Recently, various machines and tools have been miniaturized. In this trend, the size of an actuator is a very important factor. An ultrasonic actuator is different from another actuator using electromagnet force in the driving principle. The structure of an ultrasonic piezoelectric actuator is simple. An ultrasonic actuator converts the ultrasonic mechanical energy to mechanical thrust force by a friction force. Based on this idea, various ultrasonic actuators were proposed and experimentally constructed.
In this paper, the basic characteristics of a piezoelectric actuator were theoretically analyzed. The relationship between the thrust force and the weight force was clarified, and was verified by the experiments. Various prototypes of plane ultrasonic piezoelectric actuators were experimentally constructed, and the fundamental characteristics were measured.

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For three-phase synchronous generators, a new self-excitation scheme has been developed. The generator employed this scheme behaves as a flat-compound machine without any automatic voltage regulators. The stator of the generator is provided with an armature winding which generates the fundamental and 2nd-harmonic mmfs. The rotor is equipped with a field winding and a harmonic winding. The harmonic winding is magnetically coupled to the 2nd-harmonic mmf produced by the armature winding. Making the current flow in the stator armature winding by way of a three-phase set of capacitors connected across its three-phase terminals, the ac voltage is induced in the rotor harmonic winding due to the armature 2nd-harmonic mmf. By connecting the harmonic winding to the fled winding through a rectifier circuit, self-excitation of the generator is obtained. This excitation scheme is both self-excited and brushless, and no exciter is required. Additionally, the voltage regulation due to the load variation can be improved by connecting the capacitors of suitable value.
In this paper the operating principle and circuit configuration of the generator are explained, and the experimental results using a 1kVA prototype machine are shown. Then, the generator characteristics are theoretically clarified by approximate analysis, and appropriateness of the theory and the usefulness of the proposed scheme are experimentally confirmed.

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Brushless three-phase synchronous motor involving a rotating AC exciter on the same shaft as the motor and with the windings linked through a shaft-mounted rectifier is widely put to practical use as medium and large capacity machines. However, the motor needs to fit with damping windings for self-starting outside of the field winding in the rotor and needs to equip discharge resistance with complex electronic device to dispose of electromagnetic force induced in the field winding at starting. Therefore, the rotor structure is very complex, and there are disadvantages especially for robust and high reliability required generally to motor.
In order to solve this problem existing in traditional motor, authors proposed a brushless three-phase synchronous induction motor with two stators and one wound rotor. This problem is solved because the proposed motor is two stators structure: The rotor winding operates as the secondary winding of induction motor at starting and as the field winding at synchronous operation.
The motor can self-start as a wound-rotor induction motor without external secondary resistance. Therefore, discharge resistance is not necessary; the starting equipment is very simple and the rotor structure is robust. It is possible to start with high torque.
In this paper, the basic constitution of the proposed motor and the principles of operation are described in detail. The experimental results at starting and pulling into synchronism are shown for confirming the principles of operation and the experimental and the numerical results of the starting characteristics, the load ones, the generating ones are shown: the practical use of the proposed motor is confirmed.

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The concept of the variable active-passive reactance (VAPAR) has been proposed in⁽¹⁾, which behaves like a two-terminal reactive element, and the produced active virtual reactance works as a passive reactive component, including in transient state. However, in these analysis and experiments, the DC voltage source was used as an energy storage element. If a DC voltage source is replaced with a capacitor, VAPAR can be considered as a complete two-terminal element.
In this paper, authors propose the equivalent resistance control method for the capacitor DC voltage regulation when a capacitor is used as an energy storage element of VAPAR. The series equivalent resistance is added to the produced virtual inductance, and the capacitor voltage is controlled by changing the series equivalent resistance. The proposed scheme was verified by simulations and experiments.

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The finite element method (FEM) and the boundary element method (BEM) are very useful for the numerical analysis of electromagnetic phenomena. Although the FEM suits the analysis of a complicated region which could include non-linear materials or eddy currents, the physical quantities such as the magnetic flux densities B are obtained discretely. Therefore we have to make fine meshes for accurate estimation of the electromagnetic force by the Maxwell stress method. On the other hand the BEM makes it possible to derive continuous physical quantities at inner points by using analytical expressions, not by relying numerical derivation as in case of the FEM.
In this paper we first use the FEM for analyzing the electromagnetic fields of the concrete model in terms of the magnetic vector potential A and the electric scalar potental φ. Next we locate the temporary boundary enclosing the region where we desire the values of B, and apply the BEM (using the H method or the _??_ method) to this region in order to obtain B continuously. Then we can calculate the electromagnetic force accurately by the Maxwell stress method. To verify this approach, the numerical results obtained by the proposed method are compared with the theoretical values.

