Artificial upper limb development, simulation and control

Abstract

The artificial upper limbs are widespread in the amputees community and have two distinct aims: to restore the aesthetic or the mechanical function of the limb. Functional prostheses can be passive - with friction joints - or active. The last ones can be classified as "body-powered" or "externally-powered". The "externally powered" are currently supplied by electrical actuators and driven by EMG signals: if the active joints are more than one they are driven sequentially and the system includes a selector. Over a certain number of active axes this approach is stressing and produces very unnatural movements. This is one of the reasons why, at present, shoulder joints are only passive. An innovative active shoulder with two d.o.f. based on a differential gear is presented. It is a component of our total artificial limb (4 or 5 d.o.f.) for which a new approach to the driving system has been studied. In this case it is asked to the patient only to try to drive the hand in the space independently by the other joints. Discarding the sequential approach, the relative motion of head and trunk is chosen as command signal for the preliminary driving tests and a virtual reality system have been built to evaluate the driving algorithms. The head-trunk relative motion is measured by an instrumented spatial linkage. The results of two algorithms has been analyzed and compared. Future development will concern a miniaturized device for collecting kinematics data, the improvement of the command algorithms and some feedback for the prosthetic limb.