Published papers

Wireless power transfer (WPT) is a widely used technology today, and one challenge is to prevent the reduction of efficiency due to misalignment between the receiver and the transmitter. One solution is to reduce the misalignment by positioning the receiver at the position that maximizes efficiency, but this requires estimating the positional relationship between the devices. This paper aims to estimate the distance between coils by the receiving voltage value using a magnetic field resonance-type WPT device based on the modelings of mutual inductance from previous studies. Modeling of mutual inductance is performed for the coaxial and non-coaxial coil cases, and a theory is derived for estimating the coil positions from the received voltages. Accuracy is evaluated by comparing experimental data of receiving voltage and distance between coils with theoretical values.

Bilateral teleoperation is a key technology that enables to perform contact-rich tasks remotely. Bilateral teleoperation using commercial industrial manipulators has practical advantages, however, industrial manipulators have low backdrivability and no torque control, so admittance-based force control is required. 2ch admittance-based bilateral teleoperation has been proposed that is compatible with industrial manipulators. However, the conventional 2ch admittance-based type does not take into account the discrepancy of admittance control period and communication period between the leader and the follower that bring out position drift. In this paper, 4ch admittance-based bilateral teleoperation that prevents position drift is proposed, and a comparison between three constructs of admittance-based teleoperation using position-controlled industrial manipulator is conducted through experiments using commercial industrial manipulators Yaskawa GP7 and HC10DTP.

Solid-state electro-aerodynamic propulsion systems are devices that utilize atmospheric pressure corona discharge and have been actively researched in recent years as a means of achieving silent drones. However, these systems contain multiple, widely disparate time and spatial scales. Therefore, the governing equations of the systems, a three-component plasma fluid model that considers the presence of electrons, positive ions, and negative ions, constitute a stiff non-linear system of partial differential equations, challenging to solve. Here, we have developed an ANEMONE simulator capable of numerically estimating the corona inception voltage and energy conversion efficiency in three-dimensional solid-state electro-aerodynamic propulsion systems. Specifically, on the basis of the governing equations, we adopted the method of characteristics and the perturbation method to obtain the sub-problems. Furthermore, we have successfully obtained the integral equations, making the sub-problems easier to solve. Finally, we validated the prediction results based on the theoretical results in a previous study. Remarkably, ANEMONE is the first simulator in the world which predicted the two representative performance (i.e., the corona inception voltage and energy conversion efficiency) of fully three-dimensional propulsion systems. Program summary: Program Title: ANEMONE CPC Library link to program files: https://doi.org/10.17632/2sxsg2pmyp.1 Licensing provisions: MIT Programming language: C++ Nature of problem: Solid-state electro-aerodynamic propulsion system [1] ionizes the ambient air and can propel silent drones. For the rapid-prototyping of the system, it is important to utilize numerical simulation, but the spatial and temporal scales of the system are diverse; hence, the corresponding governing equations (e.g. the three-component plasma fluid model which can simultaneously consider electrons, positive and negative ions) are too stiff to solve. For example, the overall spatial scale of the system is the order of meters, while the scale of the electrodes is the order of micrometers. Moreover, the ions move between electrodes in the order of milliseconds, while the Maxwell dielectric relaxation time scale is in the order of nanoseconds. Solution method: For the issue of the spatial scales, we adopt a three-dimensional hierarchical Cartesian grid method together with the adaptive mesh refinement method. Moreover, this leads fully automatic mesh generation and ensures the grid convergence. For the issue of the temporal scales, we adopt the perturbation method [2] combined with the method of characteristics. This can decompose the original problem into many subproblems easy to solve. References: [1] Haofeng Xu, et al., Flight of an aeroplane with solid-state propulsion, Nature 563 (7732) (2018) 532–535. [2] Hisaichi Shibata, et al., Performance prediction of electrohydrodynamic thrusters by the perturbation method, Phys. Plasmas 23 (5) (2016).

Explosive loading in mountain tunneling requires automation due to a shortage of skilled workers and occupational accidents. However, automation is difficult because handling explosives demands delicate force control. This paper adopts motion reproduction based on human motion to consider the adjustment of force. Nevertheless, conventional methods fail when the hole's position differs from the recording. Therefore, a new method is proposed that detects hole positions using a stereo camera, performs calibration, and compensates for positional differences while reproducing the motion. Through experiments using industrial manipulators, it is confirmed that motions are reproduced for different hole positions from the recording.

Bilateral teleoperation is one of the teleoperation methods that enables safe contact by synchronization of position and force between the leader and follower devices. However, the controller is designed by trial and error in many cases. There are some problems in that the maximum control performance is not achieved and it may cause destabilization in contact with a hard environment. Therefore, this paper proposes the design of the gain updating law considering environmental stiffness for bilateral teleoperation. The validity of the proposal is confirmed by experiments. This paper contributes to the appropriate gain selection in each environmental stiffness.

