Damage reduction control for humanoid robot fall

1. A computer-implemented method for controlling a robot during a fall, the method comprising:

receiving, by a robot controller, a detected state of the robot;

determining based on the detected state that a fall of the robot is unavoidable;

responsive to determining that the fall of the robot is unavoidable, determining a desired rotational velocity of the robot that would cause the robot to impact the ground with a predetermined target body segment making first contact with the ground given the detected state of the robot;

generating a control signal to control motion of the robot during the fall based on the desired rotational velocity; and

outputting the control signal to actuators of the robot to cause the robot to rotate based on the desired rotational velocity such that the predetermined target body segment makes first contact with the ground.

2. The computer-implemented method of claim 1 , wherein determining the desired rotational velocity of the robot comprises:

estimating a time to a moment of impact of the target body segment with the ground based on the detected state of the robot;

estimating an orientation of the target body segment at the moment of impact under a locked joint configuration; and

determining the desired rotational velocity based on the estimated time to the moment of impact and the estimated orientation.

3. The computer-implemented method of claim 2 , further comprising:

adjusting the desired rotational velocity to an admissible velocity based on physical limitations of the robot.

4. The computer-implemented method of claim 1 , wherein generating the control signal comprises:

determining desired joint accelerations and a desired ground reaction force based on the desired rotational velocity;

determining joint torques for achieving the desired joint accelerations and the desired ground reaction force; and

generating the control signal to represent the determined joint torques.

5. The computer-implemented method of claim 1 , wherein the control signal causes the robot to rotate a swing leg in a rotational direction opposite the desired rotational velocity of the robot, and wherein the control signal causes the robot to bend backwards at the trunk.

6. The computer-implemented method of claim 1 , further comprising:

periodically re-detecting the state of the robot during the fall; and

periodically updating the determined desired rotational velocity of the robot during the fall based on the re-detected state.

7. The computer-implemented method of claim 6 , further comprising:

periodically re-generating the control signal during the fall based on the periodically updated determined desired rotational velocity, wherein a period for re-generating the control signal is smaller than a period for updating the determined desired rotational velocity; and

periodically updating the determined desired rotational velocity of the robot during the fall based on the re-detected state.

8. The computer-implemented method of claim 1 , wherein the predetermined body segment comprises a backpack.

9. A non-transitory computer-readable storage medium for storing computer program instructions for controlling a robot during a fall, the program instructions when executed by a processor cause the processor to perform steps including:

receiving, by a robot controller, a detected state of the robot;

determining based on the detected state that a fall of the robot is unavoidable;

responsive to determining that the fall of the robot is unavoidable, determining a desired rotational velocity of the robot that would cause the robot to impact the ground with a predetermined target body segment making first contact with the ground given the detected state of the robot; and

generating a control signal to control motion of the robot during the fall based on the desired rotational velocity; and

outputting the control signal to actuators of the robot to cause the robot to rotate based on the desired rotational velocity such that the predetermined target body segment makes first contact with the ground.

10. The non-transitory computer-readable storage medium of claim 9 , wherein determining the desired rotational velocity of the robot comprises:

estimating a time to a moment of impact of the target body segment with the ground based on the detected state of the robot;

estimating an orientation of the target body segment at the moment of impact under a locked joint configuration; and

determining the desired rotational velocity based on the estimated time to the moment of impact and the estimated orientation.

11. The non-transitory computer-readable storage medium of claim 10 , further comprising:

adjusting the desired rotational velocity to an admissible velocity based on physical limitations of the robot.

12. The non-transitory computer-readable storage medium of claim 9 , wherein generating the control signal comprises:

determining desired joint accelerations and a desired ground reaction force based on the desired rotational velocity;

determining joint torques for achieving the desired joint accelerations and the desired ground reaction force; and

generating the control signal to represent the determined joint torques.

13. The non-transitory computer-readable storage medium method of claim 9 , wherein the control signal causes the robot to rotate a swing leg in a rotational direction opposite the desired rotational velocity of the robot, and wherein the control signal causes the robot to bend backwards at the at the trunk.

14. The non-transitory computer-readable storage medium of claim 9 , further comprising:

periodically re-detecting the state of the robot during the fall; and

periodically updating the determined desired rotational velocity of the robot during the fall based on the re-detected state.

15. The non-transitory computer-readable storage medium of claim 14 , further comprising:

periodically re-generating the control signal during the fall based on the periodically updated determined desired rotational velocity, wherein a period for re-generating the control signal is smaller than a period for updating the determined desired rotational velocity; and

periodically updating the determined desired rotational velocity of the robot during the fall based on the re-detected state.

16. The non-transitory computer-readable storage medium of claim 9 , wherein the predetermined body segment comprises a backpack.

17. A robot controller for controlling a robot during a fall, the robot controller comprising:

a plurality of sensors determining detecting a state of the robot;

a high level controller receiving sensed information from the plurality of sensors and determining that a fall of the robot is unavoidable based on the detected state; and

a fall controller controlling motion of the robot responsive to the high-level controller determining that the fall is unavoidable, the fall controller determining a desired rotational velocity of the robot that would cause the robot to impact the ground with a predetermined target body segment making first contact with the ground given the detected state of the robot, generating a control signal to control motion of the robot during the fall based on the desired rotational velocity, and outputting the control signal to actuators of the robot to cause the robot to rotate based on the desired rotational velocity such that the predetermined target body segment makes first contact with the ground.

18. The robot controller of claim 17 , wherein the fall controller is further configured to:

estimate a time to a moment of impact of the target body segment with the ground based on the detected state of the robot;

estimate an orientation of the target body segment at the moment of impact under a locked joint configuration; and

determine the desired rotational velocity based on the estimated time to the moment of impact and the estimated orientation.

19. The robot controller of claim 18 , wherein the fall controller is further configured to adjust the desired rotational velocity to an admissible velocity based on physical limitations of the robot.

20. The robot controller of claim 17 , wherein the fall controller is further configured to:

determine desired joint accelerations and a desired ground reaction force based on the desired rotational velocity;

determine joint torques for achieving the desired joint accelerations and the desired ground reaction force; and

generate the control signal to represent the determined joint torques.