EP0685077A1 - Dispositif anticollision pour vehicules - Google Patents

Dispositif anticollision pour vehicules

Info

Publication number
EP0685077A1
EP0685077A1 EP94906333A EP94906333A EP0685077A1 EP 0685077 A1 EP0685077 A1 EP 0685077A1 EP 94906333 A EP94906333 A EP 94906333A EP 94906333 A EP94906333 A EP 94906333A EP 0685077 A1 EP0685077 A1 EP 0685077A1
Authority
EP
European Patent Office
Prior art keywords
vehicle
laser beam
rangefinder
threshold
coupled
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP94906333A
Other languages
German (de)
English (en)
Inventor
Amotz Yavnayi
Moshe Gavish
Pinchas Schechner
Israel Kantor
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Silicon Heights Ltd
Original Assignee
Silicon Heights Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/017,742 external-priority patent/US5388048A/en
Priority claimed from IL10693293A external-priority patent/IL106932A/en
Application filed by Silicon Heights Ltd filed Critical Silicon Heights Ltd
Publication of EP0685077A1 publication Critical patent/EP0685077A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/93—Lidar systems specially adapted for specific applications for anti-collision purposes
    • G01S17/931—Lidar systems specially adapted for specific applications for anti-collision purposes of land vehicles

Definitions

  • a Vehicle Anti-Collision Device A Vehicle Anti-Collision Device
  • This invention relates to a vehicle anti-collision device for aiding a driver in maintaining a safe distance between his vehicle and the one in front.
  • Passive devices warn the driver of a rear, or following, vehicle when he is approaching too close to the vehicle in front (hereinafter the "leading" vehicle) for his current road speed.
  • the warning having been provided, the initiative is now the driver's to take suitable precautionary action.
  • active devices include a servo-control system typically coupled to the throttle valve so that, in the event that the driver does not maintain a safe distance from the leading vehicle for his current road speed, the following vehicle is automatically decelerated so as to reduce its road speed to a safe stopping speed based on the reduced distance between the two vehicles.
  • U.S. Patent No. 4,706,195 (Yoshino et al.) describes such an active speed control system.
  • Yoshino et al. is based on a laser radar for measuring the distance of the following vehicle from the leading vehicle, the speed of the following vehicle being determined by a speed sensor coupled to the speedometer.
  • passive systems also must comprise at least these two elements: namely some sort of rangefinder for determining the distance between two vehicles and also means for determining the speed of the following vehicle.
  • rangefinder for determining the distance between two vehicles
  • speed of the following vehicle it has been found that both passive and active systems have proven difficult to exploit commercially for several reasons. First, it is difficult to design a system which is easily amenable to coupling to all existing vehicles without requiring special customization for each vehicle. As soon as such customization is required, this raises the price of the system.
  • a further drawback relating to the development of such systems concerns the occurrence of false alarms.
  • a false alarm is obtained with active systems, the result is not merely irritating but can even be dangerous in that it is liable to lead to a rear-end collision between the following vehicle and the one behind it. This can occur because the following vehicle abruptly slows down (or stops) for no reason, leaving the vehicle behind him insufficient time to take precautionary action and thereby leading to a collision between the two vehicles.
  • false alarms will produce similar dangerous results if the driver panics as a result of the alarm, applying his brakes too abruptly and resulting possibly in skidding of his own vehicle or, for the same reasons as explained above, a rear-end collision between his vehicle and the one behind.
  • Laser rangefinders for use in vehicle anti-collision systems are well known and must address a variety of different requirements. Thus, such rangefinders must be able to detect a target vehicle driving in the same lane as a vehicle to which the rangefinder is fitted, whilst being able to distinguish from false targets.
  • the rangefinder must be able to work reliably in adverse weather conditions and the laser must be so designed as not to represent a hearth hazard. Additionally, cost must be kept to a minimum so as to prevent the anti-collision system from being prohibitively • expensive.
  • U.S. Patent No. 4,757,450 employs a plurality of laser beams, each directed so as to cover a respective volume within the field of view whereby, in combination, a wide field of view may be covered. Appropriate calculations permit false targets to be eliminated but the resulting system is neither simple nor does it permit accurate detection in fog.
