Luigi Pinna

Piezoelectric Polymer Transducer Arrays for Flexible Tactile Sensors

The paper focuses on the manufacturing technology of modular components for large-area tactile sensors, which are made of arrays of polyvinylidene fluoride (PVDF) piezoelectric polymer taxels integrated on flexible PCBs. PVDF transducers were chosen for the high electromechanical transduction frequency bandwidth (up to 1 kHz for the given application). Patterned electrodes were inkjet printed on the PVDF film. Experimental tests on skin module prototypes demonstrate the feasibility of the proposed approach and reveal the potentiality to build large area flexible and conformable robotic skin.

A Tensor-Based Pattern-Recognition Framework for the Interpretation of Touch Modality in Artificial Skin Systems

Artificial skin systems support human-robot interactions through touch. The interpretation of touch modalities indeed represents a crucial component for the future development of robots that can properly interact with humans. Independently of the specific employed transducer, one of the key issues is how to process the massively complex and high-dimensional tactile data. In this paper, machine learning technologies (namely, support vector machines and extreme learning machines) support a pattern-recognition framework that can fully exploit the tensor morphology of the tactile signal. Furthermore, a practical strategy is provided to address the intricacies of the training procedure. Experimental results show the effectiveness of the proposed approach.

Tactile Sensing Chips With POSFET Array and Integrated Interface Electronics

PThis paper presents the advanced version of novel piezoelectric oxide semiconductor field effect transistor (POSFET) devices-based tactile sensing chip. The new version of the tactile sensing chip presented here comprises of a 4 × 4 array of POSFET touch sensing devices and integrated interface electronics (i.e., multiplexers, high compliance current sinks, and voltage output buffers). The chip also includes four temperature diodes for the measurement of contact temperature. Various components on the chip have been characterized systematically and the overall operation of the tactile sensing system has been evaluated. With new design, the POSFET devices have improved performance [i.e., linear response in the dynamic contact forces range of 0.01-3 N and sensitivity (without amplification) of 102.4 mV/N], which is more than twice the performance of their previous implementations. The integrated interface electronics result in reduced interconnections which otherwise would be needed to connect the POSFET array with off-chip interface electronic circuitry. This paper paves the way for CMOS implementation of full on-chip tactile sensing systems based on POSFETs.

CHARGE AMPLIFIER DESIGN METHODOLOGY FOR PVDF-BASED TACTILE SENSORS ¤

This paper proposes and describes a charge amplifier-based interface electronics design methodology approach for piezoelectric polymer tactile sensors to be used for humanoid robot applications. The tactile sensor–consisting of a PVDF single sensor element–is illustrated, the electromechanical thickness mode behavior is modeled and a fabricated prototype is presented. The model allows associating the PVDF charge response to the effective load applied on the outer surface of the sensor. The model is also used as a key in the proposed design methodology to estimate the charge to be detected by the charge amplifier. A case study based on the design methodology approach is reported. The system (PVDF single taxel + interface electronics) is analyzed firstly, considering it as ideal and then when the nonidealities come into play. A charge amplifier-based interface electronics prototype is also presented. The implementation is used to validate the followed approach and then defining the design specs towards the dedicated IC design. Some experimental results are also reported.

A tensor-based approach to touch modality classification by using machine learning

The use of piezoelectric sensor arrays to measure contact forces has been extensively studied in connection to robotics. In this research, Polyvinylidene Fluoride (PVDF) has been used for direct measurement of the mechanical stress and large bandwidth electromechanical transduction. Additionally, 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 classification experiment, opening interesting scenarios for the application of tensor-based models to support human-robot interactions. PVDF piezoelectric films have been used to build tactile sensor arrays.ML based pattern-recognition system is designed to treat raw data in tensor form.Different touch modalities have been collected involving 70 participants.The adopted classification tools showed good performance on a three-class experiment.

SPICE model for Piezoelectric Bender Generators

This paper presents the equivalent circuit model of PBG (Piezoelectric Bender Generator) along with its SPICE implementation. The model, made of lumped circuit elements, is valid under both parallel and series wired PBG operation modes. The model is validated by comparing the simulation results, from the transient analysis of the model in SPICE, with those obtained by using MATLAB®. An example using the proposed SPICE model is also presented.

A Tactile Sensing System Based on Arrays of Piezoelectric Polymer Transducers

Tactile sensing enables robots to interact safely and effectively with unstructured environments and humans in case of both voluntary and reactive interaction tasks. Focusing on humanoid robots, there is increasing interest in avoiding negative human feelings towards the “entity” [1], enabling robots to interact with humans in more intuitive and meaningful ways [2-4]. This requires designing methods for extracting important information from tactile stimuli leading to classification of touch modalities [5-8]. It is still unclear, however, whether touch modality actually plays an important role in the communication of social messages. A very interesting research area consists in exploring social touch for robotics through an interpretation of emotions and other social messages [9].

Towards prosthetic systems providing comprehensive tactile feedback for utility and embodiment.

The present research moves in the direction of enabling a bidirectional communication between the subject brain and the prosthetic limb, by providing the prosthesis with an artificial cutaneous sensing through an electronic skin. In this preliminary study, the skin response to the applied mechanical stimuli is conveyed to the human subject using electrotactile stimulation. Experimental tests on two healthy subjects show that a short training through reinforced learning increased considerably the success rate in the identification of the impact location. This preliminary study demonstrates the feasibility of communicating the tactile information from the electronic skin to the human subject using multichannel electrocutaneous stimulation. The result is promising since it implies that it might be possible to achieve the embodiment of the artificial skin into the body scheme of the human subject, relying on the brain ability to successfully process the artificial tactile information.

Tactile sensors with integrated piezoelectric polymer and low voltage organic thin-film transistors

This paper presents a novel approach for realizing tactile sensors by integrating a piezoelectric polymer with a low voltage Organic Thin-Film Transistor (OTFT) on flexible plastic substrates. The transducing element consists of PVDF piezoelectric film. The proposed device architecture is similar to the extended gate scheme, whereby the transducing material is connected to OTFT via extended gate. In this scheme, the OTFTs and the transducer material may be or same substrate, as in this case, or they may be on different substrates. The piezoelectric effect induced by an external mechanical stimulus modulates the output current of the OTFT. This scheme represents a simple and innovative solution for artificial sense of touch and is particularly suitable for the low-cost fabrication of so-called “electronic skin”. The electromechanical characterization shows that the sensing devices can detect forces stimuli within the range 0.5 - 8N.

Interface electronics for tactile sensing arrays

This paper presents the interface electronics design and implementation of a tactile sensing system for humanoid robot applications. The tactile system is designed to cover the human tactile sensing bandwidth ranging from 1Hz to 1kHz and to operate on a wide range of input forces/pressures. Some interface electronics prototypes have been designed and fabricated. The paper reports the experimental results and the validation of the proposed implementation. We report also results of the electro-mechanical response of the tactile sensing system (i.e. tactile sensing array + interface electronics) to external mechanical stimuli. The current implementation is a first step towards dedicated IC integration.