A free-piston engine linear generator system is expected for use as a high-efficiency generator engine. The cupper loss is decreased using resonant output distribution control which limits the maximum electric current and uses the mover inertia for power dispersion. But this causes iron loss and spring heat loss is larger due to stroke extension. Therefore, we confirmed that the total loss decrease by using its control in the theoreticaly calculation and simulation. Furthermore, the variable damper control is effective for decrease at generation time in using non-linear spring.
This paper reports on the electric power and the dynamic electromagnetic force produced by a linear vibration generator which integrates an opposite drive mechanism using magnets and coils that move continuously in opposite directions. An electric control that changes the circuit resistance of the power generation coil was able to regulate the electric power and the electromagnetic force. The generator serves as an energy regenerating damper that simultaneously performs power generation and vibration damping. By analyzing the generator`s performance in terms of its power regeneration rate and electromagnetic energy, we are able to investigate the advantages of using an opposite drive linear vibration generator.
Recently, image quality deteriorations due to vibrations have become a problem in an autonomous system. A lens-unit swing system which consists of a lens and an imaging device is a kind of image stabilization technologies that generate an inverse motion against camera shakes. This system can correct an image from camera shakes over wide rotation ranges around three axes. However, this system has some problems such as an increase in size and weight. In order to solve these problems, we proposed a novel three-degree-of-freedom actuator for image stabilization. In this paper, we create a dynamic model for the actuator. The motion equation and state equation are derived by Lagrangian method. The validity of the dynamic model is investigated by the comparison of dynamic analyses using 3-D finite element method. In addition, the optimal servo system is designed using the dynamic model, and the effectiveness of the dynamic modeling method is verified.
Electromagnetic type linear oscillatory actuators are used in many devices because of high controllability and small size. We developed a linear oscillatory actuator with two movers that can independently drive by impressing same-phase or reverse-phase currents. The proposed actuator has two difference vibration characteristics, and it effectively generates vibrations with differential frequencies. In this paper, we clarify the characteristics thorough measurements on a prototype.
Authors have proposed a three-degree-of-freedom resonant actuator that was able to be driven in three axes. However, a mutual interference of thrust was not considered in the conventional vector control. In this paper, we propose a novel vector control theory for three-degree-of-freedom resonant actuator. A mathematical model of d-q conversion is theoretically introduced and the effectiveness of the proposed method is verified by confirming the thrust linearity with respect to the mover position.
Multi-degree-of-freedom (multi-DOF) actuators have been developed for the fields of robotics and industrial machinery. We proposed an outer rotor type spherical synchronous actuator. In this actuator, permanent magnets are arranged at equal intervals inside the rotor. However, this actuator requires a spherical shell-shaped resin part for smoothing the surface of the rotor inner surface. This is because it directly supports the inside of the rotor. Due to this, there is a problem that the air gap length becomes long. In this paper, in order to remove the resin parts, an interior permanent magnet structure is applied to this actuator, and the torque characteristics are investigated. It was found that the air gap length was shortened due to an interior permanent magnet structure, and the torque was increased. In addition, by increasing the thickness of the inner yoke, the cogging torque decreased.
This study proposes a rotation control technique for a spherical motor driven by electromagnets using a torque map that expresses a rotation torque to the rotor by an electromagnet flowing unit current and is obtained in advance for various relative spatial relations between the electromagnet and the rotor. The rotation control technique determines an optimal set of currents for electromagnets arranged in the stator by solving the convex programming problem obtained from the equations expressing the relations among the currents of electromagnets and rotation torque under constraints and a convex-type objective function. The applicability of the technique is demonstrated by an example to obtain an optimal set of currents for a constant torque rotation of a spherical motor that arranges 12 permanent magnets on the surface of the rotor and 10 electromagnets in the stator.
