Achieving a target gait behavior in a legged robot
A legged robot may seek to operate according to a target gait. The legged robot may include leg members and leg joints. Possibly based on the target gait and state of the legged robot, an ordered list of gait controllers may be obtained. The gait controllers in the ordered list may define respective gaits of the legged robot, and may include respective validity checks and output parameters for the respective gaits. The ordered list may begin with a target gait controller that defines the target gait. The ordered list may be traversed in order from the target gait controller until a validity check associated with a particular gait controller passes. The legged robot may be instructed to actuate the leg members and/or leg joints according to output parameters of the particular gait controller.
1. A method comprising:
receiving, at a processor of a legged robot, sensor information from one or more sensors of the legged robot, the legged robot including leg members and leg joints;
determining, by the processor, an instantaneous state of the legged robot based on the sensor information, the instantaneous state comprising at least one of a position of the legged robot, a velocity of the legged robot, an angle associated with each leg joint, or a torque associated with each leg joint;
determining, by the processor, a target gait for operating the legged robot on a ground surface;
obtaining, by the processor, an ordered list of gait controllers based on the target gait for operating the legged robot, each gait controller associated with a respective gait for operating the legged robot and comprising:
a validity check associated with the respective gait; and
one or more output parameters associated with the respective gait;
determining, by the processor, whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for a first gait controller of the ordered list of gait controllers, the respective gait for the first gait controller comprising the target gait; and
when the instantaneous state of the legged robot satisfies the validity check associated with the target gait for the first gait controller, instructing, by the processor, the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the target gait, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the target gait,
wherein the one or more output parameters associated with the respective gait for each gait controller comprise:
target footstep locations to achieve the respective gait; and
at least one of target joint torques or target joint angles for the joints to achieve the target footstep locations.
2. The method of claim 1 , further comprising, when the instantaneous state of the legged robot does not satisfies the validity check associated with the target gait:
determining, by the processor, whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for a second gait controller of the ordered list of gait controllers, the respective gait for the second gait controller comprising a first intermediary gait for operating the legged robot to achieve the target gait; and
when the instantaneous state of the legged robot satisfies the validity check associated with the first intermediary gait for the second gait controller, instructing, by the processor, the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the first intermediary gait for the second gait controller, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the first intermediary gait.
3. The method of claim 2 , further comprising, after instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the first intermediary gait:
determining, by the processor, whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for the first gait controller of the ordered list of gait controllers, the respective gait for the first gait controller comprising the target gait; and
when the instantaneous state of the legged robot satisfies the validity check associated with the target gait for the first gait controller, instructing, by the processor, the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the respective gait, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the target gait.
4. The method of claim 2 , further comprising, when the instantaneous state of the legged robot does not satisfy the validity check associated with the first intermediary gait:
identifying, by the processor, a next gait controller in the ordered list of gait controller having an associated validity check satisfied by the instantaneous state of the legged robot; and
instructing, by the processor, the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the respective gait for the identified next gait controller, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the respective gait.
5. The method of claim 1 , wherein determining the target gait for operating the legged robot comprises receiving an input command from an external controller in communication with the processor for the legged robot, the input command comprising an instruction for the legged robot to perform the target gait.
6. The method of claim 1 , wherein determining the target gait for operating the legged robot comprises receiving an input command from an external controller in communication with the processor of the legged robot, the input command comprising an instruction to move the legged robot to a target geographical location.
7. The method of claim 1 , wherein at least one of the gait controllers of the ordered list of gait controllers comprises:
(i) a cyclic gait controller defining respective touchdown timings and positions for feet of the legged robot that cause the legged robot to operate according to the respective gait;
(ii) an acyclic gait controller defining touchdown timings and positions for the feet that cause the legged robot to transition from one gait to another gait; or
(iii) a recovery gait controller defining touchdown timings and positions for the feet that cause the legged robot to recover from deviations from a cyclic gait or an acyclic gait.
