Dielectric Electro Active Polymer Actuator Research Articles

NARMAX Approach for the Identification of a Dielectric Electroactive Polymer Actuator

NARMAX Approach for the Identification of a Dielectric Electroactive Polymer Actuator

Silicone-Based Membranes as Potential Materials for Dielectric Electroactive Polymer Actuators

This article includes an overview of the materials and a thorough analysis of the methods that are used to produce dielectric electroactive actuator membranes. The paper also presents extensive results from our experimental studies on two types of addition silicone (Silicone Mold Start 15 and Dragon Skin 10M) that are used to manufacture actuators with different active membranes of thicknesses (165 μm and 300 μm, respectively). This study explored in depth the hardware architectures and methodologies for manufacturing the selected actuators. The displacements of the actuators were compared to their responses to two types of voltage excitation: a step response and a sinusoidal signal with an increasing frequency over time. This paper graphically presents the results that we obtained for all devices, with a particular emphasis on the resonance frequencies. When comparing membranes that had the same thickness (165 μm), it was found that the mean amplitude was higher for silicone membranes with lower values for the Young’s modulus (DS = 0.57 mm and MS = 0.73 mm). All experiments were repeated for two series of measurements and the results that were obtained in this study demonstrated the successful implementation of the actuator concepts that were made from the new types of silicone, which have not yet been used for production.

Intelligent feedforward hysteresis compensation and tracking control of dielectric electro-active polymer actuator

Dielectric electro-active polymer (DEAP) actuator has been considered potentially in recent decades for many applications, especially in intelligent bio-inspired robotics. However, the viscoelastic properties including rate-dependent and asymmetrical hysteresis, creep and the uncertainties under different operating conditions are still limiting its further development. In this paper, a feedforward-feedback tracking control approach is developed. Firstly, a long short term memory (LSTM) neural network combined with empirical mode decomposition (EMD), which has the information of reference as input and the control signal as output, is constructed using the data collected from the DEAP actuator. Thus, the well trained LSTM model can precisely capture the inverse hysteresis dynamics of the DEAP actuator, which can be used as a feedforward compensator to eliminate the hysteresis nonlinearities. Then, a conventional proportional-integral-derivative feedback controller is combined to compensate for the uncertainties and creep effect. To verify the effectiveness of the proposed feedforward compensator, comparative experiments on prediction of control signal and compensation of hysteresis among the traditional artificial back propagation neural network model, the inverse rate-dependent Prandtl-Ishlinskii model and the proposed LSTM-based compensator are conducted. The results validate that the LSTM-based compensator can precisely predict the control signal and eliminate the hysteresis with best performance indexes. Moreover, the tracking control experiments further validate the effectiveness of the proposed feedforward-feedback approach.

Modeling of Dielectric Electroactive Polymer Actuators with Elliptical Shapes

Dielectric electroactive polymers have been widely used in recent applications based on smart materials. The many advantages of dielectric membranes, such as softness and responsiveness to electric stimuli, have lead to their application in actuators. Recently, researchers have aimed to improve the design of dielectric electroactive polymer actuators. The modifications of DEAP actuators are designed to change the bias mechanism, such as spring, pneumatic, and additional mass, or to provide a double cone configuration. In this work, the modification of the shape of the actuator was analyzed. In the standard approach, a circular shape is often used, while this research uses an elliptical shape for the actuator. In this study, it was shown that this construction allows a wider range of movement. The paper describes a new design of the device and its model. Further, the device is verified by the measurements.

Electromechanical Characteristics of Core Free Folded Dielectric Electro-active Polymer Soft Actuator

This paper investigates the active dynamic and electromechanical characteristics of a new thin folded dielectric electro-active polymer actuator developed by Danfoss PolyPower. The high voltage is supplied to the actuator during dynamic testing to identified the effect of the electrical field on dynamic characteristics. The electromechanical characteristics are investigated by varying the amplitude and frequency of the voltage supplied. The experimental results, such as natural frequency, amplitude response, and loss factor are presented to show the influence of such an electrical field on the characteristic of the actuator. There is a reduction of resonance frequency from 14 Hz to 12 Hz as voltage supply up to 2000 V. The actuating response of the actuator was subjected more to frequency rather than the amplitude of the voltage supplied. Hence, the results may guide the exploration of a new folded thin actuator as an active vibration controller.

