Simulation Modeling and Control of an Elastic Shaping Antagonistic Variable Stiffness Actuator

Position--stiffness regulation of antagonistic variable stiffness actuators (VSAs) involves coupled nonlinear dynamics, parameter uncertainty, and feedback states that are not directly measured. This paper addresses this challenge through a simulation-based workflow that integrates elastic shaping, model verification, and layered nonlinear control. This study builds on a previously developed actuator comprising two crossed four-bar compliant transmission elastic units. Its optimized elastic mapping provides the structural basis, with an ADAMS torque-curve root mean square error (RMSE) of 2.57\,N\!·\!mm against the target. A control-oriented analytical model is implemented in Simulink and compared with the independently executed ADAMS model under matched inputs. The maximum joint-angle RMSE across the tested cases is 4.66×10⁻³\,rad. A layered controller combines extended Kalman filtering for state reconstruction, feedback linearization for nominal decoupling, and adaptive sliding-mode control for residual compensation. At the end of the nominal simulation, the joint-angle error is approximately 3.14×10⁻⁵\,rad. The stiffness error is 3.07\,N\!·\!mm/rad relative to a target of 50\,N\!·\!mm/rad. Parameter-variation and ablation tests assess tracking performance and the effects of the controller modules within the evaluated conditions. The resulting workflow links structural-response modeling, state estimation, and robust control assessment, supporting repeatable comparisons beyond nominal tracking alone.