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Flexiforce sensor — Parallax Forums

Flexiforce sensor

cbricbri Posts: 7
edited 2007-08-25 01:42 in BASIC Stamp
Hi All, I'm looking for input on the use of a flexiforce sensor to get a real time 'force measurement' on one of the LCD screens. Does the flexiforce provide realtime data that can give me instant readings about how much force is being applied instantly?

Thanks,

Craig

Comments

  • mhackermhacker Posts: 1
    edited 2007-08-13 16:11
    Hi Craig,

    I'm using it for the same aplication, on a rocket motor test stand.

    I suggest you to download de PLX-DAQ from here: http://www.parallax.com/dl/sw/plx_daq_install.zip and try it by yourself. It's almost anything you need to do datalogging in realtime.

    The data readed from the sensor is just a resistor variance from Mohm (not force applied) to a few Ohm's when it pressed.

    The problem is to calibrate it to our own needs. I'm in this process now...

    Of course, any other sugestion or advice will be welcomed too! smile.gif

    Regards,

    Marcelo
  • steve_bsteve_b Posts: 1,563
    edited 2007-08-13 18:09
    We use contact brushes to pass electrical signal from a rotating radar dish down to a computer.
    The brush force is crucial in how long it will last....too hard and it'll wear out fast...too light, and it'll eventually wear enough that it'll have intermittant contact.
    We played a little bit with a flexiforce sensor and had a terrible time getting repeatability with measurements.

    The sensors require "pre-loading" to "condition" them so they will read. I think the sensor is basically a gel capsule with some resistive gel inside. You preload it so that the gel spreads out uniformly.

    Anyhow, we eventually gave up on using it for a brush force sensor. It would be fine for a relative reading but not something fine and exact!

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    <FONT>Steve



    What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
    Lee Travino after the second time being hit by lightning!
  • cbricbri Posts: 7
    edited 2007-08-13 18:20
    Steve did you come up with something else? I basically need something like a torque meter that I can install on a swinging arm.. I was thinking where the arm makes contact with the body of the machine I can tell how much pressure their is and stop at the same spot each time..

    Craig
  • steve_bsteve_b Posts: 1,563
    edited 2007-08-15 17:23
    Hi Craig,

    I ended up getting busy with "real work" hehe I was playing with the flexiforce sensors in hopes of rolling this out to other techs as an easy solution to knowing the brush pressure (they could just put their multimeter on the leads and they've got an equivalent reading).
    The area I need to get in to is VERY small (see attached) so the flexiforce was idea in that respect.
    *(in the pic you can see how the brushes come with a pre-bend in them..)

    Anyhow, if you have a fairly large area to get under, you might like at a piezo type force sensor (I'm sure there's one available from parallax) just be sure to build the suggest 'protection' circuit as the instantaneous voltages can be somewhat large (not much current though).

    Cheers

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    <FONT>Steve



    What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
    Lee Travino after the second time being hit by lightning!
    brushes.JPG
    855 x 512 - 63K
  • FerretMK4FerretMK4 Posts: 11
    edited 2007-08-25 01:42
    We were going to try the Flexiforce to monitor hydraulic pressure in a generating station, but haven't tested it yet.· Their rep says the sensor has a reasonable frequency response (maybe to 100 Hz is my guess) but has a temperature sensitivity and takes a "set" if held under load; ie if you put it under load the output will drift to a final value.· It's a simple two-wire device which changes resistance with pressure.· You have to be careful to distribute the pressure over the full sensor button area to get consistent results.· It's used in studies of foot, bum, and hand pressure on controls and seats and in shoes, has been used to study disc brake pad pressure distributions, is used in medical devices such as for therapy and measuring sleep apnea by measuring the pressure the chest applies to a strap when breathing.· Some of these apps require repetitive accuracy.
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