Published papers

© 2005-2012 IEEE. A stability index has been generally used in a gait system of formulaic structure. In this standardized structure, a human model has a center of gravity (COG), while a robot device has a zero moment point (ZMP) with COG as the stability standard in the walking motion. In the gait system of wearable type, the stability of human model is closely related with the robot device, in other words, the COG and ZMP are located in the limited domain of human motion and robot task. In this paper, the human and device are designed individually and the knee joint of human is unconstrained from the device work to allow the human reliance. The stability index that includes the COG and ZMP is defined. The validation of this index is guaranteed through a few tests to describe a correlation between the stability index and the human model condition. Based on the validity of the stability index, the experiment for the walking stabilization is implemented with the ZMP estimation by reaction torque observer.

© 1982-2012 IEEE. It is expected that bilateral control will find broad applications such as mobile robot exploration and operations in extreme environments. However, the transmission of vivid haptic sensation requires a rapid data-transfer rate of haptic data due to the short sampling period and high-frequency communication. The objective of this paper is aimed at the traffic reduction of haptic data by exploiting an impedance field equivalence of a standard bilateral control. The proposed approach theoretically clarifies the equivalence of the standard bilateral control and impedance control in terms of haptic transmission. Based on this equivalence, the same performance of a standard bilateral control can be achieved by only communicating the force information that determines the equilibrium position of the impedance control. The validity of the proposed approach is confirmed through both simulations and experiments. The obtained results show that the proposed approach successfully reduced the amount of communicated haptic data without any disadvantages compared with the standard acceleration-based bilateral system. This paper shows novel interpretation that haptic transmission is realized by controlling the equilibrium force, which contributes reducing data traffic in haptic transmission and understanding motion generation.

CCBY In order to realize a vivid tactile transmission in a teleoperation system, it is necessary to send and receive a lot of motion information such as position, speed, and force with extreme high frequency. In addition, in the actual use, many systems are connected to each other through a network. Against this backdrop, the explosive increase in communication traffic becomes a serious problem. The difficulty of this problem is that there exist complicated exchanges of motion information among the systems and they affect each other. Therefore, this paper proposes a novel configuration of a teleoperation system that consists of the conversion technique of transmitted and received information into a single physical quantity (equilibrium force) and the reconstruction technique of discrete data (ZOH: zero-order hold/FOH: first-order hold). The analyses and experiments revealed that 1) FOH is superior to ZOH in terms of operational force 2) FOH and ZOH are about the same performance in terms of reproducibility 3) FOH tends to be more unstable when the packet transmission period increases.

© 2020 The Institute of Electrical Engineers of Japan. Advanced rehabilitation requires a measurement system that quantitatively analyzes the actions of each individual. Joint moment is an indice used to quantitatively evaluate an individual's actions. Conventionally, force plates and highspeed cameras have been used to analyze joint moments. However, these devices need to be fixed in a laboratory, which limits the measurable motions and measurement range. Further, these sensors are expensive. Hence, it is difficult to use them in medical or nursing care facilities. Therefore, this study aimed to estimate joint moments using inexpensive and wearable sensors. This paper proposes a practical joint moments estimation system using inertial measurement units, which is a wearable sensor. The proposed method uses wearable sensors to measure continuous motion without limitation. It is also cheaper than conventional systems. The effectiveness of the proposed system was verified by comparison with the method using force sensors.

© 2019 The Institute of Electrical Engineers of Japan. In motor drive applications, a high switching frequency is required to mitigate current harmonics, which cause a copper loss. However, the high switching frequency makes the switching loss large. Hence, some switching loss reduction techniques have been studied in the past. These techniques have some problems. This paper proposes a multilevel inverter topology for switching loss reduction. Because of provision of multiple current paths, the proposed inverter realizes the zero current switching. Consequently, a loss of the whole system including an inverter and motor can be reduced with a higher switching frequency. The switching loss of the proposed inverter is smaller than that of the conventional one. It was verified that the proposed inverter has some advantages at high switching frequency, through calculations.

Mountain tunnel excavation has two problems, which are a shortage of skilled engineers and frequent industrial accidents. Automation of mountain tunnel excavation is progressing to solve these problems. However, loading explosives in mountain tunnel excavation is difficult to automate because this task requires a sense of force. Motion reproduction is an expected method to automate the process of loading explosives that takes the sense of force into account. It uses bilateral control to save and reproduce motions and has the advantage of being able to reproduce forces and teach human skills to manipulators. On the other hand, motion reproduction cannot succeed in saved tasks when the relative position of the loading hole and manipulator or the direction of the loading hole changes from the saving phase. Therefore, this paper proposes a method to compensate for variations in relative position and direction by image processing based on depth information in motion reproduction for automation of loading explosives. Experiments showed the effectiveness of the proposed method through the successful reproduction of the insertion motion despite variations in relative position and direction.

A force generation mechanism utilizing corona discharge has the advantages of being lightweight, compact, and having no moving parts. The general structure of an electrode used to generate corona discharge is a wire on the high-voltage side and a flat plate on the ground side. To gain greater force generated by corona discharge, it is necessary to install and integrate a large number of electrodes. However, if a large number of electrodes are integrated, the required volume will increase. Therefore, a method of integrating the electrodes to increase the force-to-volume ratio is needed. Therefore, this paper comprehensively examines the two-dimensional arrangement of electrodes on the ground side and investigates the relationship with the force-to-volume ratio. Specifically, the force-to-volume ratio was investigated when the ground side was made of hollow hexagons, squares, or triangles compared to the wire-plate electrode. Also, since it is known that the force is more significant when needles are used on the high-voltage side rather than wires, the high-voltage side was made into a needle for electrodes with hollow polygons. The experimental results show that the force-to-volume ratios of the needle-hollow polygon electrodes were larger when the applied voltage was low, around 20 kV, and that of the wire-plate electrode was larger when the applied voltage was higher than 30 kV. These results show the relationship between the method of integrating the electrodes and the force-to-volume ratio, which was unknown in corona discharge. They can be used as a reference in the design of actuators.