at the stage of storing in the memory 400 after AD conversion, as shown in FIG. 5D. The horizontal axis is the address on the memory 400, and the vertical axis is AD
When the converted value data is used, sinusoidal AD converted data can be created. Further, the data that has been sample-held and AD-converted by the light emission pulse train after the 102nd time becomes the data after the second cycle of 30 Hz, so if the determination result of the level determination circuit 200 is proper, the data of the previous cycle Then, the accuracy of the AD converted data can be improved by performing the averaging process of the data later.

The first sample hold circuit 221
By using the AD conversion data obtained by the above and the AD conversion data obtained by the second sample hold circuit 222, each data is subjected to Fourier transform to obtain the phase, and an arithmetic operation for averaging the values is performed, It is configured to use this average value.

Laser diode 1 executed as described above
The process from the light emission of (1) to the storage of the AD converted data in the memory 400 is performed for the external distance measuring optical path and the internal reference optical path. As shown in FIG. 5D, if is AD conversion data of the internal reference optical path and is AD conversion data of the external distance measuring optical path, the phase difference φ between the two waveforms corresponds to the optical path difference. Fourier transform is applied to each waveform, phase information of the fundamental component wave is obtained, and a precision measurement distance of 10 m unit or less can be obtained from the phase difference. Note that the rough measurement distance can also be obtained with an accuracy of 10 m from the counter difference between the counter 180 in the external distance measuring optical path and the internal reference optical path. Then, by combining the rough measurement distance and the fine measurement distance, the actual distance from the lightwave rangefinder to the measurement object can be obtained. The configuration for performing these operations corresponds to the distance measuring means.

Since the precision measurement distance is obtained by performing the Fourier transform on the AD-converted data value to obtain the phase of the fundamental wave component, the waveform to be sampled and held is not necessarily the sine wave shown in FIG. 6 does not have to be
It may be the integrated wave of (b) or the triangular wave of FIG. 6 (c). Similarly, a low pass filter may be adopted instead of the band pass filter 210.

The first embodiment constructed as described above is the AD obtained by the first sample hold circuit 221.
The conversion data and the AD conversion data obtained by the second sample hold circuit 222 are used to perform the Fourier transform on the respective data to obtain the phase, and the values are averaged. There is an outstanding effect that the offset of the second comparator 172 of the timing detection circuit 170 can be removed.

(Second Embodiment)

Next, a second embodiment will be described with reference to FIG. In the first embodiment, the first sample hold circuit 2
21 and the second sample and hold circuit 222 are used, and the first sample and hold circuit 221 samples and holds by the output signal of the rising edge detector 174, and the second sample and hold circuit 221. The sample signal 222 is sampled and held by the output signal of the falling edge detector 175.
Then, the signal after sample hold is switched by the switch 230.

The second embodiment is a sample hold circuit 22.
Only one 0 is used, the output signal of the rising edge detector 174 and the output signal of the falling edge detector 175 are switched by the switch 230, and the switched output signal is sent to the sample hold circuit 220. Has been done.

The second embodiment has a disadvantage that the same damped oscillation waveform cannot be implemented when measuring the rising edge and the falling edge, but if the alternate measurement is performed in a short time, the first embodiment There is an effect that the same operation as can be performed. The rest of the configuration and operation are the same as in the first embodiment, so a description thereof will be omitted.

In the above embodiment, the number of light pulses forming the light emission pulse train is two, but it may be composed of three or more light pulse trains. In this case, the output amplitude of the damped oscillation waveform is further increased. It has the effect of becoming larger. Then, the reception timing detection circuit 170 is preferably configured to capture the maximum slope portion of the damped oscillation waveform.

Further, in the above embodiment, only the portion g4 of the damped oscillation waveform of FIG. 4 (g) is used as the reception timing, but other cross points with 0V such as g3 and g6 are used as the reception timing. May be used. Then, by performing an averaging operation on the data obtained by g4, the second comparator 17 of the reception timing detection circuit 170
It is possible to remove the drift of the threshold level of 2 and to improve the measurement accuracy by the averaging effect.

