Self-sensing Actuator Research Articles

Piezoelectric Impedance-based Structural Damage Identification Empowered with Tunable Circuitry Integration and Multi-objective Optimization based Inverse Analysis

Abstract The piezoelectric impedance-based technique is increasingly recognized for its promise in structural health monitoring and damage identification. Built upon their self-sensing actuation capability, piezoelectric transducers can be integrated to host structures to acquire the system-level impedance information in high frequency range with small wavelength. Furthermore, the frequency-sweeping harmonic excitations in impedance measurements lead to the potential for model-based inverse identification of damage location and severity. A major challenge in damage identification, however, is that the inverse analysis is generally underdetermined, as the measurement information may not be adequate to yield a unique solution. In this research, a new methodology of tunable sensing in conjunction with multi-objective optimization inverse analysis is established. Taking advantage of the two-way electromechanical coupling of piezoelectric transducers, tunable inductance is integrated into the measurement circuit. For the same damage scenario, by tuning the inductance to a series of values, a family of impedance measurements can be acquired. Meanwhile, the inverse analysis is cast into a multi-objective optimization problem, aiming at minimizing the difference between measurement and model prediction and achieving sparsity in damage index vector. A Q-learning based multi-objective particle swarm optimization is synthesized to reach a small yet diverse solution set. We report the circuitry integration details as well as the algorithm enhancement with systematic case investigations. It is validated that the new methodology with enriched measurement can produce smaller solution set encompassing the true damage scenario, thereby providing vital information for diagnoses and prognosis.

Smart sensing hydrogel actuators conferred by MXene gradient arrangement

Smart sensing and excellent actuation abilities of natural organisms have driven scientists to develop bionic soft-bodied robots. However, most conventional robots suffer from poor electrical conductivity, limiting their application in real-time sensing and actuation. Here, we report a novel strategy to enhance the electrical conductivity of hydrogels that integrated actuation and strain-sensing functions for bioinspired self-sensing soft actuators. Conductive hydrogels were synthesized in situ by copolymerizing MXene nanosheets with thermosensitive N-isopropylacrylamide and acrylamide under a direct current electric field. The resulting hydrogels exhibited high electrical conductivity (2.11 mS/cm), good sensitivity with a gauge factor of 4.79 and long-term stability. The developed hydrogels demonstrated remarkable capabilities in detecting human motions at subtle strains such as facial expressions and large strains such as knee bending. Additionally, the hydrogel electrode patch was capable of monitoring physiological signals. Furthermore, the developed hydrogel showed good thermally induced actuation effects when the temperature was higher than 30 °C. Overall, this work provided new insights for the design of sensory materials with integrated self-sensing and actuation capabilities, which would pave the way for the development of high-performance conductive soft materials for intelligent soft robots and automated machinery.

A tactile sensing system capable of recognizing objects based on bioinspired self-sensing soft pneumatic actuator

Tactile sensors play an important role when robots perform contact tasks, such as physical information collection, force or displacement control to avoid collision. For these manipulations, excessive contact may cause damage while poor contact cause information loss between the robotic end-effector and the objects. Inspired by skin structure and signal transmission method, this paper proposes a tactile sensing system based on the self-sensing soft pneumatic actuator (S-SPA) capable of providing tactile sensing capability for robots. Based on the adjustable height and compliance characteristics of the S-SPA, the contact process is safe and more tactile information can be collected. And to demonstrate the feasibility and advantage of this system, a robotic hand with S-SPAs could recognize different textures and stiffness of the objects by touching and pinching behaviours to collect physical information of the various objects under the positive work states of the S-SPA. The result shows the recognition accuracy of the fifteen texture plates reaches 99.4%, and the recognition accuracy of the four stiffness cuboids reaches 100%by training a KNN model. This safe and simple tactile sensing system with high recognition accuracies based on S-SPA shows great potential in robotic manipulations and is beneficial to applications in domestic and industrial fields.

