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Owusu-Ansah, Prince, Yefa Hu et Rhoda Afriyie Mensah. « Active Magnetic Bearing as a Force Measurement System ». International Journal of Materials, Mechanics and Manufacturing 5, no 3 (août 2017) : 209–12. http://dx.doi.org/10.18178/ijmmm.2017.5.3.320.
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Marshall, J. T., M. E. F. Kasarda et J. Imlach. « A Multipoint Measurement Technique for the Enhancement of Force Measurement With Active Magnetic Bearings ». Journal of Engineering for Gas Turbines and Power 125, no 1 (27 décembre 2002) : 90–94. http://dx.doi.org/10.1115/1.1519268.
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Active magnetic bearings (AMBs) have the unique capability to act concurrently as support bearings and load cells for measuring shaft forces. Current state-of-the-art methods for force measurement rely on models with limited accuracy due to effects which are difficult to characterize such as fringing, leakage, and variations in material properties. In addition, these effects may be a function of actual air gaps which are difficult to determine in a dynamic operating environment. This paper discusses a new force measurement methodology that inherently accounts for these types of effects and other system uncertainties by utilizing multiple sets of current pairs in opposing actuators, in conjunction with a calculation algorithm, to accurately determine the force applied by the AMB. This new multipoint methodology allows for the determination of bearing forces from information on basic actuator geometry and control currents only, with no knowledge of actual operating air gaps required. The inherent nature of the methodology accounts for model uncertainties such as fringing, leakage, and other system unknowns. Initial static experimental test results are presented demonstrating 3% error in measuring the nominal determined bearing load, and a variation in calculated forces of less than 5% in most cases (8% in one case) when the location of the rotor within the bearing stator is modified. For the analogous conventional single-point measurements, the results show 15% error and 23% variation.
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Baun, D. O., et R. D. Flack. « A Plexiglas Research Pump With Calibrated Magnetic Bearings/Load Cells for Radial and Axial Hydraulic Force Measurement ». Journal of Fluids Engineering 121, no 1 (1 mars 1999) : 126–32. http://dx.doi.org/10.1115/1.2821992.
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A research pump intended for both flow visualization studies and direct measurement of hydrodynamic radial and axial forces has been developed. The impeller and the volute casing are constructed from Plexiglas which facilitates optical access for laser velocimetry measurements of the flow field both inside the impeller and in the volute casing. The pump housing is designed for flexibility allowing for each interchange of impellers and volute configurations. The pump rotor is supported by three radial magnetic bearings and one double acting magnetic thrust bearing. The magnetic bearings have been calibrated to characterize the force versus coil current and air gap relationship for each bearing type. Linear calibration functions valid for rotor eccentricities of up to 2/3 of the nominal bearing clearances and force level of ±58 N (13 lbf) and ±267 N (60 lbf) for the radial and axial bearings, respectively, were found. A detailed uncertainty analysis of the force calibration functions was conducted such that meaningful uncertainty bounds can be applied to in situ force measurements. Hysteresis and eddy current effects were quantified for each bearing such that their effect on the in situ force measurements could be assessed. By directly measuring the bearing reaction forces it is possible to determine the radial and axial hydraulic loads acting on the pump impeller. To demonstrate the capability of the magnetic bearings as active load cells representative hydraulic force measurements for a centered 4 vane 16 degree log spiral radial flow impeller operating in a single tongue spiral volute casing were made. At shut-off a nondimensional radial thrust of 0.084 was measured. A minimum nondimensional radial thrust of about 0.007 was observed at the nominal design flow. The nondimensional radial thrust increased to about 0.019 at 120 percent of design flow. The nondimensional axial thrust had a maximum at shut-off of 0.265 and decreased steadily to approximately 0.185 at 120 percent of design flow. Two regions of increasing axial thrust, in the flow range 75 to 100 percent of design flow, were observed. The measurements are compared to radial and axial force predictions using classical force models. The direct radial force measurements are compared to a representative set of radial force measurements from the literature. In addition, the directly measured radial force at design flow is compared to a single representative radial force measurement (obtained from the literature) calculated from the combination of static pressure and net momentum flux distribution at the impeller exit.
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Di Terlizzi, I., M. Gironella, D. Herraez-Aguilar, T. Betz, F. Monroy, M. Baiesi et F. Ritort. « Variance sum rule for entropy production ». Science 383, no 6686 (mars 2024) : 971–76. http://dx.doi.org/10.1126/science.adh1823.
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Entropy production is the hallmark of nonequilibrium physics, quantifying irreversibility, dissipation, and the efficiency of energy transduction processes. Despite many efforts, its measurement at the nanoscale remains challenging. We introduce a variance sum rule (VSR) for displacement and force variances that permits us to measure the entropy production rate σ in nonequilibrium steady states. We first illustrate it for directly measurable forces, such as an active Brownian particle in an optical trap. We then apply the VSR to flickering experiments in human red blood cells. We find that σ is spatially heterogeneous with a finite correlation length, and its average value agrees with calorimetry measurements. The VSR paves the way to derive σ using force spectroscopy and time-resolved imaging in living and active matter.
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Kurihara, Kazue. « Surface forces measurement for materials science ». Pure and Applied Chemistry 91, no 4 (24 avril 2019) : 707–16. http://dx.doi.org/10.1515/pac-2019-0101.
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Abstract This article reviews the surface forces measurement as a novel tool for materials science. The history of the measurement is briefly described in the Introduction. The general overview covers specific features of the surface forces measurement as a tool for studying the solid-liquid interface, confined liquids and soft matter. This measurement is a powerful way for understanding interaction forces, and for characterizing (sometime unknown) phenomena at solid-liquid interfaces and soft complex matters. The surface force apparatus (SFA) we developed for opaque samples can study not only opaque samples in various media, but also electrochemical processes under various electrochemical conditions. Electrochemical SFA enables us to determine the distribution of counterions between strongly bound ones in the Stern layer and those diffused in the Gouy-Chapman layer. The shear measurement is another active area of the SFA research. We introduced a resonance method, i.e. the resonance shear measurement (RSM), that is used to study the effective viscosity and lubricity of confined liquids in their thickness from μm to contact. Advantages of these measurements are discussed by describing examples of each measurement. These studies demonstrate how the forces measurement is used for characterizing solid-liquid interfaces, confined liquids and reveal unknown phenomena. The readers will be introduced to the broad applications of the forces measurement in the materials science field.
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Hoh, N. J., et R. N. Zia. « Hydrodynamic diffusion in active microrheology of non-colloidal suspensions : the role of interparticle forces ». Journal of Fluid Mechanics 785 (16 novembre 2015) : 189–218. http://dx.doi.org/10.1017/jfm.2015.602.
