Strain Gages

Discussion in 'The Projects Forum' started by Mazaag, Oct 4, 2006.

  1. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    Hi guys..
    I have already posted something with regards to this topic, but just wanted to clarify something...

    Does anyone know of Strain Gages which are small and flexible enough to be able to bend with the bending of a finger ? ( at a joint ) ie: approx 90degrees?

    basically i need some sort of a sensor to be able to measure the amount of bending in each finger.. I thought of strain gages..but heard that they can't bend that far... any ideas?

    thanks guys
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Strain gauges are easily flexible to bend with a finger. They are just resistive ribbon bonded into a plastic matrix.

    They tend to fail when they go past 5% elongation, though. They can't bend that far and function.
     
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    3
    A conductive rubber strip that changes the resistance with stretching will do the job. Have a look at something like Inastomer from Inaba or just do a search on conductive rubber pressure.
     
  4. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    Thanks for your reply guys...

    About the strain gage, I was planning of having it mounted at the joint of my finger, such that it bends when i bend my finger.. is it possible for the gage to bend that far ?


    n91028301923091281 , ( :p )
    about the Conductive rubber, any idea on the prices ? are there any other companies who sell such stuff ? or is it still at a research stage ?

    Thanks
     
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
    1,198
    3
    You could try finding the Inastomer I mentioned in my previous post. Failing that, I did a design for a company that make automatic doors for public transport systems years ago. One of the sensor that they used to detect for obstruction was the pressure rubber strip. It looked like an ordinary rubber strip, but it has resistance that changes with pressure. Unfortunately, I have no idea where they sourced it from. I imagine that the price is not that steep. They used a lot of it to line the doors.

    I also saw a rubber band once used in medical application to measure the blood pressure or something. It was tied around arm, finger or wrist and it measures the stretching of the band. I think the guy that worked with it told me that it was rubber tube filled with metal, like mercury or something. Probably quite expensive.

    Sorry I couldn't be of more help.
     
  6. peajay

    Well-Known Member

    Dec 10, 2005
    67
    0
    Someone once gave me an old Nintendo Power Glove, which had sensors the thumb and two fingers. Upon disecting it, I found these things in the fingers of the glove:

    http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=150551

    They're wonderfully easy to use, they just change their resistance as they are bent, but there's just no way I could convince myself to pay $12 for one.

    I just can't understand why they should cost so much. The one I had, which looked just like the one in the picture, seemed to be just a strip of plastic with some of the material used in potentiometers on it. I would definately look elsewhere for cheaper ones if you decide to use it.
     
  7. Mazaag

    Thread Starter Senior Member

    Oct 23, 2004
    255
    0
    hey peajay,
    do you know if those were connected to the fingers? like can you get a complete 90 bend on your fingers? or how does that work ? do you mind checking for me ?

    thanks alot
     
  8. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Hi,

    Strain Gauges won't work, instead, check out this Stretch Sensor
     
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