JPH0712938A - Laser radar equipment for vehicle - Google Patents

Abstract

PURPOSE:To improve the distance and vehicle-to-vehicle distance detecting accuracy of laser radar equipment for vehicle by using a light gathering window having a large area without affecting the design of vehicles nor requiring any special installing space. CONSTITUTION:Laser radar equipment for vehicle is constituted of a light emitting section 102 which is installed to the front face part of a vehicle 101 and emits a laser beam, light guide section 105 which is formed of a wind shield 103 and volumetric hologram 104 and guides the reflected light of the laser beam to a prescribed position, extraction prism 106 for extracting the reflected light of the laser beam guided to the prescribed position through the section 105, and light receiving section 107 which receives the reflected light of the laser beam extracted through the prism 106. The light guide section 105 guides the reflected light of the laser beam to the light receiving section 107 by diffracting the reflected light so that the light can advance in the wind shield 103 at a total reflection angle by using the shield 103 and volumetric hologram 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention emits a laser beam in front of a vehicle and receives a laser reflected beam of the laser beam,
The present invention relates to a vehicle laser radar device that detects a distance to an obstacle ahead or a distance between vehicles.

[0002]

2. Description of the Related Art As conventional laser radar devices for vehicles, there are devices shown in FIGS. 13 and 14, for example. This vehicle laser radar device 1401 includes a light transmitting unit 14
A laser beam is emitted from 02 to the front of the vehicle, the laser reflected light of the laser beam is received by the light receiving section 1403, and the distance detection circuit 1404 detects the distance to the obstacle ahead or the inter-vehicle distance. Like the vehicle 1405
Is attached to the front surface (here, the bumper section).

FIG. 14 shows the structure of the laser radar device 1401 shown in FIG. 13. A light transmitting section 1402 outputs a laser beam from a laser diode driving section 1501 and a laser diode 1502 for outputting a laser beam and a laser diode 1502. A light-transmitting lens 1503 and an emission window 150 that spread the laser light at a predetermined angle and emit the laser light.
4 and.

The light receiving section 1403 includes a daylighting window 1505 for taking in the laser reflected light and a daylighting window 150.
Honeycomb filter and infrared filter 150 for selectively passing laser reflected light from the light taken in 5
6, a condenser Fresnel lens 1507 for condensing the laser reflected light, and a PIN photodiode 15 for taking in the light (laser reflected light) as a current (signal)
08 and an amplifier 1509 that amplifies a signal photoelectrically converted by the PIN photodiode 1508.

Reference numeral 1510 in the figure is a distance detection circuit 14
A distance display device for displaying the distance obtained in 04, a vehicle speed sensor 1511, and a signal processing circuit 1512 for performing processing such as warning based on the vehicle speed and the distance.

[0006]

However, according to the above-mentioned conventional laser radar device for a vehicle, a light-receiving window for collecting the laser-reflected light is required in the light-receiving section, and in order to improve the detection accuracy, Although it is desirable to make this daylighting window large, it is not possible to provide a large area daylighting window due to vehicle design restrictions.
There is a problem in that the accuracy of distance detection and inter-vehicle distance detection is limited.

Further, according to the above-mentioned conventional laser radar device for a vehicle, a honeycomb filter, an infrared filter and a converging Fresnel lens having the same size as the daylighting window are required. However, even when the area of the daylighting window is increased, the light receiving part becomes large in proportion to the area of the daylighting window, and there is a problem that a special installation space is required.

The present invention has been made in view of the above, and detects a distance using a large-area daylighting window without affecting a vehicle design and requiring a special installation space. It is also intended to improve the accuracy of vehicle distance detection.

[0009]

In order to achieve the above object, the present invention emits a laser beam in front of a vehicle and receives a laser reflected light of the laser beam to detect a distance to an obstacle in front or A laser radar device for a vehicle that detects an inter-vehicle distance is provided with a volume hologram that is disposed on or inside a windshield and diffracts laser reflected light that has entered the windshield so that it travels within the windshield at a total reflection angle. Provided is a laser radar device for a vehicle, which collects laser reflected light using a windshield and a volume hologram.

