JPH0821872A - Laser radar device - Google Patents

Abstract

PURPOSE:To provide a laser radar capable of controlling the received light quantity in a short response time and preventing the saturation of a light detector by controlling the number of blackened regions among multiple split regions of the transmission surface of a liquid crystal. CONSTITUTION:The reflected light from an object 11 is collected by a transceiver optical system 2 and fed to a light attenuator 4a. The reflected light transmitting the light attenuator 4a is fed to a light detector 5 for photoelectric transfer. An arriving time detecting circuit 6 calculates the reciprocating time of a laser beam and calculates the distance from a device to the object 11. A light level detecting circuit 6 judges whether there is a light input of a fixed level or above or not and outputs the judged result to an attenuation quantity control circuit 8. Light attenuators 4a, 4b are provided for multiple split regions of the light transmission surface, multiple split regions are controlled to on or off based on the control signals from the attenuation quantity control circuit 8 respectively, and the attenuation quantity is set by the ratio of the split regions controlled to off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser radar device, and more particularly to a laser radar device that measures a distance to an object by using laser light and obtains three-dimensional information from the distance and the pointing direction.

[0002]

2. Description of the Related Art In a conventional laser radar device, when a distance to a desired object is measured by using a laser beam, it is assumed that a signal from a long distance is also received, and such a long distance is detected. A laser beam having an intensity capable of obtaining a sufficient reception input is used. However, if an attempt is made to measure the distance of an object at a short distance with the laser light of that intensity, the input level becomes too strong and the photodetector or the like is saturated, so that accurate distance measurement cannot be performed.

Therefore, in the conventional laser radar device,
When the approximate value of the distance to the object to be measured is known in advance, the saturation of the photodetector can be suppressed or the saturation of the photodetector can be prevented by reducing the intensity of the emitted laser light. If the input level changes within the range, CFD
(Constant Fraction Discri
It is known that a measurement is performed using a (minor) circuit to detect a peak of a received waveform regardless of the level.

Further, in the conventional laser radar device for measuring the distance to a moving object while tracking the moving object, the distance is gradually changed, and therefore the amount of attenuation to be adjusted at one time is small. When there is no time limit, such as when measuring in only one direction, the photodetector can be controlled by limiting the amount of light received using the camera's automatic diaphragm based on the input level at the previous measurement. It is also known to prevent saturation of.

Further, among conventional laser radar devices, there is known a device which limits the amount of received light by a mechanical method in order to prevent the above-mentioned photodetector from being saturated. Examples of this mechanical method include, in addition to the above automatic diaphragm, for example, a method of arranging and rotating a number of filters having different attenuation amounts on the circumference, a method of rotating a filter whose attenuation amount changes gradually, and A method of rotating one of the polarizers to change the transmission amount, a method of blocking a part of the light receiving surface of the photodetector with a knife edge, and the like have been considered.

Further, among the conventional laser radar devices, there is known a device which limits the amount of received light by an electronic method in order to prevent the above-mentioned photodetector from being saturated. This electronic method includes, for example, a method of inserting an element whose polarization state is changed by an electro-optical effect between two polarizers, and a photodetector which transmits the liquid crystal by changing the voltage applied to the liquid crystal. A method of adjusting the amount of light incident on is considered.

In the latter laser radar device using the latter liquid crystal, a control signal having an amplitude proportional to the direct current component of the output signal of the photodetector is generated by the attenuation control circuit and applied to the plate-shaped liquid crystal. By changing the amount of attenuation of the liquid crystal passing through according to the amplitude of the control signal, the background noise of the light passing through the liquid crystal and entering the photodetector does not fluctuate much even if the background noise of the incident light increases significantly. To prevent saturation of the photodetector (Japanese Patent Laid-Open No. 59-65279).

[0008]

However, among the conventional laser radar devices described above, those having means for reducing the intensity of the emitted laser beam are used when the approximate value of the distance to the object is not known in advance. Saturation of the photodetector cannot be suppressed, or a sufficient amount of received light cannot be obtained. In addition, CFD (Constant Fraction D)
It is not possible to prevent saturation of the photodetector by using an iscriminator) circuit.

Further, the conventional laser radar device which prevents saturation of the photodetector by a mechanical method has a slow response and
There is a problem that the distance may change abruptly, such as when three-dimensional information is obtained by measuring the distance while performing two-dimensional scanning, and it is not suitable for the purpose of measuring the distance at high speed.

