300 Research Article Received: 15 June 2009 Revised: 28 July 2009 Accepted: 6 August 2009 Published online in Wiley Interscience: 23 December 2009 (www.interscience.wiley.com) DOI 10.1002/pi.2752 Self-sensing ionic polymer – metal composite actuating device with patterned surface electrodes Karl Kruusam ¨ ae, a* Paola Brunetto, b Salvatore Graziani, b Andres Punning, a Giovanna Di Pasquale b and Alvo Aabloo a Abstract Electroactive polymers are materials that change their properties (e.g. size and shape) while stimulated by an electric field/current. Conversely, they produce an electrical signal if bent. As both actuators and sensors, they are considered attractive for various applications, e.g. in biomedicine and robotics. Self-sensing actuators made of these materials are still a topic of great interest among researchers. This paper proposes a new self-sensing ionic polymer – metal composite (IPMC) actuating device. By specially patterning the opposite metal electrodes of an IPMC strip, an actuator and a sensor are formed on a single piece of the material. Self-sensitivity is attained by measuring the changing resistance of the sensor part of the structure. This paper introduces the methods for patterning the surface of an IPMC strip and measuring the resistance change during the actuator work cycle, and gives experimental evidence of the suitability of the proposed method for the realization of a smart motion actuator. c  2009 Society of Chemical Industry Keywords: IPMC; self-sensing; surface patterning; surface resistance; electroactive polymer; actuator INTRODUCTION Ionic polymer – metal composites (IPMCs) are electroactive materi- als that typically consist of a thin ionic polymer membrane, plated by metal (e.g. platinum) on both sides. IPMCs bend when a voltage (typically lower than 5 V) is applied between the metal electrodes. The direction of movement is dependent on the polarity of the voltage and the amplitude of displacement depends on the level of the applied electric current. 1,2 More specifically, the electric field applied between the metal electrodes causes directional movement of mobile ions inside the polymer matrix. This uneven distribution of ions and the formation of electrical double layers make one side of the IPMC expand and the opposite one contract. This process results in the bending of the IPMC actuator. IPMC materials also exhibit the reverse effect to actuation, i.e. a sensing characteristic. 2 A conventional IPMC sensor in a cantilever configuration can be treated like an accelerometer or a motion detector. 2–5 The external bending of an IPMC strip causes movement of ions inside the polymer membrane, making it possible to collect charges at the electrodes of the IPMC strip. The charges can be registered either as open-circuit voltage or short-circuit current. 3–5 The signal produced in this way is usually quite weak and noisy. 3–5 Moreover, if a constant displacement is imposed, the difference of the charge concentration at the electrodes evens out and no signal can be measured. Hence, this kind of sensor cannot easily be used as a position sensor. In order to use an IPMC as a position sensor, the change in resistance of the surface electrodes in respect to the shape can be measured. When the IPMC bends or is bent, one of the surface electrodes is compressed and the opposite one is stretched out. It is observed that the resistance of the surface plate increases on stretching and decreases on compression. The variation of resistance depends on the material used for the electrodes and can be up to a few hundred ohms, which makes it rather easy to detect. 6 When using IPMC actuators, real-time feedback is often required. 7 This aids in determining the position and state of the actuator, which might lead to closed-loop control of the system. Since the electromechanical process of IPMCs suffers from problems of both repeatability and reproducibility, 8 the necessity of using real-time feedback to obtain reliable applications is clear. The most commonly used feedback systems include laser displacement sensors, 9 load cells 10 and video cameras, 11 although using a separate strip of IPMC as a deformation sensor 12 or other transducers 13 has also been proposed. Unfortunately the need for an off-board feedback source increases the cost and the complexity of the whole system design, which hinders the use of IPMC actuators. For example, due to their small dimensions (thickness of ca 200 μm), IPMCs are considered as good candidates for miniaturization, but having a bulky sensor as a feedback source would make the system impractical and unwieldy. ∗ Correspondence to: Karl Kruusam¨ ae, IMS Lab, Institute of Technology, Tartu University, Nooruse 1, 50411 Tartu, Estonia. E-mail: karl.kruusamae@ut.ee a IMS Lab, Institute of Technology, Tartu University, Nooruse 1, 50411 Tartu, Estonia b Dipartimento di Ingegneria Elettrica, Elettronica e dei Sistemi, Universit` a degli Studi di Catania, viale Andrea Doria 6, 95125 Catania, Italy Polym Int 2010; 59: 300–304 www.soci.org c  2009 Society of Chemical Industry