JPH0720229A - Laser radar apparatus - Google Patents

Abstract

PURPOSE:To make stable measurement possible by arranging a laser element in such a manner that the direction parallel with a junction surface of the laser element almost coincides with the direction of retraction in the attitude of a transparent plate to reduce adverse effect as caused by the reflection of the transparent plate. CONSTITUTION:The attitude of a semiconductor laser element 18 at a transmitting section 12 of a vehicle-to-vehicle distance measuring device is set with a junction surface 19 of a PN junction turned vertical. A laser light generated on the junction surface 19 is checked in solid angle of radiation with a lens 17 to be incident into a front glass 11 through a protective plate 16. The laser element 18 uses a laser diode element so that the power of a deflection component parallel with the junction surface 19 reaches as much as 90% in a total radiation does of the laser light but the power of the deflection component vertical to the junction surface 19 is only 10%. Therefore, the junction surface 19 is turned vertical to admit the deflection component parallel with the junction surface 19 into the glass 11 as P polarized component. This make possible the curtailment of an S polarized component with a high reflection rate thereof on glass 11 effectively there by minimizing the ratio of the laser light to be reflected the glass 11.

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 which emits laser light through a transparent plate having one side retracted and detects scattered light of the laser light by a front obstacle through the same transparent plate.

[0002]

2. Description of the Related Art A laser radar device that emits a laser beam in the front space and detects the scattered light of the laser beam by the front obstacle to measure the distance to the front obstacle is installed in, for example, a passenger car or a truck. It is being put to practical use as an inter-vehicle distance measuring device that measures the inter-vehicle distance to the vehicle in front. According to the inter-vehicle distance measuring device, it is possible to reduce the burden on the driver while driving and compensate for the driver's momentary inattention.

The inter-vehicle distance measuring device not only measures the inter-vehicle distance of the preceding vehicle and displays it to the driver, but (1) When the inter-vehicle distance of the preceding vehicle falls below the dangerous level, the driver is audible. It is also used for applications such as warning, (2) automatic control of speed according to the vehicle-to-vehicle distance of the preceding vehicle, and keeping the vehicle-to-vehicle distance constant.

In a laser radar type inter-vehicle distance measuring apparatus, a pulsed laser beam is usually intermittently sent to a space in front of a vehicle, and scattered light of the laser beam due to a front obstacle is detected. Then, the time difference between the sending time of the laser pulse and the receiving time of the scattered light is measured, and the inter-vehicle distance to the preceding vehicle is calculated by multiplying this time difference by the speed of light.

The inter-vehicle distance measuring device is usually constructed by adjoining a scattered light receiving part to a laser pulse sending part.
A laser diode element (LD element) can be used as the semiconductor laser element of the sending unit. For example, oscillation is started at intervals of several milliseconds and laser light is generated by continuing oscillation for several tens of nanoseconds. A laser pulse output of 10 nsec is emitted to the front space. On the other hand, the receiving unit includes a lens for converging the incident light of a predetermined front solid angle and a light receiving element for converting the converged incident light into an electric signal, and the transmitted laser light collides with the preceding vehicle. The scattered light that is formed is converted into electrical signal pulses (see Fig. 1 (a)).

Here, the time from the start timing of laser oscillation in the semiconductor laser element to the detection timing of scattered light in the light receiving element is obtained by dividing the length from the semiconductor laser element through the preceding vehicle to the receiving section again by the speed of light. Almost equals the time spent. A typical inter-vehicle distance measuring device that has been put into practical use can measure the time from laser oscillation to detection of scattered light, and can measure the inter-vehicle distance of up to 100 m with an accuracy of ± 1 m or less.

[0007]

[Problems to be Solved by the Invention] A laser radar inter-vehicle distance measuring device is (1) arranged between a roof and a rearview mirror on the center line of a vehicle body, (2) arranged in a corner of a dashboard in a vehicle interior, (3) The inter-vehicle distance measuring device is placed with a recess in the front of the vehicle body, and it is placed behind the inclined transparent plate by covering the inter-vehicle distance measuring device with a transparent resin cover that is integrated with the curve on the front of the vehicle body. There is a case.

