This paper proposes a system to trace resonance frequencies of Langevin type ultrasonic transducers. The system consists of a microcomputer, detecting circuits and a direct digital synthesizer. Fabrication of the system is reported. Step responses are described as tracing performance. Vibration amplitude modulation using the system is also indicated as an application for mechatronics.

A frequency-following servocompensator is applied to a rotary gyro with flexures gimbal to eliminate the oscillating components from the estimated signals. In the targeted gyro, a synchronous motor is fixed to a rectangular holder and a disk-type rotor is driven by the motor to generate gyroscopic couplings. The coupled two rotational motions of the holder are controlled by four electromagnets on the stator; the angular velocities are estimated from the control currents to regulate the relative displacement of the holder to the stator. The other four-degree-of-freedom motions of the holder are constrained by the flexures gimbal. Such suspension using flexures makes the system less damped so that high accuracy is expected to this gyro. However, one of the problems is that an oscillating component caused by rotor unbalance appears in the estimated signal because the estimation is based on the control input. To solve this problem, the frequency-tracking servocompensator is applied to eliminate the oscillating component. The virtually perfect elimination of the component from the estimated signal was achieved.

A compact axial active magnetic bearing with a function of two-tilt-motion control is fabricated which has a new configuration of magnetic poles. They consist of four cylindrical poles with coils and a single common pole whose opposite plane of the rotor has a permanent magnet to achieve multi-degree-of-freedom zero power control. Modal control is applied because local zero power control may make the whole system unstable when the number of control channels is larger than the number of freedoms of motion to be controlled. In the developed system, a disk-shape rotor is sandwiched between two axial magnetic bearing stators that are operated differentially. Such a configuration makes it possible to rotate the rotor without disturbing the axial motion. The characteristics of the fabricated magnetic bearing system including rotation are studied experimentally.

The fundamental characteristics and performances of alternating current (AC) magnetic suspension using magnetic resonant coupling are studied analytically and experimentally. Nowadays, wireless power transfer to the suspended object is required during non-contact suspension in some applications. Therefore, magnetic resonant coupling has been introduced for AC magnetic suspension to achieve self-stabilizing magnetic suspension and energy transfer to the floator simultaneously. The effect of circuit parameters for developing an experimental apparatus and performances are predicted from the solution of the equivalent circuits analytically. First, an equivalent magnetic circuit is derived and analyzed to characterize the self-inductance and mutual inductance with the gap. Second, an equivalent electrical circuit is analyzed to derive the current and force equations including magnetic parameters of the circuit. The derivation of these equations is numerically solved to study the characteristics of the primary current, the secondary current, and the force with respect to the gap and the applied frequency. The comparison between theoretical and experimental results is depicted, and the reason for differences is explained. The experimental and theoretical results show that positive stiffness is possible, which is essential for achieving self-stabilization. The self-stability is confirmed by the frequency response of the suspension system to disturbance experimentally.

A novel flux control magnetic suspension system that places control plates beside the magnetic source (permanent magnet) is proposed. In a conventional flux-path control magnetic suspension system, the control plates were inserted between the magnetic source and the suspended object (floator). In contrast, the control plates were placed beside the magnetic source in the proposed system. In such a configuration, the effective gap becomes larger than in the conventional system. Basic characteristics of the proposed magnetic suspension system were studied both numerically and experimentally. The numerical analyses show that the attractive force acting on the floator increases as the position of the lateral ring-shape control plate increases. The variation of the attractive force is sufficient for the stabilization of the suspension system. It is also shown that lateral force can be generated by dividing the plates into halves and moving them differentially. The predicted characteristics are confirmed experimentally in a fabricated apparatus with a three-axis force sensor and a gap adjustment mechanism.