Control design for beam stabilization with self-sensing piezoelectric actuators: managing presence and absence of hysteresis

Control design for beam stabilization with self-sensing piezoelectric actuators: managing presence and absence of hysteresis

Experimental study on synchronous detection of output force in a self-sensing giant magnetostrictive actuator

This paper systematically investigates the real-time detection of static and dynamic output forces by a self-sensing giant magnetostrictive actuator (SSGMA). The online stiffness of the actuator is perceived as the sensing signal according to the ΔE effect of Terfenol-D. Numerical simulations are carried out to analyze the effects of the driving magnetic field and the hysteresis caused by magneto-mechanical coupling on the performance of self-sensing output force. Then the prototype is fabricated and tested to verify the self-sensing characteristics of SSGMA for the output force. The noise density of prototype is tested to be below 56.92 nV √Hz−1. The experimental results illustrate that SSGMA has a self-detection sensitivity of 0.47 mV N−1 for a static force with an amplitude of nearly 120 N. The SSGMA is able to synchronize the tracking of quasi-static and low-frequency dynamic output forces, respectively. The hereby proposed SSGMA further broadens the application scenario of precision actuation systems by synchronizing the detection and control of the output force without requiring external sensors.

Thermal and light-driven soft actuators based on a conductive polypyrrole nanofibers integrated poly(N-isopropylacrylamide) hydrogel with intelligent response

The development of soft hydrogel actuators with outstanding mechanical properties, fast actuation speed, and available quantification of self-sensing actuation remains a challenging endeavor. In this work, dopamine-decorated polypyrrole nanofibers (DAPPy) were introduced into the polyethylene glycol diacrylate (PEGDA)-crosslinked poly(N-isopropyl acrylamide) network to generate a stretchable, NIR-responsive, and strain sensitive DAPPy/PNIPAM hydrogel layer. Besides, this active layer was combined with the passive ligninsulfonate sodium/polyacrylamide (LS/PAAM) to give DAPPy/PNIPAM//LS/PAAM bilayer hydrogel actuator, which exhibits ultrafast thermo-responsive actuation (19°/s) and underwater grasping and lifting performance. Moreover, the DAPPy/PNIPAM layer has excellent electrical conductivity (0.29 S/m) and thermal conversion ability (10.8 °C/min), which enable such a conductive hydrogel to act as a highly sensitive strain and temperature sensor with real-time resistance change in response to tensile strain (gauge factor up to 3.4), applied pressure, temperature, and remote NIR light irradiation. More importantly, the bilayer hydrogel actuator can integrate both actuation and self-sensing functions through the bending angle-surface temperature-relative resistance change relationship of the photothermal process. With excellent mechanical actuation and self-sensing ability, the resulting bilayer hydrogel showed a promising application potential as soft biomimetic actuating materials and soft intelligent actuators.

Three-Degree-of-Freedom Cable-Driven Parallel Manipulator with Self-Sensing Nitinol Actuators

Three-Degree-of-Freedom Cable-Driven Parallel Manipulator with Self-Sensing Nitinol Actuators

Sensor-Less Control of Mirror Manipulator Using Shape Memory Polyimide Composite Actuator: Experimental Work.

Integrated thin film-based shape memory polyimide composites (SMPICs) are potentially attractive for efficient and compact design, thereby offering cost-effective applications. The objective of this article is to design and evaluate a mirror manipulator using an SMPIC as an actuator and a sensor with control. A sensor-less control strategy using the SMPIC (a self-sensing actuator) with a proportional derivative combined variable structure controller (PD-VSC) is proposed for position control of the mirror in both the vertical and angular directions. The mirror manipulator is able to move the mirror in the vertical and angular directions by 3.39 mm and 10.5 deg, respectively. A desired fast response is obtained as the performance under control. In addition, some benefits from the proposed control realization include good tracking, stable switching, no overshoot, no steady state oscillations, and robust disturbance rejection. These superior properties are experimentally validated to reflect practical feasibility.

Liquid crystal elastomer-based all-printed actuator and sensing array systems

Liquid crystal elastomers (LCEs) are valuable in soft actuators, sensors and other emerging fields. However, it is still a huge challenge to build high-performance LCE-based functional devices in a simple and fast way to achieve the orderly and patterned integration of multiple functional layers and LCE. Herein, screen-printing technology is used to realize the multi-layer pattern deposition of silver fractal dendrites conductive ink (with excellent Joule heating effect and strain-sensing function) and carbon black conductive ink (with photothermal conversion ability) on the surface of LCE. A series of LCE-based electronic devices are prepared through customized printing patterns. The as-obtained actuator possesses excellent electric actuating performance (bending angle of 102° at 200 mA) and self-sensing function (maximum relative resistance changes of −55.0%), and also exhibits NIR light-driven self-sensing bending actuation behavior (bending angle of 81° at 1.43 W/cm2), which can be used to control the robotic arm. The as-printed NIR light sensing array system can accurately sense the intensity, spot size and position of NIR light, showing good application potential in the field of unmanned aerial vehicle flight safety. This work provides a new strategy for the efficient preparation of LCEs-based flexible electronics.

