Tactile Sensor Applications Research Articles

Investigation on voltage response and application of flexible tactile sensors based on multiple cooperative structures

Recently, flexible tactile sensors (FTSs) have gained great attention for their application prospects in human–machine interfaces and robots. However, there is a lack of effective and practical approaches to study the response and guide the design of FTSs. Establishing a valid analytical model and revealing the effect mechanism remain challengeable at present. Herein, an analytical model of an FTS based on multiple cooperative structures (FTS-MCS) is developed. The model is validated with numerical and experimental results. The relative error between the analytical and experimental results for the compression and recovery are 9.3% and 3.8%, respectively. The effect of structure parameters, including helix coil and permanent magnet, is investigated based on the analytical model. The results show that the voltage of FTS-MCS can be improved by tuning the turn, diameter, and shape of coils and the remanent flux density and dimensions of the permanent magnet. The maximum voltage is improved by 49.8% as the turn of coils grows four. The effect of the load conditions of the compression deformation and compression speed is also revealed. Then, a sensitivity analysis is performed to quantitatively analyze the effect of different parameters. Results show the diameter of coils and the compression deformation have the greatest effect on the voltage of FTS-MCS. Due to the flexibility, adaptability, and tactility, such FTS-MCS are mounted on a double-fingered claw to endow the claw with self-perception capacity. Consequently, our study gives a comprehensive understanding of such FTS-MCS and is conducive to promoting the application of FTS-MCS.

Synthesis of PDMS Chain Structure with Introduced Dynamic Covalent Bonding for High‐Performance Rehealable Tactile Sensor Application

AbstractIn addressing the increasing demand for wearable sensing systems, the performance and lifespan of such devices must be improved by enhancing their sensitivity and healing capabilities. The present work introduces an innovative method for synthesizing a healable disulfide bond contained in a polydimethylsiloxane network (PDMS−SS) that incorporates ionic salts, which is designed to serve as a highly effective dielectric layer for capacitive tactile sensors. Within the polymer network structure, the cross‐linking agent pentaerythritol tetrakis 3‐mercaptopropionate (PTKPM) forms reversible disulfide bonds while simultaneously increasing polymer softness and the dielectric constant. The incorporation of dioctyl sulfosuccinate sodium salt (DOSS) significantly improves the capacitance and sensing properties by forming an electrical double‐layer through interactions between the electrode charge and salt ions at the contact interface. The developed polymer material‐based tactile sensor shows a strong response signal at low pressure (0.1 kPa) and maintains high sensitivity (0.175 kPa−1) over a wide pressure range (0.1–10 kPa). It also maintains the same sensitivity over 10 000 repeated applications of external pressure and is easily self‐healed against mechanical deformation due to the dynamic disulfide covalent bonding, restoring ≈95% of its detection capacity.

Application and analysis of contemporary flexible tactile sensors

In order to meet the increasing demand for electronic products in contemporary society, relevant manufacturers have been continuously improving related technologies. While electronic products are convenient, they are plagued by issues such as rapid power consumption, susceptibility to damage, and inconvenience in portability. Therefore, many countries have developed foldable screen smartphones, computers, and other electronic products. In China, major brands such as OPPO and Huawei have released foldable screen smartphones, effectively addressing issues like portability. In this article, a background study of flexible tactile sensors is first conducted to ensure a thorough understanding of their applications. Secondly, based on the working principle of flexible tactile sensors and their different categories, the current research status is analyzed. The classification can be further refined according to the information transmission mechanism and application scenarios. In the former classification, detailed principal introductions are provided for each type of sensor. In the latter classification, based on the existing environment, detailed analyses of the production methods and characteristics are carried out in multiple fields such as tablets and smartphones, laying the groundwork for subsequent discussions. Furthermore, from the perspectives of preparation, characteristics, and power supply, I identify the existing problems and shortcomings that need improvement today, providing detailed explanations. Finally, relevant solutions are proposed for the aforementioned issues, and prospects for the extensive application and bright future of flexible tactile sensors are discussed, including in the fields of biointerfaces, cellular domains, and future mechanical domains.

