Coil Actuator Research Articles

Defining a vibrotactile toolkit for digital musical instruments: characterizing voice coil actuators, effects of loading, and equalization of the frequency response

The integration of vibrotactile feedback in digital music instruments (DMIs) is thought to improve the instrument’s response and make it more suitable for expert musical interactions. However, given the extreme requirements of musical performances, there is a need for solutions allowing for independent control of frequency and amplitude over a wide frequency bandwidth (40–1000 Hz) and low harmonic distortion, so that flexible and high-quality vibrotactile feedback can be displayed. In this paper, we evaluate cost-effective and portable solutions that meet these requirements. We first measure the magnitude–frequency and harmonic distortion characteristics of two vibrotactile actuators, where the harmonic distortion is quantified in the form of total harmonic distortion (THD). The magnitude–frequency and THD characteristics in two unloaded cases (actuator suspended freely or placed on a sandbag) are observed to be largely identical, with minor attenuation for actuators placed on the sandbag. Loading the actuator (when placed in a DMI) brings resonant features to its magnitude–frequency characteristics, increasing the output THD and imposing a dampening effect. To equalize the system’s frequency response, an autoregressive method that automatically estimates minimum-phase filter parameters is introduced, which by design, remains stable upon inversion A practical use of this method is demonstrated by implementing vibrotactile feedback in the poly vinyl chloride chassis of an unfinished DMI, the t-Stick. We finally compare the result of equalization by performing sinesweep measurements on the implementation and discuss the degree of equalization achieved using it.

Design of the $\mu$MAZE Platform and Microrobots for Independent Control and Micromanipulation Tasks

We present the μMAZE (μ(Micro) Magnetic Actuation Zone control Environment) platform for independent control of multiple magnetic microrobots for performing individual and collaborative micromanipulation tasks. We present a new local magnetic field generating coil system design, microrobot design, actuation scheme, and orientation control for actuating multiple magnetic microrobots independently. The new designs are validated and experiments showcasing their abilities are presented. The demonstrations include closed-loop independent and simultaneous control of four microrobots and a sample micromanipulation task involving two microrobots pushing micro-parts into a prescribed formation.

Control system and measurements of coil actuators parameters for magnetomotive micropump concept

Control system and measurements of coil actuators parameters for magnetomotive micropump concept

The influence of energy recovery on the overall efficiency of acoustic sources at low frequencies

This paper defines a criterion called the overall efficiency (OE) for evaluating the efficiency of acoustic sources. In practice, the conventional efficiency (CE), is not capable of giving a comprehensive overview of the power consumption, especially in the connected amplifier drivers. The reason for this is that the CE is defined based on the nominal input electrical power. The nominal input electrical power is defined as the real part of the power that is delivered by the electrical amplifier to the actuation unit of an acoustic source. Therefore, power loss in the amplifier unit is not included in the CE definition. With the aid of the OE criterion, the effect of power loss in the connected amplifier units is taken into account. In particular, the application of the OE is crucial for acoustic sources that operate in a low frequency range. This is due to the reactive nature of power in both actuators and connected amplifiers. In the current paper, various combinations of amplifiers and actuators are studied. In particular, voice coil actuators and piezoelectric stack elements including both Lead Zirconate Titanate (PZT) ceramics and single crystal Lead Zirconate Niobate-Lead Titanate (PZN-PT) piezoelectric materials are investigated. In addition, the effect of a connected power driver is investigated. A class AB and a class D amplifier are studied respectively as analogue and switching amplifiers. Unlike a class AB amplifier, a class D amplifier is capable of energy recovery. A perforated flat acoustic source is examined in this paper as a practical example to verify the OE criterion. The numerical simulation on a thin acoustic source shows that for a single actuator, thanks to energy recovery, the OE is higher in a class D amplifier than that in a class AB amplifier. This study reveals that if a class D amplifier is the driver, using piezoelectric actuators results in a higher OE compared to using a voice coil actuator. Measurements on the sample acoustic source verify the numerical results presented in the current study.

Long Range Six Degree-of-Freedom Magnetic Levitation Using Low Cost Sensing and Control

We have developed a magnetic levitation system which uses an array of cylindrical actuation coils and a set of three position sensing photodiode assemblies for controlled levitation of a moving platform of permanent magnets. The novelty of this system is that low cost, standard off-the-shelf commodity hardware and software components are used for position sensing and feedback control, rather than costly motion tracking sensing systems and controllers. The design and function of the system are described and controlled motion in all directions is demonstrated through motion ranges of 30 mm horizontal and 20 mm vertical translation, and 26° of roll and 43° of yaw rotation.

