Direct Torque Measurement Research Articles

Rheological measurements and transition to turbulence for moderate Reynolds number inertial suspensions

Particulate flows at moderate particle Reynolds numbers are important in critical engineering and geological applications. This experimental study explores neutrally buoyant suspensions in an outer-rotating coaxial rheometer for solid fractions, $\phi$ , from 0.1 to 0.5, and particle Reynolds number, $Re$ , from 0.5 to 800, covering laminar, transitional and turbulent regimes; $Re$ is defined in terms of the square of the particle diameter and the shear rate. For $0.1 < \phi < 0.4$ and $0.5 < Re <10$ , the direct torque measurements normalised by the laminar flow torque, $M/M_{lam}$ , are independent of $Re$ , but depend on $\phi$ . For the same range of $\phi$ and for $10< Re<100$ , the normalised torques depend on both $\phi$ and $Re$ , and show an increasing dependence on $Re$ . As $Re$ increases, the flow transitions to turbulence. Small particles delay the turbulent transition for $\phi \leqslant 0.3$ , while large particles augment the transition. A modified Reynolds number, $Re^\prime$ , that depends linearly on the particle diameter and the maximum velocity, $U_{o}$ , is introduced for both laminar and turbulent flows and shows a better correlation of the results as compared with $Re$ . For $\phi = 50\,\%$ , the normalised torque minus the torque at zero rotational speed is nearly independent of $Re^\prime$ . Rheological models based on $Re^\prime$ and the Krieger–Dougherty relative viscosity are proposed in the laminar regime for $10< Re^\prime <500$ ; in the turbulent regime, a correlation is proposed in terms of $Re^\prime$ and $\phi$ for $1000< Re^\prime < 6000$ .

On the importance of the experimental setup design in hydrodynamic journal bearing friction measurement

Improving operating conditions and reducing the friction-related power losses of hydrodynamic journal bearings could lower emissions and contribute to efforts for a faster green transition. Experimental studies play an important role in evaluating and improving the performance of plain journal bearings. The concept of the experimental setup for friction measurements of journal bearings is well defined in the relevant standards, but the actual design is always left to the researchers conducting a particular study. Our study reveals that common practical assumptions about the frictional power losses caused by components of the experimental setup can lead to misleading conclusions about the measured coefficient of friction. The research premises were tested on the developed experimental setup using two methods for measuring the coefficient of friction and different load interfaces. In particular, the direct torque measurement using strain gauges on the shaft demonstrated the strongest correlation with theoretical values. However, the result was affected by the correct evaluation of the frictional losses of the support ball bearings. Conversely, the Stribeck curves showed that the combination of the indirect cantilever method and load interface with direct radial force application led to inferior results. The intricate interactions between setup components and unknown frictional conditions made straightforward geometric corrections challenging. The study encourages researchers in the field to critically assess their experimental setups and to rely on their own assessment of frictional losses.

Focusing properties of Azimuthally Polarized Lorentz Gauss Vortex Beam through a Dielectric Interface