Design and Application of Flexible Resistive Tactile Sensor Based on Short-Circuit Effect

Resistive tactile sensor has excellent anti-interference characteristics in daily environment. Inspired by the short-circuit effect in electricity, a new design of flexible resistive tactile sensor was proposed in this study. We utilized conductive graphite paint and conductive silver paint as sensing materials to fabricate the high-impedance element (100–150 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega$ </tex-math></inline-formula> ) on the polyimide (PI) film and the low-impedance element (2– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~\Omega$ </tex-math></inline-formula> ) on the silicone rubber, respectively. The output signal depends on the contact area between the high-impedance and the low-impedance elements caused by the applied pressure, which employs the short-circuit effect for the transduction mechanism. Besides, the spherical microstructure in silicone rubber layer was used to enlarge the measuring range of pressure. The experimental results show a wide range of pressure response up to above 3 MPa, and the resolution of the sensor with spherical structure is 79.6 kPa (0.25 N). The force sensing sensitivity of the sensor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S = - 5.733\times 10^{-4}$ </tex-math></inline-formula> kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> (from 0 to 799.4 kPa) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S = - 1.744\times 10^{-4}$ </tex-math></inline-formula> kPa <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> (from 799.4 to 2834.4 kPa). Furthermore, an air gap between the high-impedance and the low-impedance elements was designed for restraining the interference of adjacent sensor arrays. Finally, we demonstrated the application in teleoperation and letter recognition, which implies that the proposed sensor has a great application potential in the field of robotics.

Design, Optimization and Application of Tactile Sensor Based on Virtual Binocular Vision

Design, Optimization and Application of Tactile Sensor Based on Virtual Binocular Vision

Triple mode and multi-purpose flexible sensor fabrication based on carbon black and thermoplastic polyurethane composite with propolis

This study reports the design, fabrication, and application of strain and tactile sensors molded with Carbon Black (CB)/Thermoplastic Polyurethane (TPU) composite ink into flexible-soft 3D printed TPU substrate. In sensor design, three different geometries, namely Straight Line/Zigzag/Wavy, are produced to investigate the effect on the sensing behavior. 3D printed molds are preferred due to their low cost and simplicity in fabrication. Additionally, propolis, which is antibacterial and has therapeutic properties for wound and fungal diseases, is added to the composite material to benefit its healing and protective properties. The sensing properties of propolis are investigated for its use as mixing and coating materials. According to electrical characterization, the fabricated structures can be used in triple mode as piezoresistive, piezocapacitive, and piezoinductive sensors. The gauge factor (GF) values for sensors using different ratios of materials varies between 3 and 10. Given conventional metallic strain gauges whose GF is typically around 2, the obtained GF values are remarkable. The distribution of the applied stress on the sensor surface is given by simulations. In addition, the characteristic changes of the samples according to the frequency are examined, and equivalent circuits are provided.

Modulating the percolation network of polymer nanocomposites for flexible sensors

Flexible sensors have been the focus of intense research efforts in academic and industrial fields for Internet-of-Things applications. In this revolution, different strategies are explored to fabricate flexible tactile sensors by leveraging the pros and cons. In this Perspective, we focus on the current achievements of conductive polymer composites with three bottle-up micro/nano-conductive network structures based on the fundamental tunneling percolation theory and their potentialities and drawbacks for tactile sensor applications. Then, we highlight how model simulations can be used to elucidate the structure and property relationship clearly and guide the modulation of the network structure of conductive composites. Finally, benefiting from the precise definition of the parameters of the composites by model simulation, we discuss the perspectives of the emerging machine learning paradigm on inverse design and development of newly conductive polymer composites in the future.

Magnetostrictive tactile sensor array for force and stiffness detection

The sense of touch, also known as tactile perception, enables enhanced ambient environment awareness for modern robots. Fe-Ga alloys have demonstrated great potential in tactile sensor applications due to their significant inverse magnetostrictive effect. This study first develops a magnetostrictive sensor unit, consisting of permanent magnets, Fe-Ga wires, and Hall sensors to detect static and dynamic forces, as well as sample stiffness. Numerical models for individual sensor units are derived for force and stiffness detection, respectively. The force measurement range of tactile sensor unit is 0 to 3 N, and the sensitivity is 126 mV/N. A tactile sensor array is then developed and validated on a commercial robotic hand. Parametric studies investigating sensor interference and sensor arrangement are completed using finite element modeling. The tactile sensor array is able to detect stiffness of both monolithic and composite samples with a measurement error less than 8.3%. The magnetostrictive tactile sensor array developed in this study can facilitate precise grasping and intelligent control for future robots.