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Hydrodynamic diffusion in the absence of Brownian motion is studied via active microrheology in the ‘pure-hydrodynamic’ limit, with a view towards elucidating the transition from colloidal microrheology to the non-colloidal limit, falling-ball rheometry. The phenomenon of non-Brownian force-induced diffusion in falling-ball rheometry is strictly hydrodynamic in nature; in contrast, analogous force-induced diffusion in colloids is deeply connected to the presence of a diffusive boundary layer even when Brownian motion is very weak compared with the external force driving the ‘probe’ particle. To connect these two limits, we derive an expression for the force-induced diffusion in active microrheology of hydrodynamically interacting particles via the Smoluchowski equation, where thermal fluctuations play no role. While it is well known that the microstructure is spherically symmetric about the probe in this limit, fluctuations in the microstructure need not be – and indeed lead to a diffusive spread of the probe trajectory. The force-induced diffusion is anisotropic, with components along and transverse to the line of external force. The latter is identically zero owing to the fore–aft symmetry of pair trajectories in Stokes flow. In a naïve first approach, the vanishing relative hydrodynamic mobility at contact between the probe and an interacting bath particle was assumed to eliminate all physical contribution from interparticle forces, whereby advection alone drove structural evolution in pair density and microstructural fluctuations. With such an approach, longitudinal force-induced diffusion vanishes in the absence of Brownian motion, a result that contradicts well-known experimental measurements of such diffusion in falling-ball rheometry. To resolve this contradiction, the probe–bath-particle interaction at contact was carefully modelled via an excluded annulus. We find that interparticle forces play a crucial role in encounters between particles in the hydrodynamic limit – as they must, to balance the advective flux. Accounting for this force results in a longitudinal force-induced diffusion $D_{\Vert }=1.26aU_{S}{\it\phi}$, where $a$ is the probe size, $U_{S}$ is the Stokes velocity and ${\it\phi}$ is the volume fraction of bath particles, in excellent qualitative and quantitative agreement with experimental measurements in, and theoretical predictions for, macroscopic falling-ball rheometry. This new model thus provides a continuous connection between micro- and macroscale rheology, as well as providing important insight into the role of interparticle forces for diffusion and rheology even in the limit of pure hydrodynamics: interparticle forces give rise to non-Newtonian rheology in strongly forced suspensions. A connection is made between the flow-induced diffusivity and the intrinsic hydrodynamic microviscosity which recovers a precise balance between fluctuation and dissipation in far from equilibrium suspensions; that is, diffusion and drag arise from a common microstructural origin even far from equilibrium.
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Nudehi, Shahin, Ranjan Mukherjee et Steven W. Shaw. « Active Vibration Control of a Flexible Beam Using a Buckling-Type End Force ». Journal of Dynamic Systems, Measurement, and Control 128, no 2 (25 mars 2005) : 278–86. http://dx.doi.org/10.1115/1.2192836.
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In this paper, we explore the use of end forces for vibration control in structural elements. The process involves vibration measurement and observer-based estimation of modal amplitudes, which are used to determine when to apply an end load such that it will remove vibration energy from the structure. For this study, we consider transverse vibration of a cantilever beam with a buckling-type end load that can be switched between two values, both of which are below the buckling load. The stability of the control system is proven using Lyapunov stability theory and its effectiveness is demonstrated using simulations and physical experiments. It is shown that the effectiveness of the approach is affected by the bandwidth of the actuator and the attendant characteristics of the filter, the level of the control force, and the level of bias in the end force. The experiments employ a beam fitted with a cable mechanism and motor for applying the end force, and a piezoelectric patch for taking vibration measurements. It is shown that the first two modes of the beam, whose natural frequencies are less than the bandwidth of the motor, are very effectively controlled by the proposed scheme.
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Wada, Nobutaka, Akihiro Takahashi, Masami Saeki et Masaharu Nishimura. « Vehicle Yaw Control Using an Active Front Steering System with Measurements of Lateral Tire Forces ». Abstracts of the international conference on advanced mechatronics : toward evolutionary fusion of IT and mechatronics : ICAM 2010.5 (2010) : 319–24. http://dx.doi.org/10.1299/jsmeicam.2010.5.319.
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Sharp, Andrew A., Blake W. Cain, Joanna Pakiraih et James L. Williams. « A system for the determination of planar force vectors from spontaneously active chicken embryos ». Journal of Neurophysiology 112, no 9 (1 novembre 2014) : 2349–56. http://dx.doi.org/10.1152/jn.00423.2014.
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Generally, a combination of kinematic, electromyographic (EMG), and force measurements are used to understand how an organism generates and controls movement. The chicken embryo has been a very useful model system for understanding the early stages of embryonic motility in vertebrates. Unfortunately, the size and delicate nature of embryos makes studies of motility during embryogenesis very challenging. Both kinematic and EMG recordings have been achieved in embryonic chickens, but two-dimensional force vector recordings have not. Here, we describe a dual-axis system for measuring force generated by the leg of embryonic chickens. The system employs two strain gauges to measure planar forces oriented with the plane of motion of the leg. This system responds to forces according to the principles of Pythagorean geometry, which allows a simple computational program to determine the force vector (magnitude and direction) generated during spontaneous motor activity. The system is able to determine force vectors for forces >0.5 mN accurately and allows for simultaneous kinematic and EMG recordings. This sensitivity is sufficient for force vector measurements encompassing most embryonic leg movements in midstage chicken embryos allowing for a more complete understanding of embryonic motility. Variations on this system are discussed to enable nonideal or alternative sensor arrangements and to allow for translation of this approach to other delicate model systems.
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Yang, Yuan Yuan, Lei Wang, Jiu Bin Tan, Xiao Yu Zhu, Bo Zhao, Guo Liang Jin, Xi Ping Zhao et Yong Meng Liu. « Self-Sensing Giant Magnetostrictive Actuator for Active Vibration Isolation ». Applied Mechanics and Materials 870 (septembre 2017) : 67–72. http://dx.doi.org/10.4028/www.scientific.net/amm.870.67.
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Giant magnetostrictive actuator (GMA) are commonly used in active vibration isolation domain for hight frequency response and large output force. GMA has a nonlinear displacement output when disturbed by vibrations. In order to compensate for the nonlinearity and improve the precision of the system, the critical process is the measurement of external disturbances which can be realized with a bridge circuit based on a traditional equivalent circuit model. However, the sensitivity is restricted because of the integral relationship between the force and the open circuit voltage. In this paper, the conception of the dynamic inductance is proposed to optimize the equivalent circuit model that is based on coupled linear magneto-mechanical constitutive equations. Then the measurement for external forces becomes effective with the improvement in the sensitivity through measuring the dynamic inductance. A dynamic simulation is carried out to test the performance of GMA based on the equivalent circuit model. The external dynamic forces can be accurately detected by calculating the impedances in the self-sensing effect of the Terfenol-D.
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Jobse, Hans, Ruud Schuurhof, Ferenc Cserep, A. Wim Schreurs et Jos J. de Koning. « Measurement of Push-Off Force and Ice Friction during Speed Skating ». International Journal of Sport Biomechanics 6, no 1 (février 1990) : 92–100. http://dx.doi.org/10.1123/ijsb.6.1.92.
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Portable equipment for active measurements of push-off force and ice friction was developed. The equipment consists of a pair of skates with three measuring elements between the shoe and the skate blade to register force in both fore/aft and normal direction. A portable computer samples the friction force and normal force signals during one or more strokes, calculates the mean coefficient of ice friction, and stores the sampled data in memory. The push-off force and ice friction force were measured. The peak push-off forces reach values of up to 140% of body weight. The magnitude of the coefficient of ice friction varies, depending on the weather conditions and preparatory method, generally between 0.003 and 0.007 when skating the straightaway. During the skating of the curves the coefficient of ice friction is 35% higher, most likely due to the different skating technique in the curves.
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Stojanović, Goran, Milan Radovanović, Dragana Vasiljević, Tijana Kojić, Bojana Pivaš, Tatjana Puškar, Sunil Kapadia et Reinhard Baumann. « Comparison of Performances of Flexible Tailor-Made Force Sensing Resistors Fabricated Using Inkjet and Xurographic Techniques ». Journal of Sensors 2019 (7 juillet 2019) : 1–8. http://dx.doi.org/10.1155/2019/9181492.
