JPH04307387A - Range finder device - Google Patents

Abstract

PURPOSE:To prevent an erroneous measurement from being made even at a short distance by changing a bias of an avalanche diode (APD) which performs a photoelectric conversion of light emitted from a laser oscillator and reflected by a target and then returned with an output of a mirror integration equipment. CONSTITUTION:A sensitivity of an APD 4 is changed by allowing a bias voltage to be varied with an output of a mirror integration equipment 9 and sensitivity becomes small at a short distance. Therefore, even if a strong reception light enters, an output of a trans-impedance amplifier 5 is not saturated and does not output any double pulses. Then, laser beam is emitted from a laser oscillator 1 and a time from that moment to a time when a target receives the reflected light is counted by a counter 10, thus enabling a distance to be known without resulting in an erroneous distance measurement.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improvement in a distance measuring device using a laser.

0002

2. Description of the Related Art FIG. 5 is a configuration diagram showing a conventional distance measuring device, in which 1 is a laser oscillator, 2 is a transmitting optical system, 3 is a receiving optical system, 4 is an APD (avalanche photodiode), and 5 is a transmitting optical system.
is a transimpedance amplifier, 6 is an AGC (auto gain control) amplifier, 7 is an amplifier, 8 is a photodetector, 9 is a Miller integrator, and 10 is a counter.

In FIG. 5, when a laser oscillator 1 oscillates a laser beam, a photodetector 8 generates an electric signal (start pulse) at the timing of laser oscillation, and this signal causes a counter 10 to start counting. On the other hand, the light emitted from the laser oscillator 1 irradiates the target via the transmission optical system 2. The laser beam reflected by the target and returned is sent to the receiving optical system 3 via APD.
The light is focused on the detection surface 4 and converted into a current signal. This current signal is converted into a voltage signal by a transimpedance amplifier 5, and further amplified by an AGC amplifier 6 and an amplifier 7, and an electric signal corresponding to the light reflected from the target (
stop pulse). This stop pulse causes the counter 10 to stop counting. In other words, the counter 10 measures the time difference from the moment the laser beam is emitted to the moment the reflected light from the target is received. Since the speed of light C is constant, this time difference t is proportional to the distance R to the target to be measured and is expressed by equation (1), so the distance R can be known. R=Ct/2 (1)

0004
On the other hand, the signal strength (stop pulse strength) of the output of the amplifier 7 is as shown in Fig. 6 a for distance measurement, and the backscatter from rain or aerosol from close range is as shown in Fig. 6 b.
Therefore, if a stop pulse is detected using a fixed threshold value such as c, backscatter from rain or aerosol will be incorrectly measured at close range. Therefore, Figure 5
If the gain of the AGC amplifier 6 is lowered at short distances and the threshold value for stop pulse detection is changed as shown in d in Figure 6, backscatter from rain or aerosol will not cause erroneous distance measurement, and the signal (stop pulse) will not be detected. It can be done by distance. This method is called TPG (Time Program
mmed Gain).

Conventionally, to apply TPG, an AGC amplifier 6 and a Miller integrator 9 are used as shown in FIG. The mirror integrator 9 starts operating from the moment the photodetector 8 issues a start pulse, and the voltage waveform as shown in e in FIG.
Add to gain control input of C amplifier 6. AGC
The gain of the amplifier 6 is lower as the voltage of the gain control input is higher, so the gain of the AGC amplifier 6 is as shown in f in Fig. 7.
It becomes as follows and operates as TPG.

[0006]

[Problem to be solved by the invention] The conventional A as described above
In a distance measuring device using a GC amplifier 6, when a short distance is measured, there is a strong received echo, and the output of the transimpedance amplifier 5 is saturated, generating a double pulse as shown in g in FIG. If this double pulse is detected using a threshold value such as h in Figure 8, it will be detected as a stop pulse from the actual target and another one.
Generates two stop pulses. In other words, there was a drawback of incorrect distance measurement.

The present invention has been made to solve the above-mentioned problems, and provides a distance measuring device that does not erroneously measure distances at short distances.

[0008]

[Means for Solving the Problems] In the distance measuring device according to the present invention, the AGC amplifier 6 is not used, and the bias of the APD 4 is changed by the output of the Miller integrator 9.

Further, the distance measuring device according to the present invention does not use the mirror integrator 9 that changes the bias of the APD, but instead includes an optical modulator between the receiving optical system 3 and the APD 4, and a drive circuit for driving the optical modulator. It is something.

0010

[Operation] This invention applies the bias of the APD to the mirror integrator 9.
Since it is controlled by the output of APD 4, the sensitivity of APD 4 changes over time and can be used for TPG. Furthermore, since the TPG lowers the sensitivity of the APD at short distances, the transimpedance amplifier 5 will not become saturated even if a strong received echo is received. In other words, the stop pulse does not become a double pulse at short distances, and there is no possibility of erroneous distance measurement.

Furthermore, when an optical modulator and a drive circuit are used, the present invention can be used in a TPG because the effective sensitivity of the APD, which is the product of the transmittance of the optical modulator and the sensitivity of the APD, changes over time. Furthermore, since the transmittance of the optical modulator decreases at short distances, even if a strong received echo enters, the effective sensitivity of the APD decreases, so the transimpedance amplifier will not become saturated and generate a double pulse.

