Light activated label dispenser

Discussion in 'The Projects Forum' started by gerstley, Nov 20, 2015.

  1. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    I am not all experienced at this sort of thing but never the less I am trying to build a device to dispense labels off a roll. I have a 12v motor that I am using to unroll labels off the roll. The motor runs until a light sensor detects a space between labels and at that point the motor should stop so a label can be removed. The operator would then press a momentary switch button to start the motor again and advance the roll to the next label. The light sensor would then stop the motor again when the next label space is detected. I was thinking of using a locking solenoid that would be activated by the switch and deactivated by the light sensor. I am not sure if that is the right approach and how I would set it all up if it is. Any help would be great!
     
  2. #12

    Expert

    Nov 30, 2010
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    The electronics are simple enough. The mechanical part is critical. Where are you going to place the sensor so it has the roll in the right position when it stops?

    I don't mean for you you answer that. Just put it as #1 on the "to do" list.
    Then we think about installing some, "idiot proof". What if light fails? The motor empties the roll.:D
    Maybe it should be, no light = no run.
    How will ambient light be accounted for?
    This is why we complicate things, like using an LED modulated at 38 KHz so the light detector can't be confused by fluorescent lights.
    How about a purely mechanical method? One push-button = one inch.
    Microswitch lever falls into hole in paper, motor stops. No paper = no motor.

    Think about these. Your ideas will mature over a few hours.;)
     
  3. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    Those are good questions. The labels come on a roll with a somewhat translucent backing paper and there is a gap of about 1/4 inch between labels on the roll. My hope was that light sensor would pick up the change in light as the label passed by. Maybe that isn't a great idea. I was going to make the sensor location positionable so the feed would stop about where I wanted it. It doesn't need to be precise.

    The motor that is advancing the labels is spooling up the backing paper so each rotation of the motor advances the label roll by a variable amount depending on how much backing paper in on the motor spool. As a result I can't see how I could use a stepper motor to advance the roll by a set distance with each button press.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    If the backing is clear and the labels not clear, then the electronics become very easy.

    There are details to address...
    - The out-feed length from the rolls.
    - the flexibility of the backing vs rigidity of the label.
    - the size if the label and speed that you need for each label to peel

    A simple DC motor can be used. A momentary push button can trigger a flipFlop (on), the motor runs until the light of an IR LED can pass through the gap between labels, that reception of light pulses the trigger of the flip flop again (off).

    It does not matter if the motor has inertia and passes the clear gap.

    The flipFlop cannot drive the motor directly but a MOSFET switch will easily turn it on.
     
  5. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    I would like to try to build this but I wouldn't know quite how. Would it be possible to sketch something for me?
     
  6. #12

    Expert

    Nov 30, 2010
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    I understand why you can't advance the major roll by x number of degrees and expect the paper to move the same amount each time. That's why pinch rollers were invented. Do you understand that principle? A pair of 0ne inch diameter pinch rollers hold the paper and a stepper motor moves the pinch roller by 1/Pi revolutions to move the paper one inch.

    How about a 2 method system as a fail-safe approach? Maybe you can have the simple light activated "stop" plus a microswitch lever which falls into the hole and also stops the process?

    We are waiting for your idea to become firm. Choose one...or two methods, and we'll get busy on the circuitry.

    Meanwhile, what kind of electricity is available? 120 volt out of a wall socket? A 12 volt battery? How much paper must move to arrive at the stop point? How wide is the roll? How big are the holes? What shape are the holes? How much different is the translucency of the sticker compared to the backing paper? What colors are involved? Are the major rolls contained in a metal cabinet? Is it bigger than a bread box? Is it mostly empty? Is the container size negotiable? What kind of motor do you have, or is it undefined until you buy something? Are you good with gears? Do you want this to be adaptable to different sizes of paper and stickers? Can you place the sensor two stickers away from the exit point?

    I think you can tell by my questions that we want YOU to start with a drawing!
     
  7. gerstley

    Thread Starter New Member

    Nov 20, 2015
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  8. GopherT

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    Nov 23, 2012
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    Do you have some info on the open questions from @#12?
     
  9. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    I attached a sketch that hopefully can help explain what I am looking at. The individual labels are 3"x7" and the backing paper is about 1/8" wider than the labels. There are no holes. The backing paper is about as translucent as waxed paper. The labels are a heavy stock paper and are pretty opaque (at least to my eye). I am thinking that by making the sensor location adjustable, I can accommodate different label sizes in the future. The whole setup will sit on a table top.

    Let me know if there is more information you need (or if you can't make sense from my sketch!)
     
  10. #12

    Expert

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    This is a $5 light level sensor, complete with light source. It might not be the one you end up with, but it demonstrates that these things exist. I merely couldn't find one with a thinner slot right now.
     
