The descent phase of the multi-rotor Unmanned Aerial Vehicles (UAVs) is one of the situations when UAVs tend to lose control because of the Vortex Ring State (VRS). The VRS is one of the states of turbulence. The VRS is a well-known phenomenon in manned helicopters and can also occur during the descent of a UAV. It is difficult to escape from the VRS without taking the VRS recovery motion. Some previous studies have proposed to avoid the VRS condition. However, those methods do not consider the effect of the wind disturbance. It is important to know the real-time turbulence information and detect the VRS to be robust to unexpected wind. This paper proposes a novel VRS detection method using the counter torque of the propeller motor to obtain real-time turbulence information. The method is verified with the bench experiments in a wind tunnel. The results show the possibility of the proposed method to detect the airflow flows into a propeller from dangerous airflow angles.

Recently, wireless power transfer (WPT) for electric mobilities has much attention. The electromagnetic field radiated by the WPT current is limited by the international regulations. In order to reduce the electromagnetic field radiated by the third harmonic current (3rd-EMF) in an SS topology WPT system, the inverter is often operated using a phase shift control whose shifted phase is fixed at π/3 rad. However, an additional DCDC converter is needed to control the WPT power. This paper proposes the two-pulse width modulation method to achieve both the voltage regulation and the 3rd-EMF reduction. The switching timing is determined by calculating the Fourier transform of the inverter output voltage waveform. The proposed method is experimentally validated using a GaN inverter which is used to generate the precise voltage waveform. The results show that the proposed method can regulate the voltage and reduce the third harmonic current simultaneously. The inverter efficiency is more than 92% when the duty ratio is more than 50% even if hard switching is conducted.

To overcome the short flight duration of drones, research on in-flight inductive power transfer has been recognized as an essential solution. Thus, it is important to accurately estimate and control the attitude of the drones which operate close to the charging surface. To this end, this paper proposes an attitude estimation method based solely on the motor current for precision flight control in the ground effect region. The model for the estimation is derived based on the motor equation when it rotates at a constant rotational speed. The proposed method is verified on the simulations and experiments. It allows simultaneous estimation of altitude and pitch angle with the accuracy of 0.30 m and 0.04 rad, respectively. The minimum transmission efficiency of the in-flight power transfer system based on the proposed estimation is calculated as 95.3 %, which is sufficient for the efficient system.

Range extension via speed trajectory optimization is an important issue for battery electric vehicles (EVs), To this end, this paper contributes a practical approach to globally minimize the energy consumption of EVs passing through multiple signalized intersections. The energy consumption is estimated using a traffic flow Gaussian mixture model (GMM) obtained from floating car data. Then, the optimal speed trajectory is generated using dynamic programming (DP). The algorithm is solved distributedly for each segment between two adjacent intersections, thereby, alleviating the computational burden. Furthermore, the proposal does not require vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication. Experimental results demonstrate that the proposed algorithm can successfully reduce energy consumption. The reductions are respectively 11.7% and 8.0% compared to the simple strategy with the constant speed and acceleration/deceleration, and the conventional method which independently minimizes the energy consumption in each road segment between two adjacent intersections.

This paper presents a two-degree-of-freedom control system for improving the attitude control performance under the existence of propeller's loss of effectiveness (LoE). To deal with the long sampling time of attitude measurements, a multirate observer is designed to estimate the attitudes at every control period of the propeller actuator. Using the estimated attitudes, the LoEs are identified via recursive least squares (RLS) algorithm. Using the identified LoEs, the propeller speed references are adjusted to compensate the fault effect on the system. Some physical parameters of the attitude dynamics are also identified to adaptively update the feedforward controller. In summary, the proposed system only consists of practical algorithms which can be implemented conveniently in real applications. Experiments using a dual-rotor testbench show that the proposed system can quickly identify the time-varying LoEs. In comparison with a conventional singlerate control system without fault tolerance, the proposed system can reduce the pitch angle and yaw angle tracking errors by 69.3 % and 39.6 %, respectively.

