Levitation Mass Method Research Articles

Development of a New Data Processing System for Increasing the Accuracy of a Levitation Mass Method (LMM) based Measurement

Levitation Mass Method (LMM) is the method as a material tester to evaluate the mechanical response of general objects against impact forces. In this method, a mass is made to collide with material to be tested and the impulse, i.e. the time integration of the impact force, is measured highly accurately as a change in momentum of the mass. To realize linear motion with sufficiently small friction acting on the mass, a pneumatic linear bearing is used. The inertial force acting on the mass is calculated from the velocity of the mass. The velocity is determined, highly accurately by means of measuring the Doppler shift frequency of a laser light beam reflected on the mass using an optical interferometer. To determine the Doppler frequency shift for LMM data processing, the method for estimating the frequency is necessary. Several methods have been developed to estimate the frequency for the LMM data processing with high accuracy, i.e. Zero-Crossing Average Method (ZAM), Zero-Crossing Fitting Method (ZFM), Sine Wave Fitting, and Zero-crossing Sine Wave Fitting. All methods realized using the zero-crossing point of the waveform obtained from the digitizer. A better method to estimate frequency on the digitized waveform will enable higher precision for a more accurate result. In this research, a new method that can improve the accuracy has been developed. The program was developed using data segmentation to obtain the frequency of the digitized waveforms. The developed program has the smallest error ( 1,98 X 10^-10 for N= 200) compare to other methods (2,31 X 10-3 for ZAM; 1,10X10-3 for ZFM; and 8,69 X10-4 for Zero-crossing Sine Wave Fitting).

Effect of Mass Added to a Force Transducer on the Dynamic-Force Correction Method

Dynamic-error caused by the mass attached to the sensing part of a force transducer is experimentally investigated using the Levitation Mass Method (LMM), in which the dynamic-force applied to the force transducer is measured based on the definition of force, i.e. the product of mass and acceleration. It is experimentally proved that the change in the dynamic correction coefficient (DCC) is proportional to the additional mass as expected by the theory. The effective mass and the effective spring constant of the transducer with the additional mass are estimated from the experimental result. It is experimentally proved that the DCC for the transducer with the additional mass can be calculated using the estimated properties, i.e. the effective mass and the effective spring constant, and the dynamic-error can be corrected with the calculated DCC.

New technique for dynamic calibration of a force transducer using a drop ball tester

A method to calibrate a force transducer under dynamic conditions has been developed. Calibration is achieved by a drop ball test based on the levitation mass method using an optical interferometer. From the conducted experiments, the output of the force transducer could be corrected, in line with the previous paper written by the authors. Moreover, the dynamic correction coefficient could be obtained by this method, even without an expensive air slider, which was used in our previous method. The calibration performed by the developed method proved to be very significant in correcting the dynamic force measurement error by the force transducer with a very small root mean square (RMS) error compared to the results of measurement in the absence of calibration and dynamic correction. The RMS error of measurement result by the force transducer with dynamic calibration and dynamic correction using the developed method is about 1.6 N. This error is equivalent to 1% of the maximum force applied to the force transducer, which is approximately 160 N.

Corrigendum

Wang Y, Shu D, Fujii Y, et al. Comparison between numerical analysis and the levitation mass method measurement test of a spherical structure early impacting water. Advances in Mechanical Engineering 2018; 10(1): 1–15. DOI: 10.1177/1687814017748076 In the above-referenced article, the names of the third, fourth, fifth, and sixth authors were displayed incorrectly. The full author list should appear as follows: Yonghu Wang, Dongwei Shu, Yusaku Fujii, Akihiro Takita, Tsuneaki Ishima and Ryosuke Araki.