A Survey of Tactile‐Sensing Systems and Their Applications in Biomedical Engineering

Over the past few decades, tactile sensors have become an emerging field of research in both academia and industry. Recent advances have demonstrated application of tactile sensors in the area of biomedical engineering and opened up new opportunities for building multifunctional electronic skin (e‐skin) which is capable of imitating the human sense‐of‐touch for medical purposes. Analyses have shown that current smart tactile sensing technology has the advantages of high performance, low‐cost, time efficiency, and ease‐of‐fabrication. Tactile sensing systems have thus sufficiently matured for integration into several fields related to biomedical engineering. Furthermore, artificial intelligence has the potential for being applied in human‐machine interfacing, for instance, in medical robotic manipulation, especially during minimally invasive robotic surgery, where tactile sensing is usually a problem. In this survey, we present a comprehensive review of the state of the art of tactile sensors. We focus on the technical details of transduction mechanisms such as piezoresistivity, capacitance, piezoelectricity, and triboelectric and highlight the role of novel and commonly used materials in tactile sensing. In addition, we discuss contributions that have been reported in the field of biomedical engineering, which includes its present and future applications in building multifunctional e‐skins, human‐machine interfaces, and minimally invasive surgical robots. Finally, some challenges and notable improvements that have been made in the technical aspects of tactile sensing systems are reported.

Monocharged Electret Nanogenerators: A Monocharged Electret Nanogenerator‐Based Self‐Powered Device for Pressure and Tactile Sensor Applications (Adv. Funct. Mater. 41/2019)

With the rapid development of the internet of things, sensors play an increasingly critical role in the measurement of force, temperature, and light. In article number 1807618, Kailiang Ren, Zhong Lin Wang, and co-workers propose a self-powered pressure sensor based on an electret nanogenerator. This device holds great promise for use in future tactile sensors and artificial skin applications.

Electrical properties of stretchable and skin–mountable PDMS/MWCNT hybrid composite films for flexible strain sensors

Flexible strain sensors based on carbon nanofillers have great potential in the application of skin-adhesive sensors, wearable sensors, and tactile sensors, due to their superior electrical properties. Herein, the electrical properties of highly sensitive PDMS/MWCNT strain sensors made by vacuum filtration method were investigated. In order to obtain the electrical percolation curve of the flexible conductive films, first different samples were made with the same surface area but with different wt. % of CNTs. Then, depending on CNT content, the obtained conductive films exhibited initial electrical resistance in the range of 12.5 KΩ to 22.8 MΩ. The piezoresistive films with the CNT concentration of 1.4 to 2.9 [Formula: see text] had shown superior resistance drop, so this interval was determined as the percolation threshold region. According to the SEM images, the nanocomposite layer thickness of the flexible strain sensors in this region was 790 nm to 1210 nm. Afterward, the percolation curve was obtained using curve fitting to the experimental data and the exact value of the percolation threshold was defined as [Formula: see text]. Finally, in order to determine the minimum gauge factor ([Formula: see text]) of the sensors in percolation region, a flexible strain sensor in the upper limit of this region was selected and the piezoresistive properties of the selected sample were investigated.

A Monocharged Electret Nanogenerator‐Based Self‐Powered Device for Pressure and Tactile Sensor Applications

AbstractThis study reports a self‐powered pressure sensor based on a monocharged electret nanogenerator (MENG). The sensor exhibits great advantages in terms of high reliability, ease of fabrication, and relatively high sensitivity. The working mechanism of the MENG sensor is studied by both theoretical derivations and finite element analyses to determine the electric potential distribution during the device operation. The MENG sensor exhibits a stable open circuit voltage ≈10 V at a 30.8 kPa pressure and a corresponding sensitivity of 325 mV kPa−1. The stability testing result shows that the device has only ≈5% attenuation after 10 000 cycles of repeated testing at 30.8 kPa pressure. Furthermore, it is found that the MENG sensor responds not only to a dynamic force but also a static force. Finally, a sensor array consisting of nine MENG sensor elements is fabricated. The testing results from the sensor array also reveal that a single touch of the sensor element can immediately light up an LED light at the corresponding position. This device holds great promise for use in future tactile sensors and artificial skin applications.