[0085]

According to the present invention configured as described above, the light source section which emits light in a pulsed manner, the optical means for sending the light from the light source section to the object to be measured, and the light source section from the object to be measured are provided. Light receiving means for receiving the reflected light and converting it into a reception pulse of an electric signal, tuning amplification means for converting the reception pulse converted by the light reception means into a damped oscillation waveform, and conversion by this tuning amplification means Reception timing detection means for forming a reception timing signal from the damped oscillation waveform,
A lightwave rangefinder comprising a lightwave rangefinder comprising a distance measuring unit for measuring a distance to a measurement object based on a time difference from the light emission of the light source section to the reception timing signal, wherein the light source section has the tuning Since it is configured to emit multiple pulses that are tuned by an amplifier circuit, it is possible to obtain a large damped oscillation waveform whose output amplitude is several times larger than that of a conventional lightwave rangefinder, and the measurement distance limit Can be extended and the measurement accuracy can be improved.

Further, since a plurality of pulses are emitted, there is an effect that the emission characteristics can be utilized to the maximum without exceeding the maximum rating of the pulse laser or the like used for the emission source.

[0087]

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a laser diode driver of this embodiment.

FIG. 4 is a diagram illustrating detection of a reception timing signal according to the present embodiment.

FIG. 5 is a diagram illustrating a phase difference measurement according to the present embodiment.

FIG. 6 is a diagram illustrating waveforms to be sampled and held in this embodiment.

FIG. 7 is a diagram illustrating the principle of a conventional optical distance meter.

FIG. 8 is a diagram illustrating a light receiving pulse of a conventional lightwave rangefinder.

FIG. 9 is a diagram illustrating a light receiving pulse of a conventional lightwave distance meter.

[Explanation of symbols]

 1 Laser Diode 2 Condenser Lens 3 Condenser Lens 41 Split Prism 42 Split Prism 5 Optical Path Switching Chopper 71 APD 8 Optical Fiber 9 Prism 10 Objective Lens 11 Corner Cube 160 Tuning Amplifier 170 Reception Timing Detection Circuit 171 First Comparator 172 Second Comparator 173 One-shot vibrator 174 Rising edge detector 175 Falling edge detector 180 Counter 190 Peak hold circuit 220 Sample hold circuit 230 Switching device 300 AD converter 400 Memory 500 CPU 1000 Processing unit

Claims (4)

[Claims] 1. A light source section which emits light in a pulsed manner, an optical means for sending light from the light source section to an object to be measured, and reflected light from the object to be measured is received to generate an electrical signal. From the light receiving means for converting into the reception pulse, the tuning amplification means for converting the reception pulse converted by the light receiving means into the damping vibration waveform, and the damping vibration waveform converted by the tuning amplification means, the reception timing signal is obtained. In the lightwave rangefinder, the light source includes a reception timing detecting means for forming a light emitting portion, and a distance measuring means for measuring a distance to a measurement object by a time difference from light emission of the light source unit to the reception timing signal. A lightwave rangefinder, wherein the section is configured to emit a plurality of pulses tuned by the tuning amplifier circuit. 2. A light source section which emits light in a pulsed manner, an optical means for sending light from the light source section to an object to be measured, and reflected light from the object to be measured is received to generate an electrical signal. Light receiving means for converting into a received pulse, tuning amplification means for converting the received pulse converted by the light receiving means into a damping vibration waveform, and a cross with respect to a threshold level of the damping vibration waveform converted by the tuning amplification means. It comprises a reception timing detection means for detecting a point and forming a reception timing signal, and a distance measurement means for measuring the distance from the light emission from the light source unit to the measurement object from the time difference of the reception timing signal. In the lightwave rangefinder, the reception timing detection means includes at least two or more cross points among the plurality of cross points detected from the damped oscillation waveform. An optical distance meter, which is configured to use a point as a reception timing signal, and wherein the light source section emits a plurality of pulses tuned by the tuning amplifier circuit. 3. When the light source section that emits light in a pulsed manner has a time T as the light source emits light and a time T ₂ as the light source that does not emit light between the light source emission is T ₂ = (2n + 1) ) T (n is an integer). 4. The time T during which the light source emits light is equal to the time between the light emission of the light source and the time when the light source does not emit light.
The lightwave rangefinder according to claim 1.