Robot Skin Research Articles

A comprehensive design for biomimetic behavior of robotic head

In robotics and human-robot interaction, the ability to express emotions and respond accurately to human emotions is essential. An important aspect of this ability involves controlling the robot’s facial actuators in a way that resonates with human emotions. This study systematically presented the construction of a robot head based on the theoretical foundation of human sustainability. Facial landmarks are extracted for various purposes, such as to determine anthropometric metrics for robot head design, a comprehensive design for the robotic head is proposed in this study including anthropometric measurements used as a theoretical basis for the design, the calculations, and design, control system, electricity, and robot skin are presented. The robotic head with 24 degrees of freedom (DoF) aims to express all human emotions, signals are fed back from strain gauge sensors and cameras to calibrate the response of the robot’s prosthetic muscles. Strain gauge sensors are set up at locations with large deformations to double-check the functioning of prosthetic muscles. The two experiments are set up to evaluate the completeness of emotions, the results showed that both experiments achieved 93.88% and 91.85% respectively.

Simulation and theory for wiring compaction of robot skin tactile sensor by frequency-selective triboelectric-piezoelectric filters

Abstract Abstract: Robots are increasingly equipped with different sensors to better identify things and interact with their environment. One such sensor is the ability to sense and receive information through touch. A significant challenge in designing tactile sensors is to create a larger and more complex network of electrical connections to cover larger partitioned surface areas, necessitating a more compaction for electrical connections. In this study, we try to reduce the number of these array connections by designing a novel triboelectric-piezoelectric pressure sensors that will function as electromechanical frequency-selective filters. The sensor cell units are created in the form of various disk-shape layers with a basic double-lamina layers, a triboelectric lamina placed over a piezoelectric lamina. The triboelectric layer, being soft, is used for static pressure measurement and more sensitivity enhancement. In addition, an electromechanical frequency-selective filter is generated by altering geometric dimensions of that lamina, such as the radius and/or thickness. An applied pressure is calculated by measuring the electric current and the cell unit admittance. The advantage of using piezo-layer geometric manipulation for generating different operating resonant frequencies is that it is a simpler design task as compared to alter the cell electrical properties, which is the focus of previous research. In this work, a theoretical model and numerical simulations are employed to obtain the electromechanical admittance of a set of three unit cell tactile sensors.

Alterable Robotic Skin Using Material Gene Expression Modulation

AbstractRobotic skins that integrate artificial tactile sensing elements can substantially complement the perception dimension of social robots, presenting an indispensable part in human‐robot interaction (HRI). However, existing design frameworks compromise between versatility and sustainability due to the restricted range of characteristics available for a single constituent. Here an alterable robotic skin constructed from homogeneous sensing units are proposed, capable of cyclically realtering their inherent characteristics across a wide spectrum. Necessary characteristics to achieve positioning and pressure sensing subunits can be encoded in the feature motifs and extracted through condition‐induced differentiation, showcasing a remarkable resemblance to the gene expression in the living system. By virtue of this, up to 100‐fold differences in feature parameters are achieved, including modulus, surface state, and conductivity, to drive the target attribute coupling. The trans‐temporal reconstruction of materials enables the superb customization of functional building blocks, advancing the flexible separation and combination of different touch modes, including location, pressure, duration, and motion pattern. As a proof of concept, the alterable robotic skin is demonstrated that integrates a position‐sensing layer and a pressure‐sensing layer. It can accurately distinguish and recognize multi‐dimensional touch motions based on less‐channel data, which showcases an efficient haptic interaction application.

Robotic skins inspired by auxetic metamaterials for programmable bending of soft actuators

This paper presents a class of robotic skins inspired by auxetic metamaterials, which enable programmable bending in soft pneumatic actuators. The efficiency of these robotic skins in controlling bending curvature and hoop expansion of the soft actuators is demonstrated through a combination of experiments and numerical simulations. Parametric studies are then performed to explore how variations in the geometric parameters of the metamaterial skin affect the performance of the bending actuators. Specifically, our study demonstrates that a range of bending curvatures (0.0077 mm−1 to 0.0097 mm−1) and cross-section diameters (38.4 mm to 44.0 mm) can be achieved by adjusting the unit cell numbers of metamaterial skin in the vertical and hoop directions for bending a 2 mm-thickness-walled inflatable cylindrical tube, which is characterized by an initial length of 104.3 mm, an initial cross-section diameter of 29.0 mm, and at an inflation volume of 75 mL. Moreover, a variety of bio-inspired soft actuators exhibiting complex bending behaviors are presented. The work demonstrates the effectiveness of the proposed strategy for achieving customized curved bending and shape-morphing by adjusting the geometric parameters and arrangement of the unit cells in the metamaterial skins.

