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device to measure a force (gauge strain ) — Parallax Forums

device to measure a force (gauge strain )

SuaadSuaad Posts: 2
edited 2013-12-17 03:40 in Robotics
Hi

I have a project to finish in 3 months

my project is basically about measuring the stiffness of the tissue and I am in process of making a device or a technique for it

So basically I am going to design a beam that is attached to a wall which is suppose to be bendable in order to position the gage strain on this beam
this beam in a way will hold the tissue in 4 directions and I will put a load over the membrane the memberane will deform and the beam suppose to get bent and gauge strain will get me the value of voltage

the dimension of the beam is undefined .. I dont know how small should it be designed...what i know is the gauge strains are in mm so should i design a beam in mm or cm ..I am really confused about it

the tissue that I am measuring is a cancer cell

Since this is my first time doing this kind of project ..I have no idea which gauge strain should i use ? and what type of the bendable beam can I design
I thought of Polycarbonates material .but I am not sure if the load that i will apply to tissue which is less than gram (i dont if this is even correct but what i mean is ..it will be a small load over the membrane ) is enough to make the beam bendable

I hope u can advise me here


Thank you So much

Comments

  • Mark_TMark_T Posts: 1,981
    edited 2013-12-09 16:11
    I guess polycarbonate isn't bad - relatively stable mechanical properties. However its very sensitive to many solvents so sticking a strain gauge to its surface might be tricky. Same goes for
    polystyrene (probably too brittle anyway). Thin metal isn't to be ignored either, stainless spring steel might be worth investigating.
  • SuaadSuaad Posts: 2
    edited 2013-12-10 00:02
    Mark_T wrote: »
    I guess polycarbonate isn't bad - relatively stable mechanical properties. However its very sensitive to many solvents so sticking a strain gauge to its surface might be tricky. Same goes for
    polystyrene (probably too brittle anyway). Thin metal isn't to be ignored either, stainless spring steel might be worth investigating.


    Thank you So much for your reply .. I really appreciate it

    So what I meant by bendable that I need a flexible beam ..So did u mean that metal could be flexible too

    I have question regerd the gauge strain ..Is there any specific type of gauge strain the provide me the force value instead of voltage ?
  • kwinnkwinn Posts: 8,697
    edited 2013-12-10 21:30
    Perhaps if you posted a rough diagram of what you have in mind along with some estimates of the dimensions and forces involved you would get some more help. I have some experience with strain gauges and load cells (as do some others on the forum), however I am having a hard time picturing what you are trying to accomplish.

    I do know there are some load cells with built in electronics that output force directly but have not come across any strain gauges that do so.
  • Beau SchwabeBeau Schwabe Posts: 6,557
    edited 2013-12-10 23:56
    Is this to be used on a patient similar to a skin durometer? ...or is the sample for a biopsy?
  • PropGuy2PropGuy2 Posts: 358
    edited 2013-12-13 05:53
    It sounds like this Is a pretty high end project, so go with the best strain gage sensor you can get. I recommend you start with Omega Engineering for a complete line of thermal, pressure and force sensors. They sell pre mounted strain gages that are calibrated and repeatable. I use the MCP3208 analog to digital chip and a quality op amp buffer (to amplify the low level strain gauge voltage) OR you can buy the whole package from Omega Engineering, but I won't be cheap.
  • Mark_TMark_T Posts: 1,981
    edited 2013-12-16 12:53
    For a strain gauge an ordinary opamp is hopeless. You need a good quality instrumentation amp.

    [that means bags of CMRR and PSRR and ultra-low offset voltage and offset-voltage drift]
  • kwinnkwinn Posts: 8,697
    edited 2013-12-16 18:32
    Mark_T wrote: »
    For a strain gauge an ordinary opamp is hopeless. You need a good quality instrumentation amp.

    [that means bags of CMRR and PSRR and ultra-low offset voltage and offset-voltage drift]

    Better yet are the chips designed to work with strain gauges. There are single chip systems that include the excitation, amplifier, adc, and digital interface.
  • ErlendErlend Posts: 612
    edited 2013-12-17 03:40
    Are you sure you want to use a strain gauge for this purpose? To get sufficient bending force from pressing against organic tissue, I would think you need a long measuring arm. Maybe you should consider other measurement principles too? What about a membrane connected to a pressure sensor, or a spring loaded rod with a linear position sensor(optical)? I would think the force to be measured is very low?
    Interesting project!

    Erlend
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