Moment Sensor Research Articles

Fault diagnosis and condition monitoring of wind turbines

SummaryThis paper describes a model‐free method for the fault diagnosis and condition monitoring of rotor systems in wind turbines. Both fault diagnosis and monitoring can be achieved without using a model for the wind turbine, applied controller, or wind profiles. The method is based on measurements from standard sensors on modern wind turbines, including moment sensors and rotor angle sensors. This approach will allow the method to be applied to existing wind turbines without any modifications.The method is based on the detection of asymmetries in the rotor system caused by changes or faults in the rotor system. A multiblade coordinate transformation is used directly on the measured flap‐wise and edge‐wise moments followed by signal modulation. Changes or faults in the rotor system will result in unique signatures in the set of modulation signals. These signatures are described through the amplitudes and phase information of the modulation signals. It is possible to detect and isolate which blade is faulty or has been changed based on these signatures. Furthermore, the faulty component can be isolated, ie, the actuator, sensor or blade, and the type of fault can be determined. The method can be used both on‐ and off‐line.

Measurement uncertainty evaluation of a hexapod-structured calibration device for multi-component force and moment sensors

As a reference measurement machine for multi-component force and moment sensors of up to six components, a hexapod-structured calibration device was developed at the Physikalisch-Technische Bundesanstalt in 2001. The machine can generate and measure forces of up to 10 kN and moments of up to 1 kN · m. In this paper, the measurement uncertainty budget of the machine is analyzed, beginning with an improved physical model and calculation of sensitivity coefficients using the implicit function theorem and the Monte Carlo method. The main influencing factors for the measurement uncertainty are discussed and suggestions for further reduction of the uncertainty are given.

Forces and moments applied during derotation of a maxillary central incisor with thinner aligners: An in-vitro study.

Recent studies have shown that therapeutic loads applied to individual teeth by aligners may substantially exceed recommended values. The primary purpose of this study was to quantify force and moment components during derotation of a maxillary central incisor when 0.3-mm-thick or 0.4-mm-thick polyethylene terephthalate glycol aligners were used instead of conventional polyethylene terephthalate glycol aligners with a minimum thickness of 0.5mm. The test setup consisted of an acrylic model of a maxilla with a separated right central incisor mounted on a 3-dimensional force and moment sensor. The force and moment components were recorded for aligners with thicknesses ranging from 0.3 to 0.75mm during ±10° rotation and derotation of the separated incisor. Moments exerted by the thinnest aligner currently available, 0.5mm, were 73.57 Nmm for the 10° mesiorotation. In comparison, the corresponding moments with the 0.4-mm and 0.3-mm aligners were 41.08 and 17.84 Nmm, respectively. Moment values for derotation of the maxillary right central incisor into neutral position showed nonlinear return curves indicating viscoelastic material behavior. A significant load reduction can be achieved with the new thinner aligners. Because of the form instability of the 0.3-mm aligner during handling, we suggest the novel sequence 0.4, 0.5, and 0.75mm for aligner systems based on sequentially increased material thickness. This sequence combines sufficiently low initial aligner stiffness and steady load increases in single setup steps. The viscoelastic behavior of polyethylene terephthalate glycol aligners observed during incisor derotation should lead to a reduction of the high initial load exerted directly after intraoral aligner insertion.

Should the Ipsilateral Hamstrings Be Used for Anterior Cruciate Ligament Reconstruction in the Case of Medial Collateral Ligament Insufficiency? Biomechanical Investigation Regarding Dynamic Stabilization of the Medial Compartment by the Hamstring Muscles

