Due to the advantages of high energy efficiency and environmental friendliness, the electro-hydraulic actuator (EHA) plays a vital role in fluid power control. One variant of EHA, double pump direct driven hydraulics (DDH), is proposed, which consists of double fixed-displacement pumps, a servo motor, an asymmetric cylinder and auxiliary components. This paper proposes an adaptive backstepping sliding mode control (ABSMC) strategy for DDH to eliminate the adverse effect produced by parametric uncertainty, nonlinear characteristics and the uncertain external disturbance. Based on theoretical analysis, the nonlinear system model is built and transformed. Furthermore, by defining the sliding manifold and selecting a proper Lyapunov function, the nesting problems (of the designed variable and adaptive law) caused by uncertain coefficients are solved. Moreover, the adaptive backstepping control and the sliding mode control are combined to boost system robustness. At the same time, the controller parameter adaptive law is derived from Lyapunov analysis to guarantee the stability of the system. Simulations of the DDH are performed with the proposed control strategy and proportional–integral–differential (PID), respectively. The results show that the proposed control strategy can achieve better position tracking and stronger robustness under parameter changing compared with PID. Full article

This paper focuses on the electromechanical properties of novel sub-micron compliant metallic thin film electrodes for dielectric elastomer membranes. Electrodes with thicknesses within the range of 10–20 nm and different residual stress states are explored. Both pure nickel films and sandwiches of nickel (Ni) and carbon (C) are deposited by direct current (DC) magnetron sputtering onto pre-stretched silicone elastomer membranes. Both 37.5% biaxial pre-stretch and 57.5% uniaxial pre-stretch under pure shear condition (PSC) are considered in the conducted investigation. After the coating process is completed, the elastomer is allowed to relax. In the contracted configuration, it exhibits a wrinkled surface. After this state is reached, the electromechanical characterization is performed. All types of films reveal a low initial resistance (around 100 Ω/square). Depending on the kind of pre-stretch and the electrode material, a strain of 100% without any major degradation is achieved. It is also shown how the residual stress of the layers can be influenced by suitable sputtering parameters. As a result, low residual film stress significantly improves the electromechanical properties of PSC pre-stretched elastomers, but have only a minor influence on the biaxially pre-stretched ones, regarding the Ni and the Ni + C thin films. This phenomenon is directly connected to the failure mechanisms observed on the two types of pre-stretched membranes. With reversed layer order, i.e., C + Ni electrodes, the residual stress state of Ni does not influence the electromechanical properties for both the biaxially pre-stretched and the PSC pre-stretched coated membranes. The results are of fundamental importance for understanding the role of residual stresses for the creation of electromechanically stable and highly conductive electrode films, to be used in dielectric elastomer (DE) applications. Full article

Shape memory alloys and polymers are a class of smart materials that remember a pre-trained shape or form when exposed to an appropriate temperature. In this work, shape memory alloys consisting of wires, 1-way springs, and 2-way springs are described; an open-loop control of shape memory alloys and polymers is also implemented. Since the amount of electric current that flows through a wire is directly proportional to temperature, control of the electric circuit is used for open-loop temperature control. The designed smart control is applied to rotate a lever mechanism through the conversion of the linear motion of the shape memory alloy (SMA) into the rotational motion of the lever through the tapping of a piezoelectric transducer to deliver the open-loop control. When the piezo transducer is deformed by mechanical stress via tapping, striking, or any other mechanical stimulus, it produces an electrical signal, which when sent to the microelectronic circuit activates the SMA. The implemented system can be applied in robotic systems and autonomous applications. Full article

The pronation/supination of the forearm are important movements to properly accomplish the activities of daily living. While several exoskeletons have been proposed for the rehabilitation of the arm, few of them have actively implemented the movements of pronation/supination. Often, the addition of this degree of freedom to the mechanism results in a bulky and heavy structure. Consequently, the overall exoskeleton is too big for a wearable solution. This paper proposes a digital prototype and kinematic evaluation of a cable-driven orthosis for pronation/supination movement assistance. The actuator is based on an open ring (semi-circle) to be attached to the forearm, while a stationary guide drives the ring into a rotary movement. By considering anthropomorphic data in the design stage, it is possible to develop a rigid, compact, and high power to weight ratio solution for the actuator responsible for pronation and supination. The proposed actuator can achieve the full range of motion for the activities of daily living and 83% of the rotation of the forearm total range of motion with a total mass of only 150 g. Full article

Electro-hydrostatic actuators (EHAs) combine the advantages of electric and hydraulic actuation, and it results in a preferable solution for heavy load actuation. The required power level of the EHA is increasing because it is being introduced to large vehicles such as submarines and heavy launch vehicles. Thus, a 30 kW EHA is under development for launch vehicles, which simultaneously require high dynamic performance, light weight, high efficiency, etc. Therefore, a dedicated multi-objective optimization design method is proposed for the preliminary design of the 30 kW EHA. In this study, firstly, the design requirements were analyzed for the launch vehicle application, and the objectives and the constraints of the optimization design were defined for the 30 kW EHA. Secondly, dedicated models were developed for evaluating each objective or constraint, including weight, bandwidth, and efficiency. Thirdly, the multi-objective EHA optimization design was implemented based on the genetic algorithm. Lastly, the optimization design results were evaluated through simulation analysis, which demonstrated that the 30 kW EHA achieved more than 10 Hz bandwidth with under 72 kg weight while the efficiency was also optimized. Full article

