JPH0734035B2 - Automotive Doppler radar - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vehicle-mounted radar device, and more particularly to a vehicle-mounted Doppler radar adapted to detect a moving object by utilizing a Doppler effect.

2. Description of the Related Art Recently, a system has been developed in which a radar is mounted on an automobile to detect an obstacle such as a vehicle traveling in front and activate an automatic braking device. It is difficult to detect only the object, and stationary objects such as guardrails on the road surface and side zones are also detected, making it difficult to derive the detection signal of the object from the radar output.

The present invention has been made in consideration of the above points, and when detecting an object using a Doppler radar, removes a reflection signal from a stationary object on the road surface and side bands to detect only a moving object. The present invention provides a vehicle-mounted Doppler radar.

To achieve the object, the present invention combines a reflected beam from an object when a beam having a fundamental frequency is emitted toward a target and a beam in which the fundamental frequency is Doppler frequency-shifted according to the vehicle speed in advance. By doing so, only the reflected beam from the moving object is extracted.

Further, in order to achieve the object, the present invention combines a beam having a fundamental frequency with a beam reflected from an object when a beam whose fundamental frequency has been Doppler frequency shifted according to the vehicle speed is emitted toward a target. By doing so, only the reflected beam from the moving object is extracted.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In the vehicle-mounted Doppler radar according to the present invention, as shown in FIG. 1, a laser device 1 for emitting a laser beam Bo frequency-modulated by a fundamental frequency fo, and the emitted laser beam Bo are distributed in two directions. A distributor 2, a light-transmitting optical system 3 for irradiating a laser beam Bo distributed in one direction in a predetermined direction, and a reflected beam Br having a frequency fr, which is Doppler frequency-shifted, from an object 4. Basic frequency distributed to the other side by the light receiving optical system 5 and the distributor 2.
Doppler shifter 6 for shifting the Doppler frequency according to the traveling speed of the vehicle based on the laser beam Bo having fo
, A light combiner 7 for combining a laser beam Bt having a frequency ft that is Doppler frequency shifted according to the traveling speed of the vehicle and a reflected beam Br received from the object 4, and the light combined beam Bm. To an electric signal Sm, and a filter and an amplifier 9 for filtering and amplifying the frequency fm component of the converted electric signal Sm.
And a frequency measuring instrument 10 for measuring the frequency fm based on the processed signal Sm ′ and outputting a signal Sv corresponding to the relative speed between the own vehicle and the object 4.

FIG. 2 shows a concrete configuration example of the Doppler shifter 6. Here, the reflected beam Bt when the laser beam Bo is irradiated onto the rotating drum 62 through the condenser lens 61 is received through the light receiving lens 63. ing. Further, the rotary drum 62 is a speed governor using a speed cable 65, which is a rotation source proportional to the rotation of the tire, taken out from the rear end of the transmission as a drive source.
The rotation speed is controlled by 64, and is kept at the rotation speed according to the traveling speed Vo (m / s) of the vehicle at that time.

In this case, assuming that the radius of the rotating drum 62 is r (m), the rotating speed thereof is N (r / s), and the speed of light is c (m / s), the Doppler value according to the following equation is calculated according to the rotation of the rotating drum 62. Frequency fd
(Hz) occurs.

fd = (2 × 2πr × N / c) · fo (1) Then, the laser beam Bo having the fundamental frequency fo irradiated on the rotating drum 62 undergoes the Doppler frequency shift, and the frequency given by the following formula A reflected beam Bt with ft will be obtained.

ft = fo + fd (2) In such a Doppler shifter 6, a Doppler frequency shift that particularly satisfies the relationship of the following equation is generated.

ft = fo (1 + 2Vo / c) (3) That is, when the tire rotation speed is M (r / s) and the tire radius is L (m), Vo = 2πLM, so (1)
From the relationship with the formula, governor so that N = LM / r is satisfied.
The rotation speed N of the rotary drum 62 is set by 64.

When the laser beam Bo is emitted through the light transmitting optical system 3 and is reflected by the object 3 in the structure as described above, it undergoes Doppler frequency shift due to the Doppler effect, and at that time, the light receiving optical system. The frequency fr of the reflected beam Br received through 5 is given by:

fr = fo {1 + 2 (Vo-Va) / c} (4) Here, Va is the moving speed (m / s) of the object 4.

