The response of NiMnGa ferromagnetic shape memory alloy to static and dynamic magnetic fields was studied. Tests involving excitation of the samples up to 10 Hz for constant stress and constant strain conditions were conducted. Based on these results, performance parameters were measured and discussed including power density, total power output and electromechanical efficiency. The effects of strain rate and material damping were also measured. It was shown that both power density and total power output were strong functions of applied stress. A maximum volumetric power density of 31 MW/m3 was measured. Once the NiMnGa behavior was characterized, an analytical model based on four experimentally measured parameters was formulated to predict the induced strain in response to a dynamic magnetic field. Comparison of the analytical model to experimental data showed good correlation for applied stresses below 0.6 MPa and above 1.33 MPa. Although requiring further refinement, the model's results are encouraging, indicating that it could be developed into a useful analytical tool for predicting NiMnGa actuator behavior.
In recent years, there have been growing applications of active materials, such as piezoelectrics and magnetostrictives, as actuators in the aerospace and automotive fields. Although these materials have high force and large bandwidth capabilities, their use has been limited due to their small stroke. The use of hydraulic amplification in conjunction with motion rectification is an effective way to overcome this problem and to develop a high force, large stroke actuator. In the hydraulic hybrid actuator concept, a hydraulic pump actuated by an active material is coupled to a conventional hydraulic cylinder, from which output work can be extracted. This actuation concept requires a high bandwidth active material with a moderate stroke. Both piezoelectrics, and magnetostrictives such as Terfenol-D and Galfenol are well suited as driving elements for this application, however, each material has its drawbacks. This paper presents a comparison of the performance of a piezoelectric, Terfenol-D and Galfenol element as the driving material in a hydraulic hybrid actuator. The performance of the actuator with each driving element is measured through systematic testing and the driving elements are compared based on input power required and actuator mass. For a pumping chamber of diameter 1” and a driving element of length 2”, the maximum output power was measured to be 2.5 W for the Terfenol-D hybrid actuator and 1.75 W for the piezoelectric hybrid actuator.
KEYWORDS: Actuators, Magnetism, Amplifiers, Velocity measurements, Control systems, Temperature metrology, Magnetostrictive materials, Control systems design, Sensors, Aerospace engineering
This paper presents the design and testing of a magnetostrictive-hydraulic hybrid actuator driven by Terfenol-D. The actuator is based on the frequency rectification of small displacements from a Terfenol-D rod by using one-directional check valves. The continuous fluid flow produced from this actuation is then used to drive a hydraulic output cylinder. A transducer was built in order to actuate the Terfenol-D rod in the pump. In addition, an active valve system was designed and built to achieve bi-directional capabilities in the actuator. Successful testing of the actuator in uni-directional and bi-directional modes was carried out. The actuator was found to have an unloaded velocity of 6 in/sec, a blocked force of 10 lbs, and a bi-directional stroke of 0.1 in/cycle at 10 Hz.
Magnetorheological (MR) fluids can be used in a variety of smart semi-active systems. MR dampers have especially great potential to mitigate environmentally induced vibration and shocks. MR fluid can be used effectively in valve networks to control the flow from a hydraulic source to enable a fully active actuator. These devices are simple, have few moving parts and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezo-pump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electro-mechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the actuator to achieve controllable damping. The design, construction and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, biviscous and Bingham-plastic representations of MR fluid behavior. Unidirectional performance, or constant velocity actuator shaft motion, is assessed analytically and compared to experimental data. A experimental assessment of the magnetorheological birectional flow control capability is also provided.
Magnetorheological (MR) fluids can be used in a variety of smart semi-active systems. The MR damper shows an especially great potential to mitigate environmentally induced vibration and shocks. Another aspect of MR fluids is the construction of MR valve networks in conjunction with a hydraulic pump resulting in a fully active actuator. Conventional hydraulic pumps, however, are bulky, contain many moving parts, and do not scale favorably with decreasing size motivating development of high energy density piezohydraulic pumps. These devices are simple, have few moving parts and can be easily miniaturized to provide a compact, high energy density pressure source. The present study describes a prototype MR-piezo hybrid actuator that combines the piezopump and MR valve actuator concepts, resulting in a self-contained hydraulic actuation device without active electro-mechanical valves. Durability and miniaturization of the hybrid device are major advantages due to its low part count and few moving parts. An additional advantage is the ability to use the MR valve network in the acuator to achieve controllable damping. The design, construction and testing of a prototype MR-piezo hybrid actuator is described. The performance and efficiency of the device is derived using ideal, biviscous and Bingham-plastic representations of MR fluid behavior, and is evaluated with experimental measurements. This will provide a design tool to develop an actuator for a specific application. The prototype actuator achieved an output velocity of 5.34mm/sec against a mass load of 5.15kg with a piezopump weighing 300gm.