This paper presents the design, fabrication and performance of origami-based folding microactuators based on NiTi films showing the one-way shape memory effect. Freestanding NiTi films are micromachined by laser cutting or photolithography to achieve double-beam structures allowing for direct Joule heating with an electrical current. The NiTi microactuators are interconnected to rigid sections (tiles) forming an initial planar system that self-folds into a predetermined 3D shape upon heating. A thermo-mechanical treatment is used for shape setting of as-received specimens to approach a maximum folding angle of 180°. The bending moments, bending radii and load-dependent folding angles upon Joule heating are evaluated. The shape setting process is particularly effective for small bending radii, which, however, generates residual plastic strain. After shape setting, unloaded beam structures show recoverable bending deflection between 0° and 140° for a maximum heating power of 900 mW. By introducing additional loads to account for the effect of the tiles, the smooth folding characteristic evolves into a sharp transition, whereby full deflection up to 180° is reached. Full article

This document reports the design, fabrication and performance of miniaturized locomotion systems employing flexible materials and 3D printed legs. The movement of the system was achieved by the first extensional mode of vibration of the platform of the robot and the inclination of the supporting legs. The structures were manufactured using a 30-mm-long piezoelectric polyvinylidene fluoride (PVDF) film as the robot platform, with manually added legs fabricated by stereolithography (SLA). Several speed measurements were performed for samples of 1- and 2-mm-long legs, at an angle of inclination of 45° and 60° to the PVDF film. The system was able to exceed a speed of 1 BL/s (body-lengths per second) to 25 V. Full article

The high work density and beneficial downscaling of shape memory alloy (SMA) actuation performance provide a basis for the development of actuators and systems at microscales. Here, we report a novel monolithic fabrication approach for the co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double-beam cantilevers are chosen for the actuator layout to enable electrothermal actuation by Joule heating. The SMA materials under investigation are NiMnGa and NiTi(Hf) films with tunable phase transformation temperatures. We show that Joule heating of the cantilevers generates increasing temperature gradients for decreasing cantilever size, which hampers actuation performance. In order to cope with this problem, a new method for design optimization is presented based on finite element modeling (FEM) simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in the perpendicular direction to the active beam cantilevers. Thereby, power consumption can be reduced by more than 35 % and maximum deflection can be increased up to a factor of 2 depending on the cantilever geometry. Full article

This paper reports the design, fabrication and performance of Micro-electromechanical Systems (MEMS) piezoelectric bidirectional conveyors featuring 3D-printed legs in bridge resonators. The structures consisted of aluminium-nitride (AlN) piezoelectric film on top of millimetre-sized rectangular thin silicon bridges and two electrode patches. The position and size of the patches were analytically optimised for wave generation, while the addition of 3D-printed legs, for a controlled contact, allowed for a further step into the manufacturing of efficient linear motors. Such hybrid devices have recently demonstrated the conveyance of sliders—surpassing several times the motor weight—with speeds of 1.7 mm/s while operated at 6 V and 19.3 kHz. However, by the optimisation of various aspects of the device such as the vibrational modes and excitation signals, speeds above 25 mm/s were demonstrated. Full article

Individuals with impaired upper limbs have motor limitations that interfere with functionality. An alternative to rehabilitation is robot-assisted therapy, a method that increases the effectiveness of treatment. New robotic actuators have been developed to assist in the rehabilitation of the upper limb. One of them aims to actively perform finger extension and flexion passively, using a servo motor coupled to a rope system. At the elbow, a direct current (DC) motor combined with a gearbox was coupled to a system of pulleys and ropes designed to actively perform flexion and extension movements. To activate the system, an Arduino-NANO^® and a mobile application for Android were used. The performance of the prototype was evaluated in four post-stroke volunteers. The ability to perform the proposed movements with the device was observed. Structural reinforcement was necessary, after twisting the elbow support structure, with pronation of the forearm, resulting in increased component weight. This work presented new robotic devices that can assist in the rehabilitation of post-stroke individuals. Full article

In recent years, several legged/wheeled robots have been developed, and their effective functionality in locomotion on uneven terrains has been proved. Many robotics researchers have been focusing on improving the locomotion speed as well as the stability and robustness of such robots. High-speed locomotion of robots is, however, subject to various design challenges, especially in the development of actuators. The robotic applications that require high-speed motion in high-torque operations along with the ability to manage dynamic physical interactions are not satisfied by the conventional robotic actuators deploying high-reduction gearings. In this work, we present a quasi-direct-drive actuator designed for continuous high-speed motions in high torque, such as wheeled motions in mobile robots or joint motions in dynamic-legged robots. The presented actuator exploits low-reduction gearing so that it can render over 26 Nm of continuous torque, while the actuator speed can exceed 37 rad/s. Such characteristics enable the exhibition of dynamic motions and can deal with large external impacts. The selection of the motor and design of the gearing unit was carried out iteratively so that commercial items with minimum customization could be employed and the outer diameters of the motor and the gearbox could match. A single-level planetary gearbox was devised for the reduction unit to ensure high back-drivability and transparency of the actuator, thereby making the actuator robust against external impacts and allowing for accurate torque control using motor current measurement. The gear set design was carried out based on the AGMA gear torque calculation. Given the radial space required for the gearbox to deal with the torque requirements, the actuator motor was chosen to be small in height (pancake type), which ensures high torque density within smaller dimensions at high-speed operation. The mechanical design of the actuator is presented in this paper, and the actuator’s specifications in terms of size and performance are compared with those of similar state-of-the-art actuators. Full article