Zwitterionic liquid crystal elastomer with unusual dependence of ionic conductivity on strain and temperature for smart wearable fabric

Stretchable ionic conductors are appealing for soft electronics, yet frequently had their conductivities limited below the level desired by many applications, and also lack the ability of simultaneously actuating and sensing their own motions, resembling living organisms’ neuromuscular behaviors. In this study, by introducing a zwitterionic chain extender into liquid crystal elastomers (LCEs) backbones, a unique type of zwitterionic LCEs (iLCEs) fiber with ionic conductivity of 2.3 S m−1 and self-sensing properties was designed. By controlling the anisotropy solvent evaporation, the iLCEs fiber with certain degree of mesogenic alignment was easily obtained. The mesogenic alignment not only enabled a reversible actuation behavior, but also boosted the formation of ionic channels for an abnormal dependence of ionic conductivity on temperature and elongation. The resultant iLCEs fibers showed an increasing resistance at high temperatures, and a decreasing resistance at large tensile strain, in contrast to the liquid-like mechanism of ion transport for ionogel systems. This combination of actuation and ionic conductance promises great potential in applications of self-sensing actuation and self-perception of soft robots.

A tri-modal dielectric elastomer actuator integrating linear actuation, sound generation, and self-sensing capabilities

This paper presents a concept of multi-modal dielectric elastomer actuator (DEA) that leverages a single voltage input to concurrently work as linear actuator and loudspeaker, while also integrating self-sensing capabilities. Low-frequency linear actuation is obtained by inducing tangential stretching of the DEA membrane surface, whereas high-frequency sound generation is concurrently achieved through transverse structural vibrations of the DEA membrane surface. Multi-mode actuation is combined with a new self-sensing paradigm: measuring the current signal arising from the dynamic acoustic excitation and processing it in real-time with capacitance estimation algorithms, the actuator low-frequency displacement can be reconstructed with no need for additional transducers or dedicated probing signals. The performance of the proposed self-sensing approach is evaluated using complex multi-harmonic driving signals, with a focus on analyzing the correlation between capacitance estimates and the low-frequency stroke of the device. Concurrent self-sensing and multi-mode actuation are finally demonstrated in a number of application scenarios, in which the intensity/frequency of the DEA acoustic output is adjusted in closed-loop as a function of externally induced deformations, such as impacts with obstacles, or interactions with a user. The multi-modality paradigm pursued in this work paves the way to new application opportunities, such as multi-sensory user interfaces (e.g. audio-tactile buttons), or highly integrated sensor-actuator units able to sense their state during operation and provide feedback (e.g., acoustic signaling) accordingly.

Self-sensing model of low-frequency magnetostrictive composites actuator based on Jiles-Atherton theory

Giant magnetostrictive powder composites (GMPCs) have important applications in electric current sensing, stress sensing, vibration damping, actuation, health monitoring and other fields. Most of the research discussed the actuation or sensing function of GMPCs merely. In this paper, GMPCs based actuator with a self-sensing function is proposed to realize direct measurement of the deformation amplitudes of the actuator in low frequency, through monitoring the voltage signal of the driving circuit. It also means the actuator can be used as a compressive stress and magnetostriction sensor. The self-sensing actuator avoids the dependence on extra sensors for actuation detection, which complements the self-sensing technique in GMPC-based actuators. It is helpful not only in the designing and controlling of self-sensing applications in actuators, but also in expanding the applications of GMPCs in the field of integrated devices.

