Human support robots are in high demand and the performance enhancement through force control has been extensively studied. However, the design of the force controller and selection of appropriate gains are sometimes difficult because they are affected by the conditions of motion such as environmental impedance or model uncertainties. This study discusses force control with a disturbance observer and applies a neural network (NN) into its controller; the NN works as both the feedback and feedforward components. The contribution of this study is to show the development method of force control using disturbance observer and a NN, which enhances the performance of force control from the perspective of both feedback and feedforward components. The structure of the controller and composition of the NN were selected through simulation results; moreover, the compensator based on NN was designed in a frequency range higher than the cutoff frequency of the observer with a small number of hidden layers. Moreover, this study discusses a training method of weights in real time . Simulations and experiments were performed for showing the effectiveness of the proposal.
In recent years, the declining birthrate and an aging population have become a serious problem in Japan. For this reason, the number of elderly people who have difficulty going outside is expected to increase. In addition, elderly people have difficulty dealing with modes of transportation such as cars and bicycles. To solve these problems, a small and easy-to-handle mobile robot, such as an inverted two-wheel vehicle is expected to be a useful device. However, the vehicle robot has difficulty moving along a path with a narrower width than that of the vehicle body. Therefore, in this paper, a trajectory planning method is proposed that makes it possible for vehicles to move laterally on narrow roads using a pivot turns in places where it is otherwise difficult to turn. The validity of the proposed method was evaluated experimentally.
This paper presents a bidirectional converter with multi-stage FETs featuring voltage balance control function using variable capacitors. The proposed converter is constructed using low-voltage Si-FETs in a series connection, and it improves the voltage balance between the drain-source voltages of the series connected FETs in the OFF period. Using the converter figure of merit (FOM), which can estimate the converter losses from the specifications of the FETs, the effectiveness of the proposed converter is compared to that of a converter using SiC-FETs. The factors of the voltage unbalance are analytically clarified using the equivalent circuit. The principle of voltage balance control function using the variable capacitor is discussed. The experimental results show that the proposed converter can achieve a maximum power conversion efficiency of 99.2%.
In this paper, a method for dead time voltage compensation is proposed. The dead time is a period for preventing short circuits in the semiconductor power devices incorporated in inverters. Owing to this dead time, an error occurs in the output voltage of the inverter with respect to the voltage command. To suppress this error, a dead time compensation signal is generally added to the voltage command. However, the accuracy of the above-mentioned compensation control may be reduced because of the switching characteristics of the power device, transmission delay of the switching command, and so on. In the proposed method, to achieve highly accurate dead time compensation, the waveform of the compensation signal is formed based on a circuit model that assumes a virtual capacitor is connected to the semiconductor power device in parallel. In addition, an automatic adjustment method was proposed for parameters such as the capacitance of the virtual capacitor. The proposed method is validated experimentally.
To efficiently and safely reuse recycling batteries from electric vehicles in distributed generation systems, it is necessary to reduce the ripple currents caused by single-phase inverters. Thus, in this paper, an active power-decoupling circuit to reduce either high- or low-frequency ripple currents is proposed. The effectiveness of the proposed circuit is verified by simulation results.
This paper presents a bidirectional non-isolated dc-dc converter based on three-level flying-capacitor converters intended to be applied to electric railway systems. It consists of several main converters with four power devices per converter, multiple auxiliary converters each of which is formed by cascaded chopper cells, and inductors for current control. The dc-dc converter can achieve zero-current switching (ZCS) for all the power devices in the main converters, not only under steady-state conditions but also under transient-state conditions including sudden changes in the supply voltage. This paper presents a current control method based on dq0 transformation and a voltage control method for the floating dc capacitors used in the auxiliary converters. The validity of the control methods proposed in this paper is verified through experiments using a 200-V, 2-kW downscaled model.
