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Actuators, Volume 8, Issue 3 (September 2019)

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Open AccessArticle
Flexible Shape-Memory Alloy-Based Actuator: Mechanical Design Optimization According to Application
Actuators 2019, 8(3), 63; https://doi.org/10.3390/act8030063
Received: 15 July 2019 / Revised: 9 August 2019 / Accepted: 9 August 2019 / Published: 14 August 2019
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Abstract
New robotic applications, among others, in medical and related fields, have in recent years boosted research in the development of new actuators in the search for solutions that are lighter and more flexible than conventional actuators. Shape-Memory Alloy (SMA)-based actuators present characteristics that [...] Read more.
New robotic applications, among others, in medical and related fields, have in recent years boosted research in the development of new actuators in the search for solutions that are lighter and more flexible than conventional actuators. Shape-Memory Alloy (SMA)-based actuators present characteristics that make them an excellent alternative in a wide variety of applications. This paper presents the design, tests (with the control description) and analysis of various configurations of actuators based on SMA wires: flexible SMA actuators, different mechanical design to multiply the displacement and different configurations for actuators with multiple SMA wires. The performance of the actuators has been analyzed using wires of different activation temperatures. The influence of the Bowden sheath of the flexible actuator has been tested, as has the thermal behavior of actuators with several wires. This work has allowed determination of the most effective configuration for the development of a flexible actuator based on SMA, from the point of view of dimensions, efficiency, and work frequency. This type of actuator has been applied in the development of soft robots and light robotic exoskeletons. Full article
(This article belongs to the Special Issue Actuators Based on Shape Memory Alloys)
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Open AccessPerspective
Recycling-Oriented Design in Soft Robotics
Actuators 2019, 8(3), 62; https://doi.org/10.3390/act8030062
Received: 24 June 2019 / Revised: 1 August 2019 / Accepted: 6 August 2019 / Published: 12 August 2019
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Abstract
Soft robotics is a novel approach in the field of robotics. Soft robots or soft actuators are typically polymer-based and are characterized by their flexibility and adaptability, which brings new far-reaching applications. Soft robotics is currently at the peak of its research. One [...] Read more.
Soft robotics is a novel approach in the field of robotics. Soft robots or soft actuators are typically polymer-based and are characterized by their flexibility and adaptability, which brings new far-reaching applications. Soft robotics is currently at the peak of its research. One circumstance that is also present in this age is constant climate change; there is a demand for sustainability. This goes hand in hand with the design of products that are suitable for recycling. Today, more is expected of an engineer than just function-oriented design. This article looks at soft robotics from the point of view of sustainability. Since nature operates in cycles, the aim is to design products in such a way that they can be introduced into cycles. Three recycling cycles for products can be distinguished, which take place during production, during product use, and after product life. Within the framework of this work, special design measures are reviewed for fluidic elastomer actuators—a characteristic type of soft actuators—so that they can be integrated into the recycling process. Full article
(This article belongs to the Special Issue Pneumatic Soft Actuators)
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Open AccessArticle
Applicability of Shape Memory Alloys in Aircraft Interiors
Actuators 2019, 8(3), 61; https://doi.org/10.3390/act8030061
Received: 10 July 2019 / Revised: 1 August 2019 / Accepted: 5 August 2019 / Published: 9 August 2019
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Abstract
This paper evaluates possible applications for SMAs (Shape Memory Alloys) based on the requirements in the field of aircraft interiors. The authors gather requirements regarding industry standards and regulations by detailed literature research and lead user interviews. They develop a classification scheme for [...] Read more.
