DEVELOPMENT OF A HAND EXOSKELETON ACTUATED WITH SMA

Shape Memory Alloys (SMAs) are innovative materials whose potential as actuators is being investigated in different fields because of their smart properties. Indeed, this material can recover a predefined shape if subjected to an appropriate thermomechanical process. The purpose of this thesis is to develop a novel hand exoskeleton actuated by SMA springs for the rehabilitation of patients affected by post-stroke hemiparesis. In the first part of the work the actual state of the art is analysed in order to identify the most suitable solutions for implementing the SMA actuation on an exoskeleton device. Afterwards, the exoskeleton is completely designed from the point of view of the mechanical structure, the electronic circuit, and the control system. From the mechanical point of view, a tendon-driven 4-bar linkage structure is implemented. Different dynamic simulations on INVENTOR confirm the structure dimensions and allow an estimation of the needed forces to overcome the stroke rigidity. The design results in an exoskeleton that actuates the two joints of the index finger and of the middle finger. On the basis of the simulations, two prototypes are realized. The characteristics of the SMA springs used for the actuation are experimentally analysed and the SMA actuator unit is implemented on one of the two prototypes to realize a fully operating exoskeleton. A MOSFET circuit is designed on LT-spice to let a PWM current flow through the SMA springs and heat them thanks to the Joule effect. A control system algorithm based on a threshold control is implemented on an Arduino board for achieving the stroke rehabilitation. The superficial electromyography (sEMG) signal is withdrawn from the healthy forearm of the patient to let the patient control the rehabilitation movement thanks to the self-motion control.