Multi-beam lidar system with polygon mirror

• US 10,324,170 B1
• Filed: 05/08/2018
• Issued: 06/18/2019
• Est. Priority Date: 04/05/2018
• Status: Active Grant

• Current Assignee: Luminar Technologies, Inc.
• Original Assignee: Luminar Technologies, Inc.
• Inventors: Engberg, Jr., John P., Engberg, Christopher A., Hughes, John G., Hughes, Sean P.
• Primary Examiner(s): Abraham, Samantha K
• Application Number:
  US15/974,153
• Time in Patent Office: 406 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 first and second beams of light, receivers to configured to detect light from the first and second beams of light and scattered by one or more remote targets, and a scanner including a first scan mirror configured to pivot along a first-mirror pivot axis to scan the first beam of light along a first direction, a second scan mirror configured to pivot along a second-mirror pivot axis to scan the second beam of light along the first direction, and a polygon with multiple reflective surfaces configured to rotate about a polygon-mirror rotation axis to scan the first and second beams of light along a second direction.

Claims

1. A lidar system comprising:

a light source configured to produce a first beam of light and a second beam of light;

a scanner configured to scan a field of regard of the lidar system using the first beam of light and the second beam of light, the scanner including;

a first scan mirror configured to;

receive the first beam of light from the light source and reflect the first beam of light toward a polygon mirror, and

pivot along a first scan-mirror pivot axis to scan the first beam of light along a first direction;

a second scan mirror configured to;

receive the second beam of light from the light source and reflect the second beam of light toward the polygon mirror; and

pivot along a second scan-mirror pivot axis to scan the second beam of light along the first direction, wherein the scanner controls at least one of a scanning speed or range of pivoting of the second scan-mirror independently of the first scan-mirror; and

the polygon mirror that comprises a plurality of reflective surfaces angularly offset from one another along a periphery of the polygon mirror, the polygon mirror configured to;

receive the first beam of light from the first scan mirror and reflect the first beam of light toward the field of regard,

receive the second beam of light from the second scan mirror and reflect the second beam of light toward the field of regard, and

rotate about a polygon-mirror rotation axis to scan the first and second beams of light along a second direction substantially orthogonal to the first direction;

a first receiver configured to detect scattered light from the first beam of light; and

a second receiver configured to detect scattered light from the second beam of light.

2. The lidar system of claim 1, wherein, for each reflection of the first and second beams of light from the polygon mirror, the first beam of light and the second beam of light are reflected from different reflective surfaces of the polygon mirror.

3. The lidar system of claim 1, wherein the polygon mirror scans the first and second beams of light synchronously, wherein a scanning speed of the first beam of light along the second direction is equal to a scanning speed of the second beam of light along the second direction.

4. The lidar system of claim 1, wherein:

the first scan mirror scans the first beam at a first scanning speed,

the second scan mirror scans the second beam at a second scanning speed,

the first scanning speed being different from the second scanning speed.

5. The lidar system of claim 1, wherein:

the first and second beams of light are scanned across respective first and second scan patterns contained within the field of regard of the lidar system, each scan pattern comprising a plurality of scan lines;

each reflection of the first beam of light from each of the reflective surfaces of the polygon mirror produces one scan line of the first scan pattern; and

each reflection of the second beam of light from each of the reflective surfaces of the polygon mirror produces one scan line of the second scan pattern.

6. The lidar system of claim 1, wherein:

the first scan-mirror pivot axis is orthogonal to the polygon-mirror rotation axis; and

the second scan-mirror pivot axis is orthogonal to the polygon-mirror rotation axis.

7. The lidar system of claim 1, wherein the scanner further comprises a motor configured to impart rotation to the polygon mirror, wherein the motor is at least partially contained within the polygon mirror.

8. The lidar system of claim 1, wherein the scanner further comprises a motor configured to impart rotation to the polygon mirror, wherein the motor is attached to a top or bottom surface of the polygon mirror with epoxy or mechanical fasteners.

9. The lidar system of claim 1, wherein the polygon mirror has a square shape with four reflective surfaces, a hexagonal shape with six reflective surfaces, or an octagonal shape with eight reflective surfaces.

10. The lidar system of claim 1, wherein the first and second scan mirrors are each driven by a galvanometer scanner.

11. The lidar system of claim 1, wherein the first and second scan mirrors are each part of a microelectromechanical systems (MEMS) device.

12. The lidar system of claim 1, wherein:

the detected scattered light from the first beam of light is first reflected from the polygon mirror toward the first scan mirror and then reflected from the first scan mirror toward the first receiver; and

the detected scattered light from the second beam of light is first reflected from the polygon mirror toward the second scan mirror and then reflected from the second scan mirror toward the second receiver.

13. The lidar system of claim 1, wherein:

the first beam of light and the detected scattered light from the first beam of light travel in approximately opposite directions and are parallel to within 1°

; and

the second beam of light and the detected scattered light from the second beam of light travel in approximately opposite directions and are parallel to within 1°

.

