JPS59142488A - Optical radar equipment - Google Patents

Abstract

PURPOSE:To detect exactly a range to a target object even in a fog, a snow, etc. by providing a sensitivity variable means which sets the receiving sensitivity of a reflected light signal to a low sensitivity at a prescribed level when light sending an optical signal increasing thereafter as time elapses. CONSTITUTION:A light sending device G emits pulse light Lt from a laser diode 12 in response to the supply of the transmitting trigger signal St of a period Tp from a control circuit F. On the other hand, a light receiving device H condenses the incident light containing reflected pulse light Lr. A photodetecting output making the reflected light Lr incident to a photodetector 17 is amplified by a pre-amplifier 18 to obtain the photodetecting signal Sr of an analog pulse and is inputted to the control circuit F. The control circuit F is constituted of a clock circuit 20, a time variable attenuating circuit 21, a wide band amplifier 22 and a signal processing circuit 23, and basing on a delay time extending from the time point of arrival of a trigger pulse Sd from the clock circuit 20 to the arrival time point of a photodetecting pulse Se, a range data DR corresponding to a range to a target object is formed by the processing circuit 23 and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical radar device that detects the distance to a target object using light.

2. Description of the Related Art Conventional optical radar devices include one shown in FIG. 1, for example.

This optical radar device consists of a control circuit X that generates and processes electrical signals, a light transmitter Y that modifies light of a certain wavelength into a sharp beam, and a condensed light beam reflected from an object that converts it into an electrical signal. It consists of a light receiver Z.

Then, as shown in FIG. 2, the pulse modulator 1 outputs a driving pulse signal a with a repetition period Tp (about 10.0 μs), a pulse width of 1-W (about 5 Qns), and a peak value Vo to the light transmitter Y. At the same time, a trigger signal generated at the same time is input to the signal processing circuit 3. The light emitting element 2 attached to the light transmitter Y is driven by high-speed pulse modulation by the drive pulse signal a, and the wavelength λ and pulse width Tw
η pulsed light Lt is generated. This pulsed light It is condensed by a lens 4, shaped into a beam having a divergence angle θt, and radiated forward.

Then, in the light receiver Z, the weak reflected pulsed light 1r from the object in front is condensed by a lens 5 with a large diameter and converged to its focal point.

The reflected pulsed light focused by the lens 5 is passed through an optical filter 6 that removes backlight noise (external light such as sunlight 9 and artificial lighting).
The light passes through the light and enters the light receiving surface of the light receiving element 7, which is mounted so that the light receiving surface is at the focal point of the lens 5, and is photoelectrically converted to produce a reflected light light receiving signal C in the form of a high-speed minute pulse.

The reflected light reception signal O is input to the broadband amplifier 8, amplified to a predetermined level, and after being shaped, becomes a high-speed pulse signal d, which is input to the signal processing circuit 3.

In the signal processing circuit 3, the propagation delay time τ of the reflected pulsed light 1-r with respect to the pulsed light Lt emitted from the light transmitter Y is detected based on the time relationship with the high-speed pulse signal d when a trigger signal is received, and the distance to the object is determined. R is calculated using the following formula.

r<=C-7:/2 (1) Here, the unit of R is m, the unit of τ is S, and C is approximately 3×108 m/s.

Applications of this optical radar device include ASCD (constant speed cruise control device), which was previously proposed by the applicant, and when used for these purposes, the optical radar device is configured. The transmitter Y and receiver Z are
The sensors are installed in the front grille of the vehicle and are used to detect the distance to preceding vehicles and obstacles in front of the vehicle.

By the way, when driving in fog, for example, as shown in FIG. 2, the reflected pulsed light 1-r reflected from the preceding vehicle
Before receiving s, reflected pulsed light 1rr scattered by fog particles is received.

The reflectance of fog is quite small compared to the reflectance of the vehicle body, but the reflected pulse light 11'f of the fog is reflected from a close distance, so its intensity is strong (the intensity of reflected light is proportional to the fourth power of the distance). (inversely proportional).

However, in the conventional optical radar device as described above, since the reception sensitivity of the reflected pulsed light 1r (determined by the characteristics of the light receiving element, the gain of the amplifier, etc.) is constant, the reflected pulsed light L1 due to the fog is A light reception signal df resulting from the reception of "[" is output, and the distance is determined based on the propagation delay time τt with respect to the light transmission pulse optical signal Lt. Such a phenomenon appears not only when fog occurs but also when it snows. This invention was made in view of the above circumstances, and its purpose is to calculate fI + snow cap as described above. Among other things, it is an object of the present invention to provide an optical radar device that can accurately detect the distance to a target object.

In order to achieve the above object, the present invention is characterized in that a sensitivity variable means is provided for setting the receiving sensitivity of the reflected optical signal to a predetermined low level at the time of transmitting light through the optical port and increasing it over time thereafter. It is something to do.

Embodiments of the present invention will be described in detail below with reference to FIG. 3 and the subsequent drawings.

FIG. 3 is a diagram showing an embodiment of the optical radar device according to the present invention.

