Object detection method and apparatus employing electro-optics

• US 4,926,170 A
• Filed: 02/12/1987
• Issued: 05/15/1990
• Est. Priority Date: 02/19/1986
• Status: Expired due to Fees

• Current Assignee: Autosense LLC
• Original Assignee: Auto-Sense. Limited
• Inventors: Beggs, George, Speck, Richard
• Primary Examiner(s): Orsino, Joseph A.
• Assistant Examiner(s): SWARTHOUT, BRENT
• Application Number:
  US07/013,812
• Time in Patent Office: 1,188 Days
• Field of Search: 340/901-904, 340/933, 340/942, 340/97, 340/555-557, 180/169, 342/455, 342/27, 342/28, 356/438, 356/439
• US Class Current: 340/904
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 2007/4975 of sensor obstruction by, e.g. dirt- or ice-coating, e.g. by reflection measurement on front-screen
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver

Abstract

Apparatus for detecting the presence of an object within an area under surveillance employs an electro-optical emitter for directing light into the area and an electro-optical receiver for sensing light reflected from the object which originates from the emitter. The emitter emits light energy of a preselected wavelength and is modulated at a preselected frequency to provide the emanating light energy with a characteristic signature. Light reflected by an object within the area under surveillance is filtered and converted to an electrical signal which varies in accordance with the magnitude of the filtered light having the preselected wavelength and modulation frequency. A selected portion of the electrical signal is amplified by a band-pass amplifier and is synchronously sampled in accordance with the modulation frequency to determine the magnitude of the filtered light which originated from the emitter. The sampled signal is compared with a threshold value to determine whether an object is present within the area under surveillance. The emitter and receiver are covered by a transparent shield to protect them against foreign matter. An electro-optic detector monitors the accumulation of foreign particulates on the shield. The apparatus may be desirably used in vehicles to detect the presence of adjacent objects, particularly within the vehicle'"'"'s "blind spots" and thereby avoid collisions.

Claims

1. Apparatus for detecting the presence of an object in an area under surveillance comprising:

emitter means for emitting light into said area;

controller means coupled to said emitter means for generating an activating signal to control the intensity of said light such that said intensity has a keyed modulation;

detector means for receiving light from said area and generating an electrical signal proportional thereto, said electrical signal having said keyed modulation;

synchronous means coupled to said detector means and to said controller means for deriving a first portion of said electrical signal having said keyed modulation;

threshold means coupled to said synchronous means for generating an indicating signal when the magnitude of said first portion exceeds a threshold value;

delay means coupled to said controller means for generating a quadrature signal phase shifted by substantially 90°

from said activating signal;

quadrature means coupled to said detector means and to said delay means for deriving a second portion of said electrical signal having a modulation corresponding to said quadrature signal; and

circuit means coupled to said quadrature means and to said synchronous means for comparing said first portion and said second portion.

2. The apparatus of claim 1 wherein said circuit means is further coupled to said threshold means for inhibiting said indicating signal when the absolute value of said second portion exceeds a predetermined ratio of said first portion.

3. A method for detecting the presence of an object within an area under surveillance comprising the steps of:

radiating light energy into said area, said energy having an intensity corresponding to a selected modulation;

receiving light energy from said area including said radiated light energy and generating an electrical signal proportional thereto;

deriving a first portion of said electrical signal corresponding to said selected modulation;

indicating the presence of an object when said first portion exceeds a threshold value;

generating a quadrature signal phase-shifted by substantially 90°

from the modulation of said intensity;

deriving a second portion of said electrical signal corresponding to said quadrature signal; and

,

inhibiting said indicating step when said second portion exceeds a predetermined value.

4. The method of claim 3 further comprising the step of varying said selected modulation over time.

5. The method of claim 4 wherein said selected modulation is frequency modulation having substantially only one frequency component.

6. The method of claim 4 wherein said selected modulation is frequency modulation having a plurality of frequency components.

7. The method of claim 3 further comprising the step of generating a predetermined ratio of said first portion as said predetermined value.

8. The method of claim 3 wherein said radiating step includes generating a plurality of angularly segregated light beams.

9. The method of claim 8 wherein said receiving step includes separate detection of each of said light beams.

10. The method of claim 8 wherein each of said light beams has a different selected modulation.

11. The method of claim 8 wherein said light beams are emitted in sequence.

12. Apparatus for detecting the presence of an object within an area under surveillance, comprising:

emitter means for emitting radiant energy into said area;

controller means coupled to said emitter means for generating an activating signal to control the intensity of said radiant energy such that said intensity has a controlled frequency spectrum;

detector means for receiving radiant energy from said area and generating an electrical signal proportional thereto;

synchronous means coupled to said detector means and to said controller means for deriving a first portion of said electrical signal having said controlled frequency spectrum;

threshold means coupled to said synchronous means for generating an indicating signal when the magnitude of said first portion exceeds a threshold value; and

,

key sequence generator means coupled to said controller means for sequentially commanding said frequency spectrum, said key sequence generator means including a read-only memory for sequentially reading out a commanded frequency spectrum.

13. The apparatus of claim 12 wherein said controlled frequency spectrum is time varying.

14. The apparatus of claim 12 wherein said controlled frequency spectrum has substantially only one component frequency, the frequency of which varies in time.

15. The apparatus of claim 12 wherein said controlled frequency spectrum has more than one component frequency.

16. The apparatus of claim 12 wherein said emitter means is adapted to emit a plurality of angularly segregated beams of said radiant energy.

17. The apparatus of claim 16 wherein each of said plurality of beams has a different controlled frequency spectrum.

18. The apparatus of claim 16 wherein said plurality of beams are emitted in sequence.

19. The apparatus of claim 16 wherein said detector means includes a plurality of channels, each channel adapted to receive radiant energy from a respective zone within said area.

20. Apparatus for detecting the presence of an object within an areas under surveillance, comprising:

emitter means for emitting radiant energy into said area;

controller means coupled to said emitter means for generating an activating signal to control the intensity of said radiant energy such that said intensity has a controlled frequency spectrum;

detector means for receiving radiant energy from said area and generating an electrical signal proportional thereto;

synchronous means coupled to said detector means and to said controller means for deriving a first portion of said electrical signal having said controlled frequency spectrum;

threshold means coupled to said synchronous means for generating an indicating signal when the magnitude of said first portion exceeds a threshold value;

delay means coupled to said controller means for generating a quadrature signal phase-shifted by substantially 90°

from said activating signal;

quadrature means coupled to said detector means and to said delay means for deriving a second portion of said electrical signal which has a frequency spectrum phase-shifted by substantially 90°

from said activating signal; and

,

circuit means coupled to said quadrature means and to said threshold means for inhibiting said indicating signal when the absolute value of said second portion exceeds a predetermined value.

21. The apparatus of claim 20 wherein said predetermined value is a predetermined ratio of said first portion.