This study presents a novel circuit topology for a single-phase inverter using an active power decoupling circuit operated in discontinuous current mode (DCM). In a conventional single-phase grid-tied inverter, bulky capacitors are used in a DC-link to absorb a power ripple with twice the grid frequency. However, electrolytic capacitors limit a converter's lifetime. In contrast, ceramic capacitors are used in the proposed circuit since the required capacitance is reduced. Furthermore, the active power decoupling circuit in DCM has no inductor inside by utilizing the current zero cross featured in DCM for power ripple compensation modes. An experimental verification using a 1-kW prototype shows a 90.2% current ripple reduction caused by the power ripple with twice the grid frequency. The efficiency exceeds 94% in the 20% region of the rated power to 1-kW through 96.0% of the 650 W maximum. According to a theoretical evaluation using a Pareto-front optimization assumed as a 3-kW system, the proposed circuit reaches the maximum power density at 20 kHz which is 115 % higher than that of the passive power decoupling method. The inductor volume in the proposed circuit is reduced by 30.4% compared to a conventional buck-type active power decoupling circuit.
The demand for robots working with humans, known as collaborative robots, has increased recently. Collaborative robots must be human-friendly; they must ensure safety and flexibly follow human’s instructions. In the industry, as the cost of high-resolution encoders has decreased, the number of devices with load-side encoders has significantly increased. However, studies on control methods using load-side encoder information are limited. Therefore, in this paper, a high backdrivable control method for geared mechatronic systems is proposed using load-side encoder information and backlash. The proposed high backdrivable control method utilizes the idling characteristics of backlash, by precise position control using both motor-side and load-side encoders. The performance of the proposed method is verified and compared to impedance control. Moreover, the advantages of employing a load-side encoder to collaborative robots are demonstrated by simulations and experiments.
Surgical robots have been studied and developed to assist surgeons. Master-slave flexible forceps robots that are components of a flexible endoscopic surgical robot are useful to realize novel minimally invasive surgical procedures that are difficult for conventional rigid medical devices. Although driving force for the tip portion of a flexible forceps robot is mechanically transmitted by wires through the flexible portion, friction and backlash changed by the posture of the flexible portion make it difficult to realize precise end effector control. Furthermore, transmission of haptic sensation is necessary to realize safer operation. In this study, a multi degrees-of-freedom (DoF) haptic forceps robot with three fingers is presented as an end effector of a flexible forceps robot. Transmission of driving force in flexible structure that causes performance deterioration is eliminated by arranging motors near the end effector. To transmit haptic sensation to operators, bilateral control is implemented to a master-slave system composed of the haptic forceps robot and a multi DoF input device. Additionally, control on modal space is implemented to verify finger dexterity. The utility of the haptic forceps robot is experimentally validated.
This presents a reactive power control strategy for the single delta bridge cell modular multilevel cascaded converter (SDBC-MMCC) for static synchronous compensator (STATCOM) under asymmetric voltage conditions. An average power balancing method is proposed to support continuous injection of reactive power under grid voltage fault conditions, considering sub-module capacitor voltage balancing and STATCOM maximum phase current protection. Analytical solutions of the STATCOM phase currents are presented. A maximum current limit control scheme is proposed to ensure continuous reactive power injection and STATCOM operation under unbalanced voltage condition. The fault-ride through capability of the SDBC STATCOM under asymmetrical condition is analyzed using the proposed method. A comparative analysis shows that the current requirement of the proposed strategy is superior to the zero-sequence current balancing technique.
This paper describes the implementation of a disturbance observer-based controller after Savitzky-Golay filters. The cutoff frequency is a bottleneck for the conventional disturbance observers in DC motors with position measurement. The measurement noise limits the cutoff frequency of the pseudo-derivative in the design of the conventional disturbance observers. This study proposes an implementation of a disturbance observer based on Savitzky-Golay filters to improve the performance in noisy conditions with respect to the cutoff frequency of the time derivative. The proposed method was verified through various numerical simulations and experiments, thereby demonstrating its applications in bilateral control.
This paper proposes a DAB converter using two transformers as a method to improve the efficiency in the lightload region when the output voltage fluctuates. In the proposed circuit, in addition to the operation mode of the conventional DAB converter, there exist three other operation modes initiated by switching the connection of these transformers as series or parallel. In the proposed circuit, the transformer-applied voltage can be changed and efficiency can be improved by switching between series-parallel, conventional, and parallel operations according to the input/output voltage ratio. The experimental results confirmed that for the input/output voltage ratios of 1.9 and 0.25, the conversion efficiencies were 96%, and 90%, respectively, the phase difference of 30◦ as the light-load condition.
