A motion-copying system is a kind of autonomous robotic system. This system reproduces human motion on the basis of haptic information (i.e., position and force information) extracted using a bilateral control system. However, in conventional motion-copying systems, control stiffness always remains constant. Thus, conventional systems show poor adaptability to differences in environmental locations during the reproduction phase. The objective of this study is to develop a motion-copying system with variable impedance. The proposed method includes an approach to determine the control stiffness of the motion-copying system on the basis of position, force, and impedance information. The haptic information is acquired using a scaled bilateral control system. For calculating the impedance, dynamic programming matching and the least-squares method are utilized. Dynamic programming matching accommodates the motion speeds in the saved data. The derived impedance is fed into a compliance control system, where it is reproduced. To validate the proposed method the task of removing a sarcoma is performed in experiments, in which three different types of target positions are set. The proposed motion-copying system succeeded in removing the sarcoma phantom, whereas the conventional method either failed to grasp it or applied excessive force. The proposed method succeeded in increasing the adaptability of the motion-copying system to different environmental locations.
This paper presents a method for suppressing the bending vibration of galvano mirrors used in laser positioning systems. Fast and highly precise positioning of the mirror is vitally important for these systems. Thus, the flatness of the mirror should be maintained to ensure highly precise laser positioning. However, mechanical resonant vibrations of the mirror, which are excited by the moment force during positioning, lead to residual vibrations after positioning; these vibrations degrade the flatness of the mirror and the laser manufacturing accuracy. In this paper, therefore, a vibration suppression method is proposed in which a piezoelectric element is mounted on the mirror so as to utilize the multifunctionality of the piezoelectric element by applying it as both actuator and sensor in the vibration suppression controller design. The applicability of the proposed approach to industrial galvano scanners has been verified by performing experiments with a prototype.
In industrial applications, reducing the stiffness caused by mechanical constraints, such as using gear, induces a vibration at the tip of a system, which can become a problem. Thus, research is ongoing on vibration control scheme based on a wave equation to suppress all resonances by eliminating reflected waves. However, the conventional method based on the wave equation does not consider robustness against a load force. This paper proposes position control of a resonant system using wave observer to enhance robustness against the load force. In the proposal, the resonant system is modeled as the wave equation containing the load force and control system design is based on the wave equation. Vibration suppression is achieved by a reflected wave rejection, which can suppress all resonances of a resonant system. Moreover, the conventional reflected wave rejection structure is modified to realize robustness against disturbance acting on the motor side. In addition, the wave observer is proposed for eliminating an effect of the load force. Finally, the validity of the proposed method is verified by experiments.
This paper proposes a circuit topology for a matrix converter with a boost-up AC chopper in the input stage in order to improve the voltage transfer ratio, which is defined as the ratio between the input and output voltages. The proposed system is applied in an IPMSM adjustable speed drive system where the application range of flux-weakening control is wide. In order to drive the motor at the rated speed in the high-torque region, there are three possible solutions: (i) applying flux-weakening control, (ii) boosting up the voltage by the AC chopper or (iii) a combination of both the solutions (i) and (ii). In terms of the total loss, the proposed system with the solutions (ii) or (iii) is compared with the conventional matrix converter by using solution (i). Consequently, the chopper loss in the AC chopper and the copper loss of the motor are calculated theoretically to evaluate the total loss. In addition, the proposed system is demonstrated as a 3.7-kW prototype by experiments. In this paper, the input voltage is degraded so that a larger boost-up ratio can be applied to the AC chopper. Further, the proposed system is compared to the conventional matrix converter by expanding the range of flux-weakening control, which depends on the input voltage. As a result, it is confirmed that the converter efficiency of the proposed system reaches 94.8% at the maximum point. Furthermore, it is revealed that the efficiency of the proposed system is higher when the rated motor voltage is greater than 107% of the input voltage.
Wireless power transfer is expected to be applied to portable devices and electric automobiles in the future. To achieve this, it is necessary to improve the transmission efficiency of the coils used in wireless power transfer, that is, to improve the quality factor and coupling coefficient of the coils. To improve the quality factor of the coils, the authors propose the use of a litz wire with a magnetoplated wire (MPW), which is a copper wire plated with a thin iron film. The MPW increases the quality factor of the coils by reducing the AC resistance owing to the proximity effect. In this study, the effect of the number of strands of a litz wire on the quality factor of the coils and efficiency characteristics is considered. Moreover, the quality factor of the coils and efficiency characteristics using three types of coil—a solid copper wire (COW), a litz wire with a copper wire (LCW), and a litz wire with an MPW (LMW)—are considered. At the transmission frequency f =13.56MHz, it is experimentally demonstrated that many strands, whose number becomes the highest in terms of the quality factor of the coils, exist. The transmission efficiencies of the COW, LCW and LMW coils at an output power of 5W and a transmission distance of 9mm are 89%, 84%, and 91%, respectively, and the efficiency of the LMW coil is the highest. Also, in this case, the temperature increases of the COW, LCW, and LMW coils are 12°, 16°, and 10°, respectively, and the LMW coil reduces the temperature increase.
