This paper presents a force sensorless workspace hybrid position/force control method with equivalent mass matrices switching for rubbing motion. The equivalent mass matrices express an interference between control axes. Since the determinant of the matrix computed from the design values of robots becomes near zero around the singular configuration of robots, the utilized matrices are often arbitrarily designed. However, inappropriate matrices conditions deteriorate control performance and could cause vibration during rubbing motion. This study reveals suitable equivalent mass matrices for rubbing motion depending on the velocity of the force control axes. Moreover, a hybrid controller with equivalent mass matrices switching depending on the expected velocity of the force control axes in tasks is proposed. The validity of the proposed hybrid controller is demonstrated by the experimental response of rubbing motion with a parallel link type direct-drive four-link manipulator.

This paper proposes a method for autonomously replanning the optimal trajectory of a teleoperated mobile robot to avoid obstacles during teleoperation with time-varying delay. Model predictive control (MPC) is applied to compensate for the time-varying delay to ensure the mobile robot autonomously avoids obstacles. An operator operates the robot while viewing the predicted model. The state of the predicted model is sequentially sent to the teleoperation system by the local system including the predicted model. This earlier received predicted state is used as a reference trajectory for MPC, and linear interpolation is performed on the lost data of the reference trajectory. When an obstacle is encountered, the path to avoid it is replanned. The constraints for obstacle avoidance, including the cost of the distance between the obstacle and the mobile robot are relaxed, making obstacle avoidance control robust to modeling errors. The mobile robot then follows a reference trajectory while maintaining the optimal distance to the obstacle. Simulations and experiments are conducted to evaluate the performance of the proposed method in comparison with conventional methods.

The force/tactile sensation (hereafter referred to as f/t sensation) has not been well defined for a long time. In the applications of real haptics, it is necessary to quantitatively evaluate the quality of the f/t sensation. The paper proposes the definition of f/t sensation as the stimulus signal. Accordingly, the instantaneous value of the stimulus signal of the f/t sensation represents the simultaneous ratio of the value of reaction force and the value of velocity. If the contact target is modeled as an inertia-damper-spring model, the stimulus signal of the f/t sensation is expressed as the equivalent circuit of the sum of the impedance (or admittance) and the voltage source (or the current source). The definition of the stimulus signal of the f/t sensation in frequency area clarifies the physical meaning. The paper presents the experimental results that confirm the viability of this novel definition on the stimulus signal of the f/t sensation.

Bilateral control realizes position synchronization and the “law of action and reaction” between two points. To advance applications of bilateral control, it is necessary to emphasize environmental adaptability, safety, and task execution. Accordingly, the bilateral system is required to consider contact with unknown environments and realize stable contact to avoid harm to the operator or the object. Thus, a bilateral control system using elastic manipulators is proposed in this paper. Moreover, the integration of mechanical and control designs for stable interaction with the operator and the environment is discussed. The proposed bilateral system with elasticity is modeled as a pair of two-mass resonant systems. Accordingly, a modal space control (MSC) is introduced with the aim of realizing the control goals, vibration suppression, and good operationality. Modal transformation independently configures the force and position controllers of each other in virtual common and differential spaces. MSC comprises reaction torque feedback loops in the modal space and modal space load-side disturbance observer (MLOB). MLOB compensates for load-side disturbance, including the interference between the common and the differential modes. It realizes disturbance suppression, decoupling control, and nominalization of parameters in the form suitable for each force and position control system.

Joint motors of legged robots and manipulators need to withstand temporary high loads during walking, posture maintenance, and contact with external objects. To only increase the torque, the gear ratio can be increased; however, this decelerates the movement. To increase the power of the motor, improving the torque-current characteristics or applying a high current is necessary. When a high current is applied, a large amount of heat is generated by the motor, which can cause motor failure. In this study, we used thermoelectric cooling as a new cooling method for robot joint motors and verified its effectiveness.

We developed a thermoelectric cooling module that can significantly cool a motor before it experiences a high current. Experiments were conducted in which a motor was subjected to a high-load motion, and the results with and without the thermoelectric cooling module were compared. It was shown that the developed thermoelectric cooling system improved the performance of the motor.

