Axial Misalignment Research Articles

Polarization Error Analysis of an All-Optical Fibre Small Current Sensor for Partial Discharge

In view of the characteristics of the small amplitude of a current signal, an all-optical fibre small-current sensor for partial discharge is devised. A novel type of sensor head with electric winding light is proposed. A complete optical model of the optical fibre current sensor is developed under the effect of polarization error factors. In addition, the effect of polarization error factors on the optical fibre sensing system is simulated. The simulation results show that as the extinction ratio increases, the output relative error of the optical fibre small-current sensor decreases. The effect of the fast and slow axis misalignment errors of a polarizing beam splitter is similar to the effect of the alignment angle error of an optical fibre polarizer. It is observed that the relative error curve follows a sine function. Meanwhile, the output relative error increases first and then oscillates with an increase in the linear birefringence. We conclude that the linear birefringence of the sensing optical fibre is the main error source for the measurement accuracy of the sensing system. Finally, an experimental system for the optical fibre small-current sensor is implemented. The experimental results show that the effect of linear birefringence on the fibre current sensing system can be suppressed by introducing a large amount of circular birefringence into the sensing optical fibre. The theoretical mechanism of these errors is analysed, which can be applied to implement corresponding measures to reduce the effect of error factors on the sensing system and further improve the measurement accuracy of the optical fibre small-current sensor.

Refined Model of a Groove Seal and Calculation of Angular Hydrodynamic Force Coefficients

We propose a solution to the problem of calculating the coefficients of the radial and angular forces in a groove seal (with the use of a refined model of a smooth groove seal) as functions of two independent variables, the eccentricity of the rotor and the angle of misalignment of the rotor axis in the seal. Unsteady turbulent flow of a viscous incompressible fluid in the channel of the seal, due to both the axial pressure drop in the seal and the nature of the travel of the inner channel wall, is investigated. The problem is solved under the assumption of small radial and angular displacements of the shaft. The coefficients for forces determined by the angular misalignments of the rotor are obtained here for the first time.

Modelado por elemento finito de la fatiga en engranes de reductores de velocidad con desalineamiento radial y axial

Este artículo presenta un análisis de fatiga en engranes de reductores de velocidad sometidos a desalineamiento radial y axial. Se empleó el método del elemento finito para el cálculo de los ciclos de vida y del estado de esfuerzos alternantes en los engranes. El desalineamiento se consideró en función del módulo del engrane, M. El desalineamiento radial fue M0.2 y M0.5 y el desalineamiento axial fue M0.2 y M0.3. El mecanismo analizado corresponde a los engranes piñón y rueda de la primera etapa del reductor de velocidad de un vehículo todo terreno. En ambas condiciones de desalineamiento la máxima reducción en los ciclos de vida ocurre en el engrane piñón causados por elevados esfuerzos alternantes a medida que se incrementa el torque. Las variaciones en la zona de contacto entre los dientes debido a los desalineamientos en los engranes provocó concentraciones de esfuerzos en la cara y la raíz del diente

Parameters of the Earth\u2019s Free Core Nutation from Diurnal Strain Tides

Earth deformation at the diurnal tidal frequencies includes the resonant tidal-forcing response caused by the Free Core Nutation (FCN), a retrograde mode related to the slight misalignment of the rotation axes of the outer core and mantle. We analyse data from four underground high-sensitivity laser extensometers, whose signal-to-noise ratio in the diurnal tidal band is particularly high, and provide an alternative independent estimate of the FCN complex frequency with respect to more usual techniques (nutation and gravity). Firstly, we differentiate displacements due to diurnal solid tides to obtain extension along any azimuthal direction in terms of three complex parameters (A, S, C) which depend on latitude and frequency. Then, we demonstrate that we can invert the FCN complex frequency and the sensitivity of Im(A) and Re(S) to the resonance from our data. Lastly we obtain the probability distributions of those four parameters. Our results are in full agreement with those from nutation and gravity, as well as with reference IERS (International Earth Rotation and Reference Systems Service) values. Sensitivities of Im(A) and Re(S) to the resonance are estimated here for the first time and are in agreement with values computed using reference Love and Shida numbers from IERS.