Mechanochromic Suction Cups for Local Stress Detection in Soft Robotics

Advancements in smart soft materials are enhancing the capabilities of robotic manipulators in object interactions and complex tasks. Mechanochromic materials, acting as lightweight sensors, offer easily interpretable visual feedback for localized stress detection, structural health monitoring, and energy‐efficient robotic skins. Herein, an innovative mechanochromic soft end‐effector capable of discerning local contact stresses during mechanical interactions with objects is presented and their relative position is ascertained. This system utilizes a reversible force‐induced color switch in a thin layer of spiropyran‐functionalized polydimethylsiloxane, which coats a silicone‐made suction cup. The mechanochromic suction cup is integrated with a 3D‐printed compact load‐transferring system and electronic color‐changing detection elements. The assembly may serve as a synthetic receptor for robotic actuators, discerning localized interaction forces down to 3 N. The system's resilience to varying environmental factors, including illumination, tilting, and interaction with objects of various shapes is verified. The results indicate potential for exteroceptive solutions in reconfigurable manipulation tasks without compromising the overall softness of the manipulator.

An intrinsic electromechanical design method for MXene-based electrodes of ultra-highly sensitive and stable pseudocapacitive pressure device

To achieve the optimal performances of flexible pressure devices, the current approaches typically involve extensive experimental trials. However, such methods lack guidance from theoretical models in a positive fashion, not only introducing unpredictability and uncertainty into results but also potentially limiting the applicability of any achieved advancements to the alternative material systems. Here, an electrical-mechanical design model, combining density functional theory and molecular dynamics simulations, was proposed for calculating the specific capacitance and mechanical strength of various modified MXene films. Based on which, the optimal hybrid film entailed the cross-linking of holey reduced graphene oxide and MXene via cysteamine was prepared. This film, upon electromechanical characterizations, has effectively overcome the issues of MXene self-stacking and brittleness, thus validating the conclusions of theoretical predictions. Subsequently, the proposed film was integrated as electrode into a pseudocapacitive pressure sensor, achieving highly sensitivity (∼143,258 kPa−1) and mechanical stability (with capacitance drift below 1.2 % after 10,000-repeated test). Ultimately, the fabricated sensors were developed into sound collection system and robotic skins, respectively, to achieve recognition of distinctive sounds and stable perception of gravity. The calculation-based approach holds enormous potential for the design of two-dementional materials-based pressure sensors.

Recent Progress on Flexible Self-Powered Tactile Sensing Platforms for Health Monitoring and Robotics.

Over the past decades, tactile sensing technology has made significant advances in the fields of health monitoring and robotics. Compared to conventional sensors, self-powered tactile sensors do not require an external power source to drive, which makes the entire system more flexible and lightweight. Therefore, they are excellent candidates for mimicking the tactile perception functions for wearable health monitoring and ideal electronic skin (e-skin) for intelligent robots. Herein, the working principles, materials, and device fabrication strategies of various self-powered tactile sensing platforms are introduced first. Then their applications in health monitoring and robotics are presented. Finally, the future prospects of self-powered tactile sensing systems are discussed.

A Digital Twin-Based Large-Area Robot Skin System for Safer Human-Centered Healthcare Robots Toward Healthcare 4.0

A Digital Twin-Based Large-Area Robot Skin System for Safer Human-Centered Healthcare Robots Toward Healthcare 4.0

A Multimodal Perception-Enabled Flexible Memristor with Combined Sensing-Storage-Memory Functions for Enhanced Artificial Injury Recognition.

With the continuous advancement of wearable technology and advanced medical monitoring, there is an increasing demand for electronic devices that can adapt to complex environments and have high perceptual sensitivity. Here, a novel artificial injury perception device based on an Ag/HfOx/ITO/PET flexible memristor is designed to address the limitations of current technologies in multimodal perception and environmental adaptability. The memristor exhibits excellent resistive switching (RS) performance and mechanical flexibility under different bending angles (BAs), temperatures, humid environment, and repetitive folding conditions. Further, the device demonstrates the multimodal perception and conversion capabilities toward voltage, mechanical, and thermal stimuli through current response tests under different conditions, enabling not only the simulation of artificial injury perception but also holds promise for monitoring and controlling the movement of robotic arms. Moreover, the logical operation capability of the memristor-based reconfigurable logic (MRL) gates is also demonstrated, proving the device has great potential applications with sensing, storage, and memory functions. Overall, this study not only provides a direction for the development of the next-generation flexible multimodal sensors, but also has significant implications for technological advancements in many fields such as robotic arms, electronic skin (e-skin), and medical monitoring.

