JPS5987383A - Light receiving circuit of laser range finder - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a false stop pulse by generating automatically a pulse having a waveform similar to that of an irregularly reflected pulse and an amplitude wider than that of this pulse each time when the irregularly reflected pulse is inputted and providing a means obtaining the difference between this generated pulse and the irregularly reflected pulse to amplify. CONSTITUTION:The irregularly reflected pulse compensating a signal generating circuit 8 receives the irregularly reflected pulse from molecules or corpuscles included in a transmission medium in air or the like and generates an irregularly reflected pulse compensating signal (e), which has a waveform similar to that of this irregularly reflected pulse and has an amplitude wider than that of this pulse, automatically each time when the irregularly reflected pulse is inputted. An irregularly reflected pulse compensating circuit 9 receives a light reception signal (c) from a light reception signal generating circuit 7 and said signal (e) and superposes and amplifies them to obtain a differential irregularly reflected pulse compensating circuit output (f), and this output is sent to a reflected pulse amplitude discriminating circuit 10. The circuit 10 discriminates the amplitude of said output (f) to extract only a laser target reflected pulse. These circuits 8-10 are provided to prevent automatically the occurrence of the false stop pulse.

Description

[Detailed description of the invention] The present invention relates to a light receiving circuit for a laser distance measuring device.

Laser range finders emit a single sharply directional laser beam pulse from a laser oscillator toward a laser target, and measure the distance to the laser target from the time difference between the reflected pulse and the laser beam pulse. well known at the time.

In such a laser i11 range device, the laser emission pulse emitted from the laser oscillator toward the laser target uses a single pulse with high energy, and the laser reflected pulse from the laser target usually uses a single pulse of high energy. A counter with a built-in reference pulse oscillator having a reference frequency is operated by a start pulse synchronized with the laser emission pulse and a stop pulse formed from the laser reflected pulse, detected by a photodetector such as a photomultiplier, and the start pulse The system is configured to measure the time difference from the number of reference pulses counted by the reference pulse and the stop pulse, and calculate the distance to the laser target from this time difference and the laser light speed.The operating principle is the same as that of a radar device. It is also well known that the same is true.

When a v-v projection pulse is emitted toward a laser target,
The intensity of the laser reflected pulse not only decreases in proportion to the square of the distance to the laser target, but also corresponds to the decrease in laser light transmittance due to absorption, scattering, etc. in the propagation medium of the laser emitted pulse, such as the atmosphere. decreases rapidly with increasing distance to the laser target. Therefore, when measuring a distance to a long-distance laser target, it is necessary to increase the intensity of the laser projection pulse of the laser range finder and also to significantly increase the gain of the light receiving circuit.

However, increasing the intensity of the laser emitting pulse and increasing the gain of the light receiving circuit will inevitably cause problems such as molecules and particles contained in the propagation medium such as the atmosphere, such as water vapor, fog, rain, snow, or dust in the atmosphere. If the diffused reflected pulse caused by the laser target is large, this will be formed as a pseudo stop pulse by the light receiving circuit of the laser range finder, which will interfere with normal ranging by the laser reflected pulse from the laser target, and therefore there is a high probability of incorrect ranging. The problem arises that the size increases.

Conventionally, as a means to remove this kind of pseudo stop pulse formed in the light receiving circuit of a laser distance measuring device, generally,
For short distances, a method is used to reduce the gain of the light receiving circuit. This is because the diffusely reflected pulse due to molecules or particles in the atmosphere is the distance at which the optical field of view of the laser projection pulse emitted through the projection optical system of the laser rangefinder matches the optical field of view of the reception optical system. After that, the laser pulse is input to the light receiving circuit, and then the range where the emitted beam of the laser emitted pulse intersects with the optical field of view of the light receiving optical system, usually a relatively limited distance range of about several 100 mm within the light receiving range. It has been clarified from a large amount of actual measurement data that it occurs over a long period of time, and its intensity rapidly reaches its maximum value at a relatively short distance, and then exhibits a characteristic of attenuating relatively slowly over the range of occurrence. In addition, it has been known from numerous measurements that the intensity characteristics of the diffusely reflected pulse as a whole have characteristics that are almost similar to the charging and discharging characteristics of a capacitor and electrical resistance. is a characteristic almost similar to a charging characteristic at a relatively short distance, and after rapidly reaching a maximum value, it attenuates with a relatively gentle attenuation characteristic almost similar to a discharging characteristic.

