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Multifunctional Soft Robotic Finger Based on a Nanoscale Flexible Temperature–Pressure Tactile Sensor for Material Recognition

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... Recognizing different contact patterns applied to the tactile sensors plays a very important role in human-machine interaction. A flexible tactile sensor is an essential tactile information acquisition medium of the robot sensor system, and it has special advantages in detecting target surface texture and physical properties [1][2][3], which is conducive to establishing a more secure and reliable humanmachine interaction system [4,5]. ...
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Recognizing different contact patterns imposed on tactile sensors plays a very important role in human–machine interaction. In this paper, a flexible tactile sensor with great dynamic response characteristics is designed and manufactured based on polyvinylidene fluoride (PVDF) material. Four contact patterns (stroking, patting, kneading, and scratching) are applied to the tactile sensor, and time sequence data of the four contact patterns are collected. After that, a fusion model based on the convolutional neural network (CNN) and the long-short term memory (LSTM) neural network named CNN-LSTM is constructed. It is used to classify and recognize the four contact patterns loaded on the tactile sensor, and the recognition accuracies of the four patterns are 99.60%, 99.67%, 99.07%, and 99.40%, respectively. At last, a CNN model and a random forest (RF) algorithm model are constructed to recognize the four contact patterns based on the same dataset as those for the CNN-LSTM model. The average accuracies of the four contact patterns based on the CNN-LSTM, the CNN, and the RF algorithm are 99.43%, 96.67%, and 91.39%, respectively. All of the experimental results indicate that the CNN‑LSTM constructed in this paper has very efficient performance in recognizing and classifying the contact patterns for the flexible tactile sensor.
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Flexible and wearable pressure sensors are of paramount importance for development of personalized medicine and electronic skin. However, the preparation of easily disposed pressure sensors is still facing with pressing challenges. Herein, we have developed an all paper-based piezoresistive (APBP) pressure sensor through a facile, cost-effective and environment-friendly method. This pressure sensor was based on tissue paper coated with silver nanowires (AgNWs) as sensing material, nanocellulose paper (NCP) as bottom substrate for printing electrodes, and NCP as top encapsulating layer. The APBP pressure sensor showed high sensitivity of 1.5 kPa-1 in the range of 0.3-30.2 kPa and retained excellent performance in bending state. Furthermore, the APBP sensor has been mounted on the human skin to monitor human physiological signals (such as arterial heart pulse and pronunciation from throat) and successfully applied as soft electronic skin to response to external pressure. Due to the use of common tissue paper, NCP, AgNWs and conductive nanosilver ink only, the pressure sensor has low-cost, facile-craft and fast-preparation advantages and can be disposed easily by incineration. We believe that the developed sensor will propel the advance of easily disposed pressure sensor and green paper-based flexible electronic devices.
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We develop a flexible and multifunctional resistive sensor integrating uniform conductive coating layers with interlaced nanofibrous structure through a large-scale and cost-efficient strategy. Elastomer nanofiber framework not only endows superior flexibility for the multi-mode sensor, but also provides abundant contact sites and contact area which can significantly enhance the sensitivity and operating range of obtained sensor. More impressively, the multilevel sensing paths comprised of both interlaminar and intrastratal signal transmissions fulfill the simultaneous and precise detection of pressure-temperature stimuli without interference to each other. The achieved sensor ultimately shows an ultrahigh pressure sensitivity of 1185.8 kPa-1 and superior reliability, enabling the rapid detection of subtle stimulus as low as 2.4 Pa and superior response behavior under 5000 cyclic loading tests. Besides, high linearity and stability are achieved for temperature sensing characteristic even under various pressure loadings. These outstanding performances are further evaluated by preparing 4×5 bimodal sensor array to synchronously monitor multiple signals, consequently demonstrating precise sensing capability with negligible interference and providing effective approach for developing multiparametric sensing platforms and wearable devices.