Application of Tactile Sensor Using Shape-memory Polymer to Robot Arm

Application of Tactile Sensor Using Shape-memory Polymer to Robot Arm

Tactile Chemomechanical Transduction Based on an Elastic Microstructured Array to Enhance the Sensitivity of Portable Biosensors

Tactile sensors capable of perceiving biophysical signals such as force, pressure, or strain have attracted extensive interest for versatile applications in electronic skin, noninvasive healthcare, and biomimetic prostheses. Despite these great achievements, they are still incapable of detecting bio/chemical signals that provide even more meaningful and precise health information due to the lack of efficient transduction principles. Herein, a tactile chemomechanical transduction strategy that enables the tactile sensor to perceive bio/chemical signals is proposed. In this methodology, pyramidal tactile sensors are linked with biomarker-induced gas-producing reactions, which transduce biomarker signals to electrical signals in real time. The method is advantageous as it enhances electrical signals by more than tenfold based on a triple-step signal amplification strategy, as compared to traditional electrical biosensors. It also constitutes a portable and general platform capable of quantifying a wide spectrum of targets including carcinoembryonic antigen, interferon-γ, and adenosine. Such tactile chemomechanical transduction would greatly broaden the application of tactile sensors toward bio/chemical signals perception which can be used in ultrasensitive portable biosensors and chemical-responsive chemomechanical systems.

Large deformation mechanics of a soft elastomeric layer compressed by a finite flat rigid punch for tactile sensor applications

In this study, we develop a large deformation analytical–empirical model for a flat finite punch pinching on an incompressible, polymeric layer under plane strain conditions. The model could further advance the predictive capabilities of enhanced tactile sensor response models. The aforementioned model is developed based on the analytical model for an infinitely long layer under uniform compression which has been presented in Kalayeh and Charalambides (2015). Related non-linear finite element (FE) simulations with large strain, large deformation assumptions are carried out in this study. Using the FE finite flat punch simulations, the uniform layer compression model is properly adjusted to predicting the finite punch layer response. The mechanics of the polymeric layer in the vicinity of the symmetry plane, under the application of a flat finite rigid punch is fully analyzed and an expression for the indentation force as a function of the applied top surface deformation is developed. The relevance of this result to modeling the non-linear tactile sensor response over a broad sensing range is discussed. The reported results are compared to FE simulations for applied surface deformation levels of up to 40 percent of the layer initial thickness, and punch half-length to layer thickness ratios of 1 to 2. Great agreement is found to exist between the analytical–empirical model and the FE simulations. For completeness, this new semi-analytical model is fully summarized in the Appendix of this work.

Tactile-Sensing Based on Flexible PVDF Nanofibers via Electrospinning: A Review.

The flexible tactile sensor has attracted widespread attention because of its great flexibility, high sensitivity, and large workable range. It can be integrated into clothing, electronic skin, or mounted on to human skin. Various nanostructured materials and nanocomposites with high flexibility and electrical performance have been widely utilized as functional materials in flexible tactile sensors. Polymer nanomaterials, representing the most promising materials, especially polyvinylidene fluoride (PVDF), PVDF co-polymer and their nanocomposites with ultra-sensitivity, high deformability, outstanding chemical resistance, high thermal stability and low permittivity, can meet the flexibility requirements for dynamic tactile sensing in wearable electronics. Electrospinning has been recognized as an excellent straightforward and versatile technique for preparing nanofiber materials. This review will present a brief overview of the recent advances in PVDF nanofibers by electrospinning for flexible tactile sensor applications. PVDF, PVDF co-polymers and their nanocomposites have been successfully formed as ultrafine nanofibers, even as randomly oriented PVDF nanofibers by electrospinning. These nanofibers used as the functional layers in flexible tactile sensors have been reviewed briefly in this paper. The β-phase content, which is the strongest polar moment contributing to piezoelectric properties among all the crystalline phases of PVDF, can be improved by adjusting the technical parameters in electrospun PVDF process. The piezoelectric properties and the sensibility for the pressure sensor are improved greatly when the PVDF fibers become more oriented. The tactile performance of PVDF composite nanofibers can be further promoted by doping with nanofillers and nanoclay. Electrospun P(VDF-TrFE) nanofiber mats used for the 3D pressure sensor achieved excellent sensitivity, even at 0.1 Pa. The most significant enhancement is that the aligned electrospun core-shell P(VDF-TrFE) nanofibers exhibited almost 40 times higher sensitivity than that of pressure sensor based on thin-film PVDF.

