JP2000075030A - Scanning laser radar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive scanning laser radar having a long lifetime by providing a laser beam control means for controlling a spreading angle control means and a scanning angle control means depending on the output from a vehicle speed sensor thereby suppressing the number of times of laser emission. SOLUTION: At the time of low speed, beam scanning angle 6 and beam spreading angle 5 are set wide. Consequently, the number of times of laser emission is suppressed thus suppressing the lowering of lifetime of a laser element. At the time of high speed, beam scanning angle 8 and beam spreading angle 7 are set narrow. Consequently, the density of laser beam can be increased and since the power of reflected light is increased, a remote detectable range can be ensured. Spreading angle and scanning angle of laser beam are set wide at the time of low speed so that a wide range can be irradiated while suppressing the number of times of laser emission and both angles are made narrower as the speed increases so that a narrow range is irradiated while increasing the power of reflected light and ensuring a detectable range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type laser radar device for detecting a detection object ahead in a traveling direction while a vehicle is traveling, and more particularly to a scanning laser radar device used as an inter-vehicle distance sensor.

[0002]

2. Description of the Related Art Scanning laser radar devices have recently been put to practical use as inter-vehicle distance sensors during vehicle running, and are used for automatically maintaining a constant inter-vehicle distance or monitoring the inter-vehicle distance during running. Used in

The basic principle is as follows. That is, a laser beam (pulse wave or amplitude modulated wave)
Is irradiated toward the detection target while scanning within a predetermined angle, and reflected light from the detection target is received. At that time, since the propagation speed of light in the atmosphere is almost constant, it is necessary to know this time by using the principle that the time required for light to be reflected by the detection target and return is proportional to the distance. Is used to measure the distance to the detection target.

The detectable distance of such an inter-vehicle distance sensor depends on the power of a signal reflected from a detection target. Here, in order to increase the power of the reflected signal in order to secure a sufficient detectable distance, it is conceivable to increase the output of the light source from which the signal is transmitted, but the laser output is legally limited in terms of safety. It is imposed, and it is virtually impossible to output a certain level of power. Therefore, in order to ensure a sufficient detectable distance, it is effective means to increase the laser density on the reflection surface of the detection target, that is, to reduce the spread angle of the laser beam.
Laser light has strong directivity, and the spread angle can be easily suppressed by using an optical system.

However, in practice, always suppressing the divergence angle of the beam increases the spatial resolution but increases the possibility of missing detection between scanning points. It is necessary to secure the number of times of laser emission, and there are problems such as a reduction in the life of the laser element and an increase in cost for securing the capability of the drive circuit.

In order to solve this problem, Japanese Patent Laid-Open Publication No.
No. 5199 describes an obstacle sensor that emits a wide beam for short-distance detection and suppresses the number of laser emission, and simultaneously emits a thin beam toward a distant place to enlarge a sensing area.

[0007]

However, the above-mentioned obstacle sensor detects a long distance and a short distance at the same time, and such a function is not necessary as an inter-vehicle distance sensor. This is because the inter-vehicle distance sensor can achieve its purpose if it can detect only a short distance in a low speed range and only a long distance in a high speed range according to the speed of the vehicle. Also,
Since a plurality of light sources are required to exhibit such a function, there is a problem that the cost increases.

Therefore, the present invention has been made in view of the above-mentioned circumstances, and makes the divergence angle and scanning angle of a laser beam variable according to the speed of a vehicle, suppresses the number of laser emission times, and provides a long life and low cost. It is a technical object to provide a scanning laser radar device.

[0009]

According to a first aspect of the present invention, there is provided a detection target object located in a predetermined area ahead of a vehicle in a traveling direction thereof. In a scanning laser radar device for detecting the distance and azimuth of the vehicle, a vehicle speed sensor for detecting the speed of the vehicle, a divergence angle control means for controlling the divergence angle of the emitted laser beam, and the scanning angle of the laser beam A scanning laser radar device comprising: a scanning angle control unit for controlling; and a laser beam control unit for controlling the divergence angle control unit and the scanning angle control unit according to the output of the vehicle speed sensor.

As described above, the laser beam control means can freely set the divergence angle and the scanning angle of the laser beam in accordance with the vehicle speed. Since the laser density can be reduced without increasing the power of the reflected light, the divergence angle of the beam is set wide, and as a result, the number of laser emission times can be reduced. As a result, the reduction in the life of the laser element can be suppressed, and the safety for eyes can be improved.

On the other hand, when the performance of detecting a long distance is required according to the vehicle speed, it is necessary to secure a sufficient detectable distance, and it is necessary to increase the power of the reflected light. It can be set to be narrow, make a narrow beam, and increase the laser density.

As described above, the optimum value of the divergence angle of the laser beam can be set according to the condition of the vehicle speed.
The number of times of laser emission can be efficiently suppressed, and a reduction in the life of the laser element can be suppressed. In addition, only one light source is required for the present invention, and it can be provided at a lower cost than a conventional device requiring a plurality of light sources.

Further, the laser beam control means according to the first aspect of the present invention, as described in the second aspect, sets the divergence angle of the laser beam and the scanning angle of the laser beam together when the speed of the vehicle is low. It is desirable to control the vehicle so as to be wide and narrow as the speed of the vehicle increases.

Generally, in the case of an inter-vehicle distance sensor, when the vehicle is running at a low speed, the detection object (preceding vehicle) is widely distributed over a short distance. Becomes faster, the detection target exists in a long distance and narrow range (for example, a road width in consideration of a lane width and a possible curve), so that a detection capability in a long distance and a narrow range is required. .

