Levitation Mass Research Articles

Dynamic analysis by FEM for a measurement system to observe viscoelasticity using levitation mass method

Dynamic analysis was carried out for a novel measurement system to obtain material viscoelasticity using the levitation mass method [Fujii and Yamaguchi, Rev Sci Instrum 75-71:119–123, 2004; Yamaguchi et al., Mech Syst Signal Process 20:1905–1922, 2006; Fujii and Yamaguchi, J Mater Sci 40-18:4785–4790, 2005], which was proposed by Fujii. For this measurement system, a viscoelastic specimen is attached to a block, which is levitated due to a pneumatic linear bearing. Impact load is applied to the levitated block, and then the movement of the block is measured by a laser interferometer. By following our proposed numerical procedure using nonlinear finite element method in our previous paper [Yamaguchi et al., Mech Syst Signal Process 20:1905–1922, 2006], the dynamic properties of the measurement system were investigated. Time histories of velocity for the block were simulated. These results were compared with experimental results. Furthermore, undesirable dynamic components for the measurement system were evaluated using the numerical model by varying pulse width of the input load.

振子機構を用いた材料試験

A practical and low cost instrument for accurately measuring small impact force is proposed. In the various industrial and research applications such as materials testing, the requirements for evaluating the mechanical characteristics of materials and structure have increased. In this paper, the mechanical characteristics of material against small impact force are determined by means of the newly developed pendulum mechanism that based on the levitation mass method (LMM). In this method, a pendulum mechanism is used as a substitute for expensive pneumatic linear bearing. A mass that is suspended using a newly developed pendulum mechanism with negligible friction and a stable restoring force, is made to collide with the object under test. A pendulum mechanism with 6 wires is used to realize the static motion of mass that is the swing part of pendulum. Mass is suspended by 3 triangles formed using 6 wires. The Doppler frequency shift of a laser beam reflecting on the mass is highly accurately measured using an optical interferometer. The velocity, position, acceleration and inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. The performance of the proposed method is demonstrated by evaluating the viscoelasticity (i.e. hysteresis curve between force and displacement, curve between force and velocity) of a small silicon-gel block under an impact load.

Evaluation of mechanical response of human palm to small impact force

AbstractA method of measuring the mechanical characteristics of the human palm for a small impact force is proposed. In the field of bioengineering, accurate quantitative analysis of the mechanical characteristics of the human body is required. In this paper, the mechanical characteristics of the human palm for a small impact force are determined by means of the Levitation Mass Method (LMM). The LMM is a method for accurately measuring varying forces without the use of force transducers. The mechanical characteristics of the human palm were measured with high accuracy by means of an instrument based on the LMM. In the measurement, the mass, which is the moving part of an aerostatic linear bearing, is made to collide with a human palm under test. During the collision measurement, only the Doppler shift frequency of the laser light reflecting on the mass is measured with high accuracy, using an optical interferometer. The velocity, position, acceleration, and inertial force of the mass are calculated from the measured time‐varying Doppler shift. The mechanical response of the human palm to the small impact load is also characterized from the measured data. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(1): 18–23, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10002

Material Tester Using a Controlled Oscillator and an Inertial Mass

In this paper, a controlled oscillation using the levitation mass method (LMM) for material with nonlinear viscoelasticity is proposed. Since LMM is a very accurate and efficient method of measuring a varying force, it has a possibility to apply to the material tester. For LMM, system identification process is introduced to grasp the nonlinear components of the restoring force. The process consists of the experiment and frequency analysis for higher modes which originate for the nonlinear restoring force. The input signal is then derived based on the identification results. By adding the proposed identification process to LMM, the arbitrary waveform of the force can be investigated even in the open-loop excitation. The effectiveness of the proposed oscillation method is verified through the LMM-based experiments.

Loss measurements on superconducting Nb by a cryogenic dual compensated calorimeter for the implementation of the kilogram standard by the levitation mass method

A cryogenic dual compensated calorimeter was constructed for energy loss measurements in superconducting materials. The losses induced by slowly varying periodic magnetic fields (amplitudes <50 mT) in field-generating coils fabricated from different niobium wires were at the level of 500 nJ/cycle. Measurable losses are caused by incomplete Meissner effect in tested superconducting materials. The results of the study show the difficulties and limitations in the implementation of the kilogram standard using the ‘superconducting magnetic levitation mass’ method.

