The skin is one of the main organs of the human body and as such it implements many different and relevant functions, e.g. protection of the inner body organs, detection of cutaneous stimuli, etc. Due to its complexity, the development of electronic skin (e-skin) is a very challenging goal which involves many different and complementary research areas.
Nonetheless, the possible application areas are many and very relevant - e.g. humanoids and industrial robotics, artificial prosthetics, biomedical instrumentation, cyber physical systems, to name a few. Due to its very peculiar features, the development of electronic skin can be effectively tackled using a holistic approach. Starting from the system specification definition, the mechanical arrangement of the skin itself (i.e. soft or rigid mechanical support, structural and functional material layers, etc.) needs to be designed and fabricated together with the electronic embedded system, to move toward aspects such as tactile data processing algorithms and the communication channel interface.
Selected publication
R. S. Dahiya, D. Cattin, A. Adami, C. Collini, L. Barboni, M. Valle, L. Lorenzelli, R. Oboe, G. Metta, F. Brunetti, Towards Tactile Sensing System on Chip for Robotic Applications, IEEE Sensors Journal, June 2011. DOI: 10.1109/JSEN.2011.2159835.
Electronic skin based on piezoelectric transducers
The aim is to build multisensory systems which integrate different physical sensors on a same patch. In particular, ROBOSKIN (EU FP7 - Skin-Based Technologies and Capabilities for Safe, Autonomous and Interactive Robots) skin system is formed by conformable patches of triangular shape, interconnected in order to form a networked structure. This application demands mechanical flexibility, conformability joint with a relatively wide frequency bandwidth (0-1 kHz). Piezoelectric transducers in the form of PVDF thin polymer films have been chosen, as they meet these requirements except from perceiving static mechanical stimuli. We are pursuing two major goals: to develop robotic skin for small area robot parts (i.e. hand of the robot) and for large area robot parts (e.g. torso, back and limbs).
Selected publications
L. Pinna, M. Valle, Charge Amplifier Design Methodology for PVDF-Based Tactile Sensors, Journal of Circuits, Systems and Computers (JCSC), vol. 22, no. 8, 2013
R. S. Dahiya, A. Adami, L. Pinna, C. Collini, M. Valle, L. Lorenzelli, Tactile Sensing Chips With POSFET Array and Integrated Interface Electronics, Sensors Journal, IEEE , Vol.14, no.10, pp.3448,3457, Oct. 2014. doi: 10.1109/JSEN.2014.2346742
Multimodal flexible platforms for customized electronic skin (piezo + organic)
The main objective is to reproduce some features of the human skin through the development and integration of advanced technologies, in order to obtain artificial multimodal sensing systems capable to detect different types of information (e.g. contact mechanics, temperature). Organic electronics represents a valuable technology for facing these issues. Organic polymers are flexible and can be processed and deposited on large areas with low-cost procedures. The employment of this technology allows us to fabricate arrays of different tactile transducers in which some of the fabricated devices (i.e. organic thin film transistors) can be employed at the same time as sensing elements and as control logic for locally addressing each single sensor element, dramatically simplifying the design and complexity of the required interface electronics.
Selected publication
A. Spanu, L. Pinna, F. Viola, L. Seminara, M. Valle, A. Bonfiglio, P. Cosseddu, A high-sensitivity tactile sensors based on piezoelectric polymer PVDF coupled to an ultra low-voltage organic transistor, Organic Electronics, Vol. 36, 2016, pp. 57-60. DOI: 10.1016/j.orgel.2016.05.034.
Tactile data processing: Machine Learning Algorithms for touch classification
A Machine Learning algorithm has been specifically designed to deal with the inherent tensor morphology of raw tactile data. An experiment involving 70 participants has been organized to collect the output signals under different modalities of touch. The proposed pattern-recognition system showed good accuracy in performing touch classification in a three-class experiment, opening interesting scenarios for the application of tensor based models to support human-robot interactions.
Selected publication
P. Gastaldo, L. Pinna, L. Seminara, M. Valle, and R. Zunino, A tensor-based pattern-recognition framework for the interpretation of touch modality in artificial skin systems, IEEE Sensors Journal Vol. 14, Issue 7, 2014, pp. 2216-2225
Tactile data processing: Solids Mechanics Algorithms for contact force reconstruction
The main task of robotic skin is recognition of tactile stimuli acting on the surface of a soft elastic layer through the outputs of embedded sensor arrays. The focus of this work is the development of an algorithm for estimating the spatial distribution of contact forces as well as their intensities and directions starting from sensor data. This requires the solution of an inverse problem where only incomplete information (e.g. normal stress on the sensors) is usually available. The proposed method discretizes external forces at the nodes of a grid. For multi-component force distributions the problem is in principle ill-posed. A solution is achieved through an optimization procedure accounting for the physical features of the problem by the use of the Moore-Penrose pseudo-inverse matrix and of a vector depending on two continuous and adjustable scalar parameters. The algorithm has been tested on simulated single-contact problems with encouraging results for both accuracy and robustness of the solution.
Selected publication
L. Seminara, M. Capurro, M. Valle, Tactile data processing method for the reconstruction of contact force distributions, Mechatronics, Vol. 27, 2015, pp. 28-37.
Embedded Tactile Sensing System
The development and optimized design of an embedded tactile sensing system is typically based on the following steps:
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- Electromechanical characterization of functional materials (i.e. piezoelectric).
- Optimized design of the interface electronics.
- Integration of piezoelectric functional devices and interface electronics on silicon platforms
- Development and hardware implementation of real-time processing algorithms.
- Experimental testing of systems and electronic circuits.
