In this paper, we deal with the problem of Robust schedUling for wireLess charger nEtworks (RULE), i.e., given a number of rechargeable devices, each of which may drift within a certain range, and a number of directional chargers with fixed positions and adjustable orientations distributed on a 2D plane, determining the orientations of the wireless chargers to maximize the overall expected charging utility while taking the charging power jittering into consideration. To address the problem, we first model the charging power as a random variable, and apply area discretization technique to divide the charging area into several subareas to approximate the charging power as the same random variable in each subarea and bound the approximation error. Then, we discretize the orientations of chargers to deal with the unlimited searching space of orientations with performance bound. Finally, by proving the submodularity of the problem after the above transformations, we propose an algorithm that achieves (1/2-ε)-approximation ratio. We conduct both simulation and field experiments, and the results show that our algorithm can perform better than other comparison algorithms by 103.25% on average.