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Taking a Closer Look at the HP Pagewide Printhead

From the Printware Blog on Friday 3rd March 2017

In case you didn’t know it yet, HP Pagewide printers threaten to disrupt the business printer industry by ensuring faster print speeds, higher colour quality and lower total cost of ownership. All this, just by swapping a moving printhead assembly for a stationary one that spans the entire width of the page. But is the engineering involved as simple as the concept?

HP Pagewide Printhead Close up To find the answer, we need to –quite literally - put the design of the HP printhead under the microscope. We need to find out how it can deliver 1200 tiny dots of ink per inch via a mind-boggling 42,240 fixed nozzles, each measuring less than the width of a human hair. Not only that, but how each nozzle can produce ink droplets at up to roughly one every 50 microseconds.

And how can HP claim that, with such a huge density of microscopic nozzles, their printhead will deliver reliably and stand the test of time?

To understand all of this first we have to look into how the Printhead is built.

Building the Pagewide Printhead

The manufacture of HP’s Printhead is made possible by their own Scalable Printing Technology (SPT). Using similar techniques used to produce integrated circuits, they define all parts of the printhead using a process called photolithograghy to create extremely small structures. As a result ink passages, chambers and nozzles are constructed with sub-micron precision.

The production also increases lifespan by providing contamination resistance, crucial to ensure the long-term overall dependability of the printhead. Also, closely placed miscroscopic pillars at the inlet forms a barrier to prevent particles entering and obstructing the ink’s intended path through the mechanism.

Managing & Maintaining a Small Army of Nozzles

With so many tiny nozzles in one small space, it seems like an incomprehensible task to monitor and maintain each one to ensure each is functioning correctly. Yet, as impossible as it sounds, as paper whizzes through the printer at up to 55 pages per minute a continuous testing process runs. Individual ink drops are monitored by optical sensors as they travel from the printhead to determine if they are as expected.

HP call this Backscatter Drop Detection. It uses innovative optics and photodetectors combined with advanced processing. Measuring the light that is reflected when an ink drop travels through a focused light beam it can determine if: a) the droplet has been produced in the first place; and b) is moving at the right speed and in the right direction. The system is sufficiently advanced to do measure several hundred ink drops each second.

This system is all the more remarkable given that:

  • A drop moves at about 33 feet (10 meters) per second
  • There are four nozzle arrays on each die positioned at different distances from the sensor
  • The measurement system must fit into a confined space close enough to the printhead to measure individual drops
  • The sensor must be highly immune to stray reflected light and electrical noise
  • Drop detection must have little impact on printer productivity

Once the data is analysed, it can be determined by the system whether the nozzle under analysis is functional, faulty, or not firing at all. At that point the issues caused by bad nozzles can be corrected.

In the near future we will revisit this topic and look at how Pagewide technology ensures such high print quality even when nozzles malfunction, and look at the variety of passive and active technologies it can use when this happens.

In the meantime, please browse our range of HP Pagewide Printers.

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