Although it depends on the characteristics of this diffuse reflection intensity and the conditions of the propagation medium such as the atmosphere, the distance measured by a laser distance measuring device is approximately several thousand meters or more. occurs at a sufficiently short range, and reaches its maximum value at even shorter distances.

Therefore, by reducing the gain of the short-distance light receiving circuit, the influence of this disturbance 5- reflected pulse can be significantly reduced0. It minimizes the gain of the time light receiving circuit, increases the gain as time passes, detects the laser target reflected pulse received from a long distance with high sensitivity, and generates a stop pulse accurately. The characteristics are made to correspond to the gain correction of the light receiving circuit described above.

For example, in the dream of using a photomultiplier as a photodetector, the photodetection characteristics can be corrected by applying a gain correction voltage that changes over time in accordance with the content to be corrected to the dynode voltage of the photomultiplier. is being carried out. However, since the dynode voltage of the photomultiplier normally uses a high voltage of about 1000V, the gain correction voltage also requires a voltage of several 100V, and the voltage control element also requires a vacuum tube or a high voltage transistor.
Therefore, it is difficult to miniaturize the light receiving circuit, and it is also difficult to improve the efficiency of the power source.

Even when using a semiconductor photodetector such as a photodiode or phototransistor as a photodetector, there are hundreds of photodetectors.
volt gain control voltage, and these photodetectors have excellent detection sensitivity but low output level, so they are combined with an amplifier to compensate for this, so each high voltage gain control voltage generation mentioned above is However, the disadvantage is that the amplifier is likely to malfunction and erroneous measurements may occur. Furthermore, any of the above-mentioned methods has the disadvantage that it is extremely difficult to completely remove the highly variable diffusely reflected pulses.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, and to automatically generate a pulse with a waveform almost similar to the diffused reflected pulse and a constant large amplitude every time the diffused reflected pulse is input to the light receiving circuit of a laser distance measuring device, and to combine this with the diffused reflected pulse. By providing a means for amplifying the difference between An object of the present invention is to provide a light receiving circuit for a laser distance measuring device with a simple structure.

The circuit of the present invention measures the distance to the laser target by determining the time difference between the laser emission pulse emitted from the laser oscillator and the laser reflection pulse received from the laser target by the laser emission pulse. In a range device, upon receiving a diffused reflection pulse from molecules or particles contained in a propagation medium such as the atmosphere, a diffused reflection pulse compensation signal whose waveform is almost similar to the diffused reflection pulse and whose amplitude is always larger than that of the diffused reflection pulse is used as the diffused reflection pulse. A diffused reflection pulse compensation signal generation circuit that automatically generates for each input, the diffused reflection pulse compensation signal generated by this diffused reflection pulse compensation signal generation circuit, and the laser reflection pulse accompanied by the diffused reflection pulse are inputted, and the difference between these two manual efforts is calculated. A diffused reflection pulse compensation circuit that compensates to remove the diffused reflection pulse by amplifying the amplitude and a laser reflection pulse of a preset level based on the difference between the two forces obtained by this diffused reflection compensation circuit. and a reflected pulse amplitude discrimination circuit that extracts a laser reflected pulse from the laser target by comparing the amplitude with a discrimination threshold value and performing amplitude discrimination.

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a circuit according to the present invention.

