Therefore, for a given voltage, a linear relationship exists between displacement and force, and the slope of this straight line depends on the stiffness of the ring bender. This actuation force, which is proportional to the applied voltage, is gradually reduced when the ring bender moves from its neutral position because of its stiffness. Like all piezo-actuators, the ring bender behaves like a spring of stiffness k rb to which a force F b (called blocking force) is applied. Figure 2b shows the force–displacement relationship of a ring bender as a function of the applied voltage ranging from 0 to + V max (a similar graph is valid for − V max ≤ V amp ≤ 0). Positive values of the voltage allow the ring bender to move in a direction, whereas negative values enable the movement in the opposite direction. Novel Servovalve ArchitectureĪ picture of a ring bender is provided in Figure 2a it is an annular disc that deforms when a voltage from an amplifier V amp (comprised between − V max and + V max) is applied to it. The transient behavior of the obtained valve configuration is finally assessed using the full numerical model solved by SimScape Fluids. This design procedure, which has general validity, is then applied to a specific case of a valve providing 65.8 L/min for a pressure drop of 210 bar. Some of these equations are then simplified and combined to obtain a simplified model allowing, for a given main spool geometry, the determination of correct values for the main geometrical parameters of the pilot stage. A full numerical model of the entire valve concept, providing the prediction of the transient behavior of the valve, is then described thoroughly. The proposed servovalve concept is described in the next section along with a discussion of the advances in the study of this novel architecture. This architecture is intended to reduce not only the complexity but also the internal leakage at null of typical two-stage servovalves, with huge advantages in terms of costs, manufacturing times, and power consumption. In the present work, we studied a novel architecture of servovalve based on the use of two ring benders in place of the torque motor. For this reason, the proposed valve can be regarded as a “clean” component for energy conversion, having lower energy consumption than commercially available servovalves. This design procedure is applied to a 7 mm diameter main spool afterward, a detailed numerical model of the entire valve, solved by SimScape Fluids software, is employed to demonstrate that the response of the main stage valve is very rapid while ensuring negligible internal leakage through the piezo-valves when the main stage is closed (resulting in lower power consumption). In particular, a simplified numerical model is developed to provide a design tool that allows, for a given main stage spool, the values of the geometrical parameters of the pilot stage to be chosen along with the characteristics of the ring bender. The valve assessment is completed in the present study, since the entire valve architecture (main stage + pilot stage) is investigated. The low complexity and the negligible internal leakage of the piezo-valves are accompanied by the high response speed typical of piezoelectric actuators. With this novel architecture, the typical drawbacks of two-stage servovalves can be overcome, such as the high complexity of the torque motor and the high internal leakage in the pilot stage when the main valve is at rest in the neutral position (null). The novelty of the proposed configuration is the torque motor being removed and replaced with two small two-way two-position (2/2) valves actuated by piezoelectric ring benders, which can effectively control the opening degree of a main spool valve. In part I of this study, we experimentally and numerically investigated the pilot stage of a novel two-stage servovalve architecture.
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