Voice Coil Research Articles

Head-Positioning Control in Triple-Stage-Actuator Enterprise Hard Disk Drives Using Mixed H2/H∞ Synthesis Methodologies

Abstract The recent rapid growth in the cloud storage industry has strongly increased the demand for high-capacity enterprise hard disk drives (HDDs). Increasing the areal density brings new challenges to the high-accuracy head-positioning control in the next generation HDD development. Triple-stage-actuator (TSA) system is one of the emerging technologies (Atsumi, 2016, “Emerging Technology for Head-Positioning System in HDDS,” IEEJ J. Ind. Appl. 5(2), pp. 117–122.) that can achieve higher bandwidth than that of a dual-stage-actuator (DSA) system and improve the track-following performance. In this paper, we focus on the TSA system with one voice coil motor (VCM) and two piezoelectric (PZT) actuators. Two types of mixed H2/H∞ synthesis methodologies based on model-based optimization and data-driven optimization are proposed to design the track-following controller for the TSA system. The simulation results show the feasibility and effectiveness of the TSA systems with a tertiary PZT actuator. We also analyze the effects of stroke limitations and resonance frequencies of the second-/third-stage PZT actuators on the head-positioning accuracy. The results might provide a guideline for the TSA mechanical design.

Development of dual-mode precision current source for macro-microcomposite actuator based on field programmable gate array.

To meet the requirements of variable input current forms, microstep adjustment, low error coefficient, high output linearity, and the low ripple of macro-microcomposite actuators developed by combining voice coil motors and a giant magnetostrictive actuator, in this study, a design scheme of dual-mode precise programmable current sources based on a field programmable gate array (FPGA) was proposed. First, according to the working principle and control characteristics of macro-microcomposite drivers, an overall circuit system model of a driving power supply was established. Second, based on the circuit operational amplifier principle, an output current equation of the power supply was obtained, and a current switching circuit and a dual-mode current sampling circuit were designed. Finally, an FPGA was used as the current control core, and an incremental PI algorithm was introduced to compensate for the current feedback. The experimental results showed that the precision current source can output two current modes (positive current 0-5A and positive and negative current -5 to 5A) under the FPGA control. The average current error coefficient of the output in the two current output modes was ε ≦ 0.006, the maximum nonlinearity was ηmax ≦ 0.005, and the error between the current adjusting step value and the preset value was less than 1%.

Investigation on the Modeling and Dynamic Characteristics of a Novel Hydraulic Proportional Valve Driven by a Voice Coil Motor

As the key control component of the water hydraulic systems, the water hydraulic proportional valve has a significant influence on the control performance of the systems. Due to the poor viscosity and lubricity of water, the valve spool resistance is large and non-linear. In this study, a novel fast-response water hydraulic proportional valve is presented. The actuator of the valve adopts a voice coil motor (VCM), which has the advantages of fast response, high control precision and small volume. In order to realize the fast control of the valve, a lever amplifier is designed to obtain enough actuation force. A detailed and precise non-linear mathematical model of the valve considering both the valve’s structural parameters and VCM electromagnetic characteristics is developed. A comprehensive performance simulation analysis has been carried out, mainly divided into an electromagnetic simulation, an analysis of the characteristics of the lever magnifier, and a dynamic performance simulation of the valve. The simulation results show that the adjusting time is about 28ms, and the maximum overshoot is about 5 %. The step response rise time is about 15 ms. The test rig of the valve and VCM have been built. The test results of the prototype show that the optimal stroke range of VCM is 4 mm to 15 mm. The maximum overshoot of the valve is around 10 %; the adjusting time is about 30 ms in the opening process and 35 ms in the closing process. The test results prove that the valve has good static and dynamic control performance.

