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Ergonomic limits for thumb and 1st finger

Ergonomic limits for thumb and 1st finger

(OP)
Hello

I am designing product that is similar to a clothespin /cloths-peg. i.e. It involves some jaws that need to be opened by a user with one hand.

I need to know:
a) What is the maximum ergonomic span between thumb and 1st (or 2nd) fingers?
b) What is the maximum acceptable for between thumb and 1st (or 2nd) fingers?

For use by male and female adults aged at least late teens on wards.

Many thanks

J



RE: Ergonomic limits for thumb and 1st finger

(OP)
Can anyone point me towards a good source of ergonomic standards?

RE: Ergonomic limits for thumb and 1st finger

ship69,

Google MIL-STD-1472, Human Engineering. You should be able to just download this.

--
JHG

RE: Ergonomic limits for thumb and 1st finger

(OP)
1. Excellent! OK I now have some thumb-finger forces data

Details:
I managed to download the "MIL-STD-1472, Human Engineering" PDF from here:
http://everyspec.com/MIL-STD/MIL-STD-1400-1499/MIL...
On page 94 the "THUMB-FINGER GRIP (PALMER)" seems to be 60 Newtons of momentary hold, 35 Newtons of sustained hold for "5th percentile male data".

Thank you. Yes, this is useful, although I shall need to scale it back to work for female hands. According to this table
http://msis.jsc.nasa.gov/sections/section04.htm#Fi... 4.9.3-5
I should reduce these numbers by 45% for to allow for women's "upper extremeties" being physically weaker then men's.

However according to this link:
http://www.theergonomicscenter.com/graphics/Workst...
Thumb & index finger strength for men is "19 lbs" ==> 8.6 Kg ==> 84 Newtons (24 Newtons more that nasa.gov link)
And women aren't far behind at "15 lbs" ==> 6.8 Kg ==> 66 Newtons

Anyhow those are good enough numbers for now on thumb-first finger strength.


2. I could not find any information about either what maximum stretch (i.e. maximum span) would be for a thumb to first finger pinch grip, nor how that interacts with strength (ideally for women).

Any suggestions?

J

RE: Ergonomic limits for thumb and 1st finger

ship69,

Maximum stretch should be easier than force. Ask some five foot tall woman in our office to stretch her fingers out, then measure them.

--
JHG

RE: Ergonomic limits for thumb and 1st finger

(OP)

Finally getting there... with a little help from the Chartered Institute of Ergonomics, I have finally discovered that for pinching between first and index finger (which is what will be required by our new product):

1). 95% of women should be able to pinch with 62+ Newtons (my 66 Newtons above wasn't far off)
2). 95% of women should be able to grasp to a width of 94+mm

What I now need to know is how much to scale back to allow for:
A) Being at near maximum width of stretch (say 94mm) ==> reduce force by 25%?
B) For say 25 repeat pinches within 5 minutes ==> reduce force by a further 20%?
C) Reasonable comfort (as opposed to maximums) ==> ?

Are there any broad ergonomic principles or rules of thumb (!) that I might apply?

Many thanks


drawoh
Yes, I like your thinking. I guess most people's hand are roughly in promotion to their height, although I notice that this can vary a fair bit. And it will be a good idea to do some usability testing on smaller, more lightly built women... who don't rock-climb(!)


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