Further, the conventional laser radar device for preventing the saturation of the photodetector by an electronic method can control the attenuation amount of the light incident on the photodetector at a high speed, and the light receiving side. Not only is it applicable to the laser transmitting side, but there is a problem that an expensive control circuit is required and the size (particularly length) increases.

Further, among the conventional laser radar devices for preventing the saturation of the photodetector by the above-mentioned electronic method, in the former device in which an element having an electro-optical effect is inserted between two polarizers. , If there is a slight difference in the voltage applied to the element that has the electro-optical effect, the amount of attenuation may change significantly.Therefore, it is not sufficient to set the amount of attenuation in advance, but based on the intensity of light actually transmitted. Need to control. However, this control is difficult with laser light having a short pulse width.

On the other hand, of the conventional laser radar devices that prevent the saturation of the photodetector by the electronic method described above, in the latter device using liquid crystal, the applied voltage and the transmittance characteristic of the liquid crystal are shown in FIG. As shown in A), the variable range in which the applied voltage and the transmittance of the liquid crystal change correspondingly is narrow, and the relationship between the applied voltage and the transmittance may change due to temperature conditions and the like. Even if the voltage corresponding to the required transmittance is applied to the liquid crystal based on the data measured under a certain condition, the transmittance as set value is not always obtained. That is, it is difficult to regulate the amount of transmitted light of the liquid crystal by the voltage applied to the liquid crystal.

The present invention has been made in view of the above points,
Instead of controlling the amount of attenuation by the voltage applied to the liquid crystal,
An object of the present invention is to provide a laser radar device capable of preventing the saturation of a photodetector by controlling the amount of received light with a fast response time by controlling the number of blackenings of a plurality of divided areas that divide the transmission surface of liquid crystal. And

[0014]

In order to achieve the above object, the present invention provides a laser oscillator for intermittently emitting a laser beam and a laser beam emitted from the laser oscillator at a predetermined beam divergence angle into a space. , A transmission / reception optical system that collects incident light from the outside, a photodetector that photoelectrically converts the received light and outputs a received light signal, and an external device based on the received light output signal of the photodetector and the output signal of the laser oscillator Arrival time detection circuit that calculates at least the arrival time to the object, the optical path of the laser light that enters the transmission / reception optical system from the laser oscillator, and the light that is received and condensed by the transmission / reception optical system and that enters the photodetector. An optical attenuator made of liquid crystal provided in at least one of the optical paths, an optical level detection circuit that detects the level of the received light output signal of the photodetector, and an optical attenuator reduction based on the output signal of the optical level detection circuit. An attenuation amount control means for setting and controlling the amount, and the light transmitting surface of the optical attenuator is divided into a plurality of divided regions, and each of the plurality of divided regions to the control signal from the attenuation amount control means. On the basis of this, the amount of attenuation is set to ON or OFF, and the attenuation amount is set according to the ratio of the divided regions that are controlled to be OFF of the plurality of divided regions.

Further, the present invention provides a calibration light source which emits calibration light and makes it enter the optical path from the transmission / reception optical system to the photodetector, and the attenuation amount control means controls the light reflected by the object. Drive the calibration light source during the period when it is not incident,
The total amount of attenuation is obtained from the level of the output light reception signal of the photodetector obtained at that time, and the amount of attenuation of the optical attenuator is corrected.

Further, according to the present invention, the output light receiving signal of the photodetector is attenuated by an attenuation amount according to the input control voltage and is output to the arrival time detection circuit, and the output signal of the voltage control attenuator is Outputs the control voltage to the voltage control attenuator so that the output signal of the voltage control attenuator is a constant level according to the output detection signal of the level detection circuit which is branched and input to detect the input level. And a control voltage generating circuit for controlling the attenuation amount.

[0017]

According to the present invention, the received light is incident on the photodetector via the optical attenuator made of liquid crystal, or the light from the laser oscillator is emitted via the optical attenuator, and is detected by the optical level detection circuit. Based on the level of the signal, the attenuation amount control means controls each of the plurality of divided regions of the optical attenuator to be turned on or off, and the attenuation amount is set by the ratio of the divided regions which are controlled to be off of the plurality of divided regions. Therefore, even if there is some temperature fluctuation, the transmittance of each divided area of the liquid crystal can be controlled accurately, and faster than the mechanical method.
Therefore, the amount of attenuation can be controlled accurately and at high speed.