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Glucose metabolism plays an important role in cell energy supply, and quantitative detection of intracellular glucose level is particularly important for understanding many physiological processes. Glucose electrochemical sensors are widely used for blood and extracellular glucose detection. However, intracellular glucose detection cannot be achieved by these sensors owing to their large size and consequent low spatial resolution. Herein, we developed a single nanowire glucose sensor for electrochemical detection of intracellular glucose by depositing Pt nanoparticles (Pt NPs) on a SiC@C nanowire and further immobilizing glucose oxidase (GOD) there on. Glucose was converted by GOD to an electroactive product H2O2 which was further electro-catalyzed by Pt NPs. The glucose nanowire sensor is endowed with high sensitivity, high spatial-temporal resolution and enzyme specificity due to its nanoscale size and enzymatic reaction. This allows the real-time monitoring of the intracellular glucose level, and the increasement of intracellular glucose level induced by a novel potential hypoglycemic agent, reinforcing its potential application in lowering the blood glucose level. This work provides a versatile method for the construction of enzyme-modified nanosensors to electrochemically detect intracellular non-electroactive molecules, which is of great benefit to the physiological and pathological studies.
Article
Recently, cellulose paper based materials are emerging for applications in wearable “green” electronics due to their earth-abundance, low cost, light weight, flexibility, and sustainability. Herein, for the first time, we develop an almost all cellulose paper based pressure sensor through a facile, cost-effective, scalable, and environment-friendly approach. The screen-printed interdigital electrodes on the flat printing paper and the carbonized crepe paper (CCP) with a good conductivity are integrated into a flexible pressure sensor as substrates and active materials, respectively. The porous and corrugated structure of the CCP endows the pressure sensor with high sensitivity (2.56-5.67 KPa⁻¹ in the range of 0-2.53 KPa), wide workable pressure range (0-20 KPa), fast response time (<30 ms), low detection limit (~0.9 Pa), and good durability (>3000 cycles). Additionally, we demonstrate the practical applications of the CCP pressure sensor in detection of finger touching, wrist pulse, respiration, phonation, and acoustic vibration, etc., and real-time monitoring of spatial pressure distribution. The proposed CCP pressure sensor has great potentials in various applications as wearable electronics. Moreover, the subtle fabrication of desired materials based on commercially available products provides new insights into the development of green electronics.
Article
Flexible and wearable pressure sensor may offer convenient, timely, and portable solutions to human motion detection, yet it is a challenge to develop cost-effective materials for pressure sensor with high compressibility and sensitivity. Herein, a cost-efficient and scalable approach is reported to prepare highly flexible and compressible conductive sponge for piezoresistive pressure sensor. The conductive sponge, PEDOT:PSS@MS, is prepared by one-step dip coating the commercial melamine sponge (MS) in an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Due to the interconnected porous structure of MS, the conductive PEDOT:PSS@MS has high compressibility and stable piezoresistive response at the compressive strain up to 80%, as well as good reproducibility over 1000 cycles. Thereafter, versatile pressure sensors fabricated using the conductive PEDOT:PSS@MS sponges are attached to the different parts of human body; the capabilities of these devices to detect a variety of human motions including speaking, finger bending, elbow bending, and walking are evaluated. Furthermore, prototype tactile sensory array based on these pressure sensors is demonstrated.
Article
Humans possess manual dexterity, motor skills, and other physical abilities that rely on feedback provided by the somatosensory system. Herein, a method is reported for creating soft somatosensitive actuators (SSAs) via embedded 3D printing, which are innervated with multiple conductive features that simultaneously enable haptic, proprioceptive, and thermoceptive sensing. This novel manufacturing approach enables the seamless integration of multiple ionically conductive and fluidic features within elastomeric matrices to produce SSAs with the desired bioinspired sensing and actuation capabilities. Each printed sensor is composed of an ionically conductive gel that exhibits both long-term stability and hysteresis-free performance. As an exemplar, multiple SSAs are combined into a soft robotic gripper that provides proprioceptive and haptic feedback via embedded curvature, inflation, and contact sensors, including deep and fine touch contact sensors. The multimaterial manufacturing platform enables complex sensing motifs to be easily integrated into soft actuating systems, which is a necessary step toward closed-loop feedback control of soft robots, machines, and haptic devices.