Therefore, the divergence angle and the scanning angle of the laser beam are set to be wide at low speeds so that the laser beam can be irradiated over a wide range while suppressing the number of laser emission. It is desirable to increase the power of the laser beam so as to be able to irradiate a narrow range while securing a detectable distance.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a detectable range of a scanning laser radar device for an inter-vehicle distance sensor according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a vehicle, and a scanning laser radar device 2 is provided in a front part of the vehicle 1.

The scanning laser radar device 2 can set the detection range of the emitted laser beam based on a signal from a vehicle speed sensor (not shown). The operation will be described later with reference to FIG. At low speeds, as shown in FIG. 3, a short range and a wide fan-shaped area larger than the road width are set as the detectable range. At high speeds, as shown in FIG. The sector area of the range is set as the detectable range. The existence range of the preceding vehicle is distributed over a short distance and a wide range in consideration of turning at low speeds, and is distributed over a long distance and a narrow range (for example, a road width in consideration of lane widths and possible curves) at high speeds. Because you do.

FIG. 2 is a diagram showing a divergence angle and a scanning angle of a laser beam emitted from a scanning laser radar device for an inter-vehicle distance sensor according to an embodiment of the present invention.
As shown in FIG. 2, at a low speed, the beam scanning angle 6 is
As in FIG. 1, the beam is set wide, and the beam divergence angle 5 is also set wide. This reduces the number of laser emissions,
A reduction in the life of the laser element can be suppressed. on the other hand,
At high speed, the beam scanning angle 8 is set to be narrow as in FIG. 1, and the beam divergence angle 7 is also set to be narrow. As a result, the density of the laser beam can be increased, and the detectable distance can be secured far away by improving the power of the reflected light.

FIG. 3 is a block diagram showing the operation principle of the scanning laser radar device for an inter-vehicle distance sensor according to one embodiment of the present invention. The scanning laser radar device 2 is provided with a microcomputer 10 (laser beam control means). When the microcomputer 10 issues a trigger signal to the driver 11, the driver 11 sends an instantaneous pulse to the pulse laser diode 11. Inject current. The pulse laser diode 11 into which the pulse current has been injected irradiates the target 16 with a laser beam (transmission pulse 14) proportional to the injected current. At the same time, the microcomputer 10 transmits a counter start signal to the interval timer / counter 19, and the interval timer / counter 19 starts a counter operation. This is the starting point of the measurement time width. Here, the peak power of the transmission pulse 14 is set to a value sufficient to satisfy the required detection distance performance of the following distance detection system,
The light emission cycle is determined by the number of samples required for the averaging process to satisfy the required distance measurement resolution and the responsiveness required by the system.

When irradiating the transmission pulse 14, the microcomputer 10 transmits a scan range control command to the scanner 13 (scan angle control means) based on the own vehicle speed data from the vehicle speed sensor 9 to correspond to the vehicle speed. The transmission pulse 14 is deflected and scanned within a scan range (scan angle). The scanning method is generally based on a polygon mirror, but a galvano mirror may be used. Further, the microcomputer 10 transmits a beam width control signal to the collimating lens 12 (spreading angle control means) based on the own vehicle speed data from the vehicle speed sensor 9, and controls the distance between the pulse laser diode 11 and the collimating lens 12. Thus, the beam width (spread angle) is adjusted according to the vehicle speed.

Received pulse 1 reflected by target 16
5 is a PIN photodiode 1 via a light receiving lens 17.
The light is condensed at 8, extracted as a photocurrent, amplified through an amplifier 18, and then supplied to an interval timer / counter 19 as a counter stop signal. The interval timer / counter 19 supplied with the counter stop signal stops the counting operation started by the counter start signal. Since this counted value is proportional to the measurement time width, that is, the distance to the target 16,
The microcomputer 10 can obtain distance data to the target 16 by multiplying this value by an appropriate coefficient.

By repeating the above operation, distance data to the target 16 at each scanning point is calculated inside the microcomputer 10 and is calculated together with the scanning angle by the scanner 13.
It is supplied to the target recognition logic in the inter-vehicle distance detection system, and can recognize the distance to the target 16 and the azimuth. This information is supplied to the inter-vehicle distance control system so that, for example, automatic control of the inter-vehicle distance can be performed.

Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the above embodiment.
It includes various aspects according to the principles of the present invention.

[0025]

According to the present invention, there is provided a scanning laser radar apparatus in which the divergence angle and scanning angle of a laser beam are made variable in accordance with the speed of a vehicle, the number of times of laser emission is suppressed, and a long-life and inexpensive laser radar apparatus is provided. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a detectable range of a scanning laser radar device for an inter-vehicle distance sensor according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a spread angle and a scan angle of a laser beam emitted by a scanning laser radar device for an inter-vehicle distance sensor according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating an operation principle of the scanning laser radar device for an inter-vehicle distance sensor according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vehicle 2 Scan type laser radar device 9 Vehicle speed sensor 10 Microcomputer (laser beam control means) 12 Collimating lens (spread angle control means) 13 Scanner (scan angle control means)

Claims (2)

[Claims] 1. A scanning type laser radar device for detecting a distance and an azimuth angle of a predetermined area in front of a vehicle in a traveling direction with respect to a detection target located in the area, and a vehicle speed sensor for detecting a speed of the vehicle. Divergence angle control means for controlling the divergence angle of the emitted laser beam, scan angle control means for controlling the scan angle of the laser beam, and the divergence angle control means and the scan angle control in accordance with the output of the vehicle speed sensor A scanning laser radar apparatus comprising a laser beam control means for controlling the means. 2. The laser beam control means increases a divergence angle of the laser beam and a scanning angle of the laser beam both when the speed of the vehicle is low, and decreases as the speed of the vehicle increases. 2. The scanning type laser radar device according to claim 1, wherein the scanning type laser radar device is controlled as follows.