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The force is one of the parameters very often measured in our life. Force sensing resistors (FSRs) can be successfully used for measuring force, especially that they can be applied in dentistry for measuring bite forces. However, it is very difficult to apply commercial FSRs for accurate measurement of bite forces and to ensure personalized approach to each patient. Because of that, design, fabrication, and characterization of tailor-made force sensing resistors intended for application in dental medicine are presented in this paper. We designed two FSRs, one with two active areas and one with four active areas (for teeth of higher volume–molars). Two different fabrication processes were applied: first additive, using inkjet printer and silver as material for conductive segments, and second subtractive, using cutter, and gold as a material for manufacturing of interdigitated structure of FSR. Performances of these FSRs have been compared, measuring resistance as a function of applied force, using in-house developed experimental set-up with an articulator.
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Carabello, Alina, Rick Henkner et Welf-Guntram Drossel. « Novel Procedure for Determining the Finger Force in Flexion Depending on the Finger Position ». Current Directions in Biomedical Engineering 8, no 2 (1 août 2022) : 384–87. http://dx.doi.org/10.1515/cdbme-2022-1098.
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Abstract Introduction: The design and development of a novel dynamic hand orthosis that allows individual and progressive adaptation to the patient’s condition require knowledge about the maximum voluntary contraction forces of the fingers. The following work presents a test setup and procedure for determination of isometric finger contraction forces during flexion depending on various finger positions and finger tasks. Methods: The test setup places hand and fingers in certain positions (position 0: grasping of a plate; position 1-3: circular grasping of cylinders of three different diameters). The force measurement is carried out using pressure sensing: A capacitive force sensor is placed on each fingertip. To perform various finger tasks, the subjects are asked for isometric contraction of defined finger groups and single fingers against the boundary system. For proof of the concept, measurements are performed with six subjects and compared with reference values from the literature. Results: The separated finger force of each finger can be captured during the finger tasks in varying positions. Furthermore, the total finger force of all active fingers can be determined. It is shown that the total finger force during contraction of all fingers (IMRLtask; 78.4N ± 25.8N, d2) is higher than during contraction of the index finger (25.8N ± 3.4N, d2). Furthermore, the single finger force of the index finger is higher than the index finger activity in IMRL-task. The results also show a tendency for the finger contraction force to increase with increasing flexion. Further investigations may require improvements to the method. In this proof of concept, this potential is revealed and discussed. However, the functionality of the test setup and procedure can be demonstrated.
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McIntyre, J., E. V. Gurfinkel, M. I. Lipshits, J. Droulez et V. S. Gurfinkel. « Measurements of human force control during a constrained arm motion using a force-actuated joystick ». Journal of Neurophysiology 73, no 3 (1 mars 1995) : 1201–22. http://dx.doi.org/10.1152/jn.1995.73.3.1201.
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1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures many more of the salient features observed in the measured human data. 6. We conclude that human subjects execute surface-following motions in a largely feedforward manner, using an a priori model of the surface geometry. The evidence does not suggest that active, real time use of force feedback is used to guide the movement or to control limb impedance. We do not exclude, however, the possibility that the internal model of the constraint is updated at somewhat longer latencies on the basis of proprioceptive information.
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Werner, Lennart, Michael Strohmeier, Julian Rothe et Sergio Montenegro. « Thrust Vector Observation for Force Feedback-Controlled UAVs ». Drones 6, no 2 (17 février 2022) : 49. http://dx.doi.org/10.3390/drones6020049.
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This paper presents a novel approach to Thrust Vector Control (TVC) for small Unmanned Aerial Vehicles (UAVs). The difficulties associated with conventional feed-forward TVC are outlined, and a practical solution to conquer these challenges is derived. The solution relies on observing boom deformations that are created by different thrust vector directions and high-velocity air inflow. The paper describes the required measurement electronics as well as the implementation of a dedicated testbed that allows the evaluation of mid-flight force measurements. Wind-tunnel tests show that the presented method for active thrust vector determination is able to quantify the disturbances due to the incoming air flow.
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Haeger, Ricarda, Felipe de Souza Leite et Dilson E. Rassier. « Sarcomere length non-uniformities dictate force production along the descending limb of the force–length relation ». Proceedings of the Royal Society B : Biological Sciences 287, no 1937 (28 octobre 2020) : 20202133. http://dx.doi.org/10.1098/rspb.2020.2133.
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The force–length relation is one of the most defining features of muscle contraction, and yet a topic of debate in the literature. The sliding filament theory predicts that the force produced by muscle fibres is proportional to the degree of overlap between myosin and actin filaments, producing a linear descending limb of the active force–length relation. However, several studies have shown forces that are larger than predicted, especially at long sarcomere lengths (SLs). Studies have been conducted with muscle fibres, preparations containing thousands of sarcomeres that make measurements of individual SL challenging. The aim of this study was to evaluate force production and sarcomere dynamics in isolated myofibrils and single sarcomeres from the rabbit psoas muscle to enhance our understanding of the theoretically predicted force–length relation. Contractions at varying SLs along the plateau (SL = 2.25–2.39 µm) and the descending limb (SL > 2.39 µm) of the force–length relation were induced in sarcomeres and myofibrils, and different modes of force measurements were used. Our results show that when forces are measured in single sarcomeres, the experimental force–length relation follows theoretical predictions. When forces are measured in myofibrils with large SL dispersions, there is an extension of the plateau and forces elevated above the predicted levels along the descending limb. We also found an increase in SL non-uniformity and slowed rates of force production at long lengths in myofibrils but not in single sarcomere preparations. We conclude that the deviation of the descending limb of the force–length relation is correlated with the degree of SL non-uniformity and slowed force development.
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Koter, Katarzyna, Martyna Samowicz, Justyna Redlicka et Igor Zubrycki. « Hand Measurement System Based on Haptic and Vision Devices towards Post-Stroke Patients ». Sensors 22, no 5 (7 mars 2022) : 2060. http://dx.doi.org/10.3390/s22052060.
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Diagnostics of a hand requires measurements of kinematics and joint limits. The standard tools for this purpose are manual devices such as goniometers which allow measuring only one joint simultaneously, making the diagnostics time-consuming. The paper presents a system for automatic measurement and computer presentation of essential parameters of a hand. Constructed software uses an integrated vision system, a haptic device for measurement, and has a web-based user interface. The system provides a simplified way to obtain hand parameters, such as hand size, wrist, and finger range of motions, using the homogeneous-matrix-based notation. The haptic device allows for active measurement of the wrist’s range of motion and additional force measurement. A study was conducted to determine the accuracy and repeatability of measurements compared to the gold standard. The system functionality was confirmed on five healthy participants, with results showing comparable results to manual measurements regarding fingers’ lengths. The study showed that the finger’s basic kinematic structure could be measured by a vision system with a mean difference to caliper measurement of 4.5 mm and repeatability with the Standard Deviations up to 0.7 mm. Joint angle limits measurement achieved poorer results with a mean difference to goniometer of 23.6º. Force measurements taken by the haptic device showed the repeatability with a Standard Deviation of 0.7 N. The presented system allows for a unified measurement and a collection of important parameters of a human hand with therapist interface visualization and control with potential use for post-stroke patients’ precise rehabilitation.
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Yao, Lei, Qingguang Gao, Dailin Zhang, Wanpeng Zhang et Youping Chen. « An Integrated Compensation Method for the Force Disturbance of a Six-Axis Force Sensor in Complex Manufacturing Scenarios ». Sensors 21, no 14 (9 juillet 2021) : 4706. http://dx.doi.org/10.3390/s21144706.