This paper describes the measurement of wall thinning by continuous wave electromagnetic acoustic resonance (CW-EMAR) and pulse wave electromagnetic acoustic resonance (PW-EMAR). Simulated pipe wall thinning specimens are measured. The two methods show accurate results in the areas with a low variation of thickness, and the accuracy decreases when the thickness changes drastically. The two methods are analyzed by using the finite element method. The results show that with the increase of the bottom inclination, the accuracy of the two methods is reduced. For thin specimens, the reason for the larger error of CW-EMAR method is due to that CW-EMAR method is more easily affected by ultrasonic scattering and nonuniform distribution of static magnetic field.
An eddy current method is a method for discriminating metals nondestructive and noncontact. It is very important to know the changes in the frequency profile of sensor coil inductance. If an air-core coil is placed to face an iron plate, the changes contain both the conductivity and permeability information. In order to find a suitable coil size, the same values of in inductance are designed for four coils which have different diameter to generate same magnetic flux at a constant current. The frequency profiles are measured with a conventional impedance analyzer, as a function of distance between the coil and metal plate. The measured values are as same as 200 μH for four coils until a few hundred Hz. When the coils are placed to face the metal, a decrease in lift off produces an increase in inductance at low frequency, and a decrease in inductance at high frequency. There is a cross frequency at which the measured value is as same as inductance of coil only. It is found that it seems to be defined by the coil diameter, not defined by the liftoff. Introducing normalized parameters, other useful considerations are also noted.
The purpose of this study is to find a suitable diameter of the coil for discrimination of non-magnetic metal plate. The same values of in inductance are designed for coils having different diameter to generate same magnetic flux at a constant current, and the discrimination of the metal plate was evaluated by the eddy current testing. The target metal is chosen only an aluminum and opposed to coil. Changes in the inductance of the coil were measured using an impedance analyzer with the distance as a parameter. To find a general solution, normalized parameters are introduced using coil diameter, coil distance and side length of the metal plate. As a result, it is preferable to increase the average diameter at the point where the distance between the coil and the metal plate is equal to the rate of the average diameter of the coil. For discrimination of non-magnetic metal plate, coil average diameter is preferably the same as the width of the metal plate.
In this paper, the results of examining the number of strands for high efficiency and low heat generation of litz wire used for transformer of LLC resonant converter are described. Converter used for switching power supplies are required to be smaller and more efficient. To reduce the size of the converter, examinations have been made by increasing the frequency of the driving frequency. However, due to the high frequency, heat generation in the winding increase due to an increase in AC resistance in the transformer, which is one of the programs of high frequency. In view of this, we study reduction in heat generation by making the wire diameter of the winding constant and changing the number of strands. As a results, it is possible to improve efficiency of the LLC converter by 0.3 % and suppress heat generation of the transformer at 37 °C.
This paper deals with research and development on a VR resolver with sheet coil structure that is thinner than the conventional VR resolver. The main topic of the paper is to propose a structure in which the rotor is sandwiched between upper and lower stators, changing the laminated electrical steel plate to dust core to use the core at high frequency operation, and proposed a theory to improve angle accuracy. Compared to conventional resolvers, the 4X-VR resolver decreased to 43% at the transformation ratio, and the variation width of the angular accuracy was 1.99 times.
In recent years, induction machine motors are operating at high speed rotation. However, an increase in iron loss occurring in the core of the induction motor when the frequency is increased poses a problem. In addition, alternating magnetic flux and rotating magnetic flux are mixed in the iron core, and this inner rotating magnetic flux leads to an increase factor of core loss. Therefore, it is important to clarify the magnetic characteristics in the motor core and to clarify the factor of the increase in core loss. In this paper we report the alternating and rotating core loss characteristics of a three-phase induction motor model iron core under high frequency excitation.
Recently, one of the most important problems is energy shortage. Therefore, it is required the high efficiency electromagnetic device like motors. One of them is interior permanent magnetic synchronous motor (IPMSM). It has a high degree of freedom of shape design because permanent magnets are placed in the interior of a rotor. This paper presents optimal design method of a rotor in IPMSM by multi-objective genetic programming (MOGP). In this method, Pareto optimal solution is composed of high dimensional data. Therefore, it is compressed into 2D with dimension reduction method. Authors investigate obtained optimal structures and usefulness of the proposed method.
