Slip detection for robotic locomotion
An example method may include i) determining a first distance between a pair of feet of a robot at a first time, where the pair of feet is in contact with a ground surface; ii) determining a second distance between the pair of feet of the robot at a second time, where the pair of feet remains in contact with the ground surface from the first time to the second time; iii) comparing a difference between the determined first and second distances to a threshold difference; iv) determining that the difference between determined first and second distances exceeds the threshold difference; and v) based on the determination that the difference between the determined first and second distances exceeds the threshold difference, causing the robot to react.
1. A method comprising:
executing, by a controller of a robot, a gait pattern according to ground reaction force control;
detecting, by the controller, that a pair of feet of the robot are in contact with a ground surface during execution of the gait pattern;
determining, by the controller, that one of a first foot or a second foot of the pair of feet slips while the pair of feet are in contact with the ground surface based on a difference between:
a first distance estimate traveled by a body of the robot relative to the one of the first foot or the second foot that slips; and
a second distance estimate traveled by the body according to an inertial measurement of the body of the robot; and
generating, by the controller, a slip reaction to the determined slip by the one of the first foot or the second foot, the slip reaction disabling ground reaction force control.
2. The method of claim 1 , further comprising:
determining, by the controller, that the slip reaction disrupts the gait pattern; and
correcting, by the controller, the slip by the one of the first foot or the second foot in subsequent steps by the pair of feet of the robot.
3. The method of claim 1 , wherein determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface comprises:
obtaining a first distance measurement and a second distance measurement, the first distance measurement between the first foot and the second foot at a first time while the pair of feet are in contact with the ground surface, the second distance measurement between the first foot and the second foot at a second time subsequent the first time while the pair of feet are in contact with the ground surface;
determining whether a difference between the first distance measurement and the second distance measurement satisfies a threshold; and
when the difference between the first distance measurement and the second distance measurement satisfies the threshold, determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface.
4. The method of claim 3 , further comprising, when the difference between the first distance measurement and the second distance measurement fails to satisfy the threshold, continuing execution of the gait pattern according to ground reaction force control.
5. The method of claim 1 , wherein determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface further comprises:
determining whether a difference between the first distance estimate and the second distance estimate satisfies a threshold; and
when the difference between the first distance estimate and the second distance estimate satisfies the threshold, determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface.
6. The method of claim 5 , wherein when the difference between the first distance estimate and the second distance estimate fails to satisfy the threshold, continuing execution of the gait pattern according to ground reaction force control.
7. The method of claim 1 , wherein determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface comprises determining that a positon of the first foot relative to the second foot while the pair of feet are in contact with the ground surface has changed by a threshold difference.
8. The method of claim 1 , further comprises logging, by the controller, the determined slip.
9. The method of claim 1 , wherein the slip reaction disabling ground reaction force control comprises prematurely causing at least one foot of the pair of feet of the robot to contact with the ground surface by terminating a swing phase of the at least one foot of the pair of feet of the robot early.
10. The method of claim 9 , further comprising, upon contact of the at least one foot of the pair of feet of the robot with the ground surface, reestablishing, by the controller, ground reaction force control.
11. A robot comprising:
a body;
a plurality of legs coupled to the body; and
a controller configured to control motion of the plurality of legs, the controller comprising a processor and memory in communication with the processor, the memory storing programming instructions that when executed on the processor perform operations comprising:
executing a gait pattern according to ground reaction force control;
detecting that a pair of feet of the robot are in contact with a ground surface during execution of the gait pattern;
determining that one of a first foot or a second foot of the pair of feet slips while the pair of feet are in contact with the ground surface based on a difference between:
a first distance estimate traveled by a body of the robot relative to the one of the first foot or the second foot that slips; and
a second distance estimate traveled by the body according to an inertial measurement of the body of the robot; and
generating a slip reaction to the determined slip by the one of the first foot or the second foot, the slip reaction disabling ground reaction force control.
12. The robot of claim 11 , wherein the operations further comprise:
determining that the slip reaction disrupts the gait pattern; and
correcting the slip by the one or the first foot or the second foot in subsequent steps by the pair of feet of the robot.
13. The robot of claim 11 , wherein determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface comprises:
obtaining a first distance measurement and a second distance measurement, the first distance measurement representing a distance between the first foot and the second foot at a first time while the pair of feet are in contact with the ground surface, the second distance measurement representing a distance between the first foot and the second foot at a second time subsequent the first time while the pair of feet are in contact with the ground surface;
determining whether a difference between the first distance measurement and the second distance measurement satisfies a threshold; and
when the difference between the first distance measurement and the second distance measurement satisfies the threshold, determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface.
14. The robot of claim 13 , further comprising, when the difference between the first measurement and the second measurement fails to satisfy the threshold, continuing execution of the gait pattern according to the ground reaction force control.
15. The robot of claim 11 , wherein the operation of determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface further comprises:
determining whether a difference between the first distance estimate and the second distance estimate satisfies a threshold; and
when the difference between the first distance estimate and the second distance estimate satisfies the threshold, determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface.
16. The robot of claim 15 , wherein when the difference between the first distance estimate and the second distance estimate fails to satisfy the threshold, continuing execution of the gait pattern according to ground reaction force control.
17. The robot of claim 11 , wherein the operation of determining that the one of the first foot or the second foot slips while the pair of feet are in contact with the ground surface comprises determining that a positon of the first foot relative to the second foot while the pair of feet are in contact with the ground surface has changed by a threshold difference.
18. The robot of claim 11 , wherein the operations further comprise logging the determined slip.
19. The robot of claim 11 , wherein the slip reaction disabling ground reaction force control comprises prematurely causing at least one foot the pair of feet of the robot to contact with the ground surface by terminating a swing phase of the at least one foot of the pair of feet of the robot early.
20. The robot of claim 19 , wherein the operations further comprise, upon contact of at least one of the pair of feet of the robot with the ground surface, reestablishing the ground reaction force control.