In this paper, a novel monolithic structural design of a piezoelectric (PZT) inchworm motor utilizing three force amplification mode (FAM) mechanisms is presented as an approach to overcome the design challenges of common PZT inchworm motors. A mechanical system model based on Simulink software was developed for a proposed inchworm motor design. The dynamic response of the motor was simulated at the moment of releasing the pre-stressed mechanism. The results showed a backlash response due to the mass acceleration of the mechanisms. Full article

To provide high output force and to reduce the installation space, the electro-hydrostatic actuator (EHA) usually adopts asymmetric cylinder. However, comprehensive effects produced by its asymmetric flow, parameter uncertainties and unknown disturbance make it difficult to achieve high-accuracy position control. This paper proposed an integral sliding mode backstepping control (ISMBC) based on extended state observer for the asymmetric EHA. Firstly, the principle of the EHA was analyzed and an EHA model was built. Furthermore, the state space equation of the EHA was established based on flow distribution analysis. Two extended state observers (ESO) were designed to achieve real-time estimation of the unmeasured system states, unmatched and matched disturbances. The backstepping method was used to compensate the matched and unmatched disturbance, and an integrated sliding mode controller was developed to eliminate the static error and to improve the response ability. Theoretical analysis indicates that the controller can guarantee the desired tracking performance for the actuator under time-varying unmatched disturbances, and can make the tracking error asymptotically converge to zero under constant matched disturbances. Finally, simulations were performed with the designed controller, backstepping controller and proportional–integral–derivative (PID) controller, respectively. Thereafter, detailed comparisons of the control performances were provided. The results show that the proposed controller can achieve better position tracking and stronger robustness in parameter changing compared with the backstepping controller and PID controller. Full article

As a result of the energy crisis and further development of the electro-hydraulic actuator, double-pump direct driven hydraulics (DDH) was brought forward, which mainly comprises a servo motor, double fixed displacement pumps, a differential cylinder, a low-pressurized tank and auxiliary valves. To address the problems caused by uncertain parameters and unknown external disturbances of DDH, this paper proposed a control method adopting active disturbance rejection control (ADRC). Firstly, a mathematical model, including a DDH unit and a micro-crane, was created and modelled in MATLAB/Simulink. Further, the model was verified by measurement. After that, the state-space equation model of the system was derived based on its mathematical model and a third-order ADRC was designed using the constructed system state-space equation. Additionally, tracking-differentiator (TD) was employed to process the input signal transiently to avoid unnecessary oscillations, and the extended state observer (ESO) was used to accurately estimate the influence of the uncertainty and compensate by nonlinear feedback control law (NFCL). Moreover, the proposed ADRC or Proportional–Integral–Differential (PID) control was combined with the mathematical model of a micro-crane. Finally, the simulations were performed under varying loads, and the system position tracking performance were analyzed and compared. The results show that the ADRC can sufficiently suppress the unknown external disturbance, has the advantages of robustness, and improves the position tracking precision. Full article

Machine-induced vibrations and their control represent, for several reasons, a crucial design issue for buildings, and especially for industrial facilities. A special attention is required, at the early design stage, for the structural and dynamic performance assessment of the load-bearing members, given that they should be optimally withstand potentially severe machinery operations. To this aim, however, the knowledge of the input vibration source is crucial. This paper investigates a case-study eyewear factory built in Italy during 2019 and characterized by various non-isolated computer numerical control (CNC) vertical machinery centers mounted on the inter-story floor. Accordingly, the structure started to suffer for pronounced resonance issues. Following the past experience, this paper reports on the efficiency of a coupled experimental-numerical method for generalized predictive and characterization studies. The advantage is that the machinery features are derived from on-site experiments on the equipment, as well as on the floor. The experimental outcomes are then assessed and integrated with the support of Finite Element (FE) numerical simulations, to explore the resonance performance of the floor. The predictability of marked resonance issues is thus analyzed, with respect to the reference performance indicators. Full article

Multistable structures that possess more than one elastically stable equilibrium state are highly attractive for advanced shape-changing (morphing) applications due to the nominal control effort required to maintain the structure in any of its specific stable shapes. The aim of the paper is to develop a bistable cross-shaped structure consisting of symmetric and unsymmetric laminate actuated using Macro Fibre Composite (MFC) actuators. The critical snap-through voltages required to change the shapes are investigated in a commercially available finite element package. The use of MFC actuators to snap the bistable laminate from one equilibrium shape to another and back again (self-resetting) is demonstrated. A new cross-shaped design of active bistable laminate with MFC actuators is proposed where the cross-shape consist of four rectangles on the four legs and a square on the middle portion. All the rectangles are made up of unsymmetric laminates, and the central portion is designed with a symmetric laminate. MFC actuators are bonded on both sides of the four legs to trigger snap-through and snap-back actions. An attempt is made to address the possible design difficulties arising from the additional stiffness contribution by MFC layers on the naturally cured equilibrium shapes of cross-shaped bistable laminates. Full article

In this paper, a mechanical system model based on Simulink software was developed for a proposed design for a stick-slip motor. Only the orientation of a cubic PZT element identifies the mode configuration of the motor. The preliminary results showed that force amplification mode exhibited roughly five times more speed, at one-hundred times more loading force, compared to the displacement amplification mode. Interestingly, when the output displacement was compared to maximum expansion of mechanical advantage mechanism, then the force amplification mode showed displacement amplification. Full article

