Hybrid hydraulic and electrically actuated mobile robot
Example embodiments may relate to a robotic system that includes a hydraulic actuator and an electric actuator both coupled to a joint of the robotic system. Operation of the actuators may be based on various factors such as based on desired joint parameters. For instance, such desired joint parameters may include a desired output torque/force of the joint, a desired output velocity of the joint, a desired acceleration of the joint, and/or a desired joint angle, among other possibilities. Given a model of power consumption as well as a model of the actuators, the robotic system may determine operating parameters such as hydraulic and electric operating parameters as well as power system parameters, among others. The robotic system may then control operation of the actuators, using the determined operating parameters, to obtain the desired joint parameters such that power dissipation in the system is minimized (i.e., maximizing actuation efficiency).
1. A system comprising:
a hydraulic actuator coupled to a joint of a robotic device;
an electric actuator coupled to the joint of the robotic device;
a sensor configured to measure a load applied at the joint; and
a controller configured to:
determine a total output velocity to be applied by the hydraulic actuator and the electric actuator;
determine hydraulic operating parameters and electric operating parameters based on the load applied at the joint and the total output velocity;
determine whether the load applied at the joint is greater than a threshold load;
determine whether the total output velocity is less than a threshold velocity; and
when the load applied at the joint is greater than the threshold load and the total output velocity is less than the threshold velocity:
activate the hydraulic actuator to operate at the hydraulic operating parameters; and
halt actuation by the electric actuator.
2. The system of claim 1 , wherein the controller is further configured to, when the load applied at the joint decreases to a value less than the threshold load and the total output velocity is greater than the threshold velocity:
deactivate the hydraulic actuator to halt operating at the hydraulic operating parameters; and
active the electric actuator to operate at the electric operating parameters.
3. The system of claim 1 , further comprising a power system configured to supply power to the hydraulic and electric actuators, wherein the controller is further configured to:
determine power system parameters based the load applied at the joint and the total output velocity; and
operate the power system according to the determined power system parameters.
4. The system of claim 3 , wherein the power system parameters comprise one or more of the following parameters: a current, a voltage, a state of charge, and a battery temperature.
5. The system of claim 1 , wherein the hydraulic operating parameters comprise one or more of the following parameters: a pressurized fluid flow of the hydraulic actuator, a pressure drop in the hydraulic actuator, and a pressure in a pressure rail to which the hydraulic actuator is connected.
6. The system of claim 1 , wherein the electric operating parameters comprise one or more of the following parameters: an output torque to be applied by the electric actuator and an output velocity to be applied by the electric actuator.
7. The system of claim 1 , wherein the controller is further configured to determine a total power dissipation by the hydraulic actuator and the electric actuator, the total power dissipation comprising a sum of a resistive power dissipation of the electric actuator and a hydraulic power dissipation of the hydraulic actuator.
8. The system of claim 7 , wherein the resistive power dissipation of the electric actuator is a product of a resistance of the electric actuator and a square of a current supplied to the electric actuator.
9. The system of claim 7 , wherein the hydraulic power dissipation of the hydraulic actuator is a product of a pressurized fluid flow of the hydraulic actuator and of a difference between a pressure in a pressure rail to which the hydraulic actuator is connected and a pressure drop in the hydraulic actuator.
10. The system of claim 1 , wherein determining hydraulic operating parameters and electric operating parameters is further based at least in part on one or more of the following constant values: a gear ratio of the electric actuator, an effective gear ratio of the hydraulic actuator, a torque constant of the electric actuator, and a resistance of the electric actuator.
11. A robotic system comprising:
a joint;
a hydraulic actuator coupled to the joint;
an electric actuator coupled to the joint;
a sensor configured to measure a load applied to the joint;
a processor; and
data storage hardware in communication with the processor, the data storage hardware storing program instructions that when executed on the processor cause the processor to perform operations comprising:
determining a total output velocity to be applied by the hydraulic actuator and the electric actuator;
determining hydraulic operating parameters and electric operating parameters based on the load applied at the joint and the total output velocity;
determining whether the load applied at the joint is greater than a threshold load;
determining whether the total output velocity is less than a threshold velocity; and
when the load applied at the joint is greater than the threshold load and the total output velocity is less than the threshold velocity:
activating the hydraulic actuator to operate at the hydraulic operating parameters; and
halting actuation by the electric actuator.
12. The robotic system of claim 11 , wherein the operations further comprise, when the load applied at the joint decreases to a value less than the threshold load and the total output velocity is greater than the threshold velocity:
deactivating the hydraulic actuator to halt operating at the hydraulic operating parameters; and
activating the electric actuator to operate at the electric operating parameters.
13. The robotic system of claim 12 , further comprising a power system configured to supply power to the hydraulic and electric actuators, wherein the operations further comprise:
determining power system parameters based the load applied at the joint and the total output velocity; and
operating the power system according to the determined power system parameters.
14. A method comprising:
receiving, at a controller, a measured load applied to a joint of a robotic device from a sensor in communication with the controller;
determining, by the controller, a total output velocity to be applied by a hydraulic actuator and an electric actuator, the hydraulic actuator and the electric actuator both coupled to the joint of the robotic device;
determining, by the controller, hydraulic operating parameters and electric operating parameters based on the load applied at the joint and the total output velocity
determining, by the controller, whether the load applied at the joint is greater than a threshold load;
determining, by the controller, whether the total output velocity is less than a threshold velocity; and
when the load applied at the joint is greater than the threshold load and the total output velocity is less than the threshold velocity:
activating, by the controller, the hydraulic actuator to operate at the hydraulic operating parameters; and
halting, by the controller, actuation by the electric actuator.
15. The method of claim 14 , further comprising, when the load applied at the joint decreases to a value less than the threshold load and the total output velocity is greater than the threshold velocity:
deactivating, by the controller, the hydraulic actuator to halt operating at the hydraulic operating parameters; and
activating, by the controller, the electric actuator to operate at the electric operating parameters.