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Automatic Blow Off For A Conveyor

Discussion in 'General Electronics Discussion' started by steve2020, Aug 4, 2017.

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  1. steve2020

    steve2020

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    Aug 4, 2017
    I have a project to do that is when a plastic bottle is off on the weight it will blow off into the scrap bin. There is no room for I/0 so i was thinking a on/off delay timer would work i think? From the scale to the air blow is about 16.56 seconds. Is there a way i can do this? I need a bit of advice. Thanks. I have a Finder timer
     
    Last edited: Aug 4, 2017
  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    A decent monostable circuit would do it. Loads of ways to skin that particular cat. Google the bold word with 'schematic'
     
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  3. shrtrnd

    shrtrnd

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    Jan 15, 2010
    Unsure, with the limited information you provided.
    I'm assuming you have worked-out the signal from the scale that will trigger the air-blow?
    I don't understand how you think a 'on/off delay timer' is going to help here.
    Can you be more specific about the process itself so we can have a better idea of exactly what it is you expect to do?
    I would think the scale would indicate an empty bottle and a trigger signal would activate the air-blow.
    What is the significance of the 16.56 second difference from the scale to the air blow?
     
  4. AnalogKid

    AnalogKid

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    Jun 10, 2015
    What power is available for the control circuit?
    What is the go/no-go signal out of the scale?
    What are the control signal requirements for the air blow?
    How fast is the line moving?
    What is the margin on the timing signal. IOW, 16.56 seconds +/- xx.xx seconds?
    What is the range of ambient air temperature around the control circuit?

    1 part in 16.56 seconds is 0.06%. You never will achieve that kind of accuracy or stability with an analog R-C timer. This can be done pretty easily in either hardware digital logic (2-3 chips) or a $1 8-pin PIC (just add software; how hard can it be?)

    ak
     
  5. Minder

    Minder

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    Apr 24, 2015
    What is meant exactly by 'No room for I/O'?
    You have run out of I/O?
    If so what is the present means of control?
    M.
     
  6. Irv

    Irv

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    Jun 7, 2017
    This leaves a lot of room for guesswork (which can be a good thing) :)
    So, if this is an assembly-line type thing, and the sensor says bottle is "empty" or whatever fault condition exists, then how many bottles will there be between the faulty bottle and the blower?
    Count bottles arriving at the blower, wait for it.
    More accurate than a timer, provided bottles don't fall off somewhere along the way.
     
  7. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I wouldn't use a timer other than the air burst duration or you'll have problems when conveyor speed slightly varies.

    If conveyor speed isn't too fast, you could alternatively use a solenoid kicker or a gate that would divert the bottle.
     
  8. steve2020

    steve2020

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    Aug 4, 2017
    So in the Jbox where i thought i could get a signal is full, but there is a hmi panel that has drives and terminal strips
     
  9. steve2020

    steve2020

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    Aug 4, 2017
    So im still looking for a signal since the jbox is full but i think i could use the relays inside the hmi panel, the scale has a horn that goes off when the weight of the bottle is off. Currently the use a manual air valve to kick the bad ones off. They want something that will automatically kick the bad bottles off and im just a tad lost
     
  10. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    You may be able to change the jbox terminals to two tiered type terminals in order to gain space.
    Where does it kick them off? At the scale or down stream on the conveyor.
     
  11. Irv

    Irv

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    Jun 7, 2017
    OK, the scale has a horn that goes off when a "bad" bottle is on it. Down the line there is someone waiting to turn or step on an air valve to blow the empty bottle off the line about 16 seconds after they hear a horn?

    Hopefully, this poor soul has some other job in addition to waiting for a horn and counting the seconds.

    If I have described this correctly, then the person involved has two things to do:
    1. Wait until the "bad" bottle is exactly in the right place to be blown off the conveyor,
    2. Turn on the air for the correct length of time so that only the "bad" bottle gets tossed out, without toppling other good bottles.

    If this is what you want, then you need:
    (A) A sensor to determine when a bottle (any bottle) is exactly in front of the air jet.
    (B) A way to know that this is the bad bottle,
    (C) A timer to open, and then close a solenoid driven air valve after a set length of time.

    A and C are off-the shelf stuff, you probably already know where to get them.
    That leaves B, the waiting "about" 16 seconds part.
    You *could* use a timer for that, started by the horn, which would wait 16 seconds (or a bit less),
    then tell sensor A to start looking for the next bottle.

    A better way would be to count bottles. You know that there are x number of bottles between the scale and the blower-person. Horn blows, (A) counts down until that many bottles have passed, then blows.

    As far as designing this circuitry - YOU are the only one here who knows what voltages, amperages, environmental conditions (electrical noise, etc) are there to be worked with. Without those specifications, no real answer can be given.
     
  12. Minder

    Minder

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    Apr 24, 2015
    ++.
    To give a practical answer system details have to be known, Electronic, Electrical, Mechanical.
    Otherwise pure guess work.:rolleyes:
    M.
     
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  13. bushtech

    bushtech

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    Sep 13, 2016
    Why not just blow the bottle off the scale?
     
  14. kellys_eye

    kellys_eye

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    Jun 25, 2010
    16.56 seconds seems pretty specific..... either the bottles are moving at one heck of a rate past the blow-off point or you've been over-egging the accuracy required.

    As for
    ??? They used to use analog monostables to create the basic digital games (i.e. pong) on TV screens using line/frame frequency triggering and μS accuracy..... 74-series monostables too!!
     
  15. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Not exactly a fair comparison because of the tolerances allowed by the two situations. 1 pixel back then was 1 part in 320. The requirement here is over 5 times more stringent.

    But I get your point. However, the capacitor for a microsecond RC timer can be a 1% polyester film or silvered mica type that is both accurate and stable over temperature, and a 1% or better resistor, both at a reasonable cost. A 16-second timer would need a 1 meg resistor and a 16 uF electrolytic. The resistor can be stable, but the capacitor initial tolerance and temperature coefficients both are way worse than anything in a video timing circuit. Plus, the leakage current can be a significant percentage of the total charging current available. This changes the required timing resistor value, and drifts with temperature separately from the basic capacitance value drift.

    ak
     
  16. Minder

    Minder

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    Apr 24, 2015
    So far it is not known if this is a professional Industrial/commercial bottling line, If so, I would expect some way of integrating it into the existing system, I can't see anyone designing something like this without some kind of allowance for future needs.
    Also are these empty bottles or weighed full?
    If full, I would not expect a puff of air to remove one.
    I worked for a time servicing the bottling lines on Canadian breweries and they have a method of detecting empty or low cans of beer, and they kept track of the can and a air operated solenoid would punch it out of the line when it passed.
    They also detected a empty bottle with a contamination still after the washer and removed a similar way.
    M.
     
    steve2020 likes this.
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