Robot Skin Research Articles

A real-time data acquisition and processing framework for large-scale robot skin

Large-scale tactile sensing applications in Robotics have become the focus of extensive research activities in the past few years, specifically for humanoid platforms. Research products include a variety of fundamentally different robot skin systems. Differences rely in technological (e.g., sensory modes and networking), system-level (e.g., modularity and scalability) and representation (e.g., data structures, coherency and access efficiency) aspects. However, differences within the same robot platform may be present as well. Different robot body parts (e.g., fingertips, forearms and a torso) may be endowed with robot skin that is tailored to meet specific design goals, which leads to local peculiarities as far as technological, system-level and representation solutions are concerned. This variety leads to the issue of designing a software framework able to: (i) provide a unified interface to access information originating from heterogeneous robot skin systems; (ii) assure portability among different robot skin solutions. In this article, a real-time framework designed to address both these issues is discussed. The presented framework, which is referred to as Skinware, is able to acquire large-scale tactile data from heterogeneous networks in real-time and to provide tactile information using abstract data structures for high-level robot behaviours. As a result, tactile-based robot behaviours can be implemented independently of the actual robot skin hardware and body-part-specific features. An extensive validation campaign has been carried out to investigate Skinware’s capabilities with respect to real-time requirements, data coherency and data consistency when large-scale tactile information is needed.

Tactile surface classification for limbed robots using a pressure sensitive robot skin

This paper describes an approach to terrain identification based on pressure images generated through direct surface contact using a robot skin constructed around a high-resolution pressure sensing array. Terrain signatures for classification are formulated from the magnitude frequency responses of the pressure images. The initial experimental results for statically obtained images show that the approach yields classification accuracies . The methodology is extended to accommodate the dynamic pressure images anticipated when a robot is walking or running. Experiments with a one-legged hopping robot yield similar identification accuracies . In addition, the accuracies are independent with respect to changing robot dynamics (i.e., when using different leg gaits). The paper further shows that the high-resolution capabilities of the sensor enables similarly textured surfaces to be distinguished. A correcting filter is developed to accommodate for failures or faults that inevitably occur within the sensing array with continued use. Experimental results show using the correcting filter can extend the effective operational lifespan of a high-resolution sensing array over 6x in the presence of sensor damage. The results presented suggest this methodology can be extended to autonomous field robots, providing a robot with crucial information about the environment that can be used to aid stable and efficient mobility over rough and varying terrains.

Self-Powered Tactile Pressure Sensors Using Ordered Crystalline ZnO Nanorods on Flexible Substrates Toward Robotic Skin and Garments

Flexible, bendable tactile pressure sensors are developed with crystalline ZnO nanorods as a robotic skin or as part of a multimodal sensing garment. The sensors are arranged in addressable arrays for detection of spatial tactile pressure variation with a resolution of 1 mm or better. The sensors are fully conformable to nonplanar surfaces. A low-temperature hydrothermal process in conjunction with thermal nanoimprint lithography is demonstrated to achieve ordered growth of ZnO nanorods placed vertically on the flexible substrate. The nanorods are fully packaged in inert polyimide for protection against dust, moisture, and mechanical shock. The sensor response to applied pressure is observed to be nearly linear and with negligible hysteresis. A peak sensitivity of 21.2 μV/kPa has been observed for tactile pressure in the 10-200 kPa range.

2A2-R03 人工皮膚下への埋め込みを想定した水晶発振回路式液体濃度センサの開発

In this paper, we report the development of liquid concentration sensor using crystal oscillator circuit embedded in a robotic artificial skin. We optimized the shape of the sensing capacitor for sensing a small quantity of liquid locally. This sensor is composed of the sensing capacitor and quartz crystal resonator (QCR). The frequency of QCR changes by a liquid in contact with the artificial skin on the sensing capacitor. Because the frequency changes relate to the electrical characteristics (dielectric constant, conductivity) of the liquid, the sensor can measure the concentration of the liquid. This sensor is expected to be applied to a sensor embedded in the robotic artificial skin.

