Nonlinear Robust Link Space Control for an Electrical Stewart Platform

The complete dynamic model in link space for a general six degree of freedom Stewart platform is developed and a multi-input multi-output (MIMO) nonlinear controller equipped with friction domination is proposed to realize high precision tracking control. Firstly, the complete model of the manipulator´s dynamics is derived by using Lagrange method that describes the motion of the upper platform and the six legs in link space. Then, the coupling force caused by the dynamics of the legs is compensated using the Newton-Euler inverse dynamic formula which makes the compensation algorithm much simple without computing the complex forward dynamics. Finally, a robust tracking control approach is shown to cope with the uncertainties including the friction and the remains of the partial compensation. This method is based on platform´s complete dynamics and has better performance than single-input single-output (SISO) control naturally. Simulation results indicate the proposed algorithm outperforms the conventional PD-gravity controller