AbstractsEngineering

Body Powered Hand Prostheses provide the user with a replacement for a missing hand. Current body powered hand prostheses are inefficient and require large input forces for the control. Improvements are needed to provide amputees with adequate body powered hand prostheses. The Delft Cylinder Hand, a promising design for an underactuated voluntary closing body powered prosthesis with hydraulic actuation, could be improved further by adding an actively movable thumb. The goal of this research is to increase the grip size of the Delft Cylinder Hand by adding an active thumb. A 1 degree of freedom mechanism is chosen to create a natural looking conical movement of the thumb. A complete design is made for an underactuated hydraulic cylinder hand with moving fingers and a moving thumb. A prototype for this design was made, tested and evaluated on the posed design requirements. The mechanism for the thumb movement adds 24 gram to the weight of the prosthesis. The total weight of the prosthetic hand (176 gram without glove and 241 gram with glove) is still 49 % lower than the lightest available voluntary closing body powered prosthesis. The prototype could grasp objects up to 99 (mm), which is a 32% increase with respect to the current grip size of 75 (mm). For objects with a size above 35 (mm) the mechanical performance is comparable to the current design of the Delft Cylinder Hand. Activation forces of 80 (N) to 90 (N) are needed to apply a pinch force of 15 (N) between the thumb and two fingers. The performance of the prototype without cosmetic glove for grasping small objects is lower than that of the Delft Cylinder Hand. Obtaining a stable pinch grip on small cylindrical objects is difficult because of the uneven movements of the finger phalanges of the prototype without cosmetic glove. Also the pinch forces are lower when grasping small objects compared to the current Delft Cylinder Hand. A pinch force of 5.5 (N) is achieved for an activation force of 100 (N) while grasping an object of 10 (mm) thick compared to a pinch force of 19 (N) with the Delft Cylinder Hand. Adding an actively movable thumb to the Delft Cylinder Hand is a promising improvement. It is possible to obtain an equilibrium between the thumb and the finger phalanges while grasping objects of various sizes with different grip types. The active thumb increases the grip size of the prosthesis. Further research is needed to develop a Delft Cylinder Hand with a movable thumb which meets the performance criteria for a larger range of object sizes.