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In order to obtain a high-precision pneumatic control system, it is necessary to study the friction force of the cylinder. However, few researchers have considered the cylinder's frictional characteristics at small-displacements. This study investigated the influence of different conditions on the cylinder friction characteristics during the process from static to small-displacement of the pneumatic double O-ring seal. A set of experimental apparatuses controlled by an electric actuator perform a seal ring small-displacement friction test to achieve the goals. The working principle of sealing rings in different deformation stages is expounded. According to experiments, the sealing ring's friction force in small-displacement movement can be separated into tilt, elastic deformation, pre-sliding, and sliding friction stages. Furthermore, the clearance characteristics between the sealing ring and the piston groove are verified, which decreases with the sealing ring thickness. Finally, the friction displacement characteristics of sealing rings under different pressures and materials during the elastic deformation stage were verified. It can be concluded that when the displacement is between 0.05 and 0.25 mm, the friction of the sealing ring is almost linear with the displacement; when the displacement reaches 0.25 mm, with the increase of the displacement, the friction force changes in a similar parabolic manner. This study provides a detailed analysis of the friction characteristics of the seal in different stages of small displacement, which plays an important reference role in overcoming cylinder friction and promotes the development of pneumatic systems in the field of accurate position and speed control. [ABSTRACT FROM AUTHOR]

The Dynamic Weighting Control Allocator (DWCA) was introduced by Sadien et al. (Control Engineering Practice, 2019) to solve the allocation problem raised by the yaw control of an on-ground aircraft. It handles the classical tradeoff between virtual reference inputs realisation and control power minimisation. But it also offers three specific features. First, the actuators reach saturation almost simultaneously, which allows an efficient recovery in case of failure. Then, several industrial requirements are taken into account, such as implementation ease, low computational cost and compatibility with certification constraints. And finally, the actuators can be prioritised, the last ones being used sparingly (to avoid overheating, fatigue, maintenance cost...) only when the virtual reference inputs cannot be realised by the first ones only. But despite its attractiveness, the DWCA is limited to the 1-dimensional case, which means that only one degree of freedom can be controlled. This is not sufficient to deal with today's challenges in the aeronautical and automotive fields, for example, where certain control problems are inherently multi-dimensional. With the progressive advent of autonomous cars, new concepts of light hybrid or electric vehicles are, for example, emerging, where both hydraulic and electric actuators are mounted on each wheel to improve the combined management of speed and steering. In this context, this paper introduces a non-trivial generalisation of the DWCA, which retains the various characteristics and advantages of the initial version and can be used in the multi-dimensional case. [ABSTRACT FROM AUTHOR]

Position-controlled systems driving repetitive tasks are of significant importance in industrial machinery. The electric actuators used in these systems are responsible for a large part of the global energy consumption, indicating that major savings can be made in this field. In this context, motion profile optimization is a very cost-effective solution as it allows for more energy-efficient machines without additional hardware investments or adaptions. In particular, mono-actuated mechanisms with position-dependent system properties have received considerable attention in literature. However, the current state-of-the-art methods often use unbounded design parameters to describe the motion profile. This both increases the computational complexity and hampers the search for a global optimum. In this paper, Chebyshev polynomials are used to describe the motion profile. Moreover, the exact bounds on the Chebyshev design parameters are derived. This both seriously reduces the computational complexity and limits the design space, allowing the application of a global optimizer such as the genetic algorithm. Experiments validate the added value of the chosen approach. In this study, it is found that the energy consumption can be reduced by 62.9% compared to a standard reference motion profile. [ABSTRACT FROM AUTHOR]

This study aims to obtain safe working condition of the electrothermal U-shaped actuator (EUA). The finite difference method is applied for modeling and solving the steady electric-thermal state and maximum temperature of the microactuator. The critical voltages causing beam buckling and overheating phenomena are determined to avoid the axial instability as well as melting deformation of the actuator. The relationships between temperature and the frequency or amplitude of the AC are analyzed. The results showed that the structure and the applied voltage levels have significant influence on the temperature distributions and the value of the stress. It is confirmed that the temperature between 300 to 600 °C is comparatively suitable for microactuator according to theoretical and experimental analysis, and the microactuator is able to provide accurate and stable number of cycles for tens of millions. [ABSTRACT FROM AUTHOR]

