WO1992021116A1

WO1992021116A1 - Vehicle collision avoidance

Info

Publication number: WO1992021116A1
Application number: PCT/GB1992/000953
Authority: WO
Inventors: Philip Needham; Christopher Francis; Peter Oakley
Original assignee: Imatronic Limited
Priority date: 1991-05-23
Filing date: 1992-05-26
Publication date: 1992-11-26
Also published as: GB9111129D0

Abstract

Vehicle collision avoidance apparatus for a motor vehicles measures the speed and distance of an approaching vehicle using a rearwardly directed laser measuring beam. A collision risk factor is computed and an appropriate display generated. The display may consist of the progressive activation of the vehicle's existing brake, rear fog and hazard warning lights. A dedicated display can be provided, visible to the driver of the rearwardly approaching vehicle.

Description

VEHICLE COLLISION AVOIDANCE

This application relates to vehicle collision avoidance and in the most important example to apparatus installed for this purpose in motor cars and other motor vehicles.

According to an existing proposal, the effectiveness of car brake lights can be improved by incorporating a progressive warning display. That is to say, as the brakes in the motor car are applied more firmly, the intensity or the area of illumination of the brake lights is increased. The driver of a rear approaching motor car is thus alerted to the need to apply his own brakes, if he or she is not to approach the braking vehicle too closely or too quickly than is safe. There are circumstances, however, where a car which is not braking, is approached by another vehicle from the rear too closely or too quickly than is safe. Under these circumstances, brake lights - whether they are conventional or progressive - offer no remedy.

Suggestions have been made for providing motor vehicles with apparatus for measuring the distance to other vehicles or to fixed objects. Specifically, radar distance measuring equipment has been proposed for this purpose. In such a known arrangement, the measuring equipment is directed forwardly and measures the distance between the equiped vehicle and the vehicle in front. The driver of the vehicle equipped with the measuring apparatus can thus be alerted if he is approaching another vehicle too closely. This equipment might be expected to reduce the risk of collisions caused by a mis-judgement or lack of concentration on the part of the driver of the vehicle which is so equipped. In circumstances where mis-judgement or lack of care is exercised by the drivers of other vehicles, the known equipment is of little use in avoiding collisions. Apparatus has also been suggested for measuring the distance to other vehicles - or to fixed objects - during close manoevring and, especially, parking.

It is an object of this invention to provide improved apparatus and methods of vehicle collision avoidance which overcome important drawbacks of the existing arrangements.

Accordingly, the invention consists in one aspect in vehicle collision avoidance apparatus for installation in a motor vehicle, comprising means for monitoring the distance between the said vehicle and an approaching vehicle; means for determining the velocity of approach of the approaching vehicle; means for assigning a collision risk factor which increases with an increase in said approach velocity and with a decrease in said distance and display means positioned in the said vehicle so as to be visible to the driver of the approaching vehicle, said display means providing an indication of the collision risk factor;

Preferably, said display means provides a progressive indication of the collision risk factor.

Advantageously, said display means operates with the successive energisation of existing warning lights in the vehicle, selected from brake lights, rear fog lights and rear hazard warning lights.

Alternatively, said display means comprises a dedicated display device.

By energising, for example, the brake lights of the vehicle, this invention serves to alert not (or not only) the driver of the vehicle which is equipped, but the driver who is approaching too quickly or too closely and on whose part braking or avoiding action is required. Operation is not dependent upon the car in front braking. The present invention will even provide the driver of the rear approaching vehicle with a warning, in circumstances where the car in front is stationary and, possibly, unoccupied. It will also provide a warning in circumstances where the need to brake or to take avoiding action arises from acceleration in the car behind, rather than deceleration - through braking - of the car in front.

Important advantages are seen in the capability of the present invention to operate through existing indicators or displays on motor vehicles. There is some economy in not requiring, necessarily, a dedicated display device. Much more important, however, is the ability of the present invention to take advantage of conditioned driver responses to brake lights and hazard warning lights. Thus the driver of a vehicle approaching too closely or too quickly a vehicle equipped in accordance with this invention, is likely to react to brake lights without immediately appreciating (or needing to appreciate) the reason for his need to brake. Thus it is immaterial, for the immediate purposes of avoiding a collision, that the driver of the approaching vehicle "thinks" that the car in front is braking. If the relative speed of approach is too great, the need for the following car to brake is the same whether the car in front is actually braking or whether the following car is simply travelling too fast, too close.

