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Constraints for cam follower in an assembly

Discussion in 'Using Alibre Design' started by raygilbert, Aug 3, 2018.

  1. raygilbert

    raygilbert Member

    File attached
    It is possible to create a cam part (e.g. Large radius + small radius + 2 tangent lines) and a follower part (circular boss) then assemble them with constraints such that when the cam is rotated about the large radius the follower will move in a linear fashion?
    I can make the parts and set up the tangent constraints but this will only constrain one of the four individual sections of the cam , not the full cam profile.
    The cam I want to simulate does have a more complex profile than the attached file.

    Attached Files:

  2. oldfox

    oldfox Alibre Super User

    I think you'll have to "Package" the assembly so the "Parts" can be seen. (File > Package > Create) This will generate a Package file. Save and upload that one.
  3. raygilbert

    raygilbert Member

    OK, have not used that before. Hope this upload works.
    I have also tried using a polyline to create the cam. The full cam surface and follower OD selected OK but no constraints are available to add a tangent constraint.

    Attached Files:

  4. oldfox

    oldfox Alibre Super User

    Good news:
    The upload is perfect. Exactly like it should be. You just learned something new this evening.

    Bad news:
    A lot of folks, including your's truly, have been sitting around until Alibre has a constraint that will do exactly what you were trying to do. So far it doesn't exist in Alibre.

    Hopefully in the future it will be available.

    More news:
    As you have probably already ascertained, you can constrain the wheel to any one segment of the cam. That works. Now, if you want motion,
    as I do, that's what we have to wait for. In the meantime you could make a static "pseudo motion" by using "configurations". You would
    make a different config for each segment of the cam. Then, and I really can't help you with this one, you would cycle through the configs,
    kinda like those old "card" movies where you would flip through a deck of cards with each one having a slightly different image than the last
    one. It would then look like motion. :cool:

    You may want to look through the examples in the Alibre Script library. There might be one there showing a bolt being threaded into a
    nut. It's another approach. Alibre Script, the old WizoScript, can do a lot. Just depends on how clever the person wanting to use it is.

    Also, if you have the capability to grab an animated GIF from the screen, you can grab one part of the moving parts and with the mouse
    rotate it around it's axis. Just another idea. Kinda like making the cylinders in an engine go up and down around the crankshaft.

    And that's pretty much it in a nutshell, albeit a fairly large nut. :D

    Good luck. And have a good weekend.
  5. JST

    JST Alibre Super User

    There is a rather limited capability to do what you want, now existing.

    But you cannot use just any cam profile. it must be made from one single form. Possibly only a circle, I have not tried any other forms. You cannot use any form which is built up of pieces, since the tangent can work on one and only one named surface.

    That issue of not passing to a new surface is what stops you from using it now except for simple form surfaces.

    EDIT: I probably should also mention the possibility of a cusp at the joins between surfaces, we know Alibre hates "cusping surfaces", that is an error message I have seen. I forget where, possibly with lofts.

    And, it does not even work with an ellipse. the "surface" of an ellipse apparently does not exist, it cannot be selected by the tangent outside command.

    Attached Files:

    Last edited: Aug 5, 2018

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