Situating interruptions in manufacturing assembly

Abstract: Interruptions have been studied extensively, with interruptions experiments where tasks performed on computers are interrupted by another task received on the same computer having receiving much of the focus. Additionally, many of the tasks used in existing research have been designed specifically to test the effect of interruptions on humans by making both the interrupting task and the task being interrupted quite difficult. The studies introduced here show that these commonly used tasks do not accurately represent some aspects of the manual tasks commonly performed by humans outside of laboratory experiments, with the experiments in this thesis focusing on manual tasks in assembly. A notable difference identified here is that interruptions in manual assembly tasks were seen to always contain a negotiation element, meaning that the person being interrupted could always modify to some extent when to respond to interruptions. Another central finding is that breakpoints for smart interruption systems need to be chosen using even more care than suggested by existing research because of an effect that can cause a notification to be completely missed when sent at a point that seemed opportune. This is due to apparent lulls in the activity containing preparation for the next action, or anticipation of action, using the Activity Theory (AT) terms used in the analysis of this effect. AT was identified as a useful tool for the analysis of manual assembly as it supports a hierarchical analysis of the activity and takes into account operator skill (task familiarity) in an easy to understand manner.AT was further used in an observational study where current approaches to interruption management were observed and explored. A surprising conclusion was that classical interruptions, as commonly defined, where one task is interrupted and another task must be completed before resuming the main (primary) task were exceedingly uncommon. This was found to be due to the high task familiarity (skill level) of the workers, the assembly activities being designed to minimise the risk of interruptions, and workers being trained to always finish the current operation before switching to another task. Workers did however engage in conversation and an interesting style of communication, dubbed ebb-and-flow style of negotiation, was identified. The differences between the results found in literature and the results of the studies were synthesised into a theoretical framework, or a collection of theories that work together to support the analysis of interruptions, and a visual support tool for the theoretical framework was created. This visual support tool, called an activity board both binds together the theories in a way that should make the theoretical framework easier to understand, and provides the beginnings of an analysis tool for interruption using the framework.