As the cam shaft rotates, the lobed portion of the cam pushes down and opens the valve. When the valve is fully open, the follower stops moving and remains idle, or dwells, momentarily. The cam then rotates further and the valve closes. For one typical revolution of the cam the follower accelerates, decelerates, dwells, accelerates, and then decelerates again. The cam surface is shaped to provide the best follower positions, velocities, accelerations, and dwells for a specific application.
Linkages are a broad class of mechanisms.
Two of the most important are the four-bar linkage and the slider crank. A four-bar linkage has four links that are connected by pin joints. One of the links is stationary and is generally formed from the machine housing. The other links consist of the input, output, and the coupler, which connects the input and output links. A crank has rotary motion, while a rocker oscillates back and forth.