Background
: In 2014, work-related musculoskeletal disorders reached approximately 365,000 cases in the United States (Bureau of Labor Statistics, 2015), highlighting the ongoing need to reduce ergonomic risk in the workplace. To optimize the match between task demands and worker capacity, designers are challenged with several tradeoffs including which body part is more important and how to address worker variability in anthropometrics and capacity. Adjustable design is a classic approach to fit a target population, in contrast to design for the average or extreme. However, adding adjustability can require capital investments, and as such typically requires convincing financial justification. While adjustability may have financial benefits as a result of reducing injury risks, impacts on performance may be more directly related to these benefits.
Purpose
: The purpose of this study was to explore if a causal relationship exist between the level of adjustability, as a variable amendable to design, and both productivity and quality.
Methods
: To simulate a drilling task common in aircraft manufacturing, we built a mock fuselage (Figure 1) that is “scaled-world” representation of the actual work. The simulated fuselage included upper, middle and lower rungs on each side, each with six holes. Adjustability level was the only variable manipulated in the experiment, and it had three levels. In the no adjustability condition (None), the midline of the fuselage was set at mean elbow height, while in the some adjustability condition (Some) it was set at mean shoulder height and two stools were provided (and intended to allow “better” reaches for the higher and lower rungs). In the high adjustability condition (High), participants were allowed to rotate the fuselage about its long axis and to choose its elevation. A commercial drill was used (Figure 2), with a load cell attached to a simulated bit. The size of the probe and holes were chosen to mimic targeted quality requirements, such that any deviation more than ±2° was considered “error”. Audible tones were used to indicate achievement of required force level, errors, and completion of a hole. Productivity was defined by fuselage completion time, with two metrics derived to quantify quality: the total number of errors and the number of defective (i.e., at least one error) holes in a fuselage.
Results and Discussion
: We expected that increasing workstation adjustability will improve both productivity and quality. However, the results suggest that the influence of increasing workstation adjustability depended on the specific level of that added adjustability. High adjustability significantly improved both quality and productivity. Yet, despite the expectation that Some adjustability would reduce postural extremes, this condition reduced productivity (both metrics) and did not have a significant influence on either quality metric.
Conclusion
: Generally, the results support the existence of a causal relationship between enhanced adjustability and improved performance. However, the noted inconsistent influence of adjustability on performance highlights the need to test the efficacy of adjustability prior to its actual implementation. Future work is recommended that more successfully and systematically varies the extent of workstation adjustability. Finally, we are currently analyzing ergonomic risk aspects of the experiment to study the association between performance and ergonomic risk, a relationship critical to financially justify ergonomic interventions.
