McKibben artificial muscle realizing variable contraction characteristics using helical shape-memory polymer fibers

McKibben artificial muscles that consist of a rubber tube and a sleeve with knitted fibers have multiple advantages, including flexibility, low cost, and lightweight. Therefore, they are a prospective driving source for devices and robots used in the medical welfare field. The McKibben artificial muscles generate contraction motion by applying pneumatic pressure, and the contraction characteristics depend on initial knitting angle of the fibers. Namely, the contraction characteristics are decided during the fabrication process. Generally, a system with multiple artificial muscles has multiple regulators or valves to drive them with different contraction amount individually. This results in increased size, weight, and cost. To solve this problem, we proposed a novel artificial muscle structure that can change contraction characteristics on site with ease. The actuator has helical shape-memory polymer (SMP) fibers as sleeve fibers. Owing to shape fixity which is a unique function of SMPs, the angle of the helical SMP fibers, that is equivalent to the knitting angle of the sleeve fibers, can be varied even after fabrication, and contraction characteristics can be changed. Different contraction characteristics of a fabricated artificial muscle were confirmed experimentally by changing the angle of the helical SMP fibers.