Low-Cost, Continuously Variable, Strain Wave Transmission Using Gecko-Inspired Adhesives

In robotics, high gear reductions are often required when using an electromagnetic motor to drive revolute joints, as in a humanoid robot. Strain wave gears (SWGs), also known as harmonic drives, are often used. However, these transmissions are relatively expensive and have a fixed gear ratio. Here, we present a low-cost transmission that maintains the high reduction of the SWG and enables a continuously variable gear ratio. We achieve this by, first, replacing the teeth of an SWG with a smooth frictional contact to enable continuous gear variation and, second, inverting the gear elements to enable high frictional torque transfer with a low preload via the capstan effect. We choose a gecko-inspired dry adhesive as the frictional material because it has high friction at low normal forces, and is not inherently tacky. We present a model describing the transmission, as well as experimental data gathered from a prototype device that verifies this model and establishes a proof of concept. Our transmission expands the possibilities for low-cost robotic systems.