The printhead is the part of a printing system that contains nozzles for jetting ink. Piezoelectric printheads are made up of an active component called the 'actuator', a series of pipes and channels collectively known as the 'fluid path' and some electronics to control the individual channels. The actuator contains a series of parallel walls that make up the channels. The se are made of a piezoelectric ceramic material that deforms when a voltage is applied to it (the reverse piezoelectric effect). In Xaar printheads moving the walls of individual channels creates acoustic pressure waves which in turn eject ink from the nozzles at the end or side of each of the channels.
The reverse piezoelectric effect results in the ceramic material deforming in one of two ways which are used to create two different printhead modes of operation: 'bend' mode and 'shear' mode.
Bend mode printheads
In bend mode printheads, a piece of piezoelectric material is glued to the roof of the ink chamber. When an electric field is applied in the same direction in which the material is poled, the piece of material either lengthens or shrinks. If one side of the material is glued to the top of an ink chamber the lengthening causes the roof to bend (technically this is transverse actuation). This creates a pressure change that displaces a volume of ink causing a drop to be ejected from the nozzle.
Shear mode printheads
In shear mode printheads the electric field is applied perpendicular to the direction in which the material is poled. The deformation creates a shear effect (trapezoid shape) as can be seen in the animation of the channel walls below. A single piece of poled material creates what is known as a monolithic cantilever – the wall is fixed at the bottom and flexes about this point.
The animation shows the walls of the channel shearing from side to side.
All Xaar 1003 printheads have an actuator that is made of 2 pieces of oppositely poled piezo material fused together. When the electric field is applied, the 2 sections of the channel walls deflect at the join to create a 'chevron' shape. This occurs at a very high frequency within the printhead. The animation is slowed down to demonstrate chevron actuation in three adjacent channel walls.
The chevron design used by Xaar is very energy efficient which reduces the required drive voltage and therefore reduces power consumption. It also offers:
- More consistent performance than a single poled material (monolithic cantilever)
- Better drop formation uniformity
- Better drop placement accuracy
- Higher print quality as a result
- Reduced mechanical stress resulting in longer actuator life .
When the channel walls are flexed (actuated) in chevron mode at a high frequency, an acoustic wave is created. This pressure wave forces the ink droplets out of the nozzles.
The animation shows acoustic waves moving up and down the channel. This method of drop ejection is very efficient. The walls vibrate at approximately 150 kHz.
Xaar's patented shared-wall design is a technique for increasing native resolution or channel density. Each channel has 2 walls made of piezoelectric material. These walls are therefore shared between adjacent channels and can be used to fire both of the adjacent channels independently. This structure is an efficient use of the piezo material leading to cost-effective, high nozzle density printheads.
The conventional design of inkjet printheads uses end shooter architecture. This means that these printheads have nozzle orifices at the end of each channel through which the ink is ejected.
Hybrid Side Shooter® architecture
Xaar's Hybrid Side Shooter® architecture has an inlet and outlet for the ink as well as a separate nozzl e in each channel. The nozzle is in the side of the ink channel and the drop is fired perpendicular to the flow of the ink.
This new architecture, which builds on Xaar's highly-successful Hybrid Side Shooter® design, optimises actuator performance to deliver unprecedented drop velocity, drop volume and drop placement profiles for consistent colour across the print swathe.