In the present invention, the attenuation control means drives the calibration light source during the non-incident period of the light reflected by the object,
Since the total amount of attenuation is calculated from the level of the received light output signal of the photodetector obtained at that time and the amount of attenuation of the optical attenuator is corrected, the pulse laser is transmitted to measure the distance to the object. Even in such a device, the actual attenuation amount of the optical attenuator can be accurately controlled to a desired set value.

Further, according to the present invention, the output light reception signal of the photodetector is input to the level detection circuit via the voltage control attenuator to detect the level, and the output signal of the voltage control attenuator is detected according to the level detection signal. The control voltage generation circuit controls the amount of attenuation of the voltage-controlled attenuator so that the output level is constant, so that the level of the received light output signal from the photodetector is not changed and the level is output to the arrival time detection circuit. can do.

[0020]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of an embodiment of the present invention.
As shown in the figure, in this embodiment, a laser oscillator 1 that emits laser light, a transmission / reception optical system 2 that condenses received laser light with a transmitted laser light having a certain beam divergence angle, and optical scanning for scanning Arrival time for detecting the arrival time to the object 11 from the device 3, the optical attenuator 4a that attenuates the received laser light, the photodetector 5, and the output detection signal of the photodetector 5 and the output signal of the laser oscillator 1. A detection circuit 6, a light level detection circuit 7 for detecting the light level of the photodetector 5, an attenuation amount control circuit 8 for electronically controlling the attenuation amount of the optical attenuator 4a, and a central processing unit (CPU) 9. It is composed of

Further, a calibration light source 10 is provided as needed. Further, instead of the optical attenuator 4a or together with the optical attenuator 4a, an optical attenuator 4b for attenuating the transmission laser light of the laser oscillator 1 may be provided.

The present embodiment has the same structure as the conventional device except for the optical attenuators 4a and 4b, the optical level detection circuit 7, the attenuation control circuit 8 and the calibration light source 10. In addition, the present embodiment uses a liquid crystal for the optical attenuator 4a, and has a first feature in its configuration and control method. Further, the second feature is that the total attenuation is accurately set using the calibration light source 10.

Next, the operation of this embodiment will be described.
The pulsed laser light that is intermittently oscillated and output from the laser oscillator 1 is radiated into space at a predetermined beam divergence angle by the transmission / reception optical system 2. At this time, depending on the situation, the optical scanning device 3
May be scanned by. The pulsed laser light emitted into the space is reflected by the object 11, and the reflected light is condensed by the transmission / reception optical system 2 and is incident on the optical attenuator 4a. When the optical scanning device 3 is used at the time of transmission, it passes through this again and then enters the transmission / reception optical system 2.

The reflected light that has passed through the optical attenuator 4a enters the photodetector 5 and is photoelectrically converted. The photodetection signal (light reception signal), which is an electric signal extracted from the photodetector 5, is supplied to the arrival time detection circuit 6 and is also supplied to the light level detection circuit 7.

The arrival time detection circuit 6 starts counting the clock signal of a constant cycle from the time when the start signal synchronized with the emission time of the pulsed laser light is supplied from the laser oscillator 1, and the received light signal of a certain level or higher is received. The round trip time of the laser light is calculated based on the count value of the counter that stops counting when supplied from the photodetector 5, and the round trip time is halved to detect the arrival time to the object 11. Then, the arrival time is further multiplied by the speed of light to calculate the distance from the device to the object 11.

Further, the light level detection circuit 7 judges whether or not there is a light input above a certain level (a level slightly lower than the saturation of the photodetector 5), and the judgment result is sent to the attenuation amount control circuit 8. Output. The attenuation amount control circuit 8 outputs a control signal for electronically controlling the attenuation amount of the optical attenuators 4a and / or 4b to the optical attenuators 4a and / or 4b based on the input determination result. In practice, the above control signal often goes through the CPU 9 for optimal control.

Further, when the transmitted laser light is attenuated by the optical attenuator 4b, it is necessary to consider damages and the like due to the laser light of high intensity.

