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Actuators, Volume 7, Issue 1 (March 2018)

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Open AccessArticle Modeling a Pull-In Instability in Micro-Machined Hybrid Contactless Suspension
Actuators 2018, 7(1), 11; https://doi.org/10.3390/act7010011
Received: 26 February 2018 / Revised: 16 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
A micro-machined hybrid contactless suspension, in which a conductive proof mass is inductively levitated within an electrostatic field, is studied. This hybrid suspension has the unique capability to control the stiffness, in particular along the vertical direction, over a wide range, which is
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A micro-machined hybrid contactless suspension, in which a conductive proof mass is inductively levitated within an electrostatic field, is studied. This hybrid suspension has the unique capability to control the stiffness, in particular along the vertical direction, over a wide range, which is limited by a pull-in instability. A prototype of the suspension was micro-fabricated, and the decrease of the vertical component of the stiffness by a factor of 25% was successfully demonstrated. In order to study the pull-in phenomenon of this suspension, an analytical model was developed. Assuming quasi-static behavior of the levitated proof mass, the static and dynamic pull-in of the suspension was comprehensively studied, also yielding a definition for the pull-in parameters of the hybrid suspension. Full article
(This article belongs to the Special Issue Micromanipulation)
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Open AccessArticle A Calibrated Lumped Element Model for the Prediction of PSJ Actuator Efficiency Performance
Actuators 2018, 7(1), 10; https://doi.org/10.3390/act7010010
Received: 16 February 2018 / Revised: 8 March 2018 / Accepted: 16 March 2018 / Published: 16 March 2018
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Abstract
Among the various active flow control techniques, Plasma Synthetic Jet (PSJ) actuators, or Sparkjets, represent a very promising technology, especially because of their high velocities and short response times. A practical tool, employed for design and manufacturing purposes, consists of the definition of
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Among the various active flow control techniques, Plasma Synthetic Jet (PSJ) actuators, or Sparkjets, represent a very promising technology, especially because of their high velocities and short response times. A practical tool, employed for design and manufacturing purposes, consists of the definition of a low-order model, lumped element model (LEM), which is able to predict the dynamic response of the actuator in a relatively quick way and with reasonable fidelity and accuracy. After a brief description of an innovative lumped model, this work faces the experimental investigation of a home-designed and manufactured PSJ actuator, for different frequencies and energy discharges. Particular attention has been taken in the power supply system design. A specific home-made Pitot tube has allowed the detection of velocity profiles along the jet radial direction, for various energy discharges, as well as the tuning of the lumped model with experimental data, where the total device efficiency has been assumed as a fitting parameter. The best fitting value not only contains information on the actual device efficiency, but includes some modeling and experimental uncertainties, related also to the used measurement technique. Full article
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Open AccessErratum Erratum: Martens, M.; Boblan, I. Modeling the Static Force of a Festo Pneumatic Muscle Actuator: A New Approach and a Comparison to Existing Models. Actuators 2017, 6, 33
Actuators 2018, 7(1), 9; https://doi.org/10.3390/act7010009
Received: 8 March 2018 / Revised: 8 March 2018 / Accepted: 8 March 2018 / Published: 13 March 2018
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Abstract
The authors would like to correct the content of Table 2 and the text above Table 2 in their article[...] Full article
Open AccessArticle Examination of High-Torque Sandwich-Type Spherical Ultrasonic Motor Using with High-Power Multimode Annular Vibrating Stator
Actuators 2018, 7(1), 8; https://doi.org/10.3390/act7010008
Received: 5 January 2018 / Revised: 13 February 2018 / Accepted: 20 February 2018 / Published: 27 February 2018
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Abstract
Spherical ultrasonic motors (SUSMs) that can operate with multiple degrees of freedom (MDOF) using only a single stator have high holding torque and high torque at low speed, which makes reduction gearing unnecessary. The simple structure of MDOF-SUSMs makes them useful as compact
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Spherical ultrasonic motors (SUSMs) that can operate with multiple degrees of freedom (MDOF) using only a single stator have high holding torque and high torque at low speed, which makes reduction gearing unnecessary. The simple structure of MDOF-SUSMs makes them useful as compact actuators, but their development is still insufficient for applications such as joints of humanoid robots and other systems that require MDOF and high torque. To increase the torque of a sandwich-type MDOF-SUSM, we have not only made the vibrating stator and spherical rotor larger but also improved the structure using three design concepts: (1) increasing the strength of all three vibration modes using multilayered piezoelectric actuators (MPAs) embedded in the stator, (2) enhancing the rigidity of the friction driving portion of the stator for transmitting more vibration force to the friction-driven rotor surface, and (3) making the support mechanism more stable. An MDOF-SUSM prototype was tested, and the maximum torques of rotation around the X(Y)-axis and Z-axis were measured as 1.48 N∙m and 2.05 N∙m, respectively. Moreover, the values for torque per unit weight of the stator were obtained as 0.87 N∙m/kg for the X(Y)-axis and 1.20 N∙m/kg for the Z-axis. These are larger than values reported for any other sandwich-type MDOF-SUSM of which we are aware. Hence, the new design concepts were shown to be effective for increasing torque. In addition, we measured the transient response and calculated the load characteristics of rotation around the rotor’s three orthogonal axes. Full article