When the laser radar device is arranged behind the inclined transparent plate, a part of the laser beam output from the laser radar device is reflected by the transparent plate and repeatedly reflected by the surrounding wall surface and the like. There is a possibility that the light will be reflected by the transparent plate again and enter the light receiving element.

The reflected light which is formed due to the reflection of the transparent plate and is incident on the light receiving element regardless of the laser beam transmitted through the transparent plate gives a pulse similar to that of the preceding vehicle to the output of the light receiving element. It is formed, and the inter-vehicle distance measurement is erroneous.

It is an object of the present invention to provide a laser radar device which has a small adverse effect due to reflection from a transparent plate, has a stable output from a light receiving element, and can prevent incorrect measurement of an inter-vehicle distance.

[0011]

A laser radar device according to claim 1 is a semiconductor laser arranged behind a transparent plate (11) having one side retracted and emitting a laser beam through the transparent plate (11). The element (18) and the transparent plate (11) are arranged on the same side as the semiconductor laser element (18), and the reflected light of the laser beam emitted by the semiconductor laser element (18) is reflected by the transparent plate (11). In a laser radar device having a light receiving means (13) for detecting through, the direction parallel to the joint surface of the laser element (18) is substantially aligned with the backward direction of the posture of the transparent plate (11), The laser element (18) is arranged.

A laser radar device according to a second aspect is the laser radar device according to the first aspect, wherein a deflection direction is set in a backward direction of a posture of the transparent plate on a laser light emitting path between the semiconductor laser element and the transparent plate. The set deflection means is provided.

[0013]

In the laser radar device of the present invention, the generation of reflected light when the laser light is emitted from the transparent plate is suppressed by utilizing the peculiar deflection characteristics of the semiconductor laser element. That is, with respect to the inclination of the transparent plate with one side retracted in the vertical, horizontal, diagonal, etc. directions, the mounting position of the semiconductor laser element is optimally selected to determine the laser light transmittance of the transparent plate. Higher and lower reflectance.

FIG. 1 is an explanatory view of an inter-vehicle distance measuring device of a first embodiment to which the laser radar device of claim 1 is applied. Here, the operation of the laser radar device according to claim 1 will be described with reference to FIG.

In the laser radar device according to the first aspect, the transparent plate 11 made of transparent glass or resin covers the front surfaces of the semiconductor laser element 18 and the light receiving means 13 in common, and is emitted from the semiconductor laser element 18. The emitted laser light is radiated forward through the transparent plate 11 and illuminates a forward obstacle (for example, a preceding vehicle). The laser light collides with a front obstacle to form scattered light, and a part of the scattered light returns to the laser radar device side, passes through the transparent plate 11, and reaches the light receiving means 13.

The transparent plate 11 is arranged, for example, with one of the top, bottom, left and right retracted. The laser light emitted from the semiconductor laser element 18 obliquely enters the transparent plate 11. The transparent plate 11 has an S-polarized component of the oblique incident light and a P-polarized component.
It has different transmittance characteristics for the deflection component, and has a greater transmittance for the P deflection component than for the S deflection component, in other words, for the S deflection component than for the P deflection component. It has a large reflectance.

Here, the P deflection component for the transparent plate 11 is an in-plane deflection component including the incident angle and is defined as a deflection component parallel to the incident surface including the normal line. On the other hand, the S deflection component for the transparent plate 11 is a deflection component orthogonal to the P deflection component and is defined as a deflection component orthogonal to the incident surface including the normal line.

On the other hand, the laser light output from the semiconductor laser element 18 has a considerably large deflection component in the direction parallel to the joint surface 19 as compared with the deflection component in the junction direction of the PN junction which constitutes the laser oscillator. Therefore, the direction parallel to the bonding surface 19 of the semiconductor laser element 18 is made substantially coincident with the inclination direction of the transparent plate 11 to increase the proportion of the P deflection component in the output of the semiconductor laser element 18.

By increasing the ratio of the P-polarized component with respect to the transparent plate 11, the ratio of the laser light output from the semiconductor laser element 18 that is transmitted through the transparent plate 11 is increased and the ratio of reflected light is decreased. .

