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 computer-implemented method when executed by a controller of a robot causes the controller to perform operations comprising:
determining a piston position difference between a desired position and a measured position of a piston of a hydraulic actuator, the piston position difference representing a piston position error;
generating a piston position signal using the piston position error;
determining a piston velocity difference between a desired velocity and a measured velocity of the piston, the piston velocity difference representing a piston velocity error;
generating a piston velocity signal using the piston velocity error;
determining a piston force difference between a desired force and a measured force applied by the piston to an external environment, the piston force difference representing a piston force error;
generating a piston force signal using the piston force error; and
generating a valve command to control a valve using the piston position signal, the piston velocity signal, and the piston force signal.
2. The method of claim 1 , wherein generating the valve command comprises summing the piston position signal, the piston velocity signal, and the piston force signal.
3. The method of claim 2 , wherein generating the valve command further comprises adjusting the sum of the piston position signal, the piston velocity signal, and the piston force signal using a slew rate limitation threshold.
4. The method of claim 1 , wherein determining the piston position difference comprises receiving sensor data from a position sensor coupled to the piston.
5. The method of claim 1 , wherein generating the piston position signal comprises:
adjusting the piston position error by a proportional position gain;
generating a piston position integrated signal using an integration of the piston position error; and
summing the adjusted piston position error and the piston position integrated signal.
6. The method of claim 1 , wherein determining the piston velocity difference comprises receiving sensor data from a velocity sensor coupled to the piston.
7. The method of claim 1 , wherein generating the piston velocity signal comprises: adjusting the piston velocity error using a first proportional velocity gain;
adjusting the desired velocity using a feedforward gain;
adjusting the measured velocity using a second proportional velocity gain; and
summing the adjusted piston velocity error, the adjusted desired velocity, and the adjusted measured velocity.
8. The method of claim 1 , wherein determining the piston force difference comprises receiving sensor data from a force sensor coupled to the piston.
9. The method of claim 1 , wherein generating the piston force signal comprises adjusting the piston force error using a proportional force gain.
10. The method of claim 1 , wherein the valve command controls opening at least one orifice of the valve.
11. A robot comprising:
a controller; and
memory hardware in communication with the controller, the memory hardware storing instructions that when executed by the controller cause the controller to perform operations comprising:
determining a piston position difference between a desired position and a measured position of a piston of a hydraulic actuator, the piston position difference representing a piston position error;
generating a piston position signal using the piston position error;
determining a piston velocity difference between a desired velocity and a measured velocity of the piston, the piston velocity difference representing a piston velocity error;
generating a piston velocity signal using the piston velocity error;
determining a piston force difference between a desired force and a measured force applied by the piston to an external environment, the piston force difference representing a piston force error;
generating a piston force signal using the piston force error; and
generating a valve command to control a valve using the piston position signal, the piston velocity signal, and the piston force signal.
12. The robot of claim 11 , wherein generating the valve command comprises summing the piston position signal, the piston velocity signal, and the piston force signal.
13. The robot of claim 12 , wherein generating the valve command further comprises adjusting the sum of the piston position signal, the piston velocity signal, and the piston force signal using a slew rate limitation threshold.
14. The robot of claim 11 , wherein determining the piston position difference comprises receiving sensor data from a position sensor coupled to the piston.
15. The robot of claim 11 , wherein generating the piston position signal comprises:
adjusting the piston position error by a proportional position gain;
generating a piston position integrated signal using an integration of the piston position error; and
summing the adjusted piston position error and the piston position integrated signal.
16. The robot of claim 11 , wherein determining the piston velocity difference comprises receiving sensor data from a velocity sensor coupled to the piston.
17. The robot of claim 11 , wherein generating the piston velocity signal comprises:
adjusting the piston velocity error using a first proportional velocity gain;
adjusting the desired velocity using a feedforward gain;
adjusting the measured velocity using a second proportional velocity gain; and summing the adjusted piston velocity error, the adjusted desired velocity, and the adjusted measured velocity.
18. The robot of claim 11 , wherein determining the piston force difference comprises receiving sensor data from a force sensor coupled to the piston.
19. The robot of claim 11 , wherein generating the piston force signal comprises adjusting the piston force error using a proportional force gain.
20. The robot of claim 11 , wherein the valve command controls opening at least one orifice of the valve.