Cable Motion Research Articles

Wear of cardiac lead outer insulation due to internal cable motion

Insulation wear in implanted cardiac leads may result in serious failure modes, including inappropriate or missing therapy. A novel test apparatus intended to simulate a range of loading conditions between cardiac lead components has been developed. Wear testing performed in an aqueous environment at loads and velocities anticipated to occur in-vivo shows that a material with decreased toughness exhibited increased wear rate. Order of magnitude variability within test groups was observed, suggesting that reliability projections should incorporate the statistical nature of the wear rate. Ranking of implantable material wear rates are possible using this methodology.

Mitigation of Wind-Rain-Induced Cable Vibration in Cable-Stayed Bridges: Measurement Error

Recent advances in structural and construction technologies have enabled engineers to use the cable efficiently in relatively large structures such as long span cable-stayed bridges. It appeared that many factors and phenomena can generate cable vibration. The cables usually possess low damping and are therefore prone to many vibration problems, even causing large displacement. The active control method has been introduced to control the cable vibration in the cable-stayed bridges. The active control method is an effective method to suppress cable vibrations by adjusting the cable tension which is varied with time. This approach utilizes the axial motion of cables supported by an actuator installed at the anchorage to produce a time-varying force in the cable. To synthesize the feedback control signal, the cable vibration is measured by an optical tracking sensor attached at the mid-span cable. The studies are carried out to investigate the measurement error features of the control method as a design guideline.

Chaos Behavior and Control of Stay-Cables

Stay-cable is infinite dimensional nonlinear dynamical system with a very complex vibration types and mechanism which are not described reasonably yet. In order to better control its dynamic behavior, it is necessary to study complex dynamic behavior carefully. Fistly, partial differential equation of the cable motion is established based on the parabolic initial configuration and is simplified into n Duffing-equations by using Galerkin method. Secondly, the chaos behaviors of the first order Duffing-equation under periodic excitation are studied by taking advantage of Melnikov method. At last , parameters may lead to chaotic motion of a true cable in laboratory are calculated and the methods of chaos control are discussed briefly. The study shows that: 1. First order vibration of cable under periodic excitation has much more complex behaviors than the freedom vibration; 2. The Melnikov method can be very effective and convenient for the analysis of chaotic motion of cable.

Wavelet thresholding technique for sEMG denoising by baseline estimation

The surface electromyography (sEMG) signal is affected by different sources of noises: current technology is considerably robust to the interferences of the power line or cable motion artefacts, but still there are many limitations in denoising the baseline. In this paper, we introduce a new technique, named baseline adaptive denoising algorithm (BADA), for denoising the sEMG signal by wavelet thresholding procedure. In particular, the thresholds are estimated using the same baseline signal with fixed and adaptive techniques. Eventually, we verify that the proposed adaptive method performs better than the standard Donoho technique and different variations, in term of noise cancellation and distortion of the signal, quantified by a new suggested indicator of the denoising quality.

A $160~\mu {\rm W}$ 8-Channel Active Electrode System for EEG Monitoring

This paper presents an active electrode system for gel-free biopotential EEG signal acquisition. The system consists of front-end chopper amplifiers and a back-end common-mode feedback (CMFB) circuit. The front-end AC-coupled chopper amplifier employs input impedance boosting and digitally-assisted offset trimming. The former increases the input impedance of the active electrode to 2 GΩ at 1 Hz and the latter limits the chopping induced output ripple and residual offset to 2 mV and 20 mV, respectively. Thanks to chopper stabilization, the active electrode achieves 0.8 μVrms (0.5-100 Hz) input referred noise. The use of a back-end CMFB circuit further improves the CMRR of the active electrode readout to 82 dB at 50 Hz. Both front-end and back-end circuits are implemented in a 0.18 μm CMOS process and the total current consumption of an 8-channel readout system is 88 μA from 1.8 V supply. EEG measurements using the proposed active electrode system demonstrate its benefits compared to passive electrode systems, namely reduced sensitivity to cable motion artifacts and mains interference.

Modeling and Analysis of Piezo-Elastica Energy Harvester in Computer Hard Disk Drives

In this paper, design and analysis of an energy harvester named piezo-elastica energy harvester (PEEH) to harvest wasted mechanical energy generated by flex cable kinetic and vibratory motions are presented. A coupled piezo-elastic model is developed for the harvester with focus given to understanding piezoelectricity generated by its PVDF layer over its underlying largely deformed flex cable elatica structure. Design for manufacturing for the proposed harvester is detailed in this work. Numerical finite element simulations and laboratory measurements using noncontact laser interferometry validate the mode with respect to the PEEH's profiles, natural frequencies and mode shapes as well as electric energy generated resulted from flex cable's dynamics. It is observed that about 25% of the power consumed by disk drive's voice coil motor can be harvested by the proposed design. Among harvested energy, it is found that 58% comes from significant change of PEEH's profile when rotary actuator swings between disk's outer diameter and inner diameter regions, 33% from PEEN's 2nd bending mode, and 9% from its 1st bending mode. The work presented in this paper suggests the possibility of scavenging and converting flex cable's mechanical vibrations and dynamics into electrical form for power conservation inside computer hard disk drives.