A PI Controller with a Robust Adaptive Law for a Dielectric Electroactive Polymer Actuator

Dielectric electroactive polymer actuators are new important transducers in control system applications. The design of a high performance controller is a challenging task for these devices. In this work, a PI controller was studied for a dielectric electroactive polymer actuator. The pole placement problem for a closed-loop system with the PI controller was analyzed. The limitations of a PI controller in the pole placement problem are discussed. In this work, the analytic PI controller gain rules were obtained, and therefore extension to adaptive control is possible. To minimize the influence of unmodeled dynamics, the robust adaptive control law is applied. Furthermore, analysis of robust adaptive control was performed in a number of simulations and experiments.

DEAP Actuator Composed of a Soft Pneumatic Spring Bias with Pressure Signal Sensing

Dielectric electroactive actuators are novel and significant smart actuators. The crucial aspect of construction of these devices is the bias mechanism. The current literature presents three main types of biases used in the construction of the DEAP actuators. In these solutions, the bias is caused by the action of a spring, a force of a permanent magnet or an applied mass. The purpose of this article is to present a novel type of DEAP bias mechanism using soft pneumatic spring. In contrast to the solutions presented so far, the soft pneumatic spring has been equipped with a sensor that measures the variable pressure of its inner chamber. We performed the modeling process of a soft pneumatic spring with the finite element method to predict its mechanical behavior. Furthermore, a prototype of the soft spring was molded and used to construct a dielectric electroactive polymer actuator. The principle of operation has been confirmed by the experiments with measurement of static and dynamics characteristics. The presented device can be used to control systems with an additional pressure-sensing feedback.

Modeling of the dynamic hysteresis in DEAP actuator using an empirical mode decomposition based long-short term memory network

As a smart material-based actuator, the dielectric electro-active polymer (DEAP) actuator is widely considered to be a potential driving mechanism for many applications, especially in intelligent bio-inspired robotics. However, the DEAP actuator demonstrates rate-dependent and asymmetrical hysteresis phenomenon which leads to great tracking inaccuracy and even oscillatory response, severely limiting its further development. Feedforward Neural Network (FNN) model has already become a widely used method to describe this kind of strong hysteresis nonlinearity in recent years. However, the FNN has no ability to remember the historical state of long period of time which is also a very important factor to restrict hysteresis phenomenon. In this paper, a novel hybrid model, Long-Short Term Memory (LSTM) network combined with Empirical Mode Decomposition (EMD), is proposed to model the dynamic hysteresis nonlinearity in DEAP actuator. At first, the original control signal sequence is preprocessed into a series of sub-sequence by the EMD method and is reshaped by one-sided dead-zone operator. Then the input space of LSTM is conducted using the original control signal, the sub-sequence, and reshaped signal. Finally, the input space and the displacement signal are applied to train the long-short term memory network. In order to verify the performance of the proposed model, the traditional artificial back propagation neural network (BPNN) model, rate-dependent Prandtl-Ishlinskii (RPI) model, and nonlinear electromechanical (NEM) model are compared from prediction accuracy. The results demonstrate that: (1) the proposed model has a higher prediction accuracy than the traditional artificial BPNN, RPI, and NEM model; and (2) the prediction accuracy of LSTM network is significantly improved by using EMD. Therefore, the long-short term memory network combined with empirical mode decomposition is a competitive method compared to the existing state-of-the-art approach.

