Visible light detection and ranging apparatus and method

• US 5,298,905 A
• Filed: 03/01/1993
• Issued: 03/29/1994
• Est. Priority Date: 06/12/1992
• Status: Expired due to Term

• Current Assignee: General Dynamics C4 Systems Incorporated (General Dynamics Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Dahl, Randy L.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/024,720
• Time in Patent Office: 393 Days
• Field of Search: 342/54, 342/205, 342/118, 342/127, 342/195, 356/5
• US Class Current: 342/54
• CPC Class Codes: G01S 7/34 Gain of receiver varied automatically during pulse-recurrence period, e.g. anti-clutter gain control
• CPC Class Codes: G01S 7/4021 of receivers
• CPC Class Codes: G01S 7/4873 by deriving and controlling a threshold value
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G01S 7/52004 Means for monitoring or calibrating short-range imaging G01S7/5205

Abstract

A lidar apparatus for detecting an object. The lidar apparatus includes a laser providing a visible light output signal over a first field of view and a photodiode having a second field of view. At least some of the first and second fields of view overlap. The photodiode provides electrical signals in response to received optical signals. A controller is coupled to the laser and to the photodiode. The controller for provides electrical signals to the laser, causing emission of visible light output signals. A time varying threshold generator is coupled to the controller. The time varying threshold generator provides a time varying threshold signal in response to signals from the controller. A threshold detector is coupled to the time varying threshold generator and to the photodiode. The threshold detector compares the time varying threshold signal to the electrical signals to provide signals indicating presence or absence of the object.

Claims

1. A method for ranging, the method comprising steps of:

(a) initiating a measurement cycle;

(b) receiving an optical signal;

(c) converting the optical signal to an electrical signal;

(d) providing specific successive values of desired sensitivity time control threshold information;

(e) comparing the specific successive values of desired sensitivity time control threshold information to the electrical signal to provide a comparison signal; and

(f) calculating a range from a delay between said step (a) and the comparison signal from said step (e).

2. A method as claimed in claim 1, wherein said step (d) further comprises substeps of:

(d1) extracting specific values of the desired sensitivity time control threshold information from a digital memory at successive time intervals to provide specific successive values of the desired sensitivity time control threshold information; and

(d2) converting the desired sensitivity time control threshold information with a digital-to-analog converter to provide an analog calibration signal; and

wherein said step (e) further comprises a substep of;

(e1) comparing the analog calibration signal to the electrical signal to provide the comparison signal.

3. A method as claimed in claim 1, wherein said step (d) further includes substeps of:

(d1) loading an addressable memory with digital calibration data from an information store in response to signals from a digital control and timing generator; and

(d2) extracting the specific successive values of the desired sensitivity time control threshold information from the addressable memory at successive time intervals to provide the specific successive values of the desired sensitivity time control threshold information.

4. A method as claimed in claim 1, wherein said step (a) comprises a substep of:

(a1) transmitting a first optical signal; and

wherein said step (b) includes a substep of;

(b1) receiving a second optical signal, said second optical signal formed by reflection of at least part of said first optical signal by an object; and

wherein there is further included a step of;

(f) calculating a range to the object from a time delay measured between said substeps (a1) and (b1).

5. A method as claimed in claim 4, wherein said step (a1) further comprises a step of transmitting a first optical signal comprising visible light.

6. A method as claimed in claim 1, wherein said step (a) includes a step (a1) of transmitting a first optical signal from a solid state laser diode.

7. A method as claimed in claim 1, wherein said step (a) includes a substep (a1) of transmitting a first optical signal having a wavelength in the range from 700 to 450 nanometers from a solid state laser diode.

