An Active Compensator for the Weakness of Superfluous Force in the Electro-hydraulic Force Control System with Perturbation of Displacement

That the output force of the electro-hydraulic force control system and the perturbation of displacement are in opposite directions causes superfluous force. Many attentions have been paid to this problem for many years and various compensation control schemes in a way of the electric controller are given. An electro-hydraulic servo valve whose movement direction of the main spool is opposite to that of the electro-hydraulic servo valve in the system is proposed as a compensation scheme here. The superfluous force is reduced by this compensation electro-hydraulic servo valve discharging the oil caused by the perturbation of displacement. With the help of mathematical modeling, a control signal expression of the compensation valve is obtained. The results of numerical simulation show that the superfluous force caused by the perturbation of displacement can be reduced by more than 97%; at the same time, it also effectively reduces the possibility that cavitation may emerge in the low pressure chamber of actuator. By taking a typical force system with a PID controller as an example, the results of numerical simulation show that the steady-state error of the force control system after the introduction of the active compensator is no more than 10%.