Article
In this study, we demonstrate a fabrication of highly sensitive flexible temperature sensor with a bioinspired octopus-mimicking adhesive. A resistor-type temperature sensor consisting of a composite of poly(N isopropylacrylamide) (pNIPAM)-temperature sensitive hydrogel, poly(3,4 ethylenedioxythiophene) polystyrene sulfonate, and carbon nanotubes, exhibits a very high thermal sensitivity of 2.6%•ºC⁻¹ between 25 and 40 °C so that the change in skin temperature of 0.5 °C can be accurately detected. At the same time, the polydimethylsiloxane adhesive layer of octopus-mimicking rim structure coated with pNIPAM, is fabricated through the formation of a single mold by utilizing undercut phenomenon in photolithography. The fabricated sensor shows stable and reproducible detection of skin-temperature under repeated attachment/detachment cycles onto skin without any skin irritation for a long time. This work suggests a high potential application of our skin-attachable temperature sensor to wearable devices for medical and healthcare monitoring.
Article
Identification of the material from which an object is made is of significant value for effective robotic grasping and manipulation. Characteristics of the material can be retrieved using different sensory modalities: vision based, tactile based or sound based. Compressibility, surface texture and thermal properties can each be retrieved from physical contact with an object using tactile sensors. This paper presents a method for collecting data using a biomimetic fingertip in contact with various materials and then using these data to classify the materials both individually and into groups of their type. Following acquisition of data, principal component analysis (PCA) is used to extract features. These features are used to train seven different classifiers and hybrid structures of these classifiers for comparison. For all materials, the artificial systems were evaluated against each other, compared with human performance and were all found to outperform human participants’ average performance. These results highlighted the sensitive nature of the BioTAC sensors and pave the way for research that requires a sensitive and accurate approach such as vital signs monitoring using robotic systems.
Article
Working together, heated and unheated temperature sensors can recognize contact with different materials and contact with the human body. As such, distributing these sensors across a robot's body could be beneficial for operation in human environments. We present a stretchable fabric-based skin with force and thermal sensors that is suitable for covering areas of a robot's body, including curved surfaces. It also adds a layer of compliance that conforms to manipulated objects, improving thermal sensing. Our open hardware design addresses thermal sensing challenges, such as the time to heat the sensors, the efficiency of sensing, and the distribution of sensors across the skin. It incorporates small self-heated temperature sensors on the surface of the skin that directly make contact with objects, improving the sensors’ response times. Our approach seeks to fully cover the robot's body with large force sensors, but treats temperature sensors as small, point-like sensors sparsely distributed across the skin. We present a mathematical model to help predict how many of these point-like temperature sensors should be used in order to increase the likelihood of them making contact with an object. To evaluate our design, we conducted tests in which a robot arm used a cylindrical end effector covered with skin to slide objects and press on objects made from four different materials. After assessing the safety of our design, we also had the robot make contact with the forearms and clothed shoulders of 10 human participants. With 2.0 s of contact, the actively-heated temperature sensors enabled binary classification accuracy over 90% for the majority of material pairs. The system could more rapidly distinguish between materials with large differences in their thermal effusivities (e.g., 90% accuracy for pine wood vs. aluminum with 0.5 s of contact). For discrimination between humans vs. the four materials, the skin's force and thermal sensing modalities achieved 93% classification accuracy with 0.5 s of contact. Overall, our results suggest that our skin design could enable robots to recognize contact with distinct task-relevant materials and humans while performing manipulation tasks in human environments.
Article
Approaching to the super-sensitivity, we herein develop a pressure sensor based on fully bubbled ultralight graphene block through a simple sparkling strategy. The obtained sparking graphene block (SGB) exhibits excellent elasticity even at 95% compressive strain and rebounds a steel ball with an ultra-fast recovery speed (~1085 mm s−1). Particularly, the SGB based sensor reveals a record pressure sensitivity of 229.8 kPa−1, much higher than other graphene materials due to the highly cavity-branched internal structure. Impressively, the pressure sensor can detect the extremely gentle pressures even beyond the real human skin, promising for ultrasensitive sensing applications.