This paper proposes the controller design for a shape memory alloy (SMA) positioning actuator system. The system utilizes spiral-formed SMA wire as the driving power source. SMA generates force via temperature-based crystalline phase transitions. The wire is deformed in the spiral form under low temperature and heated by applying direct current, it recovers to the original form and generates the recovering force, which rotates the attached load. This paper proposes using the electric resistance of the SMA, which is related to its crystalline phase status, for designing the controller of the actuator system. The feasibility of the proposed system and controller design are evaluated experimentally with a sample test device, manufactured using a 3D printer, and the device achieves the designed rotation.

We evaluate an external segment-type switched reluctance motor (ESSRM) generator via simulations and experiments on an actual ESSRM. In the simulation, the shape of ESSRM was optimized using a genetic algorithm with two shape sizes varied as parameters. As a result of calculating 480 different shapes, it is found that the model that optimized by the genetic algorithm has a 1.45% higher power generation efficiency of 95.08% and a 634W higher generated power of 2,896W than the model optimized using a single parameter. To prototype a small SRM for evaluating the validity of the simulation model, the ESSR simulation model is similarly miniaturized. We developed a small model of ESSRM and conducted power generation experiments. In the ESSRM, the maximum power generation efficiency was measured as 62.13% when the generated power was 81.20W. As a result of comparing the simulation results with the experimental results by changing the number of segments, consistently the power generation efficiency was consistently highest when the number of segments was five in both experiments and simulations. The results confirm the validity of the simulation model.

This paper presents a phase-shift control method of a triple-active-bridge converter for distributed power supply systems with multiple batteries. The experimental results show that the reactive power through the transformer can be suppressed under a wide range of conditions. The proposed phase-shift control method improves the light load loss at 500W by approximately 30% compared to the conventional method. In addition, according to the power-transmission characteristics of the proposed method, for applications in which a voltage source connected to an input port is attached and detached, the power supply and demand can be adjusted between each output port while gradually lowering the charge of the input port by utilizing the characteristics of the charging operation. Therefore, the converter can continue to operate regardless of the attachment and detachment of the input port-voltage source.

SiC devices are potential future power devices because of their higher switching speed and lower ON resistance than those of Si devices. Research and development efforts to apply them in medium- and large-capacity power conversion circuits are underway. However, SiC power devices in TO packages, which are general-purpose packages, are difficult to apply in high-current applications owing to their low current ratings. Therefore, increasing the capacity of power devices by connecting them in parallel is being studied. However, the current imbalance during switching due to the differences in device characteristics and variations in parasitic inductance is problem. This study proposed a current-balancing procedure focused on the parasitic inductances around power devices and gate drive circuit implementation. The proposed method was verified by conducting double-pulse tests at 300V and 200A.

The recent increase in residential photovoltaic (PV) power generation has become a major factor in the electricity supply instability. As a result, power balancing at the distribution level is becoming increasingly important. In Japan, storage batteries installed in residential homes along with PV systems has reached nearly 3GW and are expected to contribute to the power system stability. In this paper, we propose a method for a group of residential consumers to participate in the balancing market by managing their total meter value to match the target power. This method consists of the following two stages: bid volume optimization, which optimizes the bid volume based on the past behavior of the consumers, and demand response (DR) dispatch optimization, which quickly determines the dispatch of charging and discharging requests every 5min when DR is requested. Evaluation simulations based on the actual 1-min power data and consumer response model showed that, by aggregating 1600 consumers, the success criteria of the balancing market can be met. In other words, the total metered power in 1-min and 5-min intervals can be controlled within ±10% of the bid volume against the target power. From these experiments we have shown that the aggregation of as large as 1600 residential consumers has the potential to participate in the balancing market.

In recent years, progress in power semiconductor switching devices has created more additional advantages that can be realized using multi-phase inverter-fed motors. The authors propose a MATRIX motor to realize electric motors with higher functionalities than conventional electric motors. Since the MATRIX motor is driven by H-bride inverters connected with each phase winding, it has a high degree of freedom in control. Moreover, these inverters can change their connections to different phase coils to realize a wide operating range. The voltage equation of each mode can be expressed using the transformation matrix when the winding connection is changed. Therefore, we call the proposed motor MATRIX motor. In addition, since motors are being applied to various applications that operate within proximity of people, further quietness of the motor is required. In this paper, we propose a method to suppress vibration caused by a specific harmonic order radial direction electromagnetic force via teeth flux density control using the MATRIX motor. The specific order radial force and vibration are suppressed by utilizing two features of the MATRIX motor. One is a high degree of freedom of current control owing to multi-phase drive and the other is local flux density observation. The effectiveness of the proposed method was clarified using experimental results.