Tight focusing properties of azimuthally polarized Lorentz Gaussian vortex beam through a dielectric interface are numerically studied by vector diffraction theory. The focusing properties, such as spot size, depth of focus, and maximum intensity position, are numerically calculated by properly manipulating the Lorentz parameter with/without annular obstruction values. Thus, using annular obstruction, one can generate a highly confined focal spot of long focal depth when using an azimuthally polarized Lorentz Gaussian vortex beam. Full Text: PDF References A. Ashkin et al., "Observation of a single-beam gradient force optical trap for dielectric particles", Opt. Lett. 11, 288 (1986). CrossRef A. Ambardekar, Y.Q. Li, "Optical levitation and manipulation of stuck particles with pulsed optical tweezers", Opt. Lett. 30, 1797 (2005). CrossRef P. Zemánek, C.J. Foot, "Atomic dipole trap formed by blue detuned strong Gaussian standing wave", Opt. Commun. 146, 119(1998). CrossRef S.M. Block et al., "Bead movement by single kinesin molecules studied with optical tweezers", Nature 348, 348 (1990). CrossRef D.E. Smithet al., "The bacteriophage φ29 portal motor can package DNA against a large internal force", Nature 413, 748 (2001). CrossRef L. Oroszi et al., "Direct Measurement of Torque in an Optical Trap and Its Application to Double-Strand DNA", Phys. Rev. Lett. 97, 058301 (2006). CrossRef D.P. Biss, T.G. Brown, "Cylindrical vector beam focusing through a dielectric interface", Opt. Express 9, 490 (2001). CrossRef P. Török et al., "Electromagnetic diffraction of light focused through a planar interface between materials of mismatched refractive indices: structure of the electromagnetic field. I", J. Opt. Soc. Am. A 12, 2136 (1995). CrossRef S.H. Wiersma et al., "Comparison of different theories for focusing through a plane interface", J. Opt. Soc. Am. A 14, 1482 (1997). CrossRef L.E. Helseth, "Roles of polarization, phase and amplitude in solid immersion lens systems", Opt. Commun. 191, 161 (2001). CrossRef P. Zhou et al., "Propagation properties of a Lorentz beam array", Appl. Opt. 49, 2497 (2010). CrossRef O.E. Gawhary, S. Severini, "Lorentz beams and symmetry properties in paraxial optics", J. Opt. A: Pure Appl Opt 8, 409 (2006). CrossRef J. Yang et al., "Focusing of diode laser beams: a partially coherent Lorentz model", Proc. SPIE 6824, 68240 A (2007). CrossRef O.E. Gawhary, S. Severini, "Lorentz beams as a basis for a new class of rectangularly symmetric optical fields", Opt. Commun. 269, 274 (2007). CrossRef H. Yu, L. Xiong, B. Lü, "Nonparaxial Lorentz and Lorentz–Gauss beams", Optik 121,1455(2010). CrossRef Z. Zhang, J. Pu, X. Wang, "Tight Focusing of Radially and Azimuthally Polarized Vortex Beams through a Dielectric Interface", Chin. Phys. Lett. 25, 1664 (2008). CrossRef

Experimental Investigation on Churning Power Loss of Splash Lubricated Worm Gear

Churning power losses are a complex phenomenon that produces critical power losses when considering the splash lubrication of gear units. This article describes the method to investigate the churning power loss in a worm gearbox. A particular test rig was designed and fabricated to experiment on single start worm gear incompletely submerged in an oil bath. The direct torque measurement technique was used to determine the churning power losses. Experiments have been conducted to determine the impact of a variety of operating conditions on churning power losses, including worm speeds, gear immersion depth, lubricant temperatures, and lubricant type (mineral and synthetic). It was found that the churning losses were significantly affected by the worm shaft orientation, speed of gear, and the depth of immersion (static head). The lubricant's temperature is more essential than the type of lubricant in terms of churning power loss.

Force and torque reactions on a pitching flexible aerofoil

Experimental measurements in a wind tunnel of the unsteady force and moment that a fluid exerts on flexible flapping aerofoils are not trivial because the forces and moments caused by the aerofoil's inertia and others structural tensions at the pivot axis have to be obtained separately and subtracted from the direct measurements with a force/torque sensor. Here we derive from the nonlinear beam equation general relations for the force and torque reactions at the leading edge of a pitching aerofoil in terms of the fluid force and moment on the aerofoil and its kinematics, involving geometric and structural parameters of the flexible aerofoil. These relations are validated by comparing high-resolution numerical simulations of the flow–structure interaction of a two-dimensional flexible aerofoil pitching about its leading edge with direct force and torque measurements in a wind tunnel.

Friction dynamics of elasto-inertial turbulence in Taylor-Couette flow of viscoelastic fluids.

