Sensitive hand prosthesis in sight

Gripping comfort is to be improved by new hand prosthesis control

Professor Buchenrieder and his colleagues develop a better gripping comfort of arm prostheses © Universität der Bundeswehr München
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Direct grasping for an item with optimized force control may soon become a reality for many hand prosthesis wearers. For German researchers want to significantly improve the gripping mechanism and the electrical control of hand prostheses. The aim of the research is to determine the grip speed, gripping force and rotational movements for each opening width of a hand proportionally and independently of each other directly from the intensity of the muscle signals.

The current hand and arm prostheses use to control the electrical AC voltages that arise in the contraction of the residual muscles. These so-called myoelectric signals are measured on the skin surface with small electrodes and used to control the prosthesis. An electronic system makes it possible to switch on or off electric motors even at low contraction, which move the middle and index fingers and the thumb over a small gear.

Heretofore, for the opening or closing of a prosthetic hand, a patient must perform an alternative movement, such as extending or angling the hand, to generate control signals with the remaining muscles. To set the control parameters and to control the prosthesis, a longer training phase is necessary to coordinate and practice the movements.

Synchronization of muscle signal and gripping movement

Now, Professor Klaus Buchenrieder and his team of researchers at the Institute of Computer Engineering at the University of the Federal Armed Forces Munich intend to realize a direct grasp without prior adjustment of the desired movement. The improved synchronization of the intensity of the muscle signals and the desired gripping movement is made possible by a measuring and control system developed at the Chair of Embedded Systems and Computers in Technical Systems.

Minimize measurement errors

Buchenrieder would like to reduce the occurrence of disturbances in the measurement of muscle signals by using three instead of two contact points on the surface electrodes. By means of self-developed computer architectures, special hardware and new algorithms, the myoelectric signals should be processed faster and more realistically than previously possible for the control of the prosthesis. "Over the next six months, we will develop a low-maintenance prototype that meets these requirements and allows those affected a life with fewer restrictions, " says Buchenrieder optimistically. display

Buchenrieder also wants to further develop the previous gripping comfort of standard arm prostheses, which access the movement of a finger and the thumb as with a pair of pliers, by means of two independently movable fingers.

(idw - University of the Federal Armed Forces Munich, 15.12.2006 - AHE)