Pneumatic Muscle: Heat and Mass Transfer in the Cylindrical Membrane

A pneumatic muscle is a one-way reciprocating air motor. It is designed to create apullingforce. The pneumatic muscle return to its initial position is ensured by a reversible strain of its shell. The pneumatic muscle is based on the cylindrical membrane with a rigid bottom and a cover. The membrane cord is formed during the process of cross-spiral weaving from the super-hard synthetic fibers (for example, Kevlar). After the cord has been filled with an elastomer, a strong, deformable and elastic shell is formed. When an overpressure is provided to the internal cavity of the membrane, in a diamond-shaped cell that is formed as a result of weaving cord threads, the tangential diagonal is lengthened and the axial diagonal is shortened simultaneously. Using the pneumatic muscle cord structure of the MAS series produced by FESTO company as an example, we studied a strain of the diamond-shaped cell of the membrane and found the numerical relationships between the value of the pneumatic muscle contraction, the inner diameter of the membrane and the volume of its internal cavity of the pneumatic muscle, which allowed us to develop a mathematical model of an idealized cylindrical membrane in the dynamics of which the strain force of the elastomer that fills the diamond-shaped cell was not taken into account. The paper shows that the cylindrical membrane used in the pneumatic muscle should be considered as a thermodynamic system with full or partial heat and mass transfer. Also discusses the special aspects of using pneumatic muscles in engineering systems as applied to the type of a thermodynamic process. The study of the air movement features in throttling openings of control and management devices, as well as the changes in the state of compressed air during heat and mass transfer allowed us to estimate a length of the transient process in the pneumatic muscle that works as part of the pneumatic load positioning system. The results of the performed studies expand opportunities for predicting the pneumatic muscle dynamics at the design stage of the pneumatic control system, as well as during its operation.