The absence of the hand causes massive, physical and psychological restrictions in daily life. The use of a prosthesis can compensate for these problems and enables patients to lead a less restricted life. Meeting the functional and aesthetic requirements of a prosthesis usually entails high costs in development and construction. At the Institute for Medical Device Technology (IMT), research is being conducted into medical devices and systems from the perspective of low-cost, in order to be able to serve low-income sections of the population.
As part of the LILO-Hand project, a model of a 3D-printed prosthetic hand with an actively executed grasping movement was developed and built. A twisted string actuator (TSA) is used for actuation. The strings of the drive are twisted by the rotation of the shaft of an electric motor and a tensile force is generated. This inflects the fingers. In order to enable variable grasping, a compensating mechanism is integrated into the hand prosthesis that adapts the curvature of the fingers to the object being grasped. Thus, flexion and extension of the index finger to the little finger and the thumb can each be operated with a motor.
The components of the mechanism are manufactured using 3D printing. The construction of the two TSAs requires the calculation of the parameters for the design of the drive unit. In addition to this calculation, the appropriate electric motors as well as other purchased parts for the electronics are selected under the low-cost aspect. After the procurement and production of all components, the assembly and functional tests are carried out. After these, improvements are made to the design and construction.
Finally, by using only two electric motors and the TSAs, a lightweight and low-cost model of a hand prosthesis is built. With this model, it is possible to grasp large objects through the perimeter grip, but not with the tweezer grip. This will be implemented as part of a further development.
- Mühlbauer P, Löhnert L, Siegle C, Stewart KW, Pott PP, Demonstrator of a low-cost hand prosthesis, IFAC, 12.-17.7.2020, Berlin