Ch. 15

Use to determine how much spring force is needed to keep the follower in contact with the cam at a chosen design speed.

• the k_s of the physical return spring.
• The design has a large degree of control over k_eff

the softest spring

the spring is compressed (or extended if an extension spring) from its free length to its initial assemby length.

• Preloading creates residual force on the follower even when the cam is at its lowest displacement.
• This helps maintain good contact between the cam and follower at all times.

• For most cam-follower systems the value of c can be estimated for a first approximation to be about 0.05 to 0.10 of the critical damping c_c
• c_c = 2m(k/m)^1/2 = 2m*omega_n
• The spring constant and preload must be selected to guarantee a positive force at all points in the cycle.

push

providing the force needed to keep the joint closed during the negative acceleration portions of the follower motion.

• They will experience follower jump which is where the follower and cam will part company.
• The follower jump is also called the valve float in automotive engine valve applications.
• When they meet again it will be with large and potentially damaging impact forces.
• The follower jump will occur near the point of maximum negative acceleration.