Design and Simulation of Electromagnetic Driving Device for Voice Coil Diaphragm Pump

Design and Simulation of Electromagnetic Driving Device for Voice Coil Diaphragm Pump

Design and Analysis of a High Thrust Linear Voice Coil Motor Using for the Stiffness Test of Linear Motor Servo System

Linear voice coil motors (VCMs) are widely used in some high precision or high dynamic applications, such as lithography, digital cameras, and microscopes. In this article, a high thrust linear VCM is analyzed and designed, which is used for the position loop stiffness test of linear motor servo system. To guarantee the structural strength of coil frame and provide space for the cooling channels, the two layers’ coil arrangement is adopted. Based on 2-D finite element method (FEM), the thrust and thrust ripple performance of the motor are analyzed. Moreover, a reasonable cooling structure integrated with the coil frame is designed to further improve the thrust density. Finally, a linear VCM prototype with a thrust rating of 1000 N is manufactured and tested. The static thrust test results show that the thrust varies linearly with the coil current. The motor can provide a nearly constant thrust and thrust ripple within ±2 mm displacement is less than 1%, which agrees well with finite element simulation. In addition, the temperature test is also achieved. Compared with natural cooling condition, the thermal equilibrium can be achieved among the coil, coil frame and cooling water with the water-cooling condition, when the current density is 15.3 A/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Furthermore, a good overall cooling effect and low surface temperature rise can be realized when two heat shield cover plates are fixed onto both sides of the primary.

Dual feedback based bipolar current source with high stability for driving voice coil motors in wide temperature ranges

Bipolar current sources with a stability better than 0.1% in the temperature range of -30 to +70 °C are demanded for driving voice coil motors applied in a new ultra-quiet satellite platform, but almost none of the existing designs satisfy the harsh requirements. This paper presents a possible solution, which is essentially a floating-load, bipolar current source circuit with a dual feedback path. The key circuit is a composite amplifier (co-amp) composed of a high precision amplifier for error correction and a high power amplifier for load driving. The first feedback path comprises a specially designed four-wire current-sense resistor for current-to-voltage conversion and a discrete instrumentation amplifier for amplifying the converted voltage and closing the loop. The second feedback path is a proposed compensation network for loop stability. Error budgets for evaluating current stability and choosing key components of the circuit are comprehensively studied based on a derived rigorous current equation. Loop-stability problems attributable to the inductive load and the high open-loop gain of the co-amp are analyzed, and the proposed dual feedback compensation method is verified by theory, simulation, and measurement. All these contributions are demonstrated by three implemented prototypes with an output of up to ±2A. The measured results agree well with theoretical predictions. The best and the worst stability performances of the three prototypes at +2 and -2A are, respectively, 394 and 986 ppm in the temperature range of -30 to +70 °C, which are close to the theoretical value of 776 ppm.

A novel master-slave intraocular surgical robot with force feedback.

Intraocular surgery is one of the most challenging microsurgeries. Unintended movements of human hand and lack of force feedback can seriously affect surgical safety. We developed a novel master-slave robotic system with force feedback to assist intraocular surgeries. Isomorphism design was adopted to achieve intuitive control of the system. Contact force between instrument tip and tissues was measured with a force sensor developed by our group. Real-time force feedback was provided with one linear voice coil motor and two magnetic particle brakes in the master manipulator. Experiments were carried out to verify the proposed system. In the phantom experiment mimicking realistic surgical operations, the contact force significantly reduced by more than 30% with the force feedback when peeling the egg inner shell membranes. Experimental results demonstrate the effectiveness of force feedback and indicate the promise of the presented master-slave robotic system for intraocular surgery assistance.

An innovative MEMs peizo speaker

MEMs micro-speaker development has trailed behind MEMs microphone development by over two decades due to fabrication and acoustical challenges. While MEMs microphones only need to respond to minuscule displacement, generating sound energy requires both motor force and far higher volume velocity of the transducer mechanism. Recent development of a full bandwidth piezo-MEMs micro-speaker with a silicon diaphragm creates a rigid, light, fast responding transducer with high resistance to humidity and low thermal expansion. Fabricated using a monolithic MEMS semiconductor process eliminates calibration and driver matching. 20 Hz to 20kHz frequency response is delivered in occluded earbud, IEM, and hearing aid applications. The 20 kHz resonance peak provides a smoothly increasing response in the upper octaves. This extra amplitude allows for a significant increase in hearing aid gain and bandwidth over balanced armature transducers. The device is packaged in both top- and side-fire port configurations with earbud EVKs currently shipping. Integration of the amp, on the package substrate or SiP module, opens possibilities for more compact devices, longer battery life, lower cost, and more robust construction. The combination of audio fidelity, size, and speaker to speaker uniformity is not possible with traditional voice coil or hybrid MEMS approaches.

