Pleated Pneumatic Artificial Muscles for Robotic Applications Bram Vanderborght, Micha¨ el Van Damme, Ronald Van Ham, Bj¨ orn Verrelst and Dirk Lefeber Vrije Universiteit Brussel Department of Mechanical Engineering Pleinlaan 2, 1050 Brussel, Belgium bram.vanderborght@vub.ac.be http://lucy.vub.ac.be Abstract— This work describes the implementation of Pleated Pneumatic Artificial Muscles (PPAM) into innovative robotic applications. These actuators have a very high power to weight ratio and an inherent adaptable compliance. Two applications for which these characteristics give interesting surplus values are described. Nowadays legged robots are gaining more and more in- terest. But most of the robots use electrical drives making these machines heavy and power consuming. An actuator, such as the PPAM lowers the robot weight and the adaptable compliance of the muscles can be exploited to reduce energy consumption. In order to substantiate the benefits of the PPAM, a two-dimensional walking biped ”LUCY” has been built. For robot manipulators, which interact with humans to support them with some heavy-duty tasks, the compliance of the PPAM can assure a ”soft-touch”. Moreover it is possible to estimate exerted force and torque values by measuring the applied gauge pressures in the different artificial muscles. This provides an important tool to generate manipulator force and torque feedback without expensive and complex sensor devices. Index Terms— Pleated Pneumatic Artificial Muscle, Legged Robots, Manipulators I. THE PLEATED PNEUMATIC ARTIFICIAL MUSCLE A pneumatic artificial muscle is, essentially, a membrane that expands radially and contracts axially when inflated, while generating high pulling forces along the longitudinal axis. Different designs have been developed. The best known is the so called McKibben muscle. This muscle contains a rubber tube which will expand when inflated, while a surrounding netting transfers tension. Hysteresis, due to dry friction between the netting and the rubber tube, makes control of such a device rather complicated. Typical of this type of muscles is a threshold level of pressure before any action can take place. The main goal of the new design (Fig. 1) was to avoid both friction and hysteresis, thus making control easier while avoiding the threshold. This was achieved by arranging the membrane into radially laid out folds that can unfurl free of radial stress when inflated. Tension is transferred by stiff longitudinal fibres that are positioned at the bottom of each fold. The graph in Fig. 2 gives the generated force for different pressures of a muscle with initial length 11 cm and unloaded diam- eter 2.5 cm. Forces up to 5000 N can be generated with gauge pressure of only 300 kPa while the device weighs about 100 g. At low contraction, forces are extremely high causing excessive material loading, on the other hand the generated forces drop too low for large contraction. Thus contraction will be bounded between two limits, 5 and 35 %, in practise. Fig. 1. Photograph of 3 contraction levels of the PPAM Fig. 2. Generated forces of the PPAM The artificial muscles have specific properties that are of special interest in the field of legged robots and manipula- tors operating in direct contact with a human: • High torque/weight and power/weight ratios Proceedings of the 2006 IEEE International Conference on Robotics and Automation Orlando, Florida - May 2006 0-7803-9505-0/06/$20.00 ©2006 IEEE 4324