Help! Optical sensors, actuators and more

Discussion in 'The Projects Forum' started by bzzzt, Dec 4, 2010.

  1. bzzzt

    Thread Starter New Member

    Nov 1, 2010
    4
    0
    Hello everybody, newbie here.

    My problem: I am working on an electrically driven platform lifter. The lifting is being done by -two- linear actuators that need to always be equal in height, no matter the weight discrepancy between them.

    Retracted State
    [​IMG]

    Expanded State
    [​IMG]

    Encased in the rising boxes are two linear actuators. In order to keep the table stable, they must be rising at the exact same rate.

    To do this, I came up with an idea that would get them to rise in sync. I want to place an LED on one box, and based on which one of three sensors picks up the light, three different things will happen:

    If the middle sensor on actuator #2 picks up the light, that means that actuator 1 and actuator 2 are at the same height. Therefore, they are both risen at the same time. If the bottom sensor picks up the light, that means that actuator #2 is higher than actuator #1. Therefore, current must be turned off to actuator #2 until actuator #2 catches up in height. If the top sensor picks up the light, that means that actuator #1 is too high, and thus current is turned off to it until actuator 2 catches up.

    Heres what I'm trying to do:

    [​IMG]

    My questions:

    1. Is this design a plausible solution to my problem? Do you think it will work?
    2. If it will work, do you have suggestions on components? I think I will use solid-state relays for the optical sensors.
    3. The actuators require 10A each. How should I go about creating this current? I want this machine to work from a standard wall plug.

    Any other advice would be GREATLY appreciated... This is a great community!!


    -Bzzzt
     
  2. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    you would likely need a polarized light source, ie; laser.

    you could mechanical tie the actuators together, and save on one motor.
    you could use position feedback to accuately locate both drives.
    you could use two steppers of the same angular step, geared identically.
     
  3. radiohead

    Active Member

    May 28, 2009
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    31
  4. bzzzt

    Thread Starter New Member

    Nov 1, 2010
    4
    0
    Your idea about using the stepper motors interests me. How would some such chip detect which 'step' (tooth of the motor-gear) the particular stepper motor is on? Does the motor have an output? Could you expand on this idea and suggest a component?


    Also, I cannot use a scissor lift as it is too expensive, and I don't need all that extra height.

    -bzzzt
     
  5. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    10 amps each from a wall outlet for 2 motors??? That's roughly 3 horsepower. Just what are you lifting here? Unless you're an expert, a drive of that capacity is something you'd be much better off buying rather than building.

    As for steppers, good luck on finding any with that kind of power.

    But for synchronizing them, in theory all you have to do with steppers is wire them in electrical parallel, and they will both do the same thing.
     
  6. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    As suggested, you drive them off a common signal.

    Scissor lifts are rather simple devices. If you building the device, a scissor mechanism is not much more.
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    To raise in pillars as shown, I'd suggest a scissor assembly.

    Alternate would be a worm gear type drive, but the shaft would need to be rather stout (read: expensive). Benefit to this is no power is required for "holding", only movement.
     
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