Current Issue : April - June Volume : 2016 Issue Number : 2 Articles : 5 Articles
In order to accurately model the hysteresis and dynamic characteristics of piezoelectric stack actuators (PSAs), consider that a linear\nforce and a hysteresis force will be generated by piezoelectric wafers under the voltage applied to a PSA, and the total force suffering\nfrom creep will result in the forced vibration of the two-degree-of-freedommass-spring-damper system composed of the equivalent\nmass, stiffness, and damping of the piezoelectric wafers and the bonding layers. A modified comprehensive model for PSAs is\nput forward by using a linear function, an asymmetrical Bouc-Wen hysteresis operator, and a creep function to model the linear\nforce, the hysteresis force, and the creep characteristics, respectively. In this way, the effect of the bonding layers on the hysteresis\nand dynamic characteristics of PSAs can be analyzed via the modified comprehensive model.The experimental results show that\nthe modified comprehensive model for PSAs with the corresponding parameter identification method can accurately portray the\nhysteresis and dynamic characteristics of PSAs fabricated by different layering/stacking processes. Finally, the theoretical analyzing\non utilizing the modified comprehensive model to linearize the hysteresis characteristics and design the dynamic characteristics of\nPSAs is given....
With its unique structure, the Akiyama probe is a type of tuning fork atomic\nforce microscope probe. The long, soft cantilever makes it possible to measure soft\nsamples in tapping mode. In this article, some characteristics of the probe at its second\neigenmode are revealed by use of finite element analysis (FEA) and experiments in a\nstandard atmosphere. Although the signal-to-noise ratio in this environment is not good\nenough, the 2 nm resolution and 0.09 Hz/nm sensitivity prove that the Akiyama probe can be\nused at its second eigenmode under FM non-contact mode or low amplitude FM tapping\nmode, which means that it is easy to change the measuring method from normal tapping to\nsmall amplitude tapping or non-contact mode with the same probe and equipment....
Nowadays there is growing interest in evolving the distributed sensors concept from the more traditional one of enabling technology\nto monitor the surrounding physical environment towards Cyber Physical Systems (CPS) sensors and actuators, that is, as a suitable\ntool to measure/influence the cyber activity of possibly worldwide communities of users (e.g., any geotagged operation leaving a\ncyber footprint and any cyber physical incentive to stimulate activity as in crowdsensing). To leverage this novel perspective, we\npropose a framework to integrate at best multilayer CPS sensors and actuators as the basis for autonomic management operations on\nboth physical and cyber worlds. In this paper the specific application domain target is peer-to-peer content sharing based on social\nidentities and relationships, but we claim that the proposed CPS framework is of general applicability. In particular, our original\nmiddleware solution adopts CPS actuators to move users� content temporarily from smart home environments to high-performance\ncloud resources to minimize the access time of a dynamically selected quota of contents. Then, based on social network sensors and\nconnectivity/networking ones hosted at lightweight domestic Web servers, our CPS actuators can originally and dynamically move\ncontent back from the cloud to smart homes when appropriate, in order to both retain full ownership of user-generated content\nand reduce cloud hosting costs....
The use of wireless communications for real-time control applications poses\nseveral problems related to the comparatively low reliability of the communication channels.\nThis paper is concerned with adaptive and predictive application-level strategies for\nameliorating the effects of packet losses and burst errors in industrial sampled-data\nDistributed Control Systems (DCSs), which are implemented via one or more wireless\nand/or wired links, possibly spanning multiple hops. The paper describes an adaptive\ncompensator that reconstructs the best estimates (in a least squares sense) of a sequence of\none or more missing sensor node data packets in the controller node. At each sample time,\nthe controller node calculates the current control, and a prediction of future controls to apply\nover a short time horizon; these controls are forwarded to the actuator node every sample\ntime step. A simple design method for a digital Proportional Integral Derivative (PID)-like\nadaptive controller is also described for use in the controller node. Together these\nmechanisms give robustness to packet losses around the control loop; in addition, the\nmajority of the computational overhead resides in the controller node. An implementation of\nthe proposed techniques is applied to a case study using a Hardware in the Loop (HIL) test\nfacility, and favorable results (in terms of both performance and computational overheads)\nare found when compared to an existing robust control method for a DCS experiencing\nartificially induced burst errors....
Structural modal identification has become increasingly important in health monitoring, fault diagnosis, vibration control, and\ndynamic analysis of engineering structures in recent years. Based on an analysis of traditional optimization algorithms, this paper\nproposes a novel sensor optimization criterion that combines the effective independence (EFI) method with the modal strain energy\n(MSE) method. Considering the complex structure and enormous degrees of freedom (DOFs) of modern concrete arch dam,\na quantum genetic algorithm (QGA) is used to optimize the corresponding sensor network on the upstream surface of a dam.\nFinally, this study uses a specific concrete arch damas an example and determines the optimal sensor placement using the proposed\nmethod. By comparing the results with the traditional optimization methods, the proposed method is shown to maximize the spatial\nintersection angle among the modal vectors of sensor network and can effectively resist ambient perturbations, which will make\nthe identified modal parameters more precise....
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