Eigenfrequency Identification of the Hydraulic Cylinder

The paper is focused on the identification of the eigenfrequency of the linear hydraulic servo drive, which consists of the flow control valve and hydraulic cylinder. The behaviour of the closed loop controlled hydraulic drive is given by the dynamic properties of the control valve and hydraulic cylinder. The dynamic properties of the hydraulic cylinder determine the structure and tuning of the controller of the closed loop position control system. For that reason it is important to know the eigenfrequency of the cylinder. The eigenfrequency of the cylinder depends on the moving mass and on the stiffness of the hydraulic cylinder, that means it depends on type of the hydraulic cylinder and on hydraulic capacities of the cylinder chambers and connecting pipelines. Due to the dependence of the hydraulic capacity on the piston position the stiffness and the eigenfrequency vary with the piston position. The identification of the eigenfrequency using the self-excited oscillations by the arranging a non-linear element in the feedback is presented in the paper. The identified curve describing the eigenfrequency of the cylinder in dependence on the piston position can be used for the controller tuning.