Upper-Limb Shape Memory Alloy Orthosis for Restoration or Improvement of Basic Hand Functions

Shape Memory Alloys have been used in fields of assistive engineering, robotics, medicine and space industry for many years. This paper elaborates the possibility of a hand exoskeleton primarily designed using Shape Memory Alloy (SMA) as actuators and conceptualized around its notable structural transformation characteristics which have been displayed with an electrically induced change of temperature. In this study, an orthotic device was designed to enable hand gripping. The mechanical design of the orthotic device has been modeled in CATIA and electrical schematics have been made on Psim. Many exoskeletons have been developed using electro-mechanical actuators making them bulky. This study is concentrated on making the design simple without compromising on its functionality. The system utilizes two SMA wires, along with an indigenous mechanism to selectively actuate one of them and thus, making the process of gripping easy to perform for the user. The concept proposed removes the requirement of feedback sensors thereby, making the system compact and light. Keeping in mind the one way property of SMA, a retraction link has been included to make the system a two way process. Due to the reliance of SMA on heat to transform, this paper also provides a feasible solution for improving response time of actuators. The mechanism can be tailored to perform other hand postures like fist and point. Also the proposed concept can be used on other joints of the human anatomy and thus, helping in rehabilitation.