Multi frequency photoelectric detection system

• US 6,377,167 B1
• Filed: 05/01/2001
• Issued: 04/23/2002
• Est. Priority Date: 07/22/1997
• Status: Expired due to Fees

• Current Assignee: Autosense LLC
• Original Assignee: Autosense LLC
• Inventors: Lewis, Robert I, Mathews, Paul, Juds, Scott
• Primary Examiner(s): Wu, Daniel J.
• Assistant Examiner(s): Nguyen, Tai T.
• Application Number:
  US09/674,215
• Time in Patent Office: 357 Days
• Field of Search: 340/435, 340/436, 340/903, 340/904, 340/933, 340/942, 340/943, 340/552, 340/555, 342/70
• US Class Current: 340/435
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 2013/9315 Monitoring blind spots
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver

Abstract

Collision avoidance apparatus (28, 30) is mounted on a host vehicle (20) to detect the presence of an adjacent vehicle (22) within a monitored zone (24, 26). A sensor module (30) includes a plurality of discrete sensor systems for monitoring unique portions of the monitored zone (24, 26), each of which comprises an emitter (52) emitting a fixed frequency modulated beam (58) of light energy (54) with a predetermined burst length into its unique portion of the monitored zone (24, 26), and a receiver (68) having a field of view (62), substantially aligned with emitted beam (58) to produce a fixed optical overlap area (A), and for sensing light energy (66) and generating a received signal. A frequency generator (48) produces two or more predetermined different fixed frequencies for use by the emitter (52) to emit beams (58) at each frequency. A phase shifter (70) produces a phase shifted reference signal with a different predetermined phase delay relationship to each fixed frequency. A mixer (72) mixes each received signal and each phase shifted reference signal to produce demodulation signals from for each frequency. A processor (40) receives and processes accoupled logic level detection signals generated by a limiter amplifier (76) for each discrete sensor system at each of the fixed frequencies to determine the presence of a vehicle (22) in the monitored zone (24, 26). The fixed frequency and the predetermined phase delay are chosen to produce a null received signal resulting from reflections of the emitted beam from uniformly distributed atmospheric backscatter within the optical overlap area (A).

Claims

1. An electro-optical detection system for detecting objects within the boundaries of a monitored zone, comprising an emitter and photodetector pair, wherein the emitter emits a beam of pulses of light energy into the monitored zone, and the photodetector detects light energy including light energy from the beam that is reflected from an object within the monitored zone and generates light detection signals, and a controller for operating the emitter and photodetector pair and for generating an object detection signal when it determines that an object is in the monitored zone, characterized by

the emitter emitting a beam of pulses of light energy at multiple frequencies into the monitored zone, and

the controller generating a phase-delayed reference signal at each frequency, mixing the light detection signals and the reference signals to produce a phase difference signal for each frequency that varies in polarity sinusoidally with the distance to the object, and comparing the polarity of these phase difference signals to determine the presence of an object in the monitored zone.

2. The detection system of claim 1, further characterized by including a plurality of emitter and photodetector pairs, each monitoring a unique portion of the monitored zone.

3. The detection system of claim 2, further characterized by the controller being operable to adjust the phase delay of the reference signals for each to vary the effective boundaries of the monitored zone.

4. The detection system of claim 3, further characterized by the controller including a device for phase shifting the reference signal to equal the expected phase shift of an emitted signal reflected from an object at a boundary of the monitored zone, thereby enabling the comparator to determine whether received light energy is reflected from an object within or outside said boundary.

5. The detection system of claim 1, further characterized by the emitters and photodetectors being mounted on an outside rearview mirror of the vehicle.

6. Collision avoidance apparatus mounted on a host vehicle to detect the presence of an adjacent vehicle within a monitored zone, comprising a sensor module which includes at least one discrete sensor system for monitoring a unique portion of the monitored zone, comprising an emitter for emitting a fixed frequency modulated beam of light energy with a predetermined burst length into the unique portion of the monitored zone, and a receiver which has a field of view substantially aligned with the emitted beam and for sensing light energy and generating a received to signal, characterized by

a frequency generator for producing two or more predetermined different fixed frequencies for use by the emitter to emit beams at each of said frequencies,

a phase shifter for producing a phase shifted reference signal with a different predetermined phase delay relationship to each of said fixed frequencies,

a mixer for producing demodulation signals from each received signal and each phase shifted reference signal for each frequency,

a limiter amplifier for producing highly amplified ac coupled digital logic level detection signals from said demodulation signals, and

a processor for receiving and processing said logic level detection signals generated by each discrete sensor system at each of the fixed frequencies to determine the presence of a vehicle in the monitored zone.

7. The collision avoidance apparatus of claim 6, further characterized by the apparatus comprising six discrete sensor systems.

8. The collision avoidance apparatus of claim 6, further characterized by the frequency generating means producing three fixed frequencies for use by each emitter.

9. The collision avoidance apparatus of claim 8, further characterized by the frequencies being approximately 15 MHz, 2.5 MHz and 1.875 MHz.

10. Collision avoidance apparatus mounted on a host vehicle to detect the presence of an adjacent vehicle within a monitored zone, comprising a sensor module which includes at least one discrete sensor system for monitoring a unique portion of the monitored zone, comprising an emitter for emitting a fixed frequency modulated beam of light energy with a predetermined burst length into the unique portion of the monitored zone, and a receiver which has a field of view substantially aligned with the emitted beam and for sensing light energy and generating a received signal, characterized by

a frequency generator for producing at least one fixed frequency,

a phase shifter for producing a phase shifted reference signal with a predetermined phase delay relationship to said fixed frequency,

a mixer for producing demodulation signals from each received signal and each phase shifted reference signal,

wherein the radiation pattern of the emitted beam and the field of view of the receiver have a fixed optical overlap area, and

the fixed frequency and the predetermined phase delay are chosen to substantially produce a null received signal resulting from reflections of the emitted beam from uniformly distributed atmospheric backscatter within the optical overlap area.