Humantech--Ask the Expert

Ask the Expert--June 16th 2008 Article. See link http://www.humantech.com/resources/newsletter/currentIssue/

Designing for Ergonomics in Assembly: Considerations for the Aging Population


According to Blake McGowan, Senior Consultant and Ergonomics Engineer for Humantech, most safety professionals are concerned about ergonomics and the aging population. When asked why they are concerned, many express fears of anticipated increases in injury rates as their working population ages. However, data suggests that non-fatal occupational injury rates (sprains and strains) are higher for younger workers (≤ 25 years old) compared to the aging population (Jackson, 2001; Salminen, 2004). This is especially true for male populations.
In reality, the two most important issues safety professionals should consider as the workforce ages are:
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Decreases in production performance. Older workers often require increased task completion time, which leads to decreases in production performance (Rahman et al., 2002).
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Increases in quality errors. Many older workers experience reduced hand sensitivity, which results in reduced tactile sensation and more product assembly errors (Ranganathan et al., 2001).
Currently, many organizations understand the positive impacts of ergonomics on productivity performance (for example, lean manufacturing). Organizations have repeatedly demonstrated cycle time improvements and ergonomic risk reductions following the implementation of ergonomic improvements. However, very few have launched ergonomic initiatives focused on reducing quality errors. Several common physiological changes occur as we age that may increase quality errors:
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Movement speed slows during grasping (Carnahan et al., 1993) and reaching (Seidler-Dobrin and Stelmach, 1998
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Movement precision (deceleration) decreases (Walker et al., 1997)
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Range of motion is reduced (Chaparro et al., 2000)
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Muscle strength (grip, push, pull) decreases (Ketchum and Stelmach, 2001)
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Force control decreases, as adults grip twice as hard to compensate (Cole, 1991)
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Force perception decreases (Cole et al., 1991)
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Muscle endurance decreases
Design engineers can assist in reducing product quality errors that occur as a result of these physiological changes by applying 10 simple principles:
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Design parts with self-locating and self-aligning features (chamfers, guides, pins)
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Design for "one-way, right-way" connections (mistake-proofing)
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Design for adequate visual access (eliminate blind assemblies)
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Design for adequate hand or tool access
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Design for adequate tolerances (eliminate overlapping tolerances)
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Design for ease of handling (eliminate slippery, sharp, flexible parts)
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Design for low-force connections or insertions (snap-to-connect)
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Design to eliminate the need for precision or manual alignment
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Design to standardize hardware (minimize or integrate hardware)
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Design to reduce horizontal reach distance (≤ 16" from product edge)