Recent developments in robotics allow the design of work systems with enhanced human robot collaboration (HRC) for assembly tasks. Productivity improvements are a common aim for companies that look into the implementation of HRC. To harvest the full productivity potential of these work systems, an analysis of the HRC work processes is essential. However, a dedicated method for the analysis of productivity in HRC is missing. This paper presents an approach using 3D-cameras to observe the employee in HRC. The approach links this information to robot states. The resulting analysis aims at improving the productivity of the work system e.g. by identifying and reducing balancing losses in HRC. The method tracks the movements of the employees in the HRC area and matches the corresponding robot activities.