We propose simple homopolar magnetic bearings for a ventricular assist device. The bearings control radial position and inclination around radial axes of the outer rotor. In this paper, magnetic suspension characteristics of two types of the magnetic bearings which differ from each other in magnet arrangement or magnetization direction are compared using three-dimensional magnetic field analysis. The one is whose magnets are set on the outer rotor (Type A). The other is whose magnet is set on the stator (Type B). The radial control force and tilting control torque of Type A is 17% and 9.5% higher than that of Type B. The Type A magnetic bearing is made based on the analysis results and measured its magnetic flux density and axial restoring force. The bearing indicates the axial stiffness of about 2 N/mm.
We have developed a novel blood pump with a magnetic levitated impeller to recover cardiac function. The blood pump can increase the coronary flow by varying rotational speed of the impeller in accordance with the heartbeat. In this work, radial displacements of the rotor were measured to evaluate passive stability with improved impeller which generated stronger axial attractive force. Levitation stability of the impellers in the pump with horizontally setting was compared to that vertically setting under the condition of continuous flow and pulsatile flow in a mock flow loop with normal saline. As a result, touchdown occurred with present impeller in the condition of vertical setting and pulsatile flow, whereas touchdown did not occur with improved impeller in any condition. In the future, hemolysis test, vibration test and durability test will be carried out with improved impeller. In consideration of safely, the levitation stability of improved impeller would be improved by changing size of the permanent magnets.
Expanding degrees of freedom in vibration systems is an effective way to improve the power generation efficiency of energy-harvesting devices from the vibrating source, since the system becomes responsive for a wide frequency range due to the appearance of multiple resonant peaks. A magnetostrictive-type vibration energy harvester using an iron-gallium alloy (Galfenol) has received much attention in recent years. A bending force applied at the tip of the cantilever yields a flux change due to tensile or compression stress, and the flux variation leads to the generation of voltage on the wound coils. This energy harvesting technology has advantages over conventional types, with respect to size and efficiency, and it is extremely robust and has low electrical impedance. In this study, the differential evolution (DE), known as a kind of global optimization techniques, was introduced for the parameter design of the harvester that constituted a two-degree-of-freedom vibration system. Using DE, we numerically explored the best combination of spring constants and masses of the vibration system that maximized the electric power generation.
Recently, the number of skyscrapers is increasing in the countries with rapid economic growth. From its background, hi-speed, safe and comfortable elevators are demanded. However, in an elevator emergency stoppage, the large impact force from an emergency stop device injures passengers. Additionally, in a normal operation, the vertical vibration caused by the spring component of lifting wire deteriorates ride-comfort of an elevator. In order to reduce the impact force in an emergency stoppage, we had proposed a new structure of elevator with a magnetorheological fluid control damper by utilizing elevator’s double-cage structure. In this paper, we would like to design new controllers for reducing impact force and apply our system to improve ride-comfort. Then, we would like to verify the effect of our system from viewpoints of comfort and safety for passengers by many digital simulations with MATLAB/Simulink.
The development of spherical actuators for robots and electric devices are expected in the manipulation of machines that have multi degrees of freedom. We have developed a 2-degree-of-freedom outer rotor spherical actuator for writs of robots. In this paper, we propose a new control method to reduce the number of current phases and verify the control method through dynamic analysis and measurements on a prototype.
In order to construct a system with multi-degree of freedom by only using the motors with one degree of freedom, the same number of motors as the degree of freedom is required. On the other hand, in a spherical motor with three degrees of freedom, it is possible to realize a system with three degrees of freedom by only one spherical motor, and it is possible to reduce the size of the system. However, in many spherical motors driven by electromagnets, a spherical speed reducer is required as a device to extract and transmit the output torque. The spherical speed reducer considered in this study is composed of an output ball and an intermediate small ball to transmit the torque from the rotor. In the mechanism of the spherical speed reducer, a model of the rotation transmission to control suitably the rotor is required for a desirable rotation of the output ball. The purpose of this study is to measure angular velocities of the small ball and the output ball in order to derive a rotation transmission model. The angular velocity of each ball is measured using two optical mouse sensors. From the measurement results, a valid rotation transmission model is derived.
