• adaptive finger
• body powered prostheses

Body powered prostheses require a high input energy for their activation. This force, coming from user’s shoulder movement, makes the use of these devices during daily tasks tiring. Furthermore, body powered prostheses are often heavy and uncomfortable. This leads to a high rate of rejection and abandonment of these prostheses. Reducing the input force, the weight and the discomfort still represent a challenge for these types of devices.
In this study, carried out with my colleague Pasquale Martucci at TU Delft, a hydraulic adaptive finger mechanism for body powered prostheses was developed. The new device allows the reduction of activation force and at the same time a good gripping force.
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. In the latter the object is firmly tightened by the finger. During the first phase users exert a low amount of force to reach the object; in the second one the activation force is amplified to hold the object tightly. This is guaranteed by a pressure intensifier, which provides the amplification of the input force, coming from the shoulder movement.
The new adaptive finger has been developed and tested. The results are satisfactory for the first prototype. Despite the pinch force is lower than the expected, the operating principle is the desired one and the reduction of the input energy for the activation of the prosthesis is noticeable. Many improvements can be made to obtain higher pinch force in the range of the desired activation force.