A modular-type robotic arm design having effective torque-speed performance as configuration of coaxial-torque synthesis modules

Abstract

As the applications of robotic arms become increasingly diverse, achieving a high payload-to-weight ratio and superior speed performance has become a critical design consideration. In this study, a 7 degrees-of-freedom (DoF) robotic arm based on a coaxial-torque synthesis module (CoSMo) is introduced to meet both of these performance goals. The CoSMo consists of two sub-modules: (1) an extended-coaxial spherical joint module (E-CoSMo), and (2) a concentrically stacked modular actuator (CoSMoA). The CoSMo-based robotic arm (CoSMo-Arm) comprises a 4-DoF CoSMo for shoulder and elbow joints, and a 3-DoF CoSMo for the wrist joint. Due to its unique structural features, actuator torque can be synthesized at the output joint, enabling the CoSMo-Arm to achieve high torque performance with relatively low gear reduction. As a result, the CoSMo-Arm offers a higher payload-to-weight as well as agile motion capability. Two prototypes were fabricated for validation. The first prototype exhibits a payload-to-weight ratio at least 1.45 times greater than that of representative robotic arms referenced in this paper. The second prototype, designed with a lower gear reduction ratio, demonstrates that the proposed mechanism can maintain a high payload-to-weight ratio while also enabling agile motion feasibility. These implementations indicate that the CoSMo-based robot can be designed and adapted for various purposes and applications, particularly advantageous for mobile robotic systems.