JPH03216580A - Laser radar for detecting dynamic relative speed and relative distance - Google Patents

Abstract

PURPOSE: To improve measurement precision by branching laser beam(LB) which is poured on an object in an irradiation part, to be assumed as a reference LB, and then mixing the reference LB with a reflection LB from the target and providing multiple means which calculate relative speed by CPU process. CONSTITUTION: A laser drive part 03 drives a laser diode(LD) 04 to generate a laser beam(LB), and the LB is, through the first condenser lens 05, the first prism 06 and the first lenticular lens(LL) 07, poured on a target as LB40. LB of LD04 is reflected on the first and second prisms 06 and 08, and then made incident on a photo-detective element 09, which is used for monitoring LB, and, LB42 which has transmitted through the prism 08 comes in the third prism 12, to be reference LB. LB41 reflected on the target, through the second LL11, the prism 12 and the second condenser lens 13, reaches an LB detecting part 14, and then mixed with the reference LB 42, and, the LB41 and 42 are used for heterodyne interference effect, thus Doppler frequency is obtained for providing a relative speed with the use of a CPU 17. Thus, noise wave is avoided, and measurement precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] The present invention relates to a laser radar, and more particularly to a laser radar that detects the relative speed and distance of two moving objects, such as cars.

Conventional Radio Frequency Radar
y Radars) uses radio waves as a medium to emit toward objects. The reflected radio waves are received and processed to determine relative speed and distance. The range of use of such radars is limited because radio waves are difficult to maintain accurate direction and are easily jammed by radio noise.

Therefore, there is a movement to use laser beams as a medium for measuring distance. Recently, a laser displacement meter (Laser D
appler Displacement Meter
LDDM) was developed. About this
rs & Optronics, 1987. 9. p
It is introduced in 69-71. The advantages of LDDM are that it uses a laser beam with continuous wave frequency and is frequency stable, no optical feedback means are required, and the overall system is compact. The application of laser beams to radar devices is actively being carried out, including a collision prevention device invented by Koito Seisakusho (Japan). The device roughly measures the time a laser beam takes to travel between cars traveling in the same direction and converts this time into relative distance.

[Problem to be solved by the invention]

Since the time it takes for a laser beam to travel between cars 100 meters apart is less than 0.3 microseconds, any measurement error will render the device useless.

Although this device works to issue a warning signal to the driver to avoid an accident, it is not always reliable. This is the biggest problem with conventional radar, whether it uses radio waves or laser beams.

Another problem with conventional radars that detect the relative speed and distance of two objects is that highly accurate measurements are difficult. The reason for this is that radar captures noise waves from other objects and mixes them with reflected waves. This especially occurs when using radio electromagnetic waves as the medium. Furthermore, sometimes the propagating waves may be reflected by undesired objects, so that a warning signal may be erroneously emitted.

The main object of the present invention is to provide a laser radar that detects the relative velocity and distance of two moving objects. This objective is achieved by obtaining accurate sensing by exploiting the heterodyne interference effect between the propagated and reflected media laser beams.

Another object of the present invention is to provide a laser radar that measures Doppler frequency using the Doppler effect. The Doppler frequency contains relative velocity information that is processed by the laser radar's central processing unit.

Yet another object and very important feature of the invention is a PIN diode array or a charge-coupled device (CCO) array for detecting the reflected laser beam and at the same time obtaining information about the relative distance of two moving objects. The object of the present invention is to provide a photodetection means such as the following.

A further object of the present invention is that a distinctive feature of the laser radar of the present invention is to improve the accuracy of velocity measurements and to provide timing gating means to avoid any possible noise waves. The timing gate means suppresses the reflected laser beam corresponding to the 5p radiation received and processed by the laser radar.

[Means for Solving the Problems] Therefore, the laser radar of the present invention includes a laser beam irradiation means, a reference beam forming means for receiving the irradiation beam and converting it into a reference beam, a reference beam, and a reference beam. The laser radar of the present invention includes a light receiving means for receiving the reflected laser beam to be mixed, and a clock generating means for processing the mixed laser beam and converting it into relative velocity information.The laser radar of the present invention includes a clock generating means for generating a pulse clock for the entire system. , a laser beam drive means, and a timing gate means for controlling reception of a reflected laser beam corresponding to the irradiated laser beam. The clock generation means, laser drive means, and timing gate means are all made of electric circuits.

