Dielectric Electroactive Polymer Research Articles

NARMAX Approach for the Identification of a Dielectric Electroactive Polymer Actuator

NARMAX Approach for the Identification of a Dielectric Electroactive Polymer Actuator

Review of Soft Actuators Controlled with Electrical Stimuli: IPMC, DEAP, and MRE

Soft actuators have been developed for a variety of applications, including soft grippers, artificial muscles, wearables, tactile devices, and medical devices. In this review, we will discuss a group of chemical materials and their robotic applications in soft actuators controlled with electrical stimuli. Soft actuators provide a deformable body and allow interaction with the environment to achieve the desired actuation pattern. We will also discuss the principles of operation and functionality and focus on important real-life applications of three groups of soft actuators: ionic polymer–metal composites (IPMCs), dielectric electroactive polymers (DEAPs), and magnetorheological elastomers (MREs). This review article aims to provide researchers interested in the field of soft robotics with a guide to various state-of-the-art chemistry methods used in electrically activated soft actuators, as well as the application areas for such devices.

Voltage-tunable surface-enhanced Raman scattering substrates based on electroactive polymeric membranes containing plasmonic nanoparticles

We describe voltage-controlled surface-enhanced Raman scattering (SERS) substrates in which the SERS-signals can be actively modulated by applying voltage. These SERS-substrates employ a dielectric electroactive polymer (D-EAP) membrane with a pair of electrically-actuated active regions. When these regions are simultaneously activated, they produce an in-plane contractile strain in the regions of the D-EAP where SERS dye-coated nanoparticles are placed. We demonstrate that SERS-signals from dye-coated silver nanoparticles, deposited on the D-EAP membrane, increases by ∼100% upon application of an actuating voltage. Upon removal of the voltage, actuated active-areas move towards their original positions, leading to a decrease in the SERS-signals.

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.

Electroactive Polymer-Based Composites for Artificial Muscle-like Actuators: A Review.

Unlike traditional actuators, such as piezoelectric ceramic or metallic actuators, polymer actuators are currently attracting more interest in biomedicine due to their unique properties, such as light weight, easy processing, biodegradability, fast response, large active strains, and good mechanical properties. They can be actuated under external stimuli, such as chemical (pH changes), electric, humidity, light, temperature, and magnetic field. Electroactive polymers (EAPs), called ‘artificial muscles’, can be activated by an electric stimulus, and fixed into a temporary shape. Restoring their permanent shape after the release of an electrical field, electroactive polymer is considered the most attractive actuator type because of its high suitability for prosthetics and soft robotics applications. However, robust control, modeling non-linear behavior, and scalable fabrication are considered the most critical challenges for applying the soft robotic systems in real conditions. Researchers from around the world investigate the scientific and engineering foundations of polymer actuators, especially the principles of their work, for the purpose of a better control of their capability and durability. The activation method of actuators and the realization of required mechanical properties are the main restrictions on using actuators in real applications. The latest highlights, operating principles, perspectives, and challenges of electroactive materials (EAPs) such as dielectric EAPs, ferroelectric polymers, electrostrictive graft elastomers, liquid crystal elastomers, ionic gels, and ionic polymer–metal composites are reviewed in this article.

Modeling of a Flyback Converter Controlled by an IGBT for Generating a High-Frequency Pulse Voltage

With the rapid development of semiconductor devices, researchers have proposed different types of high-frequency pulse voltage generators based on power electronic converters to meet the requirements of microorganism inactivation, water pollution purification, and piezoelectric and dielectric electroactive polymer drives. The transient modeling of these high-voltage converters aids in understanding the electrical characteristics of the devices and optimizing their performances. This article analyzes the electrical behavior of a semiconductor switching device (i.e., an insulated gate bipolar transistor) used during the switching transient of the converter and constructs an electromagnetic transient model of the flyback converter that considers both the parasitic elements and the ferromagnetic losses of the transformer. The accuracy of the proposed model is then verified by comparing calculation results obtained using the model with experimental measurement results.

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.

A multizone cerebellar chip for bioinspired adaptive robot control and sensorimotor processing.

The cerebellum is a neural structure essential for learning, which is connected via multiple zones to many different regions of the brain, and is thought to improve human performance in a large range of sensory, motor and even cognitive processing tasks. An intriguing possibility for the control of complex robotic systems would be to develop an artificial cerebellar chip with multiple zones that could be similarly connected to a variety of subsystems to optimize performance. The novel aim of this paper, therefore, is to propose and investigate a multizone cerebellar chip applied to a range of tasks in robot adaptive control and sensorimotor processing. The multizone cerebellar chip was evaluated using a custom robotic platform consisting of an array of tactile sensors driven by dielectric electroactive polymers mounted upon a standard industrial robot arm. The results demonstrate that the performance in each task was improved by the concurrent, stable learning in each cerebellar zone. This paper, therefore, provides the first empirical demonstration that a synthetic, multizone, cerebellar chip could be embodied within existing robotic systems to improve performance in a diverse range of tasks, much like the cerebellum in a biological system.