To expand the inclusiveness of hybrid test platform research, enhance the flexibility of hybrid test platforms using various control strategies, and promote the development of hybrid test techniques, a low-cost user-configurable electric actuator hybrid test platform is established in this paper. This platform can be transferred to other medium or large electric actuator hybrid test platform, the research applications of this platform cannot be limited by their proposed setup. Firstly, the hardware system design including hybrid test facility integrated control system core architecture and all related signal routings are carried out. Then, the improved equivalent force control feedback method based on force-loading control is proposed, and the software system development including hybrid test process control system software and user-configurable STM32 microcontroller (UCSM) software are conducted. Next, the mechanical performance of viscoelastic damper is tested, and the mechanical model parameters of viscoelastic damper are regressed. The accuracy of electric actuator force control (inner control loop), of which the control tasks get executed on the UCSM is verified using the experimental substructure of viscoelastic damper. The hybrid test of viscoelastic damping system verifies the reliability and robustness of hybrid test platform (outer control loop). Finally, the developed hybrid test platform implements various hybrid tests of viscoelastic damping system under broad temperature range and different seismic intensities. The test results reveal the influence of temperature and seismic intensities on the seismic control effect of viscoelastic damper. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the preparation and several electrical properties of two ionic Liquid Crystal Elastomers. We show that iLCEs can be used as electric actuators, bending sensors and as solid electrolytes of organic electrochemical transistors. We summarise the results using one type of LCE and two types of ionic liquids. It is found that the ionic liquid that phase separates from the reactive mesogenic monomers and forms micron size ionic channels performs better than the less phase separating ionic liquid. The switching time of the order of a second was found to be possible using the ionic liquid with smaller ions and larger channels. These results provide many exciting opportunities in various areas and impact future applications, although they are far from optimised. Fine tuning of the high-performance iLCEs require an intricate compatibility between the LCE and the electrodes and appears to be laborious. On the other hand, the first promising results justify the efforts to study more type of liquid crystal elastomers, ionic liquids and compliant electrodes. [ABSTRACT FROM AUTHOR]

Dielectric elastomer actuators have attracted growing interest for soft robot due to their large deformation and fast response. However, continuous high-voltage loading tends to cause the electric breakdown of the actuator due to heat accumulation, and viscoelasticity complicates precise control. The snap-through bistability of the Venus flytrap is one of the essential inspirations for bionic structure, which can be adopted to improve the shortcoming of dielectric elastomer actuators and develop a new actuation structure with low energy consumption, variable configuration, and multi-mode actuation. Hence, in this paper, the structural design principles of electroactive bistable actuators are first presented based on the total potential energy of the structure. Following that, a feasible design parameter region is provided, the influence of crucial parameters on the actuation stroke, trigger voltage, and actuation charge are discussed. Finally, according to the coupling relationship between the bending stiffness and the bistable property of the actuator, the adjusting methods of bistable actuation are explored. A qualitative experiment was performed to verify the feasibility and correctness of the bistable design methodology and the actuation regulation strategy. This study provides significant theoretical guidance and technical support for developing and applying dielectric elastomer actuators with multi-mode, high-performance, and long-life characteristics. [ABSTRACT FROM AUTHOR]

