Braking and regeneration control in a legged robot
An example robot includes a hydraulic actuator cylinder controlling motion of a member of the robot. The hydraulic actuator cylinder comprises a piston, a first chamber, and a second chamber. A valve system controls hydraulic fluid flow between a hydraulic supply line of pressurized hydraulic fluid, the first and second chambers, and a return line. A controller may provide a first signal to the valve system so as to begin moving the piston based on a trajectory comprising moving in a forward direction, stopping, and moving in a reverse direction. The controller may provide a second signal to the valve system so as to cause the piston to override the trajectory as it moves in the forward direction and stop at a given position, and then provide a third signal to the valve system so as to resume moving the piston in the reverse direction based on the trajectory.
1. A robot comprising:
a hydraulic actuator cylinder controlling motion of a member 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 fluid and couple the second chamber to the return line to move the piston in a forward direction; and
a controller configured to:
provide a first signal to the valve system to cause the piston to follow a desired trajectory, the desired trajectory indicating movement by the piston in the forward direction from a first position until the piston stops at a second position, then move in a reverse direction;
when the piston is between the first position and the second position while moving in the forward direction:
receive sensor information from a sensor system indicative of a speed of the piston and a pressure level in the second chamber; and
provide a second signal to the valve system based on the speed of the piston and the pressure level in the second chamber, the second signal causing the piston to override the desired trajectory and stop at a third position disposed between the first position and the second position; and
prior to when the piston would have reached the third position if the piston was moving in the reverse direction according to the desired trajectory, provide a third signal to the valve system to resume moving the piston in the reverse direction based on the desired trajectory.
2. The robot of claim 1 , wherein the valve system is configured to couple the supply line to the second chamber, and couple the first chamber to the return line to move the piston in the reverse direction.
3. The robot of claim 1 , wherein the controller is configured to provide the first signal to connect the first chamber to the supply line and connect the second chamber to the return line such that hydraulic fluid flows from the supply line to the first chamber, and hydraulic fluid flows from the second chamber to the return line causing the piston to move in the forward direction based on the desired trajectory.
4. The robot of claim 1 , wherein the controller is configured to provide the second signal to connect the second chamber to the supply line and connect the first chamber to the return line such that hydraulic fluid flows from the second chamber into the supply line, and hydraulic fluid flows from the return line to the first chamber.
5. The robot of claim 1 , wherein the controller is configured to provide the second signal to connect both the first chamber and the second chamber to the return line at the same time.
6. The robot of claim 1 , wherein the controller is configured to provide the third signal to connect the second chamber to the supply line and connect 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 based on the desired trajectory.
7. The robot of claim 1 , wherein the controller is configured to provide the second signal to the valve system to cause the piston to follow a modified trajectory when moving in the forward direction until the piston stops at the third position.
8. The robot of claim 7 , wherein the piston stops at the third position according to the modified trajectory earlier than the piston would have stopped at the second position if the piston had followed the desired trajectory.
9. The robot of claim 1 , wherein the controller is configured to provide the third signal to the valve system to cause the piston to resume following the desired trajectory in the reverse direction.
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 of the robot, the hydraulic actuator cylinder comprising 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, the valve system configured to couple the first chamber to the supply line of pressurized fluid and couple the second chamber to the return line to move the piston in a forward direction, wherein the first signal to the valve system causes the piston to follow a desired trajectory, the desired trajectory indicating movement by the piston in the forward direction from a first position until the piston stops at a second position, then move in a reverse direction;
when the piston is between the first position and the second position while moving in the forward direction:
receiving sensor information from a sensor system indicative of a speed of the piston and a pressure level in the second chamber; and
providing a second signal to the valve system based on the speed of the piston and the pressure level in the second chamber, the second signal causing the piston to override the desired trajectory and stop at a third position disposed between the first position and the second position; and
prior to when the piston would have reached the third position if the piston was moving in the reverse direction according to the desired trajectory, providing a third signal to the valve system to resume moving the piston in the reverse direction based on the desired trajectory.
11. The method of claim 10 , wherein providing the first signal comprises providing the first signal to connect the first chamber to the supply line and connect the second chamber to the return line such that hydraulic fluid flows from the supply line to the first chamber, and hydraulic fluid flows from the second chamber to the return line causing the piston to move in the forward direction based on the desired trajectory.
12. The method of claim 10 , wherein providing the second signal comprises providing the second signal to connect the second chamber to the supply line and connect the first chamber to the return line such that hydraulic fluid flows from the second chamber into the supply line, and hydraulic fluid flows from the return line to the first chamber.
13. The method of claim 10 , wherein providing the second signal comprises providing the second signal to connect both the first chamber and the second chamber to the return line at the same time.
14. The method of claim 10 , wherein providing the third signal comprises providing the third signal to connect the second chamber to the supply line and connect 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 based on the desired trajectory.
15. A non-transitory computer readable medium having stored therein instructions that, in response to execution by a controller of a robot, cause the controller to perform operations comprising:
providing a first signal to a valve system, wherein the robot includes a hydraulic actuator cylinder controlling motion of a member of the robot, the hydraulic actuator cylinder comprising 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, the valve system configured to couple the first chamber to the supply line of pressurized fluid and couple the second chamber to the return line to move the piston in a forward direction, wherein the first signal to the valve system causes the piston to follow a desired trajectory, the desired trajectory indicating movement by the piston in the forward direction from a first position until the piston stops at a second position, then move in a reverse direction;
when the piston is between the first position and the second position while moving in the forward direction:
receiving sensor information from a sensor system indicative of a speed of the piston and a pressure level in the second chamber; and
providing a second signal to the valve system based on the speed of the piston and the pressure level in the second chamber, the second signal causing the piston to override the desired trajectory and stop at a third position disposed between the first position and the second position; and
prior to when the piston would have reached the third position if the piston was moving in the reverse direction according to the desired trajectory, providing a third signal to the valve system to resume moving the piston in the reverse direction based on the desired trajectory.
16. The non-transitory computer readable medium of claim 15 , wherein providing the second signal comprises providing the second signal to the valve system to cause the piston to follow a modified trajectory when moving in the forward direction until the piston stops at the third position.
17. The non-transitory computer readable medium of claim 16 , wherein the piston stops at the third position according to the modified trajectory earlier than the piston would have stopped at the second position if the piston had followed the desired trajectory.
18. The non-transitory computer readable medium of claim 16 , wherein the operation of providing the third signal comprises providing the third signal to the valve system to cause the piston to resume following the desired trajectory in the reverse direction.