Systems and methods for processing ultrasonic signals to detect the position of a piston

A method for detecting the position of a piston within a cylinder of a hydraulic actuator, the method comprising:

• providing the hydraulic actuator including the cylinder and the piston adapted to move linearly within the cylinder, the piston having a first surface and a second surface that is displaced from the first surface by a known distance, and an ultrasonic transducer adapted to detect an ultrasonic signal indicative of a position of the piston within the cylinder;
• receiving, from the ultrasonic transducer, an ultrasonic signal indicative of the position of the piston within the cylinder;
• implementing a cross-correlation function to identify a first echo and a second echo in the ultrasonic signal;
• determining a velocity of the first echo or the second echo;
• determining whether a difference between the velocity of the first echo or the second echo and a theoretical velocity is less than a threshold;
• and
• in response to determining that the difference between the velocity of the first echo or the second echo and a theoretical velocity is less than a threshold, determining the position of the piston within the cylinder based in part on a time shift between the first echo and the second echo in the ultrasonic signal.

A hydraulic actuator, comprising:

• a cylinder having a base portion;
• a piston adapted to move within an interior of the cylinder, the piston having a first surface and a second surface that is indented relative to the first surface by a known distance;
• an ultrasonic transducer disposed on the base portion and adapted to detect an ultrasonic signal indicative of a position of the piston within the cylinder;
• and
• a controller coupled to the ultrasonic transducer, the controller is adapted to:
• receive the ultrasonic signal from the ultrasonic transducer;
• implement a cross-correlation function to identify a first echo and a second echo in the ultrasonic signal;
• determine a velocity of the first echo and the second echo;
• determine whether a difference between the velocity of the first echo and the second echo and a theoretical velocity is less than a threshold;
• and
• in response to determining that the difference between the velocity of the first echo and the second echo and a theoretical velocity is less than a threshold, determine a distance between the base portion and the first surface of the piston independent of a pressure or a temperature within the interior of the cylinder.