• Welcome to engineeringclicks.com
  • mechanical linkage

    Discussion in 'The main mechanical design forum' started by oemodm, May 4, 2014.

    1. oemodm

      oemodm Active Member

      Joined:
      May 2014
      Posts:
      25
      Likes Received:
      0
      Hi Everyone,

      Having a bit, well, alot of trouble trying to design a linkage which does this (A to B in picture below). Arms move from vertical to 45 deg, and slider on each moves up at same time by 30cm.

      [​IMG]

      Tried making something up, but its unstable and a little difficult to operate.

      [​IMG]

      Tried making a drawing using scissor linkage, only to realise it would not work at all.

      [​IMG]





      Any pointers would be extremely useful.
       
    2.  
    3. Lochnagar

      Lochnagar Well-Known Member

      Joined:
      Feb 2011
      Posts:
      157
      Likes Received:
      0
      Hi,
      I am not quite sure what you are trying to achieve here nor is it clear if there are any space restrictions on where the additional links or gears can be mounted.
      However, it looks as though all you are trying to do is "open up" the two vertical bars (picture C) so that they are at 45 degrees to the horizontal (picture D). If this is the case - then do you really need the two green sliders?

      However, which ever option you are trying to achieve - you need to synchronise the system - so that the two vertical bars open out in unison. There are many ways this can be done - either with a mechanism incorporating gears on the end of the bars (at the pivot point) - and a double sided rack to drive the gears. The rack however needs to slide perpendicular to the 15cm link - and needs to be restrained to this perpendicular position which is easy to do.

      Another way - is to try and achieve the synchronisation with springs - bearing in mind that one spring will not want to extend dramatically more than the other spring. This is less perfect (and will not achieve perfect synchronisation) - but may do for your particular application.

      However, in the meantime have a look at an umbrella mechanism - to get some inspiration.

      Hope this is of some help - but if you are still needing some help - then maybe you can provide some more information on the restrictions that you may have - and what you are really trying to achieve.
       
    4. oemodm

      oemodm Active Member

      Joined:
      May 2014
      Posts:
      25
      Likes Received:
      0
      I appreciate your advice. Thank you.

      The green sliders, need to move up as they control another part of the same linkage which is currently hidden.

      Restrictions:

      1 = Depth. Mechanism for opening the bars to 45 deg + moving sliders up 30cm, should not add depth, and should fit inside/between the 2 vertical blue bars.

      2 = I wanted to stay away from gears, for 2 reasons. They will cost more than a linkage. They have more chance to wear out/fail, as the size/stress this full linkage will undergo will be quite high. That's why I favoured a linkage.

      3 = Last night I thought of a pulley system instead. That might work (instead of gears). But as yet, no major ideas...
       
    5. Lochnagar

      Lochnagar Well-Known Member

      Joined:
      Feb 2011
      Posts:
      157
      Likes Received:
      0
      Thanks for providing some further insight into the problem you have. However, there are still a few questions running through my head since you haven't provided any further information on the linkage "beyond" this mechanism - which you say is hidden.

      So just being the Devils Advocate - why do you need the 3 blue coloured bars? Why can't you have two curved rails - that allows the green coloured carriages to slide outward radially and angularly simultaneously - thereby achieving what appears to be your objective of moving the green coloured carriages from their position in your picture C to picture D?

      It would be helpful if you could provide a sketch of the mechanism you are trying to drive "beyond" the above mechanism - so that we can perhaps understand more about what you are trying to achieve.

      On the topic of gears for synchronisation - these can be very inexpensive - since they can be water jet cut - and be part of the lever. A very simple example of such a system - is a wine bottle cork puller - see example below. However, I have used this method in industrial applications.

      Hope this is of some further help.

      http://levohome.com/stainless-steel-cork-puller-red-wine-air-pressure-opener-p-418.html
       
    6. oemodm

      oemodm Active Member

      Joined:
      May 2014
      Posts:
      25
      Likes Received:
      0
      Hi Lochnagar - you really sparked thought from your initial reply. As linkages are a bit new for me, I tend to get nervous which blocks thought. So far, I'm quite content to run with this:

      [​IMG]
      A = "extra linkage" which pushes the arms up
      B = "extra linkage" in lower position
      C = Slider, at top position 30cm higher
      D = The slider at this point, gets pushed out a little further when perpendicular to the fixed pivot. Not ideal, but workable. I could over come by curving the outer arms (but this would only add cost + make other things a little more complex).