One of the features of this embodiment is that liquid crystal is used for the receiving optical attenuator 4a. However, when there is no risk of damage due to laser light, the transmitting optical attenuator 4 is used.
A liquid crystal may be used for b. The liquid crystal is an element that can control the voltage applied to the liquid crystal based on the signal that detected the received light level last time or several times before, and change the light transmittance as shown in FIG. 2 (A). is there. As used in television receivers and the like, liquid crystal has the feature that the transmittance can be controlled at a much higher speed than mechanical methods, and since it has a small thickness, it can be miniaturized. .

The relationship between the applied voltage and the transmittance of the liquid crystal is shown in FIG.
As shown in (A), the transmittance changes in accordance with the applied voltage within the voltage range shown by b to c, so that the transmittance is changed by simply controlling the applied voltage within this voltage range. be able to. However, assuming that it is used in a wide temperature range, it is possible that the above-mentioned applied voltage vs. transmittance characteristics may shift depending on the temperature, so the transmittance should be estimated only by the applied voltage without directly monitoring the transmitted light amount. Is simple but requires attention.

In the present embodiment, as a method of removing the influence of the shift of the applied voltage-transmittance characteristic due to the above temperature and reliably determining the attenuation amount (transmittance), the applied voltage-transmittance shown in FIG. In the rate characteristics, set the voltage at which the characteristic changes at both ends disappear, that is, the voltage at which the transmittance is always minimum and maximum even if there is a slight temperature change, and then turn on the liquid crystal. , OFF control is performed. In FIG. 2 (A), voltage a is an off voltage whose transmittance is controlled to be minimum even if there is some temperature fluctuation, and voltage d is controlled to be maximum even if there is some temperature fluctuation. ON voltage.

However, if the applied voltage is simply controlled to one of the on-voltage and the off-voltage, the transmittance is maximized or minimized, and the fine attenuation cannot be controlled. Therefore,
In this embodiment, the liquid crystal surface of the liquid crystal is divided into a plurality of grid-like regions as shown in FIG. 2B, or a plurality of radial regions as shown in FIG. An ON voltage or an OFF voltage is applied to each of the divided regions to individually control the transmittance to the maximum or minimum.

In FIGS. 2B and 2C, the white portion of the divided area indicates the liquid crystal area in which the ON voltage is applied and the transmittance is maximum (ON state), and the black portion indicates the OFF voltage. The liquid crystal region which is in the minimum transmittance state (off state) by being applied, that is, the divided region which is blackened is shown.

In the present embodiment, the number of blackened divided areas is controlled according to the required transmittance (attenuation). For example, if the total number of divided areas is 1
If it is 000, the black transmission number is 999 when the black transmission number is 0.
It is theoretically possible to adjust the amount of attenuation in 1/1000 units without being affected by temperature fluctuations and the like.

It is also possible to adjust the amount of attenuation in a larger range without increasing the total number of divided regions to be controlled, by making the sizes of the plurality of divided regions not the same, but by adding sizes to each other. Is.

Further, in this embodiment, since the liquid crystal surface is divided into a plurality of areas and each of the areas is controlled to be turned on / off, there is a feature that a light flux portion for attenuating the transmitted / received light can be selected. This will be described in detail with reference to FIG. In FIGS. 9A to 9E, the same components are designated by the same reference numerals.

When different optical systems are used for transmission and reception, as shown in FIG. 3 (A), the laser light emitted from the laser oscillator 1 forms a lens 15 which constitutes a part of the transmission / reception optical system 2. When the reflected light, which is radiated into the space through the light and reflected from the object, is focused by the lens 16 forming a part of the transmission / reception optical system and is incident on the photodetector 5, the laser radiated at the transmission beam divergence angle α The portion I where the light flux and the reflected light flux incident at the reception viewing angle β overlap can be received, but laser light is emitted in the short range on the lens 15 and 16 sides from the position II where they do not overlap. It is generally known that a so-called parallax occurs in which the received position and the received visual field do not match.

As a countermeasure, the ends of the transmission optical system and the reception optical system are generally brought as close as possible to each other.
There are certain limits. Further, as shown in FIG. 3B, an automatic diaphragm 17 is arranged between the lens 16 and the photodetector 5 to cut the received light from the peripheral portion and transmit it to the photodetector 5. In the method of reducing the amount of light, the center of the received light does not change, but the point where the ends of the transmission optical system and the reception optical system overlap is farther than in the case where the automatic diaphragm 17 is not provided, as indicated by III in FIG. 3B. This point III because it occurs in the position
At a shorter distance, the reception field of view and the position where the transmission light beam hits do not match, and the light cannot be received.

