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Controlling linear actuators

  1. Feb 20, 2014 #1
    I have never used a linear actuator before so I'm looking for a little help in applying one to my project.

    The question is in how to control them the way I would like. Everything seem to require you toggle and hold a switch to operate in each direction. And if you keep holding it, it'll just keep trying to move.

    I would like to be able to just use a momentary switch, have it extend to it's limit, stop and then wait until I push the button again to retract. It would be nice if it could be made to stop in the middle with the button, or stop if it got jammed up or obstructed.

    This is nothing more than every garage door opener can do, so it must not be impossible or require an SGI to handle, but I can't seem to find anything.

    Thanks for any assistance.
     
  2. jcsd
  3. Feb 20, 2014 #2

    Baluncore

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    Assuming a DC motor...
    There needs to be a limit switch at each end of the travel that prevents current to the motor.
    Each limit switch will have a diode across it so the motor can move away again.
    There will be two relays, they self latch when an up or down button is pressed.
    They drop when a stop button is pressed or a limit switch is reached.
     
  4. Feb 21, 2014 #3
    Thanks for the response.

    Are the limit switches you refer to typically built into the actuator itself? I know very little about these things and there seem to be a great number of them available, and I would be surprised if it wasn't common to have these fairly basic options built right in. I can't imagine everyone wants to stand around holding a switch every time they move the thing.

    It would be really easy to make my own travel stop switches on either end of travel that get triggered at the start and stop positions. I guess it would have to reverse polarity for the next action, but all this is so basic I can't help but think there must be something available off the shelf. I'm just hoping someone knows where to find it.

    Thanks
     
  5. Feb 21, 2014 #4

    Baluncore

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    You must check the details, or you will be surprised. Never assume anything when buying on the internet.

    Safety is important in any design. Do you have a good insurance policy?
     
  6. Feb 21, 2014 #5
    Er, what is it I should be concerned about with regard to safety??
     
  7. Feb 21, 2014 #6

    Baluncore

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    That is the question you should be asking yourself at every step of your design.

    Anything that moves under power should have safety switches that will prevent injury to people or damage to the equipment.
     
  8. Feb 21, 2014 #7
    Noted, thanks.

    I guess that takes us back to the original question, which is, how to achieve this using actuators.
     
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