Modeling hydraulic actuator mechanical dynamics from pressure measured at control valve ports

The goal of this article is to formulate and validate a model for the prediction of the mechanical dynamics of hydraulic actuators controlled by means of proportional directional valves (PDVs). The model inputs are the pressure at the PDVs ports and the current to the solenoids: no further input is required even when additional elements are installed in the line between PDV and actuator. The model finds application in closed-loop control of mobile electrohydraulic machines for load handling, construction and agriculture. These machines are typically based on open-loop control of the actuator speed. Nevertheless, these machines are often characterized by non-cyclical operation, large disturbances (e.g. drive on uneven ground) and time-varying parameters (e.g. load mass). Due to these features, closed-loop control has potential to improve the machine dynamics with consequent benefits in terms of productivity and operation safety. However, because of the harsh working conditions, the installation of feedback sensors in proximity of the hydraulic actuator is impractical and rarely exploited. The proposed model offers a solution to implement closed-loop control using pressure sensors in a compact and reliable arrangement, next to PDVs ports. The case study is a hydraulic crane using PDVs in combination with counterbalance valves (CBVs) to control the mechanical arms. The experiments were performed without altering the basic hydraulic circuit of the commercial crane and using an electronic hardware with performance comparable to standard controllers for mobile hydraulics. The results show the accuracy of the model for all operating conditions, including the assistive load condition.