It may be that with widespread use of the present invention, drivers will become accustomed to receiving, from the car in front, visual warnings of a collision risk and will react without a need to rely on conditioned responses to brake and hazard warning lights. A wide variety of technologies are available for monitoring the distance of an approaching vehicle. These include beams of electromagnetic radiation such as radar, and infrared or visible lasers and, also, ultrasonic means. It will be beneficial to adopt a measurement technology which has all weather capability.

Laser based measurement technologies are currently preferred. From repeated measurement of distance, speed can be calculated. It is also possible for speed to be measured separately, for example using a Doppler technique. Acceleration can if required be computed. The two main techniques for distance measurement which would be appropriate in this case are i) a continually modulated laser beam, where the phase shift of the reflected beam is measured and ii) a short laser pulse where the time of flight is measured. Both systems would be likely to use infrared light to avoid the risk of distraction by visible light. Whilst lasers have the advantage of very low beam divergence, it may be possible to make use of alternative light sources such as light emitting diodes.

The invention will further be described by way of example with reference to the accompanying drawings, in which :-

Figure 1 is a block diagram of apparatus according to this invention;.

Figure 2 is a schematic view of optical components forming part of apparatus according to this invention;

Figure 3 is a block diagram of apparatus according to a further embodiment of the present invention; Figure 4 is a block diagram of apparatus according to a still further embodiment of the present invention;

Figure 5 is a somewhat schematic view of an alternative optical arrangement for use in the present invention;

Figures 6a) and 6b) are diagrams illustrating modes of operation of the optical arrangement shown in Figure 5; and

Figure 7 is a plan illustrating parameters and calculations utilised in a preferred form of the present invention.

Referring initially to the schematic drawing of Figure 1 , a non-contact distance measuring device 10, preferably operating by the use of a narrow field of radiation over a long distance, is positioned at the rear of the vehicle so as to provide a measurement of the distance to an approaching vehicle shown schematically at 12. A more detailed description of alternative forms of distance measuring devices will follow. The distance signal is supplied as one input to a processor 14. The distance signal is also applied to a velocity unit 16 which provides as a second input to the processor 14 a signal indicating the rate of change with time of the distance signal, and thus the approach velocity of the vehicle 12. The processor 14 is provided, in look-up table 18, with information relating to the degree of danger associated with a particular approach velocity at a particular distance. Thus, in one example, there may be associated with each of a range of distances a maximum approach velocity beneath which no collision risk is assigned. At a particular distance, the collision risk factor would increase with an increase in approach velocity. Clearly, for a particular approach velocity, the collision risk factor will decrease with an increase in distance. The processor 14 provides an output to a display 20, the output being representative of the collision risk factor. The display is positioned so as to be visible by the driver of the vehicle 12. Typically, the display comprises existing warning or indicator lights of the vehicle. Thus, if the vehicle is fitted with a progressive brake light system, the display means 20 is arranged to energise the brake light system progressively as the collision risk factor increases. In the case of a vehicle having conventional brake lights, the display means may be adapted to energise the vehicle brake lights as the collision risk factor passes a first threshold and then succesively to energise other warning or indicator lights as the collision risk factor passes subsequent thresholds. Thus, after energisation of the brake lights, rear fog lamps and hazard warning lights can be turned on in succession.

Referring now to Figure 2, there is illustrated in schematic form, an optical arrangement for use in the present invention.

A laser 30, for example a commercially available laser diode operating in the infrared, is associated with beam-forming optics shown at 32. The beam is directed rearwardly of the motor vehicle by a mirror 34 which is adjustable in position about a pivot or pivots 36. Positioning means (not shown) are provided for controlling the position of the mirror. The mirror may be driven, for example, so as to scan the laser beam continuously. In an alternative, the mirror is controlled in position so as to direct the laser beam, possibly in a feedback loop. The mirror 34 serves additionally to direct laser light reflected from a following motor vehicle, onto the light gathering optics 38 of a detector 40. This detector may, for example, take the form of an avalanche photodiode.

The optical arrangement in this preferred example also includes a video camera 42. Image processing from the camera output will enable the direction or bearing of the following vehicle to be determined, enabling the correct direction to be selected for the laser beam. The bearing of the following vehicle - for instance, whether the vehicle is in an overtaking lane - will itself represent information that can usefully be processed in the apparatus according to this invention. A camera may also collect other forms of useful information such as the approximate size of the following vehicle.

Turning now to Figure 3, there is shown in block form one embodiment of the present invention.