Then, the received reflected beam Br and the Doppler shifter 6
Thus, the laser beam Bt that has undergone the Doppler frequency shift according to the traveling speed Vo of the host vehicle is combined in the optical combiner 7, and the combined laser beam Bm is converted into an electric signal Sm in the photoelectric converter 8.

At this time, the optical combiner 7 is configured to combine the beams Br and Bt so that the frequency fm of the electric signal Sm is given by the following equation.

fm = | ft−fr | (5) Therefore, from equations (3) and (4), fm = 2fo / c · Va (6) is given.

Finally, the converted electric signal Sm is given to the filter and amplifier 9 to filter and amplify the frequency fm component, and the processed signal Sm 'is processed by the frequency measuring instrument 10
The frequency fm is measured there and the signal Sv corresponding to the moving speed Va of the object 4 according to the equation (6) is output.

Specifically, the display is caused to display the speed based on the output signal Sv.

When the object 4 is a stationary object (Va = 0), a laser beam Bo is emitted through the light transmitting optical system 3, and is reflected by the object 4 and received by the light receiving optical system 5 as a reflected beam Br. The frequency fr is given by:

fr = fo {1 + 2Vo / c} (7) Therefore, in this case, as shown in the equation (3), the frequency of the laser beam Bt that has undergone the Doppler frequency shift in the Doppler shifter 6 according to the traveling speed Vo of the vehicle. It becomes equal to ft, and from the relationship of the equation (5), fm = 0 when fr = ft, and no output is generated from the frequency measuring instrument 10.

As described above, in the vehicle-mounted Doppler radar according to the present invention, when the vehicle-mounted Doppler radar detects the moving speed Va of the moving object 4 such as a vehicle traveling in front, the stationary Doppler radar on the road surface or side band becomes noise. The reflected signal component from the object can be surely removed, and the speed can be detected with high accuracy.

FIG. 3 shows another embodiment of the present invention. In this case, a laser beam Bt whose Doppler frequency is shifted by the Doppler shifter 6 according to the traveling speed of the vehicle is emitted through the light transmitting optical system 3 to receive light. The reflected beam Br from the object 4 received through the optical system 5 and the laser beam Bo having the fundamental frequency fo are combined in the optical combiner 7.

With such a configuration, the Doppler shifter 6 causes a Doppler frequency shift that satisfies the following expression.

ft = fo (1-2Vo / c) (8) Here, the rotation direction of the rotary drum 62 in the Doppler shifter 6 is opposite to that in the case of FIG.

In this case, however, the frequency fr of the reflected beam Br received by the light receiving optical system 5 from the object 4 is given by the following equation.

fr = ft {1 + 2 (Vo-Va) / c} (9) Further, the frequency fm of the electric signal Sm that is combined by the optical combiner 7 and converted by the photoelectric converter 8 is given by the following equation.

fm = | fr−fo | (10) Therefore, if equation (10) is transformed using equations (8) and (9), fm = | fo {2Vo / c + 4Vo (Vo−Va) / c ² } | … (11)

Electric signal Sm when the object 4 is a stationary object (Va = 0)
If the frequency of is fms, then from equation (11), fms = fo · 4Vo ² / c ² … (12).

Here, as the traveling speed Vo of the own vehicle, assuming that the maximum traveling speed of the own vehicle is 50 m / s (180 Km / h) when considering a normal traveling state, the condition of the maximum value Vo = 50 m / s And fo = 3.33 × 10 ¹⁴ (H
When z) is given, the value of fms = 37 (Hz) is obtained.

That is, the maximum value of the frequency fms of the electric signal Sm finally output from the optical converter 8 based on the reflected beam Br from the stationary object when the own vehicle is traveling at the maximum speed of 50 m / s is 37 Hz. Then, it will never exceed at least 40Hz.

fms37 <40 (Hz) (13) Therefore, a band filter is used in the filter of the next stage and the amplifier 9 to select the lower limit of the pass band to 40 Hz, and the movement obtained when the vehicle is actually traveling is obtained. If the electric signal Sm output from the photoelectric converter 8 is passed through the bandpass filter based on the turbid reflected beam Br from an object or a stationary object, the maximum value of fms by the stationary object can be cut off. , As a result, the reflected beam Br
Among these, the reflection component from the stationary object can be removed to the utmost. Also, the upper limit of the pass band is fm
By selecting a value slightly higher than the maximum value of, it becomes possible to suppress the influence of noise due to sunlight or other ambient light. Specifically, the bandwidth of the filter section is set to about 2.22 to 111 MHz.

