Last time on Amazing Inkjet – Part 1 we talked about how an inkjet cartridge uses magic to convert electrical energy into kinetic energy and fire a 50pL drop of liquid (1/160,000 the size of a raindrop) over and over again.
The underlying principle behind inkjet technology
Magic is cool (mega cool), but it’s just the basic principle – the idea that enables the technology. The real fun is turning the magic into a working ink cartridge that can print stuff.
Thermal inkjet technology (TIJ) was invented at the same time by two separate groups: one within HP and one within Canon. The Canon group was trying to use the piezo electric effect (described in part 1) to eject ink and accidentally touched a hot soldering iron to a syringe filled with ink. When the ink shot out they were like, “Woah… this is much simpler than this damn piezo nonsense.”
At the same time, HP was working on their own TIJ tech: These were some of the first experimental thermal inkjet printheads developed at HP!
Nozzle used for firing around walls
In this and future articles we’ll be focusing on HP TIJ tech. because we’re the most familiar with it. Cannon was also a pioneer in TIJ and like most technologies in the space, their technology closely mirrors HP’s.
Born in 1984, the HP 51604A was the first commercial inkjet cartridge. Initially used in the HP2225, it’s still used today in ATMs and receipt printers!
It was a pretty big deal at the time because the alternative was a noisy dot matrix printer or a mammoth laser printer. It could print 500 pages from one cartridge at 96DPI and cost $495 USD in 1985 (~$1000 USD in 2015). One of the HP2225s main selling feature was that it was portable! This guy certainly is enjoying it!
This picture explains the basic components of the 51604A. All subsequent thermal inkjet cartridges have the same basic parts and construction technique.
The orifice plate and nozzle array is the business end of the cartridge and contains the chambers that do the printing. I know you’ve been anxious to find out what a chamber actually looks like, so here’s a cutaway diagram.
The 51604A cartridge has 12 of these nozzles. This is basically nothing compared to the thousands modern cartridges have. Each nozzle is spaced at 96 nozzles per inch so that as the cartridge moves over a page it can print a 12/96 or 0.125 inch wide swath at 96DPI. After one swath the paper is fed through the printer an a new swath is printed.
Here’s a closer view of the nozzle/orifice plate and chamber.
The orifice plate is made from a piece of electro-formed
metal and is added to the cartridge last. All the layers below the Orifice plate are made using the same techniques used in IC manufacture.
Even though each resistor is powered by a small amount of current (mA’s) at a low voltage (21v), they’re so small that the heat flux on it’s surface is greater than the surface of the sun! This combined with the rapid heating and quenching of the nozzles and corrosive nature of ink lead to many issues with resistor lifetime. And these were only a few of the many issues engineers needed to overcome to build a working inkjet cartridge!
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