Robust disturbance observer based sliding mode control of a planar parallel (3-PPR) manipulator

This study proposes a robust controller in conjunction with the dynamic modeling of an existing three degrees of freedom planar parallel manipulator which can perform effectually in the presence of parameter uncertainties and external disturbances. The planar manipulator discussed here has three legs each with a prismatic-prismatic-revolute (3-PPR) joint configuration and located on the same plane connecting the moving platform which is in the form of an equilateral triangle. Each leg consists of an active prismatic joint, a passive prismatic joint and a passive rotary joint. The dynamic model has been obtained using the Euler-Lagrangian formulation method which is based on the kinetic and potential energies of the system. The proposed controller is based on a sliding mode control scheme with a nonlinear disturbance observer incorporated which aids in eliminating disturbances present in the system which is a result of both disturbances (internal and external disturbances) and parameter uncertainties which might arise due to un-modeled dynamics. Computer based numerical simulations are performed to demonstrate the effectiveness of the proposed control and results confirming the same in the presence of disturbances.