Regenerative pumping system and method

A computer implemented method for determining piston position and for monitoring and maintaining stroke rate in a hydraulic lift system comprising a lift cylinder, a reversible hydraulic pump having a swash plate, a motor, a flywheel, and an ultrasonic sensor located on an upstroke side of a piston of the lift cylinder for providing a sensed piston position;

• said computer implemented method comprising the steps of:
• i. predicting a nominal amount of fluid passing through the hydraulic pump, from swash plate position data of the swash plate of the hydraulic pump and from a speed of the motor;
• ii. estimating, from pump pressure data, a flow rate of fluid lost to the system through internal leakage in the pump;
• iii. compensating the nominal fluid flow through the hydraulic pump by the flow rate of fluid lost to the system through internal leakage to determine a leakage-compensated fluid flow;
• iv. determining, using the leakage-compensated fluid flow through the hydraulic pump and from dimensions of the lift cylinder, an estimated position of the piston;
• v. receiving the sensed piston position from the ultrasonic sensor and comparing the sensed piston position with the estimated position of the piston;
• and
• vi. adopting, if the sensed piston position is determined to be not following a target piston position or not available from the ultrasonic sensor, the estimated piston position as the piston position.