Systems and methods for traction detection and control in a self-driving vehicle
Methods and systems are provided for traction detection and control of a self-driving vehicle. The self-driving vehicle has drive motors that drive drive-wheels according to a drive-motor speed. Traction detection and control can be obtained by measuring the vehicle speed with a sensor such as a LiDAR or video camera, and measuring the wheel speed of the drive wheels with a sensor such as a rotary encoder. The difference between the measured vehicle speed and the measured wheel speeds can be used to determine if a loss of traction has occurred in any of the wheels. If a loss of traction is detected, then a recovery strategy can be selected from a list of recovery strategies in order to reduce the effects of the loss of traction.
1. A vehicle, comprising:
at least one wheel for moving the vehicle;
at least one drive motor for driving the at least one wheel with at least one drive motor speed;
a computer having a processor in communication with the at least one drive motor for adjusting the at least one drive-motor speed;
a first sensor for measuring a vehicle speed of the vehicle, the first sensor in communication with the computer; and
a second sensor for measuring a wheel speed of the at least one wheel;
wherein the processor is configured to:
receive the vehicle speed from the first sensor and the wheel speed from the second sensor;
calculate a difference between the vehicle speed and the wheel speed, the difference being indicative of a loss of traction of the at least one wheel; and
responsive to the loss of traction, selecting a strategy based on at least one of a score or a priority associated with the strategy and implementing a corrective action associated with the selected strategy, wherein the score associated with the selected strategy is based on an observed result from a previous occurrence of the selected strategy.
2. The vehicle of claim 1 , wherein the first sensor comprises a range-finding sensor and the second sensor comprises a rotary encoder.
3. The vehicle of claim 2 , wherein the range-finding sensor is a LiDAR device.
4. The vehicle of claim 3 , wherein the LiDAR device is a two-dimensional LiDAR device.
5. The vehicle of claim 1 , wherein the first sensor comprises at least one video camera.
6. The vehicle of claim 1 , wherein the first sensor comprises an inertial-measurement unit.
7. The vehicle of claim 1 , wherein the corrective action comprises decelerating the at least one wheel at a constant deceleration.
8. The vehicle of claim 1 , wherein the corrective action comprises decelerating the at least one wheel at a variable deceleration.
9. The vehicle of claim 1 , wherein the at least one wheel comprises a first wheel and a second wheel, and the at least one drive motor comprises a first drive motor for driving the first wheel with a first drive-motor speed and a second drive motor for driving the second wheel at a second drive-motor speed.
10. The vehicle of claim 9 , wherein the processor is further configured to:
determine a ratio of the first drive-motor speed to the second drive-motor speed associated with an intended vehicle path; and
wherein the corrective action comprises reducing the first drive-motor speed, and proportionately reducing the second drive-motor speed;
such that the ratio of the first drive-motor speed to the second-drive-motor speed associated with the intended vehicle path is maintained.
11. A method for traction detection and control of
a vehicle, comprising:
moving the vehicle with a drive motor operating at a drive-motor speed;
measuring, with a first sensor, a vehicle speed of the vehicle;
measuring, with a second sensor, a wheel speed of a wheel of the vehicle;
receiving, at a computer, the vehicle speed and the wheel speed;
calculating, with the computer, a speed difference based on the vehicle speed and the wheel speed, the speed difference being indicative of a loss of traction of the wheel; and
responsive to the loss of traction, selecting a strategy based on at least one of a score or a priority associated with the strategy and implementing a corrective action associated with the selected strategy, wherein the score associated with the selected strategy is based on an observed result from a previous occurrence of the selected strategy.
12. The method of claim 11 , wherein the first sensor is a range-finding sensor and the second sensor is a rotary encoder attached to the wheel.
13. The method of claim 11 , wherein the first sensor comprises at least one video camera.
14. A method for traction detection and control of a vehicle, comprising:
moving the vehicle with a first drive motor operating at a first drive-motor speed and a second drive motor operating at a second drive-motor speed, the first drive motor being attached to a first drive wheel, and the second drive motor being attached to a second drive wheel;
measuring, with a sensor, a vehicle speed of the vehicle;
measuring, with a first rotary encoder, a first wheel speed of the first drive wheel;
receiving, at a computer, the vehicle speed and the first wheel speed; calculating, with the computer, a speed difference based on the vehicle speed and the first wheel speed, the speed difference being indicative of a loss of traction of the first drive wheel; and
responsive to the loss of traction, selecting a strategy based on at least one of a score or a priority associated with the strategy and implementing a corrective action associated with the selected strategy, wherein the score associated with the selected strategy is based on an observed result from a previous occurrence of the selected strategy.
15. The method of claim 14 , wherein the corrective action comprises:
decelerating the first drive wheel to a reduced first wheel speed using at least one of the first drive motor and a first brake attached to the first drive wheel;
decelerating the second drive wheel to a reduced second wheel speed using at least one of the second drive motor and a second brake attached to the second drive wheel;
operating the first drive motor at a reduced first drive-motor speed associated with the reduced first wheel speed; and
operating the second drive motor at a reduced second drive-motor speed associated with the reduced second wheel speed.
16. The method of claim 15 , wherein the reduced first wheel speed and the reduced second wheel speed are zero.
17. The method of claim 15 , further comprising receiving, at the computer, a vehicle path;
wherein at least one of the reduced first drive-motor speed and the reduced second drive-motor speed are selected such that a ratio of the reduced first drive-motor speed to the reduced second drive-motor speed corresponds to the vehicle path.
18. The method of claim 14 , wherein the first drive motor is operating to drive the first drive wheel in a first wheel direction, and the second drive motor is operating to drive the second drive wheel in a second wheel direction opposite the first wheel direction so as to pivot the vehicle; and the corrective action comprises selecting a corrective first wheel direction that is the same as the second wheel direction, thereby preventing the vehicle from pivoting.
19. The method of claim 14 , wherein the corrective action comprises decelerating the at least one wheel at a constant deceleration.
20. The method of claim 14 , wherein the corrective action comprises decelerating the at least one wheel at a variable deceleration.