Multiple facets of tightly coupled transducer-transistor structures

The ever increasing demand for data processing requires different paradigms for electronics. Excellent performance capabilities such as low power and high speed in electronics can be attained through several factors including using functional materials, which sometimes acquire superior electronic properties. The transduction-based transistor switching mechanism is one such possibility, which exploits the change in electrical properties of the transducer as a function of a mechanically induced deformation. Originally developed for deformation sensors, the technique is now moving to the centre stage of the electronic industry as the basis for new transistor concepts to circumvent the gate voltage bottleneck in transistor miniaturization. In issue 37 of Nanotechnology, Chang et al show the piezoelectronic transistor (PET), which uses a fast, low-power mechanical transduction mechanism to propagate an input gate voltage signal into an output resistance modulation. The findings by Chang et al will spur further research into piezoelectric scaling, and the PET fabrication techniques needed to advance this type of device in the future

Tactile Sensors Based on Conductive Polymers

This paper presents results from a selection of tactile sensors that have been designed and fabricated. These sensors are based on a common approach that consists in placing a sheet of piezoresistive material on the top of a set of electrodes. We use a thin film of conductive polymer as the piezoresistive mate¬rial. Specifically, a conductive water-based ink of this polymer is deposited by spin coating on a flexible plastic sheet, giving it a smooth, homogeneous and conducting thin film. The main interest in this procedure is that it is cheap and it allows the fabrication of flexible and low cost tactile sensors. In this work we present results from sensors made using two technologies. Firstly, we have used a flexible Printed Circuit Board (PCB) technology to fabricate the set of electrodes and addressing tracks. The result is a simple, flexible tactile sensor. In addition to these sensors on PCB, we have proposed, designed and fabricated sensors with screen printing technology. In this case, the set of electrodes and addressing tracks are made by printing an ink based on silver nanoparticles. The intense characterization provides us insights into the design of these tactile sensors.This work has been partially funded by the spanish government under contract TEC2006-12376-C02

Estudio e implementación de sensores de fuerza 3D con aplicación a manos robóticas

El presente trabajo se enmarca dentro del contexto del proyecto europeo HANDLE. Dicho proyecto se está llevando a cabo por un consorcio de nueve socios de diferentes países europeos, entre los cuales se encuentra la Universidad Carlos III de Madrid. El objetivo principal es comprender como los humanos llevamos a cabo la manipulación de los objetos, con el objetivo de replicar tanto el agarre como la destreza de los movimientos en una mano arti cial antropomór ca y a partir de ahí, mover los dedos de tal manera que se consiga una mano más autónoma y efectiva en los procesos de manipulación de objetos. Para lograr este objetivo se requiere entre muchos factores la capacidad de percepción táctil. En la actualidad existen algunos dispositivos comerciales que cumplen dicha función. Sin embargo, dichos sistemas solo miden fuerzas normales, lo que limita en gran medida la aplicación de las estrategias de control para conseguir tareas de manipulación diestra de objetos con una sola mano. La necesidad de medir no solo fuerzas normales, sino también fuerzas de fricción han llevado a algunos grupos de investigación del proyecto HANDLE a estudiar y tratar de desarrollar prototipos de piel arti cial con electrodos 3D. Entre dichos grupos se encuentra el RoboticsLab de la UC3M. Con el objetivo de desarrollar piel arti cial con capacidad de medición de fuerzas 3D, el presente proyecto se encargará de analizar las diferentes tecnologías actuales que puedan ser utilizadas para dicho n. Asímismo se seleccionará la más apropiada de acuerdo a diversos criterios relacionados con el costo, escalabilidad, precisión y simplicidad de fabricación. Una vez seleccionada la tecnología base se desarrollar á un modelo teórico de un elemento sensor y se validará mediante la implementación de un prototipo con una escala su cientemente grande que facilite dicho proceso. Por ultimo se realizará un análisis crítico del prototipo que permita identi car los puntos débiles y los fuertes para el diseño de sucesivas versiones, estableciéndose unas guias para su futura interacción en una matriz de elementos sensores que pueda integrarse en forma de piel arti cial.Ingeniería Industria

