TriCoSphere: A High‑Dexterity, Large‑Volume, 3‑Finger Coaxial Spherical Manipulator

Abstract

Designing robotic manipulators often requires balancing dexterity, speed, and payload capacity. While traditional serial-link and cable-driven manipulators offer high dexterity, they struggle to concurrently achieve high speed, and often lack the strength and stiffness required for many applications. To address these limitations, we present TriCoSphere, a novel 12-degree-of-freedom, three-fingered manipulator designed to optimize all three attributes. Each 4-DoF finger employs a Coaxial Spherical Parallel Mechanism (CSPM), which positions all actuators at the base. This parallel architecture minimizes finger inertia for high-speed motion and distributes loads across multiple linkages, enhancing payload capacity. We provide a complete kinematic analysis and develop an efficient inverse kinematics solver for precise fingertip control. Experiments demonstrate that each finger can support a 4.1 kg payload and achieve a motion bandwidth of 6.5 Hz. The manipulator’s grasp range and dexterity are showcased by handling objects from a 20 mm sphere to a 300 mm acrylic ball, as well as performing complex in-hand manipulation tasks. TriCoSphere is cost-effective, robust, and open-sourced to support future research.