Rigid sphere indentation on soft materials for robotics tactile sensor application

Rigid sphere indentation on soft materials for robotics tactile sensor application

Core-shell nanofiber mats for tactile pressure sensor and nanogenerator applications

Core-shell nanofibers of PDMS ion gel /PVDF-HFP were successfully prepared by incorporating cross-linking agent during electrospinning. The electrospun nanofiber mats were used to fabricate pressure sensors to detect the static and dynamic pressures by harnessing the capacitance changes and triboelectric effects judiciously. The core-shell PDMS ion gel/PVDF-HFP nanofiber sensor functions as a capacitive pressure sensor, which offers high sensitivity of 0.43kPa−1 in the low pressure ranges from 0.01kPa to 1.5kPa. The sensitivity, flexibility, and robustness of our capacitive pressure sensor allows it to be utilized as a wrist-based pulse wave detector for heart-rate monitoring. In addition, the core-shell PDMS ion gel/PVDF-HFP nanofiber mat made a good triboelectric based pressure sensor in the high pressure range with a linear pressure sensitivity 0.068VkPa−1 from 100kPa to 700kPa, one of the best reported at present. The increase in inductive charges and the enhanced dielectric capacitance of the core-shell nanofiber layer compared to the pure PVDF-HFP nanofiber layer allows it to function in the triboelectric nanogenerator (TENG) with the maximum power density reaching 0.9W/m2, which is sufficient to light up several hundred light emitting diodes (LEDs) instantaneously.

Piezoresistivities of vapor‐grown carbon fiber/silicone foams for tactile sensor applications

AbstractDue to the growing demand for tactile sensors, the possibility of detecting an external uniaxial pressure by the piezoresistive measuring of a conductive filler/elastomer composite was investigated. A series of piezoresistive models are discussed. Novel highly sensitive piezoresistive foams with excellent elasticity were fabricated using vapor‐grown carbon fiber (VGCF), two‐component silicone elastomer and a new type of thermally expandable micro beads foaming agent to overcome the disadvantages of the silicone elastomer in the utilization of a tactile sensor. Deformations of the foams caused by uniaxial pressure were observed using scanning electron microscopy from cross‐sections. Effects of the VGCF and the foaming agent on the piezoresistivitiy were investigated. The piezoresistive mechanisms of the foams are discussed according to the measurements, and good fit was found between the theoretical calculations and the experimental piezoresistivity measurements. It is found that the addition of the micro beads foaming agent can improve the piezoresistivity of the VGCF/silicone foam and increase the sensitivity and repeatability for its application in a tactile sensor. © 2016 Society of Chemical Industry

An extremely highly selective flexible compliant tactile touch sensor sheet

One of the major challenges toward widespread application of flexible tactile pressure sensors lies in the distinction between tactile pressure stimuli and contributions from substrate bending. To this point, this issue has been a bottleneck in further advancement of this class of devices. To address this issue, we demonstrate a flexible tactile pressure sensor sheet with extremely high selectivity between tactile pressure and substrate bending: these devices are designed with strain engineering with the goal of incorporation into artificial skin applications. In addition to characterizing the mechanical and electrical performance of the sensor, a first proof of concept for tactile pressure mapping at several mechanical flex states is conducted, demonstrating that these devices are highly compliant tactile pressure sensors well‐suited to robotic skin and prosthesis applications.