Coil Actuator Research Articles

High Cycle Performance of Twisted and Coiled Polymer Actuator

High Cycle Performance of Twisted and Coiled Polymer Actuator

Retraction Note: Machine learning-based self-sensing of the stiffness of shape memory coil actuator

Retraction Note: Machine learning-based self-sensing of the stiffness of shape memory coil actuator

Compound Model of Twisted and Coiled Polymer Actuators Describing Relationship Between Output Force and Excitation Current

Compound Model of Twisted and Coiled Polymer Actuators Describing Relationship Between Output Force and Excitation Current

Coil Formation and Biomimetic Performance Characterization of Twisted Coiled Polymer Artificial Muscles

A biological muscle's force is nonlinearly constrained by its current state (force, length, and speed) and state history. To investigate if artificial muscles can mimic (i.e. biomimetic) the complete mechanical state spectrum of biological muscles, this study uses a novel method to characterize twisted coiled polymer actuators (TCPAs) mechanically. Thus, comprehensive and reproducible test procedures are established to verify artificial muscle biomimetics regarding stress, strain, and strain rate combinations intrinsic to biological muscle. A rheometer performs novel high‐precision mechanical characterization methods to comprehensively verify biomimetic performance. Sample twist level, torque, length, force, and temperature are controlled and measured during twist‐induced coiling, heatsetting/annealing, and mechanical testing. TCPAs are formed from linear low‐density polyethylene monofilament. Linear low‐density polyethylene (LLDPE) TCPAs generate larger stresses than biological muscle through the entire spectrum of strains—contracting more than 40%, exerting more than 0.3 MPa at rest length, and withstanding tension of 8 MPa without damage. Thus, the LLDPE TCPAs attain biological muscle performance statically, but additional tests are required to assess this dynamically. The mechanical performance of LLDPE TCPAs enables biomimetic actuation with an intelligent control and measurement system. Their high‐throughput textile manufacturability positions them for advanced biomechatronic applications—including prosthetics and exoskeletons.

Development of a large stroke 3-DOF piezoelectric steering mirror for optical system

The steering mirrors and the focusing mechanisms are the key components of the optical system. Traditional steering mirrors driven by voice coil actuator or piezoelectric stack actuator have the disadvantages of short stroke, self-locking difficulty and poor structural reliability. These defects limit the performance of the steering mirrors and make it difficult to be compatible with the focusing mechanism. As a result, additional focusing devices are required in the optical system, which significantly increases the complexity of the system. To simplify the optical system, a large stroke three-degree-of-freedom (3-DOF) piezoelectric steering mirror (PSM) which can realize both light path adjustment and focus adjustment is proposed in this study. Two rotational degrees of freedom of the PSM are used to adjust the light path, and a translational degree of freedom is used to adjust the focus. The screwed-typed piezoelectric actuators (STPAs) are designed to drive the PSM by exciting the travelling wave. The feasibility of the operating principle and reliability of the proposed PSM have been verified by finite element simulation. A prototype of the PSM is fabricated and tested. The experimental results show that the PSM achieves rotational degrees of freedom around the x-axis, y-axis and translational degree of freedom along the z-axis with maximum ranges of ±0.17 rad, ±0.17 rad, and ±10 mm, respectively, meeting the application requirements of the optical systems. The resolutions of the two rotary motions of the PSM are 28 μrad, and 21 μrad, respectively, and that of the translational motion is 0.5 μm. Finally, the position adjustment and focusing operations of the image are demonstrated to validate the potential application of PSM in optical systems.

