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Re: [SeattleRobotics] Re: Gripping Fragile parts with Robotic Arm

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  • Peter Balch
    ... 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
    Message 1 of 17 , Dec 3, 2012
      > 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
    • jamericanfreddy
      Here is the page for one type ,they do have others https://www.sparkfun.com/products/7902 Now to make the sensor you need a 2 tiny copper plates and some soft
      Message 2 of 17 , Dec 4, 2012
        Here is the page for one type ,they do have others
        https://www.sparkfun.com/products/7902

        Now to make the sensor you need a 2 tiny copper plates and some soft insulator material to go between them
        Its been a long time since i work on that project,but since i got a full machine shop with every machine need,like a lathe and milling machine
        Will be working on my hand design some time soon
        I am thinking thin layer of open cell foam might work,can easy get it at home depot and one side is sticky,i think the copper needs to be facing each other,
        ALSO there is circuits for capacitance to analog
        FRED
        --- 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
        >
      • jamericanfreddy
        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
        Message 3 of 17 , Dec 4, 2012
          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
          >
        • jamericanfreddy
          small search found this AD7150 capacitance to analog voltage chip with I2C buss,i think a 555 timer can work too
          Message 4 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 5 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 6 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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