Voice Coil Actuator Research Articles

Design, Development and Implementation of the Position Estimator Algorithm for Harmonic Motion on the XY Flexural Mechanism for High Precision Positioning.

This article presents a novel concept of the position estimator algorithm for voice coil actuators used in precision scanning applications. Here, a voice coil motor was used as an actuator and a sensor using the position estimator algorithm, which was derived from an electro-mechanical model of a voice coil motor. According to the proposed algorithm, the position of coil relative to the fixed magnet position depends on the current drawn, voltage across coil and motor constant of the voice coil motor. This eliminates the use of a sensor that is an integral part of all feedback control systems. Proposed position estimator was experimentally validated for the voice coil actuator in integration with electro-mechanical modeling of the flexural mechanism. The experimental setup consisted of the flexural mechanism, voice coil actuator, current and voltage monitoring circuitry and its interfacing with PC via a dSPACE DS1104 R&D microcontroller board. Theoretical and experimental results revealed successful implementation of the proposed novel algorithm in the feedback control system with positioning resolution of less than ±5 microns at the scanning speed of more than 5 mm/s. Further, proportional-integral-derivative (PID) control strategy was implemented along with developed algorithm to minimize the error. The position determined by the position estimator algorithm has an accuracy of 99.4% for single direction motion with the experimentally observed position at those instantaneous states.

Multi-Degree of Freedom Isolation System With High Frequency Roll-Off for Drone Camera Stabilization

The technological developments in the field of image based sensing have led to a vast growth in the use of drones in various domains. The drone is usually equipped with an image sensor (camera) which collect images over the target area. These images are then post-processed to extract the important information. Efficiency and accuracy of the image based sensing are largely dependent on the captured image quality. Therefore, it is important to prevent the transmission of the drone vibrations to the camera. Most of the current camera mounting systems use passive rubber mounts for isolation. However, these mounts are effective only in vertical direction and essentially adds damping to the system which degrades the performance of the isolation at high frequency. In this paper, a multi-degree of freedom isolation system, based on a Stewart platform configuration, is proposed for drone camera stabilization. The important features of the proposed isolation system are — (i) high frequency roll-off, (ii) no use of flexible joints, (iii) uses non-contact voice coil actuator thus avoiding spurious resonances of the legs, (iv) adjustable stiffness, (v) 3D printed lightweight parts and (vi) centralized control using a single sensor (inertial measurement unit). A prototype of the proposed system has been manufactured and validated experimentally. The proposed isolation system is found to reduce the response of the isolation system near resonance without compromising performance at high frequency. The application of the isolation system can be easily extended to other fields which require high quality image acquisition.

Optimized design of high efficient voice coil actuator in deformable mirror

Optimized design of high efficient voice coil actuator in deformable mirror

System modeling and identification of a balance type checkweigher compensated by voice coil actuator

The aim of this article is to investigate the characteristics of checkweigher which consists of two parts: electrical part (voice coil actuator) and mechanical part (lever-pivot mechanism). Its integrated weighing system simplified m, c, and k model, and system identification is performed through comparison of experimental results and simulated results by Simulink. m and k are attributed to the mechanical part and c is mainly due to the electromagnetic damping of voice coil actuator. Even with a determined voice coil actuator, the damping effect can be adjusted by the relocation of voice coil actuator to improve the performance of checkweigher. The validity of the simplified model is verified by comparing simulation and experimental results.

An in-plane, large-stroke, multipole electromagnetic microactuator realized by guideways stacking mechanism

In the application of cell phone cameras, it is essential to design optical image stabilizers with tiny size, in-plane motion and large stroke. Previously, small sized voice-coil actuators utilizing assembled magnets have been developed to achieve displacements up to 500 μm. Here, we propose a novel MEMS electromagnetic actuator employing a multipole permanent magnet with a finely pitched chessboard pattern and stacked multilayer Si-based guideways, enabling us to obtain a large stroke at low driving voltages. The magnet, which has multiple poles (pole number: 36) and a fine pitch (magnetization pitch: 1 mm), is realized by a combination of laser assisted heating and an external magnetic field, utilized to enhance the magnetic strength. For the support mechanism, stacked multilayered Si-based guideways are adopted to reduce the friction in the driving x- and y-directions and increase the rigidity in the non-driving z-direction. Driving experiments showed the proposed microactuator was capable of both independent 1-DOF motion and simultaneous 2-DOF motion with driving frequencies varying from 1 to 15 Hz. For the independent 1-DOF motion, an approximately straight line trajectory with a maximum stroke of 760 μm was obtained with an AC of 160 mA at a frequency of 1 Hz. In the simultaneous 2-DOF motion, a quasi-circular trajectory with a maximum stroke of 280 μm was achieved when the coil currents were set as follows: frequency of 1 Hz, current amplitude of 120 mA in the x-direction, current amplitude of 140 mA in the y-direction, phase difference of 90°between the x- and y-directions. This promising structure utilizing a finely pitched multipole permanent magnet and stacked multilayered guideways improves the stroke at a low driving voltage and in the small size.

