Types of follower motion

TYPES OF FOLLOWER MOTION

• It may be noted that the motion of the follower actually depends on the shape and size of the cam profile.

• A cam can be designed to provide any desired motion to follower. Also, theoretically, a large number of follower motions are possible. But, in actual practice, only few standard follower motions are commonly employed. Because other follower motions result in high stresses and serious vibrations in the associated components (due to extreme values of velocity, acceleration, and jerk').

• The most common follower motions, that are used in the design of cams, are:

1. Uniform velocity motion (or uniform motion),

2. Simple harmonic motion (SHM),

3. Uniform acceleration and retardation motion (UARM) (or Parabolic motion),

4. Cycloidal motion.

• Jerk and its significance:

• Jerk is nothing but the rate of change acceleration with respect to time (i.e., the time derivative of acceleration).

• It is necessary to produce a cam design that minimizes the jerk, to ensure a smooth acceleration curve, and a stable dynamic performance of the mechanism.

• In the design of cam, in addition to velocity and acceleration, the jerk is also considered, because of tribological implications and the ability of the actuated body to follow the cam profile without chatter.

• In other words, jerk characteristics produce, abruptly changing contact stresses at the bearings and on the cam surface and leads to noise, surface wear and eventual failure.

• Notations to be used in this discussion are:

y = Displacement of follower at any instant,

v = Velocity of follower,

L = Maximum displacement of follower, also called lift or stroke,

α = Acceleration of follower,

j = Jerk of follower,

θ = Cam angle, and

θ_o, or θ_r, = Angle of outstroke and angle of return respectively.