Computational model of an inclined aerial ropeway and numerical method for analyzing nonlinear cable-car interaction

The main objective of the paper is to present the computational model of a bi-cable aerial ropeway, which provides a scope for investigating the nonlinear interaction between the carrying cable motion and the swaying motion of traveling passenger carriers, depending on cable track inclination. To solve nonlinear equations of motion of two coupled sub-systems: multi-span cable and carriers idealized as physical pendulums, the special numerical method is developed, where initial vibrations of carriers (before entering a cable track) are used as a base for predicting further history of motion. Numerical analysis performed for different inclinations of a cable track led to the conclusion that nonlinear interaction effects are not significant and can be neglected to simplify the computational procedure in further research.

Stochastic optimal control of cable vibration in plane by using axial support motion

A stochastic optimal control strategy for a slightly sagged cable using support motion in the cable axial direction is proposed. The nonlinear equation of cable motion in plane is derived and reduced to the equations for the first two modes of cable vibration by using the Galerkin method. The partially averaged Ito equation for controlled system energy is further derived by applying the stochastic averaging method for quasi-non-integrable Hamiltonian systems. The dynamical programming equation for the controlled system energy with a performance index is established by applying the stochastic dynamical programming principle and a stochastic optimal control law is obtained through solving the dynamical programming equation. A bilinear controller by using the direct method of Lyapunov is introduced. The comparison between the two controllers shows that the proposed stochastic optimal control strategy is superior to the bilinear control strategy in terms of higher control effectiveness and efficiency.

Derivation of equations of motion of an unwinding cable from a cylindrical spool package

In this study, the transient analysis of a cable unwinding from a cylindrical spool package is studied. Cables are withdrawn with a constant velocity through a fixed point which is located along the axis of the package. When the cable is flown out of the package, several dynamic forces, such as inertial force, Coriolis force, centrifugal force, tensile force, and fluid-resistance force are acting on the cable. Consequently, the cable becomes to undergo very nonlinear and complex unwinding behavior which is called unwinding balloon. In this paper, to prevent the problems during unwinding such as tangling or cutting, unwinding behaviors of cables in transient state were derived and analyzed. First of all, the governing equations of motion of cables unwinding from a cylindrical spool package were systematically derived using the extended Hamilton’s principles of an open system in which mass is transported at each boundary. And the modified finite difference methods are suggested to solve the derived nonlinear partial differential equations. Time responses of unwinding cables are calculated using Newmark time integration methods.

Classical applications of the Klein–Gordon equation

The quantum mechanical origin of the Klein–Gordon equation hides its capability to model many classical systems. We consider three examples of vibrating systems whose mathematical descriptions lead to the Klein–Gordon equation. These examples are adapted to applications such as the motion of suspended cables and Inca rope suspension bridges. We also discuss the correspondence between the classical and quantum settings of this equation as a way to provide an explanation of the concept of mass.

Geometrically Exact Kirchhoff Beam Theory: Application to Cable Dynamics

In this article, the finite element simulation of cables is investigated for future applications to robotics and hydrodynamics. The solution is based on the geometrically exact approach of Cosserat beams in finite transformations, as initiated by Simo in the 1980s. However, the internal basic kinematics of the beam theory is not those of Reissner–Timoshenko but rather those of Kirchhoff. Based on these kinematics, the dynamic model adopted is a nonlinear extension of the so-called linear model of twisted and stretched Euler–Bernoulli beams. In agreement with the investigated applications, one or both of the ends of the cable are submitted to predefined motions. This model is also implemented into a computational fluid dynamics code, which solves the Reynolds-averaged Navier–Stokes equations. Regarding this last point, an implicit/iterative algorithm including a conservative load transfer for the variable hydrodynamic forces exerted all along the beam length has been used to reach a stable coupling. The relevance of the approach is tested through three advanced examples. The first is related to the prediction of cable motion in robotics. Then, the two last illustrations deal with fluid-structure interaction (FSI). A 2D classical benchmark in FSI is first investigated, and, at last, a computation illustrates the procedure in a 3D case.