Comparison between numerical analysis and the levitation mass method measurement test of a spherical structure early impacting water

In order to precisely measure water impact loads of a spherical structure vertically dropping onto a calm water surface, a new validity check of the analysis using the levitation mass method experiment is proposed. The main feature of levitation mass method experiment is to obtain a better estimation of early water impact loads through the application of Doppler effect. Experimental results of different heights are verified based on the Assessment Index and are in comparison with the classical experimental data for validation purpose. It shows that the levitation mass method measurement is useful and effective to obtain the water impact loads for the crashworthiness analysis. Besides, early water impact hydrodynamic behaviors are simulated based on the nonlinear explicit finite element method, together with application of a multi-material arbitrary Lagrangian–Eulerian solver. A penalty coupling algorithm is utilized to realize fluid–structure interaction between the spherical body and fluids. Convergence studies are performed to construct the proper finite element model by the comparison with experimental results, where mesh sensitivity, contact stiffness, and time-step size parametric studies are thoroughly investigated. The comparisons between experimental and numerical results show good consistency by the prediction of the water impact coefficients on the structure.

Precision Mechanical Measurement Using the Levitation Mass Method (LMM)

The present status and the future prospects of a method for precision mass and force measurement, the levitation mass method (LMM), are reviewed. The LMM has been proposed and improved by the authors. In the LMM, the inertial force of a mass levitated using a pneumatic linear bearing is used as the reference force applied to the objects under test, such as force transducers, materials or structures. The inertial force of the levitated mass is measured using an optical interferometer. The three typical applications of the LMM, i.e. the dynamic force calibration, the micro force material tester and the space scale, are reviewed in this paper.

Impact Response Measurement of Bamboo Shinai and CFRP Shinai

Bamboo shinai is a practice sword for kendo which is the Japanese traditional fencing. The effectiveness of the shock absorption of the bamboo shinai has been shown in our previous study. Although shinai is usually made of bamboo, it is also made of carbon fiber reinforced plastic (CFRP). The impact response of bamboo shinai and CFRP shinai is compared. As a result, the difference of peak value of impact force between bamboo shinai and CFRP shinai against similar initial velocity is small. Impact response measurement of each shinai has been carried out using the Levitation Mass Method (LMM) which has been proposed by us. In this method, a mass, which is levitated with a pneumatic linear bearing and hence affected by negligible friction, is made to collide with a shinai under test. Because bamboo is natual product, resource of suitable bamboos for shinai is limited. On the other hand, carbon-fiber-reinforced-plastic (CFRP) can be designed to be suitable for a shinai, which has a fixed shock absorption characteristic for an application to the structure of robot arms. Therefore, if the shock absorption characteristic of CFRP shinai is the same as that of bamboo shinai, CFRP shinai is more suitable for the structure of robot arms.

Impact Response Measurement of a Bamboo Sword “Shinai”

Impact response of a bamboo sword “Shinai” which is a practice sword used in a Japanese traditional fencing and has an unique and simple structure of light-weight bamboo plates for moderating the impact force to the human body, is accurately measured by means of modifying the Levitation Mass Method (LMM). In the method, a mass, which is levitated with an aerostatic linear bearing and hence encounters negligible friction, is made to collide with a bamboo sword under test. During the collision, the Doppler shift frequency of a laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, position, acceleration, and inertial force of the mass are calculated from the measured time-varying Doppler shift frequency. The measurement results show that “Shinai” considerably moderates the impact force and its unique structure might be effective for robotics and automobiles to moderate the impact force acting to the human body in the case of accidents.

Impact Response Measurement of Contact Lenses

Impact response of contact lenses is measured using the Levitation Mass Method (LMM). In the LMM, a small mass collides with contact lenses and the impact force is measured with high accuracy as the inertial force of the moving part. A pneumatic linear bearing is used to achieve linear motion with sufficiently small friction acting on the moving part. Hysteresis loop and consumed energy as mechanical characteristics of contact lenses are also calculated.

Frictional Characteristics Measurement of a Ceramic Aerostatic Linear Bearing

The resultant force acting on the moving part of the ceramic aerostatic linear bearing is measured highly accurately as the inertial force of the moving part of the bearing by means of the levitation mass method (LMM). The measurement results of the ceramic aerostatic linear bearing and metal aerostatic linear bearing of different mass are compared. The regression equation of the ceramic aerostatic linear bearing and metal aerostatic linear bearing are calculated. The ceramic linear bearing and metal linear bearing have extremely small frictional force.