Particularly, in the example of the glass material used for the windshield of an automobile, the incident angle with respect to the glass surface is 50.
Within the range of up to 60 degrees, the transmittance with respect to the P-polarized component has the property of being further reduced as compared with the case where the incident angle is 0 degrees (normal incidence). Therefore, if the proportion of the P deflection component is increased by adjusting the attitude of the semiconductor laser element 18 and the inclination of the glass surface is combined so that the incident angle of the P deflection component is within this range, the proportion of the reflected light on the glass surface is increased. It can be further reduced.

According to another aspect of the laser radar device of the present invention, the S deflection component lowered by the adjustment of the attitude of the semiconductor laser element is further blocked by the deflection means such as the resin deflection plate. As a result, the adverse effect of the reflected light of the transparent plate due to the S-polarized component is further reduced.

Particularly, in the case of the glass material used for the windshield of an automobile, the incident angle with respect to the glass surface is 50.
In the range of up to 60 degrees, the difference between the reflectances of the S deflection component and the P deflection component becomes remarkably large. Therefore, when the inclination of the glass surface is set using this range, the arrangement of the deflecting means requires a particularly large reflection light. Exert the effect of reducing.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an inter-vehicle distance measuring device of a first embodiment, FIG. 2 is an external view of an inter-vehicle distance measuring device, FIG. 3 is an explanatory diagram of a usage state of the inter-vehicle distance measuring device, and FIG. It is explanatory drawing of the relationship between a deflection component and reflectance. In FIG. 1, (a) shows the mounted state, and (b) shows the arrangement of the semiconductor laser device. In FIG.
(a) shows a front view and (b) shows a plan view. In FIG. 3, (a) shows an arrangement and (b) shows a signal. In FIG. 4, (a) shows the relationship between the deflection component and the reflectance, and (b) shows the relationship between the incident angle.

Here, an inter-vehicle distance measuring device installed in the passenger compartment of a passenger car is shown. The inter-vehicle distance measuring device emits laser light to the front of the vehicle through the windshield and detects the scattered light through the windshield.

In FIG. 1A, an inter-vehicle distance measuring device 10
Is fixed to the roof 15 of the vehicle at a position close to the center line of the vehicle body, emits laser light forward through a gap between the roof 15 and a rearview mirror (not shown), and detects scattered light from the front. Further, in FIG. 1 (a), for convenience of illustration, the sending unit 12 for outputting the laser light and the receiving unit 13 for detecting the scattered light are vertically arranged, but actually, in FIG. 2 (a). As shown in, the sending unit 12 and the receiving unit 13 are arranged side by side.

The laser light emitted from the sending section 12 is
The light passes through the windshield 11 and advances in the space in front of the vehicle to illuminate pedestrians and vehicles in front. A part of the scattered light generated by the collision of the laser light with the preceding vehicle or the like is turned back toward the own vehicle, passes through the windshield 11, and is incident on the receiving unit 13. The receiving unit 13 forms a detection signal such as a preceding vehicle according to the intensity of the incident scattered light, and detects the incident timing of the scattered light.

By the way, an automobile windshield 11
Is disposed at an angle of 40 degrees with respect to the horizontal direction, so that the laser light emitted forward from the sending unit 12 of the inter-vehicle distance measuring device 10 has an incident angle within a predetermined range centered at 50 degrees. It is incident on the windshield 11.

Most of the laser light emitted from the sending portion 12 passes through the windshield 11 and is emitted to the space in front of the vehicle, but only a small portion is reflected by the windshield 11 to illuminate the dashboard 14. To do. A small part of the scattered light generated by the collision of the laser light with the dashboard 14 is reflected by the windshield 11 and reaches the receiver 13.

The incident light of the receiving portion 13 caused by the reflection of the windshield 11 may have an intensity comparable to the scattered light traveling back and forth between the vehicles due to its short optical path length, and the normal scattering by the preceding vehicle or the like. There is a possibility that the incident timing of light may be erroneously detected.