Modeling of a Halbach Array Voice Coil Actuator via Fourier Analysis Based on Equivalent Structure

This paper presents the magnetic field analysis for the double layer Halbach array voice coil actuator (VCA). This VCA is composed of a stator and a mover supported by the flexure-based bearings. The mover gets three coils winded on the skeleton. The stator comprises the closed yoke and the double layer Halbach array permanent magnets (PMs). The boundary condition of the quadrangularly surrounded yoke and the aperiodic distribution of the Halbach array PMs complicate the magnetic analysis process. An equivalent VCA structure that has almost identical air-gap flux distribution to the original one is, therefore, proposed. For the equivalent structure, the boundary condition is simple and the Halbach array PMs is periodically distributed, thus the analysis process of air-gap flux density distribution via Fourier analysis is simplified. The equivalence between these two structures is validated by finite-element analysis (FEA). The analytical model is built by adopting Fourier analysis. The results of the FEA and experiments confirm the correctness of the developed model and prove the feasibility of the analytic method with the equivalent structure.

An Ultralow-Frequency Active Vertical Vibration Isolator With Geometric Antispring Structure for Absolute Gravimetry

The absolute gravimeter plays an important role in metrology, geophysics, and geological exploration. Seismic and environmental vibration has been one of the most serious factors limiting its performance. Consequently, an ultralow-frequency vertical vibration isolator is required to significantly improve its measurement precision. A novel active vertical vibration isolator employing geometric antispring (GAS) structure is proposed in this paper. The payload is supported by a GAS structure fixed on an inner frame, and the inner frame is hung by coil springs from the base. The relative movement of the payload with respect to the inner frame is detected, and the inner frame is driven by a voice coil actuator controlled by a feedback circuit to track the payload’s motion. The new isolator has a compact size, and it can be used for different load ranges by tuning the GAS structure. The practical closed-loop system has a resonant period of 19.2 s, compared with the period of 0.74 s in an open-loop system. Experiments showed that the new isolator has great performance in a homemade T-1 absolute gravimeter, reducing the measurement deviation by a factor of 32. It is expected to be used in both free-falling and atomic-interference absolute gravimeters. Future improvements may include optimizing the mechanical structure and integrating a temperature control subsystem.

Ultra‐fast moving coil actuator for power switches in medium‐voltage grids

The need for faster power switches leads to the following question: Which technical actuation principle has the highest acceleration potential? This study describes the investigation of electrodynamic moving coil (voice coil) actuators. This principle promises no delay for the excitation field because of permanent magnets and a very small electrical time constant of the moving coil. The aim is to find out the limits of the switching time under practicable conditions. In the study, technical limitations of the actuation principle concerning the dynamic behaviour are shown by an analytical approach. It contains the major parameters like stroke or material of the iron poles, the coil, and the permanent magnets. Furthermore, the study discusses thermal aspects and approaches for the mechanical force multiplying by cascaded arrangements. A magnetically optimised elementary unit can be combined parallel or in series. The mechanical load inertial can be divided into a sufficient number of cascaded actuation units. Consequently, only the inherent moving mass determines the acceleration capability. This optimisation was done analytically with the Lorentz force formula and with finite element method simulations. This article describes both approaches, their results, and the experimental verification. The experimental actuator reaches a switching time of 2.7 ms.

Design, Analysis and Test of a Hyperbolic Magnetic Field Voice Coil Actuator for Magnetic Levitation Fine Positioning Stage

The multi-degree-of-freedom high-precision positioning system (MHPS) is one of the key technologies in many advanced industrial applications. In this paper, a novel hyperbolic magnetic field voice coil actuator using a rhombus magnet array (HMF-VCA) for MHPS is proposed. Benefiting from the especially designed rhombus magnet array, the proposed HMF-VCA has the advantage of excellent force uniformity, which makes it suitable for multi-degree-of-freedom high-precision positioning applications. First, the basic structure and operation principles of the HMF-VCA are presented. Second, the six-degree-of-freedom force and torque characteristic of the HMF-VCA is studied by three-dimensional finite element analysis (3-D FEA). Third, the influence of structural parameters on force density and force uniformity is investigated, which is conducive to the design and optimization of the HMF-VCA. Finally, a prototype is constructed, and the comparison between the HMF-VCA and conventional VCAs proves the advantage of the proposed topology.

