Chulhee Han

A new type of a direct-drive valve system driven by a piezostack actuator and sliding spool

A direct-drive valve (DDV) system is a kind of electrohydraulic servo valve system, in which the actuator directly drives the spool of the valve. In conventional DDV systems, the spool is generally driven by an electromagnetic actuator. Performance characteristics such as frequency bandwidth of DDV systems driven by the electromagnetic actuator are limited due to the actuator response property. In order to improve the performance characteristics of conventional DDV systems, in this work a new configuration for a direct-drive valve system actuated by a piezostack actuator with a flexible beam mechanism is proposed (in short, a piezo-driven DDV system). Its benefits are demonstrated through both simulation and experiment. After describing the geometric configuration and operational principle of the proposed valve system, a governing equation of the whole system is obtained by combining the dynamic equations of the fluid part and the structural parts: the piezostack, the flexible beam, and the spool. In the structural parts of the piezostack and flexible beam, a lumped parameter modeling method is used, while the conventional rule of the fluid momentum is used for the fluid part. In order to evaluate valve performances of the proposed system, an experimental apparatus consisting of a hydraulic circuit and the piezo-driven DDV system is established. The performance characteristics are evaluated in terms of maximum spool displacement, flow rate, frequency characteristics, and step response. In addition, in order to advocate the feasibility of the proposed dynamic model, a comparison between simulation and experiment is undertaken.

Performance evaluation of a piezoactuator-based single-stage valve system subjected to high temperature

In this paper, a novel single-stage valve system activated by a piezostack actuator is proposed and experimentally evaluated at both room temperature (20 °C) and high temperature (100 °C) conditions. A hinge-lever displacement amplifier is adopted in the valve system to magnify the displacement generated from the piezostack actuator. After explaining the operating principle of the proposed piezostack-driven single-stage valve system, the geometric dimensions and mechanical properties of the valve components are discussed in details. An experimental apparatus is then manufactured to evaluate the performances of the valve system such as flow rate. The experimental apparatus consists of a heat chamber, which can regulate the temperature of the valve system and oil, pneumatic-hydraulic cylinders, a hydraulic circuit, a pneumatic circuit, electronic devices, an interface card, and a high voltage amplifier. The pneumatic-hydraulic cylinder transforms the pneumatic pressure into hydraulic pressure. The performances of the valve system regarding spool response, pressure drop, and flow rate are evaluated and presented. In addition, the performance of the valve system under high temperature condition is compared with that under room temperature condition. The experimental results are plotted in both frequency and time domains.

Dynamic characteristics and control capability of a piezostack actuator at high temperatures: experimental investigation

In this study, experiments are conducted to evaluate dynamic characteristics and position tracking control performance of a piezoelectric actuator at various temperature conditions including up to 180 °C. An experimental apparatus consisting of a heat chamber, piezostack actuator, a laser sensor, a gap sensor, a temperature sensor, a data acquisition board, a function generator and a computer is established. To obtain the dynamic characteristics of a commercial piezostack actuator, desired input signals, which are sinusoidal waveforms with several different frequencies, are generated by the function generator, and actual controlled output signals are detected by the laser sensor. In this experiment, the heat chamber regulates temperature conditions of the piezostack actuator for a sufficient time before starting next test. After discussing the temperature dependent dynamic properties such as blocking force, another experimental setup is established to evaluate control performance of the piezostack actuator at high temperatures. A proportional-integral-derivative feedback controller which does not require an exact dynamic model of the system is designed and experimentally realized using a microprocessor for the position tracking control. Control performances such as position tracking error are measured at various temperatures and presented in time domain.

A new measurement method of magnetic flux density using magnetorheological fluid characteristics and a variable resistor circuit

This work proposes a new approach with which to measure the magnetic flux density using the characteristics of magnetorheological fluid (MRF) that is integrated with a variable resistor. For convenience, it is called a magnetorheological fluid variable resistor (MRF-VR) system in this study. The mechanism of the MRF-VR is based on the interaction between ferromagnetic iron particles of the MRF due to an external magnetic field, which causes its electrical resistance to be field dependent. Using this salient principle, the proposed MRF-VR system is constructed with electrodes and MRF, and its performance is demonstrated by evaluating its electrical resistive characteristics such as dimensional influence, response time, hysteresis and frequency response. After evaluating the performance characteristics, a feedback control system with a proportional–integral–derivative (PID) controller is established, and resistance-trajectory control experiments are carried out. Based on this MRF-VR system, a magnetic field–sensing system is constructed using a Wheatstone bridge circuit, and a polynomial model for calculating the magnetic flux density is formulated from the measured voltage. Finally, the accuracy and effectiveness of the proposed sensing system associated with the empirical polynomial model is successfully verified by comparing the calculated values of magnetic flux density with those measured by a commercial tesla meter.