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As one of the key components for active compliance control and human–robot collaboration, a six-axis force sensor is often used for a robot to obtain contact forces. However, a significant problem is the distortion between the contact forces and the data conveyed by the six-axis force sensor because of its zero drift, system error, and gravity of robot end-effector. To eliminate the above disturbances, an integrated compensation method is proposed, which uses a deep learning network and the least squares method to realize the zero-point prediction and tool load identification, respectively. After that, the proposed method can automatically complete compensation for the six-axis force sensor in complex manufacturing scenarios. Additionally, the experimental results demonstrate that the proposed method can provide effective and robust compensation for force disturbance and achieve high measurement accuracy.
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Naghshineh, K., et G. H. Koopmann. « An Active Control Strategy for Achieving Weak Radiator Structures ». Journal of Vibration and Acoustics 116, no 1 (1 janvier 1994) : 31–37. http://dx.doi.org/10.1115/1.2930393.
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A general control strategy is presented for active suppression of total radiated sound power from harmonically excited structures based on the measurement of their response. Using the measured response of the structure together with knowledge of its structural mobility, an equivalent primary excitation force is found at discrete points along the structure. Using this equivalent primary force and performing a quadratic optimization of the power radiated from the structure, a set of control forces is found at selected points on the structure that results in minimum radiated sound power. A numerical example of this strategy is presented for a simply supported beam in a rigid baffle excited by a harmonic plane wave incident at an oblique angle. A comparison of the response of the beam with and without control forces shows a large reduction in the controlled response displacement magnitude. In addition, as the result of the action of the control forces, the magnitude of the wave number spectrum of the beam’s response in the supersonic region is decreased substantially. The effect of the number and location of the actuators on reductions in sound power level is also studied. The actuators located at the anti-nodes of structural modes within the supersonic region together with those lcoated near boundaries are found to be the most effective in controlling the radiation of sound from a structure.
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Lorenz, M., B. Heimann et V. Härtel. « A Novel Engine Mount with Semi-Active Dry Friction Damping ». Shock and Vibration 13, no 4-5 (2006) : 559–71. http://dx.doi.org/10.1155/2006/263251.
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In this paper the authors present a semi-active engine mount with a controllable friction damper. The normal force of the friction contact is applied by an electromagnetic actuator and can be varied dynamically. The nonlinear current-force-relation of the actuator is linearized. To account for wear and assembly tolerances, an initialization method is developed, that is based on indirect measurement of the actuators inductance. The friction contact is made up of industrial friction pads and a friction rod of steel. The friction model used is suitable especially for small oscillations of the friction damper. The control policy imitates viscous damping forces that exert a minimum of harmonics. Damping is activated only when necessary. Finally the friction mount is compared to the original mount in a row of test rack experiments and also in the car.
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Aguilera-Castells, Joan, Bernat Buscà Safont-Tria, Javier Peña López, Azahara Fort-Vanmeerhaeghe, Mònica Solana-Tramunt et Jose Morales Aznar. « Suspended lunge exercise : assessment of forces in different positions and paces ». Aloma : Revista de Psicologia, Ciències de l'Educació i de l'Esport 37, no 1 (28 mai 2019) : 57–64. http://dx.doi.org/10.51698/aloma.2019.37.1.57-64.
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The forces exerted on the suspension device have been examined in upper body exercises, like push-ups or inverted raw. For this reason, this aim of this study was to determine the effect of body position, contraction patterns and pace on force production by the lower limb during the execution of suspended lunge exercises. Ten physically active male university students (n = 10, age = 23.70±2.83 years old) performed sixteen suspended lunges in four different positions and three different paces (60, 70, and 80 beats per minute). A load cell was used to assess the forces exert on the suspension device. Force data were analyzed with the factorial repeated measurements (ANOVA). A significant main effect for position in concentric force (p= .000), average force (p= .002), and for frequency in peak force (p= .004) were found. Peak force was significantly higher for dynamic contraction type in all positions in comparison with isometric suspended lunge. In conclusion, a higher feet distance, frequencies around 70 beats per minute and the dynamic contraction type enhanced the forces exert on the suspension strap when performed the lunge exercise.
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Remme, Espen W., Anders Opdahl et Otto A. Smiseth. « Mechanics of left ventricular relaxation, early diastolic lengthening, and suction investigated in a mathematical model ». American Journal of Physiology-Heart and Circulatory Physiology 300, no 5 (mai 2011) : H1678—H1687. http://dx.doi.org/10.1152/ajpheart.00165.2010.
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We investigated the determinants of ventricular early diastolic lengthening and mechanics of suction using a mathematical model of the left ventricle (LV). The model was based on a force balance between the force represented by LV pressure (LVP) and active and passive myocardial forces. The predicted lengthening velocity ( e′) from the model agreed well with measurements from 10 dogs during 5 different interventions ( R = 0.69, P < 0.001). The model showed that e′ was increased when relaxation rate and systolic shortening increased, when passive stiffness was decreased, and when the rate of fall of LVP during early filling was decreased relative to the rate of fall of active stress. We first defined suction as the work the myocardium performed to pull blood into the ventricle. This occurred when contractile active forces decayed below and became weaker than restoring forces, producing a negative LVP. An alternative definition of suction is filling during falling pressure, commonly believed to be caused by release of restoring forces. However, the model showed that this phenomenon also occurred when there had been no systolic compression below unstressed length and therefore in the absence of restoring forces. In conclusion, relaxation rate, LVP, systolic shortening, and passive stiffness were all independent determinants of e′. The model generated a suction effect seen as lengthening occurring during falling pressure. However, this was not equivalent with the myocardium performing pulling work on the blood, which was performed only when restoring forces were higher than remaining active fiber force, corresponding to a negative transmural pressure.
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Alguacil-Diego, Isabel M., Alicia Cuesta-Gómez, David Pont, Juan Carrillo, Paul Espinosa, Miguel A. Sánchez-Urán et Manuel Ferre. « A Novel Active Device for Shoulder Rotation Based on Force Control ». Sensors 23, no 13 (5 juillet 2023) : 6158. http://dx.doi.org/10.3390/s23136158.
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This article describes a one-degree-of-freedom haptic device that can be applied to perform three different exercises for shoulder rehabilitation. The device is based on a force control architecture and an adaptive speed PI controller. It is a portable equipment that is easy to use for any patient, and was optimized for rehabilitating external rotation movements of the shoulder in patients in whom this was limited by muscle–skeletal injuries. The sample consisted of 12 shoulder rehabilitation sessions with different shoulder pathologies that limited their range of shoulder mobility. The mean and standard deviations of the external rotation of shoulder were 42.91 ± 4.53° for the pre-intervention measurements and 53.88 ± 4.26° for the post-intervention measurement. In addition, patients reported high levels of acceptance of the device. Scores on the SUS questionnaire ranged from 65 to 97.5, with an average score of 82.70 ± 9.21, indicating a high degree of acceptance. The preliminary results suggest that the use of this device and the incorporation of such equipment into rehabilitation services could be of great help for patients in their rehabilitation process and for physiotherapists in applying their therapies.
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Olgac, N., et M. Hosek. « Active Vibration Absorption Using Delayed Resonator With Relative Position Measurement ». Journal of Vibration and Acoustics 119, no 1 (1 janvier 1997) : 131–36. http://dx.doi.org/10.1115/1.2889680.
