Current Issue : April - June Volume : 2014 Issue Number : 2 Articles : 7 Articles
The paper deals with the design of control algorithms for virtual reality based telerobotic system with haptic feedback that allows\r\nfor the remote control of the vertical drilling operation. The human operator controls the vertical penetration velocity using a\r\nhaptic device while simultaneously receiving the haptic feedback from the locally implemented virtual environment. The virtual\r\nenvironment is rendered as a virtual spring with stiffness updated based on the estimate of the stiffness of the rock currently\r\nbeing cut. Based on the existing mathematical models of drill string/drive systems and rock cutting/penetration process, a robust\r\nservo controller is designed which guarantees the tracking of the reference vertical penetration velocity of the drill bit. A scheme\r\nfor on-line estimation of the rock intrinsic specific energy is implemented. Simulations of the proposed control and parameter\r\nestimation algorithms have been conducted; consequently, the overall telerobotic drilling system with a human operator controlling\r\nthe process using PHANTOM Omni haptic device is tested experimentally, where the drilling process is simulated in real time in\r\nvirtual environment....
A single-degree-of-freedom mechanical model of vibro-impact system is established. Bifurcation and chaos in the system are\r\nrevealed with the time history diagram, phase trajectory map, and Poincar�´e map. According to the bifurcation and chaos of the\r\nactual vibro-impact system, the paper puts forward external periodic force control strategy. The method of controlling chaos by\r\nexternal periodic force feedback controller is developed to guide chaotic motions towards regular motions. The stability of the\r\ncontrol system is also analyzed especially by theory. By selecting appropriate feedback coefficients, the unstable periodic orbits\r\nof the original chaotic orbit can be stabilized to the stable periodic orbits. The effectiveness of this control method is verified by\r\nnumerical simulation....
The full control system of a grid-connected current-controlled voltage-source inverter (CC-VSI) has been designed and\r\nimplemented on a field-programmable gate array (FPGA). Various control functions and implementation methods are described\r\nand discussed. The practical viability of the system is evaluated in an experimental setup, where a VSI supplies 30kW into the local\r\ngrid at 400V. A phase-locked loop (PLL) is used for grid phase tracking and evaluated for simulated abnormal grid conditions.\r\nPower factor is kept at unity, and the implemented control system is stressed with step responses in the supplied active power. A\r\nmoving-average filter is implemented to reduce the effects of noise and harmonics on the current control loops. A coupling between\r\nactive and reactive power flow is observed for the step responses but may be ignored in this context. The proposed system is fully\r\ncomparable with more conventional microprocessor-based control systems....
How to make the individual get the reasonable and practical profit among the fourth party logistics supply chain coalition system\r\nis still a question for further study. Considering the characteristics of the fourth party logistics supply chain coalition, this paper\r\ncombines Shapley Value with Distribution according to Contribution, two methods in the application, and then adjusts the profit\r\nallocated to each member reasonably based on the actual coalition situation named improved weighted Shapley Value model. In\r\nthis paper, we first analyze the fourth party logistics supply chain coalition profit allocation models, the classical Shapley value\r\nmethod. Then, we analyze the weight of individual enterprise in the coalition by the analytic hierarchy process. To each enterprise,\r\nthe weight is determined by the investment risks, information divulging risks, and failure risks. Finally, the numerical study shows\r\nthat the profit allocation method improved weighted Shapley value model is relatively rational and practical. Thus, the proposed\r\ncombined model is a useful profit allocation mechanism for the fourth party logistics supply chain coalition that the contribution\r\nand risks are fully considered....
The integrity design problem of fault tolerant control for networked control system (NCS) with actuator failures and data packet\r\ndropouts is investigated.Thedata packet dropouts in both sensor-controller (S-C) and controller-actuator (C-A) links are described\r\nby two switches, which can bemodeled as a discrete event system with known rate. After introducing thematrix of actuator failure,\r\nthe closed-loop NCS is developed, which can be viewed as asynchronous dynamical systems (ADSs). Then, the sufficiency of\r\nexponential stability for the NCS is obtained based on the theory of ADSs. The output feedback controllers that can guarantee\r\nsystemstability are also proposed. Finally, two numerical examples are given to demonstrate the validity of our proposed approach...
Distributed denial of service (DDoS) attacks are one of the major threats to the current Internet, and application-layer DDoS\r\nattacks utilizing legitimate HTTP requests to overwhelm victim resources are more undetectable. Consequently, neither intrusion\r\ndetection systems (IDS) nor victim server can detect malicious packets. In this paper, a novel approach to detect application-layer\r\nDDoS attack is proposed based on entropy of HTTP GET requests per source IP address (HRPI). By approximating the adaptive\r\nautoregressive (AAR) model, the HRPI time series is transformed into a multidimensional vector series. Then, a trained support\r\nvector machine (SVM) classifier is applied to identify the attacks. The experiments with several databases are performed and results\r\nshow that this approach can detect application-layer DDoS attacks effectively....
Three feature extraction methods of sucker-rod pump indicator card data have been studied, simulated, and compared in this\r\npaper, which are based on Fourier Descriptors (FD), GeometricMoment Vector (GMV), and Gray LevelMatrix Statistics (GLMX),\r\nrespectively.Numerical experiments show that the FourierDescriptors algorithm requires less running time and less memory space\r\nwith possible loss of information due to nonoptimal numbers of Fourier Descriptors, the Geometric Moment Vector algorithm is\r\nmore time-consuming and requires more memory space, while the Gray LevelMatrix Statistics algorithm provides low-dimension\r\nfeature vectors withmore time consumption andmore memory space. Furthermore, the characteristic of rotational invariance, both\r\nin the Fourier Descriptors algorithm and the Geometric Moment Vector algorithm, may result in improper pattern recognition of\r\nindicator card data when used for sucker-rod pump working condition diagnosis....
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