A Sarcomere-Inspired Magnetic Recruitment Array Actuator for Load-Adaptive Robotic Arm Actuation

Abstract

Artificial muscles hold considerable promise in robotics owing to their lightweight and highly compliant characteristics. Nevertheless, existing bio-inspired actuation still lack human-like functionality and struggle to balance precision with compliance. Therefore, this study designs a Sarcomere-Inspired Recruitment Array Actuator (SRAA) motivated by the fundamental motor units of human muscles. The designed actuator employs a magnetic actuation unit array to realize progressive recruitment and cooperative force generation. A hierarchical structure combined with an integrated position-force control strategy enables dynamic allocation of output according to task requirements, thereby supporting fine-grained position regulation and tunable compliance. This study develops a humanoid robotic arm platform to validate the proposed design. Experimental evaluations demonstrate that the proposed system achieves millimeter-level positioning accuracy and stable mechanical response, while also exhibiting fast dynamic performance and high task adaptability. The robotic arm achieved an MAE of 0.04 mm in the dynamic water-filling task and maintained sinusoidal tracking MAEs below 0.25 mm for actuator displacement and 0.69$^{\circ }$ for forearm angle. The design provides a new pathway for compliant, human-like actuation in humanoids and rehabilitation robots.