(This article belongs to the Special Issue Piezoelectric Actuators 2018)
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Open AccessArticle Modelling and Control of Ionic Electroactive Polymer Actuators under Varying Humidity Conditions
Actuators 2018, 7(1), 7; https://doi.org/10.3390/act7010007
Received: 29 December 2017 / Revised: 12 February 2018 / Accepted: 14 February 2018 / Published: 20 February 2018
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Abstract
In this work, we address the problem of position control of ionic electroactive polymer soft actuators under varying relative humidity conditions. The impact of humidity on the actuation performance of ionic actuators is studied through frequency response and impedance spectroscopy analysis. Considering the
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In this work, we address the problem of position control of ionic electroactive polymer soft actuators under varying relative humidity conditions. The impact of humidity on the actuation performance of ionic actuators is studied through frequency response and impedance spectroscopy analysis. Considering the uncertain performance of the actuator under varying humidity conditions, an adaptable model using the neural network method is developed. The model uses relative humidity magnitude as one of the model parameters, making it robust to different environmental conditions. Utilizing the model, a closed-loop controller based on the model predictive controller is developed for position control of the actuator. The developed model and controller are experimentally verified and found to be capable of predicting and controlling the actuators with excellent tracking accuracy under relative humidity conditions varying in the range of 10–90%. Full article
(This article belongs to the Special Issue Electrochemical and Electromechanical Actuators)
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Open AccessFeature PaperReview Structural-Parametric Model of Electromagnetoelastic Actuator for Nanomechanics
Actuators 2018, 7(1), 6; https://doi.org/10.3390/act7010006
Received: 31 October 2017 / Revised: 4 January 2018 / Accepted: 11 February 2018 / Published: 14 February 2018
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Abstract
The generalized parametric structural schematic diagram, the generalized structural-parametric model, and the generalized matrix transfer function of an electromagnetoelastic actuator with output parameters displacements are determined by solving the wave equation with the Laplace transform, using the equation of the electromagnetolasticity in the
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The generalized parametric structural schematic diagram, the generalized structural-parametric model, and the generalized matrix transfer function of an electromagnetoelastic actuator with output parameters displacements are determined by solving the wave equation with the Laplace transform, using the equation of the electromagnetolasticity in the general form, the boundary conditions on the loaded working surfaces of the actuator, and the strains along the coordinate axes. The parametric structural schematic diagram and the transfer functions of the electromagnetoelastic actuator are obtained for the calculation of the control systems for the nanomechanics. The structural-parametric model of the piezoactuator for the transverse, longitudinal, and shift piezoelectric effects are constructed. The dynamic and static characteristics of the piezoactuator with output parameter displacement are obtained. Full article
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Open AccessReview Survey on Recent Designs of Compliant Micro-/Nano-Positioning Stages
Actuators 2018, 7(1), 5; https://doi.org/10.3390/act7010005
Received: 12 January 2018 / Revised: 6 February 2018 / Accepted: 9 February 2018 / Published: 11 February 2018
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Abstract
Micromanipulation is a hot topic due to its enabling role in various research fields. In order to perform a high precision operation at a small scale, compliant mechanisms have been proposed and applied for decades. In microscale manipulation, micro-/nano-positioning is the most fundamental
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Micromanipulation is a hot topic due to its enabling role in various research fields. In order to perform a high precision operation at a small scale, compliant mechanisms have been proposed and applied for decades. In microscale manipulation, micro-/nano-positioning is the most fundamental operation because a precision positioning is the premise of subsequent operations. This paper is concentrated on reviewing the state-of-the-art research on complaint micro-/nano-positioning stage design in recent years. It involves the major processes and components for designing a compliant positioning stage, e.g., actuator selection, stroke amplifier design, connecting scheme of the multi-DOF stage and structure optimization. The review provides a reference to design a compliant micro-/nano-positioning stage for pertinent applications. Full article
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Open AccessEditorial Acknowledgement to Reviewers of Actuators in 2017
Actuators 2018, 7(1), 4; https://doi.org/10.3390/act7010004
Received: 15 January 2018 / Revised: 15 January 2018 / Accepted: 15 January 2018 / Published: 15 January 2018
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Abstract
Peer review is an essential part in the publication process, ensuring that Actuators maintains high quality standards for its published papers [...]