8. A lidar apparatus for detecting an object, said lidar apparatus comprising:

a laser providing a visible light output signal over a first field of view;

a photodiode having a second field of view, wherein at least some of said first and second fields of view overlap, said photodiode providing electrical signals in response to received optical signals;

control means coupled to said laser and to said photodiode, said control means for providing first electrical signals to said laser to cause said laser to emit said visible light output signals;

a time varying threshold generator coupled to said control means, said time varying threshold generator for providing a time varying threshold signal in response to signals from said control means; and

a threshold detector coupled to said time varying threshold generator and to said photodiode, said threshold detector for comparing said time varying threshold signal to said electrical signals to provide signals indicating presence or absence of said object.

9. An apparatus as claimed in claim 8, wherein said laser comprises a solid state laser diode.

10. An apparatus as claimed in claim 8, wherein said laser comprises a solid state laser diode providing light having a wavelength in the range from 450 to 700 nanometers.

21. An apparatus as claimed in claim 8, further comprising a sampler and analog to digital converter coupled to said photodiode, said sampler and analog to digital converter coupled to said control means and operating in response to timing signals from said control means, said sampler and analog to digital converter for converting said electrical signals to digital signals, wherein said time varying threshold generator provides a particular time varying threshold signal from a group of time varying threshold signals in response to said digital signals.

11. A method for ranging an object, said method comprising steps of:

(a) a transmitting a first signal comprising visible light from a ranging apparatus to said object;

(b) receiving a second signal comprising visible light to said object;

(c) converting the second signal to a first electrical signal;

(d) extracting specific values of desired sensitivity time control threshold information from an information store at successive time intervals to provide specific successive values of the desired sensitivity time control threshold information;

(e) converting the specific successive values to analog values to provide an analog calibration signal;

(f) comparing the analog calibration signal to the first electrical signal to provide a comparison signal; and

(g) using the comparison signal to determine a range to said object.

12. A method as claimed in claim 11, wherein said step (g) further comprises a step (h) of determining a delay between the first signal and the second signal.

13. A method as claimed in claim 12, wherein said step (h) further comprises a step (i) of measuring a range separating the ranging apparatus from a target by the delay from said step (g).

14. A method as claimed in claim 11, wherein said step (a) includes a step of transmitting the first signal from a laser diode.

15. A method as claimed in claim 11, wherein said step (a) includes a step of transmitting the first signal from a laser diode, wherein the first signal comprises coherent light having a wavelength in the range from 450 to 700 nanometers.

16. An ranging apparatus, comprising:

a signal input for receiving input signals, said input signals comprising visible light, said signal input providing electrical signals in response to said input signals;

a pre-look circuit coupled to said signal input, said pre-look circuit for providing a pre-look signal, said pre-look signal characterizing an ambient signal condition;

a memory coupled to said pre-look circuit, said memory for storing sensitivity time control data and for providing a first analog sensitivity time control signal in response to said pre-look signal; and

a first comparator coupled to said signal input and to said memory, said first comparator having an input for receiving said first analog sensitivity time control signal, said first comparator for comparing said electrical signal to said first analog sensitivity time control signal to provide a first detection signal.

17. An apparatus as claimed in claim 16, wherein said pre-look circuit comprises sampling and analog-to-digital conversion circuitry coupled to said signal input, said sampling and analog-to-digital conversion circuitry for forming a digital pre-look signal from said electrical signal.

18. An apparatus as claimed in claim 16, wherein said memory comprises:

a digital memory; and

digital-to-analog conversion circuitry coupled to said digital memory, said digital-to-analog conversion circuitry for converting said specific sensitivity time control data to said first analog sensitivity time control signal.

19. An apparatus as claimed in claim 16, further comprising:

a controller, said controller coupled to said pre-look circuit, to said memory and to said first comparator, said controller for synchronizing said pre-look circuit and said memory, said controller initiating measurement cycles; and

a laser, said laser coupled to said controller and providing coherent visible light signals in response to signals from said controller, wherein said input signals comprise reflected light from said coherent visible light signals, wherein a delay between said coherent visible light signals and said input signals comprises a measure of distance traveled by said coherent visible light signals from said laser to said signal input.

20. An apparatus as claimed in claim 19, wherein said laser comprises a solid state diode laser.