〔Example〕

FIG. 1 is a block diagram of a laser radar system according to the present invention. The present invention seeks to detect the relative speed and distance of two moving objects, particularly two cars moving in the same direction. The phenomenon of heterodyne interference effect of two mixed waves is a well-known technique, called “Differential
Laser fleterodyrLe Micro
-metrology” with the title “Optical
Engineeringmagazine”p926
-929 No. 6 vo1, 24, Nov. /De
c. This can best be understood with reference to 1985. The laser radar according to the invention uses this heterodyne interferometry to detect relative velocity information, but for the sake of brevity, details regarding the operation of the laser radar in this regard are omitted. This does not mean that the disclosure of the invention is insufficient. Further, the laser radar of the present invention utilizes the Doppler effect.

The Doppler effect is expressed by the following equations (1) and (2).

Fr=Ft ((C-V)/(C+V))"...
(1) F o = F r F t
...(2) However, Ft; Frequency of irradiated electromagnetic waves Fr; Frequency of received electromagnetic waves FD; Dobler frequency C; Speed of light V; Relative speed of two objects The frequency of the laser beam is 300,000 GHz, and the speed difference between the two cars is Change a certain relative speed from lkm/h to 100k
m/hour, Dobler frequency F is approximately 0.5 MHz
It becomes 55MHz. The Dobler frequency F, is selected to represent relative velocity information. As shown in FIG. 1, the laser radar system includes a clock means 01 for generating a control clock pulse, a synchronous high voltage generation means 02, a laser beam driving means 03, and an optical device 100, and the optical device 100 further includes a laser beam irradiation section. 101, the central processing unit 17, which includes a reference beam detector 102 and a laser beam receiver 103, performs initial settings represented by block 31, the speed of the first vehicle represented by block 32, and block 33;
the clutched or unclutched state of the first car, represented by
and other received information signals from the optical section 100. The central processing unit 17 can send signals of relative speed and distance to be displayed on the display device 18, and the speaker 1
9 can send a warning to be notified, can control the decelerator 20 of the first car, and can send a warning to the second car running in front of the first car.
The camera 21 can be controlled to capture images of the car. These control techniques are well known and are not a major feature of the present invention, so they will not be discussed in detail. Referring again to FIG. 1, the laser radar of the present invention includes a reference beam detection means 102 and a first amplifier 1 connected to the central processing unit l7.
0, a preamplifier 15, a second amplifier 151, a central processing unit 17, and a timing gate section 16 connected between the laser beam receiving section 1030.

Referring to FIG. 2, an optical part 100 is attached to the front of the vehicle, and this part generally includes a laser diode 04 that generates a laser beam, a set of condensing lenses 05, and a first prism 06. , a laser beam irradiation section 101 including a first Lenticular lens 07.

As shown in FIGS. 3(a) to 3(C), the function of the lenticular lens 07 is to transform the laser beam 40 into a beam having a spread angle of 1.5° in the horizontal direction and 0.3° in the vertical direction. It is to change it to. As a result, the laser beam 4
0 can be directed toward a moving object in front of the object without being irradiated with objects other than the object.

As shown in FIG. 2, the laser beam from the laser diode 04 is reflected by the first prism 06 and reaches the second prism 08 in the reference laser beam detection section 102.

The reference laser beam detection unit 102 includes a condensing lens 081 and a light receiving element 09, and monitors the beam irradiation device 100 to confirm whether it is operating normally. Furthermore, the beam transmitted through the second prism 08 becomes a reference radiation beam. The laser beam receiving section 103 of the optical system I 100 roughly includes a second lenticular lens 11, a third prism 12, a second condensing lens 13, and a laser beam detecting section 14. The laser beam detection unit 14 is a plurality of PIN diodes forming an array of PIN diodes or a plurality of CCDs. A commercially available CCD has 1024 elements and can detect an irradiated light beam.

The operation of the optical section 100 will be explained with reference to FIG.

A laser drive section 03 drives a laser diode 04 to generate a laser beam. The generated laser is transmitted through the condensing lens 05, the first prism 06, and the first lenticular lens 0.
7 and becomes a laser beam 40 for irradiation.

The reflected laser beam 41 passes through the second lenticular lens 11, the third prism 12, and the second condensing lens 13 of the light receiving section 103, and reaches the laser beam detecting section l4.

The received laser beam 41 is mixed with the reference light 42 from the reference light detection section 102. This reference beam 42 has optically the same properties as the irradiating laser beam 40.

Laser beams 41,42 are used for heterodyne interference effects. As a result, the Doppler frequency Fd is determined and sent to the central processing unit 17. As a result, the relative speed between the first car and the second car ahead is determined by the central processing unit 17.

