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Problem with a Loom!

Discussion in 'General Electronics Chat' started by wizard, Dec 22, 2008.

  1. eblc1388

    eblc1388 Active Member

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    No. Certainly not. It has nothing to do with strobe effect.

    I have absolutely no idea what are are talking about. As long as the shuttle is rotating, pulses will be generated.

    What made you think others are not design engineers as yourself and not taking the problem seriously? Your mention of hobbyist approach is condescending to say the least. As you have mentioned strobe effect in the post, I would say you failed to understand what is actually being proposed.
     
  2. Pommie

    Pommie Well-Known Member Most Helpful Member

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    How can you say this is a math problem. You receive a bit stream from the sensor, if too many similar bits then a shuttle has stopped. This is of a similar complexity to bit banging 19200 baud RS232.

    Does any one know the speed the shuttles orbit and there revs per orbit?

    Mike.
     
  3. Ubergeek63

    Ubergeek63 Well-Known Member

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    I said nothing of the sort. I said simply that I was trying to state it in such away that ALL here could understand.

    I understand the problem completely, a beat frequency is a beat frequency regardless of if you are talking about audio frequency modulated light or the IF generated in a tuner. Shall we take this further into a discussion of subharmonics as well?

    Dan
     
    Last edited: Dec 24, 2008
  4. dave

    Dave New Member

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  5. xanadunow

    xanadunow New Member

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    the problem v/s egos

    The “subtle” exchange between the Pommie and the Ubergeek63 were (for me) the only source of the information that “the shuttle’s rotation stops when the string is broken”, hence the desire to count pulses I could not figure out before because it was not clearly stated. Whether you do detect the missing pulses (4 transmitters/1 sensor) or the missing string (4 sensors) – we are looking at rather complex solution requiring some form of wireless communication. The comment made by eblc1388 is valid; we are here to do our best to solve the problem, not to argue about our egos.

    Would I be to presumptuous in my approach trying to replace the human operator with a sensor to sense the error in the pattern the same way the human does (1 sensor)?

    Regards,
    xanadunow
     
    Last edited: Dec 26, 2008
  6. Rolf

    Rolf Member

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    If the shuttle spool center (axle) is large enough to hold a RFID device then it shouldn't be impossible to a detect the rotation remotely without the need for batteries.
    This is of cause only possible if the center is non metallic.

    For more info on RFID devices see: Radio-frequency identification - Wikipedia, the free encyclopedia
     
  7. xanadunow

    xanadunow New Member

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    RFID tags..

    .. would require the matter not to be metalic (as you stated). I don't believe it is the case..

    Regards,
    xanadunow
     
    Last edited: Dec 26, 2008
  8. user_88

    user_88 Member

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    Optical Sensor Approach

    If a reflective facet or suitable tag could be attached to the spool circumference at some spot, you might be able to employ a laser line generator to create enough of a stimulus to activate an array configuration of photosensors .... LDR, phototransistor, or whatever seems to work.

    The photosensors would be lined up so that more than one revolution of the spool, as it traversed the entire array length, would generate a non-zero signal.
    Maybe an analog integral accumulator could be used here... or possibly a byte or two of input bits on a microcontroller. Some trial and experimentation might be necessary to get the spacing of the photosensors to work correctly.

    If the spool failed and stopped rotating, then usually, the reflective facet would fail to reflect the laser line onto any of the sensors, and the accumulator value would be zero .... leading to a machine stop command. In the rare event that the spool failed at the exact point of rotation where the reflective facet turned on all of the photosensors, an accumulator value above a certain value .... or maybe 8 bits all high .....would also send a machine halt command.
     

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  9. xanadunow

    xanadunow New Member

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    laser thingy..

    It does sound good! The four laser sources would not require any communication, just the supply power - and receptors are mounted stationary. Thumbs up user_88!

    Regards,
    xanadunow
     
    Last edited: Dec 26, 2008
  10. xanadunow

    xanadunow New Member

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    worry..

    ..is in the implementation of the "receptors", this could be costly..

    xanadunow
     
  11. user_88

    user_88 Member

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    .... Right .... getting the sensors to detect enough of a pulse signal to register .. without being activated by spurious light noise, is the first problem to look at.
    Maybe place the photosensors at some modest depth in a well or some type of light shield.

    The one significant dimension to look at is the linear distance along the great circle path that is required for the spool to make one rotation on its own axis.
    You would want to have the optical sensor array span, or maybe overlap this distance.

    ... It would be required to have at least one 'solid' sensor detection per spool revolution ...all zeros or all ones being the machine halt condition... If going analog, then you need some value that is significantly greater than zero.

    ... Increase the signal detection level by placing more than one reflective facet on the spool, maybe in pairs for symmetry.

    Consider using some sort of 'spool arrival' sensor, to produce a signal to initiate the accumulation process, and maybe a 'spool departure' sensor signal, to start the comparison calculation ....

    If you manage to get the initial configuration to perform as intended, you might even be able to eliminate all the laser/sensor arrays except for one.
    That is, you would sense the passing by of each of the four spools, in sequence. This would probably depend on your hardware choice .... An all analog version might be fast enough .... You would have to have some numbers for the spool rotation rate about its own axis, as well as that of the 'great' circle axis, and then calculate the time delay between each spool.
     