Here, if the dashboard 14 is covered with a material having a high light absorption rate, the scattered light of the dashboard 14 is suppressed, and the malfunction of the inter-vehicle distance measuring apparatus 10 can be prevented. However, there are many cases where a highly reflective object such as a map or a document is placed on the dashboard 14 during driving.
In some cases, a material having a high light absorptivity cannot be adopted from the viewpoint of the color arrangement design of the interior of the vehicle including the dashboard 14.

Therefore, as shown in FIG. 1 (b), the attitude of the semiconductor laser element 18 is determined, and the characteristic that the deflection component of the light emission is unevenly distributed in the semiconductor laser element 18 is used to suppress the reflection on the windshield 11. There is.

In FIG. 1 (b), the delivery section 12 is provided with a protective plate 16, a lens 17, a semiconductor laser element 18, etc.,
The posture of the semiconductor laser element 18 is the bonding surface 1 of the PN junction.
9 is set vertically. The laser light generated on the bonding surface 19 of the semiconductor laser element 18 is reflected by the lens 17
The solid angle of emission is suppressed by, and the light is irradiated forward through the protective plate 16 and enters the windshield 11.

A laser diode element (LD element) is used as the semiconductor laser element 18, and the power of the deflection component parallel to the joint surface 19 in the total radiation amount of the laser light reaches 90%, and The power of the deflection component perpendicular to the surface 19 is only 10%.

Therefore, with the joint surface 19 of the PN junction oriented vertically, the deflection component parallel to the joint surface 19 is applied to the windshield 1.
1 as a P deflection component, the windshield 1
The S-polarized component having a high rate of being reflected by 1 is effectively reduced,
The ratio of laser light reflected by the windshield 11 is minimized.

In FIG. 2A, the sending section 12 and the receiving section 1
3 are each made into a component, and are arranged side by side in the inter-vehicle distance measuring device 10, and are arranged on the printed circuit board 22.
And the like are connected to a circuit portion 21 having the same. The laser light generated by the semiconductor laser element 18 of the sending unit 12 is radiated forward through the lens 17 having a diameter of 30 mm and forms a detection area in the angle range shown by the diagonal lines.

The semiconductor laser element 18 continues to oscillate every tens of nanoseconds every 1 millisecond, and emits a laser pulse having a length of several tens of nanoseconds to the detection area. Semiconductor laser device 1
An electric signal for starting and sustaining the oscillation of No. 8 is generated on the printed circuit board 22 of the circuit unit 21.

On the other hand, the receiving unit 13 uses the delivery 1
A 00 mm square Fresnel lens 27 is provided, and the Fresnel lens 27 converges the scattered light entering the entrance opening onto the light receiving surface of the light receiving element 28. The light receiving element 28 is composed of a photodiode in which a PN junction is arranged on the light receiving surface and a reverse bias voltage is applied. Each time the light receiving element 28 is irradiated with scattered light on the light receiving surface, a current corresponding to the intensity of scattered light is passed. In the receiving circuit arranged on the printed circuit board 22 of the circuit section 21, a detection signal of the preceding vehicle or the like is formed based on this current signal.

On the printed circuit board 22 of the circuit section 21, the time delay amount between the detection timing of the electric signal for starting the oscillation of the semiconductor laser element 18 and the detection timing of the preceding vehicle by the light receiving element 28 is measured, and this time is measured. The delay amount is multiplied by the speed of light to calculate the inter-vehicle distance of the preceding vehicle.

The inter-vehicle distance calculated by the circuit section 21 is sent to the monitor section 24 through the wiring 21A. The monitor unit 24 numerically displays the received inter-vehicle distance on the display unit 24D. Further, the driver compares the inter-vehicle distance of the preceding vehicle with the reference inter-vehicle distance set by operating the preset knob 24A in advance, and when the reference inter-vehicle distance is interrupted, a voice warning is given through the speaker 24H. Is output. The knob 24B is used to adjust the volume of the speaker 24H.

In FIG. 3A, the inter-vehicle distance measuring device 10 mounted on the own vehicle 31 emits a laser beam in front of the own vehicle 31 to form a detection area 33. The detection area 33 is roughly 1 lane wide and 1 lane in front of the vehicle.
The shaded area occupies a space with a depth of about 100 m.

