Herein, the development of complex 3D intelligent structures such as robotic hands using innovative designs and multimaterial additive manufacturing technology is presented. The distal phalanges of the 3D printed hand presented herein have inherent soft capacitive touch or pressure sensors and embedded electronics. Materials such as thermoplastic polyurethane (TPU), silver paint, conductive polylactic acid composite, graphite ink, etc. are explored to develop five different variants of the sensors using a modified 3D printer, which is capable of extruding conductive ink, metal paste, and polymers. The best‐performing 3D printed soft capacitive touch sensors, formed with silver paint and soft rubber (Ecoflex 00‐30), are integrated on the distal phalanges of the 3D printed robotic hand. These sensors exhibit a stable response with sensitivity of 0.00348 kPa−1 for pressure <10 kPa and 0.00134 kPa−1 for higher pressure. To demonstrate the practical applicability, the 3D printed hand with embedded soft capacitive touch sensors is used for interacting with everyday objects. The tightly integrated sensing elements within the 3D printed structures, as presented herein, can pave the way for a new generation of truly smart material systems that can possibly change their appearance and shape autonomously.
Temperature sensing is an important parameter needed to be measured by the eSkin during the physical interaction of robots with real-world objects. Yet, most of the work on sensors in eSkin has focused on pressure sensing. Here we present a skin conformable printed temperature sensor with poly(3,4-ethylenedioxythiophene): poly (styr-enesulfonate) (PEDOT:PSS)-graphene oxide (GO) as a temperature sensitive layer and silver (Ag) as contact electrodes. The demonstration of PEDOT:PSS/GO as a highly temperature sensitive layer is the distinct feature of the work. The response of presented sensor observed over ∼25 • C (room temperature (RT)) to 100 • C, by measuring the variation in resistance across the GO/PEDOT:PSS layer showed ∼80% decrease in resistance. The sensitivity of the sensor was found to be 1.09% per • C. The sensor's response was also observed under static and dynamic bending (for 1000 cycles) conditions. The stable and repeatable response of sensor, in both cases, signifies strong adhesion of the layers with negligible delamination or debonding. In comparison to the commercial thermistor, the printed GO/PEDOT:PSS sensor is faster (∼73% superior) with response and recovery times of 18 s and 32 s respectively. Finally, the sensor was attached to a robotic hand to allow the robot to act by using temperature feedback.
Electronic skin (eSkin) with various types of sensors over large conformable substrates has received considerable interest in robotics. The continuous operation of large number of sensors and the readout electronics make it challenging to meet the energy requirements of eSkin. In this article, we present the first energy generating eSkin with intrinsic tactile sensing without any touch sensor. The eSkin comprises a distributed array of miniaturized solar cells and infrared light emitting diodes (IRLEDs) on soft elastomeric substrate. By innovatively reading the variations in the energy output of the solar cells and IRLEDs, the eSkin could sense multiple parameters (proximity, object location, edge detection, etc.). As a proof of concept, the eSkin has been attached to a 3-D-printed hand. With an energy surplus of 383.6 mW from the palm area alone, the eSkin could generate more than 100 W if present over the whole body (area ∼1.5 m 2 ). Further, with an industrial robot arm, the presented eSkin is shown to enable safe human−robot interaction. The novel paradigm presented in this article for the development of a flexible eSkin extends the application of solar cell from energy generation alone to simultaneously acting as touch sensors.Index Terms-Electronic skin (eSkin), energy harvesting, human−robot interaction (HRI), proximity sensing, solar cell, touch sensing. I. INTRODUCTIONElectronic skin or "eSkin" has recently emerged as a novel platform for advances in robotics, prosthesis, health diagnostics, therapeutics, and monitoring [1]. It allows robots and prosthetic limbs to gather tactile information from large area contacts and to exploit the same to operate in unstructured environment or to improve human−robot interaction (HRI) [2]-[6]. Likewise, eSkin has been explored for measurement of vital health parameters and to provide reliable, effective, and, sometimes, life-saving functions [7]-[9]. With increasing number and type of sensors (pressure, temperature, texture, proximity, etc.) and electronics associated with them on large area eSkin [10]-[13], a stable power supply is critical for practical usage [11], [14]. Thus, a realistic and accessible power source is urgently needed for a next-generation of smart, stand-alone, always-on eSkins. This is a challenge as the continuous power supply through batteries is not practical because they add weight, are not flexible, and may require redesigning of robotics platform [15], [16]. Likewise, for applications requiring intimate integration of eSkin
Herein, a novel tactile sensing device (SensAct) with a soft touch/pressure sensor seamlessly integrated on a flexible actuator is presented. The squishy touch sensor is developed with custom‐made graphite paste on a tiny permanent magnet, encapsulated in Sil‐Poxy, and the actuator (15 μ‐thick coil) is fabricated on polyimide by Lithographie Galvanoformung Abformung (LIGA) micromolding method. The actuator can operate in two modes (expansion and contraction/squeeze) and two states (vibration and nonvibration). The sensor was tested with up to 12 N applied forces and exhibited ≈70% average relative resistance variation (ΔR/Ro), ≈0.346 kPa−1 sensitivity, and ≈49 ms response time with excellent repeatability (≈12.7% coefficient of variation) at 5 N. During simultaneous sensing and actuation, the modulation of coil current, due to ΔR/Ro (≈14% at 2 N force) in the sensor, allows the close loop control (ΔI/Io ≈385%) of expansion/contraction (≈69.8 μm expansion in nonvibration state and ≈111.5 μm peak‐to‐peak in the vibration state). Finally, the soft sensor is embedded in the 3D‐printed fingertip of a robotic hand to demonstrate its use for pressure mapping along with remote vibrotactile stimulation using SensAct device. The self‐controllable actuation of SensAct could provide eSkin the ability to tune stiffness and the vibration states could be utilized for controlled haptic feedback.
This paper presents a textile-based stretchable microstrip patch antenna with intrinsic strain for e-textiles with seamlessly integrated multifunctional devices. Several microstrip antennas have been developed with the patch alone (stretchable up to 40%) or both the patch and the ground plane (stretchable up to 100%) meshed by using rectangular serpentine units. The changes in the resonant frequency of the meshed antennas, as a result of stretching, have been exploited to demonstrate the intrinsic uniaxial strain sensing. The obtained results indicate that resonant frequency decreases linearly with increasing applied strain, suggesting that the designed antennas can also be used as strain sensors with stretchability up to 100% and a sensitivity of 0.25. The results were validated through full-wave electromagnetic simulations and a two-dimensional digital image correlation (DIC) technique to model the antenna deformations during the tensile tests. In terms of stretchability, the meshed textile patch antenna on a solid ground plane showed more than a 2-fold improvement compared to a meshed gold patch antenna, showing a linear frequency shift. As potential applications, we demonstrate the use of a highly deformable fully meshed textile antenna as a strain sensor capable of measuring joint angles of a human limb. To do that, a microwave readout circuit based on RF to DC rectifier was realized. The rectifier obtained a peak conversion efficiency of 71% at 10 dBm input power overload resistor of 3 kΩ.
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