This paper proposes a simple and practical estimation method of switching losses considering the ac winding resistance of the extremely highly efficient high-power dual-active-bridge (DAB) converter with the conversion efficiency from the dc input to dc output terminals with over 99%. The extremely highly efficient high-power DAB converters are sensitive in measurements or estimations of switching losses at zero-voltage switching (ZVS) and copper losses in the magnetic devices in terms of accuracy and practicality of those. Experimental results obtained from the 850-V 100-kW 16-kHz DAB converter confirm that the proposed method makes possible to separate the switching loss easily at ZVS from the overall loss using the ac winding resistance of the magnetic devices measured accurately under the conditions assuming the actual high-current operation.

Permanent magnet linear synchronous motors (PMLSMs) are widely used in high-precision motion systems, where fast and accurate current control is essential to achieve superior thrust performance. Deadbeat predictive current control , especially multi-sampling deadbeat predictive current control (MS-DPCC), provides excellent transient response; however, its performance is highly sensitive to parameter mismatches in the motor model, which inevitably cause steady-state current errors. Although disturbance-compensated approaches have been investigated, their ability to cope with multiple parameter mismatches remains limited. To address this issue, this paper proposes a robust current control scheme that integrates a reduced-order extended state observer (ESO) into the MS-DPCC framework. An analytical investigation reveals that mismatches in stator resistance, stator inductance, and permanent-magnet flux linkage inherently induce steady-state current deviations in deadbeat predictive current control. Based on this analysis, a reduced-order ESO is designed to estimate and compensate equivalent disturbances arising from parameter mismatches, and its structure is tailored to the multisampling characteristics of MS-DPCC. Simulation results demonstrate that the proposed method reduces steady-state current deviations under various parameter mismatches while preserving the fast transient response of MS-DPCC. These results confirm that the proposed control scheme achieves both high dynamic performance and strong robustness against model uncertainties.

Environmental impedance recognition is important for abstracting human dexterous motion characteristics. One of the methods to abstract such beneficial information is bilateral teleoperation, which expresses the interaction between the human and the object. To identify the environmental impedance, injecting a probing signal with a wide range of frequency components is an effective method for improving system identification performance. However, such signals introduce vibration components that deteriorate human operability; therefore, there is a tradeoff between identification performance and operability. Hence, a probing signal autoelimination method based on the environmental impedance identification error is proposed. When the identification error is adequately small, the probing signal should be eliminated to avoid disturbance. Conversely, when the identification error increases because of environmental variation, the probing signal is reinjected. The proposed method can adaptively switch between injection and elimination of the probing signal according to changes in the environment. Furthermore, the effect of the probing signal is analytically formulated, and its characteristics are clarified. Therefore, the proposed approach overcomes the tradeoff between identification performance and operability. The effectiveness of the proposed method is experimentally validated by evaluating the convergence of identified impedance parameters and the squared identification residual under spring-type environments.

Electroaerodynamic propulsion systems, which use ionic wind resulting from corona discharge to generate thrust, have the advantages of being compact, lightweight, and silent. However, a critical challenge in improving thrust is that increasing the distance between the electrodes to increase the applied voltage increases the leakage of ions, which does not contribute to thrust, resulting in a reduced output thrust. To address this problem, this study proposes a method that uses a cylindrical Guide electrode placed at the same potential above the emitter to generate ions. As a result, this electrode changes the electric field distribution around the emitter and concentrates the electric field toward the collector, thereby suppressing ion leakage. Experimental results show that the addition of the Guide electrode significantly improves the maximum achievable thrust and thrust-to-power ratio, with a maximum thrust improvement of 36.6%. This study demonstrates a relatively more simple and effective electrode design for increasing the generated electroaerodynamic thrust and provides useful knowledge for the design of future high-efficiency and silent propulsion systems.

The motion reproduction system (MRS) transfers human dexterous motion skills to robots. Compared with other machine learning-based methods, it has an advantage in terms of the number of data points and hyperparameters. However, it may fail when the actual object of motion differs from that of acquired human motion. Conventional studies consider human stiffness, which characterizes the intention of human motion. Although they performed better than the original MRS with variable objects, they estimated human impedance using linear interpolation. Linear interpolation is insufficient for generating novel, human-like motions that are nonlinear and time-variant. In this article, more sophisticated motions were generated by fitting the relationship between environmental stiffness and position, velocity, and force nonlinearly using Gaussian process regression, which requires a smaller amount of data compared to machine learning-based schemes. Through experiments, the data number and error reduction between the true human motion and actual motion were confirmed by comparing the original and conventional MRS and the imitation learning. Therefore, the proposed method can generate motion for variable objects more precisely with a small amount of human motion data.