[0010]

In the vehicle laser radar device of the present invention, the laser reflected light of the laser light travels in the windshield at a total reflection angle by using the volume hologram and the windshield arranged on or in the windshield. And guide it to the light receiving part.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, a laser radar device for a vehicle according to the present invention will be described in the order of [Example 1], [Example 2], [Example 3], [Example 4] and [Example 5]. And will be described in detail.

[Embodiment 1] FIG. 1 shows a configuration of a laser radar device for a vehicle according to Embodiment 1, which is provided in a front portion of a vehicle 101 and has a light transmitting section 102 for emitting a laser beam,
A light guide section 105 which is formed by the windshield 103 and the volume hologram 104 and guides the laser reflected light to a predetermined position, and an extraction prism 106 for extracting the laser reflected light guided to the predetermined position by the light guide section 105.
And a light receiving section 107 that receives the laser reflected light extracted by the extraction prism 106.

Here, the windshield 103 includes a glass 103a outside the vehicle and a glass 103a inside the PVB intermediate layer 103b.
This windshield 10 is formed by joining with
A transparent volume hologram 104 is inserted between the glasses when manufacturing 3.

The extraction prism 106 is attached to the lower end portion of the windshield 103 (that is, a predetermined position of the light guide portion 105) with an optical adhesive.

Further, as shown in the figure, the light receiving portion 107 arranged in parallel with the extraction surface of the extraction prism 106 does not have a honeycomb filter, and has a daylighting window 107a and a laser for collecting the laser reflected light. Fresnel lens 10 for condensing
7b, a PIN photodiode 107c for taking in light (laser reflected light) as a current (signal), and an amplifier (not shown).

Numeral 108 is a vehicle dash panel, RL
Reference symbol o denotes laser light emitted from the light transmitting unit 102, and RLa and RLb denote reflected light (laser reflected light) of the laser light RLo.

FIG. 2 shows a method of fixing the light receiving portion 107.
In the first embodiment, the laser reflected light guided through the light guide section 105 and the extraction prism 106 receives the laser reflected light.
In order to improve the accuracy of distance detection and inter-vehicle distance detection, the light receiving unit 107 is arranged so that the positional relationship between the light receiving unit 107 and the extraction prism 106 does not change, as shown in FIG. Further, an optical adhesive is applied and fixed between the OQ surface of the extraction prism 106 and the surface of the light collection window 107a of the light receiving unit 107. In addition, as another method, for example, as shown in FIG.
The light receiving unit 107 and the light receiving unit 107 may be fixed using the blanket 201.

Next, referring to FIGS. 1, 3 and 4,
The symbols used for the description of the operation described later are defined as follows.

Θi1: Incident angle when the laser reflected light RLa is incident on the glass 103a from the atmosphere (see FIG. 1) θ'i1: When the laser reflected light RLa is incident on the point A of the volume hologram 104 from the glass 103a. Incident angle (see Fig. 1) θi2: Laser reflected light RLb from the atmosphere to glass 1
03a incident angle (see FIG. 1) θ′i2: incident angle when the laser reflected light RLb enters the volume hologram 104 at point B of the volume hologram 104 (see FIG. 1) θr: volume hologram 104 Diffraction angle = light guide 10
5 reflection angle (see FIG. 1) t: thickness of the windshield 103 (see FIG. 3) PQ surface: extraction surface (see FIGS. 1 and 3) θk: inclination angle of the extraction prism 106 (FIGS. 1 and 3)
L): length of volume hologram 104 provided in windshield 103 = length of windshield 103 (see FIG. 4) θt: inclination angle of windshield 103 (see FIG. 4) O′Q ′ surface: vertical direction Projection plane of windshield 103 on (see FIG. 4) C _air : speed of light in _air C _Glass : speed of light in glass The operation of the above configuration will be described. Since the transmission type volume hologram 104 is a hologram that selectively diffracts the laser radar wavelength, it is not colored by external light and does not interfere with the driver's vision. Therefore, since it can be provided over the entire area of the windshield 103, the relationship of the length L of the volume hologram 104 = the length L of the windshield 103 is set in the first embodiment.