We have been studying the application of amorphous metal with low loss to axial gap motors. However, since radial gap motors are the most widly used motors, a motor structure that can apply amorphous metal to a radial gap motor was studied. In our previous study, we reported the study on SPM motors with concentrated winding. In this study, we evaluated the effect of high efficiency on the distributed winding IPM motor with high magnetic flux density inside the iron core. As a result, it was confirmed that the efficiency can be improved by reducing the iron core loss.
In functional electrical stimulation, the time delay between an input voltage and the corresponding muscle force is a significant issue. This study revealed that the joint angle/voltage relationship can be modeled as a fourth-order system. This enables the inclusion of a time delay in the high-order phase delay of the force/voltage relationship, which may lead to delay recovery using a suitable controller. Accordingly, a full state feedback controller is proposed in this study, to recover the phase delays. Jerk measurement is mandatory for full state feedback controllers owing to the joint the fourth-order joint angle/voltage relationship. This issue can be solved by the recent development of high-resolution encoders. Finally, the validity of the proposed method was verified experimentally.
This study evaluated the performance of the Quasi-Zenith Satellite System (QZSS) in Japan at an early stage for its future sustainable operation. After the four satellites of QZSS Michibiki started their official operation, the fixed-position and moving vehicles simultaneously received centimeter-class positioning augmentation signals, L6D-CLAS (Centimeter-Level Augmentation Service), and L6E-MADOCA (Multi-GNSS Advanced Demonstration tool for Orbit and Clock Analysis) from Michibiki. This is the first attempts the results of real-time.
The global navigation satellite system (GNSS) is a satellite positioning system. However, when the signal is shielded by reinforced concrete or metal, it is difficult to be received indoors. This study introduces an indoor location estimation scheme based on bluetooth low energy (BLE) for pedestrian navigation that can save power and reduce the installation density. We investigated indoor positioning methods with the use of the received signal strength indicator (RSSI) in association with two BLE transmitters as the main axis. The error of the single RSSI ranging is more than several tens of meters, and is insufficient for use for pedestrian navigation. However, this error is reduced to a few meters when the proposed simple proportional correction calculation is performed for the estimated distance. The target accuracy required for pedestrian navigation for healthy people is approximately 10 m. This is equivalent to the accuracy of outdoor satellite positioning. For example, given that the size of the Shibuya underground shopping street is approximately 4,676 m2, twenty BLE beacons can cover the entire area. If this technology is established, indoor positioning can become possible within a wider range with a lower cost and lower labor effort compared with the current state-of-the-art.
Partial shading on a photovoltaic (PV) panel consisting of multiple substrings is known to trigger a significant reduction in energy yield and the occurrence of multiple maximum power points (MPPs), including one global and multiple local MPPs. Uneven irradiance on curved PV panels, such as flexible panels and solar roofs of electric vehicles, also causes characteristic mismatch, triggering the same issues. Although various kinds of differential power processing (DPP) converters have been proposed to preclude the characteristic mismatch issues, the DPP converter is separately required in addition to an existing boost converter for panel control, resulting in increased system complexity, cost, and volume. This paper proposes a novel integrated converter that realizes system simplification and circuit miniaturization by integrating a PWM boost converter and a DPP converter into a single unit. Laboratory and field tests were performed emulating partial shading and characteristic mismatch conditions. The proposed converter eliminated local MPPs and increased maximum powers while boosting the panel voltage, demonstrating the efficacy of the proposed integrated converter.
To suppress the residual vibration of the resonance frequency of a three-inertia system, this paper proposes a current control system that has a resonance damping structure focusing on the vibration modes of the three-inertia system. Because the conventional position/velocity control system based on the two-inertia model focuses only on the primary resonance frequency, its residual vibration is induced by using the conventional control system based on a two-inertia model as against the three-inertia system. The conventional current control system does not include a resonance damping structure. The proposed current control system damps the secondary resonance frequency of the three-inertia system, whereas the ordinary position/velocity control system suppresses the primary resonance frequency of the three-inertia system. The effectiveness of the position/velocity control system using the proposed current control is confirmed through experiments.
