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gmklapsing34
05-27-2011, 03:49 AM
Hello community,

I'm trying to obtain the time sequence of the sole contact area during a step. In order to do so I have a raised glass floor, an inclined high reflexion mirror below it, a high speed camera and white light strobes.

I've done many captures which do look good, but the contrast between the zone of the sole actually being in contact with the ground and those zones being just above the glass (e.g. 1 mm) is not good enough.

I've tried spilling milk, gel, paint, carrot juice, on top of the glass. Besides the mess, I get again nice pictures, but:
- I get bubbles wich can be confusing with the contact area
- When there is slipping, the sole wipes the glass. We are not able to distinguish between some of the wiped areas and the actual contact area.

I remember having seen some pictures where the contact area of the sole appears to be green. I'm not sure if this was painted afterwards or if it was a raw recording.

Now I'm thinking about some kind of spray or paint I could apply to the sole. This substance should rearrange its moleclules under load in a way that it changes reflexion or colour.

I'm now working with a grayscale camera, but I'm willing to switch to colour if this solves the problem. Ideally I would be able to use the same procedure regardless of the original colour of the sole, since nowadays it is quite common to have multicoloured soles.

I'm open to any solution and any help will be greatly appreciated.

Thank you in advance,

Gaspar

PD: I'll post a summary of responses

kkirby52
05-27-2011, 06:00 PM
Gaspar:

You may possibly try a different approach. Rather than applying fluids on top of the glass, where the sole is displacing the fluid, why not instead having the sole covered with some sort of sticky film before it strikes onto the clean glass plate, so that just a small film of fluid clearly adheres to the glass during the step? The shoes may be able to be sprayed with a paint, an adhesive spray (Cramer Tuf Skin is one brand used for tape-on-skin applications), or even a pancake syrup before the trial. Alternatively, possibly the surfaces before the glass plate could be saturated with a sticky fluid (pancake syrup seems the best here) so that the shoe sole would be coated on the step before the glass plate is walked on. This makes sense to me hypothetically, but you will need to experiment with the idea to see if it works. Good luck!

hlau65
05-27-2011, 11:14 PM
Hi Gaspar,

Sounds like a fun project to do spilling liquids all over the floor!
I guess you want to monitor the dynamic change in contact area during shoe-sole contact? If not then maybe you can just do a static print using carbon paper or spray things onto the shoe.
and what's the accuracy you need in terms of 'area' and 'time' measurement?

I would think the liquid won't recover instantly once an area of the shoe has lift off, especially when viscous liquid like gel is used => error in 'time' and 'area' measurment.
Maybe you could try coating the glass with a thin layer of water+ink, but wrap and enclose this ink reserviour with thin plastic film onto the glass.
That way the ink will get squeezed to outer parts of the reserviour when you step on, and you can see the contact area underneath.
The ink will then rush back when you step off. Hopefully bubbles won't be an issue in this setup, try distilled water if it helps.

Or...you may try a cleaner way.
Instead of using a big strobe light, try pointing an array of small LEDs to the sides of the glass.
A contact on the glass should affect the internal reflection so you may get an image with better contrast between area where its touching or not.
Some touch screens use this techquie, and you may want to read this webpage: http://fadgy4.wordpress.com/author/fadgy4/

Those are my ideas, you'll have to try and see whether they'll work or not.
If all fails, might be worth getting a pressure mat.
I'm interested to see how you get on, so keep us posted, have fun!

Hin Chung
PS: try not to waste too much good juice! :-)

cbaumgart46
05-30-2011, 03:39 AM
Hi Gaspar,

Maybe you can use "Prescale Measurement Film" for your application. You can find some informations here:
http://products.fujifilm.eu/products/prescale_films/index.html

Christian

----
Dipl.-Sporting. Ch. Baumgart
Bergische Universität Wuppertal
Fachbereich G
Arbeitsbereich Bewegungswissenschaft
www.bewegungswissenschaft.uni-wuppertal.de
Fon: 0202/439 3758
Fax: 0202/439 3125

Gebäude I-14.66
Fuhlrottstraße 10
42119 Wuppertal

Forschungszentrum für Leistungsdiagnostik und Trainingsberatung (FLT)
flt@uni-wuppertal.de
www.flt.uni-wuppertal.de
Sekretariat: 0202/439 3226

gmklapsing34
05-31-2011, 02:20 AM
Hi Christian,

thank you for your suggestion. However, as I'm trying to get the evolution of the contact area over time during a step, maybe even a slipping one, I think the film does not suit my purposes. If I'm right, the film will reflect the whole contact hisotry on it. This way I miss the instantaneous contact area.

Thank you anyway,

Gaspar

tfeix38
05-31-2011, 04:27 AM
Hey Gaspar,

did you try satined (is it the proper term?..) glass? I mean a glass which has on one side a rough surface. If you put that side upwards so that you step onto it might help. Only if you are very close to the surface then you should get a clear picture. At least it looks like this if I try it with a glass cup.

Best
Thomas