It takes two: Cargo loading plans for an autonomous unloading of trucks with skid robots

Skid robots represent a recent innovation in the field of autonomous mobile robotics. Two independent skid robots can move below a pallet, and – after being digitally linked – initiate their lifting mechanisms to jointly move the pallet omnidirectionally toward its destination. Their ability to navigate through the fork openings of a blocking pallet and retrieve a blocked pallet sideways (without requiring double handling) adds flexibility to logistics processes such as the autonomous unloading of a truck’s cargo area. Against this backdrop, this paper investigates the optimization of cargo loading plans for trucks to enable skid robots to retrieve pallets from the cargo area across a set of potential truck tours, thereby eliminating double handling. We formulate the resulting Skid Truck Loading Problem (STLP), prove structural properties, and propose an efficient mixed integer program. Using the latter, we show that skid robot usage can significantly improve unloading processes over traditional front-only unloading with forklifts.