The fluid power system is applied to various fields of modern industries because it is able both to generate great force or torque and to control precisely the movement of hydraulic actuators. Amongst those to which the fluid power is applied, active suspension system and four wheel steering system on a passenger car have the force control hydraulic servosystem.
The electro-hydraulic servo valve and the proportional pressure control valve can be used as control valve, an essential component of the force control hydraulic servosystem. The electro-hydraulic servo valve requires feedback of control output in the hydraulic servosystem. But the proportional pressure control valve does not require feedback of control output in the force control servosystem.
In this paper, the linear model of the hydraulic servosystem for force tracking control which consists of a proportional pressure control valve and a double acting cylinder is derived. The performance of the hydraulic servosystem is analysed through computer simulations. And the limitations on designing the controller in feedback control system are studied. In addition, performance of position tracking control system as well as the limitations on feedback control is examined.
In the force tracking hydraulic servosystem, the velocity of piston acts as feedback term from the position output of the cylinder to pressure differential across the piston. Therefore, the poles of the plant manifest themselves as the zeros of the open-loop transfer function. Moreover, these zeros can't be changed via feedback and simple algorithms are severely bandwidth limited. In the position tracking control system, by the stable pole-zero cancellation the poles of the plant do not appear as the zeros of the open-loop transfer function.
The result from the study shows that a simple algorithm for force tracking purposes beyond the bandwidth limitation is not suitable and the need of more advanced algorithms are confirmed. On the other hand, It is confirmed that the position control system is properly controlled by means of simple algorithms.