A Novel Hybrid Serial-Parallel Shoulder Mechanism for Humanoid Robots: Design and Workspace Analysis

This paper presents a novel 4-DOF hybrid se-rial-parallel shoulder mechanism for humanoid robots, designed to enhance workspace coverage while maintaining a compact, human-like form. The mechanism is composed of two integrated substructures: a serial chain and a fully parallel subsystem. This hybrid approach addresses the challenges of achieving large pitch, yaw, and roll ranges under size and anthropomorphic constraints. The design is tailored for the HYDROüD humanoid robot, with a focus on developing compact and smart joints suitable for human-robot interaction. To approximate anatomical constraints, the shoulder region is modeled as a conjoined conical volume representing the upper trunk and upper arm. The kinematic model is validated through numerical workspace analysis, demonstrating the hybrid architecture's effectiveness in expanding motion capabilities within a restricted envelope.