Background: Semitendinosus and gracilis muscles are frequently harvested for autologous tendon grafts for cruciate ligament reconstruction. This study investigated the joint-stabilizing effects of these hamstring muscles in cases of insufficiency of the medial collateral ligament (MCL). Hypotheses: First, both the semitendinosus and gracilis muscles can actively stabilize the joint against valgus moments in the MCL-deficient knee. Second, the stabilizing influence of these muscles decreases with an increasing knee flexion angle. Study Design: Controlled laboratory study. Methods: The kinematics was examined in 10 fresh-frozen human cadaveric knees using a robotic/universal force moment sensor system and an optical tracking system. The knee kinematics under 5- and 10-N·m valgus moments were determined in the different flexion angles of the (1) MCL-intact and (2) MCL-deficient knee using the following simulated muscle loads: (1) 0-N (idle) load, (2) 200-N semitendinosus (ST) load, and (3) 280-N (200/80-N) combined semitendinosus/gracilis (STGT) load. Results: Cutting the MCL increased the valgus angle under all tested conditions and angles compared with the MCL-intact knee by 4.3° to 8.1° for the 5-N·m valgus moment and 6.5° to 11.9° for the 10-N·m valgus moment (P < .01). The applied 200-N simulated ST load reduced the valgus angle significantly at 0°, 10°, 20°, and 30° of flexion under 5- and 10-N·m valgus moments (P < .05). At 0°, 10°, and 20° of flexion, these values were close to those for the MCL-intact joint under the respective moments (both P > .05). The combined 280-N simulated STGT load significantly reduced the valgus angle in 0°, 10°, and 20° of flexion under 5- and 10-N·m valgus moments (P < .05) to values near those for the intact joint (5 N·m: 0°, 10°; 10 N·m: 0°, 10°, 20°; P > .05). In 60° and 90° of flexion, ST and STGT loads did not decrease the resulting valgus angle of the MCL-deficient knee without hamstring loads (P > .05 vs deficient; P = .0001 vs intact). Conclusion: In this human cadaveric study, semitendinosus and gracilis muscles successfully stabilize valgus moments applied to the MCL-insufficient knee when the knee is near extension. Clinical Relevance: In the valgus-unstable knee, these data suggest that the hamstring muscles should be preserved in (multi-) ligament surgery when possible.

Development of a 6-DoF FBG force–moment sensor for a haptic interface with minimally invasive robotic surgery

A new and precise 6-Degree-of-freedom (DoF) Fiber Bragg grating (FBG) force–moment sensor integrated with a platform frame was proposed for the haptic feedback of loadings at the tip cutting tools of end-effectors of a minimally invasive surgical robot. As the platform deformed during surgery, the attached FBG pretensioned with 2000 μm strain. Strains were calculated by Finite element analyses (FEAs) and related to optical wavelength equations. Experiments integrated with sagacious ways of how to apply forces and moments for the sensor fabricated were conducted to measure the strains and wavelength changes caused in FBGs. Experimental wavelength changes correlated well in 3% to 4% error with the FEA results for all cases. A realistic design of a small 6-DoF FBG force–moment sensor was proposed using the analytic method. Wavelength changes slightly increased as temperature increased in the study of thermal compensation.

Analysis of two modeling approaches for fatigue estimation and remaining useful life predictions of wind turbine blades

Wind turbines components are subject to considerable stresses and fatigue due to extreme environmental conditions to which they are exposed, especially those located offshore. With thisaim, the present work explores two different approaches on fatigue damage estimation and remaining useful life predictions of wind turbine blades. The first approach uses the rainflow counting algorithm. The second approach comes from a fatigue damage model that describes the propagation of damage at a microscopic scale due to matrix cracks which manifests in a macroscopic scale as stiffness loss. Both techniques have been tested using the information provided by the blade root moment sensor signal obtained from the well known wind turbine simulator FAST (Fatigue, Aerodynamics, Structures and Turbulence).

An experimental investigation on the characteristics of fluid–structure interactions of a wind turbine model sited in microburst-like winds

An experimental investigation is performed to assess the characteristics of the fluid–structure interactions and microburst-induced wind loads acting on a wind turbine model sited in microburst-liked winds. The experiment study was conducted with a scaled wind turbine model placed in microburst-like winds generated by using an impinging-jet-typed microburst simulator. In addition to quantifying complex flow features of microburst-like winds, the resultant wind loads acting on the turbine model were measured by using a high-sensitive force–moment sensor as the turbine model was mounted at different radial locations and with different orientation angles with respect to the oncoming microburst-like winds. The measurement results reveal clearly that, the microburst-induced wind loads acting on the turbine model were distinctly different from those in a conventional atmospheric boundary layer (ABL) wind. With the scales of the wind turbine model and the microburst-like wind used in the present study, the dynamic wind loadings acting on the turbine model were found to be significantly higher (i.e., up to 4 times higher for the mean loads, and up to 10 times higher for the fluctuation amplitudes) than those with the same turbine model sited in ABL winds. Both the mean values and fluctuation amplitudes of the microburst-induced wind loads were found to vary significantly with the changes of the mounted site of the turbine model, the operating status (i.e., with the turbine blades stationary or freely rotating), and the orientation angle of the turbine model with respect to the oncoming microburst-like wind. The dynamic wind load measurements were correlated to the flow characteristics of the microburst-like winds to elucidate underlying physics. The findings of the present study are helpful to gain further insight into the potential damage caused by the violent microbursts to wind turbines to ensure safer and more efficient operation of the wind turbines in thunderstorm-prone areas.