Control performances of a piezoactuator direct drive valve system at high temperatures with thermal insulation

This technical note presents control performances of a piezoactuator direct drive valve (PDDV) operated at high temperature environment. After briefly discussing operating principle and mechanical dimensions of the proposed PDDV, an appropriate size of the PDDV is manufactured. As a first step, the temperature effect on the valve performance is experimentally investigated by measuring the spool displacement at various temperatures. Subsequently, the PDDV is thermally insulated using aerogel and installed in a large-size heat chamber in which the pneumatic-hydraulic cylinders and sensors are equipped. A proportional-integral-derivative feedback controller is then designed and implemented to control the spool displacement of the valve system. In this work, the spool displacement is chosen as a control variable since it is directly related to the flow rate of the valve system. Three different sinusoidal displacements with different frequencies of 1, 10 and 50 Hz are used as reference spool displacement and tracking controls are undertaken up to 150 °C. It is shown that the proposed PDDV with the thermal insulation can provide favorable control responses without significant tracking errors at high temperatures.

Two-Dimensional rGO-MoS2 Hybrid Additives for High-Performance Magnetorheological Fluid

Magnetorheological fluids (MRF) that undergo a change in their viscoelastic properties under the magnetic fields have been considered as one of most important smart functional materials for vibration dampers and shock absorbers in several engineering applications. However, the use of magnetorheological fluids in practical applications has been limited by poor sedimentation ratio and on-state yield stress. Herein, we report hybrid rGO-MoS2 additives for a high-performance magnetorheological fluid. Two different kinds of hybrid additives, which are called non-magnetic rGO-MoS2 and magnetic Fe-rGO-MoS2, were synthesized by using a hydrothermal method. The rGO-MoS2 added suspensions remained stable for the first 90 min whereas the CIP MRFs settled down quickly (65%) in the first 10 minutes. The Fe-rGO-MoS2 additives showed a 24% higher on-state shear stress as compared to CIP MRFs. On the other hand, an increase of 60% in the on-state yield stress for Fe-rGO-MoS2 MRF can be attributed to the gap-filling by the hybrid additives during columnar-structure formation. Among two-dimensional (2D) materials, Molybdenum Disulphide (MoS2) is a member of transition metal dichalcogenides (TMDCs), traditionally used as solid lubricant, while reduced graphene-oxide (rGO) is a well-known 2D material with supreme mechanical properties. We believe that this study will blaze the new way for developing a high-performance magnetorheological fluids based on various 2D material hybrids.

Design and Analysis of a Magnetorheological Damper for Airplane Landing Gear

Airplane landing gears are subjected to a wide range of excitation conditions due to variations in sink speed and road condition. An existing passive type damper for the landing gear is hard to satisfy these various conditions. A semi-active type magnetorheological (MR) damper is one of attractive solutions to resolve this problem. This work presents design and analysis of MR damper applicable to the landing gear system. MR damper is designed based on the required damping force and packaging constraints. Especially, the geometry of the magnetic core is optimized in terms of magnetic intensity at magnetic poles to achieve uniform magnetic intensity under the packaging constraints. The effectiveness of the proposed MR damper is given by presenting the field-dependent damping force and the efficiency.

Tracking Control of a Spool Displacement in a Direct Piezoactuator-Driven Servo Valve System

This paper presents tracking control performances of a piezostack direct drive valve (PDDV) operated at various temperatures. As afirst step, a spool valve and valve system are designed operated by the piezoactuator. After briefly describing about operating principle, an experimental apparatus to investigate the effect of temperaturs on the performances is set up. Subsequently, the PDDV is installed in a large-size heat chamber equipped with electric circuits and sensors. A classical proportional-integral-derivative (PID) controller is designed and applied to control the spool displacement. In addition, a fuzzt algorithm is integrated with the PID controller to enhace performance of the proposed valve system. The tracking performance of a spool displacement is tested by increasing the teperature and exciting frequency up to 150°C and 200 Hz, respectively. It is shown that the tracking performance heavily depends on both the operating temperature and the excitation frequency.

A Study on Vibration Control Performance of Macpherson Type Semi-Active Suspension System

The paper studies a comparison analysis of semi-active control strategies for a Macpherson strut type suspension system consisting of MR(magneto-rheological) damper. As a first step, in order to formulate governing, a dynamic full model of a Macpherson strut is developed considering the kinematics. The nonlinear equation of motion of the strut is then linearized around the equilibrium point. A new adaptive moving sliding model controller is developed for fast response of the system. A newly proposed adaptive moving sliding mode control strategy is then compared with conventional sliding mode controller and skyhook controller. The comparison is made for two different types of road inputs; bump and random road profiles showing superior vibration control performance in time and frequency domains.

Design and modeling of new suspension system using direct drive servo-valve system actuated by piezostack actuator

This paper proposes a new type of a direct-drive valve (DDV) suspension system for vehicle controlled by the piezostack actuator associated with displacement amplifier. In order to achieve this goal, a new type of controllable piezostack DDV damper is designed and its performance evaluation of damping force is undertaken. Next, a full vehicle suspension system consisting of sprung mass, spring, tire and the piezostack DDV damper is constructed. After deriving the governing equations of the motion for the proposed the piezostack DDV suspension system, the skyhook controller is implemented for the realization of the full vehicle. Analytical model of the whole suspension system is then derived and performance characteristics are analyzed through numerical simulation. Finally, vibration control responses of the vehicle suspension system such as vertical acceleration are evaluated under both bump and sine road conditions.