The optical radar device shown in the same figure has a control circuit F, a light transmitter G, a light receiver 1-
It is composed of 1.

The light transmitter G emits pulsed light Lt from the laser diode 12 in response to being supplied with a transmission trigger signal St with a period Tl) from the control circuit F, and is located inside a cylindrical housing. , pulse drive circuit 11. A laser diode 12 and the like are housed therein, and a convex lens 13 is fitted into an opening at one end of the housing. The pulse drive circuit 11 has a configuration as shown in FIG.

The transmission trigger signal St output from the control circuit F is transmitted to the pulse drive circuit 1 via the coaxial connector 14.
1, the transistor Q+ in this pulse drive circuit 11 is turned on as the transmission trigger is triggered by the signal St, and accordingly, this transistor Q1
The charge of high voltage Va ('=150V) stored in the capacitor C1 connected to the collector of the transistor Q1 is supplied to the laser diode 12 inserted between the emitter of the transistor Q1 and ground.

At this time, a pulse current with a pulse width of several tens of ns and a peak value of several tens of A flows through the laser diode 12, and
, pulsed laser light (pulsed light Lt) with pulse width Tp=several tens of ns and peak output W is emitted. This pulsed light 1t is shaped by the convex lens 13 into a beam having a divergence angle of θ and is irradiated forward.

In addition, at one end of the cylindrical casing of the light receiver H, there is a
A convex lens 15 is fitted, and the convex lens 15 converts the pulsed light 1t emitted from the light transmitter G into reflected pulsed light 1-r, which is reflected back to a target object such as a preceding vehicle located ahead. Collects the incident light containing the

The incident light condensed by the convex lens 15 passes through an optical filter 16 such as an interference filter, backlight noise other than the reflected pulsed light 1r is removed, and is introduced into a light receiving element (such as a PIN photodiode) 17.

The light receiving output of the pulse voltage that is output when the reflected pulsed light L" is incident on the light receiving element 17 is amplified by a preamplifier 18 with a bandwidth of several tens of MH2 and a gain of 20 to 30 dB, and then the light receiving output of the pulse voltage L" is amplified by a preamplifier 18 with a bandwidth of several tens of MHz and a gain of 20 to 30 dB. The signal Sr is output via the coaxial connector 19 and input to the control circuit F.

As shown in FIG.
and a signal processing circuit 23.

The clock circuit 20 outputs a transmission trigger signal S [to be supplied to the pre-distribution optical device G], and this transmission trigger outputs a trigger pulse Sd with a pulse width of about 2 μs in synchronization with the signal St, and the trigger pulse 3d is The signal is supplied to the time variable attenuation circuit 21 and the signal processing circuit 23.

The time variable attenuation circuit 21 is connected to the light receiver 1-1 hl.
Input the received light signal 3r output from the received light signal 3r.
The output signal is outputted after being variably attenuated over time, and has a configuration as shown in FIG. 6, for example.

The light reception signal Sr is input to the depletion type FET Q2 via the buffer circuit 24, and the trigger pulse Sd is supplied to the slope signal generation circuit 26.

As shown in FIG. 7, the slope signal generating circuit 26 operates at a negative voltage =■ppol1~ at which the FET Q2 is in the pinch A) state until t1 immediately before the arrival of the trigger pulse Sd from the clock circuit 20. Thereafter, a predetermined period of time Ts (
Ts = 400 ns), the depletion type F
This is the supply voltage to the gate of ETQ2.

The received light signal 3r input to the FET' Q 2 is voltage-divided by the drain-source resistance RdS and the resistance R8 connected to the source side, and the input impedance Zi
≧1, and is outputted via the buffer circuit 25 with output impedance zo=50Ω (this output is referred to as the attenuated light reception signal Ss).

At this time, the drain-source resistance R of the FETQ2
dS is the time tI corresponding to the change in the slope signal Sg.
The resistance value changes linearly from (Rds=oo) to time t2 (RdS20).

As a result, as shown in FIG. 7, the time variable attenuation circuit 2
1, the signal transmission rate K(K-8s pulse height value/Sr pulse wave a(a)4; & increases approximately linearly from 0% to 100% between j+ and t2 above.

Note that the power supply V1 of the slope signal generation circuit 26 (-5V
) is configured so that it can be controlled on and off by a transistor Q3. That is, transistor Q
ON/0FF applied to the base of No. 3 (No. 8 sp is ゛H
'' level, the 4;ll;1t- transistor Q3 is turned on, and the power supply of the slope signal generation circuit 26 is turned off (
'-0V), and the voltage of the slope signal S9 is not varied and is always OV.

Then, the attenuated light reception signal SS output from the time variable attenuation circuit 21 is processed by a broadband amplifier (gain of 50 to 60 dB>
The signal is amplified while limiting its amplitude, and is also waveform-shaped to become a received light signal pulse Se of a predetermined level, which is supplied to the signal processing circuit 23.

The signal processing circuit 23 calculates a distance corresponding to the distance to the target object based on the delay time τ from the time hX when the trigger pulse 3d arrives from the background check circuit 20 to the time when the light reception signal pulse Se arrives. It is generated by forming data DR.

