Below are illustrations to both open and closed inking systems.

Closed Ink System

These images illustrate the main components found on the inking system of a closed ink cup machine.

The ink pot travels horizontally forward and back, in doing so it will deposit ink into the etch and remove any excess.

Open Ink System

This was the original pad printing system. Instead of using an ink cup, this system utilizes an ink well, spatula and crucially a doctor blade. 

With the spatula floating and the doctor blade in a raised position, the machine moves forward with the spatula pushing the ink from the ink well as it goes. The machine moves forward just enough for the ink to be deposited into the etch. Once the machine reaches is desired location, the doctor blade rotates downward, applying pressure to the cliche plate. 

Now with downward pressure on the cliche plate the entire system returns to the ink well. The doctor blade drags all of the excess ink with it, leaving only the ink in the etch. Once in the home position the doctor blades once again raises, ready for the next cycle.