The Development of a Flexible Sensor for Continuum Soft-Bodied Robots

In this thesis, we investigate, develop, and verify an approach to sense over soft and flexible materials based on the use of a tomographic technique known as Electrical Impedance Tomography

Tactile perception in hydrogel-based robotic skins using data-driven electrical impedance tomography

Combining functional soft materials with electrical impedance tomography is a promising method for developing continuum sensorized soft robotic skins with high resolutions. However, reconstructing the tactile stimuli from surface electrode measurements is a challenging ill-posed modelling problem, with FEM and analytic models facing a reality gap. To counter this, we propose and demonstrate a model-free superposition method which uses small amounts of real-world data to develop deformation maps of a soft robotic skin made from a self-healing ionically conductive hydrogel, the properties of which are affected by temperature, humidity, and damage. We demonstrate how this method outperforms a traditional neural network for small datasets, obtaining an average resolution of 12.1 mm over a 170 mm circular skin. Additionally, we explore how this resolution varies over a series of 15,000 consecutive presses, during which damages are continuously propagated. Finally, we demonstrate applications for functional robotic skins: damage detection/localization, environmental monitoring, and multi-touch recognition - all using the same sensing material

Electrical Impedance Tomography: From the Traditional Design to the Novel Frontier of Wearables

Electrical impedance tomography (EIT) is a medical imaging technique based on the injection of a current or voltage pattern through electrodes on the skin of the patient, and on the reconstruction of the internal conductivity distribution from the voltages collected by the electrodes. Compared to other imaging techniques, EIT shows significant advantages: it does not use ionizing radiation, is non-invasive and is characterized by high temporal resolution. Moreover, its low cost and high portability make it suitable for real-time, bedside monitoring. However, EIT is also characterized by some technical limitations that cause poor spatial resolution. The possibility to design wearable devices based on EIT has recently given a boost to this technology. In this paper we reviewed EIT physical principles, hardware design and major clinical applications, from the classical to a wearable setup. A wireless and wearable EIT system seems a promising frontier of this technology, as it can both facilitate making clinical measurements and open novel scenarios to EIT systems, such as home monitoring

Electronic hardware design of a low cost tactile sensor device for physical Human-Robot Interactions

International audienceWe propose in this paper a low-cost method of Electrical Impedance Tomography (EIT) data acquisition from soft conductive fabric for the design of robots artificial skin. We use a simple multiplexer/demultiplexer circuit for retrieving the resistance field from the pair-wised electrical current injected and the output voltage measured from the conductive fabric. A microcontroller controls the current injection and voltage output patterns and the analog-to-numeric conversion from the tactile material. After explaining the EIT method, we present the electronics corresponding to the data acquisition and we analyze the material property. Results show that we can acquire and localize in real time spatial patterns of the tactile contact

Electronic hardware design of a low cost tactile sensor device for physical Human-Robot Interactions

International audienceWe propose in this paper a low-cost method of Electrical Impedance Tomography (EIT) data acquisition from soft conductive fabric for the design of robots artificial skin. We use a simple multiplexer/demultiplexer circuit for retrieving the resistance field from the pair-wised electrical current injected and the output voltage measured from the conductive fabric. A microcontroller controls the current injection and voltage output patterns and the analog-to-numeric conversion from the tactile material. After explaining the EIT method, we present the electronics corresponding to the data acquisition and we analyze the material property. Results show that we can acquire and localize in real time spatial patterns of the tactile contact