On the other hand, in this embodiment, as shown in FIG. 3C, the liquid crystal surface of the receiving optical attenuator 4a is divided into a plurality of divided areas in which the liquid crystal surface is sequentially blackened from the end opposite to the transmitting optical system. Since a part 18 composed of a plurality of divided areas on the side close to the transmission optical system can be used as a transmission part, the end of the transmission optical system can be formed until the transmission part 19 is composed of one last divided area. Therefore, it is not necessary to change the distance between the ends of the receiving optical system, and the field of view and the position where the laser light strikes can be matched even at a short distance. That is, in this case, the effect of parallax can be minimized.

On the other hand, contrary to the above, the receiving optical attenuator 4
As shown in FIG. 3D, the liquid crystal surface of a may be sequentially blackened from the end of the transmission optical system to the opposite end to form a blackened region 21 and a transmissive region 22. In this case, when measuring the distance of a relatively distant object through the glass window, the device may conventionally malfunction due to the reflected light from the glass window. As a result, the parallax can be intentionally increased with respect to the reflected light from the glass window at the position indicated by V in FIG. 3 (E), and the portion indicated by IV of the reflected light can be cut. Can be avoided.

In FIG. 3 (E), the optical attenuator 4a is used.
Although not shown, it is provided between the lens 16 and the photodetector 5 or on the front surface of the lens 16.

Further, even in the so-called coaxial type structure in which the transmitted light is emitted from the central portion of the receiving optical system, the optical attenuator having the radial pattern divided regions shown in FIG. 2C as the optical attenuator 4a. By sequentially cutting the light from the peripheral part or from the center part, the matching points of the visual field are adjusted,
The same effect as described above can be obtained.

When used outdoors, even if there is a light-shielding cylinder, sunlight may hit a part of the light-receiving lens.
In this case, an unnecessary current flows through the photodetector, which may cause saturation of the photodetector, etc. However, by blackening the portion of the optical attenuator 4a through which the light from the portion exposed to sunlight passes. , The effect can be minimized. In order to eliminate the influence of disturbance light from an unpredictable direction and the influence of non-uniformity of the sensitivity of the photodetector, the blackening pattern of the optical attenuator 4a is randomly arranged and changed over time to average the input. It becomes possible.

There is a limit to the light blocking characteristic of liquid crystal,
It may be possible that the total level fluctuation of the received light due to the distance change cannot be fully supported.Therefore, in the actual device, the voltage applied to the photodetector, which is a known means for suppressing the received light level, is changed to change the multiplication rate It is desirable to use a means for reducing (photomultiplier tube, avalanche photodiode, etc.) together.

In this way, in the present embodiment shown in FIG. 1, the optical attenuator 4a and / or 4b is controlled by the attenuation amount control circuit 8.
Although the saturation of the photodetector 5 is prevented by controlling the attenuation amount of, the present embodiment further uses the calibration light source 10 to accurately set the total attenuation amount.

That is, the number of blackened areas (the number of blackened areas) in the large number of divided areas of the liquid crystal surface of the optical attenuator 4a.
Is recorded in the controlling CPU 9 or the like,
Although there is no particular problem, even if the applied voltage to the photodetector 5 is measured or set, the multiplication ratio of photoelectrons to this may change. Further, it is difficult to accurately grasp the relationship between the amount of attenuation of the voltage control attenuator and the voltage and to appropriately control the light reception signal level.

Further, if it is a continuous signal, it is easy to form a feedback loop to make the level of the received light signal constant, but in the present embodiment, pulsed laser light is emitted to measure the distance to the object 11. Since the laser light only enters the transmission / reception optical system 2 for a short time, the output signal of the photodetector 5 is almost zero even if an attempt is made to obtain a direct current component. As a result, it is not possible to easily create the equivalent of the automatic gain control signal.

Therefore, it is desirable to hold a voltage corresponding to the intensity of the received laser light by using a peak hold circuit or the like and feed it back as a signal with a long pulse width (close to direct current), but various problems in practical use. There is.

