Contact Force Waveforms Research Articles

Prediction of Knee Joint Contact Forces From External Measures Using Principal Component Prediction and Reconstruction.

Abnormal loading of the knee joint contributes to the pathogenesis of knee osteoarthritis. Gait retraining is a noninvasive intervention that aims to reduce knee loads by providing audible, visual, or haptic feedback of gait parameters. The computational expense of joint contact force prediction has limited real-time feedback to surrogate measures of the contact force, such as the knee adduction moment. We developed a method to predict knee joint contact forces using motion analysis and a statistical regression model that can be implemented in near real-time. Gait waveform variables were deconstructed using principal component analysis, and a linear regression was used to predict the principal component scores of the contact force waveforms. Knee joint contact force waveforms were reconstructed using the predicted scores. We tested our method using a heterogenous population of asymptomatic controls and subjects with knee osteoarthritis. The reconstructed contact force waveforms had mean (SD) root mean square differences of 0.17 (0.05) bodyweight compared with the contact forces predicted by a musculoskeletal model. Our method successfully predicted subject-specific shape features of contact force waveforms and is a potentially powerful tool in biofeedback and clinical gait analysis.

Nonlinear dynamics of thin plates excited by a high-power ultrasonic transducer

Strong superharmonic and high-order subharmonic vibrations of thin metal plates are observed in the experiments when a high-power ultrasonic transducer is used to excite plate vibrations. A finite element model and a lumped-mass discrete parameter model are established, respectively, and numerical simulations are carried out to study the mechanism of nonlinear vibrations. The plate vibrations are characterized by time series, power spectra, phase portraits, Poincare maps and bifurcation diagram. It can be seen that the contact force waveform distortion is the reason for generating superharmonic vibration, while the intermittent contact between the thin plates and the ultrasonic transducer is the cause of subharmonic vibrations in the plates. The FEM simulation results are in agreement with the numerical results obtained from the discrete model, which have implications for the predication and control of nonlinear vibrations in ultrasonic assisted manufacturing and testing.

48 * Factors affecting catheter contact in the human left atrium and their impact on ablation efficacy

Introduction: Pre-clinical work suggests factors including catheter orientation and contact consistency during individual radiofrequency ablations influence lesion size and that impedance drop during ablation correlates with the lesion size. Our aim was to investigate factors affecting catheter contact in the human left atrium (LA) and their effects on ablation. Methods and Results: 2,900 eight second static LA mapping points were studied in 30 patients undergoing ablation for AF: 16 patients in AF, 14 in sinus rhythm (SR), 18 remote robotic navigation (RRN) procedures. A SmartTouch contact force (CF) sensing catheter (Biosense Webster, USA) was used to collect CF data. All data were analysed using custom written scripts in the Matlab (MathWorks, USA) environment. CF variability (CFV: difference between 20Hz-sampled CF waveform mean peak and trough) increased with mean CF (Spearman's rho 0.6, p<0.005), and varied by location, being highest at the LA roof. Catheter drift correlated weakly with CF (Spearman's rho −0.05, p=0.005). CFV and drift were higher in SR than AF (p<0.001 for each). In AF there was less catheter drift for RRN than manual navigation points but the converse was true in SR (p<0.001 for both). CFV was higher with RRN (p<0.005). In 747 static 30s LA ablations, the influence of contact parameters on ablation efficacy was compared by multivariate analysis of impedance drop during ablation: a lesser drop suggesting reduced efficacy (Table). Greater CFV, locational drift, perpendicular contact, SR and RRN usage were associated with reduced efficacy (p<0.005 for each), even with ablation force time integral included in this analysis. Dependent Variable: Square root of percentage impedance drop Reference Location: Right WACA A positive β value for a co-factor means that if all the other co-factors are unchanged, the impedance drop will be higher as the co-factor increases (and vice versa) . Conclusions: Beyond ablation CF magnitude and duration, the quality of catheter contact also influences ablation efficacy. Clinical catheter contact is affected by multiple factors, including contact orientation, atrial rhythm and catheter navigation mode. Ablations should be performed in parallel contact with CFV ≤10g and catheter drift ≤3.5mm to maximize efficacy. | Multivariate analysis of factors affecting impedance drop during ablation | |:-------------------------------------------------------------------------:| ------------------------------------------ | | Co-factor | Unstandardized β (95% Confidence Interval) | p-value | | Ln(Force Time Integral) g.s | 0.78 (0.77 to 0.78) | <0.005 | | Remote Robotic Navigation | −0.08 (−0.1 to −0.07) | <0.005 | | Catheter drift >3.5mm | −0.22 (−0.24 to −0.2) | <0.005 | | Contact Force Variability (g) | −0.03 (−0.03 to −0.02) | <0.005 | | Perpendicular Contact Orientation | −0.03 (−0.04 to −0.02) | <0.005 | | Sinus Rhythm | −0.07 (−0.09 to 0.05) | <0.005 | | Left Atrial Body (non-WACA) | 0.1 (0.08 to 0.11) | <0.005 | | Left WACA | 0.06 (0.05 to 0.07) | <0.005 |

Nonlinear vibrations and heating phenomena of cracks in metal plates excited by intensive ultrasonic pulses.