TACTILE SENSING WITH COMPLIANT STRUCTURES FOR HUMAN-ROBOT INTERACTION

This dissertation presents the research on tactile sensing with compliant structures towards human-robot interaction. It would be beneficial for robots working collaboratively with humans to be soft or padded and have compliant tactile sensing skins over the padding. To allow the robots to interact with humans via touch effectively and safely and to detect tactile stimuli in an unstructured environment, new tactile sensing concepts are needed that can detect a wide range of potential interactions and sense over an area. However, most highly sensitive tactile sensors are unable to cover the forces involved in human contacts, which ranges from 1 newton to thousand newtons; to implement area sensing capabilities, there have been challenges in creating traditional sensing arrays, where the associated supporting electronics become more complex with an increasing number of sensing elements. This dissertation develops a novel multi-layer cutaneous tactile sensing architecture for enhanced sensitivity and range, and employs an imaging technique based on boundary measurements called electrical impedance tomography (EIT) to achieve area tactile sensing capabilities. The multi-layer cutaneous tactile sensing architecture, which consists of stretchable piezoresistive strain-sensing layers over foam padding layers of different stiffness, allows for both sufficient sensitivity and an extended force range for human contacts. The role that the padding layer plays when placed under a stretchable sensing layer was investigated, and it was discovered that the padding layer magnifies the sensor signal under indentation compared to that obtained without padding layers. The roles of the multi-layer foams were investigated by changing stiffness and thickness, which allows tailoring the response of multi-layer architectures for different applications. To achieve both extended force range and distributed sensing, EIT technique was employed with the multi-layer sensing architecture. Machine and human touch were conducted on the developed multi-layer sensing system, revealing that the second sensing skin is required to detect the large variability in human touch. Although widely applied in the medical field for functional imaging, EIT applied in tactile sensing faces different challenges, such as unknown number and region of tactile stimuli. Current EIT tactile sensors have focused on qualitative demonstration. This dissertation aims at achieving quantitative information from piezoresistive EIT tactile sensors, by investigating spatial performance and the effect of sensor’s conductivity. A spatial correction method was developed for obtaining consistent spatial information, which was validated by both simulation and experiments from our stretchable piezoresistive EIT sensor with an underlying padding layer

A Large Area Tactile Sensor Patch Based on Commercial Force Sensors

This paper reports the design of a tactile sensor patch to cover large areas of robots and machines that interact with human beings. Many devices have been proposed to meet such a demand. These realizations are mostly custom-built or developed in the lab. The sensor of this paper is implemented with commercial force sensors. This has the benefit of a more foreseeable response of the sensor if its behavior is understood as the aggregation of readings from all the individual force sensors in the array. A few reported large area tactile sensors are also based on commercial sensors. However, the one in this paper is the first of this kind based on the use of polymeric commercial force sensing resistors (FSR) as unit elements of the array or tactels, which results in a robust sensor. The paper discusses design issues related to some necessary modifications of the force sensor, its assembly in an array, and the signal conditioning. The patch has 16 × 9 force sensors mounted on a flexible printed circuit board with a spatial resolution of 18.5 mm. The force range of a tactel is 6 N and its sensitivity is 0.6 V/N. The array is read at a rate of 78 frames per second. Finally, two simple application examples are also carried out with the sensor mounted on the forearm of a rescue robot that communicates with the sensor through a CAN bus

Design, characterization and validation of integrated bioelectronics for cellular studies: from inkjet-printed sensors to organic actuators