This paper describes the design and testing of a piezoelectric hydraulic hybrid actuator operating at a high pumping frequency. The actuator is envisaged as a potential actuator for a trailing edge flap of a full scale smart rotor system. Recent research efforts on piezoelectric hydraulic hybrid actuators have investigated devices based on large piezoelectric stacks operating at a relatively low pumping frequency. The present work focuses on the behavior of such an actuator operating at a high pumping frequency and low volumetric displacement. Challenges to achieving high pumping frequencies were identified and solutions were implemented. The actuator was driven by two piezostacks, of a total length of 36 mm and cross-sectional area 10 mm2. The actuator was tested up to a pumping frequency of 1 kHz, developing a maximum no-load velocity of 1.2 in/sec and a blocked force of 35 lbs in the uni-directional output mode. Bi-directional output performance was also measured, by incorporating a 4-way valve in the hydraulic circuit. At a frequency of 5 Hz, a no-load output displacement with an amplitude 32 mils was measured.
This paper describes the development of a compact hybrid hydraulic actuation system as a potentially high-authority compact actuator for various applications including actuation of the trailing edge flap of a smart rotor system. The actuation system is divided into two parts, a pump driven by piezostack actuators and an output hydraulic actuator. The present work focuses on the design, analysis and testing of the pump. Analytical models are developed for various elements of the system. Operating the piezostacks at a frequency of up to 250 Hz over a period of five minutes, the pump generated a maximum pressure rise of 180 psi, displacing approximately 100 ml of hydraulic fluid in the process. A maximum temperature of 55 degree(s)C was measured on the piezostack.
A magnetorheological (MR) fluid-based hydraulic power system is analyzed and experimentally validated by testing a prototype. A set of MR valves is proposed to implement within a Wheatstone bridge hydraulic power circuit to drive a hydraulic actuator using a pump. The MR valves are used in place of conventional mechanical servo valves. The proposed use of MR valves in hydraulic actuator systems has many advantages. First, MR valves have no moving parts, enhancing reliability. Second, the MR valves operate at the same speed as the actuation bandwidth (typically below twenty Hz in our applications). Third, the actuator relies on flow rates for a given pump speed, and avoids, to a large degree fluid compliance. Fourth, if a change in stroke direction is required, the flow through each of the MR valves can be controlled smoothly via changing the applied magnetic field. The performance of the Wheatstone bridge with MR valves is theoretically derived using three different models of the MR fluid behaviors: an idealized model, a Bingham-plastic model and a biviscous model. The analytical system efficiency in each case is compared, and departures from ideal behavior are recognized. The driving force and efficiency will be evaluated in the MR hydraulic power actuator system for both Bingham plastic and biviscous flows. An MR valve is designed using a magnetic finite element analysis. The magnetic flux density developed in the MR valve are verified by analytical and experimental methods. The yield stresses achieved in the MR valve due to the applied current are also measured to validate the design methodology. The overall performance of the MR fluid based hydraulic power system is described using the experimental MR valve performance data.
This paper investigates the behavior of piezoelectric elements as strain sensors. Strain is measured in terms of the charge generated by the element as a result of the direct piezoelectric effect. Strains from piezoceramic and piezofilm sensors are compared with strains from a conventional foil strain gage and the advantages of each type of sensor are discussed, along with their limitations. The sensors are surface bonded and are calibrated by means of a dynamic beam bending setup over a frequency range of 5 - 500 Hz. Correction factors to account for transverse strain and shear lag effects due to the bond layer are analytically derived and validated experimentally. Additionally, design of signal conditioning electronics to collect the signals from the piezoelectric sensors is addressed. The superior performance of piezoelectric sensors compared to conventional strain gages in terms of sensitivity and signal to noise ratio is demonstrated.
This paper investigates the behavior of piezoceramic actuators under different types of excitation and mechanical loading. The research focuses on the application of these actuators to the development of smart rotor systems. The free strain response of the actuators under DC excitation is investigated experimentally along with the associated drift of the strain over time. Effect of tensile stress on the DC response is investigated. Strain response to an AC excitation is also investigated for a free actuator and for a pair of actuators surface bonded to a host structure. The phase lag of the strain response and non-linear hysteretic effects have been observed and the power consumption has been validated by the impedance method. Additionally, depoling of the actuators is discussed, along with the feasibility of recovering performance by repoling in the event of accidental depoling.
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