Piezo printhead operation & architecture
There are different piezo printhead modes of operation: Chevron, Shear and Bend. Chevron and Shear mode are patented by Xaar.
Shear mode printheads use a single piece of poled PZT for the actuator design. The electric current is applied perpendicular to the direction in which the material is poled. The deformation creates a shear effect (trapezoid shape) – see the animation below. The animation shows the walls of the channel shearing (moving) from side to side
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.
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.
All Xaar’s latest bulk technology printheads have an actuator that is made of 2 pieces of oppositely poled piezo material joined (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
- Better drop formation uniformity
- Better drop placement accuracy
- Higher print quality as a result
- Reduced mechanical stress resulting in longer actuator life.
The conventional design of inkjet printheads uses end shooter architecture i.e. these printheads have nozzle orifices at the end of each channel through which the ink is ejected.
A printhead which uses this architecture is the Xaar 128
Hybrid side shooter architecture
Xaar's Hybrid Side Shooter printhead architecture has an inlet and outlet for the ink as well as a separate nozzle 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 unique architecture, which builds on Xaar's highly-successful Hybrid Side Shooter design, optimises actuator performance to deliver more uniform drop formation and velocity across the print swathe and therefore exceptional print quality at longer throw distances.
The printhead shape allows printheads to align with one another without increasing the depth of the array. Print zone areas are minimised, increasing print quality and decreasing cost of the printer.