Development of Bio-inspired Walking Microrobot using PVDF/PVP/PSSA-based IPMC Actuator Nguyen Kim Tien, Doyeon Hwang, Sunyong Jung Seong Young Ko, Jong-Oh Park, and Sukho Park Department of Mechanical Engineering School of Mechanical Engineering Graduate School of Chonnam National University Chonnam National University Buk-gu, Gwangju, Korea Buk-gu, Gwangju, Korea nguyenkimtien90@gmail.com spark@jnu.ac.kr Abstract - Ionic polymer-metal composite (IPMC) is used in many bio-inspired aquatic systems due to its special characteristics of wet electro-active polymer (EAP). This paper proposes an IPMC actuator using poly-vinylidene fluoride (PVDF)/polyvinyl pyrrolidone (PVP)/polystyrene sulfuric acid (PSSA) blend membrane and explains a bio-inspired walking microrobot using the proposed IPMCs as actuators. The proposed IPMC actuator was fabricated using a PVDF/PVP/PSSA solution with the mixture ratio of 30/15/55. It could generate higher tip displacement and blocking force at low DC voltages compared with Nafion-based IPMC actuator. The PVDF/PVP/PSSA-based IPMC actuators were employed for our bio-inspired walking microrobot. Finally, the bio-inspired terrestrial walking microrobot has the weight of 1.3g and can demonstrate a walking motion with a speed of 0.55mm/s on the 0.2 coefficient of friction surface. Index Terms - ionic polymer–metal composite (IPMC), smart material actuator, walking robot, biomimetic robot. I. INTRODUCTION Nowadays, electro-active polymers (EAPs) play a very important role due to its tremendous advances in polymeric materials technology. It is being used to replace conventional material such as metals and alloys in such fields as electronic, automobile, household goods, medical, etc. There are many different types of EAPs, but they can be divided into two categories, electronic EAPs and ionic EAPs. IPMCs form an important category of ionic EAPs. An IPMC sample is typically composed of a thin ion-exchange membrane (e.g. Nafion, mixture PVDF/PVP/PSSA or pure PVDF, etc.) that is chemically sandwiched between two novel metal electrodes (e.g. Platinum, gold, silver, etc.) or carbon nanotube. With ion-exchange process, positive hydrogen ion (H+) was replaced by positive Lithium ion (Li+). When the ionic polymer is hydrated, the cations (H+ or Li+) associated with the SO 3 í1 groups become mobile, allowing the polymer to conduct cations while anions (negatively charged ions) are fixed to the ionic polymer membrane. Under the electrical field, the mobile cations gathering with water molecules were redistributed from one electrode surface to the other one, resulting in the imbalance internal stress of the backbone membrane. At the anion-rich region, polymer chain contract, while at the cation-rich region, they extend, which makes the IPMC bend to the anode side. In the other hand, when applying mechanical force to the IPMC, the moving of the mobile cations causes the electrical charge at each electrode. This can explain for both actuation and sensing characteristic of IPMCs. IPMCs have attracted much interest in the last decade because of its superior characteristics such as low actuation voltage and power consumption, large tip displacement, good response time, extremely lightweight, simple fabrication process, well working in aquatic environment, ease of miniaturization, and so forth. However, the tip force generated by IPMC is very small, and loss water molecules while working in air condition are limitations of this potential actuator. Therefore, most of the bio-inspired systems using IPMC as the actuators or sensors are operated in aquatic environment where force is not problematic with the aid of buoyancy and where the system work well without any loss of water molecules inside. Fish-like robots that could swim in the water by using IPMC as the fish tail have been developed [1- 3]. A ray-like swimming robot mimicked the pectoral fin of a ray by using IPMC strip [4-5]. Najem et al. [6] and Gou et al. [7] designed the jelly fish type swimming robot by IPMCs to mimic the jelly fish motion. Ref. [8] reported a snake-like swimming robot that consist of 2 IPMC strips and applied periodic input with appropriate frequency and phase shift to make the snake-like swimming motion. Otherwise, the swimming motion with the differences, it is walking motion which could move easily in many kind of terrain not only in aquatic environment but also terrestrial environment. However, it requires the system have to have more force, especially, in bio-system using IPMCs. A lot of effort has gone into overcoming this disadvantage in order to apply this friendly potential in to the bio-microrobot, especially walking robot. Chang et al. used thick Nafion based IPMC (1mm) to generate sufficient force for walking robot. A walking robot (102×80×43 mm, 39 g) with six 2-degree-of-freedom (2-DOF) legs has been designed, implemented, and walked in water at the speed of 0.5 mm/s [9]. Many walking robots using other smart materials have been developed such as RoACH [10] (3 cm long and 2.4g), DASH [11] (10 cm long and 16g), MEDIC [12] (5.5 cm long and 5.5g), HAMR [13] (17 mm long x 23 mm wide and 90mg) and millimeter scale walking robot [14] (4×2.7×2.5 mm). They have used shape memory alloy (SMA) as actuator and demonstrated speed up to 15 body lengths per second on the flat ground. Other reports [15-16] presented the centimeter scale walking robots HAMR 2 (5.7cm long, 2g), HAMR 3 (4.7cm long, 1.7g) using PZT actuator to demonstrated the locomotion of a hexapod with speed up to 4 body lengths per second. These robots showed high-speed 49 978-1-4799-3979-4/14/$31.00 ©2014 IEEE Proceedings of 2014 IEEE International Conference on Mechatronics and Automation August 3 - 6, Tianjin, China