Need a Specific Linear Push Solenoid!!

Discussion in 'General Electronics Chat' started by Konduction2, Feb 16, 2014.

  1. Konduction2

    Thread Starter Member

    Feb 12, 2014
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    I'm looking for a linear push solenoid that can output a many different displacements in proportion to a voltage I give it. All of the solenoids I've seen, regardless what of voltage is supplied to it, either have their shafts fully extended or fully receded. But I want one that can be 0%, 25%, 86%, etc extended in proportion to the voltage I supply.
    Also, I plan to supply it a power that will go up and down a few times a second, so it must be able to oscillate somewhat quickly (moderate accuracy is OK)

    Also:
    -I want one with a displacement of between 2mm and 15mm.
    -It needs to have at least enough force to push 35 grams against gravity
    -I would prefer one that only needs 12VDC to fully extend, but this isn't necessary. I can go up to 24VDC

    Help! Is there any solenoid that fits these parameters that I can buy?? I've been trying to make one, but it's SO frustrating - I really don't want to make one if I can buy one. Please provide a purchase link if you know one; it would help soooo much and I will be forever in your debt!!!!
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    I am not aware of any such mechanism except a voice coil.
    There are linear motors but these require some form of position sensing and servo feedback control. You can also use DC motors and servo mechanisms.

    Have you tried a solenoid pulling against a spring?
     
  3. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    What force do you require from this? Maybe the head arrangement from a harddisk could work for you.
     
  4. bertus

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  5. Konduction2

    Thread Starter Member

    Feb 12, 2014
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    MrChips: I have tried that, but the ones I've built are far too weak, and the ones I've seen online don't output variable displacements. Thanks for the voice coil mention!

    Kubeek: Thanks, I've gotten that suggestion before, but I need linear displacement (I am aware I can improvise a way to get linear displacement from this, but it would be too messy)

    Bertus: Ah thanks! This seems to be what I am looking for! However, I have a concern. I went to the "operating info" section of that website, and it says
    "Required Electronics:
    Because of the very low inductance of the actuator, a DC linear servo amplifier is required to provide power to the Voice Coil. A programmable motion controller is required to close the position loop on the system."

    Would I be able to use this without the servo amplifier and the motion controller?? I want to just feed it an amplified music signal (using an LM386 audio op-amp and a TIP31c power transistor) so it can tilt a laser mirror.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This is exactly how a proportional valve works, but of course the spool is used to vary a specific hydraulic flow.
    Not sure if one could be adapted for your purpose.
    Max.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    A solenoid structure with a spring which resists the attraction might function in this application. Increasing voltage supplying the increased attraction to overcome the resistance from the spring allowing a deeper penetration while lower voltage levels would provide the opposite.
     
  8. snav

    Active Member

    Aug 1, 2011
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    I don't know how much force is available, but a Wiggy tester works that way. I assume it's balanced against the spring so Zero sum for force available. You might get the results you want with two coils and a differential voltage.
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
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    It seems like you should be able to make a hobby servo work to tilt a mirror. They are easy to control with a simple circuit. Can you convert a rotary motion to something close to linear or could you use a rotary motion to tilt your mirror?
     
  10. Konduction2

    Thread Starter Member

    Feb 12, 2014
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    Yeah, it would be logical to think spring loaded solenoids should work, but I tried one and it didn't. When I gave it 3, 5, and 9 volts, it didn't budge - then I gave it 12 volts and it went all the way. That's why I'm asking for a link to a specific solenoid, because I'm pretty sure most of them are like that, which wouldn't work. If 12v is what made it extend all the way, then I need it to be halfway extended at 6v, etc.

    I can't use a servo because they take data input, not analog voltage. If I could, then I would just get a linear servo. I am deliberately avoiding the use of a microcontroller, because I am proving to some friends that a lot can be done without software.

