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Re: Gripping Fragile parts with Robotic Arm

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  • jamericanfreddy
    small search found this AD7150 capacitance to analog voltage chip with I2C buss,i think a 555 timer can work too
    Message 1 of 17 , Dec 4, 2012
      small search found this AD7150 capacitance to analog voltage chip with I2C buss,i think a 555 timer can work too

      --- In SeattleRobotics@yahoogroups.com, "jamericanfreddy" <jamericanfreddy@...> wrote:
      >
      > Do see they are touch sensor chips
      > many circuits on the internet for capacitance to voltage
      > and if you have a really good meter it has the circuit,its great to test the capacitance sensor first and then build the circuit around it
      > most like that chip i gave a page too the front end uses that type of circuit and then add a touch on/off circuit
      >
      > --- In SeattleRobotics@yahoogroups.com, "Peter Balch" <peterbalch@> wrote:
      > >
      > > > they gave me piezo sensor and capacitive type of force sensors
      > > > if you go to [sparkfun ] sensors then capacitance you will see some chips
      > >
      > > Thanks.
      > >
      > > I can see some touch sensor chips but not any capacitive force sensors or
      > > chips.
      > >
      > > I know that capacitive force sensors exist but I haven't found an easy
      > > supply yet.
      > >
      > > Peter
      > >
      >
    • Peter Balch
      ... Excellent. I hadn t spotted that chip. When I saw touch sensor I assumed it was on/off. I haven t got my head around the data sheet yet but it seems to
      Message 2 of 17 , Dec 6, 2012
        > Here is the page for one type ,they do have others
        > https://www.sparkfun.com/products/7902

        Excellent. I hadn't spotted that chip. When I saw "touch sensor" I assumed
        it was on/off.

        I haven't got my head around the data sheet yet but it seems to imply that
        maybe one should make a sensor with a capacitance change of less than 1pF
        over the force range you're interested in.

        For two plates,
        Capacitance = permittivity * area / distance.

        If we assume permittivity = 10pF/m then, for example, plates with an area of
        1 sq cm separated by 1mm give a capacitance of 1pF. (I think I've got all
        the zeros right!)

        Of course, for a force sensor, one would be looking for a _change_ of 1pF
        and I think the chip allows a "parasitic" capacitance of 40pF on top of that
        change.

        > Now to make the sensor you need a 2 tiny copper plates and
        > some soft insulator material to go between them

        It's a nice idea to make a home-made sensor. I'd be worried that the foam
        would degrade pretty quickly. Open-cell foams often can't take many crush
        cycles (although closed-cell neoprene isn't too bad). I wonder whether a
        silicone baking sheet between two copper-clad boards would do the job. One
        of the boards could have the chip on it to keep the sensor leads short and
        stable. I'm generally measuring a max of a hundred kilos but you may be
        trying to measure less force.

        The chips are not cheap but they could well be worth it if the completed
        sensor is accurate. I think I'll buy some.

        Peter
      • jamericanfreddy
        I was over 5 years ago when a professor of physics that was the part owner of the company i worked for that ,design that sensor for a scale it measure up to
        Message 3 of 17 , Dec 7, 2012
          I was over 5 years ago when a professor of physics that was the part owner of the company i worked for that ,design that sensor for a scale
          it measure up to 100 lbs

          SO be nice to make that sensor,i know we didnt use that chip
          it might used a 555 timer to get capacitance to voltage

          I am thinking small a circuit that used in most meters is what we need.

          --- In SeattleRobotics@yahoogroups.com, "Peter Balch" <peterbalch@...> wrote:
          >
          > > Here is the page for one type ,they do have others
          > > https://www.sparkfun.com/products/7902
          >
          > Excellent. I hadn't spotted that chip. When I saw "touch sensor" I assumed
          > it was on/off.
          >
          > I haven't got my head around the data sheet yet but it seems to imply that
          > maybe one should make a sensor with a capacitance change of less than 1pF
          > over the force range you're interested in.
          >
          > For two plates,
          > Capacitance = permittivity * area / distance.
          >
          > If we assume permittivity = 10pF/m then, for example, plates with an area of
          > 1 sq cm separated by 1mm give a capacitance of 1pF. (I think I've got all
          > the zeros right!)
          >
          > Of course, for a force sensor, one would be looking for a _change_ of 1pF
          > and I think the chip allows a "parasitic" capacitance of 40pF on top of that
          > change.
          >
          > > Now to make the sensor you need a 2 tiny copper plates and
          > > some soft insulator material to go between them
          >
          > It's a nice idea to make a home-made sensor. I'd be worried that the foam
          > would degrade pretty quickly. Open-cell foams often can't take many crush
          > cycles (although closed-cell neoprene isn't too bad). I wonder whether a
          > silicone baking sheet between two copper-clad boards would do the job. One
          > of the boards could have the chip on it to keep the sensor leads short and
          > stable. I'm generally measuring a max of a hundred kilos but you may be
          > trying to measure less force.
          >
          > The chips are not cheap but they could well be worth it if the completed
          > sensor is accurate. I think I'll buy some.
          >
          > Peter
          >
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