The current study is concerned with heat transfer enhancement by electrohydrodynamic within a vertical duct enclosed by a corrugated wall. The numerical simulation was performed for different corrugation profiles and various collector electrode configurations for Rayleigh numbers between 104 and 106 and the applied voltages in the range of 14 to 18 kV. A descriptive enhancement factor: the ratio of the average Nusselt number affected by electrohydrodynamic to the average Nusselt number without electrohydrodynamic is used to evaluate the capability of the heat transfer augmentation. The results demonstrate the sensitivity of the heat transfer enhancement to the corrugation profile and the location of the collector electrode. It is shown that the enhancement factor in the presence of the electrohydrodynamic reaches about 4.73 for triangular corrugation. Also, the results indicate that the enhancement factor grows for higher applied voltages and lower Rayleigh numbers. As the main goal and the final step, the electrohydrodynamic efficiency is defined as the rate of the enhancement factor by the electrohydrodynamic actuator to the electric power consumption. The results show that the triangular corrugation is more beneficial than the other configurations at Rayleigh number of 104 and the applied voltage of 14 kV. [ABSTRACT FROM AUTHOR]

In this study, the development of a novel hydraulic robotic actuator is introduced. With the use of additive manufacturing (AM), lightweight and compact design can be achieved. A high load-to-weight ratio 3-DOF robot actuator with orthogonally connected hydraulic rotary cylinders is designed for AM. To validate the feasibility, a titanium hydraulic robot actuator is prototyped by using the metal powder bed fusion (M-PBF) AM process. A set of loading experiments are conducted on the AM-printed prototype. The study shows that system-level AM design and manufacturing methods can help gain increased output torque but with reduced weight and volume. With the use of hydraulic driving, the robotic actuator is more compact and solid to resist to tough environments as compared with the traditional actuators using electric motors. This study also implies the potential wide application of AM to design and print similar hydraulic link mechanism in heavy-duty robot or mobile humanoid robot. [ABSTRACT FROM AUTHOR]

Dielectric Elastomer Actuator (DEA) shows the complex characteristics such as the inherent nonlinearity, intricate electromechanical coupling, time-dependent viscoelastic behavior, etc., which make it difficult to establish a dynamic model. This paper proposes a dynamic model based on the physical properties of DE materials to describe the above characteristics. The Gent model and the generalized Kelvin model are used to describe the free energy and the viscoelastic characteristics of DEA, respectively. Based on the experimental results, the differential evolution algorithm is used to identify the model parameters. Comparing the experimental data with the model prediction, the validity and generalization of the model are demonstrated. [ABSTRACT FROM AUTHOR]

Nowadays, the soft material, dielectric elastomers (DEs) are being used for many engineering applications due to their exceptional properties like high strain rate sensitivity, low power consumption, capable of static force measurement and capability of changing dimensions when subjected to voltage. They have the ability of converting mechanical energy to electrical energy and vice versa. In this article, nonlinear dynamic behavior of viscoelastic tapered DE under mechanical and electromechanical loading is studied. A dynamic model based on standard linear solid model is incorporated for viscoelasticity. Strain energy density of the system is derived from Gent model of hyperelasticity. The tapered DE is analyzed with different values of damping coefficients, ratio of shear moduli of springs, width and height tapers. The effects of tapers greatly put an impact on the dynamic responses of the system. The tapered DEs exhibits damped vibration and weak nonlinearity with an increase in damping force. The dynamic stability of tapered DEs is also studied using phase diagrams, and the results indicated that with an increase in damping force, the dynamic stability changes from a state of aperiodic vibration to quasi-periodic vibration. It is also found that the resonant frequency and peak amplitude reduce with an increase in the damping force. [ABSTRACT FROM AUTHOR]

This article conducts a multiobjective optimization study for minimizing both the actuator energy and the total drag of a NASA N + 2 aircraft, the Blended-Wing-Body (BWB), during cruising, by using the three-segment Variable-Camber Continuous Trailing-Edge Flap (VCCTEF) proposed by NASA. The metric for the electric drive actuators' energy for the BWB during cruising is characterized by summing the absolute hinge moments for all actuators. A local minimum is easily obtained for the optimization problem with a least absolute sum cost function when using a gradient-based optimizer. The minimization of the total actuator energy is converted to a linear programming problem by treating the absolute hinge moments as design variables. The induced and profile drags are considered to be the largest two contributions to the total drag. Design variables for the flap rotations and the absolute hinge moments with different orders of magnitude are scaled with respect to their maximum bounds in the optimization study to avoid numerical problems. Different VCCTEF configurations of varying deflection profiles and degrees of actuation independence and traditional flaps are studied and their performance is compared. For the BWB with four representative fuel levels, 80, 50, 20 and 0% of the maximum fuel loads, all during cruising, multiobjective optimization studies show that the VCCTEF with three individual segments can achieve a minimal total drag for the BWB while requiring a minimal total actuator energy to maintain its optimal shape for the minimal total drag. [ABSTRACT FROM AUTHOR]

