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To overcome the drawbacks in the active and passive control systems, a low-powered semi-active approach based on synchronized switch damping techniques using piezoelectric materials have been developed. The synchronized switch damping (SSD) method, which consists in a nonlinear processing of the voltage on a piezoelectric actuator by switch control, is used to shift the phase and amplify the amplitude of the generated voltage on the piezoelectric element, which is helpful to enhance the energy conversion and control performance. In this paper, several new SSD control methods developed by the authors, including SSD control based on negative capacitance (SSDNC), and unsymmetrical SSD, are introduced. Moreover, two examples of application of SSD methods in aerospace engineering are given. Finally, the future directions of research in semi-active control are also summarized. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to investigate the effect of frictional materials and surface texture on the energy conversion efficiency and the mechanical output performance of the ultrasonic motor (USM).Design/methodology/approach A newly designed testing system was set up to measure the mechanical output performance of the USM. The influence of different frictional materials on the output performance of the USM was studied under the same assembly process and parameters. The surface texture was fabricated by laser ablation processing. The effects of surface texture and input parameters on the energy conversion efficiency and mechanical output performance of the USM were studied.Findings The results show that polyimide (PI) composites as frictional material can significantly improve the output performance of the USM compared to polytetrafluoroethylene (PTFE) composites. When the pre-load is 240 N, the energy conversion efficiency of the USM using textured PI composites as frictional material can reach 41.93 per cent, increased by 29.21 per cent compared to PTFE composites, and the effective output range of the USM is increased to 0.7-1.1 N m. Besides, the pre-load and surface texture have a great influence on the output performance of the USM.Originality/value PI composites can improve the mechanical output performance of the USM. Surface texture can also improve the interface tribological properties and the energy conversion efficiency based on the advanced frictional materials, which will contribute to the increment of the output performance of the USM under the same input conditions. [ABSTRACT FROM AUTHOR]

Abstract: In a structural system with piezoelectric actuators, the damping effect can be achieved by properly switching the voltage on the actuators. Semi-active synchronized switch damping (SSD) approaches are typical switched-voltage control methods, which have recently been a topic of active research. In this study, the energy conversion of a SSD control system with an arbitrary switching frequency is investigated theoretically and validated numerically. First the general expression of the switched voltage on the piezoelectric actuator is derived. The results show that maximum voltage magnitude is obtained on the piezoelectric actuator when piezoelectric is switched at every odd number of displacement extrema. Next the average converted energy per vibration cycle is derived for an arbitrary switching frequency. The results show that the efficiency of energy conversion is reduced drastically even if the switching frequency is slightly deviated from the optimal frequency. Finally numerical simulation and experiments were carried out to validate the theoretical results. [Copyright &y& Elsevier]

Abstract: The synchronized switch damping (SSD) approaches based on piezoelectric actuators have been successfully used in multimode vibration control of structures. By suppressing voltage inversion at some displacement extrema, the control performance of SSD approaches can be significantly improved. In this study, conversion of energy from mechanical to electrical in two-mode control is analyzed for different amplitude ratios and frequency ratios. The results show that the converted energy in two-mode control with voltage inversion at every extremum is smaller than the sum of the energies of the two modes in single-mode control, but the converted energy of the second mode in two-mode control may exceed that in single-mode control when the amplitude ratio of the second mode to the first mode is small enough. The influence of voltage threshold used to suppress voltage inversion on energy conversion of the system and each individual mode is also investigated. The converted energy of the first mode in two-mode control may be much larger than that in single-mode control when voltage inversion is suppressed suitably. The analytical results can successfully explain the phenomenon in the previous control experiments and can also be extended to multimode control. [Copyright &y& Elsevier]

Abstract: In this paper, a new switch control strategy based on an energy threshold is proposed for the synchronized switch damping techniques in multimode control. This strategy is derived from the total converted energy of a synchronized switch damping (SSD) system in a given time window. Using the new strategy the voltage is inverted only at those extrema where the effective distance, which is proportional to the converted energy between two neighboring extrema, exceeds the threshold. The new switch control strategy is used in both the synchronized switch damping on inductor (SSDI) technique and the synchronized switch damping on voltage source (SSDV) technique, which are applied to the two-mode control of a composite beam. Their control performances are compared with those of the single-mode control and those of classical SSDI and SSDV techniques in two-mode control. The experimental results show that voltage inversion is prevented at some of the displacement extrema to increase the total converted energy, and exhibit better global damping effect than classical SSDI and classical SSDV, respectively. In single mode, the best control performance is achieved when the voltage is inverted at every extremum. But in multimodal control, the total converted energy in a given time window is increased and the control performance is improved when some extrema are skipped. [Copyright &y& Elsevier]

