Less is more! Support of Parallel and Time-critical Assembly Tasks with Augmented Reality

Manual assembly tasks require workers to precisely assemble parts in 3D space in parallel steps. Often, additional time pressure further increases the complexity of these parallel tasks (e.g. in adhesive bonding processes). The performance in parallel tasks is heavily influenced by the capacity of the working memory, which is often overwhelmed if rules and states of too many tasks have to be remembered or perceived. Therefore, we propose to use Augmented Reality (AR) to investigate how visual assistance with parallel tasks can affect worker performance in time and spatial dependent process steps. In a user study, we compare three conditions: AR instructions presented (a) One task, (b) Two tasks, and (c) Four tasks per step on a tablet. For instructions we used selected work steps from a standardized adhesive bonding process as a representative for common time-critical assembly tasks. Our results show that instructions with multiple displayed tasks simultaneously per step can improve the process time but also increase the error rate and task load. The work instructions with less displayed tasks per work step showed better subjective results among participants, which may increase motivation, especially among less experienced workers. Our results help designers and developers to design assistance systems for time-critical and simultaneously executable assembly tasks, while considering process times, error rate and task load.