Improvement of Software for Dynamic Force Correction of Force Transducers

Software for correcting the dynamic error of the force sensor in the impact force measurement, which uses an output signal of the sensor itself, has been improved. The software corrects the output waveform of the sensor by using the output waveform itself and estimates its uncertainty. In the experiment, the dynamic error of the sensor is evaluated using the Levitation Mass Method (LMM). In the LMM, the impact force applied to the sensor is accurately determined as an inertial force of the moving part of the aerostatic linear bearing. The parameter for correcting the dynamic error is determined from the results of one set of impact measurements of the sensor. Then the validity of the parameter is evaluated by using the results of measurements of the sensor. The uncertainty of the un-corrected force and that of the corrected force are also estimated. In the previous version of the software, the user input “input text-file” which contains force that is calculated based on the static calibration results. On the other hand, the output signal from the sensor is not force. This time, the software has been modified to load input text-file which contains the output signal from the sensor.

New Method for Evaluating Dynamic Characteristics of Cantilever Spring of Vibration Sensor

Copper beryllium (CuBe)is materials that are widely used for mechanical applications. In this paper,the use of copper beryllium for cantilever spring of a vibration sensor will beinformed. Cantilever spring plays important role in a vibration sensor, becauseit transfers vibration energy of the measured system into the sensor.Therefore, it is important to know the dynamic characteristics of thecantilever spring. An optical method, called Levitation Mass Method (LMM), isproposed to measure the dynamic characteristic of the cantilever. In themethod, the force of cantilever spring is measured as the inertial force workedon a mass. A pneumatic linear bearing is used to realize a linear motion withsufficiently small friction acting on the mass, i.e., the moving part of thelinear bearing. The inertial force acting on the mass is calculated from thevelocity of the mass, and the velocity is determined highly accurately by meansof measuring the Doppler shift frequency of the laser light beam reflecting onthe mass using an optical interferometer. It is shown that the proposed methodshows the dynamic characteristic of the vibration sensor well.

Software for correcting the dynamic error of force transducers.

Software which corrects the dynamic error of force transducers in impact force measurements using their own output signal has been developed. The software corrects the output waveform of the transducers using the output waveform itself, estimates its uncertainty and displays the results. In the experiment, the dynamic error of three transducers of the same model are evaluated using the Levitation Mass Method (LMM), in which the impact forces applied to the transducers are accurately determined as the inertial force of the moving part of the aerostatic linear bearing. The parameters for correcting the dynamic error are determined from the results of one set of impact measurements of one transducer. Then, the validity of the obtained parameters is evaluated using the results of the other sets of measurements of all the three transducers. The uncertainties in the uncorrected force and those in the corrected force are also estimated. If manufacturers determine the correction parameters for each model using the proposed method, and provide the software with the parameters corresponding to each model, then users can obtain the waveform corrected against dynamic error and its uncertainty. The present status and the future prospects of the developed software are discussed in this paper.

Determination of Reaction Force in a Toothbrush Tuft using Levitation Mass Method (LMM)

The reaction force of a single toothbrush tuft (group of bristles) against the colliding ogject is measured using the Levitation Mass Method (LMM). In the experiment, a metal object with a rounded tip is made to collide with the surface of the tuft. The metal object, i.e. the moving part of the aerostatic linear bearing, moves horizontally with a suffiently small friction. Since the frictional force acting to the moving part is very small, the inertial force of the moving part is equal to the dynamic reaction force of the tuft. The tested toothbrush tuft used is made of nylon material with 25 bristles, has a length of 10 mm and a diameter of 0.2 mm. The velocity of the moving part is measured precisely from the beat frequency and the rest frequency using an optical interferometer. After getting the velocity, the other mechanical quantities, such as position, acceleration, and inertial force. are calculated numerically. The mechanical friction inside the bearing is determined using the same instrumentation with an average value of 2.05 mN.