Active Disturbance Rejection Control for Dielectric Electroactive Polymer Actuator

This paper presents the Active Disturbance Rejection Control (ADRC) designed for a Dielectric Electroactive Polymer (DEAP) actuator. ADRC has gained popularity in recent years as an effective alternative approach to solving control problem in relation to classic PID controller and the model-based approach. It is a valuable control methodology due to its simple tuning method and robustness against process parameter variations. The novelty of this article is a simple control method of DEAP actuator based on ADRC schema. This work presents a method of identifying the parameters of the actuator model necessary to develop the ADRC control. Then Linear Extended State Observer (LESO) was developed which is used for compensating the effects of total disturbance. The linear proportional-derivative (PD) controller, which in ADRC control scheme can be considered as a state feedback controller, has been implemented in the external feedback loop. This approach makes it possible to use the system with a simplified DEAP model, because the negative effects of modeling uncertainty are compensated in real time. The tuning process of ADRC parameters (performed in the terms of LESO and PD controller bandwidth) is discussed and presented graphically. The experiments show the transients of the ADRC control system and the performance indexes of the two reference trajectories in order to verify the effectiveness of the control system.

Second-order adaptive discrete-time fast terminal sliding mode control of a DEAP actuator with hysteresis nonlinearity

This paper investigates trajectory tracking control of a dielectric electro-active polymers (DEAP) actuator with hysteresis nonlinearity by using second-order adaptive discrete-time fast terminal sliding mode control (2-ADFTSMC) scheme. Taking into account that the hysteresis behaviour is asymmetric rate-dependent, a Hammerstein model is established to represent the DEAP actuator. Then, based on a novel 2-ADFTSM function and a terminal-sliding-mode-type switching control law, a 2-ADFTSMC scheme is proposed to improve the trajectory tracking performance. Furthermore, the stability of the closed-loop system is proved. Compared with discrete-time sliding mode control (DSMC) and discrete-time fast terminal sliding mode control (DFTSMC) schemes, the proposed control scheme can provide higher tracking accuracy, faster convergence speed, and stronger robustness in presence of model uncertainties and external disturbances. The effectiveness and practicality of the proposed control scheme are validated through the experiments on the DEAP actuator.

Reset Strategy for Output Feedback Multiple Models MRAC Applied to DEAP

The smart actuators are rapidly developing in the recent years. Dielectric Electroactive Polymer actuators are very important smart actuators due to their features like softness, high force ratio, fast operation and silence. In recent year a set of dynamic models for DEAP actuators have been developed by various authors. Relying on these models it is possible to design an wide range of feedback controllers. In our work, we develop the indirect adaptive controller for Dielectric Electroactive Polymer actuator exploiting the multiple models approach with second layer adaptation. The results presented in this paper prove that in the case of piecewise continuous parameters, the benefits of second level adaptation can be lost. To solve this problem, a new resetting algorithm is proposed. The efficiency of the proposed control method is verified by a simulation on a simple motivation example and DEAP actuator model.

Electromechanical characterization of a 3D printed dielectric material for dielectric electroactive polymer actuators

Dielectric electroactive polymers (DEAPs) represent a subclass of smart materials that are capable of converting between electrical and mechanical energy. These materials can be used as energy harvesters, sensors, and actuators. However, current production and testing of these devices is limited and requires multiple step processes for fabrication. This paper presents an alternate production method via 3D printing using Thermoplastic Polyurethane (TPU) as a dielectric elastomer. This study provides electromechanical characterization of flexible dielectric films produced by additive manufacturing and demonstrates their use as DEAP actuators. The dielectric material characterization of TPU includes: measurement of the dielectric constant, percentage radial elongation, tensile properties, pre-strain effects on actuation, surface topography, and measured actuation under high voltage. The results demonstrated a high dielectric constant and ideal elongation performance for this material, making the material suitable for use as a DEAP actuator. In addition, it was experimentally determined that the tensile properties of the material depend on the printing angle and thickness of the samples thereby making these properties controllable using 3D printing. Using surface topography, it was possible to analyze how the printing path affects the roughness of the films and consequently affects the voltage breakdown of the structure and creates preferential deformation directions. Actuators produced with concentric circle paths produced an area expansion of 4.73% uniformly in all directions. Actuators produced with line paths produced an area expansion of 5.71% in the direction where the printed lines are parallel to the deformation direction, and 4.91% in the direction where the printed lines are perpendicular to the deformation direction.