Atomic Resolution Imaging of Light Elements in a Crystalline Environment using Dynamic Hollow-Cone Illumination Transmission Electron Microscopy.

Multiple electron scattering and the nonintuitive nature of image formation with coherent radiation complicate the interpretation of conventional transmission electron microscopy images. Precession of the illuminating beam in transmission electron microscopy (TEM) can lead to more robust and interpretable images with some penalty to image contrast, a technique known as dynamic hollow-cone illumination TEM. We demonstrate direct and robust imaging of light and heavy atoms in a crystalline environment with this technique. This method is similar to the annular bright-field technique in scanning transmission electron microscopy, via the principle of reciprocity. Dynamic hollow-cone illumination TEM is challenging in practice due to sensitivity to the misalignment of the precession axis, microscope objective aperture, and crystal zone axis.

Design of Fixations for an Exoskeleton Device with Joint Axis Misalignments

This study aims to solve problems caused by misalignments between exoskeleton systems and the human body. Misalignments interfere with the achievement of the wearer’s motion intention by generating unintended interaction forces between the wearer and the exoskeleton system. Therefore, this study attempts to overcome this problem by applying an additional degree of freedom (DOF) to the fixation of the human body. First, we analyzed a system of a human body and exoskeleton connected by serial chains. Second, we derived all possible DOF sets for a 7-DOF exoskeleton system and determined the final DOF set based on practical applicability. Finally, we measured the interaction forces generated during the operation of the exoskeleton system to verify the effects of the fixation mechanism. The significance of the results was confirmed by a t test with a significance level of p ≤ 0.05.

Optimization of Axial Misalignment due to Glass Drilling by Statistical Methods

Flat glass has a significant utilization in the domestic appliances sector. Drilling of glass is frequently used in the white goods sector. In this research, the glass drilling method is explained in detail, the determined axial misalignment values using the tool rotation speed and the feed rate were investigated. The drilling operation with its parameters must be optimized precisely, in order to have good control over the productivity, quality, and cost aspect of the application. Using the Ø18.3 mm drill tool, drilling process was performed with different rotation speeds (rpm) and feed rates (mm/sec). The impressions of drilling parameter on output variable were investigated using Analysis of Variance (ANOVA). Probabilistic uncertainty analysis based on Monte Carlo simulation was carried out. According to the results, the suggested model and optimization method could be used for estimating axial misalignment and this investigation is reliable and proper for figuring out the problems met in machining operations. Furthermore, Monte Carlo simulations were obtained quite effective for identification of the uncertainties in axial misalignment that could not be possible to be caught by deterministic ways. The optimum axial misalignment value was found to be 0.11823 mm.

Analytical Modeling of Misalignment in Axial Flux Permanent Magnet Machine

This paper proposes an analytical model for the prediction of air gap magnetic field distribution for axial flux permanent magnet (AFPM) machine with various types of misalignments. The AFPM machine geometry is first transformed to a polar representation. Consequently, the subdomain model based on current sheet technique is developed. Then the stator coordinate system is chosen as reference coordinate to consider both static/dynamic angular and axis misalignments. The back electromagnetic forces and cogging torque are obtained accordingly based on Maxwell's equations. The results show that the proposed approach agrees with the finite-element method. The model is further validated by experiments under healthy, dynamic angular and axis misalignment conditions, which can validate the proposed approach. It turns out that the proposed approach can predict the performance of AFPM machines with types of misalignment quickly and effectively, which is greatly significant for further fault detection.