The short flight time is one of the problems hindering the development of industrial applications of drones. As a solution to this problem, in-flight wireless power transfer (WPT) has been attracting attention, especially in security and R&D operations. One of the challenges of in-flight WPT for drones is the received power control due to fluctuations of mutual inductance and the motor's required power. To control the received power, the active rectifier is usually used in WPT applications, which keeps the power by switching. However, that switching deteriorates the system efficiency. Conversely, if there is not enough power, a normal WPT system cannot control power only by receiving side. In this paper, we propose a unique received power control for in-flight drones that combines power control by the rectifier and altitude control. The performance improvements have been experimentally demonstrated on the bench system. As a result, the conversion efficiency of the rectifier improved by 4.10 % because of a reduction in the number of switching times of the rectifier. When received power was insufficient, the current increased by 1 A and exceeded the lower limit of the control target.

This study aims to develop a tactile display which can represent 2D haptic information. In our previous works, sensorless position control for a compact dual solenoid actuator (CDSA) has been proposed to realize a compact actuation system for the tactile display. To represent the haptic information, contact force control is also required. This paper proposes position/force sensorless force control using the position estimation and a reaction force observer (RFOB). The RFOB is constructed based on the motion equation of the CDSA. Experiments were conducted to validate the performance of the force control. The results show that the contact force is accurately controlled with about 5 mN error which is 6 % of the force command offset. The gain of the proposed force control becomes more than -2.6 dB when the command frequency was less than 20 Hz. The control phase delay was 14.0 ms which came from the cut-off frequency of the low pass filter in the RFOB. The experimental results with change of the mover position showed that the contact force was accurately controlled when the position was at 0.0 ~ 0.2 [mm]. This proposal is useful because a compact actuation system whose position and force are controllable without position and force sensors is realized.

This study aims to realize a tactile display which can represent 2D haptic information on the display surface. The display consists of many compact actuation systems whose position and force can be controlled. In our previous works, sensorless motion control for a compact solenoid actuator has been proposed to realize the compact actuation system. Additionally, we have proposed sensorless control method for a dual solenoid actuator (DSA) to improve the control performance. However, the proposed DSA system has a few problems such as large body, large mover mass, and large friction force. In order to solve these problems, this paper proposes a new compact dual solenoid actuator (CDSA). The proposed actuator has less number of coil turns, therefore much current is required to generate large magnetic force. On the other hand, the large current generates large thermal energy which causes change of the inductance characteristics of the dual coils. The sensorless position estimation is conducted using the relation between the mover position and the inductance. Therefore, thermal compensation method for the new CDSA is also proposed in this paper. Experiments were conducted to validate the proposal. As a result, the sensorless position estimation with less than 60μm estimation error was achieved.

In-circuit tests play a key role in manufacturing electronic devices with a high level of reliability. One of the most flexible technology for the tests is based on flying probes, in which a set of conductive needles is automatically positioned on multiple test points of the device under test. The probes are controlled at high speed within the working space, to increase the production rate, Position and contact force of probing system should be accurately controlled, to prevent damages to the parts. A force sensor is usually used in the contact detection and for controlling the contact force. However, the force sensor is weak against impact force and expensive. A Reaction Force Observer (RFOB) is often used in force control system without force sensors. This paper proposes a fast force controller for probing systems without force sensor. In this study, a MEMS accelerometer is used to improve the performance of the RFOB. Acceleration-aided Kalman Filter (aaKF) is combined with the RFOB to derive accurate estimates of the velocity and acceleration signals. The contact detection is conducted using jerk signal, which can be obtained by differentiating the acceleration. After the contact detection, a negative constant force is applied for a short period, to decelerate the motion of the probe. Finally, a force control is applied. Experiments were conducted to validate the effectiveness of the proposal. As a result, the proposed method can quickly control the contact force without overshoot, with a settling time of 10 ms. The proposed control is effective for circuit probing systems, because the force is controlled in short time, so making the in-circuit test time short.