Augmenting Perceived Softness of Haptic Proxy Objects Through Transient Vibration and Visuo-Haptic Illusion in Virtual Reality

In this article, we investigate the effects of active transient vibration and visuo-haptic illusion to augment the perceived softness of haptic proxy objects. We introduce a system combining active transient vibration at the fingertip with visuo-haptic illusions. In our hand-held device, a voice coil actuator transmits active transient vibrations to the index fingertip, while a force sensor measures the force applied on passive proxy objects to create visuo-haptic illusions in virtual reality. We conducted three user studies to understand both the vibrotactile effect and its combined effect with visuo-haptic illusions. A preliminary study confirmed that active transient vibrations can intuitively alter the perceived softness of a proxy object. Our first study demonstrated that those same active transient vibrations can generate different perceptions of softness depending on the material of the proxy object used. In our second study, we evaluated the combination of active transient vibration and visuo-haptic illusion, and found that both significantly influence perceived softness, with with the visuo-haptic effect being dominant. Our third study further investigated the vibrotactile effect while controlling for the visuo-haptic illusion. The combination of these two methods allows users to effectively perceive various levels of softness when interacting with haptic proxy objects.

Composite formation flying strategy for distributed space telescopes with an ultralarge aperture

There is increasing demand for space telescopes with ultralarge apertures in the order of 100 to 1000 m for space exploration. It is difficult to expand a space telescope beyond 100 m because of the extensive structural controls that are needed to satisfy optical interference. Large apertures can be achieved using classical formation flying satellites, but it is difficult to achieve suitable relative position and altitude control. Therefore, a novel composite formation flying strategy for distributed space telescopes that provides an ultralarge aperture and ultrahigh accuracy is presented. The proposed strategy combines coarse and fine formations (FFs) provided by support and payload modules (PMs), respectively. The support and PMs are actively connected by noncontact voice coil actuators (VCAs) in each formation satellite. A model and a VCA collision avoidance control approach are also provided for the proposed satellites. The coarse formation is controlled by small thrusters and gives the relative position accuracy in the order of centimeters. The FF is controlled by the VCAs and gives the relative position accuracy in the order of micrometers. The performance is evaluated using simulation studies.

Programmable signal path system for magnetic tracking devices for local navigation tasks

Introduction. The article is dealing with the Magnetic Tracking signal path for measurement of objects’ positions in nearby places. The basic principle of the Magnetic Tracking method is based on measurement of magnetic induction of the reference magnetic fields and the calculation of the objects position based on it.Problem analysis. Big advantages of magnetic tracking technologies are the non-line-of-sight feature compared to optical tracking and high accuracy of long time measurement compared to inertial tracking. However, a very large signal range and significant distortions due to nearby metallic objects are serious drawbacks preventing magnetic tracking from being widely used.Selection and configuration of signal path components. Taking into account the requirements of uptoday microelectronics, in particular for the sensors of the Internet of Things, the signal path of the Magnetic Tracking sensors is implemented on the concept of System on Chip. Basic components of the signal path are software Programmable Waveform Generator, Programmable Gain Amplifiers and Programmable Mixer. Configurations of the components are provided by Application Programming Interface routines.                                                                                                                                                                                                                                                                                                                                               Functional and model studies of the synchronous detector. Noise immune processing is based on synchronous detector. SPICE simulations and analysis of this detector are provided.Implementation of signal path of magnetic tracking. The signal converter has been implemented on the Programmable System on Chip PSoC 5LP (Cypress Semiconductor). The module CY8CKIT-059 Prototyping Kit has been used. The developed software for controlling the measurement process provides controlling the conversion mode, dynamic amplification switching, analog-to-digit converting, etc.Conclusions. The novelty of the solutions presented in the work is the combination of signal amplification dynamic switching and the noise immune processing. Reference magnetic fields are formed by actuator coils in the lowfrequency spectrum of electromagnetic waves. Signals are produced by sensor coils and are used for objects position calculation. Technologies of Magnetic Tracking are considered as high promising solutions for Virtual Reality, Augmented Reality and Internet of Things.