The energy conversion efficiency (ECE) of a piezoelectric generator can be denoted by its effective electromechanical coupling coefficient (EECC), which depends only on the geometry parameters with a certain boundary conditions. To obtain the optimal energy-harvesting device, the Raleigh Method was utilized to establish the analysis model of circular piezoelectric composite diaphragms. Simply supported and clamped boundary conditions were considered. The relationships between the performance parameters (EECC and natural frequency) and the structural parameters (diametric ratio β and thickness ratio α) of piezoelectric composite diaphragms were figured out. Given the correlative material parameters and boundary conditions, the performance parameters with the structural parameters as variables can be worked out. The simulation results show that the optimal structural parameters of a composite diaphragm in the case of the simply supported and clamped boundary conditions are different. A simply supported diaphragm generator tends to achieve higher effective electromechanical coupling coefficient and lower natural frequency, and is more suitable for the applications of energy harvesting. [ABSTRACT FROM AUTHOR]

A new magnetic force control method using giant magnetostrictive material (GMM) was proposed and its feasibility was confirmed in earlier studies by the authors. This new method is based on the inverse magnetostrictive effect and the magnetic force is controlled by changing the stress or strain in the magnetostrictive material. This method is expected to have lower heat generation and higher energy conversion efficiency compared to traditional methods, since a constant magnetic force can be maintained by merely applying a constant stress. In this study, the energy conversion efficiency of this method is investigated experimentally using a universal test machine. The input elastic energy was calculated from the stress-strain loading curve and the converted magnetic energy was estimated from the generated magnetic field. Since the elastic energy is strongly dependent on the history of the strain-stress loading curve, and the loading curve is affected by the applied magnetic field in the magnetostrictive material, it is important to optimize the bias magnetic field for maximum energy conversion efficiency. The relationships between the elastic modulus and the magnetic field were measured experimentally and the results show that the bias magnetic field must be carefully chosen to obtain high efficiency of energy conversion. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(1): 8–15, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10026 [ABSTRACT FROM AUTHOR]

In the field of piezoelectric energy harvesting from ambient low-frequency vibrations, frequency up-converting effect is a classical approach to improve the efficiencies of energy conversion and extraction. However, most of the frequency up-converting harvesters are implemented by either mechanical impacts or non-contact impulse-like accelerations, which needs high-level excitations and usually leads to reduced longevity or considerable noise. To address these limitations, this paper introduces and demonstrates a novel frequency up-converting energy harvester based on 1:3 internal resonance. The nonlinear harvester mainly consists of two asymmetric cantilever beams in which the ratio of their resonant frequencies is 1:3. The harvester features two vibrational degrees-of-freedom (DOFs) corresponding to the two cantilevers: The primary DOF picks up the ambient low-frequency vibrations and excites the secondary one to vibrate drastically at its resonant frequency. Because the secondary resonance is three times higher than the excited frequency, the harvester realizes the frequency up-conversion. The underlying mechanisms of this design are thoroughly analyzed in the numerical simulation and experiment. [ABSTRACT FROM AUTHOR]

Ultrasonic motor (USM) performance is dependent on the tribological characteristics of the interface between a stator and rotor, which are sensitive to ambient environments and driving parameters. Thus, the effects of vacuum and temperature on the mechanical output performance and energy conversion efficiency of a traveling wave rotary ultrasonic motor 60 (TRUM-60) with a novel micro-dimpled PI-based friction material and optimized input parameters were systematically investigated for the first time. The degree of vacuum had a negligible effect on the performance of the TRUM-60, whereas temperature influenced its mechanical output torque, rotational speed, and output power. The results can aid in the design of USM devices for aerospace applications. • Vacuum and temperature can affect the performance of an ultrasonic motor. • A mechanical model of the frictional coefficient was proposed. • Performance was experimentally investigated under various parameters. • A set of optimal parameters was determined and evaluated. [ABSTRACT FROM AUTHOR]

• Mechanism of energy conversion efficiency improvement with flexible rotors studied. • 3D finite element model with coupling among various parameters established. • Transient solution and modal analysis methods applied on TRUM-60. • Results and validated experimentally as well as using 3D vibration measurements. Flexible rotors are widely used in traveling wave rotary ultrasonic motors (TRUMs) because of their higher energy conversion efficiency; however, there have been few reports on how flexible rotors improve the energy conversion efficiency of ultrasonic motors. In this study, we investigate the improvement mechanism of energy conversion efficiency in TRUMs with flexible rotors. A 3D finite element (FE) model with full coupling among a piezoelectric coupled stator, rotor, friction layer, and the rigid–elastic contact interface of the stator and friction layer is established. To analyze the mechanism by which the efficiency of the TRUM is improved, the contact interface and rotor vibration information are extracted. Taking TRUM-60 as an example, the transient solution method and modal analysis method are used to solve the model. It is found that when the stator mode is B 09 , the flexible rotor mode is B 19. The energy conversion efficiency of the TRUM is obtained from the ratio of output power to the electrical input power of the model solution. The results are validated using 3D vibration measurements and energy conversion efficiency experiments. The simulation result shows that the motor with flexible rotor improves the energy conversion efficiency compared with the motor with rigid rotor, which can be attributed to two reasons: first, the axial amplitude ratio of the flexible rotor to the stator is reduced; second, the flexible rotor reduces the radial friction. This study reveals the influence of flexible rotor on the output efficiency and can thus provide guidance for rotor design. [ABSTRACT FROM AUTHOR]