A Numerical Model of Heating and Cooling Cycles to Study the Driven Response for Twisted and Coiled Polymer Actuator

A Numerical Model of Heating and Cooling Cycles to Study the Driven Response for Twisted and Coiled Polymer Actuator

Variable Area Jet Impingement for Enhanced Junction Temperature Control of High-Power Electronics

Abstract Convective heat transfer by jet impingement cooling offers a suitable solution for high heat flux applications. Compared to techniques that rely on bulk conduction in series with convection, direct liquid impingement reduces the thermal resistance between power device hot spots and the coolant. Although capable of highly efficient cooling, static impingement devices must be designed for the worst-case cooling requirements for a transient power profile. This can result in wasted hydraulic performance. Aircraft, highway vehicles, and heavy machinery fall into this category where a substantial factor of safety is required. This work proposes a method for improving power electronics reliability by limiting temperature fluctuations at reduced coolant pressure requirements during transient power cycling using a variable area jet. Single phase jet impingement cooling is implemented in an active control scheme using a variable diameter iris mechanism as the primary nozzle architecture. In addition to pressure drop and temperature control, the active nozzle structure introduces the ability to create pulsating jet flows to further enhance the heat transfer compared to fixed-geometry nozzles. The key underlying fluid mechanics characteristic of pulsating flows is the effect of disrupting the thermal boundary layer on the electrical device surface. By introducing a variable diameter jet, eddy formation can be fine-tuned for optimal boundary layer disruption. Using the definition of the Strouhal number, vortex shedding created by the non-steady jet flows is directly correlated with the resulting Nusselt number as a function of the iris kinematics. An experimental apparatus for jet impingement thermal-fluid testing is used to evaluate the Nusselt number versus Strouhal number for a parametric study of variable diameter iris configurations. The apparatus utilizes a voice coil actuator to achieve sine and square waveforms, to vary the amplitude of actuation, and to vary the mean of actuation. Finally, power cycling with a single emulated hot spot is performed to estimate the reliability increase as a result of maintaining constant junction temperatures with the active jet impingement scheme.

Armature Reaction Analysis and Suppression of Voice Coil Actuator Based on an Improved Magnetic Equivalent Circuit Model

The high thrust density voice coil actuator (VCA) is a key component for the deployers to determine the CubeSats' separation velocity in orbit directly. To improve the VCA's thrust density and power consumption, it is essential to analyze the armature reaction under heavy current work conditions. This paper proposes a dynamic splitting method of the magnetic equivalent circuit (MEC) model for analyzing the armature reaction of the VCA. This MEC model can effectively reveal the interaction mechanism between the dynamic winding field and the permanent magnet (PM) field, which provides an approach to readily and quickly analyze the armature reaction. Based on the understanding of the mechanism, we found an effective way to suppress the armature reaction and propose a new VCA with double PM flux circuits. The electromagnetic performances of the new configuration are evaluated by comparing it with the conventional one. Both the theoretical and experimental results show that the new structure achieves lower magnetic saturation, lower armature reaction, and higher thrust density. A research prototype was constructed and experimentally tested to verify the theoretical results of the armature reaction, magnetic field, thrust, separation velocity, and other performances. The new VCA realizes a wide and accurate modulation of separation velocity for the CubeSats.

Single layered soft skin actuated with twisted and mandrel coiled actuators for soft robotics

AbstractSoft silicone‐based artificial skin is essential in soft robotics because of high elongation, safe human interaction, low energy requirements and ease of manufacturing. Inspired by nature, several attempts have been made to fabricate morphing structures using synthetic soft skin. In this study, a novel elastomeric skin is demonstrated featuring embedded actuators and micro‐fluidic channels, that is capable of grasping objects. The actuators are twisted, and mandrel coiled nylon artificial muscles, with nichrome heaters that overcome key challenges in developing synthetic soft skin. The desired properties of a morphing skin are being low‐cost, lightweight, highly deformable, compact size, silent cyclic actuation, fast response, and long life. The actuators are fabricated from 160 μm diameter resistance wires wrapped on twisted nylon 6 fishing line precursor fibers of 800 μm diameter. The wrapped nichrome (0.42 mm pitch) along with the twisted precursor fibers are coiled on a 1.4 mm diameter mandrel rod to obtain high strain. This muscle termed twisted, and mandrel coiled polymer fishing line muscle with nichrome is embedded in soft skin samples and tested. Characterization results on the actuators (3.2 mm in diameter) showed remarkable tensile actuation of ~36% strain from loaded length at 0.99 MPa for an input power of 4.9 W, a blocked stress of 1.27 MPa, an actuation frequency of 0.04 Hz, and a lifecycle >22,000 cycles. These actuators, when embedded in the soft skin of 4 mm thick, showed ~50% bending strain within 10s and a cyclic behavior with active water cooling. A soft gripper fabricated with embedded soft skin is integrated to our child‐sized humanoid robot (HBS Robot) demonstrating its potential in grasping unconventional and deformable objects, hence advancing the progress in soft robotics.

