A Novel Series Elastic Actuator with Variable Stiffness

Recent studies proposed various robotic joint actuators with variable stiffness to enhance the physical human-robot interaction. However, these actuators were designed on the basis of the planar dynamic models, which limited the optimization of the structure and size of the actuator. This paper proposes a novel concept of incorporating a three-dimensional dynamic model in the design of variable stiffness actuators (VSAs), enabling more compact design of VSAs. A design of VSA is presented according to the proposed concept. The output torque and stiffness are modelled based on the dynamics of the actuator to identify the torque-deflection and stiffness-deflection relations. Simulation is conducted to analyse the dynamic behaviour of the proposed VSA. A prototype is created to evaluate the performance of the proposed VSA through experiments. The simulation results indicate that the proposed concept provides a reasonable principle for stiffness variation of VSAs. The torque estimation accuracy of the model is investigated by comparing the estimated torque with the torque measured by a torque sensor. The result illustrates that the model can estimate the output torque of the proposed VSA accurately. The dynamic behaviour of the proposed VSA is tested through the free vibration test.