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23-Emerald IV
TomU23-Emerald IV
23-Emerald IV
March 28, 2012
Question

Barrel Cam Modeling

  • March 28, 2012
  • 24 replies
  • 48558 views

I'm looking for ideas on how to properly model the slot in a barrel cam. I have attempted multipe techniques and I'm starting to spin my wheels. I have an idea that what I want to do can probably be done with the variable section sweep, but that feature is definitely not my area of expertise.


I've worked through the "wave washer" suggested technique on PTC's site (http://www.ptc.com/appserver/wcms/standards/freefull_cskdb.jsp?&im_dbkey=88651&icg_dbkey=900). The problem with this exampl is that the part is not a constant thickness (whereas my cam slot needs to be). To get a constant thickness, I changed the sketch profile to a single line, which created a single wavy surface, and then thickened it. Problem is, the sides are no longer vertical. To get around that, I lengthend the VSS section to include some extra on each end, then extruded inner and outer cylinder surfaces, merged everything together, and solidified. This succeeded in creating a constant thickness washer with straight sides.(See attached PDF.)


Problem is, thistechnique does not transfer well to the cam. The centersurface won't offset nearly as far as it would need to. Creating inner and outer curves and building boundary blends didn't work either.


Tom


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T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 30, 2012
Several of you have asked for more information. Here is a copy of the actual model I'm using. It has curves at the edges of all surface and the VSS shown at only 40mm thick. All the features in the model are suppressed to reduce file size. You will need to resume them after opening. The file was created in WF5 M120.

Tom U.

B
bfrandsen10-Marble
10-Marble
March 30, 2012
Hi all
I think I found a nice solution for this Barrel Cam Modeling making it in 3 features. I am not an expert in mechanism design, so I might have overlooked something, but anyway here is my suggestion:

Use VSS to create a surface perpendicular to the cylinder. The height from the base can be driven be the CAM graph (10.00 is the start value). Dimension the surface to the depth need for the CAM (5.00) and let the other end be free of the cylinder (1.00).
[cid:image002.png@01CD0E9A.373A9130]

This give a Quilt surface like this:
[cid:image003.png@01CD0E9A.373A9130]

Thicken the Quilt and define it as a Cut:
[cid:image004.png@01CD0E9A.EC9088A0][cid:image005.png@01CD0E9B.437BA9B0]

This gives a Dihedral Angle at the bottom of the groove close to 90 degrees.
[cid:image006.png@01CD0E9B.B08C0AE0]

And a constant groove width:
[cid:image007.png@01CD0E9C.912CC5D0]


/Bjarne
T
TimMcLellan12-Amethyst
12-Amethyst
March 30, 2012
Here is also a copy of the sample I sent Tom yesterday. This example also
leverages "approximate" copies for the origin & x-vector of the VSS to
reduce potential self intersecting geometry.



I had also include a "Full Round" in the model to help illustrate the cam's
performance. For those of you who are playing with this leveraging a round
on the internal edges will help you visualize if the results are as needed.
You will find that creating a simple edge round (with correct results)
should yield parallel internal tangent edges of the round throughout the cam
surface. It should also allow you to create a full round as illustrated in
this example. Switch the full round OFF and set the value to about 4 and you
should see what I am talking about on the inside surface of the cam



(WF5 & features suppressed to reduce file size).



Hope this helps others,

Tim McLellan
Mobius Innovation and Development, Inc.
P
ptc-28607371-Visitor
1-Visitor
March 30, 2012
Hi all

While I've been pondering this problem I've been trying to set up a
mechanism to be able to see the motion of the pin following the groove,
but Pro/E will not allow a cam follower connection. Does anyone know how
to go about setting it up so a pin will follow the groove for a motion
study?


Doug Barton
Mechanical Designer
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB R3T 1T4 Canada
direct 204 453 3339 x309
fax 204 452 7156
-
www.parker.com/ecd




K
KrisR1-Visitor
1-Visitor
March 30, 2012
Here is the cam-follower connection - it is in Applications->Mechanism.

[cid:image003.jpg@01CD0E74.AB30F500]
T
TimMcLellan12-Amethyst
12-Amethyst
March 30, 2012
Just keep in mind that the motion envelopes generated in Mechanism are
facetted (i.e. surface, STL...)



Tim McLellan
Mobius Innovation and Development, Inc.
P
ptc-28607371-Visitor
1-Visitor
March 30, 2012
Thanks, however I already know how to set up a cam follower connection.
What I said was Pro/E would not allow it (in this case). I believe this
is because the cam surface is curved in two directions which makes it
invalid. Although I also tried just the profile curve instead of the
surface and that didn't work either.

From Help


The question was, is there a method other than a cam follower connection
to get the pin to follow the cam profile.


Doug Barton
Mechanical Designer
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB R3T 1T4 Canada
direct 204 453 3339 x309
fax 204 452 7156
-
www.parker.com/ecd




B
blenk1-Visitor
1-Visitor
March 30, 2012
Bjarne, I applied your idea to the track I was trying to make and it appears that it works great. I used a second trajectory instead of a CAM graph. The sides of the track stay at 90 degrees even where the track cuts across the cylinder at an angle. Thank you very much for sharing this with us!

VSS created with curve on end of cylinder and pre-determined track curve:
[cid:image008.png@01CD0E77.56626B00]
P
ptc-28607371-Visitor
1-Visitor
March 30, 2012
Yes. Maybe not enough resolution to see anything worthwhile.

Here's an image of an assembly of parts. The pins are just assembled
point on curve.




Doug Barton
Mechanical Designer
Parker Hannifin Canada
Electronic Controls Division
1305 Clarence Avenue
Winnipeg, MB R3T 1T4 Canada
direct 204 453 3339 x309
fax 204 452 7156
-
www.parker.com/ecd




T
TimMcLellan12-Amethyst
12-Amethyst
March 30, 2012
Tom,



Here is your part.



Changes include:

· Converted profile to GRAPH feature. Scaled dimensions to simplify
the VSS for 360° rather than using the arc length as you had defined. This
simplifies the CAM path and allows for easy modification. Also, modified
splines and converted complete sketcher/graph to spline (one entity in
sketcher graph).

· VSS paths use new GRAPH and sweep as I had illustrated yesterday
(origin & X-vector to control orientation). Note: both VSS use same graph
to drive the path over 360°

· VSS is extended outside of outer surface and inside of inner
surface then merged.



Hope this helps everyone.

Tim McLellan
Mobius Innovation and Development, Inc.
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