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A novel active vibration absorption technique, the Delayed Resonator, has been introduced recently as a unique way of suppressing undesired oscillations. It suggests a control force on a mass-spring-damper absorber in the form of a proportional position feedback with a time delay. Its strengths consist of extremely simple implementation of the control algorithm, total vibration suppression of the primary structure against a harmonic force excitation and full effectiveness of the absorber in a semi-infinite range of disturbance frequency, achieved by real-time tuning. All this development work was done using the absolute displacements of the absorber in the feedback. These measurements, however, may be difficult to obtain and for some applications impossible. This paper deals with the operating and design repercussions caused by the substituting of an easier measurement: the relative motion of the absorber with respect to the primary structure. Although the proposition sounds like a trivial extension to the prior work it gives rise to important concerns such as system stability. Theoretical foundations for the Delayed Resonator (DR) are briefly recapitulated and its implementation on a single-degree-of-freedom primary structure disturbed by a harmonic force is discussed utilizing both absolute and relative position measurement of absorber mass. Methods for stability range analysis and transient behavior are presented as design tools. Properties observed for the same system with these two different feedbacks are compared. Another important advantage of the relative position feature is is to decouple the operation of the absorber from the primary structure entirely.
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Yun, Gyu-young, Heung Soo Kim et Jaehwan Kim. « Blocked force measurement of an electro-active paper actuator using a cantilevered force transducer ». Smart Materials and Structures 17, no 2 (19 février 2008) : 025021. http://dx.doi.org/10.1088/0964-1726/17/2/025021.
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Stone, R. S. W., et P. N. Brett. « A Sensing Technique for the Measurement of Tactile Forces in the Gripping of Dough-Like Materials ». Proceedings of the Institution of Mechanical Engineers, Part B : Journal of Engineering Manufacture 210, no 3 (juin 1996) : 261–69. http://dx.doi.org/10.1243/pime_proc_1996_210_115_02.
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This paper describes a tactile sensing technique that is devised for applications concerned with the control of the active gripping of deformable compact shaped non-rigid materials. The sensor uses measurements of thin aluminium plate deformation to determine a close representation of the force distribution applied to the surface of the workpiece and can be used to indicate deformation and slip of soft materials under the action of gripping forces. Two methods of operation are described along with the results of each of these implementations. The first method utilizes a model of the sensor mechanical structure to interpret the sensory data from the deformed shape created by the applied force of the object on the sensor surface. The second method relies on an algorithm for comparing theoretical and measured bending moments to achieve the force distribution that provides close agreement between these two entities. In this case the theoretical moment is adjusted by manipulation of the parameters used in the expression describing the force distribution.
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Rao, M. M., et T. K. Datta. « Predictive Active Control of Building Frames with a Solo Neurocontroller ». Journal of Vibration and Control 11, no 5 (mai 2005) : 627–41. http://dx.doi.org/10.1177/1077546305052316.
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We present an efficient generalized control scheme using a solo neural network controller (neuro-controller) for the predictive single mode response control of building frames subjected to earthquake excitation. The control scheme is developed by considering the time delay that exists between the measurement of response and the actual application of the control force. Response measurements are taken from only one point of the structure. The neurocontroller is directly trained to provide the control force signal for a predetermined response reduction, called the target reduction. The neurocontroller is trained such that it can provide control force for target reduction for any building frame ranging between 5 and 15 stories. As an illustrative example, a 10-story shear-building frame is considered whose period of first mode of vibration is about three times that of the second mode of vibration. The efficiency of the control scheme is demonstrated by controlling the first mode response of the frame subjected to El Centro and Treasure Island earthquake records. It is shown that the control scheme provides response reductions close to the target reductions for the unknown problem used for testing the efficiency of the control scheme.
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Prins, Robert J., Mary E. F. Kasarda et Samantha C. Bates Prins. « A System Identification Technique Using Bias Current Perturbation for Determining the Effective Rotor Origin of Active Magnetic Bearings ». Journal of Vibration and Acoustics 129, no 3 (8 novembre 2006) : 317–22. http://dx.doi.org/10.1115/1.2424976.
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Locating the effective rotor origin of an active magnetic bearing (AMB) is an important step toward accurate characterization of the bearing air gaps for field tuning, performance analyses, and some shaft force measurement techniques. Specifically, application of current-based force measurement techniques to AMBs requires accurate modeling of air gaps in order to predict dynamic forces with accuracy. This paper discusses the application of a system identification technique that employs perturbation of the bias current and allows the user to establish the location of the effective rotor origin, an important step in characterizing the actual bearing gap. The technique analyzes the AMB system’s response to the perturbation of bias currents in conjunction with a magnetic circuit model to infer the center position. The effective rotor origin identification technique developed here does not require additional hardware and is suitable for use in the general class of AMBs in field applications. For our purposes, the effective rotor origin of an electro-magnet biased magnetic bearing is defined as the unique rotor location for which a magnetic circuit based force model of the bearing is satisfied for zero position offset of the rotor along each control axis. Note that the effective rotor origin referred to here is the radial origin.
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Gao, Shuxiang, et Ying Ye. « Acute Vascular Response of Hand to Force and Vibration ». Vibration 5, no 1 (2 mars 2022) : 153–64. http://dx.doi.org/10.3390/vibration5010010.
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This study aimed to investigate the acute effect of grip and feed exertions on the vascular system at the fingers during exposure to hand-arm vibration (HAV), and to identify which active hand force situation would have the most effect on finger vascular function. A total of 12 individuals attended the test, and each of them were subjected to eight sets of force-and-vibration situations: four with combinations of forces and vibration, and four control ones with only hand forces applied. The vibration stimulus was applied on the right hand at 2.75 m/s2 with a frequency of 125 Hz for three minutes, during which the application of grip and feed forces were set at either 10 N or 50 N. The weakening of the finger vascular function was reflected by a reduction in the finger blood flow (FBF) and finger skin temperature (FST). They were tested on both hands at fixed intervals before, during and after the exposure for in-time measurement. Hand forces resulted in clear reductions in FBF and FST in exposed right fingers whether the force was exerted solely or combined with vibration. The greater the hand force (especially grip force), the stronger the vascular response, while the additional reductions in FBF and FST from vibration were not significant. In the non-exposed left fingers, no significant changes in finger circulation occurred in response to force or vibration. Generally, vibration-induced acute finger vasoconstriction was affected by the hand forces, in which hand force seemed to play a more important part than vibration. A larger grip force would lead to a greater loss in the digital circulation than feed force. Thus, the level of hand force exerted on the tool handle should be limited to reduce the risk of harm from HAV.
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Takeuchi, Akitoshi. « OS6-17 An Attempt to Measure the Force and Moment Acting on Hub-bearing with Ultrasonic Technique(Measurement Techniques using Ultrasonics (1),OS6 Ultrasonic non-destructive testing and evaluation,MEASUREMENT METHODS) ». Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics 2015.14 (2015) : 88. http://dx.doi.org/10.1299/jsmeatem.2015.14.88.
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Dąbrowa, Tomasz, Dominik Badura, Bartosz Pruchnik, Ewelina Gacka, Władysław Kopczyński, Marcin Mikulewicz, Teodor Gotszalk et Edward Kijak. « Correlation between Friction and Wear in Cylindrical Anchorages Simulated with Wear Machine and Analyzed with Scanning Probe and Electron Microscope ». Materials 16, no 5 (28 février 2023) : 1991. http://dx.doi.org/10.3390/ma16051991.
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This paper presents the possibilities of applying atomic force microscopy (AFM) techniques to the study of the wear of prosthetic biomaterials. In the conducted research, a zirconium oxide sphere was used as a test piece for mashing, which was moved over the surface of selected biomaterials: polyether ether ketone (PEEK) and dental gold alloy (Degulor M). The process was carried out with constant load force in an artificial saliva environment (Mucinox). An atomic force microscope with an active piezoresistive lever was used to measure wear at the nanoscale. The advantage of the proposed technology is the high resolution of observation (less than 0.5 nm) in the three-dimensional (3D) measurements in a working area of 50 × 50 × 10 µm. The results of nano wear measurements in two measurement setups are presented: zirconia sphere (Degulor M and zirconia sphere) and PEEK were examined. The wear analysis was carried out using appropriate software. Achieved results present a tendency coincident with the macroscopic parameters of materials.
