Published online by Cambridge University Press: 09 March 2009
A motion controller for an overhead Cartesian crane in three-dimensional Euclidean (3-D) space is designed under the constraint that the control action belong to a discrete set of assigned values. The design approach rests upon a two-step procedure: first, a constraintfree motion controller is determined that satisfies the required dynamic specifications; second, this controller is replaced with an equivalent controller satisfying the discrete action constraint. The first step is implemented by means of a heuristic 3-D extension of a well-proven 2-D controller, the second step by applying recent sliding mode results. Numerical simulations illustrate the properties of the resulting feedback system under both nominal and perturbed operating conditions.