Research on robot tracking force control algorithm based on neural networks

Purpose This study aims to propose a force control algorithm based on neural networks, which enables a robot to follow a changing reference force trajectory when in contact with human skin while maintaining a stable tracking force. Design/methodology/approach Aiming at the challenge of robots having difficulty tracking changing force trajectories in skin contact scenarios, a single neuron algorithm adaptive proportional – integral – derivative online compensation is used based on traditional impedance control. At the same time, to better adapt to changes in the skin contact environment, a gated recurrent unit (GRU) network is used to model and predict skin elasticity coefficients, thus adjusting to the uncertainty of skin environments. Findings In two robot–skin interaction experiments, compared with the traditional impedance control and robot force control algorithm based on the radial basis function model and iterative algorithm, the maximum absolute force error, the average absolute force error and the standard deviation of the force error are all decreased. Research limitations/implications As the training process of the GRU network is currently conducted offline, the focus in the subsequent phase is to refine the network to facilitate real-time computation of the algorithm. Practical implications This algorithm can be applied to robot massage, robot B-ultrasound and other robot-assisted treatment scenarios. Originality/value As the proposed approach obtains effective force tracking during robot–skin contact and is verified by the experiment, this approach can be used in robot–skin contact scenarios to enhance the accuracy of force application by a robot.

Origami-Enhanced Mechanical Properties for Worm-Like Robot.

In recent years, the exploration of worm-like robots has garnered much attention for their adaptability in confined environments. However, current designs face challenges in fully utilizing the mechanical properties of structures/materials to replicate the superior performance of real worms. In this article, we propose an approach to address this limitation based on the stacked Miura origami structure, achieving the seamless integration of structural design, mechanical properties, and robotic functionalities, that is, the mechanical properties originate from the geometric design of the origami structure and at the same time serve the locomotion capability of the robot. Three major advantages of our design are: the implementation of origami technology facilitates a more accessible and convenient fabrication process for segmented robotic skin with periodicity and flexibility, as well as robotic bristles with anchoring effect; the utilization of the Poisson's ratio effect for deformation amplification; and the incorporation of localized folding motion for continuous peristaltic locomotion. Utilizing the high geometric designability inherent in origami, our robot demonstrates customizable morphing and quantifiable mechanical properties. Based on the origami worm-like robot prototype, we experimentally verified the effectiveness of the proposed design in realizing the deformation amplification effect and localized folding motion. By comparing this to a conventional worm-like robot with discontinuous deformation, we highlight the merits of these mechanical properties in enhancing the robot's mobility. To sum up, this article showcases a bottom-up approach to robot development, including geometric design, mechanical characterization, and functionality realization, presenting a unique perspective for advancing the development of bioinspired soft robots.

Multifunctional robot skin based on liquid metal composites and electrode arrays

While human skin regulates body temperature and protects the organism, robots also need multifunctional skin that can protect their internal electronics. Currently, most of the research on robotic skin focuses on the limbs with the aim of improving their sensory functions. There is a lack of a robotic skin with protective features that can be applied to the whole body. In some complex working environments, too high or too low temperatures can directly jeopardize the operation of the robot's internal circuitry. In addition, ubiquitous electromagnetic waves can damage the electronic system of robots. Therefore, an e-skin that protects the robot from external factors was desired. In this study, with reference to the structure of human skin, a gallium-based liquid metal and a bismuth-based low-melting-point alloy were combined to prepare a highly thermally conductive e-skin that can withstand both thermal shock and low temperature. This skin not only features thermal management, but also touch positioning and electromagnetic shielding. The development of multifunctional robot skin (MFR skin) will extend the service life of robots, broaden their application areas, and enable future robots to replace humans to accomplish more complex and operationally difficult tasks.