A novel monolithic structural design of an electrostatic actuator with a multiple degree of freedom is presented as an approach for a system that is capable of performing scalable stroke and large electrostatic force beyond mN range. An electromechanical system model based on Simulink software was developed for a proposed design of the electrostatic actuator. The dynamic response of the actuator was simulated and the mechanical bouncing response due to effect of realizing extra mechanical stoppers or passivation layer was investigated. Additionally, the mechanical bouncing as well as steady state response of the actuator was investigated under various mechanical loading values. The results showed that the switching time increased as the mechanical load was increased. In addition, bouncing maximum peak increased as the collision force was increased. Full article

Earlier research demonstrated that a pump-controlled hydraulic system combines the best properties of traditional hydraulics and electric intelligence. Thus, the new system has been proposed as a replacement for conventional valve-controlled systems, to improve the energy efficiency in non-road mobile machinery in particular. One of the pump-controlled systems can be realized via direct control of hydraulic pump/motor by varying speed of prime mover. Electric motor (EM) as a prime mover attract with higher efficiency (more than 90%) and a wide range of speed regulation. These advantages allow to improve the system efficiency and decrease the energy consumption in electric and hybrid non-road mobile machinery. Further EM's efficiency improvement can be achieved by using vector control systems, which provide rotor magnetic flux control proportionally to the shaft's speed. Considering all vector control’s benefits (high accuracy of speed control, smooth~start and smooth rotation of the motor in the entire frequency range, quick response to load changes, increased control range and accuracy of regulation), the electro-hydraulic systems and influence of electric part on hydraulic one is not investigated widely. Therefore, in this paper Field Oriented Control (FOC) is analyzed as One of the most perspective vector control systems for electro-hydraulic actuator application with a Permanent Magnet Synchronous Machine (PMSM) as a prime mover. In~this study, Direct-driven hydraulics (DDH) was considered as a study case. A detailed model of the PMSM control system with DDH was built in MATLAB/Simulink. The behavior of the DDH system was investigated by transient processes analysis of EM, pump, and cylinder in the normal and failure modes. The system demonstrates a difference between reference and simulated speed about 0.33% and 11.75% of average torque fluctuations. The behavior of the system in failure mode demonstrated multiple excesses of rated parameters. Full article

The versatility of the form factors of thermal shape memory alloys (SMA) in combination with their unique actuation and sensing abilities allow for the design and construction of innovative multifunctional systems. Despite the considerable number of advantages, such as their exceptional energy density, only a few SMA-based actuator systems are commercially available. One of the main reasons for this is their inefficient thermal activation and the resulting high energy consumption. The efficiency of SMA-based actuator systems can be improved by innovative design and control approaches. In the first part of this paper, the intelligent combination of SMA actuator wires with bi-stable, nonlinear spring elements is described. This combination eliminates the commonly quoted disadvantages of SMAs—slow actuation and energy inefficiency—for a wide range of applications. In particular, two energy-free actuator configurations are realized, which can be applied to any non-proportional actuation tasks. The second approach for the realization of high-speed actuation and energy efficiency is the activation of SMA wires with high voltage pulses, which leads to actuation times in the millisecond range and energy savings of up to 80% in comparison to the suppliers’ recommendations. It is shown that even high AC voltages such as typical mains supplies can be directly used for highly efficient SMA activation. Full article

The Hands exert a vital role in the simplest to most complex daily tasks. Losing the ability to make hand movements, which is usually caused by spinal cord injury or stroke, dramatically impacts the quality of life. In order to counteract this problem, several assisting devices have been proposed, but they still present several usage limitations. The marketable orthoses are generally either the static type or over-expensive active orthosis that cannot perform the same degrees of freedom (DoF) that a hand can do. This paper presents a conceptual design of a tendon-driven mechanism for hand’s active orthosis. This study is a part of an effort to develop an effective and low-cost hand’s orthosis for people with hand paralysis. The tendon design proposed was thought to comply with some requisitions such as lightness and low volume, as well as fit with the biomechanical constraints of the hand joints to enable a comfortable use. The mechanism employs small cursors on the phalanges to allow the tendons to run on the dorsal side and by both sides of the fingers, allowing 2 DoF for each finger, and one extra tendon enlarges the hands’ adduction nuances. With this configuration, it is simple enough to execute the flexion and extension movements, which are the most used movements in daily actives, using one single DC actuator for one DoF to reduce manufacturing costs, or with more DC actuators to enable more natural hand coordination. This system of actuation is suitable to create soft exoskeletons for hands easily embedded into 3D printed parts, which could be merged over statics thermoplastic orthosis. The final orthosis design allows dexterous finger movements and force to grasp objects and perform tasks comfortably. Full article

