This study focuses on allocation of assembly tasks to the robot(s) and assembly worker(s) in human-robot collaboration assembly systems 4.0. A new method is proposed to allocate tasks of products to a robot and a worker (resources) to minimize the cycle time and hence maximize the output, the single workstation, where the safety issues are considered. Thus, it is not allowed for the worker and robot to process the same product simultaneously to avoid any direct contact between the resources. The proposed method starts with dividing the cycle time for a station into intervals with unknown and unequal lengths. Afterward, a COMSOAL heuristic is utilized to task allocation to resources. The results obtained illustrate the ability of the proposed method to minimize the workstation cycle time and improve productivity.