The windshield 103 receives laser reflected lights RLa and RLb from the front vehicle and lights of various wavelengths from all angles. Of the light beam incident on the volume hologram 104, only the wavelength component that meets the diffraction condition of the volume hologram 104 is diffracted at the diffraction angle θr. Here, the diffraction conditions of the volume hologram 104, the wavelength of the wavelength = reflected laser beam, and the incident angle theta _i is theta _t through? _T
The range is + 3 °. When the diffraction angle θr is equal to or greater than the critical angle at the glass-atmosphere interface, the light diffracted by the volume hologram 104 is totally reflected at the glass-atmosphere interface, and the windshield 103 itself serves as a light guide plate. It functions as the light guide unit 105.

The sea-side angle at the glass-atmosphere interface is shown in FIG. 5 (a).
As shown in, when the refractive index of glass is n (n = 1.52), the critical angle θ _c is _calculated by the following equation.

Sin ⁻¹ (sin θ _c × n) = 90 ° θ _c = 41.8 ° Therefore, in order to make the diffraction angle θr larger than the sea angle θ _{c in} advance, θr ≧ 41.8 ° and the volume hologram 1 is set.
04 should be produced.

The windshield 1 is guided by the light guide portion 105.
The laser reflected light (RLa and RLb) reflected and conducted to the extraction prism 106 provided at the lower end of 03 is
It is taken out of the windshield 103 from the OQ surface by the extraction prism 106. Here, the extraction prism 1
The size of 06 is defined by the thickness t of the windshield (windshield) and the hologram diffraction angle θr, and can be obtained by the following equation.

PQ length = 2 × t × tan (θr) θk = 90−θr OQ length = PQ length × sin (θk) If the light receiving portion 107 is arranged in parallel with the OQ surface of the extraction prism 106, O′Q Laser reflected light (R
La and RLb) can be received on the OQ surface. Here, the relationship between the O'Q 'length and the OQ length is O'Q' length = L × sin (θt) >> OQ length.

Further, since the volume hologram 104 has a filter effect and allows only the wavelength set at the time of exposure to pass, the honeycomb filter (1506 in FIG. 14) required in the conventional example becomes unnecessary, and the light receiving portion is eliminated. 107
Can be miniaturized.

In the light receiving section 107, the laser reflected light thus collected is supplied to the PIN photodiode 107.
At c, the light is received as a light reception signal, amplified by an amplifier, and the distance is detected by a distance detection circuit (not shown).

On the other hand, the laser reflected light captured by the PIN photodiode 107c as a received light signal is shown in FIG.
As shown in (b), the optical path difference (lag of sensing time) between the laser reflected light RLb incident on the upper side (point B) and the laser reflected light RLa incident on the lower side (point A) of the volume hologram 104. ) Exists, it is necessary to consider this optical path difference when detecting the distance based on the laser reflected light.

The delay x of the sensing time of the light incident on the points A and B is obtained by the equation 1.

[0029]

[Equation 1]

In a normal vehicle, L = 700 to 800
mm, θt = 30 to 35 °, t = 5 mm. For example, here, L = 800 mm, θt = 30, t = 5 m
Assuming that the system is configured with m and θr = 42 °, the delay x in sensing time is

[0031]

[Equation 2]

When the delay of the sensing time of 5 [nsec] is converted into the optical path difference in the atmosphere, it becomes 5 × 10 ⁻⁹ × 3 × 10 ⁸ = 1.5 m. Therefore, if the emission pulse having a proper pulse width and the sampling interval are set, the distance from the preceding vehicle can be measured within the range of measurement variation ± 1.5 / 2 [m].

