<p>We consider the issue of energy efficient data collection in the context of a mobile robot-aided delay tolerant wireless sensor network (DTSN). The latter is composed of static nodes (SNs), a fusion center (FC) and a mobile robot (MR), which acts as a data ferry in order to reduce energy consumption at the SNs, thereby increasing their lifetime. The considered wireless channel model accounts for both path loss and shadowing. We propose a method to optimise the trajectory of the MR so as to minimise the overall energy consumption of the DTSN, while controlling the latency of the end-to-end transmission and maintaining the number of bits in the SNs' buffers bounded. Simulation results show the effectiveness of the proposed solution in reducing the energy consumption of the DTSN.</p>