JPH10197635A - Laser distance measuring equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sustain the distance detection performance by enhancing the sensitivity when the distance detection performance has degraded due to bad environment, e.g. snow or rain. SOLUTION: A laser pulse L is projected from a projecting section 24 and used for scanning through an optical scanning section 25. The laser pulse L reflected on an object is received by a light receiving element 29 and a light receiving signal b amplified through a light receiving circuit 30 is integrated by an integrator 33. When a specified number of pulses of light receiving signal b are integrated, a gate circuit 34 is opened to output an integrated value f which is then compared with a threshold value Vth at a threshold value decision section 35. When the integrated value f is larger than the threshold value Vth, a detection signal c is outputted and a distance is operated at a distance calculating section 36. When the measuring environment is degraded due to snow or rain, it is detected at an environmental condition detecting section 37 and the scanning rate at the optical scanning section 25 is decreased and the period for opening the gate circuit 34 is prolonged correspondingly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a laser distance measuring apparatus (laser radar).

[0002]

2. Description of the Related Art In a pulse echo type laser distance measuring apparatus, a laser pulse is emitted from a laser distance measuring apparatus, a laser pulse reflected from an object is returned, and a laser pulse is returned. Calculate the distance to. However, under poor environmental conditions such as rain, snow, and window dirt, the light receiving level of the laser pulse is reduced, so that the distance measurement may not be performed.

Therefore, there has been proposed a laser distance measuring apparatus capable of measuring a distance even in a bad environment by changing a threshold value in a light receiving section. Such a laser ranging device is shown in FIG. The laser distance measuring device 1 includes a light emitting unit 4 including a semiconductor laser element (LD) 2 and a semiconductor laser element driving circuit (LD driving circuit) 3, an optical scanning unit (scanner) 5, and a photodiode (PD). A light receiving unit 8 including a light receiving element 6 and a light receiving circuit 7, a threshold value determining unit 9,
It comprises a distance calculator 10, a timing generator 11, and an environmental condition detector 12.

When the light emission timing signal a is output from the timing generator 11 to the semiconductor laser device driving circuit 3, the semiconductor laser device driving circuit 3 causes the semiconductor laser device 2 to emit light in pulses,
The laser pulse L emitted from the optical scanning unit 5 is scanned left and right by the optical scanning unit 5. When the laser pulse L reflected by the object is received by the light receiving element 6, a light receiving signal b is output from the light receiving element 6 and amplified by the light receiving circuit 7. The amplified light receiving signal b is compared with a predetermined threshold value Vth0 by a threshold value judging unit 9 as shown in a section A1 in FIG. 2, and when the light receiving signal b is larger than the threshold value Vth0, the distance calculation is performed. The detection signal c is output to the unit 10. On the other hand, the light emission timing signal a is also output from the timing generation unit 11 to the distance calculation unit 10, and the distance calculation unit 10 measures the delay time from emission to reception of the laser pulse L, and measures the delay time from the delay time to the object. Calculate and output the distance.

The environmental condition detecting unit 12 monitors bad environments such as snow and rain, dirt on the window of the laser distance measuring device 1, and dirt on the window of the vehicle in front of the laser distance measuring device 1. When the condition detecting unit 12 determines that the environmental condition has deteriorated, the condition detecting unit 12 outputs a signal d notifying the deterioration of the environmental condition to the threshold value determining unit 9. Upon receiving the signal d, the threshold value judging unit 9 improves the sensitivity by reducing the threshold value. That is, when the light receiving signal b is reduced due to the bad environment as in the section A2 in FIG. 2, the light receiving signal b is compared with the threshold value Vth0. Can not be calculated, but when a bad environment is detected, the threshold value is reduced to Vth1 to increase the sensitivity, and the detection signal c is output to the distance calculation unit 10,
The distance to the object can be determined.

[0006]

In the laser distance measuring apparatus as described above, the distance to the object can be obtained even in a bad environment. However, when the environment became worse, the detection performance could not be further improved. In other words, when the threshold value is further reduced, the detection signal is output also due to external noise, thermal noise of the light receiving circuit, and the like, which results in deterioration of the detection performance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above background art, and has as its object to detect deterioration of environmental conditions even when the distance detection performance is reduced due to deterioration of environmental conditions. It is an object of the present invention to provide a laser distance measuring apparatus capable of further improving sensitivity and obtaining stable distance detection performance.

