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Thread: Scissor lift with vertical cylinders

  1. #1
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    Lightbulb Scissor lift with vertical cylinders

    Hi to everybody!
    I need to design small-sized lifting mechanism, for my course project. Then I fount this US patent http://www.google.com/patents/US4113...page&q&f=false
    In that patent was mentioned about the "traditional" scissor lift. However, if we ask google "scissor lift" we can see, that in generally, "traditional" construction with one cylinder, which rise from almost horizontal position, is being used. So I hesitate in my decision... who have already concerned with question? who have any idea, why construction of scissor lifts with vertical cylinders are not so widespread?
    p.s. For my project I need lifting mechanisms to elevate 500 kg (1400 lb) in 6 meter (16,7 ft) height.

  2. #2
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    You need to think this through. Sometimes things are done for good reason and not just because it looks nice.

    Why don't you discuss with us why you think a vertical cylinder would be better or worse?

  3. #3
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    Why don't you discuss with us why you think a vertical cylinder would be better or worse?
    1. The fact that as the lift mechanism is initially elevated from its lowermost position, the hydraulic cylinder unit of the prior art hydraulic mechanism is positioned almost horizontal, and it must exert an excessively high trust on the mechanism to turn the lower-most arms and to start the vertical extension of the linkages. Then, lift is extended more and more in a vertical direction, the hydraulic lift unit pivots to an upright position, and it requires less and less thrust to move the load. This results in the need for an excessively large hydraulic lift unit in the prior art scissors lift in order to be effective to move the linkages from their retracted to their fully extended position, and it often leads to the requirement for auxiliary hydraulic lift mechanisms...
    2. As my previous calculation show, for the same load, I will need smaller beam cross-section. Not significant, but smaller.
    For disadvantages of vertical cylinder, as I think:
    One and main reason it's expensiveness, because of two cylinders, and they even may be telescopic as it showed here: http://en.wikipedia.org/wiki/File:He...cissorlift.jpg
    so, I'm still in confusion
    But fact is fact, vertical cylinder scissor lifts are very very rare, and I think, they are not produced anymore...
    Sir, may be you have more information or data about this question?

  4. #4
    Technical Fellow jboggs's Avatar
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    Vova - We are very close to violating the rules on homework here. You might want to check that out.
    But here's a tip... You seem to have a grasp of the forces and vectors involved. Investigate the physical dimensions involved. "Extended overall length" vs "retracted overall length".

  5. #5
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    jboggs thank you for answering!
    Investigate the physical dimensions involved. "Extended overall length" vs "retracted overall length".
    I have already done this. If we use telescopic vertical cylinders, "retracted overall length" the same as in traditional scissor lift. But these cylinders are known to be expensive...
    as I think, the main reason of "vertical cylinders are not so widespread?" is economical reason, not mechanical.
    Vova - We are very close to violating the rules on homework here. You might want to check that out.
    Question that I asked and discussing now is not my home task. It just for my personally fully understanding of the question ;-)

  6. #6
    Technical Fellow jboggs's Avatar
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    Quote Originally Posted by Vova View Post
    jboggs thank you for answering!

    I have already done this. If we use telescopic vertical cylinders, "retracted overall length" the same as in traditional scissor lift. But these cylinders are known to be expensive...
    as I think, the main reason of "vertical cylinders are not so widespread?" is economical reason, not mechanical.
    Most scissor lifts I have seen have an overall height of 6" or less when retracted, and an overall height of several feet when extended. I have never seen any cylinder, telescopic or otherwise, that can do that. Find any telescopic cylinder that can extend to 48" overall length. The retracted length is going to be much greater than 6". The main reason scissor lifts have angular cylinder arrangement is - simplicity.

  7. #7
    Administrator Kelly Bramble's Avatar
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    Horizontal vs. vertical hydraulic cylinder configurations both work in scissor lift designs. There are advantages and disadvantages in both approaches.

    A horizontal design approach lends itself to a more compact collapsed configuration, where a vertical design simplifies force required calculations.

    As in all engineering design – end-item specifications drive the concept approach.
    Last edited by Kelly Bramble; 10-05-2012 at 10:27 AM.

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