Modeling of Transmission Characteristics Across a Cable-Conduit System

Many robotic systems, like surgical robots, robotic hands, and exoskeleton robots, use cable passing through conduits to actuate remote instruments. Cable actuation simplifies the design and allows the actuator to be located at a convenient location, away from the end effector. However, nonlinear frictions between the cable and the conduit account for major losses in tension transmission across the cable, and a model is needed to characterize their effects in order to analyze and compensate for them. Although some models have been proposed in the literature, they are lumped parameter based and restricted to the very special case of a single cable with constant conduit curvature and constant pretension across the cable only. This paper proposes a mathematically rigorous distributed parameter model for cable-conduit actuation with any curvature and initial tension profile across the cable. The model, which is described by a set of partial differential equations in the continuous time-domain, is also discretized for the effective numerical simulation of the cable motion and tension transmission across the cable. Unlike the existing lumped-parameter-based models, the resultant discretized model enables one to accurately simulate the partial-moving/partial-sticking cable motion of the cable-conduit actuation with any curvature and initial tension profile. The model is further extended to cable-conduit actuation in pull-pull configuration using a pair of cables. Various simulations results are presented to reveal the unique phenomena like backlash, cable slacking, interaction between the two cables, and other nonlinear behaviors associated with the cable conduits in pull-pull configuration. These results are verified by experiments using two dc motors coupled with a cable-conduit pair. The experimental setup has been prepared to emulate a typical cable-actuated robotic system. Experimental results are compared with the simulations and various implications are discussed.

Multi-mode interactions in vortex-induced vibrations of flexible curved/straight structures with geometric nonlinearities

A general low-order fluid–structure interaction model capable of evaluating the multi-mode interactions in vortex-induced vibrations of flexible curved/straight structures is presented. Cross-flow motions due to unsteady lift forces of inclined sagged cables and tensioned beams in uniform currents are investigated. In contrast to a linear equation governing the transverse motion of straight beams or cables typically considered in the literature, coupled horizontal/vertical (axial/transverse) displacements and geometric nonlinearities of curved cable (straight beam) are accounted for. A distributed nonlinear wake oscillator is considered in the approximation of space–time varying hydrodynamics. This semi-empirical fluid force model in general depends on the mass-damping parameter and has further been modified to capture both the effects of varying initial curvatures of the inclined cylinder and the Reynolds number. Numerical simulations are performed in the case of varying flow velocities and parametric results highlight several meaningful aspects of vortex-induced vibrations of long flexible cylinders. These comprise multi-mode lock-in, sharing, switching and interaction features in the space and time domains, the estimated maximum modal and total amplitudes, the resonant nonlinear modes of flexible cylinders and their space–time modifications, and the influence of fluid/structure parameters. A shortcoming of single-mode or linear structural model is underlined. Some quantitative and qualitative comparisons of numerical/experimental results are discussed to demonstrate the validity and required improvement of the proposed modelling and analysis predictions.

Dynamic excitation of cables by deck and/or tower motion

Large-amplitude cable vibrations have been observed on many major cable-stayed bridges. One possible source of excitation is movement of the deck and/or tower. Of particular concern is parametric excitation, whereby small deck/tower motion at one frequency can cause large cable motion at half the frequency under certain conditions. More commonly, deck/tower motion causes direct excitation of the cable at the same frequency in the same plane. Since cables have low damping, the response amplitudes can be large and geometric non-linearities can become important. Current design guidelines treat the axial and transverse components of end motion separately, but for an inclined cable subject to vertical deck motion at the lower anchorage and/or in-plane horizontal motion at the upper anchorage, both components occur simultaneously, modifying the behaviour considerably. This paper gives simplified results of non-linear mathematical modelling of inclined cable dynamics, with experimental validation, with the aim of providing more reliable guidelines for use in design. The proposed guidelines are summarised an appendix .

Optimal Tuning of Amplitude Proportional Coulomb Friction Damper for Maximum Cable Damping

This paper investigates numerically the optimal tuning of Coulomb friction dampers on cables, where the optimality criterion is maximum additional damping in the first vibration mode. The expression for the optimal friction force level of Coulomb friction dampers follows from the linear viscous damper via harmonic averaging. It turns out that the friction force level has to be adjusted in proportion to cable amplitude at damper position which is realized by amplitude feedback in real time. The performance of this adaptive damper is assessed by simulated free decay curves from which the damping is estimated. It is found that the damping efficiency agrees well with the expected value at the theoretical optimum. However, maximum damping is larger and achieved at a force to amplitude ratio of 1.4 times the analytical value. Investigations show that the increased damping results from energy spillover to higher modes evoked by the amplitude proportional Coulomb friction damper which clamps the cable at its upper and lower positions. The resulting nonsinusoidal cable motion clearly violates the assumption of pure harmonic motion and explains why such dampers have to be tuned differently from optimal linear viscous dampers.

