Performance Evaluation of a Variable Stiffness Joint Based on Electromagnetic Force Attraction

Variable stiffness joints (VSJ) inherently exhibit non-linear stiffness characteristics, which can introduce complexity when evaluating their performance. Specialized evaluation methods and customized modeling techniques are often imperative for an accurate assessment of their behavior. In this paper, we present a performance evaluation method of a variable stiffness joint (VSJ) driven by electromagnetic force attraction (EFA). The experimental setup comprises one rotational joint with two links, a commercial electromagnet, a slider support, a permanent magnet, three contact surfaces, a camera, a ring support, and a variable weight load. The variable stiffness properties are modulated within a voltage range from zero to twelve volts, and their efficacy has demonstrated a direct correlation with the friction coefficient of the contact material. This evaluation methodology has proven effective within our design constraints, offering a practical solution for the development of variable stiffness devices using rotational joint mechanisms.