A high-adhesive and sensitive hydrogel with interpenetrating and interlocking networked structure for efficient biological signal monitoring

Smart flexible sensing materials and devices for wearable health monitoring are considered as prospective and promising areas in healthcare that are currently in high demand in the market. Conductive hydrogel-based sensors, which closely resemble human tissue, encounter notable challenges in attaining high electronic conduction, robust mechanical properties, biocompatibility, and intimate tissue adhesion simultaneously. In this work, a poly(2-acrylamide-2-methylpropane sulfonic acid-co-acrylamide)/bacterial cellulose (P(AMPS-co-AM)/BC) hydrogel with a particular interpenetrating and interlocking networked structure is reported. This hydrogel possesses all the mentioned intriguing properties plus easy degradability. It is realized by utilizing the interaction between amino, amide, and sulfonic groups on polymer molecular chains and polyhydroxy groups on bacterial cellulose. This hydrogel exhibits high strength (1.28 MPa) and tensile strain (525 %), remarkable tissue adhesion (697 kPa), exceptional antibacterial property and low cytotoxicity. Furthermore, it can degrade in the natural environment when exposed to UV light irradiation. The hydrogel-based strain sensors have demonstrated efficient human motion detection with a broad strain detection range (0–360 %) and a high sensitivity (GF = 11.36). Moreover, this hydrogel can be assembled into Triboelectric Nanogenerator for monitoring biological signals. This work presents a new avenue for human-machine interaction and electronic robotic skins.

Capacitive flexible pressure sensor based on porous GR/PDMS composite dielectric layer

Capacitive flexible pressure sensors, with the advantages of simple structure, reliable repeatability, and low energy consumption, have been widely used in wearable devices, soft robots, and other fields. This article describes the preparation of a polydimethylsiloxane (PDMS) sponge dielectric layer with a surface microstructure and dense internal bubbles by adding ammonium bicarbonate to PDMS, using sandpaper as a template, and utilizing the thermal decomposition of ammonium bicarbonate into three gases: ammonia, carbon dioxide, and water vapor (NH3, CO2, and H2O). Meanwhile, the sensitivity of the capacitive flexible pressure sensor using the sandwich structure with PDMS sponge can reach 0.4321 kPa−1 within the range of 0–3 kPa, and it has a fast response time and recovery time, good repeatability, and a wide detection range. The pressure sensor based on a porous graphene/PDMS (GR/PDMS) sponge dielectric layer can achieve human physiological signal detection and has broad application prospects in fields such as robot skin.

Electroactive composite biofilms integrating Kombucha, Chlorella and synthetic proteinoid Proto-Brains.

In this study, we present electroactive biofilms made from a combination of Kombucha zoogleal mats and thermal proteinoids. These biofilms have potential applications in unconventional computing and robotic skin. Proteinoids are synthesized by thermally polymerizing amino acids, resulting in the formation of synthetic protocells that display electrical signalling similar to neurons. By incorporating proteinoids into Kombucha zoogleal cellulose mats, hydrogel biofilms can be created that have the ability to efficiently transfer charges, perform sensory transduction and undergo processing. We conducted a study on the memfractance and memristance behaviours of composite biofilms, showcasing their capacity to carry out unconventional computing operations. The porous nanostructure and electroactivity of the biofilm create a biocompatible interface that can be used to record and stimulate neuronal networks. In addition to in vitro neuronal interfaces, these soft electroactive biofilms show potential as components for bioinspired robotics, smart wearables, unconventional computing devices and adaptive biorobotic systems. Kombucha-proteinoids composite films are a highly customizable material that can be synthesized to suit specific needs. These films belong to a unique category of 'living' materials, as they have the ability to support cellular systems and improve bioelectronic functionality. This makes them an exciting prospect in various applications. Ongoing efforts are currently being directed towards enhancing the compositional tuning of conductivity, signal processing and integration within hybrid bioelectronic circuits.

Protective and Collision‐Sensitive Gel‐Skin: Visco‐Elastomeric Polyvinyl Chloride Gel Rapidly Detects Robot Collision by Breaking Electrical Charge Accumulation Stability

Human–robot collaboration (HRC) is effective to improve productivity in industrial fields, based on the robot's fast and precise work and the human's flexible skill. To facilitate the HRC system, the first priority is to ensure safety in the event of accidents, such as collisions between robots and humans. Therefore, a protective and collision‐sensitive robot skin, named Gel‐Skin is proposed to guarantee the safety in HRC. The Gel‐Skin is composed of polyvinyl chloride (PVC) gel, which is a functional material with piezoresistive characteristics and impact absorption capability. In particular, the PVC gel has a distinctive piezoresistive property that the relation between mechanical pressure and electrical resistance is tunable depending on an applied voltage. When a voltage is applied to the PVC gel, the electrical charges are accumulated around the anode and it shows increased piezoresistive sensitivity. In this study, it is verified for the PVC gel to exhibit the 4.78 times higher sensitivity by simply applying a voltage. This novel physical phenomenon enables the Gel‐Skin to detect the collision rapidly. Finally, the Gel‐Skin is applicated to a real robot system and it is verified that the Gel‐Skin can detect a collision and absorb impact to ensure safety.