[0008]

DISCLOSURE OF THE INVENTION A laser range finder according to the present invention comprises a light projecting section for emitting laser light, a light scanning section for scanning the laser light emitted from the light projecting section, and a laser beam reflected by an object. A light receiving unit that detects the distance to the object by receiving light, and a unit that detects an environmental condition, according to the environmental condition detected by the environmental condition detecting unit,
The detection time of the laser beam in the light receiving section is changed.

In particular, the light receiving section detects a laser beam by integrating a light receiving signal output according to a light receiving amount for a predetermined detecting time and comparing the integrated value with a predetermined threshold value. It is.

Here, in order to change the detection time of the laser beam in the light receiving section, the scanning speed of the laser beam by the optical scanning section may be changed. Alternatively, the light emission cycle of the light emitting unit may be changed.

In such a laser distance measuring device,
Since the detection time is changed according to the environmental conditions, even if the measurement environmental conditions of the laser ranging device deteriorate, the detection sensitivity can be improved by increasing the detection time, and the distance to the target object can be improved. Measurement performance can be improved.

Further, according to the method of changing the detection time in accordance with the environmental conditions, there is no restriction due to extraneous noise or thermal noise as in the conventional example, and the detection performance can be improved even when the environmental conditions become very bad. can do.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 3 is a schematic block diagram showing a configuration of a laser distance measuring apparatus 21 according to an embodiment of the present invention. This laser distance measuring device 21 scans a laser beam L emitted from the semiconductor laser element 22 in a detection area by a light projecting unit 24 including a semiconductor laser element 22 and a semiconductor laser element driving circuit 23 for driving the semiconductor laser element 22. An optical scanning unit (scanner) 25 for performing light emission and a timing generation unit 28 for generating a light emission timing signal a are provided. The semiconductor laser element drive circuit 23 causes the semiconductor laser element 22 to emit pulses in synchronization with the light emission timing signal a output from the timing generation section 28 at regular intervals. The optical scanning unit 25 includes a mirror 26 for reflecting a laser pulse L and a mirror driving unit 27 for rotating the mirror 26. It is composed of a diaphragm and the like. The laser pulse L emitted from the semiconductor laser element 22 is transmitted to the optical scanning unit 2
The light is reflected by the fifth mirror 26 and scans a predetermined detection area.

Here, the light projection operation of the laser distance measuring device 21 in a normal state will be specifically described with reference to FIG.
The semiconductor laser element 22 emits light every 2 μsec by the timing generator 28 and the semiconductor laser element drive circuit 23. On the other hand, the optical scanning unit 25 scans the laser pulse L with a cycle of 50 msec over a measurement range of 200 mrad. Since the laser pulse L emits light every 25 μsec, the semiconductor laser element 22 emits 2,000 times during 50 msec of one scan, and the distance measurement of 2,000 pulses is performed. Of the 2000 pulses in one scan, 1600 pulses from 201 to 1800 are used for distance measurement, and distance measurement is not performed in end point areas (pulses 1 to 200 and pulses 1801 to 2000). 1600 pulses (20
(1st to 1800th pulses) are divided into 80 regions every 20 pulses.

Although the details are omitted, the end point area is
When the scanning direction detecting device detects the scanning direction (light emission direction) of the laser pulse L, it detects an end area of the scanning area which is a reference in the scanning direction.

The laser distance measuring device 21 further includes a light receiving element 29 such as a photodiode (PD) and a light receiving circuit 3.
A light receiving unit 32 including a signal processing unit 31 and a signal processing unit 31 is provided.
The laser pulse L emitted from the semiconductor laser element 22 and scanned by the optical scanning unit 25 is projected forward, is reflected by an object, returns to the laser distance measuring device 21, and is reflected by the light receiving element 29. Received. Light receiving element 2
The light receiving signal b output from 9 is amplified by the light receiving circuit 30 and output.

