Design and Fabrication of Millimeter-Scale Crossed-Cylinder Wrist Mechanism with Two Degrees of Freedom

This paper describes the design and fabrication of a 2-DOF wrist mechanism suitable for fabrication with maximum dimension on the order of 2–4 mm. The design is based on the idea of 2 half-cylinders in contact such that their axes lie orthogonal to each other. In that way, each cylinder can roll parallel to the other cylinder’s axis, giving 2 rotational degrees of freedom. To constrain the cylinders’ motion, unique gear teeth are designed that allow rolling motion in either orthogonal direction, but constrain all other motions. Contact can be guaranteed using a compressive force acting to push the cylinders together. We first demonstrate the design at centimeter scale using FDM 3D printing. Based on the smooth motion achieved, we fabricate a wrist with maximum dimension of 3 mm using layered sheets of carbon nanotube composite material. Each sheet is individually patterned using photolithography.