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T
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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24 replies

T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 28, 2012
Here is a PDF that shows the wave washer modeling.

Tom U.
T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 28, 2012
Digging on the web, I see that solid works has the ability to sweep one solid through another. Anyone know if there is something similar in Pro/e?

The Swept Solid function allows an actual solid shape (say a milling cutter) to be swept and cut from another solid. A Cut-Sweep only cuts a sketched profile which gives a slightly different result.

files.solidworks.com/supportfiles/Whats_new/2008/English/whatsnew.pdf

[cid:image001.png@01CD0D01.232491E0]
K
KrisR1-Visitor
1-Visitor
March 29, 2012

Could you do the washer as flat, do one section of the wave as a cut, then pattern the wave cut? I would think this would work.....


T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 29, 2012
The purpose of the wave washer wasn't to create the washer, but rather explore techniques that could translate to the cam. Here is a picture of what the cam looks like right now (though not correct yet).

[cid:image001.jpg@01CD0D7F.340D0A90]
B
blenk1-Visitor
1-Visitor
March 29, 2012
We have had similar issues trying to model this feature at our company too. I've tried to create it using VSS, using curves and surfaces, even using Pro/NC. I've even tried drawing a flat pattern in sheetmetal and forming it into a circle, but this really isn't the design intent I want to use. The best luck I have had is using the VSS and keeping the cut normal to the center axis of the cylinder but no matter how I've tried it the walls of the cut will twist as soon as they start to cut at an angle across the cylinder. Would be great if Pro/Creo/Wildfire could simply rotate a cutter normal to an axis following a tool path. Maybe it can but it is beyond me, I'd be very interested into what others have done for this.
[cid:image002.png@01CD0D80.D39A1D40]


Brandon Lenk
Senior Designer
TEAM Industries-Bagley
(218) 694-4128
-<">mailto:->
J
JonathanHodgson13-Aquamarine
13-Aquamarine
March 29, 2012
We model our barrel cams by creating a flat pattern, then using a
Toroidal Bend.



I'm fairly sure the geometry isn't 100% accurate; but it looks about
right, and since the milling guys program it from the flat pattern
anyway, it makes it easier to include that information in the drawing.





Jonathan


T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 29, 2012
I've been getting quite a bit of feedback on this issue. Unfortunately, every single solution yields cam slot surfaces that do not properly contact the roller. The ONLY thing I've found to properly orient the slot surfaces to the roller is to offset them from a center surface (created through the desired trajectory). I would like to be able to sweep something normal to the outside of a cylinder surface AND normal to the trajectory at the same time. The sketch section needs to "tip" as it moves along the trajectory so the cam surfaces stay flat to the line of contact the roller makes with the slot. Here are a few pictures that show what I'm talking about.

This first one shows how a roller will gouge the slot surface. The roller should only be in contact on the red line. This is what is created using a VSS, Toroid bend, graph with trajpar, etc.

[Description: cid:image009.jpg@01CD0D85.38920EC0]


This picture shows slots that were created by offsetting one through the center of the path. These are correct! I just can't use this approach for the real cam profile (surfaces become self-intersecting at the offset values needed.)

[Description: cid:image010.jpg@01CD0D85.38920EC0]


If there is a way to alter the VSS to allow the blue rectangle to tip as it sweeps around so it's parallel with the red line, we'd be perfect!

[Description: cid:image001.jpg@01CD0D8B.09C2A9A0]


T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 29, 2012
Someone suggested using a helical sweep. This DOES tip the sketch plane to match the pitch value. Does anyone know if there is a way to use a helical sweep but tell it to follow a graph/trajectory/curve?

[cid:image004.png@01CD0D9F.8BD2EDB0]
B
bfrandsen10-Marble
10-Marble
March 30, 2012
I have seen Creo 1.0 presentations using a graph to control the pitch of the helical sweep. Not sure if this is available in earlier releases.

Another idea could be to start creating a VSS surface with the current flat trajectory making an edge being you cam edge. Then use that edge as trajectory for the VSS that makes the solid cut holding the sketch normal to the its trajectory.

Best Regards,
Bjarne Frandsen
T
23-Emerald IV
TomU23-Emerald IVAuthor
23-Emerald IV
March 30, 2012
Barrel Cam Update


* Using a variable section sweep seems to be the best solution so far.

* The primary trajectory needs to be the cam profile wrapped or projected around the cylinder.

* There needs to be a second trajectory for use as the X-trajectory (under Horizontal/Vertical control)

[cid:image002.jpg@01CD0E68.1CEDDA30] [cid:image004.png@01CD0E60.C36703D0]

I am still struggling with how to correctly model the surfaces in the areas when the offset combined with the rotation will generate a sharp corner. The picture shown above is with the slot 45mm thick. It needs to be 40mm thick. Here is what it looks like when it's the correct thickness.
[cid:image005.png@01CD0E64.0025FB20] [cid:image008.jpg@01CD0E68.1CEDDA30]

I am presently attempting to build the top and bottom slot surface independently to see if I can overcome this issue. Thanks for all the suggestions so far.

Tom U.
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