On Theoretical and Numerical Aspects of Bifurcations and Hysteresis Effects in Kinetic Energy Harvesters

The piezoelectric energy-harvesting system with double-well characteristics and hysteresis in the restoring force is studied. The proposed system consists of a bistable oscillator based on a cantilever beam structure. The elastic force potential is modified by magnets. The hysteresis is an additional effect of the composite beam considered in this system, and it effects the modal solution with specific mass distribution. Consequently, the modal response is a compromise between two overlapping, competing shapes. The simulation results show evolution in the single potential well solution, and bifurcations into double-well solutions with the hysteretic effect. The maximal Lyapunov exponent indicated the appearance of chaotic solutions. Inclusion of the shape branch overlap parameter reduces the distance between the external potential barriers and leads to a large-amplitude solution and simultaneously higher voltage output with smaller excitation force. The overlap parameter works in the other direction: the larger the overlap value, the smaller the voltage output. Presumably, the successful jump though the potential barrier is accompanied by an additional switch between the corresponding shapes.

Modeling of wedge-pin joint for the dynamic analysis of a planar temporary demountable structure

In order to understand deeply the dynamic behavior of a Temporary Demountable Structure (TDS), a 2-D analytical model of the Wedge-Pin Joint (WPJ) is established. This model takes into account of the semi-rigidness of the vertical contact and the sliding between beam and column based on the frictional shear-slip mechanism. The analytical WPJ model is validated by comparing with the dynamic responses of the TDS modeled with that obtained from the finite element model under harmonic load. Furthermore, a thorough dynamic analysis of the TDS subjected to a bipedal walking force is conducted. Results show that the hysteretic effect of the WPJs can be induced in the system. It is strongly affected by the amplitude of excitation, and a larger excitation does not mean a stronger hysteresis. This can be interpreted by that large horizontal contact force for joints resulted from strong excitation in horizontal direction yields high friction, which enhances the clamping effects in vertical and then weakens the hysteretic effect of WPJs. In addition, the vertical slip for joint is limited to a small value due to a relative small acceleration, this small vertical slip leads to a small of hysteretic loop. Finally, it is also found that the semi-rigidness of WPJs can apparently increase the deformation and acceleration of the system in both horizontal and vertical directions. This research provides for the first time an analytical model of WPJs of TDS, which will be beneficial to the future research of human-TDS interaction.

Sliding mode observer based hysteresis compensation control for piezoelectric stacks

Piezoelectric stacks (PS) are wildly used as actuator mechanism for precise instrument in practical engineering. Nevertheless, hysteretic effect that is carried by the piezoelectric materials can degrade the control performance dramatically. For the purpose of improving the control precision, the problem of hysteresis compensation control for PS system is investigated in this paper. First, in order to compensate the hysteretic effect, two kinds of observers are proposed. The design of the observers has considered external disturbance and the creep effect in PS system. By utilizing Lyapunov function and linear matrix inequalities (LMI) technique, the observers can asymptotically estimate the hysteretic output with [Formula: see text] performance. Second, a hysteresis-compensation based back-stepping controller is established. The design of the controller has considered the observation error, and it has a certain robustness. At last, numerical and experimental simulations are carried out to verify the effectiveness of the proposed methods.

Under-Actuated Humanoid Model With Elastomeric Springs

This paper presents the mechanical modifications and simulation of a bipedal humanoid system actuated with linear springs to produce a standing equilibrium position. The original humanoid system is comprised of two leg assemblies connected by a hip bracket. Eleven pairs of springs were attached to the system in locations designed to simulate the muscles and tendons in a human body. The next evolution of the LUIGEE project is the inclusion of three servo motors per leg and a series of elastomeric springs. Although servo motors have been introduced, it is desired to maintain the passive, static aspect of the previous prototype. This paper reports on part modifications to accommodate servo motors and the introduction of polymeric springs that guarantee static stability. ABS plastic and photopolymer resin was used to produce the new model. Due to the size of the motors, some parts of the original robot were redesigned. The new design iteration was stimulated using SimWise 4D®, where the hysteretic effect of rubber was modelled with an equivalent viscous damping.

Hysteresis in Mental Workload and Task Performance

Objective: We examine how transitions in task demand are manifested in mental workload and performance in a dual-task setting. Background: Hysteresis has been defined as the ongoing influence of demand levels prior to a demand transition. Authors of previous studies predominantly examined hysteretic effects in terms of performance. However, little is known about the temporal development of hysteresis in mental workload. Method: A simulated driving task was combined with an auditory memory task. Participants were instructed to prioritize driving or to prioritize both tasks equally. Three experimental conditions with low, high, and low task demands were constructed by manipulating the frequency of lane changing. Multiple measures of subjective mental workload were taken during experimental conditions. Results: Contrary to our prediction, no hysteretic effects were found after the high- to low-demand transition. However, a hysteretic effect in mental workload was found within the high-demand condition, which degraded toward the end of the high condition. Priority instructions were not reflected in performance. Conclusion: Online assessment of both performance and mental workload demonstrates the transient nature of hysteretic effects. An explanation for the observed hysteretic effect in mental workload is offered in terms of effort regulation. Application: An informed arrival at the scene is important in safety operations, but peaks in mental workload should be avoided to prevent buildup of fatigue. Therefore, communication technologies should incorporate the historical profile of task demand.