Therefore, in this embodiment, the intensity of the reception level is detected by the optical level detection circuit 7, and the detection information is C
Notify PU9. The CPU 9 not only calculates the required attenuation amount based on the received light level information and sets the transmission amount of the optical attenuator 4a in the attenuation amount control circuit 8, but also adjusts the voltage applied to the photodetector 5 as necessary. Voltage setting and the like are performed via the attenuation amount control circuit 8.

Further, the CPU 9 drives the calibration light source 10 until the next pulse laser light arrives after receiving the pulse laser light, and emits the light emitted from this through the optical attenuator 4a. The error between the actual attenuation amount of the optical attenuator 4a and the set value of the voltage applied to the photodetector 5 is determined on the basis of the photodetection signal which is incident on the detector 5 and further input through the optical level detection circuit 7. to correct.

Since the period during which light is output from the calibration light source 10 is long, for example, about 10 μs to 100 μs, the pulse width of the calibration light source 10 is, for example, 10 to 20 ns like the laser oscillator 1. A device that outputs an extremely short pulsed laser beam cannot be used, and for example, a light emitting diode or a laser diode having a slow response is used.

As described above, by providing the above-mentioned calibration light source 10, an error does not occur between the photoelectron multiplication ratio of the photodetector 5 and the set value. As a result, in this embodiment, it is possible to set the optimum attenuation amount in the optical attenuator 4a or apply the optimum voltage to the photodetector 5.

In the above embodiment, the main purpose of attenuating the light by the optical attenuators 4a and / or 4b is as follows.
This is to prevent the photodetector 5 from being saturated, and the degree of attenuation is sufficient to prevent the saturation, but this attenuation alone cannot handle all large changes in the received light level. Therefore, in the case where all the large changes in the received light level are dealt with, it is necessary to provide a level control circuit for further attenuating the output received light signal of the photodetector 5 to keep the received light level constant.

As the level control circuit, the photodetector 5 is used.
Gain control of the amplifier for amplifying the output light reception signal of the amplifier is variably controlled so that the output signal of the amplifier becomes a constant level (AGC: Automatic Gain Control).
Control is considered first, but in this method, not only the gain of the amplifier but also the phase characteristic may change due to changing the bias voltage. In particular, in the case of amplification of a thing having a fast rise characteristic such as a pulse laser, even if an amplifier with a wide band is used, it will be used at a frequency close to the limit, but the frequency region is a region where the phase characteristic changes greatly. Therefore, distortion or the like of the amplified waveform occurs.

Therefore, in another embodiment of the present invention, a circuit having the structure shown in the block diagram of FIG. 4 is used as the level control circuit. As shown in the figure, this level control circuit is composed of an amplifier 31, a voltage controlled attenuator 32, a level detection circuit 33 and a control voltage generation circuit 34, and is provided between the photodetector 5 and the arrival time detection circuit 6. It is provided in.

To explain the operation of this level control circuit, the received light signal output from the photodetector 5 of FIG. 1 is amplified by the amplifier 31 of constant gain shown in FIG. Supplied. The voltage control attenuator 32 has a configuration in which the amount of attenuation is controlled by the control voltage from the control voltage generation circuit 34, and outputs its output signal to the arrival time detection circuit 6 of FIG. 1 and the level detection circuit of FIG. 33
Supply to

The level detection circuit 33 detects the level of the input signal and inputs the detection signal to the control voltage generation circuit 34 to generate a control voltage corresponding to the detection signal level.
The output control voltage of the control voltage generation circuit 34 is supplied to the voltage controlled attenuator 32, and the attenuation amount is controlled so that the level detected by the level detection circuit 33 becomes constant.

As a result, only the level can be controlled without changing the phase of the received light signal, and the arrival time detection circuit 6 of FIG.
Can be output to. The CPU 9 sets the voltage applied to the voltage controlled attenuator 32 via the attenuation amount control circuit 8 as necessary.

In the above embodiment, when the pulse laser is used, based on the reception level of the previous time or several times,
It is intended to make the reception level constant, and normally it can be considered that there is no large level fluctuation during that time, but strictly speaking, a slight fluctuation will occur for each light receiving pulse. Even if this variation occurs, the CFD (Constant) is provided in the arrival time detection circuit 6 so that the arrival time detection circuit 6 operates correctly.
A Fraction Discriminator) circuit is generally included, but since it has no direct relation to the gist of the present invention, its detailed description is omitted.