The embodiment shown in FIG. 1 is a Q-switched laser oscillator 1. Light transmission optical system 2. Start pulse generation circuit 3゜Pulse counting circuit 4. Flip-flop circuit5. Light receiving optical system 6. Light reception signal generation circuit 7. Diffuse reflection pulse compensation signal generation circuit 8. Diffuse reflected pulse compensation circuit 9 and reflected pulse amplitude discrimination circuit j&1
0.

Figure 2 is an operating waveform characteristic diagram showing the operating waveform characteristics of the main parts in the block diagram of the embodiment in Figure 1), (a) - (b) * (c) + (d) in Figure 2. , (e
) and (f) are the circuit portions a shown in the block diagram of FIG. 1, respectively.

The characteristics of the operating waveforms at b, c, d, e, and f are shown. The embodiment shown in FIG. 1 will be described below with reference to the operating waveform characteristic diagram shown in FIG. 2. In FIG. A di-iront pulse laser is oscillated, and the laser oscillation output 101 is transmitted to the light transmission optical system 2. The light transmitting optical system 2 gives a predetermined directivity angle to the laser oscillation output 101 through a built-in lens group, and this is emitted as a laser projection pulse 201 toward a laser target via a propagation medium such as the atmosphere.

The Q-switched laser oscillator 1 also has a laser oscillation output of 10
1 is sent to the start pulse generation circuit 3 as a start synchronization pulse 102.

The start pulse generating circuit 3 is a photodiode.

It has a pulse forming circuit, an amplifying circuit, etc., and detects the received start synchronizing pulse 102 with a photodiode.The pulse forming circuit and amplifying circuit generate a start pulse a with a predetermined pulse width and level, which is sent to a pulse counting circuit 4 and a flip-flop. is sent to the pull-up circuit 5. The start pulse a is shown in FIG. 2(a) with the elapsed time t as the time axis.

10- Now, the pulse counting circuit 4 includes a reference pulse generator that generates a reference pulse from a reference frequency, a pulse counter, a time difference counter, and a pulse that starts and stops the counting operation of this pulse counter using a start pulse and a stop pulse. In this embodiment, a start pulse a causes a pulse counter to start counting reference pulses via a pulse counter gate circuit, and a stop pulse g output from a reflected pulse amplitude discrimination circuit 10, which will be described later, is used. This start pulse a
A time difference measuring device calculates the time difference from the reference pulse counts counted by the stop pulse g and the stop pulse g, and displays this as a time difference signal 401 in a display circuit (not shown).
The distance is displayed according to this time difference.

The flip-flop circuit 5 has a monostable multivibrator circuit, which allows the level and pulse width t to be specified in advance.
. Outputs a gate pulse b having the following values. The pulse width t g Fi % of this gate pulse b is a period in which distance measurement by the laser side range sensor is unnecessary, that is, a time set in advance corresponding to a sufficiently short distance with respect to the range measurement range, and also as described above. It is set to include the time until the level of the diffusely reflected pulse reaches its maximum. FIG. 2(b) shows Kate pulse b.

Now, a laser reflected pulse 601 from a laser target is received by a light receiving optical system 6 having a lens group that forms light receiving directivity, and this light receiving power 602 is transmitted to a light receiving signal generating circuit 7.
light is sent to.

It is equipped with a light reception signal generation circuit 71d and a photodetection circuit using a photomultiplier, and converts the received light reception input 602 into an electrical signal and outputs this as a light reception signal C. This light reception signal C includes a laser target reflection pulse Po and a diffuse reflection pulse P1.

FIG. 2(c) shows the characteristics of the operating waveform of the received light signal C, in which the laser target reflected pulse P0 and the diffused reflected pulse P1 are detected by the photomultiplier with the camellia inverted.
The diffuse reflection pulse Pl rapidly increases its level after the elapse of time 11 corresponding to the distance at which the laser projection pulse 201 and the light receiving field of view of the light receiving optical system coincide, reaching the maximum value R0, and then relatively gradually increasing. Attenuating. Figure 2(b)
The pulse width t of the aforementioned gate pulse b shown in FIG. is the time when distance measurement is not required, and the diffused reflection pulse P1 is at its maximum value. The pulse width t0 is set to be approximately equal to the time taken to reach the maximum value R0, but for the reason described later, it is not necessary to set it strictly according to the time taken to reach the maximum value R0. It is sufficient to set it within the range of the setting width of the time it, which is determined in advance from the circuit characteristics etc.

