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Actuators, Volume 6, Issue 3 (September 2017)

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Research

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Open AccessArticle Modeling and Testing Strategies for an Interconnected Four-Pole Magnetic Bearing
Actuators 2017, 6(3), 21; doi:10.3390/act6030021
Received: 19 December 2016 / Revised: 14 May 2017 / Accepted: 12 June 2017 / Published: 23 June 2017
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Abstract
An unusual idea for the construction of active magnetic bearings has been recently discussed in the literature. Theoretical results predict a greater equivalent stiffness for it, when compared with traditional active magnetic bearings. The development of a mathematical model that allows these predictions
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An unusual idea for the construction of active magnetic bearings has been recently discussed in the literature. Theoretical results predict a greater equivalent stiffness for it, when compared with traditional active magnetic bearings. The development of a mathematical model that allows these predictions and the use of recently-built prototypes for testing if the expectations hold true are the main goals of this paper. Full article
(This article belongs to the Special Issue Active Magnetic Bearing Actuators)
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Open AccessArticle A Novel Mechanically Overdamped Actuator with Adjustable Stiffness (MOD-AwAS) for Safe Interaction and Accurate Positioning
Actuators 2017, 6(3), 22; doi:10.3390/act6030022
Received: 23 May 2017 / Revised: 16 June 2017 / Accepted: 19 June 2017 / Published: 28 June 2017
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Abstract
This paper presents the design and development of a novel mechanically overdamped actuator with adjustable stiffness (MOD-AwAS). The novelty of MOD-AwAS compared to other variable stiffness actuators relates to its mechanical design, which prevents oscillations at the output link. Almost all variable stiffness
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This paper presents the design and development of a novel mechanically overdamped actuator with adjustable stiffness (MOD-AwAS). The novelty of MOD-AwAS compared to other variable stiffness actuators relates to its mechanical design, which prevents oscillations at the output link. Almost all variable stiffness actuators have an overshooting problem that require a sophisticated control algorithm to be able to perform accurate positioning. MOD-AwAS can regulate the stiffness from zero to its maximum (theoretically infinite) in less than 0.2 s by changing the position of the pivot point of its lever mechanisms. MOD-AwAS employs only one rotational spring with no pre-deflection, which gives it full accessibility to its energy storage capacity. Experimental results are presented to show the ability of MOD-AwAS to control its position accurately with a wide range of stiffness adjustment. Full article
(This article belongs to the Special Issue Variable Stiffness and Variable Impedance Actuators)
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Open AccessArticle Optimization Design of Electromagnetic Actuator Applied as Fast Tool Servo
Actuators 2017, 6(3), 25; doi:10.3390/act6030025
Received: 21 June 2017 / Revised: 6 August 2017 / Accepted: 8 August 2017 / Published: 18 August 2017
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Abstract
Fast tool servos (FTS) for single point diamond turning are widely employed for machine optical free-form surfaces. A FTS with a large stroke and a high bandwidth can increase the efficiency of a machine and complexity of a work-piece. In this paper, a
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Fast tool servos (FTS) for single point diamond turning are widely employed for machine optical free-form surfaces. A FTS with a large stroke and a high bandwidth can increase the efficiency of a machine and complexity of a work-piece. In this paper, a FTS driven by a Maxwell electromagnetic actuator is developed to obtain a relatively large stroke and high bandwidth. In this study, a multi-objective optimization model is proposed based on the whole system by considering electromagnetic driving principles, kinematic model, and mechanical model. The proposed optimization model can be applied to solve the parameters of electromagnetic actuators with diverse application requirements. A sequential quadratic programming (SQP) algorithm is implemented to solve the problem. The optimization results are verified through both finite element analysis and experiments. The optimized FTS can produce 49.55 μm of full stroke with a frequency response of 3.2 kHz. Full article
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Open AccessArticle Generalization of Series Elastic Actuator Configurations and Dynamic Behavior Comparison
Actuators 2017, 6(3), 26; doi:10.3390/act6030026
Received: 1 May 2017 / Revised: 30 July 2017 / Accepted: 15 August 2017 / Published: 22 August 2017
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Abstract
The Series Elastic Actuator (SEA) has recently been developed by many research groups and applied in various fields. As SEA is the combination of motor, spring, gear and load, various types and configurations of mechanism have been developed as SEAs to satisfy many
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The Series Elastic Actuator (SEA) has recently been developed by many research groups and applied in various fields. As SEA is the combination of motor, spring, gear and load, various types and configurations of mechanism have been developed as SEAs to satisfy many requirements necessary for the applications. This paper provides a theoretical framework to categorize and compare these various configurations of SEAs. The general structure and model of SEA is provided, and SEA configurations are categorized into Force-sensing Series Elastic Actuator, Reaction Force-sensing Series Elastic Actuator and Transmitted Force-sensing Series Elastic Actuator, based on the relative location of the spring. Criteria such as Force sensitivity, Compliance and Transmissibility of SEA are derived and compared using actual SEAs that have been developed previously. Full article
(This article belongs to the Special Issue Variable Stiffness and Variable Impedance Actuators)
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Open AccessArticle Pneumatic Multi-Pocket Elastomer Actuators for Metacarpophalangeal Joint Flexion and Abduction-Adduction
Actuators 2017, 6(3), 27; doi:10.3390/act6030027
Received: 22 July 2017 / Revised: 4 September 2017 / Accepted: 6 September 2017 / Published: 19 September 2017
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Abstract
During recent years, interest has been rising towards developing fluidic fiber-reinforced elastomer actuators for wearable soft robotics used in hand rehabilitation and power-assist. However, they do not enable finger abduction-adduction, which plays an important role in activities of daily living, when grasping larger
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During recent years, interest has been rising towards developing fluidic fiber-reinforced elastomer actuators for wearable soft robotics used in hand rehabilitation and power-assist. However, they do not enable finger abduction-adduction, which plays an important role in activities of daily living, when grasping larger objects. Furthermore, the developed gloves often do not have separate control of joints, which is important for doing various common rehabilitation motions. The main obstacle for the development of a fully-assisting glove is moving a joint with multiple degrees of freedom. If the functions are built into the same structure, they are naturally coupled and affect each other, which makes them more difficult to design and complex to control than a simple flexion-extension actuator. In this study, we explored the key design elements and fabrication of pneumatic multi-pocket elastomer actuators for a soft rehabilitation glove. The goal was to gain more control over the metacarpophalangeal joint’s response by increasing the degree of actuation. Three main functional designs were tested for achieving both flexion and abduction-adduction. Five prototypes, with four different actuator geometries and four different reinforcement types, were designed and fabricated. They were evaluated by recording their free motion with motion capture and measuring their torque output using a dummy finger. Results showed the strengths and weaknesses of each design in separating the control of the two functions. We discuss the different improvements that are needed in order to make each design plausible for developing an actuator that meets the requirements for full assist of the hand’s motions. In conclusion, we show that it is possible to produce multi-pocket actuators for assisting MCP joint motion in both flexion and abduction-adduction, although coupling between the separate functions is still problematic and should be considered further. Full article
(This article belongs to the Special Issue Pneumatic Actuators)
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Review

