This paper describes semi-active assist control in the form of a smart suit for horse trainers. We have developed a soft and flexible power assist device named “smart suit” for reducing user's physical fatigue. The smart suit is a kind of semi-active and flexible power assist devices. The semi-active assist mechanism consisting of elastic materials and a small DC motor is our original technology. The assist force is basically gained by the elastic force of elastic materials, and it is controlled by adjusting the length of the elastic materials by using DC motor. In this study, we applied the smart suit to horse trainers for reducing their physical fatigue in horse training to prevent their injuries. Moreover we developed an assist force control method based on periodical input control to gain the suitable assist force.

The holding force acting on a levitated object in a near-field acoustic levitation apparatus was examined in an effort to increase acoustic levitation between opposing vibration sources. Using finite element analysis, we calculated holding force levels generated by vertically opposed vibration sources and found that when the phase difference of the opposing vibration sources was 180°, the holding force level was larger than could be produced by a single vibration source. On the other hand, when the phase difference is 0°, the holding force produced by acoustic radiation between the opposing vibration surfaces decreased. Additionally, we found that the holding force increased against the decrease of distance between the vibration surfaces. This increase in holding force between opposing vibration sources was experimentally confirmed by the position transient responses of an object detected via image processing. Hence, increases in the holding force levels produced by acoustic levitation between opposing vibration sources have been achieved.

A multidegree-of-freedom ultrasonic motor (MDOF-USM) has excellent features such as high torque at a low speed and a self-holding force, compared with other types of MDOF motor. Therefore, the MDOF-USM has been considered for applications in robot joints, multidimensional systems, and spacecraft. In previous research, the MDOF-USM consisting of a spherical rotor and a stator vibrator of various shapes has been mainly studied. In contrast, the MDOF-USM consisting of a spherical stator and a rotor of various shapes is proposed in this paper. The excitation methods for vibration modes and mode rotation using piezoelectric plates and multilayered piezoelectric actuators were examined. Furthermore, a stator support method that does not significantly affect the vibration of the sphere was devised. From the results of experiments using the fabricated prototype stator, the generation of vibration mode and mode rotation were confirmed. Therefore, the possibility of the realization of the MDOF-USM using a spherical stator was indicated.

A non-contact transport method using near-field acoustic levitation has been studied. In this research, the levitated object is transported by multiple stators in steps. This transport method requires a large number of stators, but it has the advantage of precisef positioning because the levitated object is stopped and held on each stator. In addition, by arranging stators in two dimensions, transportation in two-dimensional direction is realized, but stable operation is not obtained, such as unintended rotation in transportation. Through experiments and analysis, we clarified under what conditions the transported object rotates.

As an application of noncontact transportation utilizing the near-field acoustic levitation phenomenon, a rotary-type noncontact-synchronous ultrasonic motor (NCSyn-USM) using acoustic viscous force was examined. The NCSyn-USM consisted of six fan-shaped stators arranged in a circle and a flat fan-shaped rotor installed above stators via small an air gap. The possibility of the NCSyn-USM was investigated by both of numerical simulation and measurement. From the acoustic-structure and fluid-structure interaction analyzes by finite element method, the correlation between the sound pressure in the air gap and the rotational force was obtained, and it was found that the rotational force was increased by utilizing the acoustic resonance of the air gap. In the experiment, the change of rotational torque with respect to the rotor angular position approximately corresponded with analysis results. The rotation of the rotor by switching driving stators was actually obtained, so that a rotary-type NCSyn-USM would be realized.