This paper proposes the stability improvement of two wheeled mobile manipulator using nonlinear Proportional Derivative (PD) controller. Nonlinear PD controller is a controller which automatically adjusts its gains according to the stability conditions on running. Lyapunov function based on kinetic energy of the system and position error are used to re-schedule the gains of the nonlinear PD controller. This method will expand the stability margin of the two wheeled mobile manipulator. Further advantages of this method are reducing the parameter uncertainty and difficulty of adjusting gains due to nonlinear nature of system. In the proposed approach, virtual double inverted pendulum is introduced for the control of the two wheeled mobile manipulator. The model based on the double inverted pendulum, makes it easy to design the controller. Here, wheel control and manipulator control are designed separately and unified by using two nonlinear PD controllers. Two nonlinear PD controllers are implemented for better stability. The method proposed in this paper has used nonlinear PD controller in work space of the manipulator controller together with null space control. Here the null space control increases the control stability of manipulator configuration. The effectiveness of the proposed method was confirmed by the experiment of two wheel mobile manipulator.
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