Forces and Moments on Flat Plates of Small Aspect Ratio with Application to PV Wind Loads and Small Wind Turbine Blades

To improve knowledge of the wind loads on photovoltaic structures mounted on flat roofs at the high angles required in high latitudes, and to study starting flow on low aspect ratio wind turbine blades, a series of wind tunnel tests were undertaken. Thin flat plates of aspect ratios between 0.4 and 9.0 were mounted on a sensitive three-component instantaneous force and moment sensor. The Reynolds numbers varied from 6 × 104 to 2 × 105. Measurements were made for angles of attack between 0° and 90° both in the free stream and in wall proximity with increased turbulence and mean shear. The ratio of drag to lift closely follows the inverse tangent of the angle of incidence for virtually all measurements. This implies that the forces of interest are due largely to the instantaneous pressure distribution around the plate and are not significantly influenced by shear stresses. The instantaneous forces appear most complex for the smaller aspect ratios but the intensity of the normal force fluctuations is between 10% and 20% in the free-steam but can exceed 30% near the wall. As the wind tunnel floor is approached, the lift and drag reduce with increasing aspect ratio, and there is a reduction in the high frequency components of the forces. It is shown that the centre of pressure is closer to the centre of the plates than the quarter-chord position for nearly all cases.

Effects of bubbly flow on bending moment acting on the shaft of a gas sparged vessel stirred by a Rushton turbine

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Rushton turbine, as one of the results of fluid and structure interactions in stirred vessels, was measured using a moment sensor equipped with digital telemetry. An analysis of the shaft bending moment amplitude shows that the amplitude distribution of the bending moment, which indicates the elasticity nature of shaft material against bending deformation, follows the Weibull distribution. The trends of amplitude mean, standard deviation and peak deviation characteristics manifest an “S” shape versus gas flow. The “S” trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas–liquid stirred vessels, resulted from the competition among the nonuniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades, and the gas direct impact on the impeller when gas is introduced. A further analysis of the bending moment power spectral density shows that the rather low frequency and speed frequency are evident. The low-frequency contribution to bending moment fluctuation peaks in the complete dispersion regime.

The influence of the medial meniscus in different conditions on anterior tibial translation in the anterior cruciate deficient knee.

The purpose of this study was the evaluation of knee laxity in the ACL-deficient knee with combined meniscal tear, meniscal suture and partial medial meniscectomy. Kinematics of the intact knee were determined in 18 human cadaver specimens in response to a 134-N anterior tibial load (aTT) as well as a combined rotatory load of 10 Nm valgus and 4 Nm internal tibial rotation using a robotic/universal force moment sensor testing system. The anterior cruciate ligament was resected. Subsequently, a vertical bucket-handle medial meniscal tear was created followed by a standard meniscus repair using horizontal inside-out stitches or a partial medial meniscectomy. Knee kinematics were calculated following every sub-step. A significant increase of anterior tibial translation was found in the ACL-deficient knee compared to the intact knee at 30° and 90° of flexion (p = 0.001; p ≤ 0.001). Additional tear of the medial meniscus significantly increased anterior tibial translation (p = 0.01). In response to a simulated pivot shift, anterior tibial translation of the intact knee did not increase significantly after ACL resection (p = 0.067). However, ACL deficiency with an additional medial meniscus tear led to a significant increase compared to the intact knee at 0° of flexion (p = 0.009). Additional injury of the medial meniscus increased aTT as well as aTT under a combined rotatory load in the ACL-deficient knee whereas repair of the meniscus significantly decreased aTT. Therefore, the meniscus status does have a significant impact on knee kinematics in the ACL-deficient knee. The present biomechanical study further highlights the importance of preserving the meniscus especially in patients with additional ACL injuries.

Blade root moment sensor failure detection based on multibeam LIDAR for fault‐tolerant individual pitch control of wind turbines

AbstractDetection of blade root moment sensor failures is an important problem for fault‐tolerant individual pitch control, which plays a key role in reduction of uneven blade loads of large wind turbines. A new method for detection of blade root moment sensor failures which is based on variations induced by a vertical wind shear is described in this paper. The detection is associated with monitoring of statistical properties of the difference between amplitudes of the first harmonic of the blade load, which is calculated in two different ways. The first method is based on processing of the load sensor signal, which contains a number of harmonics. The first harmonic is recovered via least squares estimation of the blade load signal with harmonic regressor and strictly diagonally dominant (SDD) information matrix. The second method is a model‐based method of estimation of the first harmonic, which relies on the blade load model and upwind speed measurements provided by multibeam Light Detection and Ranging (LIDAR). This is a new application for future LIDAR‐enabled wind turbine technologies. Moreover, adaptation of the load model in a uniform wind field is proposed. This adaptation improves accuracy of the load estimation and hence the performance of the blade load sensor failure detection method.