  • the rangefinder itself is mounted outside of the vehicle, typically on the front fender. This is not entirely satisfactory, because dirt and grime may accumulate on the rangefinder, thereby derogating from the measurement accuracy and requiring constant maintenance and cleaning in order to avoid such errors. Also, fitting the rangefinder outside the vehicle • lends it vulnerable to tampering and theft. Yet a further consideration is that since the instrumentation relating to the anti-collision system is mounted inside the vehicle, special wiring is required in order to connect the rangefinder to the instrumentation.
  • any rangefinder system it is clearly essential in any rangefinder system to distinguish genuine targets from false targets. In the prior art systems, this is typically achieved by using a large S/N (signal to noise) ratio so that only strong reflections are interpreted as being derived from genuine targets. Whilst this approach does eliminate false targets, it reduces the resulting sensitivity of the rangefinder so that reflections from genuine targets in adverse conditions are often not sufficiently strong and are therefore rejected as noise signals. For example, fog tends to disperse the laser beam so that by the time the laser beam has been reflected from a true target vehicle, the strength of the received signal is so weak that it is misinterpreted as noise in conventional systems and is therefore rejected.
  • S/N signal to noise
  • a vehicle anti-collision device comprising: a rangefinder for mounting inside a following vehicle near to a windshield thereof for measuring a distance of said vehicle from a leading vehicle, distance sampling means coupled to the rangefinder for sampling measured distances at predetermined time intervals, self speed determination means for measuring a self speed of the following vehicle, collision time determination means coupled to the rangefinder and to the self speed determination means and responsive to the measured self speed of the following vehicle for determining a collision time between the following and leading vehicles; comparing means coupled to the collision time determination means for comparing said collision time with a predetermined threshold, and alarm means coupled to the comparing means for generating an alarm if the collision time is less than said predetermined threshold.
  • the rangefinder includes a laser light source for emitting a narrow angle beam of laser light.
  • One component of the laser beam passes through the windshield so as to be reflected by a leading vehicle, whilst a second component of the laser beam is reflected directly by the windshield back towards the device.
  • the device is responsive to a difference in time between receipt of both components for determining the distance between the following and leading vehicles.
  • a laser rancefinder for fixing to a vehicle and including therein: a laser source for directing a laser beam on to a tarcet vehicle for determinin ⁇ a distance between the two vehicles, means for successively directing the laser beam at the target vehicle at predetermined intervals of time so as to be reflected thereby as a reflected beam, means for receiving the reflected beam so as to determine successive distance measurements between the two vehicles, and comparing means for comparing the successive distance measurements or a derivative thereof with a respective safety threshold so as to generate an alarm signal if one or more of the distance measurements or its derivative is less than the respective safety threshold; the improvement wherein the safety threshold comprises a first low S/N ratio frequency adaptive threshold together with a second digital threshold set to eliminate false targets.
  • the self- speed of the following vehicle is determined by counting pulses of light reflected by a light-reflecting strip adhered to an axle of the following vehicle: such an approach being universally applicable and obviating the need for customization to different vehicles.
  • a low S/N ratio is employed so that weak signals, which may possibly result from true targets in adverse weather conditions such as fog, for example, are not rejected as they are in hitherto proposed systems. Since, nevertheless, such weak signals could derive from false targets, the resulting reflected signals are subjected to further analysis in order to distinguish true targets from false targets.