The diffuse reflection pulse P1 is shown in Fig. 2 (as is clear from cl.
It has start-up and decay characteristics similar to the charging and discharging characteristics of a capacitor using an 〇R circuit that combines a capacitor C and an electric resistance R.

Normally, in order to suppress the influence caused by such a diffused reflection pulse Pl, after the laser emission pulse 201 is emitted, the light reception detection gain by the light reception signal generation circuit 6 is lowered, and this is gradually restored over time to reduce the influence of the diffused reflection pulse Pl. A method has been used in which only the laser target reflected pulse P0 is detected with high sensitivity while suppressing the reception of the laser beam, but this method has the drawbacks described above.

Therefore, in this embodiment, a diffuse reflection pulse compensation signal generation circuit 8. The diffused reflected pulse compensation circuit 9 and the reflected pulse amplitude discrimination circuit 10 are provided to eliminate this drawback and suppress the diffused reflected pulse as follows.

The diffuse reflection pulse compensation signal generation circuit 8 includes an analog switch circuit 81. Operational amplifier circuit consisting of resistors R3, R14 and operational amplifier 82, capacitor C1 and resistor R
11 charging/discharging circuits.

The analog switch circuit 81 receives the gate pulse b output from the flip-flop circuit 5 and the light reception signal C output from the light reception signal generation circuit 7, gates the light reception signal C by the gate pulse b, and outputs it for a time t0. . The output of this analog switch circuit 81 is as shown in FIG. 2 (rd), and the light reception signal C shown in FIG. 2 (c) is generated only during time t0.
The gated analog switch circuit output pulses d and 14- are input to an operational amplifier circuit constituted by an operational amplifier 82 and resistors R3, R+4. This operational amplifier circuit has an amplification degree determined by a resistor R3゜R4 having a preset resistance value, and the input analog switch circuit output pulse d is amplified and polarized in accordance with the above-mentioned amplification degree. At the same time as outputting as a pulse, time constant τ=CIR determined by capacitor C1 and resistor R11.

The capacitor C1 is charged with a charging characteristic corresponding to , and when the input of the analog switch circuit output pulse d is cut off, the capacitor C1 is discharged with a discharging characteristic corresponding to the time constant τ, thus generating a diffuse reflection pulse compensation signal e. . This diffusely reflected pulse compensation signal e is shown in FIG. 2(e). Figure 2 (
The waveform P2 in e) shows the charging period during the charging and discharging period by the capacitor C1 and the resistor R6, and the waveform P3 shows the waveform in the discharging period, and the waveform is changed to the light receiving signal C1, that is, the waveform shown in FIG. 2(C) by a preset time constant τ. Waveform P of the diffusely reflected pulse.

It is almost equal to , and is always obtained as a pulse with a much higher level and opposite polarity.

This diffused reflection pulse compensation signal e is automatically output as a pulse having the above-mentioned characteristics when the received light signal C includes a diffused reflection pulse, and is sent to the diffused reflection pulse compensation circuit 9. It has a nine-piece diffuse reflection pulse compensation circuit, a two-man operational amplifier circuit consisting of two resistors R1 and R having the same resistance value, and an operational amplifier 91.
and a diffused reflected pulse compensation signal e, which are superimposed and amplified to obtain a differential diffused reflected pulse compensation circuit output f, which is sent to the reflected pulse amplitude discrimination circuit 10.

