Adaptive pulse rate in a lidar system

• US 10,209,359 B2
• Filed: 12/18/2017
• Issued: 02/19/2019
• Est. Priority Date: 03/28/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Russell, Austin K., Weed, Matthew D., McGregor, Liam J., Martin, Lane A., Eichenholz, Jason M.
• Primary Examiner(s): Bolda, Eric L
• Application Number:
  US15/845,552
• Publication Number:
  US 20180284278A1
• Time in Patent Office: 428 Days
• 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 17/26 wherein the transmitted pulses use a frequency-modulated or phase-modulated carrier wave, e.g. for pulse compression of received signals
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4816 of receivers alone
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/483 Details of pulse systems
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

To increase the effective pulse rate of a light source in a lidar system, a controller provides control signals to the light source to transmit a light pulse once the previous light pulse has been received. The controller may communicate with a receiver in the lidar system that detects received light signals. In response to detecting a received light signal, the receiver may provide an indication of the received light signal to the controller which may in turn provide a control signal to the light source to transmit the next light pulse. The receiver may also provide characteristics of the received light signal to the controller, such as the peak power for the received light signal, the average power for the received light signal, the pulse duration of the received light signal, etc. Then the controller may analyze the characteristics to determine whether to transmit another light pulse.

Claims

1. A method of controlling pulse rate in lidar systems, the method comprising:

emitting light pulses by a light source in a lidar system;

scanning, by a scanner in the lidar system, a field of regard of the lidar system, including directing the light pulses toward different points within the field of regard;

detecting, by a receiver of the lidar system, light from some of the light pulses scattered by one or more remote targets to generate respective pixels; and

varying a pulse rate at which the light source emits the light pulses based on when the receiver detects scattered light from the light pulses, including;

in a first instance, emitting a new light pulse in response to detecting scattered light from a first light pulse, after a time interval T1 since the first light pulse was emitted,

in a second instance, emitting a new light pulse after a time interval T2 since a second light pulse was emitted, including not receiving scattered light from the second light pulse within the time interval T2, where the time interval T1 is shorter than the time interval T2.

2. The method of claim 1, wherein the time interval T2 corresponds to a time it takes a light pulse to travel a maximum distance D and return back to the lidar system.

3. The method of claim 1, further comprising:

varying the pulse rate in view of a scan direction in which the scanner is directing the light pulses.

4. The method of claim 3, wherein varying the pulse rate includes:

adjusting the pulse rate upward based on a scan velocity of the scanner.

5. The method of claim 3, wherein varying the pulse rate includes:

adjusting the pulse rate downward based on a scan velocity of the scanner.

6. The method of claim 3, wherein varying the pulse rate includes:

adjusting the pulse rate upward for a particular region of the field of regard.

7. The method of claim 3, wherein varying the pulse rate includes:

adjusting the pulse rate downward for a particular region of the field of regard.

8. The method of claim 3, wherein the time interval T2 corresponds to a time it takes a light pulse to travel a maximum distance D and return back to the lidar system, and wherein varying the pulse rate in view of the scan direction includes adjusting a duration of the time interval T2 in view of the scan direction.

9. The method of claim 1, wherein detecting the scattered light from the first light pulse includes comparing a received light signal to a power or energy threshold value to determine whether the received light signal corresponds to the first light pulse.

10. The method of claim 9, wherein detecting the scattered light from the first light pulse includes comparing a pulse duration to a duration threshold value to determine whether the received light signal corresponds to the first light pulse.

11. The method of claim 1, wherein detecting the scattered light from the first light pulse includes:

determining an amount of power in a received light signal,

determining a pulse duration of the received light signal,

combining the determined amount of power and the determined pulse duration to generate a combined metric of the received light signal, and

comparing the combined metric to a threshold value to determine whether the received light signal corresponds to the first light pulse.

12. The method of claim 1, further comprising:

providing a signal indicative of pulse detection from the receiver to a controller, and

providing a signal from the controller to the light source to trigger emission of a new light pulse.

13. A lidar system comprising:

a light source configured to emit light pulses;

a scanner configured to scan a field of regard of the lidar system including direct the light pulses toward different points within the field of regard;

a receiver configured to detect light from some of the light pulses scattered by one or more remote targets to generate respective pixels; and

a controller configured to vary a pulse rate at which the light pulses are emitted by the light source based on when the receiver detects scattered light from the light pulses, including;

in a first instance, cause the light source to emit a new light pulse in response to detecting scattered light from a first light pulse, after a time interval T1 since the first light pulse was emitted, and

in a second instance, cause the light source to emit a new light pulse after a time interval T2 since a second light pulse was emitted, including not detecting scattered light from the second light pulse within the time interval T2, wherein the time interval T1 is shorter than the time interval T2.

14. The lidar system of claim 13, wherein to cause the light source to emit a new light pulse, the controller is configured to provide a control signal to the light source indicating when to emit the new light pulse.

15. The lidar system of claim 13, wherein to detect the scattered light from the first light pulse the controller is configured to:

receive an indication of a received light signal from the receiver including one or more characteristics of the received light signal; and

detect the scattered light from the first light pulse by analyzing the one or more characteristics of the received light signal to determine whether the received light signal corresponds to the first light pulse.

16. The lidar system of claim 15, wherein to detect the scattered light from the first light pulse by analyzing the one or more characteristics of the received light signal, the controller is configured to compare an amount of power in the received light signal to a power threshold to determine whether the received light signal corresponds to the first light pulse.

17. The lidar system of claim 13, wherein the light source includes a fiber laser or a laser diode.

18. A method of controlling a pulse rate in a lidar system, the method comprising:

scanning, by a scanner in the lidar system, a field of view of a light source across a field of regard of the lidar system;

emitting, by a light source in the lidar system, a first light pulse;

detecting, by a receiver in the lidar system, light from the first light pulse scattered by a remote target; and

emitting, by the light source, a second light pulse in response to detecting the scattered light from the first light pulse after a time interval T1 since the first light pulse was emitted.

19. The method of claim 18, further comprising:

emitting, by the light source, a third light pulse;

waiting for a time interval T2 to expire without detecting scattered light from the third light pulse; and

emitting, by the light source, a fourth light pulse in response to not detecting the scattered light from the third light pulse during the time interval T2, wherein the time interval T1 is shorter than the time interval T2.

20. The method of claim 19, wherein the time interval T2 corresponds to a time that the lidar system is configured to wait without receiving scattered light from an emitted light pulse before emitting a subsequent light pulse.