Theoretic Model and Position Solution of a Cable Mesh Mechanism

The cable mesh mechanism is a kind of flexible,parallel motion mechanism array. The motion theoretical analysis is important for the complex and coupled movement. The theoretical model of the cable mesh mechanism is setup via undigraph,and expressed in computer via adjacency list. The cable is simplified and regarded as a linear spring-sliding pair. Based on force density method,the balance equations of the active node are built,and extended to the whole cable mesh motion mechanism. The problem how to solve the balance equations is discussed,and the positional relationship between actuator ends and active nodes of the cable mesh mechanism is deduced and expressed in iterative equations. Then a position analysis method is built. By programming,the cable mesh motion mechanism of the 30 m model of the five-hundred-meter aperture spherical telescope (FAST) is modeled,and its motion is simulated. The results are same as that simulated in Adams software. The position analysis method is verified. It can be used in the real-time control arithmetic of the FAST active reflector,and can be used in precise adjustment or control of the reflector shape for other large cable mesh antennas and space deployable reflectors as well.

A study on dynamic response of cable-seabed interaction

A numerical method is developed to investigate the dynamic response of cable-seabed interaction in this paper. The motion of cable is described by the Lumped Parameter Method, while the seabed, unlike the prevailing simplified model of elastic foundation, is modeled as an irregular continuous rigid surface with rebound and friction existing, and the forces exerted by the seabed consist of normal counterforce and isotropic tangential Coulomb friction resistance. To describe the detailed dynamic response, two coefficients are introduced by analogy with the theory of rigid body collision with friction. The cable-seabed kinematic and dynamic contact conditions are formulated subsequently, and are used to incorporate the seabed effect into the cable dynamics to produce a set of ordinary differential governing equations. In this paper, we employ 4th order Runge-Kutta method to solve these equations. Several simulation cases are presented to illustrate the seabed effect. The results show that friction and impact have a prominent influence on the statics and dynamics of the cable.

Identification of Cable Forces on Cable-Stayed Bridges: A Novel Application of the MUSIC Algorithm

Proper identification of the cable’s resonant frequencies is critical to provide an accurate estimate of cable force. The MUltiple SIgnal Classification (MUSIC) algorithm is implemented to estimate cable-stayed bridge cable tensions noninvasively from measured cable motion. This algorithm performs eigenanalysis on the data sequence to estimate and eliminate noise contributions before creating its frequency spectrum, providing a more robust estimation approach than traditional Fourier based frequency spectrums. To aid in the selection of cable frequencies, a comprehensive finite difference cable model is simulated and compared to the estimated MUSIC spectrums.

Mixing Measurements on an Equatorial Ocean Mooring

Abstract Vaned, internally recording instruments that measure temperature fluctuations using FP07 thermistors, including fluctuations in the turbulence wavenumber band, have been built, tested, and deployed on a Tropical Atmosphere Ocean (TAO) mooring at 0°, 140°W. These were supplemented with motion packages that measure linear accelerations, from which an assessment of cable displacement and speed was made. Motions due to vortex-induced vibrations caused by interaction of the mean flow with the cable are small (rms < 0.15 cable diameters) and unlikely to affect estimates of the temperature variance dissipation rate χT. Surface wave–induced cable motions are significant, commonly resulting in vertical displacements of ±1 m and vertical speeds of ±0.5 m s−1 on 2–10-s periods. These motions produce an enhancement to the measurement of temperature gradient in the surface wave band herein that is equal to the product of the vertical cable speed and the vertical temperature gradient (i.e., dT/dt ∼ wcdT/dz). However, the temperature gradient spectrum is largely unaltered at higher and lower frequencies; in particular, there exists a clear scale separation between frequencies contaminated by surface waves and the turbulence subrange. The effect of cable motions on spectral estimates of χT is evaluated and determined to result in acceptably small uncertainties (< a factor of two 95% of the time, based on 60-s averages). Time series of χT and the inferred turbulent kinetic energy dissipation rate ε are consistent with historical data from the same equatorial location.

카메라를 이용한 구조물의 동특성 추출

A set of modal parameters of a stay-cable have been extracted fi:on a moving picture captured by a digital camera supported by shaking hands. It is hard to identify the center of targets attached on the cable surface from the blurred cable motion image, because of the high speed motion of cable, low sampling frequency of camera, and the shaking effect of camera. This study proposes a multi-template matching algorithm to resolve such difficulties. In addition, a sensitivity-based system identification algorithm is introduced to extract the natural frequencies and damping ratios from the ambient cable vibration data. Three sets of vibration tests are conducted to examine the validity of the proposed algorithms. The results show that the proposed technique is pretty feasible for extracting modal parameters from the severely shaking motion pictures.