Control of Pneumatic Artificial Muscle for Bicep Configuration Using IBC Lanka Udawatta * and PGS Priyadarshana * Sanjeeva Witharana † * Department of Electrical Engineering, University of Moratuwa, Sri Lanka Email: lanka@ieee.org † Institute of Particle science and Engineering, University of Leeds, UK Email: switharana@ieee.org Abstract—This paper presents a control algorithm for pneu- matic artificial muscles on bicep configuration. Due to the characteristics such as lower power to weight ratios, high strength and lightweight and easiness of employment, pneumatic artificial muscles have become more attractive actuators for robotics applications. The dynamics equations for bicep configuration were derived with the help of single muscle analysis. Nonlinear dynamic equation was linearized in order to derive the state space model. To obtain the desired tracking performance, inversion based control (IBC) concept was employed. Results show the effectiveness of the proposed methodology. I. I NTRODUCTION In robotics applications, the common actuator technology is electrical systems with very limited use of hydraulics or pneu- matics. However, electrical systems suffer from relatively low power/weight ratio and power/volume ratio. Electromagnetic motors such as dc motors, ac motors, stepper motors, and linear motors, which are widely used in robots at present, fail on the requirements to have light weight and direct transmission capabilities. High power/weight ratio is the major drawback of employing electric motors in these applications. Electric motors have power to weight ratios in the order of 100 (W/kg) and their torque to weight ratios range is more or less within 1-10 (Nm/kg) [1]. In fact hydraulic systems are relatively unreliable and expensive though they have very good power to weight ratio (2000 (W/kg) on average), especially high torques at low speeds. However, their energy source can leak due to the high operating pressures, typically around 20 (MPa) [1]. They can be directly connected to robot joints and compliance is not inherent to this type of actuation but it can be introduced by means of servo valve control. On the other hand, pneumatic actuators are having high power to weight ratios in the order of 400 (W/kg) with less controlling capabilities compared to electrical motors. They have not, however been widely applied in advanced robotics, primarily due to two interrelated problems; difficult to control accurately and compliance (sponginess). The orientation of industrial robotics toward applications needs greater proximity between the robot and the human operator [2]. This has recently led researchers to develop novel actuator sharing some analogies with natural skeletal muscle. A novel pneumatic artificial muscle (see Fig. 1) actuator has been regarded during the recent decades as an interesting alter- native to hydraulic and electric actuators [3]. But main inherent feature of pneumatic muscle actuator is non-linear behavior. The present research works are highly focused on finding out suitable control solutions regarding this. In industrial robotics, accurate positioning of a manipulator or end effecter is one of the most important features. The system is designed to meet high mechanical stiffness and high feedback gains, which improves the accuracy, the stability and the bandwidth of the position control. Gearing is needed to have high torques at low speeds, although direct drive robots, having their joints directly powered by high performance motors, are being developed. A typical DC-drive with gearbox and conventional feedback control often suits this purpose [4]. Fig. 1. A Pneumatic Muscle Robotics application imposes special requirements on the actuation in certain situations. Most importantly, it needs to be lightweight; especially in autonomous robots, adding weights to the system will create new faults like increasing required strength of supportive frame structure and energy demands. Autonomous machine operation, requiring the energy source to be carried along, is a requirement that has not to be fulfilled in a first instance but its possibility needs to be present. Autonomous machine operation can then be guaranteed in a number of ways, for an example, by using on-board small size internal combustion engines and compressors [5]. Now research works have been oriented to make robotic actuators 978-1-4244-1900-5/07/$25.00  2007 IEEE ICIAFS07 35