Hydraulic pressure variation in a legged robot

1. A robot comprising:

one or more movable members;

a hydraulic system comprising at least (i) one or more hydraulic actuators configured to operate the one or more movable members, and (ii) a source of hydraulic fluid; and

a controller configured to perform operations comprising:

determining a task to be performed by the robot, wherein the task includes a plurality of phases;

causing hydraulic fluid having a first pressure level to flow from the source to the one or more hydraulic actuators for the robot to perform a first phase of the plurality of phases of the task;

based on a second phase of the task, determining a second pressure level for the hydraulic fluid; and

adjusting, based on the second pressure level, operation of the hydraulic system before the robot begins the second phase of the task.

2. The robot of claim 1 , further comprising:

one or more sensors coupled to the robot and configured to provide information associated with an environment of the robot, wherein the operations further comprise:

receiving from the one or more sensors information indicating that a disturbance to the robot is about to occur;

based on the information, determining a third pressure level for the hydraulic fluid; and

adjusting, based on the third pressure level, operation of the hydraulic system before the disturbance occurs.

3. The robot of claim 2 , wherein the operations further comprise:

upon the robot recovering from the disturbance, adjusting operation of the hydraulic system based on a pressure level associated with a phase during which the disturbance occurred.

4. The robot of claim 1 , wherein the source is an accumulator configured to store the hydraulic fluid, wherein the hydraulic system further comprises a pump, wherein the second pressure level is higher than the first pressure level, and wherein adjusting operation of the hydraulic system comprises:

causing the pump to provide pressurized hydraulic fluid to the accumulator until the hydraulic fluid in the accumulator has a pressure level within a threshold pressure value from the second pressure level.

5. The robot of claim 4 , wherein causing the pump to provide the pressurized fluid to the accumulator comprises:

causing the pump to start providing the pressurized fluid to the accumulator at a predefined period of time before the robot begins the second phase of the task.

6. The robot of claim 5 , wherein causing the pump to start providing the pressurized fluid to the accumulator at the predefined period of time before the robot begins the second phase of the task involves the hydraulic fluid in the accumulator reaching the pressure level within the threshold pressure value from the second pressure level over a period of time less than or equal to the predefined period of time.

7. The robot of claim 1 , wherein the source is an accumulator configured to store the hydraulic fluid, wherein the hydraulic system further comprises a pump configured to provide pressurized hydraulic fluid to the accumulator, wherein the second pressure level is less than the first pressure level, and wherein adjusting operation of the hydraulic system comprises:

causing the pump to stop providing the hydraulic fluid to the accumulator at least until a pressure level of the hydraulic fluid in the accumulator is within a threshold pressure value from the second pressure level.

8. The robot of claim 1 , wherein the hydraulic system further comprises:

a reservoir containing hydraulic fluid having a given pressure level lower than a pressure level of the hydraulic fluid of the source; and

a dump valve,

wherein adjusting operation of the hydraulic system comprises, in response to determining the second pressure level to be less than the first pressure level, opening the dump valve until the pressure level of the hydraulic fluid of the source is within a threshold pressure value from the second pressure level.

9. A method comprising:

determining a task to be performed by a robot, wherein the robot includes one or more movable members and a hydraulic system, wherein the hydraulic system includes at least (i) one or more hydraulic actuators configured to operate the one or more movable members, and (ii) a source of hydraulic fluid, wherein the task includes a plurality of phases;

causing hydraulic fluid having a first pressure level to flow from the source to the one or more hydraulic actuators for the robot to perform a first phase of the plurality of phases of the task;

based on a second phase of the task, determining a second pressure level for the hydraulic fluid; and

adjusting, based on the second pressure level, operation of the hydraulic system before the robot begins the second phase of the task.

10. The method of claim 9 , further comprising:

receiving information indicating that the robot has been, or is about to be, subjected to a disturbance to a balance of the robot;

based on the information, determining a third pressure level for the hydraulic fluid; and

adjusting, based on the third pressure level, operation of the hydraulic system.

