Assembly - February 2009 - (Page 46) Workstations include torquing, applying downward force or working at unusual angles. “Sometimes, replacing the tool itself adds benefit to the user, especially if the new one is electrically or pneumatically driven,” says Verrill. “Supporting that tool via a torque arm or tool trolley is also a key factor to consider. This makes the tool readily available for the operator’s use without the need for excessive muscle strain.” Another important factor to consider with workstations is the storage of materials, supplies and other products necessary to complete an assigned task. “Organizing these items within an optimum working envelope minimizes reach and awkward motions,” explains Verrill. “As a side benefit, the added organization allows for quick identification by the user and enhances productivity. Of course, straight or angled shelving is one possible solution; but, swing arm accessories for parts cups, monitors and keyboards are even more beneficial.” Guideline Challenges Applying ergonomic guidelines to an assembly environment is not easy because of the dynamic, high-mix nature of the work. “Variability in product manufacturing and assembly requirements, as well as variations in processes and tools from line to line, make it very difficult to provide specific ergonomic guidelines,” says Waters. [“While] general ergonomic workstation layout guidelines have been provided, some customization is usually needed to make the solutions work most efficiently.” Some experts suggest tackling ergonomic guidelines as a team effort. “The first thing the team should do is acquire any existing guidelines that would be applicable to their industry or specific design project,” says Maynard. “Recommendations for designing a workstation are available. Existing guidelines can save a lot of time and [help avoid] reinventing the wheel. “The biggest mistake I see is where engineers design a new assembly operation, including equipment, without considering ergonomics and then, after [encountering] problems, spend additional funds to correct their mistakes,” notes Maynard. “Anthropometric data bases exist and references are available on recommended heights for fixed and adjustable workstations, sitting or standing. The ANSI B11 TR1 document is intended to provide useful guidance for all equipment design, not just machine tools.” Unfortunately, misunderstanding or misinterpreting ergonomic guidelines often hinders manufacturing engineers. “The human body is not as consistent as a metal structure, and people are all different,” explains Greenwald. “One of the most common answers we give engineers when asked for a ‘number’ is that it depends. “The answer may depend on the task performed, the posture the worker must use and how often it is performed,” Greenwald points out. “An answer given without all the information is most likely the wrong answer, and teaching users to see the full picture can be a challenge.” A This illustration depicts some recommended vertical work zones. The upper limit is set by the 95th percentile female’s shoulder height. The lower limit is set by the 95th percentile male’s knuckle height. The lower limit of the zone not recommended for repetitive work or heavy lifting is set by the 95th percentile male’s knee height. Illustration courtesy Ergonomics Center of North Carolina An anthropometric wheel can be used to make assembly tasks and workstations more ergonomic. Photo courtesy Ergonomics Center of North Carolina 46 ASSEMBLY / February 2009 www.assemblymag.com http://www.assemblymag.com
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