This paper presents the design of a hybrid state observer that estimates the sway angle in trolley systems with a pendulum, such as overhead cranes. In the system, sway angle signals detected by angular sensors are generally used for designing the anti-sway control of the pendulum or observing the pendulum state. By contrast, in this study, a linear state observer without sensors is applied to estimate the sway angle of the pendulum. The use of a standard asymptotic state observer leads to estimation error due to the system's nonlinearities and parametric errors. This paper proposes using a hybrid state observer design that combines discrete event sensing with a linear state observer. In the hybrid state observer, the estimation performance is improved by correcting the state of the system based on the discrete sway angle and angular velocity using discrete sensing. In addition, the parametric error of the pendulum length of the system is identified using the same hybrid setting. The effectiveness of the hybrid state observer and the parametric adaptation of the pendulum length are verified by conducting experiments using a downscaled prototype of a trolley system with a pendulum.
In position sensorless positioning servo systems, the parameter mismatch between interior permanent magnet synchronous motors (IPMSMs) and a position controller and/or a position estimator due to thermal variation and aged deterioration has not been sufficiently investigated. This paper proposes a convolutional integration-based second-order differential calculation to identify the parameters of IPMSMs for a high-performance positioning servo system in an adaptive scheme. In addition, we propose a high-frequency voltage injection strategy considering the trade-off between acoustic noise suppression and estimation performance. The effectiveness of the proposed second-order differential calculation calculation method, and the high-frequency voltage injection for the acoustic noise suppression is verified experimentally.
This paper proposes a new isolated CLLC resonant converter for automotive charging and discharging applications. The input includes a full-bridge structure, and the output battery side involves six switches to realize the rectification function. On the basis of component loss and stress, this paper compares and analyzes three battery-side rectification structures: full-bridge, dual full-bridge (eight switches), and the proposed six-switch bridge architectures. First harmonic approximation analysis indicates that these three architectures have equivalent AC circuits and are thus similar in design to the traditional full-bridge structure. Moreover, the proposed topology demonstrates lower component counts while maintaining the same advantages as those of the dual full bridge, resulting in greater efficiency and lower cost. Furthermore, employing six switches on the secondary side reduces the voltage stress of every switch by half of the output; the low on-resistance power switch is used, resulting in lower conduction loss. In addition, zero-voltage-switching of all power switches in the entire power range is realized to obtain high efficiency. Finally, the proposed 1-kW CLLC resonant converter prototype is successfully constructed and tested to verify the feasibility of the converter at the peak efficiency of 97.1%.
This paper presents an analysis of the maximum torque minimum peak phase current of the dual winding interior permanent magnet motor. Reducing the current contributes to small motor size. The peak phase current to generate the torque is reduced by the cancelation of the torque ripple generated by the two windings. The high harmonic current that does not generate torque ripple in the dual winding motor is analyzed. With the high harmonic current, the minimum peak phase current to generate a predetermined torque is calculated. The experiments were conducted to confirm the reduction of the peak phase current without increasing the torque ripple.
This paper presents a method for improving the position estimation accuracy for magnetic saliency based sensorless control. Conventional magnetic saliency based sensorless position estimation methods are based on the voltage equation of Interior Permanent Magnet Synchronous Motor without incorporation of the mutual inductances between the d-axis and q-axis of rotating reference frame synchronized with rotor. The mutual inductances are caused by magnetic saturation due to load current and high-frequency injection signal for position detection. Furthermore, the mutual inductances contain the harmonic components due to the motor structure. Consequently, the position estimation error is caused by the neglected mutual inductances. It is difficult to determine the actual value of mutual inductance, particularly the harmonic components that vary depending on the rotor position. Therefore, in this paper, a method for improvement of the position estimation accuracy by considering the cross-coupling factor without determining the mutual inductances is proposed. The experimental results demonstrate the validity of the proposed method.
The Cockcroft-Walton (CW) circuit is used in high-voltage low-current apparatuses, such as electron beam irradiation devices and insulation testing devices. The parasitic capacitance of the CW circuit is not considered in the design of a high voltage resonant converter. In the past, it has been clarified that the equivalent capacitor of the CW circuit can be utilized as a resonant capacitor to boost the output voltage. This study derives a theoretical quality factor and an output voltage of a resonant CW circuit, considering the equivalent capacitance and the equivalent conductance. Furthermore, it is revealed that parallel capacitors can improve the quality factor and the output voltage of the CW circuit. Experimental results obtained from the 5-stage resonant CW circuit verify the validity of the theoretical analysis.
