Obstacle detection system for use in vehicles

• US 4,477,184 A
• Filed: 01/18/1980
• Issued: 10/16/1984
• Est. Priority Date: 01/19/1979
• Status: Expired due to Term

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Endo, Hiroshi
• Primary Examiner(s): BUCZINSKI, STEPHEN C
• Application Number:
  US06/113,263
• Time in Patent Office: 1,733 Days
• Field of Search: 356/1, 356/4, 356/5, 356/28, 356/141, 356/152, 180/167, 180/169, 434/21, 434/22, 434/27, 350/358, 358/201, 358/63
• US Class Current: 356/141.1
• CPC Class Codes: G01S 17/931 of land vehicles

Abstract

An obstacle detection system for vehicles comprises a laser radar mounted on the front end of a vehicle and modulated by drive pulses of high rate. The laser pulses are deflected in two orthogonal directions by paired deflection signals fed from a deflection driver to paired acousto-optic light deflectors to digitally scan a space ahead of the running vehicle. The deflector driver supplies paired deflection information to arithmetic logic means. One deflection signal fed to one deflector has a rate much higher than the other and is synchronized therewith. When receiving a return pulse by a photo-detector, a video pulse of substantially constant level is reproduced by a sensitivity time control function. The distance between a target and the vehicle can be registered in a binary counter. Relevant distance information is supplied to the arithmetic logic means. The latter provides a decision of whether a possibility of collision exists and produces an alarm when the distance approaches a stopping distance. For two facing targets the arithmetic logic means calculates a spacing between them and provides decision that passing-through therebetween is impossible if the spacing is smaller than a predetermined width. For a target above the road the arithmetic logic means calculates its height and provides a decision that passing-through thereunder is impossible if that height is smaller than a predetermined height.

Claims

1. In an obstacle detection system for use in vehicles wherein decisions based upon predetermined criteria are made with respect to one or more targets existing on a course to be traveled by the vehicle in a running direction to determine whether said each target constitutes an obstacle, including:

central clock means for generating high repetition rate clock pulses;

pulse driver means responsive to said clock means for producing a sequence of drive pulses;

laser means including a single laser responsive to said pulse drive means for emitting a sequence of laser pulses;

light deflector means responsive to said clock means and said laser means for deflecting said each laser pulse in the running direction of the vehicle;

transducer means responsive to each laser pulse reflected from the one or more targets for photoelectrically converting said each returned laser pulse into an electric pulse signal; and

distance information means responsive to said clock means and said transducer means for producing information on distance up to said each target;

the improvement comprising;

means included in said light deflector means for sequentially deflecting each of said laser pulses into a high scan density, two-dimensional scanning pattern in the running direction of the vehicle and also for producing a deflection information pair corresponding to a direction of said each laser pulse as deflected; and

arithmetic logic means responsive to said deflection information pair for deriving directional information pair representing a direction of said each target with respect to a point where the laser pulse is transmitted, and further responsive to said directional information pair and said distance information as well as information indicative of the speed of the vehicle for deriving a running safety distance up to each target as well as for deriving a mutual distance between at least two targets and a height of each target to provide decision data on possibilities of (1) collision of the vehicle with each target, (2) passing of the vehicle through a laterally spaced target relative to travel direction of the vehicle, and (3) passing of the vehicle under a target.

2. A detection system as claimed in claim 1, wherein said arithmetic logic means includes means for generating an alarm signal when the distance between said target and the vehicle is determined to be less than or equal to a distance which is the sum of a predetermined marginal distance and a stopping distance, the stopping distance being the sum of a free running distance and a braking distance which are both functions of the speed of the vehicle, respectively;

and said mutual distance is derived from averaging a plurality of distances between targets.

4. A detection system as claimed in claim 1, wherein said arithmetic logic means includes means for providing a decision that passing-through between targets arranged laterally to the direction of width of the vehicle is not possible, including means for calculating the relationships ##EQU61## where d_ln is a computed minimum distance between a left-side target and the central axis of the vehicle, d_rn is an averaged minimum distance between a rightside target and said central axis, W an overall width of the vehicle, and Δ

v is a predetermined half margin in width,

the detection system further including means for producing an alarm signal if either of the foregoing relationships holds.