Self‐Sustained and Coordinated Rhythmic Deformations with SMA for Controller‐Free Locomotion

This study presents a modular, electronics‐free, and fully onboard control and actuation approach for shape memory alloy (SMA)‐based soft robots to achieve locomotion tasks. This approach exploits the nonlinear mechanics of compliant curved beams and carefully designed mechanical control circuits to create and synchronize rhythmic deformation cycles, mimicking the central pattern generators prevalent in animal locomotions. More specifically, the study elucidates a new strategy to amplify the actuation performance of the shape memory coil actuator by coupling it to a carefully designed, monostable curve beam with a snap‐through buckling behavior. Such SMA‐curved beam assembly is integrated with an entirely mechanical circuit featuring a slider mechanism. This circuit can automatically cut off and supply current to the SMA according to its deformation status, generating a self‐sustained rhythmic deformation cycle using a simple DC power supply. Finally, this study presents a new strategy to coordinate (synchronize) two rhythmic deformation cycles from two robotic modules to achieve efficient crawling locomotion but still use a single DC power. This work represents a significant step toward fully autonomous, electronics‐free SMA‐based locomotion robots with fully onboard actuation and control.

Effects of Manufacturing Parameters on Fast Actuation of Twisted and Coiled Polymer Actuators Made of Fishing Lines

Effects of Manufacturing Parameters on Fast Actuation of Twisted and Coiled Polymer Actuators Made of Fishing Lines

Design and Experimental Testing of a Moving Coil Actuator with Compensation Coils

Design and Experimental Testing of a Moving Coil Actuator with Compensation Coils

Fuzzy Proportional Integral Derivative control of a voice coil actuator system for adaptive deformable mirrors

Fuzzy Proportional Integral Derivative control of a voice coil actuator system for adaptive deformable mirrors

Triangular fin array passively actuated by bimetallic coils for CubeSat thermal control

CubeSat thermal control can be especially demanding due to volume and size constraints, high power dissipation per unit surface area, and highly variable internal and external heat loads. As such, CubeSat developers must rely on thermal control systems that meet the specific requirements of their mission and environmental conditions. Deployable radiators enable satellites to increase their radiative surface area and to reveal highly emissive surfaces during times when increased heat rejection is desired. In colder conditions, when decreased heat loss is preferable, the radiators can be stowed. Passive thermal control systems are unpowered and can increase system reliability by not relying on control electronics while offering decreased weight and power requirements. In this work, we propose a deployable array of triangular radiator panels that are independently and passively actuated by bimetallic coils in response to changes in temperature. This system demonstrates the use of bimetallic coils to passively deploy and stow the radiator fins as well as the use of multiple CubeSat radiator fins with independent actuators to provide increased redundancy. An experimental prototype of the system design was subjected to vacuum chamber testing with panels held in a fixed, deployed position to obtain temperature data used to tune a thermal simulation model. The prototype was then placed in a cryogenically cooled vacuum chamber environment with the panels free to actuate passively in response to varied heating conditions. Both steady state and transient testing were performed. Through this testing and the use of the tuned thermal simulation, the experimental prototype is determined to have a turndown ratio (largest cooling power / smallest cooling power) of 5.4. Deployment of the radiator panels serves to reduce CubeSat body temperatures by 45 °C. Results show the efficacy of the bimetallic coil actuators and radiator fin array in providing passive, dynamic thermal control to small satellites. Recommendations are made to further enhance the performance of the system. Of these recommendations, the most critical is to improve the thermal conductive path from the CubeSat body to the bimetallic coils and to the triangular radiator panels across the deployable radiator hinge. Such changes provide the possibility of increasing the maximum heat rejection, responsiveness of the thermal control system, and turndown ratio to 9 or greater.