Bending Fatigue Life Prediction of Spur Gear in Axial Misalignment Condition

Misalignment between pinions to wheel gears induces bending stresses continued influences the fatigue life of the spur gear system. Lack of research projected to the issues causes uncertain in their useful lifetime estimation. In this paper, the bending fatigue life of the spur gear in axial misalignments condition was predicted. A three teeth FEM model of spur gear with the same geometrical profiles was constructed according to ISO 6336-1:2006. The gear was subjected with five misalignment from 0.1mm to 0. 5mm at different torque loadings from 50Nm to 300 Nm. Exerted with quasi-static approach; the stress variant was analysed to stress life model as well as the damage accumulation model for fatigue life prediction in ANSYS V19. Results showed that the application of axial misalignment had a small impact significantly reduce the life of the gear, in percentage difference between 0.1 - 2%. This suggested that the bending fatigue life did not reflect to the existence of axial misalignments as the effect is very small that it is possible to be neglected.

Respon Vibrasi Overall dan Temperatur Komponen Mesin Terhadap Misalignment Axial

Misalignment is one of the problems that often occurs in rotary equipment. In this paper, the observation was done to the rotary machine model in response to changes of axial misalignment by using vibration meter and infrared thermography camera. The model was a machine series, consisting of electric motor and disc which was connected by 3 Jaw flexible coupling. The shafts were positioned into several axial misalignment conditions to see the effect on the overall vibration value and its component temperature. The result of vibration observation showed that under certain conditions, by increasing shaft misalignment then the overall vibration value tends to decrease. With the decrease of overall vibration value, the machine condition was not in better condition. This was indicated by observing the temperature of the components in this condition, which showed the opposite fact. As misalignment increases, the temperature of the engine components also increases.

Calculating loads and life-time reduction of wind turbine gearbox and generator bearings due to shaft misalignment

During the last two decades, wind turbine industries have faced high failure rates, downtimes and costly repairs. Gearbox and generator have contributed to this, especially, because their high speed shaft bearings have often failed. In this article, an analytical method is proposed to calculate the reaction loads of flexible connecting couplings installed between wind turbine gearbox and generator. Raction loads are determined from joint kinematics and metal disk pack deformations as well as axial and angular shaft misalignment. The calculations are executed for both flexible connecting couplings and a universal joint shaft and applied to the gearbox high speed shaft. The performance of flexible connecting couplings and universal joint shaft is compared with respect to the bearing loads and life-time of the gearbox high speed shaft. It is shown that the early, unplanned bearing failures of gearbox and generator high speed shaft can often be attributed to the flexible connecting couplings installed between gearbox and generator.

Cryoablation for atrial fibrillation.

Cryoballoon ablation for the treatment of atrial fibrillation has established itself as an effective and efficient modality for achieving pulmonary vein isolation. Over the past 13 years more than 100,000 Cryoballoon ablation procedures have been performed with the first to fourth generation cryoballoons. Over that time there have been significant advances in our understanding regarding the optimal procedural techniques. The purpose of this "topic in review" is to focus on the practical aspects of performing a Cryoballoon ablation procedure, within the context of the contemporary literature. Specifically there is a focus on how contemporary studies can inform clinical decision making and ensure operators are able to perform a safe and effective procedure.

Stress magnification factor for angular misalignment between plates with welding-induced curvature

The construction of lightweight structures poses new design challenges as a result of the different mechanics of deformation experienced by thinner-plated structures. Because of a reduced bending stiffness, thin plates are particularly sensitive to welding-induced distortions, which include a curvature, in addition to the axial and global angular misalignment observed on thick plates. The curvature shape and amplitude determine a local angular misalignment at the welded joint, which causes non-negligible secondary bending effects. Therefore, the commonly used stress magnification factors km solution for flat plates need a further development to include the curvature effect. This study proposes new analytical formulations, which extend the applicability of the existing solutions to the assessment of the structural stress of a curved thin plate under an axial load. The improved formulations are consistent with the geometrical non-linear finite element analysis under compression (up to sim 80% of the buckling limit) and tension (up to the yield strength). A sensitivity analysis is presented in order to show the dominant role of the curvature effect in the estimation of the km factor. Regardless of the load applied, the presence of the curvature causes a flat plate solution inaccuracy greater than 10% when the local angular misalignment is more than 1.25 times higher than the global angular misalignment in the case of a thin and slender structure.