5. A detection system as claimed in claim 1, wherein said arithmetic logic means comprises means for providing a decision that passing of the vehicle under an upper target is not possible, including means for computing the relationship

6. A detection system as claimed in claim 5, wherein said arithmetic logic means further comprises means for providing a decision that passing of the vehicle under an upper target is not possible, including means for computing the relationship

7. A detection system as claimed in claim 3, 5, 6 or 2, further comprising sub-clock means responsive to said central clock means for generating sub-clock pulses having a high rate corresponding to a predetermined sub-division of said central clock rate;

wherein said light deflector means comprises deflector driver means responsive to said sub-clock pulses, said deflector driver means including first and second variable-frequency oscillators to generate respective output signals whose repetitive periods of variation in frequency are synchronized to each other, and a pair of wideband power amplifiers to amplify said output signal into first and second deflection signals of asymmetrical form corresponding to said deflection information pair, respectively; and

first and second light deflectors responsive respectively to said first and second deflection signals for sequentially deflecting said laser pulse into first and second directions substantially orthogonal to each other so that on an imaginary plane ahead of the vehicle and substantially perpendicular to the running direction of the vehicle is provided a two-dimensional scanning pattern having a higher scan density in said first direction such that sequential spots of said laser pulse are partially overlapped with each other in said first direction so as to form a continuous trace of said laser spots in said first direction.

8. A detection system as claimed in claim 7, wherein said deflector driver means comprises a first dividing means having a first dividing factor responsive to said sub-clock means for producing a first local clock pulse train, and deflection signal pair generator means including a pair of deflection signal generator means comprising a sawtooth signal generator means and stepwise signal generator means, respectively, said sawtooth signal generator means being responsive to said first local clock for generating a sawtooth waveform signal of said first local clock rate which is supplied to said first variable-frequency oscillator, and said stepwise signal generator means being responsive to said first local clock for generating a stepwise signal of said first local clock rate which is fed to said second variable-frequency oscillator in synchronism with said sawtooth waveform signal.

9. A detection system as claimed in claim 8, wherein said deflector driver means comprises a second dividing means having a second dividing factor smaller than said first dividing factor for generating a second local clock pulse train of a rate higher than that of said first local clock pulse train, and a first counter responsive to said second local clock pulse train for producing a first binary code which corresponds to a first one of said deflection information pair of the laser pulse in the first direction of the two-dimensional scanning pattern;

and wherein said stepwise signal generator means comprises a second counter responsive to said first local clock for generating a second binary code which corresponds to a second one of said deflection information pair of the laser pulse in the second direction of said scanning pattern, and an analog-to-digital converter responsive to said second binary code from said second counter for producing said stepwise signal.

10. A detection system as claimed in claim 9, wherein said first counter of said deflector driver means is started and incremented by said second local clock and reset by said first local clock;

and said deflector driver means comprises a digital comparator, one input to which said second binary code is fed and the other input to which a binary code corresponding to a scanning range in the second direction of said scanning pattern is applied as a reference code for comparison, said digital comparator being operative to reset said second counter when its contents are equal to said reference code.

11. A detection system as claimed in claim 10, wherein said first and second variable frequency oscillators comprise a first and a second voltage-controlled oscillator, respectively.

12. A detection system as claimed in claim 9, wherein said first and second light deflectors comprise a first and a second acousto-optic light deflector for deflecting the laser pulse in said first and second directions of said scanning pattern, respectively.

13. A detection system as claimed in claim 2, 4, 5 or 6, further comprising sub-clock means responsive to said central clock means for generating sub-clock pulses having a high rate corresponding to a predetermined sub-division of said central clock rate;

wherein said light deflector means comprises deflector driver means responsive to said sub-clock pulses, said deflector driver means including a first and a second variable-frequency oscillator to generate output signals whose repetitive periods of variation in frequency are synchronized to each other, and a pair of wideband power amplifiers to amplify said output signals respectively into a first and a second deflection signal of asymetrical form corresponding to said deflection information pair, respectively, and a first and a second light deflector responsive respectively to said first and second deflection signals for sequentially deflecting said laser pulse into a first and a second direction substantially orthogonal each other so that on an imaginary plane ahead of the vehicle and substantially perpendicular to the running direction of the vehicle is provided a two-dimensional scanning pattern having a higher scan density in said first direction such that sequential spots of said laser pulse are partially overlapped to each other in said first direction so as to form a continuous trace of said laser spots in said first direction.

