Enhancement of Thin McKibben Muscle Durability Under Repetitive Actuation in a Bent State

The McKibben muscle can produce a high force-to-mass ratio, beneficial for various applications in the soft mechatronics field. The thin McKibben muscle, which has a small diameter, has the advantage of a high force-to-mass ratio and sufficient flexibility for use in a bent state. This flexibility permits the realization of flexible mechatronics. However, the thin McKibben muscle is easily broken in a bent state while it is very durable in a straight state. Over repetitive operations, the fibers within the sleeve gradually shift, causing the rubber tube inside to protrude and ultimately leading to cracking. This study investigates improvements in the durability of artificial muscles using adhesives to prevent this fiber-to-fiber misalignment. The durability test showed that the adhesive could provide a durability of up to 10,000-times greater than that of a normal thin artificial muscle in the maximum case. Using the thin McKibben muscle with the proposed method, tensegrity modules were fabricated. The durability test revealed a 500-fold increase under an applied pressure of 0.5 MPa. Furthermore, the durability of the adhesive-applied artificial muscles was also confirmed to be enhanced during the dynamic movements of a soft tensegrity robot that throws a ball with 0.7 MPa.