Modeling and Discrete-Time Terminal Sliding Mode Control of a DEAP Actuator with Rate-Dependent Hysteresis Nonlinearity

Dielectric electro-active polymer (DEAP) materials, also called artificial muscle, are a kind of EAP smart materials with extraordinary strains up to 30% at a high driving voltage. However, the asymmetric rate-dependent hysteresis is a barrier for trajectory tracking control of DEAP actuators. To overcome the barrier, in this paper, a Hammerstein model is established for the asymmetric rate-dependent hysteresis of a DEAP actuator first, in which a modified Prandtl-Ishlinskii (MPI) model is used to represent the static hysteresis nonlinear part, and an autoregressive with exogenous inputs (ARX) model is used to represent the linear dynamic part. Applying Levenberg-Marquardt (LM) algorithm identifies the parameters of the Hammerstein model. Then, based on the MPI model, an inverse hysteresis compensator is obtained to compensate the hysteresis behavior. Finally, a compound controller consisting of the hysteresis compensator and a novel discrete-time terminal sliding mode controller (DTSMC) without state observer is proposed to achieve the high-precision trajectory tracking control. Stability analysis of the closed-loop system is verified by using Lyapunov stability theorem. Experimental results based on a DEAP actuator show that the proposed controller has better tracking control performance compared with a conventional discrete-time sliding mode controller (DSMC).

Modeling, control and experimental investigation of time-average flow rate of a DEAP actuator based diaphragm pump

Over the past three decades, micropumps have been intensively interested to handle and to carry small and precise volumes of liquid in many fields of modern industry. Especially, smart actuator based diaphragm micropumps have received considerable attention because of its simple structure and operation precisely. However, hysteresis phenomenon in the smart actuator is the barrier which prevents the system functioning correctly. This study deals with a mitigation strategy of the hysteresis effects for a typical dielectric electro-active polymer actuator based diaphragm micropump in order to improve the performance of the micropump. Firstly, the forward and inverse hysteresis models are designed and optimized to describe the rate-dependent hysteresis behavior of the actuation system. The model-based control method is then developed and validated to drive the system precisely at high frequencies. Finally, experiments have been conducted to demonstrate the effectiveness of the control strategy in a real application. As a result, the hysteresis behaviors of the smart actuator are effectively compensated at the frequencies up to 1Hz and a maximum time average flow rate of 1.443 mL/min and maximum backpressure of 833.5 Pa at room temperature are recorded.

An application review of dielectric electroactive polymer actuators in acoustics and vibration control

Recent years have seen an increasing interest in the dielectric electroactive polymers (DEAPs) and their potential in actuator applications due to the large strain capabilities. This paper starts with an overview of some configurations of the DEAP actuators and follows with an in-depth literature and technical review of recent advances in the field with special considerations given to aspects pertaining to acoustics and vibration control. Significant research has shown that these smart actuators are promising replacement for many conventional actuators. The paper has been written with reference to a large number of published papers listed in the reference section.

New Incremental Actuators Based on Electroactive Polymer: Conceptual, Control, and Driver Design Considerations

This paper presents an overview of the widely used conventional linear actuator technologies and existing electroactive polymer-based linear and rotary actuators. It also provides the conceptual, control, and driver design considerations for a new dielectric electroactive polymer (DEAP)-based incremental actuator. The DEAP incremental actuator consists of three independent DEAP actuators with a unique cylindrical design that potentially simplifies mass production and scalability compared to existing DEAP actuators. To accomplish the incremental motion, a high-voltage (HV) bidirectional dc–dc converter independently charges and discharges each capacitive DEAP actuator. The topology used for the HV driver is a peak current controlled bidirectional flyback converter. The scalability of the proposed DEAP incremental actuator is discussed, and different scaled designs are provided. The estimated speeds and forces for various scaled incremental actuator designs are provided. The HV drivers are experimentally tested with a prototype of the DEAP incremental actuator. The energy efficiency measurement results of one of the HV driver are presented. The DEAP incremental actuator prototype achieved bidirectional motion with a maximum velocity of 1.5 mm/s, at 2.87 Hz incremental driving frequency, when all actuators are driven with 1.8 kV. Finally, two new improved concepts of DEAP-based incremental actuator are presented.