Dynamic properties of elasto-inertial turbulence (EIT) are studied in a Taylor-Couette geometry. EIT is a chaotic flow state that develops upon both non-negligible inertia and viscoelasticity. A combination of direct flow visualization and torque measurement allows to verify the earlier onset of EIT compared with purely inertial instabilities (and inertial turbulence). The scaling of the pseudo-Nusselt number with inertia and elasticity is discussed here for the first time. Variations in the friction coefficient, temporal frequency spectra and spatial power density spectra highlight that EIT undergoes an intermediate behaviour before transitioning to its fully developed chaotic state that requires both high inertia and elasticity. During this transition, the contribution of secondary flows to the overall friction dynamics is limited. This is expected to be of great interest in the aim of achieving efficiency mixing at low drag and low but finite Reynolds number. This article is part of the theme issue "Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical transactions paper (Part 2)".

Indirect Efficiency Measurement Method for Line-Start Permanent Magnet Synchronous Motors

Despite the great potential and the high performance of energy-efficient line-start permanent magnet synchronous motors (LSPMSMs), their developers face a great deal of difficulties, one of which is the lack of reliable and accurate testing methods for such electrical machines. In this paper, we propose a new method for indirectly determining the efficiency of LSPMSM through the summation of individual loss components. The standard input-output method usually used for these machines is based on torque measurement, requires expensive measuring equipment, and, as a rule, has great uncertainty. Contrarily, the proposed method does not require direct measurement of torque and mechanical power on the shaft and is less sensitive to measurement uncertainties. The theoretical substantiation of the proposed method and its experimental verification using a commercially available four-pole LSPMSM with a rated power of 0.55 kW are presented. Satisfactory convergence of the experimental results obtained using the standard input-output method and using the proposed indirect method is shown.

Exploiting Cyclic Angle-Dependency in a Kalman Filter-Based Torque Estimation on a Mechatronic Drivetrain

Torsional vibrations play a critical role in the design and operation of a mechanical or mechatronic drivetrain due to their impact on lifetime, performance, and cost. A magnetic spring allows one to reduce these vibrations and improve the actuator performance yet introduces additional challenges on the identification. As a direct torque measurement is generally not favourable because of its intrusive nature, this paper proposes a nonintrusive approach to identify torsional load profiles. The approach combines a physics-based lumped parameter model of the torsional dynamics of the drivetrain with measurements coming from a motor encoder and two MEMS accelerometers in a combined state/input estimation, using an augmented extended Kalman filter (A-EKF). In order to allow a generic magnetic spring torque estimation, a random walk input model is used, where additionally the angle-dependent behaviour is exploited by constructing an angle-dependent estimate and variance map. Experimental validation leads to a significant reduction in bias in the load torque estimation for this approach, compared to conventional estimators. Moreover, this newly proposed approach significantly reduces the variance on the estimated states by exploiting the angle dependency. The proposed approach provides knowledge of the torsional vibrations in a nonintrusive way, without the need for an extensive magnetic spring torque identification. Further, the approach is applicable on any drivetrain with angle-dependent input torques.

Development and Electromyographic Validation of a Compliant Human-Robot Interaction Controller for Cooperative and Personalized Neurorehabilitation.

BackgroundAppropriate training modalities for post-stroke upper-limb rehabilitation are key features for effective recovery after the acute event. This study presents a cooperative control framework that promotes compliant motion and implements a variety of high-level rehabilitation modalities with a unified low-level explicit impedance control law. The core idea is that we can change the haptic behavior perceived by a human when interacting with the rehabilitation robot by tuning three impedance control parameters.MethodsThe presented control law is based on an impedance controller with direct torque measurement, provided with positive-feedback compensation terms for disturbances rejection and gravity compensation. We developed an elbow flexion-extension experimental setup as a platform to validate the performance of the proposed controller to promote the desired high-level behavior. The controller was first characterized through experimental trials regarding joint transparency, torque, and impedance tracking accuracy. Then, to validate if the controller could effectively render different physical human-robot interaction according to the selected rehabilitation modalities, we conducted tests on 14 healthy volunteers and measured their muscular voluntary effort through surface electromyography (sEMG). The experiments consisted of one degree-of-freedom elbow flexion/extension movements, executed under six high-level modalities, characterized by different levels of (i) corrective assistance, (ii) weight counterbalance assistance, and (iii) resistance.ResultsThe unified controller demonstrated suitability to promote good transparency and render both compliant and stiff behavior at the joint. We demonstrated through electromyographic monitoring that a proper combination of stiffness, damping, and weight assistance could induce different user participation levels, render different physical human-robot interaction, and potentially promote different rehabilitation training modalities.ConclusionWe proved that the proposed control framework could render a wide variety of physical human-robot interaction, helping the user to accomplish the task while exploiting physiological muscular activation patterns. The reported results confirmed that the control scheme could induce different levels of the subject's participation, potentially applicable to the clinical practice to adapt the rehabilitation treatment to the subject's progress. Further investigation is needed to validate the presented approach to neurological patients.