14. A detection system as claimed in claim 13, wherein said deflector driver means comprises a first dividing means having a first dividing factor responsive to said sub-clock means for producing a first local clock pulse train, and deflection signal pair generator means including a pair of deflection signal generator means comprising a sawtooth signal generator means and stepwise signal generator means, respectively, said sawtooth signal generator means being responsive to said first local clock for generating a sawtooth waveform signal of said first local clock rate, which is supplied to said first variable-frequency oscillator, and said stepwise signal generator means being responsive to said first local clock for generating a stepwise signal of said first local clock rate which is fed to said second variable-frequency oscillator in synchronism with said sawtooth waveform signal.

15. A detection system as claimed in claim 14, wherein said deflector driver means comprises a second dividing means having a second dividing factor smaller than said first dividing factor for generating a second local clock pulse train of a rate higher than that of said first local clock pulse train, and a first counter responsive to said second local clock pulse train for producing a first binary code which corresponds to a first one of said deflection information pair of the laser pulse in the first direction of the two-dimensional scanning pattern;

and wherein said stepwise signal generator means comprises a second counter responsive to said first local clock for generating a second binary code which corresponds to a second one of said deflection information pair of the laser pulse in the second direction of said scanning pattern, and an analog-to-digital converter responsive to said second binary code from said second counter for producing said stepwise signal.

16. A detection system as claimed in claim 15, wherein said first counter of said deflector driver means is started and incremented by said second local clock and reset by said first local clock;

and said deflector driver means comprises a digital comparator, one input to which said second binary code is fed and the other input to which a binary code corresponding to a scanning range in the second direction of said scanning pattern is applied as a reference code for comparison, said digital comparator being operative to reset said second counter when its contents are equal to said reference code.

17. A detection system as claimed in claim 16, wherein said first and second variable frequency oscillators comprise a first and a second voltage-controlled oscillator, respectively.

18. A detection system as claimed in claim 15, wherein said first and second light deflectors comprise a first and a second acousto-optic light deflector for deflecting the laser pulse in said first and second directions of said scanning pattern, respectively.

19. A detection system as claimed in claim 12, further comprising sub-clock means responsive to said central clock means for generating sub-clock pulses having a high rate corresponding to a predetermined sub-division of said central clock rate;

wherein said laser means comprises a semiconductor laser in the form of a laser diode, and said pulse driver means comprises current switching means responsive to said sub-clock pulses and connected to one terminal of said laser diode, said current switching means comprising a parallel arrangement of a first series combination of a first electronic switch and a first constant current source of one polarity and a second series combination of a second switch and a second constant current source of the other polarity, and said first and second electronic switches being switched on in an alternating manner in response to said each sub-clock pulse.

20. A detection system as claimed in claim 19, wherein said first electronic switch is first switched on in response to said each sub-clock pulse for a predetermined first duration to enable a forward current to flow through said laser diode, and immediately after said first duration said second electronic switch is switched on for a predetermined second duration.

21. A detection system as claimed in claim 20, wherein said first and second durations are chosen substantially equal to the duration of said each sub-clock pulse to produce a laser pulse having a much steeper trailing edge and a duration which is substantially equal to that of said each sub-clock pulse.

22. A detection system as claimed in claim 19, wherein said first combination comprises a first emitter coupled logic means and said second combination comprises a second emitter coupled logic means.

23. A detection system as claimed in claim 18, further comprising sub-clock means responsive to said central clock means for generating sub-clock pulses having a high rate corresponding to a predetermined sub-division of said central clock rate;

wherein said laser means comprises a semiconductor laser in the form of a laser diode, and said pulse driver means comprises current switching means responsive to said sub-clock pulses and connected to one terminal of said laser diode, said current switching means comprising a parallel arrangement of a first series combination of a first electronic switch and a first constant current source of one polarity and a second series combination of a second switch and a second constant current source of the other polarity, and said first and second electronic switches being switched on in an alternating manner in response to said each sub-clock pulse.

