JPS62123378A - Apparatus for measuring car speed - Google Patents

Abstract

PURPOSE:To suppress the scaling-up of the titled apparatus, by a method wherein an electromagnetic wave is transmitted to a vehicle in a plurality of directions and the speed component of the vehicle in each of a plurality of directions is calculated on the basis of the difference between the frequency of the reflected wave of each running road surface and that of a transmitted electromagnetic wave. CONSTITUTION:When an electromagnet 9 is excited by an exciter 11, the movable iron core of the electromagnet 9 moves while pressing a spring 10 to allow a mirror 7 to move to the first position on the light path of laser beam. As a result, one of laser beams, obtained when the laser beam outputted from a laser beam source 1 straightly advances through beam splitters 3, 5, is reflected by a reflector 7 to be allowed to irradiate the surface 13 of the earth 13 at an angle alpha. Scattering beam obtained by reflecting said laser beam from the surface 13 of the earth is reflected by the reflector 7 to be received by a beam detector 23 through the beam splitter 5 and the reference beam reflected by mirrors 19, 21 is incident to the beam detector 23 while being synthesized with scattering beam by the beam splitter 5. The scattering beam and the reference beam from the surface 13 of the earth received by the beam detector 23 are supplied to a frequency difference detector 25 and the frequency difference between both beams is detected to be outputted. This frequency difference is substituted for a predetermined formula to make it possible to determine the speed of the front of a vehicle in the before-and-behind direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a vehicle speed measuring device that measures the ground speed of a vehicle using the Doppler effect of laser light.

[Technical background of the invention and its problems] Conventionally, a Doppler radar device is mounted on a vehicle, and electromagnetic waves are transmitted from the radar toward the road surface while the vehicle is running, and the frequency of the reflected wave from the road surface is the transmitted electromagnetic wave. The phenomenon of deviation from the frequency of
That is, a vehicle speed measuring device that detects the running speed of a vehicle using the Doppler effect is known (for example, Japanese Patent Application Laid-Open No.
-665).

FIG. 2 is a block diagram showing an example of a conventional vehicle speed measurement device using such a Doppler effect. In the figure, an excavator 31 outputs a high frequency signal having a resonance frequency fO of an ultrasonic speaker 33. The ultrasonic speaker 33 is excited by this high frequency signal and transmits an ultrasonic wave having a fundamental frequency fO at an angle θ toward the ground 35. This ultrasonic wave is reflected by the ground 35 and received by the ultrasonic microphone 37.

The output signal of the ultrasonic microphone 37 is amplified by an amplifier 39 and then supplied to a frequency difference detector 41 .

This frequency difference detector 41 detects the difference fd between the fundamental frequency [O of the transmission signal supplied from the oscillator 31 and the frequency of the reflected wave from the ground 35 supplied from the amplifier 39. This frequency difference "d" is expressed by the following equation as is well known.

fd=2Vfo-cosθ/C-<+) In this formula, C is the speed of sound and ■ is the vehicle speed.

Therefore, as described above, the vehicle speed V can be determined by detecting the frequency difference "d".

By the way, in a vehicle, for example, a four-wheel steering control device or an anti-skid control device, in particular, the two-dimensional speed of the vehicle,
In other words, it is necessary to know the longitudinal velocity V+1 and the lateral velocity ■2 with respect to the front of the vehicle.
and lateral speed V cannot be measured, and vehicle speed measurement devices equipped with Doppler radar must be installed separately in the same way as described above in order to measure longitudinal direction speed Vu and lateral direction speed Vh. However, when it is installed in a vehicle with limited space, space becomes a problem, and the price is almost twice as high, making it extremely uneconomical.

This is even more remarkable when the velocity components to be measured are in multiple directions.

[Object of the Invention] The present invention has been made in view of the above, and its object is to economically detect velocity components of a vehicle in multiple directions while suppressing the increase in size of the device. An object of the present invention is to provide a vehicle speed measuring device.