This paper discusses a super-multipolar permanent magnet reluctance generator (PMRG) for small-scale renewable power generation. The PMRG has 72 stator poles and 96 rotor poles in order to be directly connected to the turbine without a gear box. The designed PMRG has a rated power of over 1.0kW at 100rpm. The PMRG has two features to reduce torque ripple; a two-stacked structure where one rotor is shifted by an electrical angle of 180 degrees from the other rotor; and chamfered rotor pole-tips so that the torque waveform consists of only odd harmonics. This structure drastically reduces the torque ripple of the PMRG. The shape of the rotor pole-tips was first optimized by the two-dimensional finite element method (2D-FEM) coupled with a general-purpose optimization program. Next, the load characteristics of the PMRG obtained from 3D-FEM were considered. Finally, the characteristics of the developed 72/96-pole PMRG were measured.
Rare earth permanent magnets (PMs) with a large energy product are generally used in the traction motors of hybrid electric vehicles. However, developing rare-earth-free motors is necessary because of problems with rare earth materials, such as increasing prices and difficulty in their supply. This paper introduces such a rare-earth-free motor: a ferrite PM axial gap motor with a coreless rotor structure. The motor structure and the results of three-dimensional finite element analysis are described in detail.
The influence of the shearing process on the iron loss of non-oriented electrical steels with thicknesses of 0.20-0.50mm was investigated. The deterioration of material iron loss was lesser in thinner steel sheets. The distribution of the increase in hardness near the sheared edge was almost half of the sheet thickness for all tested steels. Therefore, applying thinner steel sheets for the motor core may decrease the iron loss deterioration from the punching process. This argument was supported by measuring the iron loss of a model IPMSM using steels with different thicknesses and calculating the motor iron loss through FE analysis. The magnetic properties of narrow pieces corresponding to the width of the motor's teeth and yoke were shown to be important and useful to estimating the motor iron loss more accurately.
Magnetic gears offer several advantages against conventional mechanical gears such as easy maintenance, low vibration and acoustic noise, and high reliability. For the practical application of magnetic gears, experimental studies on gear characteristics that consider real manufacturing constraints should be performed. This paper presents the loss analysis, experimental tests, and performance improvement of a surface permanent magnet (SPM) magnetic gear. The torque characteristic and the efficiency of the SPM magnetic gear were calculated using finite element analysis (FEA). Experiments were performed on a trial magnetic gear. The FEA and experimental results demonstrated the improved efficiency of the trial gear. The maximum efficiency of the improved gear was over 96%.
It is experimentally known that the efficiency of class E amplifiers deteriorates when the dc supply voltage is much lower than the designed value. However, the existing literature on efficiency and power loss analysis of class E amplifiers cannot explain the cause of this phenomenon at all. It is demonstrated in this paper that this deterioration of efficiency is caused by the influence of the nonlinearity of the output capacitance of the MOSFET. Owing to the nonlinearity of the output capacitance, the class E amplifier cannot achieve ZVS switching when dc supply voltage is lower than the designed value, even if the circuit is designed to achieve ZVS at the designed dc supply voltage. In this regard, this paper presents the power efficiency of the class E RF power amplifier as a function of dc supply voltage VDD when the shunt capacitance is nonlinear with the grading coefficient m =0.5 as a representative value. With this modeling of the nonlinear shunt capacitance, non-ZVS switching at a low dc supply voltage can be reproduced with the theoretical waveforms, and the switching loss can be calculated at a dc supply voltage that is lower than the designed dc supply voltage. Then, the total power loss including the switching loss can be calculated. The result of the efficiency calculation demonstrates a deterioration of efficiency at low dc supply voltages as expected, and there was good agreement with the experimental results.
Trains require high deceleration and stable traveling performance. Improvement in adhesion characteristics is, thus, very important for electric trains. We have previously proposed an anti-slip/skid re-adhesion control system that is based on a disturbance observer and possesses a high adhesion force utilization ratio. In the present work, we focus on the deceleration mode. Generally, a train has an electric regenerative brake (electric brake) and an air brake (mechanical brake). Under wet railway track conditions, the regenerative brake may be suspended because of the air brake response. This paper proposes a regenerative brake priority control and an electro-pneumatic blended braking control based on an estimated adhesion coefficient. Furthermore, this paper evaluates and discusses regenerative brake priority control using numerical simulations.