A Modular Variable Stiffness Co‐Bot System Achieving Tasks Flexibility and Contact Compliance

ABSTRACT Enhancing contact compliance and task flexibility is essential for expanding the real‐world use of robotic systems. This paper presents a modular collaborative robot system that combines antagonistic actuation with hybrid soft–rigid variable‐stiffness components, including a modular variable‐stiffness bending joint (mvsBJ), a modular variable‐stiffness rotational joint (mvsRJ), and a modular variable‐stiffness link (mvsL), supported by an integrated control framework. Experimental characterization shows that the mvsBJ achieves a 55.96° bending range and nearly threefold stiffness variation, from 9.16 to 24.72 Nm/rad, through fluidic pressure adjustment. The mvsRJ achieves 145° bidirectional rotation. The platform is benchmarked across repeated trials in healthcare assistance and industrial support scenarios. In an assistive feeding task, a 3‐DoF RBBL configuration operates in a low‐stiffness mode, maintaining bounded force‐tracking variation with mean error drift below 0.16 N. Collision tests across 40–60 mm/s show peak interaction forces increasing predictably from 3.93 to 5.38 N. In an industrial chamfering task, the 2‐DoF RB configuration achieves pressurized rigidity comparable to a conventional mechanical workbench. These results demonstrate plug‐and‐play reconfigurability with reliable adjustable compliance, providing a novel architecture for diverse physical human–robot collaboration applications.