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Schematic diagram of the proposed modular expandable tactile sensor: (a) sensor module array and (b) structure of single tactile cell. The tactile cell capacitance changes as the air gap is squeezed according to applied force.
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In this paper, we propose and demonstrate a modular expandable capacitive tactile sensor using polydimethylsiloxsane (PDMS) elastomer. A sensor module consists of 16times16 tactile cells with 1 mm spatial resolution, similar to that of human skin, and interconnection lines for expandability. The sensor has been fabricated by using five PDMS layers...
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... The conductors are produced from silicone rubber with a special food contact-grade carbon black. This allows us to forego brittle inelastic materials [11,43,44], hazardous or corrosive conductive liquids [45,46], as well as new and experimental particulate fillers with unclear health and environmental risks [47][48][49]. Our conductive materials are nevertheless more stretchable than those used in previous and related works [5,48,50]. ...
We present a thin and elastic tactile sensor glove for teaching dexterous manipulation tasks to robots through human demonstration. The entire glove, including the sensor cells, base layer, and electrical connections, is made from soft and stretchable silicone rubber, adapting to deformations under bending and contact while preserving human dexterity. We develop a glove design with five fingers and a palm sensor, revise material formulations for reduced thickness, faster processing and lower cost, adapt manufacturing processes for reduced layer thickness, and design readout electronics for improved sensitivity and battery operation. We further address integration with a multi-camera system and motion reconstruction, wireless communication, and data processing to obtain multimodal reconstructions of human manipulation skills.
... Figure 8 demonstrates the final thicknesses of spin-coated and cured films that are used for measuring dielectric permittivity, breakdown strength, and friction coefficients. When comparing the obtained thickness values for IP-PDMS with the spin-coated thicknesses of common PDMS compositions in the literature, the IP-PDMS thicknesses stand on the lower side of the range [35,37]. This agrees with the authors' visual observation of IP-PDMS's lower viscosity compared to commonly used PDMS Sylgard 184. ...
... Figure 8 demonstrates the final thicknesses of spin-coated and cured films that are used for measuring dielectric permittivity, breakdown strength, and friction coefficients. When comparing the obtained thickness values for IP-PDMS with the spincoated thicknesses of common PDMS compositions in the literature, the IP-PDMS thicknesses stand on the lower side of the range [35,37]. This agrees with the authors' visual observation of IP-PDMS's lower viscosity compared to commonly used PDMS Sylgard 184. ...
Recent developments in micro-scale additive manufacturing (AM) have opened new possibilities in state-of-the-art areas, including microelectromechanical systems (MEMS) with intrinsically soft and compliant components. While fabrication with soft materials further complicates micro-scale AM, a soft photocurable polydimethylsiloxane (PDMS) resin, IP-PDMS, has recently entered the market of two-photon polymerization (2PP) AM. To facilitate the development of microdevices with soft components through the application of 2PP technique and IP-PDMS material, this research paper presents a comprehensive material characterization of IP-PDMS. The significance of this study lies in the scarcity of existing research on this material and the thorough investigation of its properties, many of which are reported here for the first time. Particularly, for uncured IP-PDMS resin, this work evaluates a surface tension of 26.7 ± 4.2 mN/m, a contact angle with glass of 11.5 ± 0.6°, spin-coating behavior, a transmittance of more than 90% above 440 nm wavelength, and FTIR with all the properties reported for the first time. For cured IP-PDMS, novel characterizations include a small mechanical creep, a velocity-dependent friction coefficient with glass, a typical dielectric permittivity value of 2.63 ± 0.02, a high dielectric/breakdown strength for 3D-printed elastomers of up to 73.3 ± 13.3 V/µm and typical values for a spin coated elastomer of 85.7 ± 12.4 V/µm, while the measured contact angle with water of 103.7 ± 0.5°, Young’s modulus of 5.96 ± 0.2 MPa, and viscoelastic DMA mechanical characterization are compared with the previously reported values. Friction, permittivity, contact angle with water, and some of the breakdown strength measurements were performed with spin-coated cured IP-PDMS samples. Based on the performed characterization, IP-PDMS shows itself to be a promising material for micro-scale soft MEMS, including microfluidics, storage devices, and micro-scale smart material technologies.
... A sensor array should ideally be thin and flexible, have an adequate resolution, and be devoid of crosstalk between its sensing pixels. However, most of the existing sensor mats based on conductive polymers cannot eliminate crosstalk between sensing elements because they are composed of a uniform (i.e., blanket) pressure-sensing layer; that is, neighboring sensing pixels are activated whenever the uniform conductive polymer is deformed [27,28]. To overcome this problem, a sensor array is designed that entails stacking conductive polymers on individual electrodes. ...
