Handling gait disturbances with asynchronous timing
An example method may include i) detecting a disturbance to a gait of a robot, where the gait includes a swing state and a step down state, the swing state including a target swing trajectory for a foot of the robot, and where the target swing trajectory includes a beginning and an end; and ii) based on the detected disturbance, causing the foot of the robot to enter the step down state before the foot reaches the end of the target swing trajectory.
1. A method comprising:
identifying, by a control system for a robot, an estimated swing time for a swing phase of a gait pattern, the swing phase comprising a swing forward state when a respective foot of the robot has a forward velocity along a swing trajectory and a step down state when the respective foot of the robot approaches a ground surface from a swing height of the swing trajectory;
determining that an actual swing time for a first foot of a first leg of the robot to execute the swing phase exceeds the estimated swing time; and
when the actual swing time for the first foot exceeds the estimated swing time:
transitioning control of a second foot of a contralateral leg of the robot from a stance phase to the swing phase by disengaging ground reaction force control of the second foot;
lifting the second foot to execute the swing phase of the gait pattern for the second foot; and
executing ground reaction force control for the first foot of the robot.
2. The method of claim 1 , wherein determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds the estimated swing time occurs when the first foot reaches a range of motion limit for a joint associated with the first leg.
3. The method of claim 2 , wherein the range of motion limit corresponds to a limit of an actuator associated with the joint and configured to move the joint in a respective range of motion.
4. The method of claim 1 , further comprising:
prior to lifting the second foot to execute the swing phase of the gait pattern for the second foot:
determining a stance velocity of the second foot with respect to a body of the robot; and
generating a lift-off velocity for the second foot equal to a current forward velocity of the robot,
wherein lifting the second foot to execute the swing phase of the gait pattern occurs by applying the lift-off velocity using one or more actuators configured to control motion for the contralateral leg of the robot.
5. The method of claim 1 , wherein determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds the estimated swing time comprises determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds a threshold deviation from the estimated swing time.
6. The method of claim 1 , wherein identifying the estimated swing time for the swing phase of the gait pattern comprises determining the estimated swing time at the control system of the robot.
7. The method of claim 1 , wherein identifying the estimated swing time for the swing phase of the gait pattern comprises receiving, at the control system of the robot, a nominal swing time for the swing phase and configuring the estimated swing time to be equal to the received nominal swing time.
8. The method of claim 1 , wherein the robot is a quadruped robot with four legs.
9. The method of claim 1 , wherein the robot is a biped robot.
10. The method of claim 1 , wherein the gait pattern comprises a trotting gait.
11. A robot comprising:
a first foot;
a second foot; and
a control system comprising a processor and memory in communication with the processor, the memory storing program instructions that, when executed by the processor, cause the processor to perform operations comprising:
identifying an estimated swing time for a swing phase of a gait pattern, the swing phase comprising a swing forward state when a respective foot of the robot has a forward velocity along a swing trajectory and a step down state when the respective foot of the robot approaches a ground surface from a swing height of the swing trajectory;
determining that an actual swing time for the first foot of a first leg of the robot to execute the swing phase exceeds the estimated swing time; and
when the actual swing time for the first foot exceeds the estimated swing time:
transitioning control of the second foot of a contralateral leg of the robot from a stance phase to the swing phase by disengaging ground reaction force control of the second foot;
lifting the second foot to execute the swing phase of the gait pattern for the second foot; and
executing ground reaction force control for the first foot of the robot.
12. The system of claim 11 , wherein determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds the estimated swing time occurs when the first foot reaches a range of motion limit for a joint associated with the first leg.
13. The system of claim 12 , further comprising an actuator associated with the joint of the first leg, the actuator limited to a range of motion based on the range of motion limit.
14. The system of claim 11 , wherein the operations further comprise:
prior to lifting the second foot to execute the swing phase of the gait pattern for the second foot:
determining a stance velocity of the second foot with respect to a body of the robot; and
generating a lift-off velocity for the second foot equal to a current forward velocity of the robot,
wherein lifting the second foot to execute the swing phase of the gait pattern occurs by applying the lift-off velocity using one or more actuators configured to control motion for the contralateral leg of the robot.
15. The system of claim 11 , wherein determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds the estimated swing time comprises determining that the actual swing time for the first foot of the first leg of the robot to execute the swing phase exceeds a threshold deviation from the estimated swing time.
16. The system of claim 11 , wherein identifying the estimated swing time for the swing phase of the gait pattern comprises determining the estimated swing time at the control system of the robot.
17. The system of claim 11 , wherein identifying the estimated swing time for the swing phase of the gait pattern comprises receiving a nominal swing time for the swing phase and configuring the estimated swing time to be equal to the received nominal swing time.
18. The system of claim 11 , wherein the robot is a quadruped robot with four legs.
19. The system of claim 11 , wherein the robot is a biped robot.
20. The system of claim 11 , wherein the gait pattern comprises a trotting gait.