Controlling pulse timing to compensate for motor dynamics

• US 10,088,559 B1
• Filed: 01/22/2018
• Issued: 10/02/2018
• Est. Priority Date: 03/29/2017
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Weed, Matthew D., Campbell, Scott R., Martin, Lane A., Eichenholz, Jason M., Russell, Austin K., Cleye, Rodger W., Stauffer, Melvin L.
• Primary Examiner(s): Bolda, Eric L
• Application Number:
  US15/876,669
• Publication Number:
  US 20180284225A1
• Time in Patent Office: 253 Days
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• 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 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/484 Transmitters

Abstract

To compensate for motor dynamics in a scanner in a lidar system, a light source transmits light pulses at a variable pulse rate in accordance with a scan speed of the scanner. More specifically, the pulse rate may be directly related to the scan speed so that the light source transmits light pulses uniformly across a field of regard. A controller may determine the scan speed and provide a control signal to the light source adjusting the pulse rate accordingly.

Claims

1. A method of controlling pulse rate in lidar systems in which a scanner scans in a forward-scanning direction and a reverse-scanning direction, to compensate for motor dynamics of the scanner, the method comprising:

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

scanning, by a scanner in the lidar system, a field of view of the light source across a field of regard of the lidar system in a forward-scanning direction and a reverse-scanning direction, including;

directing the light pulses toward different points within the field of regard, and

decreasing a scan speed of the scanner as the scanner changes direction between the forward-scanning direction and the reverse-scanning direction at respective turnaround points;

adjusting a pulse rate at which the lidar system generates the light pulses in accordance with the scan speed, including transmitting the light pulses at a first pulse rate for a first scan speed and at a second pulse rate for a second scan speed; and

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.

2. The method of claim 1, wherein adjusting the pulse rate includes decreasing the pulse rate when decreasing the scan speed, so that the scanner distributes the light pulses uniformly across the field of regard.

3. The method of claim 1, wherein adjusting the pulse rate includes increasing the pulse rate when decreasing the scan speed, so that the pixel density is higher at a turnaround point.

4. The method of claim 1, wherein scanning across the field of regard includes using two or more scanners to concurrently illuminate two or more different portions of the field of regard, with each of the two or more scanners having an inner turnaround point and an outer turnaround point.

5. The method of claim 4, wherein adjusting the pulse rate includes increasing the pulse rate as the scanner approaches the inner turnaround point and decreasing the pulse rate as the scanner approaches the outer turnaround point.

6. The method of claim 4, wherein adjusting the pulse rate includes decreasing the pulse rate as the scanner approaches the inner turnaround point and increasing the pulse rate as the scanner approaches the outer turnaround point.

7. The method of claim 4, wherein the emitted light pulses are split to produce two or more output beams which are scanned by the respective two or more scanners.

8. The method of claim 4, wherein using two or more scanners includes scanning simultaneously in opposite directions.

9. The method of claim 4, wherein using two or more scanners includes scanning simultaneously in a same direction.

10. The method of claim 1, further comprising:

adjusting an amount of average power of the emitted light pulses or an amount of energy per light pulse provided by the light source based on the pulse rate.

11. The method of claim 10, wherein the amount energy per light pulse is higher for slower pulse rates.

12. The method of claim 1, further comprising:

identifying, using a controller, the scan speed of the scanner, and

providing a control signal to the light source to adjust the pulse rate according to the scan speed.

13. A lidar system comprising:

a light source configured to emit light pulses;

a scanner configured to scan a field of view of the light source across a field of regard of the lidar system in a forward-scanning direction and a reverse-scanning direction, including;

direct the light pulses toward different points within the field of regard; and

decrease a scan speed as the scanner changes direction between the forward-scanning direction and the reverse-scanning direction at respective turnaround points;

a controller configured to adjust a pulse rate at which the light pulses are emitted by the light source, including;

when the scanner scan at a first scan speed, cause the light source to emit the light pulses at a first pulse rate, and

when the scanner scans at a second scan speed, cause the light source to emit the light pulses at a second pulse rate; and

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

14. The lidar system of claim 13, wherein to adjust the pulse rate the controller is configured to decrease the pulse rate when the scan speed decreases, so that the scanner distributes the light pulses uniformly across the field of regard.

15. The lidar system of claim 13, wherein to adjust the pulse rate the controller is configured to increase the pulse rate when the scan speed decreases, so that the pixel density is higher in at a turnaround point.

16. The lidar system of claim 13, wherein the controller is further configured to receive an indication of the scan speed of the scanner and to provide a control signal to the light source to adjust the pulse rate in accordance with the scan speed.

17. The lidar system of claim 13, wherein the scanner includes two or more scanners to concurrently illuminate two or more different portions of the field of regard, with each of the two or more scanners having an inner turnaround point and an outer turnaround point.

18. The lidar system of claim 17, wherein for each of the two or more scanners, to adjust the pulse rate the controller is configured to increase the pulse rate as the scanner approaches the inner turnaround point and decrease the pulse rate as the scanner approaches the outer turnaround point.

19. The lidar system of claim 17, wherein for each of the two or more scanners, to adjust the pulse rate the controller is configured to decrease the pulse rate as the scanner approaches the inner turnaround point and increase the pulse rate as the scanner approaches the outer turnaround point.

20. The lidar system of claim 17, wherein the two or more scanners scan simultaneously in opposite directions.

21. The lidar system of claim 17, wherein the two or more scanners scan simultaneously in a same direction.

22. The lidar system of claim 13, wherein the controller is further configured to adjust an amount of average power of the emitted light pulses or an amount of energy per light pulse provided by the light source based on the pulse rate.