Electromagnetic Force Compensation Research Articles

Force-displacement measurement system with electromagnetic and electrostatic force compensation principles

Zusammenfassung Der Artikel präsentiert eine modifizierte Version des Kraft-Weg-Messgeräts, das zur Kalibrierung der Steifigkeiten von MEMS und Cantilevern sowie der von ihnen erzeugten Kräfte im Bereich von 10 nN bis 2mN verwendet wird. Weiterhin werden verbesserte Ergebnisse für die Kalibrierung von Kraftkonstanten und der Steifigkeit weicher Cantilever (Kraft bis 300 nN) mit einer erweiterten relativen Unsicherheit von 0,46 % gezeigt.

Nonlinear electromagnetic force analysis and compensation control of electromagnetic linear actuator

Nonlinear electromagnetic force is a common phenomenon in electromagnetic linear actuators (EMLA). This nonlinearity limits the application in high-precision control systems. For facilitating the controller design, the influencing factors of nonlinear electromagnetic force were analyzed, and the quadratic polynomial with unknown weights was designed to approximate the nonlinear relationship among electromagnetic force, excitation current and displacement. An adaptive integral robust control algorithm based on electromagnetic force compensation (AIRC-FC) was designed, which combined the adaptive control law of electromagnetic force nonlinear compensation, stable feedback and error signal continuous integral robust control. The tracking performance and the adaptability of the EMLA with and without compensation control were analyzed under different loads. The results show that AIRC-FC improve the tracking performance of the EMLA effectively, and maintain high control accuracy under different loads.

Stiffness Considerations for a MEMS-Based Weighing Cell

In this paper, a miniaturized weighing cell that is based on a micro-electro-mechanical-system (MEMS) is discussed. The MEMS-based weighing cell is inspired by macroscopic electromagnetic force compensation (EMFC) weighing cells and one of the crucial system parameters, the stiffness, is analyzed. The system stiffness in the direction of motion is first analytically evaluated using a rigid body approach and then also numerically modeled using the finite element method for comparison purposes. First prototypes of MEMS-based weighing cells were successfully microfabricated and the occurring fabrication-based system characteristics were considered in the overall system evaluation. The stiffness of the MEMS-based weighing cells was experimentally determined by using a static approach based on force-displacement measurements. Considering the geometry parameters of the microfabricated weighing cells, the measured stiffness values fit to the calculated stiffness values with a deviation from -6.7 to 3.8% depending on the microsystem under test. Based on our results, we demonstrate that MEMS-based weighing cells can be successfully fabricated with the proposed process and in principle be used for high-precision force measurements in the future. Nevertheless, improved system designs and read-out strategies are still required.

Microcantilever-based current balance for precise measurement of the photon force

We present a method for the quantitative determination of the photon force (PF)—the force generated by the radiation pressure of photons reflected from the surface. We propose an experimental setup integrating innovative microelectromechanical system (MEMS) optimized for the detection of photon force (pfMEMS). An active microcantilever was used as the force detector, while the measurement was conducted in a closed-loop setup with electromagnetic force compensation. In opposition to our previous works, this measurement method provides quantitative not qualitative assessment of PF interaction. Final current-balance setup is suitable for light sources from tens of microwatts to few watts. In our article, we present the results of the performed experiments, in which we measured the PF interactions in the range up to 67.5 pN with resolution of 30 fN in the static measurement.

Research on a watt balance experimental model based on a monolithic weighing converter

This research describes the main systems and nodes of the watt balance experimental model created at the D. I. Mendeleev Institute for Metrology. It presents the results of studies of metrological characteristics of the watt balance model arrangement component part that operate on the principle of electromagnetic force compensation with a monolithic weight converter and a lower suspension. The studies were conducted with the use of standards traceable to the state primary standard of the unit of mass – kilogram. The research provides the information on the joint efforts of national metrological institutes aimed at the gradual spread of the unit of mass traceable to the fundamental physical constant – Planck's constant, the fixation of the numerical value of which was adopted at the 26th General Conference on Weights and Measures in Paris on May 20, 2019. Here the necessity of carrying out work to maintain the equivalence of the national standard of the unit of mass to the best national standards of other countries is reflected, because it is also the required factor for international recognition of the measuring capabilities of the metrological institutes of Russian Federation. The findings of the metrological characteristics of the watt balance experimental model studies showed potential possibility of using the design solutions applied in this experimental model for creating the measurement standard in the Russian Federation to implement a new definition of the kilogram.