This paper evaluates possible applications for SMAs (Shape Memory Alloys) based on the requirements in the field of aircraft interiors. The authors gather requirements regarding industry standards and regulations by detailed literature research and lead user interviews. They develop a classification scheme for SMA-based actuators, which consists of SMA-specific technical attributes and requirements. This classification scheme allows one to evaluate the feasibility of using SMA-based systems in aircraft interiors. Furthermore, this paper clusters critical requirements and discusses solutions for limitations of SMAs in aircraft interiors. The authors identify critical and noncritical requirements for the implementation of SMA-based actuators. They suggest solutions for critical requirements in order to improve the possible range of applications for SMAs. The study exclusively regards the field of aircraft interiors and the currently existing industry standards and only indirectly takes laws into account. The evaluated requirements and proposed solutions can be transferred to other areas such as the automotive industry. This structured analysis of the feasibility of SMA-based systems in aircraft interiors is an innovative research work and, therefore, is valuable in order to benefit from the advantageous properties of SMAs. Full article
(This article belongs to the Special Issue Actuators Based on Shape Memory Alloys)
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Open AccessArticle
Scalable Bi-Directional SMA-Based Rotational Actuator
Actuators 2019, 8(3), 60; https://doi.org/10.3390/act8030060
Received: 9 July 2019 / Revised: 29 July 2019 / Accepted: 1 August 2019 / Published: 5 August 2019
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Abstract
In industrial applications, rotatory motions and torques are often needed. State-of-the-art actuators are based on either combustion engines, electro-motors, hydraulic, or pneumatic machines. The main disadvantages are the construction space, the high weight, and a large amount of needed peripheral devices. To overcome [...] Read more.
In industrial applications, rotatory motions and torques are often needed. State-of-the-art actuators are based on either combustion engines, electro-motors, hydraulic, or pneumatic machines. The main disadvantages are the construction space, the high weight, and a large amount of needed peripheral devices. To overcome these limitations, compact and light-weight actuator systems can be built by using shape memory alloys (SMAs), which are known for their superior energy density. In this paper, the development of a scalable bi-directional rotational actuator based on SMA wires is presented. The scalability was based on a modular design, which allowed the actuator to be adapted to various application specifications by customizing the rotational angle and the output torque. On the mechanical side, each module enabled a small rotatory motion, which added up to the total angle of the actuator. The SMA wires were arranged in an agonist-antagonist configuration to provide active rotation in both directions. The presented prototype achieved a total rotation of 100°. The modularity of the mechanical concept is also reflected in the electronics, which is discussed in this paper as well. This consideration allows the electronics to be adapted to the mechanics with minimal changes. As a result, a prototype, including the presented mechanical and electronic design, is reported in this study. Full article
(This article belongs to the Special Issue Actuators Based on Shape Memory Alloys)
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Open AccessArticle
A Critical Analysis of Valve-Compensated Hydrostatic Actuators: Qualitative Investigation
Actuators 2019, 8(3), 59; https://doi.org/10.3390/act8030059
Received: 29 May 2019 / Revised: 22 July 2019 / Accepted: 28 July 2019 / Published: 30 July 2019
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Abstract
Hydrostatic actuation has gained interest from both academia and industry due to the unquestionable energetic advantages when compared to valve-controlled actuators; the main feature being the absence of throttling losses due to the direct control of the cylinder by the pump. However, the [...] Read more.
Hydrostatic actuation has gained interest from both academia and industry due to the unquestionable energetic advantages when compared to valve-controlled actuators; the main feature being the absence of throttling losses due to the direct control of the cylinder by the pump. However, the fact that the great majority of applications are based on single-rod cylinders has been both a challenge and a source of inspiration for a variety of different circuit designs. In an attempt to compensate for the uneven flows coming in and out of differential cylinders, several solutions have been proposed, including the use of hydraulic transformers, individual pumps connected to the cylinder ports or pumps with unmatched input and output flows. The simplest approach, however, seems to be the use of compensation valves in the circuit, which is the focus of this paper. Here, we analyse some representative circuits proposed along the years in a direct and elucidative manner, showing that the definitive solution to the single-rod actuator control problem has been established, paving the road for introducing stable and trustworthy circuits, which can be commercially used in the near future. Full article
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Open AccessArticle
Soft Driving Epicyclical Mechanism for Robotic Finger
Actuators 2019, 8(3), 58; https://doi.org/10.3390/act8030058
Received: 2 April 2019 / Revised: 25 June 2019 / Accepted: 19 July 2019 / Published: 29 July 2019
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Abstract
Nowadays, the development or improvement of soft actuation mechanisms is a crucial
topic for the achievement of dexterous manipulation using. Then, a primary target of research is the
design of actuation and driving devices. Consequently, in this paper, we introduce a soft driving
[...] Read more.