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Keller, Monique M., Roline Y. Barnes et Corlia Brandt. « Activities of daily living with grasp types and force measurements during object manipulation ». South African Journal of Occupational Therapy 54, no 1 (1 avril 2024) : 15–21. http://dx.doi.org/10.17159/2310-3833/2024/vol54no1a3.
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Background: Limited scientific evidence guides hand rehabilitation towards improved hand function, and safe early return to work. Grasp types, the subunits of object manipulation and the forces which may improve functional outcomes, have been identified as missing links that may inform rehabilitation after second to fifth metacarpal fractures, through progression of basic and instrumental activities of daily living (ADL). The aim of the study was to collect ADL forces through grasp types to inform hand rehabilitation for second to fifth metacarpal fractures. Methods: This cross-sectional, quantitative study included 32 conveniently sampled healthy adults aged 20 and 59 years. Thirty-one (31) ADLs, both basic and instrumental, each associated with a predominant grasp type, were tested. The participants donned two testing gloves, with force sensing resistors (FSRs) glued to the fingertips, the ADLs were performed, and forces measured. The researcher imported the force data into an Excel spreadsheet for both descriptive and inferential analyses with STATA. Results: Fourteen males and 18 females, with a mean age of 37 years, participated. Statistically significant differences between genders were found for seven grasp types. Three thumb-adducted power palm grasps, three thumb-abduction precision pad grasps, and one thumb-abduction power palm grasp constituted the testing. Light and heavy ADLs and their associated grasp types were identified. Conclusion: To ensure optimal hand function, early safe return to ADLs should be the goal of second to fifth metacarpal fracture rehabilitation and may be achieved by incorporating active grasp types as exercises with graded resisted grasp types and ADLs. Implications for practice • Occupational therapists can incorporate grasp types in their observation during assessments of individuals who sustained second to fifth metacarpal fractures to determine the subcomponents of functional deficits. • Hand rehabilitation may be augmented by incorporating grasp types in isolation during unresisted active joint range of motion. • Occupational therapists, guided by the analysis of hand functioning, can incorporate ADLs with the predominant grasp types which may improve hand function. • Grasp force data may guide safe and early return to function.
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Tsveov, Mihail, Pavel Venev, Dimitar Chakarov et Ivanka Veneva. « Simulations and experimental evaluation of an active orthosis for interaction in virtual environments ». MATEC Web of Conferences 145 (2018) : 01006. http://dx.doi.org/10.1051/matecconf/201814501006.
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In this work, the development of a human arm active orthosis is presented. The orthosis is designed primarily for training and rehabilitation in virtual environments.The orthosis system is intended for embodiment in virtual reality where it is allowing human to perceive forces at different body parts or the weight of lifted objects. In the paper the choice of a mechanical structure is shown equivalent to the structure of the human arm. A mechanical model of the orthosis arm as haptic device is built, where kinematic and dynamic parameters are evaluated. Impedance control scheme is selected as the most suitable for force refection at the hand or arm. An open-loop impedance controller is presented in the paper. Computer experiments are carried out using the dimensions of a real arm orthosis. Computer experiments have been carried out to provide force reflection by VR, according to virtual scenario. The conducted simulations show the range of the forces on the operator hand, orthosis can provide. The results of additional measurements and experimental evaluations of physical quantities in the interaction in a virtual environment are revealed in the paper.
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Shu, Jicheng, Jianping Sun, Dingwen Zhang et Huanwei Wei. « Sequential Measurement and Analysis of Large Underground Retaining Structures by Diaphragm Wall Anchor for the Spring Area ». Advances in Civil Engineering 2019 (11 novembre 2019) : 1–21. http://dx.doi.org/10.1155/2019/5291420.
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The performance of a diaphragm wall-anchor structure in spring area in Jinan city, China, is studied. Based on field measured data, lateral wall deflections, lateral soil movements, horizontal displacement of the capping beam, the maximum lateral wall deflection, ground surface settlement, lateral earth pressures on diaphragm wall, internal force of diaphragm wall, axial anchoring forces, settlements of adjacent building, and pore-water pressure are investigated. The results indicate that the maximum deflections of the lateral wall are 0.07%∼0.18% of the excavation depth (He). The ground surface settlement influence zone extends beyond 2.5He from the pit for this project. The δv,max ranges from 0.67 δh,max to 1.0 δh,max. The maximum lateral active earth pressures on diaphragm walls above the excavation bases range between 0.4He and 0.6He. The axial anchoring forces of the top three layers of anchors change significantly during the excavation while the axial anchoring force of the fourth layer of anchor is constant. The deformation of surrounding building has three stages, including a uniform subsidence stage, an accelerated subsidence stage, and a stable subsidence stage.
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Weinhandl, Joshua T., Bobbie S. Irmischer et Zachary A. Sievert. « Effects of Gait Speed of Femoroacetabular Joint Forces ». Applied Bionics and Biomechanics 2017 (2017) : 1–7. http://dx.doi.org/10.1155/2017/6432969.
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Alterations in hip joint loading have been associated with diseases such as arthritis and osteoporosis. Understanding the relationship between gait speed and hip joint loading in healthy hips may illuminate changes in gait mechanics as walking speed deviates from preferred. The purpose of this study was to quantify hip joint loading during the gait cycle and identify differences with varying speed using musculoskeletal modeling. Ten, healthy, physically active individuals performed walking trials at their preferred speed, 10% faster, and 10% slower. Kinematic, kinetic, and electromyographic data were collected and used to estimate hip joint force via a musculoskeletal model. Vertical ground reaction forces, hip joint force planar components, and the resultant hip joint force were compared between speeds. There were significant increases in vertical ground reaction forces and hip joint forces as walking speed increased. Furthermore, the musculoskeletal modeling approach employed yielded hip joint forces that were comparable to previous simulation studies and in vivo measurements and was able to detect changes in hip loading due to small deviations in gait speed. Applying this approach to pathological and aging populations could identify specific areas within the gait cycle where force discrepancies may occur which could help focus management of care.
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Koo, Bonjin, et Placid M. Ferreira. « An active MEMS probe for fine position and force measurements ». Precision Engineering 38, no 4 (octobre 2014) : 738–48. http://dx.doi.org/10.1016/j.precisioneng.2014.03.010.
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CHEN, CHAO-JUNG, YEN-LIANG CHEN et LIANG-CHIH CHANG. « PITCH MEASUREMENT BY TRACEABLE ATOMIC FORCE MICROSCOPE ». International Journal of Nanoscience 02, no 04n05 (août 2003) : 335–41. http://dx.doi.org/10.1142/s0219581x0300136x.
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A Traceable Atomic Force Microscope (TAFM) to calibrate the pitch standards is presented. The TAFM consists of an atomic force microscope, a three-axis active compensation flexure stage, two laser interferometers, an L-shape mirror, a vibration isolator, and a super-Invar metrology frame. A test specimen is laid on the same plane of laser interferometers to eliminate the Abbe-offset. The displacements of X and Y axes are taken by the laser interferometers, the Z movement is controlled by AFM cantilever and the displacement is taken by a capacitance sensor while the flexure stage moves the specimen in X and Y axes motions. A water circulator is used to control the TAFM at 20°C. Measuring results of a standard pitch sample show that this TAFM can be used for measuring of pitch standards. A pitch standard with nominal value of 292 nm was served as a test sample. The combined standard uncertainty was 1.2 nm.
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Kim, Jaehwan, Yukeun Kang et Sungryul Yun. « Blocked force measurement of electro-active paper actuator by micro-balance ». Sensors and Actuators A : Physical 133, no 2 (février 2007) : 401–6. http://dx.doi.org/10.1016/j.sna.2006.04.019.
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Kasarda, M. E., J. Marshall et R. Prins. « Active magnetic bearing based force measurement using the multi-point technique ». Mechanics Research Communications 34, no 1 (janvier 2007) : 44–53. http://dx.doi.org/10.1016/j.mechrescom.2006.06.003.
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Wright, S., et P. G. Weyand. « The application of ground force explains the energetic cost of running backward and forward ». Journal of Experimental Biology 204, no 10 (15 mai 2001) : 1805–15. http://dx.doi.org/10.1242/jeb.204.10.1805.
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We compared backward with forward running to test the idea that the application of ground force to support the weight of the body determines the energetic cost of running. We hypothesized that higher metabolic rates during backward versus forward running would be directly related to greater rates of ground force application and the volume of muscle activated to apply support forces to the ground. Four trained males ran backward and forward under steady-state conditions at eight treadmill speeds from 1.75 to 3.50 m s(−)(1). Rates of oxygen uptake were measured to determine metabolic rates, and inverse periods of foot-ground contact (1/t(c)) were measured to estimate rates of ground force application. As expected, at all eight speeds, both metabolic rates and estimated rates of ground force application were greater for backward than for forward running. At the five slowest speeds, the differences in rates of ground force application were directly proportional to the differences in metabolic rates between modes (paired t-test, P<0.05), but at the three highest speeds, small but significant differences in proportionality were present in this relationship. At one of these three higher speeds (3.0 m s(−)(1)), additional measurements to estimate muscle volumes were made using a non-invasive force plate/video technique. These measurements indicated that the volume of muscle active per unit of force applied to the ground was 10+/−3 % greater when running backward than forward at this speed. The product of rates of ground force application and estimated muscle volumes predicted a difference in metabolic rate that was indistinguishable from the difference we measured (34+/−6 % versus 35+/−6 %; means +/− s.e.m., N=4). We conclude that metabolic rates during running are determined by rates of ground force application and the volume of muscle activated to apply support forces to the ground.
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Kohl, D., C. Kerschner et G. Schitter. « Active damping by Q-control for fast force-distance curve measurements in atomic force microscopy ». Review of Scientific Instruments 88, no 12 (décembre 2017) : 123711. http://dx.doi.org/10.1063/1.4991604.
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Achkire, Y., et A. Preumont. « Optical Measurement of Cable and String Vibration ». Shock and Vibration 5, no 3 (1998) : 171–79. http://dx.doi.org/10.1155/1998/387973.
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This paper describes a non contacting measurement technique for the transverse vibration of small cables and strings using an analog position sensing detector. On the one hand, the sensor is used to monitor the cable vibrations of a small scale mock-up of a cable structure in order to validate the nonlinear cable dynamics model. On the other hand, the optical sensor is used to evaluate the performance of an active tendon control algorithm with guaranteed stability properties. It is demonstrated experimentally, that a force feedback control law based on a collocated force sensor measuring the tension in the cable is feasible and provides active damping in the cable.
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Collins, Liam, Stephen Jesse, Jason I. Kilpatrick, Alexander Tselev, M. Baris Okatan, Sergei V. Kalinin et Brian J. Rodriguez. « Kelvin probe force microscopy in liquid using electrochemical force microscopy ». Beilstein Journal of Nanotechnology 6 (19 janvier 2015) : 201–14. http://dx.doi.org/10.3762/bjnano.6.19.
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Conventional closed loop-Kelvin probe force microscopy (KPFM) has emerged as a powerful technique for probing electric and transport phenomena at the solid–gas interface. The extension of KPFM capabilities to probe electrostatic and electrochemical phenomena at the solid–liquid interface is of interest for a broad range of applications from energy storage to biological systems. However, the operation of KPFM implicitly relies on the presence of a linear lossless dielectric in the probe–sample gap, a condition which is violated for ionically-active liquids (e.g., when diffuse charge dynamics are present). Here, electrostatic and electrochemical measurements are demonstrated in ionically-active (polar isopropanol, milli-Q water and aqueous NaCl) and ionically-inactive (non-polar decane) liquids by electrochemical force microscopy (EcFM), a multidimensional (i.e., bias- and time-resolved) spectroscopy method. In the absence of mobile charges (ambient and non-polar liquids), KPFM and EcFM are both feasible, yielding comparable contact potential difference (CPD) values. In ionically-active liquids, KPFM is not possible and EcFM can be used to measure the dynamic CPD and a rich spectrum of information pertaining to charge screening, ion diffusion, and electrochemical processes (e.g., Faradaic reactions). EcFM measurements conducted in isopropanol and milli-Q water over Au and highly ordered pyrolytic graphite electrodes demonstrate both sample- and solvent-dependent features. Finally, the feasibility of using EcFM as a local force-based mapping technique of material-dependent electrostatic and electrochemical response is investigated. The resultant high dimensional dataset is visualized using a purely statistical approach that does not require a priori physical models, allowing for qualitative mapping of electrostatic and electrochemical material properties at the solid–liquid interface.
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Leite, Felipe S., Fábio C. Minozzo, Albert Kalganov, Anabelle S. Cornachione, Yu-Shu Cheng, Nicolae A. Leu, Xuemei Han et al. « Reduced passive force in skeletal muscles lacking protein arginylation ». American Journal of Physiology-Cell Physiology 310, no 2 (15 janvier 2016) : C127—C135. http://dx.doi.org/10.1152/ajpcell.00269.2015.
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Arginylation is a posttranslational modification that plays a global role in mammals. Mice lacking the enzyme arginyltransferase in skeletal muscles exhibit reduced contractile forces that have been linked to a reduction in myosin cross-bridge formation. The role of arginylation in passive skeletal myofibril forces has never been investigated. In this study, we used single sarcomere and myofibril measurements and observed that lack of arginylation leads to a pronounced reduction in passive forces in skeletal muscles. Mass spectrometry indicated that skeletal muscle titin, the protein primarily linked to passive force generation, is arginylated on five sites located within the A band, an important area for protein-protein interactions. We propose a mechanism for passive force regulation by arginylation through modulation of protein-protein binding between the titin molecule and the thick filament. Key points are as follows: 1) active and passive forces were decreased in myofibrils and single sarcomeres isolated from muscles lacking arginyl-tRNA-protein transferase (ATE1). 2) Mass spectrometry revealed five sites for arginylation within titin molecules. All sites are located within the A-band portion of titin, an important region for protein-protein interactions. 3) Our data suggest that arginylation of titin is required for proper passive force development in skeletal muscles.
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Beltran-Carbajal, Francisco, Antonio Valderrabano-Gonzalez, Antonio Favela-Contreras, Jose Luis Hernandez-Avila, Irvin Lopez-Garcia et Ruben Tapia-Olvera. « An Active Vehicle Suspension Control Approach with Electromagnetic and Hydraulic Actuators ». Actuators 8, no 2 (24 avril 2019) : 35. http://dx.doi.org/10.3390/act8020035.
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An active vibration control approach from an online estimation perspective of unavailable feedback signals for a quarter-vehicle suspension system is introduced. The application of a new signal differentiation technique for the online estimation of disturbance trajectories due to irregular road surfaces and velocity state variables is described. It is assumed that position measurements are only available for active disturbance suppression control implementation. Real-time signal differentiation is independent of detailed mathematical models of specific dynamic systems and control force generation mechanisms. Active control forces can be supplied by electromagnetic or hydraulic actuators. Analytical and simulation results prove the effective and fast dynamic performance of the online signal estimation as well as a satisfactory active disturbance attenuation on a quarter-vehicle active suspension system.
