Braking and regeneration control in a legged robot

1. A robot comprising:

a hydraulic actuator cylinder for controlling motion of a member associated with a leg of the robot, the hydraulic actuator cylinder comprising a piston, a first chamber, and a second chamber;

a valve system configured to control hydraulic fluid flow between a supply line of pressurized hydraulic fluid, the first and second chambers, and a return line, the valve system configured to:

couple the first chamber to the supply line of pressurized hydraulic fluid and the second chamber to the return line to move the piston in a forward direction; and

couple the second chamber to the supply line of pressurized hydraulic fluid and the first chamber to the return line to move the piston in a reverse direction; and

a controller configured to:

provide a first signal to the valve system, the first signal instructing the valve system to move the piston along a target trajectory that causes the leg of the robot to undergo a swing phase of leg motion;

while the piston is moving in the forward direction along the trajectory, provide a second signal to the valve system to reduce speed until the piston stops at an intermediate position along the target trajectory causing the leg of the robot to stop prematurely during backswing of the swing phase; couple both the first chamber and second chamber to the return line at the same time; and

provide a third signal to the valve system, the third signal instructing the valve system to move the piston in the reverse direction causing the leg of the robot to swing forward toward touchdown.

2. The robot of claim 1 , wherein the controller is further configured to, while the piston is moving in the forward direction:

determine whether the piston has stopped at the intermediate position; and

when the piston has stopped at the intermediate position, provide the third signal to the valve system.

3. The robot of claim 1 , wherein the second signal:

instructs the valve system to couple the second chamber to the supply line of pressurized hydraulic fluid and the first chamber to the return line; and

causes, based on the movement by the piston in the forward direction, hydraulic fluid to flow from the second chamber into the supply line and hydraulic fluid to flow from the return line to the first chamber.

4. The robot of claim 1 , wherein, the second signal:

instructs the valve system to couple the first chamber to the return line and couple the second chamber to the return line; and

causes, based on the movement by the piston in the forward direction, hydraulic fluid to flow from the second chamber into the return line and hydraulic fluid to flow from the return line to the first chamber.

5. The robot of claim 1 , wherein the controller is configured to receive sensor information indicative of a pressure level in the second chamber and a speed of the piston, and wherein the controller is configured to provide the second signal based on the pressure level in the second chamber and the speed of the piston.

6. The robot of claim 1 , wherein the second signal instructs the valve system to couple both the first chamber and the second chamber to the return line at the same time.

7. The robot of claim 1 , wherein the controller is configured to provide the third signal to the valve system prior to when the piston would have reached the third position if the piston was moving in the reverse direction along the target trajectory.

8. The robot of claim 1 , wherein, when the third signal instructs the valve system to move the piston in the reverse direction, the valve system couples the second chamber to the supply line and couples the first chamber to the return line such that hydraulic fluid flows from the supply line to the second chamber and hydraulic fluid flows from the first chamber to the return line causing the piston to move in the reverse direction.

9. The robot of claim 1 , wherein:

the swing phase of leg motion comprises lift off at a first time instance and touchdown at a second time instance; and

the third signal causes the leg of the robot to swing forward and touchdown at the second time instance.

10. A method comprising:

providing, by a controller of a robot, a first signal to a valve system, wherein the robot includes a hydraulic actuator cylinder controlling motion of a member associated with a leg of the robot, wherein the hydraulic actuator cylinder comprises a piston, a first chamber, and a second chamber, wherein the valve system is configured to control hydraulic fluid flow between a supply line of pressurized hydraulic fluid, the first and second chambers, and a return line, wherein the first signal to the valve system instructs the valve system to move the piston along a target trajectory that causes the leg of the robot to undergo a swing phase of leg motion;

while the piston is moving in a forward direction along the trajectory, providing, by the controller, a second signal to the valve system to reduce speed until the piston stops at an intermediate position along the target trajectory causing the leg of the robot to stop prematurely during backswing of the swing phase; couple both the first chamber and second chamber to the return line at the same time; and

providing, by the controller, a third signal to the valve system, wherein the third signal instructs the valve system to move the piston in a reverse direction causing the leg of the robot to swing forward toward touchdown.

11. The method of claim 10 , further comprising, while the piston is moving in the forward direction:

determining, by the controller, whether the piston has stopped at the intermediate position; and

when the piston has stopped at the intermediate position, providing, by the controller, the third signal to the valve system.

12. The method of claim 10 , wherein, the second signal:

instructs the valve system to couple the second chamber to the supply line of pressurized hydraulic fluid and the first chamber to the return line; and

causes, based on the movement by the piston in the forward direction, hydraulic fluid to flow from the second chamber into the supply line and hydraulic fluid to flow from the return line to the first chamber.

13. The method of claim 10 , wherein, the second signal:

instructs the valve system to couple the first chamber to the return line and couple the second chamber to the return line; and

causes, based on the movement by the piston in the forward direction, hydraulic fluid to flow from the second chamber into the return line and hydraulic fluid to flow from the return line to the first chamber.

14. The method of claim 10 , further comprising receiving sensor information indicative of a pressure level in the second chamber and a speed of the piston, and wherein providing the second signal to the valve system is based on the pressure level in the second chamber and the speed of the piston.

15. The method of claim 10 , wherein the second signal instructs the valve system to couple both the first chamber and the second chamber to the return line at the same time.

16. The method of claim 10 , further comprising providing, by the controller, the third signal to the valve system prior to when the piston would have reached the third position if the piston was moving in the reverse direction along the target trajectory.

17. The method of claim 10 , wherein, when the third signal instructs the valve system to move the piston in the reverse direction, the valve system couples the second chamber to the supply line and couples the first chamber to the return line such that hydraulic fluid flows from the supply line to the second chamber and hydraulic fluid flows from the first chamber to the return line causing the piston to move in the reverse direction.

18. The method of claim 10 , wherein:

the swing phase of leg motion comprises lift off at a first time instance and touchdown at a second time instance; and

the third signal causes the leg of the robot to swing forward and touchdown at the second time instance.