Daisuke Iba

Structural vibration control by tuned mass damper using central pattern generator

This paper proposes a new control method for active mass dampers using a Central Pattern Generator in vibration mitigation. The active mass dampers (or active dynamic absorbers) have been applied to structural vibration control of high-rise buildings, bridges and so on. In this case, the mass of the active mass damper must oscillate in an appropriate phase in relation to the control object, and generally, the damper has been designed by linear control theory as pole placement method, optimal control method or H infinity control method, and all the rest. On the other hand, on walking of animate beings like mammals or insects, both side feet have appropriate phase relations; moreover, it is possible to keep moving on irregular ground. That is, algorithms for the walking would be embedded into the animate beings to control the complicated and redundant bodies with ease and robustness. In biological study, the Central Pattern Generators in bodies playing a significant role in the walking have been learned over the last few decades, and some studies said that some animate beings are able to control their feet by using the generators without their brains in the walking. Moreover, mathematical models of the pattern generators have been proposed, and some researchers have been studying to realize walking of biped-robots using the pattern generators embedded in a computer. In this study, the algorithm is installed into a controller for the active mass damper; furthermore, validation of the controller is performed by numerical simulation.

Mutual synchronization between structure and central pattern generator

This paper shows an evaluating method of synchronization between a structure and Central Pattern Generators (CPGs), which are embedded in a controller designed for an active mass damper. A neural oscillator composing the CPGs has nonlinear and entrainment properties. Therefore, the proposed controller has possibility to exhibit the characteristic of robustness, when the structural parameters, i.e. stiffness or damping, are changed by earthquakes and the like. Our earlier studies have proposed the new controller and ascertained the efficacy of vibration suppression. However, there has been no study to evaluate the controllers above-mentioned properties. For tuning into practical application, the reliability and robustness along with the controllers vibration mitigation performance must be analyzed. In this paper, phase reduction theory is tried to appraise the synchronization between a structure and the CPGs. In this case, the synchronization between the target structure and a single neural oscillator constituting the CPGs is required to be investigated. Therefore, the single neural oscillators the harmonization characteristic with sinusoidal input is firstly examined, and the synchronization region is expressed using phase response curves. In addition, the mutual synchronization between the structure and the single neural oscillator is studied under sinusoidal input using the result of the harmonization characteristic.

Nonlinear piezoelectric impedance modulation induced by a contact-type failure and its application in crack monitoring

In this paper, a self-sensing, sensitive and baseline-free structural health monitoring methodology is developed, which aims to detect and characterize local structural failures of contact type, i.e. failures which arise along with the generation, growth and/or changes of imperfect solid–solid interfaces. The nonlinear piezoelectric impedance modulation (NPIM) method presented is based on the ideas of two existing damage detection principles; a piezoelectric impedance-based methodology and a nonlinear wave modulation spectroscopy. It uses a single piezoelectric active sensor bonded on the structural surface, which is driven by a high-frequency harmonic voltage source. When the structure including a contact-type failure is subjected to a low-frequency dynamic load, the induced structural vibration causes a fluctuation of the scattering conditions for the high-frequency elastic waves at the failure because of the contact acoustic nonlinearity (CAN). This nonlinear effect of vibro-acoustic interaction yields a significant fluctuation in the driving-point impedance in the high-frequency range, which may lead to a modulation of the coupled electromechanical impedance (or admittance) of the piezoelectric active sensor. Therefore, if the sensor is driven by a fixed amplitude high-frequency harmonic voltage source, modulation of the coupled admittance can be observed as the amplitude modulation and phase modulation of the current flowing through the sensor. A simplified modeling study leads to the definition of a damage evaluation index that assesses the intensity of the stiffness fluctuation caused by the CAN. Experiments using cracked beam specimens are conducted to show how the NPIM can be observed and to examine the performance of the proposed method.

Evaluation method for a controller of active mass damper using central pattern generator

This paper proposes an evaluation method for a CPG controller designed for active mass dampers. Neural oscillators composing the CPG have nonlinear and entrainment properties. Therefore, the proposed controller has possibility to have flexibility, when the structural parameters, i.e. stiffness or damping, are changed by the effect of earthquakes and the like. However, there has been no study to evaluate the controller’s above-mentioned properties. For tuning into practical application, the reliability and flexibility along with the controller’s performance must be analyzed. In our previous study, the phase reduction theory was tried to appraise the synchronization between a structure and a single neural oscillator and the synchronization region of the neural oscillator was obtained as basic research. However, the information from the synchronization region was insufficient to evaluate the system, because the neural oscillator has a phase difference called a phase locking point between the structure and the neural oscillator during the synchronization. Then, in this paper, the phase locking point within the synchronization region between a structure and a single neural oscillator is focused on, and the phase locking point and the vibration mitigation effect are considered with the simple object model.