Driving complex flow waveforms with a linear voice coil actuator.

Oscillatory and pulsatile fluid flows for use in microfluidic applications were generated using a deformable chamber driven by a low cost linear voice coil actuator. Compliance in the fluidic system originating in the deformable chamber and the fluidic tubing produced a strong frequency dependence in the relationship between the system's input and the output flow rate. The effects of this frequency dependence were overcome by precise system calibration, enabling on-demand generation of sinusoidal oscillations in the fluid flow rate with a controlled amplitude in the range from 0.1 to over 1 ml/min across a frequency range from 0.1 Hz to 10 Hz. The calibration data further enabled the optimization of a multistage exponential smoothing model of the system that allowed the generation of arbitrary complex waveforms. This was demonstrated by combining flow modulation with a constant background flow generated by a syringe pump to mimic the pulsatile flow found in the human vascular system.

Torsion balance-based system for high-precision force measurement in horizontal plane: part II. Static and dynamic improvement

In this paper, improved static and dynamic capabilities of the torsion force measurement system (TFMS) are reported based on an earlier development presented in part I (Yan et al 2018 Meas. Sci. Technol. 29 084001) of this work. The force measurements through a closed-loop operation mode are set up, by which the cut-off frequency is improved from 0.002 Hz to 0.1 Hz. Two different actuation and compensation mechanisms are introduced; in the first case the small forces are produced electromagnetically by a commercial voice coil actuator, in the second case electrostatically using a customized capacitive actuator. We apply Newton’s polynomial interpolation to evaluate the measurement results, which reveals that the TFMS is able to resolve forces with approximately 2 nN resolution in the measuring range of ±3 µN.

Relaying the High-Frequency Contents of Tactile Feedback to Robotic Prosthesis Users: Design, Filtering, Implementation, and Validation

It is known that high-frequency tactile information conveys useful cues to discriminate important contact properties for manipulation, such as first contact and roughness. Despite this, no practical system, implementing a modality matching paradigm, has been developed so far to convey this information to users of upper-limb prostheses. The main obstacle to this implementation is the presence of unwanted vibrations generated by the artificial limb mechanics, which are not related to any haptic exploration task. In this letter, we describe the design of a digital system that can record accelerations from the fingers of an artificial hand and reproduce them on the user's skin through voice-coil actuators. Particular attention has been devoted to the design of the filter, needed to cancel all those vibrations measured by the sensors that do not convey information on meaningful contact events. The performance of the newly designed filter is also compared with the state of the art. Exploratory experiments with prosthesis users have identified some applications where this kind of feedback could lead to sensory-motor performance enhancement. Results show that the proposed system improves the perception of object-salient features such as first-contact events, roughness, and shape.

Modulation of mechanical tissue properties resulting from changes in splice variant expression of the Drosophila titin ortholog, sallimus

We are broadly interested in the many nuances of neuromuscular transduction. Work performed over the past two decades has demonstrated important non‐acto‐myosin means of modulating muscle stiffness ‐ elasticity and viscosity ‐ that can be (a) relatively rapid and long lasting, whilst (b) remaining somewhat independent of neuronal signaling. We hope to provide mechanistic explanations for historical phenomena like catch tension, the Blashko effect, and generally, muscle hysteresis. Here we report on the potential mechanical role(s) of alternative splice variants of the sallimus gene / protein in muscle tissue. Sallimus (sls) is an ortholog of vertebrate titin and like it's counterparts across Animalia (e.g. twitchin), sls possesses both compliant (i.e. Ig) and stiffer elastic domains (i.e. PEVK). There are at least ten sls isoforms described in fruit fly and several possess notably different proportions of compliant and stiff domains, potentially offering a diversity of mechanical tissue properties that could be critical to developmentally shifting motor demands. Indeed, Drosophila larvae must escape the dense, thick rinds of fruit (e.g. citrus), but have only hydrostatic soft bodies with which to do so. Stiffening the muscle could be achieved by either (a) increased neuronal output, or (b) modulation of splice variants / sls proteins. We hypothesize that modulation of sls variants, either by short‐term signalling (i.e. Ca2+) or longer‐term modified splice variant expression, could yield stiffness changes in a manner that mitigates the need to modulate neuronal output. In such a system, varied developmental motor demands could be accommodated more so by intramuscular protein modulation than motoneuronal output.We use two approaches to evaluate this hypothesis: (1) molecular and (2) physiologic / mechanical. We characterize the expression of different sls variants using several molecular approaches: qPCR, Western blots, and super resolution immunohistochemistry. Tissue mechanics are examined using a custom voice coil actuator, silicon based force beams, and motoneuronal electrical activation. Longitudinal bodywall muscles of larval Drosophila were stretched cyclically within previously described behavioral parameters. Motoneuronal stimuli were presented concurrent with various portions of the tissue length duty cycle. In some experiments, blebbistatin derivatives were utilized to interrupt acto‐myosin interactions. Tissue mechanics data suggest that short‐term modulation, independent of acto‐myosin interactions, has significant and long‐lasting effects on muscle stiffness. We used a transient anti‐sls RNAi paradigm to further evaluate our hypothesis. Interestingly, rather than knocking down all sls splice variants, molecular data suggest that transient RNAi against sls reduced overall sls expression but also induced the expression of different variants. Such a shift in variant expression, perhaps driven by neurohormonal modulation like the pre‐puparian octopaminergic surge, could be physiologically utilized to increase bodywall stiffness to a value greater than that of the fruit rind that a larva must escape.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A Linear Permanent Magnet Synchronous Motor for Large Volume Needle-Free Jet Injection

