Hierarchical route choice control for baggage handling systems

We propose a hierarchical control framework for state-of-the-art baggage handling systems where the luggage is transported by fast destination coded vehicles (DCVs). In this control framework switch controllers provide position instructions for each switch in the network. A collection of switch controllers is then supervised by a network controller that mainly takes care of the route choice instructions for DCVs. The route choice control problem is problem is a nonlinear, mixed integer optimization problem, with high computational requirements, which makes it intractable in practice. Therefore, we present an alternative approach for reducing the complexity of the computations by approximating the nonlinear optimization problem and rewriting it as a mixed integer linear programming (MILP) problem for which solvers are available that allow us to efficiently compute the global optimal solution. The solution of the MILP problem is then used in computing optimal switch control actions. For a benchmark case study we compare the hierarchical control with centralized switch control. The results indicate that the proposed hierarchical control offers a balanced trade-off between optimality and computational efficiency.