The USS Quad Damage

Explaining Inkjet Printers

I explain how inkjet printers work so people can better understand the "razor and blades" model.

Anyway, while the key word for Piezo was "cost", the key word for heating elements is "reliability".

I’ve been hearing a lot about the price of ink, on how it’s a razor and blades model, and the subsequent indignation at companies like HP profiteering and something something capitalism amirite? I want to take some time to explain the technology behind the model, and how this is the only model the technology can take. I’m not saying HP aren’t profiteering, but that this isn’t pure evil at work here.

There’s two main types of inkjet printers, piezo and heating element, and both are made of MEMS, or “Micro Electro Mechanical Systems”. This means “tiny moving things activated by using electricity”. How tiny? Well at a 600DPI printer, each nozzle is about 0.04mm in width, so that small. You have MEMS in your phone as well: Your magnetometer (compass), gyro, and various other doohickeys, including the mic itself, are all created using MEMS, which means they all sit on a little chip about 5mm square, and most of that is probably wire bonds.

What’s interesting about MEMS is how it’s built, which is mostly using the same technology as you use to build CPUs and such, except features on a CPUs are a magnitude smaller still. So imagine 20 year old CPU technology and MEMS technology looks a bit like that.

The first actuator we’ll get through is the Piezo actuator. An actuator spits out the “dot” you see on the page. Piezo actuators work by physically moving back and forth, like a piston (roughly). They have various differing properties from the heating element actuators but the one we care about is cost: Piezos are expensive. This is why you’ll see them on the printer itself. When you buy an Epson printer, this is what you get. The Epson ink is just a vial of ink, and you plug it in and the printer will pull the ink out of the ink cartridge and push it into the printhead. The printhead will then use it’s thousand or so actuators to push out each individual ink drop.

You’ll notice the Epson cartridges are cheaper than the HP ones. This is because all you’re getting is some ink. However, the ink has to be special. At the scale of the actuator, different types of ink behave very differently. If you have a dry bit or blob, or the ink separates, or anything funny happens, or the ink gets dry while it’s on the print head and being unused, there’s a chance that an actuator could get stuck or broken, and that’s pretty much it for that actuator, and you’ll see white streaks for the lifetime of that printer. Considering that on Epson you’d need to buy a whole new printer to fix the print head, you can see how it’s important to get good quality ink, especially from Epson’s perspective, who want to ensure that you get a good lifetime out of their printer and expensive print head. Having said that, the print heads can take a beating compared to the heating element ones.

The second actuator is the heating element. A heating element works by heating up the ink and it sort-of-boils and then flies out at the page. Originally Canon called this a “bubble jet” which sounds cool, but I guess it also sounds like it’d have bad quality prints so they stopped calling it that — HP called theirs an “ink jet”, despite being based on the same tech. and it sounds like it shoots “straighter”.

Anyway, while the key word for Piezo was “cost”, the key word for heating elements is “reliability”. Heating elements are cheap to make, but they are very finicky and a lot depends on the ink chemistry. For this reason, Canon and HP sell their print heads on the ink cartridges. The little thing at the bottom where you have to peel off the sticker? That’s the print head. With all the actuators on it. Without the cartridge, the “printer” is just a bunch of motors that push paper around. You could theoretically grab the ink cartridge and “do electronics” to connect it to USB and wave it around to print stuff, without ever buying the “printer”.

The print cartridges are expensive to make, is my point. This is why when you see “after market” HP ink, it’s not in an ink cartridge, you have to refill an existing ink cartridge.

These heating elements have several problems. First, in order to even squirt the ink out properly, they need special ink. Second, if an actuator tries to fire and there’s no ink there, it could burn out. If the ink dries, it could burn out. If the ink doesn’t do exactly the right thing, individual actuators start dying. Even if nothing of the sort is wrong, individual actuators could still start dying. There’s also a much tighter relationship between the actuators and the ink. They kind of “depend” upon each other.

Many people noticed that HP ink cartridges aren’t even full any more. The reason for this is that the engineers found a way to use less ink and keep it equally dark, so they did it as a cost saving exercise. However, they couldn’t give you an “extra length” cartridge because the lifetime of the actual actuators hasn’t improved. If you refill an existing HP ink cartridge, you’ll likely get streaks. The more times you refill, the more streaks you’ll get.

The interesting thing about heating element inkjets is, as an engineering product, they’re a total failure. Imagine telling your boss this stuff when describing your product: You need exactly the right kind of ink and it tends to die a lot even if other conditions are perfect, oh and don’t let it get too dry, etc. etc. Imaginative marketing and management have turned this thing from a joke to a massively profitable business.

Hilariously, HP make a massive amount of cash because their printers are so cheap, because they’re not really printers at all. Even though Epson tends to win all the awards for being highest quality, more reliable, and even cheaper to run, the initial outlay for the printer means more people still buy HP or Canon, and then whinge about how much they hate them.

So if you want a decent inkjet printer (knowing what you’re getting yourself into), get an Epson. Market pressure from HP and not getting enough business means their printers are well cheaper than they should be (even though they might still be twice the price of an HP), and the aftermarket ink doesn’t involve you messing around with the little injectors spilling ink everywhere and getting streaky printouts at the end anyway.