A pulse generator 50 supplies a control pulse to a laser driver 52, causing a pulse of laser light to be emitted from laser 54. The control pulse is passed, additionally, from the pulse generator 50 to the "start" input of a timer 56. The laser pulse passes through laser optics 58 to a laser scanning system 60. This scanning system is controlled from a control logic unit 62 in tandem with a detector scanning system 64. The two scanning systems may, as shown in Figure 2, comprise a common scanning mirror; they may alternatively be physical separate with mechanical or electronic control linkages.

Light reflected from the following vehicle and captured by the detector scanning system 64, passes through detector optics 66 to a photodetector 68. The output of this photodetector is presented, via an ampiifier 70, to an edge detector 72 providing a "stop" input to the timer 56. The control logic unit 62 receives the time-of-flight output from the timer 56, together with a range of sensor inputs shown at 62, and provides a collision risk input to the warning system 66. Examples of appropriate sensors and other parameters that are usefully taken into consideration by the control logic unit 62 in calculating the collision risk factor, will be discussed below. As has already been mentioned, the warning system 66 can take the form of an interface with existing indicators on the motor vehicle; alternatively, it may comprise a dedicated display positioned so as to be visible by the driver of the following vehicle.

An alternative embodiment is shown in rather more abbreviated form in Figure 4. A modulation oscillator 70 controls a laser driver 72 so as to generate from laser 74 a continuous laser beam of modulated amplitude. The modulated beam is directed rearwardly of the vehicle through laser optics 76 which may include suitable beam positioning or scanning mechanisms. A control output from the modulation oscillator is also taken to a phase detector 78. Light reflected from the following vehicle is collected in detector optics 80 and passed to a photodetector 80. The photodetector output is taken through amplifier 82 to the phase detector 78. An output is produced which is representative of the distance to the following vehicle. In control logic (not shown in Figure 4), speed is calculated and a collision risk factor assessed.

Since there is wide variety in the size and shape of optical target represented by the front elevation of motor vehicles, the probability of detecting a reflected signal can be increased by employing a relatively broad beam, possibly around 50cms. This can be achieved at a particular distance by de-focussing of the beam and this may be a possible where alternative means exist for defining a distance range of interest. Where a beam of constant width is employed, however, there may be practical difficulties in handling a beam of that diameter. A useful alternative is to use multiple laser beams to simulate, in certain respects, the effect of a single, larger width beam. Multiple beams can be arranged in a parallel array to give the required "footprint". The beams can also be angled so as to give the desired width over the distance range of interest. Multiple beams can be generated in separate laser diodes or through beam splitting of the output of a single laser diode.

Referring for example to Figure 5, there is shown an arrangement by which five laser beams of equal power are produced from a single laser source 90. The laser beam from source 90 is directed to a generally parallel array of five graded splitting mirrors 92,94,96,98 and 100. Each mirror has an upper portion of 100% reflectivity and a lower portion of graded reflectivity. Thus the lower portion of mirror 92 has a reflectivity of 20%, increasing to 25% for mirror 94, 33% for mirror 96, 50% for mirror 98 and 100% for mirror 100. As will be readily seen, this arrangement produces at each mirror, a rearwardly directed beam at 20% of the original beam intensity. Light reflected from the following vehicle is directed by the upper portion of each mirror to the associated detector 102.

It is proposed that a mirror adjusting mechanism be provided to enable adjustment of the mirrors 92 to 100 in two modes. In a first mode, the mirrors are deflected in unison to cause a parallel scanning movement of the five beams; in a second mode, the mirrors are deflected differentially so as adjust the divergence of the beams. One mechanism for achieving these forms of adjustment is shown schematically in Figure 5. Each of the mirrors 92 to 100 is pivotally mounted at its lower edge as shown at 104. The mounting of each mirror includes a slot 106, with the slot for mirror 96 being vertical and the slots for the mirrors on either side being inclined inwardly at increasing angies. An adjustment bar 108 is provided with a series of five pins 1 10 riding, one each, in the slots 106. The adjustment bar 108 is mounted for adjusting movement horizontally and vertically. Horizontal adjusting movement has the effect of deflecting the beams together, whilst vertical movement will adjust the divergence of the beams.

As indicated in Figure 6, multiple beams can be orientated in different ways. Figure 6a) shows an arrangement in which different angular zones are sampled simultaneously; the beam width is not however constant. In the arrangement of Figure 6b), the beam width is constant; scanning or positioning of the beam may be required.

Turning to Figure 7, there is illustrated in graphical form the parameters and computations utilised in a preferred form of the present invention. In certain practical arrangements it will be possible to dispense with some of the listed factors, whilst still achieving the required results. Equally, there may be other factors - useful in certain situations - that will occur to the skilled man.

