Discretized valve state control for multi-level hydraulic systems

1. A method comprising:

based on a load on one or more hydraulic actuators of a hydraulic drive system of a robotic device, determining, by a control system of the robotic device, an actuation pressure to actuate the one or more hydraulic actuators;

based on the determined actuation pressure, selecting, by the control system, a pressure rail from among a set of pressure rails at respective pressures, wherein the selected pressure rail supplies pressurized hydraulic fluid at a supply pressure, and wherein the supply pressure is, among the respective pressures, at a lowest pressure that exceeds the determined actuation pressure;

causing, by the control system, one or more valves to connect the selected pressure rail to a metering valve such that hydraulic fluid at approximately the supply pressure flows from the selected pressure rail to the metering valve;

causing, by the control system, the hydraulic drive system to operate in a discrete mode in which the metering valve opens such that hydraulic fluid flows from the selected pressure rail through the metering valve to the one or more hydraulic actuators at approximately the supply pressure;

receiving, by the control system, from one or more sensors on the robotic device, data indicative of one or more physical features of an environment in which the robotic device is operating; and

based on the data indicative of the one or more physical features of the environment, causing, by the control system, the hydraulic drive system to operate in a continuous mode in which the metering valve throttles the hydraulic fluid such that the supply pressure is reduced to approximately the determined actuation pressure.

2. The method of claim 1 , wherein the robotic device comprises at least one articulable leg, and wherein the at least one articulable leg comprises the one or more hydraulic actuators, the method further comprising:

based on the data indicative of the one or more physical features of the environment, determining that the robotic device is traversing uneven terrain; and

in response to determining that the robotic device is traversing uneven terrain, causing the hydraulic drive system to operate in the continuous mode.

3. The method of claim 1 , the method further comprising:

receiving data indicating a load that that the robotic device is carrying;

based on the received data, determining that the robotic device is carrying an unbalanced load; and

responsive to the determining that the robotic device is carrying the unbalanced load and based on the data indicative of the one or more physical features of the environment, causing the hydraulic drive system to operate in the continuous mode.

4. The method of claim 1 , further comprising:

receiving, from the one or more sensors on the robotic device, additional data indicative of one or more additional physical features of the environment in which the robotic device is operating;

based on the additional data indicative of the one or more additional physical features of the environment, causing the hydraulic drive system to operate in the discrete mode.

5. The method of claim 1 , wherein the robotic device comprises at least one articulable leg, and wherein the at least one articulable leg comprises the one or more hydraulic actuators, the method further comprising:

based on the data indicative of the one or more physical features of the environment, determining that the robotic device is traversing even terrain; and

in response to determining that the robotic device is traversing even terrain, causing the hydraulic drive system to operate in the discrete mode.

6. The method of claim 1 , wherein the robotic device comprises at least one articulable leg configured to move the robotic device according to a running gait, and wherein the at least one articulable leg comprises the one or more hydraulic actuators, the method further comprising:

determining that the robotic device is moving according to the running gait; and

responsive to the determining that the robotic device is moving according to the running gait, causing the hydraulic drive system to operate in the discrete mode.

7. A hydraulic drive system comprising:

one or more hydraulic actuators of a robotic device;

a plurality of pressure rails at respective pressures;

one or more valves;

a metering valve; and

a control system configured to:

based on a load on the one or more hydraulic actuators of the robotic device, determine an actuation pressure to actuate the one or more hydraulic actuators;

based on the determined actuation pressure, select a pressure rail from among the plurality of pressure rails, wherein the selected pressure rail supplies pressurized hydraulic fluid at a supply pressure, and wherein the supply pressure is, among the respective pressures, at a lowest pressure that exceeds the determined actuation pressure;

cause the one or more valves to connect the selected pressure rail to the metering valve such that hydraulic fluid at approximately the supply pressure flows from the selected pressure rail to the metering valve;

cause the hydraulic drive system to operate in a discrete mode in which the metering valve opens such that hydraulic fluid flows from the selected pressure rail through the metering valve to the one or more hydraulic actuators at approximately the supply pressure;

receiving, from one or more sensors on the robotic device, data indicative of one or more physical features of an environment in which the robotic device is operating; and

based on the data indicative of the one or more physical features of the environment, cause the hydraulic drive system to operate in a continuous mode in which the metering valve throttles the hydraulic fluid such that the supply pressure is reduced to approximately the determined actuation pressure.

8. The hydraulic drive system of claim 7 , wherein the robotic device comprises at least one articulable leg, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the control system if further configured to:

based on the data indicative of the one or more physical features of the environment, determine that the robotic device is traversing uneven terrain; and

in response to determining that the robotic device is traversing uneven terrain, cause the hydraulic drive system to operate in the continuous mode.

9. The hydraulic drive system of claim 7 , wherein the control system if further configured to:

receive data indicating a load that that the robotic device is carrying;

based on the received data, determine that the robotic device is carrying an unbalanced load; and

responsive to determining that the robotic device is carrying the unbalanced load and based on the data indicative of the one or more physical features of the environment, cause the hydraulic drive system to operate in the continuous mode.

