Cam

A cam is a projecting part of a rotating wheel or shaft that strikes a lever at one or more points on its circular path. The cam can be a simple tooth, as is used to deliver pulses of power to a steam hammer, for example, or an eccentric disc or other shape that produces a smooth oscillating motion in the follower which is a lever making contact with the cam.


The cam can be seen as a device that translates movement from circular to linear. Another common example is the camshaft of a car or automobile, which takes the rotary motion of the engine and translates it into the linear motion necessary to operate the intake and exhaust valves of the cylinders.

The opposite operation, translation of linear motion to circular motion, is done by a crank. An example is the crankshaft of a car, which takes the linear motion of the pistons and translates it into the rotary motion necessary to operate the wheels.

Certain cams can be characterized by their displacement diagrams which reflect the changing position a roller follower would make as the cam rotates about an axis. These diagrams relate angular position to the radial displacement experienced at that position. Several key terms are relevant in such a construction of plate cams: base circle, prime circle (with radius equal to the sum of the follower radius and the base circle radius), and the pitch curve which is the radial curve traced out by appling the radial displacements away from the prime circle across all angles. Displacement diagrams are traditionally presented as graphs with non-negative values.