Development of a new hydraulic servo cylinder with mechanical feedback

This paper presents a new type of hydraulic servo cylinder, which is characterized by its mechanical feedback structure. The feedback mechanism consists of two poppet valves, a plate spring and a steel ball. The hydraulic pressure in each cylinder chamber is controlled by a poppet valve, which is activated by a solenoid. The solenoid input current opens the valve, which results in a pressure drop in the corresponding cylinder chamber, and initiates the piston motion. The piston is specially designed to generate a force to close the valve in proportion to its distance from the cylinder center, by means of a steel ball and a plate spring. Finally, the piston moves to its new equilibrium position, controlled by the solenoid current. The characteristics of this hydraulic servo cylinder are studied by stability analysis, as well as the transient and steady-state responses to step inputs. Analytical studies and computer simulations are executed to verify the effects of the various design parameters on the performance. A prototype hydraulic servo cylinder is developed and tested. The results confirm the successful operation of the servo cylinder, and show consistency with the theoretical studies.