A model formulation for the prediction of churning power loss in worm gear transmission

Churning power loss is a complex process that causes significant loss of energy under splash lubrication of gear units. A set of empirical equations are available that allows for precise churning power losses calculation for only the parallel axis gears. The main objective of this study is to formulate a new mathematical model for worm gear based on the experiment result. The mathematical model is formulated using the dimensional analysis method and has been experimentally validated over a wide range of speeds in terms of revolutions, types of lubricants, lubricant temperature, and immersion depths. The simple direct torque measurement method was used to measure the churning loss. The influence of inertia force, viscous force, and gravitational forces were also investigated therefore correlations with Froude and Reynolds numbers are presented. Hardened steel and bronze were used as a material combination of worm and worm gear, respectively. A new formula for worm gear under splash lubrication has been derived and validated by comparison with experimental evidence. A very little discrepancy was found between the experiment result and the mathematical equation.

SynRM Sensorless Torque Estimation Using High-Frequency Signal Injection

Precise output torque control is often required in applications using synchronous reluctance machines. Direct measurement of torque has drawbacks due to both cost and reliability issues. To overcome these limitations, the development of torque estimation methods has received significant research attention. Most of the exiting torque estimation methods require knowledge of machine parameters, suffering, therefore, from parameter sensitivity. Load and saturation are recognized as the primary source of parameter variation. This article proposes the use of a high-frequency signal injection for the online estimation of the machine parameters required for torque estimation. The improvement in the torque estimation will be especially relevant in deep-saturation regions. The method operates without interfering with the normal operation of the machine.

Permanent Magnet Synchronous Machine Torque Estimation Using Low Cost Hall-Effect Sensors

Torque measurement/estimation in permanent magnet synchronous machines (PMSMs) is required in a large variety of applications. Direct torque measurement by means of torque transducers is typically limited to laboratory applications due to cost, reliability, and room concerns. Alternatively, torque can be estimated. Torque estimation methods require accurate knowledge of machine parameters. Injection of a high frequency (HF) signal in the stator via inverter has been shown to be a viable option for online machine parameters identification in PMSMs. However, this introduces concerns on the performance of the machine due to the noise, vibration, and additional losses produced by the HF signal. This article proposes a torque estimation method for PMSMs using low cost Hall-effect sensors. The method is based on the dependency of the leakage flux complex vector due to interaction between permanent magnet flux and stator coil flux and does not interfere with the drive operation of the machine.

Comparative Investigation of Worm Positions for Worm Gear-box Performance under No-Load Condition

The Worm Gear drive is a gear arrangement where the worm shaft meshes with a worm wheel (gear). The worm shaft plays an important role in reduction ratio & efficiency. This worm shaft can be used at the top and the bottom in the gearbox. This technical research paper provides a comprehensive comparative evaluation of Input torque analysis & heating rate of lubricant inside the gearbox for two positions of the worm shaft in the worm gearbox under no-load condition. Worm shaft at the top and worm shaft at the bottom were assessed at variable speed (1000-1400 rpm), the different splashed volume of lubricant (1.5-2.7 liter), and variable temperature of lubricant (30-50 ºC). Input torque was measured with the help of a direct torque measurement technique. Similarly, the heating rate of the lubricant was also measured with a temperature sensor for both orientations of the worm shaft. Full factorial experiments were performed on a specially designed and fabricated worm gear test rig. The experiments showed that the input torque requirement for the worm at the bottom position is 20 -25% higher than the worm at the top position at an average speed. The heating rate remains almost the same for both orientations. This study aimed to find the suitable orientation of the worm shaft which reduces the power losses and increases efficiency.