  • Fig. 1 is a block diagram showing functionally the principal compo- nents of a device according to the invention
  • Fig. 2 shows pictorially a device according to the invention mounted inside a vehicle
  • Fig. 3 shows pictorially a digital speedometer for use with the device
  • Fig. 4 is a flow diagram showing the principal steps associated with a method for determining the self-speed of a vehicle
  • Figs, ⁇ a and 5b are flow diagrams showing the principal steps associated with a method for determining the speed of a leading vehicle as well as the collision time between two vehicles;
  • Fig. 6 is a schematic diagram showing the main components in a receiver of the rangefinder shown in Fig. 1;
  • Figs. 7a, 7b and 7c are geometric diagrams showing how the system according to the invention discriminates between vehicles in different lanes;
  • Fig. 8 is a pictorial representation of a vehicle having height transduc ⁇ ers in accordance with a further embodiment of the invention
  • Fig. 9 is a geometric representation useful for explaining operation of the embodiment shown in Fig. 8;
  • Fig. 10a is a schematic representation of a prior art rangefinder
  • Fig. 10b is a graphical representation relating to the prior art range- finder shown in Fig. 10a;
  • Fig. 11 is a schematic representation of a rangefinder according to the invention.
  • Fig. 12 is a graphical representation relating to the rangefinder shown in Fig. 12;
  • Fig. 13 is a pictorial representation of a laser beam reflected from a true, moving target and a false, stationary target;
  • Fig. 14 is an intensity versus time characteristic for the situation depicted in Fig. 13;
  • Fig. 15 relates to Fig. 13 and shows a frequency versus range characteristic
  • Fig. 16 is a pictorial representation of a laser rangefinder according to the invention, fitted inside a vehicle;
  • Fig. 17 is a schematic representation of a front windshield of the vehicle shown in Fig. 16; and Fig. 18 shows schematically a detail of the windshield shown in
  • Fig. 16 having affixed thereto a prismatic element.
  • FIG. 1 there is shown a block diagram of a device depicted generally as 10 comprising an instrument 11 powered by a 12 V power supply 12.
  • the power supply 12 is built as a separate system, assembled underneath a dashboard of a vehicle, and supplies the different voltages, as required, to the instrument 11 for the operation of the different electronic systems therein.
  • the instrument 11 comprises a micro-controller 13 coupled to a laser rangefinder 14, to a speed transducer 15, to a steering angle transducer 16 and to an elevation angle transducer 17.
  • the micro-controller 13 is also coupled to a display 18 and to a buzzer 19.
  • the display 18 and the buzzer 19 are contained within the instrument 11, whilst the speed transducer 15 and the steering angle transducer .16 are provided as separate units which are externally coupled to the micro-controller 13.
  • the laser rangefinder 14 comprises a transmitter 20 coupled to a laser diode and suitable optics 21.
  • the laser diode and optics 21 emits a narrow angle laser beam which is intercepted by a leading vehicle so as to be reflected thereby and detected by an optical detector 22 an output of which is fed to a receiver 23 coupled to the micro-controller 13.
  • a sensitivity selector 24 connected to the receiver 23 permits the sensitivity of the receiver 23 to be adjusted so as to allow for varying weather conditions, such as fog, for example.
  • Figs. 2a and 2b show pictorially the instrument 11 positioned within a vehicle 25 proximate a windshield 26 thereof and preferably glued thereto.
  • the laser diode 21 (Fig. 1) emits a beam of laser light having a first component 27 which is reflected by the windshield 26 and a second component 28 which passes through the windshield 26 so as to be reflected by a leading vehicle 29 in front of the vehicle 25.
  • first and second components 27 and 28 of the laser beam strike the optical detector 22, corresponding first and second detector signals are generated thereby and fed to a timer 30 which measures an elapsed time ⁇ t between receipt of the first and second components 27 and 28 of the laser beam.
  • A. distance computer 31 coupled to the timer 30 is responsive to the elapsed time ⁇ t for determining the distance between the two vehicles.
  • Such an arrangement obviates the need for synchronization between the transmission of a laser pulse and subsequent receipt thereof, since both the first and second components 27 and 28 of the laser beam are derived from the same beam and any flight time delay between the actual emission of the laser beam and receipt of the first component 27 thereof by the detector 22 is exactly compensated for by the transit time for the second component 28 of the laser beam to reach the windshield 26 from the detector 22 during its outgoing trajectory and to reach the detector 22 from the windshield 26 on its return trajectory.
  • the timer 30 and the distance computer 31 are not provided by separate hardware circuits but, rather, are provided within the micro-controller 13.
