Silicone-Rubber-Based Tactile Sensors for the Measurement of Normal and Tangential Components of the Contact Force Alberto D’Amore, 1 Giuseppe De Maria, 2 Luigi Grassia, 1 Ciro Natale, 2 Salvatore Pirozzi 2 1 Department of Aerospace and Mechanical Engineering, The Second University of Naples, Aversa (Caserta) 81031, Italy 2 Department of Information Engineering, The Second University of Naples, Aversa (Caserta) 81031, Italy Received 28 April 2011; accepted 28 April 2011 DOI 10.1002/app.34790 Published online 11 August 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: This article presents the developmental process of a new tactile sensor. The sensor was based on the use of light-emitting diode (LED) phototransistor cou- ples and a silicone rubber layer positioned above the opto- electronics devices. The optoelectronic components were organized in a matrix structure. For each couple, the LED illuminated the reflective surface, which coincided with the bottom facet of the deformable layer. Practically, the deformable layer transduced an external force into a dis- placement variation of its bottom facet through its stiff- ness. An external force applied to the deformable layer produced local variations of the bottom surface of the elastic material, and the couples of optical devices meas- ured the vertical deformations in a discrete number of points. In particular, these vertical displacements pro- duced a variation of the reflected light intensity and, accordingly, of the photocurrent measured by the photo- detector. The realized prototype was designed and opti- mized through finite element analysis. A calibration procedure is also presented, whose results demonstrate the ability of the sensor to reconstruct the contact point and also the normal and tangential components of the contact force. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3758–3770, 2011 Key words: rubber; sensors; silicones INTRODUCTION Researchers in recent decades have made and are making a huge effort to develop more autonomous robots, that is, robots that are much more capable of making decisions by themselves. To reach this goal, it is clear that the first thing to do is improve the sensitive apparatus of the robot, that is, to increase the number of sensors through which the robot can sense the environment in which it operates and diversify the kinds of physical properties it can feel. Tactile sensors are a class of sensors on which the scientific community is focusing. In nature, tactile sensing is an essential tool, especially for human beings. Picking up an object without making it slip and moving in an unstructured time-varying envi- ronment is something humans do every moment of their lives: humans’ sensing system is designed by nature to work in such conditions, so an approach for building new-generation robots is too look at human beings’ sensing system and trying to imitate it in the realization of a robot sensing system. When one considers tactile sensors, it is useful to begin by considering the fundamental physical quantities that can only be sensed through contact with the envi- ronment. The most important quantities measured with touch sensors are shape and force. 1–4 The measurement of contact forces occurring dur- ing a manipulation is accomplished with different types of sensors, most often embedded as matrices in an elastic material on the fingertips of an end effect or a manipulator. These individual sensing elements, called taxels (the word taxel derives from the union of the words tactile and element), give in- formation about the contact status of the surface on which they are mounted. Although many techniques and technologies have been used to build tactile sen- sors, very little commercial success has been obtained so far. The complexity of many of the cur- rent technologies makes them hard to manufacture, and thus, they are very costly. The following list provides a general description of the most common sensor configurations. A more comprehensive review can be found in ref. 5: 1. Resistive sensors: These devices are usually divided in two subgroups. The sensors of the first subgroup exploit the force-resistance char- acteristic of conductive elastomers and foams. When subjected to an external force, these Correspondence to: L. Grassia (luigi.grassia@unina2.it). Contract grant sponsor: European Community’s Seventh Framework Programme (FP7/2007-2013); contract grant number: 216239 (DEXMART project). Journal of Applied Polymer Science, Vol. 122, 3758–3770 (2011) V C 2011 Wiley Periodicals, Inc.