Abstract This paper introduces a novel compact discrete variable stiffness actuator, distinguished by its design topology enabling compactness and independent stiffness adjustment regardless of position, without relying on complex stiffness tuning mechanisms. The compactness is achieved through a rotary spring module comprising six linear springs. Variation in stiffness is attained by adjusting the number of engaged elastic elements (springs) using linear actuators. The paper comprehensively covers the design, modeling, prototyping, and control of the actuator. A mathematical model, encompassing stiffness and dynamic aspects of the system, is developed and analyzed. Robust controllers are devised to ensure stability across different stiffness levels and under varying loads. Simulation and experimental findings provide empirical validation of the effectiveness of this innovative compact actuation system, underscoring its suitability for diverse applications across sectors such as manufacturing, healthcare, and assistive robotics.
Hussain et al. (2025) studied this question.