Voice Coil Research Articles

Signal Stitching Algorithm for Faster Acquisition of Long Traces in Terahertz Time Domain Spectroscopy

In this paper, an iterative algorithm is developed to combine time shifted traces in pulsed terahertz time domain spectroscopy (THz-TDS). This method intends to correct errors due to mechanical sampling in the trailing ends of the traces in systems that utilize a combination of a fast voice coil optical delay line and a slow long delay range one. The algorithm works by iteratively combining three basic modifications on the trace shape to match the overlapping areas of consecutive time windows. In order to validate the method, both simulated and experimental traces affected by ODL distortions are stitched. Proper stitching is shown to mitigate the increase of noise floor and the frequency shift of spectral resonances that arises with direct stitching, i.e. just compensating for the offset between traces. An enhancement in acquisition speed by a factor 7 in comparison to conventional lock-in detection based on a long range optical delay line is shown in tests with the experimental setup available.

A hybrid of surrogate model and MIGA method for optimization and compensation of steady-state flow force on water hydraulic HSV

In this research, a hybrid of surrogate model and Multi-island genetic algorithm (MIGA) is proposed for optimization and compensation of steady-state flow force on water hydraulic high-speed on-off valve (HSV) driven by voice coil motor. Firstly, a dynamic model on the spool of HSV is established, and the effects of spool displacement, spool half-cone angle, valve stem diameter and inlet pressure on the steady-state flow force of HSV are analyzed through the CFD simulation. Secondly, a quadratic response surface model is set up based on design of experiment (DOE) to analyze interactions of key parameters on steady-state flow force. MIGA is proposed to optimise the structural parameters of HSV, and the optimization results are analyzed and verified by CFD simulations. Simulation results demonstrate that the steady-state flow force is reduced significantly. Finally, the steady-state flow force in the optimized structure of HSV is also verified experimentally. The experiment results exhibit that the optimized spool can compensate about 71% for the steady-state flow force, then reduce about 15% the energy consumption of HSV. This research will provide the guide for the design and engineering application of HSV.

Design and Experimental Investigation of XY Compliant Mechanism for Precision Applications

A XY compliant mechanism is designed for the precision application with higher range, precision, and accuracy. In earlier work, many researchers have used different methods to design compliant mechanism. In this paper, XY positioning stage is designed using blocks method. However, the model is monolithic in nature to avoid joints. By using wire EDM, the XY model is manufactured. Voice coil actuators are used for the displacement, which give larger range. Analytical modeling is carried out and is validated with MATLAB results. Finally, experimentation is done for performance analysis. The XY model gives ±6mm with motion direction. The XY model evaluates both static and dynamic performances.

보이스코일모터를 이용한 초정밀 자기부상 스테이지

Voice coil motor is an actuator that employs a non-contact electromagnetic force between its coils and magnets, and is widely used in precision stages on account of its good linearity between current and force. Additionally, these advantages are beneficial for implementing the magnetic levitation mechanism. Unlike the case of general use of a voice coil motor where 1-DOF translational motion is applied, 6-DOF magnetic levitation causes variation in the relative position and orientation between the coil and the magnet. Accordingly, the force constant also changes. In this study, high-level precision positioning of 20 ㎚ was realized through the design and control of a magnetic levitation stage using voice coil motors. In the process, the change in the force of the voice coil motor was found to be approximately 1% within the range of motion. Therefore, the proposed design was verified to be suitable for high-precision stages.

The Delta Robot-A long travel nano-positioning stage for scanning x-ray microscopy.

A new stage design concept, the Delta Robot, is presented, which is a parallel kinematic design for scanning x-ray microscopy applications. The stage employs three orthogonal voice coils, which actuate parallelogram flexures. The design has a 3 mm travel range and achieves rms position jitter, integrated from 1 Hz to 1 kHz, of 2.8 and 1.3 nm perpendicular to the beam and 5.6 nm along the beam direction with loads up to 350 g. The Delta Robot design process used a mechatronics approach of iterative modeling and simulation to develop the system and validate performance. The design considerations, design process, stability, and operational performance on the hard x-ray nanoprobe at Diamond Light Source are presented.