Method of generating and measuring static small force using down-slope component of gravity

A method of generating and measuring static small forces at the micro-Newton level is proposed. In the method, the down-slope component of gravity acting on a mass on an inclined plane is used as a static force. To realize a linear motion of the mass with a small friction, an aerostatic linear bearing is used. The forces acting on the mass, such as the down-slope component of gravity and the dynamic frictional force, are determined by the levitation mass method. In an experiment, a static small force of approximately 183 microN is generated and measured with a standard uncertainty of approximately 2 microN.

Microforce materials tester based on the levitation mass method

The present status and the future prospects of the levitation mass method (LMM), which has been proposed and developed by the author as a precision mechanical measurement method and has been applied to dynamic force calibration and material testing, are reviewed. 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. As an example, mechanical responses of a gel block against small impact loads were evaluated using the LMM.

Impact force measurement of an actuator arm of a hard disk drive

Impact forces of an actuator arm of a hard disk drive (HDD) are measured by means of modifying the levitation mass method (LMM) whose basic concept was proposed by the first author. In the LMM, force is measured as the inertial force of a mass levitated with sufficiently small friction using an aerostatic linear bearing. The Doppler frequency shift of the laser beam reflecting from the mass is accurately calculated from the waveform recorded using a digitizer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. In the experiments, the mechanical response of an actuator arm of a HDD against an impact load and the inertial force of the actuator arm in free oscillation are measured. The importance and the problems concerning the present knowledge on the impact force of an actuator arm of a HDD are also discussed.

Evaluation of Mechanical Response of Human Palm to Small Impact Force

Method of measuring mechanical characteristics of human palm against small impact force is proposed. Medical doctors qualitatively evaluate the mechanical characteristics of the human body by manipulation and percussion. In the field of bioengineering, accurate quantitative analysis of the mechanical characteristics of the human body is required. In this paper, the mechanical characteristics of a human palm against small impact force are determined by means of the Levitation Mass Method (LMM). The LMM is a method for accurately measuring varying forces without the use of force transducers. Mechanical characteristics of a human palm were measured with high accuracy by means of an instrument based on the LMM. In the measurement, the mass, that is a moving part of an aerostatic linear bearing (a hydrostatic linear air bearing, an externally pressurized air bearing), is made to collide with a human palm under test. During the collision measurement, only the Doppler shift frequency of the laser light reflecting on the mass is highly 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. The mechanical response of a human palm against small impact loading is also characterized from the measured data.

Impact response measurement of an accelerometer

The zero-crossing averaging method (ZAM), which was originally developed for improving the measurement accuracy of force by means of the levitation mass method (LMM), is applied for evaluating the impact response of accelerometers. In the ZAM, the moment of the zero-crossing point is calculated as the average of many adjacent zero-crossing points and then the frequency is calculated. In this paper, the impulse response of an accelerometer is evaluated with high resolution and high sampling rate by means of the ZAM. The present status and future prospects of the ZAM as a method for use in calibration of accelerometers are discussed.

Method of Evaluating the Force Controllability of the Human Finger

The ability of the human finger to control force against an impact load is determined by means of a novel practical method, which is a variation of the levitation mass method. In the method, a mass that is levitated with a pneumatic linear bearing and hence encounters negligible friction is made to collide with an object under test. During the collision, the Doppler frequency shift 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. The method is characterized by the fact that preparation for the test is easy, and measurement accuracy is high. The importance of visual information is also determined by means of conducting the tests under conditions in which the subject's eyes are either opened or closed

Measurement of the electrical and mechanical responses of a force transducer against impact forces

A method for measuring the electrical and mechanical responses of force transducers to impact loads is proposed. The levitation mass method (LMM) is used to generate and measure the reference impact force used. In the LMM, a mass that is levitated using an aerostatic linear bearing (and hence encounters negligible friction) is made to collide with the force transducer under test, and the force acting on the mass is measured using an optical interferometer. The electrical response is evaluated by comparing the output signal of the force transducer with the inertial force of the mass as measured using the optical interferometer. Simultaneously, the mechanical response is evaluated by comparing the displacement of the sensing point of the transducer, which is measured using another optical interferometer, with the inertial force of the mass. To demonstrate the efficiency of the proposed method, the impact responses of a force transducer are accurately determined.