An Improved Algorithm for the Automated Design of Large-Scaled Robot Skin

A recent paper titled “On the Problem of the Automated Design of Large-Scaled Robot Skin” (Anghinolfi et al., 2013) published in the IEEE Transactions on Automation Science and Engineering addressed the problem of covering the surface of a humanoid robot with the largest number of nonoverlapping equilateral triangular sensor modules. The problem is eventually approximated by a simpler one: how to find the placement of a given polygon P on an equilateral triangular grid G that contains the largest number of the grid triangles. In this paper, we show how to improve the efficiency of the algorithm presented in that paper. Further, we show that the general problem of filling P with the largest number of disjoint equilateral triangles (all entirely contained in P and all of the same size) is not equivalent to that of finding an optimal placement of P on G. Using this result, we propose an improved heuristic for the original problem of covering the skin of a robot with the largest number of triangular sensor modules.

Flexible pressure sensing film based on ultra-sensitive SWCNT/PDMS spheres for monitoring human pulse signals.

Flexible pressure sensors are essential components of electronic skins for future attractive applications ranging from human healthcare monitoring to biomedical diagnostics to robotic skins to prosthetic limbs. Here, we report a new kind of flexible pressure sensing film based on ultrasensitive single wall carbon nanotube (SWCNT)/polydimethylsiloxane (PDMS) spheres. These spheres with the diameter of 600 ± 20 μm were prepared using the dipping method, and were further sandwiched by flexible electrodes using a stack of double-sided tape. The sensing mechanism of this device was analyzed by classic thin plate theory for circular plate deflection. Its sensitivity was further optimized by the synthesis of sensitive materials and geometrical design of device parameters. Ultimately, the developed sensing film exhibited a maximum sensitivity of 46.7% kPa-1 to resistance, great durability over 15 000 cycles, and very rapid mechanical responses (a few milliseconds). We also demonstrated that our sensing film can be used to detect the location and distribution of finger pressure, as well as to map the fingertip pulse signals, jugular venous pulse (JVP) signals and wrist pulse signals of the testers of different ages effectively.

A flexible pressure-sensitive array based on soft substrate

A 4×4 flexible pressure-sensitive array based on PET/ITO (polyethylene terephthalate/indium tin oxides) was designed and fabricated, with a size of 2.5cm×2.5cm×0.75mm. The design effectively reduces the complexity of device structure. The array shows giant negative pressure coefficient of resistivity (NPCR) effect under 0–4N (0–0.32MPa). The pressure-sensitive array exhibits high sensitivity and fast response-recovery to loads. And the response and recovery times are less than 2s. The sensitive size and azimuth of the applied loading on the pressure-sensitivity array can be accurately recognized easily. The pressure-sensitivity array is stable, low-cost and easy for fabricating large-area sensors. The designed micro array may be used for in robot skin.

Ultrasensitive Piezoresistive Pressure Sensors Based on Interlocked Micropillar Arrays

The development of wearable electronic skins is drawing many interests due to potential applications in prosthetic limbs, robotic skins, and human healthcare monitoring devices. Here, we demonstrate piezoresistive wearable electronic skins based on conductive composite elastomers with interlocked geometry of micropillar arrays. The interlocked micropillar arrays enable the huge variation of contact area and thus the contact resistance between interlocked micropillar arrays when they are deformed in response to external pressure stimuli. In this study, we show that the contact resistance is strongly affected by the variation of diameter, pitch size, and shape of micropillar arrays. The pressure sensor with optimized micropillar dimension shows an ultrahigh pressure sensitivity (−22.8 kPa−1) and response time (∼0.07 s). Finally, we demonstrate that the wearable electronic skin attached on the fingertip is capable of detecting the pressure and vibration signal simultaneously.

A new robot skin for force and position detection

Purpose – The aim of the research is to achieve a robot skin which is easy to use, and can detect both position and force interacted between robot and environments. Design/methodology/approach – The new type of robot skin proposed in this paper includes two functional modules – contact position sensor and contact force sensor. The contact position sensor module is based on the resistor divider principle, which consists of two perpendicular conductive fiber layers and insulated dot spacer between them. The contact force sensor module is based on capacitance change theory, which consists of two soft conductive plates and a viscoelastic layer between them. By combining the two modules, the soft robot skin was designed. Findings – Simulation and experiment results demonstrate that the proposed robot skin design is feasible and effective enough to sense contact position and contact force simultaneously. Practical implications – This robot skin is low-cost and easy to make and use, which provides safety solutions for most of the robot. Originality/value – For the first time, an integrated robot skin which can get contact position and force information simultaneously is designed. Unlike general tactile sensor matrices, this robot skin has only six leads. Furthermore, the number of leads does not increase with the enlarging of sensor area. Soft and simple structure of the robot skin makes it possible to cover any region of the robot body.

