We propose a miniature spherical motor using iron-gallium alloy (Galfenol). This motor consists of four rods of
Galfenol with square cross-section, a wound coil, a permanent magnet, an iron yoke and a spherical rotor placed
on the edge of the rods. The magnetomotive force of the magnet provides bias magnetostriction for the rods
and an attractive force that maintains the rotor on the rods. When currents of 180 deg phase difference flow in
pairs of opposing coils, a torque is exerted on the rotor is by pushing (expansion) and pulling (contraction) of
the rods. Rotation about a single axis is realized by a sawtooth current, such that the rotor rotates with slow
expansion and slips at the rapid contraction. The motor can be fabricated at small sizes and driven with a low
voltage, suitable for application as a microactuator for rotating the camera and mirror in endoscopes.
We propose a three-DOF magnetostrictive micro actuator using Iron-Gallium alloy (Galfenol). The actuator consists of two parallel beam structure having a Galfenol core, located at either end of a Galfenol rod of 1 mm square cross-section and length 11 mm, with two orthogonal ditches cut down it of width 0.3 mm. Around the resulting prongs are wound, and the prongs are bonded to an iron end cap to close the magnetic circuit. When current is passed through a coil wound round one of the orthogonal parallel beams, the resulting magnetostriction enables the actuator to bend in two directions. In addition, longitudinal displacement with high frequency bandwidth can be generated by excitation of two or of all four coils. Maximum displacements were observed of 8 to 10 μm in bending and 2.2 μm in the longitudinal direction. This actuator is potentially applicable in machining (drilling), positioning, and in a micro-motor using wobbling or translational motion when powered by a small power supply.
We investigate a micro bending actuator based on unimorph, lamination of Galfenol (Iron-gallium alloy) and
non-magnetic material. Galfenol C-shape yoke bonded with stainless plates (lamination) is wound coils, and
is composed close magnetic loop with connected an iron plate. The magnetostriction in longitude direction is
constrained by the stainless, thus, the laminations yield bending deformation with the current flowing. The
advantage of the actuator is simple, compact and ease of assembling including winding coil, and high tolerance
against bending, tensile and impact. We machined the yoke from a plate of 1mm thickness of polycrystalline
Galfenol (Fe81.4Ga18.6 Research grade) using ultra high precision cutting technique. The prototype, thickness of 1mm and length of 10mm, was observed the displacement 13&mgr;m and 1st resonance at 1.6 kHz, and the high bending (tensile) tolerance withstanding suspended weight of 500g.
We investigate the machining properties of Iron-Gallium alloy for microactuator. Iron-Gallium is ductile
magnetostrictive material with moderate magnetostriction ranging from 100 to 300ppm. The microactuator of Fe-Ga is
expected to have advantages of simple configuration, low voltage driving, high robustness against external force and
high temperature environment, compared with that of PZT. Here the rod of Fe-Ga prepared by FSZM technique was machined
to distributed pillars of 1mm square by milling process. The comparison of magnetostrictions of machined and
non-machined parts by strain gage confirms the strains different in pillars are inherited from the grain distribution
and the milling process does not significantly deteriorate the material properties. The measurement of displacements by
LASER Doppler vibrometer supports the validity of strain measurement. The success of the fabrication of the distributed
pillars of 0.7 and 0.5mm square exhibits the potential of the milling process for Fe-Ga with high aspect ratio suitable
for practical micro applications.
A novel configuration of composite of Terfenol-D and stack PZT actuator is proposed for coil-free magnetic force
control. This magnetic force control is based on the inverse magnetostrictive effect of magnetostrictive materials
whereby the stress resulting magnetic force is controlled by the voltage of the actuator. The advantages, zero power
consumption to maintain constant of the magnetic force and small power supply are inherited from characteristics of
piezoelectric material. In addition, the configuration of the composite without rigid structure to apply pre-stress is
simple and compact compared with our conventional one. In this paper, the measurements of the magnetic force with
different size of the magnets and pre-strain clarified the magnetic force is strongly dependent on bias magnetic field
and prestress. Linear stepping motor and magnetic levitation taking the advantage of low power consumption to maintain
the position of the mover or levitated yoke are also introduced with some experimental results to discuss the potential
of the device for practical applications.
