The virtual constraints based general design method is proposed to solve a dynamical servo control problems
for the Acrobot system, which forcing it to move along the periodic trajectory passing through the given points.The design
of virtual constraint, analysis of system zero dynamics under virtual constraint and periodic property determination of the
trajectory are combined to generate the desired periodic orbit function. Based on a Lyapunov methed, smooth feedback
controller is proposed to overcome the dependency on the analytic solution of the system zero dynamics which exists in
LQR based controller. An example is given and the simulation results show the effectiveness of the proposed general design
method.