24. A detection system as claimed in claim 23, wherein said first electronic switch is first switched on in response to said each sub-clock pulse for a predetermined first duration to enable a forward current to flow through said laser diode, and immediately after said duration said second electronic switch is switched on for a predetermined second duration.

25. A detection system as claimed in claim 24, wherein said predetermined first and second durations are chosen substantially equal to the duration of said each sub-clock pulse to produce a laser pulse having a much steeper trailing edge and duration which is substantially equal to that of said each sub-clock pulse.

26. A detection system as claimed in claim 23, wherein said first combination comprises a first emitter coupled logic means and said second combination comprises a second emitter coupled logic means.

27. A detection system as claimed in claim 22, wherein said transducer means comprises photo-detector means responsive to said each return laser pulse for generating an electric pulse signal of level which is directly dependent upon the distance between the target and the vehicle;

and variable gain amplifier means responsive to said electric pulse signal for amplifying it to a predetermined level irrespective of the distance between the target and the vehicle.

28. A detection system as claimed in claim 27, wherein said photo-detector means comprises a photo diode of electron avalanche type.

29. A detection system as claimed in claim 28, wherein said variable gain amplifier means comprises a two stage amplifier, a preceding stage thereof including a dual gate field effect transistor to a gain control gate of which a sensitivity time control signal is applied and a succeeding stage of said amplifier including a field effect transistor.

30. A detection system as claimed in claim 29, wherein a range of the distance to be measured by scanning operation of the laser pulse is dependent upon the beginning and duration of said sensitivity time control signal.

31. A detection system as claimed in claim 30, wherein said transducer means comprises a ramp function generator responsive to said each sub-clock pulse for generating a ramp signal serving as said sensitivity time control signal.

32. A detection system as claimed in claim 30, wherein said transducer means comprises a wideband amplifier responsive to said electric pulse signal as detected for amplifying its level and threshold means responsive to said amplified electric pulse signal for comparing a level of the latter with a predetermined threshold level of said comparator means.

33. A detection system as claimed in claim 31, wherein said distance information means comprises window-time means which is set by said sub-clock pulse and reset by an output of said threshold means to produce a window time signal, gating means responsive to said window time signal from said window time means for passing said central clock pulses, and distance counter means responsive to said central clock pulses for counting the number thereof as supplied for a duration of said window time signal to produce a binary code representing a distance between the vehicle and the target as scanned.

34. A detection system as claimed in claim 33, wherein said window time means comprises a flipflop.

35. A detection system as claimed in claim 26, wherein said transducer means comprises photo-detector means responsive to said each return laser pulse for generating an electric pulse signal of level which is directly dependent upon the distance between the target and the vehicle;

and variable gain amplifier means responsive to said electric pulse signal for amplifying it to a predetermined level irrespective of the distance between the target and the vehicle.

36. A detection system as claimed in claim 35, wherein said photo-detector means comprises a photo diode of electron avalanche type.

37. A detection system as claimed in claim 36, wherein said variable gain amplifier means comprises a two stage amplifier, a preceding stage thereof including a dual gate field effect transistor to a gain control gate of which a sensitivity time control signal is applied and a succeeding stage of said amplifier including a field effect transistor.

38. A detection system as claimed in claim 37, wherein a range of the distance to be measured by scanning operation of the laser pulse is dependent upon the beginning and duration of said sensitivity time control signal.

39. A detection system as claimed in claim 38, wherein said transducer means comprises a ramp function generator responsive to said each sub-clock pulse for generating a ramp signal serving as said sensitivity time control signal.

40. A detection system as claimed in claim 39, wherein said transducer means comprises a wideband amplifier responsive to said electric pulse signal as detected for amplifying its level and threshold means responsive to said amplified electric pulse signal for comparing a level of the latter with a predetermined threshold level of said comparator means.

41. A detection system as claimed in claim 40, wherein said distance information means comprises window-time means which is set by said sub-clock pulse and reset by an output of said threshold means to produce a window time signal, gating means responsive to said window time signal from said window time means for passing said central clock pulses, and distance counter means responsive to said central clock pulses for counting the number thereof as supplied for a duration of said window time signal to produce a binary code representing a distance between the vehicle and the target as scanned.

