## 3 Concept and Mechanical Design  
The items to be handled are cardboard boxes placed on a standard Euro Pallet (EPAL), in such a manner that the parcel boxes form at most four vertical layers separated by rigid interlayers. The overall depalletizing task may be subdivided into the following sequential steps:  
* Robot's self-localization within the workspace;
* Autonomous navigation towards the desired pallet;
* Pose detection of boxes on the top layer of the pallet;
* Extraction of boxes from the pallet and placement aboard the robot. A manipulation strategy based on dragging goods aboard the mobile robot is employed, in order to overcome the limitations of standard grabbing manipulation, such as a limited robot payload or the possibility of handling only packages that are able to sustain their own weight. We propose using a serial collaborative manipulator UR10e, provided by Universal Robots (www.universal-robots.com/products/ur10-robot/, accessed on 24 June 2021), installed on a Mir100 AMR, supplied by Mobile Industrial Robots (www.mobile-industrial-robots.com/en/solutions/robots/mir100/, accessed on 24 June 2021) as illustrated in Figure 1. In addition, a scissor lifting mechanism is integrated to collect boxes on board. Thus, the displacement and lifting functions are decoupled. The top of the lifting mechanism is equipped with an idler-roller conveyor to allow items to be dragged and collected. During the manipulation phase, a swivel hatch, mounted on the terminal part of the conveyor, can be set in either open or closed configuration. The former position enables items to be dragged either from the pallet to the conveyor or vice versa, whereas the latter position prevents the boxes from falling out during the AMR navigation. The operational capability of the overall system is influenced by how the cobot and the lifting mechanism are integrated on the AMR. For this reason, three different solutions were analyzed. In the first solution, the cobot is installed on a fixed support, and the installation height is selected by optimizing the cobot workspace with respect to the box locations. In this way, system stability is not excessively penalized, but the fixed cobot location limits the boxes that can be reached. In the second solution, the cobot is installed on top of the lifting mechanism, thus simplifying task execution, since the cobot base is always aligned with the conveyor and the box layer to be handled. As a drawback, a more powerful lifting mechanism is needed. The last solution requires the installation of the cobot on a telescopic actuator, thus leading to independent movements of the cobot and the lifting mechanism. However, cost-effectiveness is penalized. Moreover, in both the second and the third solution, system stability decreases when handling the higher boxes. Another aspect to be considered when choosing the optimal hardware architecture is that, due to the rectangular footprint of the MiR AMR, the cobot and the lifting mechanism can be placed in either longitudinal or transverse arrangement. The former (Figure 2a) enhances stability, but possible interference between the lifting mechanism and the cobot limits the base joint rotation. On the other hand, the latter arrangement (Figure 2b) overcomes such limitations by virtue of the larger distance of the cobot with respect to the lifting mechanism, however, AMR navigation may be more challenging because of the non-ommidirectional MiR steering system. As a result of the design analysis (with the latter being thoroughly described in [28]), we chose the installation of the cobot on a fixed support with a transverse arrangement. It is worth observing that when the AMR is close to the pallet, at most two boxes can be processed, due to the limited workspace  
Figure 1: Overview of the mobile robot and its components. of the robot arm; thus, handling the third box of the same row requires the AMR to reposition on the opposite side of the pallet. This drawback can be overcome by using a cobot with a larger workspace mounted on a larger AMR.