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dgschaefer21-Topaz II
21-Topaz II
October 29, 2014
Question

VSS with trajpar

  • October 29, 2014
  • 16 replies
  • 7142 views
Creo 2, M120

I have a VSS where I need the value of one radius to vary along the sweep from 100 at the start to 25 at half way back to 100 at the end.  Can I do this with a relation and trajpar?  If needed, I could split it into 2 sweeps where one went from 100 to 25 and the next from 25 to 100.

Thanks,

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    16 replies

    M
    mlocascio1-Visitor
    1-Visitor
    October 29, 2014
    Is there a fully defined tutorial, or technical document, on trajpar?



    MPL


    P
    ptc-8104501-Visitor
    1-Visitor
    October 29, 2014
    Hi Doug,
    Yes, you can do it with a relation and trajpar. It is easiest if it is
    one equation:

    R = 300*trajpar^2 - 300*trajpar + 100

    Is an example of a parabola that will do what you want (R is the radius
    dimension).

    I believe you can use IF statements to make a non-continuous curve but I
    have never done this before.


    If you want to do an arbitrary curve, you can use the "evalgraph" function
    so that the radius is read off a sketched graph as a function of trajpar.
    I can give some instructions on this if you need it.
    --
    Mark von Huben

    Principal Mechanical Engineer
    Cochlear Ltd
    1 University Ave
    Macquarie Park, NSW, 2113
    Australia

    p +61 2 9425 5210


      T
      TimMcLellan12-Amethyst
      12-Amethyst
      October 29, 2014
      I would also recommend looking at driving it by a "graph". Either way work great.
      Tim McLellan
      Mobius Innovation and Development, Inc.
      M
      mlocascio1-Visitor
      1-Visitor
      October 29, 2014
      Trajpar has always been kind of a mystery to me. I know that you (WE) can do
      marvelous things using trajpar. But how do we know, or learn, how to use it?




      Michael P. Locascio


      D
      dgschaefer21-Topaz IIAuthor
      21-Topaz II
      October 30, 2014
      This is great, thanks.  Can you help me dissect this a bit because I'm realizing that the values that I need may be different than 25 & 100.  How would I adapt this to different values?

      Also, I'm realizing that if it's a linear progression for high to low to high I'll likely get a peak / valley in the center, so perhaps a graph would be more appropriate.

      --
      M
      mlocascio1-Visitor
      1-Visitor
      October 30, 2014
      This is what I was asking for. Is there any kind of trajpar training course?
      I REALLY want to become more of an "expert" with this.



      Michael P. Locascio


      B
      bj6031-Visitor
      1-Visitor
      October 30, 2014
      Sounds like a graph-driven VSS might be best for your application.

      A sample Creo 2 model is attached (resume all features).

      A critical part of the process is to enter a sketch relation, such as the following:
      sd3=evalgraph("GRAPH_1", trajpar*100)

      PTCU used to have a section on driving VSS's with trajpar/graphs; ... look for the "Surfacing using Creo Parametric 2.0" course, and the section on
      "Using Trajpar and Datum Graphs with Sweep Surface features".

      Regards,

      Terry Partridge
      P
      ptc-8104501-Visitor
      1-Visitor
      October 31, 2014
      Hi Doug,
      Did Terry's model give you enough of a hint (Thanks Terry!)? To get the
      equation I just started with the equation for a parabola, y = ax^2 + bx +
      c and solved for a, b and c so it went through (0,100), (0.5, 25) and (1,
      100) where x = trajpar and varies from 0 to 1 along the origin curve (from
      start to finish, however you have defined that).

      If you find the the VSS feature isn't generating for some reason,
      sometimes it is because your sketch can't be resolved at all places along
      the curve (. An easy way to check this is to place a datum point along
      your origin curve and then placing the VSS sketch on that point.

      You can then move the datum point up and down the curve and look at the
      sketch at each location to see what is going on. I have done this to
      Terry's file and reattached it here (in the group evalgraph_method).

      It occurred to me that there was another way to do what you wanted with
      datum curves (easiest to directly sketch to the curve or you can use the
      second curve to drive a dimension) - an example is the "curve_method"
      group. Create as many curves as you want to get the desired geometry. VSS
      is very powerful - you are only limited by your imagination!



      Should you need to have the edge of a VSS tangent to a curved surface and
      ProE decides it can't do it automatically, there are ways to cheat if you
      are happy with "close enough to tangent is good enough". If needed I can
      find an example but it will take quite some time to remove confidential
      info / genericise the model. I can't do this today.

      cheers
      --
      Mark von Huben

      Principal Mechanical Engineer
      Cochlear Ltd
      1 University Ave
      Macquarie Park, NSW, 2113
      Australia

      p +61 2 9425 5210


      D
      dgschaefer21-Topaz IIAuthor
      21-Topaz II
      October 31, 2014
      Actually, I got something workable (for now) without trying it.  I’ll need to come back to it later, but I’ve got other fires to fight first.  I definitely appreciate the input and have files the emails away for that inevitability.

      I particularly liked this bit:

      “I just started with the equation for a parabola, y = ax^2 + bx + c and solved for a, b and c so it went through (0,100), (0.5, 25) and (1, 100) where x = trajpar and varies from 0 to 1 along the origin curve”

      Of course, why didn’t I think of that? 😛

      So, if I needed values of A & B instead of 25 & 100, I need to re-solve for the points (0,A), (0.5,B) and (1,A), correct?  This assumes that I can dust off my long dormant Algebra skills and figure that out. 😕

      --
      K
      kimndave91-Visitor
      1-Visitor
      November 2, 2014

      While breaking out the Algebra book can work, you may wish to try a solve block:


      SOLVE
      d1 + d2 = 500
      d1 - d2 = 0
      FOR d1 d2


      You can substitute your own functions.


      http://help.ptc.com/creo_hc/creo30_pma_hc/usascii/index.html#page/pma/fundamentals/fund_seven_sub/About_Simultaneous_Equations.html


      x

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