Ergonomics Analysis & Recommendations
Anthropometry
In order to make the Adjustable Sailing Seat able to fit several different individuals, we have decided to use the standard, average body dimensions of the 95th percentile male and 5th percentile female. The 95th percentile values for males represent the taller members of the population, and therefore the largest dimensions for which we will be designing the system. The 5th percentile values for females represent the shorter members of the population, and are therefore the smallest dimensions which the system will accommodate. Designing for these percentiles means that the design range will accommodate approximately 90% of the population.
The anthropometric databases consulted were the Anthropometric Survey (ANSUR) database, for the most part, and also the Business and Institutional Furniture Manufacturing Association (BIFMA) Ergonomic Guidelines of 2002. The latter is only available for purchase, but some good information can be found online since it was compiled specifically for the design of workplace furniture.
After calculating all dimensions of interest, Richard Ramos’ height was taken into consideration, and the average body dimensions for an individual with Richard’s height were calculated (6’9”). Richard’s overall dimensions, as well as those of the “average” Richard model were found to fall inside the 95th-5th percentile range, therefore the customer’s ergonomic needs would be accounted for.
Fig 1. Anthropometric data gathered
These measurements were then used to calculate the necessary range of adjustment needed for each subcomponent of the system in order to accommodate any user within our defined population. The resulting values were observed and evaluated for feasibility, which enabled the team to make final decisions on adjustability. These will be presented later in this report.
Fig. P12032 custom seat design and dimensions (in)
Backrest
Overall specifications of backrests indicate that the recommended backrest when sitting should adapt to the person’s spine and provide support to the back. The backrest should not be lower than the user’s shoulder blades.
In terms of motion, the backrest for a person in a sitting position should allow for a minimum rearward tilt of 10 degrees. However, studies on ergonomic hand cycling practices indicate that the straightest backrest position possible is actually preferred in this sport, since it protects the back and shoulders from possible strain or injury on the long run. This straight position also provides a better mechanical advantage than having the user tilting back.
Handles or Hand Grips
In the case of Richard, who has limited hand strength, quad gloves for hand cycling are used. These gloves are attached to the handles on the crank and these enable Richard to use his shoulder and core muscles to “cycle.”
Since this system is being designed for multiple users, the possibility of having users that are able to grip the handles is being considered. In this case, the inclusion of an ergonomic handgrip is considered. These handgrips are shaped a little differently, with a larger surface area extended to accommodate the palm of the hand better. The purpose of this extension is to prevent the user from gripping at an angle that could potentially cause injury to the wrist and the nerves.
Fig 3. Ergonomic handgrip by ERGON
Fig. Difference in wrist position
For hand cycling in particular, it is recommended that a 30 degree angle of pronation is considered when designing the hand crank system. This is another factor that prevents injury of the wrist on the long run.
References
Coming soon…