Towards the creation of tactile maps for robots and their use in robot contact motion control

The recent availability of large-scale tactile systems for robots implies the design and development of tactile representation frameworks able to inform tactile-based robot control strategies. As a matter of fact, this is a non-trivial problem in knowledge representation. Starting from the previous work, we introduce the notion of tactile maps for robots, and we propose an architecture that addresses all the various phases which allow us to implement tactile-based representation and robot control. The proposed architecture is validated using simulations, which are aimed at assessing the robustness and the performance of the chosen control strategy with respect to the accuracy of the robot skin representation as well as to the force feedback needed to implement tactile-based contact tasks.

Computational intelligence techniques for tactile sensing systems.

Tactile sensing helps robots interact with humans and objects effectively in real environments. Piezoelectric polymer sensors provide the functional building blocks of the robotic electronic skin, mainly thanks to their flexibility and suitability for detecting dynamic contact events and for recognizing the touch modality. The paper focuses on the ability of tactile sensing systems to support the challenging recognition of certain qualities/modalities of touch. The research applies novel computational intelligence techniques and a tensor-based approach for the classification of touch modalities; its main results consist in providing a procedure to enhance system generalization ability and architecture for multi-class recognition applications. An experimental campaign involving 70 participants using three different modalities in touching the upper surface of the sensor array was conducted, and confirmed the validity of the approach.

Tactile Interactions with a Humanoid Robot: Novel Play Scenario Implementations with Children with Autism

The work presented in this paper was part of our investigation in the ROBOSKIN project. The project has developed new robot capabilities based on the tactile feedback provided by novel robotic skin, with the aim to provide cognitive mechanisms to improve human–robot interaction capabilities. This article presents two novel tactile play scenarios developed for robot-assisted play for children with autism. The play scenarios were developed against specific educational and therapeutic objectives that were discussed with teachers and therapists. These objectives were classified with reference to the ICF-CY, the International Classification of Functioning—version for Children and Youth. The article presents a detailed description of the play scenarios, and case study examples of their implementation in HRI studies with children with autism and the humanoid robot KASPAR.

Development of Hybrid Piezoelectric Materials for Tactile Sensing

As the robotics is moving its interest from the machine tools for industrial production to biomimetic, even human-like systems, the need for materials that fulfill skin role arises. Skin presents a structure that has multiple roles such as protection and tact. The basic requirements for a skin mimetic material are flexibility and a measurable physical property triggered by the pressure. In this work hybrid piezoelectric materials are prepared and characterized. The flexibility of materials is assured by the polymeric matrices while ceramic oxide fillers grant a piezoelectric response. Polyvinilidene fluoride (PVDF) is used both in its piezoactive β-form and piezopassive α-form, in order to investigate the contribution of the organic phase to the overall response. Polymethylmethacrylate (PMMA) is also used in order to compare the behavior of an amorphous and a semi-crystalline polymer. Lead-based ceramics were avoided, despite they are known to be the most effective piezoelectric materials, to prevent complications in terms of toxicity. Ceramic materials with lower piezoelectric coefficient, but more suitable for human robotics such as barium titanate and zinc oxide are preferred. Organic matrices and ceramic powders are then employed for preparing composites with different compositions, microstructures and mechanical behaviors, in order to evaluate their piezoelectric response in view of their application as sensing skin for robots.

Application and Experimental Validation of Pheromone Design in Ant Colony Optimization: the Problem of Robot Skin Wiring

During the past few years, the problem of optimally routing the wiring in large-scale modular skins for robots gained much attention in the literature. From a theoretical standpoint, the problem is NP-hard. Following previous work (Anghinolfi et al. 2012; Nattero et al. 2012), we solve the skin wiring problem using an ant colony optimization approach. In this article, we specifically address the problem of designing a pheromone structure that is effective in terms of solution quality. In particular, we propose five different alternatives, which are thoroughly validated using problem instances originating from both real and theoretical (i.e., artificially generated) use cases.

