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 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.
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.
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.
The decreasing number of workers and the loss of techniques of skilled workers, associated with an aging society, which can be attributed to the falling birth rate, are serious issues. To solve these problems, human substitution by the robot technology is essential. This study proposes a bilateral control system that only transmits the force information and presents applications to scaled bilateral control, time-delay systems, and human motion preservation and reproduction. The reported study demonstrated that the structure and performance of the proposed bilateral control system are equivalent to those of the conventional four-channel bilateral control using the position/force information. In the proposed method, because the position information is not used, the amount of transmitted or stored data is reduced compared to that in the conventional four-channel bilateral control and motion reproduction using position/force information. Simulations and experiments were conducted to evaluate the proposed method.
This paper presents the external force estimation for helical motors contain the magnetic levitation system. The helical shape of helical motors induces a wide inductive gap; thus, their thrust density is 1.5 times higher than that of general cylindrical linear motors. Furthermore, by magnetically levitating the mover, the motor can be directly driven. However, owing to the variations in the magnetic attractive force acting on the mover, the accuracy of external force estimation is lower than that of cylindrical motors. To solve this problem, this study proposed the combination of the thrust and torque disturbance observers of this motor for external force estimation irrespective of the magnetic attractive force. Numerical simulations and experimental results demonstrated that the proposed method can achieve the highest precision.
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.
High-precision and high-speed tracking position control with a large stroke is required for manufacturing equipment. To this end, this study aimed to utilize pneumatic cylinders for such equipment owing to their desirable properties such as high-power-to-weight ratio, low cost, and low heat exhaust. However, there are many challenges in achieving high-precision and high-speed tracking position control with pneumatic cylinders. One challenge is to address the varying dead zones of valves. In this paper, we propose a mass flow rate control system comprising a tuned inverse model of a valve and a two-degree-of-freedom (2-DOF) structure using a fast-response flowmeter. While conventional mass flow rate control based on the feedforward structure cannot address the varying dead zone, the proposed system can compensate for it using the tuning strategy and feedback structure. Furthermore, the proposed method needs less time and effort than the conventional one to develop the inverse model. Experimental results show the effectiveness of the proposed method and indicate that the tuned inverse model reduces the error immediately and that the feedback structure removes the remaining error. As the proposed method can remove the nonlinearity in the mass flow rate loop, we expect that it to improve pressure control performance and position control performance.
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.
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%.
Energy harvesting systems have recently garnered significant attention. Mechanical vibrations are used as a type of energy source in such systems. However, it is important to improve the performance of vibration generators because they provide low power in the milliwatt or microwatt level. This study investigated the improvements in the output power using passive devices. A boost-type, current-improving passive rectifier was used in this study. Additionally, an input series inductor was employed to resonate the internal capacitor of the piezoelectric elements; consequently, the output power was increased. The validity of the proposed circuit was verified both numerically and experimentally.
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.
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.
Optimization of robotic bipedal walking widely uses simplified dynamical models to minimize the computational cost and generate fast solutions, but this poses the problem of modeling errors and increased inaccuracy. Moreover, direct methods of optimization are almost always used; however, most are not implemented to satisfy Pontryagin's Principle, which can lead to suboptimal solutions. This study presents the optimization of planar robotic bipedal walking using exact dynamics. We apply pseudospectral optimal control to optimize gait generation using two accuracy requirements: nonlinear multi-degree-of-freedom whole-body dynamics and satisfied conditions of optimality according to Pontryagin's Principle. In order to consistently achieve solvability of optimization in this type of problem, we present a novel methodology consisting of synergic techniques that address well-known numerical difficulties of optimization.
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.
In this study, the effect of enhancing white noise for parity-time-symmetric (PTS) wireless power transfer (WPT) is investigated through modeling and simulation with TopSpice. The operating principle is described using the coupled mode theory. This study specifically focuses on the coupling situation, from strong coupling to incomplete PTS matching. The voltage amplitude in the receiver circuit increases because the PTS condition is completely preserved. However, it is difficult to initiate oscillation as there is a trade-off between the voltage amplitude and highly responsive oscillation in PTS-WPT for gain in the negative resistance regime. By enhancing the white noise signal, highly responsive oscillation is achieved at a high voltage and low gain. This study focuses on the enhancement of white noise for negative resistance for WPT. The proposed enables achieving to earlier stable oscillation with a high power supply.
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.
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.
This paper proposes a DAB converter using two transformers as a method to improve the efficiency in the light-load 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.