  • a safety time threshold adjustment 33 is coupled to the distance computer 31 for adjusting the safety time threshold at which an alarm is given, in order to allow for different ambient conditions or wakefulness of the driver.
  • a frequency of the laser diode is randomly selected between predetermined lower and upper thresholds in respect of a specific instrument, the optical detector 22 being connected to a filter 32 for filtering out a received signal whose frequency differs from the selected frequency.
  • a received signal of the correct frequency is accepted and a laser beam (of different frequency) directed towards the detector 22 by another vehicle also having a laser rangefinder fitted thereto will be filtered out, thereby reducing false alarms.
  • Fig. 3 shows schematically the speed transducer 15 which comprises at least one light-reflecting strip 35 adhered to an appropriate drive shaft 36 of the vehicle.
  • the drive shaft 36 may be one of the two drive shafts on which the front wheels 37 and 38 are mounted.
  • the drive shaft 36 is constituted by the common drive shaft between the gear box and the back axle (not shown).
  • a light source 40 emits a continuous beam of light 41 towards the axle 36 in the region of the light-reflecting strip 35 so as to be reflected thereby as a reflected beam 42 which is intercepted by a detector/counter 43 which may be optically coupled to the light-reflecting strip via an optical fiber (not shown).
  • a reflected beam 42 is emitted towards the detector/counter 43 each time the light-reflecting strip 35 intercepts the beam 41.
  • the detector/counter 43 produces a pulse each time a reflected beam 42 is detected, each of the received pulses being counted.
  • the number of pulses counted in a given time in conjunction with the number of light- reflecting strips 35 provided on the axle 36, permits the number of revolutions per unit time of the axle 36 to be computed. This having been done, it is a simple matter to calculate the self-speed of the vehicle by multiplying the angular speed of the axle 36 by the radius of the wheels 37 and 38 mounted thereon.
  • the digital output thereof may be fed directly to the micro-controller 13 without the need for the components shown in Fig. 3 to be provided as separate elements.
  • the arrangement shown in Fig. 3 is capable of universal application and does not require special customization for different vehicles, apart from specifying the wheel radius which is the only variable in such a system.
  • Fig. 4 is a flow diagram showing the principal steps associated with the calculation of self-speed using the arrangement described above with reference to Fig. 3 of the drawings.
  • the system is dormant until a first pulse is received, whereupon a clock is activated, such that on receipt of subsequent pulses, the elapsed time ⁇ t between successive pulses is measured.
  • a correction factor is applied, as required, whereupon the self-speed of the vehicle is calculated in accordance with the equation:
  • Figs. 5a and 5b show the principal steps associated with the calculation of the speed V, of the leading vehicle and the collision time t col between the two vehicles.
  • a pulse is produced which activates a clock associated with the micro-controller 13.
  • a second pulse is produced when the second component of the laser beam strikes the detector 22, thereby enabling the clock to measure the elapsed time ⁇ t between the two successive pulses.
  • ⁇ V represents the closing velocity with which the following vehicle approaches the leading vehicle. Since the self- speed of the following vehicle is known, it is therefore a simple matter to calculate the actual road speed of the leading vehicle. Additionally, since the distance between the two vehicles has been determined, the collision time between the two vehicles may also be calculated. In this connection it should be noted that, strictly speaking, the collision time is equal to the distance divided by the closing velocity, ⁇ Vj. However, in practice, most traffic laws impose a stricter criterion for the calculation of "safety time" between two vehicles, requiring that, the distance between the two vehicles be sufficient to enable the driver of the following vehicle to react properly even in the event that the leading vehicle stops instantaneously. In this case, of course, the closing speed is equal to the self-speed of the following vehicle.
  • the safety time having thus been calculated, it is displayed and also compared with a threshold, a buzzer being sounded in the event that the calculated safety time is less than the threshold.
  • Fig. 6 shows the principal circuit components in the rangefinder 14 shown functionally in Fig. 1 of the drawings.
  • a silicon PIN diode detector 45 is connected to the junction 46 of a capacitor 47 connected in series with a resistor 48 and an inductance 49, a common terminal of which 50 is connected to ground GND via a capacitor 51.