Novel Multi-Electromagnetic-Force-Compensation Weighing Cell With Axis-Symmetric Structure

A Kibble balance for the realization of a redefined kilogram requires an ultraprecision weighing cell for measuring the difference between gravitational force and electromagnetic force. In this article, we propose a novel electromagnetic force compensation weighing cell for the Kibble balance at the Korea Research Institute of Standards and Science. To be compatible with the Kibble balance, the proposed weighing cell is designed axial symmetrically using a triple compound guide mechanism and a trilever mechanism based on a compliant mechanism. The weighing cell employs three independent mass measurement units to measure the test mass by dividing it, thereby improving the structural stability, weighing accuracy, and ground-tilt response. For a 1-kg test mass, the repeatability of the weighing cell was 0.74 mg in the air; it was improved to 0.20 mg when the zero-point drift was compensated. Finally, the experimental ground-tilt response of the weighing cell suggested that the ground-tilt angle can be estimated by observing the change in the compensating force of each mass measurement unit.

Deploying the high-power pulsed lasers in precision force metrology – Towards SI traceable and practical force quantization by photon momentum

Abstract Design and operational performance of table-top measurement apparatus is presented towards direct Planck constant traceable high accuracy and high precision small forces and optical power measurements within the SI unit system. Electromagnetic force compensation weighing balances, highly reflective mirrors and high-energy pulsed laser unit (static average power 20 W) are tailored together with a specially developed opto-electro-mechanical measurement infrastructure for cross-mapping the scale-systems of two different precision small force measurement methods. One of these methods obtains the force measurements by a state-of-the-art classical kinematic system employing the partial use of Kibble balance principle in the range of 10 nN to 4000 nN to be compared with forces generated due to quantum-mechanical effect namely the transfer of the momentum of photons from a macroscopic object. Detailed overview of the adapted measurement methodology, the static and the limits of dynamic measurement, the metrological traceability routes of the measurement parameters, quantities and their measurement uncertainties, parametric estimation of up (down)-scaling perspectives of the measurements are presented with respect to the state-of-the-art measurement principles and standard procedures within the newly redefined International System of Units (SI).

Adjustment concept for compensating for stiffness and tilt sensitivity of a novel monolithic electromagnetic force compensation (EMFC) weighing cell

Abstract. This paper describes the new adjustment concept of novel planar, monolithic, high-precision electromagnetic force compensation weighing cells. The concept allows the stiffness and the tilt sensitivity of the compliant mechanisms that are dependent on the nominal load on the weighing pan to be adjusted to an optimum. The new mechanism is set up and adjusted according to the developed mechanical model. For evaluation of the concept the system is tested on a high-precision tilt table and under high vacuum conditions in the environment of a commercially available mass comparator.

전자기력 보상 방식 고정밀 저울을 위한 광학식 위치 센서 개발

The electromagnetic force compensation (EMFC) measurement principle has been widely adopted in the high-precision mass metrology system due to its sensitive compliant mechanism and nanometer level position sensor. In EMFC, an electromagnetic actuator balances the gravitational weight to maintain zero (or Null) position by feedback control using a position sensor, and the weight is calculated from the current applied to the actuator. Thus, a position sensor in the EMFC system should measure the null position accurately with high sensitivity and resolution. The position sensor commonly used in EMFC balance is an optical sensor that measures the displacement of EMFC balance from the intensity of light coming through a slit using a two-segment photodiode. This paper analyzed the characteristics of an optical position sensor for EMFC balance through parametric analysis using the Fresnel diffraction model. We also evaluated the performance of the sensor and confirmed the feasibility from weighing performance of the balance prototype. Normalized sensitivity of the sensor was 0.04237 μm<SUP>-1</SUP> and measured resolution was 1.09 nm. The weighing repeatability with our optical position sensor was 4.83 mg (1σ) at 10 g measurement, which was 3 times better than the repeatability with an alternative commercial sensor.

