Model-based position tracking control for a 6-dof electrohydraulic Stewart platform

In this paper, a position tracking controller for a six-degree-of-freedom (dof) electrohydraulic Stewart platform mechanism is developed that includes a fast inner model-based force tracking loop. A full rigid body model and an electrohydraulic actuator model, including friction and servovalve characteristics are employed and described by a set of integrated system equations. The control analysis is based on a nonlinear input-output linearization control approach. The developed control law also contains a PD part, responsible for the exponential convergence of the tracking error to zero. Simulations with typical desired trajectories are presented and a good tracking performance is obtained.