  • a voltage of 75 V is fed to a free terminal of the inductance 49 via a positive supply rail 52 connected to the positive terminal of a zener diode 53 whose negative terminal is connected to GND.
  • the positive supply rail 52 is connected via a pull-down resistance 55 to a positive voltage supply of 200 V.
  • An output 56 of the laser diode 45 is connected to an input of a trans-conductance pre-amplifier shown functionally as 57, an output 58 of which is coupled via a capacitor 59 and a resistor 60 to an input 61 of a post-amplifier shown functionally as 62.
  • the resistor 60 is connected across the input 61 and GND.
  • An output 63 of the post-amplifier is connected to a first input 64 of a fast comparator 65 a second input 66 of which is connected to a voltage reference V rsf connected across a first resistor 67 in series with a capacitor 68, a low voltage terminal of which is connected to GND.
  • a switch 69 in series with the capacitor 68 and the first resistor 67 permits connection of a second resistor 67' to the voltage reference V ref instead of the first resistor 67.
  • Coupled to an output 70 of the comparator 65 is a switch shown functionally as 72 having an output thereof connected between a positive supply rail V, via a coil 75 and GND via a capacitor 76.
  • An analog-to-digital (A D) converter 78 having an output 79 is connected across the capacitor 76.
  • the operation of the circuit is as follows. An incoming laser pulse is detected by the PIN diode detector 45, an output of which is amplified by the trans-conductance pre-amplifier 57 in tandem with the post-amplifier 62. The output of the post-amplifier 63 is compared with V ref so that the fast comparator 65 produces an output only if the voltage appearing across its first input 64 exceeds the value of V ref .
  • the capacitor 68 which is fully charged sets a high threshold level for the incoming pulses, so that only very strong reflections from nearby targets are detected, thereby avoiding a major cause of false alarms.
  • the capacitor 68 discharges through the first resistor 67 and the threshold level V ref is lowered accordingly.
  • the capacitor 70 is charged through the coil 75 at a constant current.
  • charging of the capacitor 76 stops and a voltage measurement by the A/D converter 78 is performed.
  • the voltage appearing across the output 79 of the A/D converter 78 is proportional to the elapsed time ⁇ t between receipt of successive pulses by the PIN diode detector 45 and therefore to the distance between adjacent vehicles.
  • the comparator 65 together with the switch 72 constitute a threshold detector for adjusting the sensitivity of the rangefinder in accordance with the time constant of the capacitor 68 in series with the selected resistor 67 or 67'.
  • the sensitivity of the rangefinder receiver may be increased or decreased. This is particularly useful for increasing the sensitivity of the device in adverse weather conditions, such as fog, when visibility is low so that detection of weak reflections over small distances may be effected.
  • successive pulses are, in fact, derived from first and second components of the beam being reflected by the windshield 26 of the following vehicle and by the leading vehicle, respectively.
  • the elapsed time must be measured between receipt of only that component which is reflected by the leading vehicle. This requires two threshold detectors to be employed to start charging after receiving the first component pulse reflected from the windshield of the following car, and to stop charging upon receipt of the second component pulse reflected by the leading vehicle, respectively.
  • False alarms are typically caused by the rangefinder emitting a beam which is reflected not by an adjacent vehicle but, instead, by some extraneous object such as, for example, a lamp post, a tree or even another vehicle which does not represent a danger to the following vehicle.
  • Use of a laser rangefinder goes a long way to eliminating extraneous reflections by false objects since the dispersion angle of the laser beam is very small.
  • Fig. 7a shows geometrically a vehicle 80 travelling along an inner lane 81 of a two lane highway depicted generally as 82 and having an outside lane 83, the outer wheels of the vehicle 80 lying on an inside edge
  • the inner and outer lanes 81 and 83 meet at a common boundary 85 and have identical widths W.
  • ⁇ ODC sides OD and OC are known as is angle ODC.
  • the dispersion angle of the laser beam, the width W of the lane and the width m of the vehicle are all constant for a particular device since road lanes are generally of constant, known width.