In recent years, atmospheric-pressure plasmas are applied in the medical applications. Although the mechanism of action remains unclear, new biomedical applications of plasma have been found. Experiments using atmospheric pressure plasmas confirmed several effects such as burn healing with angiogenesis. In addition, umbilical cord blood is expected to be applied to the field of regenerative medicine due to the presence of mesenchymal stem cells. We have been focusing treatment of Hypoxic Ischemic Encephalopathy (HIE). HIE caused by the discontinuation of blood supplied means that a part of the brain is necrotized and a brain function is impaired. There is no fundamental therapy for HIE except for symptomatic therapy as of now. Because of preservation and recovery of brain functions can be expected, as a study on HIE treatment, we consider and report on a method of administrating atmospheric-pressure plasma and umbilical cord blood to HIE model rat.
A magnetically levitated total artificial heart has been developed. The device has a magnetic bearing and a motor stator at center of the device. The left and right impellers are connected with a rod through a center hole of the stator core. A magnetic bearing controls the axial position and tilting motion of the levitated impeller. The radial displacement of the impeller is restricted with a passive stability characteristic of the magnetic system. A repulsive permanent magnetic bearing is applied for improvement of the radial stiffness and its performance was evaluated. At the rotation speed of 2000 rpm and the flow rate of 5 L/min, the maximum radial displacement was suppressed from 0.39 mm to 0.25 mm by the repulsive permanent magnetic bearing.
A wireless sensor which is powered by a vibration energy harvester (VEH) with magnetic induction is proposed. The wireless sensor is composed of the VEH device, a voltage multiplier, boost converter and wireless communication module. The VEH device has double magnetic circuits which form almost magnetically closed paths. It is shown that the wireless sensor can work for input acceleration 0.1 G at around 30 Hz.
This paper proposes a simple method to reduce amplitude of a magnet that levitates on a high temperature superconductor (HTS). The system works by a coil set above the magnet. The vibration of the magnet induces the current in the coil, and the current creates a magnetic field in such a direction that suppresses the vibration of the magnet. The coil is connected to an electric circuit consisting of a resistance and a capacitor, and works as an electromagnetic shunt damper which converts mechanical energy to electrical energy. The optimal parameters to achieve such a result are determined from the fixed point theory, and numerically analyzed in this paper.
A strong magnetic field forming by Halbach PM array is an effective technical element for the developing of industrial magnetically actuators. In a brand new layout Halbach array using cylinder-shaped PMs, by synchronized rotation in the same direction with of all magnets, the slide of the magnetic field distribution has been confirmed. The proposal dual-cross layout Halbach array model using cylinder-shaped PMs, it can be expected multidimensional motion of the secondary conductor. However, the slide performance of magnetic field seems to depend on the forming of the magnetic flux density distribution. And, its magnetic flux density distribution is clearly dependent on the arrangement parameters of the cylinder-shaped PM of the array. In this paper, we would like to report that the forming of the magnetic field depending on arranged and layout parameters of the brand new dual-cross layout cylinder-shaped PM type linear Halbach arrays, by magnetic field simulation and measurement.
It can be widely applied if it can stably levitate and rotate the floating rotor without using automatic control or superconducting material. The diamagnetic magnetic force generated by diamagnetic substances is very small. The author found that a heavy floating rotor can be levitated by a combination of magnetic force between floating rotor magnet and radially arranged permanent magnets, and diamagnetic magnetic force between fixed magnet group and PG disk. In this paper, I will explain how to levitate the floating rotor. In addition, I show the calculation method necessary for levitation analysis and describe the usefulness of surface current method used for analysis.