Figure 4 shows a laser beam drive unit 03, a high voltage generator 02
, a circuit diagram of the clock generator Ol is shown.

The operating voltage for the system is supplied by the vehicle's battery 51. A voltage stabilizer 52 included in power supply 50 provides a stable voltage of 12VDC. The clock section 01 indicated by the dashed line 01 is a commercially available IC (number 555).
) is used. Synchronous high voltage generator 0
2 is realized by a high voltage switching power supply represented by a dashed line 02. Laser diode 04 is indicated by dashed line 0
It is connected within the circuit for laser beam driving means denoted by 3. The electric circuit shown in Fig. 4 has a clock section 0 as a whole.
A laser beam is generated from the laser diode 04 according to the control clock from 1. Since these circuits are relatively well known, their construction and operation will not be described in detail.

FIG. 5 shows a circuit diagram of the preamplifier 15. Preamplifier 1
5 is connected to the laser beam detection means 14 of the laser beam receiving section 103. In particular, in a specific example of the circuit, a plurality of PIN diodes are used as the laser beam detection means 14. Preamplifier 15 first consists of an optical frequency amplifier 150 . The number of preamplifier circuits 15 is equal to the number of PIN diodes. The output of each optical frequency amplifier 150 is simultaneously sent to an analog summer 152 and the outputs from preamplifiers 15 are summed. The output of analog adder 152 is output from connection point B.

FIG. 6 shows a circuit diagram for detecting the relative speed of two moving objects used in the laser radar of the present invention.

The circuit diagram shows a circuit embodying the timing gate means 16, which will be described in detail below. The frequency to voltage converter is represented by functional block 60. One example of this converter 60 is a frequency synthesizer (77).
) IC, 182XO) (trade name), amplifier (LF356 of National Semiconductor) (trade name)
and multiplexer (Analog Corporation's AD
532) (Trade name). The function of this frequency/voltage converter 60 is to convert the Dobler frequency, which represents information on the relative speed of two moving objects, into voltage. The voltage signal obtained from the frequency/voltage converter 60 is sent to a sample/hold circuit 6l that holds the voltage so that it can be taken in by the central processing unit 17 (CP[I). This sample and hold circuit 61 can be made by National Semiconductor's LHO53 (trade name).

The voltages corresponding to the Doppler frequencies of the irradiating beam and the receiving beam are further calculated by the central processing unit 17 to determine the relative velocity and displayed on the display device 18.

The electrical circuit shown in FIG. 6 is a timing gate circuit diagram. The purpose and function of this timing gate circuit, which embodies the timing gate section 16, is to reduce noise as much as possible by ensuring that the received laser beam 4l reflected by a moving object in front actually originates from the irradiated laser beam 40. It consists in removing. The laser beam received by the laser beam receiver 103 is mixed with a reference wave and then amplified by the preamplifier 15 . The laser beam wave containing this Doppler frequency enters the timing gate circuit at the connection point B and is saturated by the saturation amplifier 161. The timing gate circuit includes a flip-flop 162 and an RC
A delay circuit 163 is provided.

When the laser diode 04 starts oscillating and emits a laser beam, this time signal is supplied to the timing gate circuit 16 through the connection point C. This time signal is R
The timing gate circuit is controlled to delay the start time by a period determined by the RC constant of the C delay circuit 163. Therefore, the laser beam containing the Doppler frequency from connection point B is accepted after a certain time delay. Meanwhile, clock 01 is supplied from node A to the timing gate circuit to control monostable oscillator 164. The time signal for the start of laser diode 04 is also provided to this timing gate circuit from a set of flip-flops 165, 166 to ensure the start of this timing gate circuit. The waveform of the clock pulse supplied from connection point A to the timing gate circuit is shown at node a. The output of monostable oscillator 164 becomes shown at node b. The pulse width of the signal at node b is Rl,C
Based on constants determined by I, R2, and C2. This signal is supplied to analog switch 167. DG180 (product name) can be used as an analog switch, and as a result, the waveform at node C is as shown in the figure. This waveform containing Doppler frequency information is supplied to frequency to voltage converter 60 to obtain relative velocity as described above.

A photodetector element in the laser beam receiver 103 is used to detect the relative distance using the laser radar according to the present invention. 7th
As shown in the figure, the reflected laser beam 41 is received by a photodetector array l4. The photodetector array may be a series of PIN diode arrays or charge-coupled devices (CC[l
l). There are multiple pixels on the light sensing array. The laser beam reflected at the location of the vixel is considered to contain information about the relative positions of the two moving objects. In FIG. 7, a laser beam 41 reflected by a second car in front of the first car illuminates the photodetector array 14. In FIG.