Nanocellulose-mediated bilayer hydrogel actuators with thermo-responsive, shape memory and self-sensing performances

Inspired by creatures, abundant stimulus-responsive hydrogel actuators with diverse functionalities have been manufactured for applications in soft robotics. However, constructing a shape memory and self-sensing bilayer hydrogel actuator with high mechanical strength and strong interfacial bonding still remains a challenge. Herein, a novel bilayer hydrogel with a stimulus-responsive TEMPO-oxidized cellulose nanofibers/poly(N-isopropylacrylamide) (TOCN/PNIPAM) layer and a non-responsive TOCN/polyacrylamide (TOCN/PAM) layer is proposed as a thermosensitive actuator. TOCNs as a nano-reinforced phase provide a high mechanical strength and endow the hydrogel actuator with a strong interfacial bonding. Due to the incorporation of TOCNs, the TOCN/PNIPAM hydrogel exhibits a high compressive strength (~89.2 kPa), elongation at break (~170.7 %) and tensile strength (~24.0 kPa). The prepared PNIPAM/TOCN/PAM hydrogel actuator performs the roles of an encapsulation, jack, temperature-controlled fluid valve and temperature-control manipulator. The incorporation of Fe3+ further endows the bilayer hydrogel actuator with a synergistic performance of shape memory and temperature-driven, which can be used as a temperature-responsive switch to detect ambient temperature. The PNIPAM/TOCN/PAM-Fe3+ conductive hydrogel can be assembled into a flexible sensor and generate sensing signals when driven by temperature changes to achieve real-time feedback. This research may lead to new insights into the design and manufacturing of intelligent flexible soft robots.

Motion Characteristics of Self-Sensing Piezoelectric Actuator for Yarn Micro-Gripper

In order to solve the problem of low response frequency and poor consistency of conventional yarn grippers in weft accumulators, in this study, a piezoelectric yarn gripper is used instead of conventional yarn grippers and the motion characteristics of its actuator are studied. This gripper uses a bimorph piezoelectric bending actuator with a low-cost, well integrated self-sensing method based on charge measurement. The modeling of the piezoelectric micromanipulator is based on the piezoelectric and Euler–Bernoulli beam equations. The static and dynamic characteristics of the piezoelectric actuator as well as the self-sensing capability were experimentally tested. The experimental results show that the maximum output displacement at the end of the piezoelectric actuator is 834 μm, and the maximum output force is 388 μN at 150 V driving voltage. The stability and consistency of its response are also very good, with a response speed of 24 ms. The self-sensing test of the output force also proved the feasibility of the self-sensing method used, with an error of 0.74%. The piezoelectric yarn gripper studied in this paper is promising for practical clamping applications.

Precision positioning based on temperature dependence self-sensing magnetostrictive actuation mechanism

The self-sensing actuator that integrates both actuation and sensing functions is an effective way to simplify the structure of electromechanical systems. This paper proposes a temperature-dependent self-sensing actuation strategy based on a self-sensing giant magnetostrictive actuator (SSGMA) by sensing online stiffness. Utilizing the developed model considering temperature-dependent hysteresis nonlinearity, the self-sensing output characteristics of SSGMA are first evaluated. The self-sensing based control system is then designed in detail. The relationship between the self-sensing signal and the output displacement of SSGMA at different temperatures is constructed by General Regression Neural Network (GRNN) model for fast recognition by the controller. On this basis, a composite control scheme that takes into account rate-dependent asymmetric hysteresis nonlinearities and combines an adaptive feedforward controller with PID feedback controller is proposed for precision actuation of SSGMA. Finally, a temperature-controlled experimental platform is assembled for verification. Experimental results demonstrate that, based on the developed model, the SSGMA is capable of accurate self-sensing output at temperatures of 22 °C, 40 °C, and 70 °C, respectively. The SSGMA with the proposed control method enables the synchronous and precise self-sensing positioning of step and multiple-frequency sinusoidal expectations at different temperatures.

How to Easily Make Self-Sensing Pneumatic Inverse Artificial Muscles.

Wearable mechatronics for powered orthoses, exoskeletons and prostheses require improved soft actuation systems acting as 'artificial muscles' that are capable of large strains, high stresses, fast response and self-sensing and that show electrically safe operation, low specific weight and large compliance. Among the diversity of soft actuation technologies under investigation, pneumatic devices have been the focus, during the last couple of decades, of renewed interest as an intrinsically soft artificial muscle technology, due to technological advances stimulated by applications in soft robotics. As of today, quite a few solutions are available to endow a pneumatic soft device with linear actuation and self-sensing ability, while also easily achieving these features with off-the-shelf materials and low-cost fabrication processes. Here, we describe a simple process to make self-sensing pneumatic actuators, which may be used as 'inverse artificial muscles', as, upon pressurisation, they elongate instead of contracting. They are made of an elastomeric tube surrounded by a plastic coil, which constrains radial expansions. As a novelty relative to the state of the art, the self-sensing ability was obtained with a piezoresistive stretch sensor shaped as a conductive elastomeric body along the tube's central axis. Moreover, we detail, also by means of video clips, a step-by-step manufacturing process, which uses off-the-shelf materials and simple procedures, so as to facilitate reproducibility.