A wearable light-touch contact device for human balance support

There is an urgent need for the development of ways to address the major issue of falls among today’s globally aging population. The authors here outline a new approach referred to as virtual light-touch contact to mitigate postural sway during ambulatory and stationary periods, and propose a wearable light-touch (WLT) system featuring a virtual partition around the user that allows determination of virtual forces resulting from related contact. The data produced are used to create vibrotactile fingertip feedback, which supports comprehensive perception of the partition. Non-impaired subjects were recruited to support evaluation of the prototype system (incorporating tactile stimulation and motion-capture technology), with outcomes showing successful mitigation of postural sway in a heel-to-toe tandem stance. Research performed with 150 able-bodied volunteers to validate the performance of the new set-up (incorporating an acceleration sensor and a voice coil motor to render the light-touch effect) suggested that the proposed WLT approach supports human balance on a level comparable to that of the light-touch effect.

FCS technology: A novel electrodynamic transducer architecture

For a century now, acoustic electrodynamic transducers have been bound by axisymmetric motor structures for high performance due to the assumption in transducer theory that the diaphragm moves pistonically for all operating frequencies. This is of course a flawed assumption, and results in much research and development being focused on the vibro-acoustic components of the driver to minimize cone breakup at higher frequencies.A new architecture for the electrodynamic motor has been developed which helps to address this inherent problem. Flat Core Speaker (FCS) technology presents an architecture that is a rearrangement of the conventional electrodynamic motor structure with a planar voice coil and bobbin assembly that is situated between two parallel bar magnets. This results in a high aspect ratio design where the bobbin runs along the length of a flat diaphragm, leading to even force distribution, and therefore pistonic movement, while utilizing a thin profile with a flat diaphragm. COMSOL simulations and Klippel measurement data support these claims and show evidence of FCS technology having comparable performance to conventional drivers in a slimmer profile and blowing conventional high aspect ratio driver performance out of the water.

Magnetic Field Model of Macro-motion of Coaxial Integrated Macro-micro Composite Actuator

Aiming at the problem of short stroke of giant magnetostrictive actuator (GMA), a design scheme of coaxial integrated macro-micro composite actuator is proposed by combining the long-stroke characteristics of voice coil motor with the high-precision characteristics of giant magnetostrictive actuator. Based on its structure composition and working principle, the magnetic field model of macro-motion of macro-micro composite actuator is established based on the analysis method of circuit, and the change characteristics of the driving magnetic field are obtained. The finite element method is used to verify the magnetic circuit characteristics. The results show that the magnetic circuit variation characteristics of the proposed coaxial integrated macro-micro composite actuator are consistent with the theoretical calculation results, and are consistent with the expected working process of this actuator, which indicates that the established magnetic field model is correct, and that the proposed coaxial integrated design scheme of the macro-micro composite actuator is feasible.

Self-sensing of cutting forces in diamond cutting by utilizing a voice coil motor-driven fast tool servo

Cutting force measurement is important for monitoring the diamond cutting process. In this paper, a new measurement method of thrust cutting force associated with a voice coil motor (VCM) driven fast tool servo (FTS) system has been developed. Instead of integrating additional force sensors to the FTS which would influence the dynamics of the FTS, the force measurement in the proposed system is achieved associated with in-process monitoring the variation of the driving current of the VCM and pre-process determining the system parameters. In this way, the cutting forces are accurately obtained by subtracting the influences of the driving force, the spring force, the damping force and the inertial force associated with the system as well as the cutting process. Based on the proposed method, a microstructure array was machined using the developed VCM-FTS and the cutting force during the machining process was monitored in real time. The measured force signal was in good agreement with the machining result. The surface profile error of the fabricated microstructure could be clearly distinguished by the variation of the measured cutting force signal. This provides a new approach for in-process cutting force measurement associated with FTS based diamond cutting process.