The object that has entered the detection area 33 forms scattered light of the laser light, and a part thereof is folded back toward the vehicle 31. When the object that has entered the detection area 33 is the preceding vehicle 32, particularly strong scattered light is formed by the reflector 32R of the preceding vehicle, and the preceding vehicle 32 is
The inter-vehicle distance measuring apparatus 10 can easily detect the scattered light of the reflector 32R even when traveling in front of m or more.

In FIG. 3B, when the laser pulse is output at the timing of the transmission pulse 35 for activating the semiconductor laser element, scattered light is detected at a timing delayed by 36T, and the detection signal (reception signal of the preceding vehicle) (reception) is received. Pulse 3
6) is formed. The reception pulse 36 is cut out by the threshold voltage 38, and the detection timing is measured, and the time 36T corresponds to the time when the laser pulse travels back and forth between the host vehicle 31 and the preceding vehicle 32.

Therefore, from the transmission pulse 35 to the reception pulse 3
The inter-vehicle distance is obtained by dividing the distance obtained by multiplying the time 36T up to 6 by the speed of light by 2.

On the other hand, in the conventional inter-vehicle distance measuring device in which the attitude of the semiconductor laser device 18 is not taken into consideration, the laser light reflected by the windshield 11 is irradiated to the dashboard 14 or the like at a high rate. For example, when a book is placed on 14, the reception pulse 37 may be formed due to the influence of the reflected light from the windshield 11. At this time, the reception pulse 37 is detected almost at the same time as the transmission pulse 35, and the monitor unit 24 of FIG.
On the display 24D of, the inter-vehicle distance is 0 based on the time 36F.
m was displayed, and a false alarm by voice was output from the speaker 24H.

FIG. 4 (a) shows the layout of the windshield 11
The incident angle i of the light is the normal to the windshield 11.
Is defined by the intersection angle with
Of the directional components, the component that vibrates in the plane including the incident angle is P-polarized.
The directional component and the component orthogonal thereto are S-deflection components. This and
The refractive index in the air is N₁, The refractive index of the glass material is N ₂
Then, the reflectance R for the S deflection component_S, Transmittance
T_S, P Reflectance factor for deflection component R_P, Transmittance T_PIs
Each is calculated as in equations (1) to (4).

In FIG. 4B, the transmittance of the windshield 11 with respect to the S-polarized component monotonically increases as the incident angle i increases. On the other hand, the transmittance for the P-polarized component slowly increases until the incident angle i reaches 50 degrees, reaches a minimum in the range of 50 to 60 degrees, and then sharply decreases.

Therefore, the combination of the inclination of the windshield 11 and the emitting direction of the laser light of the inter-vehicle distance measuring device 10 is determined so that the incident angle i is in the range of 50 to 60 degrees, and in this state, the semiconductor laser device Adjust the posture of 18 (PN
If the joining direction of the joining is set to the horizontal direction), the maximum transmittance for the P deflection component can be effectively utilized, and the adverse effect due to the reflection of the windshield 11 can be maximally removed.

FIG. 5 is an explanatory view of an inter-vehicle distance measuring device of the second embodiment. Here, of the configurations of the first embodiment shown in FIGS. 1 to 3, the configuration shown in FIG. 1 (b) is replaced with FIG. 5 to form a second embodiment. In addition to adjusting the posture of the semiconductor laser element, a polarizing plate is provided to further suppress the influence of reflection on the windshield 11.

In FIG. 5, the sending section 12 is a protective plate 1.
In addition to 6, the lens 17 and the semiconductor laser element 18, a polarizing plate 51 is provided. The attitude of the semiconductor laser element 18 is
The junction surface 19 of the PN junction is set to be oriented vertically.
The laser light generated at the bonding surface 19 of the semiconductor laser element 18 is irradiated forward through the lens 17, the deflection plate 51, and the protection plate 16 and enters the windshield 11.

The semiconductor laser element 18 uses a laser diode element (LD element), and the power of the deflection component parallel to the joint surface 19 occupies 90% in the total radiation amount of the laser light. Therefore, with the joint surface 19 of the PN junction oriented vertically, a deflection component parallel to the joint surface 19 is made incident on the windshield 11 as a P deflection component.