Self‐Powered Multimodal Sensing Using Energy‐Generating Solar Skin for Robotics and Smart Wearables

Wearable electronic devices‐laden systems such as electronic‐skin (e‐Skin) have been explored in recent years to enable advances in applications such as Internet of Things, healthcare, and robotics. The power requirement of multitudes of devices in the e‐Skin is a major hurdle for its wider uptake. Herein, a solar cells‐based energy generating e‐Skin is presented and how the energy outputs of solar cells can be innovatively processed for multimodal sensing is demonstrated. By reading the variations and energy output patterns of the e‐Skin, present on a robotic arm, multiple parameters can be sensed including object motion, color detection, and ambient temperature. With the accurate tracking of shadow sensing, for an object moving in horizontal and vertical directions with respect to the solar skin, information can be obtained such as the velocity and acceleration of moving object. In this regard, the presented e‐Skin can also be seen to have vision capability. The presented multifunctional energy‐generating e‐Skin shows an energy surplus of >1 mW (effective module area of 20 cm2) under white light illumination of 4,450 lux, which is sufficient for continuous powering of portable low‐powered devices. Finally, we demonstrate the e‐Skin application for energy‐autonomous hand gestures recognition in robotics.

From CySkin to ProxySKIN: Design, Implementation and Testing of a Multi-Modal Robotic Skin for Human-Robot Interaction.

The Industry 5.0 paradigm has a human-centered vision of the industrial scenario and foresees a close collaboration between humans and robots. Industrial manufacturing environments must be easily adaptable to different task requirements, possibly taking into account the ergonomics and production line flexibility. Therefore, external sensing infrastructures such as cameras and motion capture systems may not be sufficient or suitable as they limit the shop floor reconfigurability and increase setup costs. In this paper, we present the technological advancements leading to the realization of ProxySKIN, a skin-like sensory system based on networks of distributed proximity sensors and tactile sensors. This technology is designed to cover large areas of the robot body and to provide a comprehensive perception of the surrounding space. ProxySKIN architecture is built on top of CySkin, a flexible artificial skin conceived to provide robots with the sense of touch, and arrays of Time-of-Flight (ToF) sensors. We provide a characterization of the arrays of proximity sensors and we motivate the design choices that lead to ProxySKIN, analyzing the effects of light interference on a ToF, due to the activity of other sensing devices. The obtained results show that a large number of proximity sensors can be embedded in our distributed sensing architecture and incorporated onto the body of a robotic platform, opening new scenarios for complex applications.

Robotic Skins With Integrated Actuation, Sensing, and Variable Stiffness

Robotic Skins With Integrated Actuation, Sensing, and Variable Stiffness

TacSuit: A Wearable Large-Area, Bioinspired Multimodal Tactile Skin for Collaborative Robots

Robots are now working more and more closely with humans outside of traditional fences in industrial scenes. Their real-time tactile interaction perception is crucial to the safety of human–robot collaboration (HRC). In this work, we present a customized, wearable and modular robot skin (TacSuit), which is scalable for large-area surface coverage of robot with easily accessible multi-modal sensors, including pressure, proximity, acceleration and temperature sensors. The TacSuit is co-designed for mechanical structure and data fusion algorithm, consisting of three levels of design: sensor, cell (of multi-modal sensors) and block (of multiple cells). These sensors are stored with custom-designed and 3D printed capsules to achieve the conformity, scalability and easy installation to the arbitrary robot surface. A multi-level event-driven data fusion algorithm enables efficient information processing for large number of tactile sensors. Furthermore, a virtual interaction force fusion method takes both the proximity and force perception information into consideration in order to achieve safety of whole interaction process before and after direct physical contacts. A humanoid robotic platform successfully realizes the TacSuit wear of 159 tactile cells. Validation experiments of obstacle detection demonstrate the effective collision avoidance capability of the TacSuit for safe HRC.