14. The lidar system of claim 1, wherein the light source comprises a laser that produces pulses of light that are split to produce the first beam of light and the second beam of light.

15. The lidar system of claim 1, wherein the light source comprises a first laser diode configured to produce the first beam of light and a second laser diode configured to produce the second beam of light.

16. The lidar system of claim 1, wherein the first and second beams of light each comprise pulses of light having:

a wavelength between 900 nanometers and 1700 nanometers;

a pulse energy of less than 10 microjoules;

a pulse repetition frequency of less than 10 MHz;

a pulse duration of 0.1 nanoseconds to 100 nanoseconds; and

a duty cycle of less than 5%.

17. The lidar system of claim 1, further comprising:

a first stationary mirror configured to receive the first beam of light from the light source and reflect the first beam of light toward the first scan mirror; and

a second stationary mirror configured to receive the second beam of light from the light source and reflect the second beam of light toward the second scan mirror.

18. The lidar system of claim 1, wherein the first and second receivers each comprise an avalanche photodiode (APD).

19. The lidar system of claim 1, further comprising a housing enclosing the light source, the scanner, the first receiver, and the second receiver, wherein the housing comprises one or more windows configured to transmit light at one or more wavelengths of the first beam of light and the second beam of light.

20. The lidar system of claim 1, further comprising a bracket adjacent to which the polygon mirror is mounted, the bracket including:

a cavity that partially encloses the polygon mirror between a first edge of the cavity and a second edge of 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 disposed at the second edge of the cavity so as to spread out a pressure wave generated by the polygon mirror during rotation.

21. The lidar system of claim 20, wherein the noise-reducing feature is a tapered feature oriented toward the pressure wave.

22. The lidar system of claim 1, further comprising a bracket in which the polygon mirror is mounted, the bracket including a cavity that partially encloses the polygon mirror between a first edge of the cavity and a second edge of cavity, 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 acoustic impulses produced by the polygon mirror during rotation do not add together in phase.

23. The lidar system of claim 22, wherein the angle is selected according to Ω

=(360/N)*(m+1/3), wherein Ω

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

24. The lidar system of claim 22, 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.

25. A method in a lidar system for scanning a field of regard, the method comprising:

pivoting a first scan mirror along a first scan-mirror pivot axis;

pivoting a second scan mirror along a second scan-mirror pivot axis, including controlling at least one of a scanning speed or range of pivoting of the second scan-mirror independently of the first scan-mirror;

rotating a polygon mirror about a polygon-mirror rotation axis substantially orthogonal to the first scan-mirror pivot axis and the second scan-mirror pivot axis, the polygon mirror including a plurality of reflective surfaces angularly offset from one another along a periphery of the polygon mirror;

concurrently directing a first beam of light toward the first scan mirror and a second beam of light toward the scan mirror, wherein the first scan mirror reflects the first beam toward the polygon mirror to scan the first beam of light along a first direction, wherein the second scan mirror reflects the second beam toward the polygon mirror to scan the second beam of light along the first direction, and wherein the polygon mirror reflects the first beam of light and the second beam of light toward a field of regard to scan the first beam of light and the second beam of light along a second direction; and

detecting the first beam of light scattered by one or more remote targets using a first detector and the second beam of light scattered by the one or more remote targets using a second detector, to generate values for a first pixel and a second pixel.

26. The method of claim 25, further comprising pivoting the first scan mirror and the second scan mirror at a same speed.

27. The method of claim 25, further comprising pivoting the first scan mirror and the second scan mirror at different speeds to generate different scan patterns with the first beam of light and the second beam light.

28. The method of claim 25, further comprising rotating the polygon mirror using a motor operating in an open-loop mode.

29. The method of claim 25, wherein:

directing the first beam of light toward the first scan mirror includes causing the first beam of light and the detected scattered light from the first beam of light to travel in approximately opposite directions and parallel to within 1°

, and

directing the second beam of light toward the second scan mirror includes causing the second beam of light and the detected scattered light from the second beam of light to travel in approximately opposite directions and parallel to within 1°

.

30. The method of claim 25, further comprising:

concurrently directing a third beam of light toward the first scan mirror and a fourth beam of light toward the scan mirror, wherein the first scan mirror reflects the third beam toward the polygon mirror to scan the third beam of light along the first direction, wherein the second scan mirror reflects the fourth beam toward the polygon mirror to scan the fourth beam of light along the first direction, and wherein the polygon mirror reflects the third beam of light and the fourth beam of light toward the field of regard to scan the third beam of light and the fourth beam of light along the second direction; and

detecting the third beam of light scattered by the one or more remote targets using a third detector and the fourth beam of light scattered by the one or more remote targets using a fourth detector, to generate values for a third pixel and a fourth pixel.