Cams Cams are used to convert rotary motion to oscillatory motion (almost always) or oscillatory motion to rotary motion (rarely) For high speed applications – example, internal combustion engines Objectives of this chapter: Learn fundamental concepts and terminology Learn how to design a cam and follower set to achieve a desired output motion.

Cam types Plate cam Wedge cam Barrel cam Face cam  y

Cam and Follower The cam and follower is a device which can convert rotary motion (circular motion) into linear motion (movement in a straight line). Cam Follower Cams Followers (valves)

Cam and Follower follower Cam Pear Heart Circular Drop The cam can have various shapes. These are know as cam profiles. Cam Pear Heart Circular Drop

Cam and Follower Follower cam Knife edge Follower Flat foot follower A follower is a component which is designed to move up and down as it follows the edge of the cam. cam Knife edge Follower Flat foot follower Off set follower Roller follower

Cam and Follower Follower Square cam The 'bumps' on a cam are called lobes. The square cam illustrated has four lobes, and lifts the follower four times each revolution. Follower Square cam Examples of other rotary cam profiles.

Cam and Follower Examples of a Rotary cams in operation. Cams used in a pump. Control the movement of the engine valves.

Cam and Follower Linear cam Distance moved by the follower The linear cam moves backwards and forwards in a reciprocating motion. Cam Follower Linear cam Distance moved by the follower

Cam and Follower Cams can also be cylindrical in shape Below a cylindrical cam and roller follower. Cam rise and Fall Max Lift Min Lift The cam follower does not have to move up and down - it can be an oscillating lever as shown above.  

Followers Knife-edge Flat-face Roller Sperical-face

Displacement diagrams Cam-follower: usually 1-DOF system y rise dwell return dwell 

Displacement diagram types Uniform motion, Constant velocity Problem: infinity acceleration at point where dwell portion starts Parabolic-uniform Can be shown that acceleration is constant Sinusoidal (simple harmonic motion) Cycloidal

Cycloidal displacement diagram

Graphical layout of cam profiles Terminology Trace point: on follower; point of fictitious knife-edge follower. Center of roller, surface of flat-faced follower. Pitch curve Locus generated by trace point as follower moves relative to cam Prime circle Smallest circle that can be drawn with center at the cam rotation axis and is tangent to the pitch circle Base circle Smallest circle centered on cam rotation axis and is tangent to the cam surface

Layout of cam profile: roller follower

Constructing cam profile: kinematic inversion principle Consider that cam is stationary and that follower rotates in the opposite direction than the cam does in reality

SVAJ diagrams: show displacement, velocity, acceleration versus 