Numerical study of polymer embedded metal hydride-based self-sensing actuator

Metal hydride actuators have amassed increasing attention over the past decade owing to their desirable operational characteristics, such as a high power-to-weight ratio, noiseless and vibration-less operation, lightweight, safety and environmental friendliness. Essentially, there are two ways in which we can attain actuation using hydrides. Primarily, actuation force is generated by the hydrogen gas pressure changes associated with charge–discharge process. Alternatively, the incompressible volumetric changes in the hydride bed during sorption can also result in actuation. However the studies reported on this type of actuators are rare and mostly deal with bimorph actuators. The present study investigates the effect of soft silicone rubber composited metal hydride bed within a hollow stainless steel spring for its potential use as a self-sensing actuator element. LaNi5 is used as the metal hydride alloy. For an equivalent quantity of hydride by mass, the estimated actuation stroke and force for the composite bed actuator are better than their powder bed counterpart (12 mm and 100 N, respectively, in contrast to 5.84 mm and 60 N), due to improved heat transfer. Bed thickness, coil pitch and coil diameter are important geometric parameters which control the performance of the device. As previously reported, hydrogen supply pressure and heat transfer coefficient are found to be important operating parameters controlling the force –stroke characteristics of the actuating element. The simulation study has been executed using COMSOL Multiphysics™ commercial code.

Dynamic Adaptive Cross-linked Elastomers with Highly Robust, Recyclable, and Conductive Abilities toward Strain Sensors and Self-Sensing Actuators

Dynamic Adaptive Cross-linked Elastomers with Highly Robust, Recyclable, and Conductive Abilities toward Strain Sensors and Self-Sensing Actuators

Functionally antagonistic polyelectrolyte for electro-ionic soft actuator

Electro-active ionic soft actuators have been intensively investigated as an artificial muscle for soft robotics due to their large bending deformations at low voltages, small electric power consumption, superior energy density, high safety and biomimetic self-sensing actuation. However, their slow responses, poor durability and low bandwidth, mainly resulting from improper distribution of ionic conducting phase in polyelectrolyte membranes, hinder practical applications to real fields. We report a procedure to synthesize efficient polyelectrolyte membranes that have continuous conducting network suitable for electro-ionic artificial muscles. This functionally antagonistic solvent procedure makes amphiphilic Nafion molecules to assemble into micelles with ionic surfaces enclosing non-conducting cores. Especially, the ionic surfaces of these micelles combine together during casting process and form a continuous ionic conducting phase needed for high ionic conductivity, which boosts the performance of electro-ionic soft actuators by 10-time faster response and 36-time higher bending displacement. Furthermore, the developed muscle shows exceptional durability over 40 days under continuous actuation and broad bandwidth below 10 Hz, and is successfully applied to demonstrate an inchworm-mimetic soft robot and a kinetic tensegrity system.

Notice of Removal: Self-Sensing Actuation Circuit for PZT Micro-actuator in HDDs

This paper presents a new self-sensing actuation (SSA) circuit for using the piezoelectric (PZT) micro-actuator as both an actuator and a sensor simultaneously. The proposed SSA circuit senses the voltage signal generated by the PZT micro-actuator at operating frequencies, while the control voltage applied to the same PZT micro-actuator is not affected. The components of the proposed SSA circuit are minimized to allow easy balancing and implementation. In simulations, the proposed SSA circuit had similar characteristics to the conventional SSA circuit. In experiments, the proposed SSA circuit was tested with a commercial hard disk drive (HDD). The results show that the proposed SSA circuit does not affect the conventional read/write (R/W) head positioning control system. The frequency response of the PZT micro-actuator measured by the proposed SSA circuit had similar to the frequency response of the R/W head displacement at both the resonant frequency and the operating frequencies. The proposed SSA circuit was also tested at various operating temperatures of the HDD. Errors in the sensing voltage signal caused by the unbalanced SSA circuit clearly correlated to the temperatures from 10 °C to 60 °C.