42. A detection system as claimed in claim 41, wherein said window time means comprises a flipflop.

43. A detection system as claimed in claim 34, wherein upon scanning in a direction from the right to the left said arithmetic logic means operates to derive and store in memory means thereof a distance between said leftside target and said central axis by calculating an arithmetic mean of all distances to central axis obtained during the last scanning period to said leftside target in the first direction of said scanning pattern, and also to derive and store in said memory means a distance between said rightside target and said central axis by calculating an arithmetic mean of all distances obtained during the first scanning period to said rightside target in the first direction of said scanning pattern, and vice versa.

44. A detection system as claimed in claim 43, wherein said arithmetic logic means comprises a microcomputer.

45. A detection system as claimed in claim 44, wherein said central clock means, said sub-clock means, said flipflop, said gating means and said distance counter of said distance information means comprise an emitter coupled logic, respectively.

46. A detection system as claimed in claim 42, wherein upon scanning in a direction from the right to the left said arithmetic logic means operates to derive and store in memory means thereof a distance between said leftside target and said central axis by calculating an arithmetic mean of all distances to central axis obtained during the last scanning period to said leftside target in the first direction of said scanning pattern, and also to derive and store in said memory means a distance between said rightside target and said central axis by calculating an arithmetic mean of all distances obtained during the first scanning period to said rightside target in the first direction of said scanning pattern, and vice versa.

47. A detection system as claimed in claim 46, wherein said arithmetic logic means comprises a microcomputer.

48. A detection system as claimed in claim 47, wherein said central clock means, said sub-clock means, said flipflop, said gating means and said distance counter of said distance information means comprise an emitter coupled logic, respectively.

3. In an obstacle detection system for use in vehicles wherein decisions based upon predetermined criteria are made with respect to one or more targets existing on a course to be traveled by the vehicle in a running direction to determine whether said each target constitutes an obstacle, including:

central clock means for generating high repetition rate clock pulses;

pulse driver means responsive to said clock means for producing a sequence of drive pulses;

laser means including a single laser responsive to said pulse drive means for emitting a sequence of laser pulses;

light deflector means responsive to said clock means and said laser means for deflecting said each laser pulse in the running direction of the vehicle;

transducer means responsive to each laser pulse reflected from the one or more targets for photoelectrically converting each said returned laser pulse into an electric pulse signal; and

distance information means responsive to said clock means and said transducer means for producing information on distance up to said each target;

the improvement comprising;

means included in said light deflector means for sequentially deflecting each of said laser pulses into a high scan density, two-dimensional scanning pattern in the running direction of the vehicle and also for producing a deflection information pair corresponding to a direction of each said laser pulse as deflected;

said transducer means responsive to each reflected laser pulse including;

means for receiving a return laser pulse from an extreme right end of a left side target and

means for receiving a return laser pulse from an extreme left end of a right side target; and

arithmetic logic means responsive to said deflection information pair for deriving directional information pair representing a direction of each said target with respect to a point where the laser pulse is transmitted, and further responsive to said directional information pair and said distance information as well as information indicative of the speed of the vehicle for deriving a running safety distance up to each target as well as for deriving a mutual distance between at least two targets and a height of each target to provide decision data on possibilities of (1) collision of the vehicle with each target, (2) passing of the vehicle through a laterally spaced target relative to travel direction of the vehicle, and (3) passing of the vehicle under a target;

said arithmetic logic means comprising;

means for

calculating R_l, a distance between said laser on the central axis of the vehicle and the extreme right end of a left side target;

calculating θ

_xl, an angle at the laser between said central axis and said extreme right end of the left side target;

calculating R_r, a distance between said laser and the extreme left end of a right side target;

calculating θ

_xr, an angle at the laser between said central axis and said extreme left end of the right side target; and

means for computing

space="preserve" listing-type="equation">R.sub.l ·

θ

.sub.xl +R.sub.r ·

θ

.sub.xr

and for determining if

space="preserve" listing-type="equation">W+δ

w≧

R.sub.l ·

θ

.sub.xl +R.sub.r ·

θ

.sub.xr

where W is an overall width of the vehicle and δ

w is a predetermined margin in width;

the detection system further comprising means for producing an alarm signal when it is determined that the aforementioned relationship holds.