0012

[Example] Example 1 Figure 1 is a block diagram showing an example of this invention.
-10 are the same as the conventional one. In FIG. 1, the operation of calculating the distance by counting the time with the counter 10 from the moment the laser beam is emitted from the laser oscillator 1 to the moment the beam is reflected by the target is exactly the same as in the conventional method. However, T.P.G.
The function is composed of APD 4 and mirror integrator 9, and as explained later, the sensitivity of APD 4 decreases at short distances, so T
Can be used as PG.

The operation of the TPG in the case of FIG. 1 will now be explained. The sensitivity of APD4 shows bias dependence as shown in FIG. Therefore, if the bias voltage of the APD 4 is changed by the output of the Miller integrator 9 as shown in a of FIG.
It can be used as a TPG with sensitivity fluctuations such as.

Furthermore, since the sensitivity of the APD 4 decreases at short distances, the output of the transimpedance amplifier 5 does not become saturated even when strong received light enters, so that no double pulses are generated and no erroneous distance measurements occur. To give concrete numerical values, while the APD of conventional distance measuring devices had a constant sensitivity of 34 A/W, in the case of this invention, the sensitivity was 0.34 A/W at short distances.
Therefore, even if there is a strong input light from a short distance, the light will be reduced to about 1/100, so that the transimpedance amplifier 5 will not be saturated.

Embodiment 2 FIG. 4 shows another embodiment of the present invention. 3, 4, and 8 are in Figure 1
is the same as Although omitted in Figure 4, 1 in Figure 1
, 2, 5, 7, and 10 are also configured in the same manner. An optical modulator 11 is provided between the receiving optical system 3 and the APD 4,
This is driven by a drive circuit 12. In this case as well, the output of the drive circuit 12 is used to change the transmittance of the optical modulator 11, that is, the effective sensitivity of the APD, and is used for the TPG. Therefore, the transmittance of the optical modulator 11 at a short distance, that is, the effective sensitivity of the APD 4,
is small, so the transimpedance amplifier 5 will not be saturated even if there is a strong optical input from a short distance.

[0016]

[Effects of the Invention] As shown above, the present invention changes the bias of the APD using the output of the mirror integrator to change the sensitivity of the APD, or changes the light transmittance by driving the optical modulator with a drive circuit. In this way, since TPG is realized, the output of the transimpedance amplifier does not saturate, and double pulses are not generated, which has the effect of preventing erroneous distance measurement.

[Brief explanation of the drawing]

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

FIG. 2 is a diagram showing the bias voltage dependence of the sensitivity of the APD used in the present invention.

FIG. 3 is a diagram showing temporal changes in the output voltage of the Miller integrator and the sensitivity of the APD used in the present invention.

FIG. 4 is a configuration diagram showing a second embodiment of the present invention.

FIG. 5 is a configuration diagram showing a conventional distance measuring device.

FIG. 6 is a diagram showing temporal changes in signal strength and threshold value of a distance measuring device.

FIG. 7 is a diagram showing temporal changes in the output voltage of a mirror integrator and the gain of an AGC amplifier in a conventional distance measuring device.

[Fig. 8] Diagram showing erroneous distance measurement due to double pulses of a conventional distance measuring device

[Explanation of symbols]

1 Laser oscillator 2 Transmission optical system 3 Receiving optical system 4 APD 5 Transimpedance amplifier 7 Amplifier 8 Photodetector 9 Miller integrator 10 Counter 11 Optical modulator 12 Drive circuit

Claims (2)

[Claims] Claim 1: A laser oscillator, a transmission optical system for irradiating the output light of the laser oscillator onto a target, and a transmission optical system that collects the output light of the laser oscillator that exits from the transmission optical system and is reflected from the target and returns. an avalanche photodiode (APD) that converts this received light into a current signal, a transimpedance amplifier that converts the current signal of this APD into a voltage signal, and an output voltage of this transimpedance amplifier. An amplifier that amplifies the signal, a photodetector that monitors the time when light is emitted from the laser oscillator and outputs an electrical signal, and counting starts with the electrical signal at the time monitored by this photodetector, and counting is performed using the output of the amplifier. A distance measuring device comprising a counter for stopping the APD, characterized in that a mirror integrator is provided between the photodetector and the APD so as to change the bias voltage of the APD over time. 2. A laser oscillator, a transmission optical system for irradiating the output light of the laser oscillator onto a target, and a transmission optical system that collects the output light of the laser oscillator that exits from the transmission optical system and is reflected from the target and returns. an avalanche photodiode (APD) that converts this received light into a current signal, a transimpedance amplifier that converts the current signal of this APD into a voltage signal, and an output voltage of this transimpedance amplifier. An amplifier that amplifies the signal, a photodetector that monitors the time when light is emitted from the laser oscillator and outputs an electrical signal, and counting starts with the electrical signal at the time monitored by this photodetector, and counting is performed using the output of the amplifier. A distance measuring device comprising a counter for stopping the APD, comprising an optical modulator provided between the receiving optical system and the APD, and a drive circuit that changes the transmittance of the optical modulator over time. distance measuring device.