Embedded Electronic Systems for Electronic Skin Applications

The advances in sensor devices are potentially providing new solutions to many applications including prosthetics and robotics. Endowing upper limb prosthesis with tactile sensors (electronic/sensitive skin) can be used to provide tactile sensory feedback to the amputees. In this regard, the prosthetic device is meant to be equipped with tactile sensing system allowing the user limb to receive tactile feedback about objects and contact surfaces. Thus, embedding tactile sensing system is required for wearable sensors that should cover wide areas of the prosthetics. However, embedding sensing system involves set of challenges in terms of power consumption, data processing, real-time response and design scalability (e-skin may include large number of tactile sensors). The tactile sensing system is constituted of: (i) a tactile sensor array, (ii) an interface electronic circuit, (iii) an embedded processing unit, and (iv) a communication interface to transmit tactile data. The objective of the thesis is to develop an efficient embedded tactile sensing system targeting e-skin application (e.g. prosthetic) by: 1) developing a low power and miniaturized interface electronics circuit, operating in real-time; 2) proposing an efficient algorithm for embedded tactile data processing, affecting the system time latency and power consumption; 3) implementing an efficient communication channel/interface, suitable for large amount of data generated from large number of sensors. Most of the interface electronics for tactile sensing system proposed in the literature are composed of signal conditioning and commercial data acquisition devices (i.e. DAQ). However, these devices are bulky (PC-based) and thus not suitable for portable prosthetics from the size, power consumption and scalability point of view. Regarding the tactile data processing, some works have exploited machine learning methods for extracting meaningful information from tactile data. However, embedding these algorithms poses some challenges because of 1) the high amount of data to be processed significantly affecting the real time functionality, and 2) the complex processing tasks imposing burden in terms of power consumption. On the other hand, the literature shows lack in studies addressing data transfer in tactile sensing system. Thus, dealing with large number of sensors will pose challenges on the communication bandwidth and reliability. Therefore, this thesis exploits three approaches: 1) Developing a low power and miniaturized Interface Electronics (IE), capable of interfacing and acquiring signals from large number of tactile sensors in real-time. We developed a portable IE system based on a low power arm microcontroller and a DDC232 A/D converter, that handles an array of 32 tactile sensors. Upon touch applied to the sensors, the IE acquires and pre-process the sensor signals at low power consumption achieving a battery lifetime of about 22 hours. Then we assessed the functionality of the IE by carrying out Electrical and electromechanical characterization experiments to monitor the response of the interface electronics with PVDF-based piezoelectric sensors. The results of electrical and electromechanical tests validate the correct functionality of the proposed system. In addition, we implemented filtering methods on the IE that reduced the effect of noise in the system. Furthermore, we evaluated our proposed IE by integrating it in tactile sensory feedback system, showing effective deliver of tactile data to the user. The proposed system overcomes similar state of art solutions dealing with higher number of input channels and maintaining real time functionality. 2) Optimizing and implementing a tensorial-based machine learning algorithm for touch modality classification on embedded Zynq System-on-chip (SoC). The algorithm is based on Support Vector Machine classifier to discriminate between three input touch modality classes \u201cbrushing\u201d, \u201crolling\u201d and \u201csliding\u201d. We introduced an efficient algorithm minimizing the hardware implementation complexity in terms of number of operations and memory storage which directly affect time latency and power consumption. With respect to the original algorithm, the proposed approach \u2013 implemented on Zynq SoC \u2013 achieved reduction in the number of operations per inference from 545 M-ops to 18 M-ops and the memory storage from 52.2 KB to 1.7 KB. Moreover, the proposed method speeds up the inference time by a factor of 43 7 at a cost of only 2% loss in accuracy, enabling the algorithm to run on embedded processing unit and to extract tactile information in real-time. 3) Implementing a robust and efficient data transfer channel to transfer aggregated data at high transmission data rate and low power consumption. In this approach, we proposed and demonstrated a tactile sensory feedback system based on an optical communication link for prosthetic applications. The optical link features a low power and wide transmission bandwidth, which makes the feedback system suitable for large number of tactile sensors. The low power transmission is due to the employed UWB-based optical modulation. We implemented a system prototype, consisting of digital transmitter and receiver boards and acquisition circuits to interface 32 piezoelectric sensors. Then we evaluated the system performance by measuring, processing and transmitting data of the 32 piezoelectric sensors at 100 Mbps data rate through the optical link, at 50 pJ/bit communication energy consumption. Experimental results have validated the functionality and demonstrated the real time operation of the proposed sensory feedback system