Measurement of airborne radiation must be performed before and after decontamination work to confirm whether decontamination has actually been performed. Conventional measurement procedures require enormous amounts of work. Without using a specific mark, it is difficult to find the same measurement location before and after the decontamination work. To overcome these problems, we developed an airborne radiation mapping system that can perform measurements precisely and quickly. The system enables the simultaneous measurement of airborne radiation at multiple heights by utilizing multiple measurement units. In addition, we developed a new navigation system to reduce workload. The airborne radiation mapping system facilitated quick measurement and easy movement.
This paper presents a method for the mathematical-model-based simulation of automotive alternators. In the proposed method, a rectifier and motor are expressed by an electrical circuit constant that includes resistance and inductance. Moreover, a power correction factor is introduced for considering the operation of the rectifier. Owing to this, the calculation accuracy can be improved over that of a conventional mathematical simulation method. To validate the effectiveness, calculation results are compared with the experimental results.
This paper proposes an integrated mechatronic system design to realize insensitivity to the current ripple of a switching current amplifier that drives electromagnetic actuators in high-precision motion systems. Switching current amplifiers are desirable for high energy efficiency with a concern that the resulting current ripple impairs the achievable positioning resolution. To eliminate this concern, a motion system is developed based on a flexure-guided voice coil actuator, which is driven by a switching current amplifier. A resonator is mounted onto the mover, creating an antiresonance at 11.3kHz. This antiresonance is used to absorb the mover vibrations stemming from the current ripple. For this purpose, pulse width modulation (PWM) is used in the current amplifier such that the switching frequency is accurately tuned to the antiresonant frequency. Experiments reveal that the developed switching current amplifier reduces the power loss by a factor of 5.6 in comparison with a linear current amplifier. However, the switching current amplifier creates a current ripple of 0.77A and oscillates the mover, resulting in a parasitic vibration of 5.1nm. The use of the antiresonance successfully eliminates this vibration, decreasing the positioning error by a factor of three to 1.6nm.
This paper presents a new control system for permanent magnet synchronous motors composed of a 2-degree-of-freedom deadbeat control with a disturbance compensation method using a field-programmable gate array (FPGA). The purpose is to achieve quick response and improve the tracking accuracy of motor current and the robustness against parameter variations. The proposed control system using a FPGA based the hardware controller with simple implementation can compute all calculation process within the dead time of an inverter, realizing ideal real time feedback control without sample delay. The performance of the proposed control strategy was verified in comparison with the conventional deadbeat control method through simulations and experimental results.
The calculation of core loss of power electronics converters requires a large number of core loss data, including the excitation frequency, flux density ripple, and DC magnetic field bias characteristic under rectangular voltage excitation. However, in the case of the conventional method (that employs a B-H analyzer with a chopper circuit), a very long time is required to collect this core loss base data, because circuit parameter tuning is needed for each measurement point. Therefore, we propose a high-speed core loss base data collection method for core loss calculation under power electronics converter excitation. The core loss base data collection time was substantially reduced upon usage of a pulse width modulated (PWM) inverter and a neural network because various core loss characteristics were expressed upon excitation of the PWM inverter, and these core losses were learned by the neural network. The core loss base data, as measured via the proposed and conventional methods, were compared to validate the measurement accuracy of the proposed method, and the difference was found to be lesser than 12%. Thus, the proposed method achieves high-speed core loss base data collection.
Flyby imaging has attracted attention as a method of small body exploration. The visual-based tracking system has been widely used to obtain high-quality images. The high relative velocity between the spacecraft and asteroid makes it difficult to track the target asteroid completely around the closest approach point. The uncertainties of the measured relative parameter cause uncertainties in the required control trajectory profiles for the asteroid tracking. This study proposes a two-degree-of-freedom control system considering the relative parameter uncertainties. In particular, this study performs localization, that is, relative position estimation between the spacecraft and asteroid. A particle filter is applied to the estimator, and its applicability and limitations are discussed through a numerical simulation of a case study.