For the longest time, valve-controlled, centralized hydraulic systems have been the state-of-the-art technology to actuate heavy-duty mobile machine (HDMM) implements. Due to the typically low energy efficiency of those systems, a high number of promising, more-efficient actuator concepts has been proposed by academia as well as industry over the last decades as potential replacements for valve control—e.g., independent metering, displacement control, different types of electro-hydraulic actuators (EHAs), electro-mechanic actuators, or hydraulic transformers. This paper takes a closer look on specific HDMM applications for these actuator concepts to figure out where which novel concept can be a better alternative to conventional actuator concepts, and where novel concepts might fail to improve. For this purpose, a novel evaluation algorithm for actuator–HDMM matches is developed based on problem aspects that can indicate an unsuitable actuator–HDMM match. To demonstrate the functionality of the match evaluation algorithm, four actuator concepts and four HDMM types are analyzed and rated in order to form 16 potential actuator–HDMM matches that can be evaluated by the novel algorithm. The four actuator concepts comprise a conventional valve-controlled concept and three different types of EHAs. The HDMM types are excavator, wheel loader, backhoe, and telehandler. Finally, the evaluation of the 16 matches results in 16 mismatch values, of which the lowest indicates the “perfect match”. Low mismatch values could be found in general for EHAs in combination with most HDMMs but also for a valve-controlled actuator concept in combination with a backhoe. Furthermore, an analysis of the concept limitations with suggestions for improvement is included. Full article

A current goal for microactuators is to extend their usually small working ranges, which typically result from mechanical connections and restoring forces imposed by cantilevers. In order to overcome this, we present a bistable levitation setup to realise free vertical motion of a magnetic proof mass. By superimposing permanent magnetic fields, we imprint two equilibrium positions, namely on the ground plate and levitating at a predefined height. Energy-efficient switching between both resting positions is achieved by the cooperation of a piezoelectric stack actuator, initially accelerating the proof mass, and subsequent electromagnetic control. A trade-off between robust equilibrium positions and energy-efficient transitions is found by simultaneously optimising the controller and design parameters in a co-design. A flatness-based controller is then proposed for tracking the obtained trajectories. Simulation results demonstrate the effectiveness of the combined optimisation. Full article

Dielectric elastomer (DE) technology opens up the possibility of constructing novel lightweight and energy-efficient mechatonic systems, whose design can be tailored to several applications. Numerous types of DE actuator (DEA) configurations, capable of high-force, high-speed, and high-stroke, have been presented in the recent literature. One relevant example is represented by membrane DEAs. This type of actuator consists of a DE film pre-loaded with a mechanical bias. In case the biasing element shows a negative slope (i.e., stiffness) in its force-displacement characteristic, the stroke of the resulting DEA can be significantly magnified. Conventional negative-stiffness biasing systems are based on pre-compressed metal beams, thus they appear as unsuitable for miniaturization to the meso- or micro-scale, as well as for the design of completely flexible actuators for wearable and soft robotics applications. To overcome those issues, a new, novel, full polymer-based DEA configuration is introduced in this work. The core element is the biasing system, which is based on a compliant silicone dome. This type of bias presents a negative stiffness region within its mechanical characteristic; thus, it can serve as a flexible alternative to metal-based biasing systems. It will be shown how the force-displacement characteristic of the dome can be geometrically tuned to match the ones of the DE. In this way, a large actuation stroke can be achieved with a full polymer-based design. After discussing system design and manufacturing, the actuator element is assembled. Finally, experimental stroke characterization is performed. Full article

A switching power amplifier is a key component of the actuator of an active magnetic bearing, and its reliability has an important impact on the performance of a magnetic bearing system. This paper analyzes the topologies of a switching power amplifier of an active magnetic bearing. In the case of different coil pair arrangements and bias current distributions, comprehensive evaluation of the different topologies of switching power amplifiers is introduced. This evaluation has a guiding role in the design of a switching power amplifier of an active magnetic bearing. Full article

Fault detection on automotive engine components is an important feature that motivates research from different engineering areas due to the interest of automakers in its potential to increase safety, reliability, and lifespan and to reduce pollutant emissions, fuel consumption, and maintenance costs. The fault detection can be applied to several types of maintenance strategies, ranging from finding the faults that generated a component failure to finding them before the failure occurs. This work is focused on predictive maintenance, which aims to constantly monitor the target component to detect a fault at the beginning, thus facilitating the prevention of target component failures. It presents the results of different machine learning methods implemented as classification predictors for fault detection tasks, including Random Forest (RF), Support Vector Machines (SVM), Artificial Neural Networks (ANN) variants, and Gaussian Processes (GP). The data used for training were generated by a simulation testbed for fault diagnosis in turbocharged petrol engine systems, whereby its operation was modeled using industrial-standard driving cycles, such as the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), New European Driving Cycle (NEDC), Extra-Urban Driving Cycle (EUDC), and the United States Environmental Protection Agency Federal Test Procedure (FTP-75). Full article

“Hi-Fi Stake” piezoelectric actuators are constructed by bonding [011]-poled d₃₂-mode lead-based relaxor-PT single crystals with polycarbonate edge guides into a square-pipe structure. They contract under positive-polarity applied voltage due to d₃₂ values being negative for [011]-poled relaxor-PT single crystals. Under quasi-static loading conditions, Hi-Fi Stake single crystal actuators exhibit highly linear displacement response with negligible hysteresis. Over the years, we have successfully developed the following three versions of Hi-Fi Stake (HFS) actuators: cost-effective (CE), large-stroke (LS) and high-load (HL), all of maximum use temperature of up to 60 °C. Of which, the LS version, of 2-level construction, displays strokes of up to 50 μm @ 240 V and the HL version, of 2-layer construction, has maximum loads allowed of 14 kg-f at room temperature and 7 kg-f at 60 °C. Additionally described in this work are the developments of Cryogenic Hi-Fi Stakes (CG-HFS) and High-Temperature Hi-Fi Stake (HT-HFS) actuators. The selection of suitable crystal compositions, recommended working conditions and measured performance of fabricated prototypes of these two new versions of Hi-Fi Stakes are presented and discussed. Full article

