Half and quarter lissajous scan patterns for LiDAR
A LiDAR system includes a fixed frame, a first platform, an electro-optic assembly including one or more laser sources and one or more detectors mounted on the first platform; a flexure assembly flexibly coupling the first platform to the fixed frame; a drive mechanism configured to translate the first platform with respect to the fixed frame in two dimensions in a plane substantially perpendicular to an optical axis of the LiDAR system; and a controller configured to cause the drive mechanism to translate the first platform in a first direction with a first frequency and in a second direction orthogonal to the first direction with a second frequency that is different from the first frequency, acquire a point cloud, and output the point cloud at a frame rate that is an integer times a difference between the second frequency and the first frequency, the integer being greater than one.
1. A scanning LiDAR system comprising:
a fixed frame;
a first platform;
an electro-optic assembly mounted on the first platform, the electro-optic assembly including one or more laser sources and one or more detectors, each respective detector corresponding a respective laser source;
a flexure assembly flexibly coupling the first platform to the fixed frame;
a drive mechanism configured to, via the flexure assembly, translate the first platform with respect to the fixed frame in two dimensions in a plane substantially perpendicular to an optical axis of the scanning LiDAR system; and
a controller coupled to the drive mechanism, the controller configured to:
cause the drive mechanism to translate the first platform in a first direction with a first frequency and in a second direction orthogonal to the first direction with a second frequency that is different from the first frequency; and
acquire a point cloud using the one or more laser sources and the one or more detectors while the first platform is being translated; and
output the point cloud at a frame rate that is an integer times a difference between the second frequency and the first frequency, the integer being greater than one.
2. The scanning LiDAR system of claim 1 wherein the integer is two, so that a trajectory of each laser source completes a half Lissajous scan pattern in each frame.
3. The scanning LiDAR system of claim 1 wherein the integer is four, so that a trajectory of each laser source completes a quarter Lissajous scan pattern in each frame.
4. The scanning LiDAR system of claim 1 wherein:
the one or more laser sources comprise a plurality of laser sources disposed as an array, and the one or more detectors comprise a plurality of detectors disposed as an array; and
the scanning LiDAR system is characterized by a field of view that comprises a plurality of sub-fields, wherein a trajectory of each respective laser source in each frame forms a respective sub-field.
5. The scanning LiDAR system of claim 4 wherein adjacent sub-fields of the plurality of sub-fields partially overlap with each other.
6. The scanning LiDAR system of claim 5 wherein an overlap between the adjacent sub-fields in the first direction is between 10% and 30%, and an overlap between the adjacent sub-fields in the second direction is between 10% and 30%.
7. The scanning LiDAR system of claim 1 wherein the flexure assembly comprises four springs, each of the four springs connecting a respective corner of the first platform to the fixed frame.
8. The scanning LiDAR system of claim 7 wherein each of the four springs comprises a flexible rod having a first resonant frequency in the first direction and a second resonant frequency in the second direction, and wherein the first frequency is substantially equal to the first resonant frequency, and the second frequency is substantially equal to the second resonant frequency.
9. The scanning LiDAR system of claim 1 wherein the flexure assembly comprises a first spring and a second spring, the first spring connecting a first lateral side of the first platform to the fixed frame, and the second spring connecting a second lateral side opposite to the first lateral side to the fixed frame.
10. The scanning LiDAR system of claim 1 wherein the drive mechanism is mechanically coupled to the first platform for translating the first platform.
11. The scanning LiDAR system of claim 10 wherein the drive mechanism comprises a voice coil motor that is mounted on the first platform.
12. A method of three-dimensional imaging using a LiDAR system, the method comprising:
scanning the LiDAR system in a first direction with a first frequency and in a second direction orthogonal to the first direction with a second frequency that is different from the first frequency, the LiDAR system including an electro-optic assembly that comprises one or more laser sources and one or more detectors, each respective detector corresponding a respective laser source, wherein the scanning of the LiDAR system in the first direction and the second directions scans a laser beam emitted by each respective laser source across a respective sub-field of view;
emitting, using each of the one or more laser sources, a plurality of laser pulses as the LiDAR system is scanned in the first direction and the second direction;
detecting, using each of the one or more detectors, a portion of each respective laser pulse of the plurality of laser pulses reflected off of one or more objects;
determining, using a processor, a time of flight for each respective laser pulse from emission to detection;
acquiring a point cloud of the one or more objects based on the times of flight of the plurality of laser pulses from each laser source; and
outputting the point cloud at a frame rate that is an integer times a difference between the second frequency and the first frequency, the integer being greater than one.
13. The method of claim 12 wherein the integer is two, so that a trajectory of each laser source completes a half Lissajous scan pattern in each frame.
14. The method of claim 12 wherein the integer is four, so that a trajectory of each laser source completes a quarter Lissajous scan pattern in each frame.
15. The method of claim 12 wherein:
the one or more laser sources comprise a plurality of laser sources disposed as an array, and the one or more detectors comprise a plurality of detectors disposed as an array; and
the LiDAR system is characterized by a field of view that comprises a plurality of sub-fields of view.
16. The method of claim 15 wherein the LiDAR system is scanned in the first direction with a first amplitude so that adjacent sub-fields in the first direction partially overlap with each other.
17. The method of claim 16 wherein the LiDAR system is scanned in the second direction with a second amplitude so that adjacent sub-fields in the second direction partially overlap with each other.
18. The method of claim 17 wherein an overlap between the adjacent sub-fields in the first direction is between 10% and 30%, and an overlap between the adjacent sub-fields in the second direction is between 10% and 30%.
19. The method of claim 12 wherein scanning the LiDAR system comprises translating the electro-optic assembly in the first direction and the second direction in a plane that is substantially perpendicular to an optical axis of the LiDAR system.
20. The method of claim 19 wherein:
the electro-optic assembly is flexibly coupled to a fixed frame via a flexure assembly that has a first resonant frequency in the first direction, and a second resonant frequency in the second direction; and
translating the electro-optic assembly is performed via the flexure assembly, and the first frequency is substantially equal to the first resonant frequency, and the second frequency is substantially equal to the second resonant frequency.