Ergonomics Standards - CoG Human Body 2

[sammybrush]

Hello,
I am currently looking for a definitive standard that can be used in the creation of a percentile ergonomic model.

I have found a NASA document that shows some of the lengths of various limbs, torso's and the suchlike. However I cannot find any reference to the center of gravity of the items.

My overall goal is to create a "simple" 2D stick model, using the lengths and sizes provided and then a overall CoG can be calculated. This stick model is then to be modelled in Adams to visualise the movement and record the new position of the centre of gravity throughout the simulation.

Does anybody know of any standards that may be able to help me in the creation of the model?

I presume that this could be completed using industry standard 3D models and simulation packages but currently I do not have the budget to support this exercise..... Hence the calculation route.

Many thanks

 

[vpl]

thread404-226046

Patricia Lougheed

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[MechEng2005]

The link Patricia supplied wasn't very helpful for finding the center of gravity though, but was certainly a start. I also did not follow the links, so maybe that's where it was more detailed...

Finding the CG would be difficult because it is (generally) significantly different for men and women (Men's is typically higher).

I suggest finding a swing or horizontal bar and laying flat across it. When you are in a position where it is easy to balance while remaining in a flat, normal position, that's about your CG... Get everybody you can and repeat to increase sample size.

I suspect that there will be significant variation, even within genders. I don't know that the data is going to supply a much more concrete answer than you could achieve by making an educated guess (mine would be at the belly button).

-- MechEng2005

 

[KENAT]

I remember reading an article about early flight and how attatching 'wings' to peoples arms put the C of P too far forward of the C of G for stability.

Anyway, the relevant part is that it claimed the C of G was around waist height.

KENAT,

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[kchan711]

Howdy,

Just as a thought, I'm pretty sure Mark's Mechanical Engineering Handbook has a human ergonomics section with measurements and such.

Other places to try might be a search on "Human Factors in Engineering", very common in Universities, and even look within the fields of medicine.

If you go to

http://www.3dcontentcentral.com

, you should be able to find some dummy models. However, I'm not sure of their accuracy.

Best of luck.

Kyle Chandler

http://www.chiefengineering.net

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[eromlignod]

I have heard that your c.g. is about where your navel is. Of course its exact location will vary from person to person and depend on weight, etc.

I'm not sure what you're looking for. I don't think you're going to find a reliable universal formula or table. It's like asking, "What is the center of gravity of a vegetable?"

Don
Kansas City

 

[btrueblood]

The c.g. of a human will move, a lot, with the placement/bending of limbs and torso. That's how gymnasts, divers, etc. do those fancy tricks. Best bet will be to find relative center distance and mass of various body parts and model them to find a c.g.; that sounds like the approach you are taking. As for finding the c.g. of various body parts, treat as cylinders of density 1.015 g/cm^3...or become a vivisectionist.

 

[rb1957]

btureblood ... sure that's accurate enough ? ... maybe 1g/cc

 

[KENAT]

Just realize the OP is more interested in C of G of body parts not just body.

I'd look at using a uniform density and estimate volume of various parts as btrue says.

You may be able to find typical mass values for some body parts, after all "the human head weighs 7 pounds" or whatever the kid in that movie said.

Are you also considering moment of inertia, now that could be fun.

KENAT,

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[GregLocock]

Pretty sure the crash test dummy people would have a good idea of this stuff.

Cheers

Greg Locock

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[btrueblood]

"btureblood ... sure that's accurate enough ? ... maybe 1g/cc "

The 1.015 is the value from the Navy paper in the "volume of a human being" thread, error is within 1%...so, you could use anything from 1.005 to 1.025, but no, not 1.000, not unless you want to be laughed at.

...

 

[btrueblood]

and, FWIW, "that Navy paper" means this one:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD657316&Location=U2&doc=GetTRDoc.pdf

 

[GregLocock]

crash test dummies -

http://www.dentonatd.com/wwregulations.html

http://www.crash-network.com/Regulations/Dummies/dummies.html

far too much for me to wade through there, but it beats chopping up your least favourite co-worker and weighing him.

Cheers

Greg Locock

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[KENAT]

"but it beats chopping up your least favourite co-worker and weighing him. " - or not, depending just how un-favourite.

That's actually darn good thinking on the test dummies Greg, perhaps star worthy.

KENAT,

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[GregLocock]

A couple of other thoughts-

http://en.wikipedia.org/wiki/Ragdoll_(computer_model)

Also, you could easily estimate mass and cg and moments of inertia for each limb, assuming it is a uniform cylinder, I doubt you'd be enough in error to matter, given that you know the total mass, and the cg location of a standing adult (roughly the bladder).



Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[sammybrush]

Thank you very much to everybody that has replied. I have managed to find a document that has some positions of CoG and masses of major body parts, head, arms, torso and upper leg. The rest of the limbs I will just have to estimate.

I have an understanding that the values will be different, dependant if the data is male or female. I am going to use the higher percentile values so that my final answer will be pessimistic.

The reason for this is finding all the information is that if I know the length and mass of the limbs and I also know the position of the centre's of gravity of each component. I can build up a stick model to estimate the CoG (from data I have found stood upright with arms down the CoG is just above your naval in the mid plane of your torso).

Now that I know the 'stood upright' CoG if I start adding the range of movements of your joints, knee's, hips and arms I can manipulate the model into the position I require and then calculate the new CoG........ That’s the plan anyway.

At the moment I am not considering moments of inertia, but may have to consider it later on

I will search the crash test stuff to see if I can glean any information off them

Again, many thanks for people’s response’s.

 

[HamishMcTavish]

you could try the following which i found using google term anthropometry

http://www.ergonomics4schools.com/lzone/anthropometry.htm

http://www.openerg.com/psz/anthropometry_data.html

http://msis.jsc.nasa.gov/sections/section03.htm

http://www.pt.ntu.edu.tw/hmchai/BM03/BMmeasure/AntrhopometricMeasure.htm

Cheers

No more things should be presumed to exist than are absolutely necessary - William of Occam

 

[HamishMcTavish]

I've just re-read your post again and noted that you asked for standards you could use. If you weren't restricted to US standards you could also search the BSI website using terms like ergonomics and anthropometric which comes up with stuff like
BS EN ISO 15535:2006 General requirements for establishing anthropometric databases
BS EN 614-1:2006 Safety of machinery. Ergonomic design principles. Terminology and general principles
BS EN ISO 6385:2004 Ergonomic principles in the design of work systems

cheers

No more things should be presumed to exist than are absolutely necessary - William of Occam

 

[CADShark]

I've looked at my old Architectural graphic Standards book and they show the CG for an average male is about 37.5 to 38" from the ground up. The CG of a human falls inside what is called the "pelvic link" which is an imaginary triangle formed by key points in the body.

If first you do succeed...try something harder.

Blair H.
SW 2008 sp2.0, HP x6400, 2.0ghz dual core xeon, 2.0 GB ram, Nvidia Quadro FX 1500

 

[chicopee]

Also Wright Patterson Air Force base is the physiology research center for the USAF. They may be able to help you out.
You can also discuss your idea with your doctor on your next physical and he may be able to guide you in the right direction.