The Dynamic Characteristics of Gelled Food Materials against Small Impact Force

The dynamic mechanical characteristics against small impact force of konjak were measured in thisstudy. Konjak is one of the popular and healthy Japanese foods and is the Gunma prefectural specialty. Thereare many studies discussing the sensory characteristics of food materials, however few of them measure thecharacteristics quantitatively and accurately. If it has been done, the detail of sensory properties will be able to bediscussed. We have done the experience and shown the characteristics. Konjak is flexible and slimy food material.We thought konjak is like rubbers and it can be measured the response against small impact force. To measurethe precise dynamic mechanical force, the levitation mass method (LMM) is used. In LMM, a pneumatic linearbearing is used to reduce friction to almost zero, and an optical interferometer is used. The acceleration, velocity,position, and inertial force of the mass are calculated from the measured time-varying frequency due to DopplerEffect, which can be calculated by using the zero-crossing fitting method (ZFM). LMM had been used to onlymeasure the dynamic forces acting on the mass before, but we utilized it to test the mechanical characteristics offood materials. Konjak has the characteristics of viscoelasticity. We have revealed the quantitative and logicalcharacteristics of konjak.

Damping response analysis for a structure connected with a nonlinear complex spring and application for a finger protected by absorbers under impact forces

This paper describes the dynamic response of a finger protected by a pair of viscoelastic absorbers under impact forces. The restoring forces of the finger and the absorbers are measured using the levitation mass method proposed by Fujii. In this study, we carry out numerical analysis of the dynamic response of a finger protected by absorbers under the same conditions as in the experiment. The absorbers and the finger are modeled by nonlinear concentrated springs using the power series of the elongations. Nonlinear complex spring constants are used to represent the changes in hysteresis as elongation progresses. This nonlinear spring is connected to a levitated block, which is modeled by three-dimensional finite elements. The experimental data are compared with the data calculated using our proposed finite element method.

Correction method for force transducers on dynamic condition with or without the Levitation Mass Method (LMM)

In this paper, calibration method for force transducers on dynamic force condition with or without the levitation mass method (LMM) is reviewed. At first, a brief review of the LMM is described. Secondly, a correction method for force transducer in dynamic force measurement using the LMM is introduced. Finally, the self-correction method for force transducer is shown with results. The most of the dynamic error of an S-shaped strain gauge transducer is effect of inertial mass of the transducer. By using the LMM, the relations between the dynamic error and transducer's output are investigated and a correction parameter is calculated. Without the LMM, the force measured by the transducer can be corrected by use of the correction parameter.

244 直列非線形複素ばねを有する弾性体のFEM応答解析 : 緩衝材で保護された生体の衝撃応答

This paper deals with dynamic responses of a finger protected by absorbers under impact forces. Restoring forces of a finger and absorbers are measured using Levitation Mass Method proposed by Fujii. In this paper, we carry out numerical analysis of dynamic responses for the finger protected by the absorbers under same conditions with the experiment using LMM. The absorbers and the finger are modeled using nonlinear concentrated springs with nonlinear hysteresis. This nonlinear spring is connected to the levitated block, which is modeled by three-dimensional finite elements. The experimental data are compared with the calculated ones using our proposed FEM.

Development of Material Tester Using Pendulum

The requirements for evaluating the mechanical characteristics of materials have increased in the various industrial, research and the applications such as materials testing. Therefore, the authors have proposed a method for measuring force acting a material using pendulum [1]. In the Material tester, the mechanical characteristics of material against small force are measured by means of the pendulum mechanism based on the levitation mass method (LMM) [2,3,4].In the LMM, the Doppler shift frequency is measured for measuring the inertial force. The Doppler shift frequency of a laser beam reflected from the mass is accurately measured by using optical interferometer. The velocity, position, acceleration and inertia force of the mass are calculated from the measured time-varying Doppler shift frequency. Thus, the accurate measure of frequency makes that of force.

Microforce Material Tester Using Small Pendulum II

A method of inexpensive material tester based on the levitation mass method is improved. The tester is composed of an interferometer with Zeeman type two frequency He-Ne laser and a small pendulum as a substitute for a pneumatic linear bearing. As an example of a material tester using the pendulum, which evaluates the mechanical response of general objects against impact forces, is developed. The characteristics of the restoring force are measured under the free-swing condition. To demonstrate the performance of the developed instrument, the viscoelasticity of a gel block under an impact load is evaluated.