Lidar system with a polygon mirror and a noise-reducing feature

• US 10,578,720 B2
• Filed: 05/08/2018
• Issued: 03/03/2020
• Est. Priority Date: 04/05/2018
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Hughes, John G., Hughes, Sean P.
• Primary Examiner(s): Ratcliffe, Luke D
• Application Number:
  US15/974,319
• Publication Number:
  US 20190310351A1
• Time in Patent Office: 665 Days
• CPC Class Codes: G01S 13/931 of land vehicles
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/4818 using optical fibres
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/4863 Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G02B 26/0816 by means of one or more reflecting elements
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G02B 26/12 using multifaceted mirrors
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors

Abstract

A lidar system includes a light source configured to produce a beam of light, a scanner configured to scan a field of regard of the lidar system, and a receiver configured to detect light from the beam of light scattered by a remote target. The scanner includes a polygon mirror having a block with a first wall, a second wall, and several reflective surfaces angularly offset from one another along a periphery of the block, the polygon mirror configured to rotate about a scan-mirror rotation axis to scan the beam of light across the field of regard. The scanner further includes a bracket adjacent to the polygon mirror, where at least one of the polygon mirror or the bracket includes a noise-reducing feature configured to reduce acoustic noise produced when pressure waves generated by the polygon mirror during rotation are incident on one or more components of the scanner.

Claims

1. A lidar system comprising:

a light source configured to produce a beam of light;

a scanner configured to scan a field of regard of the lidar system, the scanner including;

a polygon mirror having a block with a first wall, a second wall, and a plurality of reflective surfaces angularly offset from one another along a periphery of the block, the polygon mirror configured to rotate about a polygon-mirror rotation axis to scan the beam of light across the field of regard, and

a bracket adjacent to the polygon mirror, wherein the bracket includes;

a cavity that partially encloses the polygon mirror between a first edge of the cavity and a second edge of the cavity, wherein the plurality of reflective surfaces move away from the first edge and toward the second edge when the polygon mirror rotates about the polygon-mirror rotation axis; and

a noise-reducing feature configured to reduce acoustic noise produced when pressure waves generated by the polygon mirror during rotation are incident on one or more components of the scanner, wherein the noise-reducing feature is disposed at the second edge of the cavity so as to spread out the pressure waves in time; and

a receiver configured to detect light from the beam of light scattered by a remote target.

2. The lidar system of claim 1, wherein the polygon mirror further includes a plurality of chamfered or rounded corners in the block of the polygon mirror, each of the chamfered or rounded corners being bounded by a pair of adjacent reflective surfaces.

3. The lidar system of claim 1, wherein the noise-reducing feature includes a tapered feature oriented toward the pressure waves.

4. The lidar system of claim 3, wherein the noise-reducing feature includes a plurality of tapered features oriented toward the pressure waves.

5. The lidar system of claim 3, wherein the tapered feature is shaped as a triangle with substantially straight edges.

6. The lidar system of claim 3, wherein the tapered feature is shaped as a pseudo-triangle with convex or concave edges.

7. The lidar system of claim 3, wherein the noise-reducing feature includes another tapered feature disposed on the first edge and oriented in an opposite direction relative to the tapered feature disposed on the second edge.

8. The lidar system of claim 1, wherein a first line from the first edge to the polygon-mirror rotation axis and a second line from the second edge to the polygon-mirror rotation axis form an angle selected so that the pressure waves produced by the polygon mirror during rotation do not add together in phase.

9. The lidar system of claim 8, wherein the angle is selected according to a formula Ω

=(360/N)*(m+⅓

), wherein Ω

is the angle, N is a number of the plurality of reflective surfaces of the polygon mirror, and m is an integer.

10. The lidar system of claim 8, wherein the polygon mirror is a hexagonal mirror, and wherein the angle formed by the first line and the second line is approximately 200 degrees.

11. The lidar system of claim 1, wherein the bracket partially surrounds the polygon mirror.

12. A method for manufacturing a scanner for use in a lidar system, the method comprising:

forming a polygon mirror having a block with a first wall, a second wall, and a plurality of reflective surfaces angularly offset from one another along a periphery of the block;

forming a bracket including a cavity to partially enclose the polygon mirror, the cavity including a first edge and a second edge;

mounting the polygon mirror on a polygon mirror axle, so that the bracket is adjacent to the polygon mirror, to configure the polygon mirror to rotate about the polygon mirror axle and scan a beam of light from a light source across a field of regard of the scanner;

configuring the plurality of reflective surfaces to move away from the first edge and toward the second edge when the polygon mirror rotates about the polygon mirror axle;

forming a noise-reducing feature on the bracket to reduce acoustic noise produced when pressure waves generated by the polygon mirror during rotation are incident on one or more components of the scanner, wherein forming the noise-reducing feature includes placing the noise-reducing feature at the second edge of the cavity so as to spread out the pressure waves in time; and

coupling a receiver to the scanner to detect light from the beam of light scattered by a remote target.

13. The method of claim 12, further comprising forming a plurality of chamfered or rounded corners in the block of the polygon mirror, each of the chamfers being bounded by a pair of adjacent reflective surfaces.

14. The method of claim 12, wherein forming the noise-reducing feature further includes forming, at the second edge of the cavity, a tapered feature oriented toward the pressure waves.

15. The method of claim 14, further comprising forming a plurality of tapered features oriented toward the pressure waves.

16. The method of claim 14, wherein forming the noise-reducing feature further includes shaping the tapered feature as a triangle with substantially straight edges.

17. The method of claim 14, wherein forming the noise-reducing feature further includes shaping the tapered feature as a pseudo-triangle with convex or concave edges.

18. The method of claim 14, further comprising:

forming another tapered feature on the first edge, and

orienting the tapered feature on the first edge in an opposite direction relative to the tapered feature on the second edge.

19. The method of claim 12, wherein a first line from the first edge to the polygon-mirror axle and a second line from the second edge to the polygon-mirror axle form an angle;

the method further comprising;

selecting the angle so that the pressure waves produced by the polygon mirror during rotation do not add together in phase.

20. The method of claim 19, further comprising selecting the angle according to a formula Ω

=(360/N)*(m+⅓

), wherein Ω

is the angle, N is a number of the plurality of reflective surfaces of the polygon mirror, and m is an integer.

21. The method of claim 19, wherein the polygon mirror is a hexagonal mirror, and wherein the method includes selecting the angle formed by the first line and the second line to be approximately 200 degrees.