This information is input into the electrical circuit shown in FIG. 8 or 9.

As shown in FIG. 8, the output at connection point D in FIG. 5 includes information as to which element in the PIN diode is irradiated with the reflected laser beam. Each element has a different resistance value Rl, R2, R3...Rn
connected to an individual circuit with Therefore, since the signals supplied to the gain amplifier 152 are different for each individual circuit, information on different relative positions is obtained by processing by the central processing unit 17 and displayed on the display device 18.

FIG. 9 shows a case where a CCD is used as the light receiving section 103 to detect relative velocity and position. The signal is sent directly to the central processing unit to obtain relative distance information. 6th to detect relative speed
A similar sensing signal is provided through B in the circuit diagram shown.

Although the present invention has been described in terms of the preferred embodiments described above, various modifications may be made without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to specific embodiments other than those described in the claims.

〔Effect of the invention〕

As described above, according to the present invention, a laser radar that accurately detects the relative velocity and distance of two moving objects can be realized by utilizing the heterodyne interference effect.

Furthermore, by measuring the Doppler frequency, it is possible to realize a laser radar that uses the Dobler effect to accurately detect the relative speed of two moving objects.

Furthermore, by using a PIN diode array or a charge-coupled device as the light receiving means of the laser radar, information regarding the relative distance between two moving objects can be obtained at the same time.

Further, by using a timing gate means to limit the received reflected laser beam to that of the irradiated laser beam, it is possible to improve the accuracy of speed measurement and to avoid all possible noise waves.

[Brief explanation of drawings]

Fig. 1 is a system block diagram of a laser radar according to the present invention, Fig. 2 is a schematic diagram of an optical system used in a laser radar according to the present invention, and Figs. A schematic diagram, FIG. 4 is a circuit diagram of a clock generation means, a high voltage generation means, and a laser beam driving means according to the present invention, and FIG. 5 shows a laser beam receiving means of a laser radar according to the present invention and an amplification device connected thereto. 6 is a circuit diagram of the means for detecting the relative speed of two moving objects employed in the central processing unit of the laser radar according to the present invention; FIG. FIG. 8 is an explanatory diagram of detecting the relative distance of an object, and FIG. FIG. 9 shows an electric circuit employed in a central processing unit for detecting relative distance using a charge-coupled device as a light receiving means in a laser radar according to the present invention. In the figure, 14... Photodetection section, 16... Timing gate section, l7... Central processing unit, 40... Irradiated laser beam, 41... Reflected laser beam, 60... Frequency/voltage. Converter, 101... Laser beam irradiation section, 102... Laser beam reception section, 163... Delay circuit, 164... Monostable oscillator.

Claims (1)

[Claims] 1. Means for generating and irradiating a laser beam; Light receiving means having a photodetecting means for receiving a reflected laser beam in which the irradiated laser beam is reflected by one of the moving objects; Producing heterodyne interference; two moving objects, comprising: means for mixing said emitted laser beam and said reflected laser beam to obtain a mixed laser beam; and a central processing unit for processing said mixed laser beam and converting said mixed laser beam into relative velocities of the two moving objects. A laser radar that detects the relative speed of 2. The apparatus further comprises gate means for controlling the start time of the light receiving means for receiving the reflected beam, thereby ensuring that the reflected laser beam corresponds to the irradiating laser beam. Laser radar described in. 3. The laser radar according to claim 1, further comprising frequency/voltage conversion means connected to the central processing unit for converting the frequency signal of the mixed laser beam into a voltage signal. 4. The gating means further comprises a monostable oscillator and a delay circuit for generating a waveform of the mixed laser beam that effectively includes a frequency signal indicative of the relative velocity of the two moving objects. Laser radar. 5. The laser radar according to claim 1, wherein the light detection means is a PIN diode array. 6. The laser radar according to claim 1, wherein the light detection means is a charge coupled device. 7. means for generating and irradiating a laser beam, substantially in the form of a light-sensing array having a series of elements for detecting a reflected laser beam reflected by one of the moving objects; Detecting the relative distance of two moving objects, each of the elements comprising a light detection means indicating different information on the relative distance, and means for processing a signal from the light detection means and converting it into a relative distance of the two moving objects. Laser radar. 8. The laser radar according to claim 7, wherein the light detection means is a PIN diode array. 9. The laser radar according to claim 7, wherein the light detection means is a charge coupled device.