Light steering device with an array of oscillating reflective slats

• US 9,128,190 B1
• Filed: 11/26/2013
• Issued: 09/08/2015
• Est. Priority Date: 03/06/2013
• Status: Active Grant

• Current Assignee: Waymo LLC (Alphabet Inc.)
• Original Assignee: Google Inc. (Alphabet Inc.)
• Inventors: Droz, Pierre-yves, Ulrich, Drew, Lenius, Samuel
• Primary Examiner(s): Nguyen, John Q
• Assistant Examiner(s): Hutchinson, Alan D
• Application Number:
  US14/090,485
• Time in Patent Office: 651 Days
• Field of Search: 356/5.01, 359/196.1, 359/201.2, 359/223.1, 701/28
• 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 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/931 of land vehicles
• CPC Class Codes: G01S 7/4815 using multiple transmitters
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G02B 26/08 for controlling the direction of light in light guides G02B6/35
• CPC Class Codes: G02B 26/0825 the reflecting element being a flexible sheet or membrane, e.g. for varying the focus flexible mirrors for cosmetic use A45D42/24
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/085 the reflecting means being moved or deformed by electromagnetic means
• CPC Class Codes: G02B 26/105 with one or more pivoting mirrors or galvano-mirrors G02B26/101 takes precedence
• CPC Class Codes: G05D 1/0231 using optical position detecting means position-fixing by using electromagnetic waves other than radio waves, e.g. optical position detecting means G01S5/16

Abstract

A light detection and ranging (LIDAR) device scans through a scanning zone while emitting light pulses and receives reflected signals corresponding to the light pulses. The LIDAR device scans the emitted light pulses through the scanning zone by reflecting the light pulses from an array of oscillating mirrors. The mirrors are operated by a set of electromagnets arranged to apply torque on the mirrors, and an orientation feedback system senses the orientations of the mirrors. Driving parameters for each mirror are determined based on information from the orientation feedback system. The driving parameters can be used to drive the mirrors in phase at an operating frequency despite variations in moments of inertia and resonant frequencies among the mirrors.

Claims

1. A light detection and ranging (LIDAR) device comprising:

a plurality of mirrors arranged to rotate about respective axes of rotation parallel to a reflective surface of the respective mirrors, and wherein the axes of rotation of the plurality of mirrors are arranged to be aligned in parallel and in a common plane;

a plurality of electromagnets arranged to attract the plurality of mirrors via induced magnetic fields generated in the mirrors so as to apply torque on the respective mirrors about their respective axes of rotation, wherein each of the plurality of electromagnets is arranged to apply torque to only one of the plurality of mirrors such that each of the plurality of mirrors is associated with a mirror-associated set of electromagnets in the plurality of electromagnets;

a plurality of driving circuits for operating the plurality of electromagnets using a plurality of driving signals, wherein each driving circuit is configured to receive a respective input and generate, based on the respective input, a respective driving signal for operating a respective mirror-associated set of electromagnets;

a plurality of detectors configured to detect orientations of the plurality of mirrors;

a controller configured to;

(i) receive data from the plurality of detectors indicative of detected orientations of the plurality of mirrors, (ii) determine, based on the detected orientations, driving parameters sufficient to cause the plurality of driving circuits to operate the plurality of electromagnets such that the plurality of mirrors oscillate in phase at an operating frequency, and (iii) provide the determined driving parameters as input to the plurality of driving circuits; and

a light source configured to emit light pulses directed toward the plurality of mirrors such that the light pulses are reflected by the plurality of mirrors.

2. The LIDAR device according to claim 1, further comprising:

a housing for mounting the plurality of mirrors via respective pairs of connecting arms connected between the housing and respective midpoints of opposing sides of each mirror, wherein the respective pairs of connecting arms are configured to twist during rotation of the respective mirrors so as to define the respective axes of rotation of the respective mirrors.

3. The LIDAR device according to claim 2, wherein the connecting arms are configured to resist twisting and thereby bias the mirrors in a non-rotated orientation.

4. The LIDAR device according to claim 2, wherein the connecting arms are narrow strips integrally formed with respective ones of the plurality of mirrors.

5. The LIDAR device according to claim 1, wherein the plurality of detectors include a plurality of impedance sensors, wherein each impedance sensor is configured to detect impedance in a respective mirror-associated set of electromagnets.

6. The LIDAR device according to claim 1, wherein the plurality of detectors include a plurality of optical sensors, wherein each optical sensor is configured to detect light reflected from a respective mirror in the plurality of mirrors.

