Pneumatic Muscle Actuator

It is generally accepted that in the future robots will interact more closely with humans than ever before and heavy, rigid machines are not suited to this due to concerns regarding safety. This has led to the development of biomimetics (the mimicry of biology) were the trend is to try to emulate the 'soft' compliant structure of muscle, bone, tendons and skin and combine this with the power, robustness, accuracy, and endurance of traditional mechanical drives.

Organic muscle provides power for motion on land, in water and in the air, in highly variable climatic conditions and in creatures of all shapes and sizes. Unfortunately muscle is not an engineering technology and is prone to fatigue and damage, characteristics that mean it is not suitable for machine operation. The goal of our research has thus become the development of a biomimetically inspired robot actuation system able to emulate the 'soft' compliant structure of organic muscle.

A particularly interesting actuation system from the perspective of biomimetic systems is the pneumatic Muscle Actuator (pMA). The pMA is formed from a two-layered cylinder consisting of an inner containment liner usually formed from rubber and an outer woven braid material. These are clamped to endcaps that seal the open ends of the muscle and allow the input of compressed air. When pressurized the muscles become fatter and due to the weave pattern of the braided material they reduce in length and it is this motion that can be used to move robotic limbs.

The functional similarity between natural and pneumatic muscles suggests they are well suited to the field of biologically inspired robots and particularly anthropomorphic robots. Our work has developed models of the actuators, improved actuator performance and demonstrated the technology in a range of applications.

Selected publications
S. Davis, J. Canderle, P. Artrit, N. Tsagarakis, D.G. Caldwell. "Enhanced Dynamic Performance in Pneumatic Muscle Actuators". IEEE International Conference on Robotics and Automation. Washington, USA. May 2002.

S. Davis, P. Tresadern, J. Canderle, N.G. Tsagarakis, P. Dodd, and Darwin G. Caldwell. "The Biomimetic Design of 'Soft' Mechatronic Systems". IEEE International Conference on Advanced Robotics. Coimbra, Portugal. June/July 2003.

S. Davis, N. Tsagarakis, J. Canderle and D.G. Caldwell. "Enhanced Modelling and Performance in Braided pneumatic Muscle Actuators". International Journal of Robotics Research, Volume 22, Issue 3. March 2003.

S. Davis and Darwin G. Caldwell. "Braid Effects on Contractile Range and Friction Modelling in pneumatic Muscle Actuators". International Journal of Robotics Research, Volume 25, Issue 4. April 2006.