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Open AccessReview Flexible Medical Devices: Review of Controllable Stiffness Solutions
Actuators 2017, 6(3), 23; doi:10.3390/act6030023
Received: 22 May 2017 / Revised: 27 June 2017 / Accepted: 30 June 2017 / Published: 11 July 2017
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Abstract
In the medical field and in soft robotics, flexible devices are required for safe human interaction, while rigid structures are required to withstand the force application and accuracy in motion. This paper aims at presenting controllable stiffness mechanisms described in the literature for
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In the medical field and in soft robotics, flexible devices are required for safe human interaction, while rigid structures are required to withstand the force application and accuracy in motion. This paper aims at presenting controllable stiffness mechanisms described in the literature for applications with or without shape-locking performances. A classification of the solutions based on their working principle is proposed. The intrinsic properties of these adaptive structures can be modified to change their mechanical characteristics from a geometrical point of view or equivalent elastic properties (with internal mechanisms or with a change in material properties). These solutions are compared quantitatively, based on selected criteria linked to the medical field as the stiffness range, the activation time and the working conditions. Depending on the application and its requirements, the most suitable solution can be selected following the quantitative comparisons. Several applications of these tunable stiffness structures are proposed and illustrated by examples of the literature. Full article
(This article belongs to the Special Issue Variable Stiffness and Variable Impedance Actuators)
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Open AccessReview Recent Progress on BaTiO3-Based Piezoelectric Ceramics for Actuator Applications
Actuators 2017, 6(3), 24; doi:10.3390/act6030024
Received: 15 June 2017 / Revised: 14 July 2017 / Accepted: 23 July 2017 / Published: 31 July 2017
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Abstract
Due to issues with Pb toxicity, there is an urgent need for high performance Pb-free alternatives to Pb-based piezoelectric ceramics. Although pure BaTiO3 material exhibits fairly low piezoelectric coefficients, further designing of such a material system greatly enhances the piezoelectric response by
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Due to issues with Pb toxicity, there is an urgent need for high performance Pb-free alternatives to Pb-based piezoelectric ceramics. Although pure BaTiO3 material exhibits fairly low piezoelectric coefficients, further designing of such a material system greatly enhances the piezoelectric response by means of domain engineering, defects engineering, as well as phase boundary engineering. Especially after the discovery of a Ba(Zr0.2Ti0.8)O3x(Ba0.7Ca0.3)TiO3 system with extraordinarily high piezoelectric properties (d33 > 600 pC/N), BaTiO3-based piezoelectric ceramics are considered as one of the promising Pb-free substitutes. In the present contribution, we summarize the idea of designing high property BaTiO3 piezoceramic through domain engineering, defect-doping, as well as morphotropic phase boundary (MPB). In spite of its drawback of low Curie temperature, BaTiO3-based piezoelectric materials can be considered as an excellent model system for exploring the physics of highly piezoelectric materials. The relevant material design strategy in BaTiO3-based materials can provide guidelines for the next generation of Pb-free materials with even better piezoelectric properties that can be anticipated in the near future. Full article
(This article belongs to the Special Issue Electrochemical and Electromechanical Actuators)
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