  • the values of may easily be measured and stored within a memory (not shown) associated with the micro-controller 13 (Fig. 1), during manufacture of the device, whilst the values of W and m may likewise be stored upon installing the device in a vehicle for the first time.
  • the maximum distance DC is thus a function of several stored parameters and the turning radius R and constitutes a threshold, which if exceeded by a measured propagation distance, must be rejected.
  • Fig. 7c shows that the turning radius R is itself a function of the wheel base between the front and rear axles of the vehicle and the average turning angle of the front wheels which may be determined by measuring an offset angle of the steering mechanism relative to a base value when the vehicle is moving straight.
  • H is the wheel base of the vehicle
  • ⁇ is the average turning angle of the front wheels
  • FIG. 8 shows pictorially a vehicle 90 having a front fender 91 and a rear fender 92. Positioned on the front and rear fenders 91 and 92 are respective transducers 93 and 94 which are at heights h ⁇ and h 2> respectively, above a road surface 95.
  • Fig. 9 relates to the situation shown in Fig. 8, and represents geometrically the effect of varying a load distribution within the vehicle
  • the value of h 2 decreases giving rise to a new value a' between the road surface 95 and the imaginary line joining the two transducers 93 and 94.
  • the variation in the angle is computed in response to the height measurements provided by the transducers 93 and 94 and is fed to a servo system (not shown) connected to the rangefinder 14, so that the angle of the laser beam emitted by the rangefinder 14 may be varied in order to compensate for variations in the angle a.
  • Fig. 10a shows a typical prior art rangefinder discrimination system 100 wherein an input signal 111 is fed via a delay 112 and an attenuation 113 to respective positive and negative inputs of a first compara ⁇ tor 114 and to the positive input of a second comparator 115.
  • the negative input of the second comparator 115 is fed lo a variable voltage input derived by means of a variable resistance 116 connected at one end to a voltage supply V and at its other end to GND.
  • Respective outputs of the first and second comparators 114 and 115 are ANDed together by means of an AND gate 117, an output 118 of the AND gate 117 being logic "1" for a true target and logic "0" for a false target.
  • the attenuation 113 compensates for the inevitable attenuation associated with the delay 112.
  • the value of the delay 112 is so arranged that the attenuated signal 119a and the delayed signal 119b cross at half the peak value of the original pulse, the crossover point constituting a "Constant Fraction Threshold" whereby the first comparator 114 operates at only a constant fraction, in this case half, of the original pulse.
  • variable resistance 116 is adjusted so as to provide a high signal-to-noise (S/N) ratio of between approximately 4 and 5 so as to permit the first comparator 114 to eliminate false targets. However, in the process some genuine targets are likely to be eliminated also.
  • the start time corresponds to the instant of transmitting the laser pulse and is determinate.
  • the stop time corresponds to the instant that the input signal 111 is received and is not immediately determinate. This is because the input signal 111 has a non-zero rise time such that it cannot be guaranteed that measurement will commence from the zero crossing of the input signal 111 unless a zero threshold is employed. This is not practical in a real system because noise signals would be passed as bona fide signals and therefore a non-zero, positive threshold is mandatory.
  • Fig. 11 shows schematically a rangefinder system 122 in accor ⁇ dance with the invention, for comparing an input signal 123 with a reference threshold in order to determine whether the input signal 123 represents a true or false target.
  • the reference threshold is derived from the input signal 123 itself which is fed through a series combination of a Low Pass Filter 124 and an attenuation means 125 and fed to the negative input of a comparator 126.
  • the input signal 123 is fed to the positive input of the comparator 126 via a delay 127.
  • the Low Pass Filter 124 subjects the input signal 123 which is
  • SUBSTITUTE SHEET (RULE 2 ⁇ ) fed to the inverting input of the comparator 126 to an inevitable delay.
  • the delay 127 merely ensures that the signal fed to the non-inverting input of the comparator 126 is subjected to the same delay, so as thereby to cancel the undesirable effect of the delay caused by the Low Pass Filter 124.