7. The LIDAR device according to claim 1, further comprising:

a substrate oriented in parallel with the common plane of the axes of rotation of the plurality of mirrors, wherein the substrate is mounted so as to be proximate back surfaces opposite the respective reflective surfaces of the plurality of mirrors, and

wherein the plurality of electromagnets each include;

a central core formed by a ferromagnetic peg extending outward from the substrate substantially perpendicular to the back surfaces, and

a coil formed by conductive traces embedded in the substrate that wrap around the peg such that a current driven through the coil magnetizes the peg.

8. The LIDAR device according to claim 7, wherein the plurality of electromagnets are arranged in pairs such that each pair of pegs has ends distal from the substrate located approximately equidistant from the axis of rotation of a respective one of the plurality of mirrors.

9. The LIDAR device according to claim 1, wherein the plurality of mirrors are arranged side by side in a single row, and wherein, for each of the plurality of mirrors:

the reflective surface has a length dimension and a perpendicular width dimension shorter than the length dimension, and

the axis of rotation is oriented parallel to the length dimension of the reflective surface.

10. The LIDAR device according to claim 1, wherein each of the plurality of driving signals is configured to provide a respective alternating current through a respective one of the sets of mirror-associated electromagnets.

11. The LIDAR device according to claim 10, wherein the determined driving parameters define at least one of a respective phase or respective amplitude for each respective alternating current.

12. The LIDAR device according to claim 10, wherein the operating frequency is approximately 5 kilohertz.

13. The LIDAR device according to claim 1, wherein the plurality of mirrors are configured such that each oscillates through a range of orientations of approximately 2 degrees.

14. The LIDAR device according to claim 1, wherein the plurality of mirrors include a silicon steel alloy.

15. The LIDAR device according to claim 1, wherein the LIDAR device is associated with an autonomous vehicle that is configured to use returning reflected signals corresponding to the emitted light pulses to identify obstacles surrounding the autonomous vehicle and then control the autonomous vehicle to avoid the detected obstacles.

16. A method comprising:

operating a plurality of sets of mirror-associated electromagnets in a light detection and ranging (LIDAR) device such that each set of mirror-associated electromagnets is operated by a respective driving circuit in a plurality of driving circuits in the LIDAR device based on respective input, wherein each set of mirror-associated electromagnets is configured to apply torque to a respective mirror in a plurality of mirrors so as to cause the respective mirror to rotate about a respective axis of rotation parallel to a reflective surface of the respective mirror, and wherein the plurality of mirrors in the LIDAR device have axes of rotation aligned in parallel and in a common plane;

receiving, from a plurality of detectors configured to detect orientations of the plurality of mirrors, data indicative of detected orientations of the plurality of mirrors;

determining, based on the detected orientations, driving parameters sufficient to cause the plurality of driving circuits to operate the plurality of electromagnets such that the plurality of mirrors oscillate in phase at an operating frequency; and

providing the determined driving parameters as input to the plurality of driving circuits.

17. The method according to claim 16, wherein each driving circuit provides a respective alternating current through a respective one of the sets of mirror-associated electromagnets, and wherein the determined driving parameters define at least one of a respective phase or respective amplitude for each respective alternating current.

18. The method according to claim 16, further comprising:

emitting light pulses directed toward the plurality of mirrors such that the light pulses are reflected by the plurality of mirrors;

detecting returning reflected light signals corresponding to the emitted light pulses;

identifying obstacles surrounding an autonomous vehicle; and

controlling the autonomous vehicle to avoid the identified obstacles.

19. A non-transitory computer readable medium storing instructions that, when executed by one or more processors in a computing device, cause the computing device to perform operations, the operations comprising:

operating a plurality of sets of mirror-associated electromagnets in a light detection and ranging (LIDAR) device such that each set of mirror-associated electromagnets is operated by a respective driving circuit in a plurality of driving circuits in the LIDAR device based on respective input, wherein each set of mirror-associated electromagnets is configured to apply torque to a respective mirror in a plurality of mirrors so as to cause the respective mirror to rotate about a respective axis of rotation parallel to a reflective surface of the respective mirror, and wherein the plurality of mirrors in the LIDAR device have axes of rotation aligned in parallel and in a common plane;

receiving, from a plurality of detectors configured to detect orientations of the plurality of mirrors, data indicative of detected orientations of the plurality of mirrors;

determining, based on the detected orientations, driving parameters sufficient to cause the plurality of driving circuits to operate the plurality of electromagnets such that the plurality of mirrors oscillate in phase at an operating frequency; and

providing the determined driving parameters as input to the plurality of driving circuits.

20. The non-transitory computer readable medium according to claim 19, wherein the operations further comprise:

emitting light pulses directed toward the plurality of mirrors such that the light pulses are reflected by the plurality of mirrors;

detecting returning reflected light signals corresponding to the emitted light pulses;

identifying obstacles surrounding an autonomous vehicle; and

controlling the autonomous vehicle to avoid the identified obstacles.