Soft Coiled Pneumatic Actuator with Integrated Length-Sensing Function for Feedback Control

SPIRA Coil actuators are formed from thin sheets of PET plastic laminated into a coil shape that unfurls like a “party horn” when inflated, while many soft actuators require large pressures to create only modest strains, SPIRA Coils can easily be designed and fabricated to extend over dramatic distances with relatively low working pressures. Internal metalized PET strips separate in the extended portion of the actuator, creating an electrical circuit with a resistance that corresponds to the actuator length. This paper presents and experimentally validates easy-to-use design models for the actuators’ self-retracting spring stiffness, its pneumatic extension force, and its internal length-sensing electrical resistance. Testing of the self-sensing capabilities demonstrates that the embedded sensor can be used to determine the actuator length with virtually no hysteresis. Feedback control with the resistance-based sensing resulted in length-control errors within 5% of the extended actuator length (i.e., 3 cm of 60 cm).

Improved particle swarm optimisation tuned PID position control of voice coil semi-active electrohydraulic damper

Control on the variable damping coefficients in the semi-active damper enhances ride comfort and vehicle stability. The semi-active electrohydraulic damper (SEH) presented in this study incorporates voice coil-based robust valve control to modify the damping coefficients. However, the position tracking accuracy of the voice coil actuator (VCA) gets negatively influenced by the nonlinearities such as load variations due to external disturbances, back emf, and dynamic damper characteristics. Therefore, to achieve excellent position control, a restart particle swarm optimisation with the Gompertz function (PSO-RG) is presented to obtain optimal tuning control gain for the proportional integral derivative controller. The PSO-RG algorithm applies Gompertz function-based particle coefficients and restarting technique. These techniques allow the PSO-RG to overcome the limitations of standard PSO, such as premature convergence and particle entrapment in local minima. The algorithm is tested in five selected benchmark functions for 10, 30 and 50 dimensions. The test data conveys that PSO-RG outperforms the standard PSO in mean, standard deviation, the best solution, and convergence speed. The transient response on identified and validated model of VCA demonstrated a 75.21% reduction in integral absolute error value than conventional PSO. The obtained maximum sensitivity and total variation values proved the robustness and smoothness of PSO-RG tuned PID control. Furthermore, the experimental analysis on the quarter car model shows that PSO-RG tuned PID precisely tracked the reference position with a 21.66% decrease in root mean square error to conventional PSO tuned PID. The CarSim co-simulation test results in the large van model indicate the need for precise VCA position control in enhancing ride comfort and improving the roll stability of the vehicle.

Adaptive Tikhonov regularization and dynamic control points for accurate shape parameter control of plasmas

Precise control of plasma shape parameters, such as elongation and triangularity is duly needed to achieve high-performance tokamak plasmas, for which we propose adaptive search schemes of (1) optimum regularization parameter for the Tikhonov regularization, and (2) control points to specify the key shape parameters such as elongation and triangularity. Many control points that exceed the number of actuator coils become an ill-conditioned problem, which is successfully resolved by Tikhonov regularization with adaptively optimized free parameters. Furthermore, we develop dynamically changed control points by using the Cauchy Condition Surface scheme, where elongation and triangularity become direct control values. By virtue of both the adaptive Tikhonov regularization scheme and the dynamic control point, we achieved accurate shape control with elongation up to 1.93 and triangularity up to 0.65 in JT-60SA, where the allowable speed for the change of the elongation is 0.1 s−1. We also verified the resilience of our developed our logics to the noises. The sequence of the result will contribute to enhance equilibrium controllability in upcoming JT-60SA experiments and provide the robust shape parameter control scheme for ITER and DEMO.