On the other hand, the deflection direction of the polarizing plate 51 (deflection component selectively transmitted) is set to the vertical direction. Polarizing plate 51
Selectively transmits a deflection component parallel to the joint surface 19 and blocks a deflection component perpendicular to the joint surface 19. The polarizing plate 51 is
It may be arranged at a position 52 between the lens 17 and the semiconductor laser element 18, or may be formed integrally with the lens 17 by utilizing a method of attaching a polarizing film.

The polarizing plate 51 completely eliminates the deflection component in the bonding direction generated by the semiconductor laser element 18, that is, the S deflection component with respect to the windshield 11. Therefore,
Due to the synergistic effect of using the maximum transmittance of the P deflection component,
Further, it is possible to secure a minimum generation level of reflected light.

In the above embodiment, since the inter-vehicle distance measuring device is arranged on the center line of the vehicle body, the intersection angle between the laser beam and the windshield is formed exclusively in the vertical plane. On the other hand, when arranging the inter-vehicle distance measuring device on the dashboard in the right corner space seen from the driver, in addition to the vertical tilt of the windshield, the horizontal tilt is also taken into consideration in consideration of the semiconductor laser. The attitude of the element is adjusted.

That is, the joining surface of the semiconductor laser element is obliquely determined so as to be coincident with the plane including the intersecting angle between the emitted laser light and the windshield.

[0055]

According to the laser radar device of the first aspect, when the laser radar device is arranged in the passenger compartment,
When the front surface of the laser radar device is covered with an oblique transparent resin cover, it is possible to prevent the malfunction of the light receiving means caused by the reflection of the transparent plate, for example, the false detection of the preceding vehicle.

Further, since the ratio of the transmitted light of the transparent plate to the laser beam output by the semiconductor laser element increases, the intensity of the laser beam emitted to the space in front of the transparent plate without increasing the output of the semiconductor laser element. Can be increased. Therefore, for example, if it is an inter-vehicle distance measuring device,
The measurable inter-vehicle distance limit has been expanded, and it is possible to detect even distant preceding vehicles that were previously undetectable.

Further, in the space on the laser radar device side behind the transparent plate, there is no need to design in consideration of the reflected light of the transparent plate, and the degree of freedom of the installation location of the laser radar device is increased. For example, in the case of the inter-vehicle distance measuring device, it is not necessary to paint the dashboard black, and bright colors can be used. Therefore, the degree of freedom in designing the color of the interior of the vehicle is increased.

According to the laser radar device of the second aspect, the ratio of the reflection on the transparent plate is further reduced as compared with the laser radar device of the first aspect, and the malfunction of the light receiving means caused by the reflection of the transparent plate is possible. Sex is also reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an inter-vehicle distance measuring device according to a first embodiment.

FIG. 2 is an explanatory diagram of an outer appearance of an inter-vehicle distance measuring device.

FIG. 3 is an explanatory diagram of a usage state of an inter-vehicle distance measuring device.

FIG. 4 is an explanatory diagram of a relationship between a deflection component and reflectance.

FIG. 5 is an explanatory diagram of an inter-vehicle distance measuring device according to a second embodiment.

[Explanation of symbols]

 10 Inter-vehicle distance measuring device 11 Windshield 12 Transmitter 13 Receiver 14 Dashboard 15 Roof 16 Protective plate 17 Lens 18 Semiconductor laser element 19 Bonding surface

Claims (2)

[Claims] 1. A semiconductor laser device (18), which is disposed behind a transparent plate (11) having one side retracted and emits a laser beam through the transparent plate (11), and the transparent plate (11). On the other hand, a light receiving means (13) is provided on the same side as the semiconductor laser element (18) and detects reflected light of laser light emitted by the semiconductor laser element (18) through the transparent plate (11). In the laser radar device (12), the direction parallel to the joint surface (19) of the laser element (18) is made to substantially coincide with the backward direction of the posture of the transparent plate (11), and the laser element (18) is moved. A laser radar device characterized by being placed. 2. The laser radar device according to claim 1, further comprising: a deflection unit having a deflection direction set in a backward direction of a posture of the transparent plate, on a laser light emitting path between the semiconductor laser element and the transparent plate. A laser radar device characterized by that.