Design and Analysis of a Novel Variable Stiffness Continuum Robot With Built-in Winding-Styled Ropes

Continuum robots driven by rods have a wide range of applications, such as detection and maintenance tasks in unstructured environments. However, their inherent nature of flexibility also limits their function. Thus, variable stiffness mechanisms for continuum robots have consistently attracted the attention of researchers in recent years. In this letter, a winding-styled rope inspired by snakes' behavior is first built into the constraint disk of a rod-driven continuum robot. Combined with shape memory alloy (SMA) spring, the winding ropes perform a variable stiffness or 'lock' function by adjusting the friction between the ropes and rods. A maximum static friction is up to 2 times the spring tension according to the test results. Based on the fitting relationship between SMA spring tension and friction, the established kinetostatics model can predict the manipulator configuration. Furthermore, comparative experiments proved that the stiffness change is mainly caused by the proposed mechanism. By controlling the temperature of SMA, the variable stiffness of the manipulator is achieved. The C-shape has a maximum stiffness of 0.03505 N/mm and that this shape has a maximum stiffness increase of 300%.