Heat System: Canon, HP, Lexmark
The nozzle, a small tube, fills with ink by capillarity. It also contains an electrode which is heated to over 400°ree; Celsius in a fraction of a second. Little bubbles of gas form and start form a single bubble. In this very short time, the bubble dilates and pushes the ink towards the outlet, which is a hole at the end of the nozzle. This hole where the ink is expelled has been a focus of much recent development. It can, for instance, be designed in the shape of a star-shaped cone. This gives the manufacturer better control over the shape and size of the ink droplet and the way it is deposited on the paper. When the ink leaves the nozzle, the power is cut off, the electrode retracts and the system can start a new cycle.
Piezo System: Epson
Everyone has their own way of naming things. At Epson they talk of Piezo or Micro-Piezo technology. The print-head is like a system of little studs activated by a Piezo crystal, which is electrically sensitive. The crystals change shape depending on the force applied to them. When it is powered, the plate in the head moves back and forth inside the ink chamber and compresses the liquid. This pushes the ink towards the exit or a hole at one end of the head. When the power is cut, the plate returns to its original position, creating a draught which does two things: 1) it separates the ink outside the chamber from that inside to make the most perfect droplet possible, and 2) it refills the circuit with ink. The plate is referred to as vibrating because the droplet output rate depends on the frequency of the plate movement. The size of the droplets can vary and depends on the amount of pressure applied by the plate, or on the strength of the current which activates it.