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  • Open access
  • 87 Reads
Assembly and characterization of a DE-actuator based on polymeric domes as biasing element

Dielectric elastomer (DE) technology opens up the possibility of constructing novel lightweight and energy-efficient actuators, whose design can be tailored to several applications. Numerous actuator configurations, capable of high-force, high-speed, or high-stroke, have been presented in the recent literature. Some types of DE-actuators (DEAs), namely membrane DEAs, need to be pre-loaded by a mechanical biasing system in order to generate a stroke. To achieve a large deformation with such membrane DEAs, a mechanical biasing element showing a negative slope (i.e., stiffness) in its force-displacement characteristic needs to be used. Typically, negative-slope biasing systems for DEAs are realized by pre-compressed thin metal beams. Such metal elements, however, do not lend themselves to miniaturization to the meso- and micro-scale. Additionally, metal components unavoidably affect the stiffness of the overall actuator system, thus making it not suitable for applications such as wearables and soft-robotics. To overcome those issues, a new type full polymer-based DEA element is presented in this work. This type of DEAs can be used as elementary taxels in cooperative arrays of micro-actuators. In order to achieve a completely flexible structure without losing the benefits of negative-slope biasing systems, a compliant silicone-based dome element is proposed as a novel biasing system. By tuning the dome geometry, it is possible to affect its force-displacement characteristic and, in turn, to design a large-stroke DEA. After discussing the novel compliant actuator concept, the assembly process will be presented in details. Finally, experimental validation of the proposed design will be carried out. It is shown that polymeric domes are well suited for constructing large-stroke DEAs, which is an important step towards the construction of a flexible and cooperative micro-array system.

  • Open access
  • 64 Reads
Analysis of Field Oriented Control of Permanent Magnet Synchronous Motor for valveless pump-controlled actuator

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 particularly. Such pump-controlled system can be realized via direct control of hydraulic pump/motor by varying speed of prime mover. Electric motors have higher efficiency in comparison with Combustion Camera Diesel Engines also less power consumption and local pollutions. These advantages allow to improve the system efficiency and decrease the energy expenses. A Permanent Magnet Synchronous Motor (PMSM) is the one of the most attractive option of electric motor due to its size, power, and efficiency. The efficiency of the electric motor can be increased by using vector control systems, which provide rotor magnetic flux control, which is proportional to the shafts 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 electrohydraulic systems and influence of electric part on hydraulic one is not investigated enough. One of the most perspective vector control systems is Field Oriented Control (FOC) is studied in this paper. The model of PMSM control system, which is built in MATLAB/Simulink, consists of frequency converter with Pulse Width Modulation (PWM) controller, reverse Park transformation, speed controller, saturation block, cross-link compensator, reference current and torque. In this study, a fixed displacement hydraulic pump is connected to a single-rod cylinder. Additional load connected to cylinder is changing bring the simulation closer to real conditions. A behavior of the systems was investigated by transient processes analysis (response time, overshooting, transient process time etc.) of electric motor, pump and cylinder.

  • Open access
  • 34 Reads
Influence of residual stresses of sputtered thin film electrodes for dielectric elastomer applications

This paper focuses on the electromechanical properties of novel sub-micron compliant metallic thin film electrodes for dielectric elastomer membranes. Electrodes with thicknesses between 10-20 nm and different residual stress states are explored. Either pure nickel films or sandwiches of nickel (Ni) and carbon (C) are deposited by DC magnetron sputtering onto pre-stretched silicone elastomer membranes. Both, 37.5 % biaxial pre-stretch and 57.5% 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. In the conducted experiments, 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 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. For 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. Nevertheless, 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 DE applications.

  • Open access
  • 48 Reads
Co-Design and Control of a Magnetic Microactuator for Freely Moving Platforms
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A current goal in microsystem research is to overcome small working ranges, typically resulting from mechanical connections and restoring forces such as for cantilevers. In the case of predefined resting positions and unidirectional motion, pseudo-levitation as in magnetic bearings is a promising solution.