Identificazione di un modello a parametri concentrati di un sensore tattile piezoelettrico

In questa tesi, si prosegue un lavoro di analisi e modellizzazione di un sensore tattile di ultima generazione. Tale sensore, realizzato con tecnologia Posfet, verrà utilizzato su dita robotiche. Grazie quindi all’interazione tra sensori aptici e di visione, il robot così equipaggiato sarà in grado di esplorare ed interagire con l’ambiente circostante. Il sensore sottoposto ad analisi nasce dalla collaborazione tra l’Università di Trento e l’Italian Institute of Technology di Genova, ed è stato sviluppato attraverso la tesi di dottorato dell’Ing. Ravinder S. Dahiya. La novità introdotta da tale sensore, sta nell’accorpare al trasduttore, cioè un film sottile di polimero piezoelettrico, la prima unità elettronica, costituita da un transistor Mos, migliorando così le prestazioni del dispositivo rispetto alle precedenti tecnologie. Nei capitoli a seguire, verrà esposto il lavoro di identificazione di un semplice modello basato sui parametri fisici/tecnologici, eseguito sul sensore Posfet presso il Dipartimento DTG di Vicenza, in grado di simulare il sensore nel campo di frequenza di interesse. Tale modello, ne consentirà un rapido sviluppo. Permetterà infatti un re-design mirato al fine di migliorane le prestazioni, senza dover passare per la costruzione di diversi modelli di test, riducendo così tempi e costi di sviluppo. Il lavoro di modellizzazione, è inevitabilmente contraddistinto dall’introduzione di ipotesi semplificative. Si andranno quindi a trascurare alcune dinamiche ritenute irrilevanti in partenza

Tactile sensing using elastomeric sensors

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 99-111).GelSight, namely, elastomeric sensor, is a novel tactile sensor to get the 3D information of contacting surfaces. Using GelSight, some tactile properties, such as softness and roughness, could be gained through image processing techniques. In this thesis, I implemented GelSight principle to reconstruct surface geometry of tested surfaces, based on which, the roughness comparison and lump detection experiment are conducted. Roughness of five different types of sandpapers are successfully compared using GelSight Ra value. In the lump detection experiment, a visual display for tactile information is presented. To get binary feedback of lump presence or not, a simple threshold method is introduced in this thesis. To evaluate the performance of GelSight sensor, human psychological experiments are conducted. In similar tasks, GelSight sensor outperforms humans in lump detection.by Xiaodan (Stella) Jia.S.M