Nowadays, the development or improvement of soft actuation mechanisms is a crucial
topic for the achievement of dexterous manipulation using. Then, a primary target of research is the
design of actuation and driving devices. Consequently, in this paper, we introduce a soft driving
epicyclical mechanism that mimics human muscle behavior and fulfills motion requirements to
achieve grasping gestures using a robotic finger. The prototype is experimentally assessed, and
results show that our approach has enough performance for the implementation in grasping tasks.
Furthermore, we introduce the basis for a new soft epicyclical mechanism merger with shape memory
alloys to allow active stiffness control of the mechanism. Full article
Open AccessArticle
Analysis and Control of Slotless Self-Bearing Motor
Actuators 2019, 8(3), 57; https://doi.org/10.3390/act8030057
Received: 6 June 2019 / Revised: 10 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
A self-bearing motor (SBM) is an electric motor with a magnetically integrated bearing function, that is, it can provide levitation and rotation simultaneously as a single actuator. This paper presents the design, operating principle and control system for the slotless self-bearing motor (SSBM). [...] Read more.
A self-bearing motor (SBM) is an electric motor with a magnetically integrated bearing function, that is, it can provide levitation and rotation simultaneously as a single actuator. This paper presents the design, operating principle and control system for the slotless self-bearing motor (SSBM). In this design, the stator has no iron core but includes six-phase coils. The rotor consists of a permanent magnet and an enclosed iron yoke. Magnetic forces generated by the interaction between stator currents and the magnetic field of the permanent magnet are used to control the rotational speed and radial position of the rotor. In this paper, the torque and radial bearing forces are analyzed theoretically with the aim to develop an improved control system. In order to confirm the proposed control method, an experimental system was constructed and tested. Simulation and measurement results show that the SSBM can work stably in modes such as start, reverse, rotation load and external radial pulse forces. Full article
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Open AccessArticle
Position Control of Pneumatic Actuators Using Three-Mode Discrete-Valued Model Predictive Control
Actuators 2019, 8(3), 56; https://doi.org/10.3390/act8030056
Received: 1 July 2019 / Revised: 15 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
A novel discrete-valued model-predictive control (DVMPC) algorithm termed DVMPC2 for the position control of pneumatic actuators using inexpensive on/off valves is presented. DVMPC2 includes a more flexible cost function, an improved prediction strategy, and other improvements. The actuator is a double-acting cylinder with [...] Read more.
A novel discrete-valued model-predictive control (DVMPC) algorithm termed DVMPC2 for the position control of pneumatic actuators using inexpensive on/off valves is presented. DVMPC2 includes a more flexible cost function, an improved prediction strategy, and other improvements. The actuator is a double-acting cylinder with two on/off solenoid poppet valves connected to each chamber. To reduce the switching frequency and prolong the valve life, DVMPC2 directly switches the valves when necessary, instead of using relatively high-frequency pulse-width modulation. Experimental comparisons are made with the state-of-the-art sliding-mode control (SMC) algorithm and the previous DVMPC algorithm. The comparisons are based on the five performance metrics: integral of time-weighted absolute error (ITAE), root mean square error (RMSE), overshoot (OS), steady-state error (SSE), and valve switches per second (SPS). The robustness is evaluated by increasing and decreasing the total mass of the moving components while keeping the controller parameters constant. The experimental results show that the proposed algorithm is superior to the previous DVMPC and outperformed SMC by a wide margin. Specifically, DVMPC2 reduced ITAE by 80%, RMSE by 52%, OS by 43%, and SPS by 20% relative to SMC. There was no clear winner in terms of SSE. Full article
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Open AccessArticle
Electrical Performance of a Piezo-inductive Device for Energy Harvesting with Low-Frequency Vibrations
Actuators 2019, 8(3), 55; https://doi.org/10.3390/act8030055
Received: 11 June 2019 / Revised: 7 July 2019 / Accepted: 12 July 2019 / Published: 16 July 2019
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Abstract
This study presents the experimental evaluation of a piezo-inductive mechanical system for applications of energy harvesting with low-frequency vibrations. The piezo-inductive vibration energy harvester (PI-VEH) device is composed of a voice coil motor (VCM) extracted from a hard disk drive. The proposed design [...] Read more.
