Design of a Variable Mechanical Advantage Mechanism for the Delft Cylinder Hand

The Delft Cylinder Hand and similar body powered hand prostheses require an input force that is too high for daily tasks. The force is perceived as uncomfortable and leads to a high rate of users abandoning their prosthesis. Reducing the input force by increasing the mechanical advantage of the system is not feasible, as this would unfavourably increase the required input displacement to close the prosthetic hand. The goal of the research is to significantly reduce the input force, without exceeding the input displacement limit by designing a variable mechanical advantage (VMA). The VMA is specifically designed for the Delft Cylinder Hand. The input force, when applying a 30 N pinch force, should always be lower than 50±4 N, without compromising the 53 mm maximum input displacement. Two load cases are used to determine the VMA properties, the worst-geometry load case and the realistic-pinch load case. Calculations show that a VMA design is feasible for the Delft Cylinder Hand. In the case of the worst-geometry load case, a design is only feasible when friction losses are excluded, while for the realistic-pinch load case the friction losses can be included. Simulations confirm that the designed VMA mechanism is able to pinch an object with 30 N, with an input force lower than 50±4 N for the feasible loading conditions. Practical testing was too inconclusive to validate the simulation.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin