Dynamic Force Transducer Research Articles

A comparison between static and dynamic stiffness of force transducers for dynamic force calibrations

The dynamic force transducers’ stiffness is an important parameter in determining the frequency range where the force transducers can be used at the different dynamic setups. The aim of the present paper is to demonstrate a new setup and analysis method in measuring the stiffness of the dynamic force transducers under applying static force. This new approach is distinguished by its stability and accuracy as it depends on using primary measurement devices precisely assembled; dead weight machine and laser interferometer device. The measured stiffness value is compared to the dynamic stiffness measured under applying sinusoidal dynamic force to ensure its validity. Results show that there is sensible difference between static and dynamic stiffness. Static stiffness is always greater than the dynamic stiffness. Many factors are affecting the accuracy of the dynamic stiffness such as rocking modes, lateral forces, and the mechanical coupling between force transducer and the electrodynamic shaker.

A Methodology for Reconstructing Source Properties of a Conical Piezoelectric Actuator Using Array-Based Methods

We investigated the force produced by a conical piezoelectric (PZT, lead zirconate titanate) transducer actuated by high voltage pulses (HVP) in contact with a steel transfer plate. Using elastic wave propagation theory in a semi-infinite plate, we aimed to quantify the magnitude and estimate the shape of the force–time function via the body waves produced in the transfer plate using the displacement field recorded on an array of 20 absolutely calibrated PZT receivers. We first calibrated the receiver array using glass capillary fracture. We proceeded to use a conical PZT transducer to actively produce a source at the origin, allowing us to study the displacement field produced on the now calibrated PZT receiver array. We studied two types of HVP: An impulsive and step source. The calibrated receiver array was used to estimate the general shape of the force–time functions for each type of HVP. From our hypothesized force–time functions we were able to estimate the peak force produced by the PZT actuator: The impulsive source generated a force of f_{peak} = 2.90 pm 0.42 N and the step source generated f_{peak} = 1.79 pm 0.30 N, respectively, for a peak applied voltage of 273 V. This translates to an applied force of sim 0.011 N/V and 0.007 N/V for the impulse and step force–time functions, respectively, which is similar to estimates found in the literature for other conical transducers in contact with metallic transfer media. This measurement was verified directly by independent measurements of the peak force f_{peak} using a dynamic force transducer. We found that our methodology correctly estimated the magnitude of the force but is limited to transducers with incident angles theta< 53^{circ }. Beyond this angle, overestimates of the force were observed due to the lack of body wave energy produced by the source. These results allow us to quantitatively determine the forces produced by active PZT techniques using only the measurement of the displacement field captured on a calibrated conical PZT array. Quantitative understanding of active PZT sources additionally constrains the transfer functions approach, which is commonly used in the non-destructive testing of materials and in other fields, such as rock physics and laboratory seismology.

Dynamic Force Transducer Calibration Based on Electrostatic Force

Measurements of micro/nano dynamic force transducers (DFTs) in the micro-Newton range are of significant importance in many fields. In this paper, the electrostatic force in the micro-Newton range was used to generate dynamic force to calibrate the DFT, which is traceable to the International System of Units (SI). The relationship between the force input and voltage output of a DFT was investigated. The performance of DFT, such as resolution and reproducibility had been tested by the proposed method. The uncertainties, such as eccentric loading position, electrostatic force, output voltage measurement, and stiffness measurement, were estimated. The results showed that relative standard uncertainty in the determination of the calibration of the transducer was approximately 2.2%. This showed that the proposed system was very stable and repeatable.

Parametric identification of dynamic force transducers Journal of Physics: Conference Series

Knowledge of the parameters of dynamic force transducers is required to determine the response of the transducers under dynamic conditions. We describe a model representation of dynamic force transducers with different transfer functions that cover all measurement probabilities, and we introduce three identification tools depending on least-square fit with the modelling of noise. In applying these methods to different measurements, it is demonstrated that stable results can be obtained for the parameter of dynamic force transducers.

Features calibration of the dynamic force transducers

The article discusses calibration methods of dynamic forces measuring instruments. The relevance of work is dictated by need to valid definition of the dynamic forces transducers metrological characteristics taking into account their intended application. The aim of this work is choice justification of calibration method, which provides the definition dynamic forces transducers metrological characteristics under simulation operating conditions for determining suitability for using in accordance with its purpose. The following tasks are solved: the mathematical model and the main measurements equation of calibration dynamic forces transducers by load weight, the main budget uncertainty components of calibration are defined. The new method of dynamic forces transducers calibration with use the reference converter “force-deformation” based on the calibrated elastic element and measurement of his deformation by a laser interferometer is offered. The mathematical model and the main measurements equation of the offered method is constructed. It is shown that use of calibration method based on measurements by the laser interferometer of calibrated elastic element deformations allows to exclude or to considerably reduce the uncertainty budget components inherent to method of load weight.

A review of Pochhammer–Chree dispersion in the Hopkinson bar

This paper presents a detailed review of the current state of the art in Hopkinson pressure bar (HPB) data analysis. In particular, the underlying theory of the HPB is discussed, and methods of correcting signals for Pochhammer–Chree dispersion and other associated effects are described. The theory of multiple mode propagation is presented, followed by a review of the current methods for correcting multiple mode dispersion, which are especially pertinent when using the HPB as a dynamic force transducer to measure rapidly changing loading events such as explosive blast loads.

Calibration and Validation of Dynamic Force Transducers

The urgent need for a procedure to use in validation of dynamic force transducers is considered. A model of the dynamic interaction of the elements of a dynamic force transducer in the course of calibration by the test mass method is presented. Mathematical expressions that describe the calibration process are presented. A schematic diagram of a calibration plant that would be most appropriate for dynamic force transducers is proposed.

Accurate Determination of the Frequency Response Function of Submerged and Confined Structures by Using PZT-Patches†.

To accurately determine the dynamic response of a structure is of relevant interest in many engineering applications. Particularly, it is of paramount importance to determine the Frequency Response Function (FRF) for structures subjected to dynamic loads in order to avoid resonance and fatigue problems that can drastically reduce their useful life. One challenging case is the experimental determination of the FRF of submerged and confined structures, such as hydraulic turbines, which are greatly affected by dynamic problems as reported in many cases in the past. The utilization of classical and calibrated exciters such as instrumented hammers or shakers to determine the FRF in such structures can be very complex due to the confinement of the structure and because their use can disturb the boundary conditions affecting the experimental results. For such cases, Piezoelectric Patches (PZTs), which are very light, thin and small, could be a very good option. Nevertheless, the main drawback of these exciters is that the calibration as dynamic force transducers (relationship voltage/force) has not been successfully obtained in the past. Therefore, in this paper, a method to accurately determine the FRF of submerged and confined structures by using PZTs is developed and validated. The method consists of experimentally determining some characteristic parameters that define the FRF, with an uncalibrated PZT exciting the structure. These parameters, which have been experimentally determined, are then introduced in a validated numerical model of the tested structure. In this way, the FRF of the structure can be estimated with good accuracy. With respect to previous studies, where only the natural frequencies and mode shapes were considered, this paper discuss and experimentally proves the best excitation characteristic to obtain also the damping ratios and proposes a procedure to fully determine the FRF. The method proposed here has been validated for the structure vibrating in air comparing the FRF experimentally obtained with a calibrated exciter (impact Hammer) and the FRF obtained with the described method. Finally, the same methodology has been applied for the structure submerged and close to a rigid wall, where it is extremely important to not modify the boundary conditions for an accurate determination of the FRF. As experimentally shown in this paper, in such cases, the use of PZTs combined with the proposed methodology gives much more accurate estimations of the FRF than other calibrated exciters typically used for the same purpose. Therefore, the validated methodology proposed in this paper can be used to obtain the FRF of a generic submerged and confined structure, without a previous calibration of the PZT.

절삭력 진동 분석에 의한 가공조건 모니터링

This paper deals with an experimental technique for monitoring machining conditions by analyzing cutting-force vibration measured at a milling machine. This technique is based on the relationship of the cutting-force vibrations with the feed rate and cutting depth as reported earlier. The measurement system consists of dynamic force transducers and a signal amplifier. The analysis system includes an oscilloscope and a computer with a LabVIEW program. Experiments were carried out at various feed rates and cutting depths, while the rotating speed was kept constant. The magnitude of the cutting force vibration component corresponding to the number of cutting edges multiplied by the frequency of rotation was linearly correlated with the machining conditions. When one condition of machining is known, another condition can be identified by analyzing the cutting-force vibration.

An experimental study on the interaction between free-stream turbulence and a wing-tip vortex in the near-field

The effect of external free-stream turbulence was investigated experimentally in the near-field of a wing-tip vortex. A free-stream turbulent flow with 4.6% turbulence intensity was created with the aid of a grid turbulence generator, while the turbulence intensity in the base flow case with no grid was approximately 0.5%. The experiments were conducted in a closed-circuit wind tunnel while a dynamic force transducer was used to measure the aerodynamic forces on a NACA 0015 wing section in the range of 0° to 25° angle of attack. The wing section with a semi-span aspect ratio of 5.4 spanned approximately half height of the wind tunnel section and fixed vertically to the load cell at the base. Hot-wire anemometry was used to measure the velocity field downstream of the wing at crossflow planes of x/c=0.1,0.42,0.77 and 1.03 while the Reynolds number and angle of attack were set at 1.6×105 and 10°, respectively. The results of aerodynamic force measurement for the no-grid case agree fairly with other experimental and analytical works. In addition, circumferential velocity and circulation profiles inside the vortex flow-field fit well with analytical expressions proposed by others. The crossflow velocity contours show that the free-stream turbulence tends to increase the vortex diffusion at x/c=0.77 and 1.03. The inboard and upward movement of the tip vortex downstream of the wing was not significantly affected by the introduction of free-stream turbulence, while external free-stream turbulence increases the turbulence intensity peak. External turbulence also increased the circumferential velocity and vortex circulation with respect to the streamwise distance at radial locations far from the vortex center.

