Highly Dynamic 2-DOF Cable-Driven Robotic Wrist Based on a Novel Topology

Abstract

This letter presents a highly dynamic cable-driven robotic wrist with two degrees of freedom (DOFs). It is based on a novel topology that combines three passive cables for kinematic constraint and the minimal number of active cables for the full control of a movable platform in two rotational DOFs. For a certain geometry of the wrist, the workspace is analyzed using the structure matrix. To control the motion of the wrist, the use of an inertial measurement unit is proposed to directly estimate the orientation and angular velocity, contrarily to the majority of previous cable-driven mechanisms whose control relies on the forward kinematics. Based on the measured data, a standard cascaded controller calculates target torques about two fixed axes of rotation, which are converted into target tensions for the three active cables by the existing closed-form solution. The proposed concept is validated with a hardware prototype. A quasi-static experiment shows that the wrist covers a workspace of up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm 55^{\circ }$</tex-math></inline-formula> about both rotation axes. Highly dynamic rotations are demonstrated by step responses with an angular velocity of up to 700 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> /s.