Phase Change Materials for Controllable Stiffness of Robotic Joints

Snake-like manipulators are well suited for operation in restricted and confined environments where the manipulator body can bend around obstacles to place an end effector at a difficult to access location. They require high stiffness when self-supporting weight against gravity and undertake precision manipulation task, but also require soft properties when operating in complex and delicate environments. A controllable stiffness manipulator has the potential to meet the application demands as it can switch between rigid and soft state.
This thesis experimentally investigates the properties of four materials, (low melting point solder, hot-melt adhesive, low melting point alloy and granular material) as candidates for mechanically altering the stiffness of the joints/modules in snake-like manipulators. These materials were evaluated for bonding strength, repeatability, and activation time. Modules for a snake-like manipulator were fabricated using 3D printing and silicone casting techniques including, for the first time, variable stiffness joints that use hot-melt adhesive and low melting point alloy. These modules were evaluated for stiffness properties and low melting point solder based module was found to achieve a stiffness change 150X greater than the state of the art granular material approach. In addition, the proposed modules were able to support 25X of their own weight.