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Despite that multistable isolators have been demonstrated to achieve the superior isolation performance compared with the linear ones, their performances are still inferior at ultra-low frequencies with the multi-solution phenomenon. Furthermore, their performances are dependent on the variation of initial conditions. Therefore, this paper proposes a fast fixed-time sliding mode controller to solve the ineffectiveness of the bistable dual-stage vibration isolator with external disturbances facing the above issues. Firstly, the bistable dual-stage isolator is modelled in the analytical form, and simulated compared with its linear counterpart to show its problems at some conditions. Secondly, the fast fixed-time sliding mode controller is presented with the modeling of sliding manifold and control inputs. Thirdly, the numerical simulation of the bistable dual-stage isolator with the proposed control is conducted, the results of which are compared with the finite-time sliding mode control. Finally, the outstanding feature of the proposed controller is concluded that the short convergence time becomes bounded with increasing initial conditions at both low and high excitation amplitudes. This work provides a valuable method to improve the isolation performance and robustness of the multistable vibration isolators. [ABSTRACT FROM AUTHOR]

As one of the basic motion forms, rotational motion exists widely in nature and artificial mechanical structures, such as joint rotation, gear transmission and bearing rolling. Energy harvesting technology based on rotational motion has drawn much concern recently. One of the key issues in rotational energy harvesting is the mismatch between the operating frequencies and the excitation frequencies. Conventional resonance-based linear energy harvesters perform well only near their resonant frequencies, and their performance degrades sharply while the external excitation frequencies diverge from their resonant frequencies. To solve this problem, in this paper, a flexible bistable energy harvester in rotational environment with time-varying potential wells is proposed. It mainly contains a generating beam with a tip magnet and a tuning beam with a middle magnet. Under the effects of the centrifugal force, its configuration and nonlinear characteristics change with different rotational speeds. A distributed-parameter electromechanical model is derived, and numerical simulation and experiments are accomplished. The effects of rotational speed and initial magnetic spacing on the dynamic characteristics of the harvester are studied. Analytical and experimental investigations indicate that the proposed harvester performs well in terms of operating bandwidth and is suitable for broadband rotational energy harvesting. [ABSTRACT FROM AUTHOR]

Rotational energy is a type of common energy source that can be harvested for supplying low-powered electronic devices. This paper proposes and investigates a novel cam-like dielectric elastomer generator (CDEG) for high-performance rotational energy harvesting. A mushroom-head clamp is designed to form a type of advanced conical dielectric elastomer membranes (DEMs). Moreover, a type of multi-protrusion cam mechanism is designed in the CDEG to effectively convert any external rotational excitation into a linear reciprocating motion, which can be further converted into electricity through the DEMs. First, the operating principle of the system under external rotational excitation is analyzed theoretically by deducing the deformation condition of the DEMs and the electrical output of the system. Second, the prototype is fabricated, and the rotational-to-linear motion conversion rule of its cam-like mechanism and the DEM capacitance calculation approach are validated. The experimental results show that adequate charging time and discharging time of the DEMs, which can be realized through the proposed cam-like mechanisms, are beneficial to the energy harvesting (EH) performance of the system. Third, with the validated theoretical model, numerical simulations are conducted to further study the system dynamics and the influences of important system parameters on the EH performance to provide a guideline for system improvement. Finally, the genetic algorithm is adopted to obtain the optimal system parameters and the corresponding electrical output of the proposed CDEG, demonstrating its superior output power at ultralow rotational frequencies compared with other typical rotational energy harvesters in the literature. [ABSTRACT FROM AUTHOR]

Tristable energy harvesters (TEHs) have been proposed to achieve broad frequency bandwidth and superior low-frequency energy harvesting performance. However, due to the coexistence of three potential wells and the sensitivity to system conditions and external disturbances, the desired high-amplitude inter-well oscillation in the TEHs may be replaced by the chaotic or intra-well oscillations with inferior energy output. Specifically, the chaos has an unpredictable trajectory and may cause system damages, lessen the structural durability as well as require a more complicated circuit for power management. Therefore, in this paper, we firstly propose an adaptive finite-time disturbance observer (AFTDO) for performance enhancement of TEHs by detecting the external disturbances that induce the chaos, and reject them for the recovery of the desired inter-well motion. The proposed AFTDO eliminates the need to know in advance the upper bounds of imposed perturbations in conventional observers by means of the proposed adaptive protocols, leading to the higher efficacy of estimation. The mathematical model of the piezoelectric TEH system and the AFTDO is provided. To demonstrate the effectiveness of the AFTDO, a series of numerical simulations have been performed. Results show that for both cases with sinusoidal and impulsive disturbances, the AFTDO can successfully track the trajectories of the disturbance signals with the adaptive gain, and reject the disturbance to enable the TEH to sustain the periodic inter-well oscillation with effective energy harvesting performance. [ABSTRACT FROM AUTHOR]

Rotation-based energy harvesting has attracted considerable interest in recent years. This paper presents a comprehensive theoretical model to analyze a rotational impact energy harvester using the centrifugal softening effect. The harvester is composed of a centrifugal-softening driving beam that impacts two rigid piezoelectric beams to generate electrical energy through the gravity excitation. The theoretical model is derived based on Hamilton's principle and Hertzian contact theory. An impact force model is used to overcome the limitation of the previous piecewise linear model, which cannot reflect the influence of the deformations of the driving and generating beams on the impact force and the energy output. Furthermore, an analytical impact force model is originally proposed for such a harvester based on Lee's method to understand the impact mechanism. The proposed analytical model is validated through comparison with Runge–Kutta method. Both numerical and experimental results show that the centrifugal softening effect can amplify the relative motion between the driving and generating beams and increase the impact force, thus improving output power at low rotational frequencies. The maximum output power is increased by 135.5% at 11.5 Hz for the impact gap of 0.75 mm. In addition, with the large impact stiffness, the impact force can successfully prevent the inverted driving beam from continuously deflecting and suffering the static divergence. Based on the validated theoretical model, parametric studies are conducted to further investigate the effects of the impact stiffness and the centrifugal softening coefficient. [ABSTRACT FROM AUTHOR]