[Summary of the Invention] In order to achieve the above object, the present invention includes an electromagnetic wave generating means mounted on a vehicle that generates electromagnetic waves having a predetermined frequency, and a means for generating electromagnetic waves that is mounted on a vehicle and generates electromagnetic waves having a predetermined frequency, and a means for generating electromagnetic waves that is transmitted in a plurality of directions relative to the vehicle at predetermined angles with respect to the road surface. and a frequency difference detection device that receives reflected waves from the road surface when electromagnetic waves are output, and detects frequency differences between each reflected wave and the electromagnetic waves. and a calculating means for calculating speed components of the vehicle in the plurality of directions relative to the vehicle based on the frequency differences.

[Embodiments of the invention] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows a vehicle speed measuring device according to an embodiment of the present invention. This vehicle speed measuring device uses the Doppler effect of laser light to measure the longitudinal velocity Vu and the lateral velocity Vh of the front of the vehicle. In the figure, a radar light source 1 is composed of a semiconductor laser diode, a drive circuit for the laser diode, a light transmitting lens, etc., and the laser light output from the laser light source 1 is transmitted to a beam splitter 3.
It passes through and is divided into two directions. One laser beam that travels straight through the beam splitter 3 further travels straight through the beam splitter 5, is reflected by the mirror 7, and illuminates the ground 13. The mirror 7 is driven to vary its position by the iron core of an electromagnet 9 which is biased in one direction by a spring 10, with a first position (mirror 7) indicated by a solid line and a first position (mirror 7) indicated by a dotted line. The second position (mirror 7') can be moved to the second position (mirror 7'). More specifically, the electromagnet 9 is connected to the oscillator 1
1, the iron core is driven to move in the axial direction by a coil energization on/off repetitive excitation signal with a repetition frequency of 10 Hz, and when the excitation signal is turned on and driven, the mirror 7
moves to a first position on the optical path of the laser beam traveling straight ahead, and irradiates the ground 13 with the laser beam at a predetermined angle α with the ground 13 in the front-rear direction of the front of the vehicle. When the excitation signal is turned on, the mirror 7 moves to the second position (mirror 7') on the optical path of the laser beam, and directs the laser beam to the ground 13 at a predetermined angle β with the ground 13 in the left-right direction in front of the vehicle. configured to irradiate.

Further, a part of the scattered light reflected by the ground 13 of the laser beam irradiating the ground 13 in this way is reflected by the mirror 7 at the first position or the mirror 7' at the second position on the reverse path, and the beam The light is bent at right angles by the splitter 5 and is received by the photodetector 23.

On the other hand, the laser beam from the laser light source 1 that is bent in the right angle direction by the beam splitter 3 is reflected by a mirror 19, and then further reflected by another mirror 21 as a standard reference beam. The light travels straight through the beam splitter 5, is combined with the scattered light from the ground 13, and is received by the photodetector 23. That is, the photodetector 23 receives the reference light, which is the laser light as it is from the laser light source 1, and the ground 1.
The multiplexed light with the scattered light reflected from 3 is input.

The photodetector 23 includes a condenser lens, a light receiving element such as a photodiode, an amplifier, etc., and supplies the received reference light and scattered light to the frequency difference detector 25 .

The frequency difference detector 25 uses a frequency tracker to analyze the frequency of the beat signal of the reference light and the scattered light supplied from the photodetector 23, and detects and outputs the frequency difference fd between the two light waves. When this G frequency difference rd is detected, it is possible to calculate the longitudinal direction speed V11 and the lateral direction speed VL from this difference [d in a multi-continuous manner.

Next, the effect will be explained.

First, when the electromagnet 9 is excited by an excitation signal from the oscillator 11, the movable core of the electromagnet 9 presses the spring 10 to move the mirror 7 to a first position on the optical path of the laser beam. As a result, one of the laser beams output from the laser light source 1 that went straight through the beam splitter 3.5 is
The light is reflected by the mirror 7 at the first position and illuminates a plane parallel to the front-rear direction of the vehicle at an angle α with respect to the ground 13.

The scattered light reflected by the ground 13 of this irradiated laser beam is reflected by the mirror 7 at the first position as described above, is further bent in a right angle direction by the beam splitter 5, and is received by the photodetector 23. . Further, the reference light reflected by the mirror 19.21 is delivered to the photodetector 23 by the beam splitter 5.
The light is multiplexed with the scattered light and then incident. The scattered light from the ground and the reference light received by the photodetector 23 in this manner are supplied from the photodetector 23 to the frequency difference detector 25, where the frequency difference fd++ between the two light waves is detected and output.

