TriCoSphere: A High‑Dexterity, Large‑Volume, 3‑Finger Coaxial Spherical Manipulator
Runze Hu, Zhengying Zhu, Jinyu Li, Yatao Leng, Jingshuai Liu, Chenxi Xiao
AI summary
Problem
Current robotic hands struggle to simultaneously achieve high dexterity, fast motion, and strong payload capacity due to conflicting design requirements like distal inertia, cable friction, or limited workspace in parallel mechanisms.
Approach
The authors design a 12-DoF three-finger hand where each finger uses a coaxial spherical parallel mechanism with all actuators mounted at the base, minimizing inertia and distributing loads, alongside a real-time differential inverse kinematics solver.
Key results
- 12-DoF manipulator with three 4-DoF parallel-kinematic fingers
- 4.1 kg static payload capacity per finger using low-power motors
- 6.5 Hz closed-loop position-control bandwidth for high-speed motion
- Successful in-hand manipulation and grasping of objects from 20 mm to 300 mm
Why it matters
It provides a robust, cost-effective blueprint for high-performance dexterous manipulation in dynamic, human-centric robotic applications.
Abstract
Designing robotic manipulators often requires bal- ancing 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.