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. 
RadiusofCurvature  sign convention The 'sign' of the RadiusofCurvature changes when oscillatingcircle moves one side of a curve to the other side of a curve. For example, the inside to outside of a cam. Mathematically, the sign of the 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. Radius of Curvature Convention for Planar Cams Note: there are papers that discuss a 'negative' radius for the CamFollower! This means the CamFollower is a 'housing' that surrounds the cam. RadiusofCurvature ( ρ ) = 1/ Curvature ( κ ) In MechDesigner, we use the CamData FB to plot the Radiusof Curvature of the Cam1 and Cam2. 

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 radiiofcurvatures. Note: when the radius changes from '+ve' to '–ve', or vice versa It passes an inflectionpoint. At that instant, the radiusofcurvature is infinite. The graph shows as a vertical line when the radiusofcurvature changes from +infinity to negative, or vice versa. 
If the RadiusofCurvature of the cam is small, then you must make these design checks: 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 Note: in MechDesigner, the camfollower always moves with the motion as kinematically specified. In your machine, the camfollower's motion becomes controlled only by its contact with the cam, of course. Thus, if the cam profile is undercut, the camfollower cannot move with the motion as kinematically specified. In MechDesigner, you can scrutinize the model to look for a 'dovetail'  see model to the left. 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 

Video of Undercutting  Video is very Slow! 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 
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 edge of the CamFollower w 'plough' into the cam  not good. 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 alignment specification. The nominal Hertzian contactstress of a crownroller is greater than that of the cylindricalroller. However, a crownroller can be misaligned to a greater extent, so that the edge of the roller does not plough into the Cam  better. 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. 