Cam profile design 5

[hansel]

Hi,

I'm using a Cam to move a sliding mechanism.
The Cam will rotate through 90 degrees moving the slide 20mm.

The Cam will be rotated by a rotary actuator moving at constant velocity, therefore the Cam will be in control of the slide acceleration and deceleration.
I want the slide to move in a motion similar to a Sine wave (start slow, accelerate and finish slow).

I have my values from the Sine Wave moving through 90 degrees with an amplitude of 20mm but does anyone know the process of converting it to a Cam profile?
Can't remember how to do it, something to do with an involute but a bit lost after that.

Any help would be much appreciated.

Thanks,
Emmet.

 

[MikeHalloran]

No involutes involved.
Select a 'base circle' radius for the cam.
Divide the 90 degrees on the cam into N segments.
Draw a sine curve on a straight line of arbitrary length.
Divide the straight line into N segments.
Erect normals from the straight line to the sine curve at the lines between the segments.
Draw radial lines from the center to the base circle of the came, at the lines between the segments, and extend the lines out beyond the base circle.
For each radial line on the cam, and for the corresponding normal line on the sine profile, copy the length of the normal line, and lay it down on the radial line, outside the base circle. Trim the radial line beyond the line you've just added.
Connect the tips of the new radial lines to get a piecewise approximation of a sine cam. More specifically, the resulting polyline is the locus of the cam follower center.
Draw the cam follower in correct orientation at each vertex of the polyline.
The inside locus of the cam followers is the cam profile.

It's kind of fun to do all that in a simple program and plot the whole mess on a pen plotter, if you have one.




Mike Halloran
Pembroke Pines, FL, USA

 

[hansel]

Very well explained, big help!

Thanks for that Mike.

 

[hansel]

If you're still there Mike......
After modeling that Cam using the method you outlined I realized I left out an important factor, I have to use a flat follower and I think the current method is for a round follower???

You wouldn't happen to know what adjustments I need to make???

Emmet.

 

[dvd]

The following link is for an old classic cam design book. I have found the information helpful at times. Flat-faced cam followers are discussed.

http://www.camcoindex.com/ServiceManuals/CAMCO_Cam-Design_Moon-Book.pdf

 

[MikeHalloran]

Star for dvd.
That book explains more, better, than I ever could.


Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

It's tough to explain cams without pictures.

 

[Occupant]

If you are still interested: attached are the displacement functions for a modified sine curve cam - still in use today. You figure out the Displacement values based on the angular resolution you want - let's say every 5 degrees (don't use that for an actual cam - way too coarse) and add a minimum Radius for the hub or when the cam is in dwell to each value and plot a horizontal line on the Y-axis for each point and also draw rays through the center of the cam for each angle that you increment - the first one being vertical. Intersections between the displacement lines and the rays determine points on the cam curve.