10. The hydraulic drive system of claim 7 , wherein the control system if further configured to:

receive, from the one or more sensors on the robotic device, additional data indicative of one or more additional physical features of the environment in which the robotic device is operating;

based on the additional data indicative of the one or more additional physical features of the environment, cause the hydraulic drive system to operate in the discrete mode.

11. The hydraulic drive system of claim 7 , wherein the robotic device comprises at least one articulable leg, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the control system if further configured to:

based on the data indicative of the one or more physical features of the environment, determine that the robotic device is traversing even terrain; and

in response to determining that the robotic device is traversing even terrain, cause the hydraulic drive system to operate in the discrete mode.

12. The hydraulic drive system of claim 7 , wherein the robotic device comprises at least one articulable leg configured to move the robotic device according to a running gait, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the control system if further configured to:

determine that the robotic device is moving according to the running gait; and

responsive to determining that the robotic device is moving according to the running gait, cause the hydraulic drive system to operate in the discrete mode.

13. A non-transitory computer readable medium having stored thereon instructions that, when executed by a computing device, cause the computing device to perform operations comprising:

based on a load on one or more hydraulic actuators of a hydraulic drive system of a robotic device, determining, by a processor of the computing device, an actuation pressure to actuate the one or more hydraulic actuators;

based on the determined actuation pressure, selecting, by the processor, a pressure rail from among a set of pressure rails at respective pressures, wherein the selected pressure rail supplies pressurized hydraulic fluid at a supply pressure, and wherein the supply pressure is, among the respective pressures, at a lowest pressure that exceeds the determined actuation pressure;

causing, by the processor, one or more valves to connect the selected pressure rail to a metering valve such that hydraulic fluid at approximately the supply pressure flows from the selected pressure rail to the metering valve;

causing, by the processor, the hydraulic drive system to operate in a discrete mode in which the metering valve opens such that hydraulic fluid flows from the selected pressure rail through the metering valve to the one or more hydraulic actuators at approximately the supply pressure;

receiving, by the processor, from one or more sensors on the robotic device, data indicative of one or more physical features of an environment in which the robotic device is operating; and

based on the data indicative of the one or more physical features of the environment, causing, by the processor, the hydraulic drive system to operate in a continuous mode in which the metering valve throttles the hydraulic fluid such that the supply pressure is reduced to approximately the determined actuation pressure.

14. The non-transitory computer readable medium of claim 13 , wherein the robotic device comprises at least one articulable leg, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the operations further comprise:

based on the data indicative of the one or more physical features of the environment, determining that the robotic device is traversing uneven terrain; and

in response to determining that the robotic device is traversing uneven terrain, causing the hydraulic drive system to operate in the continuous mode.

15. The non-transitory computer readable medium of claim 13 , wherein the operations further comprise:

receiving data indicating a load that that the robotic device is carrying;

based on the received data, determining that the robotic device is carrying an unbalanced load; and

responsive to determining that the robotic device is carrying the unbalanced load and based on the data indicative of the one or more physical features of the environment, causing the hydraulic drive system to operate in the continuous mode.

16. The non-transitory computer readable medium of claim 13 , wherein the operations further comprise:

receiving, from the one or more sensors on the robotic device, additional data indicative of one or more additional physical features of the environment in which the robotic device is operating;

based on the additional data indicative of the one or more additional physical features of the environment, causing the hydraulic drive system to operate in the discrete mode.

17. The non-transitory computer readable medium of claim 13 , wherein the robotic device comprises at least one articulable leg configured to move the robotic device according to a running gait, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the operations further comprise:

determining that the robotic device is moving according to the running gait; and

responsive to determining that the robotic device is moving according to the running gait, causing the hydraulic drive system to operate in the discrete mode.

18. The method of claim 1 , wherein the robotic device comprises at least one articulable leg, and wherein the at least one articulable leg comprises the one or more hydraulic actuators, the method further comprising:

determining that the robotic device is moving according to a climbing gait; and

in response to determining that the robotic device is moving according to the climbing gait and based on the data indicative of the one or more physical features of the environment, causing the hydraulic drive system to operate in the continuous mode.

19. The hydraulic drive system of claim 7 , wherein the robotic device comprises at least one articulable leg, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the control system is further configured to:

determine that the robotic device is moving according to a climbing gait; and

in response to determining that the robotic device is moving according to the climbing gait and based on the data indicative of the one or more physical features of the environment, cause the hydraulic drive system to operate in the continuous mode.

20. The non-transitory computer readable medium of claim 13 , wherein the robotic device comprises at least one articulable leg, wherein the at least one articulable leg comprises the one or more hydraulic actuators, and wherein the operations further comprise:

based on the data indicative of the one or more physical features of the environment, determining that the robotic device is traversing even terrain; and

in response to determining that the robotic device is traversing even terrain, causing the hydraulic drive system to operate in the discrete mode.