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Author: john2005
Time: 05/31/07 20:57 PST
This is a reply to message no. 18806 by mdg_cam
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Request for help reducing friction and noise of a cam follower roller
Hi Mdg_cam,

Thanks for your message.

Actually, the preload is a spring load, technically it's not really an intended preload, but the cam is basically just moveing  a spring load and the starting position is most important, the cam must be oscillated  CW and CCW from it's centered home position dwell point,  & then be returned to it's exact starting position or home resting position dwell via the springs. Friction is preventing this in one direction due to various reasons. I think my only choice is to reduce roller friction as much as possible, and/or add a helper spring to overcome the friction.

The dynamic forces are very low, there's no problem with cam follower separation, the rollers are basically extending and retracting extension springs so the springs themselves constitute the entire follower load for all practical purposes. That's a simplified way of explaining the arrangement as the mass of the follower is only 1 or two pounds and the hand operated speeds are slow. I've checked into other mechanisms and must use a cam.

After leaving the dwell position, the outer roller creates a CW torque on the cam and the inner roller creates a CCW torque on the cam. The force of the inner roller returns the cam to it's home position dwell after the hand is removed from the activation lever , along with two opposing springs connected to the cam to return the cam that last little bit where the roller centers itself on the dwell, and hold the cam on the center point dwell. The inner roller is on a slider so that I can maintain zero clearance between the rollers and the cam, if manufacturing tolerances on the cam rib were to push the rollers apart, the rollers can separate due to the inner roller being mounted on the slider, and the unit will not bind.

Since the roller force is fairly high, 90 to 130 pounds on both 3/16" OD rollers, I think that's where most of the problem is coming from.

I may be able to forget the inner roller slider, and apply a counter spring force in such a way as to reduce the roller loads onto the cam. This method would require a little clearance between the rollers and the cam, but would reduce roller load and thus friction. Right now I'm building a few and am in the middle of testing them but my goal would be production quantities.

The contact stress includes the entire load, but could be reduced significantly with the counter spring I mentioned above. The drawback is that the system will work much better with zero clearance between the rollers and cam,  which is achieved by the aforementioned slider, at a cost of higher roller loads and more friction.  

Any other feedback you may have would be appreciated.

Thanks
John
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