Revisiting the limits of photon momentum based optical power measurement method, employing the case of multi-reflected laser beam

In this work, we review the viability and precision of the photon-momentum-based optical power measurement method that employs an amplification effect caused by a multi-reflected laser beam trapped in an optical cavity. Measuring the total momentum transfer of the absorbed and re-emitted photons from a highly reflective surface (reflection of the laser beam from an optical mirror) as a force provides the possibility of measuring the optical power with direct traceability to SI units. Trial measurements were performed at two different metrology laboratories: the laboratory for mass/force at the Technical University of Ilmenau, and the clean room laser radiometry laboratory at PTB, with a portable force measurement setup consisting of two electromagnetic force compensation balances. We compared the results of the optical power measurements performed with the force measurement setup, via the photon-momentum-based method, with those performed using a calibrated reference standard detector traceable to PTB’s primary standard for optical power, the cryogenic radiometer. The comparison was carried out for an optical power range between 1 W and 10 W at a wavelength of 532 nm, which corresponds to a force of approximately 2000 nN at the upper limit, yielding approximately 2.3% relative standard uncertainty in the case of 33 reflections. Thus, conflating the high-precision force metrology technique at μN to nN levels with the optical setup required to achieve specular multi-reflection configuration of the laser beam, where a macroscopic optical cavity with ultra-high reflective mirrors (>99.995%) can adjustably be suspended from the force sensors, depending on required geometry of reflections, we show that the uncertainty of the optical power measurements upon further increase of the nominally applied optical power, the number of laser beam reflections, or the reflectivity coefficient of the mirrors can be markedly reduced.

Investigations on nonlinear deformation phenomena in a force calibration system

Previous investigations show, in force calibration and measurement systems that are based on electromagnetic force compensation (EMFC), deformations of the flexure hinges can cause significant contributions to the uncertainty of the system. A Simulink model of the Planck-Balance 2 (PB2) is established in MATLAB according to the CAD model. &lt;br /&gt;The results are compared to simplified analytical models and the results obtained from measurement.

Generation of static and dynamic small calibration forces and their measurements by electromagnetic force compensation balance

The paper presents some of the results of the static and dynamic force measurements at 100 nN to sub-10 µN ranges which are generated due the photon-momentum. The force sensor with resolution about 20 nN and operating in differential measurement mode is developed by two electromagnetic force compensation balances. In order to generate these calibration forces, CW lasers with different operational modes, power levels, and wavelengths are used. Multi-reflection configuration of the laser beam inside the macroscopic cavity with highly reflective mirrors are used to test and variate the total amount of the forces.

Electromagnetic force compensation weighing cell with magnetic springs and air bearings

The electromagnetic force compensation (EMFC) principle is a state-of-the-art weighing method for precision mass measurement. In this method, the low stiffness of the flexure-based Roberval guide mechanism and high lever ratio of force transmission contribute to achieving extremely high weighing sensitivity. However, weak damping and the parasitic resonant frequencies of the flexure mechanism lead to a slow settling time after loading a weight. Moreover, the low ruggedness of the flexure mechanism limits the load capacity of the EMFC weighing cell and may result in fatigue failure under repeated loading. In this paper, we propose a novel precision weighing cell with Halbach array magnetic springs and air bearings instead of the flexure mechanism. The magnetic spring is designed for near-zero negative stiffness to increase the system bandwidth, as well as for gravity force compensation ability against deadweights. The air bearings ensure high ruggedness toward parasitic directions with high stiffness in the parasitic direction and a damping effect from the pressurized air film. The stiffness of the fabricated prototype weighing cell is −27.3 N m−1, which is tens of times lower than that of conventional EMFC weighing cells. The weighing repeatability of the weighing cell is 2.35 mg, as measured with a 10 g E2 class test mass, and the settling time within ±2% of its final value is 57 ms in air.

Influences on amplitude estimation using three-parameter sine fitting algorithm in the velocity mode of the Planck-Balance

The Planck-Balance is a table-top version of a Kibble balance. In contrast to many other Kibble balances, the coil is moved sinusoidally and an ac rather than a dc signal is generated in the velocity mode. The three-parameter sine fitting algorithm is applied to estimate the amplitudes of the induced voltage and the coil motion, which are used to determine the force factor Bl of the voice coil of the electromagnetic force compensation balance. However, the three-parameter sine fitting algorithm is not robust against some perturbations, e.g. additive Gaussian white noise, quantization error, harmonic distortion, frequency error and time jitter. These effects have influences on the accuracy of the amplitude estimation. Based on numerical simulations and correlation analyses, the effects of these perturbations are determined. By optimizing measurement and data processing approach, the bias and standard deviation of the estimated amplitude can be effectively reduced, and thus the accuracy of the force factor Bl in the velocity mode can be improved.