In order to investigate concepts for energy efficient, cooperative microactuators, which allow free motion of small objects, we present a bistable levitation setup. The system consists of a magnetic proof mass within a glass tube, a piezoelectric staple actuator, two permanent magnets and a solenoid used as an electromagnet. The movable mass is mechanically unconstrained in its upper vertical motion and is intended to switch between two predefined equilibrium positions, namely on the staple actuator and levitating at a defined upper position. The transition is accomplished by an impulse-like kick force by the staple actuator, and subsequent feedback controlled following of a trajectory via electromagnetic actuation.

The goal of this work consists of both adapting the system parameters, guaranteeing stable and preferably robust equilibrium positions for the unactuated system, and finding optimal trajectories with a short settling time and minimum input effort for the controlled transition. These design and control objectives are combined within a co-design. In this approach, the system and controller optimizations are not performed consecutively, but within a single optimization, taking into account the coupling between the design and control. Here, we apply flatness-based control combined with feedback linearization, allowing for trajectories to be tracked without error in case of the undisturbed system. Thus, the controller is solely used for disturbance compensation and the problem can be simplified by optimizing only the trajectory without the controller parameters. We show that the combined optimization process is of advantage in comparison to the sequential approach and proficiently exploits the design parameters to improve the generated trajectories.

  • Open access
  • 59 Reads
Integrated sliding mode backstepping control of an asymmetric electro-hydrostatic actuator based on extended observer

To provide high output forces and to reduce the installation space, the electro-hydrostatic actuator (EHA) usually adopts a fixed-displacement pump and an asymmetric single-rod cylinder. However, comprehensive effects produced by its asymmetric flow, and matched and unmatched uncertainties make it difficult to achieve high-accuracy position control. This paper proposed an integrated sliding mode backstepping control based on extended observer for the asymmetric EHA, compensating the imbalanced flow with pilot-operated check valves. Firstly, flow distribution was analyzed, and its state space equation was established for the asymmetric EHA. Two extended state observer (ESO) was employed to achieve real-time estimating of the unmeasured system states, unmatched and matched disturbance. 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 speed. Theoretical analysis indicates that the controller can guarantee the specified tracking performance for the actuator under time-varying unmatched disturbances, and can make the tracking error asymptotically converge to zero under constant matching disturbances. Finally, the designed EHA and controller were combined to simulate with crane dynamics model in MATLAB/Simscape. The simulation results show that the proposed controller can guarantee the position tracking performance of EHA and possess good disturbance rejection ability.

  • Open access
  • 35 Reads
Adaptive backstepping sliding mode control for direct driven hydraulics
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Due to the advantages of high energy efficiency and environmental friendliness, the electronic-hydraulic actuator (EHA) plays an important role in fluid power control. One variation of EHA, double pump direct driven hydraulic (DDH), was proposed, which consists of double fixed-displacement pumps, a servo motor, an asymmetric cylinder, and auxiliary components. This paper proposed an adaptive backstepping sliding mode control strategy for DDH to eliminate the negative effect producing by parametric uncertainty, nonlinear characteristics and the uncertain external disturbance. Firstly, the DDH model and a crane dynamics model were constructed in MATLAB/Simulink and validated by experiment. Based on theoretical analysis, the nonlinear system model was built and transformed. Further, by defining the sliding manifold and selecting a proper Lyapunov function,the nesting problems (of the designed variable and adaptive law) causing by uncertainty coefficients were solved. Moreover, the adaptive backstepping control and the sliding mode control were combined to boost system robustness. At the same time, the adaptive law with uncertain parameters was selected. Simulations of the DDH with the proposed control strategy and proportional-integral-differential (PID) were performed respectively. The simulation results show that the designed control strategy can realize better position tracking, and has stronger robustness to parameter changes compared with PID.

  • Open access
  • 56 Reads
Active Disturbance Rejection Control for Double Pump Direct Driven Hydraulics

As the energy crisis and further development of the electro-hydraulic actuator driven by servo motor, double-pump direct driven hydraulics (DDH) was brought forward, which mainly comprises of a servo motor, double fixed displacement pumps, a differential cylinder, a low-pressurized tank and auxiliary valves. To address the problems causing by uncertain parameters and unknown external disturbances of DDH, this paper proposed a control strategy adopting active disturbance rejection control (ADRC). Firstly, a system consists of a DDH unit and a micro-crane were modelled in MATLAB/Simulink and verified by measurement. Further, 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 position signal transiently to avoid unnecessary oscillations, and the extended state observer (ESO) was used to accurately estimate the influence of the uncertain by nonlinear control law. After that, the proposed ADRC or Proportional-Integral-Differential (PID) control was combined with the system. Finally, the simulations were performed under varying loads, and the system performances, including position tracking and energy efficiency, were analyzed and compared. The results show that the ADRC can sufficiently suppress the unknown external disturbance under the condition of variable load, has the advantages of robustness and improves the position tracking precision.