    Last edited: Dec 26, 2008
  12. Rolf

    Rolf Member

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    Is the string shown correctly?
    Seems like it should be on the other side of the pulley; item #33 in the illustration.

    Also, is the arm (#37) shown in the two positions, one as in normal operation and the other with no string (tension)?
     
  13. Pommie

    Pommie Well-Known Member Most Helpful Member

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    The original suggestion by eblc was to mount strong magnets in the bobbins and use 1 (stationary) coil to pickup the changing magnetic field. A very cheap and elegant solution.

    It does require that the bobbins make at least 1 revolution whilst under the coil (or multiple magnets per bobbin). Does anyone know how many revolutions the bobbins do per orbit.

    Mike.
     
  14. user_88

    user_88 Member

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    That's a relevant question ... To get the answer you might have to use a variable strobe lamp .... Find the rotation rate of the spool/bobbin about its own axis, and also measure the rotation rate of the spool about the central/sack axis.
     
  15. Leftyretro

    Leftyretro New Member

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    Wouldn't it be variable based on the amount of thread left on the spool as it plays out. Constant thread feed rate but variable RPM of the spool?

    Lefty
     
  16. xanadunow

    xanadunow New Member

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    about magnets..

    The 2*Pi*R of the produced "sock" gives the answer to the lenght of string required to come off the bobbin in one 360 degs orbit. This in turn will provide the information of the MIN (with the bobbin at the max diameter) and the MAX (with the bobbin at the min diameter) revolutions required per orbit.

    I do understand the "magnet" solution, the difficulty here is to distinguish just one broken string. Therefore, not one but four pickup coils should be mounted 90 deg. apart. The number of magnets should be increased to ensure the "pick up" of at least one pulse from each of the rotating bobbins when it is at its max diameter (the worst case).

    That pulse should trigger a monostable at each pick up point (so it is not important if there is more than one pulse present in the pick up due to variations in the diameter of the bobbin and the number of magnets).

    All four pulses from monostables are then delivered to the AND gate.

    The AND gate is checked to make the consecutive decision whether or not to continue the production or to stop the line.

    The first incoming pulse provides the means of a sync (with monostable triggered delay) to "check" the AND gate as above as we have to ensure the presence of 4 pickups from their monostables (if they are all there).

    Once the AND gate is checked - it will be ignored until bobbins progress another 90 degrees in their orbit and the whole cycle starts all over with the first incoming pulse becoming the sync trigger again.

    Monostables have to be set in such a way as to ensure there is only ONE decision made for evey 90 degrees of the orbit.

    Regards,
    xanadunow
     
    Last edited: Dec 27, 2008
  17. eblc1388

    eblc1388 Active Member

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    Why would you want to know exactly which shuttle out of four has stopped spinning?

    Isn't a single shuttle stopped spinning a "sufficient" condition for shutting down the loom?

    Can you replace it with a fully threaded spool while the others are still in service?
     
  18. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

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    Sounds logical to me.:)
     
  19. xanadunow

    xanadunow New Member

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    Which one stops is of no importance. The presence of four pulses is. The 4 sensors 90 deg apart on the orbit, ensure the point in time where the four pulses should come in.

    Monostables do take care of difference in diameters of the bobbins and the number of magnets/pulses (one pulse is all that is required to trigger).

    The check of the AND gate is done with the delay to avoid false "stop the line" triggering i.e. I am making sure there is sufficient time to have 4 monostables triggered in the 90 degs of orbit cycle.

    The first incoming pulse is the indication that all 4 bobbins have arrived at their sensing points, therefore it is my SYNC from which I can determin the time required to get positive answers from all 4 (hence the sync is delyed). If I get only 3 positive answers - it means that a string is broken/finished and the line must stop. The AND gate takes care of that.

    This is repeatble and easily tuned to the operational speed of the production line.

    Magnets don't require powering and the remainder of the hardware is stationary. The 4 sensors are only detectors really and all logic is done in another box positioned in a convenient location.

    xanadunow
     
    Last edited: Dec 27, 2008
  20. xanadunow

    xanadunow New Member

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    I need to add one more thing, there is a point that requires to mark the end of the 90 deg cycle).

    This is done easily. When a "decission" from the AND gate is made as "YES" (i.e. continue with production) and the AND gate becomes ignored for the "decision purpose" we must sense all 4 monostables with the OR gate to know when all of them do become OFF again and this is the end of the 90 deg cycle for these bobbins sensor in their 1/4 orbit. The AND gate can provide the same information except we would not know when the last activated monostable went OFF - only when the first one.

    The next pulse after that will signify the beginning of the next 90 degs cycle.

    xanadunow
     
    Last edited: Dec 27, 2008
  21. xanadunow

    xanadunow New Member

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    monoastable timing..

    .. should be set to no more than 45 degs of the orbit to ensure proper end of the 90 degs cycle. The trigger delay for decision making check of the AND gate should fall somwhere half of that value. These are "sure" values and may be trimmed much finer if required.

    You would need to play with the number of magnets on the perimeter of the bubbin shaft to ensure at least ONE single pulse in a single 90 deg of its horizontal movement cycle.. It is a monostable sensor, if there are more pulses - it does not matter, the monostable will stay "ON" way past the time the bobbin have already moved away from the sensor.

    xanadunow
     
    Last edited: Dec 27, 2008

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