Legged robot passive fluid-based ankles with spring centering

1. A robot comprising:

a first hydraulic actuator cylinder connecting a first member to a second member, wherein the first hydraulic actuator cylinder comprises a first piston and a first chamber;

a second hydraulic actuator cylinder connecting the first member to the second member, wherein the second hydraulic actuator cylinder comprises a second piston and a second chamber;

a valve system comprising a rotary valve that includes a sleeve, a spool rotatable within the sleeve, and a rotary actuator coupled to the spool for rotation the spool within the sleeve, wherein the valve system is configured to: (i) couple a supply line of pressurized hydraulic fluid to the first chamber, (ii) couple the supply line to the second chamber, (iii) couple the first chamber to a return line, and (iv) couple the second chamber to the return line; and

a controller configured to:

determine a gait state of the robot, and

based on the determined gait state, provide a signal to the valve system to select whether to (i) connect the first chamber to the supply line and connect the second chamber to the return line, (ii) connect the second chamber to the supply lint and connect the first chamber to the return line, or (iii) connect both the first chamber and the second chamber to the return line.

2. The robot of claim 1 , wherein motion of either the first piston or the second piston in a given direction is accompanied by motion of the other piston in an opposite direction resulting in rotation of the first member about a joint relative to the second member.

3. The robot of claim 1 , wherein the robot includes a leg, and wherein the first member is a foot of the leg and the second member is a shin of the leg.

4. The robot of claim 3 , wherein the controller is further configured to:

determine, based on the determined gait state, whether the leg is in a liftoff phase, a swing phase, or a touchdown phase, wherein the controller is configured to provide the signal based on whether the at least one leg is in the liftoff phase, the swing phase, or the touchdown phase.

5. The robot of claim 4 , wherein the controller determines that the at least one leg is in a swing phase or a stance position, and where the controller is configured to, in response to the leg being in the swing phase or the stance position, provide the signal to the valve system to connect both the first chamber and the second chamber to the return line.

6. The robot of claim 1 , wherein the sleeve has a plurality of openings configured along a length of the sleeve, wherein the plurality of openings includes at least a first opening configured to receive pressurized fluid from the supply line, a second opening configured to communicate fluid to the return line, a third opening configured to communicate fluid to and from the first chamber, and a fourth opening configured to communicate fluid to and from the second chamber.

7. The robot of claim 6 , wherein the spool includes a respective plurality of openings along a length of the spool corresponding to the plurality of openings of the sleeve.

8. The robot of claim 7 , wherein the rotary actuator is configured to rotate the spool, based on the signal, to a given rotary position in a clockwise or a counter-clockwise direction to cause at least a partial alignment between a subset of the respective plurality of openings of the spool and a subset of the plurality of openings of the sleeve to: (i) connect one of the first chamber and the second chamber of the hydraulic actuator to the supply line, and connect the other chamber to the return line, or (ii) connect both the first chamber and the second chamber of the hydraulic actuator to the return line or the supply line.

9. A method comprising:

determining, by a controller of a robot, a gait state of the robot, wherein the robot includes a first hydraulic actuator cylinder connecting a first member to a second member, wherein the first hydraulic actuator cylinder comprises a first piston and a first chamber, wherein a second hydraulic, actuator cylinder connects the first member to the second member, wherein the second hydraulic actuator cylinder comprises a second piston and a second chamber, wherein the robot includes a valve system configured to: (i) couple a supply line of pressurized hydraulic fluid to the first chamber, (ii) couple the supply line to the second chamber, (iii) couple the first chamber to a return line, and (iv) couple the second chamber to the return line, and wherein the valve system is further configured to couple the first chamber and the second chamber to the supply line; and

based on the gait state, providing, by the controller, a signal to the valve system to select whether to (i) connect the first chamber to the supply line and connect the second chamber to the return line, (ii) connect the second chamber to the supply line and connect the first chamber to the return line, or (iii) connect both the first chamber and the second chamber to the return line.

10. The method of claim 9 , wherein motion of either the first piston or the second piston in a given direction is accompanied by motion of the other piston in an opposite direction resulting in rotation of the first member about a joint relative to the second member.

11. The method of claim 9 , wherein the robot includes a leg, and wherein the first member is a foot of the leg and the second member is a shin of the leg.

12. The method of claim 11 , further comprising:

determining, based on the determined gait state, whether the leg is in a liftoff phase, a swing phase, or a touchdown phase, wherein providing the signal is based on whether the leg is in the liftoff phase, the swing phase, or the touchdown phase.

13. The method of claim 12 , wherein, when the leg is in a swing phase, providing the signal causes the valve system to connect both the first chamber and the second chamber to the return line.

14. 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: determining a gait state of the robot, wherein the robot includes a first hydraulic actuator cylinder connecting a first member to a second member, wherein the first hydraulic, actuator cylinder comprises a first piston and a first chamber, wherein a second hydraulic actuator cylinder connects the first member to the second member, wherein the second hydraulic actuator cylinder comprises a second piston and a second chamber, wherein the robot includes a valve system configured to: (i) couple a supply line of pressurized hydraulic fluid to the first chamber, (ii) couple the supply line to the second chamber, (iii) couple the first chamber to a return line, and (iv) couple the second chamber to the return line, and wherein the valve system is further configured to couple the first chamber and the second chamber to the supply line; and

based on the gait state, providing a signal to the valve system to select whether to (i) connect the first chamber to the supply line and connect the second chamber to the return line, (ii) connect the second chamber to the supply line and connect the first chamber to the return line, or (iii) connect both the first chamber and the second chamber to the return line.

15. The non-transitory computer readable medium of claim 14 , wherein providing the signal comprises providing the signal to select whether to connect both the first chamber and the second chamber to the supply line.