Simulated solution for the heterogeneous pallet loading problem and application with a robotic manipulator

Abstract

Palletization is the process of stacking boxes of products on a pallet for convenient transportation of multiple goods. Without the palletizing process automation, workers must manually stack the boxes on the pallet, requiring a large amount of labor and non-deterministic processing time. A fixed automation system can be applied when there is consistency between the type of boxes to load. However, the high initial investment and the significant set-up time represent the main drawback of the solution. A programmable automation system with a robotic manipulator can be introduced to decrease the set-up times when more flexibility is required. In a scenario where there is no consistency on the boxes to be shipped, so as the boxes' size or stack patterns are heterogeneous for different pallets, these solutions are not feasible. The thesis focuses on designing and implementing a flexible method for the autonomous palletization of a heterogeneous (different dimension) set of packaging boxes with a robotic manipulator. The pallet configuration and loading sequence of the boxes are defined by solving a container loading problem, given the pallet's dimension and the set of boxes. The solution is generated through a Biased Random Key Genetic Algorithm (BRKGA), an evolutionary metaheuristic for discrete sequencing problems in combinatorial optimization. The algorithm is implemented with Python and the Pymoo open-source framework. The solution's feasibility is verified on a simulated environment in CoppeliaSim, defined with Python, by exploiting the PyRep toolkit's functionalities. The method's application with a robotic manipulator system is investigated, with proper scaling of the dimensions to meet the available system's limitations. Each box is placed in the manipulator's workspace with a QR code containing its position and dimensions. A camera system is designed to collect the initial information required by the BRKGA, enabling the palletization process.