A characteristic analysis of an ultrasonic motor (USM) at the design stage has thus far been impossible. Therefore, a characteristic analysis method is suggested on the basis of a proposed model describing the complex nonlinear contact condition between the rotor and stator. The proposed contact model and analysis method can guide theoretical research on the minimization of the main disadvantages of the USM, which mainly result from the contact mechanism. The validity and usefulness of the suggested analysis method is verified by experimental data from a prototyped USM.

An electric motor is a device that changes electrical energy into mechanical energy for railway vehicles. When developing the electric motor, it used to be developed simply for structures or control methods of the motor itself without considering convergence with other devices or technologies. However, as the railway vehicles become more advanced, technology development through convergence with other devices or technologies is spreading. Therefore, based on patent data related to the electric motors applied to the railway vehicles, this research aims to carry out technical forecasting for establishing research and development (R and D) direction for new technologies by predicting vacant technologies from the point of view of technology convergence. In other words, we studied how to find the vacant technologies in a field of convergence technology for the electric motor of the railway vehicles by analyzing the patent data. More specifically, we search the patents data associated with the electric motor of the railway vehicle that contain multiple IPC codes, and use multiple IPC codes to determine the field of convergence technology. In addition, we extract keywords from the patents data related to each of the determined convergence technologies and define the vacant technologies by interpreting the field of convergence technology and the extracted keywords.