Specifically, for example, as shown in FIG.
When the pulse interval of the sampling time is set to 5 [nsec] and the pulse width is set to 5 [nsec] or less, the distance from the preceding vehicle (T × C [m]: T is the laser light emission to the laser reflection light reception Until time, C is the speed of light)
Is in the range of (T ′ × C) <(T × C) <(T ″ × C), that is, the measurement variation can be measured within the range of ± 1.5 / 2 [m].

Further, as shown in FIG. 7, when the waveform shaping process is performed, the sensing distance can be extended and the measurement accuracy can be improved while keeping the pulse width and the sampling interval as in the conventional type. Since the received pulse shape of the laser reflected light can be predicted, T ₁ and T ₂ can be calculated from the pulse intensity ratio of one or two sampled pulses, and accurate distance measurement can be performed. In FIG. 7, each symbol indicates the contents of Table 1.

[0035]

[Table 1]

However, since there is a noise level, in the conventional type, the received light pulse having a pulse intensity smaller than the noise level of 0.5 × I is buried in the noise.

Therefore, the time from the emission of the laser light to the reception of the laser reflected light is a distance of T ₂ , in other words, (T
The distance of ₂ × C) / 2 [m] cannot be measured. In comparison with this, in the hologram lighting type of the first embodiment, the pulse intensity of the laser reflected light is integrated and increased, so that T ₂
Any time greater than the noise level, (T ₂ ×
C) A distance of 2 [m] can be measured.

However, it is necessary that the delay x of the sensing time is sufficiently smaller than the pulse width T _{P of} the laser light (emitted light) pulse. If the wavelength shaping process is performed in this way, a measurement accuracy of about 1 m can be obtained at T _P = 130 to 150 nsec and a sampling time of 60 to 70 nsec. At this time, T _P >> x (x = 5 nsec).

As described above, according to the first embodiment, since the windshield 103 is used as the light guide section 105,
It is possible to secure a large-area daylighting window without specially providing a daylighting window on the front surface of the vehicle, in other words, without being restricted by the vehicle design. In addition, the filter effect of the volume hologram 104 for daylight obviates the need for the honeycomb filter and the infrared filter, so that the light receiving portion can be downsized.

Furthermore, since the windshield 103 is used as a daylighting window, it is possible to periodically remove the water droplets attached by a wiper in case of rain, etc. Not affected,
The light receiving ability is improved.

[Embodiment 2] FIG. 8 shows the structure of a laser radar device for vehicles according to Embodiment 2, in which a reflective volume hologram 801 is used in place of the transmissive volume hologram 104 of Embodiment 1. Is. The other configuration is the first embodiment.
Since it is similar to the above, illustration and description are omitted. With such a configuration, the same effect as that of the first embodiment can be obtained.

[Third Embodiment] FIG. 9 shows the structure of a laser radar device for a vehicle according to a third embodiment. The light from the extraction prism 106 is supplied to the PIN photodiode on the OQ surface of the extraction prism 106 of the first embodiment. By providing the transmissive hologram 901 that is exposed so as to collect light on the light-receiving part 107, the light-collecting Fresnel lens of the light-receiving part 107 is eliminated. In addition, 902 shows an amplifier. The other configurations are similar to those of the first embodiment, and thus illustration and description thereof are omitted. With such a configuration, not only the same effect as that of the first embodiment can be obtained, but also the transmissive hologram 901 is provided in place of the Fresnel lens for condensing, which is thick and heavy, so that the light receiving unit 107 is provided. Can be miniaturized.

[Embodiment 4] FIG. 10 shows the structure of a laser radar device for a vehicle of Embodiment 4, in which a laser radar signal wavelength (laser light wavelength) is provided on the lower end PQ surface of the windshield 103 of Embodiment 1. The transmission type volume hologram for extraction 1001 which selectively diffracts is provided, and the light guide section 105
(Wind shield 103 and volume hologram 10
4) The extraction prism and the light-collecting Fresnel lens of the light-receiving portion 107 are eliminated by diffracting the signal light transmitted through the interior to the atmosphere side. In addition, 1002 shows an amplifier. The other configurations are similar to those of the first embodiment, and thus illustration and description thereof are omitted. With such a configuration, not only the same effect as that of the first embodiment can be obtained, but also the extraction prism and the converging Fresnel lens are replaced with the extraction transmissive volume hologram 1001, so that the configuration is simplified. Can be achieved.