11. The method of claim 10 , further comprising:

upon the robot recovering from the disturbance, adjusting operation of the hydraulic system based on a pressure level associated with a phase during which the disturbance occurred.

12. The method of claim 9 , wherein the source is an accumulator configured to store the hydraulic fluid, wherein the hydraulic system further comprises a pump, wherein the second pressure level is higher than the first pressure level, and wherein adjusting operation of the hydraulic system comprises:

causing the pump to provide pressurized hydraulic fluid to the accumulator until the hydraulic fluid in the accumulator has a pressure level within a threshold pressure value above the second pressure level.

13. The method of claim 12 , wherein causing the pump to provide the pressurized fluid to the accumulator comprises:

causing the pump to start providing the pressurized fluid to the accumulator at a predefined period of time before the robot begins the second phase of the task.

14. The method of claim 13 , wherein causing the pump to start providing the pressurized fluid to the accumulator at the predefined period of time before the robot begins the second phase of the task involves the pressure level reaching the threshold pressure value from the second pressure level over a period of time less than or equal to the predefined period of time.

15. The method of claim 9 , wherein the source is an accumulator configured to store the hydraulic fluid, wherein the hydraulic system further comprises a pump configured to provide pressurized hydraulic fluid to the accumulator, wherein the second pressure level is less than the first pressure level, and wherein adjusting operation of the hydraulic system comprises:

causing the pump to stop providing the hydraulic fluid to the accumulator at least until a pressure level of the hydraulic fluid in the accumulator is within a threshold pressure value from the second pressure level.

16. The method of claim 9 , wherein the hydraulic system further comprises (i) a reservoir containing hydraulic fluid having a given pressure level lower than a pressure level of the hydraulic fluid of the source, and (ii) a dump valve, and wherein adjusting operation of the hydraulic system comprises:

in response to determining the second pressure level to be less than the first pressure level, actuating the dump valve until the pressure level of the hydraulic fluid of the source is within a threshold pressure value from the second pressure level.

17. A non-transitory computer readable medium having stored thereon instructions that, when executed by a controller of a robot, cause the robot to perform operations comprising:

determining a task to be performed by the robot, wherein the robot includes one or more movable members and a hydraulic system, wherein the hydraulic system includes at least (i) one or more hydraulic actuators configured to operate the one or more movable members, and (ii) a source of hydraulic fluid, wherein the task includes a plurality of phases;

causing hydraulic fluid having a first pressure level to flow from the source to the one or more hydraulic actuators for the robot to perform a first phase of the plurality of phases of the task;

based on a second phase of the task, determining a second pressure level for the hydraulic fluid; and

adjusting, based on the second pressure level, operation of the hydraulic system before the robot begins the second phase of the task.

18. The non-transitory computer readable medium of claim 17 , wherein the operations further comprise:

receiving information indicating that the robot has been, or is about to be, subjected to a disturbance to a balance of the robot;

based on the information, determining a third pressure level for the hydraulic fluid; and

adjusting, based on the third pressure level, operation of the hydraulic system.

19. The non-transitory computer readable medium of claim 17 , wherein the source is an accumulator configured to store the hydraulic fluid, wherein the hydraulic system further comprises a pump, wherein the second pressure level is higher than the first pressure level, and wherein adjusting operation of the hydraulic system comprises:

causing the pump to provide pressurized hydraulic fluid to the accumulator until the hydraulic fluid in the accumulator has a pressure level within a threshold pressure value above the second pressure level.

20. The non-transitory computer readable medium of claim 19 , wherein causing the pump to provide the pressurized fluid to the accumulator comprises:

causing the pump to start providing the pressurized fluid to the accumulator at a predefined period of time before the robot begins the second phase of the task such that the hydraulic fluid in the accumulator reaches the pressure level within the threshold pressure value from the second pressure level over a period of time less than or equal to the predefined period of time.