When thin metal plates are excited by intensive ultrasonic pulses, nonlinear vibration phenomena are observed in experiments. As the plates contain cracks, the frictional heating of both faces of the crack appears under the excitation of the ultrasonic pulses. Based on the experimental conditions, a finite element modeling is established and transient dynamic analyzes are performed to explore the generation mechanism of the nonlinear vibrations including superharmonics, subharmonics, and chaotics, as well as the heating phenomena of the cracks. A piezoelectric‐thermal analogy method is used to simulate the high‐power ultrasonic transducer excitation, and a contact‐impact algorithm is used to simulate the dynamical interaction between the ultrasonic horn and plate as well as between both sides of the cracks. By analyzing the vibration velocity waveforms, vibration frequency spectra, and contact force waveform, it can be found that the waveform distortion of the intermittent contact forces between the horn ...

An Experimental Study of Contact Forces During Oblique Elastic Impact

Low and high speed impacts frequently occur in many mechanical processes. Although widely studied, rarely are normal and tangential force time-waveforms measured, as generally these are very difficult measurements to do accurately. This paper presents, for the first time, a comprehensive set of experimentally obtained contact force waveforms during oblique elastic impact for a range of initial velocities and incidence angles. The experimental apparatus employed in this study was a simple pendulum consisting of a spherical steel striker suspended from a steel wire. The contact force time-waveforms were collected using a tri-axial piezoelectric force transducer sandwiched between a spherical target cap and a large block. The measured contact forces showed that loading was essentially limited to the normal and tangential directions in the horizontal plane. Analysis of the maximum normal and tangential forces for the near glancing angles of incidence indicated a friction coefficient that varies linearly with initial tangential velocity. The essential features of tangential force reversal during impact predicted by previous continuum models are confirmed by the experimental force results.

An Analytical Solution for Shear Stress Distributions During Oblique Elastic Impact of Similar Spheres

A new solution method for the oblique elastic impact of similar spheres with Coulomb friction is presented. The solution uses approximations of the shear stress distributions at each time step during impact. These distributions are solved from analytical formulations and are able to account for both full sliding and partial-slip scenarios that may both be present for this problem due to inclusion of tangential compliance and friction effects. Comparison to previous continuum models in the literature shows very good agreement for the contact force wave forms obtained. The major advantage of this method is the drastic reduction in computation time required compared to previous solutions.

Diagnosis of Overhead Contact Line based on Contact Force

Large contact force fluctuations between contact wires and pantographs cause unstable current collection conditions and so it is important to measure and estimate the contact force to obtain a better knowledge of current collection quality. Contact force waveforms are affected by the condition of equipment used on overhead contact lines, so it is to be expected that the contact force waveform represents the state of repair of an overhead contact line. This paper describes contact force waveform characteristics against the static height of Shinkansen contact wires and their application in overhead line diagnosis.

An Experimental Study of Friction During Planar Elastic Impact

Low-speed oblique elastic impacts frequently occur in heat exchangers and other equipment having loosely supported tubes or pipes. In order to experimentally study friction during such impacts, a pendulum-type impact apparatus was developed. A hardened steel sphere at the end of the pendulum collides with a flat steel surface for a range of approach velocities and angles. The present investigation examined eight velocities from 8 to 93 mm/s and impact angles (measured from the common normal) of 0 to 75 deg for each velocity. The normal and tangential contact force waveforms were measured using a triaxial piezoelectric force transducer which was dynamically calibrated. As expected, the results show that the tangential force is less than the limiting Amontons-Coulomb friction predictions at low impact angles. Two regimes of stick-slip and gross-slip friction are clearly distinguished by a new friction parameter called the specific traction ratio. Tangential force reversal was observed at low impact angles, indicating local tangential oscillations. The stick-slip results are consistent with a partial-slip model where the contact zone has a central sticking region surrounded by a ring area undergoing slip.

Studies on Impact Sound : First Report, The Sound Generated by a Ball Colliding with a Plate

Collision is one cause of mechanical sound. Impact sound occurs from an immense variety of sources, and may cause serious problems when it occurs to an objectionable extent in machines, structures, and the like. In view of the troublesome nature of impact sound, a series of studies have been undertaken in order to find a way to reduce it. This first report concerns the impact sound that is produced by the collision of a ball against a plate. Simply, a ball attached with a force transducer was collided with a square steel plate suspended freely, and the resulting impact sound and the pulse-like contact force occurring between the ball and the plate were measured simultaneously. Different kinds of ball materials and balls of differing diameters were tested at varying impact velocity, and the impact sound and contact force waveforms were observed and investigated through real time frequency analysis. As a result, the characteristics of impact sound have been clarified, providing an insight into the mechanism of its occurrence.