Atomic Force Microscopy Breaking Through the Vertical Range-Bandwidth Tradeoff

This article proposes a mechatronic system design for atomic force microscopes (AFMs) in order to realize a large range and high control bandwidth of the vertical probe motion by a flexure-guided voice coil actuator. The first mechanical resonant frequency of the actuator is decreased to 67 Hz for a large motion, whereas the second resonant frequency is maximized to 1.15 kHz. The frequency band between the resonances enables twodegree-of-freedom control with a position sensor to realize a control bandwidth of 881 Hz, which is 13 times higher than the first resonance that is the limitation of conventional AFMs. The closed-loop actuator achieves a positioning resolution of 1.7 nm and a nonlinearity of 0.02% for a motion range of 700 μm. Consequently, the actuator realizes a range-bandwidth product of 617 kHz·μm, breaking through a theoretical limit of piezoelectric actuators (567 kHz·μm). The high performance of the actuator is further confirmed by 400 μm topography measurement in the constant force mode with a bandwidth of 197 Hz. The achieved resolution of the topography measurement is 2.9 nm, and it is demonstrated by successfully imaging nanostructures on a CD-ROM disk.

SIGNAL MODEL FOR SPATIAL POSITION SENSORS IN MAGNETIC TRACKING SYSTEMS

The subject of research is the process of forming signals in magnetic tracking systems including those used for spatial position calculation within the concepts of Industry 4.0 and Industrial Internet of Things. Such systems are based on calculating the spatial position of objects upon measurements of reference magnetic fields in low-frequency electromagnetic radiation spectrum. The goal is to develop and verify a signal model for spatial position calculating in magnetic tracking systems. The signal model is developed upon experimentally obtained dependencies of the informative signals on the distances and angles between sensor and actuator coils. Objectives: analysis of signals in magnetic tracking systems, development of tools for experimental study, mathematical interpretation of the research results along with development of the signal model, verification and use of the developed model. General scientific methods were used, including experiment, measurement, analysis, synthesis, probabilistic and statistical methods. We have obtained the following results: The structure of a signal chain of the programmable magnetic tracking systems and its implementation on the basis of PSoC of 5LP Family by Cypress Semiconductor has been disclosed. Experimental results obtained at different distances and angles between the actuator and sensor coils have been presented. For spatial positions calculation signal models that describe distribution of magnetic fields and signals of sensor coils are used. We have analyzed typical inaccuracies and ways of their minimization. For verification of the introduced signal model we propose to use the mean square deviation of normalized signals. Conclusions. A signal model for the mutual position of actuators and sensors in magnetic tracking systems has been developed. The model describes functional dependencies whose main parameters are the distances and angles between coils. Further development of the presented results implies the proposed signal model to be used when solving problems of developing and specifying algorithms of spatial position calculation, system debugging and rapid analysis, optimization of calibration procedures.

High-Performance Natural Melanin/Poly(vinyl Alcohol-co-ethylene) Nanofibers/PA6 Fiber for Twisted and Coiled Fiber-Based Actuator

Twisted and coiled fiber-based actuators have drawn a great attention because their unique structure can provide mechanical response with the external thermal stimulus. Herein, an ultra-fast and light-weight twisted and coiled fiber-based actuator was designed based on a nature melanin/poly (vinyl alcohol-co-ethylene) (PVA-co-PE) nanofibers/PA6 composite fiber. In brief, PA6 was firstly coated by melanin/PVA-co-PE nanofibers using a spraying method, followed by the twisting and coating the composite fiber to obtain the actuator. The excellent photothermal property of melanin contributed to the superior performance of the actuator, whereas the PVA-co-PE nanofibers was responsible for the uniform distribution of melanin and the enhanced mechanical property of the prepared-actuator. This unique design has led to the high performance of the melanin/NFs/PA6 fiber-based actuator, whose torsion actuation can reach to 14,000 rpm, and maximum tensile actuation was − 6.36% at temperature difference of 40 ℃. In addition, the tensile stress of PA6/NFs/melanin fiber was about four times higher than PA6 filaments. Owing to the simple and environmental-benign preparation method, as well as the excellent efficiency of twisted and coiled melanin/NFs/PA6 fiber-based actuator, this study highlights the facile design of the composite fiber for high-performance fiber-based actuators. This fiber-based actuator is promising for application in energy generator.