Direct contractility measurement in cardiomyocytes via thin PDMS diaphragm integration with a moving coil actuator: Synergistic maturation through combined topographical and mechanical stimulation

Mechanical stimulation within diaphragm-based cell culture platforms presents a promising strategy to enhance cardiomyocyte maturation. However, most of the proposed techniques have met with limited success due to their inability to directly measure the contractile force of cardiomyocytes. This issue primarily stems from the typically thicker diaphragm structure which is necessary to withstand high strain ranges induced by mechanical stimulation. Herein, we propose a moving coil actuator integrated with a thin polydimethylsiloxane (PDMS) diaphragm for precise mechanical stimulation, cell culture, and drug screening applications. This mechanical stimulation system generates desired mechanical deformation to cultured cardiomyocytes without compromising the integrity of the diaphragm structure. The 10 µm thin diaphragm produces significant displacement from the contractility of cultured cardiomyocytes, which can be directly measured using a laser vibrometer system. Cardiomyocytes cultured on nanogroove PDMS diaphragms with and without stimulation and flat diaphragms with stimulation exhibited 4.25-, 2.81-, 2.39-fold enhancements in contraction force and 1.09-, 1.06-, 1.04-, and 1.32-, 1.17-, 1.16-fold enhancements in sarcomere lengths and Connexin 43 (Cx43) compared to counterparts cultured on flat and nanogroove PDMS diaphragms without stimulation. The practicality of the device as a drug screening platform is demonstrated by examining the drug-induced effects on cardiomyocytes using cardiovascular drugs.

Optimization of direct injection mixture formation for dual-fuel low speed marine engine using novel compound electric gas injection devices

For two-stroke low speed marine engines, using a natural gas-diesel dual-fuel mode can effectively reduce emissions such as NOX, SOX, and CO2, making it an important approach to promote the low-carbon and environmentally friendly development of the shipping industry. To address the issues of abnormal combustion and gas leakage faced by low-pressure gas direct injection, a novel compound electric gas injection device is proposed, which is designed with a coaxial arrangement of a moving coil actuator and a moving iron actuator. Based on this new device, a three-dimensional computational fluid dynamics (CFD) model of the low speed marine engine operating process is established to simulate the distribution characteristics of the in-cylinder flow field under 16 different scenarios, including different injection side-slip angles and lower deflection angles, and to clarify the impact of these factors on the formation, diffusion, and evolution of the mixture. Based on this, an evaluation system was established from two dimensions: mixture uniformity and gas leakage rate. An improved multi-attribute decision-making TOPSIS algorithm based on the entropy weight method was used to define the attribute importance using information entropy, and to construct an optimization evaluation model for the spatial arrangement of the injection device. The optimal arrangement angle was calculated, in which a side-slip angle was 20° and a lower deflection angle was 10°. This method avoids the problem of unreasonable decisions caused by subjective factors such as designer preferences and experience, effectively improving the in-cylinder mixture uniformity and reducing gas leakage rate.

Modeling and Experimental Investigation of an Active Angular Vibration Absorber

The active angular absorber for angular vibration control is proposed. Characteristics of the angular absorber are analyzed and an experiment is performed. The active angular absorber consists of a base and two identical voice coil actuators. The actuators have central symmetry and the coils are series connected to get the same current so that they output inertia forces with the same amplitude in opposite directions. There is a certain distance between the axes of the two actuators to produce a moment from the inertia forces, which can be employed to actively control the angular vibration. First, the mechanics of the angular absorber are presented. Then, the dynamic model of an angular vibration system with the absorber is demonstrated and the control law is proposed. Parameters of the absorber are discussed, showing that the absorber has the advantages of reliable structure and flexibility for installation. Next, numerical simulation is performed and the results show that the control method is effective and the simplification of the dynamic model is reasonable. Finally, a prototype of the absorber is produced and the angular vibration control experiment is conducted. Test results show that angular vibration with the amplitude of 1” level and at a frequency of 6 Hz can be attenuated by 93% to the level of the noise, while vibration at 0.1” level and 46 Hz can be attenuated by 80.7% to 0.01”. The control process is rapid and convergence is stable.