This study presents the experimental evaluation of a piezo-inductive mechanical system for applications of energy harvesting with low-frequency vibrations. The piezo-inductive vibration energy harvester (PI-VEH) device is composed of a voice coil motor (VCM) extracted from a hard disk drive. The proposed design allows the integration of different element types as beams and masses. The dynamic excitations in the system produce a pendular motion carried out by a hybrid arm (rigid-flexible) that generates energy with the rotations (with a coil) and the beam strains (with a piezoelectric material). The electrical assessment was performed through different working modes classified as inductive, inductive with magnetic instabilities, and piezo-inductive. The instabilities in the harvester refer to external forces induced by two magnets that repel each other. The first two inductive configurations were designed as a function of three parameters (length, mass, instability angle) to debug these using the maximum output voltage. The selected experiments were conducted in a piezo-inductive configuration. The results showed two effects on the output voltage—the first one is related to a system without resonances (higher broadband), and the second effect is associated with a multi-resonant system. As a final conclusion, it is pointed out that the electrical performance can be improved with the magnetic instabilities since these considerably amplified the output voltages. Full article
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Open AccessArticle
A Statistical State Analysis of a Marine Gas Turbine
Actuators 2019, 8(3), 54; https://doi.org/10.3390/act8030054
Received: 27 March 2019 / Revised: 1 July 2019 / Accepted: 3 July 2019 / Published: 8 July 2019
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Abstract
This paper describes the analysis, from a statistical point of view, of a maritime gas turbine, under various operating conditions, so as to determine its state. The data used concerns several functioning parameters of the turbines, such as temperatures and vibrations, environmental data, [...] Read more.
This paper describes the analysis, from a statistical point of view, of a maritime gas turbine, under various operating conditions, so as to determine its state. The data used concerns several functioning parameters of the turbines, such as temperatures and vibrations, environmental data, such as surrounding temperature, and past failures or quasi-failures of the equipment. The determination of the Mean Time Between Failures (MTBF) gives a rough estimate of the state of the turbine, but in this paper we show that it can be greatly improved with graphical and statistical analysis of data measured during operation. We apply the Laplace Test and calculate the gas turbine reliability using that data, to define the gas turbine failure tendency. Using these techniques, we can have a better estimate of the turbine’s state, and design a preventive observation, inspection and intervention plan. Full article
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Open AccessFeature PaperReview
Artificial Immune Systems: An Overview for Faulting Actuators
Actuators 2019, 8(3), 53; https://doi.org/10.3390/act8030053
Received: 31 May 2019 / Revised: 24 June 2019 / Accepted: 27 June 2019 / Published: 29 June 2019
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Abstract
This paper reviews Artificial Immune Systems (AIS) that can be implemented to compensate for actuators that are in a faulted state or operating abnormally. Eventually, all actuators will fail or wear out, and these actuator faults must be managed if a system is [...] Read more.
This paper reviews Artificial Immune Systems (AIS) that can be implemented to compensate for actuators that are in a faulted state or operating abnormally. Eventually, all actuators will fail or wear out, and these actuator faults must be managed if a system is to operate safely. The AIS are adaptive algorithms which are inherently well-suited to these situations by treating these faults as infections that must be combated. However, the computational intensity of these algorithms has caused them to have limited success in real-time situations. With the advent of distributed and cloud-based computing these algorithms have begun to be feasible for diagnosing faulted actuators and then generating compensating controllers in near-real-time. To encourage the application of AIS to these situations, this work presents research for the fundamental operating principles of AIS, their applications, and a brief case-study on their applicability to fault compensation by considering an overactuated rover with four independent drive wheels and independent front and rear steering. Full article
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Open AccessArticle
Structural-Parametric Model and Diagram of a Multilayer Electromagnetoelastic Actuator for Nanomechanics
Actuators 2019, 8(3), 52; https://doi.org/10.3390/act8030052
Received: 20 May 2019 / Revised: 22 June 2019 / Accepted: 24 June 2019 / Published: 29 June 2019
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Abstract
In this work, the parametric structural schematic diagrams of a multilayer electromagnetoelastic actuator and a multilayer piezoactuator for nanomechanics were determined in contrast to the electrical equivalent circuits of a piezotransmitter and piezoreceiver, the vibration piezomotor. The decision matrix equation of the equivalent [...] Read more.
