Velocity control of actuators in hydraulic manipulators based on a pressure-independent model with application to a telescopic handler

Hydraulic cylinders are critical components in industrial machinery, providing the large actuation forces required for lifting and positioning of heavy loads. Reliable control of hydraulic actuators is a core objective for realization of full automation as well as implementation of assistance functions enhancing efficiency, energy conservation and operational safety. Model-based approaches address the inherent challenges of nonlinear dynamics and varying external influences. However, complex models increase computational effort and the number of required sensors while giving up generality. This work presents the design of a cylinder velocity controller that incorporates a simplified model approximating the highly dynamic hydraulic system behavior. The proposed control scheme requires only cylinder position signals and consists of a feed-forward component effectively compensating the simplified system dynamics in combination with an online implementation of the Linear Quadratic Regulator for state feedback. Desired trajectories for the states of each individual cylinders result from generation of S-curves and are compared to estimated states from an Extended Kalman Filter. The resulting pressure-independent, model-based velocity control method is validated through measurements with a telescopic handler. However, the approach can be expanded and adapted to various hydraulic machinery.