Development of a new hydraulic servo cylinder with mechanical feedback

This paper presents a new type of hydraulic servo cylinder, which is charac terized by its mechanical feedback structure. The feedback mechanism consis ts of two poppet valves, a plate spring and a steel ball. The hydraulic pre ssure in each cylinder chamber is controlled by a poppet valve, which is ac tivated by a solenoid. The solenoid input current opens the valve, which re sults in a pressure drop in the corresponding cylinder chamber, and initiat es 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 i ts new equilibrium position, controlled by the solenoid current. The charac teristics of this hydraulic servo cylinder are studied by stability analysi s, as well as the transient and steady-state responses to step inputs. Anal ytical 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. (C) 1999 Elsevier Science Ltd. All rights reserved.