A Twisted Elastic Rotary-Rail Actuator (TERRA) Using a Double-Stranded Helix Structure

Mechanically compliant systems have become one of the major concerns in robotics recently. Along with advanced control techniques, various designs of compliant actuators have been steadily proposed for taking advantages of shock absorption, low reflected inertia, and capability of energy storage. One of the well-known examples is a series elastic actuator (SEA) composed of an elastic element and a force transmission mechanism connected in series. Most transmission mechanisms in SEAs use gears that show inherent limitations of backlash and non-backdrivability. While twisted string actuators (TSAs) have been proposed to address the issues of gearboxes, they have narrow speed ranges and relatively short stroke lengths. To overcome these drawbacks, we propose a twisted elastic rotary-rail actuator (TERRA) that can generate elastic contraction motions. The proposed actuator employs a structure of a double-stranded helix for effectively converting rotation to linear contraction as well as allowing for elasticity. The TERRA shows advantages of stability, efficiency, and portability.