Design and performance of a variable stiffness joint based on electromagnetic force attraction

Purpose This paper aims to introduce a novel design for a variable stiffness joint (VSJ) based on electromagnetic force attraction (EFA). The objective is to provide a compact, energy-efficient solution for real-time stiffness modulation, particularly for applications in rehabilitation robotics and human−robot interaction. Design/methodology/approach The proposed design combines electromagnetic forces, a spring support mechanism and frictional contact surfaces to control stiffness, a mathematical model is developed to describe the interaction between electromagnetic force, spring force and friction. A prototype was built and tested experimentally using materials with different friction coefficients, the data were collected using force sensors and analyzed with MATLAB. Findings The results demonstrate that materials with higher friction coefficients enable greater stiffness variability, while the integration of a PWM controller effectively mitigates overheating and ensures energy-efficient operation. The system successfully validates EFA as a precise method for stiffness control. Originality/value This research offers an innovative approach to stiffness modulation in robotic systems using EFA, unlike traditional mechanical methods, the proposed design is compact, energy-efficient and provides real-time stiffness adjustments. It holds significant potential for rehabilitation robotics and other adaptive robotic applications, particularly where compact, low-power joints with tunable stiffness are required.