In this work, the parametric structural schematic diagrams of a multilayer electromagnetoelastic actuator and a multilayer piezoactuator for nanomechanics were determined in contrast to the electrical equivalent circuits of a piezotransmitter and piezoreceiver, the vibration piezomotor. The decision matrix equation of the equivalent quadripole of the multilayer electromagnetoelastic actuator was used. The structural-parametric model, the parametric structural schematic diagram, and the matrix transfer function of the multilayer electromagnetoelastic actuator for nanomechanics were obtained. Full article
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Open AccessFeature PaperArticle
Shape Memory Polymer Composite Actuator: Modeling Approach for Preliminary Design and Validation
Actuators 2019, 8(3), 51; https://doi.org/10.3390/act8030051
Received: 6 May 2019 / Revised: 13 June 2019 / Accepted: 21 June 2019 / Published: 27 June 2019
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Abstract
The work at hand focuses on the modeling, prototyping, and experimental functionality test of a smart actuator based on shape memory polymer technology. Particular attention is paid to the specific modeling approach, here conceived as an effective predictive scheme, quick and, at the [...] Read more.
The work at hand focuses on the modeling, prototyping, and experimental functionality test of a smart actuator based on shape memory polymer technology. Particular attention is paid to the specific modeling approach, here conceived as an effective predictive scheme, quick and, at the same time, able to face those nonlinearity aspects, strictly related to the large displacements shape memory polymers usually undergo. Shape memory polymer composites (SMPCs) may play a critical role for many applications, ranging from self-repairing systems to deployable structures (e.g., solar sails, antennas) and functional subcomponents (e.g., pliers, transporters of small objects). For all these applications, it is very important to have an effective tool that may drive the designers during the preliminary definition of the main parameters of the actuation system. For the present work, a SMPC plate sample has been conceived and realized in view of aerospace applications. An external fibre optic sensor has been then fixed with special adhesive. The temperatures needed for the activation of the Shape Memory Polymer (SMP) and strain storing have been provided by a thermo-gun and complete load–unload cycles, including strain storing, have been performed. Experimental displacements and strains have been used to validate a dedicated predictive theoretical approach, suited for laminates integrated with SMP layers. Full article
(This article belongs to the Special Issue New Materials and Designs for Soft Actuators)
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Open AccessArticle
Modeling, Identification, and Control of a Discrete Variable Stiffness Actuator (DVSA)
Actuators 2019, 8(3), 50; https://doi.org/10.3390/act8030050
Received: 23 April 2019 / Revised: 25 May 2019 / Accepted: 28 May 2019 / Published: 27 June 2019
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Abstract
A branch of robotics, variable impedance actuation, along with one of its subfields variable stiffness actuation (VSA) targets the realization of complaint robotic manipulators. In this paper, we present the modeling, identification, and control of a discrete variable stiffness actuator (DVSA), which will [...] Read more.
A branch of robotics, variable impedance actuation, along with one of its subfields variable stiffness actuation (VSA) targets the realization of complaint robotic manipulators. In this paper, we present the modeling, identification, and control of a discrete variable stiffness actuator (DVSA), which will be developed for complaint manipulators in the future. The working principle of the actuator depends on the involvement of series and parallel springs. We firstly report the conceptual design of a stiffness varying mechanism, and later the details of the dynamic model, system identification, and control techniques are presented. The dynamic parameters of the system are identified by using the logarithmic decrement algorithm, while the control schemes are based on linear quadratic control (LQR) and computed torque control (CTC), respectively. The numerical simulations are performed for the evaluation of each method, and results showed the good potentialities for the system. Future work includes the implementation of the presented approach on the hardware. Full article
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