Prediction equation of hip external rotators maximum torque in healthy adults and older adults using the measure of hip extensors maximum torque

BackgroundThe use of predictive equation of muscular torque can reduce physical effort and time spent during evaluation. ObjectivesTo establish, validate, and test the accuracy of a prediction equation to estimate the hip external rotators (HER) torque in adults and older adults by means of hip extensors (HEX) torque measurement. MethodsEighty-three healthy adults (development set) were assessed to test the association of HEX and HER torques and to establish the prediction equation. A separate 36 adults and 15 older adults (validation sets) were assessed to test the ability of the equation to estimate HER torque. Hip isometric strength was assessed by a handheld dynamometer. ResultsSimple linear regression analysis revealed that HEX torque was associated with HER torque (r=0.80; p<0.0001), resulting in the following prediction equation: HERtorque=−0.02+(0.58 * HEXtorque). Paired t-test revealed no difference between directly measured and predicted values of HER torque in adults (mean difference=0.02; 95% CI=−0.115, 0.072) and older adults (mean difference=0.05; 95% CI=−0.02, 0.12). ConclusionThe HEX and HER torques were strongly correlated. The prediction equation was valid, accurate, and can be used to estimate HER muscle strength in healthy adults and older adults, requiring only the direct measurement of HEX torque.

Synergistic Coordination of Chromatin Torsional Mechanics and Topoisomerase Activity

DNA replication in eukaryotes generates DNA supercoiling, which may intertwine (braid) daughter chromatin fibers to form precatenanes, posing topological challenges during chromosome segregation. The mechanisms that limit precatenane formation remain unclear. By making direct torque measurements, we demonstrate that the intrinsic mechanical properties of chromatin play a fundamental role in dictating precatenane formation and regulating chromatin topology. Whereas a single chromatin fiber is torsionally soft, a braided fiber is torsionally stiff, indicating that supercoiling on chromatin substrates is preferentially directed in front of the fork during replication. We further show that topoisomerase II relaxation displays a strong preference for a single chromatin fiber over a braided fiber. These results suggest a synergistic coordination-the mechanical properties of chromatin inherently suppress precatenane formation during replication elongation by driving DNA supercoiling ahead of the fork, where supercoiling is more efficiently removed by topoisomerase II. VIDEO ABSTRACT.

Experimental investigation of churning power loss of single start worm gear drive through optimization technique

Worm gears have very high total power losses due to high sliding motion and strong reduction ratio resulting in low efficiency. It is currently assumed that the total power loss (TPL) is caused by the load dependent losses; it is not caused by any non-load dependent losses. To verify this hypothesis, a specific gear test rig for worm gear pair was designed to measure the total power loss and churning power loss (CPL) simultaneously by using direct torque measurement technique. Many experiments were performed using different speed of worm gear, immersion depth of lubricant and temperature of lubricant inside the gear box. Taguchi L27 orthogonal array was used for designing the series of experiments. The empirical equation for churning power loss and total power loss with process parameters was modelled by using standard regression technique. The adequacy of the developed mathematical models was checked by Analysis of Variance (ANOVA). The problem was formulated as multi-objective optimization based on statistical analysis. It was found that the churning power loss (CPL), a kind of no-load dependent loss, has significant contribution in total power loss for splash lubrication. The immersion depth and temperature of lubricant are adequately influential parameters for churning power loss. The confirmation test result demonstrates that the optimization technique is one of the best available techniques to predict the optimal input variables for better output responses.

