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A novel alternate-current (AC) magnetic suspension using magnetic resonant coupling is proposed and studied both theoretically and experimentally. An AC magnetic suspension with energy transfer function has been developed to achieve magnetic suspension and energy transfer to the suspended object simultaneously. However, the energy transfer efficiency was low in the developed system mainly because there existed a rather wide gap between the primary and secondary circuits. In contrast, the energy transfer technique using magnetic resonant coupling has high efficiency even if there is a wide gap. In this work, this technique is combined with AC magnetic suspension. The fundamental characteristics of the proposed system are studied for a basic model. It is shown analytically that the coupled circuits has two resonant frequencies and attractive force is generated at the lower resonant frequency while repulsive force is generated at the higher resonant frequency. In addition, the self-stabilizing characteristic, which is proper in the tuned LCR circuit levitation, is achievable in the proposed suspension system. A see-saw type experimental apparatus was fabricated for basic experimental study. The theoretical predictions were confirmed experimentally. The self-stabilization was achieved in the fabricated apparatus. It was also shown experimentally that the stiffness and damping characteristics depend on the gap, the amplitude and frequency of the AC voltage source.

A solar-powered magnetic suspension carrier is fabricated which achieves noncontact power supply to the carrier. There are two conventional methods of supplying power to a carrier. One is through wires or contacts such as pantograph and the other is an on-board battery in the carrier. However, the contactless property is lost in the former while stations for charging the on-board battery are necessary in the latter. These problems are overcome by the proposed carrier system using solar magnetic suspension that can achieve continuous levitation. It is assumed for the system to operate indoors like inside a factory building. The generation of power by solar cells is low so that the magnetic suspension needs power saving. A zero power control system is applied to the suspension of the floator. In addition, low-power peripheral devices are also fabricated. The developed carrier system achieved a 24-hour levitation without external power supply in a bright environment.

The completely passive levitation of a column-shaped graphite object is achieved. Graphite is a typical diamagnetic material. Diamagnetic materials have a property of generating repulsive force in magnetic field. Most diamagnetic levitation systems use high-oriented pyrolytic graphite (PG) sheets because sufficient force for levitation is easily obtained. In contrast, column-shaped graphites are proposed as the target of levitation in this work. Experimental apparatus for diamagnetic levitation is fabricated. The apparatus uses a two-dimensional Halbach array made of cubic neodymium magnets. The magnetic fields in the apparatus are analyzed numerically and experimentally. It is shown that the stable diamagnetic levitation of a column-shaped graphite can be achieved. The floator is fabricated by combining the pencil leads made from graphite. Then the diamagnetic forces acting on the floator are measured. In addition, the effects of anisotropy of graphite on the levitation characteristics are discussed.

A mass-spring system with a dynamic vibration absorber has a fixed point in its frequency response curves. A method of measuring mass using this property was proposed. It has an advantage that mass is estimated independently of the damping in the absorber. The developed system was characterized by using a phase-looked loop to achieve the tuning condition. However, because the actuator producing the harmonic force was mounted on the base, the reaction force was transmitted to the surrounding structure. It may cause a severe vibration of the surrounding structure. Therefore, it is necessary to prevent transmission of force to the surrounding structure in measuring. In this paper, a new type of mass measurement system is proposed which uses an inertial-mass vibrator to reduce the transmitted vibration. The tuning conditions are derived for both systems with a damped absorber and with an undamped absorber. The principles of measurement are described based on a mathematical model. An experimental apparatus is designed and fabricated. The efficacy of the measurement system with an inertial mass-type vibrator is studied both analytically and experimentally.

This paper discusses the feasibility of zero-power control in parallel magnetic suspension systems. In parallel magnetic suspension systems, multiple floators are suspend with a single power amplifier. The zero-power control has been used in magnetic suspension systems with permanent magnets providing bias flux. This control realizes the steady states where the attractive force produced by the permanent magnets balances the weight of the suspended object and the electromagnet coil current converges to zero. This paper shows that parallel magnetic suspension systems incorporating zero-power control can assign the poles arbitrary if the original parallel suspension systems are controllable. The feasibility of the zero-power control in a parallel magnetic suspension is demonstrated experimentally.

This paper presents a vibration isolation system using negative stiffness suspension. The vibration isolation system is developed by combining a positive stiffness suspension in series with a negative stiffness suspension. The developed system could realize zero-compliance to direct disturbance, as well as ground vibration isolation. In the previous system, the ground vibration and, the static and low frequency sinusoidal direct disturbances were efficiently suppressed. However, there was a reverse action in case of impulse or step wise disturbance. Therefore, a peak was appeared which was, sometimes, larger than the displacement caused by the step load. This unpleasant response might hamper the objective function of many advanced systems. In this research, a feedforward controller is added in combination with zero-power control to overcome this problem. Some experimental results are presented to verify the proposed control system in a vibration isolation apparatus.

A flux-path control magnetic suspension system with multiple magnetic sources is realized. The principle of the flux-path control magnetic suspension system is to control flux from a permanent magnet to the floator, and the attractive force acting on the floator by the motion control of control plates inserted between the permanent magnet and the floator. Stable suspension and 3-DOF control with a single magnetic source was achieved. However, the horizontal control force was much less than the vertical control force. Multiple magnetic source system can overcome such problem. A variable flux-path unit is developed for the realization of multiple magnetic source system. An experimental apparatus with two variable flux-path units is constructed. Stable levitation is achieved by applying PD and PID controls. In addition, stable levitation with zero-power control is also achieved.

A three-degree-of-freedom (3-DOF) active vibration isolation system using displacement cancellation control technique is developed. The displacement cancellation concept is presented and implemented in this research to obtain zero compliance of vibration isolation table against direct static force as well as to suppress the dynamic disturbances acting on the isolation table. In the displacement cancellation control technique, relative movements of the vibration free table are followed with I-PD control and movements of the middle mass respect to base are controlled with PD control. The corresponding controllers are designed in such way so that actuator can generate opposite force against disturbance to cancel the effect of displacement of the middle mass on the vibration isolation table, which finally leads zero compliance of the isolation table. Voice coil motors (VCMs) are used for getting linear actuating effect and corresponding displacements of the table are detected by eddy-current gap sensors. The experimental results showed that the developed system with displacement cancellation mode control has capability to maintain zero compliance against direct static force in the 3-DOF motions associated with horizontal translations and a vertical rotation. Moreover experiments have been conducted to measure the dynamic responses of the vibration isolation table to direct disturbance.

In series-type multiple magnetic suspension systems, multiple floators are suspended in tandem by one electromagnet. The nearest floator to the electromagnet is directly suspended by the electromagnet. The others are indirectly suspended by the attractive force due to the magnetization of the floators. The controllability and observability of series-type multiple magnetic suspension systems with an arbitrary number of floators are discussed. They are controllable and also observable even when only the displacement of the floator nearest to the electromagnet is detected. A series-type multiple magnetic suspension system was fabricated in order to verify the analyses experimentally. In the fabricated system, magnetic suspension units that are equipped with a sensor and an electromagnet are used instead of normal floators to carry out experiments in various conditions. As the first step to realize the levitation of multiple floators using one electromagnet and one sensor, a basic trial was carried out in the fabricated system.