Although cell manipulation technologies have been adopted in a wide variety of applications, at present operators must rely solely on visual information to perform such procedures without damaging the cells. Consequently, there is an increasing demand for the integration of tactile feedback. However, conventional force sensors face significant challenges in detecting ultrafine forces exerted on soft targets such as cells. In this study, we propose an admittance-based bilateral control with reaction force estimation using an optical tweezer. The results of an experimental evaluation showed that a prototype system was able to estimate and transmit forces on the order of piconewtons to facilitate ultrafine teleoperation. Thus, our results show that the proposed approach overcomes conventional limitations in measuring ultrafine forces and enables intuitive force feedback. These capabilities are expected to reduce the difficulty of specialized microscale tasks such as cell manipulation significantly.

© 2018 The Institute of Electrical Engineers of Japan. An aging society is a serious problem in many developed countries. Due to this issue, there has been a significant increase in the demand for assist devices that can support human motion. This paper proposes a novel assist device, Intelligent Tension Pole (ITP), to assist in indoor activities of daily living (ADL), and it is expected to provide support for achieving self-reliance, space saving, and stability. The structure and control system of this assist device are presented. This novel assist device is based on a movable handrail, and therefore wheels are added to the lower and upper ends of the tension pole. In addition, a ball screw, which enables the ITP to move while stretching to the floor and ceiling at any time using force control, is added. In order to improve user comfort and reduce the risk of falling down of the ITP, translation and inclination controls of the ITP are applied to the wheel control. These controls are controlled independently by the mode decoupling method. Experiments are conducted to verify the effectiveness of the proposed device and its control system.

Electrohydrodynamics (EHD) is a thrust force produced when high voltage is applied to two electrodes, and actuators using EHD are expected to reduce equipment size and the effects of friction. However, the EHD effect of multiple anode electrodes has yet to be verified and should be considered when fabricating a multi-degree-of-freedom actuator using EHD. This paper examines the relationship between the applied voltage and the generated EHD to verify the effect of multiple anode electrodes on the EHD. Experiments were conducted using a device with two anode electrodes at right angles and another with two parallel electrodes. The results showed that the two anode electrodes placed at right angles interfered with each other, and the generated forces were not superposed. The direction of the generated force was approximately 45 deg. When the electrodes were placed horizontally, it was confirmed that the generated forces were superposed, indicating that the arrangement, not the number of anode electrodes, was the cause of the interference.

There are some dangerous situations under tunnel construction. Since humans fill small halls on the surface of a tunnel with explosives by their hands, they always work with risks of injury or death due to accidents of unexpected explosions or collapses of tunnels. In order to proceed with construction, remote control robots that take the place of their work have been developed. Although they made construction safer for humans, the operation of remote control robots is difficult. This paper proposes a method to adjust the angle vertically by using mechanical power factor feedback. When the robot's arm hits the target object, it estimates an angle deviation by mechanical power. The mechanical power factor is an analogy to power factor in electronics, which is proposed to estimate an angle deviation easily instead of using an angle sensor. It makes it possible not only to evaluate a performance of robots but also estimate an angle deviation for the vertical adjustment. Thus, the proposal has advantages in terms of focusing on the mechanical power factor. By conducting simulations, the results of the estimation of angle deviation were verified.

Electroaerodynamics (EAD) is one phenomenon that manipulates gas with high voltage. Corona discharge is a typical example and is known to produce thrust quietly without moving parts. Therefore, it is expected to be utilized in various ways, such as a thrust source of drones. As thrust with corona discharge depends on the applied voltage, it is necessary to manipulate the applied voltage for thrust control. However, large-scale systems require several tens of kV, and there is little adequate research on these systems. Thus, an adequate switching method is essential, and it is also crucial to elucidate the effect of switching on thrust. Hence, this study conducted thrust control with corona discharge and analyzed the influence of switching on thrust. Specifically, a resistor is connected in series to the electrode, and a switching element is connected in parallel with the resistor. The proposed method stabilizes and limits the voltage applied to the switching element and effectively controls the thrust and the voltage applied to the electrode. Two experiments were conducted to reveal the electrical characteristics of the electrode in corona discharge and confirm the effectiveness of the proposal. The first experiment showed the potential of switching for the electrode with corona discharge on the collector side. Moreover, the second experiment demonstrated that the proposed switching method worked properly, and thrust can be controlled by changing the duty ratio of switching. The achievements of this study are expected to control levitation systems EAD, such as corona discharge, and realize stable control.