High IQ Nerd Stumped on Simple Problem 2

[DistressedNerd]

I am trying to find a product or mechanism that already exist that is basically a Chinese finger trap for a sheet of fabric. You feed the fabric into the trap/clamp/mechanism and cant be pulled out. After pondering and asking all the engineers around my office the closest thing we have thought of is a rapid tie down strap like if your securing stuff on your car rack you can pull the strap tighter (easily feeds into the mechanism one direction) but cannot be pulled out in the opposite direction. However, the rapid tie down strap has little backwards pointing or re-curved metal teeth that dig into the material, which is too harsh on the fabric. I need something that accomplishes the same goal that's not so harsh on the fabric - I would love your input on this!

What I eventually thought of was backward pointing or recurved rubber teeth that do not dig into the material but instead use friction and pressure to prevent the fabric from being pulled out. The fabric easily slips in, but when you try to pull it out the friction on the re-curved rubber teeth cause the teeth to "unfold" increasing pressure on the fabric which in turn increases friction. The harder you try to pull the fabric out of the trap the more the re-curved rubber teeth "unfold" > increased pressure > increased friction. How would I ever make this or does something like this already exist or can be modified to build a functional prototype?

Thank you in advance!!!

"Do or do not, there is no try" - Master Yoda

 

[berkshire]

Distressed Nerd.
One thing that comes to mind for what you are trying to do, is Diamond hollow braid . This material when it is compressed gets larger in diameter , and when it is pulled, gets smaller in diameter clamping tight to anything inserted into the hollow cavity.
B.E.

You are judged not by what you know, but by what you can do.

 

[racookpe1978]

Seen a similar product used for thread protectors.

 

[MikeHalloran]

I used to have a thing on my cubicle wall that would hold a reasonable number of papers side by side. I forget its name, and can't find one for sale right now. It comprised an aluminum extrusion, basically an upside down U shape, with the straight legs tapered in a few degrees. Inside it was a loose array of short cylinders made of plastic or rubber, light enough to be pushed up by the edge of a sheet of paper. When upward force on the paper was released, the rollers would fall toward the open bottom of the U, wedging themselves against the paper, holding it pretty well. You could release an individual sheet of paper by pushing it up, then down or sideways.

Something similar should work on the edge of a sheet of fabric. You might have to use a full length dowel instead of short cylinders to allow release without going out of your mind.



Mike Halloran
Pembroke Pines, FL, USA

 

[DistressedNerd]

MikeHalloran You da bomb dot com!

I could build it out in CAD like I did with the chinese fabric trap concept described above (see below), but I would love to first find the product your talking about to help guide design. I've searched far and wide on google and can't find anything - can you help me find it so I am not taking shots in the dark making 100 prototypes to figure out design principles.

 

[BUGGAR]

I've seen diamond hollow braided sleeves for use around electrical cables to transfer connection loads to the cable body, I think they're called strain relievers.
Or cable grips used on prestressing strand.

 

[gruntguru]

I guess you need a long version of the Cam-Cleat Link.

Imagine your fabric feeding through a pair of rollers with eccentric bearings.
Spring loaded?
Single roller wedging against a plane?

je suis charlie

 

[MikeHalloran]

I found it on Amazon:

http://www.amazon.com/Hangman-Clip-...eywords=cubicle+wall+accessories+paper+holder

There appear to be at least two manufacturers, producing the item in several lengths:

Hangman Clip-It Strip Magnetic Note and Paper Holder

ADVANTUS Grip-A-Strip Display Rail



Mike Halloran
Pembroke Pines, FL, USA

 

[gruntguru]

If you just want to hang the fabric as in Mike's magnetic holder, just make something like this roller in a folded channel (fabric is red). Or could be a roller constrained to a wall with two brackets.

je suis charlie

 

[Compositepro]

Look at how window screens are held into their frames by a rubber tube pressed into a groove.
Many mechanisms that work well for small areas, like a Chinese finger trap, are not suitable for long, drapeable, sheets.

 

[Jboggs]

I once designed a machine to pull outdoor chair fabric along a curved frame to form the chair bottom and back. I used a gripper device like this, a derivative of the cam device above. The edge of the fabric slipped easily under the gripper from the bottom, but any reverse motion just engaged the gripping action and even increased the gripping force. It worked perfectly. You will have to build some prototypes to develop the material selection and final geometry. You might also want an operating and release mechanism. It should work well for you.

 

[DistressedNerd]

Thank you for the thoughtful input, creativity, and innovative thinking! I've attached a sketch of the prototype I plan to build with some additional design requirements. The Chinese fabric trap needs to meet these design requirements (1) have a variable insertion length up to 4" (as in you can insert as little or as much fabric into it up to 4") (2) Needs a holding force throughout the entire 4" column. Additional insight and thoughts are appreciated, if there is a better way please let me know! Special thanks to MikeHalloran.

 

[DistressedNerd]

Additional Question - see picture.

"That which you seek, inside you will find..." -Master Yoda

 

[zeusfaber]

"Needs holding force throughout entire 4" column"

Could I be nosy, and ask why?

A.

 

[dvd]

Where is the c.g. of the sled? Does it center up - can it misalign? Keep it simple. Also, fabric will buckle more easily that paper, so keep insertion in mind.

Unrelated topic - how high is your I.Q.?

 

[IRstuff]

The sled is marginally better, but probably more prone to malfunctioning. KISS applies.

TTFN
I can do absolutely anything. I'm an expert!
homework forum: //

http://www.engineering.com/AskForum/aff/32.aspx

faq731-376 forum1529

 

[DistressedNerd]

dvd - Your post are very insightful and succinct. It seems like over the years you've always provided great information whether my post or someone else's. You know the right questions to ask and you do it not for monetary gain, but for the greater good of society - utilizing the understanding of science and engineering as your philanthropic vehicle.

I sitting around ~130-135 according to my Graduate Record Examination scores.

Here is my updated design concept it provides force throughout the column and has less moving parts compared to using rows and rows of the roller system described above.

 

[MikeHalloran]

I don't think you can lift the wedge by pushing on it with fabric, unless the fabric has a lot of sizing on it or is remarkably stiff for other reasons.
... which is yet another reason that the wedge needs to be full-width not segmented, so that you can use strings or something to lift it by the ends and bias it to one side of the cavity, so you can work the fabric into the gap. It may even be necessary to evacuate the cavity or otherwise provide an airflow to carry the fabric into the gap.


Mike Halloran
Pembroke Pines, FL, USA

 

[gruntguru]

Wedge vs roller.

Increased grip surface area does not equal stronger grip. (F = mu.N)

A lower mu between wedge and frame permits a steeper ramp angle. Steeper ramp angle has the advantage of reduced vertical displacement for a given "grip" displacement.

A planar grip region is more prone to over-constraint and high spots. Roller has line contact. Soft roller seems best option. Lightweight (hollow elastomer?) for easier fabric insertion. (why do you need

je suis charlie

 

[GregLocock]

If I were designing a one time use system, that gripped and never let go I'd use a wedge. If not, not.

Incidentally, an IQ of 140 is probably not especially high around here, and IQ is not in itself a great indicator for engineering, above a necessary minimum. Average IQ for engineering majors is 126, 1 standard deviation is around 10, you do the math.

Cheers

Greg Locock


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