Question

1. It is desired to locate a control on a machine. The control will be located right in front of the worker at shoulder height. The worker population that is going to use the machine will include both male and female workers

1. Where should the control be located to include 90% of the population?
2. If the control is located at a reach distance of 82.5 cm, what percentile of the female population is being excluded (not being able to reach normally the control).

Answer 1

Proper positioning is a very importannt decision to be made in order to include most of the workers. Height of the woarkers , their Thumb-tip reach , elbow-thumb reach , vertical reach etc are all critical factors in deciding the position of the controls for machines. In this case , the control is to be located at a shoulder height that would mean height of the worker and the horizontal reach of their hand will be the most critical factor in deciding the position of the control.

The average height of male and females should be taken care of while deciding the position of the control for that particular machine . and their elbow or thumb tip reach also will matter.

a. To include 90% of the population in working on the control, average height and horizontal reach of hand of both males and females should be taken.The average height of should be taken as the 50 th percentile of women's height should be taken i.e.163 cm and that for men is 171.5 cm. but the 5th percentile of female is as less as 152 cm and the 95th percentile of male is as high as 185 cm , so the height should be carefully measured to set up the control. 90% of the population would include all the percentiles of males and females. So the average would come close to 167.5 cm. ; the control should be set up anywhere around this . This would include almost all the males and females from the average and large percentiles, but would exclude the 5th percentile of women. they would come in the 10% cateogary that would not be included adversely. but that is the height and the control is to be set up at shoulder height so that should be 20-25 cms less than the average i.e. 149.5 cms.So to include 90% of the population of the workers the ideal position would be roughly around 149.5 cm above ground. and the horizontal reach or the reach ditance should be roughly around 69-73 cm. to enable everyone to reach the control without facing trouble in arms.

b. If the reach distance is 82.5 cms then that would consider the horizontal reach as the most critical factor or key factor. The average percentile of women's reach is of the 5th percentile ( 1 person in 20) is 68cm and the 50th percentile is 74 cm and for the 95th percentile it is 82.7 cm and for the men it is a larger number , so if the reach distance of the control is 82.5 cms , it would exclude the 5th percentile females and also the 50th percentile females .as they would not be able to reach that distance with ease. that sums up to roughly around excluding 7.3 percentile of women being excluded. 1.3 percentile of this would be able to reach but not without ease .

So, 82.5 cms reach distance is not an appropriate distance . As stated above the reach distance should be somewhere around 69-73 cms to include a larger proportion of the workers population.