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Multi-Position Solenoid

  1. Oct 11, 2013 #1
    Hi-
    I'm trying to build a simple linear motion control using a solenoid. I've replaced the typical steel core for a permanent magnet core so that I can both push the armature out and pull it back in by flipping polarity (and without using any springs). This works nicely.

    Unfortunately, it still can only go full out or full in, like a regular solenoid. I would love to be able to add a stopping point mid-way. So in effect, I could 3 positions - In, halfway out, all the way out - and still be able to go both directions.

    Is this possible? Perhaps with a core that is some combination of reversed polarity magnets and a steel core? Or with a steel ring that acts like a mid-point latch?

    Any ideas are helpful.

    Thanks!
     
    Last edited: Oct 11, 2013
  2. jcsd
  3. Oct 11, 2013 #2

    davenn

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    Science Advisor
    Gold Member

    hi there

    just a random thought ..... what about multiple coils that you could control current clow direction individually or combined. ?

    Dave
     
  4. Oct 11, 2013 #3
    I had the same idea, and I'm pretty sure that would work, the problem is that it increases the complexity of the control circuit (I would now have to control multiple EM coils and with good timing). The goal is create a large matrix of these and each additional complexity in control will result in exponential complexity in the whole system. But it is a fallback option.
     
  5. Oct 12, 2013 #4

    berkeman

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    Staff: Mentor

    Maybe think about a rachet mechanism in combination with your bidirectional solenoid. Move the shaft in rachet steps...
     
  6. Oct 13, 2013 #5
    A solenoid decreases its force with displacement whereas a spring increases its force with displacement. It seems to me if you were to put the spring back in, the more current you put through the coil, the greater the displacement that would result. At a particular current, the displacement should be constant and stable.
     
  7. Oct 13, 2013 #6
    Hmm interesting idea. The downside is that to keep it at the midpoint you would have to supply continuous current, which is not ideal.
     
  8. Oct 13, 2013 #7
    Understood, however if a solenoid were constructed with a spring for each direction were at zero displacement when the core was also at zero displacement, it should work.
     
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