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IndustryArena Forum > MetalWorking Machines > Benchtop Machines > Chinese scales to position the tool
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  1. #1
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    Chinese scales to position the tool

    I thought rather than just display the co-ordinates I should use the scales to locate the tool on the fly, so I made a computer to read them and move the table and everything else I could think of

    Rather than burden the processor reading the scales directly I decided to do it in hardware. When the scale report comes in I just read 3 bytes on an interrupt and I have it. Only one scale wired in so far but it's reading and I have the result coming out on a serial line and it agrees with the scale :wave:

    The prototype is looking a bit moth eated with all the modifications, but it works. It all wires up with cheap 8 pin patch cords so no problem if they get crunched.

    The scales have pcb's screwed to them so the flea squeak signal only has to make it half an inch before it becomes a good solid 5 volts. They also have optical end detectors so I know where to zero it should the battery go flat.

    Just got it reading the scale and felt like a quick whoopy doo because it's taken me weeks, thank you for reading to
    Attached Thumbnails Attached Thumbnails scale1.jpg  

  2. #2
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    Hardly understood a word of that but nice job; sounds very useful :cheers:

    John

  3. #3
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    yep same here not sure what you mean
    The opinions expressed in this post are my own. -Les opinions exprimé dans ce messages sont les mienne

  4. #4
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    I think Robin is explaining how he gets the measurement from the scale into his PC, meaning that the scale can be used as a cheap feedback device for closed loop position control. Neat idea to have the translation done w/ a separate micro. What is the update rate?

  5. #5
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    Not really sure I know what I mean either

    Here's the idea I had...

    I've been positioning the milling table by turning the leadscrews very precisely and trying to minimise backlash, it works okay.

    I had a notion that if the milling machine could read the table and quill positions independantly of the screws, it could position it a lot better.

    So I'm making a computer board that accepts g-code, reads the scales, turns the handles, plus a few other things that I think might be fun such as a pendant, tool height and X,Y absolute position gauges.

    It's okay to tell me that it's already been done and is available for 50 bucks from Geekware Inc. I won't mind

  6. #6
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    Quote Originally Posted by Robin Hewitt View Post
    So I'm making a computer board that accepts g-code, reads the scales, turns the handles, plus a few other things that I think might be fun such as a pendant, tool height and X,Y absolute position gauges.
    I understood what it does, it was just the how to build a computer board to do it that's beyond me. The words smart a** come to mind lol.

    John

  7. #7
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    Quote Originally Posted by Hans_G View Post
    IWhat is the update rate?

    The scales normally update about 3 times a second but you can flip them in to "fast" mode which is about 50 per second. Step on report would give me a feed rate of about 0.25mm/s, not entirely useless I usually cut at around 1.2mm/s.

  8. #8
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    Quote Originally Posted by Oldmanandhistoy View Post
    beyond me. The words smart a** come to mind lol.

    Electronics is what I do for a living so I like what you're saying. If everyone thought it was easy I wouldn't make so much money

  9. #9
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    Quote Originally Posted by Robin Hewitt View Post
    Electronics is what I do for a living so I like what you're saying. If everyone thought it was easy I wouldn't make so much money
    It most certainly was not meant as an insult; you have my repect

  10. #10
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    Quote Originally Posted by Oldmanandhistoy View Post
    It most certainly was not meant as an insult; you have my repect


    In that case I'll let you in to the secret.

    You use circuits you already know work where ever possible. If you have to break new ground you rough out a prototype and then bodge it until it works, cursing your stupidity at every silly mistake you find.

    Then you re-make it perfect with the benefit of hind sight and never show anyone the original
    Attached Thumbnails Attached Thumbnails scale2.jpg  

  11. #11
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    Very nice! I can certainly appreciate the benefit of reading table position directly, as opposed to taking table position for granted from the stepper motors.

  12. #12
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    some people are far to clever enough

  13. #13
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    Quote Originally Posted by Robin Hewitt View Post
    Then you re-make it perfect with the benefit of hind sight and never show anyone the original
    You should have seen my first CNC router

  14. #14
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    This is an excellent project - congrats! :cheers:

    So, if you can read those scales from your PC, presumably you can also read digital dial indicators which are based on a very similar looking module? I would really like to build a tramming tool that could be used to automatically unskew (unrack?) a twin screw axis...

    They would also make for ultra precise home switches - you collide with them, and then read off how far out you are, rather than creeping up to the switching point and off again.

  15. #15
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    Congratulations Robin on accomplishing what you have.

    I particularly like the caliper extension board that gives a decent cable connection.
    -Much needed.
    Would you provide details on how it was done? (like a pic w/cover off or ??)

    Keep up the good work.

    Pres

  16. #16
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    [QUOTE=digits;411869] I would really like to build a tramming tool that could be used to automatically unskew (unrack?) a twin screw axis...
    QUOTE]


    Twin screw axis?? Never saw one of those.

  17. #17
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    Quote Originally Posted by Pres View Post
    Would you provide details on how it was done? (like a pic w/cover off or ??)
    Pic with scale in upside down attached.

    The scale connects top left hand corner, if you use fine wire you can snap the plastic cover back over the top so it all looks neat and tidy.

    The chip nearby is a high impedance input comparator which buffers the clock and data lines.

    Lower down a pair of opto slots do the end detection.

    I'm reworking this one to
    Attached Thumbnails Attached Thumbnails scale3.jpg  

  18. #18
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    Quote Originally Posted by Robin Hewitt View Post
    high impedance input comparator
    Oh the old "high impedance input comparator", if you said that in the first place no one would have gotten confused. :wee::drowning:

    Nice job mate, now how much do they cost?

  19. #19
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    Quote Originally Posted by Oldmanandhistoy View Post
    Oh the old "high impedance input comparator", if you said that in the first place no one would have gotten confused. :wee::drowning:

    Nice job mate, now how much do they cost?

    A comparator is a very simple device. Basically it has two input pins and one output. It compares the input pins. If the plus input has more volts on it than the minus input then the output is high. If the minus input has more volts then the output is low. High impedance means it doesn't draw any current on it's input pins so it doesn't flatten the battery in the digital scale.

    I used an expensive TLC372CD dual comparator (two comparators in one pack), £0.45 plus tax from Rapid Electronics, cheaper if you buy ten

  20. #20
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    Quote Originally Posted by Robin Hewitt View Post
    A comparator is a very simple device. Basically it has two input pins and one output. It compares the input pins. If the plus input has more volts on it than the minus input then the output is high. If the minus input has more volts then the output is low. High impedance means it doesn't draw any current on it's input pins so it doesn't flatten the battery in the digital scale.

    I used an expensive TLC372CD dual comparator (two comparators in one pack), £0.45 plus tax from Rapid Electronics, cheaper if you buy ten
    Thanks for the explanation; I’ve learnt at least one new thing today. :cheers:When I mentioned cost I was asking the total cost for the set up not just the comparators

    John

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