At present, many industrial carrier devices utilize linear motor sliders. However, a heavier load requires a linear motor (which is an example of a direct drive device) to get higher power, compared with a rotary motor with a ball screw slider (which is an example of an indirect drive device). In order to obtain higher power at a lower cost, a linear slider with multiple motors can be utilized, for example, a gantry type linear motor slider. Moving the gantry type slider requires two linear motors that are set up in parallel to enable synchronization control. Some conventional synchronization control methods have been proposed for the parallel twin linear slider; however, a large scaled gantry type linear motor slider has two unique problems: mechanical distortion caused by the limitations of installation environment and coupling caused by joints with low stiffness. This paper proposes a control model to solve these problems, and an identification method of each parameter. Furthermore, the effectiveness of the control model is verified by comparison with simulation results and experimental results.
Atomic Force Microscope (AFM) is a scanning probe microscope with nanoscale resolution, and it is an indispensable device for nanotechnology. Since the AFM probe physically touches the sample surface, there are rising expectations for sample dynamics measurement. One common measurement mode is the force curve measurement. In the force curve measurement, the atomic force is detected by the spring constant of the cantilever. In high speed measurement, however, the cantilever oscillates at its resonance frequency and cannot detect the atomic force. This paper proposes novel methods to identify cantilever dynamics and to measure the force curve at high speed using atomic force observer (AFO). The effectiveness of the proposed measurement method is demonstrated by using simulations and experiments. Furthermore, the robustness of the AFO against modeling error and its convergence are discussed.
This paper proposes a multi-mode operation for a five-level dual active bridge (DAB) converter using a flying capacitor (FC) topology in order to achieve a wide-load-range high efficiency over a wide output voltage range. The FC inverter alternates between three types of operations: five-level waveform operation, square wave operation, and operation of square waveform with half of the input voltage. In the multi-mode operation, the output voltage waveforms of the FC inverter are changed depending on the output power. By using multi-mode operation, zero voltage switching (ZVS) is achieved at light load against the change of the output voltage. In addition, the circulating current is also reduced compared to that of a two-level DAB converter. Therefore, the efficiency is improved by the proposed method. The experimental results show that the maximum efficiency is 96.4%. At 75% of the nominal voltage, the converter loss is reduced by 24.4% compared to that in the conventional two-level DAB converter operation.
A modulation method, which consists of a conventional space vector modulation (SVM) method based on virtual AC-DC-AC conversion and a carrier signal modulation for matrix converters, was proposed by the authors, previously. The proposed SVM method can reduce the distortion of output voltage waveforms. In this paper, the proposed SVM method is explained. In addition, a mechanism for the suppression of output voltage distortion is examined by simulation. Specifically, this mechanism is clarified by the analysis of PWM patterns produced by the proposed SVM method. In addition, a mechanism for the suppression of voltage error is presented. The coincidence of simulation and experimental results confirms the validity of the simulation.
We propose a control system to be applied to a single-phase PWM inverter used in a portable engine generator. The inverter current and output voltages are detected by sensors, and the impedance voltage drop and output voltage fluctuation are compensated by estimating the filter L voltage and filter C current, respectively. Furthermore, errors are complemented through feedback control. The study precisely describes its design method in the ideal condition. In the case of linear- and nonlinear-loads, the PWM inverter designed using the method is examined through a simulation and experiment. The PWM inverter described in this paper can output the sinusoidal voltage with low total harmonic distortion.
Metallic tubes used in power plants and industrial plants may develop cracks and change in shape owing to external factors and long-term usage. To prevent accidents caused by such defects in the metallic tubes, various non destructive inspection (NDI) methods have been established. However, these conventional methods require a considerable amount of detection time and effort to inspect the long tubes. To avoid this problem, we propose a method using propagation characteristics of electromagnetic waves. In the previous paper, we proposed the new NDI method by using the electromagnetic wave. However, it was necessary to use “a reflected wave from the normal metallic tube without any defect” as a reference. In this paper, we propose an original method for obtaining precision in defect detection without the requirement of “a reflected wave from the normal metallic tube without any defect”. By using this original precisions method, we can realize more versatile detection methods.
This paper discusses torque ripple minimization for switched reluctance motors (SRMs) driven by a boost type drive circuit. Current profiles for torque ripple minimization can be obtained from the torque-current-position characteristics of SRMs, and motor current can be controlled to follow the profiles at low speeds. However, the error between current profiles and actual currents increases at high speeds because of increase in back EMF and voltage saturation. In this study, a boost type drive circuit is applied to an SRM drive system to prevent the voltage saturation at high speeds, and the validity of the proposed drive system is demonstrated through experiments.
Bearing faults account for a large majority of the faults in a three-phase induction motor. Recently, many research activities were focused on the diagnosis of bearing faults by motor current signature analysis. However, the effective frequency band is not fully understood in terms of the diagnosis of the bearing fault. Moreover, the temporal change in motor stator current spectrum with faulty bearing has not been sufficiently investigated. The purpose of this paper is to clarify the characteristic frequency band and to evaluate the temporal change in the power spectral density of stator current by using powder contaminated bearing before complete halt of the motor. Experiments were performed with normal and powder contaminated bearings in the induction motor. The diagnosis technique for the powder contaminated bearing is discussed based on the experimental results.
This paper proposes a new drive circuit for reducing the switching current ripples in a switched reluctance motor (SRM). The authors have already presented an instantaneous flat torque control for SRMs, and confirmed its effectiveness through experimental results. However, the switching current ripples also cause torque ripples, and therefore, the current ripples should be decreased to reduce the torque ripples even more. The proposed circuit with parallel capacitor can realize such a reduction. The validity of the proposed drive circuit is verified experimentally.
Katsura laboratory focuses on system design considering time and space for advancement of an engineering system in the future society. Especially, we are developing a novel synthesis method based on the infinite-order modeling and energy conversion of electromechanical integration systems. Such innovative abstraction science and engineering will be applied to complex systems and robots for direct and harmonious human support.