Structural Vibration Control by Damping Parametric Excitation

This paper proposes a new method for utilization of variable damping in a vibration system. The coefficient of variable damping can be changed as that in the case of a sine wave, i.e. parametric excitation whose frequency can be arbitrarily selected. As a results of the parametric excitation, the vibration amplitude of the system increases because of the resonance at arbitrary frequency of the external input. We have confirmed the resonance of the damping parametric excitation by simulation and experiment and proposed a method of frequency response analysis of the vibration system with the parametric excitation of damping coefficient and the external harmonic excitation. In this paper, we consider about the SDOF vibration model with the external input that includes two frequency contents, and we propose a new vibration control method that the outputs interfere with each other by the parametric excitation. Finally, we confirm the effectiveness of the proposed control method by simulation.Copyright

Frequency response analysis of vibration system with parametric excitation of damping coefficient

This paper proposes a new method for the frequency response analysis of a vibration system with parametric excitation of damping coefficient. A base-excited single-degree-of-freedom model with a variable damper is considered. The variable damping coefficient can be changed to that in the case of a sine wave, i.e., a parametric excitation whose frequency can be arbitrarily selected. One of the external forces acting on the mass through the damper from the base is equivalent to the product of the damping coefficient and the input velocity. The product of the input sine wave and the frequency-controlled sine wave for variable damping, yields a new vibration that has a frequency different from the input frequency. Therefore, the oscillation of the damping coefficient at a suitable frequency can generate a new vibrational component that has the same frequency as that of the eigen-oscillation of the vibration system. As a result, the vibration amplitude increases because of resonance. In this study, first, we carry out theoretical analysis and obtain the frequency response of the proposed system. Subsequently, we confirm the effectiveness of the proposed analysis method by comparing the analysis result with previous simulation results.

Development of three-axis inkjet printer for gear sensors

The long-term objective of our research is to develop sensor systems for detection of gear failure signs. As a very first step, this paper proposes a new method to create sensors directly printed on gears by a printer and conductive ink, and shows the printing system configuration and the procedure of sensor development. The developing printer system is a laser sintering system consisting of a laser and CNC machinery. The laser is able to synthesize micro conductive patterns, and introduced to the CNC machinery as a tool. In order to synthesize sensors on gears, we first design the micro-circuit pattern on a gear through the use of 3D-CAD, and create a program (G-code) for the CNC machinery by CAM. This paper shows initial experiments with the laser sintering process in order to obtain the optimal parameters for the laser setting. This new method proposed here may provide a new manufacturing process for mechanical parts, which have an additional functionality to detect failure, and possible improvements include creating more economical and sustainable systems.

Frequency response analysis of multi-degree-of-freedom system with harmonically varying damping

This paper analyzes effects of harmonically varying damping on a multi-degree-of freedom system. Our recent research applied the method of the harmonically varying damping to vibration mitigation of a single-degree-of-freedom structure with sinusoidal base excitation having two frequencies. In the study, an ideal variable damper is used in conjunction with the secondary sinusoidal base excitation to reduce response due to the primary base excitation. If the primary sinusoidal base excitation contains the natural frequency of the system, resonance is induced. However, another resonance can be generated by the modulated component caused by the variable damping device and the secondary base excitation. The additional resonance is adjusted to be out of phase with the primary response, resulting in effective control of the structure. However, no such study considering the multi-degree-of-freedom system has been conducted. This paper presents the effect of the harmonically varying damping on the multi-degree-of-freedom system, especially; the influence on two structures in parallel with a variable damper between there is discussed.

A Study of Elasto-Plastic Response of Single Degree of Freedom System Using Artificial Ground Motions With Given Time-Frequency Characteristics

In this paper, a number of artificial earthquake ground motions compatible with time-frequency characteristics of recorded actual earthquake ground motion as well as the given target response spectrum are generated using wavelet transform. The maximum non-dimensional displacement of elasto-plastic structures excited these artificial earthquake ground motions are calculated numerically. Displacement response, velocity response and cumulative input energy are shown in the case of the ground motion which cause larger displacement response. Under the given design response spectrum, a selection manner of generated artificial earthquake ground motion which causes lager maximum displacement response of elasto-plastic structure are suggested.Copyright

Nonlinear piezoelectric impedance modulation and its application to crack detection

In this paper, a structural health monitoring (SHM) methodology that can detect and characterize local structural damages in early stage is developed, by merging the concepts of two existing SHM principles, a piezoelectric impedance-based methodology and a nonlinear wave modulation spectroscopy. The presented SHM system mainly consists of a piezoelectric element bonded on the structural surface, a high-frequency harmonic voltage source, and a current detector. When the structure is subjected to a dynamic load at low-frequencies, it vibrates, and the scattering conditions for the high-frequency elastic waves in the vicinity of the inherent damages will change in synchronization with the structural vibration. This nonlinear effects of vibro-acoustic interaction between the low-frequency vibration and the high-frequency wave field causes the change in the driving-point impedance at the high frequency range, which can significantly modulate the coupled electro-mechanical impedance (or admittance) of the piezoelectric element. Therefore, if the piezoelectric element is driven by a fixed amplitude high-frequency harmonic voltage source, the nonlinear modulation of the coupled admittance can be observed as the amplitude and phase modulation of the current flowing through the piezoelectric element. A simplified modeling study of the above-mentioned nonlinear piezoelectric impedance modulation successfully leads to a damage evaluation index that assesses the intensity of the modulation of the modal stiffness. Experiments using a cracked beam are conducted to see how the impedance modulation can be observed and to examine the performance of the proposed method.