• body powered prostheses
• adaptive finger

Body powered prostheses work by using muscular movement of the users. By pulling a cable, linked to the harness, the terminal device opens or closes allowing the grip. These prostheses require a high cable operation force. This energy makes the use of these devices during daily tasks tiring and often harness leads to pain and vessels damage. Even if the activation force is very high, gripping performance is not satisfactory, especially considering the multi-articulated hands as a terminal device. For a finger of 80 mm length, a torque of 2400 Nmm is required to produce a pinch force of 30 N. The described factors lead to a level of rejection and abandonment of these prostheses to 45%.
In this study, carried out with Sara Cirelli at TU Delft, a hydraulic adaptive finger mechanism for body powered prostheses was developed. The operating principle is based on the concept of a biphasic system. Any handgrip could be divided in two main steps: “reaching” (or “sizing”) and “grasping” phases. The former represents the approach of the hand toward the object using the minimum amount of activation force. In the latter the object is firmly tightened by the fingers, through a minimal displacement and a high strength.
The new device allows the reduction of activation force, thanks to the Pressure Intensifier developed and tested by Cirelli, and at the same time guarantees a suitable gripping force, thanks to the Distal Cylinder, a small-sized hydraulic cylinder inserted into the fingertip.
In this thesis work the Distal Cylinder is presented, from the concept generation to the evaluation phase. Thanks to this device it is possible to eliminate the disadvantageous lever that is created during the gripping phase between the metacarpal joint and the distal part of the finger, since the force exerted by the piston acts directly on the object to be grasped.
In addition to the Distal Cylinder, in this thesis, the middle and distal phalanges were developed in order to be integrated into the Delft Cylinder Hand 4.0, available at TU Delft. The tests conducted on the Distal Cylinder (standalone) showed satisfactory results. With an activation force of 43.13±3.67 N (mean±SD) the finger is able to exert a pinch force of 23.15±2.10 N. Finally, the whole hydraulic system (including the Distal Cylinder and the Pressure Intensifier) was successfully integrated into the Delft Cylinder Hand 4.0 and tested. The functionality of the hand was improved by the new systems developed.