Robotic hands with intrinsic tactile sensing via 3D printed soft pressure sensors

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 [less than] 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

Soft eSkin:distributed touch sensing with harmonized energy and computing

Inspired by biology, significant advances have been made in the field of electronic skin (eSkin) or tactile skin. Many of these advances have come through mimicking the morphology of human skin and by distributing few touch sensors in an area. However, the complexity of human skin goes beyond mimicking few morphological features or using few sensors. For example, embedded computing (e.g. processing of tactile data at the point of contact) is centric to the human skin as some neuroscience studies show. Likewise, distributed cell or molecular energy is a key feature of human skin. The eSkin with such features, along with distributed and embedded sensors/electronics on soft substrates, is an interesting topic to explore. These features also make eSkin significantly different from conventional computing. For example, unlike conventional centralized computing enabled by miniaturized chips, the eSkin could be seen as a flexible and wearable large area computer with distributed sensors and harmonized energy. This paper discusses these advanced features in eSkin, particularly the distributed sensing harmoniously integrated with energy harvesters, storage devices and distributed computing to read and locally process the tactile sensory data. Rapid advances in neuromorphic hardware, flexible energy generation, energy-conscious electronics, flexible and printed electronics are also discussed. This article is part of the theme issue ‘Harmonizing energy-autonomous computing and intelligence’

3D printed soft and flexible insole with intrinsic pressure sensing capability

This work presents a soft, flexible, and low-cost capacitive pressure-sensitive insole developed using resource-efficient single-step 3D printing method. Developed using elastomeric materials, the soft and robust sensory insole can bend and twist in extreme angles. The insole is designed to have four sensing zones to capture the pressure information from the entire contact area. The sensors tested under different condition of applied pressure showed reliable response up to 300kPa without saturation. The sensors exhibit a sensitivity of 2.4MPa-1 for range of 0 - 60kPa and 0.526MPa-1 for 60kPa and above with average sensitivity of 1.314 MPa-1 in the entire range. The insole was also tested under varying bending and temperature conditions. Considering the excellent response over a wide pressure range, the presented insole could be used for gait analysis or with anthropomorphic robots for critical information about the terrain morphology. To show the functionality of presented insole, we have also developed an app to display the sensory information obtained via custom-made electronics circuit

Printed Temperature Sensor Based on PEDOT:PSS-Graphene Oxide Composite

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

Multi-material 3D printed bendable smart sensing structures

This paper presents a novel additive manufacturing method to obtain bendable smart sensing structures having printed strain sensors and interconnects to gain access to embedded electronic components. The presented smart structure is obtained by simultaneous printing of functional materials along with conventional polymer-based 3D printing materials. To this end, a low-cost open-source 3D printer was augmented with a silver palladium metallic paste extruder. The strain sensors in the presented 3D printed smart structure are particularly useful for wearable motion sensing applications such as knee joint motion analysis. The printed interconnects allow for electrical connection with the Light Emitting Diodes (LEDs) embedded within the 3D printed structure. With electronic components embedded in the flexible 3D printed structure, this work also demonstrates a novel method for soft packaging of electronic and sensing components. The electrical tests conducted on the smart structure show excellent electrical continuity. The 3D printed strain sensors, tested in static and dynamic bending conditions, showed a linear response of resistance. Under no strain, the resistance of the sensor was measured to be 0.9671 n (resistivity of 9.671×10 -6 Ω.m) and during testing it exhibited a gauge factor of 1. Multi-material additive manufacturing demonstrated in this paper opens a new direction for fabrication of complex 3D structures with embedded sensors and electronics and offers significant advantages for rapid prototyping and packaging

Energy generating electronic skin with intrinsic tactile sensing without touch sensors

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 m2). 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

Bioinspired distributed energy in robotics and enabling technologies

On-board sources of energy are critically needed for autonomous robots to work in unstructured environments for extended periods. Thus far, the power requirement of robots has been met through lead-acid and Li-ion batteries and energy harvesters. However, few advances such as light weight, the shape, and size of the batteries used in robotics have remained unchanged for several decades, even though if the research in energy storage has led to devices with flexible form factors. Besides being slow at adopting new energy technologies, robotics also appears to have settled with the idea of centralized energy, as evident from the battery backpack designs of several humanoids. This is in contrast with the biological world, where energy sources are distributed all over the body. Although several attempts have been made to imitate the distributed tactile skin, the energy distribution has strangely not caught attention. A robotic platform can benefit from increased energy density, lesser design complexities, improved body dynamics, and operational reliability with distributed energy. By focusing on the distributed energy, herein, the first comprehensive review supporting the benefits of bioinspired distributed energy in robotics and various energy-storage and energy-harvesting technologies that are available or are tuned to attain the same are presented