Pendulum for precision force measurement

A pendulum and a method for correcting the restoring force of the pendulum are proposed for realizing an instrument based on the levitation mass method without the use of pneumatic linear bearings. As an example 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 accurately determined using the same instrument under the free-swing condition without the object under test. To demonstrate the high performance of the developed instrument, the impact response of a gel block is accurately determined. The possible applications of the developed method are discussed.

404 外部インパクトを受ける生体の数値解析用力学モデルの同定

This report deals with nonlinear dynamics of human arms that receives impact force by a rigid object. The object having initial velocities collided with the lived human arms. And the relevant restoring forces were measured using Levitation Mass Method proposed by Fujii. A nonlinear dynamic model of this system was identified for numerical simulation to represent the experimental data (e.g. hysteresis curves, time histories of velocities). Effects of contraction/relaxation of the muscular on the mechanical properties of human arms are accurately investigated.

FEA for vibrated structures with non-linear concentrated spring having hysteresis

This paper describes vibration analysis using finite element method for structures connected with non-linear concentrated spring. The restoring force of the spring is assumed to be expressed as power series of displacement. The restoring force also has linear hysteresis damping. Thus, complex stiffness is introduced for the linear component of the restoring force. Finite element for the spring is expressed and is connected to viscoelastic structures modelled by linear solid finite elements. Further, the discretised equations in physical coordinate are transformed into the non-linear ordinary coupled equations using normal coordinate corresponding to linear natural modes. Note that modal damping is also transformed in this procedure. The transformed equations were integrated numerically in fairly small degree of freedom. This transformation yields computation efficiency. Effectiveness of this analysis was shown for a basic block-spring model. And then, this numerical method was applied for a sophisticated measurement system named as the Levitation Mass Method proposed by Fujii for evaluating viscoelastic parameters.

Method for evaluating mechanical response of human skin against micro impact force

Method for evaluating mechanical response of human skin against micro impact force is proposed. The method is a variation of the levitation mass method, which has been proposed and developed by the author. In the method, a mass that is levitated with a pneumatic linear bearing, and hence encounters negligible friction, is made to collide with an object under test, such as a skin of human hand. During the collision the Doppler frequency shift of the laser beam reflecting from the mass is accurately measured using an optical interferometer. The velocity, the position, the acceleration and the inertial force of the mass are calculated from the measured time-varying Doppler frequency shift. The method is characterized by the fact that preparation of the test is very easy and the testing time is very short.

Non-contacting conveyance of a steel plate using electromagnetic force by transverse flux linear motors

To improve the quality of products in a steel making process, the realization of a non-contacting conveyance of a steel plate has been expected. To make the total system simple, we proposed a combined lift and propulsion system by transverse flux linear induction motors. By feeding the DC biased AC to the transverse flux linear induction motor, it is possible to realize an efficient combined lift and propulsion system with a simple structure. After showing the peculiarities of the system, conveyance experiments of a steel plate are carried out. In these experiments, the equivalent mass estimation method in which the levitation mass is estimated from the gap error is applied and the effect of the method is also shown.

A high horizontal stiffness sensor as used in gravimetry

For the first time a gravity meter with a high horizontal stiffness (1000 N/m), dynamic range 10 6–10 7 and sensitivity of about ∼10 −11 g/Hz has been constructed. A position of levitation mass (LM) suspended in a magnetic field generating by two short-circuited coils is determinated by means of the cylindrical microwave cavity resonator. The gravity meter design allows for the gravity meter sensitivity variations and linear relation of the vertical stiffness and LM position (i.e. k(z)=const). The block diagrams of the gravity meter and test set-up are given as well as the techniques for measuring the gravity meter characteristics and results of its testing.