Actuation and dynamic mechanical characteristics of a core free flat dielectric electro-active polymer soft actuator

Various complex shapes of dielectric electro-active polymer (DEAP) actuator have been promoted for several types of applications. In this study, the actuation and mechanical dynamics characteristics of a new core free flat DEAP soft actuator were investigated. This actuator was developed by Danfoss PolyPower. DC voltage of up to 2000 V was supplied for identifying the actuation characteristics of the actuator and compare with the existing formula. The operational frequency of the actuator was determined by dynamic testing. Then, the soft actuator has been modelled as a uniform bar rigidly fixed at one end and attached to mass at another end. Results from the theoretical model were compared with the experimental results. It was found that the deformation of the current actuator was quadratic proportional to the voltage supplied. It was found that experimental results and theory were not in good agreement for low and high voltage with average percentage error are 104% and 20.7%, respectively. The resonance frequency of the actuator was near 14 Hz. Mass of load added, inhomogeneity and initial tension significantly affected the resonance frequency of the soft actuator. The experimental results were consistent with the theoretical model at zero load. However, due to inhomogeneity, the frequency response function’s plot underlines a poor prediction where the theoretical calculation was far from experimental results as values of load increasing with the average percentage error 15.7%. Hence, it shows the proposed analytical procedure not suitable to provide accurate natural frequency for the DEAP soft actuator.

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.

Dynamic cell culture device using electroactive polymer actuators with composite electrodes to transfer in-plane mechanical strain to cells

Living tissues in the body receive various types of stimuli, including mechanical strain, pressure, and varied chemical environments. In contrast, conventional cell cultures are processed under in vitro conditions, which are not similar to the actual body’s environment. To precisely simulate the human body environment, a dynamic cell culture device capable of applying mechanical stimulation to cells is needed. In this study, an acrylic dielectric elastomer electroactive polymer (EAP), is introduced as a driving component for a dynamic cell culture device with a simple structure. The device is composed of separated upper and lower modules with a driving film at the center, By assembling these components, the electrodes on the surface of the driving film are isolated but still connected by columns that can transfer the deformation of the driving apparatus to the culture membrane. The culturing performance of cells according to the mechanical stimuli was experimentally investigated and compared. Tensile strain was found to provide the highest improvement in cell development rate, reaching up to 32.3%. These results highlight the utility of EAPs for compact and biocompatible dynamic cell culture device design.

Ultrahigh-Voltage Switch for Bidirectional DC–DC Converter Driving Dielectric Elastomer Actuator

Specific applications, such as dielectric elastomer actuators (DEAs) or electroactive polymers, require to switch voltage levels exceeding the ratings of existing semiconductor devices. In low-power application, reversible flyback is widely used to supply DEAs. Lowering the parallel parasitic capacitance of the high-voltage switch is important to improve the energy transfer, while it becomes mandatory to increase the output voltage of flyback above 2.5 kV. In this article, a pulsed transformer gate driver (PTGD) is used to drive series-connected MOSFET and, therefore, push the limits from 4.5 to 16 kV. At these high-voltage levels, the structure reveals a drastic voltage unbalance related to the transformer interwinding parasitic capacitance. The compensation method proposed to achieve voltage balance only adds few passive components and reduces significantly the additional parallel capacitance of the switch compared to common load side voltage balancing methods. Finally, and as proof of concept, a half-bridge bidirectional converter was designed from this switch technology and drove an actual DEA at 16 kV.

The FEM Model of the Pump Made of Dielectric Electroactive Polymer Membrane

Dielectric electroactive polymers (DEAPs) undergo large deformations when subject to an electric field, which make them an attractive material for use in novel actuator systems. This article presents the possibility of using DEAPs to model an innovative pumping actuator structure. The model was used to map important object parameters at individual operating points of the modeled pump. The experimental work involved designing the membrane and testing its changes in elasticity under the influence of varying forces and voltage supplies. In the further part of the work, a finite element model (FEM) of a pumping device was implemented. In the new construction of the pump, pressure is generated by membrane deformation. This is due to electrostatic compressive force between two electrodes applied to the polymer surface and forces generated by permanent magnets. The results are presented graphically, confirming the compliance of the model with the measurements.

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.