Micro-force measurements: a new instrument at METAS

We designed and developed a new instrument for calibrating micro-force sensors. The calibration is traceable to the SI unit of mass and is realized from 1 µN–60 mN by means of electromagnetic force compensation of a balance. The expanded measurement uncertainty of our instrument comprises two contributions, an absolute contribution of 0.13 µN and a relative contribution of 2700 ppm. We verified our instrument in a bilateral comparison between METAS and PTB's instruments for forces from 40 µN up to 20 mN. The degrees of equivalence found by the two institutes are in excellent agreement.

Effect of Electromagnetic Damping on System Performance of Voice-Coil Actuator Applied to Balancing-Type Scale

Changing a time-varying magnetic field induces an electromotive force (EMF) in non-magnetic conductive materials, resulting in an eddy current across the conductor. Thus, electromagnetic damping can be used as viscous damping. This study theoretically and experimentally investigates the electromagnetic damping characteristics of a bobbin-wounded coil with an attached cantilever beam floating over a permanent magnet; the beam is balanced by electromagnetic force compensation (EMFC) instead of applied weight. System identification is carried out for the mass (m), damping coefficient (c), and spring constant (k) values. The presence of a back EMF seen in either conductive or non-conductive material responses in the experiments includes the step input and corresponding output responses to measure the electromagnetic damping force with and without a voice-coil actuator (VCA). The results were validated using bobbins of conductive (aluminum) and non-conductive (plastic) materials. The experimental results for the conductive material show that the electromagnetic damping force is 10 times greater than that of the non-conductive material; the opposite was true in the case without a VCA, where the force was almost zero for the non-conductive material. In conclusion, conductivity is directly related to the electromagnetic damping force, which affects the performance of a VCA.

Lorentz Force Velocimetry using a bulk HTS magnet system

Design of the Lorentz Force Flow-meter (LFF-meter) for weakly-conducting and slow-flowing fluids, e.g., glass melts, place stringent requirements on the magnetic field generation and force measurements. In the scope of the Research Training Group “Lorentz Force Velocimetry (LFV) and Lorentz Force Eddy Current Testing”, a LFF-meter considers: first - a magnetic field source, where NdFeB permanents magnet system is replaced with a bulk high-temperature superconductors (HTS), which promise higher flux densities (> 1 T) and thus higher output force resolution; second - a high-precision force measurements, where electromagnetic force compensation weighing balance (EMFC) setup is replaced with torsion balance based system (TFMS), which claims an increase of the force resolution up to 1 nN. Furthermore, in order to raise the issue of the limiting total mass (which is always an issue for high-precision force measurements), the bulk HTS and TFMS are merged within the cryostat. This work discusses LFV experiments, calculations and numerical simulations, where a magnetic field is generated by the bulk HTS.

Microforce measurements – a new instrument at METAS

METAS designed and developed a new instrument for calibrating microforce sensors in the range of 1 nN to 60 mN. The calibration is realised by means of electromagnetic force compensation of a balance and traceable to the SI unit of mass. The expanded measurement uncertainty (type B) of our measuring apparatus is 0.125 µN (absolute) and 2400 ppm (relative). Our measuring apparatus was verified in a bilateral comparison between METAS and PTB. The degrees of equivalence are in excellent agreement between the two institutes.

A self-calibrating multicomponent force/torque measuring system

A multicomponent self-calibrating force and torque sensor is presented. In this system, the principle of a Kibble balance is adapted for the traceable force and torque measurement in three orthogonal directions. The system has two operating modes: the velocity mode and the force/torque sensing mode. In the velocity mode, the calibration of the sensor is performed, while in the force/torque sensing mode, forces and torques are measured by using the principle of the electromagnetic force compensation. Details about the system are provided, with the main components of the sensor and a description of the operational procedure. A prototype of the system is currently being implemented for measuring forces and torques in a range of ±2 N and ±0.1 N · m respectively. A maximal relative expanded measurement uncertainty (k = 2) of 1 · 10−4 is expected for the force and torque measurements.

Reduction of the effect of floor vibrations in a checkweigher using an electromagnetic force balance system

The objective of this paper is to propose a simple dynamic model of the system and a reduction method for effect of floor vibration. The dynamics of the system with electro-magnetic force compensation is approximated by a mass-spring-damper system, and an equation of motion is also derived. Then, a comparison of a simulation result with a realistic response is carried out. Finally, effects of floor vibration are explored with the model, and the effectiveness of the proposed reduction method is confirmed.