Vergence Eye Movements: From Basic Science to Clinical Application - Foreword to the Special Issue.

The abstract book of the last European Conference on Eye Movements [1] lists abstracts of 373 presentations, but less than five percent investigate vergence eye movements, i.e. the coordination of the right and left eye. Why then a special issue on this neglected issue? Human vision under natural conditions involves both eyes in coordination controlled by interacting processes subsumed under the concept of vergence.. Further, vergence is important for people in their daily lives since disorders of vergence can have serious consequences: ophthalmologists deal with squinting patients on the basis of heterophoria and heterotropia testing, eye strain or visual complaints can be related to impaired vergence dynamic or less accurate static vergence, remediation by optometrist includes vergence training or prism eye glasses, etc.

Analytical Reason for Smaller Lateral Sway in Angled-Plane Scissor Linkage

Abstract Scissor linkages are widely used with scissor links arranged in two parallel planes. When small misalignment of revolute joint axes are permissible, the linkage can undergo lateral sway. This paper, using rigid-body kinematics and a modeling of misalignment, converts the task of finding lateral sway into a non-linear constrained optimization problem. Through linearization of the optimization problem, this paper analytically proves that (1) maximum lateral sway increases as the number of units in the parallel-plane scissor linkage increases whereas in angled-plane scissor linkage, the lateral sway tends to a finite limit as the number of units is increased and (2) the lateral sway is independent of connector length in parallel-plane scissor linkage whereas it is dependent on the length of the connector in angled-plane scissor linkage. These results are further substantiated with numerical solution of the non-linear optimization problem. The results imply that the angled-plane scissor linkage can substantially limit lateral sway in comparison to parallel-plane scissor linkage under similar conditions of joint misalignment. The analytical expression derived in this paper helps in identifying the influence of design parameters on lateral sway.

Comparison of visual and refractive outcomes of 2 trifocal intraocular lenses.

To compare clinical outcomes after cataract surgery and bilateral implantation of 2 diffractive trifocal toric intraocular lenses (IOLs). Hospital da Luz, Lisbon, Portugal. Double-arm, randomized, prospective case series. A total of 60 patients were randomly allocated to receive bilateral implantation of either the FineVision Pod FT toric IOL (PhysIOL) or the AcrySof IQ PanOptix toric IOL (Alcon). Visual and refractive outcomes, contrast sensitivity, IOL misalignment, and quality of vision outcomes (QoV questionnaire) were evaluated at 3 months postoperatively. Surgically induced astigmatic changes were evaluated by vector analysis. Each group (FineVision toric and AcrySof IQ PanOptix toric) comprised 30 patients (60 eyes). No significant differences between groups were found regarding uncorrected and corrected distance and near visual outcomes (P ≥ .333). Mean postoperative distance-corrected intermediate visual acuity at 60 cm was 0.04 ± 0.09 logarithm of the minimum angle of resolution (logMAR) and 0.09 ± 0.11 logMAR in the PanOptix and Pod FT group, respectively (P = .032). Mean IOL axis misalignment was 1.59 degrees ± 2.15 degrees (PanOptix group) and 1.89 degrees ± 3.31 degrees (Pod FT group) (P = .821). Mean magnitude of error of astigmatic correction was -0.09 diopters (D) and -0.11 D in the PanOptix group and Pod FT group, respectively (P = .333). Contrast sensitivity, QoV scores for the presence of photic phenomena, and the level of spectacle independence were similar in both groups (P > .05). Both trifocal toric IOLs allowed complete patient visual restoration, and good spectacle independence and good visual quality outcomes. The PanOptix IOL provided superior intermediate visual acuity for distances around 60 cm.

