Abstract: For many application fields of the electro-hydraulic servo control system, such as plastics injection molding machine and press machine, in addition to the requirement of high position control accuracy, it’s necessary to control the moving speed of the actuator to minimize the impact and therefore to improve the production efficiency and product quality. To meet the requirement of position and speed hybrid control in the electro-hydraulic servo system, considering the effects of the force loads on the positioning accuracy, a compound control strategy with speed feedforward and position feedback and load compensation is proposed. The speed feedforward model is deduced, which reflects the magnitude of the load and the requirement of the given speed. And the generator of the given speed and position signals is designed, by which the undisturbed switching of the speed feedforward control and the position feedback control is realized. And the force load compensation formula is obtained through experiments and data fitting. The simulation and experimental results show that the position and speed of the actuator can be controlled simultaneously. And better performance can be achieved in both forward and reverse moving directions under different loads and with different desired speeds, without adjusting any control parameters.

Key words: Electro-hydraulic servo system, Feedforward control, Load force compensation, Position and speed hybrid control