Center-based offset of a Spline

[Bouke]

Hey everybody

I've ran into a scetching problem. I am working on a cam mechanism where the cam-disk itself is mounted solid. Around it are cars running on a track in circles. Mounted with linear guides there are 2 cam-followers that run through a cavity in the top-side of the cam. These 2 cavity's over 350° the same except for the fact that one is closer to the center of the cam then the other. Nevermind the other 10°.

I'll include links to pictures of the problem at the bottom of this post.

Well, about the problem;
I've made a 2D-spline that will be used to cut-sweep the outer cavity on the top-side of the disk. Problem is I cannot just use the off-set command now to create a spline a few milimeters smaller cause it will lead to the wrong result. I've simulated the result that I want in one of the pics below by drawing a lot of lines, one each 3°.

This solution is not really a precise enough method of getting the resulting spline. And in the picture I've used a simple cam-spline while the acual spline where I need it is much more complex.

Pictures:
The spline I want a center based offset off:

http://img258.imageshack.us/img258/1177/spinecw0.jpg

Offsetting the spline to the wrong result:

http://img249.imageshack.us/img249/2941/offsettl2.jpg

Aprox. of the result I need:

http://img441.imageshack.us/img441/3158/offsettocentergf9.jpg

I hope I made my problem clear. Does anyone have a tip how to create the needed spline?

Thanks in Advance,

Bouke

Bouke Brouwers
M-Des
The Netherlands.

 

[handleman]

Cam geometry is not that simple. If your motion profile is at all important you're going to need to do some pretty involved calculations based on the geometry of the cam and followers to get the shape of each wall of each slot.

 

[Bouke]

Yeah, it's an awful lot of work. The outer cam-line is very complex and this is why I am looking for a shortcut to convert the entire cam-path to a smaller diameter.

So anything that might help would be really appriciated.

Bouke Brouwers
M-Des
The Netherlands.

 

[handleman]

I don't think that just converting the entire cam path to a smaller diameter will actually get you the correct profile. You'd be best to go ahead and calculate the true profile for at least one other wall and then see if you can find some easier way to match it.