The output f of the diffused reflection pulse compensation circuit is as shown in Figure 2).
The difference between the two inputs to the diffused reflection pulse compensation circuit 9, that is, the received light signal C and the diffused reflection pulse compensation signal e, and therefore the second
! ? ! The difference between the waveforms shown by IfC) and (e) is amplified by the amplification degree determined by the resistors R, and R2, and the polarity is reversed to form the waveform P4 and laser target reflection shown in FIG. 2(f). Pulse P. ′ is output.

The reflected pulse amplitude discrimination circuit 10 is constructed by an amplitude discrimination circuit using a Schmitt circuit having a reflected pulse amplitude discrimination threshold shown in FIG. 2(f) as a comparison reference voltage.
Amplitude discrimination of the output f of the diffused reflection pulse compensation circuit shown in f) is performed to extract only the laser target reflected pulse P0', which is further converted into a laser target reflected pulse of a desired level and waveform using a pulse shaping circuit and an amplification circuit. It is sent to the pulse counting circuit 4 as a stop pulse g.

FIG. 2(g) shows the stop pulse g obtained in this manner.

The pulse counting circuit 4 starts counting reference pulses at the same time as the laser emission pulse 201 is emitted by the above-mentioned start pulse a, finishes counting by the stop pulse g, and calculates the corresponding time from the number of reference pulses counted during this period. That is, the distance measurement time to the laser target by the laser distance measuring device, and therefore the distance information is measured.

In this case, the influence of the diffusely reflected pulse can be automatically and essentially eliminated, making it possible to perform distance measurement without errors.Furthermore, by completely eliminating the diffused reflected pulse, it is possible to eliminate the influence of the diffused reflected pulse automatically and essentially. It is much easier to detect laser reflected wave pulses whose received light level has decreased due to changes or the like than with the conventional method.

The present invention automatically generates, in the light receiving circuit of a laser distance measuring device, a pulse with a waveform almost similar to that of the diffusely reflected pulse and always having a large amplitude every time a diffusely reflected pulse is input due to molecules or particles of a laser propagation medium such as the atmosphere. The method is equipped with a means to remove the diffused reflected pulse isometrically by taking the difference between the reflected pulse and the diffused reflected pulse, and extracts only the reflected pulse from the laser target, and generates a stop pulse for the laser range finder based on this. The basic feature is to suppress the generation of pseudo stop pulses due to diffusely reflected pulses, and FIG. 1 shows a basic embodiment as an embodiment of the present invention. It is clear that the present invention can be applied to other modifications as well.

For example, in the embodiment shown in FIG. 1, the diffused reflected pulse and the diffused reflected pulse compensation signal to be superimposed are irregularly scaled. Amplifier circuit, as well as capacitor C1 and resistor R5
As mentioned above, this diffused reflection pulse compensation signal is generated by the charging/discharging circuit formed by , for example, the frequency components of the diffusely reflected pulse and the laser target reflected pulse are the second
Focusing on the large difference as shown in Figure (c), the diffused reflected pulse is amplified through a narrow-band operational amplifier circuit that allows only the diffused reflected pulse with a low frequency component to pass among both reflected pulses. It is clear that generating compensation signals, etc. can also be easily implemented.

In addition, in this embodiment, as is clear from FIG. 2 etc., when the diffuse reflection pulse compensation signal generation circuit 8 generates the diffuse reflection pulse compensation signal e shown in FIG. ) The output gate is performed in response to the time when the level of the diffusely reflected pulse shown in ) is approximately the maximum, but the waveform of the diffusely reflected pulse compensation signal is not the same as that of the diffusely reflected pulse shown by waveform Pl in Fig. 2(c). This output gate time is not necessarily required, as long as it is equal and always has a large amplitude, and moreover, it is sufficient that the diffused reflected pulse can be equivalently removed by amplifying the difference between the diffused reflected pulse and the diffused reflected pulse. It is not necessary to target the time when the diffused reflection pulse is at its maximum, and correspondingly, the gate time t0 of the gate pulse shown in FIG. c)
Time shown in 1. There is no problem in expanding and contracting over a period of 1. It is also clear that it is possible to set in advance using the circuit configuration constants of the diffuse reflection pulse compensation signal generation circuit 8, etc.