Vibration Characteristics of Thomson Coil Actuator Based on Simulation and Experiments

To meet the fast and stable operational demands of DC circuit breakers (DCCBs), an ultrafast mechanical switch (UFMS) based on a Thomson coil (TC) actuator is studied. First, a 2D finite element (FE) transient axisymmetric model of a TC actuator coupled with magnetic fields, solid mechanics and electrical circuit modules is implemented. A time-domain analysis shows that the armature bending may limit the electromagnetic coupling effects between the coil and armature at the initial stage of driving, and this motion is accompanied by the fluctuation of the displacement and stress of each part. A frequency-domain analysis shows that the dynamic response form and vibration frequency of the actuator under the action of repulsive force are consistent with those of the 4th mode, where the maximum relative displacement occurs at the armature edge. Based on this research, a new armature structure is proposed, and the relationships among armature parameters, motion characteristics, and stress distribution are studied. Finally, a 110 kV UFMS is developed, and two armatures with different parameters are built and tested to verify the accuracy of the simulation model and the effectiveness of the optimization method.

Study on the Twisted and Coiled Polymer Actuator with Strain Self-Sensing Ability.

Twisted and coiled polymer actuators (TCAs) are a kind of efficient artificial muscles, which have good prospects for application in soft robots, bionic devices, and biological, medical, and other high-tech fields. However, the inability to dynamically sense and adjust the strain of the actuator will lead to uncertainty in the accuracy of deformation and strain, resulting in imprecise target action. Herein, TCAs with strain self-sensing ability (TCASA) are prepared by integrating the stretchable optomechanical film (SOMF) sensors into TCAs, which provides a simple strategy for dynamical strain sensing. These SOMFs have a wide range of color changes during deformation of TCAs, and the strain is perceived by observing the color change according to the corresponding relationship between color change and strain. Furthermore, the proposed TCASA maintain excellent cycling stability of strain self-sensing during cyclic tests (200 cycles) and excellent strain self-sensing performance to perform strain control compared to TCAs without SOMFs. The results indicate that the proposed structure is a promising soft actuator with excellent strain self-sensing ability, which is well suited for soft robots, bionic devices, biological and medical fields, smart wearable technologies, and so forth, especially when controlled, repetitive deformations are required.

Design and Simulation of Electromagnetic Linear Actuators for Jet Dispensers

Three electromagnetic-based linear actuators, namely a solenoid actuator (SA), a moving coil actuator (MCA), and a moving magnet actuator (MMA), are proposed for driving the needle in a jet dispenser. The total resistance force acting on the needle during operation, including the damping force, the friction force, the inertia force, the compression spring force, and the backpressure, are measured by an experimental model. The thrust force required to overcome this resistance force is then predicted for each actuator using finite element analysis (FEA) simulations. Simple two-dimensional models of the SA, MCA, and MMA are constructed using the same coil dimensions in every case in order to facilitate an objective comparison between them. Simulations in ANSYS Maxwell software are then performed to adjust the specific dimensions of each actuator structure in such a way as to generate the thrust force required to drive the needle in the jet dispenser with the minimum excitation current possible. The simulation results show that for a maximum needle driving frequency of 250 Hz and a stroke length of 0.5 mm, the excitation current required to generate the necessary thrust force is equal to 1.8 A and 1.9 A for the MCA and MMA models, respectively, when a return spring is not used, and 2.2 A, 3.8 A, and 4.1 A for the SA, MCA, and MMA models, respectively, when a return spring is employed. It is additionally shown that the thrust force drop of the MCA and MMA models is far less than that of the SA model, about 0.7%, 1.8%, and 61% for three models, respectively. Three preliminary designs for jet dispensers incorporating the proposed actuators are also generated for reference purposes.

Test bed for rotation-based triboelectric nanogenerators.

The triboelectric nanogenerator (TENG) has been attracting attention for electronic devices and sensors consuming low power. Among the few operating modes of the TENG, the rotation-based TENG provides a more continuous and smoother output than the linear-motion-based TENG. To evaluate the output performance of the rotation-based TENG precisely and quantitatively, a test bed that adjusts the eccentricity error, tilt angle error, contact force, and rotational speed is proposed. The test bed includes a motor, torque sensor, 2-axis planar stage, 2-axis tilting stage, 1-axis vertical stage, 3-degree-of-freedom force/torque (3-DOF F/T) sensor, and voice coil actuator. With the proposed test bed, the effects of the eccentricity error, tilt angle error, contact force, and rotational speed on the electrical output performance of the rotation-based TENG are analyzed. The test bed is expected to be used for quantitative performance analysis and comparative study of various rotation-based TENGs, and it can help improve the performance and reliability of rotation-based TENGs.

