DESIGN 2: 'Two Cam-Follower Rollers'
There are two bearings on the same stud / shaft. These designs aim to:
With good manufacturing tolerances, the backlash can be reduced.
The rollers do not need to change their rotational directions, and thus they do not scuff/wear as much as those cam-follower that do need to change their rotational directions.
DESIGN 2A: Two Rollers - Equal Roller Radius
See image 'DESIGN 2A'.
When the roller diameters are equal, each roller must have a clearance for it non-working flank.
The cam-profile for the 'deepest' roller must be 'undercut'
DESIGN 2B: Two Rollers - Different Roller Radius
See image 'DESIGN 2B'
The cam-profile does not need to be undercut. It is easier to manufacture.
When the load is small, and the rotation speed is low, and the elimination of backlash is important, one roller can be rubber. The rubber roller can be loaded against the cam track to spring the rigid roller against the other flank of the track-cam. Also applies to Conjugate and Rib cams.
Example: Camera Lens.