A universal smart power module (USPM) has been studied as a modularization method for rapidly developing power converters with various specifications. Herein, a control method is proposed for a three-phase modular multilevel converter composed of USPMs. The autonomous balance control of the proposed control method suppresses the variation in the voltage of the cell capacitor and the disturbance caused by communication delays. This enables the application of the proposed versatile extension method. Moreover, current droop control suppresses the effects of delay variations caused by wireless communication and eliminates system instability caused by control interference between modules. Based on the experimental results of steady-state and load-fluctuation responses with a simulated wireless communication implementation, the deviation from the command values of the line and cell capacitor voltage is less than 5%. Furthermore, the autonomous balance control improved the variation in the capacitor voltage in all modules from 9.70V to 1.94V. The results validate the effectiveness of the proposed control method in wireless communication environments.

Recently, the resonant inductive coupling wireless power transfer (RIC-WPT) technique is being widely used to charge small IoT devices dispersed in a wide area, e. g., an office desk and warehouse rack. In this application, the repeater is utilized to expand the chargeable area without an additional AC power source. The repeater comprises a LC resonator commonly with a high-quality factor to induce large current in the repeater coil. However, this causes the problem that the repeater performance is highly susceptible to the variation in its resonant frequency due to the manufacturing tolerance of coil inductance and resonant capacitance as well as the variation of the magnetic coupling between the transmitter and repeater coils. To solve this problem, a previous study has proposed a concept of the autonomous resonant frequency tuning circuit to stably maximize repeater coil current, although this study implemented a part of this control system as a practical circuit. This paper aims to develop a complete autonomous resonant frequency tuning circuit that implements the aforementioned concept. The proposed circuit adjusts the resonant frequencies of the transmitter and repeater by utilizing the Automatic Tuning Assist Circuits. These frequencies are optimized using the infrared wireless signal communication from the transmitter to the repeater. Along with the operating principle of the proposed circuit, this study presents detailed circuit design as well as the experimental results, which verified the stable autonomous maximization of the repeater coil current against the variation in the resonant frequency of the repeater resonator.

This letter proposes a control strategy for reducing a ripple current in DC-link capacitor of single-phase uninterruptible power supplies (UPS). The proposed method aims to reduce the capacitor current by reducing the difference between the input and output instantaneous power. The input current waveform should satisfy harmonic current regulation and be as close as possible to the load current. Therefore, an auxiliary buck chopper was added to compensate to the ripple current in DC-link capacitor. Experimental result confirm that the proposed method reduces the RMS value of the DC-link ripple current by 27.9%.

Grid-forming inverter control plays an important role in ensuring frequency and voltage stability in a microgrid (MG). This paper proposes a novel power and voltage control in the αβ domain. The proposed method includes two control loops; an outer loop for power droop control and an inner loop for output voltage control. With the proposed controller, active and reactive powers can be controlled according to simple complex power control principles described only in the αβ-domain. Controller gain tuning for both the outer droop and the inner voltage regulator is also proposed; the droop control gains are tuned based on transfer functions around an operating point and the voltage regulator is tuned by a linear quadratic regulator (LQR). The proposed control method is investigated and validated by simulations with a C control program and by experiments with a DSP-based digital control system.

When designing electric motors, many types of performances (electrical and mechanical characteristics) must be predicted with good accuracy. In general, these performances are determined based on complex theoretical calculations, but theoretical calculations include various assumptions. Therefore, it is difficult to eliminate prediction errors when predicting performance, and it is necessary to improve accuracy by referring actual test data. Recently, with the digitalization of the manufacturing process, a large amount of actual data has been converted into a database, and it is expected to be put to effective use. Here, a neural network that predicts various performances of electric motors using a large amount of actual data as a training dataset, is constructed to achieve uniform and high-precision performance prediction via deep learning. Its practical use for actual design work is verified in this study.