      I can lift the linkage at point C also, there will be some mechanical advantage. I'm content for now, however, backup solutions need to be prepared.



      You are right. Never assume. In this case, the final use doesn't need a sharp bottom end. The 15cm wide bottom bar reduces the sharpness.


      Beyond this linkage, I would like to keep to myself for now. Since its an attempt for some mild innovation. Your cork screw gear reference, very nice. Very nice thought pattern. I know how to make this relatively cheaply
       
    7. Lochnagar

      Lochnagar Well-Known Member

      Joined:
      Feb 2011
      Posts:
      157
      Likes Received:
      0
      I think you have tried to post a picture to provide some further illustration of your mechanism - but unfortunately the picture doesn't appear in your last posting.

      I guess the other things that spring to mind about your mechanism is:-

      1)I assume the green coloured carriages will possibly need to be locked in position at the two extreme positions - or does the other linkage that is "beyond" this mechanism (which isn't shown) hold these green coloured carriages in position?

      2)What system do you envisage for "deploying/activating" - or "opening out" the mechanism? As you probably appreciate from your very early pictures - it would be possible to manually open out the blue bars (which then causes the green coloured carriages to move radially out and angularly outwards via a mechanism of some sort) - or it might be possible to manually move the green coloured carriages radially out and angularly outwards (which then causes the blue coloured bars to rotate via a mechanism of some sort). You can perhaps see where I am coming from with this question.

      3)What sort of forces are the green coloured carriages subjected too?


      Other things that might be of interest - are:-
      Over centre mechanism - which is very handy for locking things

      So - the picture below - I think does what you are looking for - but as I say you need to synchronise the bars (with the gears as I explained before) - and possibly incorporate a locking mechanism too.

      Hope this helps.

      [​IMG][/URL][/IMG]
       
    8. s.weinberg

      s.weinberg Well-Known Member

      Joined:
      Nov 2012
      Posts:
      58
      Likes Received:
      0
      The linkage in the last post looks pretty much like what you're looking for. The only thing I'd add to it would be a horizontal member that runs up and down your central vertical axis, and which has a slider pin connected to each of your green sliders, so that it remains horizontal, but they can move along it's length and rotate relative to it.

      That would synchronize your two sides, and allow either your sliders or blue bars to be the activating portion of the mechanism.
       
    9. oemodm

      oemodm Active Member

      Joined:
      May 2014
      Posts:
      25
      Likes Received:
      0
      Lochnager, thank you for your feedback and CAD drawing:

      Very good point. But I leave the minor design challenges to the end, which, as you suggest the other part of the linkage my solve itself. I've learnt to work this way. I'm thinking to have ball chain string, inside the tubes, so if you extend the linkage from either side, a ball chain could pull to unlock a locking pin from either side.

      Good point. I will use the green carriages (green, from original drawing) as they offer the most leverage to unfolding the total linkage.

      Not much. But its easy to beef them up and/or add slide bearings/bushings if needed.

      Yes. I'm new to this kind of more mechanical design. I think with the rest of the linkage hooked up, I will discover something along these lines.

      You have been a GREAT help. People like you make forums like this so utterly rewarding.

      You mean, in closed position, the horizontal members width would be as wide as the opened position for the green sliders? If so, its a nice simple idea but the closed position should be as small as possible. However, thankyou. And sorry if I mis-understood.


      This is what I'm running with. However, will move the green sliders (now greyed) pivot point, to the outside of the blue bar to reduce over opening when sliding up.



      [​IMG]
       
    10. BruceK

      BruceK New Member

      Joined:
      May 2014
      Posts:
      1
      Likes Received:
      0
      Your first linkage setup would work, if you pinned the two cross bars together in the middle.

      Bruce
       
    11. Chris Cantrell

      Chris Cantrell Member

      Joined:
      Dec 2013
      Posts:
      21
      Likes Received:
      0
      That wouldn't work, because the two cross links don't cross in their middles when the sliders are raised. Also, and more fundamentally, pinning the cross links would make it a fixed truss, not a folding linkage/mechanism.

      To the OP, if you want to ensure the two cross members in Lochnagar's post open equally, add geared teeth to the joint where the two cross members are connected, like the wine bottle opener spoken of above. Realize, too, though, that the mechanism introduced by Lochnagar will cause the original arms in your first graphic to swing further than 45 degrees away from the vertical while in transit. I don't know if that's a problem or not.
       
      Last edited: May 12, 2014

    Share This Page