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In the field of Mechatronics, small-sized actuators with multi-degrees of freedom are desired so that dextrous performance is achieved, especially for small size robot development. We have developed a wire-driven system with a linearactuator to solve this problem. The characteristics of wire-drives are rather complicated because of its unknown stiffness, backlash and friction. After parameter identification as a 2-mass model, H_∞ controller was designed for this model which has a integral function in its transfer function. The H_∞ controller shows a good performance compare with observer-based-control and sliding-mode-control. It has good rdsponse for reference and ohserving noise rejaection and it is robust.

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While a solid plate is usually adopted to the reaction plate of the linear induction motor (LIM), slits are often introduced to the plate in order to obtain the higher thrust force by enforcing eddy currents effectively. In this paper, we investigate the slit effect to find a suitable configuration of slits by the three-dimensional finite element analysis with A-φ method, and we propose a face-elements procedure with double nodes for φ at the slit to express its infinitesimal width. We also adopt a current-sheet expression, which consists of three regions for primary winding MMF, that is given by diamond coils.
Based on above approaches, we evaluate the slit effect in the LIM, and compare it with the experimental data to conform the validity of the methods, resulting follows; (1) Number of slit per slot-pitch is required more than 4 for obtaining sufficient performances. (2) Preferable slit length is a little bit longer than the stator width. (3) A belt of no slit region in the middle part of the reaction plate is proposed from the structural point of view. However, its width should be less than 40% of the stator width to enforce eddy currents effectively.

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We have studied energy transfer circuits of inductor converter circuits (ICB), which are used for power supplies for superconducting magnets. We derived analytical solutions of steady state characteristics of ICB energy transfer circuits. On the basis of the solutions, we discussed a new control method of ICB transfer circuit to reduce a voltage ripple across a load superconducting magnet. In this paper, we propose a new control for line-commutated converters of ICB energy transfer circuit for quick changes in a transfer angle and a transfer frequency for the voltage ripple reduction control. We discuss speeding-up of the proposed controls. Validity of the proposed controls are confirmed by computer simulations.

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This paper presents analysises of high power factor AC-DC converter with a boost converter operating in discontinuous conduction mode (DCM) and critical conduction mode (CRM). The converter can be expressed by a nonlinear differential equation for each mode. The equation in DCM is solved analytically by separating its variable (output voltage) into two terms of a ripple component and a direct component, and by linearizing the equation for the ripple component. On the other hand, the equation in CRM can be solved analytically. Furthermore, the source current waveform of the converter is expanded into the Fourier series. As the results, the output voltage, its ripple and the power factor of the converter in DCM and CRM are derived as a function of the circuit parameters respectivelly, and verified experimentally. These equations exhibit clearly the effect of each circuit parameter of the converter and the difference between the converter in DCM and in CRM. The converter operating in CRM produces sinusoidal ac current with unity power factor.

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The effect of the fluctuation of measurement values and the filtering characteristics on the longitudinal distance control of vehicles has been investigated. In this studies, the following three system models are considered.
(1) The system which has a distance sensor and a PID controller.
(2) The system which has a distance sensor, relative velocity sensor and a PID controller.
(3) The system which has a distance sensor, a communication tool and a PID controller.
The system can take the data of the acceleration of the preceding vehicle by the communication. The precedin vehicle measures the acceleration by a velocity sensor.
The fluctuation of the measurement values is assumed to be in the range of resolvability. The vehicle model is assumed as the system represented as a first order transfer function. The intersting results are obtained from the computer simulation.
For the short distance longitudinal control of a vehicle, the direct measurement of the distance and the relative velocity is necessary. The data of the preceding vehicle obtained by the communication are not effective when the data have even a little errors.

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The force-balanced coil using multi-helical variable pitch windings for generating the high magnetic field and applying to Superconducting Magnetic Energy Storage is proposed. This toroidal-poloidal field hybrid coil for the torus-type superconducting magnetic device can be made capable of not only greatly reducing the global electromagnetic forces in the major radius direction, but also dispersing the local over-concentration of forces with variable pitch windings. The computer code that calculates the windings pitch of the force-balanced coil by disassembling the current density to both toroidal and poloidal directions and optimizing the current distribution is developed. The feasibility of this idea was verified through the model experiments.

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One of the most important design problem of the permanent magnet (PM) motor is the reverse rotation. The conditions for the reverse rotation with a square-wave drive are investigated experimentally. Relations between the applied voltage and the pulse rate f_p at which the probability P_b of the reverse rotation takes a maximum are discussed. Effects of the initial rotor position δ and the delay-time t_d of the first pulse on the value of P_b are discussed. Calculations of reverse rotating performance are made with various conditions, and clarified the mechanism of the reverse rotation.

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