The Curvature of a curve is the degree to which it deviates from a straight line. Curvature is a property of the curve. RadiusofCurvature is the reciprocal of Curvature. By definition, a straight line has zero curvature [and an infinite RadiusofCurvature] and a circle has finite curvature [and a finite RadiusofCurvature]. I find it easier to mentally translate RadiusofCurvature as the 'RadiusoftheCurve'. The RadiusofCurvature of each point along a cam can be represented by the radius of the osculatingcircle at that point. The oscillatingcircle might be 'inside' or 'outside' the cam. 

Two Osculating Circle at two different points. One circle is outside the cam and the other is inside the cam. Think of the 'RadiusofCurvature' as the ...radius of the osculating circle. 
Sign of the RadiusofCurvature The 'sign' of the RadiusofCurvature changes when the oscillatingcircle moves one side to the other side of a curve [or inside to outside to outside a cam], or viceversa. Mathematically, the side of a curve that has a 'positive' or 'negative' RadiusofCurvature, is arbitrary. However, with Cams [curves], the convention is:
Thus, if the Cam is a Groove Cam, then one of the camflanks will have a 'positive' and the other a 'negative' RadiusofCurvature. Note: there are papers that discuss a 'negative' radius of CamFollower. This means the CamFollower is not a roller, but a 'housing' that surrounds the cam. Radius of Curvature Convention for Planar Cams RadiusofCurvature(ρ) = 1/ Curvature(κ) In MechDesigner, we use the CamData FB to plot Cam's Radiusof Curvature. 

Usually, you must make sure the: Minimum Cam RadiusofCurvature > CamFollower Radius. It is useful to consider the ratio of the Cam and CamFollower radii.
RulesofThumb
In this graph, the olive green bar identifies the radius of the cam follower. The graph shows that the camprofile has both positive and negative radiusofcurvature. Note: when the radius of a convex cam becomes concave, or vice versa, it passes a 'pointofinflection'. The cam becomes flat instantaneously flat. The graph is a vertical line as the radiusofcurvature changes from large positive to a large negative value, or vice versa. 
If the RadiusofCurvature of the cam is small, then you must make these design checks: Undercutting : If the RadiusofCurvature of the cam is less than the Roller's radius; the 'real' [physical] CamFollower cannot follow the motion you have designed for it. However, the camfollower in MechDesigner follows the motion exactly. Contact Hertzian Stress : As the RadiusofCurvature gets smaller, the ContactStress between the cam and the camfollower becomes larger. Heat Treatment : the Cam's Heat treatment is more likely to crack the steel if its RadiusofCurvature is small. FlatFaced Followers : When the camfollower is a 'FlatFaced Follower', the RadiusofCurvature of the cam must be Convex (+ve) at all times. 

Undercutting If the cam's radiusofcurvature becomes lessthan the radius of the camfollower's roller, then the camfollower cannot move with motion as specified by your design. Note: in MechDesigner, the camfollower always moves with the motion specified by the motiondesign and the kinematicchain. However, in your machine, the camfollower's motion becomes controlled only by its contact with the cam. Thus, when the cam is undercut, the camfollower cannot move with the motion specified in the model. Thus, YOU must make sure the cam DOES NOT UNDERCUT. You can check visually. However, the best way is to use the CamData FB and a Graph FB. In the Graph, make sure the you plot the correct RadiusofCurvature. Use the Yaxis dropdown in the open graph to select 'RadiusofCurvature 1', or 'RadiusofCurvature 2', for Cam 1 or Cam 2 respectively. The number of the Cam is at the contactpoint in the graphicarea. 

Interference
Cam's RadiusofCurvature × 1 < Roller Radius ...the Roller will not fit into the Cam. 

Video of Undercutting  Slow! In this case, the RadiusofCurvature is less than the radius of the Cam Follower
However, the CamFollower cannot actually not follow the specified motion as the camfollower has nothing to follow! Too much metal has been removed from the cam.

Radius of Curvature Convention for Cam and Barrel Rollers 
CrownRollers, also called Barrel Rollers, are often used with cam mechanisms when the alignment between the cam and roller cannot be guaranteed to be within the bearings alignment specification. If a cylindricalroller is not aligned with the cam's rotational axis, the operating contactstress will be significantly more than that nominal 'Hertzian' contactstress. The nominal Hertzian contactstress of a crownroller is greater than that of the cylindricalroller. However, a crownroller can be misaligned to a greater extent without the contactstress increasing. Thus, even though the nominal contactstress of a crownroller is greater than that of a cylindricalroller, it is more likely that its operating contactstress will be less for the crownroller when alignment cannot be guaranteed. 