Recent advances in miniaturized actuators and sensors have enabled the development of cooperative systems, in which a complex global task is achieved through the joint collaboration of several microunits. Achieving system miniaturization while maintaining the desired actuation/sensor and cooperative functionality, however, is generally quite challenging from a practical point of view. Smart material transducers based on dielectric elastomer (DE) membranes represent a technology with great potential for the design of high-performance microactuator systems. By designing a miniaturized array of DE taxels, their simultaneous actuation and sensing capabilities can be used to develop large deformation, energy-efficient, multi-functional, and cooperative systems. In addition, the high flexibility of DE material makes the developed system highly suitable for new application fields, such as wearables and soft robotics. To properly design, optimize, and control cooperative DE systems, accurate mathematical models need to be developed first. In this paper, we present a novel physics-based model for an array of three DE actuator taxels. Such a model represents the first step towards the development, optimization, and control of a complex cooperative matrix actuator. Through the proposed model, it is possible to describe the coupling existing between the DE elements, and predict how such coupling effects influence the complete system performance. After presenting the model, the effect of geometrical parameters on the spatial coupling response is studied by means of numerical simulations. Full article

Piezoelectric Actuators (PEAs) are devices that can support large actuation forces compared to their small size and are widely used in high-precision applications where micro- and nano-positioning are required. Nonetheless, these actuators have undeniable non-linearities, the well-known ones being creep, vibration dynamics, and hysteresis. The latter originate from a combination of mechanical strain and electric field action; as a consequence, these can affect the PEA tracking performance and even reach instability. The scope of this paper is to reduce the hysteresis effect using and comparing different control strategies like feedback with a Feed-Forward (FF) structure, which is often used to compensate the non-linearities and diminish the errors due to uncertainties. In this research, black-box models are analyzed; subsequently, a classic feedback control like Proportional-Integral (PI) control is combined with the FF methods proposed separately and embedded into a dSpace platform to perform real-time experiments. Results are analyzed in-depth in terms of the error, the control signal, and the Integral of the Absolute Error (IAE). It is found that with the proposed methods, the hysteresis effect could be diminished to acceptable ranges for high-precision tracking with a satisfactory control signal. Full article

Lower-limb prostheses have an important function to partially recover the leg movement after amputation. In order to improve the mechanical joint behavior towards a healthy human knee, compliant elements have been introduced to the active prostheses, comprised of the well-known Series Elastic Actuators (SEAs). SEAs are used in lower-limb assistive devices due to their ability to tolerate impacts and passive store mechanical energy during ground-walking. Based on the healthy human knee in the stance phase of walking, this paper brings the design, prototyping, and analysis of a customized planar torsional spring. To enhance the compliance of a rigid active knee prosthesis, the proposed spring will substitute a torque flange between the transmission and the output of the actuator, and this carries a series of constraints to the design. The finite element method (FEM) is applied to the development and exploration of the three initially proposed geometries and the material selection along with its heat treatment is based on the maximum stress obtained in the simulations. The proposed geometry, chosen by comparison of the three, is made of austempered AISI 4340 steel and using two springs in parallel and it has a torsional stiffness of 250 N.m/rad with maximum angular displacement of ± 2.5° and 0.153 kg. In future work, we intend to compare the results of the rigid actuator against the SEA one during walking over the ground. Full article

It is difficult to describe precisely, and thus control satisfactorily, the dynamics of an electrohydraulic actuator to drive a high thrust liquid launcher engine, whose structural resonant frequency is usually low due to its heavy inertia and its complicated mass distribution. A generalized model is therefore put forward for maximum simplification and sufficient approximation, where a second-order transfer function is used to model the heavy mass-spring nature of the large engine body outside of the rod position loop, another second-order transfer function with two zeros and two poles representing the hydro-mechanical composite resonance effect in the closed rod position loop. A combined control strategy is applied to meet the stringent specification of static and dynamic performances, including a notch filter, a piecewise or nonlinear proportional, integral and differential (PID) controller and a feed-forward compensation. The control algorithm is implemented in digital signal processors with the same software structure but different parameters for different aerospace actuators. Compared to other approaches, this one makes it easier to grasp the system resonance nature, and, most importantly, the traditional dynamic pressure feedback (DPF) is replaced with the convenient digital algorithm, bringing prominent benefits such as a simplified design, reduced hardware cost and inherent higher reliability. The approach has been validated by simulation, experiments and successful flights. Full article

Soft actuators are compliant material-based devices capable of producing large deformations upon external stimuli. Dielectric elastomer actuators (DEAs) are a type of soft actuators that operate on voltage stimuli. Apart from soft robotics, these actuators can serve many novel applications, such as tunable optical gratings, lens, diffusers, smart windows and so on. This article presents our current work on tunable smart windows which can regulate light transmittance and sound absorption. This smart window can promote daylighting while maintaining privacy by electrically switching between being transparent and opaque. As a tunable optical surface scatters, it turns transparent with smooth surfaces like a flat glass; however, it turns opaque (translucent) with the micro-rough surface. The surface roughness is varied, employing surface microwrinkling or unfolding by using dielectric elastomer actuation. In addition, this smart window is equipped with another layer of transparent microperforated dielectric elastomer actuators (DEAs), which act like Helmholtz resonators, serving as a tunable and broader sound absorber. It can electrically tune its absorption spectrum to match the noise frequency for maximum acoustic absorption. The membrane tension and perforation size are tuned using DEA activation to tune its acoustic resonant frequency. Such a novel smart window can be made as cheap as glass due to its simple, all-solid-state construction. In the future, they might be used in smart green building and could potentially enhance urban livability. Full article