  • the attenuation 125 together with the delay 127 compensate for the inevitable attenuation associated with the delay 127.
  • the input signal 123 and the delayed signal 128 are of equal amplitude and their respective peaks are separated in time by an amount dependent on the value of the delay 127.
  • the delayed signal 128 is fed to the non-inverting input of the comparator 126 whilst to the inverting input thereof is fed a signal 129 being the attenuated output of the Low Pass Filter 124.
  • the signal 129 constitutes the threshold of the system 122 and, unlike the constant fraction threshold associated with Figs. 10a and 10b, varies according to the amplitude of the input signal 123.
  • the system 122 thus constitutes an adaptive, frequency-based threshold detector.
  • Fig. 13 shows pictorially a target vehicle 130 moving in front of . a vehicle 131 inside of which is fitted a laser rangefinder according to the invention. Also shown is a side wall 132 constituting a false target, reflections from which must be eliminated.
  • the target vehicle 130 travels in a direction which is substantially normal to the vehicle 131 so that a laser beam 133 directed towards the target vehicle 130 strikes an area of the target vehicle 130 so as to be reflected by the area substantially simultaneously.
  • the reflected beam may be construed as a plurality of component reflections, all of which reach the vehicle 131 substantially at the same time.
  • the laser beam shown as 133 strikes an area of the wall 132 at a non-normal angle, such that, again considering the laser beam 133 to be composed of a plurality of component beams, different ones of the component beams are reflected from the wall 132 at different instances of time. Consequently, the rangefinder (not shown) situated within the vehicle 131 receives a plurality of reflected pulses, spread out in time, each representing a different distance from the vehicle 131.
  • Fig. 14 shows an intensity versus time characteristic for the reflected pulse from the vehicle 130 and the wall 132.
  • the intensity time characteristic for the laser beam reflected from the vehicle is shown as 135 whilst that for the laser beam reflected from the wall 132 is shown as 136
  • the pulse reflected from the vehicle 130 is a relatively sharp, high intensity spike whilst the reflection 136 from the wall has a low median intensity and is somewhat spread out in time. If a threshold is now imposed on the reflected signal and it is passed through a low pass filter, the signal returning from the wall will virtually be passed in its entirety, whilst that reflected from the vehicle 130 will be significantly blocked.
  • both the signal and the threshold contain unavoidable electronic noise and there is therefore white noise superimposed on the difference signal.
  • different amplification factors are required for both channels.
  • the low pass filter subjects the electronic signal to a delay and so, in order to conform the time scales of the two channels, a like delay is imposed in the signal channel as shown in Fig. 11.
  • Fig. 15 shows a frequency range distribution for successively measured ranges relating to the moving vehicle 130 and the stationary wall 132. Since, in practice, both of the vehicles 130 and 131 are moving, over a relatively short period of time the inter-vehicle separation remains relatively constant, at least compared to the distance between the vehicle 131 and a stationary target, for which, of course, the mutual separation is constantly changing. Consequently, a spike 137 in the frequency-range characteristic denotes a moving, true target whose distance from the vehicle 131 is D. On the other hand, the spread out characteristic 138 denotes a stationary target whose distance from the vehicle 131 is constantly changing.
  • the frequency range characteristic constitutes a digital threshold for determining whether a target is true or false.
  • the efficacy of the digital threshold depends on all possible valid signals being passed in the first place. This is ensured by the selection of the analog threshold, which ensures a sufficiently low S/N ratio to allow all possible valid signals to pass.
  • Both the analog and digital thresholds may be changed so as to negate the effects of temperature-dependent noise, such as might be caused by ambient heating and sun illumination.
  • a third threshold constituting a safety threshold is generally employed in anti-collision systems so as to provide a warning if the separating distance between two vehicle is less than the so-called "safety distance".
  • the safety threshold may likewise be varied so as to adjust the collision safety time which is different for moving and stationary targets, since moving targets also require time for stopping.
  • Figs. 16, 17 and 18 show a vehicle 140 having a laser rangefinder 141 fitted therein so as to direct a laser beam 142 through a front windshield 143 of the vehicle 140.
