12 April 2017

Cam terminology


CAM Nomenclature

Definitions of terms that used in cam profile nomenclature :

  • Base circle :
It is the smallest circle drawn a tangent to the cam profile from the centre.

  • Tracepoint :
It is a reference point on the follower to trace the cam profile such as the knife-edge of a knife-edge follower and centre of the roller follower.

  • Pitch curve :
It is the curve drawn by the tracepoint assuming that the cam is fixed and the tracepoint of the follower rotates around the cam.

  • Pressure angle :
It is the angle between the normal to the pitch curve at a point and the direction of the follower motion.
Pressure angle representing the steepness of the cam profile.

  • Pitch point :
It is the point on the pitch curve at which the pressure angle is maximum.

  • Pitch circle :
It is the circle passing through the pitch point and concentric with the base circle.

  • Prime circle :
The smallest circle drawn a tangent to the pitch curve is known as the prime circle.

Displacement diagram :

Displacement diagram

As a cam rotates about the axis, it imparts a specific motion to the follower which is repeated with each revolution of the cam. It is enough to know the motion of follower for only one revolution.
The motion of the cam can be represented on a graph the x-axis represents the can rotation and the y-axis represents the displacement of the follower. Now we discuss the follower displacement diagram and its terms :

  • The angle of ascent :
It is the angle through which the cam turns during the timing of the follower rising. 
In the above figure angle of ascent represent by Ɵri.

  • The angle of dwell :
It is the angle through which the cam turns at the same time follower remains stationary at the highest or the lowest position.
In figure angle of dwell represent for the highest position by Ɵd1.

  • The angle of descent :
It is the angle through which the cam turns during the timing when the follower returns to its initial position.
In figure angle of descent represent by Ɵre.

  • Angle of action :
It is the angle through which the cam turns during the time between the beginning of rise and the end of the return of the follower. In fact angle of action is the total angle moved by the cam.
In figure angle of action represent by Ɵ.

For variation of cam types and different types of followers motions there are also different different displacement diagram are made.