Measurement of Axial Impact Force of Pipeline Transporting Thick Pastes

Due to alternating work mode of twin-cylinder of solid pump during high pressure pipeline transporting thick pastes, largde axial impact force is exerted on the pipeline, which makes pipe clamps, supports and bolts of flange damage to failure. By using twin dynamic force transducers and designing coresponding installation components for the transducers, impact forces at different flow rates, positions of the pipeline and transportation pressures were measured. Conclusions can be drawn as following: impact force increases with increasing flow rate, and decreases with increasing distance from the outlet of pump. The increased amount of impact force with increasing flow rate is larger under larger transportation pressure than that under samller transportation pressure. It is better to transport thick pastes at low system pressure, and to install more pipe clamps in the front part, and reverse in the back part of pipeline.

Nondestructive Assessment of Axial Load–Deflection Behavior of Drilled Shafts for a Suspension Bridge

The new Rio Cuarto Bridge, currently under construction in the Province of Cordoba, Argentina, consists of a 110-m long, cable-stayed main span with a prestressed concrete deck, steel pylons, and two 50-m–long side spans founded on groups of drilled shafts. The construction method, structural configuration of the superstructure, and post-tensioning sequence of the cables required a detailed characterization of the axial load behavior of the drilled shafts, both for the temporary support shafts and the foundation piers. Small-strain and working load level predictions were made during design, on the basis of conventional site investigation information and in situ geophysical testing. A series of nondestructive evaluations, coupled with nonlinear extrapolations calibrated to represent the measured small-strain range, were carried out in lieu of conventional verification of design predictions by means of more cumbersome large-strain testing. The testing program consisted on monitoring accelerations generated at the top of the shaft as a result of a small amplitude dynamic load measured by means of a dynamic force transducer. A nonlinear numerical model was then calibrated so as to reproduce the initial stiffness measured during the small-strain testing program to extrapolate the load-deflection curve into the service load range and thus define load-deflection curves of the shafts at each pier location up to service load levels. To obtain an experimental validation of the approach at the site, a conventional static load test, carried up to the service load level, was performed on a main pier shaft. Results showed a reasonable agreement between the nondestructive evaluation with nonlinear extrapolation, large-strain measurements, and design predictions for the main pier shafts, whereas some differences were observed between the design predictions and small-strain measurements at other locations, primarily as a result of as-built conditions unforeseen in the original design. Thus, the nondestructive testing program was instrumental in the verification of the as-built behavior of the shafts and allowed the development of load-deflection curves for the drilled shafts that accurately represented the behavior up to the service load level.

Efficacy of Securing Cannulae with Different Taping Methods

This study compared locally available adhesive tapes and dressings in a block randomized, blinded study to determine the force required to dislodge a cannula. In the first stage of the study, various tapes and taping methods were used to secure a cannula to a polyvinylchloride (PVC) pipe. The cannula was attached to a section of a giving set which in turn was attached to a dynamic force transducer. The force required to dislodge the cannula, together with the methods of dislodgement were recorded. In stage two the best taping technique for each type of tape was tested by attaching a cannula to the surface of the forearm of an adult male volunteer. Of the tapes tested we found Leukoplast to be the most effective tape for securing the cannula to the PVC model. On the adult forearm Sleek was as effective as Leukoplast. Orientating the tape parallel to the long axis of the cannula and taping the cannula hub-giving set connection both improved the adherence of the cannula. Under the conditions tested, sterile adhesive dressings and tapes were relatively ineffective in securing the cannulae.

LATWAK: Impact Test to Obtain Pile Lateral Static Stiffness

The LATWAK test consists of hitting in the horizontal direction the side of a pile on which a horizontal velocity transducer is attached. The blow is delivered with a sledge hammer equipped with a dynamic force transducer. The force time signal from the hammer (input) and the velocity time signal from the pile (output) are recorded during the impact. The experimental mobility curve is obtained as a function of frequency by calculating the modulus of the complex valued ratio of velocity over force using Discrete Fourier Transforms. Theoretically it is assumed that the pile is an elastic member with mass and that the soil can be represented by linear springs and viscous damping. The problem of the steady state forced vibration of the pile in such a soil is solved mathematically. It leads to the theoretical mobility curve for the pile-soil system. The experimental mobility curve obtained in the LATWAK test on the pile is matched with the theoretical mobility curve. A system identification technique is used t...

A traceable dynamic force transducer

A traceable dynamic force measurement system built at the National Physical Laboratory (NPL) for the frequency range of 0.1 to 100 Hz, is described.

On the use of quartz crystals in dynamic stress and force transducers

An important consideration in determining the veracity of data obtained from X-cut quartz crystals used to measure nominally one-dimensional load states is the role which spatial nonuniformity of the normal stress distribution on the crystal will play in determining the transducer output signal. This role was found to be minor both for crystals located 0.74 mm below a surface subjected to impact by spherical steel strikers and for 25.4-mm-diam crystals positioned in a 12.7-mm-diam Hopkinson bar through which a longitudinal wave was travelling.