Needle-free jet injection allows delivery of liquid drugs through the skin in the form of a narrow fluid jet traveling at high speed, minimizing the risk of accidents. The use of a controllable actuator to drive this process has many advantages, but the voice coil actuators previously used are too large and heavy for practical use with common injection volumes (1 mL). We instead propose a compact slotless tubular linear permanent magnet synchronous motor design for jet injection. The design was determined by utilizing a semi-analytical electromagnetic modeling technique to predict the performance of any given motor design, an optimization scheme for the motor mass at a given power dissipation, and an automated routine for estimating cogging force using finite-element analysis. A prototype motor was constructed, with a nominal mass of 322 g, a stroke of 80 mm, and a target operating power of 1.2 kW; experimental data show that the motor constant is within 10% of the target, and that the cogging force is in close agreement with the model. Test ejection of water into a force sensor verified that the motor is fit for needle-free injection. The design methodology explained here shows the benefits to integrated design optimization of both the actuator and the load, particularly in systems that drive fluid pressure loads, and also opens the door to controllable injector designs for larger volumes.

Comparative Finite Element Analysis of a Voice Coil Actuator and a Hybrid Reluctance Actuator

Comparative Finite Element Analysis of a Voice Coil Actuator and a Hybrid Reluctance Actuator

Integrated structure and precision control of flat voice coil actuator for non‐contact satellite

The disturbance caused by actuator is an important factor affecting the performance of the high-precision payload, and a new actuator is urgently required for the non-contact satellite. First, a flat voice coil actuator (VCA) with high precision and high bandwidth is proposed for the non-contact ultra-quiet satellite, and the principle of the eddy current sensor is analysed. Second, an optimised integrated structure is proposed with the flat actuator to output high-precision forces and the eddy current sensor to measure the distance of the displacement. The mathematical model of the VCA is established, and the precision of output force is studied. Third, the attitude control using six actuators in Stewart configuration is discussed, and the compensation method of unbalanced torque is provided. Finally, physical test is taken on the principle prototype, and numerical simulations are implemented to verify the effectiveness of the integrated structure and the control methodology.

Multiphysics Modeling of Voice Coil Actuators With Recurrent Neural Network

In order to accurately model the behaviors of a voice coil actuator (VCA), the three-dimensional (3-D) method is preferred over a lumped model. However, building a 3-D model of a VCA is often very computationally expensive. The computation efficiency can be limited by the spatial discretization, the multiphysics nature, and the nonlinearities of the VCA. In this paper, we propose incorporating the recurrent neural network (RNN) into the multiphysics simulation to enhance its computation efficiency. In the proposed approach, the multiphysics problem is first solved with the finite element method (FEM) at full 3-D accuracy within a portion of the required time steps. An RNN is then trained and validated with the obtained transient solutions. Once the training completes, the RNN can make predictions on the transient behaviors of the VCA in the remaining portion of the required time steps. With the proposed approach, it avoids solving the 3-D multiphysics problem at all time steps such that a significant reduction of computation time can be achieved. The training cost of the RNN model can be amortized when a longer duration of transient behaviors is required. A loudspeaker example is used to demonstrate the enhancement of the computation efficiency by using RNN in the multiphysics modeling. Various structures of neural networks and tunable parameters are investigated with the numerical example in order to optimize the performance of the RNN model.

