Annals of DAAAM for 2011 & Proceedings of the 22nd International DAAAM Symposium, Volume 22, No. 1, ISSN 1726-9679 ISBN 978-3-901509-83-4, Editor B. Katalinic, Published by DAAAM International, Vienna, Austria, EU, 2011 Make Harmony between Technology and Nature, and Your Mind will Fly Free as a Bird Annals & Proceedings of DAAAM International 2011 BIO-INSPIRED SMART SENSORS FOR A HEXAPOD ROBOT MAIBOHM, C[hristian] & BILBERG, A[rne] Abstract: EMICAB (Embodied Motion Intelligence for Cognitive, Autonomous Robots) is an EU founded project where a consortium of 4 Universities is working together to integrate smart body mechanics and sensors with intelligent planning and motor behavior in order to make a holistic approach to artificial cognitive systems. This contribution provides information and the first experimental results about smart material sensors done at the Mads Clausen Institute at the University of Southern Denmark, where the aim is to make a distributed smart sensor network with a redundancy of sensors mimicking that found on limbs of for instance stick insects. Key words : Smart sensor material, distributed sensor network, bio-mechatronics, DEAP 1. INTRODUCTION Inspired by the agility, versatility and adaptability of walking insects, autonomous legged robots based on biological principles have seen a considerable interest in the last years (Delcomyn & Nelson 2000). One of the key interest points in successful biological systems is their ability to move across rough terrain outperforming even the most agile robot. This lacking in performance of the robot can partly be contributed to a main focus on generating a predefined stable gait for the robot with a minimal influence from sensory feedback. On the other hand biological systems usually rely heavily on a redundancy of sensors which provides the insect with sensory feedback for adaptive locomotion. The aim of the EMICAB project is bridging this gab by taking a holistic approach to implementing bio-inspired artificial cognitive systems onto a legged hexapod robot seen in Fig 1. The Mads Clausen Institute part of the EMICAB project is the design and implementation of a sensory network where a redundancy of smart material sensors will mimic functions of sensor organs found on insect legs. This combined with planning and motor behavior will generate an intelligent platform for agile movements where the hexapod robot interacts with and learns from the surroundings through sensory feedback. Fig 1: Full scale plastic model of the EMICAB hexapod robot. The final hexapod will be made in carbon fiber and is about 60 cm long and weighs around 11 kg fully equipped 2. LIMB SENSOR ORGANS FOR LOCOMOTION Before describing the technical aspects of the project a brief review of sensor types mimicked in the project will be given. On an insect limb two main categories of sense organs can be found; mechanoreceptors and chemoreceptors, where only the former type are thought to have influence on agile locomotion (Delcomyn, F. et al. 1996). Mechanoreceptors can again be divided into overlapping subcategories; proprioceptors (position and motion of body parts in respect to each other), tactile receptors (contact with and to another object) and stress receptors (stress in the exoskeleton and also contact to another object). The final version of the developed sensors and sensor network in the project should perform the tasks of the above mentioned sensor receptors types. 3. DEAP AS SMART MATERIAL FOR SENSORS The material chosen for all three sensor types are a subcategory of so-called EAP (Electro Activated polymer) materials namely DEAP (Dielectric -EAP). Since the beginning of the 1990s EAP materials have seen a growing interest as active material in both actuators and sensors (Bar-Cohen, Y. 2004; Kornbluh, R. et al. 2004). We have chosen DEAP as the sensor material because of its large strain capabilities, environmental tolerance and low cost. The specific DEAP material used for sensors in this project is produced by the Danish company PolyPower A/S***. 3.1 General functionality of DEAP Basically a dielectric elastomer device functions as a plate capacitor where an incompressible and highly deformable material is sandwiched between two electrodes as seen on the left in Fig 2. If an electric field in the order of kilo volts is placed across the electrodes the so-called Maxwell stress causes the electrodes to move closer squeezing the material between them thereby causing actuation (Samatham, R et al. 2010). If used as a sensor an outside pressure, P seen on the left in Fig 2, deforms the DEAP device by moving the plates closer together inducing a capacitance change which is correlated to magnitude of P. In the general case the deformation will be uniform in the plane perpendicular to the force and therefore non-directional. If instead both the plates and the dielectric material between them are structured in order to make, an anisotropic compliant to the force a platform for smart sensor are created. The DEAP material used in the project is corrugated in one direction making the sheet nearly unidirectional compliant which means that the thickness strain s t is approximately equal to the negative of the compliant strain s comp (Sommer-Larsen, P. & Benslimane, M. 2008):      (1) Here Y is the Young’s modulus (≈ 1MPa) and P the pressure. The capacity change of the deformed device is given by: 1311