    Anyway, I hear a voice coil actuator might work. So far, it seems to be what I'm looking for. However, I still need to clear something up: can I use it without software, and just feed it an amplified music signal (using an LM386 audio op-amp and a TIP31c power transistor) so it can tilt a laser mirror??
     
  11. inwo

    Well-Known Member

    Nov 7, 2013
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    I'm sure that someone can supply a circuit to drive a servo with a voltage controlled pulse generator.

    Not involving a microprocessor.

    Have you searched on here?
     
  12. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    This may be a dumb solution, but here goes. Since this is a music driven project, why not use a small speaker to move the mirror? A speaker like out of a headphone set. Hot glue a stiff wire, like bailing or mechanics wire to the dust cover (center dome) of the speaker. Then link that to the mirror.

    To move different mirrors to different frequencies of music, small crossover filters could be made, for the separate mirrors.
     
  13. MaxHeadRoom

    Expert

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    Proportional valve amplifiers and servo drives use ±10vdc analogue also.
    Max.
     
  14. ronv

    AAC Fanatic!

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    You can build a pulser for the servo using a single 556 IC and supply the analog voltage to the control voltage pin to adjust the pulse to get the desired rotation.
    Moving coils and springs probably won't do it as the motion is load dependent and won't follow the voltage in a linear fashion.
    There is an example circuit in the TI datasheet for the output 555 then you just need another to trigger it at a 20 ms rate. I'm not sure the hobby linear servos are closed loop. I think they just spin in one direction or the other until you stop them.
     
    Last edited: Feb 17, 2014
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  15. Konduction2

    Thread Starter Member

    Feb 12, 2014
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    Inwo: Yeah I've heard I can use an NE555 timer IC to take my voltage input and generate a specific PWM that might run a servo, but I don't see why I would go through that all that trouble when I might instead be able to just get a device that directly takes voltage and outputs displacement, lol.

    Shortbus: Actually, using a speaker driver is exactly what I wish I could do, especially as they are so easy to buy and I know already exactly how they work. The problem is that the only ones that output a big enough displacement are too expensive and way too big.

    MaxHeadRoom: Really? Of those two, which would be better? Do they fit the parameters I listed in the very first post? If yes, could you please give me a purchase link?

    Ronv: Would coils not work even if its specified output force is high enough? And I thought servos are controlled by a specific data signal, not simply varying pulse frequencies?

    ***Can someone please answer this question please: Would a voice coil actuator work if I just feed it an amplified music signal??***
     
  16. strantor

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    Oct 3, 2010
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    Yes. Watch videos on YouTube . Search "voice coil linear actuator"
     
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  17. ronv

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    I haven't heard you say you want to play music on it. What I have heard is that you want to apply a voltage and hold a position, or change a position quickly. If you apply DC to a speaker it will just go to one extreme like the solenoids.
    The hobby servos work with a pulse width of 1.5ms for the center position, 1 ms for rotation in one direction and 2 ms for rotation in the other direction. In between are all the positions typically between about 0 to 270 degrees.
     
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  18. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Not exactly. The speaker voice coil and diaphragm are sprung to the centre, so the deflection +/- away from centre depends on the strength of the magnetic field, which is determined by the +/- current through the coil.

    However what yo said is true for cases where you apply too much DC current, it will move the coil +/- until it hits the end stop.
     
  19. MaxHeadRoom

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    Motor or inductive loads.
    http://www.a-m-c.com/products/analog_brush.html
    Max.
     
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  20. shortbus

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    Sep 30, 2009
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    I may have a wrong idea of the size of your "laser mirror". Of the laser mirrors I've seen in movies, TV science shows, etc, the mirror is only about one inch square. Is yours going to be bigger?

    The movement,displacement, of a speaker cone is small, I grant you. But that is where 'mechanics' comes into the picture. A 1" mirror, pivoted in the middle, with the link to the speaker cone close to the pivot point will move the outside edge much farther. Kind of like a rocker arm or bell crank movement.
     
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