A study on the effect of surface topography on the actuation performance of stacked-rolled dielectric electro active polymer actuator

Dielectric electro active polymer (DEAP) is a suitable actuator material that finds wide applications in the field of robotics and medical areas. This material is highly controllable, flexible, and capable of developing large strain. The influence of geometrical behavior becomes critical when the material is used as miniaturized actuation devices in robotic applications. The present work focuses on the effect of surface topography on the performance of flat (single sheet) and stacked-rolled DEAP actuators. The non-active areas in the form of elliptical spots that affect the performance of the actuator are identified using scanning electron microscope (SEM) and energy dissipated X-ray (EDX) experiments. Performance of DEAP actuation is critically evaluated, compared, and presented with analytical and experimental results.

Artificial Muscle Devices: Innovations and Prospects for Fecal Incontinence Treatment.

Fecal incontinence describes the involuntary loss of bowel content, which is responsible for stigmatization and social exclusion. It affects about 45% of retirement home residents and overall more than 12% of the adult population. Severe fecal incontinence can be treated by the implantation of an artificial sphincter. Currently available implants, however, are not part of everyday surgery due to long-term re-operation rates of 95% and definitive explantation rates of 40%. Such figures suggest that the implants fail to reproduce the capabilities of the natural sphincter. This article reviews the artificial sphincters on the market and under development, presents their physical principles of operation and critically analyzes their performance. We highlight the geometrical and mechanical parameters crucial for the design of an artificial fecal sphincter and propose more advanced mechanisms of action for a biomimetic device with sensory feedback. Dielectric electro-active polymer actuators are especially attractive because of their versatility, response time, reaction forces, and energy consumption. The availability of such technology will enable fast pressure adaption comparable to the natural feedback mechanism, so that tissue atrophy and erosion can be avoided while maintaining continence during daily activities.

Bidirectional Resonant DC–DC Step-Up Converters for Driving High-Voltage Actuators in Mobile Microrobots

Electroactive polymer (EAP) actuators have been investigated to convert electrical energy into mechanical deformation in autonomous microrobots. The use of dielectric EAP actuators comes with several challenges to address requirements such as high excitation voltages, explicit driving signals, and low conversion efficiency. External bulky and heavy power sources are used to generate and provide required excitation voltages. The development of a miniature, high voltage gain, and highly efficient power electronic interface is required to overcome such challenges and enable autonomous operation of miniature robots. In this paper, a bidirectional single-stage resonant dc–dc step-up converter is introduced and developed to efficiently drive high-voltage EAP actuators in mobile microrobots. The converter utilizes resonant capacitors and a coupled inductor as a soft-switched LC network to step up low input voltage. High-frequency soft-switching operation owing to LC resonance allows small footprint of the circuit without suffering from switching losses, which in turn increases the efficiency. The circuit is capable of generating explicit high-voltage actuation signals, with capability of recovering unused energy from EAP actuators. A 4-mm × 8-mm, 100-mg, and 600-mW prototype has been designed and fabricated to drive an in-plane gap-closing electrostatic inchworm motor. Experimental validations have been carried out to verify the circuit's ability to step up voltage from 2 to 100 V and generate two 1-kHz, 100-V driving voltages at 2-nF capacitive loads.

Electromechanical characteristic analysis of a dielectric electroactive polymer (DEAP) actuator

To assist in the design and optimization of dielectric electroactive polymer (DEAP) actuators, an analytical model for the electromechanical response of cone DEAP actuators is developed. Using the Yeoh form strain energy potential and the Maxwell stress tensor, the constitutive relationship of the DEAP that accounts for the electromechanical coupling behavior is deduced. The equilibrium equations of DEAP actuators with a cone configuration are derived and an analytical model is then proposed. With this model, the actuation characteristics of the DEAP actuator, including actuation displacement, force output and efficiency can be calculated. Additionally, the principal stresses and principal stretch ratio of the membrane under different actuation voltages can be determined, along with the wrinkling failure mode of DEAP actuators. The experimental results for the DEAP actuator matched the numerical results determined using the proposed model. As such, the proposed work is beneficial as a guide for the design optimization of DEAP actuators.