Analysis and Experimental Study on Closed-loop Stiffness of Hydraulic Servo System

A kind of valve controlled asymmetric cylinder system is modeled as a six order state space model by bond graphs. Based on the closed loop transfer function, the stiffness characteristic and influencing factors of the hydraulic servo system is studied. An analytical expression of the closed-loop stiffness of the hydraulic servo system is finally obtained. It is proposed that the closed loop stiffness of the hydraulic positioning servo system is only related to the pressure of the oil supply, and it is not related to the initial position of the cylinder piston and the proportional gain. And the load force is inversely proportional to the square of displacement increment of servo cylinder piston. An experimental study is conducted on the closed-loop stiffness of the hydraulic servo system. In different conditions of oil supply pressure, proportional gain and initial position of servo cylinder piston, the displacement response process of servo cylinder is tested under external load. The experimental results show that the closed-loop stiffness of the hydraulic positioning servo system is significantly related to the oil supply pressure, and it is not obviously related to the initial position of the cylinder piston and the proportional gain. In addition, the load force is approximately in inverse proportion to the square of the displacement increment of the servo cylinder. © 2018 Journal of Mechanical Engineering.