When 0 <Vo <50 (m / s) and 1 <Va <50 (m / s), the ratio of each term in the relationship of the equation (11) is Becomes

In the relationship of equation (11), the term of 4Vo (Vo−Va) / c ² is so small that it can be ignored compared to the term of 2Va / c, so that term can be omitted. , (11) can be approximated as follows.

fm ≈ fo · 2Va / c (14) That is, when the moving speed of the object 4 is 1 m / s or more, 0.
The frequency fm is the moving speed Va of the object 4 with an error of 01% or less.
Can be approximated as being approximately proportional to.

Therefore, if such an approximation is performed, the moving speed of the object 4 can be directly obtained from the frequency fm measured by the frequency measuring device 10, and there is almost no influence of the running speed of the own vehicle, and Up to now, it becomes possible to directly measure the moving speed of the object 4.

FIG. 4 shows a concrete configuration example of the vehicle-mounted Doppler radar according to the present invention. The laser device 1 has an optical wavelength λ = 900n.
A laser diode LD having m is used, and half mirrors HM1 and HM2 are used for the distributor 2 and the optical combiner 7, respectively. Further, the light transmitting optical system 3 and the light receiving optical system 5
A PIN type photodiode PD is used for the photoelectric converter 8 by using a combination of lenses L1 and L2 as shown in FIG. In the figure, reference numeral 11 denotes a display for displaying the moving speed of the object 4 based on the value measured by the frequency measuring device (frequency counter) 10.

In the above embodiments, the case where a laser beam is used has been described, but it goes without saying that a beam of radio waves, ultrasonic waves, or the like can be used as the laser medium.

As described above, in the vehicle-mounted Doppler radar according to the present invention, it is mounted in an automobile or the like, a beam having a fundamental frequency is emitted, and a reflected beam subjected to Doppler frequency shift by an object is received to change its frequency. When measuring the moving speed of an object such as a vehicle ahead from the minute, the reflected beam component from a stationary object is removed by adding a beam whose fundamental frequency is Doppler frequency shifted according to the running speed of the vehicle in advance. Therefore, with a simple configuration, it is possible to reliably detect the moving speed itself of a target moving object such as a vehicle traveling ahead by excluding the reflected beam from a stationary object such as a guardrail on the road surface and side bands. It has the excellent advantage of

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a vehicle-mounted Doppler radar according to the present invention, FIG. 2 is a simplified diagram showing an example of the configuration of a Doppler shifter used in the same embodiment, and FIG. 3 is another embodiment of the present invention. FIG. 4 is a block diagram showing the configuration, and FIG. 4 is a diagram showing a specific configuration example of the optical system. 1 ... Laser device, 2 ... Distributor, 3 ... Light-transmitting optical system,
4 ... Object, 5 ... Receiving optical system, 6 ... Doppler shifter,
7 ... Optical combiner, 8 ... Photoelectric converter, 9 ... Filter and amplifier, 10 ... Frequency measuring device, 11 ... Display device

Claims (2)

[Claims] 1. A means for emitting a beam having a fundamental frequency, a means for receiving a reflected beam from an object, and a means for shifting a beam having a fundamental frequency in advance according to the speed of the vehicle. An in-vehicle Doppler radar including means for synthesizing the beam subjected to the Doppler frequency shift and a reflected beam from the received object, and means for measuring the frequency of the synthesized beam to detect the moving speed of the object. 2. A means for shifting a beam having a fundamental frequency according to the speed of the vehicle, a means for emitting the beam subjected to the doppler frequency shift, and a means for receiving a reflected beam from an object. For vehicle use, which is composed of means for synthesizing the reflected beam from the received object and a beam having a fundamental frequency, and means for approximately detecting the moving speed of the object by measuring the frequency of the synthesized beam Doppler radar.