This paper presents a study on design and development of an alternating pressure overlay consists of inflatable mini air bladders, which could be used in relieving and reducing tissue pressure for the treatment of pressure ulcers. Pressure ulcers, which are predominant in the bony prominences of the body, is a skin deformity due to the limitation of blood circulation to the muscle tissues as a result of high pressures applied on the skin for longer duration. This research aims to design miniaturised air bladders which could provide alternating pressure sequences for the treatment of the pressure ulcers. The optimally designed air bladders provide proper envelopment of the patient’s body and create a high resolution of pressure distribution. The optimum geometry and the 3-D deformation profile of the air bladders are analysed using the finite element method. Based on the interface pressure the pressure overlay has been divided into five pressure zones. Furthermore, the real-time interface pressure profile between the body and the overlay is mapped by using the back pressure of mini air bladders. The actuator system includes an integrated control unit that regulates the internal pressures via electropneumatic valves operated based on the back pressure sensor feedback. This actuator system provides the alternating pressure patterns required for inflation and deflation of the mini air bladders controlling the airflow of the support surface, providing proper pressure distributions to heal the ulcers. Full article

“HAPA” stands for High-Authority Piezoelectric Actuator, which describes high-performance piezoelectric actuators of large stroke and blocking force. “HAPAs” are made possible by high-bending-stiffness connectors that connect multiple units of piezoceramic stacks into a 2-level actuation structure. Present HAPA actuators are fitted with commercial piezoceramic stacks. For instance, a “HAPA-(2+2)” comprises 4 lead zirconate titanate (PZT) stacks, 2 in the upper level with displacement projecting upward and 2 in the lower level with displacement projecting downward. They not only double the axial displacement of individual stacks with only fractional increase in device length but also are of 1.5 to 3 larger blocking force depending on the actual design. “FTA” stands for Flextensional Actuator, in which the horizontal extensional displacement of PZT stacks is amplified to yield much larger contractional vertical displacement via a diamond-shaped elastic frame structure. A range of new FTAs has been developed by us using single or multiple units of PZT stacks, of which the performances are described in this work. “HD-FTA” stands for HAPA-Driven Flextensional Actuator, in which HAPA piezoelectric actuators are used as the motor section to drive diamond-shaped elastic members of various designs for further displacement amplification. Several HD-FTAs, driven by a HAPA-(2+2) actuator, have been developed. Compared with standard FTAs of comparable stroke, HD-FTAs display a higher working load but of smaller overall length. “HAPA”, “FTA”, and “HD-FTA” piezoelectric actuators find applications when a smaller actuator length is advantageous in addition to the required moderate-to-large displacement and working load. Full article

This paper presents a low-cost, small-scale, electrohydrostatic actuator (EHA). This actuator leverages low-cost, mass-produced hydraulic components from the radio-controlled model industry, combined with a novel 3D printed valve. The system is capable of relatively high bandwidth operation, with much higher power- and force-density than comparable electrical actuators. This paper presents a dynamic system model, investigating the range of stability. Full article

A novel self-contained, electro-hydraulic cylinder drive capable of passive load-holding, four-quadrant operations, and energy recovery was presented recently and implemented successfully. This solution greatly improved energy efficiency and motion control in comparison to the state-of-the-art, valve-controlled systems typically used in mobile and offshore applications. The passive load-holding function was realized by two pilot-operated check valves placed on the cylinder ports, where their pilot pressure was selected by a dedicated on/off electrovalve. These valves can maintain the actuator position without consuming energy, as demonstrated on a single-boom crane. However, a reduced drop of about 1 mm was observed in the actuator position when the load-holding valves were disengaged to enable the piston motion using closed-loop position control. Such a sudden variation in the piston position that was triggered by switching the load-holding valves could increase up to 4 mm when open-loop position control was chosen. For these reasons, this research paper proposes an improved control strategy for disengaging the passive load-holding functionality smoothly (i.e., by removing this unwanted drop of the piston). A two-step pressure control strategy is used to build up pressure before disengaging the pilot-operated check valves. The proposed experimental validation of this method eliminates the piston position’s drop highlighted before and improves motion control when operating the crane in open-loop position control. These outcomes benefit those systems where the kinematics amplify the piston motion significantly (e.g., in aerial platforms) increasing, therefore, operational safety. Full article

Increased performance in modern hydraulics is achieved by crucial investigation of possible enhancements of its components. Previous research has pointed out that electromechanical actuators can represent an alternative to hydraulic pilot control systems. Since an additional pilot circuit is complex and expensive, there are advantages, especially for systems which currently rely on a separate hydraulic pilot circuit. Actuators for large sized valves have to meet various requirements, such as applying high forces over large strokes. A functional structure of the “valve and its actuation system” has been derived to define these requirements effectively in order to develop an innovative valve actuator. The general function of the system is divided into elementary functions using this design method. Besides common actuators consisting of a switch and an energy converter, even more alternative actuator designs were pointed out by the comprehensive analysis of the functional structure. Since every actuator needs to be attached on any regular hydraulic valve, the designed actuator is presented, and the most significant construction details are explained. In conclusion, this paper summarizes significant steps during the design process of alternative electromechanical actuators of hydraulic valves. It is intended to serve as a basis for the further development of innovative valve actuators. Full article