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Li, Yiming, Keyu Li, Fang Fu, Yao Li et Bing Li. « The Functions of Phasic Wing-Tip Folding on Flapping-Wing Aerodynamics ». Biomimetics 9, no 3 (18 mars 2024) : 183. http://dx.doi.org/10.3390/biomimetics9030183.
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Insects produce a variety of highly acrobatic maneuvers in flight owing to their ability to achieve various wing-stroke trajectories. Among them, beetles can quickly change their flight velocities and make agile turns. In this work, we report a newly discovered phasic wing-tip-folding phenomenon and its aerodynamic basis in beetles. The wings’ flapping trajectories and aerodynamic forces of the tethered flying beetles were recorded simultaneously via motion capture cameras and a force sensor, respectively. The results verified that phasic active spanwise-folding and deployment (PASFD) can exist during flapping flight. The folding of the wing-tips of beetles significantly decreased aerodynamic forces without any changes in flapping frequency. Specifically, compared with no-folding-and-deployment wings, the lift and forward thrust generated by bilateral-folding-and-deployment wings reduced by 52.2% and 63.0%, respectively. Moreover, unilateral-folding-and-deployment flapping flight was found, which produced a lateral force (8.65 mN). Therefore, a micro-flapping-wing mechanism with PASFD was then designed, fabricated, and tested in a motion capture and force measurement system to validate its phasic folding functions and aerodynamic performance under different operating frequencies. The results successfully demonstrated a significant decrease in flight forces. This work provides valuable insights for the development of flapping-wing micro-air-vehicles with high maneuverability.
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Full, R., et A. Ahn. « Static forces and moments generated in the insect leg : comparison of a three-dimensional musculo-skeletal computer model with experimental measurements ». Journal of Experimental Biology 198, no 6 (1 juin 1995) : 1285–98. http://dx.doi.org/10.1242/jeb.198.6.1285.
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As a first step towards the integration of information on neural control, biomechanics and isolated muscle function, we constructed a three-dimensional musculo-skeletal model of the hind leg of the death-head cockroach Blaberus discoidalis. We tested the model by measuring the maximum force generated in vivo by the hind leg of the cockroach, the coxa­femur joint angle and the position of this leg during a behavior, wedging, that was likely to require maximum torque or moment production. The product of the maximum force of the leg and its moment arm yielded a measured coxa­femur joint moment for wedging behavior. The maximum musculo-apodeme moment predicted by summing all extensor muscle moments in the model was adequate to explain the magnitude of the coxa­femur joint moment produced in vivo by the cockroach and occurred at the same joint angle measured during wedging. Active isometric muscle forces predicted from our model varied by 3.5-fold among muscles and by as much as 70 % with joint angle. Sums of active and passive forces varied by less than 3.5 % over the entire range of possible joint angles (0­125 °). Maximum musculo-apodeme moment arms varied nearly twofold among muscles. Moment arm lengths decreased to zero and switched to the opposite side of the center of rotation at joint angles within the normal range of motion. At large joint angles (>100 °), extensors acted as flexors. The effective mechanical advantage (musculo-apodeme moment arm/leg moment arm = 0.10) resulted in the six femoral extensor muscles of the model developing a summed force (1.4 N) equal to over 50 times the body weight. The model's three major force-producing extensor muscles attained 95 % of their maximum force, moment arm and moment at the joint angle used by the animal during wedging.
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Skalak, Richard, Cheng Dong et Cheng Zhu. « Passive Deformations and Active Motions of Leukocytes ». Journal of Biomechanical Engineering 112, no 3 (1 août 1990) : 295–302. http://dx.doi.org/10.1115/1.2891187.
Texte intégralRésumé :
The purpose of this paper is to review the development of continuum mechanics models of single leukocytes in both passive deformations and active motions and to indicate some future directions. Models of passive deformations describe the overall rheological behavior of single leukocytes under externally applied forces and predict the average mechanical properties from experimental data. Various “apparent” viscoelastic coefficients are obtained depending on the models assumed and the types of test used. Models of spontaneous motions postulate active driving mechanisms which must be derived internally from the cell itself and probably have different bases for different kind of motions. For pseudopod protrusion on leukocytes, energy transduction from chemical potential to mechanical work associated with actin polymerization at the tip of the projection is assumed to supply the motive power. For pseudopod retraction, active contraction due to actin-myosin interaction is assumed to be the driving force. The feasibility of the hypotheses are tested via numerical examples and comparison of the theoretical results with experimental measurements.
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Hefter, Harald, Sara Samadzadeh, Dietmar Rosenthal et Osman Tezayak. « Analysis of Single-Leg Hopping in Long-Term Treated Patients with Neurological Wilson’s Disease : A Controlled Pilot Study ». Medicina 58, no 2 (7 février 2022) : 249. http://dx.doi.org/10.3390/medicina58020249.
Texte intégralRésumé :
Background and Objectives: In long-term treated patients with neurological Wilson’s disease, the ability to perform single-leg hopping was analyzed to quantify motor deficits. Materials and Methods: Twenty-nine long-term treated Wilson patients had to stand on one leg for at least 3 s and then perform at least five consecutive hops on this leg. Ground reaction forces and temporal patterns of hopping were recorded using an Infotronic® walking system, which consists of soft tissue shoes with a solid, but flexible plate containing eight force transducers allowing measurement of ground reaction forces (GRF) and temporal patterns of foot ground contact. Parameters of hopping were correlated with clinical scores and parameters of copper metabolism and liver enzymes. Patients’ hopping data were compared with those of an age- and sex-matched control group. Results: Five severely affected Wilson patients were unable to hop. Time to the peak was significantly (p < 0.03) shorter in the remaining 24 patients compared to controls, but there was no difference in hopping frequency, the amplitude of ground forces and duration of foot contact. Twelve patients produced a second, sharp, initial “impact” force peak during ground contact in addition to the usual “active” force peak. Variability of the amplitude of the “active” peak was significantly inversely correlated with urinary copper elimination. Conclusions: The majority of long-term treated patients with neurological Wilson’s disease was able to perform single-leg hopping. The presence of a sharp initial “impact” peak in the GRF-curves of hopping may indicate a mild deficit of limb/trunk coordination and subclinical cerebellar impairment.
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Maciak, Adam, Magda Kubuśka et Tadeusz Moskalik. « Instantaneous Cutting Force Variability in Chainsaws ». Forests 9, no 10 (22 octobre 2018) : 660. http://dx.doi.org/10.3390/f9100660.
Texte intégralRésumé :
Chainsaws with chipper-type chains are widely used in timber harvesting. While existing research on such saws assumes a continuous cutting process, the objectives of the present study were to determine whether or not that is true, as well as to measure instantaneous cutting forces and active cutting time (the time during which the chainsaw cutters are actually engaged with the wood sample). Tests were conducted on a special experimental stand enabling cutting force measurement with a frequency of 60 kHz. The test material was air-dry pine wood. The feed force range was 51–118 N. The chain was tensioned. The study revealed considerable variability in instantaneous cutting force, which was correlated with the rotational speed of the chainsaw engine, as indicated by frequency analysis. Furthermore, the process of cutting with chainsaws was shown to be discontinuous, and a cutter engagement time ratio was defined as the proportion of active cutting time to the overall time of chainsaw operation when making the cut. It was also found that active cutting time was directly proportionate to the applied feed force and inversely proportionate to the rotational speed of the chainsaw engine. The results may be practically applied to establish an optimum range of rotational speed that should be maintained by the operator to maximize cutting efficiency.