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

  2. #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.

  3. #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

  4. #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.

  5. #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  

  6. #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?

  7. #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

  8. #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

  9. #21
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    Robin,

    Very nice work.

    I've been playing with a similar idea, but took the approach of grabbing the position after it has been processed by the DRO. Your way is MUCH better. Also, buffering the signal back at the source is brilliant. It solves one of the biggest problems people have with their DROs, noise.

    For faster positioning (I'm sure you've already considered this), you could do a hybrid control operation, where you use the stepper w/o feedback to get close, pause while the scale catches up, then finish with the scale providing the feedback.

    May I be your US distributor?

    - Don

  10. #22
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    Quote Originally Posted by dleroi View Post
    May I be your US distributor?
    Of course you can, but maybe I should finish it first

    I'm now writing a quick g-code interpreter and 24 bit x,y,z positioning system in machine code. I've already done it in Borland C, it's not hard. Accelerations will be much easier without having to compete with Bill Gates for the cpu timer interrupt

    My brother is a computer wizard and has given me a zippy algorythm for 'next point on an arc' without square roots. Can't wait to try it out

  11. #23
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    Smile Outstanding Idea

    This is a groundbreaking project, and rightly so it is currently focused at the electronically gifted.
    Possibly after it is completed I hope it can be simplified for us among the electronically challenged.

    Keep the photos and details comming.

  12. #24
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    great thread!

    at first i thought you mean scales as in weight, which could also be great for setting z depth? if you picked a scale that also had rs-232

    Here is something that i put together along the same lines (using existing computer interfaces that is)

    ibm trackpoint mouse used as an edge locater

    [ame="http://www.youtube.com/watch?v=3q58oVZCmB0"]YouTube - Find Center Of Slot - Edge Probe Mach 3[/ame]

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