Soft pneumatic devices for blood circulation improvement

The research activity I am presenting in this thesis lies within the framework of a cooperation between the University of Cagliari (Applied Mechanics and Robotics lab, headed by professor Andrea Manuello Bertetto, and the research group of physicians referencing to professor Alberto Concu at the Laboratory of Sports Physiology, Department of Medical Sciences), and the Polytechnic of Turin (professor Carlo Ferraresi and his equipe at the Group of Automation and Robotics, Department of Mechanical and Aerospace Engineering) This research was also funded by the Italian Ministry of Research (MIUR – PRIN 2009). My activity has been mainly carried on at the Department of Mechanics, Robotics lab under the supervision of prof. Manuello; I have also spent one year at the Control Lab of the School of Electrical Engineering at Aalto University (Helsinki, Finland). The tests on the patients were taken at the Laboratory of Sports Physiology, Cagliari. I will be describing the design, development and testing of some soft pneumatic flexible devices meant to apply an intermittent massage and to restore blood circulation in lower limbs in order to improve cardiac output and wellness in general. The choice of the actuators, as well as the pneumatic circuits and air distribution system and PLC control patterns will be outlined. The trial run of the devices have been field--‐tested as soon a prototype was ready, so as to tune its features step--‐by--‐ step. I am also giving a characterization of a commercial thin force sensor after briefly reviewing some other type of thin pressure transducer. It has been used to gauge the contact pressure between the actuator and the subject’s skin in order to correlate the level of discomfort to the supply pressure, and to feed this value back to regulate the supply air flow. In order for the massage to be still effective without causing pain or distress or any cutoff to the blood flow, some control objective have been set, consisting in the regulation of the contact force so that it comes to the constant set point smoothly and its value holds constant until unloading occurs. The targets of such mechatronic devices range from paraplegic patients lacking of muscle tone because of their spinal cord damage, to elite endurance athletes needing a circulation booster when resting from practicing after serious injuries leading to bed rest. Encouraging results have been attained for both these two categories, based on the monitored hemodynamic variables

Design and fabrication of flexible tactile sensing and feedback interface for communication by deafblind people

Humans generally interact and communicate using five basic sensory modalities and mainly through vision, touch and audio. However, this does not work for deafblind people as they have both impaired hearing and vision modalities, and hence rely on touch-sensing. This necessitates the development of alternative means that allows them to independently interact and communicate. To do this requires a solution which has the capability for tactile sensing and feedback. Therefore, tactile interface becomes a critical component of any assistive device usable by deafblind people for interaction and communication. Given that existing solutions mainly use rigid and commercial components, there is a need to tap into the advancements in flexible electronics in order develop more effective and conformable solutions. This research involves the development of flexible tactile communication interface usable in assistive communication devices for deafblind people. First, commercial sensors and actuators were utilised as a proof-of-concept and then four novel tactile interfaces were explored which include two similar touch-sensitive electromagnetic actuators, one capacitive tactile sensing array, and a facile flexible inductance-based pressure sensor. The two fabricated touch-sensitive electromagnetic actuators (Type 1 and 2) are both based on electromagnetic principle and capable of simultaneous tactile sensing and feedback. Each comprises of a tandem combination of two main modules - the touch-sensing and the actuation module, with both modules integrated as a single device in each case. The actuation module employs a flexible planar spiral coil and a Neodymium magnet assembled in a soft Polydimethylsiloxane (PDMS) structure, while the touch-sensing module is a planar capacitive metal- insulator-metal structure of copper. The flexible coil (~17µm thick and with 45 turns) was fabricated on a Polyimide sheet using Lithographie Galvanoformung Abformung (LIGA) process. The results of characterisation of these actuators at frequencies ranging from 10Hz to 200Hz, shows a maximum displacement (~ 190µm) around 40Hz. Evaluation of this by 40 (20 deafblind and 20 sighted and hearing) participants show that they can feel vibration at this range. Another tactile interface fabricated is an 8 x 8 capacitive tactile sensing array. The sensor was developed on a flexible Polyvinyl Chloride (PVC) sheet with column electrodes deposited on one side and row electrodes on the reverse side. It is intended for use as an assistive tactile communication interface for deafblind people who communicate using deafblind manual alphabets as well as the English block letters. An inductance-based pressure sensor was also designed, fabricated and characterised for use as an input interface for finger Braille as well as other tactile communication methods for deafblind people. It was realised with a soft ferromagnetic elastomer and a 17µm-thick coil fabricated on a flexible 50 µm-thick polyimide sheet. The ferromagnetic elastomer acts as the core of the coil, which when pressed, sees the metal particles moving closer to each other, leading to changes in the inductance. The coil, with 75µm conductor and 25µm pitch, was also realised using LIGA micromolding technique. Seven different sensors were fabricated using different ratios (1:1, 1:2, 1:3, 1:5, 2:1, 3:1, and 5:1) of Ecoflex to Iron particles. The performance of each sensor was investigated and generally, sensors with higher Iron particles gave better sensitivity, linear as well as dynamic range. In comparison with all other fabricated sensors, the sensor made with 1:5DD was recommended for application as a tactile interface

