Finite Element Analysis and Utilization of MCKibben Artificial Pneumatic Muscles for a Robotic Lower Leg Model

Pneumatic actuators have been established to behave like real life muscles. Although these types of actuators have been around since the 20th century, and is commercially available, the researchers of this study fabricated their own McKibben pneumatic muscle actuator from commercially available PET braided sleeving, latex penrose tubing, and 3D printed end fixtures. The use of CAD software, like Autodesk Inventor and Autodesk Fusion 360, made it possible to model components required to make a working actuator and also perform a static structural finite element analysis in ANSYS Mechanical to evaluate its performance in isotonic and isometric contractions. Moreover, this software enabled the researchers to model and fabricate a robotic lower leg model that imitate the bone structure and the number of muscles in a human lower leg. The finite element model shows good correspondence with the theoretical and experimental models used in this study. For a pressure of 40 psi (0.27579 MPa), the contraction ratio of the muscle is around 25% for a load of 10N and is used as the minimum contraction of the muscles for lower leg model. This contraction was used as a baseline in calculating the minimum working length of the McKibben PAM. The researchers were able to imitate the movement of the foot. Good correspondence was evident for motions involving inversion, eversion, and dorsal flexion when compared to humans. However, the range of motion for plantar flexion was not achieved due to an inadequate pressure required to contract the muscles to achieve the desired motion.