  • the laser beam 142 is directed through a substan- tially central portion 144 which is constantly swept by a windshield wiper 145 so as to be cleaned from the outside and prevent the buildup of dirt and grime.
  • the laser beam 142 is reflected from the inside surface of the windshield 143 so as to produce a reflected component 146 and a transmitted component 147 which, in turn, is reflected by a target vehicle.
  • the energy associated with the transmitted component 147 is less than the original energy associated with the laser beam 142 by the energy associated with the reflected component 146. It is therefore desirable to reduce as much as possible the energy associated with the reflected component 146.
  • Fig. 18 shows an alternative approach whereby a prism 148 is glued to the front windshield 143 using an optical glue, the laser beam 142 being directed substantially normally to a surface 149 of the prism 148 so that the incident beam 142 is directed through the prism 148 and is refracted throuch the front windshield 143 without being reflected.
  • the prism 148 is coated with an anti-reflection coating so as to reduce even further stray reflections and increase the power of the transmitted component of the beam.
  • the glue utilized for adhering the prism 148 to the front windshield 143 should have the same refractive index as the prism 148 so as to prevent total internal reflections within the prism 148. Reflections from the front surface of the prism 148 are minimized by applying an appropriate anti-reflection coating thereto.
  • reflections from the front windshield 143 are reduced to a minimum, thereby increasing the transmit- tance of the laser beam through the front windshield 143 and permitting a relatively low power laser to be employed, commensurate with safety considerations.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Optical Radar Systems And Details Thereof (AREA)

Abstract

Un dispositif anticollision (10) pour véhicules comprend un télémètre à laser (14, 122) monté à l'intérieur d'un véhicule (25, 131) près de son pare-brise (26, 143). La distance du véhicule (25, 131) au véhicule qui précède (29, 130) est constamment calculée et échantillonnée à des intervalles de temps prédéterminés, ce qui permet de calculer la vitesse de rapprochement avec le véhicule qui précède. Un indicateur de vitesse numérique (15) détermine la vitesse propre du véhicule, ce qui permet de calculer le temps de sécurité entre les deux véhicules. Le temps de sécurité est affiché et une alarme sonore est déclenchée lorsque le temps de sécurité calculé est inférieur à un seuil de sécurité prédéterminé. Le télémètre (14, 122) est de préférence couplé au mécanisme de direction du véhicule de manière à tenir compte de l'angle de braquage du véhicule pour distinguer deux véhicules se déplaçant sur la même voie et sur des voies différentes. De même, on a prévu un moyen (17) pour compenser l'angle d'élévation du faisceau du télémètre lorsque la répartition des charges dans le véhicule est modifiée. Le seuil de sécurité du télémètre comporte un premier seuil adaptatif en fréquence avec un rapport signal/bruit bas, et un second seuil numérique réglé pour éliminer les fausses cibles.
EP94906333A 1993-02-16 1994-02-16 Dispositif anticollision pour vehicules Withdrawn EP0685077A1 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US17742 1993-02-16
US08/017,742 US5388048A (en) 1993-02-16 1993-02-16 Vehicle anti-collison device
IL10693293 1993-09-06
IL10693293A IL106932A (en) 1993-09-06 1993-09-06 Laser rangefinder
PCT/GB1994/000309 WO1994019705A1 (fr) 1993-02-16 1994-02-16 Dispositif anticollision pour vehicules

Publications (1)

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EP0685077A1 true EP0685077A1 (fr) 1995-12-06

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EP94906333A Withdrawn EP0685077A1 (fr) 1993-02-16 1994-02-16 Dispositif anticollision pour vehicules

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EP (1) EP0685077A1 (fr)
JP (1) JPH08507371A (fr)
AU (1) AU6008594A (fr)
WO (1) WO1994019705A1 (fr)

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Also Published As

Publication number Publication date
JPH08507371A (ja) 1996-08-06
AU6008594A (en) 1994-09-14
WO1994019705A1 (fr) 1994-09-01

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