  11. GopherT

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    Nov 23, 2012
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    Something like this...


    image.jpg

    It would also benefit from a PWM speed controller to tune for your needs. Let's get their at a later step.
     
  12. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    Thanks for the schematic. I can try to build it but I have a few questions.

    I have a 12v power supply for the motor but I see the control circuit shows 5v. Do I need a transformer to bring the 12 v down to 5v or how would that be done?

    Is it possible to vary the sensitivity of the photo transistor (or the intensity of the LED) so it functions properly?

    I have attached a photo of my labels. The space between labels is 1/8". If the labels are moving at say 5"/sec, the 'light period' would be about 1/40 sec. Would the circuit respond as I want with the label moving that fast?
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @gerstley

    If you use a CD4027 / SCL4027 or MC14027 or HEF4027 (you get the idea) as your JK flip flop, you can use 12V for the whole circuit.

    You can change the sensitivity. I would put the phototransistor on the back of the label and the IR LED shining down on the top of the label. Do not use reflection (both on same side or your printing will screw things up). Order a range of resistor sizes to replace the 330 ohm. If you are going with transmission through the label (preferred) I would use a 100 ohm resistor and a 1000 (1k) ohm potentiometer (connected as a rheostat) to tune in the resistance that works best. The 100 ohm resistor insures that you always have some resistance, even with the potentiometer is turned all the way down.

    Also, the two 100k resistors may/may not work perfectly. You should order a pair of 10k, 33k and 100k resistors to insure that you can tune as needed to get a reasonable pulse to the flip flop. Likewise, order a pair of 1nF, 10 nF, 33 nF and 100 nF capacitors - these are the things that you will have to play with in the field and turn your project a little. I am not sure how sharply the edge of the label will appear and pass a pulse to the Flipflop. You will have to find a good combination once it is set up.

    The flip flop will respond to short pulses. The slowest thing there is the photo-transistor and it will clearly see a pulse of 1/38000 second.

    We may have to add a motor speed control for you with braking. I am concerned that you want to accelerate at 10" per second per second so a label is available after 1 second (average speed of 5"/second) ranging from zero to 10 m/second) and then stop. How long do you think it will take to stop. The more rotational inertia in your system, the longer it will take to stop.

    If needed, we can add braking and motor speed control (once you get this first step figured out).

    All else can stay the same. Also, what metro-area of the country do you live in?
     
  14. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    I purchased this motor:
    http://www.amazon.com/12Vdc-Right-A..._UL160_SR141,160_&refRID=1681Y4YV4SNRJJZFZ03V

    and also purchased this speed controller:
    http://www.amazon.com/RioRand-Contr...236_img_2?ie=UTF8&refRID=19H2HCKWNSYSQQE7BVVM

    The motor is a gear motor and stops turning very quickly. It should never be spinning more than about 4 ounces of backing paper at a time.
    An inch or two of movement after the motor stops is acceptable. I guess maybe I should be concerned more that the motor will accelerate so fast that it will tear the backing paper. The label roll may keep turning longer (it is free to spin) but I should be able to manage that with some kind of a friction brake.
    I am located in upstate NY - central NY
     
  15. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    The motor & control look good.
    I tried a slot detector, IR emitter & photo transistor in common package to detect space between labels.which are 4 in. X 6 in. with 1/8 in. separation. With gap in slot. adjusted IR current to give a low output , 20K on ohmmeter. With label & translucent backing in slot output at half scale, 100k. Feeding output into a comparator should give reliable sensing
    Maybe a spring loaded idler roller would ease startup tension of supply reel. Also
    if labels went over a sharp edge at end of advance it would release an edge of a label
    for quick removal.
     
    Last edited: Nov 21, 2015
  16. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    Sorry, I am a novice at this. The schematic GopherT drew didn't have a comparator (I think). Should I be looking at modifying what he had? Also, when I looked to purchase a photo transistor and MOSFET, there are many choices. Are there specific parts I should be looking for?
     
  17. GopherT

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    @Bernard
    The novice made me try for minimal parts but you are right, the comparitor will make it easiest. The triggering will be accurate every time that way.

    If you plan to order parts, you may as well get the motor speed control bits at the same time. Only a few bucks more.
     
  18. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    +This has been a great help and I really appreciate it, however being a novice, I am not quite sure how to incorporate the comparator circuit. Also, I am puzzled over exactly which transistors and MOSFET I should order. My wife (who is actually going to be using this gadget) doesn't trust me to pick out the right parts. Of course, she wouldn't do much better if you ask me.
     
  19. Bernard

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    No time today but here is my sketch: Label Feeder 00000.jpg
     
  20. gerstley

    Thread Starter New Member

    Nov 20, 2015
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    Thanks Bernard. I am looking at another option now so I am going to put this on hold for the time being. Thanks for the ideas.
     
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