Giant Tunneling Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive and Multimodal Electronic Skins

The development of flexible electronic skins with high sensitivities and multimodal sensing capabilities is of great interest for applications ranging from human healthcare monitoring to robotic skins to prosthetic limbs. Although piezoresistive composite elastomers have shown great promise in this area of research, typically poor sensitivities and low response times, as well as signal drifts with temperature, have prevented further development of these materials in electronic skin applications. Here, we introduce and demonstrate a design of flexible electronic skins based on composite elastomer films that contain interlocked microdome arrays and display giant tunneling piezoresistance. Our design substantially increases the change in contact area upon loading and enables an extreme resistance-switching behavior (ROFF/RON of ∼10(5)). This translates into high sensitivity to pressure (-15.1 kPa(-1), ∼0.2 Pa minimum detection) and rapid response/relaxation times (∼0.04 s), with a minimal dependence on temperature variation. We show that our sensors can sensitively monitor human breathing flows and voice vibrations, highlighting their potential use in wearable human-health monitoring systems.

The Bioinspiration Design Paradigm: A Perspective for Soft Robotics

Abstract Biological inspiration is a key design approach for the development of innovative robots. Flapping wings, sensitized robotic skins, insect-inspired compound eyes, and artificial muscles ar...

Organic Bendable and Stretchable Field Effect Devices for Sensing Applications

In this paper we propose a detailed investigation on the electrical response to mechanical deformations of organic field effect transistors assembled on flexible plastic substrates. We demonstrate that through applying a surface deformation by an external mechanical stimulus we induce morphological and structural changes in the organic semiconductor giving rise to a marked, reproducible and reversible variation of the device output current. We show how the intrinsic properties of the employed active layers play a crucial role in determining the final sensitivity to the mechanical deformation. Finally we also demonstrate that the fabricated flexible system can be successfully employed for different applications that go from the detection of bio-mechanical parameters (e.g., joint motion, breath rate, etc.) in the wearable electronics field to tactile transduction for the realization of artificial robot skin.

Flexible Fabric Sensor Toward a Humanoid Robot's Skin: Fabrication, Characterization, and Perceptions

We have developed a fabric sensor knitted of tension-sensitive electro-conductive yarns. Each yarn has an elastic core, around which is wound two other separate, tension-sensitive electro-conductive threads, making this sensor inherently flexible and stretchable and allowing it to conform to any complicated surface on a robot, acting as a robotic skin. The pile-shaped surface of the sensor enhances its ability to detect tangential traction, while also enabling it to sense a normal load. Our aim is to use this sensor in applications involving relative sliding between its surface and a touched object, such as contact recognition, slip detection, and surface identification through a sliding motion. We carefully analyzed the static and dynamic characteristics of this sensor while varying the load and stretching force to fully understand its response and determine its degree of flexibility and stretchability. We found that a discrete wavelet transformation may be used to indicate stick/slip states while the sensor is sliding over surfaces. This method was then used to detect slippage events acting on the sensor's surface, and to decode textures in a classification test using an artificial neural network. Because of its flexibility and sensitivity, this sensor can be used widely as a robotic skin in humanoid robots.

On the Problem of the Automated Design of Large-Scale Robot Skin

This paper describes automated procedures for the design and deployment of artificial skin for humanoid robots. This problem is challenging under different perspectives: on the one hand, different robots are characterized by different shapes, thereby requiring a high degree of skin customization; on the other hand, it is necessary to define optimal criteria specifying how the skin must be placed on robot parts. This paper addresses the problem of optimally covering robot parts with tactile sensors, discussing possible solutions with reference to a specific artificial skin technology for robots, which has been developed in the past few years. Results show that it is possible to automate the majority of the required steps, with promising results in view of a future complete automation of the process.

Development of a tactile sensing system using piezoelectric robot skin materials

Since service robots perform their functions in close proximity to humans, they are much more likely than other types of robot to come into contact with humans. This means that safety regarding robot–human interaction is of particular concern and requires investigation. Existing tactile sensing methods are very effective at detecting external dangerous loadings; however, until now, they have been very expensive. Recently, a new type of self-sensing tactile technology for service robots has been introduced, which harnesses the piezoelectric effect of several robot skin materials. In these kinds of system, relatively cheap materials are used as sensors themselves. In this research, a robot system with a self-sensing tactile technology was developed using piezoelectric robot skin materials. The test results indicate that this type of system is appropriate for application to service robots.