Stockouts constitute a major challenge in the retail industry. Stockouts are caused by errors related to manual stockkeeping and by the misplacement of items on shelves. Such errors account for up to 4% of lost sales. Real-time inventory management systems for misplaced items or missing stock detection in retail stores are limited. Accordingly, a conductive polymer-based interactive shelving system for real-time inventory management is developed. The system comprises an 80 × 48 sensor array fabricated by screen-printing a piezoresistive carbon-based conductive polymer layer onto gold interdigitated electrodes deposited on a flexible substrate. Each sensing pixel has dimensions of 5 mm × 5 mm and a sensing area of 4 mm × 4 mm. The sensor mat can detect the shape and weight features of stockkeeping units (SKUs), which can then be analyzed by a TensorFlow model for SKU identification. The developed system is characterized for functional resistance range, uniformity, repeatability, and durability. The accuracy of SKU identification achieved using shape features only and the accuracy of SKU identification achieved using both shape and weight features is 95% and 99.2%, respectively. The key novelty of the work is the development of a deep learning-embedded interactive smart shelving system for retail inventory management by using the shape and weight features of SKU. Also, the developed system helps to detect the SKU if they are stacked one over the other. Furthermore, multiple sensor mats implemented on various shelves in a retail store can be modularized and integrated for monitoring under the control of a single PC. Accordingly, the proposed retail inventory tracking system can facilitate the development of automated “humanless” shops.
... As discussed in [31], a thickness of 25 µm guarantees an excellent electrical insulation between the conductive layers. The PDMS thickness mainly depends on spin speed and duration [32], [33]. In this work, this thickness has been obtained by depositing in sequence 2 layers of PDM, each obtained through a spin coating with a speed of 2000 rpm and a duration of 5 min. ...
Capacitive sensors are widely used in robotics for their compactness, high resolution, high sensitivity and large dynamic range. In this paper we present a design solution for the manufacturing of capacitive tactile sensors with enhanced dynamic range and sensitivity. Herein, we adopted the approach of exploiting the vertical direction of the sensors by creating stacks of capacitors. The validation of the proposed model is conducted by means of finite element simulations and the effectiveness of stacked capacitors in sub-optimal configurations has been experimentally tested by using inkjet printing and spin coating- based fabrication techniques. Results show that these sensors exhibit an enhanced dynamic range and sensitivity with respect to common single capacitors, for a given sensors area budget. Sensitivity increases of 235% passing from 1 stack to 2 stack capacitor (from 5.75 fF/kPa to 19.3 fF/kPa) and a growth of 23% from 2 stack to 3 stack capacitor (from 19.3 fF/kPa to 23.7 fF/kPa). These results suggest that the proposed methodology could be adopted for designing tactile sensors with higher spatial resolution and higher transduction sensitivity and dynamic range, in perspective of an integration over large areas.
... In that sense, the sensor is partly piezo-resistive. Despite this, the sub-kPa pressure sensitivity ( Z/Z)/P is 0.14 kPa −1 and compares well with sensitivity values published in many previous studies: 0.05 kPa −1 [19], 0.008 kPa −1 [20], 0.005 kPa −1 [21], 0.02 kPa −1 [22]. A recent study [23] of the capacitive pressure response of a microstructured PDMS film gave a larger sensitivity value of 0.55 kPa −1 ; however, here again the behaviour was nonlinear and the device contained a thermoplastic top electrode, a PET substrate and hence was not stretchable. ...
... Different sensing mechanisms have been proposed and the basic principle is to capture the sensor deformation caused by contact force. A large number of tactile sensors capture the deformation by electric signals, such as capacitive sensors [9], [10], and resistive sensors [11], [12]. These sensors are in the form of sensor arrays. ...
Tactile sensors are believed to be essential in robotic manipulation, and prior works often rely on experts to reason the sensor feedback and design a controller. With the recent advancement in data-driven approaches, complicated manipulation can be realised, but an accurate and efficient tactile simulation is necessary for policy training. To this end, we present an approach to model a commonly used pressure sensor array in simulation and to train a tactile-based manipulation policy with sim-to-real transfer in mind. Each taxel in our model is represented as a mass-spring-damper system, in which the parameters are iteratively identified as plausible ranges. This allows a policy to be trained with domain randomisation which improves its robustness to different environments. Then, we introduce encoders to further align the critical tactile features in a latent space. Finally, our experiments answer questions on tactile-based manipulation, tactile modelling and sim-to-real performance.
... c. In the third step, after outgassing, PDMS was spin-coated on the surface of the coated PET polyethylene terephthalate (PET substrate for a spin time of 30 s at a spinning speed of 2000 rpm to obtain a thickness of 20-25 lm range [28]. d. ...
We report a flexible triboelectric nanogenerator (TENG) sprayed with spherical Au nanoparticles. Indium tin oxide (ITO)-coated polyethylene terephthalate (PET) was used as a flexible substrate on which layers of Ti (100 nm) and Al (80 nm) were deposited by thermal vapor deposition. The other layer of polydimethyl siloxane has been deposited on ITO-coated PET using spin coating. These thin layers of metal and polymer are then joined together to create a TENG device using a sponge as a spacer. The thin layers were characterized using field-emission scanning electron microscopy, energy–dispersive X-ray analysis, and mapping to study their physical and structural properties. Current–voltage (I–V) and power–voltage (P–V) measurements were performed for different load resistances with the application of an external force applied through a setup comprising a linear actuator. The maximum values of the open-circuit voltage, short-circuit current, and maximum power (under load conditions) were approximately 350 mV, 302 µA, and 0.29 mW, respectively. The proposed TENG device is suitable for providing sustained power in wearable electronic applications with stable output performance, mechanical strength, and hydrophobic properties.
... Typical sensors applicable in tactile sensing include capacitive sensors, piezoresistive sensors, optical methods, and piezoelectric devices [1][2][3]. Capacitive tactile sensors are designed to settle capacitors between two electrodes, so that the electrostatic capacity changes when force is applied and the distance between the electrodes changes [4,5]. The capacitive sensors have the advantages of high frequency response, precise load measurement, and wide dynamic range, but they tend to be susceptible to external noise. ...
The authors have developed a micro-vibration actuator using filiform SMA wire electrically driven by periodic electric current. While applying the SMA actuators to tactile displays, we discovered a phenomenon that the deformation caused by a given stress to an SMA wire generated a change in the electrical resistance. With this characteristic, the SMA wire works as a micro-force sensor with high sensitivity, while generating micro-vibration. In this paper, the micro-force sensing ability of an SMA transducer is described and discussed. Experiments are conducted by sliding the SMA sensor on the surface of different objects with different speeds, and the sensing ability is evaluated to be related with human tactile sensation.
... There has been a significant amount of research aiming to improve the motor control of prosthetics including its tactile sensory feedback system. Efforts in this field have been focused on developing various types of tactile sensors (e.g., capacitive [6], resistive [7] and piezoelectric [8]), and on designing efficient interface electronics [9]. However, to our knowledge, no study has focused on the communication channel from sensors to the electrotactile stimulator. ...
In this paper we propose and validate a tactile sensory feedback system for prosthetic applica-tions based on an optical communication link. The optical link features a low power and wide transmission bandwidth, which makes the feedback system suitable for a large number and vari-ety of tactile sensors. The low power transmission derives from the employed UWB-based optical modulation technique. A system prototype, consisting of digital transmitter and receiver boards and acquisition circuits to interface 32 piezoelectric sensors, has been implemented and experi-mentally tested. The system functionality has been demonstrated by processing and transmitting data from the piezoelectric sensor at 100 Mbps data rate through the optical link measuring a communication energy consumption of 50 pJ/bit. The reported experimental results validate the functionality of the proposed sensory feedback system and demonstrate its real time operation capabilities.
... Fig. 2 a shows the thickness variation of films fabricated from ExSil 100 by spin coating at different speeds and durations of rotation. The film thickness was observed to decrease with increasing rotation speed and spinning time, as is typically observed in spin coating [39]. For ease of approximation of the spin-coating conditions, Eq. (1) was simplified to Eq. (2): ...
The exploration and identification of new polymeric materials that can serve as components for soft and stretchable electronic devices complying with various demands such as ultrasoftness, ultrastretchability and skin conformality, has attracted much attention. In this study, a commercially available silicone elastomer, ExSil 100, which exhibits ultrastretchability, ultrasoftness and characteristic surface adhesion due to uncrosslinked highly entangled polymeric chains, has been used for the first time to fabricate soft and stretchable electronics. Liquid metals are compelling electrodes because they can maintain electrical conductivity when strained. Although elastomers with microchannels are typically used to create soft devices by injecting liquid metal into the channels, the resulting topographic structures of ExSil 100 are prone to collapse owing to the ultrasoftness of the elastomer. The oxidized liquid metal, which showed excellent wetting behavior, was therefore patterned by forced wetting through stencils onto the substrate. The desirable properties of the elastomer have thus been synergistically harnessed with the “infinite stretchability” of the liquid metal to fabricate a variety of multifunctional electronic devices, illustrating successful utilization of this system in the field of soft and stretchable electronics.
