Artificial muscles: actuators for biorobotic systems

Abstract

Thesis (Ph. D.)--University of Washington, 1999Biorobotic research seeks to develop new robotic technologies based on the performance of human and animal neuromuscular systems. The development of one component of a biorobotic system, an artificial muscle and tendon, is documented here. The device is based on known static and dynamic properties of biological muscle and tendon which were extracted from the literature and used to mathematically describe the unique force, length, and velocity relationships. As biological tissue exhibits wide variation in performance, ranges are identified which encompass typical behavior for design purposes.The McKibben pneumatic actuator is proposed as the contractile element of the artificial muscle. A model is presented that includes not only the geometric properties of the actuator, but also the material properties of the actuator's inner bladder and frictional effects. Experimental evidence is presented that validates the model and shows the force-length properties to be muscle-like, while the force-velocity properties are not. The addition of a hydraulic damper is proposed to improve the actuator's velocity-dependent properties, complete with computer simulations and experimental evidence validating the design process. Furthermore, an artificial tendon is proposed to serve as connective tissue between the artificial muscle and a skeleton. A series of experimental tests verifies that the design provides suitable tendon-like performance.A complete model of the artificial musculo-tendon system is then presented which predicts the expected force-length-velocity performance of the artificial system. Based on the model predictions, an artificial muscle was assembled and subjected to numerous performance tests. The results exhibited muscle-like performance in general higher activation pressures yielded higher output forces, faster concentric contractions resulted in lower force outputs, faster eccentric contractions produced higher force outputs, and output forces were higher at longer muscle lengths than shorter lengths. Furthermore, work loop tests used to experimentally measure the sustained work output during typical stretch-shortening cycles indicate the capacity to perform work increases with the magnitude of activation and is a function of both velocity and activation timing