Article
In this review, PEDOT-PSS is mainly a commercially available PEDOT-PSS, which is a water-dispersible form of the intrinsically conducting PEDOT doped with the water-soluble PSS, including its derivatives, copolymers, analogs (PEDOT:PSSs), even their composites via the chemical or physical modification toward the structure of PEDOT and/or PSS. First, we will focus on discussing the scientific importance of PEDOT-PSS in conjunction with its extraordinary properties and broad multidisciplinary applications in organic/polymeric electronics and optoelectronics from the viewpoint of the historical development and the promising application of representative ECPs. Subsequently, versatile film-forming techniques for the preparation of PEDOT-PSS film electrode were described in details, including common coating approaches and printing techniques, and many emerging preparative methods were mentioned. Then challenges (e.g., conductivity, stability in Water, adhesion to substrate electrode) of PEDOT-PSS film electrode for devices under the high humidity/watery circumstances, especially electrochemical devices are discussed. Fourth, we take PEDOT-PSS film electrode for a relatively new application in sensors as an example, mainly summarized advances in the development of various sensors based on PEDOT-PSSs and their composites in combination with its preparative methods and extraordinary properties. Finally, we give the outlook of PEDOT-PSS for possible applications with the emphasis on PEDOT-PSS film electrode for electrochemical devices, including sensors. (c) 2016 Wiley Periodicals, Inc.
Article
Bending and pressure sensors are very essential for evaluating external stimuli in human motions; however, most of them are separate devices. Here, two orthogonal carbon nanotube–polyurethane sponge strips (CPSSs) are used, each of which has different resistances when bent or pressed, to fabricate a multi-functional stretchable sensor capable of detecting omnidirectional bending and pressure independently. Due to the shape of the strip, the resistance of CPSS changes differently when bent along different directions. Based on this feature, two perpendicular CPSSs can reflect information of both bending distance and bending direction. After basic measurement data are obtained, a function set can be formulated to calculate bending distance and bending direction simultaneously. The errors of bending distance and bending angle can be controlled to less than 4%. With the help of the triboelectric effect, which only happens when the device is pressed, the sensor can differentiate bending and pressure effectively, ensuring the device works in complex situations.
Article
An ultra-stretchable and force-sensitive hydrogel with surface self-wrinkling microstructure is demonstrated by in situ synthesizing polyacrylamide (PAAm) and polyaniline (PANI) in closely packed swollen chitosan microspheres, exhibiting ultra-stretchability (>600%), high sensitivity (0.35 kPa(-1) ) for subtle pressures (<1 kPa), and can detect force in a broad range (10(2) Pa-10(1) MPa) with excellent electrical stability and rapid response speed, potentially finding applications for E-skin.
Article
Stretchable and multifunctional sensors can be applied in multifunctional sensing devices, safety forewarning equipment, and multiparametric sensing platforms. However, a stretchable and multifunctional sensor was hard to fabricate until now. Herein, a scalable and efficient fabrication strategy is adopted to yield a sensor consisting of ZnO nanowires and polyurethane fibers. The device integrates high stretchability (tolerable strain up to 150%) with three different sensing capabilities, i.e., strain, temperature, and UV. Typically achieved specifications for strain detection are a fast response time of 38 ms, a gauge factor of 15.2, and a high stability of >10 000 cyclic loading tests. Temperature is detected with a high temperature sensitivity of 39.3% °C−1, while UV monitoring features a large ON/OFF ratio of 158.2. With its fiber geometry, mechanical flexibility, and high stretchability, the sensor holds tremendous prospect for multiparametric sensing platforms, including wearable devices.
Article
Wearable human-interactive devices are advanced technologies that will improve the comfort, convenience, and security of humans, and have a wide range of applications from robotics to clinical health monitoring. In this study, a fully printed wearable human-interactive device called a “smart bandage” is proposed as the first proof of concept. The device incorporates touch and temperature sensors to monitor health, a drug-delivery system to improve health, and a wireless coil to detect touch. The sensors, microelectromechanical systems (MEMS) structure, and wireless coil are monolithically integrated onto flexible substrates. A smart bandage is demonstrated on a human arm. These types of wearable human-interactive devices represent a promising platform not only for interactive devices, but also for flexible MEMS technology.
