Design of compliant robot leg using variable stiffness mechanism

The importance of legged robots is emphasized, as legged robot locomotion allows highly precise performance and wide spectrum of application, even in rough, unstructured terrain.
However, the present challenges in legged robot locomotion are the trade-off between versatility and robustness, and the trade-off between energy efficiency and locomotion speed.
Attempts were made to overcome the challenges of these trade-off, especially by exploiting natural dynamics. Natural dynamics, or also called as passive dynamics, is a dynamic behavior of a system without external interference.
We can observe very often in nature, that human, and animals exploit natural dynamics especially in periodical movements. By exploiting natural dynamics, the system can achieve improvement in lcomotion speed and energy efficiency.

Biological system possess Kinematik structure that allows to exploit natural dynamics without sacrificing versatility, which is antagonistic actuation in muscular system.
The varying elastic actuation, therefore, could be a good solution for the versatility. In order to overcome the second trade-off between versatility and robustness, the idea of using a variable stiffness mechanism in the design of a legged robot is suggested.
VSMs can be seen as an extension of VIAs for more than one DOF by using actuation antagonism inside a PKM structure. To allow stiffness changes, nonlinear springs on joint level are required.