Nonlinear Contour Tracking of a Voice Coil Motors-Driven Dual-Axis Positioning Stage Using Fuzzy Fractional PID Control with Variable Orders

This study aims to develop a variable-order fuzzy fractional proportional-integral-differential (VOFFPID) control system for controlling the mover position of a newly designed voice coil motors- (VCMs-) driven dual-axis positioning stage. First, the operation principle and dynamics of the stage are analyzed. After that, the design of a fuzzy fractional proportional-integral-differential (FFPID) control system is introduced on the basis of a fractional calculus and fuzzy logic system. With an additional degree of freedom to the control parameters and fuzzy operation, the FFPID control system can upgrade the contour tracking performance of a conventional proportional-integral-differential (PID) control system with respect to the specified dynamics of the stage. Moreover, the VOFFPID control system is designed to further improve the tracking responses of the FFPID control system. In this system, the five control parameters are optimized with the cuckoo search algorithm via an adaptive strategy. Lastly, nominal and payload conditions attributed to two nonlinear contour demands are provided to evaluate the contouring performance of the PID, FFPID, and VOFFPID control systems. The experimental results subjected to different performance measures demonstrate that the proposed VOFFPID controller outperforms PID and FFPID controllers in terms of the designed VCMs-driven dual-axis positioning stage under both conditions.

Active vibration isolation of ultra-stable optical reference cavity of space optical clock

Space optical clocks with frequency instability better than 1×10−15 are increasingly demanded for PNT (positioning, navigation, and timing) and space physical science. Inevitably, the micro-vibration level in the order of micro-g (μg) is required for ultra-stable optical reference cavity of space optical clocks. The realization of such a strict micro-vibration requirement over broadband frequencies is still technically challenging under complex space disturbances in the order of milli-g (mg). This paper thus proposes a multi-degree of freedom (DOF) active vibration isolation approach for the ultra-stable optical reference cavity to satisfy the stringent micro-vibration requirement. Non-contact voice coil actuators are designed as the driving unit of active vibration isolation. The robust vibration isolation controller is presented considering the control uncertainty caused by the voice coil clearance and the low frequency drift of accelerometers. The loop shaping technology is used to avoid the current drift and achieve high accuracy vibration isolation over the designed bandwidth. The active vibration isolation experimental platform is further developed, and the experimental results validate the effectiveness of the designed multi-DOF active vibration isolation scheme.

Method for reducing waveform distortion by increasing damping strength for electromagnetic vibrators

Voice coil motors are frequently used as force drivers in electromagnetic vibrators. As a constant current is applied, the generated driving force is not constant but varies with displacement due to the inhomogeneous magnetic field within the stroke range. When a sinusoidal current is applied to the voice coil motors, the above effect can lead to a severe waveform distortion on the output acceleration. In order to find an effective method to reduce it, a general nonlinear dynamic model has been established and analyzed with a focus on the effect of the damping strength of the vibrator on the waveform distortion. The numerical calculations show that the waveform distortion can be efficiently reduced by increasing the damping strength under various working conditions. Based on these results, an eddy current damper (ECD) was designed with a maximized damping coefficient and applied to our home-made vibrator. Once the ECD is incorporated, the waveform distortion of the output acceleration is significantly reduced, which validates our modeling.

Interlaboratory validation of a hanging pendulum thrust balance for electric propulsion testing.

A hanging pendulum thrust balance has been developed by Imperial College London in collaboration with the European Space Agency (ESA) to characterize a wide range of static fire electric propulsion and chemical micro-propulsion devices with thrust in the range of 1 mN to 1 N. The thrusters under investigation are mounted on a pendulum platform, which is suspended from the support structure using stainless steel flexures. The displacement of the platform is measured using an optical laser triangulation sensor. Thermal stability is ensured by a closed loop self-compensating heating system. The traceability and stability of the calibration are ensured using two separate calibration subsystems: a voice coil actuator and a servomotor pulley system. Two nearly identical thrust balances have been constructed, with one being tested in the Imperial Plasma Propulsion Laboratory and the other in the ESA Propulsion Laboratory. Both balances show a high degree of linearity in the range of 0.5 mN-100 mN. Both instruments have demonstrated a stable calibration over several days, with an estimated standard deviation on thrust measurements better than 0.27 mN for low thrust measurements. The same electric propulsion test article was used during both tests: a Quad Confinement Thruster (QCT) variant called QCT Phoenix. This thruster differed from previous QCT designs by having a newly optimized magnetic topology. The device produced thrust up to 2.21 ± 0.22 mN with a maximum specific impulse of 274 ± 41 s for an anode power range of 50 W-115 W.