[Embodiment 5] FIG. 11 shows the configuration of a laser radar device for a vehicle of Embodiment 5, in which the laser radar signal wavelength (laser light wavelength) is provided on the surface opposite to the lower end PQ surface of the windshield 103 of Embodiment 1. A transmission type volume hologram for extraction 1101 for selectively diffracting (wavelength) is provided, and the extraction prism and the converging Fresnel lens of the light receiving unit 107 are eliminated. In addition, 1102 shows an amplifier. The other configurations are similar to those of the first embodiment, and thus illustration and description thereof are omitted. With such a configuration, the fourth embodiment
The same effect as can be obtained.

FIG. 12 shows the structure of a laser radar device for a vehicle related to the present invention, in which a volume hologram 1302 is provided on a headlamp cover 1301 to function as a light guide for daylighting of the laser radar device for a vehicle. It was made. In the figure, 1303 is a transmission type volume hologram for extraction which selectively diffracts a laser radar signal wavelength (wavelength of laser light), and 1304 is a PIN for taking in light (laser reflected light) as a current (signal).
A photodiode, 1305 is an amplifier, and 1306 is a headlamp. With such a configuration, the same effect as that of the first embodiment can be obtained.

[0046]

As described above, according to the present invention,
Since the laser reflected light of the laser light is diffracted so that it travels in the windshield at a total reflection angle by using the volume hologram and the windshield arranged on the windshield surface or inside, it is guided to the light receiving unit. The accuracy of distance detection and inter-vehicle distance detection can be improved by using a large-area daylighting window without affecting the design and without requiring a special installation space.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is an explanatory diagram showing a method of fixing a light receiving unit.

FIG. 3 is an explanatory diagram for defining terms used in Example 1.

FIG. 4 is an explanatory diagram for defining terms used in Example 1.

FIG. 5 (a) is an explanatory diagram showing a water surface angle at a glass-atmosphere interface, and FIG. 5 (b) is an explanatory diagram showing an optical path difference.

FIG. 6 is an explanatory diagram showing an example of setting an emission pulse having an appropriate pulse width and a sampling time.

FIG. 7 is an explanatory diagram showing an example in which a waveform shaping process is performed.

FIG. 8 is a configuration diagram of a second embodiment.

FIG. 9 is a configuration diagram of a third embodiment.

FIG. 10 is a configuration diagram of a fourth embodiment.

FIG. 11 is a configuration diagram of a fifth embodiment.

FIG. 12 is an explanatory diagram showing a configuration of a vehicle laser radar device related to the invention.

FIG. 13 is an explanatory diagram showing a configuration of a conventional vehicle laser radar device.

FIG. 14 is a configuration diagram of a conventional vehicle laser radar device.

[Explanation of symbols]

 101 Vehicle 102 Light Transmitting Section 103 Wind Shield 104 Volume Hologram 105 Light Guide Section 106 Extraction Prism 107 Light Receiving Section 801 Volume Hologram 901 Transmission Hologram 1001 Extraction Transmission Volume Hologram 1101 Extraction Transmission Volume Hologram

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G08G 1/16 E 7531-3H

Claims (1)

[Claims] 1. A laser radar device for a vehicle, which emits a laser beam in front of a vehicle and receives a laser reflected light of the laser beam to detect a distance to an obstacle ahead or an inter-vehicle distance. A volume hologram is provided which diffracts laser reflected light incident on the windshield so as to travel within the windshield at a total reflection angle, and collects laser reflected light using the windshield and the volume hologram. Laser radar device for vehicles characterized by.