Actuator limit controller

A non-transitory computer readable medium having stored thereon executable instructions that, upon execution by a controller, cause the controller to perform functions comprising:

• receiving a command for moving a piston of a hydraulic actuator at a given speed in a given direction, wherein the hydraulic actuator includes a first chamber and a second chamber;
• based on the command, providing a signal to operate a valve assembly that controls flow of hydraulic fluid to the first chamber and controls flow of hydraulic fluid out of the second chamber so as to cause motion of the piston at the given speed in the given direction;
• receiving position information indicative of the piston reaching a first position at a first threshold distance from an end-stop of the hydraulic actuator;
• in response, making a first modification to the signal to the valve assembly so as to reduce a speed of the piston;
• receiving position information indicative of the piston reaching a second position at a second threshold distance closer to the end-stop of the hydraulic actuator;
• and
• in response, making a second modification to the signal to the valve assembly to cause the hydraulic fluid within the second chamber to apply a force on the piston in a direction away from the end-stop.

A system comprising:

• a source of pressurized hydraulic fluid;
• a return line;
• a hydraulic actuator cylinder having a piston slidably accommodated in the hydraulic actuator cylinder, the piston including a piston head and a rod extending from the piston head along a central axis direction, and an inside of the hydraulic actuator cylinder being divided into a first chamber and a second chamber by the piston head;
• a valve assembly that couples the source of pressurized hydraulic fluid to the first chamber and couples the second chamber to the return line;
• at least one processor;
• and
• a memory having stored thereon executable instructions that, upon execution by the at least one processor, cause the at least one processor to perform functions comprising:
• receiving a command for moving the piston at a given speed in a given direction;
• based on the command, providing a signal to operate the valve assembly to provide the pressurized hydraulic fluid to the first chamber and allow hydraulic fluid in the second chamber to flow from the second chamber to the return line so as to cause motion of the piston at the given speed in the given direction;
• receiving position information indicative of the piston reaching a first position at a first threshold distance from an end-stop of the hydraulic actuator cylinder;
• in response, making a first modification to the signal to the valve assembly so as to apply a first force on the piston in a direction away from the end-stop so as to reduce a speed of the piston;
• receiving position information indicative of the piston reaching a second position at a second threshold distance closer to the end-stop of the hydraulic actuator cylinder;
• and
• in response, making a second modification to the signal to the valve assembly so as to apply a second force on the piston in the direction away from the end-stop so as to further reduce the speed of the piston.