We have been proposing a magnetic force control method using the inverse magnetostrictive effect of magnetostrictive materials. With a parallel magnetic circuit consisting of iron yokes and permanent magnet, the magnetic force exerting on the yoke can be varied by the mechanical stress applied to the magnetostrictive material. The characteristics of the magnetic force, such as stress-sensitivity and range of the variation, are mostly dependent on the material properties of the magnetostrictive material. So far we have mainly investigated the magnetic force using Terfenol-D (Tb-Dy-Fe alloy) and demonstrated its usefulness in practical applications. Recently, Galfenol, Iron-Gallium is widely noticed for alternative for the Terfenol with several advantages. Even lower magnetostriction, it is superior to the Terfenol with high piezomagnetic constant, low hysteresis loss, high saturation and good machinability. In this paper, we investigate the potential of the Galfenol for the magnetic force control method which can enlarge the variation range of the magnetic force and increase the stress-sensitively. The formulation of the magnetic force and experimental results of fundamental material properties and magnetic force of the Galfenol and Terfenol clarifies the merits of the Galfenol inherited from high saturation and high piezomagnetic constant. The correlation between the piezomagnetic constant and bias field is verified, providing magnetic circuit design strategy to make full use of the material properties of the Galfenol for future applications.
A high sensitive and heat-resistive magnetic sensor using a magnetostrictive/piezoelectric laminate composite is investigated. The sensing principle is based on the magnetostrictive- and piezoelectric effect, whereby a detected yoke displacement is transduced into a voltage on the piezoelectric materials. The sensor is intended to detect the displacement of a ferromagnetic object in a high temperature environment, where conventional magnetic sensors are not useful. Such applications include sensors in engine of automobile and machinery used in material processing. The sensor features combination of a laminate composite of magnetostrictive/piezoelectric materials with high Curie temperatures and an appropriate magnetic circuit to convert mechanical displacement to sensor voltages and suppress temperature fluctuation. This paper describes the sensing principle and shows experimental results using a composite of Terfenol-D and Lithium Niobate to assure high sensitivity of 50V/mm at bias gap of 0.1mm and a temperature operating range over 200 °C.
KEYWORDS: Magnetism, Ferroelectric materials, Magnetic sensors, Sensors, Actuators, Magnetostrictive materials, Electrodes, Piezoelectric effects, Finite element methods, Control systems
This paper presents novel magnetic actuator and sensor devices with a magnetostrictive/piezoelectric laminate. Both actuator and sensor are based on the conversion of electric and magnetic energies of piezoelectric and magnetostrictive materials via mechanical coupling, thus the advantages of the piezoelectric material, low power consumption and high speed response, are reflected on both functions. Here, several devices, laminations of Tb-Dy-Fe alloys and PZTs with different geometries or properties integrated into a magnetic circuit, are fabricated and their capabilities of magnetic force controlling and displacement sensing are investigated.
A magnetic force control device with laminate composite of giant magnetostrictive material (GMM) and piezo-electric material (PZT) is proposed. This magnetic force control is based on inverse magnetostrictive effect of a magnetic material, whereby the variation of stress applied on the material is converted to that of magnetic force via magnetic circuits. For the purpose of realizing the method in practical applications, disks of GMM and PZT are laminated to control the stress of GMM by electric field on PZT. Due to the capacitive properties of PZT, the device requires little electric energy hence generates no heat to maintain constant force. Furthermore compared with conventional electromagnetics, the device can be fabricated easily and in small size to be suitable for microactuators. This paper presents the principle of the magnetic force control by the lamination of GMM and PZT and investigates the static and dynamic characteristics of several devices to demonstrate their capabilities of the magnetic force control.
A magneto-electric composite element of two functional materials: giant magnetostrictive (GMM) and piezoelectric materials, is developed for coil-less magnetic force control. This force control is based on the inverse magnetostrictive effect of GMM and realized by composing a closed parallel magnetic circuit with a permanent magnet in magnetic yoke. The magnetic force between two yokes can be adjusted by controlling the strain in the magnetostrictive rod. For the purpose of efficiently controlling the strain of the GMM rod, a magneto-electric composite element is constructed, in which the two functional materials: a giant magnetostrictive rod and a stack piezoelectric actuator, are mechanically coupled via strain. The magnetization in the GMM rod can be controlled by adjusting the voltage of the piezoelectric actuator. It is confirmed that this element works to adjust magnetic force and has wide frequency bandwidth. As an application of this element, a magnetic levitation system is proposed and the movable yoke was levitated by simple PD control. This system has advantages of low power consumptions and low heat generation compared with a conventional system with electromagnetic coils.
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