Pulsed light optical rangefinder

• US 9,417,326 B2
• Filed: 06/18/2010
• Issued: 08/16/2016
• Est. Priority Date: 06/22/2009
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Motor Europe SA (Toyota Motor Corporation)
• Inventors: Niclass, Cristiano, Charbon, Edoardo, Soga, Mineki, Yanagihara, Hiromichi
• Primary Examiner(s): RATCLIFFE, LUKE D
• Application Number:
  US13/376,336
• Publication Number:
  US 20120075615A1
• Time in Patent Office: 2,251 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22, 356/28, 356/28.5
• US Class Current: 1/1
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/4863 Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/489 Gain of receiver varied automatically during pulse-recurrence period
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

An optical rangefinder based on time-of-flight measurement, radiates pulsed light toward an object (70), and receives reflected light from the object, the receiver operating in a photon counting mode, so as to generate a pulse for a detected photon. There is a variable probability of a photon detection on the receiver, and a controller (370, 380, 390; 365, 470, 475, 380, 390; 570, 580, 590, 390) controls the photon detection probability of the receiver, based on a light level. By controlling the detection probability according to a light level, the receiver can have an increased dynamic range, and without the expense of using optical components. This can apply even while detecting very weak signals since the receiver can still be in a photon counting mode while the detection probability is controlled. The light level can be indicated by an output of the receiver itself, or by another detector external to the receiver.

Claims

1. An optical rangefinder based on time-of-flight measurement, comprising

an illumination device radiating pulsed light toward an object, and having a light receiver arranged to receive light from the object, wherein the light receiver is configured to operate in a photon counting mode, and to generate a pulse for a detected photon and requiring a variable probability of a photon detection on the light receiver;

and

a controller, wherein the controller is configured to control the photon detection probability of the receiver based on a light level output from the light receiver contemporaneously with real-time range-finding measurements.

2. The optical rangefinder of claim 1, the controller comprising an input from an output of the receiver to indicate the light level, as well as optionally any kind of noise level.

3. The optical rangefinder of claim 1, the controller comprising a device configured to count the pulses over a period of time and compare the count with a threshold, the controller being further configured to use the output of the comparison to increase or reduce the photon detection probability.

4. The optical rangefinder of claim 1, the receiver comprising an optical receiving component having a means for changing the photon detection probability, and wherein the controller is arranged to control the photon detection probability by changing the photon detection probability.

5. The optical rangefinder of claim 4, the optical receiving component comprising an avalanche photo diode, and wherein the controller is arranged to control the photon detection probability by changing a reverse bias voltage of the avalanche photo diode.

6. The optical rangefinder of claim 1, further comprising a memory configured to store a record of each of the pulses during a predefined duration, an adder configured to total the pulses recorded in the memory, and a comparator configured to compare an output of the counter with a threshold.

7. The optical rangefinder of claim 6 wherein the memory is a shift register configured to store a most recent record of each of the pulses during a predefined duration.

8. The optical rangefinder of claim 1, and having a differential counter configured to increment a count number when the pulse from the receiver is input, and to decrement a count number at intervals of a predefined duration.

9. The optical rangefinder of claim 1, comprising a histogram circuit configured to distinguish wanted signals from noise according to a histogram, and to determine a time of flight of the wanted signals.

10. A method of using a receiver adapted to receive pulsed light from an object generated by radiating pulsed light towards the object, the method comprising:

operating the receiver in a photon counting mode, so as to generate a pulse for a detected received photon of the received light, there being a variable probability of a photon detection on the receiver; and

controlling the photon detection probability of the receiver, based on a light level from the receiver contemporaneously with real-time range-finding measurements.

11. The method of claim 10 further comprising determining a time of flight of the light received.

12. The method of claim 10, further comprising counting the pulses over a period of time and comparing the count with a threshold;

and

increasing or reducing the photon detection probability in response to the output of the comparison.

13. The method of claim 10, further comprising storing a most recent record of each of the pulses during a predefined duration.