Analysis of structure strength for direct current high-speed switch based on flexible body theory

The Thomson coil actuator has an important application prospect in direct current high-speed switch due to its short respond time and fast operation speed. However, the large electromagnetic impact force during the opening process may bring the stress deformation of movable components and thus cause damage to the mechanism. Therefore, the dynamic stress and strain evaluation of the moving parts is very important for the design and optimization of direct current high-speed switch. In this article, a novel method of structure strength analysis based on the flexible body theory is established for direct current high-speed switch. The electromagnetic and buffer forces in the rapid opening process are calculated, and then the stress and strain distribution of the key components are obtained. Finally, the strain test circuit of the key components is built. By comparing the simulation and experimental results of dynamic strain, the validity of the established simulation model is verified.

Parametric Study of the Design Variables Involved in the EMF Process of Sheet Metal

This study carries out a numerical parametric analysis on some key variables of an electromagnetic forming (EMF) system designed for free bulging of circular metal sheets, aiming a high and adequate distribution of electromagnetic pressure produced by the EMF system using a spiral actuator coil with a single-layer. The proposed methodology considers fully coupled electric-magnetic problems but uncoupled with the mechanical phenomenon, and solves the equations related to the coupled electrical circuits, identifying the influence of their parameters on the EMF process. Further, a calculation method is presented for the time-dependent electromagnetic pressure intensities and distributions along the radial direction, regarding their dependency in relation to the EMF system parameters. The research methodology is suitable to aid in the EMF systems design, evidencing the parametric influences, considering the pulse unit, and the EMF system geometry. The numerical results show that there exists an optimum time for the maximum electromagnetic pressure to occur producing higher sheet displacements and this optimum time is related to the spiral coil geometry, and mainly to pulse unit parameters. In other words, there exists an optimum discharge current frequency for each EMF process.

Discretely assembled walking machines

We introduce a discrete approach to robotic construction that enables the integration of structure, mechanism, and actuation and offers a promising route to on-demand robot fabrication. We demonstrate this with the assembly of two centimeter-scale electromechanical systems: a Discretely Assembled Walking Motor (DAWM) capable of producing large scale linear or rotary motion from five millimeter-scale part types as well as a Modular Tiny Locomoting Element (MOTILE) that can locomote on a variety of ferrous surfaces. The five part types each embody a limited capability including rigid (strut and node), flexural, magnetic, or coil. Through their arrangement in a three-dimensional lattice, we demonstrate the assembly of actuated mechanical degrees-of-freedom in useful small-scale machines. This work extends prior research in discrete material systems with the inclusion of flexural and actuation components. Actuation is accomplished with the use of voice coil actuator components that produce up to 42 mN of force and strokes of 2 mm. This performance compares well with other millimeter scale actuators and provides sufficient force to lift 28 connected nodes in our assembled lattice, or 7 other actuator components. DAWM is capable of stepping at rates of up to 35 Hz, resulting in velocities of up to 25 mm/s. Multiple DAWM systems can be stacked to add force and can be driven in-phase or out-of-phase to produce intermittent or continuous force, respectively. MOTILE can climb vertical surfaces at speeds of 2.46 body-lengths per second, representing the fastest vertical climbing robot in recently reported research. This approach to robot fabrication discretizes robotic systems at a much finer granularity than prior work in modular robotics and demonstrates the possibility of assembling useful small-scale machines from a limited set of standard part types.

Active stabilization of unmanned aerial vehicle imaging platform

The advancement in technology has seen a rapid increase in the use of unmanned aerial vehicles for various applications. These unmanned aerial vehicles are often equipped with the imaging platform like a camera. During the unmanned aerial vehicle flight, the camera is subjected to vibrations which hamper the quality of the captured images/videos. The high-frequency vibrations from the unmanned aerial vehicle are transmitted to the camera. Conventionally, passive rubber mounts are used to isolate the camera from the drone vibrations. The passive mounts are able to provide reduction in response near the resonance. However, this comes at the cost of amplification of response at the higher frequency. This article proposes an active vibration isolation system which exhibits improved performance at the higher frequencies than the conventional system. The active isolation system consists of a contact-less voice coil actuator supported by four springs. Experiments are carried out to study the effect of vibrations on the quality of images captured. The characterization of drone vibrations is also carried out by recording the acceleration during different flight modes. The performance of the proposed isolation system is experimentally validated on a real drone camera subjected to the recorded drone acceleration spectrum. The isolation system is found to perform better than the conventional rubber mounts and is able to reduce the vibrations to a factor of one-fourth. It can be effectively used to improve the image acquisition quality of the unmanned aerial vehicles.

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.