The signal processing section 31 includes an integrator 33, a gate circuit 34, a threshold value judging section 35, and a distance calculating section 36. The light receiving signal b output from the light receiving circuit 30 is integrated by the integrator 33 as shown in FIGS. 5A and 5B, and is output as an integrated value e. As shown in FIG. 5C, the gate circuit 34 is opened for each one area (usually, 20 pulses) divided into 80 areas. Then, the integrated value (gate output) f for one area is output to the threshold value judging section 35 at a constant period. When the integrated value for one area is output, the integrated value of the integrator 33 is cleared to zero. The threshold value judging section 35 compares the integrated value (gate output) f output from the gate circuit 34 with the threshold value Vth, and if the integrated value f of the light receiving signal b is equal to or larger than the threshold value Vth, the light receiving element 2
9 determines that the laser pulse L has been received, and outputs a detection signal to the distance calculation unit 36. On the other hand, the timing generation unit 2
8, the light emission timing signal a is also output to the distance calculation unit 36, and the distance calculation unit 36 measures the delay time from the emission of the laser pulse L to the reception of the laser pulse L reflected back from the object. Then, the distance to the object is calculated based on the delay time.

The laser distance measuring device 21 is used for snow, rain,
Dirt on window of laser distance measuring device 21, laser distance measuring device 2
The system includes an environmental condition detecting section 37 for monitoring a bad environment such as a stain on a window of a vehicle in front of the vehicle 1 and a detection time control section 38 for controlling a detection time. According to the present invention, the detection time is changed by changing the number of laser pulses included in one area according to a change in the distance measurement environment condition. In particular, in this embodiment, the detection time is changed by changing the scanning speed of the laser pulse L according to the change in the environmental conditions. The cycle of opening the gate circuit 34 is controlled.

When the environmental condition detecting unit 37 detects that the measurement environmental condition has deteriorated, the environmental condition detecting unit 37 notifies the detection time control unit 38 of the deterioration of the environmental condition. Upon detecting that the environmental condition has deteriorated, the detection time control unit 38 slows down the scanning speed of the optical scanning unit 25 and opens the gate circuit 34 so as to output an integrated value for each area in response to the slowing down. Increase the cycle. For example, the scanning speed of the laser pulse L is reduced to 1/2.
Then, the laser pulse L is increased from 20 samples to 40 samples in each of the divided regions of the scanning region into 80 regions. Correspondingly, the timing at which the gate circuit 34 opens doubles. As a result, the total detection time is doubled. As a result, the integral value f output to the threshold value judging section 35 is increased, the sensitivity is improved by √2 times, and the distance of the object can be measured even in a bad environment. Becomes

Further, even if the environmental conditions deteriorate,
The scanning speed is further reduced, the period in which the gate circuit 34 is opened is correspondingly further increased, and the detection time is further increased, whereby the sensitivity is improved and stable distance performance can be secured.

Further, according to the method of changing the threshold as described with reference to FIG. 2, when the signal level is close to the noise level, it is difficult to separate the signal and the noise even if the threshold is changed. However, according to the method of the present invention, the difference between the integrated value of the noise and the integrated value of the signal can be increased by lengthening the detection time, so that the distance measurement performance is further improved.

(Second Embodiment) FIG. 6 shows another embodiment of the present invention, in which the gate circuit 34 is changed according to a change in environmental conditions (with the scanning speed of the laser pulse L unchanged). This is a laser distance measuring device 41 that changes the opening cycle. That is, when the environmental condition detection unit 37 detects that the measurement environment condition has deteriorated, the environmental condition detection unit 37 notifies the detection time control unit 38 of the deterioration of the environmental condition.
Upon detecting that the environmental conditions have deteriorated, the detection time control unit 3
8 lengthens the cycle of opening the gate circuit 34. For example,
If the cycle of opening the gate circuit 34 is doubled, the integrator 33
Since the number of laser pulses integrated by the above expression doubles from 20 pulses to 40 pulses, the integrated value output to the threshold value judging section 35 increases, the sensitivity increases, and even in a bad environment, the The distance can be measured.

In this embodiment, since only the cycle of opening the gate circuit 34 is changed, the sensitivity can be improved, but the direction in which the object can be detected is reduced when the environmental conditions are poor (for example, the gate circuit 34 is not changed). If the opening cycle is doubled, one area is obtained by 40 pulses, so that the total is 8
However, the first embodiment is characterized in that the direction in which the object can be detected does not change, and the resolution in the detection direction does not decrease.