Mención Internacional en el título de doctorAdvances in bioinspired and biomimetic electronics have enabled coupling engineering devices to biological systems with unprecedented integration levels. Major efforts, however, have been devoted to interface malleable electronic devices externally to the organs and tissues. A promising alternative is embedding electronics into living tissues/organs or, turning the concept inside out, lading electronic devices with soft living matters which may accomplish remote monitoring and control of tissue’s functions from within. This endeavor may unleash the ability to engineer “living electronics” for regenerative medicine and biomedical applications. In this context, it remains a challenge to insert electronic devices efficiently with living cells in a way that there are minimal adverse reactions in the biological host while the electronics maintaining the engineered functionalities. In addition, investigating in real-time and with minimal invasion the long-term responses of biological systems that are brought in contact with such bioelectronic devices is desirable. In this work we introduce the development (design, fabrication and characterization) and validation of sensors and actuators mechanically soft and compliant to cells able to properly operate embedded into a cell culture environment, specifically of a cell line of human epithelial keratinocytes. For the development of the sensors we propose moving from conventional microtechnology approaches to techniques compatible with bioprinting in a way to support the eventual fabrication of tissues and electronic sensors in a single hybrid plataform simultaneously. For the actuators we explore the use of electroactive, organic, printing-compatible polymers to induce cellular responses as a drug-free alternative to the classic chemical route in a way to gain eventual control of biological behaviors electronically. In particular, the presented work introduces inkjet-printed interdigitated electrodes to monitor label-freely and non-invasively cellular migration, proliferation and cell-sensor adhesions of epidermal cells (HaCaT cells) using impedance spectroscopy and the effects of (dynamic) mechanical stimulation on proliferation, migration and morphology of keratinocytes by varying the magnitude, frequency and duration of mechanical stimuli exploiting the developed biocompatible actuator. The results of this thesis contribute to the envision of three-dimensional laboratory-growth tissues with built-in electronics, paving exciting avenues towards the idea of living smart cyborg-skin substitutes.En los útimos años los avances en el desarrollo de dispositivos electrónicos diseñados imitando las propiedades de sistemas vivos han logrado acoplar sistemas electrónicos y órganos/tejidos biológicos con un nivel de integración sin precedentes. Convencionalmente, la forma en que estos sistemas bioelectrónicos son integrados con órganos o tejidos ha sido a través del contacto superficial entre ambos sistemas, es decir acoplando la electrónica externamente al tejido. Lamentablemente estas aproximaciones no contemplan escenarios donde ha habido una pérdida o daño del tejido con el cual interactuar, como es el caso de daños en la piel debido a quemaduras, úlceras u otras lesiones genéticas o producidas. Una alternativa prometedora para ingeniería de tejidos y medicina regenerativa, y en particular para implantes de piel, es embeber la electrónica dentro del tejido, o presentado de otra manera, cargar el sistema electrónico con células vivas y tejidos fabricados por ingeniería de tejidos como parte innata del propio dispositivo. Este concepto permitiría no solo una monitorización remota y un control basado en señalizaciones eléctricas (sin químicos) de tejidos biológicos fabricados mediante técnicas de bioingeniería desde dentro del propio tejido, sino también la fabricación de una “electrónica viva”, biológica y eléctricamente funcional. En este contexto, es un desafío insertar de manera eficiente dispositivos electrónicos con células vivas sin desencadenar reacciones adversas en el sistema biológico receptor ni en el sistema electrónico diseñado. Además, es deseable monitorizar en tiempo real y de manera mínimamente invasiva las respuestas de dichos sistemas biológicos que se han añadido a tales dispositivos bioelectrónicos. En este trabajo presentamos el desarrollo (diseño, fabricación y caracterización) y validación de sensores y actuadores mecánicamente suaves y compatibles con células capaces de funcionar correctamente dentro de un entorno de cultivo celular, específicamente de una línea celular de células epiteliales humanas. Para el desarrollo de los sensores hemos propuesto utilizar técnicas compatibles con la bioimpresión, alejándonos de la micro fabricación tradicionalmente usada para la manufactura de sensores electrónicos, con el objetivo a largo plazo de promover la fabricación de los tejidos y los sensores electrónicos simultáneamente en un mismo sistema de impresión híbrido. Para el desarrollo de los actuadores hemos explorado el uso de polímeros electroactivos y compatibles con impresión y hemos investigado el efecto de estímulos mecánicos dinámicos en respuestas celulares con el objetivo a largo plazo de autoinducir comportamientos biológicos controlados de forma electrónica. En concreto, este trabajo presenta sensores basados en electrodos interdigitados impresos por inyección de tinta para monitorear la migración celular, proliferación y adhesiones célula-sustrato de una línea celular de células epiteliales humanas (HaCaT) en tiempo real y de manera no invasiva mediante espectroscopía de impedancia. Por otro lado, este trabajo presenta actuadores biocompatibles basados en el polímero piezoeléctrico fluoruro de poli vinilideno y ha investigado los efectos de estimular mecánicamente células epiteliales en relación con la proliferación, migración y morfología celular mediante variaciones dinámicas de la magnitud, frecuencia y duración de estímulos mecánicos explotando el actuador biocompatible propuesto. Ambos sistemas presentados como resultado de esta tesis doctoral contribuyen al desarrollo de tejidos 3D con electrónica incorporada, promoviendo una investigación hacia la fabricación de sustitutos equivalentes de piel mitad orgánica mitad electrónica como tejidos funcionales biónicos inteligentes.The main works presented in this thesis have been conducted in the facilities of the Universidad Carlos III de Madrid with support from the program Formación del Profesorado Universitario FPU015/06208 granted by Spanish Ministry of Education, Culture and Sports. Some of the work has been also developed in the facilities of the Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration (IZM) and University of Applied Sciences (HTW) in Berlin, under the supervision of Prof. Dr. Ing. H-D. Ngo during a research visit funded by the Mobility Fellows Program by the Spanish Ministry of Education, Culture, and Sports. This work has been developed in the framework of the projects BIOPIELTEC-CM (P2018/BAA-4480), funded by Comunidad de Madrid, and PARAQUA (TEC2017-86271-R) funded by Ministerio de Ciencia e Innovación.Programa de Doctorado en Ingeniería Eléctrica, Electrónica y Automática por la Universidad Carlos III de MadridPresidente: José Antonio García Souto.- Secretario: Carlos Elvira Pujalte.- Vocal: María Dimak