This paper presents a method for controlling the position, velocity, and acceleration of a rigid and flexible four bar coupler. The dynamic model is formulated using a new form of Kane's equations of motion for constrained systems. The formulation results in equations of motion that are separated in the accelerations. Lyapunov theory is then applied to the dynamic model to develop nonlinear tracking control laws for the rigid and flexible couplers. Numerical simulation is used to demonstrate the system performance showing a significant reduction in the flexible coupler vibration when using active control based on the flexible dynamic system model.