Published papers

Proximity and tactile sensors have been widely used to control robots. However, each of these sensors has its own shortcomings. Visual sensors have blind spots, whereas tactile sensors cannot acquire information when non-contact. To overcome these problems, this study develops an optical sensor that can measure the distance and two-axis forces using a beam structure and photo reflectors. The sensor is inexpensive owing to its simple structure. Moreover, the sensor is demonstrated to have sufficient accuracy for both the distance and force measurements at 0.2, 0.5, and 1.0 Hz. Additionally, the usefulness of the sensor is confirmed based on reduced impact control at the time of contact and force control.

Proximity sensors measure the distance to an object and detect contact. Hence, proximity sensors are typically mounted and used in end-effectors. There might be situations where it is necessary to acquire information on not only distance and contact; but also the normal force and shear force. The conventional proximity/biaxial force sensor utilizes beam deflection but brittle material and interference limit its performance. Here we present a novel proximity/decoupled biaxial force sensor made of sturdy materials, springs, and photo reflectors. We demonstrate this sensor's performance and advantage of the proposed sensor in teleoperation and during a task requiring rubbing an object.

In recent years, wireless power transfer (WPT) has become popular from the viewpoint of easy charging. Among them, magnetic field resonance WPT is being researched and developed due to its high efficiency. However, there are magnetic fluxes that cannot be used for power supply and are leaking out in magnetic field resonance WPT. Therefore, this paper applies a special magnet arrangement, a Halbach array, for transmission coils. The Halbach array transmission coils can concentrate the magnetic fluxes on one side. This feature allows the magnetic fluxes to be concentrated to increase the amount of magnetic fluxes chained to the receiving coil. It has a significant effect on efficiency. Since the size of the transmission and receiving coils also affects efficiency, this paper changes the size of the coils and analyzes its effect on efficiency. The efficiency of the Halbach array transmission coils will be confirmed by comparison with conventional transmission coils.

A method to generate wind based on electrohy-drodynamics (EHD) using corona discharge has been applied to various thrust-producing devices. However, the relationship between electrode structure and wind-induced thrust is still unclear, and electrode design guidelines have not yet been established. Therefore, this paper aims to formulate the relationship between the thrust and electrodes' configuration by taking continuous data from experiments. Experiments were conducted to investigate the change in thrust when the gap between electrodes was varied continuously, and when changing the shape of electrodes, after a preliminary experiment on the relationship between voltage polarity and thrust. Experiments revealed that thrust increased as the gap decreased at the same voltage, thrust began to be generated at a lower voltage when the emitter electrode was needles than when it was a wire. From these experimental results, it was demonstrated that the thrust was expressed as a linear equation of voltage, that there is an inverse proportion-like relationship between the gap and thrust, and that the corona discharge inception voltage became lower when needles were used as the emitter electrode, where the voltage applied, instead of a wire. These findings and considerations will greatly help to establish guidelines for designing devices using this method, which generates thrust without any moving parts.

This paper presents a framework for intuitive teleoperation of a 1-degree-of-freedom (DOF) robotic gripper using hand gesture data, focusing on dimensionality reduction, impedance control, and reaction force prediction. High-dimensional hand kinematics are compressed into a 1-dimensional (D) latent command using a combination of Principal Component Analysis (PCA) and Autoencoder (AE) for robust mapping. The gripper operates under impedance control to perform grasping on soft objects. A Long Short-Term Memory (LSTM) network is trained to predict reaction forces using past gripper positions, user commands, and object labels, using ground-truth torque provided by a Reaction Force Observer (RFOB). The model relies only on static position data and temporal context, omitting velocity and acceleration to reduce complexity. This lightweight approach allows virtual force feedback to be generated directly from hand gestures without physical force sensors. Experiments show accurate gripper control, noise robustness, and real-time performance. The force prediction model achieves an R2 score of 0.9778, and PCA-Autoencoder (PCA-AE) outperforms conventional methods in balancing variance capture and noise robustness. The framework is suitable for force-sensorless teleoperation systems and virtual environments, such as surgical training or simulation, where realistic force interaction is required without hardware feedback. Additionally, predicted forces can support safety mechanisms, such as overgripping prevention, by estimating contact forces before execution.

As the world has become increasingly electrified in recent years, wireless power transfer (WPT) has been gaining attention as a novel charging method. Among various WPT methods, the magnetic resonant coupling type is used in applications such as electric vehicles (EVs). However, the magnetic resonant coupling type has the problem that only half of the magnetic flux of the coil contributes to the power supply, resulting in magnetic flux leakage. Therefore, this paper focuses on a magnet arrangement called a Halbach array, which strengthens the magnetic flux on one side and weakens the magnetic flux on the other side. This paper applies the Halbach array coils as a receiver to improve the power-transfer efficiency in WPT system. Experimental results confirm that the proposed receiver with Halbach array coils achieves higher efficiency than the conventional square coil receiver across air gaps of 10 mm to 70 mm at constant dc input power.