Biomechanical evaluation of knee kinematics after anatomic single- and anatomic double-bundle ACL reconstructions with medial meniscal repair.

To evaluate knee laxity after anatomic ACL reconstruction with additional suture repair of a medial meniscus tear. Kinematics of the intact knee were determined in 12 human cadaver specimens in response to a 134-N anterior tibial load (aTT) and a combined rotatory load of 10 Nm valgus and 4 Nm internal tibial rotation (aTTPS) using a robotic/universal force moment sensor testing system. Subsequently, the ACL was resected following the creation of a standardized tear of the medial meniscus, a standard meniscus repair and an ACL reconstruction using an anatomic single-bundle (6) or an anatomic double-bundle technique (6). Knee kinematics were determined following every sub-step. Significant increase of aTT in the ACL-deficient knee was found (p ≤ 0.001) with a further increase in the ACL-deficient knee with additional medial meniscal rupture (p ≤ 0.001). ACL reconstructions significantly decreased aTT compared with the ACL and meniscus-ruptured knee. No significant differences were seen between the intact knee and the ACL-reconstructed knee with additional meniscal repair (p < 0.05). In response to a simulated pivot shift, aTTPS in the intact knee significantly increased in the ACL-deficient knee and meniscus-ruptured knee (p = 0.005). No significant differences in knee kinematics were found between SB as well as DB ACL reconstruction with additional medial meniscal repair compared with the intact knee. Comparison of SB versus DB ACL reconstruction did not reveal any significant differences in a simulated Lachman test or simulated pivot shift test (n.s.). aTT as well as aTTPS significantly increased with ACL deficiency compared with the intact knee; additional medial meniscal rupture further increased aTT. Anatomic ACL reconstruction with medial meniscal repair did not reveal significant differences in knee kinematics compared with the intact knee. Comparison of anatomic SB versus DB ACL reconstruction with additional repair of the medial meniscus did not show significant differences neither in a simulated Lachman nor in a simulated pivot shift test.

Effect of gas flow on the bending moment acting on a shaft in a sparged vessel stirred by a Pitched Blade Turbine

The bending moment acting on the overhung shaft of a gas-sparged vessel stirred by a Pitched Blade Turbine, as one of the results of Fluid–Structure Interactions (FSI) in stirred vessels, was measured using a moment sensor equipped with digital telemetry. The amplitude and Power Spectral Density of the shaft bending moment were analyzed. It shows that the gas flow has a considerable influence on the characteristics of the bending moment, such as the amplitude mean, distribution, Standard Deviation and peak, and the low-frequency and speed frequency contributions to the fluctuation. The relative mean bending moment initially increases with gas rate till the transition from complete dispersion to loading regimes, approaching a peak, then decreases to a valley and again rises gradually, going through the transition from loading to flooding regimes. The “S” trend of the relative mean bending moment over gas flow rate, depending on the flow regime in gas–liquid stirred vessels, results from the competition among the nonuniformity of bubbly flow around the impeller, the formation of gas cavities behind the blades and the gas direct impact on the impeller as gas is introduced.

Characteristics of the Bending Moment Acting on an Overhung Shaft in a Stirred Vessel

Abstract The bending moment acting on an overhung shaft in an impeller stirred vessel was measured using a moment sensor equipped with digital telemetry. The results show that the characteristics of bending moment, such as the mean amplitudes, the amplitude and frequency distributions and the intensity of the amplitude fluctuations are influenced by both the ratio of operational speed to resonant speed (n/nr) and the impeller type. Analysis of the bending moment amplitude shows that the dimensionless shaft bending moment decreases for low values of n/nr and increases with increasing n/nr for higher values of n/nr. The value of the n/nr transition point depends on the type of impeller used in the experiments. Analysis of the power spectral density of bending moment fluctuation shows that the main contributions to the bending moment for low impeller speeds (i.e. well below the first resonant frequency) come from factors related to the fluid flow while the impeller imbalance becomes steadily more dominant as the speed increases.