Collision avoidance is a crucial function for all ground vehicles, and using integrated chassis systems to support the driver presents a growing opportunity in active safety. With actuators such as in-wheel electric motors, active front steer and individual wheel brake control, there is an opportunity to develop integrated chassis systems that fully support the driver in safety critical situations. Here we consider the scenario of an impending frontal collision with a stationary or slower moving vehicle in the same driving lane. Traditionally, researchers have approached the required collision avoidance manoeuver as a hierarchical scheme, which separates the decision-making, path planning and path tracking. In this context, a key decision is whether to perform straight-line braking, or steer to change lanes, or indeed perform combined braking and steering. This paper approaches the collision avoidance directly from the perspective of constrained dynamic optimisation, using a single optimisation procedure to cover these aspects within a single online optimisation scheme of model predictive control (MPC). While the new approach is demonstrated in the context of a fully autonomous safety system, it is expected that the same approach can incorporate driver inputs as additional constraints, yielding a flexible and coherent driver assistance system. [ABSTRACT FROM AUTHOR]

The hysteresis nonlinearity in piezoelectric materials brings difficulties in controlling the systems. In order to mitigate the effect of hysteresis, such nonlinearity needs to be characterized and modeled under different load circumstances. For this purpose, the actuator is modeled in terms of a mass-spring-damper system utilizing the stop operator as one of the operators of the Prandtl-Ishlinskii (PI) model. Merging the structural model with the nonlinear hysteresis model, we observe that the results demonstrate better correspondence to the measured output compared to that of the classical PI model for a wide range of working conditions, i.e., different input frequency and amplitude. [ABSTRACT FROM PUBLISHER]

Actuators based on piezoelectric effects have received great attention for their broad applications in sensors and actuators. In this study, a piezoelectric layer is adhered to a substrate to form a bi-layered composite beam. Electric voltage is applied to the piezoelectric layer, resulting in a bending moment on the bi-layered composite beam. A static analysis basing on the theories of elasticity and piezoelectricity is performed to determine the stress distribution in the composite beam induced by the piezoelectric layer. The theoretical predictions are compared with the numerical results of the finite element method to demonstrate the validation of the proposed method. A numerical study is conducted to investigate the effects of the thickness and Young's modulus on the stress distribution of the composite beam. Numerical results show that the stress distribution across the thickness is heavily dependent on the ratios of the thickness and Young's modulus between the two layers. [ABSTRACT FROM AUTHOR]

In this paper, an optimal torque distribution approach is proposed for electric vehicle equipped with four independent wheel motors to improve vehicle handling and stability performance. A novel objective function is formulated which works in a multifunctional way by considering the interference among different performance indices: forces and moment errors at the centre of gravity of the vehicle, actuator control efforts and tyre workload usage. To adapt different driving conditions, a weighting factors tuning scheme is designed to adjust the relative weight of each performance in the objective function. The effectiveness of the proposed optimal torque distribution is evaluated by simulations with CarSim and Matlab/Simulink. The simulation results under different driving scenarios indicate that the proposed control strategy can effectively improve the vehicle handling and stability even in slippery road conditions. [ABSTRACT FROM AUTHOR]

This paper resumes the content of the invited talk of the author, read at the occasion of the International Workshop on Relaxor Ferroelectrics, IWRF 14, held on October 12–16, 2014 in Stirin, Czech Republic. It reviews the recent advances in materials, designing concepts, and new applications of piezoelectric actuators, as well as the future perspectives of this area. [ABSTRACT FROM PUBLISHER]

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