Degrees of freedom

grabcad

Issues with current prostheses include: a) lack of adaptability to object shapes, necessitating replacement terminals; rigid connection to drive mechanisms causing motion blockage in other fingers when one is in contact with an object. b) Holding force proportionality to cable tension is uncertain. Raptor-type prostheses are suited for small items but lack large holding forces. A potential solution: a hydraulic system with flexible, bendable fluid pressure fingers, valves, feedback sensors, and a controller. Though expensive, a mechanical approximation can be created by adding an extra degree of freedom for adaptability. First, the finger itself, able to capture objects due to its bicycle-chain-like design, allowing 20 degrees of bending towards the palm side. Flexion is provided by nonelastic cable and returned to neutral by elastic cables, with each finger element printable. The second adaptive element is a spiral spring, which bends when a finger touches an object, maintaining force and diameter until further cable movement reduces diameter and increases holding force. This concept requires further improvement and production preparation.