A novel long-stroke fast tool servo system with counterbalance and its application to the ultra-precision machining of microstructured surfaces

This paper presents a novel long-stroke fast tool servo (FTS) system with counterbalance and its application to the diamond machining of microstructured surfaces. The FTS system is driven by a voice coil motor and guided by air bearings. A hybrid control algorithm which combines PID control, sliding mode control and feed-forward control was specifically designed for the system and ensures that it has less than 1% tracking error and achieves ± 1 mm stroke and 105 Hz bandwidth. The counterbalance is achieved by the symmetric arrangement of two of the same FTS systems. System vibration decreased significantly from ± 3 μm to ± 0.145 μm when the counterbalance was working. Machining experiments were conducted using the FTS system on a diamond turning machine. A microstructured surface simulation model was built and information about the workpiece surface tested and collected. When the counterbalance was working, error in the machine axes decreased from micron-level to nano-level and the surface roughness of the microstructured surface was also reduced. The system achieves ± 1 mm (±0.5 mm) stroke at 30 Hz (40 Hz) with 0.35% (0.68%) tracking error during machining processes, and the depth error of the machined microstructured surface was measured at 1.4% (2.3%).

Calculation, simulation and fast estimation of thermal resistance of rotary voice coil actuators

Rotary voice coil actuator (RVCA) is mainly used for reciprocating drive of small inertia loads in a limited range of angle, which is widely used in aerospace and other fields. Thermal resistance is one of the most important parameters of RVCAs, which is directly related to the steady-state temperature rising and operation reliability. Because the thermal resistance cannot be measured directly, the analytical method is usually used to calculate the thermal resistance of the RVCA. However, due to the particularity of the thermal circuit calculation, the calculation is complicated and the result is not accurate. It is not conducive for engineering applications of this kind of actuator. In this paper, a series of rotary voice coil motor is selected as the research object. Through analytical calculation and thermal simulation, a more accurate thermal resistance calculation correction model and thermal resistance value of RVCAs are obtained, and the accuracy of the estimation results is verified by experiments. On this basis, the effective volume of the coil frame of the RVCA is selected as the variable, and the concise variation law of the series thermal resistance data is obtained. This paper provides a fast and accurate estimation method for the thermal resistance of RVCA, which has an important reference value for expanding the engineering applications of RVCAs.

Understanding the Effect of Speed on Human Emotion Perception in Mediated Social Touch Using Voice Coil Actuators

Touch as a modality in social communication has been getting more attention with recent developments in wearable technology and an increase in awareness of how limited physical contact can lead to touch starvation and feelings of depression. Although several mediated touch methods have been developed for conveying emotional support, the transfer of emotion through mediated touch has not been widely studied. This work addresses this need by exploring emotional communication through a novel wearable haptic system. The system records physical touch patterns through an array of force sensors, processes the recordings using novel gesture-based algorithms to create actuator control signals, and generates mediated social touch through an array of voice coil actuators. We conducted a human subject study (N= 20) to understand the perception and emotional components of this mediated social touch for common social touch gestures, including poking, patting, massaging, squeezing, and stroking. Our results show that the speed of the virtual gesture significantly alters the participants' ratings of valence, arousal, realism, and comfort of these gestures with increased speed producing negative emotions and decreased realism. The findings from the study will allow us to better recognize generic patterns from human mediated touch perception and determine how mediated social touch can be used to convey emotion. Our system design, signal processing methods, and results can provide guidance in future mediated social touch design.

Reduction of the Influence of Non-Repeatable Run-Out in X-Y Plane of Machining Surface

In recent years, the quality of the machined surfaces of molds for optical or medical instruments has needed improvement, and the fabrication of mirrored surfaces by means of cutting only has been gaining in importance. In order to obtain smooth surfaces, it is necessary to reduce various vibrations in the machine tool during the machining process. Many factors cause vibration in a machine tool, including feed mechanisms, pumps, and chatter. A high-speed spindle for precision machining is one source of vibration, but it is a challenge to avoid the non-repeatable run-out (NRRO) of a spindle. This study has developed an excitation system that can reduce the influence of non-repeatable run-out on machining surfaces. This paper presents a newly-developed excitation system with an excitation unit for each the X and Y direction. The excitation units consist of a voice coil motor and leaf springs, fixed on a spindle head. The tool run-out and vibration of the spindle head are measured by a displacement sensor and an acceleration sensor fixed on the spindle head, and their NRRO components are obtained through extraction using band-pass filters. By using these NRRO components as feedback signals, the excitation unit generates the force to cancel the NRRO of the tool. In order to determine the performance of the developed system, experimental evaluation was performed on a vertical 3-axis machining center. Since the spindle used for evaluation had three bearings, the measured NRRO of the tool had three peaks in the frequency domain. First, we conducted evaluation experiments under non-machining conditions, and all NRRO peaks were reduced by applying the developed system. Furthermore, there was no interference of the excitation units in the X and Y directions. Next, we evaluated the influence of the NRRO of the tool on the machining surface under finish machining conditions. The reduction in NRRO components in the measured surface profiles was observed through feedback. It was concluded that the developed system can reduce the influence of NRRO on machining surfaces.

Discrete Cutaneous Feedback for Reducing Dimensions of Wearable Haptic Devices

In this article, we explore alternative cutaneous haptic feedback for rendering modulation of the grasping force. The aim of the study was to reduce power requirements and in turn dimensions of the actuators, in wearable devices applied to virtual or teleoperated manipulation. This is critical in certain rehabilitation or training scenarios where haptics should not interfere with dexterity of the user. In the study, we experimented discrete, pulsed cutaneous force feedback and compared it with conventional continuous proportional feedback, in a virtual pick and place task. We made use of wearable thimbles based on voice coil actuators in order to provide high-quality, low-noise haptic feedback to the participants. The evaluation was performed on the basis of both objective measurements of task performance (measured virtual forces and correct ratio) and a questionnaire evaluating participants’ preferences for the different feedback conditions. On the basis of the obtained results, in the article, we discuss the possibility of providing high-frequency, discretized cutaneous feedback only, driven by modulation of the grasping force. The opportunity is to reduce volume and mass of the actuators and also to consider alternative design solutions, due to the different requirements in terms of static and high-frequency components of the output force.

VERTEX – versatile in-situ testing rig for X-ray scanners

In this contribution, we introduce a next-generation in-situ loading stage VERTEX (VERsatile in-situ TEsting rig for X-ray scanners) allowing for both high load capacity and high resolution tomographical imaging in a broad range of experiments including uni-axial, flexural, torque testing, and their combinations. The device is designed as a double column testing rig with two individually controlled rotary stages. It consists of 6 individual function blocks (two loading columns, two rotary stages, two cross-head beams) ensuring easy manipulation and reasonable portability. The function blocks can be assembled into different geometrical configurations (uni-axial on-axis, uni-axial off-axis, flexural) while additional loading modules can be mounted onto the rotary stages (e.g., voice coil vibration loading stage). In comparison with the conventional existing devices having the identical arrangement (two columns, two rotary stages), the loading capacity of the VERTEX is several times higher while dimensions and robustness of the device still do not significantly limit the achievable resolution.

Decoupled identification and compensation of nonlinear hysteresis cascading with linear dynamic in a moving magnet voice coil actuator.

The moving magnet voice coil actuator (MMVCA) is a promising choice for the long stroke nanopositioning stage with the advantage of low moving mass. However, the hysteresis observed in MMVCA limits further improvement on tracking performance. The hysteresis is cascading with the linear dynamic of the positioning stage, which makes common hysteresis identification inapplicable. In this paper, the cause and influence of hysteresis in MMVCA are analyzed, which reveal that the magnetic hysteresis leads to a hysteresis of force and causes motion accuracy to degrade. A modified rate-dependent Prandtl-Ishlinskii (P-I) model is proposed to describe the hysteresis in MMVCA. The decoupled method is implemented to identify the parameters of the linear dynamic model and nonlinear hysteresis model. The experimental results validate the feasibility of the proposed P-I model. Based on the hysteresis compensation, the peak-to-peak tracking errors are reduced by 30% and the root-mean-square (rms) tracking errors are decreased by 41% on average for the trajectories with amplitudes from 1 to 3mm and frequencies from 1 to 5Hz.

토크 밀도 향상을 위한 제한된 각도 토크 모터의 하이브리드 구조

The limited angle torque motor (LATM) is an electromagnetic actuator that rotates within a limited angle of less than ±90°. In this study, the advantages of permanent magnet (PM) type and reluctance type LATM are combined to create a hybrid LATM with high torque density for the same volume. The proposed hybrid LATM structure combines structural advantages using a PM with a high magnetic flux density of a PM type LATM and voice coil winding with a high fill factor of reluctance type, as well as making a prototype and conducting a torque test.

