Published papers

This article proposes a new multi-level inverter (MLI) based on flying capacitor inverter (FCI), with focused on high-precision positioning control for a voice coil motor (VCM). Multi-level inverters (MLIs) have the characteristic that increasing the number of output voltage levels reduces the output voltage error. However, as the number of levels increases, the number of circuit elements increases, and the circuit becomes more complex. In addition, the output voltage amplitude for each level is constant in conventional inverters. As a result, such as high-precision positioning control of VCM, designing an appropriate inverter for a reference wave that contains a large amount of low-voltage components increases the number of circuit elements. Therefore, this paper proposes a MLI with two unbalanced dc-input voltages, referred to as unbalanced MLIs (UMLIs) hereinafter. This topology uses two different dc-input voltages, and it is possible to reduce the output voltage level in extremely low-voltage range compared to other voltage levels. Simulation results when the high-precision positioning control of the VCM confirm that the proposed UMLIs improves the control performance compared to the conventional FCIs with equal number of output voltage levels and uniform level widths.

Environmental recognition has an important role in tele-operation. It contributes to the stabilization of complex interactions of robots with the environment. Previous studies have focused on the vision-based method. However, subject dynamics, expressed as stiffness or viscosity, can not be obtained from visual information. One method to determine this is to apply a probing signal to the system and satisfy persistent excitation (PE). However, it comes with the disadvantage of deteriorating operationality for the vibration. Thus, this paper proposed a probing signal compensation method for a 4ch bilateral control system by using a band-pass filter (BPF). Therefore, dynamics identification was accomplished with sufficient PE derived from the probing signal. While on the leader device, oscillations were suppressed and operationality was guaranteed. The proposal contributes to compatible environmental recognition and operationality indemnification for tele-operation systems.

Motion reproduction is a motion generation method in robotics characterized by the small amount of required data and its adaptability to environmental variations. However, completing the task is difficult when the environmental position variation is significant. Therefore, the proposed method generates motion data that is adaptive to environmental fluctuations by performing motion reproduction, with data integrating the position and velocity responses when motion reproduction is performed and the original force response. In simulations, it successfully made contact with the environment even when the distance to the environment was varied. In other words, the proposed method can create motions such that the task succeeded using the failed reproduction data.

Wireless power transmission (WPT) is a major technology and is mainly used in transmitting power to small electronic devices. WPT is also expected to be used for larger, higher-power devices such as EVs. One of the problems with the use of WPT is the loss of efficiency due to the misalignment of the transmitter and receiver coils. Previous studies focus on circuital methods to prevent efficiency loss such as impedance matching or frequency tuning. However, these methods do not solve the coil misalignment itself. The purpose of this paper is to propose a two-axis position estimation method in order to eliminate the misalignment. The two axes mean the parallel and vertical directions of the coils. Knowing coil position information in two axes will contribute significantly to position adjustment between coils, compared to the case of only one axis position information. This paper also verified the accuracy of the proposed method experimentally.