Contactless direct torque measurement system for a single cylinder engine transient test cell

This paper describes the design and implementation of a low cost, contacless, reliable and sensitive direct torque measurement system applied to small single cylinder engine transient test cell. The experimental set-up consists of a three-phase induction machine, used as a transient a.c. dynamometer, and non-regenerative frequency inverter connected to an internal combustion engine. Coupling the engine to the dynamometer is by a low stiffness PA-6 nylon shaft with magnetic pickups at its ends. The sensors phase are zero when torque in PA-6 nylon shaft is null, adjusted in static conditions and engine/dynamometer turned off. Contactless torque measurement occurs by magnetic pickup phase difference during PA-6 nylon shaft torsion promoted by engine in operation. Engine speed is measurement by frequency of magnetic pickup signal. PA-6 nylon shaft torsion promotes a misalignment between sensors phase, proportional to torque application in both direction.The electronic capture unit using pulse train rising edge detection measures this phase change (time shift) in pulses. An embedded microcontroller development kit acquires the time-shifted pulses. This board has circuits for A/D signal conditioning, pulse width modulate channels, and a specific circuit for magnetic pickups signals conditioning, which can measure less then 0.09 Nm resolution, taking 96 time-shifts values. The design and implementation of all embedded electronics and data acquisition system follows electromagnetic compatibility premises, which have resulted in an adequate signal-to-noise ratio so that common and differential mode noises have not edges with amplitude approximately equal to the output magnetic sensors signals. The maximum measurement uncertainty associated with the contacless direct torque measurement system were calculated at ±0.54% to 99% confidence interval.The performance is presented under different load conditions, defined by engine throttle position and the results are compared with the engine datasheet performance curves.

Synergistic Coordination of Chromatin Torsional Mechanics and Topoisomerase Activity

DNA replication in eukaryotes generates DNA supercoiling, which may intertwine (braid) daughter chromatin fibers to form precatenanes, posing topological challenges during chromosome segregation. The mechanisms that limit precatenane formation remain unclear. By making direct torque measurements, we demonstrate that the intrinsic mechanical properties of chromatin play a fundamental role in dictating precatenane formation and regulating chromatin topology. Whereas a single chromatin fiber is torsionally soft, a braided fiber is torsionally stiff, indicating that supercoiling on chromatin substrates is preferentially directed in front of the fork during replication. We further show that topoisomerase II relaxation displays a strong preference for a single chromatin fiber over a braided fiber. These results suggest a synergistic coordination-the mechanical properties of chromatin inherently suppress precatenane formation during replication elongation by driving DNA supercoiling ahead of the fork, where supercoiling is more efficiently removed by topoisomerase II. VIDEO ABSTRACT.

Determination of Optimum Working Parameters for Multiple Response Characteristics of Worm Gear Box

The reason for this task is to optimize the multiple response of single start worm gear using three working parameters to improve its performance. As the input torque and lubricant heating time are the most effective responses of worm gear box to reduce the no-load dependent losses, they are taken as the response parameters in this research. Taguchi Grey Relational Analysis (GRA) is the method used to determine the influence of type of lubricant, volume of lubricant and speed of worm gear on multiple responses (input torque &amp; lubricant heating time) of worm gear. The specific test rig is developed based on direct torque measurement technique to measure the input torque and lubricant heating time of worm gear box. Experimental results have shown that the input torque and lubricant heating time can be improved effectively through Taguchi-Grey Relational Analysis. The result is validated using the Confirmation Test. ANOVA determines the important of parameters. It has been found that the type of lubricant and speed of worm gear are influential parameters for worm gear performance. By selecting these parameters, efficiency of the worm gearbox can be increased.

Influences on torque measurement in nacelle test benches and their effect on the measurement uncertainty and consequences of a torque calibration

Torque measurement in the MN·m range is important in nacelle test benches, as it constitutes the primary value for the efficiency determination of wind turbine drive trains. However, no traceable measurement is possible above 1.1 MN·m. At the moment, alternatives to direct torque measurement in the MN·m range are, therefore, used. Several of these torque measurement methods are presented and discussed in this paper with respect to traceability and measurement uncertainty. It was found that these methods cannot fully substitute direct measurements. Therefore, detailed recommendations for a torque calibration procedure based on the specific conditions in nacelle test benches (such as rotation and additional mechanical loads) are given so as to enable the traceability of torque measurement using a torque transfer standard.