Article
Soft robots actuated by inflation of a pneumatic network (a “pneu-net”) of small channels in elastomeric materials are appealing for producing sophisticated motions with simple controls. Although current designs of pneu-nets achieve motion with large amplitudes, they do so relatively slowly (over seconds). This paper describes a new design for pneu-nets that reduces the amount of gas needed for inflation of the pneu-net, and thus increases its speed of actuation. A simple actuator can bend from a linear to a quasi-circular shape in 50 ms when pressurized at ΔP = 345 kPa. At high rates of pressurization, the path along which the actuator bends depends on this rate. When inflated fully, the chambers of this new design experience only one-tenth the change in volume of that required for the previous design. This small change in volume requires comparably low levels of strain in the material at maximum amplitudes of actuation, and commensurately low rates of fatigue and failure. This actuator can operate over a million cycles without significant degradation of performance. This design for soft robotic actuators combines high rates of actuation with high reliability of the actuator, and opens new areas of application for them.
Article
This paper reports on the preliminary experimental results of using polydimethylsiloxane (PDMS) to manufacture a visual pulsating heat pipe with length, width and internal diameter of 56mm, 50mm and 2mm, respectively, including the manufacturing process, the vacuuming management for filling and packaging. The experiment used methanol and ethanol as working fluids. A fix filled ratio (about 60%) and different heating power values (3–8W) were used to test the thermal performance. A high-speed video camera was used to record the working situation of the working fluid inside the channel. The results are discussed and analyzed.The experiment shows that methanol, in a vertical orientation, shows the most efficient results. When the heating power is 3W, the thermal resistance is more than 4.5°C/W below the value for ethanol as the working fluid. For a heating power of 4W, the average temperature decreases to 15°C in the evaporator. Also, gravity will have an impact on the PHP performance: the vertical orientation is better as compared to the horizontal orientation.
Article
silicon nanowires (SiNWs) with well orientation and crystallization are synthesized by the vapor-liquid-solid (VLS) process, and doped as n-type by an ex situ process using spin on dopant (SOD) technique. The ex situ doping process using SOD was based on solid-state diffusion, which comprised two stages: pre-coating and drive in. The phosphorous concentration in SiNWs was controlled by appropriate selections of the drive in temperature and the time period, which are 950 o C and 5-60 min in the present studies. The doped nanowire can be readily made into a temperature sensor with much better resolution and response. Calibration of the SiNW temperature sensor at different doping level has been performed. With a concentration of 4 x 10 15 atoms/cm 3 the SiNW sensor has the best temperature resolution (6186 :� / o C) and sensitivity in this study. Keywords-SiNWs; VLS synthesis; Ex situ doping; SOD;
Article
We demonstrated the first application of a pyroelectric nanogenerator as a self-powered sensor (or active sensor) for detecting a change in temperature. The device consists of a single lead zirconate titanate (PZT) micro/nanowire that is placed on a thin glass substrate and bonded at its two ends, and it is packaged by polydimethylsiloxane (PDMS). By using the device to touch a heat source, the output voltage linearly increases with an increasing rate of change in temperature. The response time and reset time of the fabricated sensor are about 0.9 and 3 s, respectively. The minimum detecting limit of the change in temperature is about 0.4 K at room temperature. The sensor can be used to detect the temperature of a finger tip. The electricity generated under a large change in temperature can light up a liquid crystal display (LCD).
Article
Electron microscopy studies are used to explore the morphology of thin poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) films. The figures show that the films are composed of grains with diameters in the range of about 50 nm. Energy dispersive X-ray spectroscopy analysis reveals that individual grains have a PEDOT-rich core and a PSS-rich shell with a thickness of about 5–10 nm. Atomic force microscopy (AFM) is then used to analyze the topography of fracture surfaces of ruptured PEDOT:PSS tensile specimens. These AFM scans also show that the films are composed of grains dispersed in a matrix. The investigations presented herein yield a picture of PEDOT:PSS morphology with unprecedented clarity.