Design and Positioning Control of a Flexure-Based Nano-positioning Stage Driven by Halbach Array Voice Coil Actuator

Design and Positioning Control of a Flexure-Based Nano-positioning Stage Driven by Halbach Array Voice Coil Actuator

Investigation of control algorithm for long-stroke fast tool servo system

Fast tool servo (FTS) is an efficient and reliable method in precision machining for fabricating freeform surfaces or microarrays with sub-micrometric form accuracy. In this paper, a Lorentz force FTS is designed where the voice coil motor is located inside the slide, and four air bearings are used as support components. Three different control algorithms, namely conventional PID control, advanced PID control with velocity/acceleration feed-forward (FF) and sliding mode control (SMC) are implemented in the system, and corresponding Simulink simulation models are built including for both mechanical and electrical systems. The results show that advanced PID and SMC can reduce phase error and overshoot, and tracking error can be controlled at 3.13% at 50 Hz. A new hybrid control algorithm (PID + SMC + FF) is developed, with system tracking error subsequently decreased to 0.871% at 50 Hz. In addition, with a suitable compensation method, the steady state tracking error is further decreased to 0.029%. Consistent results from testing with signals of different input frequency also indicate the general effectiveness of the algorithm.

Fuzzy Broad Learning Adaptive Control for Voice Coil Motor Drivers

Fuzzy Broad Learning Adaptive Control for Voice Coil Motor Drivers

High-bandwidth controller design for dual-stage actuator system in hard disk drives

Large-capacity hard disk drives are important for the development of an information society. The capacities of hard disk drives depend on the positioning accuracy of magnetic heads, which read and write digital data, in disk-positioning control systems. Therefore, it is necessary to improve positioning accuracy to develop hard disk drives with large capacities. Hard disk drives employ dual-stage actuator systems to accurately control the magnetic heads. A dual-stage actuator system consists of a voice coil motor and micro-actuator. In micro-actuators, there is a trade-off between head-positioning accuracy and stroke limitation. In particular, in a conventional controller design, the micro-actuator is required to actuate such that it compensates for low-frequency vibration. To overcome this trade-off, this study proposes a high-bandwidth controller design for the micro-actuator in a dual-stage actuator system. The proposed method can reduce the required stroke of the micro-actuator by increasing the gain of the feedback controller of the voice coil motor at low frequencies. Although the voice coil motor control loop becomes unstable, the micro-actuator stabilizes the entire feedback loop at high frequencies. As a result, the control system improves the positioning accuracy compared to that achieved by conventional control methods, and the required micro-actuator stroke is reduced.

IDENTIFICATION OF THE ELECTRICAL IMPEDANCE OF AN IMMOBILIZED TRANSDUCER AND THE MECHANICAL IMPEDANCE OF AN ELECTRODYNAMIC LOUDSPEAKER USING AUTOMATIC FIT OF THE FORCE FACTOR BL

This paper describes a method for determining mechanical and electrical impedances of an electrodynamic transducer based on the automatic brute-force search of the force factor Bl. Also, the way of identifying electrical apparent resistance and apparent inductance of the voice coil is shown as an example of deeper loudspeaker analysis that proposed method allows to achieve. The measured signals are voltage on speaker terminals, voice coil current and membrane displacement. Measuring displacement in addition to voltage and current allows to completely separate transducer mechanical subsystem from electrical and apply various known modeling approaches to them separately.

A Modified Triaxial Apparatus for Soils under High-Frequency, Low-Amplitude Vibrations

Abstract A modified triaxial apparatus was developed to explore the behavior of cohesionless soil subjected to high-frequency, low-amplitude vibrations, such as those induced by high-speed trains. It was based on a conventional Bishop-type triaxial apparatus to utilize its existing static loading module. The major modification was an added dynamic loading module with a low-inertia linear voice coil actuator mounted coaxially with the vertical loading rod. Through a signal generator and an amplifier connected to the voice coil actuator, a vibration input with wide range of frequencies and amplitudes could be superimposed to a monotonic loading process. A series of tests under different conditions were performed to demonstrate the effectiveness and performance of the modified triaxial apparatus, with the focus being placed on the reduction of shear resistance and accumulative deformation of sand induced by high-frequency, low-amplitude vibrations.

Dual-stage nanopositioner augmented with feedforward control

A piezoelectric walking stage is retrofitted with a secondary stage for precisely tracking ramp position references. Fine motion control of the secondary stage shuttle is achieved using a voice coil actuator to correct for small, periodic deviations in position produced by the walking motion of the piezoelectric drive modules. The shuttle position tracking error is more than an order of magnitude smaller than the walking stage error for velocities less than 1.0 mm/s, however, the shuttle error remains dominated by harmonics of the walking stage stepping frequency. A feedforward controller using a modulated-demodulated implementation is designed to augment the high-bandwidth (300 Hz) shuttle controller to reject three dominant disturbance modes. When the system is tracking a 1.0 mm/s position ramp reference, the modulated-demodulated controller reduces the RMS shuttle position error from 44 to 21 nm. The reported system is under development to meet the scanning requirements of spaceborne Fourier Transform spectrometers.