Cam Nomenclature
A radial cam with reciprocating roller follower is shown in Fig. (above). The following nomenclature is used in reference to planar cam mechanisms :
Base circle : It is the smallest circle tangent to the cam profile drawn from the centre of rotation of a radial cam.
Prime circle : It is the smallest circle drawn tangent to the pitch curve from the centre of rotation of the cam.
Pitch point : It is a point on the pitch curve having the maximum pressure angle.
Pitch circle : It is the circle drawn through the centre and passing through pitch point.
Trace point : It is a reference point on the follower and is used to generate the pitch curve. In the case of a knife edge follower, it is the knife edge, and in the case of a roller follower, it is the centre of the roller.
Pitch curve : It is the curve generated by the trace point as the follower moves relative to the cam. Pitch curve can be assumed to be drawn by the trace point assuming that the cam is fixed, and the trace point of the follower rotates around the cam.
Pressure angle : It is the angle between the normal to the pitch curve and the instantaneous direction of the follower motion. This angle is important in cam design because it represents the steepness of the cam profile. It varies in magnitude at all instants of the follower motion. A high value of the maximum pressure angle is not desired as it might jam the follower in the bearings.
Stroke or Throw : The greatest distance or angle through which the follower moves or rotates. It is also called as lift of the cam.
Cam profile : The surface in contact with the follower is known as the cam profile.
Angle of ascent : It is the angle of rotation of the cam during which the follower rises up.
Angle of dwell : The angle of dwell is the angle through which the cam turns while the follower remains stationary at the highest or the lowest position.
Angle of descent : It is the angle of rotation of the cam during which the follower returns to its initial position.
Angle of action : The angle of action is the total angle moved by the cam during the time, between the beginning of rise and the end of the return of the follower.
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