Two pneumatic cylinders – Same speed


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    Hello all,

    I am in a predicament at work, and I thought that some of you might have some clever ideas about how to make my day better!
    Here is the situation: in a current telecom project, I am using two 25mm heavy duty (with two pins in addition to the rod) cylinders, distant from about 500 mm from each other. I could not use a single cylinder since I have a lot of connectors to connect (the cylinders pulls a device towards test connectors).
    I have clearly underrated the speed difference problem between two cylinders. I thought that, considering the forces at stake, and the guiding pins helping, that any mismatch would be "eaten" by the cylinders themselves. Well, it works in most cases, but it does become problem at some point, randomly. One goes quicker than the other one, and both cylinders stop due to the side load they are subject to.
    I could redesign quite a lot, to better link mechanically these cylinders, or by having some kind of dampener that could take care of the non parallelism, but my project is in a very critical phase with virtually no time at all. Only a few days to have a concrete solution.

    It is pretty obvious that the problem disappears when the cylinders work at high speed. But since I test connectors in place, I must be "gentle" with them. But my first idea is still to make the cylinders go quickly enough to prevent the current trouble, but not so quick that the connectors are worn out quickly.

    But thinking about the speed of the cylinders, I thought of the other way around. Since the pins in the cylinders allow quite a lot of side load, it might just work to make the cylinders move very slowly. In that case, one will not "have the time" to go first all the way until getting stuck. It would so that the other one has enough time to move before the first one get stuck, and this during the whole pulling process.
    Am I totally dreaming?

    Another obvious thing is that some preloading on the cylinders help them to go down well. I haven't tested with my device on (it is a 15 pound device) so it might just work directly, but I was wondering if any of you guys had similar "preloading" experience.

    And at last, I cannot be the first one to encounter this problem. A few of my colleagues have had it before, but none of them really solved it (they all redesigned heavily). I cannot believe that there is not one "somehow quick" fix considering that the whole thing is working already, and it feels as if I am so close to something stable.

    Oh, anf for those wondering, I use separate speed cylinders and vavles for each cylinder, that I tune until the cylinders go at the very same time. But it is only an eye tuning, those tens of seconds that I lose might be the very reason why the whole thing is not stable after a few minutes.

    Any idea / support would be greatly appreciated! Pneumatics rock, but this has got to be one of their major drawbacks.
    Thanks a lot to everybody reading this message!

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