By substituting this frequency difference fd1+ into the following equation, the longitudinal velocity Vl of the front of the vehicle can be determined.

Vu = fcl+1 ・λ/(2・CO5α)
...<2) In this equation, λ is the wavelength of the laser beam.

Further, when the excitation signal from the oscillator 11 is off and the electromagnet 9 is not excited, the OJ iron core of the electromagnet 9 is pushed back by the spring 10 and moves, moving the mirror 7 to the second position on the optical path of the laser beam. . As a result, one of the laser beams that has gone straight through the beam splitter 3.5 of the laser beam output from the laser light source 1 is reflected by the mirror 7' at the second position, and is reflected onto a plane parallel to the left-right direction in front of the vehicle. is illuminated at an angle β with the ground 13. The ground 13 of this irradiated laser light
As described above, the scattered light reflected by the mirror 7' is reflected by the mirror 7' located at the second position, is further bent in the right angle direction by the beam splitter 5, and is received by the photodetector 23 together with the reference light. The scattered light from the ground and the reference light received by the photodetector 23 in this manner are supplied from the photodetector 23 to the frequency difference detector 25, where the frequency difference fdh between the two light waves is detected and output. By substituting this frequency difference fd into the following equation, it is possible to determine the left-right direction speed (2) of the front of the vehicle.

Vt = fd on ・λ / (2-CO3(2
) ・ (3) As mentioned above, oscillator 1
The electromagnet 9 is controlled by the excitation signal from the laser light source 1, and the mirror 7 is moved to the first position and the second position by the action of the movable iron core, and the laser light from the laser light source 1 is directed to the front of the vehicle at these positions. The ground 13 is irradiated at a predetermined angle α with respect to the ground 13 in the front-rear direction, and the ground 13 is irradiated in the left-right direction in front of the vehicle.
The ground 13 is irradiated at a predetermined angle β with respect to the ground 13, the scattered light from the ground 13 is received, and the longitudinal velocity V11 and the lateral velocity ■ of the front of the vehicle are measured in a time-sharing manner from the frequency difference fd with the reference light. It is possible.

In the above embodiment, a method using an 8m stone 9 was described as a switching means for moving the mirror 7 to the first and second positions, but the present invention is not limited to this.
For example, a motor and a rack-and-binion may be used.

Furthermore, an acousto-optic deflection element or the like may be used as means for dividing the laser beam into two directions.

Further, in the above embodiment, only velocity components in two-dimensional directions of the vehicle were measured, but the present invention is not limited to this, and it is of course possible to measure velocity components in two or more directions.

[Effects of the Invention] As explained above, according to the present invention, electromagnetic waves are distributed to a vehicle in a plurality of directions and selectively transmitted, and the reflected waves from each traveling road surface when transmitted in each direction are Since each velocity component in the plurality of directions relative to the vehicle is calculated based on the difference between the frequency of It is possible to perform economical speed detection without increasing the size of the device.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a vehicle speed measuring device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional vehicle speed measuring device. 1... Laser light source, 3, 5... Beam splitter,
7.19.21... Mirror, 9... Electromagnet, 11.
...Oscillator, 13...Ground, 23...Photodetector, 2
5...Frequency difference detector.

Claims (3)

[Claims] (1) An electromagnetic wave generation means mounted on the vehicle that generates electromagnetic waves having a predetermined frequency; and an output means that selectively outputs the electromagnetic waves to the vehicle in a plurality of directions so as to form predetermined angles with the road surface. , frequency difference detection means for receiving reflected waves from a running road surface when electromagnetic waves are output, and detecting frequency differences between each reflected wave and the electromagnetic waves; A vehicle speed measuring device comprising: calculation means for calculating speed components of the vehicle in the plurality of directions. (2) The vehicle speed measuring device according to claim 1, wherein the output means selectively outputs electromagnetic waves in the front-rear direction and left-right direction of the front of the vehicle. (3) The vehicle speed measuring device according to any one of claims 1 to 2, wherein the calculating means has a function of calculating the traveling speed of the vehicle from the calculated speed component.