In this paper, the system dynamics of an overhead crane are inverted by servo-constraints. The inversion provides a feedforward control for trajectory tracking of the system output. The overhead crane is inherently underactuated and modeled as a two-dimensional mechanical system with nonlinear system dynamics. Actuators are modeled as first-order systems to simplify implementation and account for velocity-controlled drives. The control based on servo-constraints is shown to be an effective method of trajectory control for overhead cranes. It will be demonstrated that the formulation is solvable in real-time using linear implicit Euler integration. The feedforward solution is made robust by an augmentation with LQR as well as a sliding mode controller. Experiments are conducted on a laboratory crane of 13 m motion range.