  • Open access
  • 55 Reads
Effect of Mechanical Loading and Increased Gap on the Dynamic Response of Multiple Degree of Freedom Electrostatic Actuator

Electrostatic inchworm motor based on gap-closing variable capacitor provides potential solution for larger force actuation compared to area overlapping one. Unlike the constant electrostatic force in area overlapping variable capacitor, the generated electrostatic force in gap-closing variable capacitor increases as the displacement is increased.

However, due to the pull-in phenomena the system stability and controllability is critical design challenges. Various designs of complex electrostatic actuators based on gap-closing variable capacitor were developed as linear inchworm motor [1-2]. However, the force actuation capability is still in mN range.

In this paper, a novel monolithic structural design of electrostatic actuator with multiple degree of freedom is presented as an approach for a system that is capable of performing large electrostatic force and scalable stroke. The actuator is a kind of mechanical oscillator can be driven in xy-directions by three voltage electrodes. One voltage electrode is used to apply vertical displacement in order to release or clutch the comb-like structure side with interdigitated shaft, while other voltage electrodes are used to perform displacement in the lateral direction. Multiple actuators can be used to increase
the overall applied electrostatic force on the shaft.

In this work, an electromechanical system model based on Simulink software was developed for a proposed design of 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. Also, the mechanical bouncing as well as steady state response of the actuator was investigated under various mechanical loading values. The switching time increased as the mechanical load was increased. Bouncing amplitude increased as the impact force was increased. Both switching time and bouncing amplitudes are important factors for the oscillation stability of the actuated shaft, knowing that the final system contains multiple actuator units.

Literature
[1] S.-H. Kim, Il-H. Hwang, K.-W. Jo, E.-S. Yoon, J.-H. Lee; High resolution inchworm linear motor based on electrostatic twisting microactuators, Journal of Micromechanics and Microengineering 2005, 15, pp. 1674-1682; 2005.
[2] M. A. Erismis, H. P. Neves, R. Puers, C. V. Hoof; A low voltage large displacement large force inchworm actuator; Journal of Microelectromechanical Systems 2008; 17, 6, pp. 1294-1301; 2008.
[3] I. Penskiy, S. Bergbreiter; Optimized electrostatic inchworm motors using a flexible driving arm; Journal of Micromechanics and Microengineering 2013, 23, 015018; 2013.
[4] K. Saito, D. S. Contreras, Y. Takeshiro, Y. Okamoto, S. Hirao, Y. Nakata, T. Tanaka, S. Kawamura, M. Kaneko, F. Uchikoba, Y. Mita, K. S. J. Pister; Study on electrostatic inchworm motor device for a heterogeneous integrated microrobot system; Transactions of The Japan Institute of Electronics Packaging 2019, 12; 2019.

  • Open access
  • 65 Reads
A Generalized Control Model and Its Digital Algorithm for Aerospace Electrohydraulic Actuators
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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 PID and a feed-forward compensation. The control algorithm is implemented in digital signal processors with a same software structure but different parameters for different aerospace actuators. Compared to other approaches, it is easier this way to grasp the system resonance nature, and most importantly, the traditional dynamic pressure feedback is replaced with the convenient digital algorithm, bringing prominent benefits of simplified design, reduced hardware cost and inherent higher reliability. The approach has been validated by simulation, experiments and successful flights.

  • Open access
  • 68 Reads
Temperature Homogenization of Co-Integrated Shape Memory – Silicon Bimorph Actuators
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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 on a novel approach to combine SMA film deposition and micromachining with silicon (Si) technology in a monolithic fabrication process for co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double beam cantilevers are chosen for the actuator layout to enable electro-thermal actuation by Joule heating. 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 FEM simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in 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.

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