Efficiency testing of hydraulic artificial muscles with variable recruitment using a linear dynamometer

When a task calls for consistent, large amounts of power output, hydraulic actuation is a popular choice. However, for certain systems that require short bursts of high power, followed by a period of low power, the inefficiencies of hydraulics become apparent. One system that fits this description is a legged robot. McKibben muscles prove to be a wise choice for use on legged robots due to their light weight, high force capability, and inherent compliance. Variable recruitment, another novel concept for hydraulic actuation, offers the ability to further improve efficiency for hydraulic systems. This paper will discuss the efficiency characterization of variable recruitment McKibben muscles intended for use on a bipedal robot, but will focus on the novel test apparatus to do so. This device is a hydraulic linear dynamometer that will be controlled such that the muscles experience similar force-stroke levels to what will be required on a bipedal robot. The position of the dynamometer's drive cylinder will be controlled so that the muscles experience the proper position trajectory that will be needed on the robot. The pressure of the muscles will be controlled such that the force they experience will mimic the forces that occur on the robot while walking. Hence, these dynamic tests will ensure that the muscle bundles will meet the force-stroke requirements for the given robot. Once these muscle bundles are integrated onto the walking robot, the power savings of variable recruitment McKibben muscle bundles compared to the traditional hydraulic system will be demonstrated.