The Effects of Human Interface Design on Wrist Biomechanics during Scanning

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Two window, or “bi-optic” scanners have ergonomic potential to minimize cumulative trauma disorders (CTDs) among grocery checkers. However, not all checkers utilize both windows when scanning. Four, two window scanners were tested to see whether the number of windows used had an effect on wrist acceleration, one of the most predictive indicators of CTD risk. Out of 32 subjects, 14 used only one window while scanning. These subjects were seen to have significantly higher cumulative peak wrist accelerations than those subjects that used both windows. In addition, the productivity of the one window users was significantly lower than two window users. The results indicate that two window scanners can not only increase productivity, but can reduce the risk of CTDs. However, this will only occur if checkers appreciate and choose to use both windows in their scanning activity. The large number of subjects (14 out of 32) that only used one window when scanning indicates a serious human interface problem with these types of scanners. This paper identifies the need for better scanner designs that will indicate to the user the three-dimensional scan zone created by the two windows. The design should influence one to use both windows while scanning so that wrist motions will be reduced. Most importantly, this paper identifies the importance of the relationship between cognitive and biomechanical issues when approaching a human interface problem in a product's design.