Feedback Control Design for VCM

A design of PD feedback control law for a class of the second order system to satisfy the desired performance requirements is presented. It is achieved by using root-locus approach. The desired specifications of the step-input system response are first transformed into a required region for the poles of the PD control closed-loop system. Ranges of the corresponding PD control gains are then derived to guarantee the poles of the closed-loop system lie within the targeted region. Besides, the proposed control law is also applied to the feedback control of Voice Coil Motor (VCM) to support the function of the so-called “Optical Image Stabilization (OIS).” Numerical results by using a referenced VCM model have demonstrated the success of the proposed design.

A wearable elbow exoskeleton for tremor suppression equipped with rotational semi-active actuator

Pathological tremor is a common neuromuscular disorder that affects millions of people around the globe. This disease largely affects the quality of activities of daily living such as drinking, eating, and writing, such that patients suffering from pathological tremor often have a problem in self-care. This work presents a wearable elbow exoskeleton for tremor suppression (WEETS), which offers an alternative assistive technology to the conventional treatments based on surgery and drug therapy. The WEETS system uses a novel configuration and controllable rotational semi-active actuator (RSAA) based on magnetorheological fluid to suppress the tremor in the elbow joint. The RSAA is characterized by its compact structure, lightweight and enough output torque (about 3.5 Nm). The performance of the WEETS system is validated with simulations and a series of experiments. The results show that the WEETS has the capability to attenuate the elbow tremor regarding the magnitude of angular velocity and acceleration by 61.55% and 61.68%, respectively. Furthermore, for better evaluation of the WEETS system, an instrument based on voice coil actuator is developed to generate mechanical signals simulating pathological tremors, which is a novel method to show the validation of the exoskeleton system for tremor suppression. Overall, the results from the experimental setup and simulations confirm the effectiveness of WEETS on tremor suppression.

Research and Analysis of a Novel Voice Coil Motor With Wireless Power Supply

The moving-coil type voice coil motor (VCM) has very light moving mass, which can achieve higher reciprocating frequency and work efficiency. However, the power supply lead connected to the moving coil can be easily broken under long-term reciprocating motion, so it is rarely used in compressor drive systems. The core technology of the compressor development trend is a driving motor with high-efficiency, high reciprocating frequency, certain piston stroke, and light moving mass. Due to its structural characteristics, the moving-coil type VCM has broad application prospects. This article proposes a new structure for power supply of a moving coil VCM based on the principle of electromagnetic induction. The proposed VCM can overcome the problems of aging and disconnection of power supply lines caused by reciprocating motion, and meet the requirements of high-frequency and long-term repetitive action of the moving coil. The content of this article is as follows. First, the construction of the proposed VCM is introduced. Second, the power-driven circuit based on interleaving double switch forward converter is provided. Finally, two working modes of drive circuit for reciprocating motion are proposed. Simulation and experimental results verify the effectiveness of the method.

Fluid-Structure Coupling Effects in a Dual U-Tube Coriolis Mass Flow Meter.

Coriolis mass flowmeters are highly customized products involving high-degree fluid-structure coupling dynamics and high-precision manufacture. The typical delay from from order to shipment is at least 4 months. This paper presents some important design considerations through simulation and experiments, so as to provide manufacturers with a more time-efficient product design and manufacture process. This paper aims at simulating the fluid-structure coupling dynamics of a dual U-tube Coriolis mass flowmeter through the COMSOL simulation package. The simulation results are experimentally validated using a dual U-tube CMF manufactured by Yokogawa Co., Ltd. in a TAF certified flow testing factory provided by FineTek Co., Ltd. Some important design considerations are drawn from simulation and experiment. The zero drift will occur when the dual U-tube structure is unbalanced and therefore the dynamic balance is very important in the manufacturing of dual U-tube CMF. The fluid viscosity can be determined from the driving current of the voice coil actuator or the pressure loss between the inlet and outlet of CMF. Finally, the authors develop a simulation application based on COMSOL’s development platform. Users can quickly evaluate their design through by using this application. The present application can significantly shorten product design and manufacturing time.