Furthermore, in this embodiment, the Schmitt circuit is used for amplitude discrimination in the reflected pulse amplitude discrimination circuit 10, but this is based on a preset reflected pulse amplitude discrimination threshold, that is, the second
It is clear that the same implementation can be achieved by using other circuits having an equivalent function capable of amplitude discrimination in comparison with the reflected pulse amplitude discrimination threshold shown in FIG.

Note that although this embodiment describes the case where a photomultiplier is used to detect the light received by the light received signal generation circuit 7, the same effect can be obtained even when another photodetection element such as a semiconductor light receiving element is used for this light reception detection. It is clear that the implementation is possible, and the diffused reflection pulse compensation signal generation circuit 8. Diffuse reflected pulse compensation circuit 9 and reflected pulse amplitude discrimination circuit 10
It is also possible to easily configure all or any combination of these as an integrated structure, and the present invention is not limited to the light receiving circuit of a laser distance measuring device, but is applicable to laser distance measuring devices. It is obvious that the present invention can be applied to other devices such as laser radars and other light receiving circuits, and all of the above can be easily implemented without detracting from the spirit of the present invention.

As explained above, according to the present invention, in the light receiving circuit of a laser distance measuring device, each time a diffused reflected pulse is inputted by molecules or particles of a laser propagation medium such as the atmosphere, the waveform of this diffused reflected pulse is almost similar to that of the diffused reflected pulse, and the amplitude is always constant. By automatically ordering a large pulse and amplifying the difference between this pulse and the diffusely reflected pulse, the system automatically eliminates distance measurement errors caused by the diffusely reflected pulse. This eliminates the need for high-voltage gain correction voltages, making it possible to miniaturize the circuit configuration and improve power supply efficiency. This has the effect of realizing a light receiving circuit for a laser distance measuring device that can easily detect fluctuations in laser reflected pulses, especially level drops, while completely eliminating the influence of diffusely reflected pulses.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an operating waveform characteristic diagram showing operating waveform characteristics of main parts in the embodiment of FIG. 1... Q-switch laser oscillator, 2... Group light transmission optical system, 3... Start pulse generation circuit, 4
... Pulse counting circuit, 5 ... Flip-flop circuit, 6 ... Light receiving optical system, 7 ...
... Light reception signal generation circuit, 8...22- ... Diffuse reflection pulse compensation signal generation circuit, 9. Group diffused reflection pulse compensation circuit, 10. Group reflection pulse amplitude discrimination circuit, 81...・Analog switch circuit, 82.9
1... Operational amplifier. 23-

Claims (1)

[Claims] In a laser ranging device that measures the distance to a laser target by determining the time difference between a laser emission pulse emitted from a laser oscillator and a laser reflection pulse received from the laser target using the laser emission pulse, In response to a diffused reflection pulse from molecules or particles contained in a propagation medium, a diffused reflection pulse compensation signal whose waveform is almost similar to the diffused reflection pulse and whose amplitude is always larger than that of the diffused reflection pulse is automatically generated for each input of the diffused reflection pulse. inputting the generated diffused reflection pulse compensation signal generation circuit, the diffused reflection pulse compensation signal generated by the diffused reflection pulse compensation signal generation circuit, and the laser reflection pulse accompanied by the diffused reflection pulse, and amplified the difference between these two manual forces; A diffused reflection pulse compensation circuit that compensates to remove the diffused reflection pulse, and a difference between the two human powers obtained by this diffused reflection compensation circuit, and this amplitude is compared with a laser reflected pulse discrimination threshold at a preset level. A reflected pulse amplitude discrimination circuit that extracts a laser reflected pulse from the laser target by performing amplitude discrimination, and prevents the laser distance measuring device from measuring pb due to the diffusely reflected pulse. Light receiving circuit of distance device.