Abstract
As a promising application of cobots in labor-intensive warehouses, human-robot collaborative order picking systems provide a flexible and human-friendly picking solution by capitalizing on the best attributes of human pickers and robots. Few studies have determined operation modes of human-robot collaborative order picking systems to be beneficial to efficiency, cost, and the well-being of human workers. We identify four human-robot collaborative modes for order picking: single robot to single picker (couple), single robot to multiple pickers (SR-to-MP), single picker to multiple robots (SP-to-MR), and multiple pickers to multiple robots. For each mode, we establish a fork-join queuing network (FJQN) model to analyze system performance and apply a fatigue-recovery model to estimate the fatigue of the pickers. The proposed FJQN and fatigue-recovery model are validated by simulation. Although the throughput time and picker fatigue in the SR-to-MP mode can benefit from an appropriate zoning policy, we find, interestingly, that the zoning policy cannot reduce the throughput time in the SP-to-MR mode. The SP-to-MR mode is economical if a warehouse does not pursue a swift throughput time. A well-capitalized warehouse can adopt the SR-to-MP mode to improve the throughput time further in a more human-friendly manner.