Estimating refractive index structure constant and extinction coefficient under misalignment

This paper presents two methods, named the irradiance fitting method and the irradiance integration method, for the estimation of refractive index structure constant (Cn2) and extinction coefficient under misalignment. Validations of the methods are carried out based on experimentally obtained speckle images. These two methods are feasible and accurate regardless of whether the optical axis misalignment distance is calibrated, which provides an effective and convenient approach for free space optical communication (FSOC) atmospheric channel research.

Peak Power Assessment of Isokinetic Knee Flexor and Extensor Tests – Pitfalls of a Dynamometer-based Assessment

ABSTRACTMany sports demand high forces at high movement speeds. Joint power combines these two measures and is frequently analyzed by isokinetic tests. However, various concepts of assessing joint power lead to conflicting results. The aim was to examine different methods to calculate peak power during isokinetic knee tests of sixty-one healthy male participants (20 y, 182 cm, 76 kg). Unilateral movements of the eccentrically working hamstrings and the concentrically working quadriceps at 150°/s were captured by high-speed cameras. Peak power derived from isokinetic data was significantly higher (p < 0.01, d > 1.54) compared to the camera-based kinematic procedures. To achieve best accuracy, peak power should be derived from the camera-based joint angular velocity and the measured moment at time of peak power during the dynamometer’s isokinetic range of motion. A meaningful assessment of isokinetic joint power should incorporate a camera-based kinematic analysis to account for potential measuring inaccuracies owing to anatomical features, axis misalignment, and tissue deformation.

Effects of Defects on Effective Material Properties of Triaxial Braided Textile Composite

In this study, the effects of defects in a triaxial braided textile composite was studied at unit cell level using three-dimensional finite element analysis. The manufacturing defects such as void defect and tow misalignments were considered in the model and the effect of their presence at different scale on the effective material properties were studied. The configuration of the finite element model was based on the geometric data extracted from an experimental test specimen. The representative unit cells (RUC) that repeat itself to build the whole braid were sliced out from the full interlaced geometry of axial and bias tows. Periodic boundary condition (PBC) was used to simulate the repeating nature of the unit cells. Then, numerical tests were performed to compute three-dimensional effective material properties for triaxial braided RUCs with predetermined void volume fractions and axial tow misalignment under uniaxial tension and shear loadings in different directions. It was observed that the void defects severely affected the out-of-plane properties of the material, while the tow misalignments influenced the axial modulus mostly.

Angular limit for coronal joint deformity correction using intramedullary guidance in total knee arthroplasty. A pilot study.

Introduction: Post-operative misalignment of the lower limb mechanical axis following total knee arthroplasty (TKA) is thought to be associated with clinical failure. In a balanced knee, a neutral global mechanical axis following the use of intra-medullary (IM) guidance does not necessarily imply a horizontal TKA joint line. Using femoral and tibial axes separately would be more accurate in evaluating TKA alignment. Thus, the aim of the study is to define a pre-operative mechanical tibial and/or femoral angle threshold value for post-operative optimal alignment correction using IM guides. Methods: This single-center prospective continuous pilot study included 50 patients treated with a TKA for primitive osteoarthritis. Femoral and tibial cuts were performed using intramedullary (IM) guide. Three angles were calculated and analyzed pre and post-operatively on standing antero-posterior views using long-leg radiographs: femorotibial angle (FTA), mechanical femoral angle (MFA), and mechanical tibial angle (MTA). Statistical analysis was performed for the whole sample and for the three following FTA subgroups; normo-axial, varus and valgus. Results: The pre-operative MTA is the only parameter for which a threshold value was observed; when pre-operative MTA exceeded the value of 94°, an optimal correction might not be obtained post-operatively. Discussion: Our results suggest that the bony correction obtained via IM guiding depends exclusively on the primary deformation of the tibia. In cases of a varus of more than 94°, the IM guide was found to yield sub-optimal corrections. Thus, other solutions need to be investigated.