For the next generation of soft robotics, novel materials are needed that overcome the limitations of established active materials, such as shape memory alloys or dielectric elastomer actuators. These new actuator types should offer fast actuation and good electromechanical coupling. In this publication, the manufacturing process and the resulting prototype of a helical dielectric polymer actuator are presented. The actuator material consists of several layers of thermoplastic elastomer and thermoplastic polymer layers with conductive fillers that are then thermally bonded and stretched, which leads to self-coiling into a helical configuration. In the targeted setup, the thermoplastic dielectric layer, which is compressed by Maxwell pressure, is significantly thinner but much easier to handle than silicone films frequently used in dielectric elastomer actuators. Several manufacturing strategies are discussed and experimentally evaluated. This includes the use of different materials, their preliminary treatment, the implementation of electrically conducting layers functioning as electrodes, and the contact of the conducting layers. By identifying feasible settings and properties for these parameters, potential defects occurring during manufacturing or high-voltage activation can be minimized. By pre-stretching and then releasing a thin strip of the laminate structure, a helix is formed. The resulting prototype actuator setup is characterized under voltages of 2 to 5 kV and shows high-speed actuation at deformation speeds of >5%/s. Due to the helical configuration, the observed contraction is orders of magnitude higher than the theoretical value for the corresponding flat configuration, showing the potential of the newly developed actuator material. Full article

A control circuit for inductive levitation micro-actuators was developed in this research, the circuit’s performance and its electrical parameters are discussed. The developed control circuit was fabricated on a four-layer printed circuit board (PCB) board with a size of 60 × 60 × 25 mm. It consisted of a generator based on high-speed Flip-Flop components and a current amplifier build on a H-bridge configuration. The circuit was able to generate an AC current with a squared waveform in a frequency range from 8 to 43 MHz and with a peak-to-peak amplitude of up to 420 mA. To demonstrate the efficiency of developed circuit and its compatibility with a micro-actuation system, an inductive levitation micro-actuator was fabricated by using 3D micro-coil technology. The device was composed of two solenoidal coil designs, a levitation and a stabilization coil, with outer diameters of 2 and 3.8 mm, respectively. A 25 μm diameter gold wire was used to fabricate the coils, with the levitation coil having 20 turns and the stabilization coil having 12 turns, similar to the micro-structure presented previously by our group. Using the developed control circuit, the micro-actuator was successfully excited and it demonstrated the actuation of aluminum disc-shaped micro-objects with diameters of 2.8 and 3.2 mm and, for the first time, an aluminum square-shaped object with a side length of 2.8 mm at a frequency of 10 MHz. To characterize the actuation, the levitation height and the current amplitude were measured. In particular, we demonstrated that the square-shaped micro-object could be lifted up to a height of 84 μm with a current of 160 mA. The characterization was supported by a simulation using a 3D model based on the quasi-finite element model (FEM) approach. Full article

Acoustic levitation forces can be used to manipulate small objects and liquid without mechanical contact or contamination. To use acoustic levitation for contactless robotic grippers, automated insertion of objects into the acoustic pressure field is necessary. This work presents analytical models based on which concepts for the controlled insertion of objects are developed. Two prototypes of acoustic grippers are implemented and used to experimentally verify the lifting of objects into the acoustic field. Using standing acoustic waves and by dynamically adjusting the acoustic power, the lifting of high-density objects (>7 g/cm${}^3$) from acoustically transparent surfaces is demonstrated. Moreover, a combination of different acoustic traps is used to lift lower-density objects from acoustically reflective surfaces. The provided results open up new possibilities for the implementation of acoustic levitation in robotic grippers, which have the potential to be used in a variety of industrial applications. Full article

In recent years, soft robots, such as those with high human affinity and those that excellently imitate the movements of natural creatures, have gained considerable attention. In soft robots, structurally flexible soft actuators need to be used, not conventional motors or hydraulic/pneumatic cylinders. Various types of soft actuators have been developed depending on the driving principle. A pneumatic rubber artificial muscle is a kind of soft actuator that acquires power through injection of a working fluid, such as air, into an elastic structure, such as rubber. In this study, the authors developed an actuator, namely, the straight-fiber-type artificial muscle, which exhibits excellent contraction characteristics. This artificial muscle consists of a rubber tube that contains reinforcing fibers arranged in the axial direction. When air pressure is applied to the rubber tube, the artificial muscle expands only in the radial direction and contracts in the axial direction due to the restraining effect of the reinforcing fiber. While this artificial muscle exhibits excellent contraction properties, it has some drawbacks. One is the difficulty in enclosing the reinforced fibers that have accumulated in the rubber tube, making this artificial muscle difficult to manufacture. In this study, we investigated short-fiber-reinforced artificial muscles that can be easily manufactured. First, a short-fiber-reinforced rubber was prepared, and anisotropy was evaluated via a tensile test. Then, the short-fiber-reinforced artificial muscles were prepared, and their contractions rates were evaluated. The results confirmed that a short-fiber-reinforced rubber can be useful for the manufacture of artificial muscles. Full article