Caracterización, Modelado y Diseño de Sensores Táctiles Piezorresistivos

Un sensor táctil es un dispositivo con el que se obtiene información del entorno mediante el contacto con él. Su implementación se basa en distribuir una serie de unidades sensoriales de fuerza, a las que denominamos tácteles, de forma matricial; de modo que al contactar con un objeto se detecta la distribución de fuerzas, su forma, su orientación, etc. El campo de aplicación de estos sensores es muy amplio, por ejemplo en medicina, robótica, o tele-presencia, siendo especialmente necesarios en entornos complejos, no estructurados o peligros. En el presente trabajo se proponen diferentes sensores basados en polímeros piezorresistivos, cuya estructura se basa en una matriz flexible de electrodos sobre la que se coloca una lámina de un material electro-activo que disminuye su resistencia con el aumento de la presión aplicada. Se analizan y caracterizan los sensores, que están orientados a aplicaciones de gran área con tecnologías de bajo coste. Para la elaboración de las matrices de electrodos se utilizan dos tecnologías: una placa de circuito impreso sobre un sustrato flexible (tecnología PCB), y técnicas de serigrafía sobre un sustrato plástico (tecnología screen-printing). Los sensores fabricados se caracterizan desde el punto de vista de su respuesta, evaluando parámetros como la sensibilidad, la linealidad, la histéresis, el tiempo de respuesta, la deriva y la dispersión; y analizando también la influencia que ciertos factores de diseño, como el tamaño y geometría de los electrodos, o la conductividad del material activo, tienen sobre estas características. Para los sensores fabricados con la tecnología de screen-printing (construidos mediante la superposición de capas de diferentes materiales) se propone un método de control de la sensibilidad y rango en base a la constante elástica de dos de las capas. Para explicar los resultados experimentales se hace uso de una herramienta de análisis de elementos finitos y del modelo de Winkler, que permite modelar las rugosidades en la interfaz de contacto entre los electrodos y el material piezorresistivo. Por otro lado, se proponen, diseñan y fabrican dos estructuras que superpuestas a los sensores anteriores les dotan de la capacidad de detectar fuerzas tanto normales como tangenciales. Las componentes de las fuerzas tangenciales se obtienen del desequilibrio de fuerzas que registran los tácteles del sensor que hace de base. Ambas propuestas se analizan con una herramienta de análisis de elementos finitos. Además, se muestran resultados experimentales de los prototipos fabricados para ilustrar su viabilidad. Por último, se describe un trabajo concreto de fabricación de un sensor de gran área para cubrir el brazo de un robot de rescate haciendo uso de elementos discretos de fuerza comerciales (FSR). En él se proponen, implementan y evalúan algunas estrategias de diseño que mejoran la respuesta de los FSR. De todo el trabajo desarrollado, se adquiere un conocimiento acerca de cómo abordar el diseño de este tipo de sensores táctiles y de aquellos realizados con tecnologías similares, extrayendo conclusiones y reglas de diseño básicas. Así mismo, se describen las diversas plataformas de test para los sensores táctiles que han sido fabricadas y que en su conjunto constituyen una infraestructura automatizada de caracterización, muy útil para futuros trabajos