Design and Analysis of a Linear Digital Variable Stiffness Actuator

In this paper, a novel variable stiffness mechanism (VSM) based on specially designed S-springs made from shape memory alloy (SMA) is developed. Based on the stiffness model, by changing the state combination of the SMA S-springs with different thicknesses, the actuator’s stiffness can be discretely adjusted online. The stiffness adjustment range of the actuator can be conveniently extended almost from 0 N/m to infinity by changing the preset spring angle manually offline without a complex mechanical mechanism or replacing any parts. A linear digital variable stiffness actuator (LDVSA) is also designed with the VSM. Some tests of the SMA S-springs, as well as the actuator’s stiffness under different configurations, comparisons with other actuators and its trajectory tracking capacity are conducted to verify its design. Then, a dynamic model of the actuator is established and its bandwidth is analysed. Based on this, explosive experiments are designed and performed to explore the application potential of the actuator. Experimental results are provided to illustrate the explosive capacity and energy efficiency of the proposed design.