8. The method of claim 1 , wherein the respective gaits for the gait controllers comprise one of a standing gait, a slow-walk-to-stand gait, a slow-trot-to-stand gait, a slow walk gait, a slow trot gait, a medium-walk-to-slow-walk gait, a medium-trot-to-slow-trot gait, a medium walk gait, or a medium trot gait.
9. A legged robot comprising:
leg members connected by leg joints;
one or more sensors;
a processor in communication with the one or more sensors; and
a non-transitory computer-readable medium in communication with the processor and storing instructions, that when executed by the processor, cause the processor to perform operations comprising:
receiving sensor information from the one or more sensors;
determining an instantaneous state of the legged robot based on the sensor information, the instantaneous state comprising at least one of a position of the legged robot, a velocity of the legged robot, an angle associated with each leg joint, or a torque associated with each leg joint;
determining a target gait for operating the legged robot on a ground surface;
obtaining an ordered list of gait controllers based on the target gait for operating the legged robot, each gait controller associated with a respective gait for operating the legged robot and comprising:
a validity check associated with the respective gait; and
one or more output parameters associated with the respective gait;
determining whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for a first gait controller of the ordered list of gait controllers, the respective gait for the first gait controller comprising the target gait; and
when the instantaneous state of the legged robot satisfies the validity check associated with the target gait for the first gait controller, instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the target gait, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the target gait,
wherein the one or more output parameters associated with the respective gait for each gait controller comprise:
target footstep locations to achieve the respective gait; and
at least one of target joint torques or target joint angles for the joints to achieve the target footstep locations.
10. The legged robot of claim 9 , wherein the operations further comprise, when the instantaneous state of the legged robot does not satisfies the validity check associated with the target gait:
determining whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for a second gait controller of the ordered list of gait controllers, the respective gait for the second gait controller comprising a first intermediary gait for operating the legged robot to achieve the target gait; and
when the instantaneous state of the legged robot satisfies the validity check associated with the first intermediary gait for the second gait controller, instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the first intermediary gait for the second gait controller, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the first intermediary gait.
11. The legged robot of claim 10 , wherein the operations further comprise, after instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the first intermediary gait:
determining whether the instantaneous state of the legged robot satisfies the validity check associated with the respective gait for the first gait controller of the ordered list of gait controllers; and
when the instantaneous state of the legged robot satisfies the validity check associated with the target gait for the first gait controller, instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the respective gait, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the target gait.
12. The legged robot of claim 10 , wherein the operations further comprise, when the instantaneous state of the legged robot does not satisfy the validity check associated with the first intermediary gait:
identifying a next gait controller in the ordered list of gait controller having an associated validity check satisfied by the instantaneous state of the legged robot; and
instructing the leg members and/or the leg joints to actuate based on the one or more output parameters associated with the respective gait for the identified next gait controller, the actuation of the leg members and/or the leg joints causing the legged robot to achieve the respective gait.
13. The legged robot of claim 9 , wherein determining the target gait for operating the legged robot comprises receiving an input command from an external controller in communication with the processor for the legged robot, the input command comprising an instruction for the legged robot to perform the target gait.
14. The legged robot of claim 9 , wherein determining the target gait for operating the legged robot comprises receiving an input command from an external controller in communication with the processor of the legged robot, the input command comprising an instruction to move the legged robot to a target geographical location.
15. The legged robot of claim 9 , wherein at least one of the gait controllers of the ordered list of gait controllers comprises:
(i) a cyclic gait controller defining respective touchdown timings and positions for feet of the legged robot that cause the legged robot to operate according to the respective gait;
(ii) an acyclic gait controller defining touchdown timings and positions for the feet that cause the legged robot to transition from one gait to another gait; or
(iii) a recovery gait controller defining touchdown timings and positions for the feet that cause the legged robot to recover from deviations from a cyclic gait or an acyclic gait.
16. The legged robot of claim 9 , wherein the respective gaits for the gait controllers comprise one of a standing gait, a slow-walk-to-stand gait, a slow-trot-to-stand gait, a slow walk gait, a slow trot gait, a medium-walk-to-slow-walk gait, a medium-trot-to-slow-trot gait, a medium walk gait, or a medium trot gait.