A camera 200 will offer lane boundary detection 202 as well as determinations of vehicle size 204 and vehicle location 206. Distance measurement and beam positioning unit 208 serves through receipt of information concerning the location of the following vehicle, to direct the laser beam appropriately. A distance measurement is taken and information, optionally combined with "own vehicle" speed from sensor 210, is passed to the following vehicle distance measurement unit 212. This passes a value direct to the warning threshold calculation unit 214, as well as to speed and acceleration calculation units 216,218 provided further values to the warning threshold calculation unit 214.

It has been explained how a collision risk factor can be assessed from the distance and relative speed of the approaching vehicle, modified by additional information such as rates of acceleration or deceleration. In an important addition to the preferred form of this invention, the collision risk is modified according to an estimate of the braking distance of the approaching vehicle. To achieve this, information from the vehicle size determination unit 204 is taken to a following vehicle braking distance estimation unit together with information from "ambient" sensors such as ambient temperature sensor 222, fog detector 224, rain detector 226 and snow detector 228. This information is processed in warning threshold calculation unit 214 which operates warning activation 230 as appropriate preset thresholds of collision risk are exceeded.

It should be understood that this invention has been described by way of examples only and a wide variety of modifications are possible without departing from the scope of the invention. Thus the described methods by which a collision risk factor is assigned are but examples of possible arrangements. As an alternative to the mentioned look-up table, an algorithm can be used to derive a value for the collision risk factor for comparison with preset or individually computed thresholds.

The use of existing vrhicle warning or indicator lights represents a convenient method of fitting apparatus according to this invention, but it will be understood that the display could additionally or alternatively comprise a dedicated display device. Such a display device may be adapted for fitting to the rear windscreen of an existing vehicle. A display in red which increases in intensity or in illumination area, offers the advantage of familiarity, through its association with existing brake light systems. Other display arrangements can of course be devised within the bounds of the invention, including alphanumerical dislays. In a vehicle designed to receive apparatus according to this invention, there is of course greater scope for variation in design. A slave display or other - possibly audible - warning device may be useful to provide information to the driver of the vehicle equipped in accordance with this invention.

There exist a wide variety of distance measurement technologies beyond those specifically mentioned and whilst optical methods are preferred, they are not essential to the performance of this invention. Techniques for "intelligent" positioning of the measuring beam are useful, but again not essential. The camera described for this purpose can operate in different ways, such as for example by identifying through appropriate filters the appearance on the following vehicle of a "dot" from the measuring beam. Moreover, the role of the camera - both in determining the lateral postion of the following vehicle and in estimating its size - can to certain degrees be replaced by other arrangements such as multiple beams with differential detectors. The use of multiple beams can, as has been mentioned be separately useful in increasing the effective beam width.

Claims

» 1 . Vehicle collision avoidance apparatus for installation in a motor vehicle, comprising means for monitoring the distance between the said vehicle and an approaching vehicle; means for determining the velocity of approach of the approaching vehicle; means for assigning a collision risk factor which increases with an increase in said approach velocity and with a decrease in said distance and display means positioned in the said vehicle so as to be visible to the driver of the approaching vehicle, said display means providing an indication of the collision risk factor;

2. Apparatus according to Claim 1 , wherein said display means provides a progressive indication of the collision risk factor.

3. Apparatus according to Claim 2, wherein said display means operates with the successive energisation of existing warning lights in the vehicle, selected from brake lights, rear fog lights and rear hazard warning lights.

4. Apparatus according to Claim 2, wherein said display means comprises a dedicated display device.

5. Apparatus according to any one of the preceding claims, further comprising means for providing to said collision risk assigning means an estimation of the braking distance of the approaching vehicle.

6. Apparatus according to Claim 5, wherein said means for providing an estimation of the braking distance of the approaching vehicle, comprises means for sensing ambient conditions.

7. Apparatus according to any one of the preceding claims, further comprising means for determining the lateral position of the approaching vehicle.

8. A method for motor vehicle collision avoidance comprising the steps of measuring from a first vehicle the distance and speed of approach of a second vehicle approaching the first vehicle from the rear; assigning a collision risk factor; and displaying an indication of said factor in the first vehicle so as to be visible from the second vehicle.

9. A method according to Claim 8, wherein said collision risk factor is assigned taking into consideration ambient conditions likely to affect braking distances.

10. A method according to Claim 8 or Claim 9, wherein the step of displaying an indication of said collision risk factor comprises the successive energisation of existing warning lights in the vehicle, selected from brake lights, rear fog lights and rear hazard warning lights .