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Help needed with an interesting mechanism!

  1. Oct 24, 2008 #1
    Hi guys,
    I've been dropped in at the deep end at work, tasked with designing a latching mechanism for an armrest on a luxury aircraft seat - It has to work on a remote latch principle, ie by pushing a sprung-loaded button downwards to actuate a link arm via a pivot, which then retracts the remote (actron) latch from its striker, enabling the armrest to be opened/rotated on its hinge.

    I have some pretty good sketches of the parts of the mechanism as I see it, however I need someone to have a look over it & give me their guidance on how I should proceed. I'm not a mechanism designer - I normally don't get concept design work, but I want to rise to the challenge & produce something which works well.

    I can send loads of scanned sketches via email if anyone feels they would like to help me out here - I would appreciate some guidance. Thanks in advance. James
     
  2. jcsd
  3. Oct 24, 2008 #2

    Danger

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    Welcome to PF, James.
    I doubt that anyone is willing to give out their e-mail address, but you can post the pictures here by using Image Shack or a similar service. It would definitely help people to think up solutions.
     
  4. Oct 24, 2008 #3
    Hi,

    OK thanks for the good advice, I will get my sketches scanned & put them online.

    Cheers,

    James
     
  5. Oct 24, 2008 #4

    Mapes

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    I think you should check with your boss before publishing your company's designs. I doubt the principals would appreciate the implicit statement that their design reviews are conducted by soliciting comments on an Internet forum.
     
  6. Oct 25, 2008 #5

    Danger

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    That's a good point, Mapes. I never think of things like that when answering.
    The principals might, however, appreciate that this isn't just any old internet site. It's pretty much the most prestigious science forum in the world, with world-class engineers, physicists, mathematicians and biologists available. Although some bad advice will probably be given, people who know better will shoot that down immediately. Something as inherently simple as an armrest can potentially make the difference between life and death in an aeroplane accident. No one here will ever take that lightly.
    I can come up with a basic mechanism, but there are structural and aerospace engineers who will most assuredly analyze the situation and point out any flaws.
     
  7. Oct 26, 2008 #6
    Do you have an existing seat design with movable arm rests? Does it have a local latch? If it already has a local latch that has passed acceptance testing, and and the issue is to change to remote release, you will likely find people more will to offer suggestions.
     
  8. Oct 27, 2008 #7
    Hi all,
    Thanks for the constructive points so far. Just to clarify - it is not my intention to go into huge detail or expose confidential design material, I merely need some assistance in the process of constructing a basic mechanism. Pointers / help, thats all.

    I have a blank sheet of paper - no existing design. I have designed a bezel & button which sit on top of a leather covered armrest, the passenger pushes down on the button from the top (max 30N force to actuate) & I need advice on translating the vertical motion to horizontal motion to actuate a remote latch. I am thinking of using a cam / rod arrangement maybe. I can define basic dimensions - if anyone could give me some pointers on how I should start defining the mech I would be grateful.

    I'm just starting out in my engineering career - we all have to start somewhere. Thanks for any advice you can offer.

    James
     
  9. Oct 27, 2008 #8

    Danger

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    Sounds like a simple bell-crank should do it. If there's any significant resistance to be met, such as 'torque-lock', I'd recommend that it be set to pull, rather than push, the latch. That would eliminate flexing of the tie-rod.
     
  10. Oct 31, 2008 #9
    Danger, thanks for the reply. I had been thinking along those lines also. I'm working on some basic sketches & will upload them to webspace tomorrow (Sat), I need to get this figured out over the coming weekend so I know where I am going next week. Its getting there! Cheers for the advice so far.
     
  11. Nov 1, 2008 #10

    Danger

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    Well, I'll be around for a while. Keep in mind that I have no formal education, so if anyone disagrees with my advice, you should listen to them.
     
  12. Nov 1, 2008 #11
    Hi all,

    Here are some basic sketches of the button / latch positions I have to work with. I have uploaded them to auctionpix.com webspace for ease of viewing.

    Application 1 arrangement...
    http://auctionpix.co.uk/users/kvq1336679.jpg

    Application 2 arrangement...
    http://auctionpix.co.uk/users/vap1336680.jpg

    My initial thoughts on a bell crank...
    http://auctionpix.co.uk/users/chw1336681.jpg

    Scenario - I have to translate a 30N downward force into horizontal motion to retract 2 x remote latches. I envisage a bell crank with tie rods, working in tension to pull back the latch bolts by 0.30". The button has around the same distance to depress in its housing.

    I have two arrangements to design for - the latch / button relationships are different between the two.

    I am looking for help / advice on defining the mechanism. How do I make this thing work! Any help / advice very gratefully received. James
     
  13. Nov 1, 2008 #12
    PS - I forgot to mention (although it is a small note on one of my sketches!) the whole mech has to be encapsulated within a 0.90" height due to being housed within the armrest. J
     
  14. Nov 2, 2008 #13

    Danger

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    Hi again.
    After seeing the sketches, and learning of the encapsulation size restriction, I've changed my mind. I think that a bell-crank link is overly complicated for this application.
    It would be simpler to just mount your button on a sturdy 'stem' (think rectangular mushroom) that extends through a pilot bushing with a nylon wedge on the bottom. That could then be used to cam a horizontal follower plate back to pull the tie rods. You'd just need a couple of guide slots to keep the follower straight. One moderate compression spring around the stem would be enough to ensure button return.
     
  15. Nov 2, 2008 #14
    Danger, Thanks for the advice - I see the benefits, especially due to the height restriction - getting the bell crank packaged in such a small space was going to be a headache. Will keep you posted. Cheers again.
     
  16. Nov 3, 2008 #15

    Danger

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    Just got another idea for further simplification, but I don't know if it conforms to your requirements.
    Does the depression of the button have to be straight downward? If not, you could just angle the button 'well' so that it slides backward as it goes down. Then you could connect the button stem directly to the tie rods.
     
  17. Nov 3, 2008 #16
    Thanks thats something I had not considered - will look into it. James
     
  18. Nov 8, 2008 #17

    Danger

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    To extrapolate even further, is there any particular reason that the button has to be on the top of the armrest? If not, putting it on the front would allow a straight rearward depression that could directly pull the tie rods.
     
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