Abstract
Abstract
The fatigue life of pneumatic artificial muscles (PAMs) is a limitation to the development of reliability-intensive applications of soft robots in fields such as medical robotics, transportation, and industrial manufacturing. This article aims at improving the fatigue life of PAMs by (1) providing design principles for durable PAMs under high strains and (2) demonstrating these design principles by developing a representative optimal extensible pneumatic muscle (EPM) in the context of a soft surgical robot case study. Representative performance requirements are derived from an image-guided surgical robot taken as a case study. An experimental design study over relevant EPM geometries reveals three basic fatigue principles governing the failure of PAMs: fatigue limit, abrasion wear, and Hertz contact stress. Using these principles, a new extensible pneumatic muscle made of a silicone tube and a continuous orthotropic restraining sleeve is designed and characterized in terms of performance and fatigue life. Fatigue experiments confirm that the fatigue-optimized EPM can reach 50% elongation for 229,000 cycles, a 10 × improvement in fatigue life compared with currently available PAMs. Other than being optimized for fatigue, the proposed EPM also shows a linear force–displacement behavior and its hollow construction allows for easy integration of a position sensor as well as a telescopic guide that increases static force. The application of the proposed design principles offers a solution to the usual compromise between soft actuators' strain and durability. These principles can be applied to the design of any durable high-strain soft actuator or compliant structure.
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