JAMS: A high-dexterity 3-DoF bionic joint actuator with multi-drive hierarchical output and spherical rotation mechanism

Achieving anthropomorphic agility in robotic systems remains a fundamental challenge, heavily constrained by the mechanical limitations of conventional serial-link actuators. Current joint architectures suffer from an inherent trade-off between torque density, structural compactness, and kinematic singularity, failing to replicate the complex and coupled spherical motion of biological joints. To bridge this gap, this paper proposes a high-dexterity 3-DoF dexterous joint actuator (JAMS) by in-depth mimicking the bionic advantages of the human hip. Unlike traditional decoupled designs, JAMS introduces a load-adaptive hierarchical actuation strategy that synthesizes power from three parallel motors via customized differential bevel gear and spherical gear trains. This architecture enables omnidirectional rotation around a spatially fixed center, effectively resolving the kinematic redundancy and structural bulkiness of serial equivalents. A comprehensive kinematic model is derived to map the complex gear coupling, facilitating the development of an effectively singularity-free motion control algorithm implemented on a custom dual-MCU embedded controller board. Experimental results demonstrate that JAMS achieves an extensive operational space of 360 ° × 250 °×360° and a theoretical rated torque of 21.5 N·m, exhibiting high torque density within a compact volume. Trajectory tracking experiments verify the actuator’s capability to track selected human hip reference trajectories under scaled-duration gait-cycle conditions, with a composite kinematic-fidelity score of 95.1%, demonstrating its fundamental kinematic feasibility. By integrating multi-drive hierarchical output and spherical rotation mechanism, this work presents a validated mechatronic solution that overcomes long-standing engineering bottlenecks, offering a modularized architecture for multi-DoF robotic joint design, with potential relevance to humanoid robots, robotic arms, and future wearable mechanisms.