(Third Embodiment) FIG. 7 shows still another embodiment of the present invention, in which a light emitting cycle of the semiconductor laser element 22 is changed according to a change in environmental conditions. It is a distance measuring device 42. That is, the detection time control unit 38 controls the timing generation unit 28 according to the signal from the environmental condition detection unit 37, and changes the cycle of the light emission timing signal a output from the timing generation unit 28. . For example, when the environmental condition detecting unit 37 detects that the measurement environmental condition has deteriorated, the environmental condition detecting unit 37 notifies the detection time control unit 38 of the deterioration of the environmental condition. Upon detecting that the environmental condition has deteriorated, the detection time control unit 38 controls the timing generation unit 28 so that the cycle of the light emission timing signal a is doubled. As a result, the number of laser pulses for one scan increases from 2,000 pulses to 4000 pulses, and the laser pulse L for one region integrated by the integrator 33 also increases from 20 pulses to 40 pulses. Thus, the integrated value output to is increased, the sensitivity is increased, and the distance to the object can be measured even in a bad environment.

Moreover, in this embodiment, since the direction (the number of regions) in which the object can be detected does not change, the resolution in the detection direction does not decrease and the response speed does not decrease.

(Other Embodiments) CW (Continuous-W
In an ave) type or FM-CW type laser distance measuring device (not shown), the irradiation laser light for distance measurement is a continuous wave, and therefore, the light receiving bandwidth is varied in the light receiving portion to determine the environmental conditions. It is possible to respond to changes. In other words, when the environmental condition detection unit detects that the measurement environment condition is deteriorating, the sensitivity can be improved by narrowing the light receiving bandwidth in the light receiving unit, and when the environmental condition is deteriorated. But you can make it measurable.

In an optical heterodyne type laser distance measuring apparatus, it is necessary to make the wavefronts of the laser beam on the light emitting side and the laser beam on the light receiving side coincide with each other. Scanning is synchronized. Such a laser distance measuring apparatus can respond to changes in environmental conditions by changing the scanning speed of the light receiving unit. That is, when the scanning speed in the light receiving unit is high, the incident angle of the laser light reflected back from the target object is broken, and the sensitivity is reduced. Conversely, the sensitivity can be further improved by reducing the scanning speed in the light receiving section. Therefore, when the environmental condition detection unit detects that the measurement environment condition is deteriorating, the sensitivity can be improved by reducing the scanning speed in the light receiving unit, and even when the environmental condition is degraded. The distance can be measured.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a laser distance measuring device described as a background art.

FIG. 2 is a diagram for explaining the operation of the laser distance measuring device according to the first embodiment;

FIG. 3 is a block diagram illustrating a configuration of a laser distance measuring apparatus according to an embodiment of the present invention.

FIG. 4 is a diagram illustrating a laser pulse emitted from the laser distance measuring device according to the first embodiment.

FIGS. 5A to 5D are views for explaining signal processing in a signal processing unit of the laser distance measuring device according to the first embodiment.

FIG. 6 is a block diagram showing a configuration of a laser distance measuring apparatus according to another embodiment of the present invention.

FIG. 7 is a block diagram showing a configuration of a laser distance measuring apparatus according to still another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 22 semiconductor laser element 24 light emitting section 25 optical scanning section 29 light receiving element 31 signal processing section 32 light receiving section 33 integrator 34 gate circuit 35 threshold value determination section 36 distance calculation section 37 environmental condition detection section 38 detection time control section

Claims (4)

[Claims] A light projecting unit for emitting a laser beam, a light scanning unit for scanning the laser beam emitted from the light projecting unit, and a distance to the object by receiving the laser beam reflected by the object. A light receiving unit for detecting the laser beam, and a means for detecting an environmental condition, wherein the laser light detection time in the light receiving unit is changed in accordance with the environmental condition detected by the environmental condition detecting means. Distance measuring device. 2. The method according to claim 1, wherein the light receiving unit integrates a light receiving signal output according to a light receiving amount for a predetermined detection time, and detects the laser light by comparing the integrated value with a predetermined threshold value. The laser distance measuring apparatus according to claim 1, wherein: 3. The detection time of the laser beam in the light receiving unit is changed by changing a scanning speed of the laser beam by the optical scanning unit.
A laser distance measuring device according to item 1. 4. The laser distance measuring apparatus according to claim 1, wherein a detection period of the laser beam in the light receiving unit is changed by changing a light emitting cycle in the light projecting unit.