A cam is a mechanical member used to impart desired motion or displacement to a follower by direct contact. It is widely used inautomobile industries to direct opening and closing of inlet and exhaust valves at desire time. Cams are either in rotary or reciprocating or oscillating motion. The driver member in cam follower mechanism is called cam and driven member is called follower. Cam mechanism belong to higher pair mechanism because the cam and follower makes point contact. When we study about cam follower mechanism, some common terminology like prime circle, base circle, pressure angle etc. are used to describe a cam. These are as follow.
Cam Terminology and Displacement Diagram:
Base circle is the smallest circle that can be drawn tangentially to the cam profile.
A trace point is a theoretical point on the follower. It’s motion describing the movement of the follower. For example a knife edge follower, the trace point is at the knife edge.
It is the curve drawn by the trace point assuming that the cam is fixed and the trace point of the follower rotates around the cam.
It represents the steepness of the cam profile. The angle between the direction of the follower movement and the normal to the pitch curve at any point is called pressure angle.
A pitch point correspond to the point of maximum pressure angle. Its
A circle drawn with its center at the cam center and pass through the pitch point is known as the pitch circle.
The prime circle is the smallest circle that can be drawn from the center of cam and it is tangential to the pitch curve.
Angle of Ascent:
It is the angle through which the cam turns during the time the follower rises.
Angle of Dwell:
Angle of dwell is the angle through which the cam turns while the follower remains stationary at the highest or the lowest point.
Angle of Descent:
Angle of descent is the angle through which the cam turns while follower returns to the initial position.
Angle of Action:
This is the total angle moved by the cam during the time between the beginning of rise and the end of return of the follower.