Measurement of ultrashort laser pulses with rapid-scanning frequency-resolved optical gating device

Frequency-resolved optical gating (FROG) is now one of the main methods of characterizing the ultrashort laser pulses. There are mainly three SHG-FROG methods, i.e. the standard FROG, the single-shot FROG and GRENOUILLE, each of which has its own features and application areas. Although the standard SHG-FROG has balanced advantages in sensitivity, accuracy and applicability for various test pulses, its speed is much slower than the others’: it often takes a few seconds or even minutes to record the FROG trace, which is dependent on the size of FROG image. Nowadays continuous development of the technique of digital imaging brings to high resolution CCD/CMOS image cameras with tens of millions pixels and fast refreshing rate. Unfortunately the standard FROG cannot make use of these image cameras for the real-time measurement of ultrashort pulses. To solve this problem, in this paper a rapid-scanning FROG device based on the standard SHG-FROG is demonstrated, where sinusoidal waves from a signal generator synchronously drive a voice coil actuator and a galvo-scanner, so that the spectra of the autocorrelation at different delays are successively reflected onto an area camera. As long as the camera is triggered to shoot continuously, the entire FROG trace can be recorded quickly within 1 s. Furthermore, several guidelines for good performance with this device are provided, including the settings of the amplitude and frequency of the driving sinusoidal waves, the selections of the focuses of the collimating lens F<sub>1</sub> and the focusing lens F<sub>2</sub>, and the method of delay calibration. This device is suitable for the real-time measurement of ultrashort pulses with large chirps or complex structures where large-size FROG images need to be captured. In order to show the capability of this device, femtosecond pulses delivered directly from a home-made Kerr-lens mode-locked Ti: sapphire laser as well as the chirp pulses dispersed by a 200 mm-thick BK7 slab are measured. Two scan ranges are selected in order to achieve enough effective data points in the FROG traces of these two test pulses. Using standard procedure of pulse retrieval of FROG, the two pulses are reconstructed with pulse widths 58 fs and 492 fs, respectively. From the retrieved spectral phases of these test pulses, the GDD value of the BK7 slab can be deduced to be 8740 fs<sup>2</sup>, which is in good agreement with the theoretical value of 8815 fs<sup>2</sup>. Thus the experimental results confirm the accuracy and applicability of this FROG device.

Investigation on a two-stage platform of large stroke for broadband vertical vibration isolation

For the purpose of preventing vibration-sensitive optical switches from malfunction caused by broadband vertical vibration, a novel two-stage vibration isolation platform is proposed. The primary stage is a bellows-type isolator of large stroke and low isolation frequency, and the secondary stage is a small-stroke hybrid isolator composed of bellows and voice-coil actuators. In the primary stage, two pre-compressed horizontal bellows and one vertical bellows are used to counter the weight of the switch and to reduce the total height of the isolator. The static properties of the primary stage are analyzed, and the vibration isolation of the platform is investigated. Numerical results indicate that the two-stage platform is effective in isolating vertical vibration. Experiments are also conducted to verify the performance of the platform. It is exhibited that the transmissibility is less than 0 dB over 2 Hz, and the attenuation rate reaches −35 dB/dec at high frequencies. The frequency range of test is 2–200 Hz, and the maximum displacement is 10 mm at 2 Hz. In the secondary stage, the actuators can substantially suppress the resonance peak, and promote isolation performance at low frequencies.

A two-axis tilt control system on a turntable for rotating-optical-cavity experiments.

Many precision measurements using rotating optical cavities have tight requirement on the level of a rotating platform on which the cavities are installed. We develop a single-stage tilt control system as one part of the experimental setup for testing Lorentz invariance using two optical cavities that are perpendicular to each other. Home built voice-coil actuators, together with a tilt sensor and control electronics, are adopted to simultaneously suppress the tilt of the rotating platform in two orthogonal directions. The large cross coupling between two orthogonal axes is observed, and its mechanism is examined. By adding a compensating weight, the loop instability resulting from the cross coupling is effectively removed. With the active control, the variation of the tilt around each of the two axes is reduced from the free-running value of ±30 µrad to within ±0.2 µrad, independently measured by using a second tilt sensor. This residual tilt has a component at the rotational frequency with an amplitude of 0.1 µrad, which contributes a systematical offset of 1.8 × 10-17 to the Lorentz violating parameter κ e- ZZ, estimated by assuming that the tilt sensitivity of the optical cavity is 1 × 10-16/μrad. Further improvement is still possible by using piezo-electric actuators that exhibit higher resonant frequencies, a different approach that will suppress the residual variation of the tilt to within ±0.01 µrad and allow a reduced systematical offset of 1.8 × 10-18 for κ e- ZZ.