Effect of the impeller imbalance on the bending moment acting on a shaft in a stirred vessel

The bending moment acting on an overhung shaft equipped with an unbalanced impeller, as one of the results of the lateral Fluid-Structure Interactions (FSI) in stirred vessels, was measured using a moment sensor, equipped with digital telemetry. The results show that the imbalance of impeller has a considerable influence on the characteristics of bending moment, such as the mean amplitude and the intensity of amplitude fluctuation. Analysis of the amplitude distribution shows that the distribution is well fitted by a Weibull distribution, which tends to flatten and become more symmetrical about the mean as the imbalance increases. Further analysis of the bending moment power spectral density shows that the speed frequency of the bending moment, whose contribution to the bending moment fluctuation increases with the increasing imbalance, is caused by the imbalance of the stirring structure. These results can be applied to the mechanical design process for the shaft and the stirred vessel supporting it, and the manufacturing control of impeller balance quality.

Industrial valves with electric actuators: Technical diagnostics by a moment sensor within smart actuator worm-and-wheel gearbox

This paper considers the technical diagnostics problem for industrial valves with electric actuators. We provide a mathematical description for dynamic processes running in electric actuators of industrial valves with a moment measurement mechanism whose sensing element represents a spring-loaded worm of an electric actuator worm-and-wheel gearbox.

Biomechanical Evaluation Of Knee Kinematics After ACL Reconstruction In Anatomic SB- And DB – Technique With Additional Medial Meniscus Suture

Biomechanical Evaluation Of Knee Kinematics After ACL Reconstruction In Anatomic SB- And DB – Technique With Additional Medial Meniscus Suture

Influence of the Meniscus Status on Knee Kinematics in the ACL-Deficient Knee (SS-64)

Evaluation of knee laxity in the ACL-deficient knee with combined meniscal tear, meniscal suture and partial medial meniscectomy. Kinematics of the intact knee were determined in 20 human cadaver specimens in response to a 134-N anterior tibial load (aTT) as well as a combined rotatory load of 10 Nm valgus and 4 Nm internal tibial rotation using a robotic/universal force moment sensor testing system. The anterior cruciate ligament was resected. Subsequently, a medial meniscus tear was created following a standard meniscus repair using horizontal inside-out stitches or a partial medial meniscectomy. Knee kinematics were calculated following every sub-step. Significant increase of anterior tibial translation was found in the ACL-deficient knee compared to the intact knee at 30° and 90° of flexion (p=.003;p=.009). Additional rupture of the medial meniscus significantly increased anterior tibial translation (p=.0001). In response to a simulated pivot shift, anterior tibial translation of the intact knee did not increase significantly after ACL resection. However, ACL deficiency with an additional medial meniscus tear led to a significant increase compared to the intact knee at 30° of flexion (p=.05). The meniscus status does have a significant impact on knee kinematics in the ACL-deficient knee. Additional injury of the medial meniscus increased aTT as well as aTT under a combined rotatory load.

Apparatus for measurement of pitch and yaw damping derivatives in high Reynolds number blowdown wind tunnel

The pitch/yaw apparatus designed for the measurement of the moment derivative due to an aircraft or missile model angular oscillatory motion in a wind tunnel test section is presented. A model is forced to oscillate with the primary angular oscillation around its transversal axis (pitch or yaw). Damping derivatives are obtained as a difference between total damping measured in the presence of aerodynamic load and mechanical damping measured in the absence of aerodynamic load. The main requirements for a new apparatus were: high load capacity, high structural rigidity, high range of the experimental frequencies and high sensors sensitivity. The choice of the hydraulic drive is made considering these requirements. Amplitude of the excitation moment is measured either by internal wind tunnel balance or by a specially designed excitation moment sensor. The T-38 wind tunnel data for the Modified Basic Finner Model and Basic Finner Model obtained using the pitch/yaw apparatus are shown.

Experimental Investigation on Adaptive Robust Controller Designs Applied to Constrained Manipulators

In this paper, two interlaced studies are presented. The first is directed to the design and construction of a dynamic 3D force/moment sensor. The device is applied to provide a feedback signal of forces and moments exerted by the robotic end-effector. This development has become an alternative solution to the existing multi-axis load cell based on static force and moment sensors. The second one shows an experimental investigation on the performance of four different adaptive nonlinear ℋ∞ control methods applied to a constrained manipulator subject to uncertainties in the model and external disturbances. Coordinated position and force control is evaluated. Adaptive procedures are based on neural networks and fuzzy systems applied in two different modeling strategies. The first modeling strategy requires a well-known nominal model for the robot, so that the intelligent systems are applied only to estimate the effects of uncertainties, unmodeled dynamics and external disturbances. The second strategy considers that the robot model is completely unknown and, therefore, intelligent systems are used to estimate these dynamics. A comparative study is conducted based on experimental implementations performed with an actual planar manipulator and with the dynamic force sensor developed for this purpose.