In the optical radar device configured as described above, due to the fog, the reflected light signal scattered by the fog appears before the reflected light signal 1rs from the target object, as shown in FIG. Assume that 1-rf is received. This fog reflected light signal 1-1”f is
Since the intensity of the optical signal reflected from a distance weakens, the waveform becomes a waveform whose amplitude gradually decreases as shown in the figure.

At this time, the light receiver 3r outputs a light reception signal 3r as shown in FIG. is compressed by the transmissibility characteristics.

Then, as shown in FIG. 3(e), the time-variable attenuation circuit 21 uniformly outputs the sheath reflected light reception signal 3rf with an extremely small amplitude, and this attenuated reception signal SS is sent to the broadband amplifier 22. As the light passes through, as shown in the figure ([), the component of the fog reflected light reception signal 3rr disappears, and only the reflected light reception signal 3rs component from the target object is obtained.

As a result, the signal processing circuit 23 generates a light reception pulse signal 3es based on the reflected light reception signal 3rs from the target object.
Based on this, the distance data DR is formed, making it possible to accurately detect the distance to the target object even in fog or snowfall.

Note that when a preceding vehicle is present at a short distance ahead in dense fog, the intensity of the reflected pulsed light from the preceding vehicle is sufficiently greater than the level of the sheath's foul light, so even if such attenuation control is performed, the actual It goes without saying that it is possible to detect a nearby preceding vehicle without any problem.

Next, FIG. 9 shows how the above optical radar device is connected to the vehicle's ΔSCD.
(Constant speed traveling control device) is a block diagram showing an example of application.

The ASCD 27 is activated by operating a predetermined switch, and automatically performs control to keep the vehicle running speed at a constant speed based on the output of the vehicle speed sensor, such as when driving on a highway. It is used when traveling at a constant speed for a long period of time.

The Δ5CD 27 shown in the figure is configured to vary the running speed in response to the speed instruction signal Sx supplied from the microcomputer 26.

Based on the distance data I) R supplied from the control circuit F, the micro combi coater 26 determines whether the distance to the preceding vehicle is greater than or equal to the safe distance #, and determines whether the distance between the vehicles is equal to or greater than the safe distance #. If the following distance is less than the safe distance, IA
The system outputs a speed instruction signal SX that reduces the speed and performs control to maintain a safe inter-vehicle distance.

Further, from this microcomputer 26, for example, at a period 10 times the period Tp of the transmission 1 to trigger signal St,
A 1'' level pulse is output and supplied to the 1-transistor Q3 in the time variable attenuation circuit 21 as an ON/OFF signal Sp.

As a result, the time variable attenuation circuit 21 stops the variable attenuation operation once every ten times the transmission trigger signal St occurs.

Therefore, when driving in fog, the distance data DR output from the control circuit F includes the distance data DRs to the target object and the difference between the fog and the distance data DRs. Distance data DR using 11 signals
f appears at a ratio of 9:1.

Therefore, the microcomputer 26 determines that the driver is driving in fog if the value of the manually entered distance data DR shows a significant change compared to the previously input distance data. , a driving instruction signal Sx at a speed of 111 (for example, 40 klll/11) faster than the normal driving speed is supplied to the ASCD 27 to ensure safe driving suitable for poor visibility conditions.

As explained in detail above, the optical radar device of the present invention is provided with a sensitivity variable means that sets the reception sensitivity of the reflected optical signal to a predetermined low level when transmitting the optical signal and then increases it over time. By doing so, it is possible to prevent the detection of the distance to the target object from being obstructed by fog, snowfall, etc. and from being unable to perform accurate distance detection, and it is possible to improve the distance detection performance.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional optical radar device, FIG. 2 is a waveform diagram showing its main output, and FIG. 3 is a diagram showing the configuration of an embodiment of the optical radar device according to the present invention. 4 is a circuit diagram showing a specific configuration of the pulse drive circuit in FIG. 3, FIG. 5 is a block diagram showing a specific configuration of the control circuit in FIG. 34,
FIG. 6 is a block diagram showing the specific configuration of the time variable attenuation circuit 21 in FIG. 5, FIG. 7 is a dimensional waveform diagram showing the operation of the time variable attenuation circuit, and FIG. 8 is shown in FIG. FIG. 9 is a waveform diagram showing the operation of the optical radar device, and FIG. 9 is a block diagram showing an example of application of the optical radar i@. F... Control circuit G... Light transmitter 1-1... Light receiver L (... Light transmission signal L r... Reflected light signal 21... Time variable attenuation circuit 26... Slope signal generation circuit Q2... Depletion type FET Patent applicant Nissan Motor Co., Ltd. Figure 4 Figure 5, F Figure 6 Figure 7

Claims (1)

[Claims] (1) While transmitting a pulsed optical signal, receiving a reflected optical signal from a target object, and detecting the distance to the target object based on the relationship between the transmitted and received optical signals (in an optical radar device; An optical radar device characterized in that it is provided with a variable sensitivity means (1c) for setting the reception sensitivity of an optical signal to a predetermined low level at the time of transmitting the optical signal and increasing it over time thereafter.