Development of a Hydraulic Artificial Muscle With High Force Density

Abstract

The actuation of mechanism like exoskeletons or devices for medical rehabilitation by means of fluid artificial muscles are convincing solutions due to their light weight, exceptional power capacity, remarkable resiliency, and low investment costs. The artificial muscle consist of an inner elastomeric hose surrounded by a textile, braided and reinforced by aramid fibers. The muscle is activated by fluid supply with a radial expansion of the inner pressurized hose accompanied by a corresponding axial contraction. Consequently circumferential stress in the textile reinforcement of the muscle converts into axial contraction force. The focus of this project is the development of high power hydraulic muscles that enable a significant higher pressure level as well as force density than known artificial muscles. Prototypes of new hydraulic artificial muscles have been developed and experimentally evaluated by means of a customized hydraulic test setup. Relating to the initial length of the muscle without fittings, a contraction of 32% has been measured. In this experiment the associated pressure level is 5 MPa. In a second experimental test the force depending on pressure has been measured and a high force density per mass of 60 kN/kg has been calculated.