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Open AccessArticle Comprehensive Analytical Approximations of the Pull-In Characteristics of an Electrostatically Actuated Nanobeam under the Influences of Intermolecular Forces
Actuators 2018, 7(1), 3; https://doi.org/10.3390/act7010003
Received: 14 December 2017 / Revised: 4 January 2018 / Accepted: 9 January 2018 / Published: 12 January 2018
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Abstract
In this paper, analytical closed-form expressions to accurately estimate the pull-in characteristics of an electrostatically-actuated doubly-clamped nanobeam are derived and examined. In this regard, a coupled electro-mechanical problem for the nano-actuator is first presented assuming a single mode approximation while taking into account
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In this paper, analytical closed-form expressions to accurately estimate the pull-in characteristics of an electrostatically-actuated doubly-clamped nanobeam are derived and examined. In this regard, a coupled electro-mechanical problem for the nano-actuator is first presented assuming a single mode approximation while taking into account all the possible structural, electrical and nanoscale effects: the fringing of the electrical actuating force, the geometric mid-plane stretching and intermolecular (van der Walls and Casimir) forces. The complicated nonlinear resultant equations are numerically approximated in order to derive the closed-form expressions for the important nano-actuator pull-in characteristics: i.e., the detachment length, the minimum reachable gap size before the collapse and the respective pull-in voltage. The resulting closed-form expressions are first quantitatively validated with other previously published results, and comparisons showed an acceptable agreement. Unlike the reported expressions in the literature, the proposed closed-form expressions in this work are proper approximations, fairly accurate and, more importantly, provide a quick estimate of the critical design pull-in parameters of the nano-actuator. In addition, the analysis of these expressions demonstrated that the consideration of the intermolecular forces together with the fringe effect tends to significantly reduce the threshold pull-in voltage, whereas the mid-plane stretching parameter tends to the contrary to increase the voltage at the pull-in collapse. The derived expressions of these analytical/approximate solutions could hopefully be appropriately used by NEMS engineers as simple/quick procedures for successful design and fabrication of electrostatically-actuated nano-devices. Full article
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Open AccessArticle Piezoelectric Motor Using In-Plane Orthogonal Resonance Modes of an Octagonal Plate
Actuators 2018, 7(1), 2; https://doi.org/10.3390/act7010002
Received: 26 September 2017 / Revised: 1 December 2017 / Accepted: 4 December 2017 / Published: 6 January 2018
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Abstract
Piezoelectric motors use the inverse piezoelectric effect, where microscopically small periodical displacements are transferred to continuous or stepping rotary or linear movements through frictional coupling between a displacement generator (stator) and a moving (slider) element. Although many piezoelectric motor designs have various drive
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Piezoelectric motors use the inverse piezoelectric effect, where microscopically small periodical displacements are transferred to continuous or stepping rotary or linear movements through frictional coupling between a displacement generator (stator) and a moving (slider) element. Although many piezoelectric motor designs have various drive and operating principles, microscopic displacements at the interface of a stator and a slider can have two components: tangential and normal. The displacement in the tangential direction has a corresponding force working against the friction force. The function of the displacement in the normal direction is to increase or decrease friction force between a stator and a slider. Simply, the generated force alters the friction force due to a displacement in the normal direction, and the force creates movement due to a displacement in the tangential direction. In this paper, we first describe how the two types of microscopic tangential and normal displacements at the interface are combined in the structures of different piezoelectric motors. We then present a new resonance-drive type piezoelectric motor, where an octagonal plate, with two eyelets in the middle of the two main surfaces, is used as the stator. Metallization electrodes divide top and bottom surfaces into two equal regions orthogonally, and the two driving signals are applied between the surfaces of the top and the bottom electrodes. By controlling the magnitude, frequency and phase shift of the driving signals, microscopic tangential and normal displacements in almost any form can be generated. Independently controlled microscopic tangential and normal displacements at the interface of the stator and the slider make the motor have lower speed–control input (driving voltage) nonlinearity. A test linear motor was built by using an octagonal piezoelectric plate. It has a length of 25.0 mm (the distance between any of two parallel side surfaces) and a thickness of 3.0 mm, which can produce an output force of 20 N. Full article
(This article belongs to the Special Issue Electrochemical and Electromechanical Actuators)
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Open AccessArticle A New and Versatile Adjustable Rigidity Actuator with Add-on Locking Mechanism (ARES-XL)
Actuators 2018, 7(1), 1; https://doi.org/10.3390/act7010001
Received: 12 November 2017 / Revised: 21 December 2017 / Accepted: 3 January 2018 / Published: 5 January 2018
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Abstract
Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled
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Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled compliant actuator, an adjustable rigidity with embedded sensor and locking mechanism actuator (ARES-XL) is presented in this paper. This compliant system is intended to be implemented in a gait exoskeleton for children with neuro muscular diseases (NMDs) to exploit the intrinsic dynamics during locomotion. This paper describes the mechanics and initial evaluation of the ARES-XL, a novel variable impedance actuator (VIA) that allows the implementation of an add-on locking mechanism to this system, and in combination with its zero stiffness capability and large deflection range, provides this novel joint with improved properties when compared to previous prototypes developed by the authors and other state-of-the-art (SoA) devices. The evaluation of the system proves how this design exceeds the main capabilities of a previous prototype as well as providing versatile actuation that could lead to its implementation in multiple joints. Full article
(This article belongs to the Special Issue Robotic Actuators)
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