A compact twisted string actuation system for robotic applications

Abstract

The research presented here, focus on the development of a compact twisted string actuation system for robotic applications. When coupled to a motor, a twisted string system acts as a high ratio rotary to linear motion convertor. This dissertation starts with a brief description of existing applications of twisted string mechanisms. Then, the first prototype of the twisted string actuation system, built for this research, is presented. The prototype was used for the development of a better understanding of the mechanism and to find its capabilities. Afterwards, and based on experiments performed with the first prototype, a two-phase twisted string actuation system that benefits from an overtwist phase is proposed. In this way, a higher contraction ratio compared to the state of the art could be achieved. Furthermore, since none of the previous mathematical models could predict the linear displacement of the system, for the overtwist phase, an improved mathematical model was developed that can accurately predict the linear displacement over the entire range of motion. Afterwards, the twisted string system was applied for the actuation of a robotic hand. The high contraction ratio that was achieved with the two-phase twisted string system, resulted in a compact and light rotary to linear motion conversion mechanism that could fit inside the palm of a robotic hand, which has around the same size of an adult human hand. Finally, there will be an overview of the most important achievements and conclusions of this research work, along with some future plans for further investigation.