The present invention is not limited to the above-mentioned embodiment, and for example, the division shape of a large number of division areas of the liquid crystal surface of the optical attenuator 4a may be a square shape shown in FIG. It is not limited to the radial (trapezoidal) shape of (C),
Of course, for example, concentric circles, polygonal shapes, and other shapes can be used.

[0060]

As described above, according to the present invention,
The attenuation amount is set according to the ratio of the divided regions that are controlled to be off of the plurality of divided regions of the optical attenuator composed of liquid crystal,
Even if there is some temperature fluctuation, the transmittance of each divided area of the liquid crystal can be controlled accurately and at a higher speed than mechanical methods, so the attenuation can be controlled accurately and at a high speed. It is possible to prevent saturation of the detector.

Further, according to the present invention, the attenuation amount control means drives the calibration light source during the non-incident period of the light reflected by the object, and the level of the received light output signal of the photodetector obtained at that time By calculating the total amount of attenuation and correcting the amount of attenuation of the optical attenuator, it is possible to accurately control the actual photoelectron multiplication amount of the photodetector, the amount of attenuation of the voltage control attenuator, etc. to the desired set values. Therefore, the attenuation amount of the optical attenuator can be set to always be the optimum attenuation amount.

Further, according to the present invention, since the voltage control attenuator is used to output the light-receiving signal output from the photodetector to the arrival time detection circuit with a constant level without changing the phase, the photodetector is provided. The waveform of the incident light can be faithfully output as a constant level to the arrival time detection circuit, and the measurement accuracy can be improved compared to the conventional case.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram of an optical attenuator of an embodiment of the present invention and a diagram showing each example of a pattern.

FIG. 3 is a diagram for explaining the features of one embodiment of the present invention.

FIG. 4 is a block diagram of a main part of another embodiment of the present invention.

[Explanation of symbols]

 1 Laser Oscillator 2 Transmitting / Receiving Optical System 3 Optical Scanning Device 4a, 4b Optical Attenuator 5 Photodetector 6 Arrival Time Detection Circuit 7 Optical Level Detection Circuit 8 Attenuation Control Circuit 9 Central Processing Unit (CPU) 10 Calibration Light Source 32 Voltage Control Attenuator 33 Level detection circuit 34 Control voltage generation circuit

Claims (3)

[Claims] 1. A laser oscillator that intermittently emits a laser beam, and a transmission / reception optical system that radiates the laser beam from the laser oscillator into a space at a predetermined beam divergence angle and collects incident light from the outside. A photodetector for photoelectrically converting received light and outputting a light reception signal, and arrival time detection for calculating at least the arrival time to an external object based on the output light reception signal of the photodetector and the output signal of the laser oscillator A circuit, an optical path of laser light incident from the laser oscillator to the transmission / reception optical system, and an optical path of light received and condensed by the transmission / reception optical system and incident on the photodetector. An optical attenuator made of liquid crystal, an optical level detection circuit for detecting the level of an output light reception signal of the photodetector, and a setting control of an attenuation amount of the optical attenuator based on an output signal of the optical level detection circuit. And a configuration in which the light transmitting surface of the optical attenuator is divided into a plurality of divided areas, and each of the plurality of divided areas is based on a control signal from the attenuation amount control means. Control on or off,
A laser radar device, wherein the attenuation amount is set according to a ratio of a divided area controlled to be off of the plurality of divided areas. 2. A calibration light source that emits calibration light to enter the optical path from the transmission / reception optical system to the photodetector is provided, and the attenuation amount control means receives the light reflected by an object. The calibration light source is driven for a period during which the light attenuation is not performed, and the total attenuation is obtained from the level of the output light reception signal of the photodetector obtained at that time to correct the attenuation of the optical attenuator. The laser radar device according to claim 1. 3. A voltage control attenuator for attenuating an output light reception signal of the photodetector with an attenuation amount according to an input control voltage and outputting the attenuated signal to the arrival time detection circuit, and an output signal of the voltage control attenuator is branched. And a level detection circuit for detecting the input level of the voltage control attenuator so that the output signal of the voltage control attenuator becomes a constant level according to the output detection signal of the level detection circuit. 3. The laser radar device according to claim 1, further comprising a control voltage generation circuit which outputs the control voltage to the control voltage generation circuit to control the attenuation amount.